Design and Control of Concrete Mixtures, 14th Ed

Design and Control

of Concrete

Mixtures

1 4 t h e d i t i o n

ENGINEERING BULLETIN 001

Design and Control of Concrete Mixtures

FOURTEENTH EDITION

by Steven H. Kosmatka, Beatrix Kerkhoff, and William C. Panarese

5420 Old Orchard RoadSkokie, Illinois 60077-1083 USA

Voice: 847.966.6200Fax: 847.966.9781Internet: www.cement.org

An organization of cement companies to improve andextend the uses of portland cement and concrete throughmarket development, engineering, research, education,and public affairs work.

Fourteenth Edition Print HistoryFirst Printing 2002, Revised 2003

© Portland Cement Association 2003

All rights reserved. No part of this book may be reproducedin any form without permission in writing from the pub-lisher, except by a reviewer who wishes to quote brief pas-sages in a review written for inclusion in a magazine ornewspaper.

Library of Congress Cataloging-in-Publication Data

Kosmatka, Steven H.Design and control of concrete mixtures / by Steven H.

Kosmatka, Beatrix Kerkhoff, and William C. Panarese.—14th ed.

p. cm.ISBN 0-89312-217-3 (pbk. : alk. paper)1. Concrete. 2. Concrete—Additives. 3. Portland cement.

I. Kerkhoff, Beatrix. II. Panarese, William C. III. Title. TA439 .K665 2002666'.893—dc21

2001007603

PCA R&D Serial Number SN2561

Printed in the United States of America

EB001.14

WARNING: Contact with wet (unhardened) concrete,mortar, cement, or cement mixtures can cause SKINIRRITATION, SEVERE CHEMICAL BURNS (THIRD-DEGREE), or SERIOUS EYE DAMAGE. Frequent expo-sure may be associated with irritant and/or allergic con-tact dermatitis. Wear waterproof gloves, a long-sleevedshirt, full-length trousers, and proper eye protection whenworking with these materials. If you have to stand in wetconcrete, use waterproof boots that are high enough tokeep concrete from flowing into them. Wash wet con-crete, mortar, cement, or cement mixtures from your skinimmediately. Flush eyes with clean water immediatelyafter contact. Indirect contact through clothing can be asserious as direct contact, so promptly rinse out wet con-crete, mortar, cement, or cement mixtures from clothing.Seek immediate medical attention if you have persistentor severe discomfort.

This publication is intended SOLELY for use by PROFES-SIONAL PERSONNEL who are competent to evaluate thesignificance and limitations of the information providedherein, and who will accept total responsibility for theapplication of this information. The Portland CementAssociation DISCLAIMS any and all RESPONSIBILITY andLIABILITY for the accuracy of and the application of theinformation contained in this publication to the full extentpermitted by law.

The authors of this engineering bulletin are:Steven H. Kosmatka, Managing Director, Research and Technical Services, PCABeatrix Kerkhoff, Civil Engineer, Product Standards and Technology, PCAWilliam C. Panarese, former Manager, Construction Information Services, PCA

ii

KEYWORDS: admixtures, aggregates, air-entrained concrete, batching, cement, cold weather, curing, durability, fibers,finishing, high-performance concrete, hot weather, mixing, mixing water, mixture proportioning, placing, portland cementconcrete, properties, special concrete, standards, supplementary cementing materials, tests, and volume changes.

ABSTRACT: This book presents the properties of concrete as needed in concrete construction, including strength anddurability. All concrete ingredients (cementing materials, water, aggregates, admixtures, and fibers) are reviewed for theiroptimal use in designing and proportioning concrete mixtures. Applicable ASTM, AASHTO, and ACI standards arereferred to extensively. The use of concrete from design to batching, mixing, transporting, placing, consolidating, finishing,and curing is addressed. Special concretes, including high-performance concretes, are also reviewed.

REFERENCE: Kosmatka, Steven H.; Kerkhoff, Beatrix; and Panarese, William C.; Design and Control of Concrete Mixtures,EB001, 14th edition, Portland Cement Association, Skokie, Illinois, USA, 2003.

Cover photos show ready mixed concrete being elevated by bucket andcrane to the 39th floor of a high-rise building in Chicago. (69991, 70015)

Preface and Acknowledgements . . . . . . . . . . . . . . . . . . . . ix

Chapter 1Fundamentals of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Freshly Mixed Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Mixing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Workability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Bleeding and Settlement . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Consolidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Hydration, Setting Time, and Hardening . . . . . . . . . . . . . 4

Hardened Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Curing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Drying Rate of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Permeability and Watertightness . . . . . . . . . . . . . . . . . . . . 9Abrasion Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Volume Stability and Crack Control. . . . . . . . . . . . . . . . . 11

Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Resistance to Freezing and Thawing . . . . . . . . . . . . . . . . 12Alkali-Aggregate Reactivity . . . . . . . . . . . . . . . . . . . . . . . 13Carbonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Chloride Resistance and Steel Corrosion. . . . . . . . . . . . . 14Chemical Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Sulfate Attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Seawater Exposures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Ettringite and Heat Induced

Delayed Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . 17Heat Induced Delayed Expansion . . . . . . . . . . . . . . . . 17

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Chapter 2Portland, Blended, and Other Hydraulic Cements . . . 21

The Beginning of an Industry. . . . . . . . . . . . . . . . . . . . . . . . 21Manufacture of Portland Cement. . . . . . . . . . . . . . . . . . . . . 24Types of Portland Cement. . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Type I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Type II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Type III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Type IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Type V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Air-Entraining Portland Cements. . . . . . . . . . . . . . . . . . . 30White Portland Cements . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Blended Hydraulic Cements. . . . . . . . . . . . . . . . . . . . . . . . . 31Type IS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Type IP and Type P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Type I (PM). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Type S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Type I (SM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Hydraulic Cements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Type GU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Type HE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Type MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Type HS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Type MH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Type LH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Hydraulic Slag Cements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Modified Portland Cements . . . . . . . . . . . . . . . . . . . . . . . . . 33Special Cements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Masonry and Mortar Cements . . . . . . . . . . . . . . . . . . . . . 33Plastic Cements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Finely-Ground Cements (Ultrafine Cements) . . . . . . . . . 35Expansive Cements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Oil-Well Cements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Cements with Functional Additions . . . . . . . . . . . . . . . . 36Water-Repellent Cements . . . . . . . . . . . . . . . . . . . . . . . . . 36Regulated-Set Cements . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Geopolymer Cements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Ettringite Cements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Rapid Hardening Cements . . . . . . . . . . . . . . . . . . . . . . . . 37Calcium Aluminate Cements . . . . . . . . . . . . . . . . . . . . . . 37Magnesium Phosphate Cements . . . . . . . . . . . . . . . . . . . 37Sulfur Cements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Selecting and Specifying Cements . . . . . . . . . . . . . . . . . . . . 37Availability of Cements . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Drinking Water Applications . . . . . . . . . . . . . . . . . . . . . . 38Canadian and European Cement

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Chemical Compounds and Hydration

of Portland Cement . . . . . . . . . . . . . . . . . . . . . . . . . . 39Tricalcium Silicate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Dicalcium Silicate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Tricalcium Aluminate . . . . . . . . . . . . . . . . . . . . . . . . . . 42Tetracalcium Aluminoferrite . . . . . . . . . . . . . . . . . . . . . 42Calcium Sulfate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Water (Evaporable and Nonevaporable) . . . . . . . . . . . . . 42Physical Properties of Cement . . . . . . . . . . . . . . . . . . . . . . . 43

Particle Size and Fineness . . . . . . . . . . . . . . . . . . . . . . . . . 43Soundness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Consistency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Setting Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Early Stiffening (False Set and Flash Set). . . . . . . . . . . . . 46Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Heat of Hydration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Loss on Ignition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Density and Relative Density

(Specific Gravity) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Bulk Density. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Thermogravimetric Analysis (TGA). . . . . . . . . . . . . . . . . 51Differential Thermal Analysis (DTA) . . . . . . . . . . . . . . . . 51Differential Scanning Calorimetry (DSC) . . . . . . . . . . . . 51

Virtual Cement Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Transportation and Packaging . . . . . . . . . . . . . . . . . . . . . . . 52Storage of Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Hot Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

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Table of Contents

Chapter 3Fly Ash, Slag, Silica Fume, and Natural Pozzolans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Fly Ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Slag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Silica Fume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Natural Pozzolans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Effects on Freshly Mixed Concrete. . . . . . . . . . . . . . . . . . . . 61

Water Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61Workability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Bleeding and Segregation . . . . . . . . . . . . . . . . . . . . . . . . . 62Air Content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62Heat of Hydration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Setting Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Finishability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Pumpability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Plastic Shrinkage Cracking . . . . . . . . . . . . . . . . . . . . . . . . 64Curing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Effects on Hardened Concrete . . . . . . . . . . . . . . . . . . . . . . . 64Strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Impact and Abrasion Resistance. . . . . . . . . . . . . . . . . . . . 65Freeze-Thaw Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . 65Deicer-Scaling Resistance . . . . . . . . . . . . . . . . . . . . . . . . . 66Drying Shrinkage and Creep . . . . . . . . . . . . . . . . . . . . . . 67Permeability and Absorption . . . . . . . . . . . . . . . . . . . . . . 68Alkali-Aggregate Reactivity . . . . . . . . . . . . . . . . . . . . . . . 68Sulfate Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Corrosion of Embedded Steel . . . . . . . . . . . . . . . . . . . . . . 69Carbonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Chemical Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Soundness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69Concrete Color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Concrete Mix Proportions . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Chapter 4Mixing Water for Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Alkali Carbonate and Bicarbonate . . . . . . . . . . . . . . . . . . . . 74Chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74Sulfate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75Other Common Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75Iron Salts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75Miscellaneous Inorganic Salts. . . . . . . . . . . . . . . . . . . . . . . . 75Seawater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75Acid Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76Alkaline Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76Wash Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76Industrial Wastewater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76Waters Carrying Sanitary Sewage . . . . . . . . . . . . . . . . . . . . 77Organic Impurities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77Sugar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77Silt or Suspended Particles . . . . . . . . . . . . . . . . . . . . . . . . . . 77Oils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77Algae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77Interaction with Admixtures. . . . . . . . . . . . . . . . . . . . . . . . . 77References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Chapter 5Aggregates for Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Characteristics of Aggregates . . . . . . . . . . . . . . . . . . . . . . . . 80Grading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80Fine-Aggregate Grading . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Fineness Modulus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84Coarse-Aggregate Grading . . . . . . . . . . . . . . . . . . . . . . . . 84Combined Aggregate Grading . . . . . . . . . . . . . . . . . . . . . 86Gap-Graded Aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . 86Particle Shape and Surface Texture . . . . . . . . . . . . . . . . . 87Bulk Density (Unit Weight) and Voids. . . . . . . . . . . . . . . 87Relative Density (Specific Gravity) . . . . . . . . . . . . . . . . . 87Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Absorption and Surface Moisture . . . . . . . . . . . . . . . . . . 88

Bulking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Resistance to Freezing and Thawing . . . . . . . . . . . . . . . . 89Wetting and Drying Properties. . . . . . . . . . . . . . . . . . . . . 90Abrasion and Skid Resistance. . . . . . . . . . . . . . . . . . . . . . 90Strength and Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . 91Resistance to Acid and Other

Corrosive Substances. . . . . . . . . . . . . . . . . . . . . . . . . 91Fire Resistance and Thermal Properties. . . . . . . . . . . . . . 92

Potentially Harmful Materials . . . . . . . . . . . . . . . . . . . . . . . 92Alkali-Aggregate Reactivity . . . . . . . . . . . . . . . . . . . . . . . . . 93

Alkali-Silica Reaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93Visual Symptoms of Expansive ASR . . . . . . . . . . . . . . 93Mechanism of ASR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94Factors Affecting ASR . . . . . . . . . . . . . . . . . . . . . . . . . . 94Test Methods for Identifying ASR Distress . . . . . . . . . 94Control of ASR in New Concrete . . . . . . . . . . . . . . . . . 94Identification of Potentially

Reactive Aggregates. . . . . . . . . . . . . . . . . . . . . . . . . . 95Materials and Methods to Control ASR. . . . . . . . . . . . 95

Alkali-Carbonate Reaction . . . . . . . . . . . . . . . . . . . . . . . . 95Mechanism of ACR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95Dedolomitization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98Test Methods for Identifying ACR Distress . . . . . . . . . 98Materials and Methods to Control ACR . . . . . . . . . . . 98

Aggregate Beneficiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98Handling and Storing Aggregates . . . . . . . . . . . . . . . . . . . . 98Marine-Dredged Aggregate . . . . . . . . . . . . . . . . . . . . . . . . . 99Recycled-Concrete Aggregate . . . . . . . . . . . . . . . . . . . . . . . . 99References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Chapter 6Admixtures for Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . 105

Air-Entraining Admixtures . . . . . . . . . . . . . . . . . . . . . . . . . 107Water-Reducing Admixtures. . . . . . . . . . . . . . . . . . . . . . . . 107Mid-Range Water Reducing Admixtures. . . . . . . . . . . . . . 109High-Range Water Reducing Admixtures . . . . . . . . . . . . . 109Plasticizers for Flowing Concrete . . . . . . . . . . . . . . . . . . . . 110Retarding Admixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113Hydration-Control Admixtures . . . . . . . . . . . . . . . . . . . . . 113Accelerating Admixtures. . . . . . . . . . . . . . . . . . . . . . . . . . . 113Corrosion Inhibitors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114Shrinkage-Reducing Admixtures . . . . . . . . . . . . . . . . . . . . 115Chemical Admixtures to Reduce Alkali-

Aggregate Reactivity (ASR Inhibitors) . . . . . . . . . . 115Coloring Admixtures (Pigments) . . . . . . . . . . . . . . . . . . . . 115Dampproofing Admixtures . . . . . . . . . . . . . . . . . . . . . . . . . 116Permeability-Reducing Admixtures . . . . . . . . . . . . . . . . . . 116

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Pumping Aids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116Bonding Admixtures and Bonding Agents . . . . . . . . . . . . 116Grouting Admixtures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117Gas-Forming Admixtures . . . . . . . . . . . . . . . . . . . . . . . . . . 117Air Detrainers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117Fungicidal, Germicidal, and

Insecticidal Admixtures . . . . . . . . . . . . . . . . . . . . . . 117Antiwashout Admixtures . . . . . . . . . . . . . . . . . . . . . . . . . . 117Compatibility of Admixtures and

Cementitious Materials . . . . . . . . . . . . . . . . . . . . . . 117Storing and Dispensing Chemical

Admixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

Chapter 7Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Advantages and Disadvantagesof Using Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Types and Properties of Fibers andTheir Effect on Concrete . . . . . . . . . . . . . . . . . . . . . 122

Steel Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122Glass Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124Synthetic Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125Natural Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

Unprocessed Natural Fibers . . . . . . . . . . . . . . . . . . . . 126Wood Fibers (Processed Natural Fibers) . . . . . . . . . . 126

Multiple Fiber Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

Chapter 8Air-Entrained Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

Properties of Air-Entrained Concrete. . . . . . . . . . . . . . . . . 129Freeze-Thaw Resistance . . . . . . . . . . . . . . . . . . . . . . . . . 129Deicer-Scaling Resistance . . . . . . . . . . . . . . . . . . . . . . . . 132

Air Drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134Treatment of Scaled Surfaces . . . . . . . . . . . . . . . . . . . 134

Sulfate Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134Resistance to Alkali-Silica Reactivity . . . . . . . . . . . . . . . 134Strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134Workability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136

Air-Entraining Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 136Factors Affecting Air Content . . . . . . . . . . . . . . . . . . . . . . . 137

Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137Coarse Aggregate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138Fine Aggregate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138Mixing Water and Slump . . . . . . . . . . . . . . . . . . . . . . . . 138Slump and Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141Concrete Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . 142Supplementary Cementitious Materials . . . . . . . . . . . . 142Admixtures and Coloring Agents . . . . . . . . . . . . . . . . . 142Mixing Action. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143Transporting and Handling . . . . . . . . . . . . . . . . . . . . . . 144Finishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

Tests for Air Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144Air-Void Analysis of Fresh Concrete . . . . . . . . . . . . . . . 145

Recommended Air Contents. . . . . . . . . . . . . . . . . . . . . . . . 145References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

Chapter 9Designing and ProportioningNormal Concrete Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . 149

Selecting Mix Characteristics . . . . . . . . . . . . . . . . . . . . . . . 149

Water-Cementing Materials Ratioand Strength Relationship . . . . . . . . . . . . . . . . . . . . 149

Strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150Water-Cementitious Material Ratio . . . . . . . . . . . . . . . . 151Aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151Air Content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

Mild Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153Moderate Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . 153Severe Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

Slump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153Water Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155Cementing Materials Content and Type . . . . . . . . . . . . 156Admixtures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157

Proportioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157Proportioning from Field Data . . . . . . . . . . . . . . . . . . . . 157Proportioning by Trial Mixtures . . . . . . . . . . . . . . . . . . . 158Measurements and Calculations. . . . . . . . . . . . . . . . . . . 159

Density (Unit Weight) and Yield. . . . . . . . . . . . . . . . . 159Absolute Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

Examples of Mixture Proportioning. . . . . . . . . . . . . . . . . . 160Example 1. Absolute Volume Method

(Metric) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160Conditions and Specifications. . . . . . . . . . . . . . . . . . . 160Strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160Water to Cement Ratio. . . . . . . . . . . . . . . . . . . . . . . . . 160Air Content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160Slump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160Water Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160Cement Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160Coarse-Aggregate Content . . . . . . . . . . . . . . . . . . . . . 161Admixture Content . . . . . . . . . . . . . . . . . . . . . . . . . . . 161Fine-Aggregate Content . . . . . . . . . . . . . . . . . . . . . . . 161Moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161Trial Batch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161Batch Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162

Example 2. Absolute Volume Method(Inch-Pound Units) . . . . . . . . . . . . . . . . . . . . . . . . . 163

Conditions and Specifications. . . . . . . . . . . . . . . . . . . 163Strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163Water to Cement Ratio. . . . . . . . . . . . . . . . . . . . . . . . . 163Coarse-Aggregate Size. . . . . . . . . . . . . . . . . . . . . . . . . 163Air Content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163Slump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163Water Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163Cement Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163Coarse-Aggregate Content . . . . . . . . . . . . . . . . . . . . . 163Admixture Content . . . . . . . . . . . . . . . . . . . . . . . . . . . 163Fine-Aggregate Content . . . . . . . . . . . . . . . . . . . . . . . 163Moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164Trial Batch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164Batch Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165Water Reducers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166Pozzolans and Slag . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

Example 3. Laboratory Trial MixtureUsing the PCA Water-CementRatio Method (Metric) . . . . . . . . . . . . . . . . . . . . . . . 166

Conditions and Specifications. . . . . . . . . . . . . . . . . . . 166Durability Requirements . . . . . . . . . . . . . . . . . . . . . . . 166Strength Requirements . . . . . . . . . . . . . . . . . . . . . . . . 166Aggregate Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

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Contents, continued

Air Content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166Slump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166Batch Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166Workability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166Mixture Proportions. . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Example 4. Laboratory Trial MixtureUsing the PCA Water-CementRatio Method (Inch-Pound Units) . . . . . . . . . . . . . 168

Conditions and Specifications. . . . . . . . . . . . . . . . . . . 168Water-Cement Ratio. . . . . . . . . . . . . . . . . . . . . . . . . . . 168Aggregate Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168Air Content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168Slump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168Batch Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168Workability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168Mixture Proportions. . . . . . . . . . . . . . . . . . . . . . . . . . . 169Mixture Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . 169

Example 5. Absolute Volume MethodUsing Multiple Cementing Materialsand Admixtures (Metric) . . . . . . . . . . . . . . . . . . . . . 172

Conditions and Specifications. . . . . . . . . . . . . . . . . . . 172Strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173Water to Cementing Materials Ratio . . . . . . . . . . . . . 173Air Content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173Slump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173Water Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173Cementing Materials Content . . . . . . . . . . . . . . . . . . . 173Coarse-Aggregate Content . . . . . . . . . . . . . . . . . . . . . 173Admixture Content . . . . . . . . . . . . . . . . . . . . . . . . . . . 173Fine-Aggregate Content . . . . . . . . . . . . . . . . . . . . . . . 173Moisture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174Trial Batch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

Concrete for Small Jobs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174Design Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

Chapter 10Batching, Mixing, Transporting, andHandling Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179

Batching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179Mixing Concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180

Stationary Mixing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180Ready Mixed Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . 180Mobile Batcher Mixed Concrete

(Continuous Mixer) . . . . . . . . . . . . . . . . . . . . . . . . . 183Remixing Concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

Transporting and Handling Concrete . . . . . . . . . . . . . . . . 183Delays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183Early Stiffening and Drying Out. . . . . . . . . . . . . . . . . 183Segregation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

Methods and Equipment for Transportingand Handling Concrete . . . . . . . . . . . . . . . . . . . . . . 184

Choosing the Best Method . . . . . . . . . . . . . . . . . . . . . . . 188Work At and Below Ground Level . . . . . . . . . . . . . . . . . 188Work Above Ground Level . . . . . . . . . . . . . . . . . . . . . . . 188

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

Chapter 11Placing and Finishing Concrete . . . . . . . . . . . . . . . . . . . 191

Preparation Before Placing . . . . . . . . . . . . . . . . . . . . . . . . . 191Depositing the Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . 192Placing Concrete Underwater. . . . . . . . . . . . . . . . . . . . . . . 193

Special Placing Techniques . . . . . . . . . . . . . . . . . . . . . . . . . 194Consolidating Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194

Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195Internal Vibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195External Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197Consequences of Improper Vibration. . . . . . . . . . . . . 198

Concrete Slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198Subgrade Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . 199Subbase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199Vapor Retarders and

Moisture-Problem Prevention. . . . . . . . . . . . . . . . . 199Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200Rain Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200Placing and Spreading. . . . . . . . . . . . . . . . . . . . . . . . . . . 200Screeding (Strikeoff) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200Bullfloating or Darbying . . . . . . . . . . . . . . . . . . . . . . . . . 201Edging and Jointing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202Floating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202Troweling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202Brooming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203Curing and Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

Placing on Hardened Concrete . . . . . . . . . . . . . . . . . . . . . . 204Bonded Construction Joints in

Structural Concrete . . . . . . . . . . . . . . . . . . . . . . . . . 204Preparing Hardened Concrete . . . . . . . . . . . . . . . . . . . . 204Bonding New to Previously

Hardened Concrete . . . . . . . . . . . . . . . . . . . . . . . . . 205Making Joints in Floors and Walls . . . . . . . . . . . . . . . . . . . 206

Isolation Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206Contraction Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206Construction Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208

Joint Layout for Floors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209Filling Floor Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209Unjointed Floors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210Removing Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210Patching Cleaning, and Finishing. . . . . . . . . . . . . . . . . . . . 210

Holes, Defects, and Overlays . . . . . . . . . . . . . . . . . . . . . 210Curing Patches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212Cleaning Concrete Surfaces. . . . . . . . . . . . . . . . . . . . . . . 212Finishing Formed Surfaces . . . . . . . . . . . . . . . . . . . . . . . 213

Special Surface Finishes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 213Patterns and Textures . . . . . . . . . . . . . . . . . . . . . . . . . . . 213Exposed-Aggregate Concrete . . . . . . . . . . . . . . . . . . . . . 213Colored Finishes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215Stains, Paints, and Clear Coatings . . . . . . . . . . . . . . . . . 215

Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215Protect Your Head and Eyes . . . . . . . . . . . . . . . . . . . . 215Protect Your Back . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216Protect Your Skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216

Chapter 12Curing Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

Curing Methods and Materials. . . . . . . . . . . . . . . . . . . . . . 220Ponding and Immersion . . . . . . . . . . . . . . . . . . . . . . . . . 221Fogging and Sprinkling. . . . . . . . . . . . . . . . . . . . . . . . . . 221Wet Coverings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221Impervious Paper. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222Plastic Sheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222Membrane-Forming Curing Compounds . . . . . . . . . . . 223

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Contents, continued

Internal Moist Curing . . . . . . . . . . . . . . . . . . . . . . . . . . . 224Forms Left in Place . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224Steam Curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224Insulating Blankets or Covers. . . . . . . . . . . . . . . . . . . . . 225Electrical, Oil, Microwave, and

Infrared Curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225Curing Period and Temperature. . . . . . . . . . . . . . . . . . . . . 225Sealing Compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228

Chapter 13Hot-Weather Concreting . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

When to Take Precautions. . . . . . . . . . . . . . . . . . . . . . . . . . 229Effects of High Concrete Temperatures . . . . . . . . . . . . . . . 230Cooling Concrete Materials. . . . . . . . . . . . . . . . . . . . . . . . . 231Supplementary Cementitious Materials . . . . . . . . . . . . . . 234Preparation Before Concreting . . . . . . . . . . . . . . . . . . . . . . 234Transporting, Placing, Finishing. . . . . . . . . . . . . . . . . . . . . 235Plastic Shrinkage Cracking . . . . . . . . . . . . . . . . . . . . . . . . . 235Curing and Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237Admixtures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238Heat of Hydration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238

Chapter 14Cold-Weather Concreting. . . . . . . . . . . . . . . . . . . . . . . . . . 239

Effect of Freezing Fresh Concrete . . . . . . . . . . . . . . . . . . . . 239Strength Gain of Concrete at

Low Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . 240Heat of Hydration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241Special Concrete Mixtures. . . . . . . . . . . . . . . . . . . . . . . . . . 242Air-Entrained Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242Temperature of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . 243

Temperature of Concrete as Mixed. . . . . . . . . . . . . . . . . 243Aggregate Temperature. . . . . . . . . . . . . . . . . . . . . . . . 244Mixing-Water Temperature . . . . . . . . . . . . . . . . . . . . . 244

Temperature of Concrete asPlaced and Maintained . . . . . . . . . . . . . . . . . . . . . . 245

Cooling After Protection . . . . . . . . . . . . . . . . . . . . . . . . . 245Control Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245Concreting on Ground. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246Concreting Aboveground . . . . . . . . . . . . . . . . . . . . . . . . . . 247Enclosures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249Insulating Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250Heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251Duration of Heating. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253

Moist Curing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253Terminating the Heating Period . . . . . . . . . . . . . . . . . . . 253

Form Removal and Reshoring . . . . . . . . . . . . . . . . . . . . . . 253Maturity Concept. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255

Chapter 15Volume Changes of Concrete. . . . . . . . . . . . . . . . . . . . . . 257

Early Age Volume Changes . . . . . . . . . . . . . . . . . . . . . . . . 257Chemical Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257Autogenous Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . 258Subsidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259Plastic Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259Swelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259Early Thermal Expansion . . . . . . . . . . . . . . . . . . . . . . . . 260

Moisture Changes (Drying Shrinkage)of Hardened Concrete . . . . . . . . . . . . . . . . . . . . . . . 260

Effect of Concrete Ingredients onDrying Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . 263

Effect of Curing on Drying Shrinkage . . . . . . . . . . . . . . 264Temperature Changes of

Hardened Concrete . . . . . . . . . . . . . . . . . . . . . . . . . 264Low Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265High Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265

Curling (Warping) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266Elastic and Inelastic Deformation. . . . . . . . . . . . . . . . . . . . 267

Compression Strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267Modulus of Elasticity. . . . . . . . . . . . . . . . . . . . . . . . . . . . 267Deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268Poisson’s Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268Shear Strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268Torsional Strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268

Creep. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268Chemical Changes and Effects . . . . . . . . . . . . . . . . . . . . . . 270

Carbonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270Sulfate Attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270Alkali-Aggregate Reactions. . . . . . . . . . . . . . . . . . . . . . . 270

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

Chapter 16Control Tests for Concrete . . . . . . . . . . . . . . . . . . . . . . . . 275

Classes of Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275Frequency of Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275Testing Aggregates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276

Sampling Aggregates. . . . . . . . . . . . . . . . . . . . . . . . . . . . 276Organic Impurities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276Objectionable Fine Material . . . . . . . . . . . . . . . . . . . . . . 277Grading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277Moisture Content of Aggregates. . . . . . . . . . . . . . . . . . . 277

Testing Freshly Mixed Concrete . . . . . . . . . . . . . . . . . . . . . 279Sampling Freshly Mixed Concrete . . . . . . . . . . . . . . . . . 279Consistency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279Temperature Measurement . . . . . . . . . . . . . . . . . . . . . . . 280Density and Yield. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280Air Content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280Strength Specimens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282Time of Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283Accelerated Compression Tests to

Project Later-Age Strength . . . . . . . . . . . . . . . . . . . 284Chloride Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284Portland Cement Content, Water Content,

and Water Cement Ratio . . . . . . . . . . . . . . . . . . . . . 284Supplementary Cementitious

Materials Content. . . . . . . . . . . . . . . . . . . . . . . . . . . 284Bleeding of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284

Testing Hardened Concrete. . . . . . . . . . . . . . . . . . . . . . . . . 285Strength Tests of Hardened Concrete. . . . . . . . . . . . . . . 285

Evaluation of Compression Test Results . . . . . . . . . . 287Air Content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287Density, Relative Density (Specific

Gravity), Absorption, and Voids. . . . . . . . . . . . . . . 288Portland Cement Content . . . . . . . . . . . . . . . . . . . . . . . . 289Supplementary Cementitious Material and

Organic Admixture Content . . . . . . . . . . . . . . . . . . 289Chloride Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289Petrographic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

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Volume and Length Change . . . . . . . . . . . . . . . . . . . . . . 290Durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290

Frost Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290Sulfate Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290Alkali-Silica Reactivity. . . . . . . . . . . . . . . . . . . . . . . . . 290Alkali-Carbonate Reactivity . . . . . . . . . . . . . . . . . . . . 290Corrosion Resistance . . . . . . . . . . . . . . . . . . . . . . . . . 290Abrasion Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . 290

Moisture Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291Carbonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291pH Testing Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292Nondestructive Test Methods . . . . . . . . . . . . . . . . . . . . . 292

Rebound Number Tests . . . . . . . . . . . . . . . . . . . . . . . . 292Penetration Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293Maturity Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293Pullout Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293Break-Off Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293Dynamic or Vibration Tests. . . . . . . . . . . . . . . . . . . . . 294Other Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295

Chapter 17High-Performance Concrete . . . . . . . . . . . . . . . . . . . . . . . 299

High-Early-Strength Concrete . . . . . . . . . . . . . . . . . . . . . . 300High-Strength Concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . 303

Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305Supplementary Cementing Materials . . . . . . . . . . . . . . 305Aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305Admixtures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306Proportioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306Mixing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306Placing, Consolidation, and Curing . . . . . . . . . . . . . . . . 307Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

High-Durability Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . 308Abrasion Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308Blast Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309Carbonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309Temperature Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309Freeze-Thaw Resistance . . . . . . . . . . . . . . . . . . . . . . . . . 310Chemical Attack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310Alkali-Silica Reactivity . . . . . . . . . . . . . . . . . . . . . . . . . . 310Resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

Self-Compacting Concrete. . . . . . . . . . . . . . . . . . . . . . . . . . 311Reactive Powder Concrete . . . . . . . . . . . . . . . . . . . . . . . . . 312References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

Chapter 18Special Types of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . 315

Structural Lightweight Concrete . . . . . . . . . . . . . . . . . . . . 315Structural Lightweight Aggregates . . . . . . . . . . . . . . . . 316Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . 316Entrained Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317Mixing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317Workability and Finishability . . . . . . . . . . . . . . . . . . . . . 317Slump . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317Placing, Finishing, and Curing . . . . . . . . . . . . . . . . . . . . 317

Insulating and Moderate-StrengthLightweight Concretes. . . . . . . . . . . . . . . . . . . . . . . 318

Group I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318Group II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318Group III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

Mixture Proportions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318Workability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319Mixing and Placing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319Thermal Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320Strength. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320Resistance to Freezing and Thawing . . . . . . . . . . . . . . . 321Drying Shrinkage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321Expansion Joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

Autoclaved Cellular Concrete. . . . . . . . . . . . . . . . . . . . . . . 321High-Density Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

High-Density Aggregates . . . . . . . . . . . . . . . . . . . . . . . . 322Additions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322Properties of High-Density Concrete . . . . . . . . . . . . . . . 322Proportioning, Mixing, and Placing . . . . . . . . . . . . . . . . 322

Mass Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323Preplaced Aggregate Concrete . . . . . . . . . . . . . . . . . . . . . . 325No-Slump Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325Roller-Compacted Concrete . . . . . . . . . . . . . . . . . . . . . . . . 326

Water Control Structures . . . . . . . . . . . . . . . . . . . . . . . . . 326Pavements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326

Soil-Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327Shotcrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327Shrinkage-Compensating Concrete . . . . . . . . . . . . . . . . . . 328Pervious Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328White and Colored Concrete. . . . . . . . . . . . . . . . . . . . . . . . 329

White Concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329Colored Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

Dry-Shake Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . 329Polymer-Portland Cement Concrete . . . . . . . . . . . . . . . . . 330Ferrocement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330

Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335ASTM Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341AASHTO Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346Metric Conversion Factors . . . . . . . . . . . . . . . . . . . . . . . . . 348Cement and Concrete Resources . . . . . . . . . . . . . . . . . . . . 349

Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

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Concrete’s versatility, durability, and economy have madeit the world’s most used construction material. The UnitedStates uses about 260 million cubic meters (340 millioncubic yards) of ready mixed concrete each year. It is usedin highways, streets, parking lots, parking garages,bridges, high-rise buildings, dams, homes, floors, side-walks, driveways, and numerous other applications.

Design and Control of Concrete Mixtures has been thecement and concrete industry’s primary reference on con-crete technology for over 75 years. Since the first editionwas published in the early 1920s, the U.S. version has beenupdated 14 times to reflect advances in concrete technolo-gy and to meet the growing needs of architects, engineers,builders, concrete producers, concrete technologists,instructors, and students.

This fully revised 14th edition was written to providea concise, current reference on concrete, including themany advances that occurred since the last edition waspublished in 1988. The text is backed by over 85 years ofresearch by the Portland Cement Association. It reflects thelatest information on standards, specifications, and testmethods of the American Society for Testing and Materials(ASTM), the American Association of State Highway andTransportation Officials (AASHTO), and the AmericanConcrete Institute (ACI).

Besides presenting a 50% increase in new informationover the previous edition, this edition has added metricunits that are currently required on most federal govern-ment projects and many state projects; AASHTO stan-dards commonly used by many state departments oftransportation are provided alongside ASTM standards;internet addresses are provided for many references forinstant access; new photographs have been added to illus-trate modern technology; and included are appendices onmetric unit conversion, ASTM and AASHTO standards,and a listing of key concrete organizations and their webaddresses. New chapters on supplementary cementingmaterials, fibers, and high-performance concrete have alsobeen added.

Acknowledgements. The authors wish to acknowledgecontributions made by many individuals and organiza-tions who provided valuable assistance in the writingand publishing of the 14th edition. A special thanks toKen Hover, Cornell University, for extensive technicalrecommendations; Howard “Buck” Barker, RVT En-gineering Services, for photography and text edits; and

Cheryl Taylor, Consultant, for months of desktop layout.Additional thanks for technical assistance, references, pho-tography, and editorial reviews goes to: Norm MacLeod,former Cement Association of Canada; Rick McGrath,Cement Association of Canada; John Bickley, John A.Bickley Associates, Ltd.; Hamid Farzam, ConstructionTechnology Laboratories (CTL); Colin Lobo, NationalReady Mixed Concrete Association; Linda Hills, CTL(SEM); Connie Field, PCA; Bill Burns, PCA; John Shaw,PCA; Basile Rabbat, PCA; Arlene Zapata, PCA (coverdesign); Wes Ikezoe, PCA; Richard Small, PCA; BruceMcIntosh, PCA; Susan Pepitone, PCA; Dale McFarlane,PCA; Paul Tennis, PCA; John Melander, PCA; Jamie Farny,PCA; Carmaline Spurrier, PCA; Martin McGovern, PCA;Terry Collins, PCA; Michelle Wilson, PCA; Tony Fiorato,CTL; Vagn Johansen, CTL; Wally Klemm, formerly of CTL;Peter Marlo, CTL; Ron Bard, CTL; Manoj Bharucha, CTL;Javed Bhatty, CTL; Jennifer DeStrampe, Ground Heaters,Inc.; Jim Shilstone, Shilstone Companies, Inc.; Robert E.Neal, Lehigh Portland Cement Co.; Gregory S. Barger, AshGrove Cement Co.; Mark Luther, Holcim (US) Inc.; Fred Cohrs,Florida Rock Industries, Inc.; Phil Zacarias, LafargeCanada, Inc.; Terry Holland, Silica Fume Association;Oscar Manz, Consultant; Jon Mullarky, FHWA; KarenGruber, Hercules, Inc.; Mike Pistilli, Prairie Group; SamTyson, American Coal Ash Association; Craig Plunk,Mineral Solutions; Jim Jensen, Mineral Solutions; JohnRivisto, AVR, Inc.; Charlie Misslin, County Concrete Corp.;Jamison Langdon, Cemstone; Kerry Smith, James Cape &Sons Co.; David Meyer, Lafarge North America, Inc.; LewKollmansberger, Mead & Hunt, Inc.; Tim Roble, MidwayConcrete Corp.; George Barker, River Valley Testing Corp.;Dan Large, SI Concrete Systems; EJ Streu, StreuConstruction; Len Swederski, Swederski Concrete Const.,Inc.; Pat Bauer, W. R. Grace Co.; Darrin G. Stanke, ZenithTech, Inc.; Scott Zignego, Zignego Ready Mix, Inc.; PeterWaisamen, Trow Engineers; Mette Geiker, Technical Uni-versity of Denmark; and numerous others who have pro-vided comments and suggestions on EB001 over the pastseveral years. Thanks also goes to ASTM, AASHTO, andACI for the use of their material and documents referencedthroughout the book.

The authors have tried to make this edition of Designand Control of Concrete Mixtures a concise and current ref-erence on concrete technology. Readers are encouraged tosubmit comments to improve future printings and edi-tions of this book.

ix

Preface and Acknowledgements

Concrete is basically a mixture of two components: aggre-gates and paste. The paste, comprised of portland cementand water, binds the aggregates (usually sand and gravelor crushed stone) into a rocklike mass as the paste hardensbecause of the chemical reaction of the cement and water(Fig. 1-1). Supplementary cementitious materials andchemical admixtures may also be included in the paste.*

Aggregates are generally divided into two groups: fineand coarse. Fine aggregates consist of natural or manufac-tured sand with particle sizes ranging up to 9.5 mm (3⁄8 in.);coarse aggregates are particles retained on the 1.18 mm(No. 16) sieve and ranging up to 150 mm (6 in.) in size. Themaximum size of coarse aggregate is typically 19 mm or25 mm (3⁄4 in. or 1 in.). An intermediate-sized aggregate,around 9.5 mm (3⁄8 in.), is sometimes added to improve theoverall aggregate gradation.

CHAPTER 1

Fundamentals of Concrete

The paste is composed of cementitious materials,water, and entrapped air or purposely entrained air. Thepaste constitutes about 25% to 40% of the total volume ofconcrete. Fig. 1-2 shows that the absolute volume of cementis usually between 7% and 15% and the water between 14%and 21%. Air content in air-entrained concrete ranges fromabout 4% to 8% of the volume.

Since aggregates make up about 60% to 75% of thetotal volume of concrete, their selection is important.Aggregates should consist of particles with adequatestrength and resistance to exposure conditions and shouldnot contain materials that will cause deterioration of theconcrete. A continuous gradation of aggregate particlesizes is desirable for efficient use of the paste. Throughoutthis text, it will be assumed that suitable aggregates arebeing used, except where otherwise noted.

The quality of the concrete depends upon the qualityof the paste and aggregate, and the bond between the two.In properly made concrete, each and every particle ofaggregate is completely coated with paste and all of thespaces between aggregate particles are completely filledwith paste, as illustrated in Fig. 1-3.

* This text addresses the utilization of portland cement in the production ofconcrete. The term “portland cement” pertains to a calcium silicate hydrauliccement produced by heating materials containing calcium, silicon,aluminum, and iron. The term “cement” used throughout the text pertains toportland cement or blended hydraulic cement unless otherwise stated. Theterm “cementitious materials” means portland or blended cement, used withor without supplementary cementitious materials.

Fig. 1-1. Concrete components: cement, water, fine aggre-gate and coarse aggregate, are combined to form concrete.(55361)

Air-�entrained�concrete

Non-air-�entrained�concrete

Cement�15%

Water�18%

Fine agg.�28%

Coarse agg.�31%

Air�8%

7% 14% 4% 24% 51%

15% 21% 3% 30% 31%

7% 16% 1% 25% 51%

Mix 1

Mix 2

Mix 3

Mix 4

Fig. 1-2. Range in proportions of materials used in concrete,by absolute volume. Bars 1 and 3 represent rich mixes withsmall size aggregates. Bars 2 and 4 represent lean mixeswith large size aggregates.

1

The freshly mixed (plastic) and hardened properties ofconcrete may be changed by adding chemical admixturesto the concrete, usually in liquid form, during batching.Chemical admixtures are commonly used to (1) adjustsetting time or hardening, (2) reduce water demand, (3) in-crease workability, (4) intentionally entrain air, and (5) ad-just other fresh or hardened concrete properties.

After completion of proper proportioning, batching,mixing, placing, consolidating, finishing, and curing, con-crete hardens into a strong, noncombustible, durable, abra-sion-resistant, and watertight building material that re-quires little or no maintenance. Furthermore, concrete is anexcellent building material because it can be formed into awide variety of shapes, colors, and textures for use in anunlimited number of applications.

FRESHLY MIXED CONCRETE

Freshly mixed concrete should be plastic or semifluid andgenerally capable of being molded by hand. A very wetconcrete mixture can be molded in the sense that it can becast in a mold, but this is not within the definition of “plas-tic”—that which is pliable and capable of being molded orshaped like a lump of modeling clay.

In a plastic concrete mixture all grains of sand andpieces of gravel or stone are encased and held in suspen-sion. The ingredients are not apt to segregate during trans-port; and when the concrete hardens, it becomes ahomogeneous mixture of all the components. During plac-ing, concrete of plastic consistency does not crumble butflows sluggishly without segregation.

In construction practice, thin concrete members andheavily reinforced concrete members require workable, butnever soupy, mixes for ease of placement. A plastic mixtureis required for strength and for maintaining homogeneityduring handling and placement. While a plastic mixture issuitable for most concrete work, plasticizing admixturesmay be used to make concrete more flowable in thin orheavily reinforced concrete members.

For any particular set of materials and conditions ofcuring, the quality of hardened concrete is strongly influ-enced by the amount of water used in relation to theamount of cement (Fig. 1-4). Unnecessarily high water con-tents dilute the cement paste (the glue of concrete).Following are some advantages of reducing water content:

• Increased compressive and flexural strength• Lower permeability, thus lower absorption and in-

creased watertightness• Increased resistance to weathering• Better bond between concrete and reinforcement• Reduced drying shrinkage and cracking• Less volume change from wetting and drying

The less water used, the better the quality of theconcrete—provided the mixture can be consolidated prop-erly. Smaller amounts of mixing water result in stiffermixtures; but with vibration, stiffer mixtures can be easilyplaced. Thus, consolidation by vibration permits improve-ment in the quality of concrete.

2

Design and Control of Concrete Mixtures � EB001

Fig. 1-3. Cross section of hardened concrete made with (left) rounded siliceous gravel and (right) crushed limestone. Cement-and-water paste completely coats each aggregate particle and fills all spaces between particles. (1051, 1052)

Fig. 1-4. Ten cement-paste cylinders with water-cementratios from 0.25 to 0.70. The band indicates that eachcylinder contains the same amount of cement. Increasedwater dilutes the effect of the cement paste, increasingvolume, reducing density, and lowering strength. (1071)

Mixing

In Fig. 1-1, the basic components of concrete are shownseparately. To ensure that they are combined into a homo-geneous mixture requires effort and care. The sequence ofcharging ingredients into a concrete mixer can play an im-portant part in uniformity of the finished product. Thesequence, however, can be varied and still produce a qual-ity concrete. Different sequences require adjustments in thetime of water addition, the total number of revolutions ofthe mixer drum, and the speed of revolution. Other impor-tant factors in mixing are the size of the batch in relation tothe size of the mixer drum, the elapsed time between batch-ing and mixing, and the design, configuration, and condi-tion of the mixer drum and blades. Approved mixers,correctly operated and maintained, ensure an end-to-endexchange of materials by a rolling, folding, and kneadingaction of the batch over itself as concrete is mixed.

Workability

The ease of placing, consolidating, and finishing freshlymixed concrete and the degree to which it resists segrega-tion is called workability. Concrete should be workable butthe ingredients should not separate during transport andhandling (Fig. 1-5).

The degree of worka-bility required for properplacement of concrete iscontrolled by the place-ment method, type of con-solidation, and type ofconcrete. Different types ofplacements require differ-ent levels of workability.

Factors that influencethe workability of concreteare: (1) the method andduration of transportation;(2) quantity and character-istics of cementitious ma-terials; (3) concrete consis-tency (slump); (4) grading,shape, and surface textureof fine and coarse aggre-gates; (5) entrained air; (6)water content; (7) concreteand ambient air temperatures; and (8) admixtures. A uni-form distribution of aggregate particles and the presence ofentrained air significantly help control segregation andimprove workability. Fig. 1-6 illustrates the effect of castingtemperature on the consistency, or slump, and potentialworkability of concrete mixtures.

Properties related to workability include consistency,segregation, mobility, pumpability, bleeding, and finishabil-ity. Consistency is considered a close indication of workabil-ity. Slump is used as a measure of the consistency or wetnessof concrete. A low-slump concrete has a stiff consistency. If

the consistency is too dry and harsh, the concrete will bedifficult to place and compact and larger aggregate particlesmay separate from the mix. However, it should not beassumed that a wetter, more fluid mix is necessarily moreworkable. If the mix is too wet, segregation and honey-combing can occur. The consistency should be the driestpracticable for placement using the available consolidationequipment. See Powers (1932) and Scanlon (1994).

Bleeding and Settlement

Bleeding is the development of a layer of water at the top orsurface of freshly placed concrete. It is caused by sedimen-tation (settlement) of solid particles (cement and aggregate)and the simultaneous upward migration of water (Fig. 1-7).Bleeding is normal and it should not diminish the quality ofproperly placed, finished, and cured concrete. Some bleed-ing is helpful to control plastic shrinkage cracking.

3

Chapter 1 � Fundamentals of Concrete

Casting temperature, °F

Casting temperature, °C

32 52 72 92200

150

100

50

0 0

Slu

mp,

mm

Slu

mp,

in.

8

6

4

2

Cement A

Cement B

0 10 20 30 40

Fig. 1-5. Workable concreteshould flow sluggishly intoplace without segregation.(59292)

Fig. 1-6. Effect of casting temperature on the slump (andrelative workability) of two concretes made with differentcements (Burg 1996).

Fig. 1-7. Bleed water on the surface of a freshly placedconcrete slab. (P29992)

with paste and the less aggregate surface area there is tocoat with paste; thus less water and cement are needed.Concrete with an optimally graded aggregate will be easierto consolidate and place (Fig. 1-8 left). Consolidation ofcoarser as well as stiffer mixtures results in improved qual-ity and economy. On the other hand, poor consolidation canresult in porous, weak concrete (Fig. 1-9) with poor durabil-ity (Fig. 1-8 right).

Mechanical vibra-tion has many advan-tages. Vibrators make itpossible to economi-cally place mixturesthat are impractical toconsolidate by handunder many conditions.As an example, Fig.1-10 shows concrete of astiff consistency (lowslump). This concretewas mechanically vi-brated in forms contain-ing closely spaced rein-forcement. With handrodding, a much wetterconsistency would havebeen necessary.

Hydration, Setting Time, and Hardening

The binding quality of portland cement paste is due to thechemical reaction between the cement and water, calledhydration.

Portland cement is not a simple chemical compound, itis a mixture of many compounds. Four of these make up90% or more of the weight of portland cement: tricalciumsilicate, dicalcium silicate, tricalcium aluminate, and tetra-calcium aluminoferrite. In addition to these major com-pounds, several others play important roles in the hydrationprocess. Each type of portland cement contains the samefour major compounds, but in different proportions.

Excessive bleeding increases thewater-cement ratio near the top surface;a weak top layer with poor durabilitymay result, particularly if finishing oper-ations take place while bleed water ispresent. A water pocket or void candevelop under a prematurely finishedsurface.

After evaporation of all bleed water,the hardened surface will be slightlylower than the freshly placed surface.This decrease in height from time ofplacement to initial set is called settle-ment shrinkage.

The bleeding rate and bleedingcapacity (total settlement per unit oforiginal concrete height) increases withinitial water content, concrete height,and pressure. Use of properly graded aggregate, certainchemical admixtures, air entrainment, supplementary ce-mentitious materials, and finer cements, reduces bleeding.Concrete used to fill voids, provide support, or providewatertightness with a good bond should have low bleed-ing properties to avoid formation of water pockets. SeePowers (1939), Steinour (1945), and Kosmatka (1994).

Consolidation

Vibration sets into motion the particles in freshly mixedconcrete, reducing friction between them, and giving themixture the mobile qualities of a thick fluid. The vibratoryaction permits use of a stiffer mixture containing a largerproportion of coarse and a smaller proportion of fine aggre-gate. The larger the maximum size aggregate in concretewith a well-graded aggregate, the less volume there is to fill

4


100

80

60

40

20

0

0 5 10 15 20 25 30

Voids, %

Compressive strength

Flexural strength

Modulus of elasticity

Red

uctio

n in

con

cret

e pr

oper

ties,

%

Fig. 1-9. Effect of voids in concrete due to a lack of consoli-dation on modulus of elasticity, compressive strength, andflexural strength.

Fig. 1-8. Good consolidation (left) is needed to achieve a dense and durableconcrete. Poor consolidation (right) can result in early corrosion of reinforcingsteel and low compressive strength. (70016, 68806)

Fig. 1-10. Concrete of a stiffconsistency (low slump). (44485)

When clinker (the kiln product that is ground to makeportland cement) is examined under a microscope, most ofthe individual cement compounds can be identified andtheir amounts determined. However, the smallest grainselude visual detection. The average diameter of a typicalcement particle is approximately 15 micrometers. If allcement particles were average, portland cement wouldcontain about 300 billion particles per kilogram, but in factthere are some 16,000 billion particles per kilogram becauseof the broad range of particle sizes. The particles in a kilo-gram of portland cement have a surface area of approxi-mately 400 square meters.

The two calcium silicates, which constitute about 75%of the weight of portland cement, react with water to formtwo new compounds: calcium hydroxide and calcium sili-cate hydrate. The latter is by far the most important cement-ing component in concrete. The engineering properties ofconcrete—setting and hardening, strength, and dimen-sional stability—depend primarily on calcium silicatehydrate. It is the heart of concrete.

The chemical composition of calcium silicate hydrate issomewhat variable, but it contains lime (CaO) and silicate(SiO2) in a ratio on the order of 3 to 2. The surface area ofcalcium silicate hydrate is some 300 square meters pergram. In hardened cement paste, the calcium silicatehydrate forms dense, bonded aggregations between theother crystalline phases and the remaining unhydratedcement grains; they also adhere to grains of sand and topieces of coarse aggregate, cementing everything together(Copeland and Schulz 1962).

As concrete hardens, its gross volume remains almostunchanged, but hardened concrete contains pores filledwith water and air that have no strength. The strength is inthe solid part of the paste, mostly in the calcium silicatehydrate and crystalline compounds.

The less porous the cement paste, the stronger theconcrete. When mixing concrete, therefore, no more waterthan is absolutely necessary to make the concrete plasticand workable should be used. Even then, the water used isusually more than is required for complete hydration of thecement. About 0.4 grams of water per gram of cement areneeded to completely hydrate cement (Powers 1948 and1949). However, complete hydration is rare in fieldconcrete due to a lack of moisture and the long period oftime (decades) required to achieve complete hydration.

Knowledge of the amount of heat released as cementhydrates can be useful in planning construction. In winter,the heat of hydration will help protect the concrete againstdamage from freezing temperatures. The heat may be harm-ful, however, in massive structures such as dams because itmay produce undesirable temperature differentials.

Knowledge of the rate of reaction between cement andwater is important because it determines the rate of hard-ening. The initial reaction must be slow enough to allowtime for the concrete to be transported and placed. Oncethe concrete has been placed and finished, however, rapid

hardening is desirable. Gypsum, added at the cement millwhen clinker is ground, acts as a regulator of the initial rateof setting of portland cement. Other factors that influencethe rate of hydration include cement fineness, admixtures,amount of water added, and temperature of the materialsat the time of mixing. Fig. 1-11 illustrates the setting prop-erties of a concrete mixture at different temperatures.

HARDENED CONCRETE

Curing

Increase in strength with age continues provided (1) un-hydrated cement is still present, (2) the concrete remainsmoist or has a relative humidity above approximately 80%(Powers 1948), (3) the concrete temperature remains favor-able, and (4) sufficient space is available for hydration prod-ucts to form. When the relative humidity within the concretedrops to about 80%, or the temperature of the concrete dropsbelow freezing, hydration and strength gain virtually stop.Fig. 1-12 illustrates the relationship between strength gainand moist curing, while Fig. 1-13 illustrates the relationshipbetween strength gain and curing temperature.

If concrete is resaturated after a drying period, hydra-tion is resumed and strength will again increase. However,it is best to moist-cure concrete continuously from the timeit is placed until it has attained the desired quality; onceconcrete has dried out it is difficult to resaturate. Fig. 1-14illustrates the long-term strength gain of concrete in anoutdoor exposure. Outdoor exposures often continue toprovide moisture through ground contact and rainfall.Indoor concretes often dry out after curing and do notcontinue to gain strength (Fig. 1-12).

5


0

1

2

3

4

5

6

7

0

10

20

30

40

0 2 4 6 8 10 12 14

Pen

etra

tion

resi

stan

ce, 1

000

psi

Pen

etra

tion

resi

stan

ce, M

Pa

Time, hr

Cured at 32°C (90°F)

23°C (73°F)

10°C (50°F)

Initial Set

Final Set

ASTM C 403(AASHTO T 22)

Fig. 1-11. Initial and final set times for a concrete mixture atdifferent temperatures (Burg 1996).

For example, as mentioned, concrete must continue to holdenough moisture throughout the curing period for thecement to hydrate to the extent that desired properties areachieved. Freshly cast concrete usually has an abundanceof water, but as drying progresses from the surface inward,strength gain will continue at each depth only as long asthe relative humidity at that point remains above 80%.

A common illustration of this is the surface of aconcrete floor that has not had sufficient moist curing.Because it has dried quickly, concrete at the surface is weakand traffic on it creates dusting. Also, when concrete dries,it shrinks as it loses water (Fig. 1-15), just as wood and claydo (though not as much). Drying shrinkage is a primarycause of cracking, and the width of cracks is a function ofthe degree of drying, spacing or frequency of cracks, andthe age at which the cracks occur.

While the surface of a concrete element will dry quiterapidly, it takes a much longer time for concrete in the inte-rior to dry. Fig. 1-15 (top) illustrates the rate of drying atvarious depths within concrete cylinders exposed to labo-ratory air. Field concrete elements would have differentdrying profiles due to environmental conditions, sizeeffects, and concrete properties.

The moisture content of concrete depends on theconcrete’s constituents, original water content, dryingconditions, and the size of the concrete element (Heden-blad 1997 and 1998). After several months of drying in airwith a relative humidity of 50% to 90%, moisture content isabout 1% to 2% by mass of the concrete. Fig. 1-15 illustratesmoisture loss and resulting shrinkage.

Size and shape of a concrete member have an impor-tant bearing on the rate of drying. Concrete elements withlarge surface area in relation to volume (such as floor slabs)

Drying Rate of Concrete

Concrete does not harden or cure by drying. Concrete (or moreprecisely, the cement in it) needs moisture to hydrate andharden. When concrete dries out, it ceases to gain strength; thefact that it is dry is no indication that it has undergone sufficienthydration to achieve the desired physical properties.

Knowledge of the rate of drying is helpful in under-standing the properties or physical condition of concrete.

6


60

50

40

30

20

10

00 7 28 91 365

8

6

4

2

0

Age at test, days

Moist-cured entire time

In air after 28 days moist curing


In laboratory air entire time

Com

pres

sive

stre

ngth

, MP

a

Com

pres

sive

stre

ngth

, 100

0 ps

i

Fig. 1-12. Concrete strength increases with age as long asmoisture and a favorable temperature are present forhydration of cement (Gonnerman and Shuman 1928).

Outdoor exposure - Skokie, Illinois150-mm (6-in.) modified cubesType I cement

0

20

40

60

80

100

Com

pres

sive

str

engt

h, p

si

Com

pres

sive

str

engt

h, M

Pa

w/c = 0.40

w/c = 0.53

w/c = 0.71

3d 7d 28d 3m 1y 3y 5y 10y 20yAge at Test

14000

12000

10000

8000

6000

4000

2000

0

Fig. 1-14. Concrete strength gain versus time for concreteexposed to outdoor conditions. Concrete continues to gainstrength for many years when moisture is provided byrainfall and other environmental sources (Wood 1992).

0

10

20

30

40

50

0 10 20 30

Com

pres

sive

str

engt

h, M

Pa

Com

pres

sive

str

engt

h, p

si

Age, days

10/10 (50/50)

23/10 (73/50)

23/23 (73/73)

32/32 (90/90)

Casting/curing temperature, °C °(F)

7000

6000

5000

4000

3000

2000

1000

0

Fig. 1-13. Effect of casting and curing temperature onstrength development. Note that cooler temperatures resultin lower early strength and higher later strength (Burg,1996).

dry faster than voluminous concrete members with rela-tively small surface areas (such as bridge piers).

Many other properties of hardened concrete also areaffected by its moisture content; these include elasticity,creep, insulating value, fire resistance, abrasion resistance,electrical conductivity, frost resistance, scaling resistance,and resistance to alkali-aggregate reactivity.

Strength

Compressive strength may be defined as the measuredmaximum resistance of a concrete specimen to axial load-

ing. It is generally expressed in megapascals (MPa) orpounds per square inch (psi) at an age of 28 days. Onemegapascal equals the force of one newton per squaremillimeter (N/mm2) or 1,000,000 N/m2. Other test ages arealso used; however, it is important to realize the relation-ship between the 28-day strength and other test ages.Seven-day strengths are often estimated to be about 75% ofthe 28-day strength and 56-day and 90-day strengths areabout 10% to 15% greater than 28-day strengths as shownin Fig. 1-16. The specified compressive strength is desig-nated by the symbol ˘, and ideally is exceeded by theactual compressive strength, ¯.

The compressive strength that a concrete achieves, ¯,results from the water-cement ratio (or water-cementitiousmaterials ratio), the extent to which hydration hasprogressed, the curing and environmental conditions, andthe age of the concrete. The relationship between strengthand water-cement ratio has been studied since the late1800s and early 1900s (Feret 1897 and Abrams 1918). Fig.1-17 shows compressive strengths for a wide range ofconcrete mixtures and water-cement ratios at an age of 28days. Note that strengths increase as the water-cementratios decrease. These factors also affect flexural and tensilestrengths and bond of concrete to steel.

The water-cement ratio compressive strength relation-ships in Fig. 1-17 are for typical non-air-entrained con-cretes. When more precise values for concrete are required,graphs should be developed for the specific materials andmix proportions to be used on the job.

For a given workability and a given amount of cement,air-entrained concrete requires less mixing water than non-air-entrained concrete. The lower water-cement ratio possi-ble for air-entrained concrete tends to offset the somewhatlower strengths of air-entrained concrete, particularly inlean to medium cement content mixes.

7


50

60

70

80

90

100R

elat

ive

hum

idity

, per

cent

0

200

400

600

800

Shr

inka

ge, m

illio

nths

0

0.1

0.2

0.3

0.4

0.5

0.6

0 75 150 225 300 375

Mas

s lo

ss, k

g

Time of drying, days

Normal-density concrete


Cement content: 270 kg/m3 (454 lb/cu yd)Normal-density concretew/c ratio: 0.66

75 mm (3 in.) depth

45 (13/4)

6 (1/4)20 (3/4)

Fig. 1-15. Relative humidity distribution, drying shrinkage,and mass loss of 150 x 300-mm (6 x 12-in.) cylinders moistcured for 7 days followed by drying in laboratory air at 23°C(73°F) (Hanson 1968).

0

20

40

60

80

100

120

140

160

180

1 10 100 1000 10000

Per

cent

of 2

8-da

y st

reng

th

Age, days

28 days

Concrete cylinders

Fig. 1-16. Compressive strength development of variousconcretes illustrated as a percentage of the 28-day strength(Lange 1994).

The torsional strength for concrete is related to themodulus of rupture and the dimensions of the concreteelement. Hsu (1968) presents torsional strength correlations.

Shear strength–compressive strength relationships arediscussed in the ACI 318 building code. The correlationbetween compressive strength and flexural, tensile,torsional, and shear strength varies with concrete ingredi-ents and environment.

Modulus of elasticity, denoted by the symbol E, maybe defined as the ratio of normal stress to correspondingstrain for tensile or compressive stresses below the propor-tional limit of a material. For normal-weight concrete, Eranges from 14,000 to 41,000 MPa (2 to 6 million psi) andcan be approximated as 5,000 times the square root of thecompressive strength in megapascals (57,000 times thesquare root of the compressive strength in pounds persquare inch). Like other strength relationships, the modu-lus of elasticity to compressive strength relationship is mix-ingredient specific and should be verified in a laboratory(Wood 1992).

Density

Conventional concrete, normally used in pavements, build-ings, and other structures, has a density (unit weight) in therange of 2200 to 2400 kg/m3 (137 to 150 lb/ft3). The densityof concrete varies, depending on the amount and density ofthe aggregate, the amount of air that is entrapped or pur-posely entrained, and the water and cement contents,which in turn are influenced by the maximum size of theaggregate. Reducing the cement paste content (increasingaggregate volume) increases density. Values of the densityof fresh concrete are given in Table 1-1. In the design of re-inforced concrete structures, the combination of conven-tional concrete and reinforcing steel is commonly assumedto weigh 2400 kg/m3 (150 lb/ft3).

To determine compressive strength, tests are made onspecimens of mortar or concrete; in the United States,unless otherwise specified, compression tests of mortar aremade on 50-mm (2-in.) cubes, while compression tests ofconcrete are made on cylinders 150 mm (6 in.) in diameterand 300 mm (12 in.) high (see Fig. 1-18). Smaller cylinders,100 x 200 mm (4 x 8 in.) are also used for concrete.

Compressive strength of concrete is a primary physicalproperty and frequently used in design calculations forbridges, buildings, and other structures. Most general-useconcrete has a compressive strength between 20 and 40MPa (3000 and 6000 psi). Compressive strengths of 70 to140 MPa (10,000 to 20,000 psi) have been used in specialbridge and high-rise building applications.

The flexural strength or modulus of rupture ofconcrete is used to design pavements and other slabs onground. Compressive strength, which is easier to measurethan flexural strength, can be used as an index of flexuralstrength, once the empirical relationship between them hasbeen established for the materials and the size of theelement involved. The flexural strength of normal-weightconcrete is often approximated as 0.7 to 0.8 times the squareroot of the compressive strength in megapascals (7.5 to 10times the square root of the compressive strength inpounds per square inch). Wood (1992) illustrates the rela-tionship between flexural strength and compressivestrength for concretes exposed to moist curing, air curing,and outdoor exposure.

The direct tensile strength of concrete is about 8% to12% of the compressive strength and is often estimated as0.4 to 0.7 times the square root of the compressive strengthin megapascals (5 to 7.5 times the square root of thecompressive strength in pounds per square inch). Splittingtensile strength is 8% to 14% of the compressive strength(Hanson 1968). Splitting tensile strength versus time ispresented by Lange (1994).

8


28-day strengthMoist cured cylinders

0

10

20

30

40

50

60

70

80

0.25 0.35 0.45 0.55 0.65 0.75 0.85

Com

pres

sive

stre

ngth

, MP

a

Com

pres

sive

stre

ngth

, psi

Water-cement ratio

10000

8000

6000

4000

2000

0

Fig. 1-17. Range of typical strength to water-cement ratiorelationships of portland cement concrete based on over100 different concrete mixtures cast between 1985 and 1999.

Fig. 1-18. Testing a 150 x 300-mm (6 x 12-in.) concretecylinder in compression. The load on the test cylinder isregistered on the display. (68959)

The weight of dry concrete equals the weight of thefreshly mixed concrete ingredients less the weight of mixwater that evaporates into the air. Some of the mix watercombines chemically with the cement during the hydrationprocess, converting the cement into cement gel. Also, someof the water remains tightly held in pores and capillariesand does not evaporate under normal conditions. Theamount of mix water that will evaporate from concreteexposed to ambient air at 50% relative humidity is about1⁄2% to 3% of the concrete weight; the actual amountdepends on initial water content of the concrete, absorptioncharacteristics of the aggregates, and size and shape of theconcrete element.

Aside from conventional concrete, there is a wide spec-trum of special concretes to meet various needs; they rangefrom lightweight insulating concretes with a density of aslittle as 240 kg/m3 (15 lb/ft3) to heavyweight concrete witha density of up to 6000 kg/m3 (375 lb/ft3) used for coun-terweights or radiation shielding.

Permeability and Watertightness

Concrete used in water-retaining structures or exposed toweather or other severe exposure conditions must be virtu-ally impermeable or watertight. Watertightness is oftenreferred to as the ability of concrete to hold back or retainwater without visible leakage. Permeability refers to theamount of water migration through concrete when thewater is under pressure or to the ability of concrete to resist

penetration by water or other substances (liquid, gas, orions). Generally, the same properties of concrete that makeit less permeable also make it more watertight.

The overall permeability of concrete to water is a func-tion of: (1) the permeability of the paste; (2) the permeabil-ity and gradation of the aggregate; (3) the quality of thepaste and aggregate transition zone; and (4) the relativeproportion of paste to aggregate. Decreased permeabilityimproves concrete’s resistance to freezing and thawing,resaturation, sulfate, and chloride-ion penetration, andother chemical attack.

The permeability of the paste is particularly importantbecause the paste envelops all constituents in the concrete.Paste permeability is related to water-cement ratio, degreeof cement hydration, and length of moist curing. A low-permeability concrete requires a low water-cement ratioand an adequate moist-curing period. Air entrainment aidswatertightness but has little effect on permeability.Permeability increases with drying.

The permeability of mature hardened cement pastekept continuously moist ranges from 0.1 x 10-12 to 120 x 10-12

cm per sec. for water-cement ratios ranging from 0.3 to 0.7(Powers and others 1954).The permeability of rockcommonly used as concrete aggregate varies from approx-imately 1.7 x 10-9 to 3.5 x 10-13 cm per sec. The permeabilityof mature, good-quality concrete is approximately 1 x 10-10

cm per sec.The relationship between permeability, water-cement

ratio, and initial curing for 100 x 200-mm (4 x 8-in.) cylin-drical concrete specimens tested after 90 days of air drying

9


Maximum Density, kg/m3**size of Air Relative density of aggregate†

aggregate, content, Water, Cement,mm percent kg/m3 kg/m3 2.55 2.60 2.65 2.70 2.75

19 6.0 168 336 2194 2227 2259 2291 232337.5 4.5 145 291 2259 2291 2339 2371 240375 3.5 121 242 2307 2355 2387 2435 2467

Table 1-1. Observed Average Density of Fresh Concrete (SI Units)*

* Source: Bureau of Reclamation 1981, Table 4.** Air-entrained concrete with indicated air content.† On saturated surface-dry basis. Multiply relative density by 1000 to obtain density of aggregate particles in kg/m3.

Maximum Density, lb/ft 3**size of Air Specific gravity of aggregate†

aggregate, content, Water, Cement,in. percent lb/yd3 lb/yd3 2.55 2.60 2.65 2.70 2.753⁄4 6.0 283 566 137 139 141 143 145

11⁄2 4.5 245 490 141 143 146 148 1503 3.5 204 408 144 147 149 152 154

Table 1-1. Observed Average Density of Fresh Concrete (Inch-Pound Units)*

* Source: Bureau of Reclamation 1981, Table 4.** Air-entrained concrete with indicated air content.† On saturated surface-dry basis. Multiply specific gravity by 62.4 to obtain density of aggregate particles in lb/ft3.

greatly reduced or completely removed, producing a highvolume of air voids. Pervious concrete has been used intennis courts, pavements, parking lots, greenhouses, anddrainage structures. Pervious concrete has also been usedin buildings because of its thermal insulation properties.

Abrasion Resistance

Floors, pavements, and hydraulic structures are subjectedto abrasion; therefore, in these applications concrete musthave a high abrasion resistance. Test results indicate thatabrasion resistance is closely related to the compressivestrength of concrete. Strong concrete has more resistance to

and subjected to 20 MPa (3000 psi) of water pressure isillustrated in Fig. 1-19. Although permeability valueswould be different for other liquids and gases, the relation-ship between water-cement ratio, curing period, andpermeability would be similar.

Test results obtained by subjecting 25-mm (1-in.) thicknon-air-entrained mortar disks to 140-kPa (20-psi) waterpressure are given in Fig. 1-20. In these tests, there was nowater leakage through mortar disks that had a water-cement ratio of 0.50 by weight or less and were moist-curedfor seven days. Where leakage occurred, it was greater inmortar disks made with high water-cement ratios. Also, foreach water-cement ratio, leakage was less as the length ofthe moist-curing period increased. In disks with a water-cement ratio of 0.80, the mortar still permitted leakage afterbeing moist-cured for one month. These results clearlyshow that a low water-cement ratio and a reasonableperiod of moist curing significantly reduce permeability.

Fig. 1-21 illustrates the effect of different water to ce-ment ratios on concrete’s resistance to chloride ion penetra-tion as indicated by electrical conductance. The total chargein coulombs was significantly reduced with a low water tocement ratio. Also, the results showed that a lower chargepassed when the concrete contained a higher air content.

A low water-cement ratio also reduces segregation andbleeding, further contributing to watertightness. Of coursewatertight concrete must also be free from cracks, honey-comb, or other large visible voids.

Occasionally, pervious concrete—no-fines concretethat readily allows passage of water—is designed forspecial applications. In these concretes, the fine aggregate is

10


0

10

20

30

40

50

0.3 0.4 0.5 0.6 0.7 0.8

Hyd

raul

ic p

erm

eabi

lity,

cm

/sec

x 1

0-1

0

Water-cement ratio, by mass

1 day moist, 90 daysin air

7 days moist, 90days in air

Non-air-entrained concrete

Specimens: 100 x 200-mm (4 x 8-in.) cylinders

Water pressure: 20 MPa (3000 psi)

Curing:

Fig. 1-19. Relationship between hydraulic (water) perme-ability, water-cement ratio, and initial curing on concretespecimens (Whiting 1989).

0.0

2.5

5.0

7.5

10.0

12.5

0.0

0.5

1.0

1.5

2.0

2.5

0 7 14 21 28

Leak

age,

kg/

(m2 •

h),

ave

rage

for

48 h

ours

Leak

age,

psf

per

hou

r

Period of moist curing and age at test, days

w/c ratio: 0.80

Non-air-entrained concreteSpecimens: 25 x 150-mm (1 x 6-in.)

mortar disksPressure: 140 kPa (20 psi)

w/c ratio: 0.64

w/c ratio: 0.50

Fig. 1-20. Effect of water-cement ratio (w/c) and curingduration on permeability of mortar. Note that leakage isreduced as the water-cement ratio is decreased and thecuring period increased (McMillan and Lyse 1929 and PCAMajor Series 227).

3000

4000

2000

1000

0

Water to cement ratio

Cum

ulat

ive

char

ge, c

oulo

mbs

0.2 0.3 0.4 0.5

2%4%6%

Air content

ASTM C 1202

Fig. 1-21. Total charge at the end of the rapid chloridepermeability test as a function of water to cement ratio(Pinto and Hover 2001).

abrasion than does weak concrete. Since compressivestrength depends on water-cement ratio and curing, a lowwater-cement ratio and adequate curing are necessary forabrasion resistance. The type of aggregate and surfacefinish or treatment used also have a strong influence onabrasion resistance. Hard aggregate is more wear resistantthan soft aggregate and a steel-troweled surface resistsabrasion better than a surface that had not been troweled.

Fig. 1-22 shows results of abrasion tests on concretes ofdifferent compressive strengths and aggregate types. Fig.1-23 illustrates the effect hard steel troweling and surface

treatments, such as metallic or mineral aggregate surfacehardeners, have on abrasion resistance. Abrasion tests canbe conducted by rotating steel balls, dressing wheels, ordisks under pressure over the surface (ASTM C 779). Onetype of test apparatus is pictured in Fig. 1-24. Other typesof abrasion tests are also available (ASTM C 418 and C 944).

Volume Stability and Crack Control

Hardened concrete changes volume due to changes intemperature, moisture, and stress. These volume or lengthchanges may range from about 0.01% to 0.08%. Thermalvolume changes of hardened concrete are about the sameas those for steel.

Concrete under stress will deform elastically. Sus-tained stress will result in additional deformation calledcreep. The rate of creep (deformation per unit of time)decreases with time.

Concrete kept continually moist will expand slightly.When permitted to dry, concrete will shrink. The primaryfactor influencing the amount of drying shrinkage is thewater content of the freshly mixed concrete. Drying shrink-age increases directly with increases in this water content.The amount of shrinkage also depends upon several other

11


0

2

4

6

8

10

20 30 40 50 60 70

3 4 5 6 7 8 9 10

Abr

asio

n-er

osio

n lo

ss, p

erce

nt b

y m

ass

Compressive strength, MPa

Compressive strength, 1000 psi

Aggregate type

LimestoneQuartziteTraprockChert

Fig. 1-22. Effect of compressive strength and aggregate typeon the abrasion resistance of concrete (ASTM C 1138). High-strength concrete made with a hard aggregate is highlyresistant to abrasion (Liu 1981).

0

20

40

60

80

100

120

0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.500

Tim

e, m

inut

es

Depth of abrasion, mm

Dressing-wheel abrasion test

Traprocktopping

Traprock surfacetreatment

Metallic aggregatesurface treatment

Monolithic single-course slab

Fig. 1-23. Effect of hard steel troweling and surface treat-ments on the abrasion resistance of concrete (ASTM C 779).Base slab compressive strength was 40 MPa (6000 psi) at 28days. All slabs were steel troweled (Brinkerhoff 1970).

Fig. 1-24. Test apparatus for measuring abrasion resistanceof concrete. The machine can be adjusted to use eitherrevolving disks or dressing wheels. With a differentmachine, steel balls under pressure are rolled over thesurface of the specimen. The tests are described in ASTM C779. (44015)

of those ingredients, interactions between the ingredients,and placing and curing practices determine the ultimatedurability and life of the concrete.

Resistance to Freezing and Thawing

Concrete used in structures and pavements is expected tohave long life and low maintenance. It must have gooddurability to resist anticipated exposure conditions. Themost potentially destructive weathering factor is freezingand thawing while the concrete is wet, particularly in thepresence of deicing chemicals. Deterioration is caused bythe freezing of water and subsequent expansion in thepaste, the aggregate particles, or both.

With air entrainment, concrete is highly resistant to thistype of deterioration as shown in Fig. 1-25. During freezing,the water displaced by ice formation in the paste is accom-modated so that it is not disruptive; the microscopic airbubbles in the paste provide chambers for the water to enterand thus relieve the hydraulic pressure generated.

When freezing occurs in concrete containing saturatedaggregate, disruptive hydraulic pressures can also be gener-ated within the aggregate. Water displaced from the aggre-gate particles during the formation of ice cannot escape fastenough to the surrounding paste to relieve pressure.However, under most exposure conditions, a good-qualitypaste (low water-cement ratio) will prevent most aggregateparticles from becoming saturated. Also, if the paste is air-entrained, it will accommodate the small amounts of excesswater that may be expelled from aggregates, thus protectingthe concrete from freeze-thaw damage.

Fig. 1-26 illustrates, for a range of water-cement ratios,that (1) air-entrained concrete is much more resistant tofreeze-thaw cycles than non-air-entrained concrete, (2) con-crete with a low water-cement ratio is more durable than

factors, such as: (1) the amount of aggregate used; (2) prop-erties of the aggregate; (3) size and shape of the concreteelement; (4) relative humidity and temperature of theambient air; (5) method of curing; (6) degree of hydration;and (7) time.

Two basic causes of cracks in concrete are: (1) stressdue to applied loads and (2) stress due to drying shrinkageor temperature changes when concrete is restrained.

Drying shrinkage is an inherent, unavoidable propertyof concrete; therefore, properly positioned reinforcing steelis used to reduce crack widths, or joints are used to prede-termine and control the location of cracks. Thermal stressdue to fluctuations in ambient temperature also can causecracking, particularly at an early age.

Concrete shrinkage cracks can occur because ofrestraint. When drying shrinkage occurs and there is norestraint, the concrete does not crack. Restraint comesfrom several sources. Drying shrinkage is always greaternear the surface of concrete; the moist inner portionsrestrain the concrete near the surface, which can causecracking. Other sources of restraint are reinforcing steelembedded in concrete, the interconnected parts of aconcrete structure, and the friction of the subgrade onwhich concrete is placed.

Joints. Joints are the most effective method of controllingunsightly cracking. If a sizable expanse of concrete (a wall,slab, or pavement) is not provided with properly spacedjoints to accommodate drying shrinkage and temperaturecontraction, the concrete will crack in a random manner.

Contraction (shrinkage control) joints are grooved,formed, or sawed into sidewalks, driveways, pavements,floors, and walls so that cracking will occur in these jointsrather than in a random manner. Contraction joints permitmovement in the plane of a slab or wall. They extend to adepth of approximately one-quarter the concrete thickness.

Isolation joints separate a concrete placement fromother parts of a structure and permit horizontal and verti-cal movements. They should be used at the junction offloors with walls, columns, footings, and other pointswhere restraint can occur. They extend the full depth ofslabs and include a premolded joint filler.

Construction joints occur where concrete work isconcluded for the day; they separate areas of concreteplaced at different times. In slabs-on-ground, constructionjoints usually align with, and function as, control or isola-tion joints. They may require dowels for load transfer.

DURABILITY

The durability of concrete may be defined as the ability ofconcrete to resist weathering action, chemical attack, andabrasion while maintaining its desired engineering proper-ties. Different concretes require different degrees of dura-bility depending on the exposure environment and theproperties desired. The concrete ingredients, proportioning

12


Fig. 1-25. Air-entrained concrete (bottom bar) is highlyresistant to repeated freeze-thaw cycles. (P25542)

concrete with a high water-cement ratio, and (3) a dryingperiod prior to freeze-thaw exposure substantially bene-fits the freeze-thaw resistance of air-entrained concrete.Air-entrained concrete with a low water-cement ratioand an air content of 5% to 8% will withstand a greatnumber of cycles of freezing and thawing withoutdistress (Woods 1956).

Freeze-thaw durability can be determined by labora-tory test procedure ASTM C 666, Standard Test Method forResistance of Concrete to Rapid Freezing and Thawing(AASHTO T 161). From the test, a durability factor is calcu-lated that reflects the number of cycles of freezing andthawing required to produce a certain amount of deterio-ration. Deicer-scaling resistance can be determined byASTM C 672, Standard Test Method for Scaling Resistance ofConcrete Surfaces Exposed to Deicing Chemicals.

Alkali-Aggregate Reactivity

Alkali-aggregate reactivity is a type of concrete deteriora-tion that occurs when the active mineral constituents ofsome aggregates react with the alkali hydroxides in theconcrete. The reactivity is potentially harmful only when itproduces significant expansion. Alkali-aggregate reactivityoccurs in two forms—alkali-silica reaction (ASR) andalkali-carbonate reaction (ACR). Alkali-silica reaction is ofmore concern than alkali-carbonate reaction because theoccurrence of aggregates containing reactive silica mineralsis more common.

Indications of the presence of alkali-aggregate reactiv-ity may be a network of cracks, closed or spalling joints, ordisplacement of different portions of a structure (Fig. 1-27).Because deterioration due to alkali-aggregate reaction is aslow process, the risk of catastrophic failure is low. Alkali-aggregate reaction can cause serviceability problems andexacerbate other deterioration mechanisms, such as thosethat occur in frost, deicer, or sulfate exposures.

Current practices to control alkali-silica reactivityinclude the use of supplementary cementitious materials orblended cements proven by testing to control the reaction.Supplementary cementitious materials include fly ash,ground granulated blast-furnace slag, silica fume, andnatural pozzolans (Fig. 1-28). Blended cements also containthese materials to control alkali-silica reactivity. This prac-tice allows the use of locally available aggregates andcementitious materials. Reduction of the alkali content ofthe concrete can also control the reaction.

Use of supplementary cementitious materials orblended cements does not control alkali-carbonate reaction.Fortunately this reaction is rare. If aggregate testing indi-cates that an aggregate is susceptible to alkali-carbonatereactivity, the reaction can be controlled through the use ofselective quarrying, aggregate blending, reducing maxi-mum aggregate size, or using special chemical compoundsthat inhibit the reaction.

13


0

1000

2000

3000

4000

0

1000

2000

3000

4000

5000

6000

Air-entrainedconcrete

Non-air-entrainedconcrete

0.3 0.4 0.5 0.6 0.7 0.8 0.9

Cyc

les

of fr

eezi

ng a

nd th

awin

g to

25%

loss

in m

ass

Water-cement ratio, by mass

Fog cured 14 days

Dried 76 days at 50% RH

Fog cured 28 days

No drying period

Fig. 1-26. Relationship between freeze-thaw resistance,water-cement ratio, and drying for air-entrained and non-air-entrained concretes made with Type I cement. Highresistance to freezing and thawing is associated withentrained air, low water-cement ratio, and a drying periodprior to freeze-thaw exposure (Backstrom and others 1955).

Fig. 1-27. Cracking, joint closing, spalling, and lateral offsetare caused by severe alkali-silica reactivity in this parapetwall. (56586)

ACI 318 building code, provides reinforcing steel coverrequirements for different exposures.

Chloride Resistance and Steel Corrosion

Concrete protects embedded steel from corrosion through itshighly alkaline nature. The high pH environment in concrete(usually greater than 12.5) causes a passive and noncorrod-ing protective oxide film to form on steel. However, the pres-ence of chloride ions from deicers or seawater can destroy orpenetrate the film. Once the chloride corrosion threshold(about 0.15% water-soluble chloride by mass of cement) isreached, an electric cell is formed along the steel or betweensteel bars and the electrochemical process of corrosionbegins. Some steel areas along the bar become the anode,discharging current in the electric cell; from there the irongoes into solution. Steel areas that receive current are thecathodes where hydroxide ions are formed. The iron andhydroxide ions form iron hydroxide, FeOH, which furtheroxidizes to form rust (iron oxide). Rusting is an expansiveprocess—rust expands up to four times its originalvolume—which induces internal stress and eventualspalling of the concrete over reinforcing steel. The cross-sectional area of the steel can also be significantly reduced.

Once it starts, the rate of steel corrosion is influenced bythe concrete’s electrical resistivity, moisture content, and therate at which oxygen migrates through the concrete to thesteel. Chloride ions alone can also penetrate the passive film

See Farny and Kosmatka (1997) for more informationon alkali-silica reaction and alkali-carbonate reaction.

Carbonation

Carbonation of concrete is a process by which carbon diox-ide in the ambient air penetrates the concrete and reactswith the hydroxides, such as calcium hydroxide, to formcarbonates (Verbeck 1958). In the reaction with calciumhydroxide, calcium carbonate is formed. Carbonation andrapid drying of fresh concrete may affect surface durability,but this is prevented by proper curing. Carbonation ofhardened concrete does not harm the concrete matrix.However, carbonation significantly lowers the alkalinity(pH) of the concrete. High alkalinity is needed to protectembedded steel from corrosion; consequently, concreteshould be resistant to carbonation to help prevent steelcorrosion.

The amount of carbonation is significantly increased inconcrete that has a high water to cement ratio, low cementcontent, short curing period, low strength, and highlypermeable (porous) paste. The depth of carbonation ingood-quality, well-cured concrete is generally of little prac-tical significance as long as embedded steel has adequateconcrete cover (Fig. 1-29). Finished surfaces tend to haveless carbonation than formed surfaces. Carbonation offinished surfaces is often observed to a depth of 1 to 10 mm(0.04 to 0.4 in.) and for formed surfaces, between 2 and 20mm (0.1 and 0.9 in.) after several years of exposure,depending on the concrete properties, ingredients, age, andenvironmental exposure (Campbell, Sturm, and Kosmatka1991). ACI 201.2R, Guide to Durable Concrete, has moreinformation on atmospheric and water carbonation and the

14


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30 40

Exp

ansi

on a

t 30

mon

ths,

per

cent

Fly ash dosage, percent

Type II cement, alkali = 1.00%Class F fly ashRhyolitic reactive aggregateASTM C 227 mortar bars

Failure criterion

Fig. 1-28. Certain fly ashes at appropriate dosages cancontrol alkali-silica reactivity.

Fig. 1-29. Carbonation destroys concrete’s ability to protectembedded steel from corrosion. All concrete carbonates toa small depth, but reinforcing steel must have adequateconcrete cover to prevent carbonation from reaching thesteel. This reinforcing bar in a wall had less than 10 mm (0.4in.) of concrete cover; the ACI building code requires aminimum of 38 mm (11⁄2 in.). After years of outdoor exposure,the concrete carbonated to the depth of the bar, allowing thesteel to rust and spall the concrete surface. (68340)

on the reinforcement; they combine with iron ions to form asoluble iron chloride complex that carries the iron into theconcrete for later oxidation (rust) (Whiting 1997, Taylor,Whiting, and Nagi 2000 and Whiting, Taylor and Nagi 2002).

The resistance of concrete to chloride is good; however,it can be increased by using a low water-cement ratio (0.40),at least seven days of moist curing, and supplementarycementitious materials, such as silica fume, to reducepermeability. Increasing the concrete cover over the steelalso helps slow down the migration of chlorides.

Other methods of reducing steel corrosion include theuse of corrosion inhibiting admixtures, epoxy-coated rein-forcing steel (ASTM D 3963 or AASHTO M 284), surfacetreatments, concrete overlays, and cathodic protection.

Epoxy-coated reinforcing steel works by preventingchloride ions from reaching the steel (Fig. 1-30). Surfacetreatments and concrete overlays attempt to stop or reducechloride ion penetration at the concrete surface. Silanes,siloxanes, methacrylates, epoxies, and other materials areused as surface treatments.

Impermeable materials, such as most epoxies, shouldnot be used on slabs on ground or other concrete wheremoisture can freeze under the coating. The freezing watercan cause surface delamination under the impermeablecoating. Latex-modified portland cement concrete, low-slump concrete, and concrete with silica fume are used inoverlays to reduce chloride-ion ingress.

Cathodic protection methods reverse the corrosioncurrent flow through the concrete and reinforcing steel.This is done by inserting a nonstructural anode in theconcrete and forcing the steel to be the cathode by electri-cally charging the system. The anode is connected to thepositive pole of a rectifier. Since corrosion occurs where thecurrent leaves the steel, the steel cannot corrode if it isreceiving the induced current.

Chloride present in plain concrete (not containingsteel) is generally not a durability concern.

Corrosion of nonferrous metals in concrete is dis-cussed by Kerkhoff (2001).

Chemical Resistance

Portland cement concrete is resistant to most natural envi-ronments; however, concrete is sometimes exposed tosubstances that can attack and cause deterioration. Concretein chemical manufacturing and storage facilities is especiallyprone to chemical attack. The effect of sulfates and chloridesis discussed in this chapter. Acids attack concrete by dissolv-ing cement paste and calcareous aggregates. In addition tousing concrete with a low permeability, surface treatments canbe used to keep aggressive substances from coming in contactwith concrete. Effects of Substances on Concrete and Guide toProtective Treatments (Kerkhoff 2001) discusses the effects ofhundreds of chemicals on concrete and provides a list oftreatments to help control chemical attack.

Sulfate Attack

Excessive amounts of sulfates in soil or water can attackand destroy a concrete that is not properly designed.Sulfates (for example calcium sulfate, sodium sulfate, andmagnesium sulfate) can attack concrete by reacting withhydrated compounds in the hardened cement paste. Thesereactions can induce sufficient pressure to disrupt thecement paste, resulting in disintegration of the concrete(loss of paste cohesion and strength). Calcium sulfateattacks calcium aluminate hydrate and forms ettringite.Sodium sulfate reacts with calcium hydroxide and calciumaluminate hydrate forming ettringite and gypsum.Magnesium sulfate attacks in a manner similar to sodiumsulfate and forms ettringite, gypsum, and also brucite(magnesium hydroxide). Brucite forms primarily on theconcrete surface; it consumes calcium hydroxide, lowersthe pH of the pore solution, and then decomposes thecalcium silicate hydrates (Santhanam and others 2001).

Thaumasite may form during sulfate attack in moistconditions at temperatures usually between 0°C and 10°C(32°F to 50°F) and it occurs as a result of a reaction betweencalcium silicate hydrate, sulfate, calcium carbonate, andwater (Report of the Thaumasite Expert Group 1999). Inconcretes where deterioration is associated with excessthaumasite formation, cracks can be filled with thaumasiteand haloes of white thaumasite are present around aggre-gate particles. At the concrete/soil interface the surfaceconcrete layer can be “mushy” with complete replacementof the cement paste by thaumasite (Hobbs 2001).

Like natural rock formations such as limestone, porous concrete is susceptible to weathering caused by saltcrystallization. These salts may or may not contain sulfatesand they may or may not react with the hydratedcompounds in concrete. Examples of salts known to causeweathering of field concrete include sodium carbonate andsodium sulfate (laboratory studies have also related satu-rated solutions of calcium chloride and other salts toconcrete deterioration). The greatest damage occurs withdrying of saturated solutions of these salts, often in an envi-ronment with specific cyclic changes in relative humidityand temperature that alter mineralogical phases. In perme-able concrete exposed to drying conditions, salt solutions

15

Chapter 1 ◆ Fundamentals of Concrete

Fig. 1-30. Epoxy-coated reinforcing steel used in a bridgedeck. (69915)

For the best defense against external sulfate attack:(1) design concrete with a low water to cementitious mate-rials ratio (around 0.4), and (2) use cements speciallyformulated for sulfate environments, such as ASTM C 150(AASHTO M 85) Type II or V cements, C 595 (AASHTO M240) moderate sulfate resistant cements, or C 1157 TypesMS or HS. The superior sulfate resistance of ASTM C 150Type II and V cements is shown in Fig. 1-33.

can rise to the surface by capillary action and subse-quently—as a result of surface evaporation—the solutionphase becomes supersaturated and salt crystallizationoccurs, sometimes generating pressures large enough tocause cracking. If the rate of migration of the salt solutionthrough the pores is lower than the rate of evaporation, adrying zone forms beneath the surface and salt crystalliza-tion occurs in the pores causing expansion and scaling(Mehta 2000). Both aggregate particles and cement pastecan be attacked by salts.

Sulfate attack andsalt crystallization aremore severe at locationswhere the concrete isexposed to wetting anddrying cycles, than con-tinuously wet exposures.This is often seen inconcrete posts where theconcrete has deterioratedonly a few centimetersabove and below the soilline. The portion of con-crete deep in the soil(where it is continuouslywet) is in good condi-tion (Fig. 1-31 and 1-32).However, if the sul-fate exposure is severeenough, with time even

the continuously moist sections can be attacked by sulfatesif the concrete is not properly designed.

16


Fig. 1-32. Concrete beams after seven years of exposure to sulfate-rich wet soil in a Sacramento, California, test plot. The beamsin better condition have low water-cementitious materials ratios, and most have sulfate resistant cement. The inset shows twoof the beams tipped on their side to expose decreasing levels of deterioration with depth and moisture level. (66900, 58499)

Rating:1.0 = no deterioration5.0 = severe deterioration

5.0

4.0

3.0

2.0

1.0

0.3 0.4 0.5 0.6 0.7 0.8

Vis

ual r

atin

g

Water-cement ratio by mass

ASTM Type I

ASTM Type II

ASTM Type V

Fig. 1-33. Average 16-yr ratings of concrete beams in sulfatesoils for three portland cements at various water-cementratios (Stark 2002).

Fig. 1-31. Sulfate attack is oftenthe most severe at the locationof the most wetting and drying,which is usually near the soilline. Here concrete posts havebeen attacked by sulfates nearthe soil line. Also see the insetin Fig. 1-32. The concrete is inbetter condition deep within the soil where it is moist. (43093)

Seawater Exposures

Concrete has been used in seawater exposures for decadeswith excellent performance. However, special care in mixdesign and material selection is necessary for these severeenvironments. A structure exposed to seawater or seawaterspray is most vulnerable in the tidal or splash zone wherethere are repeated cycles of wetting and drying and/orfreezing and thawing. Sulfates and chlorides in seawaterrequire the use of low permeability concrete to minimizesteel corrosion and sulfate attack (Fig. 1-34).

A cement resistant to moderate sulfate exposure ishelpful. Portland cements with tricalcium aluminate (C3A)contents that range from 4% to 10% have been found toprovide satisfactory protection against seawater sulfateattack, as well as protection against corrosion of reinforce-ment by chlorides. Proper concrete cover over reinforcingsteel must be provided (see ACI 318). Water-cementitiousmaterial ratios should not exceed 0.40. In northernclimates, the concrete must be properly air entrained withat least 6% air. High-strength concrete should be consid-ered where large ice formations abrade the structure. SeeStark (1995 and 2001), Farny (1996), and Kerkhoff (2001).

fate within 24 hours (Klemm and Miller 1997). At this stageettringite is uniformly and discretely dispersed throughoutthe cement paste at a submicroscopic level (less than amicrometer in cross-section). This ettringite is often calledprimary ettringite.

If concrete is exposed to moisture for long periods oftime (many years), the ettringite can slowly dissolve andreform in less confined locations. Upon microscopic exam-ination, harmless white needle-like crystals of ettringite canbe observed lining air voids. This reformed ettringite isusually called secondary ettringite (Fig. 1-35).

Concrete deterioration accelerates the rate at whichettringite leaves its original location in the paste to go intosolution and recrystallize in larger spaces such as air voidsor cracks. Both water and sufficient space must be presentfor the crystals to form. Cracks can form due to damagecaused by frost action, alkali-aggregate reactivity, dryingshrinkage, thermal effects, strain due to excessive stress, orother mechanisms.

Ettringite crystals in air voids and cracks are typicallytwo to four micrometers in cross section and 20 to 30micrometers long. Under conditions of extreme deteriora-tion or decades in a moist environment, the white ettringitecrystals can appear to completely fill voids or cracks.However, secondary ettringite, as large needle-like crystals,should not be interpreted as being harmful to the concrete(Detwiler and Powers-Couche 1997).

Heat Induced Delayed Expansion. Heat induced delayedexpansion (HIDE)—also called delayed ettringite forma-tion (DEF)—refers to a rare condition of internal sulfateattack* in which mature concretes undergo expansion and

17


Fig. 1-34. Concrete bridges in seawater exposure must bespecially designed for durability. (68667)

Fig. 1-35. White secondary ettringite deposits in void. Fieldwidth 64µµm. (69547)

*Internal sulfate attack refers to deterioration mechanisms occurring inconnection with sulfate that is in the concrete at the time of placement.

Ettringite and Heat Induced Delayed Expansion

Ettringite, one form of calcium sulfoaluminate, is found inall portland cement paste. Calcium sulfate sources, such asgypsum, are added to portland cement during final grind-ing at the cement mill to prevent rapid setting and improvestrength development. Sulfate is also present in supple-mentary cementitious materials and admixtures. Gypsumand other sulfate compounds react with calcium aluminatein cement to form ettringite within the first few hours aftermixing with water. Most of the sulfate in cement isnormally consumed to form ettringite or calcium monosul-

REFERENCES

Abrams, D. A., Design of Concrete Mixtures, Lewis Institute,Structural Materials Research Laboratory, Bulletin No. 1,PCA LS001, http://www.portcement.org/pdf_files/LS001.pdf, 1918, 20 pages.

Abrams, M. S., and Orals, D. L., Concrete Drying Methodsand Their Effect on Fire Resistance, Research DepartmentBulletin RX181, Portland Cement Association, http://www.portcement.org/pdf_files/RX181.pdf, 1965.

ACI Committee 201, Guide to Durable Concrete, ACI 201.2R-92, American Concrete Institute, Farmington Hills,Michigan, 1992.

ACI Committee 318, Building Code Requirements forStructural Concrete and Commentary, ACI 318-02, AmericanConcrete Institute, Farmington Hills, Michigan, 2002.

ACI Manual of Concrete Practice, American ConcreteInstitute, Farmington Hills, Michigan, 2001.

Backstrom, J. E.; Burrow, R. W.; and Witte, L. P., Investigationinto the Effect of Water-Cement Ratio on the Freezing-ThawingResistance of Non-Air- and Air-Entrained Concrete, ConcreteLaboratory Report No. C-810, Engineering LaboratoriesDivision, U.S. Department of the Interior, Bureau ofReclamation, Denver, November 1955.

Brinkerhoff, C. H., “Report to ASTM C-9 Subcommittee III-M (Testing Concrete for Abrasion) Cooperative AbrasionTest Program,” University of California and PortlandCement Association, 1970.

cracking. Only concretes of particular chemical makeup areaffected when they have achieved high temperatures,usually after the first few hours of placement (between70°C and 100°C [158°F to 212°F] depending on the concreteingredients and the time the temperature is achieved aftercasting). This can occur because the high temperaturedecomposes any initial ettringite formed and holds thesulfate and alumina tightly in the calcium silicate hydrate(C-S-H) gel of the cement paste. The normal formation ofettringite is thus impeded.

In the presence of moisture, sulfate desorbs from theconfines of the C-S-H and reacts with calcium monosulfo-aluminate to form ettringite in cooled and hardenedconcrete. After months or years of desorption, ettringiteforms in confined locations within the paste. Such ettringitecan exert crystallization pressures because it forms in alimited space under supersaturation. One theory: sinceconcrete is rigid and if there are insufficient voids to accom-modate the ettringite volume increase, expansion andcracks can occur. In addition, some of the initial (primary)ettringite may be converted to monosulfoaluminate at hightemperatures and upon cooling revert back to ettringite.Because ettringite takes up more space than monosulfoalu-minate from which it forms, the transformation is an expan-sive reaction. The mechanism causing expansion in thepaste is not fully understood at this time; the true influenceof ettringite formation on this expansion is still being inves-tigated. Some research indicates that there is little relation-ship between ettringite formation and expansion.

As a result of an increase in paste volume, separationof the paste from the aggregates is usually observed withheat induced delayed expansion. It is characterized by thedevelopment of rims of ettringite around the aggregates(Fig. 1-36). At early stages of heat induced delayed expan-sion, the voids between paste and aggregate are empty (noettringite present). It should be noted that concrete cansustain a small amount of this expansion without harm.Only extreme cases result in cracking, and often heatinduced delayed expansion is associated with other deteri-oration mechanisms, especially alkali-silica reactivity.

Only concretes in massive elements that retain the heatof hydration or elements exposed to very high tempera-tures at an early age are at risk of HIDE; and of these onlya few have the chemical makeup or temperature profile tocause detrimental expansion. Normal sized concreteelements cast and maintained near ambient temperaturescannot experience HIDE when sound materials are used.

Fly ash and slag may help control heat induceddelayed expansion, along with control over early-agetemperature development. For more information, see Lerch(1945), Day (1992), Klemm and Miller (1997), Thomas(1998), and Famy (1999).

18

Design and Control of Concrete Mixtures ◆ EB001

Fig. 1-36. Heat induced delayed expansion is characterizedby expanding paste that becomes detached from non-expansive components, such as aggregates, creating gapsat the paste-aggregate interface. The gap can subsequentlybe filled with larger opportunistic ettringite crystals asshown here. Photo courtesy of Z. Zhang and J. Olek. (69154)

Bureau of Reclamation, Concrete Manual, 8th Edition, U.S.Bureau of Reclamation, Denver, 1981, page 33.

Burg, Ronald G., The Influence of Casting and CuringTemperature on the Properties of Fresh and Hardened Concrete,Research and Development Bulletin RD113, PortlandCement Association, 1996, 20 pages.

Campbell, Donald H.; Sturm, Ronald D.; and Kosmatka,Steven H., “Detecting Carbonation,” Concrete TechnologyToday, PL911, Portland Cement Association, http://www. portcement.org/pdf_files/PL911.pdf, March 1991, 5 pages.

Copeland, L. E., and Schulz, Edith G., Electron OpticalInvestigation of the Hydration Products of Calcium Silicates andPortland Cement, Research Department Bulletin RX135,Portland Cement Association, http://www.portcement.org/pdf_files/RX135.pdf, 1962, 12 pages.

Day, Robert L., The Effect of Secondary Ettringite Formation onthe Durability of Concrete: A Literature Analysis, Research andDevelopment Bulletin RD108, Portland Cement Asso-ciation, 1992, 126 pages.

Detwiler, Rachel J., and Powers-Couche, Laura, “Effect ofEttringite on Frost Resistance,” Concrete Technology Today,PL973, Portland Cement Association, http://www.portcement.org/pdf_files/PL973.pdf, 1997, pages 1 to 4.

Famy, Charlotte, Expansion of Heat-Cured Mortars, thesis,University of London, 1999, 310 pages.

Farny, Jamie, “Treat Island, Maine—The Army Corps’Outdoor Durability Test Facility,” Concrete Technology Today,PL963, http://www.portcement.org/pdf_files/PL963.pdf,December 1996, pages 1 to 3.

Farny, James A., and Kosmatka, Steven H., Diagnosis andControl of Alkali-Aggregate Reactions in Concrete, IS413,Portland Cement Association, 1997, 24 pages.

Feret, R., “Etudes Sur la Constitution Intime Des MortiersHydrauliques” [Studies on the Intimate Constitution ofHydraulic Mortars], Bulletin de la Societe d’EncouragementPour Industrie Nationale, 5th Series, Vol. 2, Paris, 1897, pages1591 to 1625.

Gonnerman, H. F., and Shuman, E. C., “Flexure andTension Tests of Plain Concrete,” Major Series 171, 209, and210, Report of the Director of Research, Portland CementAssociation, November 1928, pages 149 and 163.

Hanson, J. A., Effects of Curing and Drying Environments onSplitting Tensile Strength of Concrete, Development Depart-ment Bulletin DX141, Portland Cement Association,http://www.portcement.org/pdf_files/DX141.pdf, 1968,page 11.

Hedenblad, Göran, Drying of Construction Water in Concrete,T9, Swedish Council for Building Research, Stockholm,1997.

Hedenblad, Göran, “Concrete Drying Time,” ConcreteTechnology Today, PL982, Portland Cement Association,http://www.portcement.org/pdf_files/PL982.pdf, 1998,pages 4 to 5.

Hobbs, D. W., “Concrete deterioration: causes, diagnosis,and minimizing risk,” International Materials Review, 2001,pages 117 to 144.

Hsu, Thomas T. C., Torsion of Structural Concrete—PlainConcrete Rectangular Sections, Development DepartmentBulletin DX134, Portland Cement Association, http://www.portcement.org/pdf_files/DX134.pdf, 1968.

Kerkhoff, Beatrix, Effects of Substances on Concrete and Guideto Protective Treatments, IS001, Portland Cement Associa-tion, 2001, 36 pages.

Kirk, Raymond E., and Othmer, Donald F., eds., “Cement,”Encyclopedia of Chemical Technology, 3rd ed., Vol. 5, JohnWiley and Sons, Inc., New York, 1979, pages 163 to 193.

Klemm, Waldemar A., and Miller, F. MacGregor,“Plausibility of Delayed Ettringite Formation as a DistressMechanism—Considerations at Ambient and ElevatedTemperatures,” Paper 4iv059, Proceedings of the 10thInternational Congress on the Chemistry of Cement, Gothen-burg, Sweden, June 1997, 10 pages.

Kosmatka, Steven H., “Bleeding,” Significance of Tests andProperties of Concrete and Concrete-Making Materials, STP169C, American Society for Testing and Materials, WestConshohocken, Pennsylvania, 1994, pages 88 to 111. [Alsoavailable as PCA RP328].

Kosmatka, Steven H., Portland, Blended, and Other Hy-draulic Cements, IS004, Portland Cement Association, 2001,31 pages.

Lange, David A., Long-Term Strength Development ofConcrete, RP326, Portland Cement Association, 1994.

Lerch, William, Effect of SO3 Content of Cement on Durabilityof Concrete, R&D Serial No. 0285, Portland CementAssociation, 1945.

Liu, Tony C., “Abrasion Resistance of Concrete,” Journal ofthe American Concrete Institute, Farmington Hills, Michigan,September-October 1981, pages 341 to 350.

McMillan, F. R., and Lyse, Inge, “Some PermeabilityStudies of Concrete,” Journal of the American Concrete Insti-tute, Proceedings, vol. 26, Farmington Hills, Michigan,December 1929, pages 101 to 142.

McMillan, F. R., and Tuthill, Lewis H., Concrete Primer, SP-1,3rd ed., American Concrete Institute, Farmington Hills,Michigan, 1973.

Mehta, P. Kumar, “Sulfate Attack on Concrete: SeparatingMyth from Reality,” Concrete International, FarmingtonHills, Michigan, August 2000, pages 57 to 61.

19

Chapter 1 ◆ Fundamentals of Concrete

Stark, David, Durability of Concrete in Sulfate-Rich Soils, Re-search and Development Bulletin RD097, Portland CementAssociation, http://www.portcement.org/pdf_files/RD097.pdf, 1989, 16 pages.

Stark, David, Long-Time Performance of Concrete in a SeawaterExposure, RP337, Portland Cement Association, 1995,58 pages.

Stark, David, Long-Term Performance of Plain and ReinforcedConcrete in Seawater Environments, Research and Develop-ment Bulletin RD119, Portland Cement Association, 2001,14 pages.

Stark, David, Performance of Concrete in Sulfate Environ-ments, PCA Serial No. 2248, Portland Cement Association,2002.

Steinour, H. H., Further Studies of the Bleeding of PortlandCement Paste, Research Department Bulletin RX004, Port-land Cement Association, http://www.portcement.org/pdf_files/RX004.pdf, 1945.

Taylor, Peter C.; Whiting, David A.; and Nagi, MohamadA., Threshold Chloride Content for Corrosion of Steel inConcrete: A Literature Review, PCA Serial No. 2169, PortlandCement Association, http://www.portcement.org/pdf_files/SN2169.pdf, 2000.

Thomas, M. D. A., Delayed Ettringite Formation in Concrete—Recent Developments and Future Directions, University ofToronto, 1998, 45 pages.

Verbeck, G. J., Carbonation of Hydrated Portland Cement,Research Department Bulletin RX087, Portland CementAssociation, http://www.portcement.org/pdf_files/RX087.pdf, 1958, 20 pages.

Whiting, D., Origins of Chloride Limits for Reinforced Concrete,PCA Serial No. 2153, Portland Cement Association, http://www.portcement.org/pdf_files/SN2153.pdf, 1997.

Whiting, D., “Permeability of Selected Concretes,” Perme-ability of Concrete, SP108, American Concrete Institute,Farmington Hills, Michigan, 1989, pages 195 to 222.

Whiting, David A.; Taylor, Peter C.; and Nagi, Mohamad,A., Chloride Limits in Reinforced Concrete, PCA Serial No.2438, Portland Cement Association, http://www.portcement.org/pdf_files/SN2438.pdf, 2002.

Wood, Sharon L., Evaluation of the Long-Term Properties ofConcrete, Research and Development Bulletin RD102,Portland Cement Association, 1992, 99 pages.

Woods, Hubert, Observations on the Resistance of Concrete toFreezing and Thawing, Research Department Bulletin RX067,Portland Cement Association, http://www.portcement.org/pdf_files/RX067.pdf, 1956.

Pinto, Roberto C. A., and Hover, Kenneth C., Frost andScaling Resistance of High-Strength Concrete, Research andDevelopment Bulletin RD122, Portland CementAssociation, 2001, 70 pages.

Powers, T. C., “Studies of Workability of Concrete,” Journalof the American Concrete Institute, Vol. 28, Farmington Hills,Michigan, February 1932, page 419.

Powers, T. C., The Bleeding of Portland Cement Paste, Mortar,and Concrete, Research Department Bulletin RX002, Port-land Cement Association, http://www.portcement.org/pdf_files/RX002.pdf, 1939.

Powers, T. C., A Discussion of Cement Hydration in Relation tothe Curing of Concrete, Research Department BulletinRX025, Portland Cement Association, http://www.portcement.org/pdf_files/RX025.pdf, 1948, 14 pages.

Powers, T. C., The Nonevaporable Water Content of HardenedPortland Cement Paste—Its Significance for Concrete Researchand Its Method of Determination, Research DepartmentBulletin RX029, Portland Cement Association, http://www.portcement.org/pdf_files/RX029.pdf, 1949, 20 pages.

Powers, T. C., Topics in Concrete Technology, ResearchDepartment Bulletin RX174, Portland Cement Association,http://www.portcement.org/pdf_files/RX174.pdf, 1964.

Powers, T. C., The Nature of Concrete, Research DepartmentBulletin RX196, Portland Cement Association, http://www.portcement.org/pdf_files/RX196.pdf, 1966.

Powers, T. C., and Brownyard, T. L., Studies of the PhysicalProperties of Hardened Portland Cement Paste, ResearchDepartment Bulletin RX022, Portland Cement Association,http://www.portcement.org/pdf_files/RX022.pdf, 1947.

Powers, T. C.; Copeland, L. E.; Hayes, J. C.; and Mann,H. M., Permeability of Portland Cement Pastes, Research De-partment Bulletin RX053, Portland Cement Association,http://www.portcement.org/pdf_files/RX053.pdf, 1954.

Report of the Thaumasite Expert Group, The thaumasiteform of sulfate attack: Risks, diagnosis, remedial works andguidance on new construction, Department of the Environ-ment, Transport and the Regions, DETR, London, 1999.

Santhanam, Manu; Cohen, Menahi D.; and Olek, Jan, “Sul-fate attack research—whither now?,” Cement and ConcreteResearch, 2001, pages 845 to 851.

Scanlon, John M., “Factors Influencing Concrete Work-ability,” Significance of Tests and Properties of Concrete andConcrete-Making Materials, STP 169C, American Society forTesting and Materials, West Conshohocken, Pennsylvania,1994, pages 49 to 64.

20


Portland cements are hydraulic cements composed prima-rily of hydraulic calcium silicates (Fig. 2-1). Hydrauliccements set and harden by reacting chemically with water.During this reaction, called hydration, cement combineswith water to form a stonelike mass, called paste. When thepaste (cement and water) is added to aggregates (sand andgravel, crushed stone, or other granular material) it acts asan adhesive and binds the aggregates together to formconcrete, the world’s most versatile and most widely usedconstruction material.

Hydration begins as soon as cement comes in contactwith water. Each cement particle forms a fibrous growth onits surface that gradually spreads until it links up with thegrowth from other cement particles or adheres to adjacentsubstances. This fibrous build up results in progressivestiffening, hardening, and strength development. The stiff-ening of concrete can be recognized by a loss of workabil-ity that usually occurs within three hours of mixing, but isdependent upon the composition and fineness of thecement, any admixtures used, mixture proportions, andtemperature conditions. Subsequently, the concrete setsand becomes hard.

Hydration continues as long as favorable moisture andtemperature conditions exist (curing) and space for hydra-tion products is available. As hydration continues, concrete

CHAPTER 2

Portland, Blended, and Other Hydraulic Cements

becomes harder and stronger. Most of the hydration andstrength development take place within the first month,but then continues, though more slowly, for a long timewith adequate moisture and temperature. Continuousstrength increases exceeding 30 years have been recorded(Washa and Wendt 1975 and Wood 1992).

THE BEGINNING OF AN INDUSTRY

Early builders used clay to bind stones together into a solidstructure for shelter and protection. The oldest concrete dis-covered so far dates from around 7000 BC and was found in1985 when a concrete floor was uncovered during the con-struction of a road at Yiftah El in Galilee, Israel. It consistedof a lime concrete, made from burning limestone to producequicklime, which when mixed with water and stone, hard-ened to form concrete (Brown 1996 and Auburn 2000).

A cementing material was used between the stoneblocks in the construction of the Great Pyramid at Gizain Ancient Egypt around 2500 BC. Some reports say it wasa lime mortar while others say the cementing material wasmade from burnt gypsum. By 500 BC, the art of making lime-based mortar arrived in Ancient Greece. The Greeks usedlime-based mate-rials as a binderbetween stone andbrick and as arendering materialover porous lime-stones commonlyused in the con-struction of theirtemples and pal-aces.

Examples ofearly Roman con-crete have beenfound dating backto 300 BC. Thevery word con-

Fig. 2-1. Portland cement is a fine powder that when mixedwith water becomes the glue that holds aggregates togetherin concrete. (58420)

Fig. 2-2. Isle of Portland quarry stone(after which portland cement wasnamed) next to a cylinder of modernconcrete. (68976)

21

22


Fig. 2-3. Steps in the traditional manufacture of portland cement.

23

Chapter 2 � Portland, Blended, and Other Hydraulic Cements

Fig. 2-4. Steps in the modern dry-process manufacture of portland cement.

Aspdin was the first to prescribe a formula for port-land cement and the first to have his product patented.However, in 1845, I. C. Johnson, of White and Sons, Swans-combe, England, claimed to have “burned the cement rawmaterials with unusually strong heat until the mass wasnearly vitrified,” producing a portland cement as we nowknow it. This cement became the popular choice during themiddle of the 19th century and was exported from Englandto various parts of the world. Production also began inBelgium, France, and Germany about the same time andexport of these products from Europe to North Americabegan about 1865. The first recorded shipment of portlandcement to the United States was in 1868. The first portlandcement manufactured in the United States was produced ata plant in Coplay, Pennsylvania, in 1871.

MANUFACTURE OF PORTLAND CEMENT

Portland cement is produced by pulverizing clinker whichconsists primarily of hydraulic calcium silicates. Clinkeralso contains some calcium aluminates and calcium alu-minoferrites and one or more forms of calcium sulfate(gypsum) is interground with the clinker to make thefinished product.

Materials used in the manufacture of portland cementmust contain appropriate amounts of calcium, silica,alumina, and iron components. During manufacture,chemical analyses of all materials are made frequently toensure a uniformly high quality cement.

Steps in the manufacture of cement are illustrated inthe flow charts in Figs. 2-3 and 2-4. While the operations ofall cement plants are basically the same, no flow diagramcan adequately illustrate all plants. There is no typical port-land cement manufacturing facility; every plant has signif-icant differences in layout, equipment, or general ap-pearance (Fig. 2-5).

Selected raw materials (Table 2-1) are transported fromthe quarry (Fig. 2-6), crushed (Fig. 2-7), milled, and propor-tioned so that the resulting mixture has the desired chemi-cal composition. The raw materials are generally a mixture

crete is derived from the Latin word “concretus” meaninggrown together or compounded. The Romans perfected theuse of pozzolan as a cementing material. Sometime duringthe second century BC the Romans quarried a volcanic ashnear Pozzuoli; thinking it was sand, they mixed it with limeand found the mixture to be much stronger than they hadproduced previously. This discovery was to have a signifi-cant effect on construction. The material was not sand, buta fine volcanic ash containing silica and alumina, whichwhen combined chemically with lime, produced whatbecame known as pozzolanic cement. This material wasused by builders of the famous Roman walls, aqueductsand other historic structures including the Theatre atPompeii (seating 20,000 spectators), and the Colosseumand Pantheon in Rome. Pozzolan seems to have beenignored during the Middle Ages when building practiceswere much less refined than earlier and the quality ofcementing materials deteriorated. The practice of burninglime and the use of pozzolan was not introduced againuntil the 1300s.

Efforts to determine why some limes possess hy-draulic properties while others (those made from essen-tially pure limestones) do not were not made until the 18thcentury. John Smeaton, often referred to as the “father ofcivil engineering in England,” concentrated his work inthis field. He found that an impure, soft limestone, contain-ing clay minerals made the best hydraulic cement. Thiscombined with a pozzolan, imported from Italy, was usedin his project to rebuild the Eddystone Lighthouse in theEnglish Channel, southwest of Plymouth England. Theproject took three years to complete and began operation in1759; it was recognized as a significant accomplishment inthe development of the cement industry. A number ofdiscoveries followed as efforts within a growing naturalcement industry were now directed to the production of aconsistent quality material.

The difference between a hydraulic lime and naturalcement is a function of the temperature attained duringcalcination. Furthermore, a hydraulic lime can hydrate in a“lump” form, whereas natural cements must be crushedand finely ground before hydration can take place. Naturalcement is stronger than hydraulic lime but weaker thanportland cement. Natural cement was manufactured inRosendale, New York in the early 1800s (White 1820) andwas first used to build the Erie Canal in 1818 (Snell andSnell 2000).

The development of portland cement was the result ofpersistent investigation by science and industry to producea superior quality natural cement. The invention of port-land cement is generally credited to Joseph Aspdin, anEnglish mason. In 1824, he obtained a patent for his prod-uct, which he named portland cement because when set, itresembled the color of the natural limestone quarried onthe Isle of Portland in the English Channel (Fig. 2-2)(Aspdin 1824). The name has endured and is used through-out the world, with many manufacturers adding their owntrade or brand names.

24


Fig. 2-5. Aerial view of a cement plant. (70000)

the kiln at a rate controlled by the slope and rotationalspeed of the kiln. Burning fuel (powdered coal, new orrecycled oil, naturalgas, rubber tires, andby-product fuel) isforced into the lowerend of the kilnwhere temperaturesof 1400°C to 1550°Cchange the rawmaterial chemicallyinto cement clinker,grayish-black pel-lets predominantlythe size of marbles(Fig. 2-9). Fig. 2-10

of calcareous (cal-cium carbonatebearing) material,such as limestone,

and an argillaceous (silica and alumina) material such asclay, shale, fly ash, or blast-furnace slag. Either a dry or awet process is used. In the dry process, grinding and blend-ing are done with dry materials. In the wet process, thegrinding and blending operations are done with the mate-rials mixed with water in a slurry form. In other respects,the dry and wet processes are very much alike. Fig. 2-4illustrates important technological developments that canimprove significantly the productivity and energy effi-ciency of dry-process plants.

After blending, the ground raw material is fed into theupper end of a kiln (Fig. 2-8). The raw mix passes through

25


Fig. 2-7. Quarry rock is trucked to theprimary crusher. (59893)

Fig. 2-6. Limestone, a primary rawmaterial providing calcium in makingcement, is quarried near the cementplant. (59894)

Table 2-1. Sources of Raw Materials Used in Manufacture of Portland Cement

Calcium Iron Silica Alumina SulfateAlkali waste Blast-furnace flue dust Calcium silicate Aluminum-ore refuse* AnhydriteAragonite* Clay* Cement rock Bauxite Calcium sulfateCalcite* Iron ore* Clay* Cement rock Gypsum*Cement-kiln dust Mill scale* Fly ash Clay*Cement rock Ore washings Fuller’s earth Copper slagChalk Pyrite cinders Limestone Fly ash*Clay Shale Loess Fuller’s earthFuller’s earth Marl* GranodioriteLimestone* Ore washings LimestoneMarble Quartzite LoessMarl* Rice-hull ash Ore washingsSeashells Sand* Shale*Shale* Sandstone SlagSlag Shale* Staurolite

SlagTraprock

Note: Many industrial byproducts have potential as raw materials for the manufacture of portland cement.*Most common sources.

Fig. 2-8. Rotary kiln (furnace) for manufacturing portland cement clinker. Insetview inside the kiln. (58927, 25139)

Fig. 2-9. Portland cement clinker isformed by burning calcium and sil-iceous raw materials in a kiln. Thisparticular clinker is about 20 mm (3⁄4in.) in diameter. (60504)

26


Fig. 2-10. Process of clinker production from raw feed to the final product (Hills 2000).

shows the clinkerproduction processfrom raw feed to thefinal product.

The clinker iscooled and thenpulverized. Duringthis operation asmall amount ofgypsum (Fig. 2-11)is added to regulatethe setting time ofthe cement and to

improve shrinkage and strength development properties(Lerch 1946 and Tang 1992). In the grinding mill, clinker isground so fine that nearly all of it passes through a 45micrometer (No. 325 mesh) sieve. This extremely fine graypowder is portland cement (Fig. 2-1).

TYPES OF PORTLAND CEMENT

Different types of portland cement are manufactured tomeet various normal physical and chemical requirementsfor specific purposes. Portland cements are manufacturedto meet the specifications of ASTM C 150, AASHTO M 85,or ASTM C 1157.

ASTM C 150, Standard Specification for Portland Cement,provides for eight types of portland cement using Romannumeral designations as follows:

Type I NormalType IA Normal, air-entrainingType II Moderate sulfate resistanceType IIA Moderate sulfate resistance, air-entrainingType III High early strengthType IIIA High early strength, air-entrainingType IV Low heat of hydrationType V High sulfate resistanceAASHTO M 85, Specification for Portland Cement, also

uses type designations I through V for portland cement. Therequirements of M 85 are almost identical to ASTM C 150.AASHTO specifications are used by some state depart-ments of transportation in lieu of ASTM standards.

ASTM C 1157, Performance Specification for HydraulicCements, provides for six types of portland cement asdiscussed under “Hydraulic Cements” below.

A detailed review of ASTM C 150 and AASHTO M 85cements follows.

Type I

Type I portland cement is a general-purpose cement suit-able for all uses where the special properties of other typesare not required. Its uses in concrete include pavements,floors, reinforced concrete buildings, bridges, tanks, reser-voirs, pipe, masonry units, and precast concrete products(Fig. 2-12).

Type II

Type II portland cement is used where precaution againstmoderate sulfate attack is important. It is used in normalstructures or elements exposed to soil or ground waterswhere sulfate concentrations are higher than normal butnot unusually severe (see Table 2-2, and Figs. 2-13 to Fig.2-15). Type II cement has moderate sulfate resistant prop-erties because it contains no more than 8% tricalciumaluminate (C3A).

Sulfates in moist soil or water may enter the concreteand react with the hydrated C3A, resulting in expansion,scaling, and cracking of concrete. Some sulfate compounds,such as magnesium sulfate, directly attack calcium silicatehydrate.

Use of Type II cement in concrete must be accompa-nied by the use of a low water to cementitious materialsratio and low permeability to control sulfate attack. Fig.2-13 (top) illustrates the improved sulfate resistance ofType II cement over Type I cement.

Concrete exposed to seawater is often made withType II cement. Seawater contains significant amounts ofsulfates and chlorides. Although sulfates in seawater arecapable of attacking concrete, the presence of chloridesinhibits the expansive reaction that is characteristic ofsulfate attack. Chloride competes with sulfate for thealuminate phases, after which they exist together in the

27


Fig. 2-11. Gypsum, a source of sulfate,is interground with portland clinker toform portland cement. It helps controlsetting, drying shrinkage properties,and strength development. (60505)

Fig. 2-12. Typical uses for normal or general use cements include (left to right) highway pavements, floors, bridges, andbuildings. (68815, 68813, 63303, 68809)

0 2 4 6 8 10 12 14 16Age, years

1

2

3

4

5

Vis

ual r

atin

g

w/c = 0.38

w/c = 0.47w/c = 0.68

concrete. The reaction products of sulfate attack are alsomore soluble in a chloride solution and can leach out of theconcrete. Observations from a number of sources showthat the performance of concretes in seawater with port-land cements having C3A contents as high as 10%, haveshown satisfactory durability, providing the permeabilityof the concrete is low and the reinforcing steel hasadequate cover.

Type II cements specially manufactured to meet themoderate heat option of ASTM C 150 (AASHTO M 85) willgenerate heat at a slower rate than Type I or most Type IIcements. The requirement of moderate heat of hydrationcan be specified at the option of the purchaser. A cement inwhich heat-of-hydration maximums are specified can beused in structures of considerable mass, such as large piers,large foundations, and thick retaining walls (Fig. 2-16). Itsuse will reduce temperature rise and temperature relatedcracking, which is especially important when concrete isplaced in warm weather.

Because of its increased availability, Type II cement issometimes used in all aspects of construction, regardless ofthe need for sulfate resistance or moderate heat genera-tion. Some cements may be labeled with more than onetype designation, for example Type I/II. This simplymeans that such a cement meets the requirements of bothcement Types I and II.

Type III

Type III portland cement provides strength at an earlyperiod, usually a week or less. It is chemically and physi-cally similar to Type I cement, except that its particles havebeen ground finer. It is used when forms need to beremoved as soon as possible or when the structure must beput into service quickly. In cold weather its use permits areduction in the length of the curing period (Fig. 2-17).Although higher-cement content mixes of Type I cementcan be used to gain high early strength, Type III mayprovide it easier and more economically.

28


0 2 4 6 8 10 12 14 16Age, years

1

2

3

4

5

Vis

ual r

atin

g

ASTM Type Vw/c = 0.37

ASTM Type IIw/c = 0.38

ASTM Type Iw/c = 0.39

Cement content = 390 kg/m3 (658 lbs/yd3)

Fig. 2-13. (top) Performance of concretes made with differentcements in sulfate soil. Type II and Type V cements have lowerC3A contents that improve sulfate resistance. (bottom) Im-proved sulfate resistance results from low water to cemen-titious materials ratios as demonstrated over time for concretebeams exposed to sulfate soils in a wetting and drying envi-ronment. Shown are average values for concretes containing awide range of cementitious materials, including cement TypesI, II, V, blended cements, pozzolans, and slags. See Fig. 2-15 forrating illustration and a description of the concrete beams(Stark 2002).

Table 2-2. Types of Cement Required for Concrete Exposed to Sulfates in Soil or Water

Minimum designWater-soluble Maximum water- compressive

Sulfate sulfate (SO4) in soil, Sulfate (SO4) cementitious material strength,exposure percent by mass in water, ppm Cement type** ratio, by mass f'c, MPa (psi)

Negligible Less than 0.10 Less than 150 No special type required — —

Moderate* 0.10 to 0.20 150 to 1500 II, MS, IP(MS), IS(MS), P(MS), 0.50 28 (4000)I(PM)(MS), I(SM)(MS)

Severe 0.20 to 2.00 1500 to10,000 V, HS 0.45 31 (4500)

Very severe Over 2.00 Over 10,000 V, HS 0.40 35 (5000)

* Seawater.** Pozzolans or slags that have been determined by test or service record to improve sulfate resistance may also be used.

Test method: Method for Determining the Quantity of Soluble Sulfate in Solid (Soil or Rock) and Water Samples, Bureau of Reclamation, 1977. Source: Adapted from Bureau of Reclamation 1981 and ACI 318.

Type IV

Type IV portland cement is used where the rate andamount of heat generated from hydration must be mini-mized. It develops strength at a slower rate than othercement types. Type IV cement is intended for use inmassive concrete structures, such as large gravity dams,where the temperature rise resulting from heat generated

during hardening must be minimized (Fig. 2-16). Type IVcement is rarely available.

Type V

Type V portland cement is used in concrete exposed tosevere sulfate action—principally where soils or ground-waters have a high sulfate content (Figs. 2-13 to 2-15). Itgains strength more slowly than Type I cement. Table 2-2lists sulfate concentrations requiring the use of Type Vcement. The high sulfate resistance of Type V cement isattributed to a low tricalcium aluminate content, not morethan 5%. Use of a low water to cementitious materials ratioand low permeability are critical to the performance of anyconcrete exposed to sulfates. Even Type V cement concretecannot withstand a severe sulfate exposure if the concretehas a high water to cementitious materials ratio (Fig. 2-15

29


Fig. 2-14. Moderate sulfate resistant cements and high sulfate resistant cements improve the sulfate resistance of concreteelements, such as (left to right) slabs on ground, pipe, and concrete posts exposed to high-sulfate soils. (68985, 52114, 68986)

Fig. 2-15. Specimens used in the outdoor sulfate test plot inSacramento, California, are 150 x 150 x 760-mm (6 x 6 x 30-in.)beams. A comparison of ratings is illustrated: (top) a rating of5 for 12-year old concretes made with Type V cement and awater-to-cement ratio of 0.65; and (bottom) a rating of 2 for 16-year old concretes made with Type V cement and a water-to-cement ratio of 0.39 (Stark 2002). (68840, 68841)

Fig. 2-16. Moderate heat and low heat cements minimize heatgeneration in massive elements or structures such as (left)very thick bridge supports, and (right) dams. Hoover dam,shown here, used a Type IV cement to control temperaturerise. (65258, 68983)

White Portland Cements

White portland cement is a true portland cement thatdiffers from gray cement chiefly in color. It is made toconform to the specifications of ASTM C 150, usually TypeI or Type III; the manufacturing process is controlled so thatthe finished product will be white. White portland cementis made of selected raw materials containing negligibleamounts of iron and magnesium oxides—the substancesthat give cement its gray color. White portland cement isused primarily for architectural purposes in structuralwalls, precast and glass fiber reinforced concrete (GFRC)facing panels, terrazzo surfaces, stucco, cement paint, tilegrout, and decorative concrete (Fig. 2-18). Its use is recom-mended wherever white or colored concrete, grout, ormortar is desired. White portland cement should be speci-fied as: white portland cement meeting the specifications ofASTM C 150, Type [I, II, III, or V]. White cement is also usedto manufacture white masonry cement meeting ASTM C 91and white plastic cement meeting ASTM C 1328 (PCA1999). White cement was first manufactured in the UnitedStates in York, Pennsylvania in 1907. See Farny (2001) formore information.

top). Type V cement, like other portland cements, is notresistant to acids and other highly corrosive substances.

ASTM C 150 (AASHTO M 85) allows both a chemicalapproach and a physical approach (ASTM C 452 expansiontest) to assure the sulfate resistance of Type V cement.Either the chemical or the physical approach can be speci-fied, but not both.

Air-Entraining Portland Cements

Specifications for three types of air-entraining portlandcement (Types IA, IIA, and IIIA) are given in ASTM C 150and AASHTO M 85. They correspond in composition toASTM Types I, II, and III, respectively, except that smallquantities of air-entraining material are interground withthe clinker during manufacture. These cements produceconcrete with improved resistance to freezing and thawing.Such concrete contains minute, well-distributed, and com-pletely separated air bubbles. Air entrainment for mostconcretes is achieved through the use of an air-entrainingadmixture, rather than through the use of air-entrainingcements. Air-entraining cements are available only incertain areas.

30


Fig. 2-17. High early strength cements are used where early concrete strength is needed, such as in (left to right) cold weatherconcreting, fast track paving to minimize traffic congestion, and rapid form removal for precast concrete. (65728, 59950, 68668)

Fig. 2-18. White portland cement is used in white or light-colored architectural concrete, ranging from (left to right) terrazzo forfloors shown here with white cement and green granite aggregate (68923), to decorative and structural precast and cast-in-place elements (68981), to building exteriors. The far right photograph shows a white precast concrete building housing theASTM Headquarters in West Conshohocken, Pennsylvania. Photo courtesy of ASTM.

BLENDED HYDRAULIC CEMENTS

Blended cements are used in all aspects of concreteconstruction in the same manner as portland cements.Blended cements can be used as the only cementitiousmaterial in concrete or they can be used in combinationwith other supplementary cementitious materials added atthe concrete plant. Blended cements are often designed tobe used in combination with local pozzolans and slags. If ablended cement or portland cement is used alone or incombination with added pozzolans or slags, the concreteshould be tested for strength, durability, and other proper-ties required in project specifications (PCA 1995 andDetwiler, Bhatty, and Bhattacharja 1996).

Blended hydraulic cements are produced by inti-mately and uniformly intergrinding or blending two ormore types of fine materials. The primary materials areportland cement, ground granulated blast-furnace slag, flyash, silica fume, calcined clay, other pozzolans, hydratedlime, and preblended combinations of these materials (Fig.2-19). Blended hydraulic cements must conform to therequirements of ASTM C 595 (AASHTO M 240), Specifi-cation for Blended Hydraulic Cements, or ASTM C 1157, Per-formance Specification for Hydraulic Cement.

ASTM C 595 recognizes five primary classes ofblended cements as follows:

Type IS Portland blast-furnace slag cement Type IP and Type P Portland-pozzolan cement Type I(PM) Pozzolan-modified portland cement Type S Slag cement Type I(SM) Slag-modified portland cement

Types IS, IP, P, I(PM), and I(SM) are general purposecements (Fig. 2-12); these and subcategory types are re-viewed in the discussion below.

AASHTO M 240 also uses the above class designationsfor blended cement. The requirements of M 240 are almostidentical to those in ASTM C 595.

ASTM C 1157 provides for six types of blended cementas discussed under “Hydraulic Cements” below. Blendedcements meeting the requirements of C 1157 meet physicalperformance test requirements without prescriptive restric-tions on ingredients or cement chemistry. This allows thecement manufacturer to optimize strength and durabilityproperties through use of a variety of cementitious materi-als, such as portland clinker, fly ash, slag, silica fume, andcalcined clay (Fig. 2-19).

A detailed review of ASTM C 595 and AASHTO M 240blended cements follows:

Type IS

Portland blast-furnace slag cement, Type IS, may be used ingeneral concrete construction. Historical use of slag blendedcements dates back to the beginning of the 20th century inEurope, Japan, and North America (Abrams 1925). Inproducing these cements, granulated blast-furnace slag iseither interground with portland cement clinker, separatelyground and blended with portland cement, or producedwith a combination of intergrinding and blending. Theblast-furnace slag content of this cement is between 25%and 70% by mass. Subcategory types (optional special prop-erties) such as air-entrainment, moderate sulfate resistance,or moderate heat of hydration may be specified by addingthe suffixes A, MS, or MH. For example, an air-entrainingportland blast-furnace slag cement that has moderatesulfate resistance would be designated as Type IS-A(MS).See Klieger and Isberner (1967) and PCA (1995).

Type IP and Type P

Portland-pozzolan cements are designated as Type IP orType P. Type IP may be used for general construction andType P is used in construction not requiring high earlystrengths. These cements are manufactured by intergrind-ing portland cement clinker with a suitable pozzolan, byblending portland cement or portland blast-furnace slagcement and a pozzolan, or by a combination of intergrind-ing and blending. The pozzolan content of these cements isbetween 15% and 40% by mass. Laboratory tests indicatethat performance of concrete made with Type IP cement asa group is similar to that of Type I cement concrete. Type IPmay be designated as air-entraining, moderate sulfateresistant, or with moderate heat of hydration by adding thesuffixes A, MS, or MH. Type P may be designated as lowheat of hydration (LH), moderate sulfate resistant (MS), orair entraining (A).

Type I (PM)Pozzolan-modified portland cement, Type I(PM), is used ingeneral concrete construction. The cement is manufactured

31


Fig. 2-19. Blended cements (ASTM C 595, AASHTO M 240, andASTM C 1157) use a combination of portland cement or clinkerand gypsum blended or interground with pozzolans, slag, orfly ash. ASTM C 1157 allows the use and optimization of allthese materials, simultaneously if necessary, to make acement with optimal properties. Shown is blended cement(center) surrounded by (right and clockwise) clinker, gypsum,portland cement, fly ash, slag, silica fume, and calcined clay.(68988)

chemistry as found in other cement specifications. ASTM C1157 provides for six types of hydraulic cement as follows:

Type GU General useType HE High early strengthType MS Moderate sulfate resistanceType HS High sulfate resistanceType MH Moderate heat of hydrationType LH Low heat of hydration

In addition, these cements can also have an Option R—Low Reactivity with Alkali-Reactive Aggregates—speci-fied to help control alkali-silica reactivity. For example,Type GU-R would be a general use hydraulic cement withlow reactivity with alkali-reactive aggregates.

When specifying a C 1157 cement, the specifier usesthe nomenclature of “hydraulic cement,” “portlandcement,” “air-entraining portland cement,” “modifiedportland cement” or “blended hydraulic cement” alongwith a type designation. For example, a specification maycall for a Hydraulic Cement Type GU, a Blended HydraulicCement Type MS, or a Portland Cement Type HS. If a typeis not specified, then Type GU is assumed.

ASTM C 1157 defines a blended cement as having morethan 15% mineral additive and a modified portland cementas containing up to 15% mineral additive. The mineral addi-tive usually prefixes the modified portland cement nomen-clature, for example, slag-modified portland cement.

ASTM C 1157 also allows a strength range to be speci-fied from a table in the standard. If a strength range is notspecified, only the minimum strengths apply. Strengthranges are rarely applied in the United States.

A detailed review of ASTM C 1157 cements follows:

Type GUType GU is a general-purpose cement suitable for all useswhere the special properties of other types are not required.Its uses in concrete include pavements, floors, reinforcedconcrete buildings, bridges, pipe, precast concrete products,and other applications where Type I is used (Fig. 2-12).

Type HEType HE cement provides higher strengths at an early age,usually a week or less. It is used in the same manner as TypeIII portland cement (Fig. 2-17).

Type MSType MS cement is used where precaution against moderatesulfate attack is important, as in drainage structures where sul-fate concentrations in ground waters are higher than normalbut not unusually severe (see Table 2-2). It is used in the samemanner as Type II portland cement (Fig. 2-14). Like Type II,Type MS cement concrete must be made with a low water-cementitious materials ratio to provide sulfate resistance.

by combining portland cement or portland blast-furnaceslag cement and a fine pozzolan. This may be accom-plished by either (1) blending portland cement with apozzolan, (2) blending portland blast-furnace slag cementwith a pozzolan, (3) intergrinding portland cement clinkerand a pozzolan, or (4) a combination of intergrinding andblending. The pozzolan content is less than 15% by mass ofthe finished cement. Air-entrainment, moderate sulfateresistance, or moderate heat of hydration may be desig-nated in any combination by adding the suffixes A, MS, orMH. An example of an air-entraining, moderate-heat-of-hydration Type I(PM) cement would be designated as TypeI (PM)-A(MH).

Type SSlag cement, Type S, is used with portland cement inmaking concrete or with lime in making mortar, but is notused alone in structural concrete. Slag cement is manufac-tured by either (1) blending ground granulated blast-furnace slag and portland cement, (2) blending groundgranulated blast-furnace slag and hydrated lime, or (3)blending a combination of ground granulated blast-furnace slag, portland cement, and hydrated lime. Theminimum slag content is 70% by mass of the slag cement.Air-entrainment may be designated in a slag cement byadding the suffix A, for example, Type S-A.

Type I (SM)Slag-modified portland cement, Type I(SM), is used forgeneral concrete construction. This cement is manufac-tured by either (1) intergrinding portland cement clinkerand granulated blast-furnace slag, (2) blending portlandcement and finely ground granulated blast-furnace slag, or(3) a combination of intergrinding and blending. Slag is lessthan 25% by mass of the finished cement. Type I(SM) maybe designated with air-entrainment, moderate sulfateresistance, or moderate heat of hydration by adding thesuffixes A, MS, or MH. An example would be Type I(SM)-A(MH) for an air-entraining, slag-modified portland ce-ment with moderate heat of hydration.

HYDRAULIC CEMENTSHydraulic cements set and harden by reacting chemicallywith water. They also stay hard and maintain their stabilityunder water. They are used in all aspects of concrete con-struction. All portland and blended cements are hydrauliccements. “Hydraulic cement” is merely a broader term. Seealso ASTM C 219 for terms relating to hydraulic cements.

The 1990s saw the creation of a performance specifica-tion for hydraulic cements—ASTM C 1157, PerformanceSpecification for Hydraulic Cements. This specification is de-signed generically for hydraulic cement to include port-land cement, modified portland cement, and blendedhydraulic cement. Cements meeting the requirements of C1157 meet physical performance test requirements, as op-posed to prescriptive restrictions on ingredients or cement

32


Type HS

Type HS cement is used in concrete exposed to severe sulfateaction—principally where soils or ground waters have ahigh sulfate content (see Table 2-2). It is used in the samemanner as Type V portland cement (Fig. 2-14).

Type MH

Type MH cement is used where the concrete needs to havea moderate heat of hydration and a controlled temperaturerise. Type MH cement is used in the same manner as amoderate heat Type II portland cement (Fig. 2-16).

Type LH

Type LH cement is used where the rate and amount of heatgenerated from hydration must be minimized. It developsstrength at a slower rate than other cement types. Type LHcement is intended for use in massive concrete structureswhere the temperature rise resulting from heat generatedduring hardening must be minimized. It is used in thesame manner as Type IV portland cement (Fig. 2-16).

Table 2-3 provides a matrix of commonly used cementsand where they are used in concrete construction.

HYDRAULIC SLAG CEMENTS

Hydraulic slag cements are like other cements that set andharden by a chemical interaction with water. Concrete madewith hydraulic slag cement is used for the same appli-cations as concrete made with other hydraulic cements.Hydraulic slag cements consist of ground granulated blast-furnace slag that contains many of the same chemical con-

stituents as portland cement. They are often blended withhydrated lime or portland cement. Combining hydraulicslag cement with water produces essentially the same bind-ing material (calcium silicate hydrate) that portland cementalone makes when combined with water. Hydraulic slagcements conform to ASTM C 595 Types IS and S, ASTM C989, or ASTM C 1157.

MODIFIED PORTLAND CEMENTS

The term “modified portland cement” usually refers to ablended cement containing mostly portland cement alongwith a small amount, less than 15%, of mineral additive.However, some local areas have modified portlandcements that do not contain a mineral additive. The modi-fication merely refers to a special property that cement hasor a cement that has the characteristics of more than onetype of portland cement. See the discussions above forType I(SM) slag-modified portland cement and Type I(PM)pozzolan-modified portland cement and the discussionson “Hydraulic Cements” for more information.

SPECIAL CEMENTS

Special cements are produced for particular applications.Table 2-4 summarizes the special cements discussed below.See Odler (2000) and Klemm (1998) for more information.

Masonry and Mortar Cements

Masonry cements and mortar cements are hydrauliccements designed for use in mortar for masonry construc-tion (Fig. 2-20). They consist of a mixture of portland

33


Table 2-3. Applications for Commonly Used Cements

Applications*

Moderate Moderate Resistance toCement General heat of High early Low heat of sulfate High sulfate alkali-silica

specification purpose hydration strength hydration resistance resistance reactivity (ASR)**ASTM C 150 I II (moderate III IV II V Low alkali

(AASHTO M 85) heat option) optionportland cements

ASTM C 595 IS IS(MH) P(LH) IS(MS) Low reactivity(AASHTO M 240) IP IP(MH) IP(MS) option

blended I(PM) I(PM)(MH) P(MS)hydraulic I(SM) I(SM)(MH) I(PM)(MS)cements S, P I(SM)(MS)

ASTM C 1157 GU MH HE LH MS HS Option Rhydraulic

cements***

* Check the local availability of specific cements as all cements are not available everywhere. ** The option for low reactivity with ASR susceptible aggregates can be applied to any cement type in the columns to the left.

*** For ASTM C 1157 cements, the nomenclature of hydraulic cement, portland cement, air-entraining portland cement, modified portlandcement, or blended hydraulic cement is used with the type designation.

34


Table 2-4. Applications for Special Cements

Special cements Type ApplicationWhite portland cements, I, II, III, V White or colored concrete, masonry, ASTM C 150 mortar, grout, plaster, and stuccoWhite masonry cements, M, S, N White mortar between masonry unitsASTM C 91Masonry cements, ASTM C 91 M, S, N Mortar between masonry units,*

plaster, and stuccoMortar cements, ASTM C 1329 M, S, N Mortar between masonry units*Plastic cements, ASTM C 1328 M, S Plaster and stucco**Expansive cements, ASTM C 845 E-1(K), E-1(M), E-1(S) Shrinkage compensating concreteOil-well cements, API-10 A, B, C, D, E, F, G, H Grouting wellsWater-repellent cements Tile grout, paint, and stucco finish coatsRegulated-set cements Early strength and repair***Cements with functional General concrete construction needingadditions, ASTM C 595 special characteristics such as; water-(AASHTO M 240), ASTM C 1157 reducing, retarding, air entraining, set

control, and accelerating propertiesFinely ground (ultrafine) cement Geotechnical grouting***Calcium aluminate cement Repair, chemical resistance, high

temperature exposuresMagnesium phosphate cement Repair and chemical resistanceGeopolymer cement General construction, repair, waste

stabilization***Ettringite cements Waste stabilization***Sulfur cements Repair and chemical resistanceRapid hardening hydraulic cement VH, MR, GC General paving where very rapid

(about 4 hours) strength developmentis required

* Portland cement Types I, II, and III and blended cement Types IS, IP, and I(PM) are also used in making mortar.** Portland cement Types I, II, and III and blended cement Types IP, I(SM) and I(PM) are also used in making plaster.

*** Portland and blended hydraulic cements are also used for these applications.

cement or blended hydraulic cement and plasticizing mate-rials (such as limestone or hydrated or hydraulic lime),together with other materials introduced to enhance one ormore properties such as setting time, workability, waterretention and durability. These components are propor-tioned and packed at a cement plant under controlled con-ditions to assure uniformity of performance.

Masonry cements meet the requirements of ASTM C91, which classifies masonry cements as Type N, Type S,and Type M. White masonry cement and colored masonrycements meeting ASTM C 91 are also available in someareas. Mortar cements meet the requirements of ASTM C1329, which also classifies mortar cements as Type N, TypeS, and Type M. A brief description of each type follows:

Type N masonry cement and Type N mortar cementare used in ASTM C 270 Type N and Type O mortars. Theymay also be used with portland or blended cements toproduce Type S and Type M mortars.

Type S masonry cement and Type S mortar cementare used in ASTM C 270 Type S mortar. They may also beused with portland or blended cements to produce TypeM mortar.

Type M masonry cement and Type M mortar cementare used in ASTM C 270 Type M mortar without the addi-tion of other cements or hydrated lime.

Types N, S, and M generally have increasing levels ofportland cement and higher strength, Type M having thehighest strength. Type N is used most commonly.

Fig. 2-20. Masonry cement and mortar cement are used tomake mortar to bond masonry units together. (68807)

The increased use of masonry in demanding structuralapplications, such as high seismic areas, resulted in the re-cent development of mortar cement. Mortar cement is simi-lar to masonry cement in that it is a factory-preparedcement primarily used to produce masonry mortar.However, ASTM C 1329 places lower maximum air contentlimits on mortar cement than permitted for masonrycements; also, ASTM C 1329 is the only ASTM masonrymaterial specification that includes bond strength perform-ance criteria.

The workability, strength, and color of masonrycements and mortar cements stay at a high level of unifor-mity because of manufacturing controls. In addition tomortar for masonry construction, masonry cements andmortar cements are used for parging. Masonry cements arealso used in portland-cement based plaster or stucco (Fig.2-21) construction (see ASTM C 926). Masonry cement andmortar cement should not be used for making concrete.

Plastic Cements

Plastic cement is a hydraulic cement that meets the require-ments of ASTM C 1328. It is used to make portland cement-

based plaster or stucco (ASTM C 926), usually in the south-west and west coast of the United States (Fig. 2-21). Plasticcements consist of a mixture of portland and blendedhydraulic cement and plasticizing materials (such as lime-stone, hydrated or hydraulic lime), together with materialsintroduced to enhance one or more properties such assetting time, workability, water retention, and durability.

ASTM C 1328 defines separate requirements for a TypeM and a Type S plastic cement with Type M having higherstrength requirements. The Uniform Building Code (UBC)25-1 does not classify plastic cement into different types,but defines just one set of requirements which correspondto those of an ASTM C 1328 Type M plastic cement. Whenplastic cement is used, no lime or other plasticizer may beadded to the plaster at the time of mixing.

The term “plastic” in plastic cement does not refer tothe inclusion of any organic compounds in the cement;rather, “plastic” refers to the ability of the cement to impartto the plaster a high degree of plasticity or workability.Plaster made from this cement must remain workable for along enough time for it to be reworked to obtain the desireddensification and texture. Plastic cement should not be usedto make concrete. For more information on the use of plas-tic cement and plaster, see Melander and Isberner (1996).

Finely-Ground Cements (Ultrafine Cements)

Finely-ground cements, also calledultrafine cements, are hydraulic ce-ments that are ground very fine for usein grouting into fine soil or thin rockfissures (Fig. 2-22). The cement parti-cles are less than 10 micrometers indiameter with 50% of particles lessthan 5 micrometers. Blaine finenessoften exceeds 800 m2/kg. These veryfine cements consist of portland ce-ment, ground granulated blast-furnaceslag, and other mineral additives.

35


Fig. 2-21. Masonry cement and plastic cement are used to make plaster or stucco for commercial, institutional, and residentialbuildings. Shown are a church and home with stucco exteriors. Inset shows a typical stucco texture. (69389, 67878, 68805)

Fig. 2-22. (left) A slurry of finely ground cement and water can be injected into theground, as shown here, to stabilize in-place materials, to provide strength forfoundations, or to chemically retain contaminants in soil. (68810) Illustration (right) ofgrout penetration in soil.

Oil-Well Cements

Oil-well cements, used for oil-well grouting, often calledoil-well cementing, are usually made from portland cementclinker or from blended hydraulic cements. Generally theymust be slow-setting and resistant to high temperaturesand pressures. The American Petroleum Institute’sSpecification for Cements and Materials for Well Cementing(API Specification 10A) includes requirements for eightclasses of well cements (Classes A through H) and threegrades (Grades O—ordinary, MSR—moderate sulfateresistant, and HSR—high sulfate resistant). Each class isapplicable for use at a certain range of well depths, temper-atures, pressures, and sulfate environments. The petroleumindustry also uses conventional types of portland cementwith suitable cement-modifiers. Expansive cements havealso performed adequately as well cements.

Cements with Functional Additions

Functional additions can be interground with cementclinker to beneficially change the properties of hydrauliccement. These additions must meet the requirements ofASTM C 226 or C 688. ASTM C 226 addresses air-entrain-ing additions while ASTM C 688 addresses the followingtypes of additions: water-reducing, retarding, accelerating,water-reducing and retarding, water-reducing and acceler-ating, and set-control additions. Cement specificationsASTM C 595 (AASHTO M 240) and C 1157 allow functionaladditions. These cements can be used for normal or specialconcrete construction, grouting, and other applications.Gajda (1996) studied a functional addition to control alkali-silica reactivity.

Water-Repellent Cements

Water-repellent cements, sometimes called waterproofedcements, are usually made by adding a small amount ofwater-repellent additive such as stearate (sodium, alumi-num, or other) to cement clinker during final grinding (Lea1971). Manufactured in either white or gray color, water-repellent cements reduce capillary water transmissionwhen there is little to no pressure but do not stop water-vapor transmission. They are used in tile grouts, paint, andstucco finish coats.

Regulated-Set Cements

Regulated-set cement is a calcium fluoroaluminatehydraulic cement that can be formulated and controlled toproduce concrete with setting times from a few minutes toan hour and with corresponding rapid early strengthdevelopment (Greening and others 1971). It is a portland-based cement with functional additions that can be manu-factured in the same kiln used to manufacture conventionalportland cement. Regulated-set cement incorporates setcontrol and early-strength-development components. Finalphysical properties of the resulting concrete are in most

Expansive Cements

Expansive cement is a hydraulic cement that expandsslightly during the early hardening period after setting. Itmust meet the requirements of ASTM C 845 in which it isdesignated as Type E-1. Currently, three varieties of expan-sive cement are recognized and have been designated as K,M, and S, which are added as a suffix to the type. Type E-1(K) contains portland cement, tetracalcium trialuminosul-fate, calcium sulfate, and uncombined calcium oxide(lime). Type E-1(M) contains portland cement, calciumaluminate cement, and calcium sulfate. Type E-1(S) con-tains portland cement with a high tricalcium aluminatecontent and calcium sulfate. Type E-1(K) is the most read-ily available expansive cement in North America.

Expansive cement may also be made of formulationsother than those mentioned. The expansive properties ofeach type can be varied over a considerable range.

When expansion is restrained, for example by reinforc-ing steel, expansive cement concrete (also called shrinkagecompensating concrete) can be used to (1) compensate forthe volume decrease due to drying shrinkage, (2) inducetensile stress in reinforcement (post-tensioning), and (3)stabilize the long-term dimensions of post-tensionedconcrete structures with respect to original design.

One of the major advantages of using expansivecement in concrete is noted in (1) above; when you cancompensate for volume change due to drying shrinkageyou can control and reduce drying shrinkage cracks. Fig.2-23 illustrates the length change (early expansion anddrying shrinkage) history of shrinkage-compensatingconcrete and conventional portland cement concrete. Formore information see Pfeifer and Perenchio (1973), Russell(1978), and ACI (1998).

36


0.10

0.08

0.06

0.04

0.02

0

-0.02

-0.04

-0.06

Leng

th c

hang

e, p

erce

nt

0 7 50 100 150 200Time, days

Moist-cured for 7 days, followed byair drying at 23°C (73°F)

Restrained by reinforcing steel, p = 0.35%

Shrinkage-compensatingconcrete

Portland cementconcrete

Fig. 2-23. Length-change history of shrinkage compensatingconcrete containing Type E-1(S) cement and Type I portlandcement concrete (Pfeifer and Perenchio 1973).

respects similar to comparable concretes made with port-land cement.

Geopolymer CementsGeopolymer cements are inorganic hydraulic cements thatare based on the polymerization of minerals (Davidovits,Davidovits, and James 1999). The term more specificallyrefers to alkali-activated alumino-silicate cements, alsocalled zeolitic or polysialate cements. They have been usedin general construction, high-early strength applications,and waste stabilization. These cements do not containorganic polymers or plastics.

Ettringite CementsEttringite cements are calcium sulfoaluminate cements thatare specially formulated for particular uses, such as thestabilization of waste materials (Klemm 1998). They can beformulated to form large amounts of ettringite to stabilizeparticular metallic ions within the ettringite structure.Ettringite cements have also been used in rapid settingapplications, including use in coal mines. Also see“Expansive Cements” above.

Rapid Hardening CementsRapid hardening, high-early strength, hydraulic cement isused in construction applications, such as fast-trackpaving, where fast strength development is needed (designor load carrying strength in about four hours). Thesecements often use calcium sulfoaluminate to obtain earlystrength. They are classified as Types VH (very high-earlystrength), MR (middle range high-early strength), and GC(general construction).

Calcium Aluminate CementsCalcium aluminate cement is not portland cement based.It is used in special applications for early strength gain(design strength in one day), resistance to high tempera-tures, and resistance to sulfates, weak acids, and seawater.Portland cement and calcium aluminate cement combina-tions have been used to make rapid setting concretes andmortars. Typical applications for calcium aluminatecement concrete include: chemically resistant, heat resist-ant, and corrosion resistant industrial floors; refractorycastables; and repair applications. Standards addressingthese cements, include British Standard BS 915-2 or FrenchStandard NF P15-315.

Calcium aluminate cement concrete must be used atlow water-cement ratios (less than 0.40); this minimizes theconversion of less stable hexagonal calcium aluminate hy-drate (CAH10) to the stable cubic tricalcium aluminatehydrate (C3AH6), hydrous alumina (AH3), and water. Withtime and particular moisture conditions and temperatures,this conversion causes a 53% decrease in volume of hyd-rated material. However, this internal volume changeoccurs without a dramatic alteration of the overall dimen-

sions of a concrete element, resulting in increased pasteporosity and decreased compressive strength. At lowwater-cement ratios, there is insufficient space for all thecalcium aluminate to react and form CAH10. The releasedwater from conversion reacts with more calcium alumi-nate, partially compensating for the effects of conversion.Concrete design strength must therefore be based on theconverted strength. Because of eventual conversion,calcium aluminate cement is often used in nonstructuralapplications and used with caution (or not at all) in struc-tural applications (Taylor 1997).

Magnesium Phosphate Cements

Magnesium phosphate cement is a rapid setting, earlystrength gain cement. It is usually used for special applica-tions, such as repair of pavements and concrete structures,or for resistance to certain aggressive chemicals. It does notcontain portland cement.

Sulfur Cements

Sulfur cement is used with conventional aggregates to makesulfur cement concrete for repairs and chemically resistantapplications. Sulfur cement melts at temperatures between113°C and 121°C (235°F and 250°F). Sulfur concrete is main-tained at temperatures around 130°C (270°F) during mixingand placing. The material gains strength quickly as it coolsand is resistant to acids and aggressive chemicals. Sulfurcement does not contain portland or hydraulic cement.

SELECTING AND SPECIFYING CEMENTS

When specifying cements for a project, be sure to check theavailability of cement types as discussed below; specifica-tions should allow flexibility in cement selection. Limitinga project to only one cement type, one brand, or one stan-dard cement specification can result in project delays and itmay not allow for the best use of local materials. Cementswith special properties should not be required unlessspecial characteristics are necessary. In addition, the use ofsupplementary cementing materials should not inhibit theuse of any particular portland or blended cement. The proj-ect specifications should focus on the needs of the concretestructure and allow use of a variety of materials to accom-plish those needs. A typical specification may call for port-land cements meeting ASTM C 150 (AASHTO M 85) or C1157, or for blended cements meeting ASTM C 595(AASHTO M 240) or C 1157.

If no special properties, (such as low-heat generationor sulfate resistance) are required, all general use cementsshould be allowed, such as Types I, GU, IS, IP, I(SM), orI(PM). Also, it should be noted that some cement typesmeet the requirements of other types as well; for example,all Type II cements meet the requirements of Type I, but notall Type I cements meet the requirements of Type II. SeeTables 2-3 and 2-4 for guidance on using different cements.

37


cement and concrete meet the special requirements of theAmerican National Standards Institute/National SanitationFoundation standard ANSI/NSF 61, Drinking Water SystemComponents—Health Effects. ANSI/NSF 61 is being adoptedby nearly every state in the United States to assure thatproducts such as pipe, coatings, process media, and plumb-ing fittings are safe for use in public drinking water systems.Cement is used in drinking water system components suchas pipe and tanks, and therefore, is subject to testing underANSI/NSF 61. Kanare (1995) outlines the specifications andtesting program required to certify cement for drinkingwater applications. Consult the local building code or localofficials to determine if National Sanitation Foundationcertified cements are required for water projects such asconcrete pipe and concrete tanks (Fig. 2-24).

Canadian and European CementSpecifications

In some instances, projects in the United States designed byengineering firms from other countries refer to cement stan-dards other than those in ASTM or AASHTO. For example,the European cement standard, EN 197, sometimes appearson project specifications. EN 197 cement Types CEM I, II, III,IV, and V do not correspond to the cement types in ASTM C150, nor can ASTM cements be substituted for EN specifiedcement without the designer’s approval. CEM I is a port-land cement and CEM II through V are blended cements.EN 197 also has strength classes and ranges (32.5, 42.5, and52.5 MPa).

There is no direct equivalency between ASTM andother cement standards of the world because of differencesin test methods and limits on required properties. EN 197cements are usually not available in the United States; there-fore, the best approach is to inform the designer as to whatcements are locally available and ask for a change in theproject specifications to allow use of an ASTM or AASHTOcement.

Availability of Cements

Some types of cement may not be readily available in allareas of the United States. Before specifying a type of ce-ment, its availability should be determined.

ASTM C 150 Type I portland cement is usually carriedin stock and is furnished when a type of cement is not spec-ified. Type II cement is usually available, especially in areasof the country where moderate sulfate resistance is needed.Cement Types I and II represent about 90% of the cementshipped from plants in the United States. Some cements aredesignated as both Type I and II (Type I/II), meaning thatthey meet specification requirements for both types. TypeIII cement and white cement are usually available in largermetropolitan areas and represent about 4% of cementproduced. Type IV cement is manufactured only whenspecified for particular projects (massive structures likedams) and therefore is usually not readily available. Type Vcement is available only in particular regions of the coun-try where it is needed to resist high sulfate environments.Air-entraining cements are sometimes difficult to obtain.Their use has decreased as the popularity of air-entrainingadmixtures has increased. Masonry cement is available inmost areas. See PCA (2002) for statistics on cement use.

If a given cement type is not available, comparableresults frequently can be obtained with one that is avail-able. For example, high-early-strength concrete can bemade by using mixtures with higher cement contents andlower water-cement ratios. Also, the effects of heat ofhydration can be minimized by using lean mixtures,smaller placing lifts, artificial cooling, or by adding apozzolan to the concrete. Type V cement may at times bedifficult to obtain, but due to the range of compoundspermitted in cement specifications, a Type II cement maymeet the requirements of a Type V.

About half the state departments of transportation re-quire AASHTO cement specifications, therefore, AASHTOdesignated cements are not available everywhere.

Blended cements can be obtained throughout most ofthe United States; however, certain types of blendedcement may not be available in some areas. When blendedcements are required, but are not available, similar proper-ties may be obtained by adding pozzolans (ASTM C 618 orAASHTO M 295) or finely ground granulated blast-furnaceslag (ASTM C 989 or AASHTO M 302) to the concrete at aready mix plant using normal portland cement. Like anyconcrete mixture, these mixes should be tested for time ofset, strength gain, durability, and other properties prior touse in construction.

Drinking Water Applications

Concrete has demonstrated decades of safe use in drinkingwater applications. Materials in contact with drinking watermust meet special requirements to control elements enter-ing the water supply. Some localities may require that

38


Fig. 2-24. Concrete has demonstrated decades of safe use indrinking water applications such as concrete tanks. (69082)

Canadian CSA A5 cement Types 10, 20, 30, 40, and 50are essentially the same as ASTM C 150 (AASHTO M 85)Types I through V, respectively, except for the allowance ofup to 5% limestone in Type 10 and Type 30 cements.

The four types of blended hydraulic cementsaddressed in CSA A362 are:

Portland blast-furnace slag cement (S)Portland fly ash cement (F)Portland silica fume cement (SF)Ternary blend cementThe nomenclature and naming practice used for

Canadian blended cements is as follows:TE-A/B

whereT = the equivalent performance to Type 10, 20, 30, 40,

or 50 portland cement;E = an indication that the cement has equivalent

performance for the physical properties specifiedin CSA A362, Table 2;

A = the predominant supplementary material; andB = the secondary supplementary material, only spe-

cified in a ternary blend.Examples:

10E-S a portland blast furnace slag cement having anequivalent performance to that of a Type 10 portlandcement.

40E-F a portland fly ash cement having an equivalentperformance to that of a Type 40 portland cement.

50E-S/SF a ternary blend cement having an equivalentperformance to that of a Type 50 portland cement with slagbeing the predominant supplementary cementing materialand silica fume the secondary supplementary cementingmaterial.

CHEMICAL COMPOUNDS ANDHYDRATION OF PORTLAND CEMENTDuring the burning operation in the manufacture of port-land cement clinker, calcium combines with the other com-

ponents of the raw mix to form four principal compoundsthat make up 90% of cement by mass. Gypsum (4% to 6%),or other calcium sulfate source, and grinding aids are alsoadded during grinding. Cement chemists use the followingchemical shorthand (abbreviations) to describe compounds:

A= Al2O3, C=CaO, F= Fe2O3, H=H2O, M=MgO, S= SiO2,and … = SO3.

The term “phase” rather than “compounds” can also beused to describe the components of clinker. Following arethe four primary compounds in portland cement, their ap-proximate chemical formulas, and abbreviations:

Tricalcium silicate 3CaO•SiO2 = C3SDicalcium silicate 2CaO•SiO2 = C2STricalcium aluminate 3CaO•Al2O3 = C3ATetracalcium

aluminoferrite 4CaO•Al2O3•Fe2O3 = C4AF

Following are the forms of calcium sulfate, their chem-ical formulas, and abbreviations:

Anhydrous calciumsulfate CaSO4 = CaO•SO3 = C…

Calcium sulfatedihydrate (gypsum) CaSO4 •2H2O =

CaO•SO3•2H2O = C…H2

Calcium sulfatehemihydrate CaSO4 • 1⁄2 H2O =

CaO•SO3•1⁄2 H2O = C…H1/2

Gypsum, calcium sulfate dihydrate, is the predomi-nant source of sulfate used in cement.

C3S and C2S in clinker are also referred to as alite andbelite, respectively. Alite constitutes 50% to 70% of theclinker, whereas belite accounts for only 15% to 30%.Aluminate compounds constitute about 5% to 10% of theclinker and ferrite compounds 5% to 15% (Taylor 1997).These and other compounds may be observed andanalyzed through the use of microscopical techniques (seeFig. 2-25, ASTM C 1356, and Campbell 1999).

39


Fig. 2-25. (left) Polished thin-section examination of portland clinker shows alite (C3S) as light, angular crystals. The darker,rounded crystals are belite (C2S). Magnification 400X. (right) Scanning electron microscope (SEM) micrograph of alite (C3S)crystals in portland clinker. Magnification 3000X. (54049, 54068)

due primarily to calcium silicate hydrate (Fig. 2-27). C3Areacts with water and calcium hydroxide to form tetracal-cium aluminate hydrates. C4AF reacts with water to formcalcium aluminoferrite hydrates. C3A, sulfates (gypsum,anhydrite, or other sulfate source), and water combine toform ettringite (calcium trisulfoaluminate hydrate), calciummonosulfoaluminate, and other related compounds. Thesebasic compound transformations are shown in Table 2-5.Brunauer (1957), Copeland and others (1960), Lea (1971),

In the presence of water, these compounds hydrate(chemically combined with water) to form new compoundsthat are the infrastructure of hardened cement paste inconcrete (Fig. 2-26). The calcium silicates, C3S and C2S,hydrate to form the compounds calcium hydroxide andcalcium silicate hydrate (archaically called tobermorite gel).Hydrated portland cement contains 15% to 25% calciumhydroxide and about 50% calcium silicate hydrate by mass.The strength and other properties of hydrated cement are

40


Fig. 2-26. Electron micrographs of (left) dicalcium silicate hydrate, (middle) tricalcium silicate hydrate, and (right) hydratednormal portland cement. Note the fibrous nature of the calcium silicate hydrates. Broken fragments of angular calciumhydroxide crystallites are also present (right). The aggregation of fibers and the adhesion of the hydration particles isresponsible for the strength development of portland cement paste. Reference (left and middle) Brunauer 1962 and (right)Copeland and Schulz 1962. (69110, 69112, 69099)

Table 2-5. Portland Cement Compound Hydration Reactions (Oxide Notation)

2 (3CaO•SiO2) + 11 H2O = 3CaO•2SiO2•8H2O + 3 (CaO•H2O)Tricalcium silicate Water Calcium silicate Calcium hydroxide

hydrate (C-S-H)

2 (2CaO•SiO2) + 9 H2O = 3CaO•2SiO2•8H2O + CaO•H2ODicalcium silicate Water Calcium silicate Calcium hydroxide

hydrate (C-S-H)

3CaO•Al2O3 + 3 (CaO•SO3•2H2O) + 26 H2O = 6CaO•Al2O3•3SO3•32H2OTricalcium aluminate Gypsum Water Ettringite

2 (3CaO•Al2O3) + 6CaO•Al2O3•3SO3•32H2O + 4 H2O = 3 (4CaO•Al2O3•SO3•12H2O)Tricalcium aluminate Ettringite Water Calcium monosulfoaluminate

3CaO•Al2O3 + CaO•H2O + 12 H2O = 4CaO•Al2O3•13H2OTricalcium aluminate Calcium hydroxide Water Tetracalcium aluminate hydrate

4CaO• Al2O3•Fe2O3 + 10 H2O + 2 (CaO•H2O) = 6CaO•Al2O3•Fe2O3•12H2OTetracalcium aluminoferrite Water Calcium hydroxide Calcium aluminoferrite hydrate

Note: This table illustrates only primary transformations and not several minor transformations. The composition of calcium silicate hydrate (C-S-H) is not stoichiometric (Tennis and Jennings 2000).

Powers and Brownyard (1947), Powers (1961), and Taylor(1997) addressed the pore structure and chemistry of cementpaste. Fig. 2-28 shows estimates of the relative volumes ofthe compounds in hydrated portland cement pastes.

A web-based computer model for hydration andmicrostructure development can be found at NIST (2001)[http://vcctl.cbt.nist.gov]. The Concrete MicroscopyLibrary (Lange and Stutzman 1999) provides a collection ofmicrographs of cement hydration and concrete athttp://www.cee.ce.uiuc.edu/lange/micro.

The approximate percentage of each compound can becalculated from a chemical oxide analysis (ASTM C 114 orAASHTO T 105) of the unhydrated cement per ASTM C150 (AASHTO M 85) (Bogue calculations). Due to the inac-

curacies of Bogue calculations, X-ray diffraction techniquescan be used to more accurately determine compound per-centages (ASTM C 1365). Table 2-6 shows typical elementaland compound composition and fineness for each of theprincipal types of portland cement.

Although elements are reported as simple oxides forstandard consistency, they are usually not found in thatoxide form in the cement. For example, sulfur from thegypsum is reported as SO3 (sulfur trioxide), however,cement does not contain any sulfur trioxide. The amount ofcalcium, silica, and alumina establish the amounts of theprimary compounds in the cement and effectively theproperties of hydrated cement. Sulfate is present to control

41

Chapter 2 ◆ Portland, Blended, and Other Hydraulic Cements

Fig. 2-27. Scanning-electron micrographs of hardened cement paste at (left) 500X, and (right) 1000X. (A7112, A7111)

0

25

50

75

100

0 25 50 75 100

Degree of hydration, %

Rela

tive v

olu

me, %

other

capillaryporosity

C-S-H

calciumhydroxide

AFt andAFm

calciumsulfate

C4 AF

C3 A

C2S

C3S

Porosity

Am

ount

C-S-H

Ca(OH)2

C4(A, F)H13

Ettringite

Age: Minutes Hours Days

0 5 30 7 2 6 7 2 7 28 90

Monosulfate

Fig. 2-28. Relative volumes of the major compounds in the microstructure of hydrating portland cement pastes (left) as afunction of time (adapted from Locher, Richartz, and Sprung 1976) and (right) as a function of the degree of hydration asestimated by a computer model for a water to cement ratio of 0.50 (adapted from Tennis and Jennings 2000). Values are givenfor an average Type I cement composition (Gebhardt 1995): C3S=55%, C2S=18%, C3A=10% and C4AF=8%. “AFt and AFm”includes ettringite (AFt) and calcium monosulfoaluminate (AFm) and other hydrated calcium aluminate compounds. See Table2-5 for compound transformations.

Dicalcium Silicate, C2S, hydrates and hardens slowly andcontributes largely to strength increase at ages beyond oneweek.Tricalcium Aluminate, C3A, liberates a large amount ofheat during the first few days of hydration and hardening.It also contributes slightly to early strength development.Cements with low percentages of C3A are more resistant tosoils and waters containing sulfates.Tetracalcium Aluminoferrite, C4AF, is the product result-ing from the use of iron and aluminum raw materials toreduce the clinkering temperature during cement manu-facture. It contributes little to strength. Most color effectsthat make cement gray are due to C4AF and its hydrates.Calcium Sulfate, as anhydrite (anhydrous calcium sul-fate), gypsum (calcium sulfate dihydrate), or hemihydrate,often called plaster of paris or bassanite (calcium sulfatehemihydrate) is added to cement during final grinding toprovide sulfate to react with C3A to form ettringite (calciumtrisulfoaluminate). This controls the hydration of C3A.Without sulfate, a cement would set rapidly. In addition tocontrolling setting and early strength gain, the sulfate alsohelps control drying shrinkage and can influence strengththrough 28 days (Lerch 1946).

In addition to the above primary cement compounds,numerous other lesser compound formulations also exist(PCA 1997, Taylor 1997, and Tennis and Jennings 2000).

Water (Evaporable and Nonevaporable)

Water is a key ingredient of pastes, mortars, and concretes,as the phases in portland cement must chemically reactwith water to develop strength. The amount of wateradded to a mixture controls the durability as well. The

setting, as well as drying shrinkage and strength gain (Tang1992). Minor and trace elements and their effect on cementproperties are discussed by Bhatty (1995) and PCA (1992).Present knowledge of cement chemistry indicates that theprimary cement compounds have the following properties:

Tricalcium Silicate, C3S, hydrates and hardens rapidlyand is largely responsible for initial set and early strength(Fig. 2-29). In general, the early strength of portland cementconcrete is higher with increased percentages of C3S.

42


C3S

C3A

C4AF

Overall

C2S

0 20 40 60 80 100Age, days

100%

80%

60%

40%

20%

0%

Deg

ree

of r

eact

ion,

% b

y m

ass

Fig. 2-29. Relative reactivity of cement compounds. Thecurve labeled “overall” has a composition of 55% C3S, 18%C2S, 10% C3A, and 8% C4AF, an average Type I cementcomposition (Tennis and Jennings 2000).

Table 2-6. Chemical and Compound Composition and Fineness of Cements*

Type of Chemical composition, % Potential compound composition,% Blaineportland fineness, cement SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O eq C3S C2S C3A C4AF m2/kg

I (min-max) 18.7-22.0 4.7-6.3 1.6-4.4 60.6-66.3 0.7-4.2 1.8-4.6 0.11-1.20 40-63 9-31 6-14 5-13 300-421I (mean) 20.5 5.4 2.6 63.9 2.1 3.0 0.61 54 18 10 8 369II** (min-max) 20.0-23.2 3.4-5.5 2.4-4.8 60.2-65.9 0.6-4.8 2.1-4.0 0.05-1.12 37-68 6-32 2-8 7-15 318-480II** (mean) 21.2 4.6 3.5 63.8 2.1 2.7 0.51 55 19 6 11 377III (min-max) 18.6-22.2 2.8-6.3 1.3-4.9 60.6-65.9 0.6-4.6 2.5-4.6 0.14-1.20 46-71 4-27 0-13 4-14 390-644III (mean) 20.6 4.9 2.8 63.4 2.2 3.5 0.56 55 17 9 8 548IV (min-max) 21.5-22.8 3.5-5.3 3.7-5.9 62.0-63.4 1.0-3.8 1.7-2.5 0.29-0.42 37-49 27-36 3-4 11-18 319-362IV (mean) 22.2 4.6 5.0 62.5 1.9 2.2 0.36 42 32 4 15 340V (min-max) 20.3-23.4 2.4-5.5 3.2-6.1 61.8-66.3 0.6-4.6 1.8-3.6 0.24-0.76 43-70 11-31 0-5 10-19 275-430V (mean) 21.9 3.9 4.2 63.8 2.2 2.3 0.48 54 22 4 13 373White (min-max) 22.0-24.4 2.2-5.0 0.2-0.6 63.9-68.7 0.3-1.4 2.3-3.1 0.09-0.38 51-72 9-25 5-13 1-2 384-564White (mean) 22.7 4.1 0.3 66.7 0.9 2.7 0.18 63 18 10 1 482

* Values represent a summary of combined statistics. Air-entraining cements are not included. For consistency in reporting, elements arereported in a standard oxide form. This does not mean that the oxide form is present in the cement. For example, sulfur is reported as SO3,sulfur trioxide, but, portland cement does not have sulfur trioxide present. “Potential Compound Composition” refers to ASTM C 150(AASHTO M 85) calculations using the chemical composition of the cement. The actual compound composition may be less due to incom-plete or altered chemical reactions.

** Includes fine grind cements.Adapted from PCA (1996) and Gebhardt (1995).

space initially taken up by water in a cementitious mixtureis partially or completely replaced over time as the hydra-tion reactions proceed (Table 2-5). If more than about 35%water by mass of cement—a water to cement ratio of 0.35—is used, then porosity in the hardened material will remain,even after complete hydration. This is called capillary por-osity. Fig. 2-30 shows that cement pastes with high and lowwater to cement ratios have equal masses after drying(evaporable water was removed). The cement consumedthe same amount of water in both pastes resulting in morebulk volume in the higher water-cement ratio paste. As thewater to cement ratio increases, the capillary porosityincreases, and the strength decreases. Also, transport prop-erties such as permeability and diffusivity are increased,allowing detrimental chemicals to more readily attack theconcrete or reinforcing steel.

Water is found in cementitious materials in severalforms. Free water is mixing water that has not reacted withthe cement phases. Bound water is chemically combined inthe solid phases or physically bound to the solid surfaces.A reliable separation of the chemically combined from thephysically adsorbed water is not possible. ThereforePowers (1949) distinguished between evaporable andnonevaporable water. The nonevaporable water is theamount retained by a sample after it has been subjected toa drying procedure intended to remove all the free water(traditionally, by heating to 105°C). Evaporable water wasoriginally considered to be free water, but it is now recog-nized that some bound water is also lost upon heating tothis temperature. All nonevaporable water is bound water,but the opposite is not true.

For complete hydration of portland cement, onlyabout 40% water (a water-to-cement ratio of 0.40) isneeded. If a water-to-cement ratio greater than about 0.40is used, the excess water not needed for cement hydrationremains in the capillary pores or evaporates. If a water-to-

cement ratio less than about 0.40 is used, some cement willremain unhydrated.

To estimate the degree of hydration of a hydrated ma-terial the nonevaporable water content is often used. Toconvert the measured nonevaporable water into degrees ofhydration, it is necessary to know the value of nonevap-orable water-to-cement ratio (wn/c) at complete hydration.Experimentally, this can be determined by preparing a highwater-to-cement ratio cement paste (for example, 1.0) andcontinuously grinding while it hydrates in a roller mill. Inthis procedure, complete hydration of the cement will typi-cally be achieved after 28 days.

Alternatively, an estimate of the value of nonevap-orable water-to-cement ratio (wn/c) at complete hydrationcan be obtained from the potential Bogue composition ofthe cement. Nonevaporable water contents for the majorcompounds of portland cement are provided in Table 2-7.For a typical Type I cement, these coefficients will generallyresult in a calculated wn/c for completely hydrated cementsomewhere between 0.22 and 0.25.

PHYSICAL PROPERTIES OF CEMENT

Specifications for cement place limits on both its physicalproperties and often chemical composition. An under-standing of the significance of some of the physical proper-ties is helpful in interpreting results of cement tests. Tests ofthe physical properties of the cements should be used toevaluate the properties of the cement, rather than theconcrete. Cement specifications limit the properties withrespect to the type of cement. Cement should be sampledin accordance with ASTM C 183 (AASHTO T 127). Duringmanufacture, cement is continuously monitored for itschemistry and the following properties:

Particle Size and Fineness

Portland cement consists of individual angular particleswith a range of sizes, the result of pulverizing clinker in thegrinding mill (Fig. 2-31 left). Approximately 95% of cementparticles are smaller than 45 micrometers, with the averageparticle around 15 micrometers. Fig. 2-31 (right) illustratesthe particle size distribution for a portland cement. The

43


Fig. 2-30. Cement paste cylinders of equal mass and equalcement content, but mixed with different water to cementratios, after all water has evaporated from the cylinders. (1072)

Table 2-7. Nonevaporable Water Contents for FullyHydrated Major Compounds of Cement

NonevaporableHydrated cement (combined) water content

compound (g water/g cement compound)C3S hydrate 0.24C2S hydrate 0.21C3A hydrate 0.40

C4AF hydrate 0.37Free lime (CaO) 0.33

sieve (ASTM C 430 or AASHTO T 192—Fig. 2-33) or the150-µm (No. 100) and 75-µm (No. 200) sieve (ASTM C 184or AASHTO T 128), and the electronic (x-ray or laser) parti-cle size analyzer (Fig. 2-34) can also be used to test fineness.Blaine fineness data are given in Table 2-6.

Soundness

Soundness refers to the ability of a hardened paste toretain its volume. Lack of soundness or delayed destructiveexpansion can be caused by excessive amounts of hard-burned free lime or magnesia. Most specifications for port-land cement limit the magnesia (periclase) content and themaximum expansion as measured by the autoclave-expan-sion test. Since adoption of the autoclave-expansion test(ASTM C 151 or AASHTO T 107) in 1943, there have beenexceedingly few cases of abnormal expansion attributed tounsound cement (Fig. 2-35) (Gonnerman, Lerch, and White-side 1953).

overall particle size distribution of cement is called “fine-ness.” The fineness of cement affects heat released and therate of hydration. Greater cement fineness (smaller particlesize) increases the rate at which cement hydrates and thusaccelerates strength development. The effects of greaterfineness on paste strength are manifested principally duringthe first seven days.

In the early 1900s, cement fineness was expressed asthe mass of cement per fractional size (percent weightretained on specific sieve sizes). Today, fineness is usuallymeasured by the Blaine air-permeability test (ASTM C 204or AASHTO T 153—Fig. 2-32) that indirectly measures thesurface area of the cement particles per unit mass. Cementswith finer particles have more surface area in square metersper kilogram of cement. The older use of square centime-ters per gram for reporting fineness is now consideredarchaic. Except for AASHTO M 85, most cement standardsdo not have a maximum limit on fineness, only a mini-mum. The Wagner turbidimeter test (ASTM C 115 orAASHTO T 98—Fig. 2-32), the 45-micrometer (No. 325)

44


Fig. 2-32. Blainetest apparatus(left) and Wagnerturbidimeter(right) for deter-mining the fine-ness of cement.Wagner finenessvalues are a littlemore than half ofBlaine values.(40262, 43815)

Cum

ulat

ive

mas

s, p

erce

nt

100

80

60

40

20

0100 50 20 10 5 2 1 0.5

Equivalent spherical diameter, µm

Typical particle size distributioncurve for Type I or Type II cement

Fig. 2-31. (left) Scanning-electron micrograph of powdered cement at 1000X and (right) particle size distribution of portlandcement. (69426)

Consistency

Consistency refers tothe relative mobility ofa freshly mixed cementpaste or mortar or to itsability to flow. Duringcement testing, pastesare mixed to normalconsistency as definedby a penetration of 10 ±1 mm of the Vicatplunger (see ASTM C187 or AASHTO T 129and Fig. 2-36). Mortarsare mixed to obtaineither a fixed water-cement ratio or to yield aflow within a prescribedrange. The flow is deter-mined on a flow table asdescribed in ASTM C230 (AASHTO M 152)and ASTM C 1437 (Fig.2-37). Both the normalconsistency method andthe flow test are used toregulate water contentsof pastes and mortars,respectively, to be usedin subsequent tests; bothallow comparing dis-similar ingredients withthe same penetrabilityor flow.

Setting Time

The object of the settingtime test is to determine(1) the time that elapsesfrom the moment wateris added until the pasteceases to be fluid andplastic (called initial set)and (2) the time requiredfor the paste to acquire acertain degree of hardness (called final set).

To determine if a cement sets according to the timelimits specified in cement specifications, tests areperformed using either the Vicat apparatus (ASTM C 191or AASHTO T 131—Fig. 2-38) or the Gillmore needle(ASTM C 266 or AASHTO T 154—Fig. 2-39).

The Vicat test governs if no test method is specified bythe purchaser. Initial set of cement paste must not occurtooearly and final set must not occur too late. The settingtimesindicate that a paste is or is not undergoing normal hydra-

45


Fig. 2-33. Quick tests, such as washing cement over this 45-micrometer sieve, help monitor cement fineness duringproduction. Shown is a view of the sieve holder with an insettop view of a cement sample on the sieve before washingwith water. (68818, 68819)

Fig. 2-34. A laser particle analyzer uses laserdiffraction to determine the particle sizedistribution of fine powders. Fig. 2-31 (right)illustrates typical results. (69390)

Fig. 2-35. In the soundness test, 25-mm square bars are exposed to hightemperature and pressure in theautoclave to determine the volumestability of the cement paste. (23894)

Fig. 2-36. Normal consistencytest for paste using the Vicatplunger. (68820)

Fig. 2-37. Consistency test formortar using the flow table. Themortar is placed in a small brassmold centered on the table (in-set). For skin safety the tech-nician wears protective gloveswhile handling the mortar. Afterthe mold is removed and thetable undergoes a succession ofdrops, the diameter of the pat ismeasured to determine consis-tency. (68821, 68822)

dehydrates in the cement mill to form plaster. Stiffening iscaused by the rapid crystallization of interlocking needle-like secondary gypsum. Additional mixing without addedwater breaks up these crystals to restore workability.Ettringite precipitation can also contribute to false set.

Flash set or quick set is evidenced by a rapid and earlyloss of workability in paste, mortar, or concrete. It is usuallyaccompanied by the evolution of considerable heat result-ing primarily from the rapid reaction of aluminates. If theproper amount or form of calcium sulfate is not available tocontrol the calcium aluminate hydration, stiffening be-comes apparent. Flash set cannot be dispelled, nor can theplasticity be regained by further mixing without the addi-tion of water.

Proper stiffening results from the careful balance of thesulfate and aluminate compounds, as well as the tempera-ture and fineness of the materials (which control the hydra-tion and dissolution rates). The amount of sulfate formedinto plaster has a significant effect. For example, with oneparticular cement, 2% plaster allowed a 5 hour set time,while 1% plaster caused flash set to occur, and 3% allowedfalse set to occur (Helmuth and others 1995).

Cements are tested for early stiffening using ASTM C451 (paste method) (AASHTO T 186), and ASTM C 359(mortar method) (AASHTO T 185), which use the penetra-tion techniques of the Vicat apparatus. However, these testsdo not address all the mixing, placing, temperature, andfield conditions that can cause early stiffening. They alsodo not address early stiffening caused by interactions withother concrete ingredients. For example, concretes mixedfor very short periods, less than a minute, tend to be moresusceptible to early stiffening (ACI 225).

tion reactions. Sulfate(from gypsum or othersources) in the cementregulates setting time,but setting time is alsoaffected by cement fine-ness, water-cement ratio,and any admixtures thatmay be used. Settingtimes of concretes donot correlate directlywith setting times ofpastes because of waterloss to the air or sub-strate, presence of ag-gregate, and because oftemperature differencesin the field (as con-trasted with the con-trolled temperature in atesting lab). Fig. 2-40 il-lustrates mean set timesfor portland cements.

Early Stiffening (False Set and Flash Set)

Early stiffening is the early development of stiffness in theworking characteristics or plasticity of cement paste, mortar,or concrete. This includes both false set and flash set.

False set is evidenced by a significant loss of plasticitywithout the evolution of much heat shortly after mixing.From a placing and handling standpoint, false-set ten-dencies in cement will cause no difficulty if the concrete ismixed for a longer time than usual or if it is remixed with-out additional water before being transported or placed.False set occurs when a significant amount of gypsum

46


Type V*

Type IV**

Type III

Type II

Type I

Initial set

Final set

0 50 100 150 200 250 030 350 400 450Time of set, minutes (Vicat Method)

*Average of two values for final set�**Average of two values for initial set; one value for final set

Fig. 2-40. Time of set for portland cements (Gebhardt 1995and PCA 1996).

Fig. 2-38. Time of set test forpaste using the Vicat needle.(23890)

Fig. 2-39. Time of set as determined by the Gillmoreneedle. (23892)

Fig. 2-41. 50-mm (2-in.) mortar cubes are cast (left) andcrushed (right) to determine strength characteristics of ce-ment. (69128, 69124)

Compressive Strength

Compressive strength as specified by ASTM cement stan-dards is that obtained from tests of 50-mm (2-in.) mortarcubes tested in accordance with ASTM C 109 (AASHTO T106) (Fig. 2-41). These cubes are made and cured in aprescribed manner using a standard sand.

Compressive strength is influenced by the cementtype, or more precisely, the compound composition andfineness of the cement. ASTM C 1157 has both minimumand maximum strength requirements while ASTM C 150and C 595 (AASHTO M 85 and M 240) set only a minimumstrength requirement. Minimum strength requirements incement specifications are exceeded comfortably by mostmanufacturers. Therefore, it should not be assumed thattwo types of cement meeting the same minimum require-ments will produce the same strength of mortar or concretewithout modification of mix proportions.

In general, cement strengths (based on mortar-cubetests) cannot be used to predict concrete strengths with agreat degree of accuracy because of the many variables inaggregate characteristics, concrete mixtures, constructionprocedures, and environmental conditions in the field(Weaver, Isabelle and Williamson 1970 and DeHayes 1990).Figs. 2-42 and 2-43 illustrate the strength development forstandard mortars made with various types of portlandcement. Wood (1992) provides long-term strength proper-ties of mortars and concretes made with portland andblended cements. The strength uniformity of a cement froma single source may be determined by following the proce-dures outlined in ASTM C 917.

Heat of Hydration

Heat of hydration is the heat generated when cement andwater react. The amount of heat generated is dependent

47


0 5 10 15 20 25 30

60

50

40

30

100

90

80

70

20

10

0

Str

engt

h as

a p

erce

nt o

f 28-

day

stre

ngth

1990s cement

Time, days

ASTM C 109 mortarw/c = 0.485

Cement

Type I

Type II

Type III

Type IV

Type V

Fig. 2-42. Relative strength development of portland cementmortar cubes as a percentage of 28-day strength. Meanvalues adapted from Gebhardt 1995.

chiefly upon the chemical composition of the cement, withC3A and C3S being the compounds primarily responsiblefor high heat evolution. The water-cement ratio, fineness ofthe cement, and temperature of curing also are factors. Anincrease in the fineness, cement content, and curingtemperature increases the heat of hydration. Althoughportland cement can evolve heat for many years, the rate ofheat generation is greatest at early ages. A large amount ofheat evolves within the first three days with the greatestrate of heat liberation usually occurring within the first 24hours (Copeland and others 1960). The heat of hydration istested in accordance with ASTM C 186 or by conductioncalorimetry (Figs. 2-44).

For most concrete elements, such as slabs, heat gener-ation is not a concern because the heat is quickly dissipatedinto the environment. However, in structures of consider-able mass, greater than a meter (yard) thick, the rate andamount of heat generated are important. If this heat is notrapidly dissipated, a significant rise in concrete tempera-ture can occur. This may be undesirable since, after hard-ening at an elevated temperature, nonuniform cooling ofthe concrete mass to ambient temperature may createundesirable tensile stresses. On the other hand, a rise inconcrete temperature caused by heat of hydration is oftenbeneficial in cold weather since it helps maintain favorablecuring temperatures.

Table 2-8 provides heat of hydration values for a vari-ety of portland cements. This limited data show that TypeIII cement has a higher heat of hydration than other typeswhile Type IV has the lowest. Also note the difference inheat generation between regular Type II cements andmoderate heat Type II cements.

48


Table 2-8. ASTM C 186 Heat of Hydration for Selected Portland Cements from the 1990s, kJ/kg*

Type IImoderate Type V

Type I cement Type II cement heat cement Type III cement Type IV cement cement7 day 28 day 7 day 28 day 7 day 7 day 28 day 7 day 28 day 7 day

No. ofsamples 15 7 16 7 4 2 2 3 1 6

Average 349 400 344 398 263 370 406 233 274 310Maximum 372 444 371 424 283 372 414 251 — 341Minimum 320 377 308 372 227 368 397 208 — 257

% of Type I 100 99 75 106 67 89(7 day)

*This table is based on very limited data.1 cal/g = 4.184 kJ/kg. PCA (1997).

0 5 10 15 20 25 30

60

50

40

30

20

10

0

Str

engt

h, M

Pa

Str

engt

h, p

si

Time, days

Type I cementASTM C 109 mortarw/c = 0.485

8000

7000

6000

5000

4000

3000

2000

1000

00 5 10 15 20 25 30

60

50

40

30

20

10

0

Str

engt

h, M

Pa

Str

engt

h, p

si

Time, days

Type III cementASTM C 109 mortarw/c = 0.485

8000

7000

6000

5000

4000

3000

2000

1000

0

60

50

40

30

20

10

0

Str

engt

h, M

Pa

0 5 10 15 20 25 30Time, days

Type II cementASTM C 109 mortarw/c = 0.485

Str

engt

h, p

si

8000

7000

6000

5000

4000

3000

2000

1000

0

0 5 10 15 20 25 30

60

50

40

30

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0

Str

engt

h, M

Pa

Str

engt

h, p

si

Time, days

Type IV cementASTM C 109 mortarw/c = 0.485

8000

7000

6000

5000

4000

3000

2000

1000

00 5 10 15 20 25 30

60

50

40

30

20

10

0S

tren

gth,

MP

a

Str

engt

h, p

si

Time, days

Type V cementASTM C 109 mortarw/c = 0.485

8000

7000

6000

5000

4000

3000

2000

1000

0

Fig. 2-43. Strength development of portland cement mortar cubes from combined statistics. The dashed line represents themean value and the shaded area the range of values (adapted from Gebhardt 1995).

Fig. 2-44. Heat of hydration can be determined by (left) ASTM C 186 or by (right) a conduction calorimeter. (68823, 68824)

Cements do not generate heat at a constant rate. Theheat output during hydration of a typical Type I portlandcement is illustrated in Fig. 2-45. The first peak shown inthe heat profile is due to heat given off by the initial hydra-tion reactions of cement compounds such as tricalciumaluminate. Sometimes called the heat of wetting, this firstheat peak is followed by a period of slow activity known asthe induction period. After several hours, a broad secondheat peak attributed to tricalcium silicate hydrationemerges, signaling the onset of the paste hardeningprocess. Finally, there is the third peak due to the renewedactivity of tricalcium aluminate; its intensity and locationnormally dependent on the amount of tricalcium alumi-nate and sulfate in the cement.

In calorimetry testing, the first heat measurements areobtained about 7 minutes after mixing the paste; as a resultonly the down slope of the first peak is observed (Stage 1,Fig. 2-45). The second peak (C3S peak) often occursbetween 6 and 12 hours. The third peak (renewed C3A peakon conversion of AFt to AFM) occurs between 12 and 90hours. This information can be helpful when trying tocontrol temperature rise in mass concrete (Tang 1992).

When heat generation must be minimized in concrete,designers should choose a lower heat cement, such as anASTM C 150 (AASHTO M 85) Type II portland cementwith the optional moderate heat of hydration require-ments. Not all Type II cements are made for a moderatelevel of heat development, however, so the moderate heatoption must be specifically requested. Type IV cement canalso be used to control temperature rise, but it is rarelyavailable. Moderate-heat and low-heat cements are alsoavailable in ASTM C 595 (AASHTO M 240) and C 1157 spe-cifications. Supplementary cementitious materials can alsobe used to reduce temperature rise.

ASTM C 150 (AASHTO M 85) has both a chemicalapproach and a physical approach to control heat of hydra-tion. Either approach can be specified, but not both. ASTMC 595 (AASHTO M 240) and ASTM C 1157 use physicallimits. See PCA (1997) for more information.

Loss on Ignition

Loss on ignition (LOI) of portland cement is determined byheating a cement sample of known weight to between900°C and 1000°C until a constant weight is obtained. Theweight loss of the sample is then determined. Normally, ahigh loss on ignition is an indication of prehydration andcarbonation, which may be caused by improper orprolonged storage, or adulteration during transport. Thetest for loss on ignition is performed in accordance withASTM C 114 (AASHTO T 105) (Fig. 2-46). LOI values rangefrom 0 to 3%.

Density and Relative Density(Specific Gravity)

The density of cement is defined as the mass of a unitvolume of the solids or particles, excluding air betweenparticles. It is reported as megagrams per cubic meter orgrams per cubic centimeter (the numeric value is the samefor both units). The particle density of portland cementranges from 3.10 to 3.25, averaging 3.15 Mg/m3. Portland-blast-furnace-slag and portland-pozzolan cements havedensities ranging from 2.90 to 3.15, averaging 3.05 Mg/m3.The density of a cement, determined by ASTM C 188(AASHTO T 133) (Fig. 2-47), is not an indication of thecement’s quality; its principal use is in mixture proportion-ing calculations.

For mixture proportioning, it may be more useful toexpress the density as relative density (also called specificgravity). The relative density is a dimensionless number

49


Stage 1

Stage 2 Stages 3 and 4 Stage 5C3S hydration

C3A hydration

Time

Hea

t evo

lutio

n

Fig. 2-45. Heat evolution as a function of time for cementpaste. Stage 1 is heat of wetting or initial hydrolysis (C3Aand C3S hydration). Stage 2 is a dormant period related toinitial set. Stage 3 is an accelerated reaction of thehydration products that determines rate of hardening andfinal set. Stage 4 decelerates formation of hydrationproducts and determines the rate of early strength gain.Stage 5 is a slow, steady formation of hydration productsestablishing the rate of later strength gain. Fig. 2-46. Loss on ignition test of cement. (43814)

THERMAL ANALYSIS

Thermal analysis techniques have been available for yearsto analyze hydraulic reactions and the interactions ofcement with both mineral and chemical admixtures (Figs.2-45 and 2-49). Traditionally, thermal analysis was not partof a routine test program for cement. However, thermalanalysis has gained recent popularity in analyzing chemi-cal and physical properties of cementitious materials andraw materials for cement manufacture (Bhatty 1993,Shkolnik and Miller 1996, and Tennis 1997).

Thermal analysis involves heating a small sample at acontrolled rate to high temperature (up to 1000°C or more).As compounds react or decompose, changes that occur asa function of time or temperature are recorded. As thesample’s temperature changes, various reactions occur thatcause a change in the sample’s weight, temperature,energy, or state. A solid can melt, vaporize, decompose to agas with a residual solid, or react with a gas (at elevatedtemperatures) to form a different solid or a different solidand another gas.

Typical uses for thermal analysis include:• identifying which hydration products have formed

and in what quantities• solving early stiffening problems• identifying impurities in raw materials• determining the amount of weathering in clinker or

cement• estimating the reactivity of pozzolans and slags for use

in blended cements• identifying the organic matter content and variations

in a quarry• quantifying the amount of carbonation that has taken

place in an exposed sample• analyzing durability problems with concrete.

Specific thermal analysis techniques are discussedbelow.

determined by dividing the cement density by the densityof water at 4°C. The density of water at 4°C is 1.0 Mg/m3

(1.0 g/cm3 or 1000 kg/m3). A relative density of 3.15 is assumed for portland ce-

ment in volumetric computations of concrete mix propor-tioning. However, as mix proportions list quantities ofconcrete ingredients in kilograms or pounds, the relativedensity must be multiplied by the density of water at 4°Cstated as 1000 kg/m3 (62.4 lb/ft3) to determine the particledensity in kg/m3 or lb/ft3. This product is then dividedinto the mass or weight of cement to determine theabsolute volume of cement in cubic meters or cubic feet.

Bulk Density

The bulk density of cement is defined as the mass ofcement particles plus air between particles per unitvolume. The bulk density of cement can vary considerablydepending on how it is handled and stored. Portlandcement that is fluffed up may weigh only 830 kg/m3

(52 pcf), where-as when consoli-dated by vibra-tion, the samecement can weighas much as 1650kg/m3 (103 pcf)(Toler 1963). Forthis reason, goodpractice dictatesthat cement mustbe weighed foreach batch of con-crete produced, asopposed to use ofa volumetric mea-sure (Fig. 2-48).

50


Fig. 2-49. Thermal analysis equipment. (69116)

Fig. 2-47. Density of cement can be determined by (left) usinga Le Chatelier flask and kerosine or by (right) using a heliumpycnometer. (68825, 68826)

Fig. 2-48. Both 500-mL beakers contain500 grams of dry powdered cement. Onthe left, cement was simply poured intothe beaker. On the right, cement wasslightly vibrated—imitating consolida-tion during transport or packing whilestored in a silo. The 20% difference inbulk volume demonstrates the need tomeasure cement by mass instead ofvolume for batching concrete. (68970)

Thermogravimetric Analysis (TGA)

Thermogravimetric analysis (TGA) is a technique thatmeasures the mass (weight) of a sample as it is beingheated (or cooled) at a controlled rate. The weight changeof a sample depends on the composition of the sample, thetemperature, the heating rate, and the type of gas in thefurnace (air, oxygen, nitrogen, argon, or other gas). Achange in mass within a specific temperature range identi-fies the presence of a particular chemical compound. Themagnitude of the weight change indicates the amount ofthe compound in the sample.

A sample’s free water will evaporate, lowering themass of the sample, as the temperature is raised from roomtemperature to about 100°C. The sample will also lose someof the water bound in hydration products, particularlysome of the water in the aluminate hydrates.

Between about 100°C and 400°C, water bound in thehydration products, primarily the C-S-H gel, will be lost,together with the remainder of water in the aluminatehydrates. Between about 400°C and 500°C, calciumhydroxide provides a relatively distinct weight loss as itdecomposes to calcium oxide (a solid) and water vapor.The amount of this weight loss can be used to determinehow much calcium hydroxide was originally present in thesample. Above 500°C, a small amount of additional watermay be lost from the hydration products. Carbonatedphases lose carbon dioxide around 800°C.

By quantifying the amount of calcium hydroxide, aTGA gives an indication of the degree of hydration that hastaken place in a sample. The reactivity of pozzolans can beassessed by tracking the disappearance of calcium hydrox-ide due to pozzolanic reaction.

Differential Thermal Analysis (DTA)

Differential thermal analysis (DTA) is an analytical methodin which the difference in temperature between a sampleand a control is measured as the samples are heated. Thecontrol is usually an inert material, like powdered alumina,that does not react over the temperature range being stud-ied. If a sample undergoes a reaction at a certain tempera-ture, then its temperature will increase or decrease relativeto the (inert) control as the reaction gives off heat (exother-mic) or adsorbs heat (endothermic). A thermocouple meas-ures the temperature of each material, allowing thedifference in temperature to be recorded. DTA is ideal formonitoring the transformation of cement compoundsduring hydration. DTA can be performed simultaneouslywith TGA.

Differential Scanning Calorimetry (DSC)

In differential scanning calorimetry (DSC), the heatabsorbed or released is measured directly as a function oftemperature or time and compared to a reference. An

51


20 m

w

a

b

Exo

ther

mic

Temperature, °C100 200 300 400 500

C

C

S

S

E

G

E

Fig. 2-50. Differential scanning calorimetry thermogram of aportland cement paste after (a) 15 minutes and (b) 24 hoursof hydration. C = calcium hydroxide; E = ettringite; G =gypsum; and S = syngenite.

advantage of DTA and DSC methods is that no masschange is required; thus if a sample melts without vaporiz-ing, measurements can still be made.

Like DTA, DSC can be used to determine whatcompounds are present at different stages of hydration.Fig. 2-50 shows two differential scanning calorimetrycurves or thermograms. The upper curve (a) shows a port-land cement paste after 15 minutes of reaction. The peaksin the curve between 100°C and 200°C are due to theendothermic (heat adsorbing) decomposition of gypsumand ettringite, while the peak around 270°C is due tosyngenite (potassium calcium sulfate hydrate). Near 450°C,a smaller peak can be seen, due to calcium hydroxide.

The lower curve (b) in Fig. 2-50 shows the same cementpaste after 24 hours of hydration. Note the disappearanceof the peak due to gypsum, the reduction in the size of thepeak due to syngenite and the growth of those due toettringite and calcium hydroxide. The size of the areasunder the curves are related to the quantity of the materialin the sample.

VIRTUAL CEMENT TESTING

Computer technology now allows simulation of cementcompounds (Fig. 2-51), hydration, microstructure develop-ment, and physical properties. Combinations of materials,cement compounds, or particle size distributions can beexamined to predict cement performance. Just some of theproperties that can be simulated and predicted include heatof hydration, adiabatic heat signature, compressivestrength, setting time, rheology (yield stress and viscosity),

percolation, porosity, diffusivity, thermal conductivity, elec-trical conductivity, carbonation, elastic properties, dryingprofiles, susceptibility to degradation mechanisms, autoge-nous shrinkage, and volumes of hydration reactants andproducts as a function of time. The effects of varying sulfateand alkali contents can be examined, along with interactionwith supplementary cementitious materials and chemicaladmixtures. Computer modeling predicts performancewithout the expense and time requirements of physicaltesting (NIST 2001).

TRANSPORTATION AND PACKAGING

Around 100 million metric tons of cement are shipped peryear throughout the United States. Most portland cementsare shipped in bulk by rail, truck, barge, or ship (Fig. 2-52).Pneumatic (pressurized air) loading and unloading of thetransport vehicle is the most popular means of handling

52


Fig. 2-51. Two-dimensional image of portland cement. Colorsare: red–tricalcium silicate, aqua–dicalcium silicate, green–tricalcium aluminate, yellow–tetracalcium aluminoferrite,pale green–gypsum, white–free lime, dark blue–potassiumsulfate, and magenta–periclase. The image was obtained bycombining a set of SEM backscattered electron and X-rayimages (NIST 2001).

Fig. 2-52. Portland cements are shipped from the plant silos to the user in bulk by (left to right) rail, truck, or water. (59899,59355, 59891)

bulk cement. However, the recent introduction of largesacks holding one to twelve tons of cement provides a newalternative to bulk cement handling. Bulk cement is meas-ured by the metric ton (1000 kg) or short ton (2000 lb).

Cement is also bagged for convenient use at construc-tion sites (Fig. 2-53) and for small jobs. In the United Statesa bag of portland cement has a mass of 42 kg (92.6 lb) anda volume of 28 liters. Traditionally a U. S. bag contains 94 lb(42.6 kg) and has a volume of one cubic foot. The mass ofmasonry cement and mortar cement by the bag is 36 kg forType M, 34 kg for Type S, and 32 kg for Type N. Plasticcement has a mass of 42 kg for Type M and 35 kg for TypeS. All bag weights are based on a 28 liter volume standard.Information for quantities of blended and specialtycements can be found on the bag. Partial bag sizes are alsoavailable in some areas.

In Canada, a bag of portland cement has a mass of 40kg, and in other countries a bag of cement can have a massof 25 kg or 50 kg.

Because of the variability of bag sizes and the presenceof supplementary cementitious materials, cement bagfactor terminology, such as “a six bag mix” should not beused to describe the cement content of concrete mixtures.

In the 1800s and early 1900s, cement was shipped inbarrels; one barrel contained 4 bags (171 kg or 376 lbs or 4cu ft) of cement. Use of the barrel unit is archaic and shouldnot be used.

STORAGE OF CEMENT

Cement is a moisture-sensitive material; if kept dry, it willretain its quality indefinitely. Cement stored in contact withdamp air or moisture sets more slowly and has lessstrength than cement that is kept dry. At the cement plant,and at ready mixed concrete facilities, bulk cement is storedin silos. The relative humidity in a warehouse or shed usedto store bagged cement should be as low as possible. Allcracks and openings in walls and roofs should be closed.Cement bags should not be stored on damp floors butshould rest on pallets. Bags should be stacked closetogether to reduce air circulation but should never be

stacked against outside walls. Bags to be stored for longperiods should be covered with tarpaulins or other water-proof covering. Bags should be stored so that the first in arethe first out.

On small jobs where a shed is not available, bagsshould be placed on raised wooden platforms (pallets)above the ground. Waterproof coverings should fit over thepile and extend over the edges of the platform to preventrain from reaching the cement and the platform (Fig. 2-54).Rain-soaked platforms can damage the bottom bags ofcement.

Cement stored for long periods may develop what iscalled warehouse pack. This can usually be corrected byrolling the bags on the floor. At the time of use, cementshould be free-flowing and free of lumps. If lumps do notbreak up easily, the cement should be tested before it isused in important work. Standard strength tests or loss-on-ignition tests should be made whenever the quality of acement is doubtful.

Ordinarily, cement does not remain in storage long,but it can be stored for long periods without deterioration.Bulk cement should be stored in weathertight concrete orsteel bins or silos. Dry low-pressure aeration or vibrationshould be used in bins or silos to keep the cement flowableand avoid bridging. Due to fluffing of cement, silos mayhold only about 80% of rated capacity.

HOT CEMENT

When cement clinker is pulverized in the grinding millduring cement manufacture, the friction generates heat.Freshly ground cement is therefore hot when placed instorage silos at the cement plant. This heat dissipatesslowly, therefore, during summer months when demand ishigh, cement may still be hot when delivered to a ready

mixed concrete plant or jobsite. Tests have shown that theeffect of hot cement on the workability and strength devel-opment of concrete is not significant (Lerch 1955). Thetemperatures of the mixing water and aggregates play amuch greater role in establishing the final temperature ofthe concrete as mixed.

53


Fig. 2-53. A small amount of cement is shipped in bags,primarily for mortar applications and for small projects.(59411)

Fig. 2-54. When stored on the job, cement should beprotected from moisture. (36052)

REFERENCES

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ACI Committee 223, Standard Practice for the Use ofShrinkage Compensating Concrete, ACI 223, American Con-crete Institute, Farmington Hills, Michigan, 1998, 28 pages.

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Copeland, L. E., and Schulz, Edith G., Electron OpticalInvestigation of the Hydration Products of Calcium Silicates andPortland Cement, Research Department Bulletin RX135,Portland Cement Association, http://www.portcement.org/pdf_files/RX135.pdf, 1962.

Davidovits, Joseph; Davidovits, Ralph; and James, Claude,editors, Geopolymer ‘99, The Geopolymer Institute,http://www.geopolymer.org, Insset, Université de Pic-ardie, Saint-Quentin, France, July 1999.

DeHayes, Sharon M., “C 109 vs. Concrete Strengths” Pro-ceedings of the Twelfth International Conference on CementMicroscopy, International Cement Microscopy Association,Duncanville, Texas, 1990.

Detwiler, Rachel J.; Bhatty, Javed I.; Barger, Gregory; andHansen, Eric R., “Durability of Concrete Containing Cal-cined Clay,” Concrete International, April 2001, pages 43 to 47.

Detwiler, Rachel J.; Bhatty, Javed I.; and Bhattacharja,Sankar, Supplementary Cementing Materials for Use in BlendedCements, Research and Development Bulletin RD112,Portland Cement Association, 1996, 108 pages.

EN 197-1, European Standard for Cement—Part 1: Composi-tion, Specifications and Common Cements, European Commit-tee for Standardization (CEN), Brussels, 2000.

EN 197-2, European Standards for Cement—Part 2: ConformityEvaluation, European Committee for Standardization (CEN),Brussels, 2000.

Farny, James A., White Cement Concrete, EB217, PortlandCement Association, 2001, 32 pages.

Gajda, John, Development of a Cement to Inhibit Alkali-SilicaReactivity, Research and Development Bulletin RD115,Portland Cement Association, 1996, 58 pages.

Gebhardt, R. F., “Survey of North American PortlandCements: 1994,” Cement, Concrete, and Aggregates, AmericanSociety for Testing and Materials, West Conshohocken,Pennsylvania, December 1995, pages 145 to 189.

Gonnerman, H. F., Development of Cement Performance Testsand Requirements, Research Department Bulletin RX093,Portland Cement Association, http://www.portcementorg/pdf_files/RX093.pdf, 1958.

Gonnerman, H. F., and Lerch, William, Changes in Charac-teristics of Portland Cement As Exhibited by Laboratory TestsOver the Period 1904 to 1950, Research Department BulletinRX039, Portland Cement Association, http://www.portcement.org/pdf_files/RX039.pdf, 1952.

Gonnerman, H. F.; Lerch, William; and Whiteside, ThomasM., Investigations of the Hydration Expansion Characteristics ofPortland Cements, Research Department Bulletin RX045,Portland Cement Association, http://www.portcement.org/pdf_files/RX045.pdf, 1953.

Barger, Gregory S.; Lukkarila, Mark R.; Martin, David L.;Lane, Steven B.; Hansen, Eric R.; Ross, Matt W.; andThompson, Jimmie L., “Evaluation of a Blended Cementand a Mineral Admixture Containing Calcined ClayNatural Pozzolan for High-Performance Concrete,” Pro-ceedings of the Sixth International Purdue Conference onConcrete Pavement Design and Materials for High Performance,Purdue University, West Lafayette, Indiana, November1997, 21 pages.

Bentz, Dale P., and Farney, Glenn P., User’s Guide to the NISTVirtual Cement and Concrete Testing Laboratory, Version 1.0,NISTIR 6583, November. 2000.

Bhatty, Javed I., “Application of Thermal Analysis toProblems in Cement Chemistry,” Chapter 6, Treatise onAnalytical Chemistry, Part 1, Volume 13, J. D. Winefordnereditor, John Wiley & Sons, 1993, pages 355 to 395.

Bhatty, Javed I., Role of Minor Elements in CementManufacture and Use, Research and Development BulletinRD109, Portland Cement Association, 1995, 48 pages.

Brown, Gordon E., Analysis and History of Cement, GordonE. Brown Associates, Keswick, Ontario, 1996, 259 pages.

Brunauer, S., Some Aspects of the Physics and Chemistry ofCement, Research Department Bulletin RX080, PortlandCement Association, http://www.portcement.org/pdf_files/RX080.pdf, 1957.

Brunauer, Stephen, Tobermorite Gel—The Heart of Concrete,Research Department Bulletin RX138, Portland CementAssociation, http://www.portcement.org/pdf_files/RX138.pdf, 1962, 20 pages.

Bureau of Reclamation, Concrete Manual, 8th ed., U.S.Bureau of Reclamation, Denver, Colorado, revised 1981.

BS 915-2, Specification for High Alumina Cement, BritishStandards Institution, 1972.

Campbell, Donald H., Microscopical Examination andInterpretation of Portland Cement and Clinker, SP030, PortlandCement Association, 1999.

Clausen, C. F., Cement Materials, Research DepartmentReport MP-95, Portland Cement Association, 1960.

Copeland, L.E., and Hayes, John C., The Determination ofNon-evaporable Water in Hardened Portland Cement Paste,Research Department Bulletin RX047, Portland CementAssociation, http://www.portcement.org/pdf_files/RX047.pdf, 1953.

Copeland, L. E.; Kantro, D. L.; and Verbeck, George,Chemistry of Hydration of Portland Cement, ResearchDepartment Bulletin RX153, Portland Cement Association,http://www.portcement.org/pdf_files/RX153.pdf, 1960.

54


Greening, Nathan R.; Copeland, Liewellyn E.; and Verbeck,George J., Modified Portland Cement and Process, UnitedStates Patent No. 3,628,973, Issued to Portland CementAssociation, December 21, 1971.

Hansen, W. C.; Offutt, J. S.; Roy, D. M.; Grutzeck, M. W.;and Schatzlein, K. J., Gypsum & Anhydrite in PortlandCement, United States Gypsum Company, Chicago, 1988,104 pages.

Helmuth, Richard; Hills, Linda M.; Whiting, David A.; andBhattacharja, Sankar, Abnormal Concrete Performance in thePresence of Admixtures, RP333, Portland Cement Associa-tion, 1995, 94 pages.

Hills, Linda M., “Clinker Formation and the Value of Mi-croscopy,” Proceedings of the Twenty-Second International Con-ference on Cement Microscopy, Montreal, 2000, pages 1 to 12.

Johansen, Vagn, and Idorn, G. M., “Cement Production andCement Quality,” Material Science of Concrete I, Edited by J.Skalny, American Ceramic Society, 1989, pages 27 to 72.

Kanare, Howard M., Certifying Portland Cement to ANSI/NSF61 for Use in Drinking Water System Components, SP117, Port-land Cement Association, 1995, 253 pages.

Kanare, Howard M., and West, Presbury B., “Leachabilityof Selected Chemical Elements from Concrete,” EmergingTechnologies Symposium on Cement and Concrete in the GlobalEnvironment, SP114, Portland Cement Association, 1993,366 pages.

Klemm, Waldemar A., Ettringite and Oxyanion-SubstitutedEttringites—Their Characterization and Applications in theFixation of Heavy Metals: A Synthesis of the Literature, Re-search and Development Bulletin RD116, Portland CementAssociation, 1998, 80 pages.

Klieger, Paul, and Isberner, Albert W., Laboratory Studies ofBlended Cements—Portland Blast-Furnace Slag Cements, Re-search Department Bulletin RX218, Portland Cement Asso-ciation, http://www.portcement.org/pdf_files/RX218.pdf, 1967.

Lange, D. and Stutzman, P., The Concrete Microscopy Library,http://www.cee.ce.uiuc.edu/lange/micro, 1999.

Lea, F. M., The Chemistry of Cement and Concrete, 3rd ed.,Chemical Publishing Co., Inc., New York, 1971.

Lerch, William, Hot Cement and Hot Weather Concrete Tests,IS015, Portland Cement Association, http://www.portcement.org/pdf_files/IS015.pdf, 1955.

Lerch, William, The Influence of Gypsum on the Hydration andProperties of Portland Cement Pastes, Research DepartmentBulletin RX012, Portland Cement Association, http://www.portcement.org/pdf_files/RX012.pdf, 1946.

Locher, F. W.; Richartz, W.; and Sprung, S., “Setting of Ce-ment–Part I: Reaction and Development of Structure;” ZKGINTERN. 29, No. 10, 1976, pages 435 to 442.

McMillan, F. R.; Tyler, I. L.; Hansen, W. C.; Lerch, W.; Ford,C. L.; and Brown, L. S., Long-Time Study of Cement Perform-ance in Concrete, Research Department Bulletin RX026,Portland Cement Association, 1948.

Melander, John M. and Isberner, Albert W. Jr., PortlandCement Plaster (Stucco) Manual, EB049, Portland CementAssociation, 1996, 60 pages.

Nehdi, Moncef, “Ternary and Quaternary Cements for Sus-tainable Development,” Concrete International, April 2001,pages 35 to 42.

NF P15-315, Hydraulic Binders. High Alumina MeltedCement, AFNOR Association française de normalisation,1991.

NIST, Virtual Cement and Concrete Testing Laboratory,http://vcctl.cbt.nist.gov, 2001.

Odler, Ivan, Special Inorganic Cements, E&FN Spon, NewYork, 2000, 420 pages.

PCA, An Analysis of Selected Trace Metals in Cement and KilnDust, SP109, Portland Cement Association, 1992, 60 pages.

PCA, Emerging Technologies Symposium on Cements for the21st Century, SP206, Portland Cement Association, 1995,140 pages.

PCA, “Portland Cement: Past and Present Characteristics,”Concrete Technology Today, PL962, Portland CementAssociation, http://www.portcement.org/pdf_files/PL962.pdf, July 1996, pages 1 to 4.

PCA, “Portland Cement, Concrete, and the Heat ofHydration,” Concrete Technology Today, PL972, PortlandCement Association, http://www.portcement.org/pdf_files/PL972.pdf, July 1997, pages 1 to 4.

PCA, “What is White Cement?,” Concrete Technology Today,PL991, Portland Cement Association, http://www.portcement.org/pdf_files/PL991.pdf, April 1999, 4 pages.

PCA, U.S. Cement Industry Fact Sheet, Portland CementAssociation, 2002.

Perenchio, William F., and Klieger, Paul, Further LaboratoryStudies of Portland-Pozzolan Cements, Research and Devel-opment Bulletin RD041, Portland Cement Association,http://www.portcement.org/pdf_files/RD041.pdf, 1976.

Pfeifer, Donald W., and Perenchio, W. F., Reinforced ConcretePipe Made with Expansive Cements, Research and Devel-opment Bulletin RD015, Portland Cement Association,http://www.portcement.org/pdf_files/RD015.pdf, 1973.

Powers, T. C., Some Physical Aspects of the Hydration ofPortland Cement, Research Department Bulletin RX125,Portland Cement Association, http://www.portcement.org/pdf_files/RX125.pdf, 1961.

55


Taylor, H. F. W., Cement Chemistry, Thomas Telford Pub-lishing, London, 1997, 477 pages.

Tennis, Paul D., “Laboratory Notes: Thermal Analysis byTGA, DTA, and DSC,” Concrete Technology Today, PL971,Portland Cement Association, http://www.portcement.org/pdf_files/PL971.pdf, April 1997, pages 6 and 7.

Tennis, Paul D., and Jennings, Hamlin M., “A Model forTwo Types of Calcium Silicate Hydrate in the Micro-structure of Portland Cement Pastes,” Cement and ConcreteResearch, Pergamon, June 2000, pages 855 to 863.

Toler, H. R., Flowability of Cement, Research DepartmentReport MP-106, Portland Cement Association, October,1963.

Verbeck, G. J., Field and Laboratory Studies of the SulphateResistance of Concrete, Research Department Bulletin RX227,Portland Cement Association, http://www.portcement.org/pdf_files/RX227.pdf, 1967.

Washa, George W., and Wendt, Kurt F., “Fifty YearProperties of Concrete,” ACI Journal, American ConcreteInstitute, Farmington Hills, Michigan, January 1975, pages20 to 28.

Weaver, W. S.; Isabelle, H. L.; and Williamson, F., “A Studyof Cement and Concrete Correlation,” Journal of Testing andEvaluation, American Society for Testing and Materials,West Conshohocken, Pennsylvania, January 1974, pages260 to 280.

White, Canvass, Hydraulic Cement, U. S. patent, 1820.


Powers, T. C., The Nonevaporable Water Content of HardenedPortland-Cement Paste–Its Significance for Concrete Researchand Its Method of Determination, Research DepartmentBulletin RX029, Portland Cement Association, http://www.portcement.org/pdf_files/RX029.pdf, 1949.

Powers, T. C., and Brownyard, T. L., Studies of the PhysicalProperties of Hardened Portland Cement Paste, Research De-partment Bulletin RX022, Portland Cement Association,http://www.portcement.org/pdf_files/RX022.pdf, 1947.

Russell, H. G., Performance of Shrinkage-Compensating Con-cretes in Slabs, Research and Development Bulletin RD057,Portland Cement Association, http://www.portcement.org/pdf_files/RD057.pdf, 1978.

Shkolnik, E., and Miller, F. M., “Differential ScanningCalorimetry for Determining the Volatility and Combust-ibility of Cement Raw Meal Organic Matter,” World CementResearch and Development, May 1996, pages 81 to 87.

Snell, Luke M., and Snell, Billie G., The Erie Canal—America’s First Concrete Classroom, http://www.siue.edu/~lsnell/erie.htm, 2000.

Stark, David, Durability of Concrete in Sulfate-Rich Soils,Research and Development Bulletin RD097, Portland Ce-ment Association, http://www.portcement.org/pdf_files/RD097.pdf, 1989.

Stark, David, Performance of Concrete in Sulfate Environments,R&D Serial No. 2248, Portland Cement Association, 2002.

Tang, Fulvio J., Optimization of Sulfate Form and Content,Research and Development Bulletin RD105, PortlandCement Association, 1992, 44 pages.

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CHAPTER 3

Fly Ash, Slag, Silica Fume,and Natural Pozzolans

Fly ash, ground granulated blast-furnace slag, silica fume,and natural pozzolans, such as calcined shale, calcined clayor metakaolin, are materials that, when used in conjunc-tion with portland or blended cement, contribute to theproperties of the hardened concrete through hydraulic orpozzolanic activity or both (Fig. 3-1). A pozzolan is asiliceous or aluminosiliceous material that, in finelydivided form and in the presence of moisture, chemicallyreacts with the calcium hydroxide released by the hydra-tion of portland cement to form calcium silicate hydrateand other cementitious compounds. Pozzolans and slagsare generally catergorized as supplementary cementitiousmaterials or mineral admixtures. Table 3-1 lists the appli-cable specifications these materials meet. The use of thesematerials in blended cements is discussed in Chapter 2 andby Detwiler, Bhatty, and Bhattacharja (1996).

The practice of using supplementary cementitiousmaterials in concrete mixtures has been growing in NorthAmerica since the 1970s. There are similarities betweenmany of these materials in that most are byproducts ofother industrial processes; their judicious use is desirablenot only from the national environmental and energy

conservation standpoint but also for the technical benefitsthey provide concrete.

Supplementary cementitious materials are added toconcrete as part of the total cementitious system. They maybe used in addition to or as a partial replacement of portlandcement or blended cement in concrete, depending on theproperties of the materials and the desired effect on concrete.

Supplementary cementitious materials are used toimprove a particular concrete property, such as resistance toalkali-aggregate reactivity. The optimum amount to useshould be established by testing to determine (1) whether thematerial is indeed improving the property, and (2) the correctdosage rate, as an overdose or underdose can be harmful ornot achieve the desired effect. Supplementary cementitiousmaterials also react differently with different cements.

Traditionally, fly ash, slag, calcined clay, calcined shale,and silica fume were used in concrete individually. Today,due to improved access to these materials, concrete produc-ers can combine two or more of these materials to optimizeconcrete properties. Mixtures using three cementitiousmaterials, called ternary mixtures, are becoming more

Fig. 3-1. Supplementary cementitious materials. From leftto right, fly ash (Class C), metakaolin (calcined clay), silicafume, fly ash (Class F), slag, and calcined shale. (69794)

Fig. 3-2. Scanning electron microscope (SEM) micrographof fly ash particles at 1000X. Although most fly ashspheres are solid, some particles, called cenospheres,are hollow (as shown in the micrograph). (54048)

57

area is typically 300 to 500 m2/kg, although some fly ashescan have surface areas as low as 200 m2/kg and as high as700 m2/kg. For fly ash without close compaction, the bulkdensity (mass per unit volume including air betweenparticles) can vary from 540 to 860 kg/m3 (34 to 54 lb/ft3),whereas with close packed storage or vibration, the rangecan be 1120 to 1500 kg/m3 (70 to 94 lb/ft3).

Fly ash is primarily silicate glass containing silica,alumina, iron, and calcium. Minor constituents are magne-sium, sulfur, sodium, potassium, and carbon. Crystallinecompounds are present in small amounts. The relativedensity (specific gravity) of fly ash generally rangesbetween 1.9 and 2.8 and the color is generally gray or tan.

ASTM C 618 (AASHTO M 295) Class F and Class C flyashes are commonly used as pozzolanic admixtures forgeneral purpose concrete (Fig. 3-4). Class F materials aregenerally low-calcium (less than 10% CaO) fly ashes with

common. Supplementary cementitious materials are used inat least 60% of ready mixed concrete (PCA 2000). ASTM C311 provides test methods for fly ash and natural pozzolansfor use as supplementary cementitious material in concrete.

FLY ASH

Fly ash, the most widely used supplementary cementitiousmaterial in concrete, is a byproduct of the combustion ofpulverized coal in electric power generating plants. Uponignition in the furnace, most of the volatile matter andcarbon in the coal are burned off. During combustion, thecoal’s mineral impurities (such as clay, feldspar, quartz,and shale) fuse in suspension and are carried away fromthe combustion chamber by the exhaust gases. In theprocess, the fused material cools and solidifies into spheri-cal glassy particles called fly ash (Fig. 3-2). The fly ash isthen collected from the exhaust gases by electrostaticprecipitators or bag filters. Fly ash is a finely dividedpowder resembling portland cement (Fig. 3-3).

Most of the fly ash particles are solid spheres and someare hollow cenospheres. Also present are plerospheres,which are spheres containing smaller spheres. Groundmaterials, such as portland cement, have solid angularparticles. The particle sizes in fly ash vary from less than1 µm (micrometer) to more than 100 µm with the typicalparticle size measuring under 20 µm. Only 10% to 30% ofthe particles by mass are larger than 45 µm. The surface

58


Fig. 3-4. Fly ash, slag, and calcined clay or calcined shale are used in general purpose construction, such as (left to right)walls for residential buildings, pavements, high-rise towers, and dams. (67279, 48177, 69554, 69555)

Fig. 3-3. Fly ash, a powder resembling cement, has beenused in concrete since the 1930s. (69799)

Table 3-1. Specifications and Classes ofSupplementary Cementitious Materials

Ground granulated iron blast-furnace slags—ASTM C 989(AASHTO M 302)

Grade 80Slags with a low activity index

Grade 100Slags with a moderate activity index

Grade 120Slags with a high activity index

Fly ash and natural pozzolans—ASTM C 618 (AASHTO M 295)

Class NRaw or calcined natural pozzolans including:Diatomaceous earthsOpaline cherts and shalesTuffs and volcanic ashes or pumicitesCalcined clays, including metakaolin, and shales

Class FFly ash with pozzolanic properties

Class CFly ash with pozzolanic and cementitious properties

Silica fume—ASTM C 1240

carbon contents usually less than 5%, but some may be ashigh as 10%. Class C materials are often high-calcium (10%to 30% CaO) fly ashes with carbon contents less than 2%.Many Class C ashes when exposed to water will hydrateand harden in less than 45 minutes. Some fly ashes meetboth Class F and Class C classifications.

Fly ash is used in about 50% of ready mixed concrete(PCA 2000). Class F fly ash is often used at dosages of 15%to 25% by mass of cementitious material and Class C flyash is used at dosages of 15% to 40% by mass of cementi-tious material. Dosage varies with the reactivity of the ashand the desired effects on the concrete (Helmuth 1987 andACI 232 1996).

SLAG

Ground granulated blast-furnace slag (Fig. 3-5), also calledslag cement, is made from iron blast-furnace slag; it is anonmetallic hydraulic cement consisting essentially of sili-cates and aluminosilicates of calcium developed in amolten condition simultaneously with iron in a blastfurnace. The molten slag at a temperature of about 1500°C(2730°F) is rapidly chilled by quenching in water to form a

glassy sandlike granulated material. The granulated mate-rial, which is ground to less than 45 microns, has a surfacearea fineness of about 400 to 600 m2/kg Blaine. The relativedensity (specific gravity) for ground granulated blast-furnace slag is in the range of 2.85 to 2.95. The bulk densityvaries from 1050 to 1375 kg/m3 (66 to 86 lb/ft3).

The rough and angular-shaped ground slag (Fig. 3-6)in the presence of water and an activator, NaOH or CaOH,both supplied by portland cement, hydrates and sets in amanner similar to portland cement. However, air-cooledslag does not have the hydraulic properties of water-cooled slag.

Granulated blast furnace slag was first developed inGermany in 1853 (Malhotra 1996). Ground slag has beenused as a cementitious material in concrete since the begin-ning of the 1900s (Abrams 1925). Ground granulated blast-furnace slag, when used in general purpose concrete inNorth America, commonly constitutes between 30% and45% of the cementing material in the mix (Fig. 3-4) (PCA2000). Some slag concretes have a slag component of 70%or more of the cementitious material. ASTM C 989(AASHTO M 302) classifies slag by its increasing level ofreactivity as Grade 80, 100, or 120 (Table 3-1). ASTM C 1073covers a rapid determination of hydraulic activity of

59

Chapter 3 � Fly Ash, Slag, Silica Fume, and Natural Pozzolans

Fig. 3-5. Ground granulated blast-furnace slag. (69800) Fig. 3-7. Silica fume powder. (69801)

Fig. 3-6. Scanning electron microscope micrograph of slagparticles at 2100X. (69541)

Fig. 3-8. Scanning electron microscope micrograph of silica-fume particles at 20,000X. (54095)

NATURAL POZZOLANS Natural pozzolans have been used for centuries. The term“pozzolan” comes from a volcanic ash mined at Pozzuoli,a village near Naples, Italy, following the 79 AD eruptionof Mount Vesuvius. However, the use of volcanic ash andcalcined clay dates back to 2000 BC and earlier in othercultures. Many of the Roman, Greek, Indian, and Egyptianpozzolan concrete structures can still be seen today, attest-ing to the durability of these materials.

The North American experience with naturalpozzolans dates back to early 20th century public worksprojects, such as dams, where they were used to controltemperature rise in mass concrete and provide cementi-tious material. In addition to controlling heat rise, naturalpozzolans were used to improve resistance to sulfate attackand were among the first materials to be found to mitigatealkali-silica reaction.

The most common natural pozzolans used today areprocessed materials, which are heat treated in a kiln andthen ground to a fine powder (Figs. 3-10, 3-11, and 3-12); theyinclude calcined clay, calcined shale, and metakaolin.

ground granulated blast furnace slag and ACI 233 (1995)provides an extensive review of slag.

SILICA FUMESilica fume, also referred to as microsilica or condensedsilica fume, is a byproduct material that is used as a poz-zolan (Fig. 3-7). This byproduct is a result of the reductionof high-purity quartz with coal in an electric arc furnace inthe manufacture of silicon or ferrosilicon alloy. Silica fumerises as an oxidized vapor from the 2000°C (3630°F)furnaces. When it cools it condenses and is collected inhuge cloth bags. The condensed silica fume is thenprocessed to remove impurities and to control particle size.

Condensed silica fume is essentially silicon dioxide(usually more than 85%) in noncrystalline (amorphorous)form. Since it is an airborne material like fly ash, it has aspherical shape (Fig. 3-8). It is extremely fine with particlesless than 1 µm in diameter and with an average diameterof about 0.1 µm, about 100 times smaller than averagecement particles.

Condensed silica fume has a surface area of about20,000 m2/kg (nitrogen adsorption method). For compari-son, tobacco smoke’s surface area is about 10,000 m2/ kg.Type I and Type III cements have surface areas of about 300to 400 m2/kg and 500 to 600 m2/kg (Blaine), respectively.

The relative density of silica fume is generally in therange of 2.20 to 2.5. Portland cement has a relative densityof about 3.15. The bulk density (uncompacted unit weight)of silica fume varies from 130 to 430 kg/m3 (8 to 27 lb/ft3).

Silica fume is sold in powder form but is morecommonly available in a liquid. Silica fume is used inamounts between 5% and 10% by mass of the total cemen-titious material. It is used in applications where a highdegree of impermeability is needed (Fig. 3-9) and in high-strength concrete. Silica fume must meet ASTM C 1240.ACI 234 (1994) and SFA (2000) provide an extensive reviewof silica fume.

60


Fig. 3-9. Although they can be used in general construction, silica fume and metakaolin are often used in applications suchas (left) bridges and (right) parking garages to minimize chloride penetration into concrete. (68681, 69542)

Fig. 3-10. Scanning electron microscope micrograph ofcalcined shale particles at 5000X. (69543)

Calcined clays are used in general purpose concreteconstruction much the same as other pozzolans (Fig. 3-4).They can be used as a partial replacement for the cement,typically in the range of 15% to 35%, and to enhance resist-ance to sulfate attack, control alkali-silica reactivity, andreduce permeability. Calcined clays have a relative densityof between 2.40 and 2.61 with Blaine fineness ranging from650 m2/kg to 1350 m2/kg. Calcined shale may contain onthe order of 5% to 10% calcium, which results in the mate-rial having some cementing or hydraulic properties on itsown. Because of the amount of residual calcite that is notfully calcined, and the bound water molecules in the clayminerals, calcined shale will have a loss on ignition (LOI) ofperhaps 1% to 5%. The LOI value for calcined shale is not ameasure or indication of carbon content as would be thecase in fly ash.

Metakaolin, a special calcined clay, is produced by low-temperature calcination of high purity kaolin clay. The prod-uct is ground to an average particle size of about 1 to 2

micrometers. Metakaolin is used in special applicationswhere very low permeability or very high strength is re-quired. In these applications, metakaolin is used more as anadditive to the concrete rather than a replacement of cement;typical additions are around 10% of the cement mass.

Natural pozzolans are classified by ASTM C 618(AASHTO M 295) as Class N pozzolans (Table 3-1). ACI 232(2000) provides a review of natural pozzolans. Table 3-2illustrates typical chemical analysis and selected propertiesof pozzolans.

EFFECTS ON FRESHLY MIXED CONCRETE

This section provides a brief understanding of the freshlymixed concrete properties that supplementary cementi-tious materials affect and their degree of influence. First itshould be noted that these materials vary considerably intheir effect on concrete mixtures. The attributes of thesematerials when added separately to a concrete mixture

can also be found inblended cements usingsupplementary cementi-tious materials.

WaterRequirements

Concrete mixtures con-taining fly ash generallyrequire less water (about1% to 10% less at normaldosages) for a givenslump than concretecontaining only port-land cement. Higherdosages can result ingreater water reduction(Table 3-3). However,some fly ashes can in-

61


Fig. 3-11. Metakaolin, a calcined clay. (69803) Fig. 3-12. Scanning electron microscope micrograph ofcalcined clay particles at 2000X. (69544)

Table 3-2. Chemical Analysis and Selected Properties of Typical Fly Ash, Slag, Silica Fume, Calcined Clay, Calcined Shale, and Metakaolin

Class F Class C Ground Silica Calcined Calcinedfly ash fly ash slag fume clay shale Metakaolin

SiO2, % 52 35 35 90 58 50 53Al2O3, % 23 18 12 0.4 29 20 43Fe2O3, % 11 6 1 0.4 4 8 0.5CaO, % 5 21 40 1.6 1 8 0.1SO3, % 0.8 4.1 9 0.4 0.5 0.4 0.1Na2O, % 1.0 5.8 0.3 0.5 0.2 — 0.05K2O, % 2.0 0.7 0.4 2.2 2 — 0.4Total Na

eq. alk, % 2.2 6.3 0.6 1.9 1.5 — 0.3Loss on

ignition, % 2.8 0.5 1.0 3.0 1.5 3.0 0.7Blaine fineness,

m2/kg 420 420 400 20,000 990 730 19,000Relative

density 2.38 2.65 2.94 2.40 2.50 2.63 2.50

62

bleed water is primarily due to the reducedwater demand in fly ash concretes. Geblerand Klieger (1986) correlate reduced bleed-ing of concrete to the reduced waterrequirement of fly ash mortar.

Concretes containing ground slags ofcomparable fineness to that of the cementtend to show an increased rate and amountof bleeding than plain concretes, but thisappears to have no adverse effect on segre-gation. Slags ground finer than cementreduce bleeding.

Silica fume is very effective in reduc-ing both bleeding and segregation; as aresult, higher slumps may be used. Cal-cined clays, calcined shales, and metakao-lin have little effect on bleeding.

Air Content

The amount of air-entraining admixturerequired to obtain a specified air content is

normally greater when fly ash is used. Class C ash requiresless air-entraining admixture than Class F ash and tends tolose less air during mixing (Table 3-5). Ground slags havevariable effects on the required dosage rate of air-entrain-ing admixtures. Silica fume has a marked influence on theair-entraining admixture requirement, which in most casesrapidly increases with an increase in the amount of silicafume used in the concrete. The inclusion of both fly ashand silica fume in non-air-entrained concrete will generallyreduce the amount of entrapped air.

crease water demand up to 5% (Gebler and Klieger 1986).Fly ash reduces water demand in a manner similar toliquid chemical water reducers (Helmuth 1987). Groundslag usually decreases water demand by 1% to 10%,depending on dosage.

The water demand of concrete containing silica fumeincreases with increasing amounts of silica fume, unless awater reducer or plasticizer is used. Some lean mixes maynot experience an increase in water demand when only asmall amount (less than 5%) of silica fume is present.

Calcined clays and calcined shalesgenerally have little effect on water de-mand at normal dosages; however, othernatural pozzolans can significantly in-crease or decrease water demand.

Workability

Fly ash, slag, and calcined clay and shalegenerally improve the workability ofconcretes of equal slump. Silica fume maycontribute to stickiness of a concretemixture; adjustments, including the use ofhigh-range water reducers, may be re-quired to maintain workability and permitproper compaction and finishing.

Bleeding and Segregation

Concretes using fly ash generally exhibitless bleeding and segregation than plainconcretes (Table 3-4). This effect makes theuse of fly ash particularly valuable inconcrete mixtures made with aggregatesthat are deficient in fines. The reduction in


Table 3-4. Effect of Fly Ash on Bleeding of Concrete (ASTM C 232, AASHTO T 158)*

* All mixtures had cementitious materials contents of 307 kg/m3 (517 lb/yd3), a slumpof 75 ± 25 mm (3 ± 1 in.), and an air content of 6 ± 1%. Fly ash mixtures contained25% ash by mass of cementitious material (Gebler and Klieger 1986).

** Volume of bleed water per surface area.

Fly ash mixtures BleedingIdentification Class of fly ash Percent mL/cm2**

A C 0.22 0.007B F 1.11 0.036C F 1.61 0.053D F 1.88 0.067E F 1.18 0.035F C 0.13 0.004G C 0.89 0.028H F 0.58 0.022I C 0.12 0.004J F 1.48 0.051

Average of:Class C 0.34 0.011Class F 1.31 0.044

Control mixture 1.75 0.059

Table 3-3. Effect of Fly Ash on Mixing Water Requirements forAir-Entrained Concrete

All mixtures had cementitious materials contents of 335 kg/m3 (564 lb/yd3), a slump of125 ± 25 mm (5 ± 1 in.), and an air content of 6 ± 1%. Water to cement plus fly ash ratiosvaried from 0.40 to 0.48 (Whiting 1989).

Fly ash content, Change in mixingFly ash mix Class of % by mass of water requirement

identification fly ash cementitious material compared to control, %

C1A C 25 -6C1D F 25 -2C1E F 25 -6C1F C 25 -8C1G C 25 -6C1J F 25 -6C2A C 50 -18C2D F 50 -6C2E F 50 -14C2F C 50 -16C2G C 50 -12C2J F 50 -10

The amount of air-entraining admixture required for acertain air content in the concrete is a function of the fine-ness, carbon content, alkali content, organic materialcontent, loss on ignition, and presence of impurities in thefly ash. Increases in alkalies decrease air-entraining agentdosages, while increases in the other properties increasedosage requirements. The Foam Index test provides anindication of the required dosage of air-entraining admix-ture for various fly ashes relative to non-ash mixtures; it canalso be used to anticipate the need to increase or decreasethe dosage based on changes in the foam index (Gebler andKlieger 1983).

The air-entraining dos-age and air retention char-acteristics of concretes con-taining ground slag ornatural pozzolans are sim-ilar to mixtures made onlywith portland cement.

Heat of Hydration

Fly ash, natural pozzolans,and ground slag have alower heat of hydrationthan portland cement; con-sequently their use will re-duce the amount of heatbuilt up in a concrete struc-ture (Fig. 3-13). Calcinedclay imparts a heat of hy-dration similar to mod-erate heat cement (Bargerand others 1997). Some

pozzolans have a heat of hydration of only 40% that ofType I portland cement. This reduction in temperature riseis especially beneficial in concrete used for massive struc-tures. Silica fume may or may not reduce the heat of hydra-tion. Detwiler and others (1996) provide a review of theeffect of pozzolans and slags on heat generation.

Setting Time

The use of fly ash and ground granulated blast-furnaceslag will generally retard the setting time of concrete (Table3-6). The degree of set retardation depends on factors such

63


Table 3-5. Effect of Fly Ash on Air-Entraining Admixture Dosage and Air Retention

Concretes had a cementitious materials content of 307 kg/m3 (517 lb/yd3) and a slump of 75 ± 25 mm (3 ± 1 in.). Fly ash mixtures contained 25% ash by mass of cementitious material (Gebler and Klieger 1983).

Percent of air-entraining

admixture Fly ash mixtures relative to control Air content, %

Minutes after initial mixingIdentification Class of fly ash 0 30 60 90

A C 126 7.2 6.0 6.0 5.8B F 209 5.3 4.1 3.4 3.1C F 553 7.0 4.7 3.8 2.9D F 239 6.6 5.4 4.2 4.1E F 190 5.6 4.6 4.3 3.8F C 173 6.8 6.5 6.3 6.4G C 158 5.5 4.8 4.5 4.2H F 170 7.6 6.9 6.5 6.6I C 149 6.6 6.5 6.5 6.8J F 434 5.5 4.2 3.8 3.4

Control mixture 100 6.6 6.0 5.6 5.3

Fly ash test mixtures Setting time, hr:min Retardation relative to control, hr:minIdentification Class of fly ash Initial Final Initial Final

A C 4:30 5:35 0:15 0:05B F 4:40 6:15 0:25 0:45C F 4:25 6:15 0:10 0:45D F 5:05 7:15 0:50 1:45E F 4:25 5:50 0:10 0:20F C 4:25 6:00 0:10 0:30G C 4:55 6:30 0:40 1:00H F 5:10 7:10 0:55 1:40I C 5:00 6:50 0:45 1:20J F 5:10 7:40 0:55 2:10

Average of:Class C 4:40 6:15 0:30 0:45Class F 4:50 6:45 0:35 1:15

Control mixture 4:15 5:30 — —

Table 3-6. Effect of Fly Ash on Setting Time of Concrete

Concretes had a cementitious materials content of 307 kg/m3 (517 lb/yd3). Fly ash mixtures contained 25% ash by mass of cementitious mate-rial. Water to cement plus fly ash ratio = 0.40 to 0.45. Tested at 23°C (73°F) (Gebler and Klieger 1986).

containing supplementary cementing materials are similarto the effects on concrete made with only portland cement;however, the curing time may need to be longer for certainmaterials with slow-early-strength gain.

High dosages of silica fume can make concrete highlycohesive with very little aggregate segregation or bleeding.With little or no bleed water available at the concrete surfacefor evaporation, plastic cracking can readily develop, espe-cially on hot, windy days if special precautions are not taken.

Proper curing of all concrete, especially concrete con-taining supplementary cementing materials, should com-mence immediately after finishing. A seven-day moist cureor membrane cure should be adequate for concretes withnormal dosages of most supplementary cementitiousmaterials. As with portland cement concrete, low curingtemperatures can reduce early-strength gain (Gebler andKlieger 1986).

EFFECTS ON HARDENED CONCRETE

Strength

Fly ash, ground granulated blast-furnace slag, calcined clay,metakaolin, calcined shale, and silica fume contribute to thestrength gain of concrete. However, the strength of concretecontaining these materials can be higher or lower than thestrength of concrete using portland cement as the onlycementing material. Fig. 3-14 illustrates this for various flyashes. Tensile, flexural, torsional, and bond strength areaffected in the same manner as compressive strength.

as the amount of portland cement, water requirement, thetype and reactivity of the slag or pozzolan dosage, and thetemperature of the concrete. Set retardation is an advan-tage during hot weather, allowing more time to place andfinish the concrete. However, during cold weather, pro-nounced retardation can occur with some materials, sig-nificantly delaying finishing operations. Acceleratingadmixtures can be used to decrease the setting time.Calcined shale and clay have little effect on setting time.

Finishability

Concrete containing supplementary cementing materialswill generally have equal or improved finishabilitycompared to similar concrete mixes without them. Mixesthat contain high dosages of cementitious materials—andespecially silica fume—can be sticky and difficult to finish.

Pumpability

The use of supplementary cementing materials generallyaids the pumpability of concrete. Silica fume is the mosteffective, especially in lean mixtures.

Plastic Shrinkage Cracking

Because of its low bleeding characteristics, concrete con-taining silica fume may exhibit an increase in plastic shrink-age cracking. The problem may be avoided by ensuring thatsuch concrete is protected against drying, both during andafter finishing. Other pozzolans and slag generally havelittle effect on plastic shrinkage cracking. Supplementarycementing materials that significantly increase set time canincrease the risk of plastic shrinkage cracking.

Curing

The effects of temperature and moisture conditions onsetting properties and strength development of concretes

64


7

14

21

28

35

42

1

2

3

4

5

6

1 10 100

Com

pres

sive

str

engt

h, M

Pa

Com

pres

sive

str

engt

h, 1

000

psi

Age, days

NoneFly ash AFly ash DFly ash EFly ash FFly ash GFly ash J

Fig. 3-14. Compressive strength development at 1, 3, 7, 28,and 90 days of concrete mixtures containing 307 kg/m3

(517 lb/yd3) of cementitious materials with a fly ash dosageof 25% of the cementitious materials (Whiting 1989).

0

20

40

60

80

100

120

0 5 10 15 20 25 30Hea

t, pe

rcen

t of T

ype

I cem

ent a

t 28

days

Time, days

ASTM Type I cement

70% slag

Fig. 3-13. Effect of a slag on heat of hydration at 20°C (68°F)compared to a Type I cement.

Because of the slow pozzolanic reaction of somesupplementary cementing materials, continuous wetcuring and favorable curing temperatures may need to beprovided for longer periods than normally required.However, concrete containing silica fume is less affected bythis and generally equals or exceeds the one-day strengthof a cement-only control mixture. Silica fume contributes tostrength development primarily between 3 and 28 days,during which time a silica fume concrete exceeds thestrength of a cement-only control concrete. Silica fume alsoaids the early strength gain of fly ash-cement concretes.

The strength development of concrete with fly ash,ground slag, calcined clay, or calcined shale, is similar tonormal concrete when cured around 23°C (73°F). Fig. 3-15illustrates that the rate of strength gain of concrete with flyash, relative to its 28-day strength, is similar to concretewithout fly ash. Concretes made with certain highly reac-tive fly ashes (especially high-calcium Class C ashes) orground slags can equal or exceed the control strength in 1to 28 days. Some fly ashes and natural pozzolans require28 to 90 days to exceed a 28-day control strength, depend-ing on the mixture proportions. Concretes containing ClassC ashes generally develop higher early-age strength thanconcretes with Class F ashes.

Strength gain can be increased by: (1) increasing theamount of cementitious material in the concrete; (2) addinghigh-early strength cementitious materials; (3) decreasingthe water-cementing materials ratio; (4) increasing the cur-ing temperature; or (5) using an accelerating admixture.Fig. 3-16 illustrates the benefit of using fly ash as an addi-tion instead of a cement replacement to improve strengthdevelopment in cold weather. Mass concrete design oftentakes advantage of the delayed strength gain of pozzolansas these structures are often not put into full service imme-diately. Slow early strength gain resulting from the use ofsome supplementary cementitious materials is an advan-tage in hot weather construction as it allows more time toplace and finish the concrete. With appropriate mixtureadjustments, all supplementary cementitious materials canbe used in all seasons.

65


0

20

40

60

80

100

120

140

160

180

1 10 100 1000 10000

Com

pres

sive

str

engt

h,pe

rcen

t of 2

8-da

y st

reng

th

Age, days

With fly ash

Without fly ash

28 days

Fig. 3-15. Compressive strength gain as a percentage of28-day strength of concretes with and without fly ash(Lange 1994).

20

25

30

35

40

45

50

55

60

2900

3600

4300

5000

5700

6400

7100

7800

8500

0 10 20 30 40 50 60 70 80 90

Com

pres

sive

str

engt

h, M

Pa

Com

pres

sive

str

engt

h, p

si

Age, days

Control

Fly Ash A 20% S

Fly Ash A 20% P

Fly Ash A 20% A

Cold weather cure: First 24 hrs at 23°C (73°F) Remainder at 4°C (39°F)

Fig. 3-16. Compressive strengths for concretes cured at 23°C(73°F) for the first 24 hours and 4°C (40°F) for the remainingtime. Control had a cement content of 332 kg/m3 (560 lb/yd3)and w/c of 0.45. The fly ash curves show substitution forcement (S), partial (equal) substitution for cement and sand(P), and addition of fly ash by mass of cement (A). The use ofpartial cement substitution or addition of fly ash increasesstrength development comparable to the cement-onlycontrol, even in cold weather (Detwiler 2000).

Supplementary cementing materials are often essen-tial to the production of high-strength concrete. Fly ash,especially, has been used in production of concrete withstrengths up to 100 MPa (15,000 psi). With silica fume,ready mix producers now have the ability to make concretewith strengths up to 140 MPa (20,000 psi), when used withhigh-range water reducers and appropriate aggregates(Burg and Ost 1994).

Impact and Abrasion Resistance

The impact resistance and abrasion resistance of concreteare related to compressive strength and aggregate type.Supplementary cementing materials generally do notaffect these properties beyond their influence on strength.Concretes containing fly ash are just as abrasion resistantas portland cement concretes without fly ash (Gebler andKlieger 1986). Fig. 3-17 illustrates that abrasion resistanceof fly ash concrete is related to strength.

Freeze-Thaw Resistance

It is imperative for development of resistance to deteriora-tion from cycles of freezing and thawing that a concretehave adequate strength and entrained air. For concretecontaining supplementary cementing materials to providethe same resistance to freezing and thawing cycles as aconcrete made using only portland cement as a binder,four conditions for both concretes must be met:

4. They must be air-dried for one month prior to expo-sure to saturated freezing conditions.

Table 3-7 shows equal frost resistance for concrete withand without fly ash. Fig. 3-18 illustrates the long termdurability of concretes with fly ash, slag, or shale.

Deicer-Scaling Resistance

Decades of field experience have demonstrated that air-entrained concretes containing normal dosages of fly ash,slag, silica fume, calcined clay, or calcined shale are resistantto scaling caused by the application of deicing salts in afreeze-thaw environment. Laboratory tests also indicate thatthe deicer-scaling resistance of concrete made with sup-plementary cementing materials is often equal to concretemade without supplementary cementing materials.

Scaling resistance can decrease as the amount of cer-tain supplementary cementing materials increases. How-ever, concretes that are properly designed, placed, andcured, have demonstrated good scaling resistance evenwhen made with high dosages of some of these materials.

Deicer-scaling resistance of all concrete is significantlyimproved with the use of a low water-cement ratio, a mod-erate portland cement content, adequate air entrainment,proper finishing and curing, and an air-drying period priorto exposure of the concrete to salts and freezing tempera-tures. Lean concrete with only about 240 kg/m3 (405lb/yd3) or less of cementitious material can be especiallyvulnerable to deicer scaling. A minimum of 335 kg/m3

66


A C

B D

Fig. 3-18. View of concrete slabs in PCA outdoor test plot (Skokie, Illinois) containing (A) fly ash, (B) slag, (C) calcined shale, and(D) portland cement after 30 years of deicer and frost exposure. These samples demonstrate the durability of concretescontaining various cementitious materials. Source: RX 157, LTS Cement No. 51, slabs with 335 kg/m3 (564 lb/yd3) of cementingmaterial and air entrainment. (69714, 69716, 69715, 69717)

1. They must have the same compressive strength.2. They must have an adequate entrained air content

with proper air-void characteristics.3. They must be properly cured.

1.0

1.2

1.4

1.6

1.8

2.0

2.2

20 25 30 35 40

Dep

th o

f wea

r, m

m

28-Day moist-cured compressive strength, MPa

28-Day moist-cured compressive strength, 1000 psi3 4 5 6

Fig. 3-17. Comparison of abrasion resistance and compressivestrength of various concretes with 25% fly ash. Abrasionresistance increases with strength (Gebler and Klieger 1986).

(564 lb/yd3) of cementitious material and a maximumwater to cementitious materials ratio of 0.45 is recom-mended. A satisfactory air-void system is also critical.

The importance of using a low water-cement ratio forscale resistance is demonstrated in Fig. 3-19. The effect ofhigh fly ash dosages and low cementing material contentsis demonstrated in Fig. 3-20. The performance of scale-resistant concretes containing fly ash at a dosage of 25% of

cementing material by mass is presented in Table 3-7. Thetable demonstrates that well designed, placed and curedconcretes with and without fly ash can be equally resistantto deicer scaling.

The ACI 318 building code states that the maximumdosage of fly ash, slag, and silica fume should be 25%, 50%,and 10% by mass of cementing materials, respectively fordeicer exposures. Total supplementary cementing materi-als should not exceed 50% of the cementitious material.Dosages less than or higher than these limits have beenshown to be durable in some cases and not in others.Different materials respond differently in different envi-ronments. The selection of materials and dosages shouldbe based on local experience and the durability should bedemonstrated by field or laboratory performance.

Drying Shrinkage and Creep

When used in low to moderate amounts, the effect of flyash, ground granulated blast-furnace slag, calcined clay,calcined shale, and silica fume on the drying shrinkage andcreep of concrete is generally small and of little practicalsignificance. Some studies indicate that silica fume mayreduce creep (Burg and Ost 1994).

67


0

1

2

3

4

5

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2

Sca

le r

atin

g at

50

cycl

es

Water to portland cement ratio

Moist cure

ASTM C 672

Fig. 3-19. Relationship between deicer-scaling resistanceand water to portland cement ratio for several air-entrainedconcretes with and without fly ash. A scale rating of 0 is noscaling and 5 is severe scaling (Whiting 1989).

Table 3-7. Frost and Deicer-Scaling Resistance of Fly Ash Concrete

Results at 300 cyclesFrost resistance in water, Deicer scaling resistance,

Fly ash mixtures* ASTM C 666 Method A (AASHTO T 161) ASTM C 672**Class of Expansion, Mass loss, Durability Water Curing

Identification fly ash % % factor cure compoundA C 0.010 1.8 105 3 2B F 0.001 1.2 107 2 2C F 0.005 1.0 104 3 3D F 0.006 1.3 98 3 3E F 0.003 4.8 99 3 2F C 0.004 1.8 99 2 2G C 0.008 1.0 102 2 2H F 0.006 1.2 104 3 2I C 0.004 1.7 99 3 2J F 0.004 1.0 100 3 2

Average of:Class C 0.006 1.6 101 3 2Class F 0.004 1.8 102 3 2

Control mixture 0.002 2.5 101 2 2

* Concrete mixtures had a cementitious materials content of 307 kg/m3 (517lbs/yd3), a water to cementitious materials ratio of 0.40 to 0.45, a target aircontent of 5% to 7%, and a slump of 75 mm to 100 mm (3 in. to 4 in.). Flyash dosage was 25% by mass of cementitious material.Gebler and Klieger 1986a.

** Scale rating (see at right)0 = No scaling1 = Slight scaling2 = Slight to moderate scaling3 = Moderate scaling4 = Moderate to severe scaling5 = Severe scaling (2718)

Alkali-Aggregate Reactivity

Alkali-silica reactivity can be controlled through the use ofcertain supplementary cementitious materials. Silica fume,fly ash, ground granulated blast-furnace slag, calcined clay,calcined shale, and other pozzolans have been reported tosignificantly reduce alkali-silica reactivity (Figs. 3-21 and3-22). Low calcium Class F ashes have reduced reactivity

Permeability and Absorption

With adequate curing, fly ash, ground slag, and naturalpozzolans generally reduce the permeability and absorptionof concrete. Silica fume and metakaolin are especially effec-tive in this regard. Silica fume and calcined clay can provideconcrete with a chloride resistance of under 1000 coulombsusing the ASTM C 1202 rapid chloride permeability test(Barger and others 1997). Tests show that the permeability ofconcrete decreases as the quantity of hydrated cementingmaterials increases and the water-cementitious materialsratio decreases. The absorption of fly-ash concrete is aboutthe same as concrete without ash, although some ashes canreduce absorption by 20% or more.

68


0

0.05

0.10

0.15

0.20

0.25

ASTM

C 1

260

expa

nsio

n at

14

days

, per

cent

Control15% 25% 15% 25% 15% 25% 35% 50%Low-CaOfly ash

Medium-CaOfly ash

High-CaOfly ash

Slag

Fig. 3-21. Effect of different fly ashes and slag on alkali-silicareactivity. Note that some ashes are more effective thanothers in controlling the reaction and that dosage of the ashor slag is critical. A highly reactive natural aggregate wasused in this test. A less reactive aggregate would require lessash or slag to control the reaction. A common limit for eval-uating the effectiveness of pozzolans or slags is 0.10%expansion using this rapid mortar bar test (Detwiler 2002).

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 2 4 6 8 10 12

Exp

ansi

on, p

erce

nt

Age, months

No pozzolan

20% Calcined shale

20% Calcined clay

ASTM C 441Cement: 0.92% alkaliPyrex glass

Fig. 3-22. Reduction of alkali-silica reactivity by calcinedclay and calcined shale (Lerch 1950).

None A D E F G J0

1

2

3

4

5S

cale

ratin

g at

150

cyc

les

(AS

TM C

672

)

Fly ash

250 kg/m3

(417 lb/yd3)

305 kg/m3

(508 lb/yd3)

335 kg/m3

(588 lb/yd3)

25% replacementMoist cure

Cementitiousmaterial

None A D E F G J0

1

2

3

4

5

Sca

le ra

ting

at 1

50 c

ycle

s (A

STM

C 6

72)

Fly ash

50%replacementMoist cure

250 kg/m3

(417 lb/yd3)

305 kg/m3

(508 lb/yd3)

335 kg/m3

(588 lb/yd3)

Cementitiousmaterial

Fig. 3-20. Relationship between deicer-scaling resistance and dosage of fly ash for air-entrained concretes made withmoderate to high water-cementitious materials ratios. Replacement of portland cement with fly ash: (left) 25% and (right)50%. A scale rating of 0 is no scaling and 5 is severe scaling (Whiting 1989).

expansion up to 70% or more in some cases. At optimumdosage, Class C ashes can also reduce reactivity but to alesser degree than most Class F ashes. Supplementarycementing materials provide additional calcium silicatehydrate to chemically tie up the alkalies in the concrete(Bhatty 1985, and Bhatty and Greening 1986). Determin-ation of optimum supplementary cementing materialsdosage is important to maximize the reduction in reactivityand to avoid dosages and materials that can aggravate reac-tivity. Dosage rates should be verified by tests, such asASTM C 1260 (AASHTO T 303) or ASTM C 1293.

Supplementary cementing materials that reducealkali-silica reactions will not reduce alkali-carbonate reac-tions, a type of reaction involving cement alkalies andcertain dolomitic limestones.

Descriptions of aggregate testing and preventivemeasures to be taken to prevent deleterious alkali-aggre-gate reaction are discussed in Farny and Kosmatka (1997),PCA (1998), and AASHTO (2000).

Sulfate Resistance

With proper proportioning and material selection, silicafume, fly ash, calcined shale, and ground slag can improvethe resistance of concrete to sulfate or seawater attack. Thisis done primarily by reducing permeability and by reducingthe amount of reactive elements (such as calcium) neededfor expansive sulfate reactions. For improved sulfate resist-ance of lean concrete, one study showed that for a particularClass F ash, an adequate amount was approximately 20% ofthe cement plus fly ash; this illustrates the need to determineoptimum ash contents, as higher ash contents were detri-mental (Stark 1989).

The sulfate resistance of high-cement-content, lowwater-cement ratio concrete made with a sulfate resistantcement is so great that fly ash has little opportunity toimprove resistance. Concretes with Class F ashes are gener-ally more sulfate resistant than those made with Class Cashes. Some Class C ashes have been shown to reduce sul-fate resistance at normal dosage rates.

Ground slag is generally considered beneficial insulfate environments. However, one long-term study in avery severe environment showed a slight reduction insulfate resistance in concrete containing ground slagcompared to concrete containing only portland cement asthe cementing material (Stark 1986 and 1989). One reasonfor decreased performance with slag in this study is thatthe mixtures may not have been optimized for sulfateresistance.

Other studies indicate that concrete with ground slaghas a sulfate resistance equal to or greater than concretemade with Type V sulfate-resistant portland cement (ACI233 and Detwiler, Bhatty, and Bhattacharja 1996). Calcinedclay has been demonstrated to provide sulfate resistancegreater than high-sulfate resistant Type V cement (Bargerand others 1997).

Corrosion of Embedded Steel

Some supplementary cementing materials reduce steelcorrosion by reducing the permeability of properly curedconcrete to water, air, and chloride ions. Fly ash can signif-icantly reduce chloride-ion ingress. Silica fume greatlydecreases permeability and chloride-ion ingress and alsosignificantly increases electrical resistivity, thereby reduc-ing the electrochemical reaction of corrosion. Concretecontaining silica fume or metakaolin is often used in over-lays and full-depth slab placements on bridges and park-ing garages; these structures are particularly vulnerable tocorrosion due to chloride-ion ingress.

Carbonation

Carbonation of concrete is a process by which carbon diox-ide from the air penetrates the concrete and reacts with thehydroxides, such as calcium hydroxide, to form carbon-ates. In the reaction with calcium hydroxide, calciumcarbonate is formed. Carbonation lowers the alkalinity ofconcrete. High alkalinity is needed to protect embeddedsteel from corrosion; consequently, concrete should beresistant to carbonation to help prevent steel corrosion.

The amount of carbonation is significantly increasedin concretes with a high water-cementing materials ratio,low cement content, short curing period, low strength, anda highly permeable or porous paste. The depth of carbona-tion of good quality concrete is generally of little practicalsignificance. At normal dosages, fly ash is reported toslightly increase carbonation, but usually not to a signifi-cant amount in concrete with short (normal) moist-curingperiods (Campbell, Sturm, and Kosmatka 1991).

Chemical Resistance

Supplementary cementing materials often reduce chemicalattack by reducing the permeability of concrete. Althoughmany of these materials may improve chemical resistance,they do not make concrete totally immune to attack.Concrete in severe chemical exposure should be protectedusing barrier systems. Kerkhoff (2001) provides a discus-sion of methods and materials to protect concrete fromaggressive chemicals and exposures.

Soundness

Normal dosages of fly ash, slag, silica fume and naturalpozzolans do not affect the soundness of concrete.Concrete soundness is protected by soundness require-ments, such as autoclave expansion limits, on the materi-als. Dosages in concrete should not exceed dosagesdeemed safe in the autoclave test.

Concrete Color

Supplementary cementitious materials may slightly alterthe color of hardened concrete. Color effects are related to

69


STORAGE

In most cases, moisture will not affect the physicalperformance of supplementary cementing materials. Thesematerials should, however, be kept dry to avoid difficultiesin handling and discharge. Class C fly ash and calcinedshale must be kept dry as they will set and harden whenexposed to moisture. Equipment for handling and storingthese materials is similar to that required for cement.Additional modifications may be required where usingsilica fume, which does not have the same flowing charac-teristics as other supplementary cementing materials (andmay be supplied as a liquid).

These materials are usually kept in bulk storage facili-ties or silos, although some products are available in bags.Because the materials may resemble portland cement incolor and fineness, the storage facilities should be clearlymarked to avoid the possibility of misuse and contamina-tion with other materials at the batch plant. All valves andpiping should also be clearly marked and properly sealedto avoid leakage and contamination. Fly ash, slag, andnatural pozzolans should be weighed after the portland orblended cement in the batching sequence to avoid over-dosing in case valves stick.

REFERENCES

AASHTO, Guide Specification on Alkali-Silica Reaction,Section 56, http://leadstates.tamu.edu/ASR/library/gspec.stm, 2000.

Abrams, Duff A., “Effect of Hydrated Lime and OtherPowdered Admixtures in Concrete,” Proceedings of theAmerican Society for Testing Materials, Vol. 20, Part 2, 1920.Reprinted with revisions as Bulletin 8, Structural MaterialsResearch Laboratory, Lewis Institute, June 1925, 78 pages.Available through PCA as LS08.

ACAA, http://www.acaa-usa.org, American Coal AshAssociation, Alexandria, Virginia, 2001.

ACI, Concrete Durability, Katherine and Bryant MatherInternational Conference, SP100, American Concrete Insti-tute, Farmington Hills, Michigan, 1987.

ACI Committee 211, Standard Practice for SelectingProportions for Normal, Heavyweight, and Mass Concrete, ACI211.1-91, American Concrete Institute, Farmington Hills,Michigan, 1991, 38 pages.

ACI Committee 211, Standard Practice for Selecting Pro-portions for Structural Lightweight Concrete, ACI 211.2-98,American Concrete Institute, Farmington Hills, Michigan,1998, 14 pages.

ACI Committee 211, Guide for Selecting Proportions for HighStrength Concrete with Portland Cement and Fly Ash, ACI211.4R-93, American Concrete Institute, Farmington Hills,Michigan, 1993, 13 pages.

the color and amount of the material used in concrete.Many supplementary cementing materials resemble thecolor of portland cement and therefore have little effect oncolor of the hardened concrete. Some silica fumes may giveconcrete a slightly bluish or dark gray tint and tan fly ashmay impart a tan color to concrete when used in largequantities. Ground slag and metakaolin can make concretewhiter. Ground slag can initially impart a bluish or green-ish undertone.

CONCRETE MIX PROPORTIONS

The optimum amounts of supplementary cementing mate-rials used with portland cement or blended cement aredetermined by testing, by the relative cost and availability ofthe materials, and by the specified properties of the concrete.

Several test mixtures are required to determine theoptimum amount of pozzolan or slag. These mixturesshould cover a range of blends to establish the relationshipbetween strength and water to cementing materials ratio.These mixtures should be established according to ACIStandard 211.1 or 211.2, taking into account the relativedensities of the supplementary cementing materials. Theseare usually different from the relative density of portlandcement. The results of these tests will be a family ofstrength curves for each age at which the concrete isrequired to meet certain specified requirements. Thedosage of a cementitious material is usually stated as amass percentage of all the cementitious materials in aconcrete mixture.

Typical practice in the United States uses fly ash, slag,silica fume, calcined clay, or calcined shale as an additionto portland cement or as a partial replacement for some ofthe portland cement. Blended cements, which alreadycontain pozzolans or slag, are designed to be used with orwithout additional supplementary cementitious materials.

Concrete mixtures with more than one supplementarycementitious material are also used. For example, a concretemixture may contain portland cement, fly ash, and silicafume. Such mixes are called ternary concretes. When flyash, slag, silica fume, or natural pozzolans are used incombination with portland or blended cement, the propor-tioned concrete mixture should be tested to demonstratethat it meets the required concrete properties for the project.

AVAILABILITY

All supplementary cementitious materials may not beavailable in all areas. Consult local material suppliers onavailable materials. Class F fly ashes are usually availablein the Eastern United States, while Class C ashes are avail-able in the Midwest and West. Silica fume is available inmost locations because only small dosages are used.Calcined clays and shales are available in select areas.Ground granulated slags are available in most regions.

70


ACI Committee 232, Use of Fly Ash in Concrete, ACI 232.2R-96, American Concrete Institute, Farmington Hills,Michigan, 1996, 34 pages.

ACI Committee 232, Use of Raw or Processed NaturalPozzolans in Concrete, ACI 232.1R-00, American ConcreteInstitute, Farmington Hills, Michigan, 2000, 24 pages.

ACI Committee 233, Ground Granulated Blast-Furnace Slagas a Cementitious Constituent in Concrete, ACI 233R-95,American Concrete Institute, Farmington Hills, Michigan,1995, 18 pages.

ACI Committee 234, Guide for the Use of Silica Fume inConcrete, ACI 234R-96, American Concrete Institute,Farmington Hill, Michigan, 1996, 51 pages.

Barger, Gregory S.; Lukkarila, Mark R.; Martin, David L.;Lane, Steven B.; Hansen, Eric R.; Ross, Matt W.; andThompson, Jimmie L., “Evaluation of a Blended Cementand a Mineral Admixture Containing Calcined ClayNatural Pozzolan for High-Performance Concrete,“Proceedings of the Sixth International Purdue Conference onConcrete Pavement Design and Materials for High Performance,Purdue University, West Lafayette, Indiana, 1997, 21 pages.

Bhatty, M. S. Y., “Mechanism of Pozzolanic Reactions andControl of Alkali-Aggregate Expansion,” Cement, Concrete,and Aggregates, American Society for Testing and Materials,West Conshohocken, Pennsylvania. Winter 1985, pages 69to 77.

Bhatty, M. S. Y., and Greening, N. R., “Some Long TimeStudies of Blended Cements with Emphasis on Alkali-Aggregate Reaction,” 7th International Conference on Alkali-Aggregate Reaction, 1986.

Buck, Alan D., and Mather, Katharine, Methods forControlling Effects of Alkali-Silica Reaction, Technical ReportSL-87-6, Waterways Experiment Station, U.S. Army Corpsof Engineers, Vicksburg, Mississippi, 1987.

Burg, R. G., and Ost, B. W., Engineering Properties ofCommercially Available High-Strength Concretes (IncludingThree-Year Data), Research and Development BulletinRD104, Portland Cement Association, 1994, 62 pages.

Campbell, D. H.; Sturm, R. D.; and Kosmatka, S. H.,“Detecting Carbonation,” Concrete Technology Today, PL911;Portland Cement Association, http://www.portcement.org/pdf_files/PL911.pdf, March 1991, pages 1 to 5.

Carette, G. G., and Malhotra, V. M., “Mechanical Properties,Durability, and Drying Shrinkage of Portland CementConcrete Incorporating Silica Fume,” Cement, Concrete, andAggregates, American Society for Testing and Materials,West Conshohocken, Pennsylvania, Summer 1983.

Cohen, Menashi, D., and Bentur, Arnon, “Durability ofPortland Cement-Silica Fume Pastes in Magnesium Sulfateand Sodium Sulfate Solutions,” ACI Materials Journal,

American Concrete Institute, Farmington Hills, Michigan,May-June 1988, pages 148 to 157.

Detwiler, Rachel J., “Controlling the Strength Gain of FlyAsh Concrete at Low Temperature,” Concrete TechnologyToday, CT003, Portland Cement Association, http://www.portcement.org/pdf_files/CT003.pdf, 2000, pages 3 to 5.

Detwiler, Rachel J., Documentation of Procedures for PCA’sASR Guide Specification, SN 2407, Portland Cement Associ-ation, 2002.

Detwiler, Rachel J.; Bhatty, Javed I.; and Bhattacharja,Sankar, Supplementary Cementing Materials for Use inBlended Cements, Research and Development BulletinRD112, Portland Cement Association, 1996, 108 pages.

Farny, J. A., and Kosmatka, S. H., Diagnosis and Control ofAlkali-Aggregate Reactivity, IS413, Portland Cement Asso-ciation, 1997, 24 pages.

Gaynor, R. D., and Mullarky, J. I., “Survey: Use of Fly Ashin Ready-Mixed Concrete,” NRMCA Technical InformationLetter No. 426, National Ready Mixed Concrete Associa-tion, Silver Spring, Maryland, June 1985.

Gebler, S. H., and Klieger, P., Effect of Fly Ash on the Air-VoidStability of Concrete, Research and Development BulletinRD085, Portland Cement Association, http://www.portcement.org/pdf_files/RD085.pdf, 1983, 40 pages.

Gebler, Steven H., and Klieger, Paul, Effect of Fly Ash onSome of the Physical Properties of Concrete, Research and De-velopment Bulletin RD089, Portland Cement Association,http://www.portcement.org/pdf_files/RD089.pdf, 1986,48 pages.

Gebler, Steven H., and Klieger, Paul, Effect of Fly Ash on theDurability of Air-Entrained Concrete, Research and Develop-ment Bulletin RD090, Portland Cement Association, http://www.portcement.org/pdf_files/RD090.pdf, 1986a, 44 pages.

Helmuth, Richard A., Fly Ash in Cement and Concrete,SP040T, Portland Cement Association, 1987, 203 pages.

Hogan, F. J., and Meusel, J. W., “Evaluation for Durabilityand Strength Development of a Ground Granulated BlastFurnace Slag,” Cement, Concrete, and Aggregates, Vol. 3, No. 1,American Society for Testing and Materials, WestConshohocken, Pennsylvania, Summer 1981, pages 40 to 52.

Kerkhoff, Beatrix, Effect of Substances on Concrete and Guideto Protective Treatments, IS001, Portland Cement Asso-ciation, 2001, 36 pages.

Klieger, Paul, and Isberner, Albert W., Laboratory Studies ofBlended Cements—Portland Blast-Furnace Slag Cements,Research Department Bulletin RX218, Portland CementAssociation, http://www.portcement.org/pdf_files/RX218.pdf, 1967.

Klieger, Paul, and Perenchio, William F., Laboratory Studiesof Blended Cement: Portland-Pozzolan Cements, Research and

71


Development Bulletin RD013, Portland Cement Association,http://www.portcement.org/pdf_files/RD013.pdf, 1972.

Lange, David A., Long-Term Strength Development of Concrete,RP326, Portland Cement Association, 1994.

Lerch, William, Studies of Some Methods of Avoiding theExpansion and Pattern Cracking Associated with the Alkali-Aggregate Reaction, Research Department Bulletin RX031,Portland Cement Association, http://www.portcement.org/pdf_files/RX031.pdf, 1950.

Malhotra, V. M., Pozzolanic and Cementitious Materials,Gordon and Breach Publishers, Amsterdam, 1996, 208 pages.

PCA, Survey of Mineral Admixtures and Blended Cements inReady Mixed Concrete, Portland Cement Association, 2000,16 pages.

PCA Durability Subcommittee, Guide Specification to Con-trol Alkali-Silica Reactions, IS415, Portland Cement Associa-tion, 1998, 8 pages.

SFA, http://www.silicafume.org, Silica Fume Association,Fairfax, Virginia, 2000.

Stark, David, Longtime Study of Concrete Durability in SulfateSoils, Research and Development Bulletin RD086, PortlandCement Association, http://www.portcement.org/pdf_files/RD086.pdf, 1982.

Stark, David, Durability of Concrete in Sulfate-Rich Soils,Research and Development Bulletin RD097, Portland Ce-ment Association, http://www.portcement.org/pdf_files/RD097.pdf, 1989, 14 pages.

Tikalsky, P. J., and Carrasquillo, R. L., Effect of Fly Ash on theSulfate Resistance of Concrete Containing Fly Ash, ResearchReport 481-1, Center for Transportation Research, Austin,Texas, 1988, 92 pages.

Tikalsky, P. J., and Carrasquillo, R. L., The Effect of Fly Ashon the Sulfate Resistance of Concrete, Research Report 481-5,Center for Transportation Research, Austin, Texas, 1989,317 pages.

Whiting, D., Strength and Durability of Residential ConcretesContaining Fly Ash, Research and Development BulletinRD099, Portland Cement Association, http://www.portcement.org/pdf_files/RD099.pdf, 1989, 42 pages.

72


Almost any natural water that is drinkable and has nopronounced taste or odor can be used as mixing water formaking concrete (Fig. 4-1). However, some waters that arenot fit for drinking may be suitable for use in concrete.

Six typical analyses of city water supplies and seawa-ter are shown in Table 4-1. These waters approximate thecomposition of domestic water supplies for most of thecities over 20,000 population in the United States andCanada. Water from any of these sources is suitable formaking concrete. A water source comparable in analysisto any of the waters in the table is probably satisfactory foruse in concrete (Fig. 4-2).

Water of questionable suitability can be used formaking concrete if mortar cubes (ASTM C 109 or AASHTOT 106) made with it have 7-day strengths equal to at least90% of companion specimens made with drinkable ordistilled water. In addition, ASTM C 191 (AASHTO T 131)tests should be made to ensure that impurities in themixing water do not adversely shorten or extend thesetting time of the cement. Acceptable criteria for water tobe used in concrete are given in ASTM C 94 (AASHTO M157) and AASHTO T 26 (see Tables 4-2 and 4-3).

CHAPTER 4

Mixing Water for Concrete

Excessive impurities in mixing water not only mayaffect setting time and concrete strength, but also maycause efflorescence, staining, corrosion of reinforcement,volume instability, and reduced durability. Therefore,certain optional limits may be set on chlorides, sulfates,

Table 4-1. Typical Analyses of City Water Supplies and Seawater, parts per million

Analysis No.

Chemicals 1 2 3 4 5 6 Seawater*

Silica (SiO2) 2.4 0.0 6.5 9.4 22.0 3.0 —Iron (Fe) 0.1 0.0 0.0 0.2 0.1 0.0 —Calcium (Ca) 5.8 15.3 29.5 96.0 3.0 1.3 50 to 480Magnesium (Mg) 1.4 5.5 7.6 27.0 2.4 0.3 260 to 1410 Sodium (Na) 1.7 16.1 2.3 183.0 215.0 1.4 2190 to 12,200Potassium (K) 0.7 0.0 1.6 18.0 9.8 0.2 70 to 550Bicarbonate (HCO3) 14.0 35.8 122.0 334.0 549.0 4.1 —Sulfate (SO4) 9.7 59.9 5.3 121.0 11.0 2.6 580 to 2810Chloride (Cl) 2.0 3.0 1.4 280.0 22.0 1.0 3960 to 20,000Nitrate (NO3) 0.5 0.0 1.6 0.2 0.5 0.0 —Total dissolved solids 31.0 250.0 125.0 983.0 564.0 19.0 35,000

Fig. 4-1. Water that is safe to drink is safe to use in con-crete. (44181)

* Different seas contain different amounts of dissolved salts.

73

effects of mix water impurities can be found in Steinour(1960) and Abrams (1924). Over 100 different compoundsand ions are discussed.

Following is a synopsis of the effects of certain impu-rities in mixing water on the quality of normal concrete:

ALKALI CARBONATE ANDBICARBONATE

Carbonates and bicarbonates of sodium and potassiumhave different effects on the setting times of differentcements. Sodium carbonate can cause very rapid setting,bicarbonates can either accelerate or retard the set. In largeconcentrations, these salts can materially reduce concretestrength. When the sum of the dissolved salts exceeds1000 ppm, tests for their effect on setting time and 28-daystrength should be made. The possibility of aggravatedalkali-aggregate reactions should also be considered.

CHLORIDE

Concern over a high chloride content in mixing water ischiefly due to the possible adverse effect of chloride ionson the corrosion of reinforcing steel or prestressingstrands. Chloride ions attack the protective oxide filmformed on the steel by the highly alkaline (pH greater than12.5) chemical environment present in concrete. The acid-

alkalies, and solids in the mixing water or appropriatetests can be performed to determine the effect the impu-rity has on various properties. Some impurities may havelittle effect on strength and setting time, yet they canadversely affect durability and other properties.

Water containing less than 2000 parts per million(ppm) of total dissolved solids can generally be used satis-factorily for making concrete. Water containing more than2000 ppm of dissolved solids should be tested for its effecton strength and time of set. Additional information on the

74


Fig. 4-2. Laboratory analysis of water, in this case using anatomic absorption spectrophotometer to detect concentra-tion of elements. (44182)

Table 4-2. Acceptance Criteria for Questionable Water Supplies (ASTM C 94 or AASHTO M 157)

Limits Test method

Compressive strength, minimum percentage of 90 C 109* or T 106control at 7 days

Time of set, deviation from control, hr:min. from 1:00 earlier to 1:30 later C 191* or T 131

*Comparisons should be based on fixed proportions and the same volume of test water compared to a control mixture using city water ordistilled water.

Table 4-3. Chemical Limits for Wash Water used as Mixing Water (ASTM C 94 or AASHTO M 157)

Maximum TestChemical or type of construction concentration, ppm* method**

Chloride, as Cl ASTM D 512

Prestressed concrete or concrete in bridge decks 500†

Other reinforced concrete in moist environments or containingaluminum embedments or dissimilar metals or with stay-in-place 1,000†galvanized metal forms

Sulfate, as SO4 3,000 ASTM D 516

Alkalies, as (Na2O + 0.658 K2O) 600

Total solids 50,000 AASHTO T 26

* Wash water reused as mixing water in concrete can exceed the listed concentrations of chloride and sulfate if it can be shown that the concen-tration calculated in the total mixing water, including mixing water on the aggregates and other sources, does not exceed the stated limits.

** Other test methods that have been demonstrated to yield comparable results can be used.† For conditions allowing use of CaCl2 accelerator as an admixture, the chloride limitation may be waived by the purchaser.

soluble chloride ion level at which steel reinforcementcorrosion begins in concrete is about 0.2% to 0.4% by massof cement (0.15% to 0.3% water soluble). Of the total chlo-ride-ion content in concrete, only about 50% to 85% iswater soluble; the rest becomes chemically combined incement reactions (Whiting 1997, Whiting, Taylor, and Nagi2002, and Taylor, Whiting, and Nagi 2000).

Chlorides can be introduced into concrete with theseparate mixture ingredients—admixtures, aggregates,cementitious materials, and mixing water—or throughexposure to deicing salts, seawater, or salt-laden air incoastal environments. Placing an acceptable limit on chlo-ride content for any one ingredient, such as mixing water,is difficult considering the several possible sources of chlo-ride ions in concrete. An acceptable limit in the concretedepends primarily upon the type of structure and theenvironment to which it is exposed during its service life.

A high dissolved solids content of a natural water issometimes due to a high content of sodium chloride orsodium sulfate. Both can be tolerated in rather large quan-tities. Concentrations of 20,000 ppm of sodium chlorideare generally tolerable in concrete that will be dry in serv-ice and has low potential for corrosive reactions. Waterused in prestressed concrete or in concrete that is to havealuminum embedments should not contain deleteriousamounts of chloride ion. The contribution of chloridesfrom ingredients other than water should also be consid-ered. Calcium chloride admixtures should be avoided insteel reinforced concrete.

The ACI 318 building code limits water soluble chlo-ride ion content in reinforced concrete to the followingpercentages by mass of cement:

Prestressed concrete 0.06%Reinforced concrete exposed to

chloride in service 0.15%Reinforced concrete that will be dry or

protected from moisture in service 1.00%Other reinforced concrete construction 0.30%

ACI 318 does not limit the amount of chlorides inplain concrete, that is concrete not containing steel.Additional information on limits and tests can be found inACI 222, Corrosion of Metals in Concrete. The acid-solubleand water-soluble chloride content of concrete can bedetermined by using ASTM C 1152 and C 1218.

SULFATE

Concern over a high sulfate content in mix water is due topossible expansive reactions and deterioration by sulfateattack, especially in areas where the concrete will beexposed to high sulfate soils or water. Although mixingwaters containing 10,000 ppm of sodium sulfate havebeen used satisfactorily, the limit in Table 4-3 should beconsidered unless special precautions are taken.

OTHER COMMON SALTS

Carbonates of calcium and magnesium are not very solu-ble in water and are seldom found in sufficient concentra-tion to affect the strength of concrete. Bicarbonates ofcalcium and magnesium are present in some municipalwaters. Concentrations up to 400 ppm of bicarbonate inthese forms are not considered harmful.

Magnesium sulfate and magnesium chloride can bepresent in high concentrations without harmful effects onstrength. Good strengths have been obtained using waterwith concentrations up to 40,000 ppm of magnesium chlo-ride. Concentrations of magnesium sulfate should be lessthan 25,000 ppm.

IRON SALTS

Natural ground waters seldom contain more than 20 to 30ppm of iron; however, acid mine waters may carry ratherlarge quantities. Iron salts in concentrations up to 40,000ppm do not usually affect concrete strengths adversely.

MISCELLANEOUS INORGANIC SALTS

Salts of manganese, tin, zinc, copper, and lead in mixingwater can cause a significant reduction in strength andlarge variations in setting time. Of these, salts of zinc,copper, and lead are the most active. Salts that are espe-cially active as retarders include sodium iodate, sodiumphosphate, sodium arsenate, and sodium borate. All cangreatly retard both set and strength development whenpresent in concentrations of a few tenths percent by massof the cement. Generally, concentrations of these salts upto 500 ppm can be tolerated in mixing water.

Another salt that may be detrimental to concrete issodium sulfide; even the presence of 100 ppm warrantstesting. Additional information on the effects of other saltscan be found in the references.

SEAWATER

Seawater containing up to 35,000 ppm of dissolved salts isgenerally suitable as mixing water for concrete notcontaining steel. About 78% of the salt is sodium chloride,and 15% is chloride and sulfate of magnesium. Althoughconcrete made with seawater may have higher earlystrength than normal concrete, strengths at later ages(after 28 days) may be lower. This strength reduction canbe compensated for by reducing the water-cement ratio.

Seawater is not suitable for use in making steel rein-forced concrete and it should not be used in prestressedconcrete due to the risk of corrosion of the reinforcement,particularly in warm and humid environments. If seawa-ter is used in plain concrete (no steel) in marine applica-

75

Chapter 4 � Mixing Water for Concrete

provided quick set is not induced. Higher concentrations,however, may reduce concrete strength.

Potassium hydroxide in concentrations up to 1.2% bymass of cement has little effect on the concrete strengthdeveloped by some cements, but the same concentrationwhen used with other cements may substantially reducethe 28-day strength.

The possibility for increased alkali-aggregate reactiv-ity should be considered.

WASH WATER

The U.S. Environmental Protection Agency and state agen-cies forbid discharging into the nation’s waterwaysuntreated wash water used in reclaiming sand and gravelfrom returned concrete or mixer washout operations. Washwater is commonly used as mixing water in ready mixedconcrete (Fig. 4-4) (Yelton 1999). Wash water should meetthe limits in Tables 4-2 and 4-3.

INDUSTRIAL WASTEWATER

Most waters carrying industrial wastes have less than4000 ppm of total solids. When such water is used asmixing water in concrete, the reduction in compressivestrength is generally not greater than about 10%-15%.Wastewaters such as those from tanneries, paint factories,coke plants, and chemical and galvanizing plants maycontain harmful impurities. It is best to test any waste-water that contains even a few hundred parts per millionof unusual solids.

tions, moderate sulfate resistant cements, Types II or MS,should be used along with a low water-cement ratio.

Sodium or potassium in salts present in seawaterused for mix water can aggravate alkali-aggregate reactiv-ity. Thus, seawater should not be used as mix water forconcrete with potentially alkali-reactive aggregates.

Seawater used for mix water also tends to cause efflo-rescence and dampness on concrete surfaces exposed toair and water (Steinour 1960). Marine-dredged aggregatesare discussed in Chapter 5.

ACID WATERS

Acceptance of acid mixing water should be based on theconcentration (in parts per million) of acids in the water.Occasionally, acceptance is based on the pH, which is ameasure of the hydrogen-ion concentration on a log scale.The pH value is an intensity index and is not the bestmeasure of potential acid or base reactivity. The pH ofneutral water is 7.0; values below 7.0 indicate acidity andthose above 7.0 alkalinity (a base).

Generally, mixing waters containing hydrochloric,sulfuric, and other common inorganic acids in concentra-tions as high as 10,000 ppm have no adverse effect onstrength. Acid waters with pH values less than 3.0 maycreate handling problems and should be avoided if possi-ble. Organic acids, such as tannic acid, can have a signifi-cant effect on strength at higher concentrations (Fig. 4-3).

ALKALINE WATERS

Waters with sodium hydroxide concentrations of 0.5% bymass of cement do not greatly affect concrete strength

76


0

20

40

60

80

100

0 1.0 2.0 3.0 4.0 5.0

Str

engt

h, p

erce

nt o

f con

trol

Tannic acid, percent of mass of mixing water

28 day testsConcrete cylinders:

75 mm x 150 mm(3 in. x 6 in.)

Fig. 4-3. Effect of tannic acid on the strength of concrete(Abrams 1920).

Fig. 4-4. Reclaiming system allows immediate reuse ofwash water in batching. (69901)

WATERS CARRYING SANITARY SEWAGE

A typical sewage may contain about 400 ppm of organicmatter. After the sewage is diluted in a good disposalsystem, the concentration is reduced to about 20 ppm orless. This amount is too low to have any significant effecton concrete strength.

ORGANIC IMPURITIES

The effect of organic substances on the setting time ofportland cement or the ultimate strength of concrete is aproblem of considerable complexity. Such substances, likesurface loams, can be found in natural waters. Highlycolored waters, waters with a noticeable odor, or those inwhich green or brown algae are visible should be regardedwith suspicion and tested accordingly. Organic impuritiesare often of a humus nature containing tannates or tannicacid (Fig. 4-3).

SUGAR

Small amounts of sucrose, as little as 0.03% to 0.15% bymass of cement, usually retard the setting of cement. Theupper limit of this range varies with different cements.The 7-day strength may be reduced while the 28-daystrength may be improved. Sugar in quantities of 0.25% ormore by mass of cement may cause rapid setting and asubstantial reduction in 28-day strength. Each type ofsugar influences setting time and strength differently.

Less than 500 ppm of sugar in mix water generallyhas no adverse effect on strength, but if the concentrationexceeds this amount, tests for setting time and strengthshould be made.

SILT OR SUSPENDED PARTICLES

About 2000 ppm of suspended clay or fine rock particlescan be tolerated in mixing water. Higher amounts mightnot affect strength but may influence other properties ofsome concrete mixtures. Before use, muddy water shouldbe passed through settling basins or otherwise clarified toreduce the amount of silt and clay added to the mixture byway of the mix water. When cement fines are returned tothe concrete in reused wash water, 50,000 ppm can betolerated.

OILS

Various kinds of oil are occasionally present in mixingwater. Mineral oil (petroleum) not mixed with animal orvegetable oils probably has less effect on strength devel-opment than other oils. However, mineral oil in concen-

trations greater than 2.5% by mass of cement may reducestrength by more than 20%.

ALGAE

Water containing algae is unsuited for making concretebecause the algae can cause an excessive reduction instrength. Algae in water leads to lower strengths either byinfluencing cement hydration or by causing a largeamount of air to be entrained in the concrete. Algae mayalso be present on aggregates, in which case the bondbetween the aggregate and cement paste is reduced. Amaximum algae content of 1000 ppm is recommended.

INTERACTION WITH ADMIXTURES

When evaluating waters for their effect on concrete prop-erties, it is important to also test the water with chemicaladmixtures that will be used in the job concrete. Certaincompounds in water can influence the performance andefficiency of certain admixtures. For example, the dosageof air-entraining admixture may need to be increasedwhen used with hard waters containing high concentra-tions of certain compounds or minerals.

REFERENCES

Abrams, Duff A., Effect of Tannic Acid on the Strength ofConcrete, Bulletin 7, Structural Materials ResearchLaboratory, Lewis Institute, Chicago, http://www.portcement.org/pdf_files/LS007.pdf, 1920, 34 pages (avail-able through PCA as LS007).

Abrams, Duff A., Tests of Impure Waters for Mixing Concrete,Bulletin 12, Structural Materials Research Laboratory,Lewis Institute, Chicago, http://www.portcement.org/pdf_files/LS012.pdf, 1924, 50 pages (available through PCA as LS012).

ACI Committee 201, Guide to Durable Concrete, ACI 201.2R-92, American Concrete Institute, Farmington Hills, Mich-igan, 1992, 41 pages.

ACI Committee 222, Corrosion of Metals in Concrete, ACI222R-96, American Concrete Institute, Farmington Hills,Michigan, 1997, 30 pages.

ACI Committee 318, Building Code Requirements forStructural Concrete and Commentary, ACI 318-02, AmericanConcrete Institute, Farmington Hills, Michigan, 2002, 369pages. Available through PCA as LT125.

Bhatty, Javed I., Effects of Minor Elements on CementManufacture and Use, Research and Development BulletinRD109, Portland Cement Association, 1995, 48 pages.

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Chapter 4 � Mixing Water for Concrete

Bhatty, J.; Miller, F.; West, P.; and Ost, B., Stabilization ofHeavy Metals in Portland Cement, Silica Fume/PortlandCement and Masonry Cement Matrices, RP348, PortlandCement Association, 1999, 106 pages.

Gaynor, Richard D., “Calculating Chloride Percentages,”Concrete Technology Today, PL983, Portland Cement Asso-ciation, http://www.portcement.org/pdf_files/PL983.pdf,December, 1998, 2 pages.

Meininger, Richard C., Recycling Mixer Wash Water,National Ready Mixed Concrete Association, SilverSpring, Maryland.

NRMCA, A System for 100% Recycling of Returned Concrete:Equipment, Procedures, and Effects on Product Quality,National Ready Mixed Concrete Association, SilverSpring, Maryland, 1975.

Steinour, H. H., Concrete Mix Water—How Impure Can ItBe?, Research Department Bulletin RX119, Portland Ce-ment Association, http://www.portcement.org/pdf_files/RX119.pdf, 1960, 20 pages.

Taylor, Peter C.; Whiting, David A.; and Nagi, MohamadA., Threshold Chloride Content of Steel in Concrete, R&DSerial No. 2169, Portland Cement Association, http://www.portcement.org/pdf_files/SN2169.pdf, 2000, 32 pages.

Whiting, David A., Origins of Chloride Limits for ReinforcedConcrete, R&D Serial No. 2153, Portland Cement Associa-tion, http://www.portcement.org/pdf_files/SN2153.pdf,1997, 18 pages.

Whiting, David A.; Taylor, Peter C.; and Nagi, MohamadA., Chloride Limits in Reinforced Concrete, R&D Serial No.2438, Portland Cement Association, 2002, 96 pages.

Yelton, Rick, “Answering Five Common Questions aboutReclaimers,” The Concrete Producer, Addison, Illinois, Sep-tember, 1999, pages 17 to 19.

78


The importance of using the right type and quality ofaggregates cannot be overemphasized. The fine andcoarse aggregates generally occupy 60% to 75% of theconcrete volume (70% to 85% by mass) and strongly influ-ence the concrete’s freshly mixed and hardened proper-ties, mixture proportions, and economy. Fine aggregates(Fig. 5-1) generally consist of natural sand or crushedstone with most particles smaller than 5 mm (0.2 in.).Coarse aggregates (Fig. 5-2) consist of one or a com-

CHAPTER 5

Aggregates for Concrete

bination of gravels or crushed stone with particlespredominantly larger than 5 mm (0.2 in.) and generallybetween 9.5 mm and 37.5 mm (3⁄8 in. and 11⁄2 in.). Somenatural aggregate deposits, called pit-run gravel, consistof gravel and sand that can be readily used in concreteafter minimal processing. Natural gravel and sand areusually dug or dredged from a pit, river, lake, or seabed.Crushed stone is produced by crushing quarry rock, boul-ders, cobbles, or large-size gravel. Crushed air-cooledblast-furnace slag is also used as fine or coarse aggregate.

The aggregates are usually washed and graded at thepit or plant. Some variation in the type, quality, cleanli-ness, grading, moisture content, and other properties isexpected. Close to half of the coarse aggregates used inportland cement concrete in North America are gravels;most of the remainder are crushed stones.

Naturally occurring concrete aggregates are a mixtureof rocks and minerals (see Table 5-1). A mineral is a natu-rally occurring solid substance with an orderly internalstructure and a chemical composition that ranges withinnarrow limits. Rocks, which are classified as igneous, sedi-mentary, or metamorphic, depending on origin, are gener-ally composed of several minerals. For example, granitecontains quartz, feldspar, mica, and a few other minerals;most limestones consist of calcite, dolomite, and minoramounts of quartz, feldspar, and clay. Weathering anderosion of rocks produce particles of stone, gravel, sand,silt, and clay.

Recycled concrete, or crushed waste concrete, is afeasible source of aggregates and an economic reality,especially where good aggregates are scarce. Conven-tional stone crushing equipment can be used, and newequipment has been developed to reduce noise and dust.

Aggregates must conform to certain standards foroptimum engineering use: they must be clean, hard,strong, durable particles free of absorbed chemicals, coat-ings of clay, and other fine materials in amounts that couldaffect hydration and bond of the cement paste. Aggregateparticles that are friable or capable of being split are unde-sirable. Aggregates containing any appreciable amountsof shale or other shaly rocks, soft and porous materials,

Fig. 5-1. Closeup of fine aggregate (sand). (69792)

Fig. 5-2. Coarse aggregate. Rounded gravel (left) andcrushed stone (right). (69791)

79

should be avoided; certain types of chert should be espe-cially avoided since they have low resistance to weather-ing and can cause surface defects such as popouts.

Identification of the constituents of an aggregatecannot alone provide a basis for predicting the behavior ofaggregates in service. Visual inspection will often discloseweaknesses in coarse aggregates. Service records areinvaluable in evaluating aggregates. In the absence of aperformance record, the aggregates should be testedbefore they are used in concrete. The most commonly usedaggregates—sand, gravel, crushed stone, and air-cooledblast-furnace slag—produce freshly mixed normal-weightconcrete with a density (unit weight) of 2200 to 2400kg/m3 (140 to 150 lb/ft3). Aggregates of expanded shale,clay, slate, and slag (Fig. 5-3) are used to produce struc-tural lightweight concrete with a freshly mixed densityranging from about 1350 to 1850 kg/m3 (90 to 120 lb/ft3).Other lightweight materials such as pumice, scoria,perlite, vermiculite, and diatomite are used to produceinsulating lightweight concretes ranging in density fromabout 250 to 1450 kg/m3 (15 to 90 lb/ft3). Heavyweightmaterials such as barite, limonite, magnetite, ilmenite,hematite, iron, and steel punchings or shot are used toproduce heavyweight concrete and radiation-shieldingconcrete (ASTM C 637 and C 638). Only normal-weightaggregates are discussed in this chapter. See Chapter 18for special types of aggregates and concretes.

Normal-weight aggregates should meet the require-ments of ASTM C 33 or AASHTO M 6/M 80. These speci-fications limit the permissible amounts of deleterioussubstances and provide requirements for aggregate char-acteristics. Compliance is determined by using one ormore of the several standard tests cited in the followingsections and tables. However, the fact that aggregatessatisfy ASTM C 33 or AASHTO M 6/M 80 requirementsdoes not necessarily assure defect-free concrete.

For adequate consolidation of concrete, the desirableamount of air, water, cement, and fine aggregate (that is,the mortar fraction) should be about 50% to 65% byabsolute volume (45% to 60% by mass). Rounded aggre-gate, such as gravel, requires slightly lower values, whilecrushed aggregate requires slightly higher values. Fineaggregate content is usually 35% to 45% by mass orvolume of the total aggregate content.

CHARACTERISTICS OF AGGREGATES

The important characteristics of aggregates for concrete arelisted in Table 5-2 and most are discussed in the followingsection:

Grading

Grading is the particle-size distribution of an aggregate asdetermined by a sieve analysis (ASTM C 136 or AASHTO

80


Table 5-1. Rock and Mineral Constituents inAggregates

Minerals Igneous rocks Metamorphic rocks

Silica Granite MarbleQuartz Syenite MetaquartziteOpal Diorite Slate Chalcedony Gabbro Phyllite Tridymite Peridotite Schist Cristobalite Pegmatite Amphibolite

Silicates Volcanic glass Hornfels Feldspars Obsidian Gneiss Ferromagnesian Pumice Serpentinite

Hornblende TuffAugite Scoria

Clay PerliteIllites PitchstoneKaolins FelsiteChlorites BasaltMontmorillonites

Mica Sedimentary rocks

Zeolite ConglomerateCarbonate Sandstone

Calcite QuartziteDolomite Graywacke

Sulfate SubgraywackeGypsum ArkoseAnhydrite Claystone, siltstone,

Iron sulfide argillite, and shalePyrite CarbonatesMarcasite LimestonePyrrhotite Dolomite

Iron oxide MarlMagnetite ChalkHematite ChertGoethitelmeniteLimonite

For brief descriptions, see “Standard Descriptive Nomenclature ofConstituents of Natural Mineral Aggregates” (ASTM C 294).

Fig. 5-3. Lightweight aggregate. Expanded clay (left) andexpanded shale (right). (69793)

T 27). The range of particle sizes in aggregate is illustratedin Fig. 5-4. The aggregate particle size is determined byusing wire-mesh sieves with square openings. The sevenstandard ASTM C 33 (AASHTO M 6/M 80) sieves for fineaggregate have openings ranging from 150 µm to 9.5 mm(No. 100 sieve to 3⁄8 in.). The 13 standard sieves for coarseaggregate have openings ranging from 1.18 mm to 100 mm

(0.046 in. to 4 in.). Tolerances for the dimensions of open-ings in sieves are listed in ASTM E 11 (AASHTO M 92).

Size numbers (grading sizes) for coarse aggregatesapply to the amounts of aggregate (by mass) in percent-ages that pass through an assortment of sieves (Fig. 5-5).For highway construction, ASTM D 448 (AASHTO M 43)lists the same 13 size numbers as in ASTM C 33

81

Chapter 5 � Aggregates for Concrete

Table 5.2. Characteristics and Tests of Aggregate

Characteristic Significance Test designation* Requirement or item reportedResistance to abrasion Index of aggregate quality; ASTM C 131 (AASHTO T 96) Maximum percentage ofand degradation wear resistance of floors and ASTM C 535 weight loss. Depth of wear

pavements ASTM C 779 and time

Resistance to freezing Surface scaling, roughness, ASTM C 666 (AASHTO T 161) Maximum number of cyclesand thawing loss of section, and ASTM C 682 or period of frost immunity;

aesthetics (AASHTO T 103 durability factor

Resistance to disintegration Soundness against ASTM C 88 (AASHTO T 104) Weight loss, particlesby sulfates weathering action exhibiting distress

Particle shape and Workability of fresh ASTM C 295 Maximum percentage of flatsurface texture concrete ASTM D 3398 and elongated particles

Grading Workability of fresh concrete; ASTM C 117 (AASHTO T 11) Minimum and maximumeconomy ASTM C 136 (AASHTO T 27) percentage passing

standard sieves

Fine aggregate degradation Index of aggregate quality; ASTM C 1137 Change in gradingResistance to degradationduring mixing

Uncompacted void content Workability of fresh ASTM C 1252 (AASHTO T 304) Uncompacted voids andof fine aggregate concrete specific gravity values

Bulk density Mix design calculations; ASTM C 29 (AASHTO T 19) Compact weight and(unit weight) classification loose weight

Relative density Mix design calculations ASTM C 127 (AASHTO T 85) —(specific gravity) fine aggregate

ASTM C 128 (AASHTO T 84)coarse aggregate

Absorption and surface Control of concrete quality ASTM C 70 —moisture (water-cement ratio) ASTM C 127 (AASHTO T 85)

ASTM C 128 (AASHTO T 84)ASTM C 566 (AASHTO T 255)

Compressive and flexural Acceptability of fine ASTM C 39 (AASHTO T 22) Strength to exceed 95% ofstrength aggregate failing other tests ASTM C 78 (AASHTO T 97) strength achieved with purified

sand

Definitions of constituents Clear understanding and ASTM C 125 —communication ASTM C 294

Aggregate constituents Determine amount of ASTM C 40 (AASHTO T 21) Maximum percentage alloweddeleterious and organic ASTM C 87 (AASHTO T 71) of individual constituentsmaterials ASTM C 117 (AASHTO T 11)

ASTM C 123 (AASHTO T 113)ASTM C 142 (AASHTO T 112)ASTM C 295

Resistance to alkali Soundness against ASTM C 227 Maximum length change,reactivity and volume volume change ASTM C 289 constituents and amountchange ASTM C 295 of silica, and alkalinity

ASTM C 342ASTM C 586ASTM C 1260 (AASHTO T 303)ASTM C 1293

* The majority of the tests and characteristics listed are referenced in ASTM C 33 (AASHTO M 6/M 80). ACI 221R-96 presents additional testmethods and properties of concrete influenced by aggregate characteristics.

aggregate proportions as well as cement and waterrequirements, workability, pumpability, economy, poros-ity, shrinkage, and durability of concrete. Variations ingrading can seriously affect the uniformity of concretefrom batch to batch. Very fine sands are often uneconomi-cal; very coarse sands and coarse aggregate can produceharsh, unworkable mixtures. In general, aggregates thatdo not have a large deficiency or excess of any size andgive a smooth grading curve will produce the most satis-factory results.

The effect of a collection of various sizes in reducingthe total volume of voids between aggregates is illustratedby the simple method shown in Fig. 5-7. The beaker on theleft is filled with large aggregate particles of uniform size

(AASHTO M 6/ M 80) plus an additional six more coarseaggregate size numbers. Fine aggregate or sand has onlyone range of particle sizes for general construction andhighway work.

The grading and grading limits are usually expressedas the percentage of material passing each sieve. Fig. 5-6shows these limits for fine aggregate and for one size ofcoarse aggregate.

There are several reasons for specifying grading limitsand nominal maximum aggregate size; they affect relative

82


Fig. 5-4. Range of particle sizes found in aggregate for usein concrete. (8985)

Fig. 5-5. Making a sieve analysis test of coarse aggregatein a laboratory. (30175-A)

Coa

rse

aggr

egat

eSi

ze N

o. 5

7

Fine

san

d

Optional,see text

150 µ

m

300 µ

m

600 µ

m

1.18 m

m

2.36 m

m

4.75 m

m

12.5

mm25

mm

37.5

mm

No. 10

0

No. 50

No. 30

No. 16

No. 8

No. 4

1 /2 in.

1 in.

11 /2 in.

Sieve sizes

Per

cent

pas

sing

, by

mas

s

100

80

60

40

20

0

Fine

agg

rega

teCo

arse

san

d

Fig. 5-6. Curves indicate the limits specified in ASTM C 33for fine aggregate and for one commonly used size number(grading size) of coarse aggregate.

Fig. 5-7. The level of liquid in the graduates, representingvoids, is constant for equal absolute volumes of aggre-gates of uniform but different size. When different sizes arecombined, the void-content decreases. The illustration isnot to scale.

and shape; the middle beaker is filled with an equalvolume of small aggregate particles of uniform size andshape; and the beaker on the right is filled with particlesof both sizes. Below each beaker is a graduate with theamount of water required to fill the voids in that beaker.Note that when the beakers are filled with one particle sizeof equal volume, the void content is constant, regardless ofthe particle size. When the two aggregate sizes arecombined, the void content is decreased. If this operationwere repeated with several additional sizes, a furtherreduction in voids would occur. The cement paste require-ment for concrete is related to the void content of thecombined aggregates.

During the early years of concrete technology it wassometimes assumed that the smallest percentage of voids(greatest density of aggregates) was the most suitable forconcrete. At the same time, limits were placed on theamount and size of the smallest particles. It is now knownthat, even on this restricted basis, this is not the best targetfor the mix designer. However, production of satisfactory,economical concrete requires aggregates of low voidcontent, but not the lowest. Voids in aggregates can betested according to ASTM C 29 or AASHTO T 19.

In reality, the amount of cement paste required inconcrete is greater than the volume of voids between theaggregates. This is illustrated in Fig. 5-8. Sketch A repre-sents large aggregates alone, with all particles in contact.Sketch B represents the dispersal of aggregates in a matrixof paste. The amount of paste is necessarily greater thanthe void content of sketch A in order to provide workabil-ity to the concrete; the actual amount is influenced by theworkability and cohesiveness of the paste.

Fine-Aggregate Grading

Requirements of ASTM C 33 or AASHTO M 6/M 43 per-mit a relatively wide range in fine-aggregate gradation,but specifications by other organizations are sometimesmore restrictive. The most desirable fine-aggregate grad-ing depends on the type of work, the richness of themixture, and the maximum size of coarse aggregate. Inleaner mixtures, or when small-size coarse aggregates areused, a grading that approaches the maximum recom-mended percentage passing each sieve is desirable forworkability. In general, if the water-cement ratio is keptconstant and the ratio of fine-to-coarse aggregate is chosencorrectly, a wide range in grading can be used withoutmeasurable effect on strength. However, the best economywill sometimes be achieved by adjusting the concretemixture to suit the gradation of the local aggregates.

Fine-aggregate grading within the limits of ASTM C33 (AASHTO M 6) is generally satisfactory for mostconcretes. The ASTM C 33 (AASHTO M 6) limits withrespect to sieve size are shown in Table 5-3.

83


A

B

Fig. 5-8. Illustration of the dispersion of aggregates in co-hesive concrete mixtures.

Table 5-3. Fine-Aggregate Grading Limits(ASTM C 33/AASHTO M 6)

Sieve size Percent passing by mass

9.5 mm (3⁄8 in.) 1004.75 mm (No. 4) 95 to 1002.36 mm (No. 8) 80 to 1001.18 mm (No. 16) 50 to 85

600 µm (No. 30) 25 to 60300 µm (No. 50) 5 to 30 (AASHTO 10 to 30)150 µm (No. 100) 0 to 10 (AASHTO 2 to 10)

The AASHTO specifications permit the minimumpercentages (by mass) of material passing the 300 µm (No.50) and 150 µm (No. 100) sieves to be reduced to 5% and0% respectively, provided:

1. The aggregate is used in air-entrained concretecontaining more than 237 kilograms of cement percubic meter (400 lb of cement per cubic yard) andhaving an air content of more than 3%.

2. The aggregate is used in concrete containing morethan 297 kilograms of cement per cubic meter (500 lbof cement per cubic yard) when the concrete is not air-entrained.

3. An approved supplementary cementitious material isused to supply the deficiency in material passingthese two sieves.

Other requirements of ASTM C 33 (AASTHO M 6) are:

1. The fine aggregate must not have more than 45%retained between any two consecutive standardsieves.

2. The fineness modulus must be not less than 2.3 normore than 3.1, nor vary more than 0.2 from the typicalvalue of the aggregate source. If this value is ex-

given maximum-size coarse aggregate can be varied overa moderate range without appreciable effect on cementand water requirement of a mixture if the proportion offine aggregate to total aggregate produces concrete ofgood workability. Mixture proportions should be changedto produce workable concrete if wide variations occur inthe coarse-aggregate grading. Since variations are difficultto anticipate, it is often more economical to maintainuniformity in manufacturing and handling coarse aggre-gate than to reduce variations in gradation.

The maximum size of coarse aggregate used in con-crete has a bearing on the economy of concrete. Usuallymore water and cement is required for small-size aggre-gates than for large sizes, due to an increase in total aggre-gate surface area. The water and cement required for aslump of approximately 75 mm (3 in.) is shown in Fig. 5-9for a wide range of coarse-aggregate sizes. Fig. 5-9 showsthat, for a given water-cement ratio, the amount of cementrequired decreases as the maximum size of coarse aggre-gate increases. The increased cost of obtaining and/or

ceeded, the fine aggregate should be rejected unlesssuitable adjustments are made in proportions of fineand coarse aggregate.

The amounts of fine aggregate passing the 300 µm(No. 50) and 150, µm (No. 100) sieves affect workability,surface texture, air content, and bleeding of concrete. Mostspecifications allow 5% to 30% to pass the 300 µm (No. 50)sieve. The lower limit may be sufficient for easy placingconditions or where concrete is mechanically finished,such as in pavements. However, for hand-finishedconcrete floors, or where a smooth surface texture is de-sired, fine aggregate with at least 15% passing the 300 µm(No. 50) sieve and 3% or more passing the 150 µm (No.100) sieve should be used.

Fineness Modulus. The fineness modulus (FM) of eitherfine or coarse aggregate according to ASTM C 125 is calcu-lated by adding the cumulative percentages by massretained on each of a specified series of sieves and divid-ing the sum by 100. The specified sieves for determiningFM are: 150 µm (No. 100), 300 µm (No. 50), 600 µm (No.30), 1.18 mm (No. 16), 2.36 mm (No. 8), 4.75 mm (No. 4),9.5 mm (3⁄8 in.), 19.0 mm (3⁄4 in.), 37.5 mm (11⁄2 in.), 75 mm(3 in.) and, 150 mm (6 in.).

FM is an index of the fineness of an aggregate—thehigher the FM, the coarser the aggregate. Different aggre-gate grading may have the same FM. FM of fine aggregateis useful in estimating proportions of fine and coarseaggregates in concrete mixtures. An example of how theFM of a fine aggregate is determined (with an assumedsieve analysis) is shown in Table 5-4.

Degradation of fine aggregate due to friction andabrasion will decrease the FM and increase the amount ofmaterials finer than the 75 µm (No. 200) sieve.

Coarse-Aggregate Grading

The coarse aggregate grading requirements of ASTM C 33(AASHTO M 80) permit a wide range in grading and avariety of grading sizes (see Table 5-5). The grading for a

84


Table 5-5. Grading Requirements for Coarse Aggregates (ASTM C 33 and AASHTO M 80)

Amounts finer than each laboratory sieve, mass percent passingSize Nominal size, sieves 100 mm 90 mm 75 mm 63 mm 50 mm

number with square openings (4 in.) (31⁄2 in.) (3 in.) (21⁄2 in.) (2 in.)

1 90 to 37.5 mm (31⁄2 to 11⁄2 in.) 100 90 to 100 — 25 to 60 —2 63 to 37.5 mm (21⁄2 to 11⁄2 in.) — — 100 90 to 100 35 to 703 50 to 25.0 mm (2 to 1 in.) — — — 100 90 to 100

357 50 to 4.75 mm (2 in. to No. 4) — — — 100 95 to 1004 37.5 to 19.0 mm (11⁄2 to 3⁄4 in.) — — — — 100

467 37.5 to 4.75 mm (11⁄2 in. to No. 4) — — — — 1005 25.0 to 12.5 mm (1 to 1⁄2 in.) — — — — —56 25.0 to 9.5 mm (1 to 3⁄8 in.) — — — — —57 25.0 to 4.75 mm (1 in. to No. 4) — — — — —6 19.0 to 9.5 mm (3⁄4 to 3⁄8 in.) — — — — —67 19.0 to 4.75 mm (3⁄4 in. to No. 4) — — — — —7 12.5 to 4.75 mm (1⁄2 in. to No. 4) — — — — —8 9.5 to 2.36 mm (3⁄8 in. to No. 8) — — — — —

Table 5-4. Determination of Fineness Modulus ofFine Aggregates

Percentageof individual Cumulative

fraction Percentage percentageretained, passing, retained,

Sieve size by mass by mass by mass9.5 mm (3⁄8 in.) 0 100 04.75 mm (No. 4) 2 98 22.36 mm (No. 8) 13 85 151.18 mm (No. 16) 20 65 35600 µm (No. 30) 20 45 55300 µm (No. 50) 24 21 79150 µm (No. 100) 18 3 97

Pan 3 0 —Total 100 283

Fineness modulus= 283 ÷ 100 = 2.83

handling aggregates much larger than 50 mm (2 in.) mayoffset the savings in using less cement. Furthermore,aggregates of different maximum sizes may give slightlydifferent concrete strengths for the same water-cementratio. In some instances, at the same water-cement ratio,concrete with a smaller maximum-size aggregate couldhave higher compressive strength. This is especially truefor high-strength concrete. The optimum maximum sizeof coarse aggregate for higher strength depends on factorssuch as relative strength of the cement paste, cement-aggregate bond, and strength of the aggregate particles.

The terminology used to specify size of coarse aggre-gate must be chosen carefully. Particle size is determinedby size of sieve and applies to the aggregate passing thatsieve and not passing the next smaller sieve. When speak-ing of an assortment of particle sizes, the size number (orgrading size) of the gradation is used. The size numberapplies to the collective amount of aggregate that passesthrough an assortment of sieves. As shown in Table 5-5,the amount of aggregate passing the respective sieves isgiven in percentages; it is called a sieve analysis.

Because of past usage, there is sometimes confusionabout what is meant by the maximum size of aggregate.ASTM C 125 and ACI 116 define this term and distinguishit from nominal maximum size of aggregate. The maxi-mum size of an aggregate is the smallest sieve that all of aparticular aggregate must pass through. The nominalmaximum size of an aggregate is the smallest sieve sizethrough which the major portion of the aggregate mustpass. The nominal maximum-size sieve may retain 5% to15% of the aggregate depending on the size number. Forexample, aggregate size number 67 has a maximum size of25 mm (1 in.) and a nominal maximum size of 19 mm (3⁄4in.). Ninety to one hundred percent of this aggregate mustpass the 19-mm (3⁄4-in.) sieve and all of the particles mustpass the 25-mm (1-in.) sieve.

The maximum size of aggregate that can be usedgenerally depends on the size and shape of the concretemember and the amount and distribution of reinforcingsteel. The maximum size of aggregate particles generallyshould not exceed:

85


3/8

4.75 9.5 12.5 19.0 25.0 37.5 50.0 75.0 112.0

1/2 3/4 1 11/2 43/82 33/16


Air-entrained concrete



Slump approximately 75 mm (3 in.)w/c ratio: 0.54 by mass

Slump approximately 75 mm (3 in.)w/c ratio: 0.54 by mass

Maximum nominal size of aggregate, mm

Maximum nominal size of aggregate, in.

300

200

100

450

400

350

300

250

200

0

500

400

300

200

100

700

600

500

400

0

Cem

ent,

kg/m

3 W

ater

, kg/

m3

Cem

ent,

lb/y

d3

Wat

er, l

b/yd

3

Fig. 5-9. Cement and water contents in relation to maximumsize of aggregate for air-entrained and non-air-entrained con-crete. Less cement and water are required in mixtures havinglarge coarse aggregate (Bureau of Reclamation 1981).

37.5 mm 25.0 mm 19.0 mm 12.5 mm 9.5 mm 4.75 mm 2.36 mm 1.18 mm(11⁄2 in.) (1 in.) (3⁄4 in.) (1⁄2 in.) (3⁄8 in.) (No. 4) (No. 8) (No. 16)

0 to 15 — 0 to 5 — — — — —0 to 15 — 0 to 5 — — — — —35 to 70 0 to 15 — 0 to 5 — — — —

— 35 to 70 — 10 to 30 — 0 to 5 — —90 to 100 20 to 55 0 to 15 — 0 to 5 — — —95 to 100 — 35 to 70 — 10 to 30 0 to 5 — —

100 90 to 100 20 to 55 0 to 10 0 to 5 — — —100 90 to 100 40 to 85 10 to 40 0 to 15 0 to 5 — —100 95 to 100 — 25 to 60 — 0 to 10 0 to 5 —— 100 90 to 100 20 to 55 0 to 15 0 to 5 — —— 100 90 to 100 — 25 to 55 0 to 10 0 to 5 —— — 100 90 to 100 40 to 70 0 to 15 0 to 5 —— — — 100 85 to 100 10 to 30 0 to 10 0 to 5

• The optimum mixture has the least particle interfer-ence and responds best to a high frequency, highamplitude vibrator.

However, this optimum mixture cannot be used forall construction due to variations in placing and finishingneeds and availability. Crouch (2000) found in his studieson air-entrained concrete that the water-cement ratiocould be reduced by over 8% using combined aggregategradation. Shilstone (1990) also analyzes aggregate grada-tion by coarseness and workability factors to improveaggregate gradation.

Gap-Graded Aggregates

In gap-graded aggregates certain particle sizes are inten-tionally omitted. For cast-in-place concrete, typical gap-graded aggregates consist of only one size of coarseaggregate with all the particles of fine aggregate able topass through the voids in the compacted coarse aggregate.Gap-graded mixes are used in architectural concrete toobtain uniform textures in exposed-aggregate finishes.They can also used in normal structural concrete becauseof possible improvements in some concrete properties, andto permit the use of local aggregate gradations (Houston1962 and Litvin and Pfeifer 1965).

For an aggregate of 19-mm (3⁄4-in.) maximum size, the4.75 mm to 9.5 mm (No. 4 to 3⁄8 in.) particles can be omit-ted without making the concrete unduly harsh or subjectto segregation. In the case of 37.5 mm (11⁄2 in.) aggregate,usually the 4.75 mm to 19 mm (No. 4 to 3⁄4 in.) sizes areomitted.

Care must be taken in choosing the percentage of fineaggregate in a gap-graded mixture. A wrong choice canresult in concrete that is likely to segregate or honeycombbecause of an excess of coarse aggregate. Also, concretewith an excess of fine aggregate could have a high waterdemand resulting in a low-density concrete. Fine aggregateis usually 25% to 35% by volume of the total aggregate. Thelower percentage is used with rounded aggregates and thehigher with crushed material. For a smooth off-the-formfinish, a somewhat higher percentage of fine aggregate tototal aggregate may be used than for an exposed-aggregatefinish, but both use a lower fine aggregate content thancontinuously graded mixtures. Fine aggregate content alsodepends upon cement content, type of aggregate, andworkability.

Air entrainment is usually required for workabilitysince low-slump, gap-graded mixes use a low fine aggre-gate percentage and produce harsh mixes withoutentrained air.

Segregation of gap-graded mixes must be preventedby restricting the slump to the lowest value consistent withgood consolidation. This may vary from zero to 75 mm (to3 in.) depending on the thickness of the section, amount ofreinforcement, and height of casting. Close control of grad-ing and water content is also required because variationsmight cause segregation. If a stiff mixture is required, gap-

1. One-fifth the narrowest dimension of a concretemember

2. Three-quarters the clear spacing between reinforcingbars and between the reinforcing bars and forms

3. One-third the depth of slabs

These requirements may be waived if, in the judg-ment of the engineer, the mixture possesses sufficientworkability that the concrete can be properly placed with-out honeycomb or voids.

Combined Aggregate Grading

Aggregate is sometimes analyzed using the combinedgrading of fine and coarse aggregate together, as they existin a concrete mixture. This provides a more thoroughanalysis of how the aggregates will perform in concrete.Sometimes mid-sized aggregate, around the 9.5 mm (3⁄8in.) size, is lacking in an aggregate supply, resulting in aconcrete with high shrinkage properties, high waterdemand, poor workability, poor pumpability, and poorplaceability. Strength and durability may also be affected.

Fig. 5-10 illustrates an ideal gradation; however, aperfect gradation does not exist in the field—but we cantry to approach it. If problems develop due to a poorgradation, alternative aggregates, blending, or specialscreening of existing aggregates, should be considered.Refer to Shilstone (1990) for options on obtaining optimalgrading of aggregate.

The combined gradation can be used to better controlworkability, pumpability, shrinkage, and other propertiesof concrete. Abrams (1918) and Shilstone (1990) demon-strate the benefits of a combined aggregate analysis:

• With constant cement content and constant consis-tency, there is an optimum for every combination ofaggregates that will produce the most effective waterto cement ratio and highest strength.

86


37.5

25.0

19.0

12.5 9.5

4.75

2.36

1.18

0.60

00.

300

0.15

0

0.07

50.

045

25

20

15

10

5

0

Per

cent

ret

aine

d

Sieve size in mm

Fig. 5-10. Optimum combined aggregate grading forconcrete.

graded aggregates may produce higher strengths thannormal aggregates used with comparable cement contents.Because of their low fine-aggregate volumes and lowwater-cement ratios, gap-graded mixtures might beconsidered unworkable for some cast-in-place construc-tion. When properly proportioned, however, these con-cretes are readily consolidated with vibration.

Particle Shape and Surface Texture

The particle shape and surface texture of an aggregateinfluence the properties of freshly mixed concrete morethan the properties of hardened concrete. Rough-textured,angular, elongated particles require more water toproduce workable concrete than do smooth, rounded,compact aggregates. Hence, aggregate particles that areangular require more cement to maintain the same water-cement ratio. However, with satisfactory gradation, bothcrushed and noncrushed aggregates (of the same rocktypes) generally give essentially the same strength for thesame cement factor. Angular or poorly graded aggregatescan also be more difficult to pump.

The bond between cement paste and a given aggre-gate generally increases as particles change from smoothand rounded to rough and angular. This increase in bondis a consideration in selecting aggregates for concretewhere flexural strength is important or where highcompressive strength is needed.

Void contents of compacted fine or coarse aggregatecan be used as an index of differences in the shape andtexture of aggregates of the same grading. The mixingwater and cement requirement tend to increase as aggre-gate void content increases. Voids between aggregate par-ticles increase with aggregate angularity.

Aggregate should be relatively free of flat and elon-gated particles. A particle is called flat and elongatedwhen the ratio of length to thickness exceeds a specifiedvalue. See ASTM D 4791 for determination of flat, and/orelongated particles. ASTM D 3398 provides an indirectmethod of establishing a particle index as an overall meas-ure of particle shape or texture, while ASTM C 295provides procedures for the petrographic examination ofaggregate.

Flat and elongated aggregate particles should beavoided or at least limited to about 15% by mass of the totalaggregate. This requirement is equally important for coarseand for crushed fine aggregate, since fine aggregate madeby crushing stone often contains flat and elongated parti-cles. Such aggregate particles require an increase in mixingwater and thus may affect the strength of concrete, particu-larly in flexure, if the water-cement ratio is not adjusted.

A number of automated test machines are availablefor rapid determination of the particle size distribution ofaggregate. Designed to provide a faster alternative to thestandard sieve analysis test, these machines capture andanalyze digital images of the aggregate particles to deter-mine gradation. Fig. 5-11 shows a videograder that meas-ures size and shape of an aggregate by using line-scan

cameras wherein two-dimensional images are constructedfrom a series of line images. Other machines use matrix-scan cameras to capture two-dimensional snapshots of thefalling aggregate. Maerz and Lusher (2001) developed adynamic prototype imaging system that provides particlesize and shape information by using a miniconveyorsystem to parade individual fragments past two orthogo-nally oriented, synchronized cameras.

Bulk Density (Unit Weight) and Voids

The bulk density or unit weight of an aggregate is themass or weight of the aggregate required to fill a containerof a specified unit volume. The volume referred to here isthat occupied by both aggregates and the voids betweenaggregate particles.

The approximate bulk density of aggregate com-monly used in normal-weight concrete ranges from about1200 to 1750 kg/m3 (75 to 110 lb/ft3). The void contentbetween particles affects paste requirements in mix design(see preceding sections, “Particle Shape and SurfaceTexture” and “Grading”). Void contents range from about30% to 45% for coarse aggregates to about 40% to 50% forfine aggregate. Angularity increases void content whilelarger sizes of well-graded aggregate and improved grad-ing decreases void content (Fig. 5-7). Methods of deter-mining the bulk density of aggregates and void contentare given in ASTM C 29 (AASHTO T 19). In these stan-dards, three methods are described for consolidating theaggregate in the container depending on the maximumsize of the aggregate: rodding, jigging, and shoveling. Themeasurement of loose uncompacted void content of fineaggregate is described in ASTM C 1252.

Relative Density (Specific Gravity)

The relative density (specific gravity) of an aggregate is theratio of its mass to the mass of an equal absolute volume of

87

Chapter 5 ◆ Aggregates for Concrete

Fig. 5-11. Videograder for measuring size and shape ofaggregate. (69545)

aggregates in order to accurately meet the water require-ment of the mix design. If the water content of the concretemixture is not kept constant, the water-cement ratio willvary from batch to batch causing other properties, such asthe compressive strength and workability to vary frombatch to batch.

Coarse and fine aggregate will generally have absorp-tion levels (moisture contents at SSD) in the range of 0.2%to 4% and 0.2% to 2%, respectively. Free-water contents willusually range from 0.5% to 2% for coarse aggregate and 2%to 6% for fine aggregate. The maximum water content ofdrained coarse aggregate is usually less than that of fineaggregate. Most fine aggregates can maintain a maximumdrained moisture content of about 3% to 8% whereas coarseaggregates can maintain only about 1% to 6%.

Bulking. Bulking is the increase in total volume of moistfine aggregate over the same mass dry. Surface tension inthe moisture holds the particles apart, causing an increasein volume. Bulking of a fine aggregate (such as sand)occurs when it is shoveled or otherwise moved in a dampcondition, even though it may have been fully consoli-

water. It is used in certain computations for mixtureproportioning and control, such as the volume occupied bythe aggregate in the absolute volume method of mixdesign. It is not generally used as a measure of aggregatequality, though some porous aggregates that exhibit accel-erated freeze-thaw deterioration do have low specific grav-ities. Most natural aggregates have relative densitiesbetween 2.4 and 2.9 with corresponding particle (mass)densities of 2400 and 2900 kg/m3 (150 and 181 lb/ft3).

Test methods for determining relative densities forcoarse and fine aggregates are described in ASTM C 127(AASHTO T 85) and ASTM C 128 (AASHTO T 84), respec-tively. The relative density of an aggregate may be deter-mined on an ovendry basis or a saturated surface-dry (SSD)basis. Both the ovendry and saturated surface-dry relativedensities may be used in concrete mixture proportioningcalculations. Ovendry aggregates do not contain anyabsorbed or free water. They are dried in an oven to con-stant weight. Saturated surface-dry aggregates are those inwhich the pores in each aggregate particle are filled withwater but there is no excess water on the particle surface.

Density

The density of aggregate particles used in mixture propor-tioning computations (not including voids between parti-cles) is determined by multiplying the relative density(specific gravity) of the aggregate times the density ofwater. An approximate value of 1000 kg/m3 (62.4 lb/ft3) isoften used for the density of water. The density of aggre-gate, along with more accurate values for water density,are provided in ASTM C 127 (AASHTO T 85) and ASTMC 128 (AASHTO T 84). Most natural aggregates haveparticle densities of between 2400 and 2900 kg/m3 (150and 181 lb/ft3).

Absorption and Surface Moisture

The absorption and surface moisture of aggregates shouldbe determined according to ASTM C 70, C 127, C 128, andC 566 (AASHTO T 255) so that the total water content ofthe concrete can be controlled and correct batch weightsdetermined. The internal structure of an aggregate particleis made up of solid matter and voids that may or may notcontain water.

The moisture conditions of aggregates are shown inFig. 5-12. They are designated as:

1. Ovendry—fully absorbent2. Air dry—dry at the particle surface but containing

some interior moisture, thus still somewhat absorbent3. Saturated surface dry (SSD)—neither absorbing water

from nor contributing water to the concrete mixture4. Damp or wet—containing an excess of moisture on

the surface (free water)

The amount of water added at the concrete batchplant must be adjusted for the moisture conditions of the

88


Ovendry Air drySaturated,surface dry

Dampor wetState

None Less thanpotential

absorption

Equal topotential

absorption

Greaterthan

absorption

Totalmoisture:

Fig. 5-12. Moisture conditions of aggregate.

0 5 10 15 20Percent of moisture added by mass

to dry, rodded fine aggregate

Fine grading

Medium grading

Coarse grading

Per

cent

incr

ease

in v

olum

e ov

er d

ry,

rodd

ed fi

ne a

ggre

gate

40

30

20

10

0

Fig. 5-13. Surface moisture on fine aggregate can causeconsiderable bulking; the amount varies with the amount ofmoisture and the aggregate grading (PCA Major Series 172and PCA ST20).

dated beforehand. Fig. 5-13 illustrates how the amount ofbulking of fine aggregate varies with moisture content andgrading; fine gradings bulk more than coarse gradings fora given amount of moisture. Fig. 5-14 shows similar infor-mation in terms of weight for a particular fine aggregate.Since most fine aggregates are delivered in a damp condi-tion, wide variations can occur in batch quantities if batch-ing is done by volume. For this reason, good practice haslong favored weighing the aggregate and adjusting formoisture content when proportioning concrete.


The frost resistance of an aggregate, an important charac-teristic for exterior concrete, is related to its porosity,absorption, permeability, and pore structure. An aggre-gate particle may absorb so much water (to critical satura-tion) that it cannot accommodate the expansion andhydraulic pressure that occurs during the freezing ofwater. If enough of the offending particles are present, theresult can be expansion of the aggregate and possibledisintegration of the concrete. If a single problem particleis near the surface of the concrete, it can cause a popout.Popouts generally appear as conical fragments that breakout of the concrete surface. The offending aggregate parti-cle or a part of it is usually found at the bottom of the void.Generally it is coarse rather than fine aggregate particles

with higher porosity values and medium-sized pores (0.1to 5 µm) that are easily saturated and cause concrete dete-rioration and popouts. Larger pores do not usually be-come saturated or cause concrete distress, and water invery fine pores may not freeze readily.

At any freezing rate, there may be a critical particle sizeabove which a particle will fail if frozen when criticallysaturated. This critical size is dependent upon the rate offreezing and the porosity, permeability, and tensile strengthof the particle. For fine-grained aggregates with low perme-ability (cherts for example), the critical particle size may bewithin the range of normal aggregate sizes. It is higher forcoarse-grained materials or those with capillary systemsinterrupted by numerous macropores (voids too large tohold moisture by capillary action). For these aggregates thecritical particle size may be sufficiently large to be of noconsequence, even though the absorption may be high. Ifpotentially vulnerable aggregates are used in concretesubjected to periodic drying while in service, they maynever become sufficiently saturated to cause failure.

Cracking of concrete pavements caused by the freeze-thaw deterioration of the aggregate within concrete iscalled D-cracking. This type of cracking has been ob-served in some pavements after three or more years ofservice. D-cracked concrete resembles frost-damagedconcrete caused by paste deterioration. D-cracks areclosely spaced crack formations parallel to transverse andlongitudinal joints that later multiply outward from thejoints toward the center of the pavement panel (Fig. 5-15).D-cracking is a function of the pore properties of certaintypes of aggregate particles and the environment in whichthe pavement is placed. Due to the natural accumulationof water under pavements in the base and subbase layers,the aggregate may eventually become saturated. Then

89


Mass of fine aggregate and water in oneunit of volume measured loose in air

Moisture in fine aggregate, percent by mass

0 2 4 6 8 10 12 14 16 18 20

Bul

k de

nsity

, kg/

m3

Bul

k de

nsity

, lb/

ft3

2480

2280

2080

1880

1680

1480

1280

150

140

130

120

110

90

80

100

Bul

king

, per

cent

by

volu

me

30

20

10

0

Fig. 5-14. Bulk density is compared with the moisture con-tent for a particular sand (PCA Major Series 172).

Fig. 5-15. D-cracking along a transverse joint caused byfailure of carbonate coarse aggregate (Stark 1976). (30639)

ovendried and the percentage of weight loss calculated.Unfortunately, this test is sometimes misleading.Aggregates behaving satisfactorily in the test mightproduce concrete with low freeze-thaw resistance;conversely, aggregates performing poorly might produceconcrete with adequate resistance. This is attributed, atleast in part, to the fact that the aggregates in the test arenot confined by cement paste (as they would be inconcrete) and the mechanisms of attack are not the same asin freezing and thawing. The test is most reliable for strat-ified rocks with porous layers or weak bedding planes.

An additional test that can be used to evaluate aggre-gates for potential D-cracking is the rapid pressure releasemethod. An aggregate is placed in a pressurized chamberand the pressure is rapidly released causing the aggregatewith a questionable pore system to fracture (Janssen andSnyder 1994). The amount of fracturing relates to thepotential for D-cracking.

Wetting and Drying Properties

Weathering due to wetting and drying can also affect thedurability of aggregates. The expansion and contractioncoefficients of rocks vary with temperature and moisturecontent. If alternate wetting and drying occurs, severestrain can develop in some aggregates, and with certaintypes of rock this can cause a permanent increase involume of the concrete and eventual breakdown. Claylumps and other friable particles can degrade rapidly withrepeated wetting and drying. Popouts can also developdue to the moisture-swelling characteristics of certainaggregates, especially clay balls and shales. While nospecific tests are available to determine this tendency, anexperienced petrographer can often be of assistance indetermining this potential for distress.

Abrasion and Skid Resistance

The abrasion resistance of an aggregate is often used as ageneral index of its quality. Abrasion resistance is essentialwhen the aggregate is to be used in concrete subject toabrasion, as in heavy-duty floors or pavements. Low abra-sion resistance of an aggregate may increase the quantityof fines in the concrete during mixing; consequently, thismay increase the water requirement and require an adjust-ment in the water-cement ratio.

The most common test for abrasion resistance is theLos Angeles abrasion test (rattler method) performed inaccordance with ASTM C 131 (AASHTO T 96) or ASTM C535. In this test a specified quantity of aggregate is placedin a steel drum containing steel balls, the drum is rotated,and the percentage of material worn away is measured.Specifications often set an upper limit on this mass loss.However, a comparison of the results of aggregate abra-sion tests with the abrasion resistance of concrete madewith the same aggregate do not generally show a clear

with freezing and thawing cycles, cracking of the concretestarts in the saturated aggregate (Fig. 5-16) at the bottomof the slab and progresses upward until it reaches thewearing surface. This problem can be reduced either byselecting aggregates that perform better in freeze-thawcycles or, where marginal aggregates must be used, byreducing the maximum particle size. Also, installation ofeffective drainage systems for carrying free water outfrom under the pavement may be helpful.

The performance of aggregates under exposure tofreezing and thawing can be evaluated in two ways: (1)past performance in the field, and (2) laboratory freeze-thaw tests of concrete specimens. If aggregates from thesame source have previously given satisfactory servicewhen used in concrete, they might be considered suitable.Aggregates not having a service record can be consideredacceptable if they perform satisfactorily in air-entrainedconcretes subjected to freeze-thaw tests according toASTM C 666 (AASHTO T 161). In these tests concrete spe-cimens made with the aggregate in question are subjectedto alternate cycles of freezing and thawing in water.Deterioration is measured by (1) the reduction in thedynamic modulus of elasticity, (2) linear expansion, and(3) weight loss of the specimens. An expansion failurecriterion of 0.035% in 350 freeze-thaw cycles or less is usedby a number of state highway departments to help indi-cate whether or not an aggregate is susceptible to D-crack-ing. Different aggregate types may influence the criterialevels and empirical correlations between laboratoryfreeze-thaw tests. Field service records should be made toselect the proper criterion (Vogler and Grove 1989).

Specifications may require that resistance to weather-ing be demonstrated by a sodium sulfate or magnesiumsulfate test (ASTM C 88 or AASHTO T 104). The testconsists of a number of immersion cycles for a sample ofthe aggregate in a sulfate solution; this creates a pressurethrough salt-crystal growth in the aggregate pores similarto that produced by freezing water. The sample is then

90


Fig. 5-16. Fractured carbonate aggregate particle as asource of distress in D-cracking (magnification 2.5X) (Stark1976). (30639-A)

correlation. Mass loss due to impact in the rattler is oftenas much as that due to abrasion. The wear resistance ofconcrete is determined more accurately by abrasion testsof the concrete itself (see Chapter 1).

To provide good skid resistance on pavements, thesiliceous particle content of the fine aggregate should be atleast 25%. For specification purposes, the siliceous particlecontent is considered equal to the insoluble residuecontent after treatment in hydrochloric acid under stan-dardized conditions (ASTM D 3042). Certain manufac-tured sands produce slippery pavement surfaces andshould be investigated for acceptance before use.

Strength and Shrinkage

The strength of an aggregate is rarely tested and generallydoes not influence the strength of conventional concrete asmuch as the strength of the paste and the paste-aggregatebond. However, aggregate strength does become importantin high-strength concrete. Aggregate stress levels in concreteare often much higher than the average stress over the entirecross section of the concrete. Aggregate tensile strengthsrange from 2 to 15 MPa (300 to 2300 psi) and compressivestrengths from 65 to 270 MPa (10,000 to 40,000 psi).

Different aggregate types have different compressibil-ity, modulus of elasticity, and moisture-related shrinkagecharacteristics that can influence the same properties inconcrete. Aggregates with high absorption may have highshrinkage on drying. Quartz and feldspar aggregates,along with limestone, dolomite, and granite, are consid-ered low shrinkage aggregates; while aggregates withsandstone, shale, slate, hornblende, and graywacke areoften associated with high shrinkage in concrete (Fig. 5-17).

Resistance to Acid and Other Corrosive Substances

Portland cement concrete is durable in most natural envi-ronments; however, concrete in service is occasionallyexposed to substances that will attack it.

Most acidic solutions will slowly or rapidly disinte-grate portland cement concrete depending on the type andconcentration of acid. Certain acids, such as oxalic acid, areharmless. Weak solutions of some acids have insignificanteffects. Although acids generally attack and leach away thecalcium compounds of the cement paste, they may notreadily attack certain aggregates, such as siliceous aggre-gates. Calcareous aggregates often react readily with acids.However, the sacrificial effect of calcareous aggregates isoften a benefit over siliceous aggregate in mild acid expo-sures or in areas where water is not flowing. With calcare-ous aggregate, the acid attacks the entire exposed concretesurface uniformly, reducing the rate of attack on the pasteand preventing loss of aggregate particles at the surface.Calcareous aggregates also tend to neutralize the acid,especially in stagnant locations. Acids can also discolor

concrete. Siliceous aggregate should be avoided whenstrong solutions of sodium hydroxide are present, as thesesolutions attack this type of aggregate.

Acid rain (often with a pH of 4 to 4.5) can slightly etchconcrete surfaces, usually without affecting the perform-ance of exposed concrete structures. Extreme acid rain orstrong acid water conditions may warrant special concretedesigns or precautions, especially in submerged areas.Continuous replenishment in acid with a pH of less than4 is considered highly aggressive to buried concrete, suchas pipe (Scanlon 1987). Concrete continuously exposed toliquid with a pH of less than 3 should be protected in amanner similar to concrete exposed to dilute acid solu-tions (ACI 515.1R).

Natural waters usually have a pH of more than 7 andseldom less than 6. Waters with a pH greater than 6.5 maybe aggressive if they contain bicarbonates. Carbonic acidsolutions with concentrations between 0.9 and 3 parts permillion are considered to be destructive to concrete (ACI515.1R and Kerkhoff 2001).

A low water-cement ratio, low permeability, and low-to-moderate cement content can increase the acid or corro-sion resistance of concrete. A low permeability resultingfrom a low water-cement ratio or the use of silica fume orother pozzolans, helps keep the corrosive agent frompenetrating into the concrete. Low-to-moderate cementcontents result in less available paste to attack. The use ofsacrificial calcareous aggregates should be consideredwhere indicated.

Certain acids, gases, salts, and other substances thatare not mentioned here also can disintegrate concrete.Acids and other chemicals that severely attack portlandcement concrete should be prevented from coming incontact with the concrete by using protective coatings(Kerkhoff 2001).

91


Sandstone Slate Granite Limestone Quartz

0.14

0.12

0.10

0.08

0.06

0.04

0.02

0.00

Dry

ing

shrin

kage

afte

r 1

year

in p

erce

nt

Fig. 5-17. Concretes containing sandstone or slate producea high shrinkage concrete. Granite, limestone and quartz,are low shrinkage-producing aggregates (ACI 221R).

Fire Resistance and Thermal Properties

The fire resistance and thermal properties of concrete—conductivity, diffusivity, and coefficient of thermal expan-sion—depend to some extent on the mineral constituentsof the aggregates used. Manufactured and some naturallyoccurring lightweight aggregates are more fire resistantthan normal-weight aggregates due to their insulatingproperties and high-temperature stability. Concretecontaining a calcareous coarse aggregate performs betterunder fire exposure than a concrete containing quartz orsiliceous aggregate such as granite or quartzite. At about590°C (1060°F), quartz expands 0.85% causing disruptiveexpansion (ACI 216 and ACI 221). The coefficient of ther-mal expansion of aggregates ranges from 0.55 x 10-6 per °Cto 5 x 10-6 per °C (1 x 10-6 per °F to 9 x 10-6 per °F). Formore information refer to Chapter 15 for temperature-induced volume changes and to Chapter 18 for thermalconductivity and mass concrete considerations.

POTENTIALLY HARMFUL MATERIALS

Harmful substances that may be present in aggregatesinclude organic impurities, silt, clay, shale, iron oxide, coal,lignite, and certain lightweight and soft particles (Table5-6). In addition, rocks and minerals such as some cherts,strained quartz (Buck and Mather 1984), and certain dolo-mitic limestones are alkali reactive (see Table 5-7). Gypsumand anhydrite may cause sulfate attack. Certain aggre-gates, such as some shales, will cause popouts by swelling(simply by absorbing water) or by freezing of absorbedwater (Fig. 5-18). Most specifications limit the permissibleamounts of these substances. The performance history ofan aggregate should be a determining factor in setting thelimits for harmful substances. Test methods for detectingharmful substances qualitatively or quantitatively arelisted in Table 5-6.

Aggregates are potentially harmful if they containcompounds known to react chemically with portlandcement concrete and produce any of the following: (1)significant volume changes of the paste, aggregates, orboth; (2) interference with the normal hydration ofcement; and (3) otherwise harmful byproducts.

Organic impurities may delay setting and hardeningof concrete, may reduce strength gain, and in unusualcases may cause deterioration. Organic impurities such aspeat, humus, and organic loam may not be as detrimentalbut should be avoided.

Materials finer than the 75-µm (No. 200) sieve, espe-cially silt and clay, may be present as loose dust and mayform a coating on the aggregate particles. Even thin coat-ings of silt or clay on gravel particles can be harmfulbecause they may weaken the bond between the cementpaste and aggregate. If certain types of silt or clay are pres-ent in excessive amounts, water requirements mayincrease significantly.

92


Effect on TestSubstances concrete designation

Organic Affects setting ASTM C 40 (AASHTO T 21)impurities and hardening, ASTM C 87 (AASHTO T 71)

may cause deterioration

Materials finer Affects bond, ASTM C 117 (AASHTO T 11)than the 75-µm increases water (No. 200) sieve requirement

Coal, lignite, Affects durability, ASTM C 123 (AASHTO T 113)or other may causelightweight stains andmaterials popouts

Soft particles Affects durability ASTM C 235

Clay lumps Affects work- ASTM C 142 (AASHTO T 112)and friable ability andparticles durability, may

cause popouts

Chert of less Affects ASTM C 123 (AASHTO T 113)than 2.40 durability, may ASTM C 295relative density cause popouts

Alkali-reactive Causes ASTM C 227aggregates abnormal ASTM C 289

expansion, ASTM C 295map cracking, ASTM C 342and popouts ASTM C 586

ASTM C 1260 (AASHTO T 303)ASTM C 1293

Table 5-6. Harmful Materials in Aggregates

Table 5-7. Some Potentially Harmful ReactiveMinerals, Rock, and Synthetic Materials

Alkali-carbonateAlkali-silica reactive substances* reactive substances**

Andesites Opal Calcitic dolomitesArgillites Opaline shales Dolomitic limestonesCertain siliceous Phylites Fine-grained dolomites

limestones Quartzitesand dolomites Quartzoses

Chalcedonic cherts ChertsChalcedony RhyolitesCristobalite SchistsDacites Siliceous shalesGlassy or Strained quartz

cryptocrystalline and certainvolcanics other forms

Granite gneiss of quartzGraywackes Synthetic andMetagraywackes natural silicious

glassTridymite

* Several of the rocks listed (granite gneiss and certain quartz for-mations for example) react very slowly and may not show evi-dence of any harmful degree of reactivity until the concrete is over20 years old.

** Only certain sources of these materials have shown reactivity.

There is a tendency for some fine aggregates todegrade from the grinding action in a concrete mixer; thiseffect, which is measured using ASTM C 1137, may altermixing water, entrained air and slump requirements.

Coal or lignite, or other low-density materials such aswood or fibrous materials, in excessive amounts will affectthe durability of concrete. If these impurities occur at ornear the surface, they might disintegrate, pop out, orcause stains. Potentially harmful chert in coarse aggregatecan be identified by using ASTM C 123 (AASHTO T 113).

Soft particles in coarse aggregate are especially objec-tionable because they cause popouts and can affect dura-bility and wear resistance of concrete. If friable, they couldbreak up during mixing and thereby increase the amountof water required. Where abrasion resistance is critical,such as in heavy-duty industrial floors, testing may indi-cate that further investigation or another aggregate sourceis warranted.

Clay lumps present in concrete may absorb some ofthe mixing water, cause popouts in hardened concrete,and affect durability and wear resistance. They can alsobreak up during mixing and thereby increase the mixing-water demand.

Aggregates can occasionally contain particles of ironoxide and iron sulfide that result in unsightly stains onexposed concrete surfaces (Fig. 5-19). The aggregateshould meet the staining requirements of ASTM C 330(AASHTO M 195) when tested according to ASTM C 641;the quarry face and aggregate stockpiles should not showevidence of staining.

As an additional aid in identifying staining particles,the aggregate can be immersed in a lime slurry. If stainingparticles are present, a blue-green gelatinous precipitatewill form within 5 to 10 minutes; this will rapidly changeto a brown color on exposure to air and light. The reactionshould be complete within 30 minutes. If no brown gelat-inous precipitate is formed when a suspect aggregate is

placed in the lime slurry,there is little likelihood ofany reaction taking place inconcrete. These tests shouldbe required when aggregateswith no record of successfulprior use are used in archi-tectural concrete.

ALKALI-AGGREGATEREACTIVITY

Aggregates containing certainconstituents can react withalkali hydroxides in concrete.The reactivity is potentiallyharmful only when it produces significant expansion(Mather 1975). This alkali-aggregate reactivity (AAR) hastwo forms—alkali-silica reaction (ASR) and alkali-carbonatereaction (ACR). ASR is of more concern than ACR becausethe occurrence of aggregates containing reactive silicaminerals is more common. Alkali-reactive carbonate aggre-gates have a specific composition that is not very common.

Alkali-silica reactivity has been recognized as a poten-tial source of distress in concrete since the late 1930s(Stanton 1940 and PCA 1940). Even though potentiallyreactive aggregates exist throughout North America, ASRdistress in structural concrete is not common. There are anumber of reasons for this:

• Most aggregates are chemically stable in hydraulic-cement concrete.

• Aggregates with good service records are abundant inmany areas.

• Most concrete in service is dry enough to inhibit ASR.• Use of certain pozzolans or slags can control ASR.• In many concrete mixtures, the alkali content of the

concrete is low enough to control harmful ASR.• Some forms of ASR do not produce significant delete-

rious expansion.

To reduce ASR potential requires understanding theASR mechanism; properly using tests to identify poten-tially reactive aggregates; and, if needed, taking steps tominimize the potential for expansion and related cracking.

Alkali-Silica Reaction

Visual Symptoms of Expansive ASR. Typical indicatorsof ASR might be any of the following: a network of cracks(Fig. 5-20); closed or spalled joints; relative displacementsof different parts of a structure; or fragments breaking outof the surface of the concrete (popouts) (Fig. 5-21). BecauseASR deterioration is slow, the risk of catastrophic failure islow. However, ASR can cause serviceability problems andcan exacerbate other deterioration mechanisms such asthose that occur in frost, deicer, or sulfate exposures.

93


Fig. 5-18. A popout is the breaking away of a small frag-ment of concrete surface due to internal pressure thatleaves a shallow, typically conical depression. (113)

Fig. 5-19. Iron oxide staincaused by impurities in thecoarse aggregate. (70024)

Mechanism of ASR. The alkali-silica reaction forms a gelthat swells as it draws water from the surrounding cementpaste. Reaction products from ASR have a great affinityfor moisture. In absorbing water, these gels can inducepressure, expansion, and cracking of the aggregate andsurrounding paste. The reaction can be visualized as atwo-step process:

1. Alkali hydroxide + reactive silica gel → reaction prod-uct (alkali-silica gel)

2. Gel reaction product + moisture → expansion

The amount of gel formed in the concrete depends onthe amount and type of silica and alkali hydroxideconcentration. The presence of gel does not always coin-cide with distress, and thus, gel presence does not neces-sarily indicate destructive ASR.

Factors Affecting ASR. For alkali-silica reaction to occur,the following three conditions must be present:

1. reactive forms of silica in the aggregate,2. high-alkali (pH) pore solution, and3. sufficient moisture.

If one of these conditions is absent, ASR cannot occur.

Test Methods for Identifying ASR Distress. It is impor-tant to distinguish between the reaction and damageresulting from the reaction. In the diagnosis of concretedeterioration, it is most likely that a gel product will beidentified. But, in some cases significant amounts of gel areformed without causing damage to concrete. To pinpointASR as the cause of damage, the presence of deleteriousASR gel must be verified. A site of expansive reaction canbe defined as an aggregate particle that is recognizablyreactive or potentially reactive and is at least partiallyreplaced by gel. Gel can be present in cracks and voids andmay also be present in a ring surrounding an aggregateparticle at its edges. A network of internal cracks connect-ing reacted aggregate particles is an almost certain indica-tion that ASR is responsible for cracking. A petrographicexamination (ASTM C 856) is the most positive method foridentifying ASR gel in concrete (Powers 1999).Petrography, when used to study a known reactedconcrete, can confirm the presence of reaction productsand verify ASR as an underlying cause of deterioration(Fig. 5-22).

Control of ASR in New Concrete. The best way to avoidASR is to take appropriate precautions before concrete isplaced. Standard concrete specifications may requiremodifications to address ASR. These modifications shouldbe carefully tailored to avoid limiting the concrete pro-ducer’s options. This permits careful analysis of cementi-tious materials and aggregates and choosing a controlstrategy that optimizes effectiveness and the economicselection of materials. If the aggregate is not reactive byhistorical identification or testing, no special requirementsare needed.

94


Fig. 5-20 (top and bottom). Cracking of concrete from alkali-silica reactivity. (69549, 58352)

Fig. 5-21. Popouts caused by ASR of sand-sized particles.Inset shows closeup of a popout. (51117, 51118)Fig. 5-21. Popouts caused by ASR of sand-sized particles.Inset shows closeup of a popout. (51117, 51118)

Identification of Potentially Reactive Aggregates. Fieldperformance history is the best method of evaluating thesusceptibility of an aggregate to ASR. For the most defini-tive evaluation, the existing concrete should have been inservice for at least 15 years. Comparisons should be madebetween the existing and proposed concrete’s mix propor-tions, ingredients, and service environments. This processshould tell whether special requirements are needed, arenot needed, or whether testing of the aggregate or jobconcrete is required. The use of newer, faster test methodscan be utilized for initial screening. Where uncertaintiesarise, lengthier tests can be used to confirm results. Table5-8 describes different test methods used to evaluatepotential alkali-silica reactivity. These tests should not beused to disqualify use of potentially reactive aggregates,as reactive aggregates can be safely used with the carefulselection of cementitious materials as discussed below.Materials and Methods to Control ASR. The most effec-tive way of controlling expansion due to ASR is to designmixtures specifically to control ASR, preferably usinglocally available materials. The following options are notlisted in priority order and, although usually not neces-sary, they can be used in combination with one another.

In North America, current practices include the use ofa supplementary cementitious material or blended cementproven by testing to control ASR or limiting the alkalicontent of the concrete. Supplementary cementitious mate-rials include fly ash, ground granulated blast-furnace slag,silica fume, and natural pozzolans. Blended cements useslag, fly ash, silica fume, and natural pozzolans to controlASR. Low-alkali portland cement (ASTM C 150) with analkali content of not more than 0.60% (equivalent sodiumoxide) can be used to control ASR. Its use has been success-ful with slightly reactive to moderately reactive aggre-gates. However, low-alkali cements are not available in allareas. Thus, the use of locally available cements in combi-nation with pozzolans, slags, or blended cements is prefer-able for controlling ASR. When pozzolans, slags, orblended cements are used to control ASR, their effective-

ness must be determined by tests such as ASTM C 1260(modified) or C 1293. Where applicable, different amountsof pozzolan or slag should be tested to determine the opti-mum dosage. Expansion usually decreases as the dosageof the pozzolan or slag increases (see Fig. 5-23). Lithium-based admixtures are also available to control ASR. Lime-stone sweetening (the popular term for replacingapproximately 30% of the reactive sand-gravel aggregatewith crushed limestone) is effective in controlling deterio-ration in some sand-gravel aggregate concretes. SeeAASHTO (2001), Farny and Kosmatka (1997), and PCA(1998) for more information on tests to demonstrate theeffectiveness of the above control measures.

Alkali-Carbonate Reaction

Mechanism of ACR. Reactions observed with certaindolomitic rocks are associated with alkali-carbonate reac-tion (ACR). Reactive rocks usually contain large crystals ofdolomite scattered in and surrounded by a fine-grainedmatrix of calcite and clay. Calcite is one of the mineralforms of calcium carbonate; dolomite is the commonname for calcium-magnesium carbonate. ACR is relativelyrare because aggregates susceptible to this reaction areusually unsuitable for use in concrete for other reasons,such as strength potential. Argillaceous dolomitic lime-stone contains calcite and dolomite with appreciableamounts of clay and can contain small amounts of reactivesilica. Alkali reactivity of carbonate rocks is not usuallydependent upon its clay mineral composition (Hadley1961). Aggregates have potential for expansive ACR if thefollowing lithological characteristics exist (Ozol 1994 andSwenson 1967):

95


Fig. 5-22. Polished section view of an alkali reactive aggregatein concrete. Observe the alkali-silica reaction rim around thereactive aggregate and the crack formation. (43090)

Control20 30 56 35 50 65 7.5 10 12.5

0

0.05

0.1

0.15

0.2

0.25

0.3

14-D

ay e

xpan

sion

, %

% Fly ash % Slag % Silica fume

0.10% expansion limit for evaluatingeffectiveness of supplementarycementitious materials against AAR

Sudbury aggregate

Fig. 5-23. Influence of different amounts of fly ash, slag,and silica fume by mass of cementing material on mortarbar expansion (ASTM C 1260) after 14 days when usingreactive aggregate (Fournier 1997).

96


Table 5-8. Test Methods for Alkali-Silica Reactivity (Farny and Kosmatka 1997)

Test name Purpose Type of test Type of sampleASTM C 227, To test the susceptibility of Mortar bars stored over At least 4 mortar bars ofPotential alkali-reactivity cement-aggregate com- water at 37.8°C (100°F) standard dimensions:of cement-aggregate binations to expansive and high relative 25 x 25 x 285 mmcombinations reactions involving humidity (1 x 1 x 111⁄4 in.)(mortar-bar method) alkalies

ASTM C 289, To determine potential Sample reacted with Three 25-gram samplesPotential alkali-silica reactivity of siliceous alkaline solution at 80°C (176°F) of crushed and sievedreactivity of aggregates aggregates aggregate(chemical method)

ASTM C 294, To give descriptive Visual identification Varies, but should beConstituents of nomenclature for the representative of entirenatural mineral more common or impor- sourceaggregates tant natural minerals—an

aid in determining theirperformance

ASTM C 295, To outline petrographic Visual and microscopic Varies with knowledge ofPetrographic examination procedures examination of prepared quarry: cores 53 to 100 mmexamination of for aggregates—an aid in samples—sieve analysis, in diameter (21⁄8 to 4 in.)aggregates determining their per- microscopy, scratch or 45 kg (100 lb) or 300for concrete formance acid tests pieces, or 2 kg (4 lb)

ASTM C 342, To determine the poten- Mortar bars stored in Three mortar bars perPotential volume tial ASR expansion of water at 23°C (73.4°F) cement-aggregatechange of cement- cement-aggregate combination of standardaggregate combinations dimensions: 25 x 25 x 285 mmcombinations (1 x 1 x 111⁄4 in.)ASTM C 441, To determine effectiveness Mortar bars—using Pyrex At least 3 mortar barsEffectiveness of mineral of supplementary cementing glass as aggregate— and also 3 mortar barsadmixtures or GBFS in materials in controlling stored over water at of control mixturepreventing excessive expansion from ASR 37.8°C (100°F) andexpansion of concrete high relative humiditydue to alkali-silica reactionASTM C 856, To outline petrographic Visual (unmagnified) At least one 150-mmPetrographic examination procedures and microscopic exam- diameter by 300-mm longexamination of for hardened concrete— ination of prepared core (6-in. diameter by hardened concrete useful in determining samples 12-in. long)

condition or performance

ASTM C 856 To identify products of Staining of a freshly- Varies: core with lapped(AASHTO T 299), ASR in hardened exposed concrete surface, core withAnnex uranyl-acetate concrete surface and viewing broken surfacetreatment procedure under UV light

Los Alamos staining To identify products of Staining of a freshly-exposed Varies: core with lappedmethod ASR in hardened concrete surface with two surface, core with(Powers 1999) concrete different reagents broken surface

ASTM C 1260 To test the potential for Immersion of mortar At least 3 mortar bars(AASHTO T 303), deleterious alkali-silica bars in alkalinePotential alkali-reactivity reaction of aggregate solution at 80°C (176°F)of aggregates (mortar- in mortar barsbar method)ASTM C 1293, To determine the Concrete prisms stored Three prisms per cement-Determination of length potential ASR expansion over water at 38°C (100.4°F) aggregate combination ofchange of concrete of cement-aggregate standard dimensions:due to alkali-silica combinations 75 x 75 x 285 mmreaction (concrete (3 x 3 x 111⁄4 in.)prism test)Accelerated concrete To determine the Concrete prisms stored Three prisms per cement-prism test (modified potential ASR expansion stored over water aggregate combination ofASTM C 1293) of cement-aggregate at 60°C (140°F) standard dimensions:

combinations 75 x 75 x 285 mm(3 x 3 x 111⁄4 in.)

97


Duration of test Measurement Criteria CommentsVaries: first measure- Length change Per ASTM C 33, maximum Test may not produce signif-ment at 14 days, then 1,2, 0.10% expansion at 6 months, icant expansion, especially3,4,6,9, and 12 months; or if not available for a 6- for carbonate aggregate.every 6 months after month period, maximum of Long test duration.that as necessary 0.05% at 3 months Expansions may not be

from AAR.24 hours Drop in alkalinity Point plotted on graph falls Quick results.

and amount of in deleterious or potentially Some aggregates give lowsilica solubilized deleterious area expansions even though

they have high silica content.Not reliable.

Short duration—as long Description of type Not applicable These descriptions are usedas it takes to visually and proportion of to characterize naturally-examine the sample minerals in aggregate occurring minerals that make

up common aggregatesources.

Short duration—visual Particle character- Not applicable Usually includes opticalexamination does not istics, such as shape, microscopy. Also may includeinvolve long test size, texture, color, XRD analysis, differentialperiods mineral composition, thermal analysis, or infrared

and physical condition spectroscopy—see ASTM C 294for descriptive nomenclature.

52 weeks Length change Per ASTM C 33, unsatis- Primarily used for aggregatesfactory aggregate if expan- from Oklahoma, Kansas,sion equals or exceeds Nebraska, and Iowa.0.200% at 1 year

Varies: first measure- Length change Per ASTM C 989, minimum Highly reactive artificialment at 14 days, then 1,2, 75% reduction in expansion aggregate may not represent3,4,5,9, and 12 months; or 0.020% maximum expan- real aggregate conditions.every 6 months after sion or per ASTM C 618, com- Pyrex contains alkalies.that as necessary parison against low-alkali

controlShort duration—includes Is the aggregate known See measurement—this Specimens can be examinedpreparation of samples to be reactive? examination determines with stereomicroscopes,and visual and micro- Orientation and if ASR reactions have polarizing microscopes,scope examination geometry of cracks. taken place and their metallographic microscopes,

Is there any gel effects upon the concrete. and scanning electronpresent? Used in conjunction with microscope.

other tests.Immediate results Intensity of Lack of fluorescence Identifies small amounts of

fluorescence ASR gel whether they causeexpansion or not.Opal, a natural aggregate,and carbonated paste can

Immediate results Color of stain Dark pink stain corresponds glow—interpret resultsto ASR gel and indicates an accordingly.advanced state of Tests must be supplemented degradation by petrographic examination

and physical tests for deter-mining concrete expansion.

16 days Length change If greater than 0.10%, Very fast alternative to C 227.go to supplementary test Useful for slowly reactingprocedures; if greater than aggregates or those that0.20%, indicative of poten- produce expansion late intial deleterious expansion the reaction.

Varies: first measure- Length change Per Appendix X1, potentially Requires long test durationment at 7 days, then 28 deleteriously reactive if ex- for meaningful results.and 56 days, then 3,6,9, pansion equals or exceeds Use as a supplement to C 227,and 12 months; every 0.04% at one year C 295, C 289, and C 1260.6 months as after that as Similar to CSA A23.2-14A.necessary3 month (91 days) Length change Potentially deleteriously Fast alternative to C 227.

reactive if expansion Good correlation to ASTMequals or exceeds 0.04% C 227 for carbonate andat 91 days sedimentary rocks.

minerals and water proportioned to have a relative density(specific gravity) less than that of the desirable aggregateparticles but greater than that of the deleterious particles.The heavier particles sink to the bottom while the lighterparticles float to the surface. This process can be used whenacceptable and harmful particles have distinguishable rela-tive densities.

Jigging separates particles with small differences indensity by pulsating water current. Upward pulsations ofwater through a jig (a box with a perforated bottom) movethe lighter material into a layer on top of the heavier mate-rial; the top layer is then removed.

Rising-current classification separates particles withlarge differences in density. Light materials, such as woodand lignite, are floated away in a rapidly upward movingstream of water.

Crushing is also used to remove soft and friable parti-cles from coarse aggregates. This process is sometimes theonly means of making material suitable for use. Unfortun-ately, with any process some acceptable material is alwayslost and removal of all harmful particles may be difficultor expensive.

HANDLING AND STORING AGGREGATES

Aggregates should be handled and stored in a way thatminimizes segregation and degradation and preventscontamination by deleterious substances (Fig. 5-24). Stock-piles should be built up in thin layers of uniform thicknessto minimize segregation. The most economical andacceptable method of forming aggregate stockpiles is thetruck-dump method, which discharges the loads in a waythat keeps them tightly joined. The aggregate is then re-claimed with a front-end loader. The loader should re-move slices from the edges of the pile from bottom to topso that every slice will contain a portion of each horizon-tal layer.

• clay content, or insoluble residue content, in the rangeof 5% to 25%;

• calcite-to-dolomite ratio of approximately 1:1;• increase in the dolomite volume up to a point at

which interlocking texture becomes a restrainingfactor; and

• small size of the discrete dolomite crystals (rhombs)suspended in a clay matrix.

Dedolomitization. Dedolomitization, or the breakingdown of dolomite, is normally associated with expansiveACR (Hadley 1961). Concrete that contains dolomite andhas expanded also contains brucite (magnesium hydrox-ide, Mg(OH)2), which is formed by dedolomitization. De-dolomitization proceeds according to the followingequation (Ozol 1994):

CaMgCO3 (dolomite) + alkali hydroxide solution →MgOH2 (brucite) + CaCO3 (calcium carbonate) + K2CO3 (potassium carbonate) + alkali hydroxide

The dedolomitization reaction and subsequent crystalliza-tion of brucite may cause considerable expansion.Whether dedolomitization causes expansion directly orindirectly, it’s usually a prerequisite to other expansiveprocesses (Tang, Deng, Lon, and Han 1994).

Test Methods for Identifying ACR Distress. The threetest methods commonly used to identify potentially alkali-carbonate reactive aggregate are:

• petrographic examination (ASTM C 295);• rock cylinder method (ASTM C 586); and• concrete prism test (ASTM C 1105).

See Farny and Kosmatka (1997) for detailed information.

Materials and Methods to Control ACR. ACR-suscepti-ble aggregate has a specific composition that is readilyidentified by petrographic testing. If a rock indicates ACR-susceptibility, one of the following preventive measuresshould be taken:

• selective quarrying to completely avoid reactive ag-gregate;

• blend aggregate according to Appendix in ASTM C1105; or

• limit aggregate size to smallest practical.

Low-alkali cement and pozzolans are generally not veryeffective in controlling expansive ACR.

AGGREGATE BENEFICIATION

Aggregate processing consists of: (1) basic processing—crushing, screening, and washing—to obtain proper grada-tion and cleanliness; and (2) beneficiation—upgradingquality by processing methods such as heavy media sepa-ration, jigging, rising-current classification, and crushing.

In heavy media separation, aggregates are passedthrough a heavy liquid comprised of finely ground heavy

98


Fig. 5-24. Stockpile of aggregate at a ready mix plant. (69552)

When aggregates are not delivered by truck, accept-able and inexpensive results can be obtained by formingthe stockpile in layers with a clamshell bucket (cast-and-spread method); in the case of aggregates not subject todegradation, spreading the aggregates with a rubber-tiredozer and reclaiming with a front-end loader can be used.By spreading the material in thin layers, segregation isminimized. Whether aggregates are handled by truck,bucket loader, clamshell, or conveyor belt, stockpilesshould not be built up in high, cone-shaped piles since thisresults in segregation. However, if circumstances necessi-tate construction of a conical pile, or if a stockpile hassegregated, gradation variations can be minimized whenthe pile is reclaimed; in such cases aggregates should beloaded by continually moving around the circumferenceof the pile to blend sizes rather than by starting on oneside and working straight through the pile.

Crushed aggregates segregate less than rounded(gravel) aggregates and larger-size aggregates segregatemore than smaller sizes. To avoid segregation of coarseaggregates, size fractions can be stockpiled and batchedseparately. Proper stockpiling procedures, however,should eliminate the need for this. Specifications providea range in the amount of material permitted in any sizefraction partly because of segregation in stockpiling andbatching operations.

Washed aggregates should be stockpiled in sufficienttime before use so that they can drain to a uniform mois-ture content. Damp fine material has less tendency tosegregate than dry material. When dry fine aggregate isdropped from buckets or conveyors, wind can blow awaythe fines; this should be avoided if possible.

Bulkheads or dividers should be used to avoidcontamination of aggregate stockpiles. Partitions betweenstockpiles should be high enough to prevent interminglingof materials. Storage bins should be circular or nearlysquare. Their bottoms should slope not less than 50degrees from the horizontal on all sides to a center outlet.When loading the bin, the material should fall verticallyover the outlet into the bin. Chuting the material into a binat an angle and against the bin sides will cause segregation.Baffle plates or dividers will help minimize segregation.Bins should be kept as full as possible since this reducesbreakage of aggregate particles and the tendency to segre-gate. Recommended methods of handling and storingaggregates are discussed at length in Matthews (1965 to1967), NCHRP (1967), and Bureau of Reclamation (1981).

MARINE-DREDGED AGGREGATE

Marine-dredged aggregate from tidal estuaries and sandand gravel from the seashore can be used with caution insome concrete applications when other aggregate sourcesare not available. Aggregates obtained from seabeds havetwo problems: (1) seashells and (2) salt.

Seashells may be present in the aggregate source.These shells are a hard material that can produce goodquality concrete, however, a higher cement content maybe required. Also, due to the angularity of the shells, addi-tional cement paste is required to obtain the desired work-ability. Aggregate containing complete shells (uncrushed)should be avoided as their presence may result in voids inthe concrete and lower the compressive strength.

Marine-dredged aggregates often contain salt from theseawater. The primary salts are sodium chloride andmagnesium sulfate and the amount of salt on the aggregateis often not more than about 1% of the mass of the mixingwater. The highest salt content occurs in sands located justabove the high-tide level. Use of these aggregates withdrinkable mix water often contributes less salt to themixture than the use of seawater (as mix water) with salt-free aggregates.

Marine aggregates can be an appreciable source ofchlorides. The presence of these chlorides may affect theconcrete by (1) altering the time of set, (2) increasing dryingshrinkage, (3) significantly increasing the risk of corrosionof steel reinforcement, and (4) causing efflorescence.Generally, marine aggregates containing large amounts ofchloride should not be used in reinforced concrete.

Marine-dredged aggregates can be washed with freshwater to reduce the salt content. There is no maximumlimit on the salt content of coarse or fine aggregate;however, the chloride limits presented in Chapter 9should be followed.

RECYCLED-CONCRETE AGGREGATE

In recent years, the concept of using old concrete pave-ments, buildings, and other structures as a source of aggre-gate has been demonstrated on several projects, resultingin both material and energy savings (ECCO 1999). Theprocedure involves (1) breaking up and removing the oldconcrete, (2) crushing in primary and secondary crushers(Fig. 5-25), (3) removing reinforcing steel and other embed-

99


Fig. 5-25. Heavily reinforced concrete is crushed with abeamcrusher. (69779)

adequate compressive strength. The use of recycled fineaggregate can result in minor compressive strength reduc-tions. However, drying shrinkage and creep of concretemade with recycled aggregates is up to 100% higher thanconcrete with a corresponding conventional aggregate.This is due to the large amount of old cement paste andmortar especially in the fine aggregate. Therefore, consid-erably lower values of drying shrinkage can be achievedusing recycled coarse aggregate with natural sand(Kerkhoff and Siebel 2001). As with any new aggregatesource, recycled-concrete aggregate should be tested fordurability, gradation, and other properties.

Recycled concrete used as coarse aggregate in newconcrete possesses some potential for alkali-silica-reactionif the old concrete contained alkali-reactive aggregate. The

ded items, (4) grading and washing, and (5) finally stock-piling the resulting coarse and fine aggregate (Fig. 5-26).Dirt, gypsum board, wood, and other foreign materialsshould be prevented from contaminating the final product.

Recycled concrete is simply old concrete that has beencrushed to produce aggregate. Recycled-concrete aggre-gate is primarily used in pavement reconstruction. It hasbeen satisfactorily used as an aggregate in granularsubbases, lean-concrete subbases, soil-cement, and in newconcrete as the only source of aggregate or as a partialreplacement of new aggregate.

Recycled-concrete aggregate generally has a higherabsorption and a lower specific gravity than conventionalaggregate. This results from the high absorption of porousmortar and hardened cement paste within the recycledconcrete aggregate. Absorption values typically rangefrom 3% to 10%, depending on the concrete being recy-cled; this absorption lies between those values for naturaland lightweight aggregate. The values increase as coarseparticle size decreases (Fig. 5-27). The high absorption ofthe recycled aggregate makes it necessary to add morewater to achieve the same workability and slump than forconcrete with conventional aggregates. Dry recycledaggregate absorbs water during and after mixing. Toavoid this, recycled aggregate should be prewetted orstockpiles should be kept moist.

The particle shape of recycled-concrete aggregate issimilar to crushed rock as shown in Fig. 5-28. The relativedensity decreases progressively as particle size decreases.The sulfate content of recycled-concrete aggregate shouldbe determined to assess the possibility of deleterioussulfate reactivity. The chloride content should also bedetermined where applicable.

New concrete made from recycled-concrete aggregategenerally has good durability. Carbonation, permeability,and resistance to freeze-thaw action have been found to bethe same or even better than concrete with conventionalaggregates. Concrete made with recycled coarse aggre-gates and conventional fine aggregate can obtain an

100


Fig. 5-26. Stockpile of recycled-concrete aggregate. (69813)

12

10

8

6

4

2

0

Wat

er a

bsor

ptio

n in

% b

y m

ass

150 µm to4.75 mm

(No. 100 toNo. 4)

2.36 mm to9.5 mm(No. 8 to3/8 in.)

2.36 mm to9.5 mm(No. 8 to3/8 in.)

2.36 mm to9.5 mm(No. 8 to3/8 in.)

4.75 mm to19 mm

(No. 4 to3/4 in.)

Recycled Natural Lightweight

Aggregate size

Fig. 5-27. Comparison of water absorption of three differentrecycled aggregate particle sizes and one size of natural andlightweight coarse aggregate. (Kerkhoff and Siebel 2001)

Fig. 5-28. Recycled-concrete aggregate. (69812)

alkali content of the cement used in the old concrete haslittle effect on expansion due to alkali-silica-reaction. Forhighly reactive aggregates made from recycled concrete,special measures discussed under “Alkali-Silica Reaction”should be used to control ASR. Also, even if expansiveASR did not develop in the original concrete, it can not beassumed that it will not develop in the new concrete ifspecial control measures are not taken. Petrographicexamination and expansion tests are recommended tomake this judgment (Stark 1996).

Concrete trial mixtures should be made to check thenew concrete’s quality and to determine the propermixture proportions. One potential problem with usingrecycled concrete is the variability in the properties of theold concrete that may in turn affect the properties of thenew concrete. This can partially be avoided by frequentmonitoring of the properties of the old concrete that isbeing recycled. Adjustments in the mixture proportionsmay then be needed.

REFERENCES

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Abrams, D. A., Design of Concrete Mixtures, Lewis Institute,Structural Materials Research Laboratory, Bulletin No. 1,PCA as LS001, Chicago, http://www.portcement.org/pdf_files/LS001.pdf, 1918, 20 pages.

ACI Committee 116, Cement and Concrete Technology, ACI116R-00, ACI Committee 116 Report, American ConcreteInstitute, Farmington Hills, Michigan, 2000, 73 pages.

ACI Committee 201, Guide to Durable Concrete, ACI 201.2R-92, reapproved 1997, American Concrete Institute, Farm-ington Hills, Michigan, 1992.

ACI Committee 216, Guide for Determining the Fire Endur-ance of Concrete Elements, ACI 216R-89, reapproved 1994,American Concrete Institute, Farmington Hills, Michi-gan, 1989.

ACI Committee 221, Guide for Use of Normal Weight Aggre-gates in Concrete, ACI 221R-96, American Concrete Insti-tute, Farmington Hills, Michigan, 1996.

ACI Committee 221, Guide to Alkali Aggregate Reactions,ACI 221.1-98, American Concrete Institute, FarmingtonHills, Michigan, 1998.

ACI Committee 515, A Guide to the Use of Waterproofing,Dampproofing, Protective, and Decorative Barrier Systems forConcrete, ACI 515.1R-79, revised 1985, American ConcreteInstitute, Farmington Hills, Michigan, 1979.

Barksdale, Richard D., The Aggregate Handbook, NationalStone Association, Washington D.C., 1991.

Bérubé, M. A.; Fournier, B.; and Durant, B., Alkali-Aggre-gate Reaction in Concrete, 11th International Conference,Québec City, Canada, June 2000.

Bhatty, Muhammad S. Y., “Mechanism of PozzolanicReactions and Control of Alkali-Aggregate Expansion,”Cement, Concrete, and Aggregates, American Society forTesting and Materials, West Conshohocken, Pennsylvania,Winter 1985.

Brown, L. S., Some Observations on the Mechanics of Alkali-Aggregate Reaction, Research Department Bulletin RX054,Portland Cement Association, http://www.portcement.org/pdf_files/RX054.pdf, 1955.

Buck, Alan D., “Recycled Concrete as a Source ofAggregate,” ACI Journal, American Concrete Institute,Farmington Hills, Michigan, May 1977, pages 212 to 219.

Buck, Alan D., and Mather, Katharine, Reactivity of Quartzat Normal Temperatures, Technical Report SL-84-12,Structures Laboratory, Waterways Experiment Station,U.S. Army Corps of Engineers, Vicksburg, Mississippi,July 1984.

Buck, Alan D.; Mather, Katharine; and Mather, Bryant,Cement Composition and Concrete Durability in Sea Water,Technical Report SL-84-21, Structures Laboratory, Water-ways Experiment Station, U.S. Army Corps of Engineers,Vicksburg, Mississippi, December 1984.

Bureau of Reclamation, Concrete Manual, 8th ed., U.S.Bureau of Reclamation, Denver, 1981.

Crouch, L. K.; Sauter, Heather J.; and Williams, Jakob A.,“92-Mpa Air-entrained HPC,” TRB-Record 1698, Concrete2000, page 24.

ECCO (Environmental Council of Concrete Organizations),“Recycling Concrete and Masonry,” EV 22, Skokie, Illinois,http://www.ecco.org/pdfs/ev22.pdf, 1999, 12 pages.

EPA, Acid Rain, Research Summary, EPA-600/8-79-028, U.S.Environmental Protection Agency, Washington, D.C.,October 1979.

EPA, Final Report, U.S. EPA Workshop on Acid DepositionEffects on Portland Cement Concrete and Related Materials,Atmospheric Sciences Research Laboratory, U.S. Environ-mental Protection Agency, Research Triangle Park, NorthCarolina, February 1986.

Farny, James A. and Kosmatka, Steven H., Diagnosis andControl of Alkali-Aggregate Reactions, IS413, Portland Ce-ment Association, 1997, 24 pages.

Fournier, B., CANMET/Industry Joint Research Program onAlkali-Aggregate Reaction—Fourth Progress Report, CanadaCentre for Mineral and Energy Technology, Ottawa, 1997.

101

Chapter 5 ◆ Aggregates for Concrete

National Cooperative Highway Research Program(NCHRP), Effects of Different Methods of Stockpiling andHandling Aggregates, NCHRP Report 46, TransportationResearch Board, Washington, D.C., 1967.

Ozol, Michael A., “Alkali-Carbonate Rock Reaction,”Significance of Tests and Properties of Concrete and Concrete-Making Materials, ASTM STP 169C, edited by Klieger, Pauland Lamond, Joseph F., American Society for Testing andMaterials, Philadelphia, 1994, pages 372 to 387.

PCA, Tests of Concrete Road Materials from California, MajorSeries 285, Research Reports, Portland Cement Associa-tion, April 1940.

PCA, Recycling D-Cracked Pavement in Minnesota, PL146,Portland Cement Association, 1980.

PCA, “Popouts: Causes, Prevention, Repair,” Concrete Tech-nology Today, PL852, Portland Cement Association, http://www.portcement.org/pdf_files/PL852.pdf, June 1985.

PCA Durability Subcommittee, Guide Specification forConcrete Subject to Alkali-Silica Reactions, IS415, PortlandCement Association, 1998.

PCA, “Controlling ASR,” Concrete Technology Today, PL971,Portland Cement Association, http://www.portcement.org/pdf_files/PL971.pdf, April 1997.

Powers, Laura J., “Developments in Alkali-Silica GelDetection,” Concrete Technology Today, PL991, Portland Ce-ment Association, http://www.portcement.org/pdf_files/PL991.pdf, April 1999.

Scanlon, John M., Concrete Durability, Proceedings of theKatherine and Bryant Mather International Conference, SP100,American Concrete Institute, Farmington Hills, Michigan,1987.

Shilstone, James M., “Changes in Concrete AggregateStandards,” The Construction Specifier, Alexandria, Vir-ginia, July 1994, pages 119 to 128.

Shilstone, James M., Sr., “Concrete Mixture Optimiza-tion,” Concrete International, American Concrete Institute,Farmington Hills, Michigan, June 1990, pages 33 to 39.

Stanton, Thomas E., “Expansion of Concrete throughReaction between Cement and Aggregate,” Proceedings,American Society of Civil Engineers, Vol. 66, New York, 1940,pages 1781 to 1811.

Stark, David, Characteristics and Utilization of CoarseAggregates Associated with D-Cracking, Research and Devel-opment Bulletin RD047, Portland Cement Association,http://www.portcement.org/pdf_files/RD047.pdf, 1976.

Stark, D. C., Alkali-Silica Reactivity: Some Reconsiderations,Research and Development Bulletin RD076, PortlandCement Association, http://www.portcement.org/pdf_files/RD076.pdf, 1981.

Galloway, Joseph E., Jr., “Grading, Shape and SurfaceProperties,” Significance of Tests and Properties of Concreteand Concrete-Making Materials, ASTM STP 169C, edited byKlieger, Paul and Lamond, Joseph F., American Society forTesting and Materials, West Conshohocken, Pennsylvania,1994, pages 401 to 410.

Hadley, D. W., “Alkali Reactivity of Carbonate Rocks—Expansion and Dedolomitization,” Research DepartmentBulletin RX139, Portland Cement Association, http://www.portcement.org/pdf_files/RX139.pdf, 1961.

Helmuth, Richard, Alkali-Silica Reactivity: An Overview ofResearch, SHRP-C-342, Strategic Highway ResearchProgram, Washington, D. C., 1993. Also PCA PublicationLT177, 105 pages.

Houston, B. J., Investigation of Gap-Grading of ConcreteAggregates; Review of Available Information, Technical Re-port No. 6-593, Report 1, Waterways Experiment Station,U.S. Army Corps of Engineers, Vicksburg, Mississippi,February 1962.

Janssen, Donald J., and Snyder Mark B., “Resistance of Con-crete to Freezing and Thawing,” SHRP-C-391, Strategic High-way Research Program, Washington, D.C., 1994, 201 pages.

Kerkhoff, Beatrix, Effects of Substances on Concrete andGuide to Protective Treatments, IS001, Portland CementAssociation, 2001, 24 pages.

Kerkhoff, Beatrix and Siebel, Eberhard, “Properties ofConcrete with Recycled Aggregates (Part 2),” Beton 2/2001,Verlag Bau + Technik, 2001, pages 105 to 108.

Kong, Hendrik, and Orbison, James G., “ConcreteDeterioration Due to Acid Precipitation,” ACI MaterialsJournal, American Concrete Institute, Farmington Hills,Michigan, March-April 1987.

Litvin, Albert, and Pfeifer, Donald W., Gap-Graded Mixesfor Cast-in-Place Exposed Aggregate Concrete, DevelopmentDepartment Bulletin DX090, Portland Cement Associa-tion, http://www.portcement.org/pdf_files/DX090.pdf,1965.

Maerz, Norbert H., and Lusher, Mike, “Measurement offlat and elongation of coarse aggregate using digital imageprocessing,” 80th Annual Meeting, Transportation ResearchBoard, Washington D.C., 2001, pages 2 to 14.

Mather, Bryant, New Concern over Alkali-Aggregate Re-action, Joint Technical Paper by National Aggregates Asso-ciation and National Ready Mixed Concrete Association,NAA Circular No. 122 and NRMCA Publication No. 149,Silver Spring, Maryland, 1975.

Matthews, C. W., “Stockpiling of Materials,” Rock Prod-ucts, series of 21 articles, Maclean Hunter PublishingCompany, Chicago, August 1965 through August 1967.

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Stark, David, “The Use of Recycled-Concrete Aggregate fromConcrete Exhibiting Alkali-Silica Reactivity,” Research andDevelopment Bulletin RD114, Portland Cement Associa-tion, 1996.

Stark, David, and Klieger, Paul, Effect of Maximum Size ofCoarse Aggregate on D-Cracking in Concrete Pavements, Re-search and Development Bulletin RD023, Portland Ce-ment Association, http://www.portcement.org/pdf_files/RD023.pdf, 1974.

Stark, David, Eliminating or Minimizing Alkali-Silica Re-activity, SHRP-C-343, Strategic Highway Research Pro-gram, Washington, D. C., 1993. Also PCA PublicationLT178, 266 pages.

Swenson, E. G., and Gillott, J. E., “Alkali Reactivity ofDolomitic Limestone Aggregate,” Magazine of ConcreteResearch, Vol. 19, No. 59, Cement and Concrete Associa-tion, London, June 1967, pages 95 to 104.

Tang, Mingshu; Deng, Min; Lon, Xianghui; and Han,Sufeng, “Studies on Alkali-Carbonate Reaction,” ACIMaterials Journal, American Concrete Institute, FarmingtonHills, Michigan, January-February 1994, pages 26 to 29.

Thomas, M. D. A.; Hooton, R. Doug; and Rogers, C. A.,“Prevention of Damage Due to Alkali-Aggregate Reaction(AAR) in Concrete Construction—Canadian Approach,”Cement, Concrete, and Aggregates, American Society forTesting and Materials, West Conshohocken, Pennsylvania,1997, pages 26 to 30.

Thomas, M. D. A., and Innis, F. A., “Effect of Slag onExpansion Due to Alkali-Aggregate Reaction in Con-crete,” ACI Materials Journal, American Concrete Institute,Farmington Hills, Michigan, November-December 1998.

Touma, W. E.; Fowler, D. W.; and Carrasquillo, R. L.,Alkali-Silica Reaction in Portland Cement Concrete: TestingMethods and Mitigation Alternatives, Research Report ICAR301-1F, University of Texas, Austin, 2001, 520 pages.

Verbeck, George, and Landgren, Robert, Influence ofPhysical Characteristics of Aggregates on Frost Resistance ofConcrete, Research Department Bulletin RX126, PortlandCement Association, http://www.portcement.org/pdf_files/RX126.pdf, 1960.

Vogler, R. H., and Grove, G. H., “Freeze-thaw testing ofcoarse aggregate in concrete: Procedures used by Mich-igan Department of Transportation and other agencies,”Cement, Concrete, and Aggregates, American Society forTesting and Materials, West Conshohocken, Pennsylvania,Vol. 11, No. 1, Summer 1989, pages 57 to 66.

103


Admixtures are those ingredients in concreteother than portland cement, water, and aggre-gates that are added to the mixture immediatelybefore or during mixing (Fig. 6-1). Admixturescan be classified by function as follows:

1. Air-entraining admixtures2. Water-reducing admixtures3. Plasticizers 4. Accelerating admixtures5. Retarding admixtures6. Hydration-control admixtures7. Corrosion inhibitors8. Shrinkage reducers9. Alkali-silica reactivity inhibitors

10. Coloring admixtures11. Miscellaneous admixtures such as workabil-

ity, bonding, dampproofing, permeability re-ducing, grouting, gas-forming, antiwashout,foaming, and pumping admixtures

Table 6-1 provides a much more extensive classification ofadmixtures.

Concrete should be workable, finishable, strong,durable, watertight, and wear resistant. These qualities canoften be obtained easily and economically by the selectionof suitable materials rather than by resorting to admixtures(except air-entraining admixtures when needed).

The major reasons for using admixtures are:

1. To reduce the cost of concrete construction2. To achieve certain properties in concrete more effec-

tively than by other means3. To maintain the quality of concrete during the stages

of mixing, transporting, placing, and curing in ad-verse weather conditions

4. To overcome certain emergencies during concretingoperations

CHAPTER 6

Admixtures for Concrete

Fig. 6-1. Liquid admixtures, from left to right: antiwashout admixture,shrinkage reducer, water reducer, foaming agent, corrosion inhibitor,and air-entraining admixture. (69795)

Despite these considerations, it should be borne inmind that no admixture of any type or amount can beconsidered a substitute for good concreting practice.

The effectiveness of an admixture depends uponfactors such as type, brand, and amount of cementingmaterials; water content; aggregate shape, gradation,and proportions; mixing time; slump; and temperatureof the concrete.

Admixtures being considered for use in concreteshould meet applicable specifications as presented inTable 6-1. Trial mixtures should be made with the admix-ture and the job materials at temperatures and humiditiesanticipated on the job. In this way the compatibility of theadmixture with other admixtures and job materials, aswell as the effects of the admixture on the properties of thefresh and hardened concrete, can be observed. Theamount of admixture recommended by the manufactureror the optimum amount determined by laboratory testsshould be used.

105

106


Table 6-1. Concrete Admixtures by Classification

Type of admixture Desired effect Material

Accelerators Accelerate setting and early-strength Calcium chloride (ASTM D 98 and AASHTO M 144)(ASTM C 494 and development Triethanolamine, sodium thiocyanate, calcium formate,AASHTO M 194, Type C) calcium nitrite, calcium nitrate

Air detrainers Decrease air content Tributyl phosphate, dibutyl phthalate, octyl alcohol, water-insoluble esters of carbonic and boric acid, silicones

Air-entraining admixtures Improve durability in freeze-thaw, Salts of wood resins (Vinsol resin), some synthetic(ASTM C 260 and deicer, sulfate, and alkali- detergents, salts of sulfonated lignin, salts of petroleumAASHTO M 154) reactive environments acids, salts of proteinaceous material, fatty and resinous

Improve workability acids and their salts, alkylbenzene sulfonates, salts ofsulfonated hydrocarbons

Alkali-aggregate reactivity Reduce alkali-aggregate reactivity Barium salts, lithium nitrate,inhibitors expansion lithium carbonate, lithium hydroxide

Antiwashout admixtures Cohesive concrete for underwater Cellulose, acrylic polymerplacements

Bonding admixtures Increase bond strength Polyvinyl chloride, polyvinyl acetate, acrylics,butadiene-styrene copolymers

Coloring admixtures Colored concrete Modified carbon black, iron oxide, phthalocyanine, umber,(ASTM C 979) chromium oxide, titanium oxide, cobalt blue

Corrosion inhibitors Reduce steel corrosion activity in a Calcium nitrite, sodium nitrite, sodium benzoate, certainchloride-laden environment phosphates or fluosilicates, fluoaluminates, ester amines

Dampproofing admixtures Retard moisture penetration into dry Soaps of calcium or ammonium stearate or oleateconcrete Butyl stearate

Petroleum products

Foaming agents Produce lightweight, foamed Cationic and anionic surfactantsconcrete with low density Hydrolized protein

Fungicides, germicides, Inhibit or control bacterial and fungal Polyhalogenated phenolsand insecticides growth Dieldrin emulsions

Copper compounds

Gas formers Cause expansion before setting Aluminum powder

Grouting admixtures Adjust grout properties for specific See Air-entraining admixtures, Accelerators, Retarders,applications and Water reducers

Hydration control Suspend and reactivate cement Carboxylic acidsadmixtures hydration with stabilizer and activator Phosphorus-containing organic acid salts

Permeability reducers Decrease permeability LatexCalcium stearate

Pumping aids Improve pumpability Organic and synthetic polymersOrganic flocculentsOrganic emulsions of paraffin, coal tar, asphalt, acrylicsBentonite and pyrogenic silicasHydrated lime (ASTM C 141)

Retarders (ASTM C 494 Retard setting time Ligninand AASHTO M 194, BoraxType B) Sugars

Tartaric acid and salts

Shrinkage reducers Reduce drying shrinkage Polyoxyalkylene alkyl etherPropylene glycol

Superplasticizers* Increase flowability of concrete Sulfonated melamine formaldehyde condensates(ASTM C 1017, Type 1) Reduce water-cement ratio Sulfonated naphthalene formaldehyde condensates

LignosulfonatesPolycarboxylates

AIR-ENTRAINING ADMIXTURES

Air-entraining admixtures are used to purposely introduceand stabilize microscopic air bubbles in concrete. Air-entrainment will dramatically improve the durability ofconcrete exposed to cycles of freezing and thawing (Fig.6-2). Entrained air greatly improves concrete’s resistance tosurface scaling caused by chemical deicers (Fig. 6-3). Fur-thermore, the workability of fresh concrete is improvedsignificantly, and segregation and bleeding are reduced oreliminated.

Air-entrained concrete contains minute air bubblesthat are distributed uniformly throughout the cementpaste. Entrained air can be produced in concrete by use ofan air-entraining cement, by introduction of an air-entraining admixture, or by a combination of both meth-ods. An air-entraining cement is a portland cement withan air-entraining addition interground with the clinkerduring manufacture. An air-entraining admixture, on theother hand, is added directly to the concrete materialseither before or during mixing.

The primary ingredients used in air-entraining ad-mixtures are listed in Table 6-1. Specifications and meth-ods of testing air-entraining admixtures are given in

ASTM C 260 and C 233 (AASHTO M 154 and T 157). Air-entraining additions for use in the manufacture of air-entraining cements must meet requirements of ASTM C226. Applicable requirements for air-entraining cementsare given in ASTM C 150 and AASHTO M 85. See Chapter8, Air-Entrained Concrete, Klieger (1966), and Whitingand Nagi (1998) for more information.

WATER-REDUCING ADMIXTURES

Water-reducing admixtures are used to reduce the quan-tity of mixing water required to produce concrete of acertain slump, reduce water-cement ratio, reduce cementcontent, or increase slump. Typical water reducers reducethe water content by approximately 5% to 10%. Adding awater-reducing admixture to concrete without reducingthe water content can produce a mixture with a higherslump. The rate of slump loss, however, is not reducedand in most cases is increased (Fig. 6-4). Rapid slump lossresults in reduced workability and less time to placeconcrete.

An increase in strength is generally obtained withwater-reducing admixtures as the water-cement ratio is

107

Chapter 6 � Admixtures for Concrete

Table 6-1. Concrete Admixtures by Classification (Continued)

Type of admixture Desired effect Material

Superplasticizer* and Increase flowability with retarded set See superplasticizers and also water reducersretarder (ASTM C 1017, Reduce water–cement ratioType 2)

Water reducer Reduce water content at least 5% Lignosulfonates(ASTM C 494 and Hydroxylated carboxylic acidsAASHTO M 194, Type A) Carbohydrates

(Also tend to retard set so accelerator is often added)

Water reducer and Reduce water content (minimum 5%) See water reducer, Type A (accelerator is added)accelerator (ASTM C 494 and accelerate setand AASHTO M 194,Type E)

Water reducer and Reduce water content (minimum 5%) See water reducer, Type A (retarder is added)retarder (ASTM C 494 and and retard setAASHTO M 194, Type D)

Water reducer—high Reduce water content (minimum See superplasticizersrange (ASTM C 494 and 12%)AASHTO M 194, Type F)

Water reducer—high Reduce water content (minimum See superplasticizers and also water reducersrange—and retarder 12%) and retard set(ASTM C 494 andAASHTO M 194, Type G)

Water reducer—mid Reduce water content (between Lignosulfonatesrange 6 and 12%) without retarding Polycarboxylates

* Superplasticizers are also referred to as high-range water reducers or plasticizers. These admixtures often meet both ASTM C 494 (AASHTOM 194) and ASTM C 1017 specifications.

cracks in concrete. Using a water reducer to reduce thecement and water content of a concrete mixture—whilemaintaining a constant water-cement ratio—can result inequal or reduced compressive strength, and can increaseslump loss by a factor of two or more (Whiting andDziedzic 1992).

Water reducers decrease, increase, or have no effect onbleeding, depending on the chemical composition of theadmixture. A reduction of bleeding can result in finishingdifficulties on flat surfaces when rapid drying conditionsare present. Water reducers can be modified to give vary-ing degrees of retardation while others do not signifi-

reduced. For concretes of equal cement content, air content,and slump, the 28-day strength of a water-reducedconcrete containing a water reducer can be 10% to 25%greater than concrete without the admixture. Despite re-duction in water content, water-reducing admixtures maycause increases in drying shrinkage. Usually the effect ofthe water reducer on drying shrinkage is small comparedto other more significant factors that cause shrinkage

108


Fig. 6-2. Frost damage (crumbling) at joints of a pavement(top), frost induced cracking near joints (bottom), andenlarged view of cracks (inset). (61621, 67834, 67835)

Fig. 6-2. Frost damage (crumbling) at joints of a pavement(top), frost induced cracking near joints (bottom), andenlarged view of cracks (inset). (61621, 67834, 67835)

Fig. 6-3. Scaled concrete surface resulting from lack of airentrainment, use of deicers, and poor finishing and curingpractices. (52742)

Slu

mp,

mm

125

100

75

50

25

0

Slu

mp,

in.

5

4

3

2

1

00 20 40 60 80 100 120 140

ControlWater reducer LWater reducer H

Elapsed time, minutes

Fig. 6-4. Slump loss at 23°C (73°F) in concretes containingconventional water reducers (ASTM C 494 and AASHTOM 194 Type D) compared with a control mixture (Whitingand Dziedzic 1992).

cantly affect the setting time. ASTM C 494 (AASHTO M194) Type A water reducers can have little effect on setting,while Type D admixtures provide water reduction withretardation, and Type E admixtures provide water reduc-tion with accelerated setting. Type D water-reducingadmixtures usually retard the setting time of concrete byone to three hours (Fig. 6-5). Some water-reducing admix-tures may also entrain some air in concrete. Lignin-basedadmixtures can increase air contents by 1 to 2 percentagepoints. Concretes with water reducers generally havegood air retention (Table 6-2).

The effectiveness of water reducers on concrete is afunction of their chemical composition, concrete tempera-ture, cement composition and fineness, cement content,and the presence of other admixtures. The classificationsand components of water reducers are listed in Table 6-1.See Whiting and Dziedzic (1992) for more information onthe effects of water reducers on concrete properties.

MID-RANGE WATER REDUCING ADMIXTURES

Mid-range water reducers were first introduced in 1984.These admixtures provide significant water reduction(between 6 and 12%) for concretes with slumps of 125 to200 mm (5 to 8 in.) without the retardation associated withhigh dosages of conventional (normal) water reducers.Normal water reducers are intended for concretes withslumps of 100 to 125 mm (4 to 5 in.). Mid-range waterreducers can be used to reduce stickiness and improvefinishability, pumpability, and placeability of concretescontaining silica fume and other supplementary cement-ing materials. Some can also entrain air and be used in lowslump concretes (Nmai, Schlagbaum, and Violetta 1998).

HIGH-RANGE WATER REDUCING ADMIXTURES

High-range water reducers, ASTM C 494 (AASHTO M194) Types F (water reducing) and G (water reducing andretarding), can be used to impart properties induced byregular water reducers, only much more efficiently. Theycan greatly reduce water demand and cement contentsand make low water-cement ratio, high-strength concretewith normal or enhanced workability. A water reductionof 12% to 30% can be obtained through the use of theseadmixtures. The reduced water content and water-cementratio can produce concretes with (1) ultimate compressivestrengths in excess of 70 MPa (10,000 psi), (2) increasedearly strength gain, (3) reduced chloride-ion penetration,and (4) other beneficial properties associated with lowwater-cement ratio concrete (Fig. 6-6).

109


4

3

2

1

0

Ret

arda

tion,

hou

rs

L H N M B X

Initial set

Admixture

Cement 1

Cement 2

3

2

1

0

Ret

arda

tion,

hou

rs

L H N M B X

Final set

Admixture

Cement 1

Cement 2

Fig. 6-5. Retardation of set in cement-reduced mixturesrelative to control mixture. Concretes L and H contain con-ventional water reducer, concretes N, M, B, and X containhigh-range water reducer (Whiting and Dziedzic 1992).

Fig. 6-6. Low water to cement ratio concrete with lowchloride permeability—easily made with high-range waterreducers—is ideal for bridge decks. (69924)

High-range water reducers are generally more effec-tive than regular water-reducing admixtures in producingworkable concrete. A significant reduction of bleeding canresult with large reductions of water content; this can resultin finishing difficulties on flat surfaces when rapid dryingconditions are present. Some of these admixtures can causesignificant slump loss (Fig. 6-7). Significant retardation isalso possible, but can aggravate plastic shrinkage crackingwithout proper protection and curing (Fig. 6-5). Dryingshrinkage, chloride permeability, air retention (Table 6-2),and strength development of concretes with high-rangewater reducers are comparable to concretes without themwhen compared at constant water-cement ratios (reducedcement and water contents) (Fig. 6-8).

Concretes with high-range water reducers can havelarger entrained air voids and higher void-spacing factorsthan normal air-entrained concrete. This would generallyindicate a reduced resistance to freezing and thawing;however, laboratory tests have shown that concretes with amoderate slump using high-range water reducers have

110


6

5

4

3

2

1

0

Slu

mp,

mm

Slu

mp,

in.

150

125

100

75

50

25

00 20 40 60 80 100 120 140

CNMBX


Fig. 6-7. Slump loss at 23°C (73°F) in mixtures containinghigh-range water reducers (N, M, B, and X) compared withcontrol mixture (C) (Whiting and Dziedzic 1992).

9

8

6

7

5

4

3

2

1

Com

pres

sive

str

engt

h, M

Pa

Com

pres

sive

str

engt

h, 1

000

psi

60

50

40

30

20

10

101 100 1000

CNMX

Age, days

Fig. 6-8. Compressive strength development in cement-reduced concretes: control mixture (C) and concretes con-taining high-range water reducers (N, M, and X) (Whitingand Dziedzic 1992).

Table 6-2. Loss of Air from Cement Reduced Concrete Mixtures

Initial air Final air Percent air Rate of air loss,Mixture content, %* content, %† retained % /minute

C Control 5.4 3.0 56 0.020L Water 7.0 4.7 67 0.038H � reducer 6.2 4.6 74 0.040N

High-range6.8 4.8 71 0.040

M water

6.4 3.8 59 0.065B reducer 6.8 5.6 82 0.048X

�6.6 5.0 76 0.027

* Represents air content measured after addition of admixture.† Represents air content taken at point where slump falls below 25 mm (1 in.).Whiting and Dziedzic 1992.

good freeze-thaw durability, even with slightly highervoid-spacing factors. This may be the result of lower water-cement ratios often associated with these concretes.

When the same chemicals used for high-range waterreducers are used to make flowing concrete, they areoften called plasticizers or superplasticizers (see discus-sion below).

PLASTICIZERS FOR FLOWINGCONCRETE

Plasticizers, often called superplasticizers, are essentiallyhigh-range water reducers meeting ASTM C 1017; theseadmixtures are added to concrete with a low-to-normalslump and water-cement ratio to make high-slump flow-ing concrete (Fig. 6-9). Flowing concrete is a highly fluidbut workable concrete that can be placed with little or novibration or compaction while still remaining essentially

(3-in.) slump concrete can easily produce a concrete with a230-mm (9-in.) slump. Flowing concrete is defined byASTM C 1017 as a concrete having a slump greater than190 mm (71⁄2 in.), yet maintaining cohesive properties.

ASTM C 1017 has provisions for two types of admix-tures: Type 1—plasticizing, and Type 2—plasticizing andretarding. Plasticizers are generally more effective thanregular or mid-range water-reducing admixtures in pro-ducing flowing concrete. The effect of certain plasticizersin increasing workability or making flowing concrete isshort-lived, 30 to 60 minutes; this period is followed by arapid loss in workability or slump loss (Fig. 6-11). Hightemperatures can also aggravate slump loss. Due to theirpropensity for slump loss, these admixtures are some-

111


Fig. 6-9. Flowable concrete with a high slump (top) is easilyplaced (middle), even in areas of heavy reinforcing steelcongestion (bottom). (47343, 69900, 47344)

Fig. 6-10. Plasticized, flowing concrete is easily placed inthin sections such as this bonded overlay that is not muchthicker than 11⁄2 diameters of a quarter. (69874)

Slu

mp,

mm

250

200

150

100

50

0

Slu

mp,

in.

10

8

6

4

2

00 20 40 60 80 100 120 140

TCTNTMTBTX


Fig. 6-11. Slump loss at 32°C (90°F) in flowing concretes(TN, TM, TB, and TX) compared with control mixture (TC)(Whiting and Dziedzic 1992).

free of excessive bleeding or segregation. Following are afew of the applications where flowing concrete is used:(1) thin-section placements (Fig. 6-10), (2) areas of closelyspaced and congested reinforcing steel, (3) tremie pipe(underwater) placements, (4) pumped concrete to reducepump pressure, thereby increasing lift and distance capac-ity, (5) areas where conventional consolidation methodsare impractical or can not be used, and (6) for reducinghandling costs. The addition of a plasticizer to a 75-mm

times added to the concrete mixer at the jobsite. They areavailable in liquid and powder form. Extended-slump-lifeplasticizers added at the batch plant help reduce slump-loss problems. Setting time may be accelerated or retardedbased on the admixture’s chemistry, dosage rate, andinteraction with other admixtures and cementing materi-als in the concrete mixture. Some plasticizers can retardfinal set by one to almost four hours (Fig. 6-12). Strengthdevelopment of flowing concrete is comparable to normalconcrete (Fig. 6-13).

While it was previously noted that flowing concretesare essentially free of excessive bleeding, tests have shownthat some plasticized concretes bleed more than controlconcretes of equal water-cement ratio (Fig. 6-14); but plas-ticized concretes bleed significantly less than control con-cretes of equally high slump and higher water content.High-slump, low-water-content, plasticized concrete hasless drying shrinkage than a high-slump, high-water-content conventional concrete; however this concrete hassimilar or higher drying shrinkage than conventional low-

112


4

3

2

1

0

Ret

arda

tion,

hou

rs

N M B X

N M B X

Initial set

Admixture

Cement 1

Cement 2

4

3

1

0

Ret

arda

tion,

hou

rs

2

Final set

Admixture

Cement 1

Cement 2

Fig. 6-12. Retardation of set in flowing concrete with plas-ticizers (N, M, B, and X) relative to control mixture (Whitingand Dziedzic 1992).

Com

pres

sive

str

engt

h, M

Pa

50

40

30

20

10

Com

pres

sive

str

engt

h, 1

000

psi

8

7

6

5

4

3

2

1101 100 1000

CFNFMFX

Age, days

Fig. 6-13. Compressive strength development in flowingconcretes. C is the control mixture. Mixtures FN, FM, andFX contain plasticizers (Whiting and Dziedzic 1992).

15

10

5

0

Ble

edin

g, p

erce

nt

C N M B XAdmixture

Fig. 6-14. Bleeding of flowing concretes with plasticizers (N,M, B, and X) compared to control (C) (Whiting and Dziedzic1992).

slump, low-water-content concrete (Whiting 1979, Gebler1982, and Whiting and Dziedzic 1992).

The effectiveness of the plasticizer is increased withan increasing amount of cement and fines in the concrete.It is also affected by the initial slump of the concrete.

Plasticized flowing concrete can have largerentrained air voids and greater void-spacing factors thanconventional concrete. Air loss can also be significant.Some research has indicated poor frost- and deicer-scal-ing resistance for some flowing concretes when exposedto a continuously moist environment without the benefitof a drying period (Whiting and Dziedzic 1992). How-ever, field performance of flowing concretes with lowwater to portland cement ratios has been good in mostfrost environments.

Table 6-1 lists the primary components and specifica-tions for plasticizing (superplasticizer) admixtures.

RETARDING ADMIXTURES

Retarding admixtures are used to delay the rate of settingof concrete. High temperatures of fresh concrete (30°C[86°F]) are often the cause of an increased rate of harden-ing that makes placing and finishing difficult. One of themost practical methods of counteracting this effect is toreduce the temperature of the concrete by cooling themixing water and/or the aggregates. Retarders do notdecrease the initial temperature of concrete. The bleedingrate and bleeding capacity of concrete is increased withretarders.

Retarding admixtures are useful in extending the set-ting time of concrete, but they are often also used inattempts to decrease slump loss and extend workability,especially prior to placement at elevated temperatures.The fallacy of this approach is shown in Fig. 6-15, wherethe addition of a retarder resulted in an increased rate ofslump loss compared to the control mixtures (Whiting andDziedzic 1992).

Retarders are sometimes used to: (1) offset the accel-erating effect of hot weather on the setting of concrete;(2) delay the initial set of concrete or grout when difficultor unusual conditions of placement occur, such as placingconcrete in large piers and foundations, cementing oilwells, or pumping grout or concrete over considerabledistances; or (3) delay the set for special finishing tech-niques, such as an exposed aggregate surface.

The amount of water reduction for an ASTM C 494(AASHTO M 194) Type B retarding admixture is normally

less than that obtained with a Type A water reducer. TypeD admixtures are designated to provide both water reduc-tion and retardation.

In general, some reduction in strength at early ages(one to three days) accompanies the use of retarders. Theeffects of these materials on the other properties of con-crete, such as shrinkage, may not be predictable. There-fore, acceptance tests of retarders should be made withactual job materials under anticipated job conditions. Theclassifications and components of retarders are listed inTable 6-1.

HYDRATION-CONTROL ADMIXTURES

Hydration controlling admixtures became available in thelate 1980s. They consist of a two-part chemical system:(1) a stabilizer or retarder that essentially stops the hydra-tion of cementing materials, and (2) an activator thatreestablishes normal hydration and setting when added tothe stabilized concrete. The stabilizer can suspend hydra-tion for 72 hours and the activator is added to the mixturejust before the concrete is used. These admixtures makeit possible to reuse concrete returned in a ready-mix truckby suspending setting overnight. The admixture is alsouseful in maintaining concrete in a stabilized non-hard-ened state during long hauls. The concrete is reactivatedwhen it arrives at the project. This admixture presentlydoes not have a standard specification (Kinney 1989).

ACCELERATING ADMIXTURES

An accelerating admixture is used to accelerate the rate ofhydration (setting) and strength development of concreteat an early age. The strength development of concrete canalso be accelerated by other methods: (1) using Type III orType HE high-early-strength cement, (2) lowering thewater-cement ratio by adding 60 to 120 kg/m3 (100 to 200lb/yd3) of additional cement to the concrete, (3) using awater reducer, or (4) curing at higher temperatures.Accelerators are designated as Type C admixtures underASTM C 494 (AASHTO M 194).

Calcium chloride (CaCl2) is the chemical most com-monly used in accelerating admixtures, especially for non-reinforced concrete. It should conform to the requirementsof ASTM D 98 (AASHTO M 144) and should be sampledand tested in accordance with ASTM D 345.

The widespread use of calcium chloride as an acceler-ating admixtures has provided much data and experienceon the effect of this chemical on the properties of concrete.Besides accelerating strength gain, calcium chloridecauses an increase in drying shrinkage, potential rein-forcement corrosion, discoloration (a darkening of con-crete), and an increase in the potential for scaling.

Calcium chloride is not an antifreeze agent. When used inallowable amounts, it will not reduce the freezing point ofconcrete by more than a few degrees. Attempts to protect

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Slu

mp,

mm

125

100

75

50

25

0

Slu

mp,

in.

5

4

3

2

1

00 20 40 60 80 100 120 140

No admixture, 23°C (73°F)No admixture, 32°C (90°F)Retarder, 32°C (90°F)


Fig. 6-15. Slump loss at various temperatures for conven-tional concretes prepared with and without set-retardingadmixture (Whiting and Dziedzic 1992).

over reinforcing steel, and a lower water-cement ratio. Stark(1989) demonstrated that concretes made with 1%CaCl2•2H2O by mass of cement developed active steel corro-sion when stored continuously in fog. When 2% CaCl2•2H2Owas used, active corrosion was detected in concrete stored ina fog room at 100% relative humidity. Risk of corrosion wasgreatly reduced at lower relative humidities (50%). Gaynor(1998) demonstrates how to calculate the chloride content offresh concrete and compare it with recommended limits.

Several nonchloride, noncorrosive accelerators areavailable for use in concrete where chlorides are notrecommended (Table 6-1). However, some nonchlorideaccelerators are not as effective as calcium chloride.Certain nonchloride accelerators are specially formulatedfor use in cold weather applications with ambient temper-atures down to -7°C (20°F).

CORROSION INHIBITORS

Corrosion inhibitors are used in concrete for parkingstructures, marine structures, and bridges where chloridesalts are present. The chlorides can cause corrosion of steelreinforcement in concrete (Fig. 6-16). Ferrous oxide andferric oxide form on the surface of reinforcing steel inconcrete. Ferrous oxide, though stable in concrete’s alka-line environment, reacts with chlorides to form complexesthat move away from the steel to form rust. The chlorideions continue to attack the steel until the passivating oxidelayer is destroyed. Corrosion-inhibiting admixtures chem-ically arrest the corrosion reaction.

Commercially available corrosion inhibitors include:calcium nitrite, sodium nitrite, dimethyl ethanolamine,amines, phosphates, and ester amines. Anodic inhibitors,such as nitrites, block the corrosion reaction of the chlo-ride-ions by chemically reinforcing and stabilizing thepassive protective film on the steel; this ferric oxide film iscreated by the high pH environment in concrete. The

concrete from freezing by this method are foolhardy. In-stead, proven reliable precautions should be taken duringcold weather (see Chapter 14, Cold-Weather Concreting).

When used, calcium chloride should be added to theconcrete mixture in solution form as part of the mixingwater. If added to the concrete in dry flake form, all of thedry particles may not be completely dissolved duringmixing. Undissolved lumps in the mix can cause popoutsor dark spots in hardened concrete.

The amount of calcium chloride added to concreteshould be no more than is necessary to produce the de-sired results and in no case exceed 2% by mass of cement-ing material. When calculating the chloride content ofcommercially available calcium chloride, it can beassumed that:

1. Regular flake contains a minimum of 77% CaCl2

2. Concentrated flake, pellet, or granular forms containa minimum of 94% CaCl2

An overdose can result in placement problems andcan be detrimental to concrete. It may cause: rapid stiffen-ing, a large increase in drying shrinkage, corrosion of rein-forcement, and loss of strength at later ages (Abrams 1924and Lackey 1992).

Applications where calcium chloride should be usedwith caution:

1. Concrete subjected to steam curing2. Concrete containing embedded dissimilar metals,

especially if electrically connected to steel reinforce-ment

3. Concrete slabs supported on permanent galvanized-steel forms

4. Colored concreteCalcium chloride or admixtures containing soluble

chlorides should not be used in the following:

1. Construction of parking garages2. Prestressed concrete because of possible steel corro-

sion hazards3. Concrete containing embedded aluminum (for exam-

ple, conduit) since serious corrosion of the aluminumcan result, especially if the aluminum is in contactwith embedded steel and the concrete is in a humidenvironment

4. Concrete containing aggregates that, under standardtest conditions, have been shown to be potentiallydeleteriously reactive

5. Concrete exposed to soil or water containing sulfates6. Floor slabs intended to receive dry-shake metallic

finishes7. Hot weather generally8. Massive concrete placements

The maximum chloride-ion content for corrosion protec-tion of prestressed and reinforced concrete as recommendedby the ACI 318 building code is presented in Table 6-3. Re-sistance to the corrosion of embedded steel is furtherimproved with an increase in the depth of concrete cover

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Table 6-3. Maximum Chloride-Ion Content forCorrosion Protection of Reinforcement*

Maximum water solublechloride-ion (CI-) inconcrete, percent by

Type of member mass of cement

Prestressed concrete 0.06

Reinforced concrete exposed tochloride in service 0.15

Reinforced concrete that will bedry or protected from moisture 1.00in service

Other reinforced concreteconstruction 0.30

* Requirements from ACI 318 tested per ASTM C 1218.

nitrite-ions cause the ferric oxide to become more stable.In effect, the chloride-ions are prevented from penetratingthe passive film and making contact with the steel.

A certain amount of nitrite can stop corrosion up tosome level of chloride-ion. Therefore, increased chloridelevels require increased levels of nitrite to stop corrosion.

Cathodic inhibitors react with the steel surface tointerfere with the reduction of oxygen. The reduction ofoxygen is the principal cathodic reaction in alkaline envi-ronments (Berke and Weil 1994).

SHRINKAGE-REDUCING ADMIXTURES

Shrinkage-reducing admixtures, introduced in the 1980s,have potential uses in bridge decks, critical floor slabs, andbuildings where cracks and curling must be minimized fordurability or aesthetic reasons (Fig. 6-17). Propylene glycoland polyoxyalkylene alkyl ether have been used as shrink-

age reducers. Drying shrinkage reductions of between 25%and 50% have been demonstrated in laboratory tests.These admixtures have negligible effects on slump and airloss, but can delay setting. They are generally compatiblewith other admixtures (Nmai, Tomita, Hondo andBuffenbarger 1998 and Shah, Weiss and Yang 1998).

CHEMICAL ADMIXTURES TO REDUCEALKALI-AGGREGATE REACTIVITY(ASR INHIBITORS)

Chemical admixtures to control alkali-silica reactivity(alkali-aggregate expansion) were introduced in the 1990s(Fig. 6-18). Lithium nitrate, lithium carbonate, lithiumhydroxide, lithium aluminum silicate (decrepitatedspodumene), and barium salts have shown reductions ofalkali-silica reaction (ASR) in laboratory tests (Thomasand Stokes 1999 and AASHTO 2001). Some of these mate-rials have potential for use as an additive to cement (Gajda1996). There is little long-term field experience availableon the effectiveness of these materials.

115


Fig. 6-16. The damage to this concrete parking structure re-sulted from chloride-induced corrosion of steel reinforce-ment. (50051)

Fig. 6-17. Shrinkage cracks, such as shown on this bridgedeck, can be reduced with the use of good concretingpractices and shrinkage reducing admixtures. (69883)

0.70

0.50

0.60

0.40

0.30

0.20

0.10

0.00

Exp

ansi

on, p

erce

nt

Age, months12 1860 24 30 36

None0.250.501.00

Li2CO3 dosage(% by mass of cement)

ASTM C 227

Fig. 6-18. Expansion of specimens made with lithium car-bonate admixture (Stark 1992).

COLORING ADMIXTURES (PIGMENTS)

Natural and synthetic materials are used to color concretefor aesthetic and safety reasons (Fig. 6-19). Red concrete isused around buried electrical or gas lines as a warning toanyone near these facilities. Yellow concrete safety curbsare used in paving applications. Generally, the amount ofpigments used in concrete should not exceed 10% byweight of the cement. Pigments used in amounts less than6% generally do not affect concrete properties.

concrete. One of the best methods of decreasing perme-ability in concrete is to increase the moist-curing periodand reduce the water-cement ratio to less than 0.5. Mostadmixtures that reduce water-cement ratio consequentlyreduce permeability.

Some supplementary cementing materials, especiallysilica fume, reduce permeability through the hydration andpozzolanic-reaction process. Other admixtures that act toblock the capillaries in concrete have been shown to be ef-fective in reducing concrete corrosion in chemically ag-gressive environments. Such admixtures, designed for usein high-cement content/low-water-cement ratio concretes,contain aliphatic fatty acid and an aqueous emulsion ofpolymeric and aromatic globules (Aldred 1988).

PUMPING AIDS

Pumping aids are added to concrete mixtures to improvepumpability. Pumping aids cannot cure all unpumpable con-crete problems; they are best used to make marginallypumpable concrete more pumpable. These admixturesincrease viscosity or cohesion in concrete to reduce dewater-ing of the paste while under pressure from the pump.

Some pumping aids may increase water demand,reduce compressive strength, cause air entrainment, orretard setting time. These side effects can be corrected byadjusting the mix proportions or adding another admix-ture to offset the side effect.

A partial list of materials used in pumping aids isgiven in Table 6-1. Some admixtures that serve otherprimary purposes but also improve pumpability are air-entraining agents, and some water-reducing and retardingadmixtures.

BONDING ADMIXTURES AND BONDING AGENTS

Bonding admixtures are usually water emulsions of organicmaterials including rubber, polyvinyl chloride, polyvinylacetate, acrylics, styrene butadiene copolymers, and otherpolymers. They are added to portland cement mixtures toincrease the bond strength between old and new concrete.Flexural strength and resistance to chloride-ion ingress arealso improved. They are added in proportions equivalent to5% to 20% by mass of the cementing materials; the actualquantity depending on job conditions and type of admix-ture used. Some bonding admixtures may increase the aircontent of mixtures. Nonreemulsifiable types are resistantto water, better suited to exterior application, and used inplaces where moisture is present.

The ultimate result obtained with a bonding admix-ture will be only as good as the surface to which theconcrete is applied. The surface must be dry, clean, sound,free of dirt, dust, paint, and grease, and at the propertemperature. Organic or polymer modified concretes are

Unmodified carbon black substantially reduces aircontent. Most carbon black for coloring concrete containsan admixture to offset this effect on air. Before a coloringadmixture is used on a project, it should be tested for colorfastness in sunlight and autoclaving, chemical stability incement, and effects on concrete properties. Calcium chlo-ride should not be used with pigments to avoid colordistortions. Pigments should conform to ASTM C 979.

DAMPPROOFING ADMIXTURES

The passage of water through concrete can usually betraced to the existence of cracks or areas of incompleteconsolidation. Sound, dense concrete made with a water-cement ratio of less than 0.50 by mass will be watertight ifit is properly placed and cured.

Admixtures known as dampproofing agents includecertain soaps, stearates, and petroleum products. Theymay, but generally do not, reduce the permeability ofconcretes that have low cement contents, high water-cement ratios, or a deficiency of fines in the aggregate.Their use in well-proportioned mixes, may increase themixing water required and actually result in increasedrather than reduced permeability.

Dampproofing admixtures are sometimes used toreduce the transmission of moisture through concrete thatis in contact with water or damp earth. Many so-calleddampproofers are not effective, especially when used inconcretes that are in contact with water under pressure.

PERMEABILITY-REDUCING ADMIXTURES

Permeability-reducing admixtures reduce the rate atwhich water under pressure is transmitted through

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Fig. 6-19. Red and blue pigments were used to color thisterrazzo floor. (69873)

acceptable for patching and thin-bonded overlayment,particularly where feather-edged patches are desired.

Bonding agents should not be confused with bondingadmixtures. Admixtures are an ingredient in the concrete;bonding agents are applied to existing concrete surfacesimmediately before the new concrete is placed. Bondingagents help “glue” the existing and the new materialstogether. Bonding agents are often used in restoration andrepair work; they consist of portland cement or latex-modified portland cement grout or polymers such asepoxy resins (ASTM C 881 or AASHTO M 235) or latex(ASTM C 1059).

GROUTING ADMIXTURES

Portland cement grouts are used for a variety of purposes:to stabilize foundations, set machine bases, fill cracks andjoints in concrete work, cement oil wells, fill cores ofmasonry walls, grout prestressing tendons and anchorbolts, and fill the voids in preplaced aggregate concrete. Toalter the properties of grout for specific applications, vari-ous air-entraining admixtures, accelerators, retarders, andnonshrink admixtures are often used.

GAS-FORMING ADMIXTURES

Aluminum powder and other gas-forming materials aresometimes added to concrete and grout in very smallquantities to cause a slight expansion of the mixture priorto hardening. This may be of benefit where the completegrouting of a confined space is essential, such as undermachine bases or in post-tensioning ducts of prestressedconcrete. These materials are also used in larger quantitiesto produce autoclaved cellular concretes. The amount ofexpansion that occurs is dependent upon the amount ofgas-forming material used, the temperature of the freshmixture, the alkali content of the cement, and other vari-ables. Where the amount of expansion is critical, carefulcontrol of mixtures and temperatures must be exercised.Gas-forming agents will not overcome shrinkage afterhardening caused by drying or carbonation.

AIR DETRAINERS

Air-detraining admixtures reduce the air content inconcrete. They are used when the air content cannot bereduced by adjusting the mix proportions or by changingthe dosage of the air-entraining agent and other admix-tures. However, air-detrainers are rarely used and theireffectiveness and dosage rate should be established ontrial mixes prior to use on actual job mixes. Materials usedin air-detraining agents are listed in Table 6-1.

FUNGICIDAL, GERMICIDAL, ANDINSECTICIDAL ADMIXTURES

Bacteria and fungal growth on or in hardened concretemay be partially controlled through the use of fungicidal,germicidal, and insecticidal admixtures. The most effec-tive materials are polyhalogenated phenols, dieldrinemulsions, and copper compounds. The effectiveness ofthese materials is generally temporary, and in highdosages they may reduce the compressive strength ofconcrete.

ANTIWASHOUT ADMIXTURES

Antiwashout admixtures increase the cohesiveness of con-crete to a level that allows limited exposure to water withlittle loss of cement. This allows placement of concrete inwater and under water without the use of tremies. The ad-mixtures increase the viscosity of water in the mixtureresulting in a mix with increased thixotropy and resistanceto segregation. They usually consist of water soluble cellu-lose ether or acrylic polymers.

COMPATIBILITY OF ADMIXTURES ANDCEMENTITIOUS MATERIALS

Fresh concrete problems of varying severity are encoun-tered due to cement-admixture incompatibility andincompatibility between admixtures. Incompatibilitybetween supplementary cementing materials and admix-tures or cements can also occur. Slump loss, air loss, earlystiffening, and other factors affecting fresh concrete prop-erties can result from incompatibilities. While these prob-lems primarily affect the plastic-state performance ofconcrete, long-term hardened concrete performance mayalso be adversely affected. For example, early stiffeningcan cause difficulties with consolidation of concrete, there-fore compromising strength.

Reliable test methods are not available to adequatelyaddress incompatibility issues due to variations in materi-als, mixing equipment, mixing time, and environmentalfactors. Tests run in a laboratory do not reflect the condi-tions experienced by concrete in the field. When incom-patibility is discovered in the field, a common solution isto simply change admixtures or cementing materials(Helmuth, Hills, Whiting, and Bhattacharja 1995, Tagni-Hamou and Aítcin 1993, and Tang and Bhattacharja 1997).

STORING AND DISPENSING CHEMICAL ADMIXTURES

Liquid admixtures can be stored in barrels or bulk tankers.Powdered admixtures can be placed in special storagebins and some are available in premeasured plastic bags.Admixtures added to a truck mixer at the jobsite are often

117


REFERENCES

AASHTO, “Portland Cement Concrete Resistant toExcessive Expansion Caused by Alkali-Silica Reaction,”Section 56X, Guide Specification For Highway Construction,http://leadstates.tamu.edu/ASR/library/gspec.stm, Ameri-can Association of State Highway and TransportationOfficials, Washington, D.C., 2001.

Abrams, Duff A., Calcium Chloride as an Admixture inConcrete, Bulletin 13 (PCA LS013), Structural MaterialsResearch Laboratory, Lewis Institute, Chicago, http://www.portcement.org/pdf_files/LS013.pdf, 1924.

ACI Committee 212, Chemical Admixtures for Concrete, ACI212.3R-91, American Concrete Institute, Farmington Hills,Michigan, 1991.

ACI Committee 212, Guide for the Use of High-Range Water-Reducing Admixtures (Superplasticizers) in Concrete, ACI212.4R-93 (Reapproved 1998), American Concrete Insti-tute, Farmington Hills, Michigan, 1998.

ACI Committee 222, Corrosion of Metals in Concrete, ACI222R-96, American Concrete Institute, Farmington Hills,Michigan, 1996.

ACI Committee 318, Building Code Requirements forStructural Concrete and Commentary, ACI 318-02, AmericanConcrete Institute, Farmington Hills, Michigan, 2002.

ACI E4, Chemical and Air-Entraining Admixtures for Concrete,ACI Education Bulletin No. E4-96, American ConcreteInstitute, Farmington Hills, Michigan, 1999, 16 pages.

Aldred, James M., “HPI Concrete,” Concrete International,American Concrete Institute, Farmington Hills, Michigan,November 1988.

Berke, N. S., and Weil, T. G., “World Wide Review ofCorrosion Inhibitors in Concrete,” Advances in ConcreteTechnology, CANMET, Ottawa, 1994, pages 891 to 914.

Chou, Gee Kin, “Cathodic Protection: An EmergingSolution to the Rebar Corrosion Problem,” Concrete Con-struction, Addison, Illinois, June 1984.

Gajda, John, Development of a Cement to Inhibit Alkali-SilicaReactivity, Research and Development Bulletin RD115,Portland Cement Association, 1996, 58 pages.

Gaynor, Richard D., “Calculating Chloride Percentages,”Concrete Technology Today, PL983, Portland Cement Associ-ation, http://www.portcement.org/pdf_files/PL983.pdf,1998, pages 4 to 5.

Gebler, S. H., The Effects of High-Range Water Reducers on theProperties of Freshly Mixed and Hardened Flowing Concrete,Research and Development Bulletin RD081, PortlandCement Association, http://www.portcement.org/pdf_files/RD081.pdf, 1982.

in plastic jugs or bags. Powdered admixtures, such as cer-tain plasticizers, or a barrel of admixture may be stored atthe project site.

Dispenser tanks at concrete plants should be properlylabeled for specific admixtures to avoid contaminationand avoid dosing the wrong admixture. Most liquidchemical admixtures should not be allowed to freeze;therefore, they should be stored in heated environments.Consult the admixture manufacturer for proper storagetemperatures. Powdered admixtures are usually lesssensitive to temperature restrictions, but may be sensitiveto moisture.

Liquid chemical admixtures are usually dispensedindividually in the batch water by volumetric means (Fig.6-20). Liquid and powdered admixtures can be measuredby mass, but powdered admixtures should not be meas-ured by volume. Care should be taken to not combinecertain admixtures prior to their dispensing into the batchas some combinations may neutralize the desired effect ofthe admixtures. Consult the admixture manufacturer con-cerning compatible admixture combinations or performlaboratory tests to document performance.

118


Fig. 6-20. Liquid admixture dispenser at a ready mix plantprovides accurate volumetric measurement of admixtures.(44220)

Helmuth, Richard; Hills, Linda M.; Whiting, David A.;and Bhattacharja, Sankar, Abnormal Concrete Performance inthe Presence of Admixtures, RP333, Portland Cement Asso-ciation, http://www.portcement.org/pdf_files/RP333.pdf,1995.

Hester, Weston T., Superplasticizers in Ready Mixed Concrete(A Practical Treatment for Everyday Operations), NationalReady Mixed Concrete Association, Publication No. 158,Silver Spring, Maryland, 1979.

Kinney, F. D., “Reuse of Returned Concrete by HydrationControl: Characterization of a New Concept,” Superplas-ticizers and Other Chemical Admixtures in Concrete, SP119,American Concrete Institute, Farmington Hills, Michigan,1989, pages 19 to 40.

Klieger, Paul, Air-Entraining Admixtures, Research Depart-ment Bulletin RX199, Portland Cement Association,http://www.portcement.org/pdf_files/RX199.pdf, 1966,12 pages.

Kosmatka, Steven H., “Discoloration of Concrete—Causesand Remedies,” Concrete Technology Today, PL861, PortlandCement Association, http://www.portcement.org/pdf_files/PL861.pdf, 1986.

Lackey, Homer B., “Factors Affecting Use of CalciumChloride in Concrete,” Cement, Concrete, and Aggregates,American Society for Testing and Materials, West Consho-hocken, Pennsylvania, Winter 1992, pages 97 to 100.

Nmai, Charles K.; Schlagbaum, Tony; and Violetta, Brad,“A History of Mid-Range Water-Reducing Admixtures,”Concrete International, American Concrete Institute, Farm-ington Hills, Michigan, April 1998, pages 45 to 50.

Nmai, Charles K.; Tomita, Rokuro; Hondo, Fumiaki; andBuffenbarger, Julie, “Shrinkage-Reducing Admixtures,”Concrete International, American Concrete Institute, Farm-ington Hills, Michigan, April 1998, pages 31 to 37.

Ramachandran, V. S., Concrete Admixtures Handbook,Noyes Publications, Park Ridge, New Jersey, 1995.

Rixom, M. R., and Mailvaganam, N. P., Chemical Admix-tures for Concrete, E. & F. N. Spon, New York, 1986.

Shah, Surendra P.; Weiss, W. Jason; and Yang, Wei,“Shrinkage Cracking—Can it be Prevented?,” ConcreteInternational, American Concrete Institute, FarmingtonHills, Michigan, April 1998, pages 51 to 55.

Stark, David, Influence of Design and Materials on Corrosion Re-sistance of Steel in Concrete, Research and Development Bul-letin RD098, Portland Cement Association, http://www.portcement.org/pdf_files/RD098.pdf, 1989, 44 pages.

Stark, David C., Lithium Salt Admixtures—An AlternativeMethod to Prevent Expansive Alkali-Silica Reactivity, RP307,Portland Cement Association, 1992, 10 pages.

Tagnit-Hamou, Arezki, and Aítcin, Pierre-Claude, “Ce-ment and Superplasticizer Compatibility,” World Cement,Palladian Publications Limited, Farnham, Surrey, Eng-land, August 1993, pages 38 to 42.

Tang, Fulvio J., and Bhattacharja, Sankar, Development of anEarly Stiffening Test, RP346, Portland Cement Association,1997, 36 pages.

Thomas, Michael D. A., and Stokes, David B., “Use of aLithium-Bearing Admixture to Suppress Expansion inConcrete Due to Alkali-Silica Reaction,” TransportationResearch Record No. 1668, Transportation Research Board,Washington, D.C., 1999, pages 54 to 59.

Whiting, David, Effects of High-Range Water Reducers onSome Properties of Fresh and Hardened Concretes, Researchand Development Bulletin RD061, Portland CementAssociation, http://www.portcement.org/pdf_files/RD061.pdf, 1979.

Whiting, David A., Evaluation of Super-Water Reducers forHighway Applications, Research and Development BulletinRD078, Portland Cement Association, http://www.portcement.org/pdf_files/RD078.pdf, 1981, 169 pages.

Whiting, D., and Dziedzic, W., Effects of Conventional andHigh-Range Water Reducers on Concrete Properties, Researchand Development Bulletin RD107, Portland Cement Asso-ciation, 1992, 25 pages.

Whiting, David A., and Nagi, Mohamad A., Manual on theControl of Air Content in Concrete, EB116, National ReadyMixed Concrete Association and Portland Cement Asso-ciation, 1998, 42 pages.

119


Fibers have been used in construction materials for manycenturies. The last three decades have seen a growinginterest in the use of fibers in ready-mixed concrete, pre-cast concrete, and shotcrete. Fibers made from steel,plastic, glass, and natural materials (such as wood cellu-lose) are available in a variety of shapes, sizes, and thick-nesses; they may be round, flat, crimped, and deformedwith typical lengths of 6 mm to 150 mm (0.25 in. to 6 in.)and thicknesses ranging from 0.005 mm to 0.75 mm(0.0002 in. to 0.03 in.) (Fig. 7-1). They are added to concreteduring mixing. The main factors that control the perform-ance of the composite material are:

1. Physical properties of fibers and matrix2. Strength of bond between fibers and matrix

Although the basic governing principles are the same,there are several characteristic differences between con-ventional reinforcement and fiber systems:

1. Fibers are generally distributed throughout a givencross section whereas reinforcing bars or wires areplaced only where required

2. Most fibers are relatively short and closely spaced ascompared with continuous reinforcing bars or wires

3. It is generally not possible to achieve the same area ofreinforcement to area of concrete using fibers as com-pared to using a network of reinforcing bars or wires

Fibers are typically added to concrete in low volumedosages (often less than 1%), and have been shown to beeffective in reducing plastic shrinkage cracking.

Fibers typically do not significantly alter freeshrinkage of concrete, however at high enough dosagesthey can increase the resistance to cracking and decreasecrack width (Shah, Weiss, and Yang 1998).

ADVANTAGES AND DISADVANTAGES OF USING FIBERS

Fibers are generally distributed throughout the concretecross section. Therefore, many fibers are inefficientlylocated for resisting tensile stresses resulting from appliedloads. Depending on fabrication method, random orienta-tion of fibers may be either two-dimensional (2-D) orthree-dimensional (3-D). Typically, the spray-up fabrica-tion method has a 2-D random fiber orientation where asthe premix (or batch) fabrication method typically has a3-D random fiber orientation. Also, many fibers areobserved to extend across cracks at angles other than 90ºor may have less than the required embedment length fordevelopment of adequate bond. Therefore, only a smallpercentage of the fiber content may be efficient in resistingtensile or flexural stresses. “Efficiency factors” can be aslow as 0.4 for 2-D random orientation and 0.25 for 3-Drandom orientation. The efficiency factor depends on fiberlength and critical embedment length. From a conceptualpoint of view, reinforcing with fibers is not a highly effi-cient method of obtaining composite strength.

Fiber concretes are best suited for thin section shapeswhere correct placement of conventional reinforcementwould be extremely difficult. In addition, spraying of fiberconcrete accommodates the fabrication of irregularlyshaped products. A substantial weight savings can be real-ized using relatively thin fiber concrete sections having

CHAPTER 7

Fibers

Fig. 7-1. Steel, glass, synthetic and natural fibers with dif-ferent lengths and shapes can be used in concrete. (69965)

121

Steel fibers do not affect free shrinkage. Steel fibersdelay the fracture of restrained concrete during shrinkageand they improve stress relaxation by creep mechanisms(Altoubat and Lange 2001).

The durability of steel-fiber concrete is contingent onthe same factors as conventional concrete. Freeze-thawdurability is not diminished by the addition of steel fibersprovided the mix is adjusted to accommodate the fibers,the concrete is properly consolidated during placement,and is air-entrained. With properly designed and placedconcrete, little or no corrosion of the fibers occurs. Anysurface corrosion of fibers is cosmetic as opposed to astructural condition.

Steel fibers have a relatively high modulus of elas-ticity (Table 7-1). Their bond to the cement matrix can beenhanced by mechanical anchorage or surface roughnessand they are protected from corrosion by the alkalineenvironment in the cement matrix (ACI 544.1R-96).

Steel fibers are most commonly used in airport pave-ments and runway/taxi overlays. They are also used inbridge decks (Fig. 7-3), industrial floors, and highwaypavements. Structures exposed to high-velocity waterflow have been shown to last about three times longerthan conventional concrete alternatives. Steel fiber con-crete is also used for many precast concrete applicationsthat make use of the improved impact resistance or tough-ness imparted by the fibers. In utility boxes and septictanks, steel fibers replace conventional reinforcement.

Steel fibers are also widely used with shotcrete inthin-layer applications, especially rock-slope stabilizationand tunnel linings. Silica fume and accelerators haveenabled shotcrete to be placed in thicker layers. Silicafume also reduces the permeability of the shotcrete mate-rial (Morgan 1987). Steel-fiber shotcrete has been success-fully applied with fiber volumes up to 2%.

Slurry-infiltrated concrete (SIFCON) with fiber vol-umes up to 20% has been used since the late 1970s. Slurry-

the equivalent strength of thicker conventionally rein-forced concrete sections.

TYPES AND PROPERTIES OF FIBERSAND THEIR EFFECT ON CONCRETE

Steel Fibers

Steel fibers are short, discrete lengths of steel with anaspect ratio (ratio of length to diameter) from about 20 to100, and with any of several cross sections. Some steelfibers have hooked ends to improve resistance to pulloutfrom a cement-based matrix (Fig. 7-2).

ASTM A 820 classifies four different types based ontheir manufacture. Type I – Cold-drawn wire fibers are themost commercially available, manufactured from drawnsteel wire. Type II – Cut sheet fibers are manufactured asthe name implies: steel fibers are laterally sheared off steelsheets. Type III – Melt-extracted fibers are manufacturedwith a relatively complicated technique where a rotatingwheel is used to lift liquid metal from a molten metal sur-face by capillary action. The extracted molten metal is thenrapidly frozen into fibers and thrown off the wheel by cen-trifugal force. The resulting fibers have a crescent-shapedcross section. Type IV – Other fibers. For tolerances forlength, diameter, and aspect ratio, as well as minimum ten-sile strength and bending requirement, see ASTM A 820.

Steel-fiber volumes used in concrete typically rangefrom 0.25% to 2%. Volumes of more than 2% generallyreduce workability and fiber dispersion and require spe-cial mix design or concrete placement techniques.

The compressive strength of concrete is only slightlyaffected by the presence of fibers. The addition of 1.5% byvolume of steel fibers can increase the direct tensilestrength by up to 40% and the flexural strength up to 150%.

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Fig. 7-2. Steel fibers with hooked ends are collated intobundles to facilitate handling and mixing. During mixingthe bundles separate into individual fibers. (69992) Fig. 7-3. Bridge deck with steel fibers. (70007)

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Chapter 7 � Fibers

Modulus ofRelative density Diameter, µµm Tensile strength, MPa elasticity, MPa Strain at

Fiber type (specific gravity) (0.001 in.) (ksi) (ksi) failure, %

Steel 7.80 100-1000 500-2600 210,000 0.5-3.5(4-40) (70-380) (30,000)

Glass

E 2.54 8-15 2000-4000 72,000 3.0-4.8(0.3-0.6) (290-580) (10,400)

AR 2.70 12-20 1500-3700 80,000 2.5-3.6(0.5-0.8) (220-540) (11,600)

Synthetic

Acrylic 1.18 5-17 200-1000 17,000-19,000 28-50(0.2-0.7) (30-145) (2,500-2,800)

Aramid 1.44 10-12 2000-3100 62,000-120,000 2-3.5(0.4-0.47) (300-450) (9,000-17,000)

Carbon 1.90 8-0 1800-2600 230,000-380,000 0.5-1.5(0.3-0.35) (260-380) (33,400-55,100)

Nylon 1.14 23 1000 5,200 20(0.9) (140) (750)

Polyester 1.38 10-80 280-1200 10,000-18,000 10-50(0.4-3.0) (40-170) (1,500-2,500)

Polyethylene 0.96 25-1000 80-600 5,000 12-100(1-40) (11-85) (725)

Polypropylene 0.90 20-200 450-700 3,500-5,200 6-15(0.8-8) (65-100) (500-750)

Natural

Wood cellulose 1.50 25-125 350-2000 10,000-40,000(1-5) (51-290) (1,500-5,800)

Sisal 280-600 13,000-25,000 3.5(40-85) (1,900-3,800)

Coconut 1.12-1.15 100-400 120-200 19,000-25,000 10-25(4-16) (17-29) (2,800-3,800)

Bamboo 1.50 50-400 350-500 33,000-40,000(2-16) (51-73) (4,800-5,800)

Jute 1.02-1.04 100-200 250-350 25,000-32,000 1.5-1.9(4-8) (36-51) (3,800-4,600)

Elephant grass 425 180 4,900 3.6(17) (26) (710)

Table 7-1. Properties of Selected Fiber Types

Adapted from PCA (1991) and ACI 544.1R-96.

infiltrated concrete can be used to produce a component orstructure with strength and ductility that far exceeds thatof conventionally mixed or sprayed fiber concrete.SIFCON is not inexpensive and needs fine-tuning, but itholds potential for applications exposed to severe condi-tions and requiring very high strength and toughness.These applications include impact and blast-resistantstructures, refractories, protective revetment, and taxiwayand pavement repairs (Fig. 7-4). Table 7-2 shows a SIFCONmix design.

Cement 1000 kg/m3 (1686 lb/yd3)

Water 330 kg/m3 (556 lb/yd3)

Siliceous Sand ≤ 0.7 mm (≤ 0.028 in.) 860 kg/m3 (1450 lb/yd3)

Silica Slurry 13 kg/m3 (1.3 lb/yd3)

High-Range Water Reducer 35 kg/m3 (3.7 lb/yd3)

Steel Fibers (about 10 Vol.-%) 800 kg/m3 (84 lb/yd3)

Table 7-2. SIFCON Mix Design.

Fiber modifications to improve long-term durabilityinvolve (1) specially formulated chemical coatings to helpcombat hydration-induced embrittlement, and (2) em-ployment of a dispersed microsilica slurry to adequatelyfill fiber voids, thereby reducing potential for calciumhydroxide infiltration.

A low-alkaline cement has been developed in Japanthat produces no calcium hydroxide during hydration.Accelerated tests with the cement in alkali-resistant-glassfiber-reinforced concrete samples have shown greaterlong-term durability than previously achieved.

Metakaolin can be used in glass-fiber-reinforced con-crete without significantly affecting flexural strength,strain, modulus of elasticity, and toughness. (Marikunte,Aldea, Shah 1997).

The single largest application of glass-fiber concretehas been the manufacture of exterior building façade panels(Fig. 7-5). Other applications are listed in PCA (1991).

Glass Fibers

The first research on glass fibers in the early 1960s usedconventional borosilicate glass (E-glass) (Table 7-1) andsoda-lime-silica glass fibers (A-glass). The test resultsshowed that alkali reactivity between the E-glass fibersand the cement-paste reduced the strength of the concrete.Continued research resulted in alkali-resistant glass fibers(AR-glass) (Table 7-1), that improved long-term durability,but sources of other strength-loss trends were observed.One acknowledged source was fiber embrittlement stem-ming from infiltration of calcium hydroxide particles, by-products of cement hydration, into fiber bundles. Alkalireactivity and cement hydration are the basis for the fol-lowing two widely held theories explaining strength andductility loss, particularly in exterior glass fiber concrete:

• Alkali attack on glass-fiber surfaces reduces fiber ten-sile strength and, subsequently, lowers compressivestrength.

• Ongoing cement hydration causes calcium hydroxideparticle penetration of fiber bundles, therebyincreasing fiber-to-matrix bond strength and embrit-tlement; the latter lowers tensile strength by inhibit-ing fiber pullout.

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Fig. 7-5. (top) Glass-fiber-reinforced concrete panels are lightand strong enough to reduce this building’s structuralrequirements. (bottom) Spray-up fabrication made it easy tocreate their contoured profiles. (60671, 46228)

Fig. 7-4. Tightly bunched steel fibers are placed in a form,before cement slurry is poured into this application ofslurry-infiltrated steel-fiber concrete (SIFCON). (60672)

Synthetic Fibers

Synthetic fibers are man-made fibers resulting fromresearch and development in the petrochemical and textileindustries. Fiber types that are used in portland cementconcrete are: acrylic, aramid, carbon, nylon, polyester,polyethylene, and polypropylene. Table 7-1 summarizesthe range of physical properties of these fibers.

Synthetic fibers can reduce plastic shrinkage and sub-sidence cracking and may help concrete after it is frac-tured. Ultra-thin whitetopping often uses synthetic fibersfor potential containment properties to delay potholedevelopment. Problems associated with synthetic fibersinclude: (1) low fiber-to-matrix bonding; (2) inconclusiveperformance testing for low fiber-volume usage withpolypropylene, polyethylene, polyester and nylon; (3) alow modulus of elasticity for polypropylene and polyeth-ylene; and (4) the high cost of carbon and aramid fibers.

Polypropylene fibers (Fig. 7-6), the most popular ofthe synthetics, are chemically inert, hydrophobic, andlightweight. They are produced as continuous cylindricalmonofilaments that can be chopped to specified lengths orcut as films and tapes and formed into fine fibrils of rec-tangular cross section (Fig. 7-7).

Used at a rate of at least 0.1 percent by volume of con-crete, polypropylene fibers reduce plastic shrinkagecracking and subsidence cracking over steel reinforcement(Suprenant and Malisch 1999). The presence of polypropy-lene fibers in concrete may reduce settlement of aggregateparticles, thus reducing capillary bleed channels.Polypropylene fibers can help reduce spalling of high-strength, low-permeability concrete exposed to fire in amoist condition.

New developments show that monofilament fibersare able to fibrillate during mixing if produced with both,polypropylene and polyethylene resins. The two poly-

mers are incompatible and tend to separate when manip-ulated. Therefore, during the mixing process each fiberturns into a unit with several fibrils at its end. The fibrilsprovide better mechanical bonding than conventionalmonofilaments. The high number of fine fibrils alsoreduces plastic shrinkage cracking and may increase theductility and toughness of the concrete (Trottier andMahoney 2001).

Acrylic fibers have been found to be the most prom-ising replacement for asbestos fibers. They are used incement board and roof-shingle production, where fibervolumes of up to 3% can produce a composite withmechanical properties similar to that of an asbestos-cement composite. Acrylic-fiber concrete compositesexhibit high postcracking toughness and ductility.Although lower than that of asbestos-cement composites,acrylic-fiber-reinforced concrete’s flexural strength isample for many building applications.

Aramid fibers have high tensile strength and a hightensile modulus. Aramid fibers are two and a half times asstrong as E-glass fibers and five times as strong as steelfibers. A comparison of mechanical properties of differentaramid fibers is provided in PCA (1991). In addition toexcellent strength characteristics, aramid fibers also haveexcellent strength retention up to 160°C (320°F), dimen-sional stability up to 200°C (392°F), static and dynamicfatigue resistance, and creep resistance. Aramid strand isavailable in a wide range of diameters.

Carbon fibers were developed primarily for their highstrength and elastic modulus and stiffness properties forapplications within the aerospace industry. Comparedwith most other synthetic fibers, the manufacture ofcarbon fibers is expensive and this has limited commercialdevelopment. Carbon fibers have high tensile strengthand modulus of elasticity (Table 7-1). They are also inert to

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Fig. 7-7. Polypropylene fibers are produced either as (left)fine fibrils with rectangular cross section or (right) cylin-drical monofilament. (69993)

Fig. 7-6. Polypropylene fibers. (69796)

ufacture of low-fiber-content concrete and occasionallyhave been used in thin-sheet concrete with high-fiber con-tent. For typical properties of natural fibers see Table 7-1.

Unprocessed Natural Fibers. In the late 1960s, researchon the engineering properties of natural fibers, and con-crete made with these fibers was undertaken; the resultwas these fibers can be used successfully to make thinsheets for walls and roofs. Products were made with port-land cement and unprocessed natural fibers such ascoconut coir, sisal, bamboo, jute, wood, and vegetablefibers. Although the concretes made with unprocessednatural fibers show good mechanical properties, theyhave some deficiencies in durability. Many of the naturalfibers are highly susceptible to volume changes due tovariations in fiber moisture content. Fiber volumetricchanges that accompany variations in fiber moisture con-tent can drastically affect the bond strength between thefiber and cement matrix.

Wood Fibers (Processed Natural Fibers). The proper-ties of wood cellulose fibers are greatly influenced by themethod by which the fibers are extracted and the refiningprocesses involved. The process by which wood isreduced to a fibrous mass is called pulping. The kraftprocess is the one most commonly used for producingwood cellulose fibers. This process involves cookingwood chips in a solution of sodium hydroxide, sodiumcarbonate, and sodium sulfide. Wood cellulose fibers haverelatively good mechanical properties compared to manymanmade fibers such as polypropylene, polyethylene,polyester, and acrylic. Delignified cellulose fibers (ligninremoved) can be produced with a tensile strength of up toapproximately 2000 MPa (290 ksi) for selected grades ofwood and pulping processes. Fiber tensile strength ofapproximately 500 MPa (73 ksi) can be routinely achievedusing a chemical pulping process and the more common,less expensive grades of wood.

MULTIPLE FIBER SYSTEMS

For a multiple fiber system, two or more fibers areblended into one system. The hybrid-fiber concrete com-bines macro- and microsteel fibers. A common macrofiberblended with a newly developed microfiber, which is lessthan 10 mm (0.4 in.) long and less than 100 micrometer(0.004 in.) in diameter, leads to a closer fiber-to-fiberspacing, which reduces microcracking and increases ten-sile strength. The intended applications include thinrepairs and patching (Banthia and Bindiganavile 2001). Ablend of steel and polypropylene fibers has also been usedfor some applications. This system is supposed to com-bine the toughness and impact-resistance of steel fiberconcrete with the reduced plastic cracking of polypropy-lene fiber concrete. For a project in the Chicago area(Wojtysiak and others 2001), a blend of 30 kg/m3

(50 lb/yd3) of steel fibers and 0.9 kg/m3 (11⁄2 lb/yd3) of fib-

most chemicals. Carbon fiber is typically produced instrands that may contain up to 12,000 individual fila-ments. The strands are commonly prespread prior toincorporation in concrete to facilitate cement matrix pene-tration and to maximize fiber effectiveness.

Nylon fibers exist in various types in the marketplacefor use in apparel, home furnishing, industrial, and textileapplications. Only two types of nylon fiber are currentlymarketed for use in concrete, nylon 6 and nylon 66. Nylonfibers are spun from nylon polymer and transformedthrough extrusion, stretching, and heating to form an ori-ented, crystalline, fiber structure. For concrete applica-tions, high tenacity (high tensile strength) heat and lightstable yarn is spun and subsequently cut into shorterlength. Nylon fibers exhibit good tenacity, toughness, andelastic recovery. Nylon is hydrophilic, with moistureretention of 4.5 percent, which increases the waterdemand of concrete. However, this does not affect con-crete hydration or workability at low prescribed contentsranging from 0.1 to 0.2 percent by volume, but should beconsidered at higher fiber volume contents. This compar-atively small dosage has potentially greater reinforcingvalue than low volumes of polypropylene or polyesterfiber. Nylon is relatively inert and resistant to a widevariety of organic and inorganic materials includingstrong alkalis.

Synthetic fibers are also used in stucco and mortar.For this use the fibers are shorter than synthetic fibersused in concrete. Usually small amounts of 13-mm (1⁄2-in.)long alkali-resistant fibers are added to base coat plastermixtures. They can be used in small line stucco andmortar pumps and spray guns. They should be addedto the mix in accordance with manufacturer’s recom-mendation.

For further details about chemical and physicalproperties of synthetic fibers and properties of syntheticfiber concrete, see ACI 544.1R-96. ASTM C 1116 classifiesSteel, Glass, and Synthetic Fiber Concrete or Shotcrete.

The technology of interground fiber cement takesadvantage of the fact that some synthetic fibers are notdestroyed or pulverized in the cement finishing mill. Thefibers are mixed with dry cement during grinding wherethey are uniformly distributed; the surface of the fibers isroughened during grinding, which offers a better mechan-ical bond to the cement paste (Vondran 1995).

Natural Fibers

Natural fibers were used as a form of reinforcement longbefore the advent of conventional reinforced concrete.Mud bricks reinforced with straw and mortars reinforcedwith horsehair are just a few examples of how naturalfibers were used long ago as a form of reinforcement.Many natural reinforcing materials can be obtained at lowlevels of cost and energy using locally available manpowerand technical know-how. Such fibers are used in the man-

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rillated polypropylene fibers were used for slabs on grade.The concrete with blended fibers had a lower slump com-pared to plain concrete but seemed to have enhancedelastic and post-elastic strength.

REFERENCES

ACI Committee 544, State-of-the-Art Report on FiberReinforced Concrete, ACI 544.1R-96, American ConcreteInstitute, Farmington Hills, Michigan, 1997.

Altoubat, Salah A., and Lange, David A., “Creep,Shrinkage, and Cracking of Restrained Concrete at EarlyAge,” ACI Materials Journal, American Concrete Institute,Farmington Hills, Michigan, July-August 2001, pages 323to 331.

Banthia, Nemkumar, and Bindiganavile, Vivek, “Repairingwith Hybrid-Fiber-Reinforced Concrete,” Concrete Inter-national, American Concrete Institute, Farmington Hills,Michigan, June 2001, pages 29 to 32.

Bijen, J., “Durability of Some Glass Fiber ReinforcedCement Composites,” ACI Journal, American ConcreteInstitute, Farmington Hills, Michigan, July-August 1983,pages 305 to 311.

Hanna, Amir N., Steel Fiber Reinforced ConcreteProperties and Resurfacing Applications, Research and De-velopment Bulletin RD049, Portland Cement Association,http://www.portcement.org/pdf_files/RD049.pdf,1977, 18 pages.

Johnston, Colin D., Fiber Reinforced Cement and Concretes,LT249, Gordon & Breach, Amsterdam, 2000, 368 pages.

Marikunte, S.; Aldea, C.; and Shah, S., “Durability of GlassFiber Reinforced Cement Composites: Effect of SilicaFume and Metakaolin,” Advanced Cement Based Materials,Volume 5, Numbers 3/4, April/May 1997, pages 100to 108.

Morgan, D. R., “Evaluation of Silica Fume Shotcrete,”Proceedings, CANMET/CSCE International Workshop onSilica Fume in Concrete, Montreal, May 1987.

Monfore, G. E., A Review of Fiber Reinforcement of PortlandCement Paste, Mortar and Concrete, Research DepartmentBulletin RX226, Portland Cement Association, http://www.portcement.org/pdf_files/RX226.pdf, 1968, 7 pages.

PCA, Fiber Reinforced Concrete, SP039, Portland CementAssociation, 1991, 54 pages.

PCA, “Steel Fiber Reinforced Concrete,” Concrete Tech-nology Today, PL931 Portland Cement Association, http://www.portcement.org/pdf_files/PL931.pdf, March 1993,pages 1 to 4.

Panarese, William C., “Fiber: Good for the ConcreteDiet?,” Civil Engineering, American Society of CivilEngineers, New York, May 1992, pages 44 to 47.

Shah, S. P.; Weiss, W. J.; and Yang, W., “ShrinkageCracking – Can it be prevented?,” Concrete International,American Concrete Institute, Farmington Hills, Michigan,April 1998, pages 51 to 55.

Suprenant, Bruce A., and Malisch, Ward R., “The fiberfactor,” Concrete Construction, Addison, Illinois, October1999, pages 43 to 46.

Trottier, Jean-Francois, and Mahoney, Michael, “InnovativeSynthetic Fibers,” Concrete International, American Con-crete Institute, Farmington Hills, Michigan, June 2001,pages 23 to 28

Vondran, Gary L., “Interground Fiber Cement in the Year2000,” Emerging Technologies Symposium on Cements for the21st Century, SP206, Portland Cement Association, March1995, pages 116 to 134.

Wojtysiak, R.; Borden, K. K.; and Harrison P., Evaluation ofFiber Reinforced Concrete for the Chicago Area – A Case Study,2001.

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CHAPTER 8

Air-Entrained Concrete

One of the greatest advances in concrete technology wasthe development of air-entrained concrete in the mid-1930s. Today air entrainment is recommended for nearlyall concretes, principally to improve freeze-thaw resist-ance when exposed to water and deicing chemicals.However, there are other important benefits of entrainedair in both freshly mixed and hardened concrete.

Air-entrained concrete is produced by using either anair-entraining cement or adding an air-entraining admix-ture during batching. The air-entraining admixture stabi-lizes bubbles formed during the mixing process,enhances the incorporation of bubbles of various sizes bylowering the surface tension of the mixing water,impedes bubble coalescence, and anchors bubbles tocement and aggregate particles.

Anionic air-entraining admixtures are hydrophobic(repel water) and are electrically charged (nonionic or no-charge admixtures are also available). The negative elec-tric charge is attracted to positively charged cementgrains, which aids in stabilizing bubbles. The air-entraining admixture forms a tough, water-repelling film,

similar to a soap film, with sufficient strength and elas-ticity to contain and stabilize the air bubbles and preventthem from coalescing. The hydrophobic film also keepswater out of the bubbles. The stirring and kneading actionof mechanical mixing disperses the air bubbles. The fineaggregate particles also act as a three-dimensional grid tohelp hold the bubbles in the mixture.

Entrained air bubbles are not like entrapped air voids,which occur in all concretes as a result of mixing, han-dling, and placing and are largely a function of aggregatecharacteristics. Intentionally entrained air bubbles areextremely small in size, between 10 to 1000 µm in diam-eter, while entrapped voids are usually 1000 µm (1 mm) orlarger. The majority of the entrained air voids in normalconcrete are between 10 µm and 100 µm in diameter. Asshown in Fig. 8-1, the bubbles are not interconnected; theyare well dispersed and randomly distributed. Non-air-entrained concrete with a 25-mm (1-in.) maximum-sizeaggregate has an air content of approximately 11⁄2%. Thissame mixture air entrained for severe frost exposurewould require a total air content of about 6%, made up ofboth the coarser “entrapped” air voids and the finer“entrained” air voids.

PROPERTIES OF AIR-ENTRAINEDCONCRETE

The primary concrete properties influenced by air entrain-ment are presented in the following sections. A brief sum-mary of other properties not discussed below is presentedin Table 8-1.


The resistance of hardened concrete to freezing andthawing in a moist condition is significantly improved bythe use of intentionally entrained air, even when variousdeicers are involved. Convincing proof of the improve-

Fig. 8-1. Polished section of air-entrained concrete as seenthrough a microscope. (67840)

129

ment in durability effected by air entrainment is shown inFigs. 8-2 and 8-3.

As the water in moist concrete freezes, it producesosmotic and hydraulic pressures in the capillaries andpores of the cement paste and aggregate. If the pressureexceeds the tensile strength of the paste or aggregate, thecavity will dilate and rupture. The accumulative effect ofsuccessive freeze-thaw cycles and disruption of paste and

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Properties Effect

Abrasion Little effect; increased strength increasesabrasion resistance

Absorption Little effectAlkali-silica reactivity Expansion decreases with increased airBleeding Reduced significantlyBond to steel DecreasedCompressive strength Reduced approximately 2% to 6% per per-

centage point increase in air; harsh or leanmixes may gain strength

Creep Little effectDeicer scaling Significantly reducedDensity Decreases with increased air Fatigue Little effectFinishability Reduced due to increased cohesion (sticki-

ness)Flexural strength Reduced approximately 2% to 4% per per-

centage point increase in airFreeze-thaw Significantly improved resistance to

resistance water-saturated freeze-thaw deterioration Heat of hydration No significant effectModulus of elasticity Decreases with increased air

(static) approximately 720 to 1380 MPa (105,000to 200,000 psi) per percentage point of air

Permeability Little effect; reduced water-cement ratioreduces permeability

Scaling Significantly reduced Shrinkage (drying) Little effect Slump Increases with increased air approximately

25 mm (1 in.) per 1⁄2 to 1 percentage pointincrease in air

Specific heat No effectSulfate resistance Significantly improved Stickiness Increased cohesion—harder to finishTemperature of wet No effect

concreteThermal conductivity Decreases 1% to 3% per percentage point

increase in air Thermal diffusivity Decreases about 1.6% per percentage

point increase in air Water demand of wet Decreases with increased air;

concrete for equal approximately 3 to 6 kg/m3 (5 to 10slump lb/yd3) per percentage point of air

Watertightness Increases slightly; reduced water-cementratio increases watertightness

Workability Increases with increased air

Air content, percentC

ycle

s of

free

zing

and

thaw

ing

for

50%

redu

ctio

n in

dyn

amic

mod

ulus

of e

last

icity

00

200

400

600

800

1000

1200

1400

1600

1800

2000

1 2 3 4 5 6

Symbols: Non-air-entrained Air-entrained

Fig. 8-2. Effect of entrained air on the resistance of concrete tofreezing and thawing in laboratory tests. Concretes were madewith cements of different fineness and composition and withvarious cement contents and water-cement ratios (Bates andothers 1952, and Lerch 1960).

Table 8-1. Effect of Entrained Air on ConcreteProperties

Note: The table information may not apply to all situations.

aggregate eventually cause significant expansion anddeterioration of the concrete. Deterioration is visible in theform of cracking, scaling, and crumbling (Fig. 8-3). Powers(1965) and Pigeon and Pleau (1995) extensively review themechanisms of frost action.

Hydraulic pressures are caused by the 9% expansionof water upon freezing; in this process growing ice crystalsdisplace unfrozen water. If a capillary is above critical sat-uration (91.7% filled with water), hydraulic pressuresresult as freezing progresses. At lower water contents, nohydraulic pressure should exist.

Osmotic pressures develop from differential concen-trations of alkali solutions in the paste (Powers 1965a). Aspure water freezes, the alkali concentration increases inthe adjacent unfrozen water. A high-alkali solution,through the mechanism of osmosis, draws water fromlower-alkali solutions in the pores. This osmotic transferof water continues until equilibrium in the fluids’ alkaliconcentration is achieved. Osmotic pressure is considereda minor factor, if present at all, in aggregate frost action,whereas it may be dominant in certain cement pastes.Osmotic pressures, as described above, are considered tobe a major factor in “salt scaling.”

Capillary ice (or any ice in large voids or cracks)draws water from pores to advance its growth. Also, sincemost pores in cement paste and some aggregates are too

small for ice crystals to form, water attempts to migrate tolocations where it can freeze.

Entrained air voids act as empty chambers in thepaste where freezing and migrating water can enter, thusrelieving the pressures described above and preventingdamage to the concrete. Upon thawing, most of the waterreturns to the capillaries due to capillary action and pres-sure from air compressed in the bubbles. Thus the bubblesare ready to protect the concrete from the next cycle offreezing and thawing (Powers 1955, Lerch 1960, andPowers 1965).

The pressure developed by water as it expandsduring freezing depends largely upon the distance thewater must travel to the nearest air void for relief.Therefore, the voids must be spaced close enough toreduce the pressure below that which would exceed thetensile strength of the concrete. The amount of hydraulicpressure is also related to the rate of freezing and the per-meability of the paste.

The spacing and size of air voids are important factorscontributing to the effectiveness of air entrainment in con-crete. ASTM C 457 describes a method of evaluating theair-void system in hardened concrete. Most authoritiesconsider the following air-void characteristics as represen-tative of a system with adequate freeze-thaw resistance(Powers 1949, Klieger 1952, Klieger 1956, Mielenz and

others 1958, Powers 1965, Klieger 1966, Whiting and Nagi1998, and Pinto and Hover 2001):

1. Calculated spacing factor, ¿, (an index related to thedistance between bubbles but not the actual averagespacing in the system)—less than 0.200 mm (0.008 in.)(Powers 1954 and 1965)

2. Specific surface, α, (surface area of the air voids)—24square millimeters per cubic millimeter (600 sq in. percubic inch) of air-void volume, or greater.

Current U.S. field quality control practice usually in-volves only the measurement of total air volume in freshlymixed concrete; this does not distinguish air-void size inany way. In addition to total air volume, Canadian prac-tice also requires attainment of specific spacing factors.Fig. 8-4 illustrates the relationship between spacing factorand total air content. Measurement of air volume alonedoes not permit full evaluation of the important charac-teristics of the air-void system; however, air-entrainmentis generally considered effective for freeze-thaw resistancewhen the volume of air in the mortar fraction of the con-crete—material passing the 4.75-mm (No. 4) sieve—isabout 9 ± 1% (Klieger 1952) or about 18% by paste volume.For equal admixture dosage rates per unit of cement, theair content of ASTM C 185 (AASHTO T 137) mortar wouldbe about 19% due to the standard aggregate’s properties.

131

Chapter 8 � Air-Entrained Concrete

Fig. 8-3. Effect of weathering on boxes and slabs on ground at the Long-Time Study outdoor test plot, Project 10, PCA,Skokie, Illinois. Specimens at top are air-entrained, specimens at bottom exhibiting severe crumbling and scaling are non-air-entrained. All concretes were made with 335 kg (564 lb) of Type I portland cement per cubic meter (cubic yard).Periodically, calcium chloride deicer was applied to the slabs. Specimens were 40 years old when photographed (seeKlieger 1963 for concrete mixture information). (69977, 69853, 69978, 69854)

resistant with a low water-cement ratio. Fig. 8-5 illustratesthe effect of water-cement ratio on the durability of non-air-entrained concrete.

Concrete elements should be properly drained andkept as dry as possible as greater degrees of saturationincrease the likelihood of distress due to freeze-thawcycles. Concrete that is dry or contains only a small amountof moisture in service is essentially not affected by even alarge number of cycles of freezing and thawing. Refer tothe sections on “Deicer-Scaling Resistance” and “Recom-mended Air Contents” in this chapter and to Chapter 9 formixture design considerations.

Deicer-Scaling Resistance

Deicing chemicals used for snow and ice removal cancause and aggravate surface scaling. The damage is pri-marily a physical action. Deicer scaling of inadequatelyair-entrained or non-air-entrained concrete duringfreezing is believed to be caused by a buildup of osmoticand hydraulic pressures in excess of the normal hydraulicpressures produced when water in concrete freezes. Thesepressures become critical and result in scaling unless en-trained air voids are present at the surface and throughoutthe sample to relieve the pressure. The hygroscopic (mois-ture absorbing) properties of deicing salts also attractwater and keep the concrete more saturated, increasingthe potential for freeze-thaw deterioration. However,properly designed and placed air-entrained concrete willwithstand deicers for many years.

Studies have also shown that, in absence of freezing,the formation of salt crystals in concrete (from externalsources of chloride, sulfate, and other salts) may con-tribute to concrete scaling and deterioration similar to thecrumbling of rocks by salt weathering. The entrained airvoids in concrete allow space for salt crystals to grow; thisrelieves internal stress similar to the way the voids relievestress from freezing water in concrete (ASCE 1982 andSayward 1984).

Deicers can have many effects on concrete and theimmediate environment. All deicers can aggravate scalingof concrete that is not properly air entrained. Sodium chlo-ride (rock salt) (ASTM D 632 or AASHTO M 143), calciumchloride (ASTM D 98 or AASHTO M 144), and urea are themost frequently used deicers. In the absence of freezing,sodium chloride has little to no chemical effect on concretebut can damage plants and corrode metal. Calcium chlo-ride in weak solutions generally has little chemical effecton concrete and vegetation but does corrode metal.

Studies have shown that concentrated calcium chloridesolutions can chemically attack concrete (Brown and Cady1975). Urea does not chemically damage concrete, vegeta-tion, or metal. Nonchloride deicers are used to minimizecorrosion of reinforcing steel and minimize groundwaterchloride contamination. The use of deicers containing am-monium nitrate and ammonium sulfate should be strictlyprohibited as they rapidly attack and disintegrate concrete.

The air content of concrete with 19-mm (3⁄4-in.) maximum-size aggregate would be about 6% for effective freeze-thaw resistance.

The relationship between air content of standardmortar and concrete is illustrated by Taylor (1948). Pintoand Hover (2001) address paste air content versus frostresistance. The total required concrete air content for dura-bility increases as the maximum-size aggregate is reduced(due to greater paste volume) and the exposure conditionsbecome more severe (see “Recommended Air Contents”later in this chapter).

Freeze-thaw resistance is also significantly increasedwith the use of the following: (1) a good quality aggregate,(2) a low water to cementing materials ratio (maximum0.45), (3) a minimum cementitious materials content of335 kg/m3 (564 lb/yd3), (4) proper finishing and curingtechniques, and (5) a compressive strength of 28 MPa(4,000 psi) when exposed to repeated freeze-thaw cycles.Even non-air-entrained concretes will be more freeze-thaw

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100

80

60

40

20

00 50 100 150 200 250 300 350

Number of freeze–thaw cycles

Rel

ativ

e dy

nam

ic m

odul

us, %

0.300.350.400.450.50

Water tocement ratio

ASTM C 666

Fig. 8-5. Durability factors vs. number of freeze-thaw cycles forselected non-air-entrained concretes (Pinto and Hover 2001).

1100

1000

900

800

700

600

500

400

300

200

1001 2 3 4 5 6 7

Air content in concrete, %

Spa

cing

fact

or, m

icro

met

ers

Non-air-entrained mixtures

Air-entrained mixtures

Fig. 8-4. Spacing factor as a function of total air content inconcrete (Pinto and Hover 2001).

Mixture Control Fly ash (Class F) Slag Calcined shale Calcined shale

Mass replacementof cement, % 0 15 40 15 25

Scale rating at25 cycles 1 1 1 1 1

Scale rating at50 cycles 2 2 1 2 1

Magnesium chloride deicers have come under recent criti-cism for aggravating scaling. One study found that mag-nesium chloride, magnesium acetate, magnesium nitrate,and calcium chloride are more damaging to concrete thansodium chloride (Cody, Cody, Spry, and Gan 1996).

The extent of scaling depends upon the amount ofdeicer used and the frequency of application. Relativelylow concentrations of deicer (on the order of 2% to 4% bymass) produce more surface scaling than higher concentra-tions or the absence of deicer (Verbeck and Klieger 1956).

Deicers can reach concrete surfaces in ways otherthan direct application, such as splashing by vehicles anddripping from the undersides of vehicles. Scaling is moresevere in poorly drained areas because more of the deicersolution remains on the concrete surface during freezingand thawing. Air entrainment is effective in preventingsurface scaling and is recommended for all concretes thatmay come in contact with deicing chemicals (Fig. 8-6).

A good air-void system with a low spacing factor(maximum of 200 micrometers) is perhaps more importantto deicer environments than saturated frost environmentswithout deicers. The relationship between spacing factorand deicer scaling is illustrated in Fig. 8-7. A low water toportland cement ratio helps minimize scaling, but is notsufficient to control scaling at normal water-cement ratios.

Fig. 8-8 illustrates the overriding impact of air contentover water-cement ratio in controlling scaling.

To provide adequate durability and scale resistance insevere exposures with deicers present, air-entrained con-crete should be composed of durable materials and havethe following: (1) a low water to cementitious materialsratio (maximum 0.45), (2) a slump of 100 mm (4 in.) or lessunless a plasticizer is used, (3) a cementitious materialscontent of 335 kg/m3 (564 lb/yd3), (4) proper finishingafter bleed water has evaporated from the surface,(5) adequate drainage, (6) a minimum of 7 days moistcuring at or above 10°C (50°F), (7) a compressive strengthof 28 MPa (4000 psi) when exposed to repeated freeze-thaw cycling, and (8) a minimum 30-day drying periodafter moist curing if concrete will be exposed to freeze-thaw cycles and deicers when saturated. Target air con-tents are discussed in “Recommended Air Contents” atthe end of this chapter.

Normal dosages of supplementary cementitiousmaterials should not effect scaling resistance of properlydesigned, placed, and cured concrete (Table 8-2). The ACI318 building code allows up to 10% silica fume, 25% flyash, and 50% slag as part of the cementitious materials fordeicer exposures. However, abuse of these materials along

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2.0 0.4

0.3

0.2

0.1

1.81.61.41.21.00.80.60.40.2

0.00 10 20 30 40 50

Number of cycles

Cum

ulat

ive

mas

s lo

ss, k

g/m

2

Cum

ulat

ive

mas

s lo

ss, l

b/ft

2

2%4%6%

Air content

ASTM C 672deicer scaling test

Fig. 8-6. Cumulative mass loss for mixtures with a waterto cement ratio of 0.45 and on-time finishing (Pinto andHover 2001).

5

4

3

2

1

00 400200 800600

Spacing factor, µm

Vis

ual r

atin

g


Rating:0 = no scaling5 = severe scaling

Fig. 8-7. Visual rating as a function of spacing factor, for aconcrete mixture with a water to cement ratio of 0.45 (Pintoand Hover 2001).

Concrete had 335 kg of cementing materials per cubic meter (565 lb/yd3), a Type I portland cement, a water to cementing materials ratio of 0.50,a nominal slump of 75 mm (3 in.), and a nominal air content of 6%. Test method: ASTM C 672. Results are for specific materials tested in 2000and may not be representative of other materials. Scale rating: 1 = very slight scaling (3 mm depth maximum) with no coarse aggregate visible,2 = slight to moderate scaling.

Table 8-2. Deicer Scaling Resistance (Visual Ratings) of Concrete with Selected Supplementary Cementing Materials

The effect of mix design, surface treatment, curing, orother variables on resistance to surface scaling can be eval-uated by ASTM C 672.

Sulfate Resistance

Sulfate resistance of concrete is improved by air entrain-ment, as shown in Figs. 8-9 and 8-10, when advantage istaken of the reduction in water-cement ratio possible withair entrainment. Air-entrained concrete made with a lowwater-cement ratio, an adequate cement content and a sul-fate-resistant cement will be resistant to attack from sulfatesoils and waters.

Resistance to Alkali-Silica Reactivity

The expansive disruption caused by alkali-silica reactivityis reduced through the use of air-entrainment (Kretsinger1949). Alkali hydroxides react with the silica of reactiveaggregates to form expansive reaction products, causingthe concrete to expand. Excessive expansion will disruptand deteriorate concrete. As shown in Fig. 8-11, the expan-sion of mortar bars made with reactive materials is re-duced as the air content is increased.

Strength

When the air content is maintained constant, strengthvaries inversely with the water-cement ratio. Fig. 8-12shows a typical relationship between 28-day compressivestrength and water-cement ratio for concrete that has therecommended percentages of entrained air. As air contentis increased, a given strength generally can be maintainedby holding the voids (air + water) to cement ratio con-stant; this may, however, necessitate some increase incement content.

Air-entrained as well as non-air-entrained concretecan readily be proportioned to provide similar moderatestrengths. Both generally must contain the same amount

with poor placing and curing practices can aggravatescaling. Consult local guidelines on allowable dosagesand practices for using these materials in deicer environ-ments as they can vary from ACI 318 requirements.

Air Drying. The resistance of air-entrained concrete tofreeze-thaw cycles and deicers is greatly increased by anair drying period after initial moist curing. Air dryingremoves excess moisture from the concrete which in turnreduces the internal stress caused by freeze-thaw condi-tions and deicers. Water-saturated concrete will deterio-rate faster than an air-dried concrete when exposed tomoist freeze-thaw cycling and deicers. Concrete placed inthe spring or summer has an adequate drying period.Concrete placed in the fall season, however, often does notdry out enough before deicers are used. This is especiallytrue of fall paving cured by membrane-forming com-pounds. These membranes remain intact until worn off bytraffic; thus, adequate drying may not occur before theonset of winter. Curing methods, such as use of plasticsheets, that allow drying at the completion of the curingperiod are preferable for fall paving on all projects wheredeicers will be used. Concrete placed inthe fall should be allowed at least 30days for air drying after the moist-curingperiod. The exact length of time for suf-ficient drying to take place may varywith climate and weather conditions.

Treatment of Scaled Surfaces. If sur-face scaling (an indication of an inade-quate air-void system or poor finishingpractices) should develop during thefirst frost season, or if the concrete is ofpoor quality, a breathable surface treat-ment can be applied to the dry concreteto help protect it against further damage.Treatment often consists of a penetratingsealer made with boiled linseed oil(ACPA 1996), breathable methacrylate,or other materials. Nonbreathable for-mulations should be avoided as they cancause delamination.

134


Fig. 8-9. Effect of entrained air and cement content (Type II) on performance ofconcrete specimens exposed to a sulfate soil. Without entrained air thespecimens made with lesser amounts of cement deteriorated badly. Specimensmade with the most cement and the lowest water-cement ratio were furtherimproved by air entrainment. Specimens were 5 years old when photographed(Stanton 1948 and Lerch 1960).

Without air With air

5

4

3

2

1

00.2 0.30.25 0.4 0.45 0.50.35


Ave

rage

mas

s lo

ss, k

g/m

21.0

0.8

0.6

0.4

0.2

Ave

rage

mas

s lo

ss, l

b/ft22%

4%6%

Air content


Fig. 8-8. Measured mass loss of concrete after 40 cycles ofdeicer and frost exposure at various water to cement ratios(Pinto and Hover 2001).

222 kg/m3

(375 lb/yd3)

306 kg/m3

(515 lb/yd3)

392 kg/m3

(660 lb/yd3)

Cementcontent

135


1

2

3

4

5

6

657517376Cement content, lb/yd3

390307223Cement content, kg/m3

Vis

ual r

atin

g

Cementtype

I

I

II

II

V

V

Rating:1 – no deterioration6 – failure

Air-entrained concreteNon-air-entrained concrete

150 x 150 x 760-mm (6 x 6 x 30-in.)beams exposed for 11 years to soil containing approximately 10% sodium sulfate

Fig. 8-10. Performance of a variety of air-entrained and non-air-entrained concretes exposed to sulfate soil. Sulfateresistance is increased with the use of Types II and Vcements, a higher cement content, lower water-cementratio, and air entrainment (Stark 1984).

70

60

50

40

30

20

10

02 4 6 8 10 12 14

Air content, percent

Red

uctio

n in

exp

ansi

on a

t one

yea

r, pe

rcen

t

50 x 50 x 250-mm(2 x 2 x 10-in.) mortar bars1: 2 mortarwater to cement ratio = 0.4019% of the sand by masscontained reactive siliceousmagnesian limestone

Fig. 8-11. Effect of air content on the reduction of expansiondue to alkali-silica reaction (Kretsinger 1949).

35 5

3

428

21

0.50 0.55 0.60Water to cement ratio, by mass

Com

pres

sive

str

engt

h, M

Pa

Com

pres

sive

str

engt

h, 1

000

psi

Air-entrained concreteCement: Type IAge: 28 days

Fig. 8-12. Typical relationship between 28-day compressivestrength and water-cement ratio for a wide variety of air-entrained concretes using Type I cement.

of coarse aggregate. When the cement content and slumpare held constant, air entrainment reduces the sand andwater requirements as illustrated in Fig. 8-13. Thus, air-entrained concretes can have lower water-cement ratiosthan non-air-entrained concretes; this minimizes thereductions in strength that generally accompany airentrainment. At constant water-cement ratios, increases inair will proportionally reduce strength (Fig. 8-14). Pintoand Hover (2001) found that for a decrease in strength of10 MPa (1450 psi), resulting from a four percentage pointdecrease in air, the water-cement ratio had to be decreasedby 0.14 to maintain strength. Some reductions in strengthmay be tolerable in view of other benefits of air, such asimproved workability. Reductions in strength becomemore significant in higher-strength mixes, as illustrated inFig. 8-15. In lower-cement-content, harsh mixes, strengthis generally increased by entrainment of air in properamounts due to the reduced water-cement ratio andimproved workability. For moderate to high-strength con-crete, each percentile of increase in entrained air reducesthe compressive strength about 2% to 9% (Cordon 1946,Klieger 1952, Klieger 1956, Whiting and Nagi 1998, andPinto and Hover 2001). Actual strength varies and isaffected by the cement source, admixtures, and other con-crete ingredients.

Attainment of high strength with air-entrained con-crete may be difficult at times. Even though a reduction inmixing water is associated with air entrainment, mixtureswith high cement contents require more mixing waterthan lower-cement-content mixtures; hence, the increasein strength expected from the additional cement is offsetsomewhat by the additional water. Water reducers canoffset this effect.

Workability

Entrained air improves the workability of concrete. It isparticularly effective in lean (low cement content) mixesthat otherwise might be harsh and difficult to work. In onestudy, an air-entrained mixture made with natural aggre-gate, 3% air, and a 37-mm (11⁄2-in.) slump had about thesame workability as a non-air-entrained concrete with 1%air and a 75-mm (3-in.) slump, even though less cementwas required for the air-entrained mix (Cordon 1946).Workability of mixes with angular and poorly gradedaggregates is similarly improved.

Because of improved workability with entrained air,water and sand content can be reduced significantly (Fig.8-13). A volume of air-entrained concrete requires lesswater than an equal volume of non-air-entrained concreteof the same consistency and maximum size aggregate.Freshly mixed concrete containing entrained air is cohe-sive, looks and feels fatty or workable, and can usually behandled with ease; on the other hand, high air contentscan make a mixture sticky and more difficult to finish.Entrained air also reduces segregation and bleeding infreshly mixed and placed concrete.

AIR-ENTRAINING MATERIALS

The entrainment of air in concrete can be accomplished byadding an air-entraining admixture at the mixer, by usingan air-entraining cement, or by a combination of these

136


10 2 3 4 5 6 7 8 9

40

30

20

10

0

5

4

3

2

1

6


Com

pres

sive

str

engt

h, M

Pa

Com

pres

sive

str

engt

h, 1

000

psi

364 kg/m3 (613 lb/yd3)

308 kg/m3 (519 lb/yd3)

252kg/m3 (425 lb/yd3)

150 x 300-mm (6 x 12-in.) cylinders

Fig. 8-15. Relationship between air content and 28-daycompressive strength for concrete at three cement con-tents. Water content was reduced with increased air contentto maintain a constant slump (Cordon 1946).

70 10

8

6

60

50

400 1 2 3 4 5 6 7


Com

pres

sive

stre

ngth

at 9

0 da

ys, M

Pa

Com

pres

sive

stre

ngth

at 9

0 da

ys, 1

000

psi

0.250.300.350.400.450.50


Fig. 8-14. Relationship between compressive strength at 90days and air content (Pinto and Hover 2001).

60

40

30

20

10

0

75

50

25

0

100

80

60

40

20

0

2.0

1.5

1.0

0.5

0

250 350 500Cement content, kg/m3

Cement content, lb/yd3W

ater

red

uctio

n, k

g/m

3

Wat

er r

educ

tion,

lb/y

d3S

and

redu

ctio

n, ft

3 /yd

3

San

d re

duct

ion,

dm

3 /m

3

300

400 600 800

400 400

Cement content, lb/yd3

400 600 800

250 350 500Cement content, kg/m3

300 400 400

8% air

6

8% air

6

4

2

4

2

Fig. 8-13. Reduction of water and sand content obtained atvarious levels of air and cement contents (Gilkey 1958).

methods. Regardless of the method used, adequate con-trol and monitoring is required to ensure the proper aircontent at all times.

Numerous commercial air-entraining admixtures,manufactured from a variety of materials, are available.Most air-entraining admixtures consist of one or more ofthe following materials: wood resin (Vinsol resin), sul-fonated hydrocarbons, fatty and resinous acids, and syn-thetic materials. Chemical descriptions and performancecharacteristics of common air-entraining agents are shownin Table 8-3. Air-entraining admixtures are usually liquidsand should not be allowed to freeze. Admixtures addedat the mixer should conform to ASTM C 260 (AASHTOM 154).

Air-entraining cements comply with ASTM C 150 andC 595 (AASHTO M 85 and M 240). To produce such ce-ments, air-entraining additions conforming to ASTM C 226are interground with the cement clinker during manufac-ture. Air-entraining cements generally provide an ade-quate amount of entrained air to meet most job conditions;however, a specified air content may not necessarily beobtained in the concrete. If an insufficient volume of air isentrained, it may also be necessary to add an air-entraining admixture at the mixer.

Each method of entraining air has certain advantages.On jobs where careful control is not practical, air-entraining cements are especially useful to ensure that asignificant portion of the required air content will alwaysbe obtained. They eliminate the possibility of human ormechanical error that can occur when adding an admix-ture during batching. With air-entraining admixtures, the

volume of entrained air can be readily adjusted to meetjob conditions by changing the amount of admixtureadded at the mixer.

Variations in air content can be expected with varia-tions in aggregate proportions and gradation, mixing time,temperature, and slump. The order of batching and mixingconcrete ingredients when using an air-entraining admix-ture has a significant influence on the amount of airentrained; therefore, consistency in batching is needed tomaintain adequate control.

When entrained air is excessive, it can be reduced byusing one of the following defoaming (air-detraining)agents: tributyl phosphate, dibutyl phthalate, octyl alcohol,water-insoluble esters of carbonic acid and boric acid, andsilicones. Only the smallest possible dosage of defoamingagent should be used to reduce the air content to the speci-fied limit. An excessive amount might have adverse effectson concrete properties (Whiting and Stark 1983).

FACTORS AFFECTING AIR CONTENT

Cement

As cement content increases, the air content decreases for aset dosage of air-entraining admixture per unit of cementwithin the normal range of cement contents (Fig. 8-16). Ingoing from 240 to 360 kilogram of cement per cubic meter(400 to 600 lb of cement per cubic yard), the dosage ratemay have to be doubled to maintain a constant air content.However, studies indicate that when this is done the air-void spacing factor generally decreases with an increase in

137


Classification Chemical description Notes and performance characteristicsWood derived acid salts Alkali or alkanolamine salt of:Vinsol® resin A mixture of tricyclic acids, Quick air generation. Minor air gain with initial mixing. Air

phenolics, and terpenes. loss with prolonged mixing. Mid-sized air bubbles formed.Compatible with most other admixtures.

Wood rosin Tricyclic acids-major component. Same as above.Tricyclic acids-minor component.

Tall oil Fatty acids-major component. Slower air generation. Air may increase with prolongedTricyclic acids-minor component. mixing. Smallest air bubbles of all agents. Compatible

with most other admixtures.Vegetable oil acids Coconut fatty acids, alkanolamine salt. Slower air generation than wood rosins. Moderate air

loss with mixing. Coarser air bubbles relative to woodrosins. Compatible with most other admixtures.

Synthetic detergents Alkyl-aryl sulfonates and sulfates Quick air generation. Minor air loss with mixing. Coarser(e.g., sodium bubbles. May be incompatible with some HRWR. Alsododecylbenzenesulfonate). applicable to cellular concretes.

Synthetic workability aids Alkyl-aryl ethoxylates. Primarily used in masonry mortars.Miscellaneous Alkali-alkanolamine acid salts All these are rarely used as concrete air-entraining

of lignosulfonate. agents in current practice.Oxygenated petroleum residues.Proteinaceous materials.Animal tallows.

Table 8-3. Classification and Performance Characteristics of Common Air-Entraining Admixtures(Whiting and Nagi 1998)

the amount of fine aggregate causes more air to beentrained for a given amount of air-entraining cement oradmixture (more air is also entrapped in non-air-entrained concrete).

Fine-aggregate particles passing the 600 µm to 150 µm(No. 30 to No. 100) sieves entrap more air than either veryfine or coarser particles. Appreciable amounts of materialpassing the 150 µm (No. 100) sieve will result in a signifi-cant reduction of entrained air.

Fine aggregates from different sources may entrapdifferent amounts of air even though they have identicalgradations. This may be due to differences in shape andsurface texture or contamination by organic materials.

Mixing Water and Slump

An increase in the mixing water makes more water avail-able for the generation of air bubbles, thereby increasingthe air content as slumps increase up to about 150 or175 mm (6 or 7 inches). An increase in the water-cementratio from 0.4 to 1.0 can increase the air content by fourpercentage points. A portion of the air increase is due tothe relationship between slump and air content. Air con-tent increases with slump even when the water-cementratio is held constant. The spacing factor, ¿, of the air-voidsystem also increases, that is, the voids become coarser athigher water-cement ratios, thereby reducing concretefreeze-thaw durability (Stark 1986).

The addition of 5 kg of water per cubic meter (8.4 lbsof water per cubic yard) of concrete can increase the slumpby 25 mm (one inch). A 25-mm (1-in.) increase in slump in-creases the air content by approximately one-half to one

cement content; and for a given air content the specific sur-face increases, thus improving durability.

An increase in cement fineness will result in adecrease in the amount of air entrained. Type III cement, avery finely ground material, may require twice as muchair-entraining agent as a Type I cement of normal fineness.

High-alkali cements may entrain more air than lowalkali cements with the same amount of air-entrainingmaterial. A low-alkali cement may require 20% to 40%(occasionally up to 70%) more air-entraining agent than ahigh-alkali cement to achieve an equivalent air content.Precautions are therefore necessary when using more thanone cement source in a batch plant to ensure that properadmixture requirements are determined for each cement(Greening 1967).

Coarse Aggregate

The size of coarse aggregate has a pronounced effect onthe air content of both air-entrained and non-air-entrainedconcrete, as shown in Fig. 8-16. There is little change in aircontent when the size of aggregate is increased above37.5 mm (11⁄2 in.).

Fine Aggregate

The fine-aggregate content of a mixture affects the per-centage of entrained air. As shown in Fig. 8-17, increasing

138


Air

cont

ent,

perc

ent

6

5

4

3

2

1

020 24 28 32 36 40 44


Non-air-entrained concrete(entrapped air only)

Cement: Type I – 280 to 335 kg/m3 (470 to 565 lb/yd3)Slump: 80 to 100 mm (3 to 5 in.)

Fine aggregate content, percent of total aggregate

Fig. 8-17. Relationship between percentage of fine aggre-gate and air content of concrete. PCA Major Series 336.

Air

cont

ent,

perc

ent

12

10

8

6

4

2

09.5 12.5 19.0 25.0 37.5 50 63

3/8 1/2 3/4 1 11/2 2 21/2

Maximum-size aggregate, mm

Maximum-size aggregate, in.

222 kg/m3 (375 lb/yd3)

306 kg/m3 (515 lb/yd3)

388 kg/m3 (655 lb/yd3)

222 kg/m3 (375 lb/yd3)

388 kg/m3 (655 lb/yd3)

Air-entrained concreteNon-air-entrained concrete(entrapped air only)

Cement: Type ISlump: 50 to 80 mm (2 to 3 in.)

Fig. 8-16. Relationship between aggregate size, cementcontent, and air content of concrete. The air-entrainingadmixture dosage per unit of cement was constant for air-entrained concrete. PCA Major Series 336.

Por

tland

cem

ent

Sup

plem

enta

ry c

emen

titio

us m

ater

ials

Che

mic

al a

dmix

ture

sA

ggre

gate

percentage point for concretes with a low-to-moderateslump and constant air-entraining admixture dosage.However, this approximation is greatly affected by con-crete temperature, slump, and the type and amount ofcement and admixtures present in the concrete. A low-slump concrete with a high dosage of water-reducing andair-entraining admixtures can undergo large increases in

slump and air content with a small addition of water. Onthe other hand, a very fluid concrete mixture with a 200 to250-mm (8 to 10-in.) slump may lose air with the additionof water. Refer to Tables 8-4 and 8-5 for more information.

The mixing water used may also affect air content.Algae-contaminated water increases air content. Highlyalkaline wash water from truck mixers can affect air con-

139


Characteristic/Material Effects Guidance

Alkali content Air content increases with increase Changes in alkali content or cement source requirein cement alkali level. that air-entraining agent dosage be adjusted.

Less air-entraining agent dosage Decrease dosage as much as 40% for high-alkalineeded for high-alkali cements. cements.

Air-void system may be more unstablewith some combinations of alkali leveland air-entraining agent used.

Fineness Decrease in air content with increased Use up to 100% more air-entraining admixture forfineness of cement. very fine (Type III) cements. Adjust admixture if

cement source or fineness changes.

Cement content in Decrease in air content with increase Increase air-entraining admixture dosage rate asmixture in cement content. cement content increases.

Smaller and greater number of voidswith increased cement content.

Contaminants Air content may be altered by contam- Verify that cement meets ASTM C 150 (AASHTO M 85)ination of cement with finish mill oil. requirements on air content of test mortar.

Fly ash Air content decreases with increase in Changes in LOI or fly ash source require that air-loss on ignition (carbon content). entraining admixture dosage be adjusted.

Perform “foam index” test to estimate increase indosage.

Air-void system may be more unstable Prepare trial mixes and evaluate air-void systems.with some combinations of fly ash/cement/air-entraining agents.

Ground granulated Decrease in air content with increased Use up to 100% more air-entraining admixture forblast-furnace slag fineness of GGBFS. finely ground slags.Silica fume Decrease in air content with increase Increase air-entraining admixture dosage up to 100%

in silica fume content. for fume contents up to 10%.Metakaolin No apparent effect. Adjust air-entraining admixture dosage if needed.

Water reducers Air content increases with increases in Reduce dosage of air-entraining admixture.dosage of lignin-based materials.

Select formulations containing air-detraining agents.Spacing factors may increase when Prepare trial mixes and evaluate air-void systems.water-reducers used.

Retarders Effects similar to water-reducers. Adjust air-entraining admixture dosage.Accelerators Minor effects on air content. No adjustments normally needed.High-range water Moderate increase in air content when Only slight adjustments needed.reducers (Plasticizers) formulated with lignosulfonate.

Spacing factors increase. No significant effect on durability.

Maximum size Air content requirement decreases Decrease air content.with increase in maximum size.Little increase over 37.5 mm (11⁄2 in.)maximum size aggregate.

Sand-to-total aggregate Air content increases with increased Decrease air-entraining admixture dosage for ratio sand content. mixtures having higher sand contents.Sand grading Middle fractions of sand promote air- Monitor gradation and adjust air-entraining admixture

entrainment. dosage accordingly.

Table 8-4. Effect of Mixture Design and Concrete Constituents on Control of Air Content in Concrete

140


Tran

spor

t an

d de

liver

yP

rodu

ctio

n pr

oced

ures

Procedure/Variable Effects GuidanceBatching sequence Simultaneous batching lowers air Add air-entraining admixture with initial water or

content. on sand.Cement-first raises air content.

Mixer capacity Air increases as capacity is approached. Run mixer close to full capacity. Avoid overloading.Mixing time Central mixers: air content increases Establish optimum mixing time for particular mixer.

up to 90 sec. of mixing.Truck mixers: air content increases Avoid overmixing.with mixing.Short mixing periods (30 seconds) Establish optimum mixing time (about 60 seconds).reduce air content and adversely affectair-void system.

Mixing speed Air content gradually increases up to Follow truck mixer manufacturer recommendations.approx. 20 rpm.Air may decrease at higher mixing Maintain blades and clean truck mixer.speeds.

Admixture metering Accuracy and reliability of metering Avoid manual-dispensing or gravity-feed systemssystem will affect uniformity of air and timers. Positive-displacement pumps interlockedcontent. with batching system are preferred.

Transport and delivery Some air (1% to 2%) normally lost Normal retempering with water to restore slump willduring transport. restore air.Loss of air in nonagitating equipment If necessary, retemper with air-entraining admixtureis slightly higher. to restore air.

Dramatic loss in air may be due to factors other thantransport.

Haul time and agitation Long hauls, even without agitation, Optimize delivery schedules. Maintain concretereduce air, especially in hot weather. temperature in recommended range.

Retempering Regains some of the lost air. Retemper only enough to restore workability. AvoidDoes not usually affect the air-void addition of excess water.system. Higher admixture dosage is needed for jobsiteRetempering with air-entraining ad- admixture additions.mixtures restores the air-void system.

Table 8-5. Effect of Production Procedures, Construction Practices, and Environment on Control of AirContent in Concrete

Mix

wat

er a

nd s

lum

p

Characteristic/Material Effects GuidanceWater chemistry Very hard water reduces air content. Increase air entrainer dosage.

Batching of admixture into concrete Avoid batching into wash water.wash water decreases air.Algae growth may increase air.

Water-to-cement ratio Air content increases with increased Decrease air-entraining admixture dosage as waterwater to cement ratio. to cement ratio increases.

Slump Air increases with slumps up to about Adjust air-entraining admixture dosages for slump.150 mm (6 in.).Air decreases with very high slumps. Avoid addition of water to achieve high-slump con-

crete.Difficult to entrain air in low-slump Use additional air-entraining admixture; up to ten concretes. times normal dosage.

Table 8-4. Effect of Mixture Design and Concrete Constituents on Control of Air Content in Concrete(Continued)

tents. The effect of water hardness in most municipalwater supplies is generally insignificant; however, veryhard water from wells, as used in rural communities, maydecrease the air content in concrete.

Slump and Vibration

The effect of slump and vibration on the air content of con-crete is shown in Fig. 8-18. For a constant amount of air-entraining admixture, air content increases as slumpincreases up to about 150 or 175 mm (6 or 7 inches); then itbegins to decrease with further increases in slump. At allslumps, however, even 15 seconds of vibration (the ACI 309limit) will cause a considerable reduction in air content.Prolonged vibration of concrete should be avoided.

The greater the slump, air content, and vibration time,the larger the percentage of reduction in air contentduring vibration (Fig. 8-18). However, if vibration is prop-erly applied, little of the intentionally entrained air is lost.The air lost during handling and moderate vibration con-sists mostly of the larger bubbles that are usually undesir-able from the standpoint of strength. While the averagesize of the air voids is reduced, the air-void spacing factorremains relatively constant.

Internal vibrators reduce air content more thanexternal vibrators. The air loss due to vibration increasesas the volume of concrete is reduced or the vibration fre-quency is significantly increased. Lower vibration fre-quencies (8000 vpm) have less effect on spacing factors

141


Air

cont

ent,

perc

ent

9.0

8.0

7.0

6.0

5.0

4.0

3.0

2.0

1.00 10 20 30 40 50

25-mm (1-in.) immersion-type vibrator.All mixes contained same amountof air-entraining admixture.

137-mm (5.4-in.) slump



Vibration time, seconds

Fig. 8-18. Relationship between slump, duration of vibra-tion, and air content of concrete (Brewster 1949).

Pla

cem

ent

tech

niqu

esFi

nish

ing

and

envi

ronm

ent

Procedure/Variable Effects GuidanceBelt conveyors Reduces air content by an average Avoid long conveyed distance if possible.

of 1%. Reduce the free-falling effect at the end of conveyor.Pumping Reduction in air content ranges from Use of proper mix design provides a stable air-void

2% to 3%. system.Does not significantly affect air-void Avoid high slump, high air content concrete.system. Keep pumping pressure as low as possible.Minimum effect on freeze-thaw Use loop in descending pump line.resistance.

Shotcrete Generally reduces air content in wet- Air content of mix should be at high end of targetprocess shotcrete. zone.

Internal vibration Air content decreases under prolonged Do not overvibrate. Avoid high-frequency vibratorsvibration or at high frequencies. (greater than 10,000 vpm). Avoid multiple passes of

vibratory screeds.Proper vibration does not influence the Closely spaced vibrator insertion is recommendedair-void system. for better consolidation.

Finishing Air content reduced in surface layer by Avoid finishing with bleed water still on surface.excessive finishing. Avoid overfinishing. Do not sprinkle water on surface

prior to finishing. Do not steel trowel exterior slabs.Temperature Air content decreases with increase in Increase air-entraining admixture dosage as temper-

temperature. ature increases.Changes in temperature do not signifi-cantly affect spacing factors.

Table 8-5. Effect of Production Procedures, Construction Practices, and Environment on Control of AirContent in Concrete (Continued)

concrete increases, particularly as slump is increased. Thiseffect is especially important during hot-weather con-creting when the concrete might be quite warm. Adecrease in air content can be offset when necessary byincreasing the quantity of air-entraining admixture.

In cold-weather concreting, the air-entraining admix-ture may lose some of its effectiveness if hot mix water isused during batching. To offset this loss, such admixturesshould be added to the batch after the temperature of theconcrete ingredients have equalized.

Although increased concrete temperature duringmixing generally reduces air volume, the spacing factorand specific surface are only slightly affected.

Supplementary Cementitious Materials

The effect of fly ash on the required dosage of air-entrainingadmixtures can range from no effect to an increase in dosageof up to five times the normal amount (Gebler and Klieger1986). Large quantities of slag and silica fume can double thedosage of air-entraining admixtures (Whiting and Nagi 1998).

Admixtures and Coloring Agents

Coloring agents such as carbon black usually decrease theamount of air entrained for a given amount of admixture.This is especially true for coloring materials withincreasing percentages of carbon (Taylor 1948).

Water-reducing and set-retarding admixtures gener-ally increase the efficiency of air-entraining admixtures by50% to 100%; therefore, when these are used, less air-entraining admixture will usually give the desired air con-tent. Also, the time of addition of these admixtures intothe mix affects the amount of entrained air; delayed addi-tions generally increasing air content.

Set retarders may increase the air-void spacing in con-crete. Some water-reducing or set-retarding admixtures arenot compatible with some air-entraining admixtures. Ifthey are added together to the mixing water before beingdispensed into the mixer, a precipitate may form. This willsettle out and result in large reductions in entrained air.The fact that some individual admixtures interact in thismanner does not mean that they will not be fully effectiveif dispensed separately into a batch of concrete.

Superplasticizers (high-range water reducers) mayincrease or decrease the air content of a concrete mixturebased on the admixture’s chemical formulation and theslump of the concrete. Naphthalene-based superplasti-cizers tend to increase the air content while melamine-based materials may decrease or have little effect on aircontent. The normal air loss in flowing concrete duringmixing and transport is about 2 to 4 percentage points(Whiting and Dziedzic 1992).

Superplasticizers also affect the air-void system ofhardened concrete by increasing the general size of theentrained air voids. This results in a higher-than-normal

and air contents than high vibration frequencies (14,000vpm). High frequencies can significantly increase spacingfactors and decrease air contents after 20 seconds of vibra-tion (Brewster 1949 and Stark 1986).

For pavements, specified air contents and uniform airvoid distributions can be achieved by operating withinpaving machine speeds of 1.22 to 1.88 meters per minute(4 to 6 feet per minute) and with vibrator frequencies of5,000 to 8,000 vibrations per minute. The most uniformdistribution of air voids throughout the depth of concrete,in and out of the vibrator trails, is obtained with the com-bination of a vibrator frequency of approximately 5,000 vi-brations per minute and a slipform paving machineforward track speeds of 1.22 meters per minute (4 feet perminute). Higher frequencies of speeds singularly or incombination can result in discontinuities and lack of re-quired air content in the upper portion of the concretepavement. This in turn provides a greater opportunity forwater and salt to enter the pavement and reduce the dura-bility and life of the pavement (Cable, McDaniel,Schlorholtz, Redmond, and Rabe 2000).

Concrete Temperature

Temperature of the concrete affects air content, as shownin Fig. 8-19. Less air is entrained as the temperature of the

142


Air

cont

ent,

perc

ent

7

6

5

4

3

2

1

0

50 60 70 80 90

10 15 20 25 30 355Concrete temperature, °C

Concrete temperature, °F

125-mm (5-in.) slump

175-mm (7-in.) slump

75-mm (3-in.) slump

25-mm (1-in.) slump

Cement: 335 kg/m3 (565 lb/yd3)Aggregate: 37.5-mm (11/2-in.) max. size

Fig. 8-19. Relationship between temperature, slump, and aircontent of concrete. PCA Major Series 336 and Lerch 1960.

spacing factor, occasionally higher than what may be con-sidered desirable for freeze-thaw durability. However,tests on superplasticized concrete with slightly higherspacing factors have indicated that superplasticized con-cretes have good freeze-thaw durability. This may be dueto the reduced water-cement ratio often associated withsuperplasticized concretes.

A small quantity of calcium chloride is sometimesused in cold weather to accelerate the hardening of con-crete. It can be used successfully with air-entrainingadmixtures if it is added separately in solution form to themix water. Calcium chloride will slightly increase air con-tent. However, if calcium chloride comes in direct contactwith some air-entraining admixtures, a chemical reactioncan take place that makes the admixture less effective.Nonchloride accelerators may increase or decrease aircontent, depending upon the individual chemistry of theadmixture, but they generally have little effect onair content.

Mixing Action

Mixing action is one of the most important factors in theproduction of entrained air in concrete. Uniform distribu-tion of entrained air voids is essential to produce scale-resistant concrete; nonuniformity might result frominadequate dispersion of the entrained air during shortmixing periods. In production of ready mixed concrete, itis especially important that adequate and consistentmixing be maintained at all times.

The amount of entrained air varies with the type andcondition of the mixer, the amount of concrete beingmixed, and the rate and duration of mixing. The amountof air entrained in a given mixture will decrease appre-ciably as the mixer blades become worn, or if hardenedconcrete is allowed to accumulate in the drum or on theblades. Because of differences in mixing action and time,concretes made in a stationary mixer and those made in atransit mixer may differ significantly in amounts of airentrained. The air content may increase or decrease whenthe size of the batch departs significantly from the ratedcapacity of the mixer. Little air is entrained in very smallbatches in a large mixer; however, the air content increasesas the mixer capacity is approached.

Fig. 8-20 shows the effect of mixing speed and dura-tion of mixing on the air content of freshly mixed con-cretes made in a transit mixer. Generally, more air isentrained as the speed of mixing is increased up to about20 rpm, beyond which air entrainment decreases. In thetests from which the data in Fig. 8-20 were derived, the aircontent reached an upper limit during mixing and agradual decrease in air content occurred with prolongedmixing. Mixing time and speed will have different effectson the air content of different mixes. Significant amountsof air can be lost during mixing with certain mixtures andtypes of mixing equipment.

Fig. 8-21 shows the effect of continued mixer agita-tion on air content. The changes in air content with pro-longed agitation can be explained by the relationshipbetween slump and air content. For high-slump con-cretes, the air content increases with continued agitationas the slump decreases to about 150 or 175 mm (6 or 7 in.).Prolonged agitation will decrease slump further anddecrease air content. For initial slumps lower than150 mm (6 in.), both the air content and slump decreasewith continued agitation. When concrete is retempered(the addition of water and remixing to restore originalslump), the air content is increased; however, after4 hours, retempering is ineffective in increasing air con-tent. Prolonged mixing or agitation of concrete is accom-panied by a progressive reduction in slump.

143


Air

cont

ent,

perc

ent

5

4

3

2

1

0100 20 30 40 50 60

11 rpm

4 rpm

Cement: 305 kg/m3 (510 lb/yd3)Mixer: 4 m3 (6 yd3) transit mixerMixing time: starts after charging completed

Mixing time, minutes

Fig. 8-20. Relationship between mixing time and air contentof concrete. PCA Major Series 336.

Air

cont

ent,

perc

ent

8

7

6

5

410 20 30 40 50 60 70 80 90

100-mm (4-in.) initial slump

225-mm (9-in.) initial slump

Agitating speeds: 2 or 4 rpmTransit mixer: 4.5 and 6.1 m3 (6 and 8 yd3)Initial mixing: 70 rev. at 10 rpm

Agitating time, minutes (after initial mixing)

Fig. 8-21. Relationship between agitating time, air content,and slump of concrete. PCA Major Series 336.

When aggregates larger than 50 mm (2 in.) are used,they should be removed by hand and the effect oftheir removal calculated in arriving at the total aircontent.

3. Gravimetric method (ASTM C 138 or AASHTO T 121,Standard Test Method for Unit Weight, Yield, and AirContent [Gravimetric] of Concrete)—requires accurateknowledge of relative density and absolute volumesof concrete ingredients.

4. Chace air indicator (AASHTO T 199, Standard Methodof Test for Air Content of Freshly Mixed Concrete by theChace Indicator)—a very simple and inexpensive wayto check the approximate air content of freshly mixedconcrete. This pocket-size device tests a mortar samplefrom the concrete. This test is not a substitute, however,for the more accurate pressure, volumetric, and gravi-metric methods.

The foam-index test can be used to measure the rela-tive air-entraining admixture requirement for concretescontaining fly ash-cement combinations (Gebler andKlieger 1983).

Transporting and Handling

Generally, some air—approximately 1 to 2 percentagepoints—is lost during transportation of concrete from themixer to the jobsite. The stability of the air content duringtransport is influenced by several variables including con-crete ingredients, haul time, amount of agitation or vibra-tion during transport, temperature, slump, and amount ofretempering.

Once at the jobsite, the concrete air content remainsessentially constant during handling by chute discharge,wheelbarrow, power buggy, and shovel. However, con-crete pumping, crane and bucket, and conveyor-belt han-dling can cause some loss of air, especially withhigh-air-content mixtures. Pumping concrete can cause aloss of up to 3 percentage points of air (Whiting and Nagi1998).

Finishing

Proper screeding, floating, and general finishing practicesshould not affect the air content. McNeal and Gay (1996)and Falconi (1996) demonstrated that the sequence andtiming of finishing and curing operations are critical to sur-face durability. Overfinishing (excessive finishing) mayreduce the amount of entrained air in the surface region ofslabs—thus making the concrete surface vulnerable toscaling. However, as shown in Fig. 8-22, early finishingdoes not necessarily affect scale resistance unless bleedwater is present (Pinto and Hover 2001). Concrete to beexposed to deicers should not be steel troweled.

TESTS FOR AIR CONTENT

Four methods for determining the air content of freshlymixed concrete are available. Although they measure onlytotal air volume and not air-void characteristics, it hasbeen shown by laboratory tests that these methods areindicative of the adequacy of the air-void system.

Acceptance tests for air content of freshly mixed con-crete should be made regularly for routine control pur-poses. Samples should be obtained and tested inaccordance with ASTM C 172 (AASHTO T 141).

Following are methods for determining the air con-tent of freshly mixed concrete:

1. Pressure method (ASTM C 231 or AASHTO T 152,Standard Test Method for Air Content of Freshly MixedConcrete by the Pressure Method)—practical for field-testing all concretes except those made with highlyporous and lightweight aggregates.

2. Volumetric method (ASTM C 173 or AASHTO T 196,Standard Test Method for Air Content of Freshly MixedConcrete by the Volumetric Method)—practical for field-testing all concretes, but particularly useful for con-cretes made with lightweight and porous aggregates.

144


5

3

4

2

1

0

Water-to-cement ratio

Vis

ual r

atin

g

0.50 0.45 0.40 0.35 0.30 0.25

Time offinishing

early on-time

Bleed water

3

4

5

2

1

0


Vis

ual r

atin

g

0.50 0.45 0.40 0.35 0.30 0.25

Time offinishing

early on-time

Fig. 8-22. Effect of early finishing—magnesium floating 20minutes after casting—on scale resistance for: (top) 6% air-entrained concrete; (bottom) non-air-entrained concrete.

The air-void characteristics of hardened concrete canbe determined by ASTM C 457 methods. This test is usedto determine void spacing factor, specific surface of voids,and number of voids per length of traverse.

Air-Void Analysis of Fresh Concrete

The conventional methods for analyzing air in fresh con-crete, such as the pressure method noted above, measurethe total air content only; consequently, they provide noinformation about the parameters that determine thequality of the air-void system. These parameters—the sizeand number of voids and spacing between them—can bemeasured on polished samples of hardened concrete(ASTM C 457); but the result of such analysis will only beavailable several days after the concrete has hardened.Therefore, test equipment called an air-void analyzer(AVA) has been developed to determine the standardASTM C 457 air-void parameters in fresh samples of air-entrained concrete (Fig. 8-23). The test apparatus deter-mines the volume and size distributions of entrained airvoids; thus an estimation of the spacing factor, specificsurface, and total amount of entrained air can be made.

In this test method, air bubbles from a sample of freshconcrete rise through a viscous liquid, enter a column ofwater above it, then rise through the water and collectunder a submerged buoyancy recorder (Fig. 8-24). The vis-cous liquid retains the original bubble sizes. Large bubbles

rise faster than small ones through the liquids. The changein buoyancy is recorded as a function of time and can berelated to the number of bubbles of different size.

Fresh concrete samples can be taken at the ready mixplant and on the jobsite. Testing concrete before and afterplacement into forms can verify how the applied methodsof transporting, placing, and consolidation affect the air-void system. Since the samples are taken on fresh con-crete, the air content and air-void system can be adjustedduring production.

Currently, no standard exists for this method. TheAVA was not developed for measuring the total air-con-tent of concrete, and because of the small sample size, maynot give accurate results for this quantity. However, thisdoes not mean the AVA is not useful as a method forassessing the quality of the air-void system; it gives goodresults in conjunction with traditional methods for meas-uring air content (Aarre 1998).

RECOMMENDED AIR CONTENTS

The amount of air to be used in air-entrained concretedepends on a number of factors: (1) type of structure,(2) climatic conditions, (3) number of freeze-thaw cycles,(4) extent of exposure to deicers, and (5) the design life ofthe structure.

The ACI 318 building code states that concrete thatwill be exposed to moist freezing and thawing or deicerchemicals shall be air entrained with the target air contentof Table 8-6 for severe exposure. Furthermore, the waterto cementitious materials ratio should not exceed 0.45.ACI 318 allows a one percentage point reduction in targetair contents for concretes with strengths over 34 MPa(5,000 psi) and presumably very low water-cement ratios.

145

Chapter 8 ◆ Air-Entrained Concrete

Fig. 8-23. Equipment for the air-void analyzer. (67961)

Fig. 8-24. Air bubbles rising through liquids in column.(67962)

ACI 318 limits the amounts of pozzolans and slag—10% for silica fume, 25% for fly ash, 50% for slag—as partof the cementitious material for deicer exposures.However, mix designers should consult local practices asto allowable dosages to prevent frost and deicer damage.Combinations of materials without historical record canbe analyzed using ASTM C 666 (AASHTO T 161) andASTM C 672. Pinto and Hover (2001) evaluate the appli-cability of the ACI 318 requirements for frost resistance ofportland cement concrete mixtures with water to cementratios from 0.25 to 0.50. Fig. 8-26 illustrates the effect ofincreased air content with respect to aggregate size onreducing expansion due to saturated freezing andthawing; it emphasizes the need to follow the require-ments of Table 8-6 for severe exposure.

When entrained air is not required for protectionagainst freeze-thaw cycles or deicers, the target air con-tents for mild exposure given in Table 8-6 can be used.Higher air contents can also be used as long as the designstrength is achieved. As noted earlier, entrained air helpsto reduce bleeding and segregation and can improve theworkability of concrete.

More information on air-entrained concrete can befound in Whiting and Nagi (1998).

Fig. 8-25 illustrates how deicer-scaling resistance isimpacted by air content and low water to portland cementratios (strengths ranging from 40 to 59 MPa [5,800 to 8,600psi]). This illustrates that concretes with very low water toportland cement ratios are more frost and deicer resistant;hence, they may allow use of lower air contents. This rela-tionship (Fig. 8-25) was not established for concretes con-taining supplementary cementitious materials as theywere not studied (Pinto and Hover 2001).

146


Nominal maximum Air content, percent*

size aggregate, Severe Moderate Mildmm (in.) exposure** exposure† exposure††

<9.5 (3⁄8) 9 7 59.5 (3⁄8) 71⁄2 6 41⁄212.5 (1⁄2) 7 51⁄2 419.0 (3⁄4) 6 5 31⁄225.0 (1) 6 41⁄2 337.5 (11⁄2) 51⁄2 41⁄2 21⁄250 (2)‡ 5 4 275 (3)‡ 41⁄2 31⁄2 11⁄2

Table 8-6. Recommended Total Target Air Contentfor Concrete

* Project specifications often allow the air content of the concrete to bewithin -1 to +2 percentage points of the table target values.

** Concrete exposed to wet-freeze-thaw conditions, deicers, or otheraggressive agents.

† Concrete exposed to freezing but not continually moist, and not incontact with deicers or aggressive chemicals.

†† Concrete not exposed to freezing conditions, deicers, or aggressiveagents.

‡ These air contents apply to the total mix, as for the preceding aggre-gate sizes. When testing these concretes, however, aggregate largerthan 37.5 mm (11⁄2 in.) is removed by handpicking or sieving and aircontent is determined on the minus 37.5 mm (11⁄2 in.) fraction of mix.(Tolerance on air content as delivered applies to this value.)

3.0

2.0

1.0

0.0

0.6

0.4

0.2

0.01 32 5 6 74

Total air content, percent

Ave

rage

mas

s lo

ss a

t 40

cycl

es, k

g/m

2

Ave

rage

mas

s lo

ss a

t 40

cycl

es, l

b/ft2

0.400.350.300.25


ASTM C 672

Fig. 8-25. Measured mass loss after 40 cycles of deicersand freeze-thaw exposures at various air contents (Pintoand Hover 2001).

0.20

0.18

0.16

0.14

0.12

0.10

0.08

0.06

0.04

0.02

00 2 4 6 8 10 12 14

Exp

ansi

on, p

erce

nt

Freeze–thaw cycles: 300Specimens: 75 x 75 x 280-mm (3 x 3 x 111/4-in.) concrete prismsCement: Type I, 310 kg/m3

(517 lb/yd3)Slump: 50 to 75 mm (2 to 3 in.)

Maximum-size aggregate9.5-mm (3/8-in.)19.0-mm (3/4-in.)37.5-mm (11/2-in.)


Fig. 8-26. Relationship between air content and expansionof concrete test specimens during 300 cycles of freezingand thawing for various maximum aggregate sizes. Smalleraggregate sizes require more air (Klieger 1952).

REFERENCES

Aarre, Tine, “Air-Void Analyzer,” Concrete TechnologyToday, PL981, Portland Cement Association, http://www.portcement.org/pdf_files/PL981.pdf, April 1998, page 4.

ACI Committee 201, Guide to Durable Concrete, ACI 201.2R-92, reapproved 1997, ACI Committee 201 Report, Amer-ican Concrete Institute, Farmington Hills, Michigan, 1992.

ACI Committee 308, Standard Practice for Curing Concrete,ACI 308-92, reapproved 1997, ACI Committee 308 Report,American Concrete Institute, Farmington Hills, Mich-igan, 1992.

ACI Committee 309, Guide for Consolidation of Concrete,ACI 309R-96, ACI Committee 309 Report, American Con-crete Institute, Farmington Hills, Michigan, 1996.

ACI Committee 318, Building Code Requirements for Struc-tural Concrete and Commentary, ACI 318-02, ACI Commit-tee 318 Report, American Concrete Institute, FarmingtonHills, Michigan, 2002.

ACPA, Scale-Resistant Concrete Pavements, IS117, AmericanConcrete Pavement Association, Skokie, Illinois, 1996.

ASCE, “Entrained Air Voids in Concrete Help Prevent SaltDamage,” Civil Engineering, American Society of CivilEngineers, New York, May 1982.

Bates, A. A.; Woods, H.; Tyler, I. L.; Verbeck, G.; and Powers,T. C., “Rigid-Type Pavement,” Association of HighwayOfficials of the North Atlantic States, 28th AnnualConvention Proceedings, pages 164 to 200, March 1952.

Bloem, D. L., Air-Entrainment in Concrete, National Sandand Gravel Association and National Ready MixedConcrete Association, Silver Spring, Maryland, 1950.

Brewster, R. S., Effect of Vibration Time upon Loss of EntrainedAir from Concrete Mixes, Materials Laboratories Report No.C-461, Research and Geology Division, Bureau ofReclamation, Denver, November 25, 1949.

Brown, F. P., and Cady, P. D., “Deicer Scaling Mechanismsin Concrete,” Durability of Concrete, ACI SP-47, AmericanConcrete Institute, Farmington Hills, Michigan, 1975,pages 101 to 119.

Cable, J. K.; McDaniel, L.; Schlorholtz, S.; Redmond, D.;and Rabe, K., Evaluation of Vibrator Performance vs. ConcreteConsolidation and Air Void System, Serial No. 2398, PortlandCement Association, http://www.portcement.org/pdf_files/SN2398.pdf, 2000, 60 pages.

Cody, Rober D.; Cody, Anita M.; Spry, Paul G.; and Gan,Guo-Liang, “Concrete Deterioration by Deicing Salts: AnExperimental Study,” http://www.ctre.iastate.edu/pubs/semisesq/index.htm, Semisequicentennial TransportationConference Proceedings, Center for Transportation Researchand Education, Ames, Iowa, 1996.

Cordon, W. A., Entrained Air—A Factor in the Design ofConcrete Mixes, Materials Laboratories Report No. C-310,Research and Geology Division, Bureau of Reclamation,Denver, March 15, 1946.

Elfert, R. J., Investigation of the Effect of Vibration Time on theBleeding Property of Concrete With and Without Entrained Air,Materials Laboratories Report No. C-375, Research andGeology Division, Bureau of Reclamation, Denver,January 26, 1948.

Falconi, M. I., Durability of Slag Cement Concretes Exposedto Freezing and Thawing in the Presence of Deicers, Mastersof Science Thesis, Cornell University, Ithaca, New York,306 pages.

Gebler, S. H., and Klieger, P., Effect of Fly Ash on the Air-VoidStability of Concrete, Research and Development BulletinRD085, Portland Cement Association, http://www.portcement.org/pdf_files/RD085.pdf, 1983.

Gebler, Steven H., and Klieger, Paul, Effect of Fly Ash onDurability of Air-Entrained Concrete, Research and Develop-ment Bulletin RD090, Portland Cement Association, http://www.portcement.org/pdf_files/RD090.pdf, 1986

Gilkey, H. J., “Re-Proportioning of Concrete Mixtures forAir Entrainment,” Journal of the American Concrete Institute,Proceedings, vol. 29, no. 8, Farmington Hills, Michigan,February 1958, pages 633 to 645.

Gonnerman, H. F., “Durability of Concrete in EngineeringStructures,” Building Research Congress 1951, collectedpapers, Division No. 2, Section D, Building ResearchCongress, London, 1951, pages 92 to 104.

Gonnerman, H. F., Tests of Concretes Containing Air-Entraining Portland Cements or Air-Entraining MaterialsAdded to Batch at Mixer, Research Department BulletinRX013, Portland Cement Association, http://www.portcement.org/pdf_files/RX013.pdf, 1944.

Greening, Nathan R., Some Causes for Variation in RequiredAmount of Air-Entraining Agent in Portland Cement Mortars,Research Department Bulletin RX213, Portland CementAssociation, http://www.portcement.org/pdf_files/RX213.pdf, 1967.

Klieger, Paul, Air-Entraining Admixtures, Research Depart-ment Bulletin RX199, Portland Cement Association,http://www.portcement.org/pdf_files/RX199.pdf, 1966.

Klieger, Paul, Extensions to the Long-Time Study of CementPerformance in Concrete, Research Department BulletinRX157, Portland Cement Association, 1963.

Klieger, Paul, Further Studies on the Effect of Entrained Air onStrength and Durability of Concrete with Various Sizes ofAggregate, Research Department Bulletin RX077, PortlandCement Association, http://www.portcement.org/pdf_files/RX077.pdf, 1956.

Klieger, Paul, Studies of the Effect of Entrained Air on theStrength and Durability of Concretes Made with VariousMaximum Sizes of Aggregates, Research DepartmentBulletin RX040, Portland Cement Association, http://www.portcement.org/pdf_files/RX040.pdf, 1952.

Kretsinger, D. G., Effect of Entrained Air on Expansion ofMortar Due to Alkali-Aggregate Reaction, Materials Labor-atories Report No. C-425, Research and Geology Division,U. S. Bureau of Reclamation, Denver, February 16, 1949.

147

Chapter 8 ◆ Air-Entrained Concrete

South Dakota Department of Transportation, Investigationof Low Compressive Strength of Concrete in Paving, Precastand Structural Concrete, Study SD 1998-03, PCA Serial No.52002-17, Pierre, South Dakota, 2000.

Stanton, Thomas E., “Durability of Concrete Exposed toSea Water and Alkali Soils-California Experience,” Journalof the American Concrete lnstitute, Farmington Hills, Mich-igan, May 1948.

Stark, David C., Effect of Vibration on the Air-System andFreeze-Thaw Durability of Concrete, Research and Develop-ment Bulletin RD092, Portland Cement Association, http://www.portcement.org/pdf_files/RD092.pdf, 1986.

Stark, David, Longtime Study of Concrete Durability inSulfate Soils, Research and Development Bulletin RD086,Portland Cement Association, http://www.portcement.org/pdf_files/RD086.pdf, 1984.

Taylor, Thomas G., Effect of Carbon Black and Black Iron Oxideon Air Content and Durability of Concrete, Research De-partment Bulletin RX023, Portland Cement Association,http://www.portcement.org/pdf_files/RX023.pdf, 1948.

Verbeck, G. J., Field and Laboratory Studies of the SulphateResistance of Concrete, Research Department BulletinRX227, Portland Cement Association, http://www.portcement.org/pdf_files/RX227.pdf, 1967.

Verbeck, George, and Klieger, Paul, Studies of “Salt” Scalingof Concrete, Research Department Bulletin RX083, PortlandCement Association, http://www.portcement.org/pdf_files/RX083.pdf, 1956.

Walker, S., and Bloem, D. L., Design and Control of Air-Entrained Concrete, Publication No. 60, National ReadyMixed Concrete Association, Silver Spring, Maryland, 1955.

Wang, Kejin; Monteiro, Paulo J. M.; Rubinsky, Boris; andArav, Amir, “Microscopic Study of Ice Propagation inConcrete,” ACI Materials Journal, July-August 1996, Amer-ican Concrete Institute, Farmington Hills, Michigan, pages370 to 376.

Whiting, D., and Stark, D., Control of Air Content inConcrete, National Cooperative Highway Research Pro-gram Report No. 258 and Addendum, TransportationResearch Board and National Research Council, Wash-ington, D.C., May 1983.

Whiting, David A., and Nagi, Mohamad A., Manual onControl of Air Content in Concrete, EB116, National ReadyMixed Concrete Association and Portland CementAssociation, 1998, 42 pages.

Whiting, D., and Dziedzic, D., Effects of Conventional andHigh-Range Water Reducers on Concrete Properties, Researchand Development Bulletin RD107, Portland Cement Asso-ciation, 1992, 25 pages.

Woods, Hubert, Observations on the Resistance of Concrete toFreezing and Thawing, Research Department BulletinRX067, Portland Cement Association, http://www.portcement.org/pdf_files/RX067.pdf, 1954.

Lerch, William, Basic Principles of Air-Entrained Concrete,T-101, Portland Cement Association, 1960.

McNeal, F., and Gay, F., “Solutions to Scaling Concrete,”Concrete Construction, Addison, Illinois, March 1996, pages250 to 255.

Menzel, Carl A., and Woods, William M., An Investigationof Bond, Anchorage and Related Factors in Reinforced ConcreteBeams, Research Department Bulletin RX042, PortlandCement Association, 1952.

Mielenz, R. C.; Wokodoff, V. E.; Backstrom, J. E.; and Flack,H. L., “Origin, Evolution, and Effects of the Air-VoidSystem in Concrete. Part 1-Entrained Air in UnhardenedConcrete,” July 1958, “Part 2-Influence of Type andAmount of Air-Entraining Agent,” August 1958, “Part 3-Influence of Water-Cement Ratio and Compaction,”September 1958, and “Part 4-The Air-Void System in JobConcrete,” October 1958, Journal of the American ConcreteInstitute, Farmington Hills, Michigan, 1958.

Pigeon, M. and Pleau, R., Durability of Concrete in ColdClimates, E&FN Spon, New York, 1995, 244 pages.

Pinto, Roberto C. A., and Hover, Kenneth C., Frost andScaling Resistance of High-Strength Concrete, Research andDevelopment Bulletin RD122, Portland Cement Asso-ciation, 2001, 70 pages.

Powers, T. C., “The Mechanism of Frost Action inConcrete,” Stanton Walker Lecture Series on the MaterialsSciences, Lecture No. 3, National Sand and GravelAssociation and National Ready Mixed ConcreteAssociation, Silver Spring, Maryland, 1965a.

Powers, T. C., and Helmuth, R. A., Theory of Volume Changesin Hardened Portland Cement Paste During Freezing, ResearchDepartment Bulletin RX046, Portland Cement Association,http://www.portcement.org/pdf_files/RX046.pdf, 1953.

Powers, T. C., Basic Considerations Pertaining to Freezing andThawing Tests, Research Department Bulletin RX058,Portland Cement Association, http://www.portcement.org/pdf_files/RX058.pdf, 1955.

Powers, T. C., The Air Requirement of Frost-ResistantConcrete, Research Department Bulletin RX033, PortlandCement Association, http://www.portcement.org/pdf_files/RX033.pdf, 1949.

Powers, T. C., Topics in Concrete Technology:… (3) MixturesContaining Intentionally Entrained Air; (4) Characteristics ofAir-Void Systems, Research Department Bulletin RX174,Portland Cement Association, http://www.portcement.org/pdf_files/RX174.pdf, 1965.

Powers, T. C., Void Spacing as a Basis for Producing Air-Entrained Concrete, Research Department Bulletin RX049,Portland Cement Association, http://www.portcement.org/pdf_files/RX049.pdf, 1954

Sayward, John M., Salt Action on Concrete, Special Report84-25, U.S. Army Cold Regions Research and EngineeringLaboratory, Hanover, New Hampshire, August 1984.

148


The process of determining required and specifiable char-acteristics of a concrete mixture is called mix design.Characteristics can include: (1) fresh concrete properties;(2) required mechanical properties of hardened concretesuch as strength and durability requirements; and (3) theinclusion, exclusion, or limits on specific ingredients. Mixdesign leads to the development of a concrete specification.

Mixture proportioning refers to the process of deter-mining the quantities of concrete ingredients, using localmaterials, to achieve the specified characteristics of theconcrete. A properly proportioned concrete mix shouldpossess these qualities:

1. Acceptable workability of the freshly mixed concrete2. Durability, strength, and uniform appearance of the

hardened concrete3. Economy

Understanding the basic principles of mixture designis as important as the actual calculations used to establishmix proportions. Only with proper selection of materialsand mixture characteristics can the above qualities beobtained in concrete construction (Fig. 9-1) (Abrams 1918,Hover 1998, and Shilstone 1990).

CHAPTER 9

Designing and Proportioning Normal Concrete Mixtures

SELECTING MIX CHARACTERISTICS

Before a concrete mixture can be proportioned, mixturecharacteristics are selected based on the intended use ofthe concrete, the exposure conditions, the size and shapeof building elements, and the physical properties of theconcrete (such as frost resistance and strength) requiredfor the structure. The characteristics should reflect theneeds of the structure; for example, resistance to chlorideions should be verifiable and the appropriate testmethods specified.

Once the characteristics are selected, the mixture canbe proportioned from field or laboratory data. Since mostof the desirable properties of hardened concrete dependprimarily upon the quality of the cementitious paste, thefirst step in proportioning a concrete mixture is the selec-tion of the appropriate water-cementing materials ratiofor the durability and strength needed. Concrete mixturesshould be kept as simple as possible, as an excessivenumber of ingredients often make a concrete mixture dif-ficult to control. The concrete technologist should not,however, overlook the opportunities provided by modernconcrete technology.

Water-Cementing Materials Ratio andStrength Relationship

Strength (compressive or flexural) is the most universallyused measure for concrete quality. Although it is an impor-tant characteristic, other properties such as durability, per-meability, and wear resistance are now recognized as beingequal and in some cases more important, especially whenconsidering life-cycle design of structures.

Within the normal range of strengths used in concreteconstruction, the compressive strength is inversely relatedto the water-cement ratio or water-cementing materialsratio. For fully compacted concrete made with clean,sound aggregates, the strength and other desirable prop-

Fig. 9-1. Trial batching (in-set) verifies that a concretemixture meets design re-quirements prior to use inconstruction.(69899, 70008).

149

Strength

The specified compressive strength, ˘, at 28 days is thestrength that is expected to be equal to or exceeded by theaverage of any set of three consecutive strength tests. ACI318 requires for ˘ to be at least 17.5 MPa (2500 psi). Noindividual test (average of two cylinders) can be morethan 3.5 MPa (500 psi) below the specified strength. Spe-cimens must be cured under laboratory conditions for anindividual class of concrete (ACI 318). Some specificationsallow alternative ranges.

The average strength should equal the specifiedstrength plus an allowance to account for variations inmaterials; variations in methods of mixing, transporting,and placing the concrete; and variations in making,curing, and testing concrete cylinder specimens. Theaverage strength, which is greater than ˘, is called Â ; itis the strength required in the mix design. Requirementsfor Â are discussed in detail under “Proportioning” laterin this chapter. Tables 9-1 and 9-2 show strength require-ments for various exposure conditions.

erties of concrete under given job conditions are governedby the quantity of mixing water used per unit of cement orcementing materials (Abrams 1918).

The strength of the cementitious paste binder inconcrete depends on the quality and quantity of thereacting paste components and on the degree to which thehydration reaction has progressed. Concrete becomesstronger with time as long as there is moisture and a favor-able temperature available. Therefore, the strength at anyparticular age is both a function of the original water-cementitious material ratio and the degree to which thecementitious materials have hydrated. The importance ofprompt and thorough curing is easily recognized.

Differences in concrete strength for a given water-cementing materials ratio may result from: (1) changes inthe aggregate size, grading, surface texture, shape,strength, and stiffness; (2) differences in types and sourcesof cementing materials; (3) entrained-air content; (4) thepresence of admixtures; and (5) the length of curing time.

150


Table 9-1. Maximum Water-Cementitious Material Ratios and Minimum Design Strengths for Various ExposureConditions

Maximum water-cementitious material Minimum design compressive strength,Exposure condition ratio by mass for concrete f'c, MPa (psi)

Concrete protected from exposure to Select water-cementitious material ratio Select strength based on structuralfreezing and thawing, application of on basis of strength, workability, requirementsdeicing chemicals, or aggressive and finishing needssubstances

Concrete intended to have low permeability when exposed to water 0.50 28 (4000)

Concrete exposed to freezing and thawing in a moist condition or deicers 0.45 31 (4500)

For corrosion protection for reinforced concrete exposed to chlorides from

0.40 35 (5000)deicing salts, salt water, brackish water,seawater, or spray from these sources

Adapted from ACI 318 (2002).

Table 9-2. Requirements for Concrete Exposed to Sulfates in Soil or Water

Minimum designWater-soluble Maximum water- compressive

Sulfate sulfate (SO4) in soil, Sulfate (SO4) cementitious material strength,exposure percent by mass* in water, ppm* Cement type** ratio, by mass f'c, MPa (psi)

Negligible Less than 0.10 Less than 150 No special type required — —

Moderate† 0.10 to 0.20 150 to 1500 II, MS, IP(MS), IS(MS), P(MS), 0.50 28 (4000)I(PM)(MS), I(SM)(MS)

Severe 0.20 to 2.00 1500 to10,000 V, HS 0.45 31 (4500)

Very severe Over 2.00 Over 10,000 V, HS 0.40 35 (5000)

* Tested in accordance with the Method for Determining the Quantity of Soluble Sulfate in Solid (Soil and Rock) and Water Samples, Bureauof Reclamation, Denver, 1977.

** Cement Types II and V are in ASTM C 150 (AASHTO M 85), Types MS and HS in ASTM C 1157, and the remaining types are in ASTM C 595(AASHTO M 240). Pozzolans or slags that have been determined by test or service record to improve sulfate resistance may also be used.

† Seawater.

Flexural strength is sometimes used on paving proj-ects instead of compressive strength; however, flexuralstrength is avoided due to its greater variability. For moreinformation on flexural strength, see “Strength” in Chap-ter 1 and “Strength Specimens” in Chapter 16.

Water-Cementitious Material Ratio

The water-cementitious material ratio is simply the massof water divided by the mass of cementitious material(portland cement, blended cement, fly ash, slag, silicafume, and natural pozzolans). The water-cementitiousmaterial ratio selected for mix design must be the lowestvalue required to meet anticipated exposure conditions.Tables 9-1 and 9-2 show requirements for various expo-sure conditions.

When durability does not control, the water-cementi-tious materials ratio should be selected on the basis ofconcrete compressive strength. In such cases the water-cementitious materials ratio and mixture proportions for therequired strength should be based on adequate field data ortrial mixtures made with actual job materials to determinethe relationship between the ratio and strength. Fig. 9-2 orTable 9-3 can be used to select a water-cementitious mate-rials ratio with respect to the required average strength, Â,for trial mixtures when no other data are available.

In mix design, the water to cementitious materialsratio, W/CM, is often used synonymously with water tocement ratio (W/C); however, some specifications differen-tiate between the two ratios. Traditionally, the water tocement ratio referred to the ratio of water to portlandcement or water to blended cement.

Aggregates

Two characteristics of aggregates have an important influ-ence on proportioning concrete mixtures because theyaffect the workability of the fresh concrete. They are:

1. Grading (particle size and distribution)2. Nature of particles (shape, porosity, surface texture)

Grading is important for attaining an economical mix-ture because it affects the amount of concrete that can bemade with a given amount of cementitious materials andwater. Coarse aggregates should be graded up to thelargest size practical under job conditions. The maximumsize that can be used depends on factors such as the sizeand shape of the concrete member to be cast, the amountand distribution of reinforcing steel in the member, andthe thickness of slabs. Grading also influences the work-ability and placeability of the concrete. Sometimes mid-sized aggregate, around the 9.5 mm (3⁄8 in.) size, is lackingin an aggregate supply; this can result in a concrete with

151

Chapter 9 � Designing and Proportioning Normal Concrete Mixtures

0.3 0.4 0.5 0.6 0.7 0.8 0.9Water to cementitious materials ratio

60

50

40

30

20

10

0

8

6

4

2

0

28-d

ay c

ompr

essi

ve s

tren

gth,

MP

a

28-d

ay c

ompr

essi

ve s

tren

gth,

100

0 ps

i



Fig. 9-2. Approximate relationship between compressivestrength and water to cementing materials ratio for concreteusing 19-mm to 25-mm (3⁄4-in. to 1-in.) nominal maximumsize coarse aggregate. Strength is based on cylinders moistcured 28 days per ASTM C 31 (AASHTO T 23). Adapted fromTable 9-3, ACI 211.1, ACI 211.3, and Hover 1995.

Compressive Water-cementitious materials ratio by mass

strength at Non-air-entrained Air-entrained28 days, psi concrete concrete

7000 0.33 —6000 0.41 0.325000 0.48 0.404000 0.57 0.483000 0.68 0.592000 0.82 0.74

Table 9-3 (Inch-Pound Units). Relationship BetweenWater to Cementitious Material Ratio andCompressive Strength of Concrete

Strength is based on cylinders moist-cured 28 days in accordancewith ASTM C 31 (AASHTO T 23). Relationship assumes nominalmaximum size aggregate of about 3⁄4 in. to 1 in.Adapted from ACI 211.1 and ACI 211.3.

Compressive Water-cementitious materials ratio by mass

strength at Non-air-entrained Air-entrained28 days, MPa concrete concrete

45 0.38 0.3040 0.42 0.3435 0.47 0.3930 0.54 0.4525 0.61 0.5220 0.69 0.6015 0.79 0.70

Table 9-3 (Metric). Relationship Between Water toCementitious Material Ratio and CompressiveStrength of Concrete

Strength is based on cylinders moist-cured 28 days in accordancewith ASTM C 31 (AASHTO T 23). Relationship assumes nominalmaximum size aggregate of about 19 to 25 mm.Adapted from ACI 211.1 and ACI 211.3.

size is about 19 mm (3⁄4 in.). Higher strengths can alsosometimes be achieved through the use of crushed stoneaggregate rather than rounded-gravel aggregate.

The most desirable fine-aggregate grading willdepend upon the type of work, the paste content of themixture, and the size of the coarse aggregate. For leanermixtures, a fine grading (lower fineness modulus) is desir-able for workability. For richer mixtures, a coarse grading(higher fineness modulus) is used for greater economy.

In some areas, the chemically bound chloride inaggregate may make it difficult for concrete to pass chlo-ride limits set by ACI 318 or other specifications.However, some or all of the chloride in the aggregatemay not be available for participation in corrosion ofreinforcing steel, thus that chloride may be ignored.ASTM PS 118 (to be redesignated ASTM C 1500), Soxhletextracted chloride test, can be used to evaluate theamount of chloride available from aggregate. ACI 222.1also provides guidance.

The bulk volume of coarse aggregate can be deter-mined from Fig. 9-3 or Table 9-4. These bulk volumes arebased on aggregates in a dry-rodded condition as des-cribed in ASTM C 29 (AASHTO T 19); they are selectedfrom empirical relationships to produce concrete with adegree of workability suitable for general reinforced con-crete construction. For less workable concrete, such asrequired for concrete pavement construction, they may beincreased about 10%. For more workable concrete, such asmay be required when placement is by pump, they maybe reduced up to 10%.

Air Content

Entrained air must be used in all concrete that will be ex-posed to freezing and thawing and deicing chemicals andcan be used to improve workability even where not required.

high shrinkage properties, high water demand, and poorworkability and placeability. Durability may also beaffected. Various options are available for obtainingoptimal grading of aggregate (Shilstone 1990).

The maximum size of coarse aggregate should notexceed one-fifth the narrowest dimension between sides offorms nor three-fourths the clear space between individualreinforcing bars or wire, bundles of bars, or prestressingtendons or ducts. It is also good practice to limit aggregatesize to not more than three-fourths the clear space betweenreinforcement and the forms. For unreinforced slabs onground, the maximum size should not exceed one third theslab thickness. Smaller sizes can be used when availabilityor economic consideration require them.

The amount of mixing water required to produce aunit volume of concrete of a given slump is dependent onthe shape and the maximum size and amount of coarseaggregate. Larger sizes minimize the water requirementand thus allow the cement content to be reduced. Also,rounded aggregate requires less mixing water than acrushed aggregate in concretes of equal slump (see“Water Content”).

The maximum size of coarse aggregate that will pro-duce concrete of maximum strength for a given cementcontent depends upon the aggregate source as well as itsshape and grading. For high compressive-strength con-crete (greater than 70 MPa or 10,000 psi), the maximum

152


0 25 50 75Nominal maximum aggregate size, mm

Nominal maximum aggregate size, in.

0.9

0.8

0.7

0.6

0.5

0.4

Bul

k vo

lum

e fr

actio

n of

coa

rse

aggr

egat

e to

con

cret

e vo

lum

e 0 0.5 1 1.5 2 2.5 3

Fineness modulus = 2.4




Fig. 9-3. Bulk volume of coarse aggregate per unit volumeof concrete. Bulk volumes are based on aggregates in adry-rodded condition as described in ASTM C 29 (AASHTOT 19). For more workable concrete, such as may be re-quired when placement is by pump, they may be reducedup to 10%. Adapted from Table 9-4, ACI 211.1 and Hover(1995 and 1998).

Nominal Bulk volume of dry-rodded coarsemaximum aggregate per unit volume of concrete for

size of different fineness moduli of fine aggregate*aggregate,mm (in.) 2.40 2.60 2.80 3.00

9.5 (3⁄8) 0.50 0.48 0.46 0.4412.5 (1⁄2) 0.59 0.57 0.55 0.53

19 (3⁄4) 0.66 0.64 0.62 0.6025 (1) 0.71 0.69 0.67 0.65

37.5 (11⁄2) 0.75 0.73 0.71 0.6950 (2) 0.78 0.76 0.74 0.7275 (3) 0.82 0.80 0.78 0.76

150 (6) 0.87 0.85 0.83 0.81

Table 9-4. Bulk Volume of Coarse Aggregate Per UnitVolume of Concrete

*Bulk volumes are based on aggregates in a dry-rodded condition asdescribed in ASTM C 29 (AASHTO T 19). Adapted from ACI 211.1.

Air entrainment is accomplished by using an air-entraining portland cement or by adding an air-entrainingadmixture at the mixer. The amount of admixture shouldbe adjusted to meet variations in concrete ingredients andjob conditions. The amount recommended by the admix-ture manufacturer will, in most cases, produce the desiredair content.

Recommended target air contents for air-entrainedconcrete are shown in Fig. 9-4 and Table 9-5. Note that theamount of air required to provide adequate freeze-thawresistance is dependent upon the nominal maximum sizeof aggregate and the level of exposure. In properly pro-portioned mixes, the mortar content decreases as maxi-mum aggregate size increases, thus decreasing the re-quired concrete air content. This is evident in Fig. 9-4. Thelevels of exposure are defined by ACI 211.1 as follows:

Mild Exposure. This exposure includes indoor or outdoorservice in a climate where concrete will not be exposed tofreezing or deicing agents. When air entrainment isdesired for a beneficial effect other than durability, such asto improve workability or cohesion or in low cement con-tent concrete to improve strength, air contents lower thanthose needed for durability can be used.

Moderate Exposure. Service in a climate where freezingis expected but where the concrete will not be continuallyexposed to moisture or free water for long periods prior tofreezing and will not be exposed to deicing or otheraggressive chemicals. Examples include exterior beams,columns, walls, girders, or slabs that are not in contactwith wet soil and are so located that they will not receivedirect applications of deicing chemicals.

Severe Exposure. Concrete that is exposed to deicing orother aggressive chemicals or where the concrete maybecome highly saturated by continual contact with mois-ture or free water prior to freezing. Examples includepavements, bridge decks, curbs, gutters, sidewalks, canallinings, or exterior water tanks or sumps.

When mixing water is held constant, the entrainmentof air will increase slump. When cement content andslump are held constant, the entrainment of air results inthe need for less mixing water, particularly in leaner con-crete mixtures. In batch adjustments, in order to maintaina constant slump while changing the air content, the watershould be decreased by about 3 kg/m3 (5 lb/yd3) for eachpercentage point increase in air content or increased3 kg/m3 (5 lb/yd3) for each percentage point decrease.

A specific air content may not be readily or repeatedlyachieved because of the many variables affecting air con-tent; therefore, a permissible range of air contents arounda target value must be provided. Although a range of ±1%of the Fig. 9-4 or Table 9-5 values is often used in projectspecifications, it is sometimes an impracticably tight limit.The solution is to use a wider range, such as –1 to +2 per-

153


0 10 20 30 40 50 60 70

Nominal maximum aggregate size, mm

Nominal maximum aggregate size, in.0 0.5 1 1.5 2 2.5 3

8

7

6

5

4

3

2

1

0

Targ

et a

ir co

nten

t, %

Severe exposure (deicers)

Moderate exposure

Mild exposure


Fig. 9-4. Target total air content requirements for concretesusing different sizes of aggregate. The air content in jobspecifications should be specified to be delivered within –1to +2 percentage points of the target value for moderateand severe exposures. Adapted from Table 9-5, ACI 211.1and Hover (1995 and 1998).

centage points of the target values. For example, for atarget value of 6% air, the specified range for the concretedelivered to the jobsite could be 5% to 8%.

Slump

Concrete must always be made with a workability, consis-tency, and plasticity suitable for job conditions. Workabil-ity is a measure of how easy or difficult it is to place,consolidate, and finish concrete. Consistency is the abilityof freshly mixed concrete to flow. Plasticity determinesconcrete’s ease of molding. If more aggregate is used in aconcrete mixture, or if less water is added, the mixturebecomes stiff (less plastic and less workable) and difficultto mold. Neither very dry, crumbly mixtures nor verywatery, fluid mixtures can be regarded as having plasticity.

The slump test is used to measure concrete consis-tency. For a given proportion of cement and aggregatewithout admixtures, the higher the slump, the wetter themixture. Slump is indicative of workability whenassessing similar mixtures. However, slump should not beused to compare mixtures of totally different proportions.When used with different batches of the same mix design,a change in slump indicates a change in consistency and inthe characteristics of materials, mixture proportions,water content, mixing, time of test, or the testing itself.

154


Water, pounds per cubic yard of concrete, for indicated sizes of aggregate*

Slump, in. 3⁄8 in. 1⁄2 in. 3⁄4 in. 1 in. 11⁄2 in. 2 in.** 3 in.** 6 in.**


1 to 2 350 335 315 300 275 260 220 1903 to 4 385 365 340 325 300 285 245 2106 to 7 410 385 360 340 315 300 270 —

Approximate amount of entrapped air in non-air- 3 2.5 2 1.5 1 0.5 0.3 0.2entrained concrete, percent


1 to 2 305 295 280 270 250 240 205 1803 to 4 340 325 305 295 275 265 225 2006 to 7 365 345 325 310 290 280 260 —

Recommended average total air content, percent, for level of exposure:†

Mild exposure 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0Moderate exposure 6.0 5.5 5.0 4.5 4.5 3.5 3.5 3.0Severe exposure 7.5 7.0 6.0 6.0 5.5 5.0 4.5 4.0

Table 9-5 (Inch-Pound Units). Approximate Mixing Water and Target Air Content Requirements for DifferentSlumps and Nominal Maximum Sizes of Aggregate

* These quantities of mixing water are for use in computing cement factors for trial batches. They are maximums for reasonably well-shapedangular coarse aggregates graded within limits of accepted specifications.

** The slump values for concrete containing aggregates larger than 11⁄2 in. are based on slump tests made after removal of particles larger than11⁄2 in. by wet screening.

† The air content in job specifications should be specified to be delivered within –1 to +2 percentage points of the table target value for mod-erate and severe exposures.

Adapted from ACI 211.1. Hover (1995) presents this information in graphical form.

Water, kilograms per cubic meter of concrete, for indicated sizes of aggregate*

Slump, mm 9.5 mm 12.5 mm 19 mm 25 mm 37.5 mm 50 mm** 75 mm** 150 mm**


25 to 50 207 199 190 179 166 154 130 11375 to 100 228 216 205 193 181 169 145 124

150 to 175 243 228 216 202 190 178 160 —Approximate amount of entrapped air in non-air- 3 2.5 2 1.5 1 0.5 0.3 0.2entrained concrete, percent


25 to 50 181 175 168 160 150 142 122 10775 to 100 202 193 184 175 165 157 133 119

150 to 175 216 205 197 184 174 166 154 —Recommended average total air content, percent, for level of exposure:†

Mild exposure 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0Moderate exposure 6.0 5.5 5.0 4.5 4.5 4.0 3.5 3.0Severe exposure 7.5 7.0 6.0 6.0 5.5 5.0 4.5 4.0

Table 9-5 (Metric). Approximate Mixing Water and Target Air Content Requirements for Different Slumps andNominal Maximum Sizes of Aggregate

* These quantities of mixing water are for use in computing cementitious material contents for trial batches. They are maximums for reason-ably well-shaped angular coarse aggregates graded within limits of accepted specifications.

** The slump values for concrete containing aggregates larger than 37.5 mm are based on slump tests made after removal of particles largerthan 37.5 mm by wet screening.

† The air content in job specifications should be specified to be delivered within –1 to +2 percentage points of the table target value for mod-erate and severe exposures.

Adapted from ACI 211.1 and ACI 318. Hover (1995) presents this information in graphical form.

Different slumps are needed for various types of con-crete construction. Slump is usually indicated in the jobspecifications as a range, such as 50 to 100 mm (2 to 4 in.),or as a maximum value not to be exceeded. ASTM C 94addresses slump tolerances in detail. When slump is notspecified, an approximate value can be selected fromTable 9-6 for concrete consolidated by mechanical vibra-tion. For batch adjustments, the slump can be increased byabout 10 mm by adding 2 kilograms of water per cubicmeter of concrete (1 in. by adding 10 lb of water per cubicyard of concrete).

Water Content

The water content of concrete is influenced by a number offactors: aggregate size, aggregate shape, aggregate texture,slump, water to cementing materials ratio, air content,cementing materials type and content, admixtures, andenvironmental conditions. An increase in air content andaggregate size, a reduction in water-cementing materialsratio and slump, and the use of rounded aggregates, water-reducing admixtures, or fly ash will reduce water demand.On the other hand, increased temperatures, cement con-tents, slump, water-cement ratio, aggregate angularity, anda decrease in the proportion of coarse aggregate to fineaggregate will increase water demand.

The approximate water contents in Table 9-5 andFig. 9-5, used in proportioning, are for angular coarse

aggregates (crushed stone). For some concretes and aggre-gates, the water estimates in Table 9-5 and Fig. 9-5 can bereduced by approximately 10 kg (20 lb) for subangularaggregate, 20 kg (35 lb) for gravel with some crushed par-ticles, and 25 kg (45 lb) for a rounded gravel to producethe slumps shown. This illustrates the need for trial batchtesting of local materials, as each aggregate source is dif-ferent and can influence concrete properties differently.

155


0 0.5 1 1.5 2 2.5 3


Nominal maximum aggregate size, mm0 10 20 30 40 50 60 70

250

200

150

100

Wat

er r

equi

rem

ent (

kg/m

3 )

Wat

er r

equi

rem

ent (

lb/y

d3)

400

350

300

250

200

169


150 to 175 mm (6 to 7 in.) slump



0 0.5 1 1.5 2 2.5 3


Nominal maximum aggregate size, mm0 10 20 30 40 50 60 70

250

200

150

100

Wat

er r

equi

rem

ent (

kg/m

3 )

Wat

er r

equi

rem

ent (

lb/y

d3)

400

350

300

250

200

169





Fig. 9-5. Approximate water requirement for various slumps and crushed aggregate sizes for (left) non-air-entrainedconcrete and (right) air-entrained concrete. Adapted from Table 9-5, ACI 211.1 and Hover (1995 and 1998).

Slump, mm (in.)

Concrete construction Maximum* Minimum

Reinforced foundation walls and footings 75 (3) 25 (1)

Plain footings, caissons, andsubstructure walls 75 (3) 25 (1)

Beams and reinforced walls 100 (4) 25 (1)

Building columns 100 (4) 25 (1)

Pavements and slabs 75 (3) 25 (1)

Mass concrete 75 (3) 25 (1)

Table 9-6. Recommended Slumps for Various Types of Construction

*May be increased 25 mm (1 in.) for consolidation by hand methods,such as rodding and spading.

Plasticizers can safely provide higher slumps.Adapted from ACI 211.1.

tity of cementing materials to be used should be not lessthan shown in Table 9-7.

To obtain economy, proportioning should minimizethe amount of cement required without sacrificing con-crete quality. Since quality depends primarily on water-cementing materials ratio, the water content should beheld to a minimum to reduce the cement requirement.Steps to minimize water and cement requirements includeuse of (1) the stiffest practical mixture, (2) the largest prac-tical maximum size of aggregate, and (3) the optimumratio of fine-to-coarse aggregate.

Concrete that will be exposed to sulfate conditionsshould be made with the type of cement shown in Table 9-2.

Seawater contains significant amounts of sulfates andchlorides. Although sulfates in seawater are capable of at-tacking concrete, the presence of chlorides in seawaterinhibits the expansive reaction that is characteristic of sulfateattack. This is the major factor explaining observations froma number of sources that the performance of concretes inseawater have shown satisfactory durability; this is despitethe fact these concretes were made with portland cementshaving tricalcium aluminate (C3A) contents as high as 10%,and sometimes greater. However, the permeability of theseconcretes was low, and the reinforcing steel had adequatecover. Portland cements meeting a C3A requirement of notmore than 10% or less than 4% (to ensure durability of rein-forcement) are acceptable (ACI 357R).

Supplementary cementitious materials have variedeffects on water demand and air contents. The addition offly ash will generally reduce water demand and decreasethe air content if no adjustment in the amount of air-entraining admixture is made. Silica fume increases waterdemand and decreases air content. Slag and metakaolinhave a minimal effect at normal dosages.

It should be kept in mind that changing the amount ofany single ingredient in a concrete mixture normallyeffects the proportions of other ingredients as well as alterthe properties of the mixture. For example, the addition of2 kg of water per cubic meter will increase the slump byapproximately 10 mm (10 lb of water per cubic yard willincrease the slump by approximately 1 in.); it will also in-crease the air content and paste volume, decrease the ag-gregate volume, and lower the density of the concrete. Inmixture adjustments, for the same slump, a decrease in aircontent by 1 percentage point will increase the waterdemand by about 3 kg per cubic meter of concrete (5 lb percu yd of concrete).

Cementing Materials Content and Type

The cementing materials content is usually determined fromthe selected water-cementing materials ratio and water con-tent, although a minimum cement content frequently isincluded in specifications in addition to a maximum water-cementing materials ratio. Minimum cement content re-quirements serve to ensure satisfactory durability andfinishability, to improve wear resistance of slabs, and toguarantee a suitable appearance of vertical surfaces. Thisis important even though strength requirements may bemet at lower cementing materials contents. However,excessively large amounts of cementing materials shouldbe avoided to maintain economy in the mixture and to notadversely affect workability and other properties.

For severe freeze-thaw, deicer, and sulfate exposures,it is desirable to specify: (1) a minimum cementing mate-rials content of 335 kg per cubic meter (564 lb per cubicyard) of concrete, and (2) only enough mixing water toachieve the desired consistency without exceeding themaximum water-cementing materials ratios shown inTables 9-1 and 9-2. For placing concrete underwater, usu-ally not less than 390 kg of cementing materials per cubicmeter (650 lb of cementing materials per cubic yard) ofconcrete should be used with a water to cementing mate-rials ratio not exceeding 0.45. For workability, finishability,abrasion resistance, and durability in flatwork, the quan-

156


Nominal maximum size Cementing materials,of aggregate, mm (in.) kg/m3 (lb/yd3)*

37.5 (11⁄2) 280 (470) 25 (1) 310 (520) 19 (3⁄4) 320 (540)

12.5 (1⁄2) 350 (590) 9.5 (3⁄8) 360 (610)

Table 9-7. Minimum Requirements of CementingMaterials for Concrete Used in Flatwork

* Cementing materials quantities may need to be greater for severeexposure. For example, for deicer exposures, concrete should con-tain at least 335 kg/m3 (564 lb/yd3) of cementing materials.

Adapted from ACI 302.

Maximum percent of Cementitious total cementitious

materials* materials by mass**

Fly ash and natural pozzolans 25

Slag 50

Silica fume 10

Total of fly ash, slag, silica fumeand natural pozzolans 50†

Total of natural pozzolans andsilica fume 35†

Table 9-8. Cementitious Materials Requirements forConcrete Exposed to Deicing Chemicals

* Includes portion of supplementary cementing materials in blendedcements.

** Total cementitious materials include the summation of portlandcements, blended cements, fly ash, slag, silica fume and other poz-zolans.

† Silica fume should not constitute more than 10% of total cementi-tious materials and fly ash or other pozzolans shall not constitutemore than 25% of cementitious materials.


Table 9-8 shows limits on the amount of supplemen-tary cementing materials in concrete to be exposed todeicers. Local practices should be consulted as dosagessmaller or larger than those shown in Table 9-8 can beused without jeopardizing scale-resistance, depending onthe exposure severity.

Admixtures

Water-reducing admixtures are added to concrete to reducethe water-cementing materials ratio, reduce cementingmaterials content, reduce water content, reduce paste con-tent, or to improve the workability of a concrete withoutchanging the water-cementing materials ratio. Waterreducers will usually decrease water contents by 5% to 10%and some will also increase air contents by 1⁄2 to 1 per-centage point. Retarders may also increase the air content.

High-range water reducers (plasticizers) reduce watercontents between 12% and 30% and some can simultane-ously increase the air content up to 1 percentage point;others can reduce or not affect the air content.

Calcium chloride-based admixtures reduce watercontents by about 3% and increase the air content by about1⁄2 percentage point.

When using a chloride-based admixture, the risks ofreinforcing steel corrosion should be considered. Table 9-9provides recommended limits on the water-soluble chlo-ride-ion content in reinforced and prestressed concrete forvarious conditions.

When using more than one admixture in concrete, thecompatibility of intermixing admixtures should beassured by the admixture manufacturer or the combina-tion of admixtures should be tested in trial batches. Thewater contained in admixtures should be considered partof the mixing water if the admixture’s water content is suf-

ficient to affect the water-cementing materials ratio by 0.01or more.

An excessive use of multiple admixtures should beminimized to allow better control of the concrete mixturein production and to reduce the risk of admixture incom-patibility.

PROPORTIONING

The design of concrete mixtures involves the following:(1) the establishment of specific concrete characteristics,and (2) the selection of proportions of available materialsto produce concrete of required properties, with thegreatest economy. Proportioning methods have evolvedfrom the arbitrary volumetric method (1:2:3—cement:sand: coarse aggregate) of the early 1900s(Abrams 1918) to the present-day weight and absolute-volume methods described in ACI’s Committee 211Standard Practice for Selecting Proportions for Normal,Heavyweight and Mass Concrete (ACI 211.1).

Weight proportioning methods are fairly simple andquick for estimating mixture proportions using an assumedor known weight of concrete per unit volume. A more accu-rate method, absolute volume, involves use of relative den-sity (specific gravity) values for all the ingredients tocalculate the absolute volume each will occupy in a unitvolume of concrete. The absolute volume method will beillustrated. A concrete mixture also can be proportionedfrom field experience (statistical data) or from trial mixtures.

Other valuable documents to help proportion con-crete mixtures include the Standard Practice for SelectingProportions for Structural Lightweight Concrete (ACI 211.2);Guide for Selecting Proportions for No-Slump Concrete (ACI211.3); Guide for Selecting Proportions for High-StrengthConcrete with Portland Cement and Fly Ash (ACI 211.4R);and Guide for Submittal of Concrete Proportions (ACI 211.5).Hover (1995 and 1998) provides a graphical process fordesigning concrete mixtures in accordance with ACI 211.1.

Proportioning from Field Data

A presently or previously used concrete mixture designcan be used for a new project if strength-test data andstandard deviations show that the mixture is acceptable.Durability aspects previously presented must also be met.Standard deviation computations are outlined in ACI 318.The statistical data should essentially represent the samematerials, proportions, and concreting conditions to beused in the new project. The data used for proportioningshould also be from a concrete with an ˘ that is within7 MPa (1000 psi) of the strength required for the proposedwork. Also, the data should represent at least 30 consecu-tive tests or two groups of consecutive tests totaling atleast 30 tests (one test is the average strength of two cylin-ders from the same sample). If only 15 to 29 consecutivetests are available, an adjusted standard deviation can be

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Maximum water-soluble chloride ion (Cl-) in

concrete, percent by Type of member mass of cement*

Prestressed concrete 0.06

Reinforced concrete exposed to chloride in service 0.15

Reinforced concrete that will bedry or protected from moisture 1.00in service

Other reinforced concrete construction 0.30

Table 9-9. Maximum Chloride-Ion Content forCorrosion Protection

*ASTM C 1218.Adapted from ACI 318.

are insufficient or not available, the mixture should beproportioned by the trial-mixture method. The approvedmixture must have a compressive strength that meets orexceeds Â. Three trial mixtures using three differentwater to cementing materials ratios or cementing mate-rials contents should be tested. A water to cementingmaterials ratio to strength curve (similar to Fig. 9-2) canthen be plotted and the proportions interpolated from thedata. It is also good practice to test the properties of thenewly proportioned mixture in a trial batch.

ACI 214 provides statistical analysis methods formonitoring the strength of the concrete in the field toensure that the mix properly meets or exceeds the designstrength, ˘.

Proportioning by Trial Mixtures

When field test records are not available or are insufficientfor proportioning by field experience methods, the con-crete proportions selected should be based on trial mix-tures. The trial mixtures should use the same materialsproposed for the work. Three mixtures with three differentwater-cementing materials ratios or cementing materialscontents should be made to produce a range of strengthsthat encompass Â. The trial mixtures should have a slumpand air content within ±20 mm (±0.75 in.) and ± 0.5%,respectively, of the maximum permitted. Three cylindersfor each water-cementing materials ratio should be madeand cured according to ASTM C 192 (AASHTO T 126). At28 days, or the designated test age, the compressive

obtained by multiplying the standard deviation (S) for the15 to 29 tests and a modification factor from Table 9-10.The data must represent 45 or more days of tests.

The standard or modified deviation is then used inEquations 9-1 to 9-3. The average compressive strengthfrom the test record must equal or exceed the ACI 318required average compressive strength, Â, in order forthe concrete proportions to be acceptable. The Â for theselected mixture proportions is equal to the larger ofEquations 9-1 and 9-2 (for ˘ ≤ 35 MPa [5000 psi]) orEquations 9-1 and 9-3 (for ˘ > 35 MPa [5000 psi]).

Â = ˘ + 1.34S Eq. 9-1Â = ˘ + 2.33S – 3.45 (MPa) Eq. 9-2Â = ˘ + 2.33S – 500 (psi) Eq. 9-2Â = 0.90 ˘ + 2.33S Eq. 9-3

where

Â = required average compressive strength of concreteused as the basis for selection of concrete propor-tions, MPa (psi)

˘ = specified compressive strength of concrete, MPa(psi)

S = standard deviation, MPa (psi)

When field strength test records do not meet the pre-viously discussed requirements, Â can be obtained fromTable 9-11. A field strength record, several strength testrecords, or tests from trial mixtures must be used for doc-umentation showing that the average strength of the mix-ture is equal to or greater than Â.

If less than 30, but not less than 10 tests are available,the tests may be used for average strength documentationif the time period is not less than 45 days. Mixture pro-portions may also be established by interpolating betweentwo or more test records if each meets the above andproject requirements. If a significant difference existsbetween the mixtures that are used in the interpolation, atrial mixture should be considered to check strength gain.If the test records meet the above requirements and limi-tations of ACI 318, the proportions for the mixture maythen be considered acceptable for the proposed work.

If the average strength of the mixtures with the statis-tical data is less than Â, or statistical data or test records

158


Modification factor forNumber of tests* standard deviation**

Less than 15 Use Table 9-11

15 1.16

20 1.08

25 1.03

30 or more 1.00

Table 9-10. Modification Factor for StandardDeviation When Less Than 30 Tests Are Available

* Interpolate for intermediate numbers of tests. ** Modified standard deviation to be used to determine required

average strength, f'cr.Adapted from ACI 318.

Required average Specified compressive compressive strength,

strength, f'c, MPa f'cr, MPa

Less than 21 f'c + 7.0

21 to 35 f'c + 8.5

Over 35 1.10 f'c + 5.0

Table 9-11 (Metric). Required Average CompressiveStrength When Data Are Not Available to Establish aStandard Deviation


Required average Specified compressive compressive strength,

strength, f'c, psi f'cr, psi

Less than 3000 f'c + 1000

3000 to 5000 f'c + 1200

Over 5000 1.10 f'c + 700

Table 9-11 (Inch-Pound Units). Required AverageCompressive Strength When Data Are Not Availableto Establish a Standard Deviation


strength of the concrete should be determined by testingthe cylinders in compression. The test results should beplotted to produce a strength versus water-cementingmaterials ratio curve (similar to Fig. 9-2) that is used to pro-portion a mixture.

A number of different methods of proportioning con-crete ingredients have been used at one time or another,including:

Arbitrary assignment (1:2:3), volumetric Void ratio Fineness modulus Surface area of aggregates Cement content

Any one of these methods can produce approximatelythe same final mixture after adjustments are made in thefield. The best approach, however, is to select proportionsbased on past experience and reliable test data with anestablished relationship between strength and water to ce-menting materials ratio for the materials to be used in theconcrete. The trial mixtures can be relatively small batchesmade with laboratory precision or job-size batches madeduring the course of normal concrete production. Use ofboth is often necessary to reach a satisfactory job mixture.

The following parameters must be selected first:(1) required strength, (2) minimum cementing materialscontent or maximum water-cementing materials ratio,(3) nominal maximum size of aggregate, (4) air content, and(5) desired slump. Trial batches are then made varying therelative amounts of fine and coarse aggregates as well asother ingredients. Based on considerations of workabilityand economy, the proper mixture proportions are selected.

When the quality of the concrete mixture is specifiedby water-cementitious material ratio, the trial-batch proce-dure consists essentially of combining a paste (water,cementing materials, and, generally, a chemical admixture)of the correct proportions with the necessary amounts offine and coarse aggregates to produce the required slumpand workability. Representative samples of the cementingmaterials, water, aggregates, and admixtures must be used.

Quantities per cubic meter (cubic yard) are then calcu-lated. To simplify calculations and eliminate error causedby variations in aggregate moisture content, the aggregatesshould be prewetted then dried to a saturated surface-dry(SSD) condition; place the aggregates in covered containers

to keep them in this SSD condition until they are used. Themoisture content of the aggregates should be determinedand the batch weights corrected accordingly.

The size of the trial batch is dependent on the equip-ment available and on the number and size of test speci-mens to be made. Larger batches will produce moreaccurate data. Machine mixing is recommended since itmore nearly represents job conditions; it is mandatory ifthe concrete is to contain entrained air. The mixing proce-dures outlined in ASTM C 192 (AASHTO T 126) shouldbe used.

Measurements and Calculations

Tests for slump, air content, and temperature should bemade on the trial mixture, and the following measure-ments and calculations should also be performed:

Density (Unit Weight) and Yield. The density (unitweight) of freshly mixed concrete is expressed in kilo-grams per cubic meter (pounds per cubic foot). The yieldis the volume of fresh concrete produced in a batch, usu-ally expressed in cubic meters (cubic feet). The yield is cal-culated by dividing the total mass of the materials batchedby the density of the freshly mixed concrete. Density andyield are determined in accordance with ASTM C 138.

Absolute Volume. The absolute volume of a granularmaterial (such as cement and aggregates) is the volume ofthe solid matter in the particles; it does not include thevolume of air spaces between particles. The volume(yield) of freshly mixed concrete is equal to the sum of theabsolute volumes of the concrete ingredients—cementingmaterials, water (exclusive of that absorbed in the aggre-gate), aggregates, admixtures when applicable, and air.The absolute volume is computed from a material’s massand relative density (specific gravity) as follows:

Absolute volume

= mass of loose materialrelative density of a material x density of water

A value of 3.15 can be used for the relative density(specific gravity) of portland cement. Blended cementshave relative densities ranging from 2.90 to 3.15. The rel-ative density of fly ash varies from 1.9 to 2.8, slag from2.85 to 2.95, and silica fume from 2.20 to 2.25. The relativedensity of water is 1.0 and the density of water is

159


Temperature, °C Density, kg/m3 Temperature, °F Density, lb/ft3

16 998.93 60 62.36818 998.58 65 62.33720 998.1922 997.75 70 62.30224 997.27 75 62.26126 996.7528 996.20 80 62.216

30 995.61 85 62.166

Table 9-12. Density of Water Versus Temperature

Air-entrainingadmixture: Wood-resin type (ASTM C 260 or

AASHTO M 154).

Water reducer: ASTM C 494 (AASHTO M 194). Thisparticular admixture is known to re-duce water demand by 10% whenused at a dosage rate of 3 g (or 3 mL)per kg of cement. Assume that thechemical admixtures have a densityclose to that of water, meaning that1 mL of admixture has a mass of 1 g.

From this information, the task is to proportion a trial mix-ture that will meet the above conditions and specifications.

Strength. The design strength of 35 MPa is greater thanthe 31 MPa required in Table 9-1 for the exposure condi-tion. Since no statistical data is available, Â (requiredcompressive strength for proportioning) from Table 9-11 isequal to˘ + 8.5. Therefore, Â = 35 + 8.5 = 43.5 MPa.

Water to Cement Ratio. For an environment with moistfreezing and thawing, the maximum water to cementi-tious material ratio should be 0.45. The recommendedwater to cementitious material ratio for an Â of 43.5 MPais 0.31 from Fig. 9-2 or interpolated from Table 9-3 [{(45 –43.5)(0.34 – 0.30)/(45 – 40)} + 0.30 = 0.31]. Since the lowerwater to cement ratio governs, the mix must be designedfor 0.31. If a plot from trial batches or field tests had beenavailable, the water to cement ratio could have beenextrapolated from that data.

Air Content. For a severe freeze-thaw exposure, Table 9-5recommends a target air content of 6.0% for a 25-mmaggregate. Therefore, design the mix for 5% to 8% air anduse 8% (or the maximum allowable) for batch proportions.The trial-batch air content must be within ±0.5 percentagepoints of the maximum allowable air content.

Slump. The slump is specified at 25 mm to 75 mm. Use75 mm ±20 mm for proportioning purposes.

Water Content. Table 9-5 and Fig. 9-5 recommend that a75-mm slump, air-entrained concrete made with 25-mmnominal maximum-size aggregate should have a watercontent of about 175 kg/m3. However, rounded gravelshould reduce the water content of the table value by about25 kg/m3. Therefore, the water content can be estimated tobe about 150 kg/m3 (175 kg/m3 minus 25 kg/m3). In addi-tion, the water reducer will reduce water demand by 10%resulting in an estimated water demand of 135 kg/m3.

Cement Content. The cement content is based on themaximum water-cement ratio and the water content.Therefore, 135 kg/m3 of water divided by a water-cementratio of 0.31 requires a cement content of 435 kg/m3; thisis greater than the 335 kg/m3 required for frost resistance(Table 9-7).

1000 kg/m3 (62.4 lb/ft3) at 4°C (39°F)—accurate enoughfor mix calculations at room temperature. More accuratewater density values are given in Table 9-12. Relativedensity of normal aggregate usually ranges between2.4 and 2.9.

The relative density of aggregate as used in mix-design calculations is the relative density of either satu-rated surface-dry (SSD) material or ovendry material.Relative densities of admixtures, such as water reducers,can also be considered if needed. Absolute volume is usu-ally expressed in cubic meters (cubic feet).

The absolute volume of air in concrete, expressed ascubic meters per cubic meter (cubic feet per cubic yard), isequal to the total air content in percent divided by 100 (forexample, 7% ÷ 100) and then multiplied by the volume ofthe concrete batch.

The volume of concrete in a batch can be determinedby either of two methods: (1) if the relative densities of theaggregates and cementing materials are known, these canbe used to calculate concrete volume; or (2) if relative den-sities are unknown, or they vary, the volume can be com-puted by dividing the total mass of materials in the mixerby the density of concrete. In some cases, both determina-tions are made, one serving as a check on the other.

EXAMPLES OF MIXTUREPROPORTIONING

Example 1. Absolute Volume Method(Metric)

Conditions and Specifications. Concrete is required fora pavement that will be exposed to moisture in a severefreeze-thaw environment. A specified compressivestrength, ˘, of 35 MPa is required at 28 days. Air entrain-ment is required. Slump should be between 25 mm and75 mm. A nominal maximum size aggregate of 25 mm isrequired. No statistical data on previous mixes are avail-able. The materials available are as follows:

Cement: Type GU (ASTM C 1157) with a rela-tive density of 3.0.

Coarse aggregate: Well-graded, 25-mm nominal max-imum-size rounded gravel (ASTM C33 or AASHTO M 80) with an ovendryrelative density of 2.68, absorption of0.5% (moisture content at SSD condi-tion) and ovendry rodded bulk den-sity (unit weight) of 1600 kg/m3. Thelaboratory sample for trial batchinghas a moisture content of 2%.

Fine aggregate: Natural sand (ASTM C 33 or AASHTOM 6) with an ovendry relative densityof 2.64 and absorption of 0.7%. The lab-oratory sample moisture content is 6%.The fineness modulus is 2.80.

160


Coarse-Aggregate Content. The quantity of 25-mmnominal maximum-size coarse aggregate can be estimatedfrom Fig. 9-3 or Table 9-4. The bulk volume of coarse ag-gregate recommended when using sand with a finenessmodulus of 2.80 is 0.67. Since it has a bulk density of 1600kg/m3, the ovendry mass of coarse aggregate for a cubicmeter of concrete is

1600 x 0.67 = 1072 kg

Admixture Content. For an 8% air content, the air-entraining admixture manufacturer recommends a dosagerate of 0.5 g per kg of cement. From this information, theamount of air-entraining admixture per cubic meter of con-crete is

0.5 x 435 = 218 g or 0.218 kg

The water reducer dosage rate of 3 g per kg of cementresults in

3 x 435 = 1305 g or 1.305 kg of water reducerper cubic meter of concrete

Fine-Aggregate Content. At this point, the amounts ofall ingredients except the fine aggregate are known. In theabsolute volume method, the volume of fine aggregate isdetermined by subtracting the absolute volumes of theknown ingredients from 1 cubic meter. The absolutevolume of the water, cement, admixtures and coarseaggregate is calculated by dividing the known mass ofeach by the product of their relative density and the den-sity of water. Volume computations are as follows:

Water = 1351 x 1000 = 0.135 m3

Cement = 4353.0 x 1000 = 0.145 m3

Air = 8.0100 = 0.080 m3

Coarse aggregate = 10722.68 x 1000 = 0.400 m3

Total volume of known ingredients 0.760 m3

The calculated absolute volume of fine aggregate is then

1 – 0.76 = 0.24 m3

The mass of dry fine aggregate is

0.24 x 2.64 x 1000 = 634 kg

The mixture then has the following proportions beforetrial mixing for one cubic meter of concrete:

Water 135 kgCement 435 kgCoarse aggregate (dry) 1072 kgFine aggregate (dry) 634 kg

Total mass 2276 kg

Air-entraining admixture 0.218 kgWater reducer 1.305 kg

Slump 75 mm (±20 mm for trial batch)

Air content 8% (±0.5% for trial batch)

Estimated concrete = 135 + 435 + (1072 x 1.005*)density (using + (634 x 1.007*)SSD aggregate) = 2286 kg/m3

The liquid admixture volume is generally too insig-nificant to include in the water calculations. However, cer-tain admixtures, such as shrinkage reducers, plasticizers,and corrosion inhibitors are exceptions due to their rela-tively large dosage rates; their volumes should be included.

Moisture. Corrections are needed to compensate for mois-ture in and on the aggregates. In practice, aggregates willcontain some measurable amount of moisture. The dry-batch weights of aggregates, therefore, have to be in-creased to compensate for the moisture that is absorbed inand contained on the surface of each particle and betweenparticles. The mixing water added to the batch must bereduced by the amount of free moisture contributed by theaggregates. Tests indicate that for this example, coarse-aggregate moisture content is 2% and fine-aggregate mois-ture content is 6%.

With the aggregate moisture contents (MC) indicated, thetrial batch aggregate proportions become

Coarse aggregate (2% MC) = 1072 x 1.02 = 1093 kg

Fine aggregate (6% MC) = 634 x 1.06 = 672 kg

Water absorbed by the aggregates does not become part ofthe mixing water and must be excluded from the wateradjustment. Surface moisture contributed by the coarseaggregate amounts to 2% – 0.5% = 1.5%; that contributedby the fine aggregate is, 6% – 0.7% = 5.3%. The estimatedrequirement for added water becomes

135 – (1072 x 0.015) – (634 x 0.053) = 85 kg

The estimated batch weights for one cubic meter of con-crete are revised to include aggregate moisture as follows:

Water (to be added) 85 kgCement 435 kgCoarse aggregate (2% MC, wet) 1093 kgFine aggregate (6% MC, wet) 672 kg

Total 2285 kg

Air-entraining admixture 0.218 kgWater reducer 1.305 kg

Trial Batch. At this stage, the estimated batch weightsshould be checked by means of trial batches or by full-sizefield batches. Enough concrete must be mixed for appro-priate air and slump tests and for casting the three cylin-ders required for 28-day compressive-strength tests, plusbeams for flexural tests if necessary. For a laboratory trialbatch it is convenient, in this case, to scale down theweights to produce 0.1 m3 of concrete as follows:

161


* (0.5% absorption ÷ 100) + 1 = 1.005(0.7% absorption ÷ 100) + 1 = 1.007

batch and reduce the water content by 2 kg/m3 for each10 mm reduction in slump. The adjusted mixture waterfor the reduced slump and air content is

(3 kg water x 1 percentage point difference for air) – (2 kgwater x 25/10 for slump change) + 129 = 127 kg of water

With less mixing water needed in the trial batch, lesscement also is needed to maintain the desired water-cement ratio of 0.31. The new cement content is

1270.31 = 410 kg

The amount of coarse aggregate remains unchangedbecause workability is satisfactory. The new adjusted batchweights based on the new cement and water contents arecalculated after the following volume computations:

Water = 1271 x 1000 = 0.127 m3

Cement = 4103.0 x 1000 = 0.137 m3

Coarse aggregate = 1072(dry) 2.68 x 1000 = 0.400 m3

Air = 8100 = 0.080 m3

Total 0.744 m3

Fine aggregate volume = 1 – 0.744 = 0.256 m3

The weight of dry fine aggregate required is0.256 x 2.64 x 1000 = 676 kg

Air-entraining admixture (the manufacturer suggestsreducing the dosage by 0.1 g to reduce air 1 percentagepoint) = 0.4 x 410 = 164 g or mL

Water reducer = 3.0 x 410 = 1230 g or mL

Adjusted batch weights per cubic meter of concrete are

Water 127 kgCement 410 kgCoarse aggregate (dry) 1072 kgFine aggregate (dry) 676 kg

Total 2285 kg

Air-entraining admixture 164 g or mLWater reducer 1230 g or mL

Estimated concrete = 127 + 410 + (1072 x 1.005)density (aggregates + (676 x 1.007)at SSD) = 2295 kg/m3

After checking these adjusted proportions in a trialbatch, it was found that the concrete had the desiredslump, air content, and yield. The 28-day test cylindershad an average compressive strength of 48 MPa, whichexceeds the Â of 43.5 MPa. Due to fluctuations in mois-ture content, absorption rates, and relative density (spe-cific gravity) of the aggregate, the density determined byvolume calculations may not always equal the densitydetermined by ASTM C 138 (AASHTO T 121). Occasion-

Water 85 x 0.1 = 8.5 kgCement 435 x 0.1 = 43.5 kgCoarse aggregate (wet) 1093 x 0.1 = 109.3 kgFine aggregate (wet) 672 x 0.1 = 67.2 kg

Total 228.5 kg

Air-entrainingadmixture 218 g x 0.1 = 21.8 g or 21.8 mL

Water reducer 1305 g x 0.1 = 130 g or 130 mL

The above concrete, when mixed, had a measuredslump of 100 mm, an air content of 9%, and a density of2274 kg per cubic meter. During mixing, some of the pre-measured water may remain unused or additional watermay be added to approach the required slump. In thisexample, although 8.5 kg of water was calculated to beadded, the trial batch actually used only 8.0 kg. The mix-ture excluding admixtures therefore becomes

Water 8.0 kgCement 43.5 kgCoarse aggregate (2% MC) 109.3 kgFine aggregate (6% MC) 67.2 kg

Total 228.0 kg

The yield of the trial batch is

228.0 kg2274 kg/m3 = 0.10026 m3

The mixing water content is determined from the addedwater plus the free water on the aggregates and is calcu-lated as follows:

Water added 8.0 kg

Free water on coarse aggregate

= 109.3 = 1.61 kg1.02 x 0.015*

Free water on fine aggregate

= 67.2 = 3.36 kg1.06 x 0.053*

Total water 12.97 kg

The mixing water required for a cubic meter of the sameslump concrete as the trial batch is

12.970.10026 = 129 kg

Batch Adjustments. The measured 100-mm slump of thetrial batch is unacceptable (above 75 mm ±20 mm max.),the yield was slightly high, and the 9.0% air content asmeasured in this example is also too high (more than 0.5%above 8.5% max.). Adjust the yield and reestimate theamount of air-entraining admixture required for an 8% aircontent and adjust the water to obtain a 75-mm slump.Increase the mixing water content by 3 kg/m3 for each 1%by which the air content is decreased from that of the trial

162


*(2% MC – 0.5% absorption) ÷ 100 = 0.015(6% MC – 0.7% absorption) ÷ 100 = 0.053

ally, the proportion of fine to coarse aggregate is kept con-stant in adjusting the batch weights to maintain worka-bility or other properties obtained in the first trial batch.After adjustments to the cementitious materials, water,and air content have been made, the volume remaining foraggregate is appropriately proportioned between the fineand coarse aggregates.

Additional trial concrete mixtures with water-cementratios above and below 0.31 should also be tested todevelop a strength to water-cement ratio relationship. Fromthat data, a new more economical mixture with a compres-sive strength closer to Â and a lower cement content can beproportioned and tested. The final mixture would probablylook similar to the above mixture with a slump range of25 mm to 75 mm and an air content of 5% to 8%. Theamount of air-entraining admixture must be adjusted tofield conditions to maintain the specified air content.

Example 2. Absolute Volume Method(Inch-Pound Units)

Conditions and Specifications. Concrete is required fora building foundation. A specified compressive strength,˘, of 3500 psi is required at 28 days using a Type I cement.The design calls for a minimum of 3 in. of concrete coverover the reinforcing steel. The minimum distance betweenreinforcing bars is 4 in. The only admixture allowed is forair entrainment. No statistical data on previous mixes areavailable. The materials available are as follows:

Cement: Type I, ASTM C 150, with a relativedensity of 3.15.

Coarse aggregate: Well-graded 3⁄4-in. maximum-sizegravel containing some crushed par-ticles (ASTM C 33) with an ovendryrelative density (specific gravity) of2.68, absorption of 0.5% (moisturecontent at SSD condition) and oven-dry rodded bulk density (unit weight)of 100 lb per cu ft. The laboratorysample for trial batching has a mois-ture content of 2%.

Fine aggregate: Natural sand (ASTM C 33) with anovendry relative density (specificgravity) of 2.64 and absorption of0.7%. The laboratory sample mois-ture content is 6%. The fineness mod-ulus is 2.80.

Air-entrainingadmixture: Wood-resin type, ASTM C 260.

From this information, the task is to proportion a trial mix-ture that will meet the above conditions and specifications.

Strength. Since no statistical data is available, Â (re-quired compressive strength for proportioning) from

Table 9-11 is equal to ˘ + 1200. Therefore, Â = 3500 + 1200= 4700 psi.

Water to Cement Ratio. Table 9-1 requires no maximumwater to cement ratio. The recommended water to cementratio for an Â of 4700 psi is 0.42 interpolated from Fig. 9-2or Table 9-3 [water to cement ratio = {(5000 – 4700)(0.48 –0.40)/(5000 – 4000)} + 0.40 = 0.42].

Coarse-Aggregate Size. From the specified information,a 3⁄4-in. nominal maximum-size aggregate is adequate as itis less than 3⁄4 of the distance between reinforcing bars andbetween the rebars and forms (cover).

Air Content. A target air content of 6.0% is specified in thisinstance not for exposure conditions but to improve work-ability and reduce bleeding. Therefore, design the mix for6% ±1.0% air and use 7% (or the maximum allowable) forbatch proportions. The trial batch air content must bewithin ±0.5 percentage points of the maximum allowableair content.

Slump. As no slump was specified, a slump of 1 to 3 in.would be adequate as indicated by Table 9-6. Use 3 in. forproportioning purposes, the maximum recommended forfoundations.

Water Content. Fig. 9-5 and Table 9-5 recommend that a3-in. slump, air-entrained concrete made with 3⁄4-in. nom-inal maximum-size aggregate should have a water contentof about 305 lb per cu yd. However, gravel with somecrushed particles should reduce the water content of thetable value by about 35 lb. Therefore, the water content canbe estimated to be about 305 lb minus 35 lb, which is 270 lb.

Cement Content. The cement content is based on themaximum water-cement ratio and the water content.Therefore, 270 lb of water divided by a water-cement ratioof 0.42 requires a cement content of 643 lb.

Coarse-Aggregate Content. The quantity of 3⁄4-in. nom-inal maximum-size coarse aggregate can be estimatedfrom Fig. 9-3 or Table 9-4. The bulk volume of coarseaggregate recommended when using sand with a finenessmodulus of 2.80 is 0.62. Since it weighs 100 lb per cu ft, theovendry weight of coarse aggregate for a cubic yard ofconcrete (27 cu ft) is

100 x 27 x 0.62 = 1674 lb per cu yd of concrete

Admixture Content. For a 7% air content, the air-entraining admixture manufacturer recommends a dosagerate of 0.9 fl oz per 100 lb of cement. From this informa-tion, the amount of air-entraining admixture is

0.9 x 643 = 5.8 fl oz per cu yd100

Fine-Aggregate Content. At this point, the amount of allingredients except the fine aggregate are known. In theabsolute volume method, the volume of fine aggregate isdetermined by subtracting the absolute volumes of theknown ingredients from 27 cu ft (1 cu yd). The absolutevolume of the water, cement, and coarse aggregate is cal-

163


With the aggregate moisture contents (MC) indicated, thetrial batch aggregate proportions become

Coarse aggregate (2% MC) = 1674 x 1.02 = 1707 lb

Fine aggregate (6% MC) = 1236 x 1.06 = 1310 lb

Water absorbed by the aggregates does not become part ofthe mixing water and must be excluded from the wateradjustment. Surface moisture contributed by the coarseaggregate amounts to 2% – 0.5% = 1.5%; that contributedby the fine aggregate is 6% – 0.7% = 5.3%. The estimatedrequirement for added water becomes

270 – (1674 x 0.015) – (1236 x 0.053) = 179 lb

The estimated batch weights for one cubic yard of con-crete are revised to include aggregate moisture as follows:

Water (to be added) 179 lbCement 643 lbCoarse aggregate (2% MC, wet) 1707 lbFine aggregate (6% MC, wet) 1310 lb

Total 3839 lb

Air-entraining admixture 5.8 fl oz

Trial Batch. At this stage, the estimated batch weightsshould be checked by means of trial batches or by full-sizefield batches. Enough concrete must be mixed for appro-priate air and slump tests and for casting the three cylin-ders required for compressive-strength tests at 28 days.For a laboratory trial batch it is convenient, in this case, toscale down the weights to produce 2.0 cu ft of concrete or2⁄27 cu yd.

Water 179 x 227 = 13.26 lb

Cement 643 x 227 = 47.63 lb

Coarse aggregate (wet) 1707 x 227 = 126.44 lb

Fine aggregate (wet) 1310 x 227 = 97.04 lb

Total 284.37 lb

Air-entraining admixture 5.8 x 227

= 0.43 fl oz

[Laboratories often convert fluid ounces to milliliters bymultiplying fluid ounces by 29.57353 to improve meas-urement accuracy. Also, most laboratory pipets used formeasuring fluids are graduated in milliliter units]

The above concrete, when mixed, had a measuredslump of 4 in., an air content of 8%, and a density (unitweight) of 141.49 lb per cubic foot. During mixing, some ofthe premeasured water may remain unused or additionalwater may be added to approach the required slump. Inthis example, although 13.26 lb of water was calculated tobe added, the trial batch actually used only 13.12 lb. Themixture excluding admixture therefore becomes:

culated by dividing the known weight of each by theproduct of their relative density (specific gravity) and thedensity of water. Volume computations are as follows:

Water = 2701 x 62.4 = 4.33 cu ft

Cement = 6433.15 x 62.4 = 3.27 cu ft

Air = 7.0100 x 27 = 1.89 cu ft

Coarse aggregate = 16742.68 x 62.4 = 10.01 cu ft

Total volume of known ingredients = 19.50 cu ft

The liquid admixture volume is generally too insignif-icant to include in these calculations. However, certainadmixtures such as shrinkage reducers, plasticizers, andcorrosion inhibitors are exceptions due to their relativelylarge dosage rates; their volumes should be included.

The calculated absolute volume of fine aggregate is then

27 – 19.50 = 7.50 cu ft

The weight of dry fine aggregate is

7.50 x 2.64 x 62.4 = 1236 lb

The mixture then has the following proportions beforetrial mixing for one cubic yard of concrete:

Water 270 lbCement 643 lbCoarse aggregate (dry) 1674 lbFine aggregate (dry) 1236 lb

Total weight 3823 lb


Slump 3 in. (±3⁄4 in. for trial batch)

Air content 7% (±0.5% for trial batch)

Estimated density = [270 + 643 + (1674 x 1.005*)(using SSD + (1236 x 1.007*)] ÷ 27aggregate) = 142.22 lb per cubic foot

Moisture. Corrections are needed to compensate for mois-ture in the aggregates. In practice, aggregates will containsome measurable amount of moisture. The dry-batchweights of aggregates, therefore, have to be increased tocompensate for the moisture that is absorbed in and con-tained on the surface of each particle and between parti-cles. The mixing water added to the batch must be reducedby the amount of free moisture contributed by the aggre-gates. Tests indicate that for this example, coarse-aggregatemoisture content is 2% and fine-aggregate moisture con-tent is 6%.

164


*(0.5% absorption ÷ 100) + 1 = 1.005;(0.7% absorption ÷ 100) + 1 = 1.007

Water 13.12 lbCement 47.63 lbCoarse aggregate (2% MC) 126.44 lbFine aggregate (6% MC) 97.04 lb

Total 284.23 lb

The yield of the trial batch is

284.23141.49 = 2.009 cu ft

The mixing water content is determined from the addedwater plus the free water on the aggregates and is calcu-lated as follows:

Water added = 13.12 lb

Free water on coarse = 126.44 x 0.015**aggregate 1.02*= 1.86 lb

Free water on fine = 97.04 x 0.053**aggregate 1.06*= 4.85 lb

Total = 19.83 lb

The mixing water required for a cubic yard of the sameslump concrete as the trial batch is

19.83 x 27 = 267 lb2.009

Batch Adjustments. The measured 4-in. slump of thetrial batch is unacceptable (more than 0.75 in. above 3-in.max.), the yield was slightly high, and the 8.0% air contentas measured in this example is also too high (more than0.5% above 7% max.). Adjust the yield, reestimate theamount of air-entraining admixture required for a 7% aircontent, and adjust the water to obtain a 3-in. slump.Increase the mixing water content by 5 lb for each 1% bywhich the air content is decreased from that of the trialbatch and reduce the water content by 10 lb for each 1-in.reduction in slump. The adjusted mixture water for thereduced slump and air content is

(5 x 1) – (10 x 1) + 267 = 262 lb per cu yd

With less mixing water needed in the trial batch, less ce-ment also is needed to maintain the desired water-cementratio of 0.42. The new cement content is

2620.42 = 624 lb per cu yd

The amount of coarse aggregate remains unchangedbecause workability is satisfactory. The new adjusted batchweights based on the new cement and water contents arecalculated after the following volume computations:

Water = 2621 x 62.4 = 4.20 cu ft

Cement = 6243.15 x 62.4 = 3.17 cu ft

Coarse aggregate = 16742.68 x 62.4 = 10.01 cu ft

Air = 7.0100 x 27 = 1.89 cu ft

Total = 19.27 cu ft

Fine aggregate volume = 27 – 19.27 = 7.73 cu ft

The weight of dry fine aggregate required is7.73 x 2.64 x 62.4 = 1273 lb

An air-entraining admixture dosage of 0.8 fluid ouncesper 100 pounds of cement is expected to achieve the 7% aircontent in this example. Therefore, the amount of air-entraining admixture required is:

= 0.8 x 624 = 5.0 fl oz100

Adjusted batch weights per cubic yard of concrete are

Water 262 lbCement 624 lbCoarse aggregate (dry) 1674 lbFine aggregate (dry) 1273 lb

Total 3833 lb


Estimated concrete density (unit weight) with the aggre-gates at SSD:

= [262 + 624 + (1674 x 1.005) + (1273 x 1.007)]27

= 142.60 lb per cu ft

Upon completion of checking these adjusted propor-tions in a trial batch, it was found that the proportions wereadequate for the desired slump, air content, and yield. The28-day test cylinders had an average compressive strengthof 4900 psi, which exceeds the Â of 4700 psi. Due to fluc-tuations in moisture content, absorption rates, and specificgravity of the aggregate, the density determined by volumecalculations may not always equal the unit weight deter-mined by ASTM C 138 (AASHTO T 121). Occasionally, theproportion of fine to coarse aggregate is kept constant inadjusting the batch weights to maintain workability orother properties obtained in the first trial batch. Afteradjustments to the cement, water, and air content have beenmade, the volume remaining for aggregate is appropriatelyproportioned between the fine and coarse aggregates.

Additional trial concrete mixtures with water-cementratios above and below 0.42 should also be tested todevelop a strength curve. From the curve, a new more eco-nomical mixture with a compressive strength closer to Â,can be proportioned and tested. The final mixture wouldprobably look similar to the above mixture with a slumprange of 1 in. to 3 in. and an air content of 5% to 7%. The

165


* 1 + (2% MC/100) = 1.02; 1 + (6% MC/100) = 1.06;** (2% MC – 0.5% absorption)/100 = 0.015; (6% MC – 0.7% absorp-

tion)/100 = 0.053

Example 3. Laboratory Trial Mixture Using the PCA Water-Cement RatioMethod (Metric)

With the following method, the mix designer developsthe concrete proportions directly from the laboratory trialbatch rather than the absolute volume of the constituentingredients.

Conditions and Specifications. Concrete is required fora plain concrete pavement to be constructed in NorthDakota. The pavement specified compressive strength is35 MPa at 28 days. The standard deviation of the concreteproducer is 2.0 MPa. Type IP cement and 19-mm nominalmaximum-size coarse aggregate is locally available. Pro-portion a concrete mixture for these conditions and checkit by trial batch. Enter all data in the blank spaces on a trialmixture data sheet (Fig. 9-6).

Durability Requirements. The pavement will be exposedto freezing, thawing, and deicers and therefore shouldhave a maximum water to cementitious material ratio of0.45 (Table 9-1) and at least 335 kg of cement per cubicmeter of concrete.

Strength Requirements. For a standard deviation of2.0 MPa, the Â (required compressive strength for pro-portioning) must be the larger of

Â = ˘ + 1.34S = 35 + 1.34(2.0) = 37.7 MPa

or

Â = ˘ + 2.33S – 3.45 = 35 + 2.33(2.0) – 3.45 = 36.2 MPa

Therefore the required average compressive strength= 37.7 MPa.

Aggregate Size. The 19-mm maximum-size coarse aggre-gate and the fine aggregate are in saturated-surface drycondition for the trial mixtures.

Air Content. The target air content should be 6% (Table9-5) and the range is set at 5% to 8%.

Slump. The specified target slump for this project is40 (±20) mm.

Batch Quantities. For convenience, a batch containing 10kg of cement is to be made. The quantity of mixing waterrequired is 10 x 0.45 = 4.5 kg. Representative samples offine and coarse aggregates are measured in suitable con-tainers. The values are entered as initial mass in Column 2of the trial-batch data sheet (Fig. 9-6).

All of the measured quantities of cement, water, andair-entraining admixture are used and added to the mixer.Fine and coarse aggregates, previously brought to a satu-rated, surface-dry condition, are added until a workableconcrete mixture with a slump deemed adequate for place-ment is produced. The relative proportions of fine andcoarse aggregate for workability can readily be judged byan experienced concrete technician or engineer.

Workability. Results of tests for slump, air content, den-sity, and a description of the appearance and workabilityare noted in the data sheet and Table 9-13.

amount of air-entraining admixture must be adjusted tofield conditions to maintain the specified air content.

Water Reducers. Water reducers are used to increaseworkability without the addition of water or to reduce thewater-cement ratio of a concrete mixture to improve per-meability or other properties.

Using the final mixture developed in the last example,assume that the project engineer approves the use of awater reducer to increase the slump to 5 in. to improveworkability for a difficult placement area. Assuming thatthe water reducer has a manufacturer’s recommendeddosage rate of 4 oz per 100 lb of cement to increase slump2 in., the admixture amount becomes

624100 x 4 = 25.0 oz per cu yd

The amount of air-entraining agent may also need to bereduced (up to 50%), as many water reducers also entrainair. If a water reducer was used to reduce the water-cement ratio, the water and sand content would also needadjustment.

Pozzolans and Slag. Pozzolans and slag are sometimesadded in addition to or as a partial replacement of cementto aid in workability and resistance to sulfate attack andalkali reactivity. If a pozzolan or slag were required for theabove example mixture, it would have been entered in thefirst volume calculation used in determining fine aggre-gate content. For example:

Assume that 75 lb of fly ash with a relative density (specificgravity) of 2.5 were to be used in addition to the originallyderived cement content. The ash volume would be

752.5 x 62.4 = 0.48 cu ft

The water to cementing materials ratio would be W C + P = 27

6430

+ 75 = 0.38 by weight

The water to portland cement only ratio would still beWC = 270

643 = 0.42 by weight

The fine aggregate volume would have to be reduced by0.48 cu ft to allow for the volume of ash.

The pozzolan amount and volume computation couldalso have been derived in conjunction with the first ce-ment content calculation using a water to cementing mate-rials ratio of 0.42 (or equivalent). For example, assume15% of the cementitious material is specified to be a poz-zolan and

W/ CM or W/ (C + P) = 0.42.Then with W = 270 lb and C + P = 643 lb,

P = 643 x 15100 = 96 lb

and C = 643 – 96 = 547 lb Appropriate proportioning computations for these andother mix ingredients would follow.

166


The amounts of fine and coarse aggregates not usedare recorded on the data sheet in Column 3, and mass ofaggregates used (Column 2 minus Column 3) are noted inColumn 4. If the slump when tested had been greater than

that required, additional fine or coarse aggregates (orboth) would have been added to reduce slump. Had theslump been less than required, water and cement in theappropriate ratio (0.45) would have been added to in-

crease slump. It is impor-tant that any additionalquantities be measuredaccurately and recordedon the data sheet.

Mixture Proportions.Mixture proportions fora cubic meter of concreteare calculated in Column5 of Fig. 9-6 by using thebatch yield (volume) anddensity (unit weight).For example, the numberof kilograms of cementper cubic meter is deter-mined by dividing onecubic meter by thevolume of concrete inthe batch and multi-plying the result by thenumber of kilograms ofcement in the batch. Thepercentage of fine aggre-gate by mass of totalaggregate is also calcu-lated. In this trial batch,the cement content was341 kg/m3 and the fineaggregate made up 38%of the total aggregate bymass. The air contentand slump were accept-able. The 28-day strengthwas 39.1 MPa, greaterthan Â. The mixture inColumn 5, along withslump and air contentlimits of 40 (±20) mmand 5% to 8%, respec-tively, is now ready forsubmission to the projectengineer.

167


Fig. 9-6. Trial mixture data sheet (metric).

Fine aggregate,Air content, Density, Cement percent of total

Batch no. Slump, mm percent kg/m3 content, kg/m3 aggregate Workability

1 50 5.7 2341 346 28.6 Harsh2 40 6.2 2332 337 33.3 Fair3 45 7.5 2313 341 38.0 Good4 36 6.8 2324 348 40.2 Good

*Water-cement ratio was 0.45.

Table 9-13. Example of Results of Laboratory Trial Mixtures (Metric)*

For a standard deviation of 300 psi,Â must be the larger of

Â = ˘ + 1.34S = 4000 + 1.34(300) = 4402 psi

or

Â = ˘ + 2.33S – 500 = 4000 + 2.33(300) – 500 = 4199 psi

Therefore, Â = 4400 psi

From Fig. 9-7, the water-cement ratio for air-entrained concrete is 0.55 for an Â of 4400 psi. This isgreater than the 0.50 permitted for the exposure condi-tions; therefore, the exposure requirements govern. Awater-cement ratio of 0.50 must be used, even though thismay produce strengths higher than needed to satisfystructural requirements.

Aggregate Size. Assuming it is economically available,11⁄2-in. maximum-size aggregate is satisfactory; it is lessthan 1⁄5 the wall thickness and less than 3⁄4 the clear distancebetween reinforcing bars and between reinforcing bars andthe form. If this size were not available, the next smalleravailable size would be used. Aggregates are to be in a sat-urated surface-dry condition for these trial mixtures.

Air Content. Because of the exposure conditions and toimprove workability, a moderate level of entrained air isneeded. From Table 9-5, the target air content for con-crete with 11⁄2-in. aggregate in a moderate exposure is4.5%. Therefore, proportion the mixture with an air con-tent range of 4.5% ±1% and aim for 5.5% ±0.5% in thetrial batch.

Slump. The recommended slump range for placing a rein-forced concrete foundation wall is 1 in. to 3 in., assumingthat the concrete will be consolidated by vibration (Table9-6). Batch for 3 in. ±0.75 in.

Batch Quantities. For convenience, a batch containing 20lb of cement is to be made. The quantity of mixing waterrequired is 20 x 0.50 = 10 lb. Representative samples of fineand coarse aggregates are weighed into suitable con-tainers. The values are entered as initial weights inColumn 2 of the trial-batch data sheet (Fig. 9-8).

All of the measured quantities of cement, water, andair-entraining admixture are used and added to the mixer.Fine and coarse aggregates, previously brought to a satu-rated surface-dry condition, are added in proportions sim-ilar to those used in mixes from which Fig. 9-7 wasdeveloped. Mixing continues until a workable concretewith a 3-in. slump deemed adequate for placement is pro-duced. The relative proportions of fine and coarse aggre-gate for workability can readily be judged by anexperienced concrete technician or engineer.

Workability. Results of tests for slump, air content, unitweight, and a description of the appearance and worka-bility (“Good” for this example) are noted on the datasheet.

The amounts of fine and coarse aggregates not usedare recorded on the data sheet in Column 3, and masses ofaggregates used (Column 2 minus Column 3) are noted inColumn 4. If the slump when tested had been greater thanthat required, additional fine or coarse aggregates (or

Example 4. Laboratory Trial Mixture Using the PCA Water-Cement RatioMethod (Inch-Pound Units)

With the following method, the mix designer develops theconcrete proportions directly from a laboratory trial batch,rather than the absolute volume of the constituent ingre-dients as in Example 2.

Conditions and Specifications. Air-entrained concrete isrequired for a foundation wall that will be exposed to mod-erate sulfate soils. A compressive strength, ˘, of 4000 psi at28 days using Type II cement is specified. Minimum thick-ness of the wall is 10 in. and concrete cover over 1⁄2-in.-diameter reinforcing bars is 3 in. The clear distancebetween reinforcing bars is 3 in. The water-cement ratioversus compressive strength relationship based on fieldand previous laboratory data for the example ingredientsis illustrated by Fig. 9-7. Based on the test records of thematerials to be used, the standard deviation is 300 psi. Pro-portion and evaluate by trial batch a mixture meeting theabove conditions and specifications. Enter all data in theappropriate blanks on a trial-mixture data sheet (Fig. 9-8).

Water-Cement Ratio. For these exposure conditions,Table 9-2 indicates that concrete with a maximum water-cement ratio of 0.50 should be used and the minimumdesign strength should be 4000 psi.

The water-cement ratio for strength is selected from agraph plotted to show the relationship between the water-cement ratio and compressive strength for these specificconcrete materials (Fig. 9-7).

168


6000

5000

4400

4000

3000

2000


0.4 0.5 0.6 0.7 0.80.55

Water-cement ratio

Compressive strength, psi

Fig. 9-7. Relationship between strength and water tocement ratio based on field and laboratory data for specificconcrete ingredients.

both) would have been added to reduce slump. Had theslump been less than required, water and cement in theappropriate ratio (0.50) would have been added to in-crease slump. It is important that any additional quantitiesbe measured accurately and recorded on the data sheet.

Mixture Proportions. Mixture proportions for a cubicyard of concrete are calculated in Column 5 of Fig. 9-8 byusing the batch yield (volume) and density (unit weight).For example, the number of pounds of cement per cubicyard is determined by dividing 27 cu ft (1 cu yd) by the

volume of concrete in thebatch and multiplyingthe result by the numberof pounds of cement inthe batch. The per-centage of fine aggregateby weight of total aggre-gate is also calculated. Inthis trial batch, thecement content was 539lb per cubic yard and thefine aggregate made up33.5% of the total aggre-gate by weight. The aircontent and slump wereacceptable. The 28-daystrength was 4950 psi(greater than Â). Themixture in Column 5,along with slump and aircontent limits of 1 in. to 3in. and 3.5% to 5.5%,respectively, is nowready for submission tothe project engineer.

Mixture Adjustments.To determine the mostworkable and econom-ical proportions, addi-tional trial batches couldbe made varying the per-centage of fine aggregate.In each batch the water-cement ratio, aggregategradation, air content,and slump should re-main about the same.Results of four such trialbatches are summarizedin Table 9-14.

169


Fig. 9-8. Trial mixture data sheet (inch-pound units).

Fine aggregate,Air content, Density, Cement content, percent of total

Batch no. Slump, in. percent lb/cu ft3 lb/cu yd3 aggregate Workability

1 3 5.4 144 539 33.5 Good2 23⁄4 4.9 144 555 27.4 Harsh3 21⁄2 5.1 144 549 35.5 Excellent4 3 4.7 145 540 30.5 Excellent

*Water-cement ratio was 0.50.

Table 9-14. Example of Results of Laboratory Trial Mixtures (Inch-Pound Units)*

illustrate the relationship between ingredients and prop-erties. This is especially useful when optimizing concretemixtures for best economy or to adjust to specification ormaterial changes (Fig. 9-9).

Table 9-15 illustrates the change in mix proportionsfor various types of concrete mixtures using a particularaggregate source. Information for concrete mixtures usingparticular ingredients can be plotted in several ways to

170


1000

900

800

700

600

500

400

300

7

6

5

4

3

2

1

0

550

500

450

400

350

300

250

200

150

175

150

125

100

75

50

25

0

240 260 280 300 320 340 360 380

150 160 170 180 190 200 210 220 230

Water content, kg/m3

Water content, lb/yd3

Cem

ent c

onte

nt, l

b/yd

3

Cem

ent c

onte

nt, k

g/m

3

Slu

mp,

in.

Slu

mp,

mm


Nominal maximum aggregate size, mm (in.)

w/c = 0.40

0.45

0.50

0.55

0.60

0.65

0.70

50 m

m (2

in.)

37.5

mm

(11 /2

in.)

25 m

m (1

in.)

19 m

m (

3 /4 in

.)

12.5

mm

(1 /2

in.)

9.5

mm

(3 /8

in.)

Fig. 9-9. Example graphical relationship for a particular aggregate source demonstrating therelationship between slump, aggregate size, water to cement ratio, and cement content (Hover 1995).

171


Table 9-15 (Metric). Example Trial Mixtures for Air-Entrained Concrete of Medium Consistency, 75-mm to 100-mm slump

With fine sand, With coarse sand,fineness modulus = 2.50 fineness modulus = 2.90

Nominal Fine Fine Coarse Fine Fine CoarseWater- maximum Water, kg Cement, kg aggregate, aggregate, aggregate, aggregate, aggregate, aggregate,cement size of Air per cu per cu percent kg per cu kg per cu percent kg per cu kg per curatio, kg aggregate, content, meter of meter of of total meter of meter of of total meter of meter ofper kg mm percent concrete concrete aggregate concrete concrete aggregate concrete concrete0.40 9.5 7.5 202 505 50 744 750 54 809 684

12.5 7.5 194 485 41 630 904 46 702 83319.0 6 178 446 35 577 1071 39 648 100025.0 6 169 424 32 534 1151 36 599 108637.5 5 158 395 29 518 1255 33 589 1184

0.45 9.5 7.5 202 450 51 791 750 56 858 68412.5 7.5 194 387 43 678 904 47 750 83319.0 6 178 395 37 619 1071 41 690 100025.0 6 169 377 33 576 1151 37 641 108637.5 5 158 351 31 553 1225 35 625 1184

0.50 9.5 7.5 202 406 53 833 750 57 898 68412.5 7.5 194 387 44 714 904 49 785 83319.0 6 178 357 38 654 1071 42 726 100025.0 6 169 338 34 605 1151 38 670 108637.5 5 158 315 32 583 1225 36 654 1184

0.55 9.5 7.5 202 369 54 862 750 58 928 68412.5 7.5 194 351 45 744 904 49 815 83319.0 6 178 324 39 678 1071 43 750 100025.0 6 169 309 35 629 1151 39 694 108637.5 5 158 286 33 613 1225 37 684 1184

0.60 9.5 7.5 202 336 54 886 750 58 952 68412.5 7.5 194 321 46 768 904 50 839 83319.0 6 178 298 40 702 1071 44 773 100025.0 6 169 282 36 653 1151 40 718 108637.5 5 158 262 33 631 1225 37 702 1184

0.65 9.5 7.5 202 312 55 910 750 59 976 68412.5 7.5 194 298 47 791 904 51 863 83319.0 6 178 274 40 720 1071 44 791 100025.0 6 169 261 37 670 1151 40 736 108637.5 5 158 244 34 649 1225 38 720 1184

0.70 9.5 7.5 202 288 55 928 750 59 994 68412.5 7.5 194 277 47 809 904 51 880 83319.0 6 178 256 41 738 1071 45 809 100025.0 6 169 240 37 688 1151 41 753 108637.5 5 158 226 34 660 1225 38 732 1184

Table 9-15 (Inch-Pound Units). Example Trial Mixtures for Air-Entrained Concrete of Medium Consistency, 3-in. to 4-in. slump


Nominal Fine Fine Coarse Fine Fine CoarseWater- maximum Water, lb Cement, lb aggregate, aggregate, aggregate, aggregate, aggregate, aggregate,cement size of Air per cu per cu percent lb per cu lb per cu percent lb per cu lb per curatio, lb aggregate, content, yd of yd of of total yd of yd of of total yd of yd ofper lb in. percent concrete concrete aggregate concrete concrete aggregate concrete concrete0.40 3⁄8 7.5 340 850 50 1250 1260 54 1360 1150

1⁄2 7.5 325 815 41 1060 1520 46 1180 14003⁄4 6 300 750 35 970 1800 39 1090 16801 6 285 715 32 900 1940 36 1010 1830

11⁄2 5 265 665 29 870 2110 33 990 19900.45 3⁄8 7.5 340 755 51 1330 1260 56 1440 1150

1⁄2 7.5 325 720 43 1140 1520 47 1260 14003⁄4 6 300 665 37 1040 1800 41 1160 16801 6 285 635 33 970 1940 37 1080 1830

11⁄2 5 265 590 31 930 2110 35 1050 1990

Slag: Grade 120, ASTM C 989 (AASHTO M302). Relative density of 2.90.

Coarse aggregate: Well-graded 19-mm nominal max-imum-size crushed rock (ASTM C 33or AASHTO M 80) with an ovendryrelative density of 2.68, absorption of0.5%, and ovendry density of 1600kg/m3. The laboratory sample has amoisture content of 2.0%. This aggre-gate has a history of alkali-silica reac-tivity in the field.

Fine aggregate: Natural sand with some crushed par-ticles (ASTM C 33 or AASHTO M 6)with an ovendry relative density of 2.64and an absorption of 0.7%. The labora-tory sample has a moisture content of6%. The fineness modulus is 2.80.

Air entrainer: Synthetic, ASTM C 260 (AASHTO M154).

Retarding water Type D, ASTM C 494 (AASHTO Mreducer: 194). Dosage of 3 g per kg of cement-

ing materials.

Example 5. Absolute Volume Method Using Multiple Cementing Materials and Admixtures (Metric)

The following example illustrates how to develop a mixusing the absolute volume method when more than onecementing material and admixture are used.

Conditions and Specifications. Concrete with a struc-tural design strength of 40 MPa is required for a bridge tobe exposed to freezing and thawing, deicers, and verysevere sulfate soils. A coulomb value not exceeding 1500 isrequired to minimize permeability to chlorides. Water re-ducers, air entrainers, and plasticizers are allowed. Ashrinkage reducer is requested to keep shrinkage under300 millionths. Some structural elements exceed a thick-ness of 1 meter, requiring control of heat development.The concrete producer has a standard deviation of 2 MPafor similar mixes to that required here. For difficult place-ment areas, a slump of 200 mm to 250 mm is required. Thefollowing materials are available:Cement: Type HS, silica fume modified portland

cement, ASTM C 1157. Relative densityof 3.14. Silica fume content of 5%.

Fly ash: Class F, ASTM C 618 (AASHTO M295). Relative density of 2.60.

172


Table 9-15 (Inch-Pound Units). Example Trial Mixtures for Air-Entrained Concrete of Medium Consistency, 3-in. to 4-in. slump (Continued)


Nominal Fine Fine Coarse Fine Fine CoarseWater- maximum Water, lb Cement, lb aggregate, aggregate, aggregate, aggregate, aggregate, aggregate,cement size of Air per cu per cu percent lb per cu lb per cu percent lb per cu lb per curatio, lb aggregate, content, yd of yd of of total yd of yd of of total yd of yd ofper lb in. percent concrete concrete aggregate concrete concrete aggregate concrete concrete0.50 3⁄8 7.5 340 680 53 1400 1260 57 1510 1150

1⁄2 7.5 325 650 44 1200 1520 49 1320 14003⁄4 6 300 600 38 1100 1800 42 1220 16801 6 285 570 34 1020 1940 38 1130 1830

11⁄2 5 265 530 32 980 2110 36 1100 19900.55 3⁄8 7.5 340 620 54 1450 1260 58 1560 1150

1⁄2 7.5 325 590 45 1250 1520 49 1370 14003⁄4 6 300 545 39 1140 1800 43 1260 16801 6 285 520 35 1060 1940 39 1170 1830

11⁄2 5 265 480 33 1030 2110 37 1150 19900.60 3⁄8 7.5 340 565 54 1490 1260 58 1600 1150

1⁄2 7.5 325 540 46 1290 1520 50 1410 14003⁄4 6 300 500 40 1180 1800 44 1300 16801 6 285 475 36 1100 1940 40 1210 1830

11⁄2 5 265 440 33 1060 2110 37 1180 19900.65 3⁄8 7.5 340 525 55 1530 1260 59 1640 1150

1⁄2 7.5 325 500 47 1330 1520 51 1450 14003⁄4 6 300 460 40 1210 1800 44 1330 16801 6 285 440 37 1130 1940 40 1240 1830

11⁄2 5 265 410 34 1090 2110 38 1210 19900.70 3⁄8 7.5 340 485 55 1560 1260 59 1670 1150

1⁄2 7.5 325 465 47 1360 1520 51 1480 14003⁄4 6 300 430 41 1240 1800 45 1360 16801 6 285 405 37 1160 1940 41 1270 1830

11⁄2 5 265 380 34 1110 2110 38 1230 1990

Plasticizer: Type 1, ASTM C 1017. Dosage of 30 gper kg of cementing materials.

Shrinkage reducer: Dosage of 15 g per kg of cementingmaterials.

Strength. For a standard deviation of 2.0 MPa, the Âmust be the greater of

Â = ˘ + 1.34S = 40 + 1.34(2) = 42.7

or

Â = 0.9 ˘ + 2.33S = 36 + 2.33(2) = 40.7

therefore Â = 42.7

Water to Cementing Materials Ratio. Past field recordsusing these materials indicate that a water to cementingmaterials ratio of 0.35 is required to provide a strengthlevel of 42.7 MPa.

For a deicer environment and to protect embeddedsteel from corrosion, Table 9-1 requires a maximum waterto cementing materials ratio of 0.40 and a strength of atleast 35 MPa. For a severe sulfate environment, Table 9-2requires a maximum water to cementing materials ratio of0.40 and a strength of at least 35 MPa. Both the water tocementing materials ratio requirements and strengthrequirements are met and exceeded using the above deter-mined 0.35 water to cementing materials ratio and 40 MPadesign strength.

Air Content. For a severe exposure, Fig. 9-4 suggests atarget air content of 6% for 19-mm aggregate. Therefore,design the mix for 5% to 8% and use 8% for batch propor-tions. The trial batch air content must be within ±0.5 per-centage points of the maximum allowable air content.

Slump. Assume a slump of 50 mm without the plasticizerand a maximum of 200 mm to 250 mm after the plasticizeris added. Use 250 ± 20 mm for proportioning purposes.

Water Content. Fig. 9-5 recommends that a 50-mm slump,air-entrained concrete with 19-mm aggregate should havea water content of about 168 kg/m3. Assume the retardingwater reducer and plasticizer will jointly reduce waterdemand by 15% in this case, resulting in an estimatedwater demand of 143 kg per cubic meter, while achievingthe 250-mm slump.

Cementing Materials Content. The amount of cementingmaterials is based on the maximum water-cementingmaterials ratio and water content. Therefore, 143 kg ofwater divided by a water-cementing materials ratio of 0.35requires a cement content of 409 kg. Fly ash and slag willbe used to help control alkali-silica reactivity and controltemperature rise. Local use has shown that a fly ashdosage of 15% and a slag dosage of 30% by mass of ce-menting materials are adequate. Therefore, the suggestedcementing materials for one cubic meter of concrete areas follows:

Cement: 55% of 409 = 225 kgFly ash: 15% of 409 = 61 kgSlag: 30% of 409 = 123 kg

These dosages meet the requirements of Table 9-8(2.8% silica fume from the cement + 15% fly ash + 30% slag= 47.8% which is less than the 50% maximum allowed).

Coarse-Aggregate Content. The quantity of 19-mmnominal maximum-size coarse aggregate can be estimatedfrom Fig. 9-3. The bulk volume of coarse aggregate rec-ommended when using sand with a fineness modulus of2.80 is 0.62. Since the coarse aggregate has a bulk densityof 1600 kg/m3, the ovendry mass of coarse aggregate for acubic meter of concrete is

1600 x 0.62 = 992 kg/m3

Admixture Content. For an 8% air content, the air-entraining admixture manufacturer recommends a dosageof 0.5 g per kg of cementing materials. The amount of airentrainer is then

0.5 x 409 = 205 g = 0.205 kg

The retarding water reducer dosage rate is 3 g per kg ofcementing materials. This results in

3 x 409 = 1227 g or 1.227 kg of water reducer per cubicmeter of concrete.

The plasticizer dosage rate is 30 g per kg of cementingmaterials. This results in

30 x 409 = 12,270 g or 12.270 kg of plasticizer per cubicmeter of concrete.

The shrinkage reducer dosage rate is 15 g per kg ofcementing materials. This results in

15 x 409 = 6135 g or 6.135 kg of shrinkage reducer percubic meter of concrete.

Fine-Aggregate Content. At this point, the amounts of allingredients except the fine aggregate are known. Thevolume of fine aggregate is determined by subtracting theabsolute volumes of all known ingredients from 1 cubicmeter. The absolute volumes of the ingredients is calcu-lated by dividing the known mass of each by the productof their relative density and the density of water. Assume arelative density of 1.0 for the chemical admixtures. Assumea density of water of 997.75 kg/m3 as all materials in thelaboratory are maintained at a room temperature of 22°C(Table 9-12). Volumetric computations are as follows:

Water (including= 143

chemical 1.0 x 997.75 = 0.143 m3

admixtures)

Cement = 2253.14 x 997.75 = 0.072 m3

Fly ash = 612.60 x 997.75 = 0.024 m3

Slag = 1232.90 x 997.75 = 0.043 m3

Air = 8.0100 = 0.080 m3

Coarse aggregate = 9922.68 x 997.75 = 0.371 m3

Total = 0.733 m3

173


The batch quantities for one cubic meter of concreteare revised to include aggregate moisture as follows:

Water (to be added) 71 kgCement 225 kgFly ash 61 kgSlag 123 kgCoarse aggregate (2% MC) 1012 kgFine aggregate (6% MC) 745 kgAir entrainer 0.205 kgWater reducer 1.227 kgPlasticizer 12.27 kgShrinkage reducer 6.14 kg

Trial Batch. The above mixture is tested in a 0.1 m3 batchin the laboratory (multiply above quantities by 0.1 to ob-tain batch quantities). The mixture had an air content of7.8%, a slump of 240 mm, a density of 2257 kg/m3, a yieldof 0.1 m3, and a compressive strength of 44 MPa. Rapidchloride testing resulted in a coulomb value of 990 (ASTMC 1202 or AASHTO T 277). A modified version of ASTM C1260 was used to evaluate the potential of the mix foralkali-silica reactivity, resulting in an acceptable expansionof 0.02%. Temperature rise was acceptable and shrinkagewas within specifications. The water-soluble chloride con-tent was 0.06%, meeting the requirements of Table 9-9. Thefollowing mix proportions meet all applicable require-ments and are ready for submission to the project engineerfor approval:

Water added 123 kg (143 kg total includingadmixtures)

Cement, Type HS 225 kgFly ash, Class F 61 kgSlag, Grade 120 123 kgCoarse aggregate 992 kg (ovendry) or 997 kg (SSD)Fine aggregate 703 kg (ovendry) or 708 kg (SSD)Air entrainer* 0.205 kg Water reducer* 1.227 kgPlasticizer* 12.27 kgShrinkage reducer* 6.14 kgSlump 200 mm to 250 mmAir content 5% to 8%Density (SSD agg.) 2257 kg/m3

Yield 1 m3

Water-cementingmaterials ratio 0.35

*Liquid admixture dosages are often provided in liters ormilliliters in mix proportion documents.

CONCRETE FOR SMALL JOBS

Although well-established ready mixed concrete mixturesare used for most construction, ready mix is not alwayspractical for small jobs, especially those requiring onecubic meter (yard) or less. Small batches of concrete mixedat the site are required for such jobs.

The calculated absolute volume of fine aggregate is then1 – 0.733 = 0.267 m3

The mass of dry fine aggregate is 0.267 x 2.64 x 997.75 = 703 kg

The admixture volumes are

Air entrainer = 0.205(1.0 x 997.75) = 0.0002 m3

Water reducer = 1.227(1.0 x 997.75) = 0.0012 m3

Plasticizer = 12.270(1.0 x 997.75) = 0.0123 m3

Shrinkage reducer = 6.135(1.0 x 997.75) = 0.0062 m3

Total = 19.84 kg of admixture with a volume of 0.0199 m3

Consider the admixtures part of the mixing water

Mixing water minus admixtures = 143 – 19.84 = 123 kg

The mixture then has the following proportions beforetrial mixing for 1 cubic meter of concrete:

Water 123 kgCement 225 kgFly ash 61 kgSlag 123 kgCoarse aggregate (dry) 992 kgFine aggregate (dry) 703 kgAir entrainer 0.205 kgWater reducer 1.227 kgPlasticizer 12.27 kgShrinkage reducer 6.135 kgTotal = 2247 kg

Slump = 250 mm (± 20 mm for trial batch)

Air content = 8% (± 0.5% for trial batch)

Estimated concrete density using SSD aggregate (addingabsorbed water)

= 123 + 225 + 61 + 123 + (992 x 1.005) + (703 x 1.007) + 20(admixtures) = 2257 kg/m3

Moisture. The dry batch weights of aggregates have to beincreased to compensate for the moisture on and in theaggregates and the mixing water reduced accordingly. Thecoarse aggregate and fine aggregate have moisture con-tents of 2% and 6%, respectively. With the moisture con-tents indicated, the trial batch aggregate proportionsbecome

Coarse aggregate (2% MC) = 992 x 1.02 = 1012 kgFine aggregate (6% MC) = 703 x 1.06 = 745 kg

Absorbed water does not become part of the mixingwater and must be excluded from the water adjustment.Surface moisture contributed by the coarse aggregateamounts to 2% – 0.5% = 1.5% and that contributed by thefine aggregate, 6% – 0.7% = 5.3%. The estimated addedwater becomes

123 – (992 x 0.015) – (703 x 0.053) = 71 kg

174


175

Chapter 9 ◆ Designing and Proportioning Normal Concrete Mixtures

Table 9-16 (Metric). Proportions by Mass to Make One Tenth Cubic Meter of Concrete for Small Jobs

Nominal Air-entrained concrete Non-air-entrained concretemaximum

size coarse Wet fine Wet coarse Wet fine Wet coarseaggregate, Cement, aggregate, aggregate, Water, Cement, aggregate, aggregate, Water,

mm kg kg kg* kg kg kg kg kg9.5 46 85 74 16 46 94 74 18

12.5 43 74 88 16 43 85 88 1819.0 40 67 104 16 40 75 104 1625.0 38 62 112 15 38 72 112 1537.5 37 61 120 14 37 69 120 14

*If crushed stone is used, decrease coarse aggregate by 5 kg and increase fine aggregate by 5 kg.

Table 9-16 (Inch-Pound). Proportions by Mass to Make One Cubic Foot of Concrete for Small Jobs


size coarse Wet fine Wet coarse Wet fine Wet coarseaggregate, Cement, aggregate, aggregate, Water, Cement, aggregate, aggregate, Water,

in. lb lb lb* lb lb lb lb lb3⁄8 29 53 46 10 29 59 46 111⁄2 27 46 55 10 27 53 55 113⁄4 25 42 65 10 25 47 65 101 24 39 70 9 24 45 70 10

11⁄2 23 38 75 9 23 43 75 9

*If crushed stone is used, decrease coarse aggregate by 3 lb and increase fine aggregate by 3 lb.

Table 9-17. Proportions by Bulk Volume* of Concrete for Small Jobs


size coarseaggregate, Wet fine Wet coarse Wet fine Wet coarse

mm (in.) Cement aggregate aggregate Water Cement aggregate aggregate Water9.5 (3⁄8) 1 21⁄4 11⁄2 1⁄2 1 21⁄2 11⁄2 1⁄2

12.5 (1⁄2) 1 21⁄4 2 1⁄2 1 21⁄2 2 1⁄219.0 (3⁄4) 1 21⁄4 21⁄2 1⁄2 1 21⁄2 21⁄2 1⁄225.0 (1) 1 21⁄4 23⁄4 1⁄2 1 21⁄2 23⁄4 1⁄237.5 (11⁄2) 1 21⁄4 3 1⁄2 1 21⁄2 3 1⁄2

*The combined volume is approximately 2⁄3 of the sum of the original bulk volumes.

If mixture proportions or mixture specifications arenot available, Tables 9-16 and 9-17 can be used to selectproportions for concrete for small jobs. Recommendationswith respect to exposure conditions discussed earliershould be followed.

The proportions in Tables 9-16 and 9-17 are only aguide and may need adjustments to obtain a workablemix with locally available aggregates (PCA 1988). Pack-aged, combined, dry concrete ingredients (ASTM C 387)are also available.

DESIGN REVIEW

In practice, concrete mixture proportions will be gov-erned by the limits of data available on the properties ofmaterials, the degree of control exercised over the pro-duction of concrete at the plant, and the amount of super-

vision at the jobsite. It should not be expected that fieldresults will be an exact duplicate of laboratory trialbatches. An adjustment of the selected trial mixture isusually necessary on the job.

The mixture design and proportioning procedurespresented here and summarized in Fig. 9-10 are applicableto normal-weight concrete. For concrete requiring somespecial property, using special admixtures or materials—lightweight aggregates, for example—different propor-tioning principles may be involved.

Internet web sites also provide assistance withdesigning and proportioning concrete mixtures (Bentz2001). Many of these web sites are internationally orientedand assume principles not used in North America.Therefore, appropriate cautions should be taken whenusing the internet to design concrete mixtures.

176


Concrete production facility has field strengthtest records for the specified class of concreteor within 7 MPa (1000 psi) of the specified class.

Calculate S

Results representone mixture

Submit for approval

Results represent twoor more mixtures

Calculate average SCalculate and increase

using Table 9-10

≥ 30 consecutivetests

Two groups of consecutivetests (total ≥ 30)

Required average strengthfrom Eq. (9-1) or (9-2) or (9-3)

Field record of at least ten consecutivetest results using similar materials and

under similar conditions is available

Average ≥requiredaverage

Plot average strength versusproportions and interpolate for

required average strength

Plot average strength versusproportions and interpolate for

required average strength

Required average strengthfrom Table 9-11

Make trial mixtures using at least three differentw/cm ratios or cementing materials contents

15 to 29 consecutivetests

or

No

NoYes NoYes NoYes

Yes

No

Yes

No

Yes

No

Yes

(No datafor S)

Fig. 9-10. Flowchart for selection and documentation of concrete proportions.

REFERENCES

Abrams, D. A., Design of Concrete Mixtures, Lewis Institute,Structural Materials Research Laboratory, Bulletin No. 1,PCA LS001, Chicago, http://www.portcement.org/pdf_files/LS001.pdf, 1918, 20 pages.

ACI Committee 211, Standard Practice for SelectingProportions for Normal, Heavyweight and Mass Concrete, ACI211.1-91, American Concrete Institute, Farmington Hills,Michigan, 1991.

ACI Committee 211, Guide for Selecting Proportions forHigh-Strength Concrete with Portland Cement and Fly Ash,ACI 211.4R-93, American Concrete Institute, FarmingtonHills, Michigan, 1993.

ACI Committee 211, Guide for Submittal of ConcreteProportions, ACI 211.5R-96, American Concrete Institute,Farmington Hills, Michigan, 1996.

ACI Committee 211, Guide for Selecting Proportions for No-Slump Concrete, ACI 211.3R-97, American Concrete Insti-tute, Farmington Hills, Michigan, 1997.

ACI Committee 211, Standard Practice for SelectingProportions for Structural Lightweight Concrete, ACI 211.2-98, American Concrete Institute, Farmington Hills, Mich-igan, 1998.

ACI Committee 214, Recommended Practice for Evaluation ofStrength Test Results of Concrete, ACI 214-77, reapproved1997, American Concrete Institute, Farmington Hills,Michigan, 1977.

ACI Committee 301, Specifications for Structural Concrete,ACI 301-99, American Concrete Institute, FarmingtonHills, Michigan, 1999.

177


ACI Committee 302, Guide for Concrete Floor and SlabConstruction, ACI 302.1R-96, American Concrete Institute,Farmington Hills, Michigan, 1996.

ACI Committee 318, Building Code Requirements for Struc-tural Concrete, ACI 318-02, and Commentary, ACI 318R-02,American Concrete Institute, Farmington Hills, Mich-igan, 2002.

ACI Committee 357, Guide for the Design and Constructionof Fixed Offshore Concrete Structures, ACI 357R-84, Amer-ican Concrete Institute, Farmington Hills, Michigan, 1984.

Bentz, Dale, Concrete Optimization Software Tool, http://ciks.cbt.nist.gov/bentz/fhwa, National Institute of Stan-dards and Technology, 2001.

Hover, Ken, “Graphical Approach to Mixture Proportion-ing by ACI 211.1-91,” Concrete International, American Con-crete Institute, Farmington Hills, Michigan, September,1995, pages 49 to 53.

Hover, Kenneth C., “Concrete Design: Part 1, FindingYour Perfect Mix,” http://www.cenews.com/edconc0998.html, CE News, September 1998.

Hover, Kenneth C., “Concrete Design: Part 2,Proportioning Water, Cement, and Air,” http://www.cenews.com/edconc1098.html, CE News, October 1998.

Hover, Kenneth C., “Concrete Design: Part 3, Propor-tioning Aggregate to Finish the Process,” http://www. cenews.com/edconc1198.html, CE News, November 1998.

PCA, Concrete for Small Jobs, IS174, Portland CementAssociation, http://www.portcement.org/pdf_files/IS174.pdf, 1988.

Shilstone, James M., Sr., “Concrete Mixture Optimiza-tion,” Concrete International, American Concrete Institute,Farmington Hills, Michigan, June 1990, pages 33 to 39.

The specification, production, and delivery of concreteare achieved in different ways. The basic processes andcommon techniques are explained here. ASTM C 94 pro-vides standard specifications for the manufacture anddelivery of freshly mixed concrete. Standards of theConcrete Plant Manufacturers Bureau, Truck Mixer Manu-facturers Bureau, and Volumetric Mixer ManufacturersBureau can be found on the National Ready MixedConcrete Association’s website at http://www.nrmca.org.

Three options for ordering or specifying concrete aredescribed in ASTM C 94:

1. Option Ais performance based. It requires the purchaserto specify the compressive strength only, while the con-crete producer selects the mixture proportions needed toobtain the required compressive strength.

2. Option B is prescription based. The purchaser specifiesmixture proportions, including cement, water andadmixture contents.

3. Option C is a mixed option. It requires the concreteproducer to select the mix proportions with the min-imum allowable cement content and compressivestrength specified by the purchaser.

BATCHING

Batching is the process of measuring concrete mix ingre-dients by either mass or volume and introducing theminto the mixer. To produce concrete of uniform quality, theingredients must be measured accurately for each batch.Most specifications require that batching be done by massrather than by volume (ASTM C 94 or AASHTO M 157).Water and liquid admixtures can be measured accuratelyby either volume or mass. Volumetric batching (ASTM C685 or AASHTO M 241) is used for concrete mixed in con-tinuous mixers.

Specifications generally require that materials bemeasured for individual batches within the following

CHAPTER 10

Batching, Mixing, Transporting, andHandling Concrete

percentages of accuracy: cementitious material ±1%,aggregates ± 2%, water ±1%, and admixtures ± 3%.

Equipment should be capable of measuring quanti-ties within these tolerances for the smallest batch regu-larly used as well as for larger batches (Fig. 10-1). Theaccuracy of scales and batching equipment should bechecked periodically and adjusted when necessary.

Liquid chemical admixtures should be charged intothe mixture as aqueous solutions. The volume of liquid, ifsignificant, should be subtracted from the batched quan-tity of mixing water. Admixtures that cannot be added insolution can be either batched by mass or volume asdirected by the manufacturer. Admixture dispensersshould be checked frequently since errors in dispensingadmixtures, particularly overdoses, can lead to seriousproblems in both fresh and hardened concrete.

Fig. 10-1. Control room for batching equipment in a typicalready mixed concrete plant. (69894)

179

with a swinging discharge chute. Many stationarymixers have timing devices, some of which can be setfor a given mixing time and locked so that the batchcannot be discharged until the designated mixing timehas elapsed.

Careful attention should be paid to the requiredmixing time. Many specifications require a minimummixing time of one minute plus 15 seconds for everycubic meter (yard), unless mixer performance testsdemonstrate that shorter periods are acceptable and willprovide a uniform concrete mixture. Short mixing timescan result in nonhomogenous mixtures, poor distributionof air voids (resulting in poor frost resistance), poorstrength gain, and early stiffening problems. The mixingperiod should be measured from the time all cement andaggregates are in the mixer drum, provided all the wateris added before one-fourth of the mixing time has elapsed(ACI 304R-00).

Under usual conditions, up to about 10% of themixing water should be placed in the drum before thesolid materials are added. Water then should be addeduniformly with the solid materials, leaving about 10% tobe added after all other materials are in the drum. Whenheated water is used in cold weather, this order ofcharging may require some modification to prevent pos-sible rapid stiffening when hot water contacts the cement.In this case, addition of the cementitious materials shouldbe delayed until most of the aggregate and water haveintermingled in the drum. Where the mixer is chargeddirectly from a batch plant, the materials should be addedsimultaneously at such rates that the charging time isabout the same for all materials. If supplementarycementing materials are used, they should be added afterthe cement.

If retarding or water-reducing admixtures are used,they should be added in the same sequence in thecharging cycle each time. If not, significant variations inthe time of initial setting and percentage of entrained airmay result. Addition of the admixture should be com-pleted not later than one minute after addition of water tothe cement has been completed or prior to the start of thelast three-fourths of the mixing cycle, whichever occursfirst. If two or more admixtures are used in the same batchof concrete, they should be added separately; this isintended to avoid any interaction that might interfere withthe efficiency of any of the admixtures and adverselyaffect the concrete properties. In addition, the sequence inwhich they are added to the mix can be important too.

Ready Mixed Concrete

Ready mixed concrete is proportioned and mixed off theproject site and is delivered to the construction area in afreshly mixed and unhardened state. It can be manufac-tured by any of the following methods:

MIXING CONCRETE

All concrete should be mixed thoroughly until it is uni-form in appearance, with all ingredients evenly distrib-uted. Mixers should not be loaded above their ratedcapacities and should be operated at the mixing speedrecommended by the manufacturer. Increased outputshould be obtained by using a larger mixer or additionalmixers, rather than by speeding up or overloading theequipment on hand. If the blades of a mixer become wornor coated with hardened concrete, mixing action will beless efficient. These conditions should be corrected.

If concrete has been adequately mixed, samples takenfrom different portions of a batch will have essentially thesame density, air content, slump, and coarse-aggregatecontent. Maximum allowable differences to evaluatemixing uniformity within a batch of ready mixed concreteare given in ASTM C 94 (AASHTO M 157).

Structural low-density concrete can be mixed the sameway as normal-density concrete when the aggregates haveless than 10% total absorption by mass or when the absorp-tion is less than 2% by mass during the first hour afterimmersion in water. For aggregates not meeting theselimits, mixing procedures are described in PCA (1986).

Stationary Mixing

Concrete is sometimes mixed at the jobsite in a stationarymixer or a paving mixer (Fig. 10-2). Stationary mixersinclude both onsite mixers and central mixers in readymix plants. They are available in sizes up to 9.0 m3

(12 yd3) and can be of the tilting or nontilting type or theopen-top revolving blade or paddle type. All types maybe equipped with loading skips and some are equipped

180


Fig. 10-2. Concrete can be mixed at the jobsite in a station-ary mixer. (58642)

1. Central-mixed concrete is mixed completely in a sta-tionary mixer (Fig. 10-3) and is delivered either in atruck agitator (Fig. 10-4 bottom), a truck mixer oper-ating at agitating speed (Fig. 10-3), or a nonagitatingtruck (Fig. 10-4 top). Fig. 10-5 illustrates a central mixready mix plant.

2. Shrink-mixed concrete is mixed partially in a sta-tionary mixer and completed in a truck mixer.

3. Truck-mixed concrete is mixed completely in a truckmixer (Fig. 10-6).

ASTM C 94 (AASHTO M 157) notes that when a truckmixer is used for complete mixing, 70 to 100 revolutions ofthe drum or blades at the rate of rotation designated bythe manufacturer as mixing speed are usually required toproduce the specified uniformity of concrete. All revolu-tions after 100 should be at a rate of rotation designated bythe manufacturer as agitating speed. Agitating speed is usu-ally about 2 to 6 rpm, and mixing speed is generally about6 to 18 rpm. Mixing at high speeds for long periods oftime, about 1 or more hours, can result in concretestrength loss, temperature rise, excessive loss of entrainedair, and accelerated slump loss.

When truck mixers are used, ASTM C 94 (AASHTO M157) also limits the time between batching and completedischarge of the concrete at the job site; this time is 11⁄2hours or before the drum has revolved 300 times afterintroduction of water to the cement and aggregates or thecement to the aggregates. Mixers and agitators shouldalways be operated within the limits for volume and speedof rotation designated by the equipment manufacturer.

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Fig. 10-3. Central mixing in a stationary mixer of the tiltingdrum type with delivery by a truck mixer operating atagitating speed. (69926)

Fig 10-4. (top) Nonagitating trucks are used with central-mix batch plants where short hauls and quick concretedischarge allows the rapid placement of large volumes ofconcrete. (bottom) Truck agitators are also used withcentral-mix batch plants. Agitation mixing capabilities allowtruck agitators to supply concrete to projects with slowrates of concrete placement and at distances greater thannonagitating trucks. (69897, 69898)

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setting becomes a persistent problem, a retarder may beused to control early hydration, especially in high-cement-content mixes. Mixture adjustments at the jobsitefor air entrainment, and the addition of other admix-tures, is permitted, followed by sufficient mixing.

Indiscriminate addition of water to make concretemore fluid should not be allowed because this lowers thequality of concrete. The later addition of water andremixing to retemper the mixture can result in markedstrength reduction.

TRANSPORTING AND HANDLING CONCRETE

Good advanced planning can help choose the appro-priate handling method for an application. Consider thefollowing three occurrences that, should they occurduring handling and placing, could seriously affect thequality of the finished work:

Delays. The objective in planning any work schedule isto produce the fastest work with the best labor force andthe proper equipment for the work at hand. Machines fortransporting and handling concrete are being improvedall the time. The greatest productivity will be achieved ifthe work is planned to get the most out of personnel andequipment and if the equipment is selected to reduce thedelay time during concrete placement.

Early Stiffening and Drying Out. Concrete begins tostiffen as soon as the cementitious materials and water aremixed, but the degree of stiffening that occurs in the first30 minutes is not usually a problem; concrete that is keptagitated generally can be placed and compacted within 11⁄2hours after mixing unless hot concrete temperatures or

Mobile Batcher Mixed Concrete(Continuous Mixer)

Mobile volumetric mixers are special trucks (Fig. 10-7)that batch by volume and continuously mix concrete asthe dry concrete ingredients, water, and admixtures arecontinuously fed into a mixing trough, typically an augersystem. The concrete must conform to ASTM C 685(AASHTO M 241) specifications and is proportioned andmixed at the jobsite in the quantities needed. The concretemixture is also easily adjusted for project placement andweather conditions.

Remixing Concrete

Fresh concrete that is left to agitate in the mixer drumtends to stiffen before initial set develops. Such concretemay be used if upon remixing it becomes sufficientlyplastic to be compacted in the forms. ASTM C 94(AASHTO M 157) allows water to be added to remix theconcrete when the truck arrives on the jobsite and theslump is less than specified providing the following con-ditions are met: (1) maximum allowable water-cementratio is not exceeded as calculated including surfacewater on aggregates as well as batch water and wateradded on site; (2) maximum allowable slump is notexceeded; (3) maximum allowable mixing and agitatingtime (or drum revolutions) are not exceeded; and (4) con-crete is remixed for a minimum of 30 revolutions atmixing speed or until the uniformity of the concrete iswithin the limits described in ASTM C 94 (AASHTO M157). Water should not be added to a partial load. If early

Fig. 10-6. Truck-mixed concrete is mixed completely in atruck mixer. (1153)

Fig. 10-7. Mobile batcher measures materials by volumeand continuously mixes concrete as the dry ingredients,water, and admixtures are fed into a mixing trough at therear of the vehicle. (54087)

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high cement contents speed up hydration excessively.Planning should eliminate or minimize any variables thatwould allow the concrete to stiffen to the extent that fullconsolidation is not achieved and finishing becomes diffi-cult. Less time is available during conditions that hastenthe stiffening process, such as hot and dry weather, use ofaccelerators, and use of heated concrete.

Segregation. Segregation is the tendency for coarseaggregate to separate from the sand-cement mortar. Thisresults in part of the batch having too little coarse aggre-gate and the remainder having too much. The former islikely to shrink more and crack and have poor resistance

to abrasion. The latter may be too harsh for full consolida-tion and finishing and is a frequent cause of honey-combing. The method and equipment used to transportand handle the concrete must not result in segregation ofthe concrete materials.

Methods and Equipment for Transporting and Handling Concrete

Table 10-1 summarizes the most common methodsand equipment for moving concrete to the point whereit is needed.

Table 10-1. Methods and Equipment for Transporting and Handling ConcreteType and range of work for

Equipment which equipment is best suited Advantages Points to watch for

Belt conveyors For conveying concrete Belt conveyors have adjustable End-discharge arrangementshorizontally or to a higher or reach, traveling diverter, and variable needed to prevent segregationlower level. Usually positioned speed both forward and reverse. and leave no mortar on return belt.between main discharge point Can place large volumes of concrete In adverse weather (hot, windy)and secondary discharge point. quickly when access is limited. long reaches of belt need cover.

Belt conveyors For conveying concrete to a Conveying equipment arrives with the End-discharge arrangementsmounted on lower, horizontal, or higher concrete. Adjustable reach and needed to prevent segregationtruck mixers level. variable speed. and leave no mortar on return belt.

Buckets Used with cranes, cableways, Enables full versatility of cranes, cable- Select bucket capacity to conformand helicopters for construction ways, and helicopters to be exploited. to size of the concrete batch andof buildings and dams. Convey Clean discharge. Wide range of capacity of placing equipment.concrete directly from central capacities. Discharge should be controllable.discharge point to formwork orto secondary discharge point.

Chutes on For conveying concrete to a Low cost and easy to maneuver. No Slopes should range between 1 totruck mixers lower level, usually below power required; gravity does most of 2 and 1 to 3 and chutes must be

ground level, on all types of the work. adequately supported in all posi-concrete construction. tions. End-discharge arrangements

(downpipe) needed to prevent segregation.

Cranes and The right equipment for work Can handle concrete, reinforcing steel, Has only one hook. Careful sched-buckets above ground level. formwork, and sundry items in bridges uling between trades and opera-

and concrete-framed buildings. tions is needed to keep crane busy.

Dropchutes Used for placing concrete in Dropchutes direct concrete into form- Dropchutes should have sufficientlyvertical forms of all kinds. work and carry it to bottom of forms large, splayed-top openings intoSome chutes are one piece without segregation. Their use avoids which concrete can be dischargedtubes made of flexible rubber- spillage of grout and concrete on rein- without spillage. The cross sectionized canvas or plastic, others forcing steel and form sides, which is of dropchute should be chosen toare assembled from articulated harmful when off-the-form surfaces permit inserting into the formworkmetal cylinders (elephant are specified. They also will prevent without interfering with reinforcingtrunks). segregation of coarse particles. steel.

Mobile batcher Used for intermittent production A combined materials transporter and Trouble-free operation requiresmixers of concrete at jobsite, or mobile batching and mixing system for good preventive maintenance pro-

where only small quantities quick, precise proportioning of spe- gram on equipment. Materials mustare required. cified concrete. One-man operation. be identical to those in original mix

design.

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Table 10-1. Methods and Equipment for Transporting and Handling Concrete (Continued)

Type and range of work for Equipment which equipment is best suited Advantages Points to watch for

Nonagitating Used to transport concrete on Capital cost of nonagitating equipment Concrete slump should be limited.trucks short hauls over smooth is lower than that of truck agitators or Possibility of segregation. Height is

roadways. mixers. needed for high lift of truck bodyupon discharge.

Pneumatic guns Used where concrete is to be Ideal for placing concrete in freeform Quality of work depends on skill of(shotcrete) placed in difficult locations and shapes, for repairing structures, for those using equipment. Only ex-

where thin sections and large protective coatings, thin linings, and perienced nozzlemen should beareas are needed. building walls with one-sided forms. employed.

Pumps Used to convey concrete Pipelines take up little space and can Constant supply of freshly-mixeddirectly from central discharge be readily extended. Delivers concrete concrete is needed with averagepoint at jobsite to formwork or in continuous stream. Pump can move consistency and without anyto secondary discharge point. concrete both vertically and horizon- tendency to segregate. Care must

tally. Truck-mounted pumps can be be taken in operating pipeline todelivered when necessary to small or ensure an even flow and to cleanlarge projects. Tower-crane mounted out at conclusion of each operation.pump booms provide continuous Pumping vertically, around bends,concrete for tall building construction. and through flexible hose will con-

siderably reduce the maximumpumping distance.

Screw spreaders Used for spreading concrete With a screw spreader a batch Screw spreaders are normallyover large flat areas, such as of concrete discharged from a bucket used as part of a paving train.in pavements and bridge or truck can be quickly spread over They should be used for spreadingdecks. a wide area to a uniform depth. The before vibration is applied.

spread concrete has good uniformityof compaction before vibration is usedfor final compaction.

Tremies For placing concrete under- Can be used to funnel concrete down Precautions are needed to ensurewater. through the water into the foundation that the tremie discharge end is

or other part of the structure being always buried in fresh concrete,cast. so that a seal is preserved be-

tween water and concrete mass.Diameter should be 250 to 300 mm(10 to 12 in.) unless pressure isavailable. Concrete mixture needsmore cement, 390 kg/m3 (658lb/yd3), and greater slump, 150 to230 mm (6 to 9 in.), because concrete must flow and consolidatewithout any vibration.

Truck agitators Used to transport concrete for Truck agitators usually operate from Timing of deliveries should suit joball uses in pavements, struc- central mixing plants where quality organization. Concrete crew andtures, and buildings. Haul dis- concrete is produced under controlled equipment must be ready onsitetances must allow discharge of conditions. Discharge from agitators to handle concrete.concrete within 11⁄2 hours, but is well controlled. There is uniformitylimit may be waived under and homogeneity of concrete on dis-certain circumstances. charge.

Truck mixers Used to transport concrete for No central mixing plant needed, only Timing of deliveries should suit jobuses in pavements, struc- a batching plant, since concrete is organization. Concrete crew andtures, and buildings. Haul dis- completely mixed in truck mixer. Dis- equipment must be ready onsitetances must allow discharge of charge is same as for truck agitator. to handle concrete. Control of con-concrete within 11⁄2 hours, but crete quality is not as good as withlimit may be waived under central mixing.certain circumstances.

Wheelbarrows For short flat hauls on all types Very versatile and therefore ideal in- Slow and labor intensive.and buggies of onsite concrete construction, side and on jobsites where placing

especially where accessibility conditions are constantly changing.to work area is restricted.

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There have been few, if any, major changes in the prin-ciples of conveying concrete during the last 75 years. Whathas changed is the technology that led to development ofbetter machinery to do the work more efficiently. Thewheelbarrow and buggy, although still used, haveadvanced to become the power buggy (Fig. 10-8); thebucket hauled over a pulley wheel has become the bucketand crane (Fig. 10-9); and the horse-drawn wagon is nowthe ready mixed concrete truck (Figs. 10-10 and 10-11).

Fig. 10-8. Versatile power buggy can move all types ofconcrete over short distances. (54088)

Fig. 10-9. Concrete is easily lifted to its final location bybucket and crane. (69687)

Fig. 10-10. Ready mixed concrete can often be placed in itsfinal location by direct chute discharge from a truck mixer.(54955)

Fig. 10-11. In comparison to conventional rear-dischargetrucks, front-discharge truck mixers provide the driver withmore mobility and control for direct discharge into place.(70006)

Years ago concrete was placed in reinforced concretebuildings by means of a tower and long chutes. This wasa guyed tower centrally placed on the site with a hopperat the top to which concrete was hauled by winch. A seriesof chutes suspended from the tower allowed the concreteto flow by gravity directly to the point required. As con-crete-framed buildings became taller, the need to hoistreinforcement and formwork as well as concrete to higherlevels led to the development of the tower crane—afamiliar sight on the building skyline today (Fig. 10-12). Itis fast and versatile, but the fact that it has only one hookmust be considered when planning a job.

The conveyer belt is old in concept and much changedover the years (Fig. 10-13). Recently, truck-mixer-mountedconveyor belts have come into use (Fig. 10-14). The pneu-matic process for shotcreting was patented in 1911 and is

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Chapter 10 ◆ Batching, Mixing, Transporting, and Handling Concrete

literally unchanged (see Chapter 18). The first mechanicalconcrete pump was developed and used in the 1930s andthe hydraulic pump was developed in the 1950s. Theadvanced mobile pump with hydraulic placing boom(Fig. 10-15) is probably the single most important innova-tion in concrete handling equipment. It is economical touse in placing both large and small quantities of concrete,depending on jobsite conditions. For small to medium sizeprojects, a combination of truck mixer and boom pumpcan be used to transport and place concrete. The screwspreader (Fig. 10-16) has been very effective in placing anddistributing concrete for pavements. Screw spreaders canplace a uniform depth of concrete quickly and efficiently.

Fig. 10-13. The conveyor belt is an efficient, portablemethod of handling concrete. A dropchute preventsconcrete from segregating as it leaves the belt; a scraperprevents loss of mortar. Conveyor belts can be operated inseries and on extendable booms of hydraulic cranes.(69896)

Fig. 10-14. A conveyor belt mounted on a truck mixer placesconcrete up to about 12 meters (40 feet) without the needfor additional handling equipment. (53852)

Fig. 10-12. The tower crane and bucket can easily handleconcrete for tall-building construction. (69969)

Fig. 10-15. (top) A truck-mounted pump and boom canconveniently move concrete vertically or horizontally to thedesired location. (bottom) View of concrete dischargingfrom flexible hose connected to rigid pipeline leading fromthe pump. Rigid pipe is used in pump booms and in pipe-lines to move concrete over relatively long distances. Up to8 m (25 ft) of flexible hose may be attached to the end of arigid line to increase placement mobility. (69968, 69966)

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See Panarese (1987) for extensive information on methodsto transport and handle concrete.

Choosing the Best Method

The first thing to look at is the type of job, its physical size,the total amount of concrete to be placed, and the timeschedule. Studying the job details further will tell howmuch of the work is below, at, or above ground level. Thisaids in choosing the concrete handling equipment neces-sary for placing concrete at the required levels.

Concrete must be moved from the mixer to the pointof placement as rapidly as possible without segregation orloss of ingredients. The transporting and handling equip-ment must have the capacity to move sufficient concreteso that cold joints are eliminated.

Work At and Below Ground Level

The largest volumes of concrete in a typical job usually areeither below or at ground level and therefore can beplaced by methods different from those employed on thesuperstructure. Concrete work below ground can varyenormously—from filling large-diameter bored piles ormassive mat foundations to the intricate work involved inbasement and subbasement walls. A crane can be used tohandle formwork, reinforcing steel, and concrete.However, the crane may be fully employed erecting form-work and reinforcing steel in advance of the concrete, andother methods of handling the concrete may have to beused to place the largest volume in the least time.

Possibly the concrete can be chuted directly from thetruck mixer to the point needed. Chutes should be metalor metal lined. They must not slope greater than 1 verticalto 2 horizontal or less than 1 vertical to 3 horizontal. Long

chutes, over 6 meters (20 ft), or those not meeting slopestandards must discharge into a hopper before distribu-tion to point of need.

Alternatively, a concrete pump can move the concreteto its final position (Fig. 10-15). Pumps must be of ade-quate capacity and capable of moving concrete withoutsegregation. The loss of slump caused by pressure thatforces mix water into the aggregates as the mix travelsfrom pump hopper to discharge at the end of the pipelinemust be minimal—not greater than 50 mm (2 in). The aircontent generally should not be reduced by more than2 percentage points during pumping. Air loss greater thanthis may be caused by a boom configuration that allowsthe concrete to fall excessively. In view of this, specifica-tions for both slump and air content should be met at thedischarge end of the pump. Pipelines must not be made ofaluminum or aluminum alloys to avoid excessive entrain-ment of air; aluminum reacts with cement alkali hydrox-ides to form hydrogen gas which can result in seriousreduction in concrete strength.

Belt conveyors are very useful for work near groundlevel. Since placing concrete below ground is frequently amatter of horizontal movement assisted by gravity, light-weight portable conveyors can be used for high output atrelatively low cost.

Work Above Ground Level

Conveyor belt, crane and bucket, hoist, pump, or the ulti-mate sky-hook, the helicopter, can be used for lifting con-crete to locations above ground level (Fig. 10-17). Thetower crane (Fig. 10-12) and pumping boom (Fig. 10-18)are the right tools for tall buildings. The volume of con-crete needed per floor as well as boom placement andlength affect the use of a pump; large volumes minimizepipeline movement in relation to output.

The specifications and performance of transportingand handling equipment are being continuouslyimproved. The best results and lowest costs will be real-ized if the work is planned to get the most out of theequipment and if the equipment is flexibly employed toreduce total job cost. Any method is expensive if it doesnot get the job done. Panarese (1987) is very helpful indeciding which method to use based on capacity andrange information for various methods and equipment.

Fig. 10-16. The screw spreader quickly spreads concreteover a wide area to a uniform depth. Screw spreaders areused primarily in pavement construction. (69895)

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REFERENCES

ACI Committee 304, Guide for Measuring, Mixing,Transporting, and Placing Concrete, ACI 304R-00, ACICommittee 304 Report, American Concrete Institute,Farmington Hills, Michigan, 2000.

ACI Committee 304, Placing Concrete by Pumping Methods,ACI 304.2R-96, ACI Committee 304 Report, AmericanConcrete Institute, Farmington Hills, Michigan, 1996.

ACI Committee 304, Placing Concrete with Belt Conveyors,ACI 304.4R-95, ACI Committee 304 Report, AmericanConcrete Institute, Farmington Hills, Michigan, 1995.

ACI Committee 301, Specifications for Structural Concrete,ACI 301-99, ACI Committee 301 Report, AmericanConcrete Institute, Farmington Hills, Michigan, 1999.

Haney, James T., and Meyers, Rodney A., Ready MixedConcrete—Plant and Truck Mixer Operations and QualityControl, NRMCA Publication No. 172, National ReadyMixed Concrete Association, Silver Spring, Maryland,May 1985.

Panarese, William C., Transporting and Handling Concrete,IS178, Portland Cement Association, 1987.

PCA, Concrete for Small Jobs, IS174, Portland CementAssociation, http://www.portcement.org/pdf_files/IS174.pdf, 1988.

PCA, Structural Lightweight Concrete, IS032, PortlandCement Association, http://www.portcement.org/pdf_files/IS032.pdf, 1986.

Fig. 10-17. For work aboveground or at inaccessible sites,a concrete bucket can be lifted by helicopter. (Source:Paschal)

Fig. 10-18. A pump boom mounted on a mast and locatednear the center of a structure can frequently reach allpoints of placement. It is especially applicable to tallbuildings where tower cranes cannot be tied up withplacing concrete. Concrete is supplied to the boom througha pipeline from a ground-level pump. Concrete can bepumped hundreds of meters (feet) vertically with thesepumping methods. (49935)

PREPARATION BEFORE PLACING

Preparation prior to placing concrete for pavements orslabs on grade includes compacting, trimming, and mois-tening the subgrade (Figs. 11-1, 11-2, and 11-3); erectingthe forms; and setting the reinforcing steel and otherembedded items securely in place. Moistening the sub-grade is important, especially in hot, dry weather to keepthe dry subgrade from drawing too much water from theconcrete; it also increases the immediate air-moisture levelthereby decreasing the amount of evaporation from theconcrete surface. The strength or bearing capacity of thesubgrade should be adequate to support anticipatedstructural loads.

In cold weather, concrete must not be placed on afrozen subgrade. Snow, ice, and other debris must beremoved from within the forms before concrete is placed.Where concrete is to be deposited on rock or hardened con-crete, all loose material must be removed, and cut facesshould be nearly vertical or horizontal rather than sloping.

Recently placed concrete requiring an overlay is usu-ally roughened shortly after hardening to produce a better

CHAPTER 11

Placing and Finishing Concrete

Fig. 11-1. A base course foundation for concrete pavementis shaped by an auto-trimmer to design grades, crosssection and alignment by automatic sensors that followstring lines. (69935)

Fig. 11-2. Water trucks with spray-bars are used to moistensubgrades and base course layers to achieve adequatecompaction and to reduce the amount of water drawn out ofconcrete as it’s placed. (69931)

Fig. 11-3. (top) Adequate compaction of a base coursefoundation for concrete pavement can be achieved by usinga vibratory roller. (bottom) Vibratory plate compactors arealso used to prepare subgrades under slabs. (69934, 69930)

191

bond with the next placement. As long as no laitance (aweak layer of concrete), dirt, or loose particles are present,newly hardened concrete requires little preparation priorto placing freshly mixed concrete on it. When in servicefor a period of time, old hardened concrete usuallyrequires mechanical cleaning and roughening prior toplacement of new concrete. The subject of placing freshlymixed concrete on hardened concrete is discussed in moredetail under the sections entitled “Placing on HardenedConcrete” and “Construction Joints.”

Forms should be accurately set, clean, tight, ade-quately braced, and constructed of or lined with materialsthat will impart the desired off-the-form finish to the hard-ened concrete. Wood forms, unless oiled or otherwisetreated with a form-release agent, should be moistenedbefore placing concrete, otherwise they will absorb waterfrom the concrete and swell. Forms should be made forremoval with minimum damage to the concrete. Withwood forms, use of too large or too many nails should beavoided to facilitate removal and reduce damage. Forarchitectural concrete, the form-release agent should be anonstaining material. See Hurd (1979) and ACI Commit-tee 347 (1999) for more information on formwork.

Reinforcing steel should be clean and free of loose rustor mill scale when concrete is placed. Unlike subgrades,reinforcing steel can be colder than 0ºC (32ºF) with specialconsiderations. See “Concreting Aboveground” inChapter 14 for more details. Mortar splattered on rein-forcing bars from previous placements need not beremoved from steel and other embedded items if the nextlift is to be completed within a few hours; loose, driedmortar, however, must be removed from items that will beencased by later lifts of concrete.

All equipment used to place concrete must be cleanand in good working condition. Standby equipmentshould be available in the event of a breakdown.

DEPOSITING THE CONCRETE

Concrete should be deposited continuously as near as pos-sible to its final position without objectionable segregation(Figs. 11-4, 11-5, 11-6, 11-7, and 11-8). In slab construction,placing should be started along the perimeter at one endof the work with each batch discharged against previouslyplaced concrete. The concrete should not be dumped inseparate piles and then leveled and worked together; norshould the concrete be deposited in large piles and movedhorizontally into final position. Such practices result insegregation because mortar tends to flow ahead of thecoarser material.

In general, concrete should be placed in walls, thickslabs, or foundations in horizontal layers of uniform thick-ness; each layer should be thoroughly consolidated beforethe next is placed. The rate of placement should be rapidenough so that previously placed concrete has not yet setwhen the next layer of concrete is placed upon it. Timelyplacement and adequate consolidation will prevent flowlines, seams, and planes of weakness (cold joints) that result

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Fig. 11-4. Wheelbarrows are used to place concrete in areasthat are not easily accessed by other placement methods.(69929)

Fig. 11-5. The swing arm on a conveyor belt allows freshconcrete to be placed fairly evenly across a deck. (70002)

Fig. 11-6. Dump trucks deposit concrete ahead of a slip-form paver that places the entire width of a street in onepass. Epoxy coated dowels on metal chairs are positionedat a joint and spiked down to the base course just ahead ofthe paver. (69936)

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Chapter 11 � Placing and Finishing Concrete

from placing freshly mixed concrete on concrete past initialset. Layers should be about 150 to 500 mm (6 to 20 in.) thickfor reinforced members and 380 to 500 mm (15 to 20 in.)thick for mass work; the thickness will depend on the widthbetween forms and the amount of reinforcement.

To avoid segregation, concrete should not be movedhorizontally over too long a distance as it is being placedin forms or slabs. In some work, such as placing concretein sloping wingwalls or beneath window openings inwalls, it is necessary to move the concrete horizontallywithin the forms, but this should be kept to a minimum.

Where standing water is present, concrete should beplaced in a manner that displaces the water ahead of theconcrete but does not allow water to be mixed in with theconcrete; to do so will reduce the quality of the concrete.In all cases, water should be prevented from collecting atthe ends, in corners, and along faces of forms. Careshould be taken to avoid disturbing saturated subgrade

soils so they maintain sufficient bearing capacity to sup-port structural loads.

Chutes and dropchutes are used to move concrete tolower elevations without segregation and spattering ofmortar on reinforcement and forms. Properly designedconcrete has been allowed to drop by free fall into caissons.Results of a field test to determine if concrete could bedropped vertically 15 meters (50 ft) into a caisson withoutsegregation proved that there was no significant differencein aggregate gradation between control samples as deliv-ered and free-fall samples taken from the bottom of thecaisson (Turner 1970). More recent field studies indicatethat free fall of concrete from heights of up to 46 m(150 ft)—directly over reinforcing steel or at a highslump—does not result in segregation of the concreteingredients nor reduce compressive strength (Suprenant2001). However, if a baffle is not used to control the flow ofconcrete onto sloped surfaces at the end of an inclinedchute, segregation can occur.

Concrete is sometimes placed through openings,called windows, in the sides of tall, narrow forms. When achute discharges directly through the opening withoutcontrolling concrete flow at the end of the chute there isdanger of segregation. A collecting hopper should be usedoutside the opening to permit the concrete to flow moresmoothly through the opening; this will decrease the ten-dency to segregate.

When concrete is placed in tall forms at a fairly rapidrate, some bleed water may collect on the top surface, espe-cially with non-air-entrained concrete. Bleeding can bereduced by placing more slowly and by using concrete of astiffer consistency, particularly in the lower portion of theform. When practical, concrete should be placed to a level300 mm to 400 mm (about a foot) below the top of tallforms and an hour or so allowed for the concrete to par-tially set. Placing should resume before the surface hardensto avoid formation of a cold joint. If practical to workaround vertical reinforcing steel, it is good practice to over-fill the form by 25 mm (an inch) or so and cut off the excessconcrete after it has stiffened and bleeding has ceased.

In monolithic placement of deep beams, walls, orcolumns, to avoid cracks between structural elements,concrete placement should stop (usually about 1 hr) toallow settlement of the deep element before concreting iscontinued in any slabs, beams, or girders framing intothem. The delay should be short enough to allow the nextlayer of concrete to knit with the previous layer by vibra-tion, thus preventing cold joints and honeycombing (ACICommittee 304 2000). Haunches and column capitals areconsidered part of the floor or roof slab and should beplaced integrally with them.

PLACING CONCRETE UNDERWATER

Concrete should be placed in the air rather than under-water whenever possible. When it must be placed under-water, the work should be done under experienced

Fig. 11-7. Curb machines continuously extrude low-slumpconcrete into a shape that immediately stands withoutsupport of formwork. (69937)

Fig. 11-8. Concrete should be placed as near as possible toits final position. (70009)

are described in Chapter 18. No matter what method isused, the basics of mixing, placing, consolidating, andcuring apply to all portland cement concretes.

CONSOLIDATING CONCRETE

Consolidation is the process of compacting fresh concrete;to mold it within the forms and around embedded itemsand reinforcement; and to eliminate stone pockets, honey-comb, and entrapped air (Fig. 11-9). It should not removesignificant amounts of intentionally entrained air in air-en-trained concrete.

Consolidation is accomplished by hand or by mechan-ical methods. The method chosen depends on the consis-tency of the mixture and the placing conditions, such ascomplexity of the formwork and amount and spacing ofreinforcement. Generally, mechanical methods using eitherinternal or external vibration are the preferred methods ofconsolidation.

Workable, flowing mixtures can be consolidated byhand rodding, that is, thrusting a tamping rod or othersuitable tool repeatedly into the concrete. The rod shouldbe long enough to reach the bottom of the form or lift andthin enough to easily pass between the reinforcing steeland the forms. Low-slump concrete can be transformedinto flowing concrete for easier consolidation through theuse of superplasticizers without the addition of water tothe concrete mixture.

Spading can be used to improve the appearance offormed surfaces. A flat, spadelike tool should be repeat-edly inserted and withdrawn adjacent to the form. Thisforces the larger coarse aggregates away from the formsand assists entrapped air voids in their upward move-ment toward the top surface where they can escape. Amixture designed to be readily consolidated by handmethods should not be consolidated by mechanicalmethods; otherwise, the concrete is likely to segregateunder intense mechanical action.

supervision. The basic principles for normal concretework in the dry apply, with common sense, to underwaterconcreting. The following special points, however, shouldbe observed:

The slump of the concrete should be specified at 150to 230 mm (6 to 9 in.) and the mixture should have a max-imum water-cementitious materials ratio of 0.45. Gen-erally, the cementitious materials content will be 390kg/m3 (600 lb/yd3) or more.

It is important that the concrete flow without segrega-tion; therefore, the aim in proportioning should be toobtain a cohesive mixture with high workability. Anti-washout admixtures can be used to make concrete cohe-sive enough to be placed in limited depths of water, evenwithout tremies. Using rounded aggregates, a higher per-centage of fines, and entrained air should help to obtainthe desired consistency.

The current in the water through which the concreteis deposited should not exceed 3 m (10 ft) per minute.

Methods for placing concrete underwater include thefollowing: tremie, concrete pump, bottom-dump buckets,grouting preplaced aggregate, toggle bags, bagwork, andthe diving bell.

A tremie is a smooth, straight pipe long enough toreach the lowest point to be concreted from a workingplatform above the water. The diameter of the tremie pipeshould be at least 8 times the diameter of the maximumsize of aggregate. A hopper to receive the concrete isattached to the top of the pipe. The lower end of the tremieshould be kept buried in the fresh concrete to maintain aseal below the rising top surface and to force the concreteto flow in beneath it by pressure. Placing should be con-tinuous with as little disturbance to the previously placedconcrete as possible. The top surface should be kept aslevel as possible. See ACI Committee 304 (2000) for addi-tional information.

Mobile concrete pumps with a variable radius boommakes easy work of placing concrete underwater. Becausethe flexible hose on a concrete pump is similar to a tremie,the same placement techniques apply.

With the grouting preplaced aggregate method, theforms are first filled with clean coarse aggregate, then thevoids in the coarse aggregate are filled with a grout toproduce concrete. Grouting preplaced aggregate hasadvantages when placing concrete in flowing water.Concrete can be placed more quickly and economicallythan by conventional placement methods. However, themethod is very specialized and should only be performedby qualified experienced personnel.

Sand bags half full of plastic concrete can be used forsmall jobs, filling gaps, or temporary work. The tied endshould face away from the outside.

SPECIAL PLACING TECHNIQUES

Concrete may be placed by methods other than the usualcast-in-place method. These methods, such as shotcreting,

194


Fig. 11-9. Honeycomb and rock pockets are the results ofinadequate consolidation. (50207)

Even in highly reinforced elements, proper mechan-ical consolidation makes possible the placement of stiffmixtures with the low water-cementitious materials ratiosand high coarse-aggregate contents associated with high-quality concrete (Fig. 11-10). Among the mechanicalmethods are centrifugation, used to consolidate moderate-to-high-slump concrete in making pipes, poles, and piles;shock or drop tables, used to compact very stiff low-slumpconcrete in the manufacture of architectural precast units;and vibration—internal and external.

Vibration

Vibration, either internal or external, is the most widelyused method for consolidating concrete. When concrete isvibrated, the internal friction between the aggregate parti-cles is temporarily destroyed and the concrete behaveslike a liquid; it settles in the forms under the action ofgravity and the large entrapped air voids rise more easilyto the surface. Internal friction is reestablished as soon asvibration stops.

Vibrators, whether internal or external, are usuallycharacterized by their frequency of vibration, expressed asthe number of vibrations per second (Hertz), or vibrationsper minute (vpm); they are also designated by the ampli-tude of vibration, which is the deviation in millimeters(inches) from the point of rest. The frequency of vibrationcan be measured using a vibrating reed tachometer.

When vibration is used to consolidate concrete, astandby vibrator should be on hand at all times in theevent of a mechanical breakdown.

Internal Vibration. Internal or immersion-type vibrators,often called spud or poker vibrators (Figs. 11-10 and 11-11),are commonly used to consolidate concrete in walls,columns, beams, and slabs. Flexible-shaft vibrators consistof a vibrating head connected to a driving motor by a flex-ible shaft. Inside the head, an unbalanced weight con-

nected to the shaft rotates at high speed, causing the headto revolve in a circular orbit. The motor can be powered byelectricity, gasoline, or air. The vibrating head is usuallycylindrical with a diameter ranging from 20 to 180 mm(3⁄4 to 7 in.). Some vibrators have an electric motor builtright into the head, which is generally at least 50 mm (2 in.)in diameter. The dimensions of the vibrator head as well asits frequency and amplitude in conjunction with the work-ability of the mixture affect the performance of a vibrator.

Small-diameter vibrators have high frequenciesranging from 160 to 250 Hz (10,000 to 15,000 vpm) and lowamplitudes ranging between 0.4 and 0.8 mm (0.016 and0.03 in.). As the diameter of the head increases, the fre-quency decreases and the amplitude increases. The effec-tive radius of action of a vibrator increases with increasingdiameter. Vibrators with a diameter of 20 to 40 mm (3⁄4 to11⁄2 in.) have a radius of action in freshly mixed concreteranging between 75 and 150 mm (3 and 6 in.), whereas theradius of action for vibrators of 50- to 80-mm (2- to 3-in.)diameter ranges between 180 and 350 mm (7 and 14 in.).Table 11-1 shows the range of characteristics and applica-tions for internal vibrators for various applications.

Proper use of internal vibrators is important for bestresults. Vibrators should not be used to move concretehorizontally since this causes segregation. Whenever pos-sible, the vibrator should be lowered vertically into theconcrete at regularly spaced intervals and allowed todescend by gravity. It should penetrate to the bottom ofthe layer being placed and at least 150 mm (6 in.) into anypreviously placed layer. The height of each layer or liftshould be about the length of the vibrator head or gener-ally a maximum of 500 mm (20 in.) in regular formwork.

In thin slabs, the vibrator should be inserted at anangle or horizontally in order to keep the vibrator headcompletely immersed. However, the vibrator should notbe dragged around randomly in the slab. For slabs ongrade, the vibrator should not make contact with the sub-

195


Fig. 11-10. Proper vibration makes possible the placementof stiff concrete mixtures, even in heavily-reinforced con-crete members. (55806)

Fig. 11-11. Internal vibrators are commonly used to consol-idate concrete in walls, columns, beams, and slabs. (69970)

Suggested values of Approximate values of

Recommended Eccentric Rate ofDiameter frequency, moment, Average Centrifugal Radius of concreteof head, vibrations mm-kg amplitude, force, action,† placement,

Group mm (in.) per minute** in.-lb (10–3) mm (in.) kg (lb) mm (in.) m3/h (yd3/h)‡ ApplicationPlastic and flowing concrete in very thinmembers and confined places. May be

20-40 3.5-12 0.4-0.8 45-180 80-150 0.8-4 used to supplement larger vibrators,1 9000-15,000 especially in prestressed work where (3⁄4-11⁄2) (0.03-0.10) (0.015-0.03) (100-400) (3-6) (1-5)

cables and ducts cause congestion in forms. Also used for fabricating laboratory test specimens.Plastic concrete in thin walls, columns,

230-60

8500-12,5009-29 0.5-1.0 140-400 130-250 2.3-8 beams, precast piles, thin slabs, and along

(11⁄4-21⁄2) (0.08-0.25) (0.02-0.04) (300-900) (5-10) (3-10) construction joints. May be used to supple-ment larger vibrators in confined areas.Stiff plastic concrete (less than 80-mm [3-in.] slump) in general construction such as walls, columns, beams, pre-

350-90

8000-12,00023-81 0.6-1.3 320-900 180-360 4.6-15 stressed piles, and heavy slabs. Auxiliary

(2-31⁄2) (0.20-0.70) (0.025-0.05) (700-2000) (7-14) (6-20) vibration adjacent to forms of mass con-crete and pavements. May be gangmounted to provide full-width internalvibration of pavement slabs.Mass and structural concrete of 0 to 50-mm(2-in.) slump deposited in quantities upto 3 m3 (4 yd3) in relatively open forms of

480-150

7000-10,5008-290 0.8-1.5 680-1800 300-510 11-31 heavy construction (powerhouses, heavy

(3-6) (0.70-2.5) (0.03-0.06) (1500-4000) (12-20) (15-40) bridge piers, and foundations). Also usedfor auxiliary vibration in dam constructionnear forms and around embedded itemsand reinforcing steel.Mass concrete in gravity dams, large piers,massive walls, etc. Two or more vibrators

5130-150

5500-8500260-400 1.0-2.0 1100-2700 400-610 19-38 will be required to operate simultaneously

(5-6) (2.25-3.50) (0.04-0.08) (2500-6000) (16-24) (25-50) to mix and consolidate quantities of con-crete of 3 m3 (4 yd3) or more deposited atone time into the form.

of a thin film of mortar on the top surface, and the cessa-tion of large bubbles of entrapped air escaping at the sur-face. Internal vibration may significantly affect theentrained-air-void system in concrete (Stark 1986, andHover 2001). Detailed guidance for proper vibrationshould be followed (ACI Committee 309).

Allowing a vibrator to remain immersed in concreteafter paste accumulates over the head is bad practice andcan result in nonuniformity. The length of time that avibrator should be left in the concrete will depend on theworkability of the concrete, the power of the vibrator, andthe nature of the section being consolidated.

In heavily-reinforced sections where an internal vi-brator cannot be inserted, it is sometimes helpful tovibrate the reinforcing bars by attaching a form vibrator to

grade. The distance between insertions should be about11⁄2 times the radius of action so that the area visiblyaffected by the vibrator overlaps the adjacent previouslyvibrated area by a few centimeters (inches).

The vibrator should be held stationary until adequateconsolidation is attained and then slowly withdrawn. Aninsertion time of 5 to 15 seconds will usually provide ade-quate consolidation. The concrete should move to fill thehole left by the vibrator on withdrawal. If the hole doesnot refill, reinsertion of the vibrator at a nearby pointshould solve the problem.

Adequacy of internal vibration is judged by experi-ence and by changes in the surface appearance of the con-crete. Changes to watch for are the embedment of largeaggregate particles,general batch leveling, the appearance

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Table 11-1. Range of Characteristics, Performance, and Applications of Internal* Vibrators

* Generally, extremely dry or very stiff concrete does not respond well to internal vibrators.** While vibrator is operating in concrete.† Distance over which concrete is fully consolidated.‡ Assumes the insertion spacing is 11⁄2 times the radius of action, and that vibrator operates two-thirds of time concrete is being placed. These

ranges reflect not only the capability of the vibrator but also differences in workability of the mix, degree of deaeration desired, and otherconditions experienced in construction.


their exposed portions. This practice eliminates air andwater trapped under the reinforcing bars and increasesbond between the bars and surrounding concrete; use thismethod only if the concrete is still workable under theaction of vibration. Internal vibrators should not beattached to reinforcing bars for this purpose because thevibrators may be damaged.

Revibration of previously compacted concrete can bedone to both fresh concrete as well as any underlyinglayer that has partially hardened. Revibration is used toimprove bond between concrete and reinforcing steel,release water trapped under horizontal reinforcing bars,and remove additional entrapped air voids. In general, ifconcrete becomes workable under revibration, the prac-tice is not harmful and may be beneficial.

External Vibration. External vibrators can be form vibra-tors, vibrating tables, or surface vibrators such as vibra-tory screeds, plate vibrators, vibratory roller screeds, orvibratory hand floats or trowels. Form vibrators, designedto be securely attached to the outside of the forms, areespecially useful (1) for consolidating concrete in mem-bers that are very thin or congested with reinforcement,(2) to supplement internal vibration, and (3) for stiff mixeswhere internal vibrators cannot be used.

Attaching a form vibrator directly to the form gener-ally is unsatisfactory. Rather, the vibrator should beattached to a steel plate that in turn is attached to steelI-beams or channels passing through the form stiffenersthemselves in a continuous run. Loose attachments canresult in significant vibration energy losses and inade-quate consolidation.

Form vibrators can be either electrically or pneumat-ically operated. They should be spaced to distribute theintensity of vibration uniformly over the form; optimumspacing is best found by experimentation. Sometimes itmay be necessary to operate some of the form vibratorsat a different frequency for better results; therefore, it isrecommended that form vibrators be equipped with con-trols to regulate their frequency and amplitude. Durationof external vibration is considerably longer than forinternal vibration—generally between 1 and 2 minutes.A reed tachometer can not only determine frequency ofvibration, but also give a rough estimate of amplitude ofvibration by noting the oscillation of the reed at variouspoints along the forms. This will assist in identifyingdead spots or weak areas of vibration. A vibrographcould be used if more reliable measurements of fre-quency and amplitude are needed.

Form vibrators should not be applied within the topmeter (yard) of vertical forms. Vibration of the top of theform, particularly if the form is thin or inadequately stiff-ened, causes an in-and-out movement that can create agap between the concrete and the form. Internal vibratorsare recommended for use in this area of vertical forms.

Vibrating tables are used in precasting plants. Theyshould be equipped with controls so that the frequency

and amplitude can be varied according to the size of theelement to be cast and the consistency of the concrete.Stiffer mixtures generally require lower frequencies(below 6000 vpm) and higher amplitudes (over 0.13 mm[0.005 in.]) than more workable mixtures. Increasing thefrequency and decreasing the amplitude as vibration pro-gresses will improve consolidation.

Surface vibrators, such as vibratory screeds (Figs.11-12, 11-13, and 11-14), are used to consolidate concrete infloors and other flatwork. Vibratory screeds give positivecontrol of the strikeoff operation and save a great deal oflabor. When using this equipment, concrete need not haveslumps in excess of 75 mm (3 in.). For greater than 75 mmslumps, care should be taken because surface vibration ofsuch concrete will result in an excessive accumulation ofmortar and fine material on the surface; this may reducewear resistance. For the same reason, surface vibrators

197


Fig. 11-12. Vibratory screeds such as this truss-type unitreduce the work of strikeoff while consolidating the con-crete. (55801)

Fig. 11-13. Where floor tolerances are not critical, an exper-ienced operator using this vibratory screed does not needscreed poles supported by chairs to guide the screed. In-stead, he visually matches elevations to forms or previouspasses. The process is called wet screeding. (69938)

Segregation from striking reinforcing steel without ade-quate vibration may also contribute to streaking.

Cold joints are a discontinuity resulting from a delayin placement that allowed one layer to harden before theadjacent concrete was placed. The discontinuity canreduce the structural integrity of a concrete member if thesuccessive lifts did not properly bond together. The con-crete can be kept alive by revibrating it every 15 minutesor less depending on job conditions. However, once thetime of initial setting approaches, vibration should be dis-continued and the surface should be suitably prepared forthe additional concrete.

Placement lines or “pour” lines are dark lines be-tween adjacent placements of concrete batches. They mayoccur if, while vibrating the overlying layer, the vibratordid not penetrate the underlying layer enough to knit thelayers together.

Subsidence cracking may occur at or near the initialsetting time as concrete settles over reinforcing steel in rel-atively deep elements that have not been adequatelyvibrated. Revibration at the latest time that the vibratorwill sink into the concrete under its own weight may elim-inate these cracks.

Defects from overvibration include: (1) segregation asvibration and gravity causes heavier aggregates to settlewhile lighter aggregates rise; (2) sand streaks; (3) loss ofentrained air in air-entrained concrete; (4) excessive formdeflections or form damage; and (5) form failure causedby excessive pressure from vibrating the same location toolong and/or placing concrete more quickly than the de-signed rate of pour.

Undervibration is more often a problem than over-vibration.

CONCRETE SLABS

Concrete slabs can be finished in many ways, dependingon the intended service use. Various colors and textures,such as exposed-aggregate or a pattern-stamped surface,may be called for. Some surfaces may require onlystrikeoff and screeding to proper contour and elevation,while for other surfaces a broomed, floated, or troweledfinish may be specified. Details are given in ACI Commit-tee 302, Kosmatka (1991), Panarese (1995), PCA (1980a),and Farny (2001).

The mixing, transporting, and handling of concrete forslabs should be carefully coordinated with the finishingoperations. Concrete should not be placed on the subgradeor into forms more rapidly than it can be spread, struck off,consolidated, and bullfloated or darbied. In fact, concreteshould not be spread over too large an area before strikeoff,nor should a large area be struck off and bleed waterallowed to accumulate before bullfloating or darbying.

Finishing crews should be large enough to correctlyplace, finish, and cure concrete slabs with due regard forthe effects of concrete temperature and atmospheric con-

should not be operated after the concrete has been ade-quately consolidated.

Because surface vibration of concrete slabs is leasteffective along the edges, a spud or poker-type vibratorshould be used along the edge forms immediately beforethe vibratory screed is applied.

Vibratory screeds are used for consolidating slabs upto 250 mm (10 in.) thick, provided such slabs are nonrein-forced or only lightly reinforced (welded-wire fabric).Internal vibration or a combination of internal and surfacevibration is recommended for reinforced slabs. Moredetailed information regarding internal and externalvibration of concrete can be obtained from ACICommittee 309.

Consequences of Improper Vibration. Following aresome of the worst defects caused by undervibration:(1) honeycomb; (2) excessive amount of entrapped airvoids, often called bugholes; (3) sand streaks; (4) coldjoints; (5) placement lines; and (6) subsidence cracking.

Honeycomb results when the spaces between coarseaggregate particles do not become filled with mortar.Faulty equipment, improper placement procedures, a con-crete mix containing too much coarse aggregate, or con-gested reinforcement can cause honeycomb.

Excessive entrapped air voids are similar to, but notas severe as honeycomb. Vibratory equipment and oper-ating procedures are the primary causes of excessiveentrapped air voids, but the other causes of honeycombapply too.

Sand streaks results when heavy bleeding washesmortar out from along the form. A wet, harsh mixture thatlacks workability because of an insufficient amount ofmortar or fine aggregate may cause sand streaking.

198


Fig. 11-14. A laser level stimulating the sensors on thisscreed guides the operator as he strikes off the concrete.Screed poles and chairs are not needed and fewer workersare required to place concrete. Laser screeds interfacedwith total station surveying equipment can also strike offsloped concrete surfaces. (69939)

ditions on the setting time of the concrete and the size ofthe placement to be completed.

Subgrade Preparation

Cracks, slab settlement, and structural failure can often betraced to an inadequately prepared and poorly compactedsubgrade. The subgrade on which a slab on ground is tobe placed should be well drained, of uniform bearingcapacity, level or properly sloped, and free of sod, organicmatter, and frost. The three major causes of nonuniformsupport are: (1) the presence of soft unstable saturatedsoils or hard rocky soils, (2) backfilling without adequatecompaction, and (3) expansive soils. Uniform supportcannot be achieved by merely dumping granular materialon a soft area. To prevent bridging and settlementcracking, soft or saturated soil areas and hard spots (rocks)should be dug out and filled with soil similar to the sur-rounding subgrade or if a similar soil is not available, withgranular material such as sand, gravel, or crushed stone.All fill materials must be compacted to provide the sameuniform support as the rest of the subgrade. Proof rollingthe subgrade using a fully-loaded dump truck or similarheavy equipment is commonly used to identify areas ofunstable soils that need additional attention.

During subgrade preparation, it should be remem-bered that undisturbed soil is generally superior to com-pacted material for supporting concrete slabs. Expansive,compressible, and potentially troublesome soils should beevaluated by a geotechnical engineer; a special slab designmay be required.

The subgrade should be moistened with water inadvance of placing concrete, but should not contain pud-dles or wet, soft, muddy spots when the concrete is placed.

Subbase

A satisfactory slab on ground can be built without a sub-base. However, a subbase is frequently placed on the sub-grade as a leveling course to equalize minor surfaceirregularities, enhance uniformity of support, bring thesite to the desired grade, and serve as a capillary breakbetween the slab and the subgrade.

Where a subbase is used, the contractor should placeand compact to near maximum density a 100-mm (4-in.)thick layer of granular material such as sand, gravel,crushed stone, or slag. If a thicker subbase is needed forachieving the desired grade, the material should be com-pacted in thin layers about 100 mm (4 in.) deep unless testsdetermine compaction of thicker a lift is possible (Fig. 11-15).Subgrades and subbases can be compacted with small platevibrators, vibratory rollers, or hand tampers. Unless thesubbase is well compacted, it is better not to use a subbase;simply leave the subgrade uncovered and undisturbed.

Vapor Retarders and Moisture-Problem Prevention

Many of the moisture problems associated with enclosedslabs on ground (floors) can be minimized or eliminatedby (1) sloping the landscape away from buildings, (2) us-ing a 100-mm (4-in.) thick granular subbase to form acapillary break between the soil and the slab, (3) pro-viding drainage for the granular subbase to preventwater from collecting under the slab, (4) installing foun-dation drain tile, and (5) installing a vapor retarder, oftenpolyethylene sheeting.

For years vapor retarders have been mistakenly calledvapor barriers. A vapor retarder slows the movement ofwater vapor by use of a 0.15 to 0.25 mm (6 to 10 mil) poly-ethylene film that is overlapped approximately 150 mm(6 in.) at the edges. A vapor retarder does not stop 100% ofvapor migration; a vapor barrier does. Vapor barriers arethick, rugged multiple-ply-reinforced membranes that aresealed at the edges. Vapor retarders are discussed in thistext because they are more commonly used; but many ofthe following principles apply to vapor barriers as well.

A vapor retarder should be placed under all concretefloors on ground that are likely to receive an impermeablefloor covering such as sheet vinyl tile or be used for anypurpose where the passage of water vapor through thefloor might damage moisture-sensitive equipment ormaterials in contact with the floor. However, a few projectsites with deep groundwater tables and sandy soils con-taining very low silt or clay contents may not require theuse of a vapor retarder under concrete slabs.

Vapor retarders placed directly under concrete slabsmay increase the time delay before final finishing due tolonger bleeding times, particularly in cold weather. Tominimize this effect, a minimum 75-mm (3-in.) thick layer

199


Fig. 11-15. Nuclear gauges containing radioactive sourcesused to measure soil density and moisture can determine ifa subbase has been adequately compacted. (69932)

ifications often require insulation at the perimeter of afloor slab. Placing insulation under the entire slab onground for energy conservation alone usually cannot bejustified economically. For more details, see PCA (1985).

Forms

Edge forms and intermediate screeds should be set accu-rately and firmly to the specified elevation and contour forthe finished surface. Slab edge forms are usually metal orwood braced firmly with wood or steel stakes to keepthem in horizontal and vertical alignment. The formsshould be straight and free from warping and have suffi-cient strength to resist concrete pressure without bulging.They should also be strong enough to support anymechanical placing and finishing equipment used.

Rain Protection

Prior to commencing placing of concrete, the owner andcontractor should be aware of procedures to be followedin the event of rain during the placing operation.Protective coverings such as polyethylene sheets or tar-paulins should be available and onsite at all times. Whenrain occurs, all batching and placing operations shouldstop and the fresh concrete should be covered to the extentthat the rain does not indent the surface of the concrete orwash away the cement paste. When rain ceases, the cov-ering should be removed and remedial measures takensuch as surface retexturing or reworking in-place plasticconcrete, before concrete placing resumes.

Placing and Spreading

Placement should start at the far point of a slab and pro-ceed toward the concrete supply source. The concrete,which should be placed as close as possible to its finalposition, should slightly overfill the forms and be roughlyleveled with square ended shovels or concrete rakes.Large voids trapped in the concrete during placing shouldbe removed by consolidation.

Screeding (Strikeoff)

Screeding or strikeoff is the process of cutting off excessconcrete to bring the top surface of a slab to proper grade.The template used in the manual method is called astraightedge, although the lower edge may be straight orslightly curved, depending on the surface specified. Itshould be moved across the concrete with a sawingmotion while advancing forward a short distance witheach movement. There should be a surplus (surcharge) ofconcrete against the front face of the straightedge to fill inlow areas as the straightedge passes over the slab. A 150-mm (6-in.) slab needs a surcharge of about 25 mm (1 in.).Straightedges are sometimes equipped with vibrators that

of approved granular, self-draining compactible subbasematerial should be placed over the vapor barrier (or insu-lation if present) (ACI Committee 302). Some contractorsfind only 75 mm of granular sand over polyethylenesheeting to be slippery, somewhat dangerous, and difficultto keep in place while concreting. A 150 to 200 mm (6 to 8in.)-thick subbase will alleviate this problem. The subbaseover a vapor retarder must be kept from getting saturatedby rain or construction activities to prevent excessivevapor migration after the concrete slab is placed.

If concrete is placed directly on a vapor retarder, thewater-cementitious materials ratio should be kept low(0.45 or less) because excess mix water can only escape tothe surface as bleed water. Because of a longer bleedingperiod, settlement cracking over reinforcement andshrinkage cracking is more likely. For more informationsee ACI (2001) and ACI Committee 302.

Good quality, well-consolidated concrete at least100-mm (4-in.) thick is practically impermeable to the pas-sage of liquid water unless the water is under consider-able pressure; however, such concrete—even concreteseveral times as thick—is not impermeable to the passageof water vapor.

Water vapor that passes through a concrete slab evap-orates at the surface if it is not sealed. Floor coverings suchas linoleum, vinyl tile, carpeting, wood, and synthetic sur-facing effectively seal the moisture within the slab; even-tually this moisture may deteriorate latex adhesivescausing the floor covering to loosen, buckle, or blister.

To prevent problems with floor covering materialscaused by moisture within the concrete, the followingsteps should be taken: (1) use a low water-cement ratioconcrete, (2) moist-cure the slab for 7 days, (3) allow theslab a 2-or-more-month drying period (Hedenblad 1997and 1998), and (4) test the slab moisture condition beforeinstalling the floor covering.

In one commonly used test (ASTM F 1869), the mois-ture vapor emission rate from a concrete slab is deter-mined by taping a domed plastic vapor barrier with adesiccant under it to the floor. After about 72 hours thedesiccant is weighed and the moisture vapor emission rateis calculated. The slab is considered dry enough forplacing a flooring material if the moisture vapor emissionrate is below either 1.4 or 2.3 kg/m2/1000 m2 (3 or 5lbs/ft2/1000 ft2) depending on the type of floor coveringto be installed. Flooring-material manufacturers oftenhave their own recommended test and specified moisturelimits for installing their product. For more informationand additional tests for water vapor transmission, see“Moisture Testing” in Chapter 16, Kosmatka (1985), andPCA (2000).

Insulation is sometimes installed over the vapor bar-rier to assist in keeping the temperature of a concrete floorabove the dew point; this helps prevent moisture in the airfrom condensing on the slab surface. This practice alsocreates a warm floor for thermal comfort. Codes and spec-

200


consolidate the concrete and assist in reducing thestrikeoff work. This combination of straightedge and vi-brator is called a vibratory screed (Fig. 11-12). Vibratoryscreeds are discussed earlier in this chapter under“Consolidating Concrete.” Screeding, consolidation, andbullfloating must be completed before excess bleed watercollects on the surface.

Bullfloating or Darbying

To eliminate high and low spots and to embed large aggre-gate particles, a bullfloat or darby (Fig. 11-16 top) shouldbe used immediately after strikeoff. The long-handle bull-float (Fig. 11-16 bottom) is used on areas too large to reachwith a short-handle darby. Highway straightedges areoften used to obtain very flat surfaces (Fig. 11-17). For non-air-entrained concrete, these tools can be made of wood;for air-entrained concrete they should be of aluminum ormagnesium alloy.

Bullfloating or darbying must be completed beforebleed water accumulates on the surface. Care must betaken not to overwork the concrete as this could result ina less durable surface.

The preceeding operations should level, shape, andsmooth the surface and work up a slight amount of cementpaste. Although sometimes no further finishing is required,on most slabs bullfloating or darbying is followed by one ormore of the following finishing operations: edging, jointing,floating, troweling, and brooming. A slight hardening of theconcrete is necessary before the start of any of these fin-ishing operations. When the bleed-water sheen has evapo-rated and the concrete will sustain foot pressure with onlyabout 6-mm (1⁄4-in.) indentation, the surface is ready for con-tinued finishing operations (Fig. 11-18).

201


Fig. 11-16. (top) Darbying brings the surface to the spe-cified level and is done in tight places where a bullfloatcannot reach. (bottom) Bullfloating must be completedbefore any bleed water accumulates on the surface. (70010,69940, 70011)

Fig. 11-17. Highway straightedges are used on highwaypavement and floor construction where very flat surfacesare desired. (69941)

Fig. 11-18. Power floating using walk-behind and ride-onequipment. Footprints indicate proper timing. When thebleedwater sheen has evaporated and the concrete willsustain foot pressure with only slight indentation, the surfaceis ready for floating and final finishing operations. (69942)

ishing operations. The concrete should not be overworkedas this may bring an excess of water and fine material tothe surface and result in subsequent surface defects.

Hand floats usually are made of fiberglass, magne-sium, or wood. The metal float reduces the amount ofwork required because drag is reduced as the float slidesmore readily over the concrete surface. A magnesium floatis essential for hand-floating air-entrained concretebecause a wood float tends to stick to and tear the concretesurface. The light metal float also forms a smoother sur-face than the wood float.

The hand float should be held flat on the concrete sur-face and moved with a slight sawing motion in asweeping arc to fill in holes, cut off lumps, and smoothridges. When finishing large slabs, power floats can beused to reduce finishing time.

Floating produces a relatively even (but not smooth)texture that has good slip resistance and is often used as afinal finish, especially for exterior slabs. Where a floatfinish is the desired final finish, it may be necessary to floatthe surface a second time after it has hardened a little more.

Marks left by hand edgers and groovers are normallyremoved during floating unless the marks are desired fordecorative purposes; in such cases the edger and groovershould be used again after final floating.

Troweling

Where a smooth, hard, dense surface is desired, floatingshould be followed by steel troweling (Fig. 11-19).Troweling should not be done on a surface that has notbeen floated; troweling after only bullfloating or darbyingis not an adequate finishing procedure.

It is customary when hand-finishing large slabs tofloat and immediately trowel an area before moving the

Warning: One of the principal causes of surface defects in con-crete slabs is finishing while bleed water is on the surface. If bleedwater is worked into the surface, the water-cement ratio is sig-nificantly increased which reduces strength, entrained-air con-tent, and watertightness of the surface. Any finishing operationperformed on the surface of a concrete slab while bleed water ispresent can cause crazing, dusting, or scaling (PCA 2001).Floating and troweling the concrete (discussed later) beforethe bleeding process is completed may also trap bleedwater under the finished surface producing a weakenedzone or void under the finished surface; this occasionallyresults in delaminations. The use of low-slump concretewith an adequate cement content and properly graded fineaggregate will minimize bleeding and help ensure mainte-nance-free slabs. For exterior slabs, air entrainment alsoreduces bleeding. ACI Committee 302 and Farny (2001)present the placing and finishing techniques in more detailand PCA (2001) discusses defects.

Edging and Jointing

Edging is required along all edge forms and isolation andconstruction joints in floors and outdoor slabs such aswalks, drives, and patios. Edging densifies and compactsconcrete next to the form where floating and troweling areless effective, making it more durable and less vulnerableto scaling, chipping, and popouts.

In the edging operation, the concrete should be cutaway from the forms to a depth of 25 mm (1 in.) using apointed mason trowel or a margin trowel. Then an edgershould be held almost flat on the surface and run with thefront of the tool slightly raised to prevent the edger fromleaving too deep an impression. Edging may be requiredafter each subsequent finishing operation for interior slabs.

Proper jointing practices can eliminate unsightlyrandom cracks. Contraction joints, also called controljoints, are made with a hand groover or by inserting stripsof plastic, wood, metal, or preformed joint material intothe unhardened concrete. When hand methods are used toform control joints in exterior concrete slabs, mark theforms to accurately locate the joints. Prior to bullfloating,the edge of a thin strip of wood or metal may be used toknock down the coarse aggregate where the joint will behand tooled. The slab should then be jointed immediatelyafter bullfloating or in conjunction with the edging opera-tion. Control joints also can be made in hardened concreteby sawing. Jointing is discussed further under the heading“Making Joints in Floors and Walls” later in this chapter.

Floating

After the concrete has been hand-edged and hand-jointed,it should be floated with a hand float or with a finishingmachine using float blades (Fig. 11-18).

The purpose of floating is threefold: (1) to embedaggregate particles just beneath the surface; (2) to removeslight imperfections, humps, and voids; and (3) to compactthe mortar at the surface in preparation for additional fin-

202


Fig. 11-19. Hand floating (right hand) the surface with ahand float held flat on the concrete surface and moved in asweeping arc with a slight sawing motion. Troweling (lefthand) with blade tilted is performed before moving thekneeboards. (69933)

kneeboards. These operations should be delayed until theconcrete has hardened sufficiently so that water and finematerial are not brought to the surface. Too long a delay,of course, will result in a surface that is too hard to floatand trowel. The tendency, however, is to float and trowelthe surface too soon. Premature floating and troweling cancause scaling, crazing, or dusting and a surface withreduced wear resistance.

Spreading dry cement on a wet surface to take upexcess water is a bad practice and can cause crazing.Such wet spots should be avoided, if possible, by adjust-ments in aggregate gradation, mix proportions, and con-sistency. When wet spots do occur, finishing operationsshould be delayed until the water either evaporates or isremoved with a rubber floor squeegee or by dragging asoft rubber garden hose. If a squeegee or hose is used,care must be taken so that excess cement paste is notremoved with the water.

The first troweling may produce the desired surface freeof defects. However, surface smoothness, density, and wearresistance can all be improved by additional trowelings.There should be a lapse of time between successive trowel-ings to permit the concrete to become harder. As the surfacestiffens, each successive troweling should be made withsmaller trowels, using progressively more tilt and pressureon the trowel blade. The final pass should make a ringingsound as the trowel moves over the hardening surface.

A power trowel is similar to a power float, except thatthe machine is fitted with smaller, individual steel trowelblades that are adjustable for tilt and pressure on the con-crete surface. When the first troweling is done by machine,at least one additional troweling by hand should be doneto remove small irregularities. If necessary, tooled edgesand joints should be rerun after troweling to maintain uni-formity and true lines.

Exterior concrete should not be troweled for severalreasons: (1) because it can lead to a loss of entrained aircaused by overworking the surface, and (2) troweled sur-faces can be slippery when wet. Floating and broomingshould be sufficient for outdoor concrete.

Brooming

Brooming should be performed before the concrete hasthoroughly hardened, but it should be sufficiently hard toretain the scoring impression to produce a slip-resistantsurface (Fig. 11-20). Rough scoring can be achieved with arake, a steel-wire broom, or a stiff, coarse, fiber broom;such coarse-textured brooming usually follows floating. Ifa finer texture is desired, the concrete should be floated toa smooth surface and then brushed with a soft-bristledbroom. Interior concrete could also be troweled beforebrooming. Best results are obtained with brooms that arespecially made for texturing concrete. Slabs are usuallybroomed transversely to the main direction of traffic.

Highway pavements are textured by “tining” the sur-face with stiff wires; this improves traction and reduceshydroplaning (Fig. 11-21).

Curing and Protection

All newly placed and finished concrete slabs should becured and protected from drying, from extreme changes intemperature, and from damage by subsequent construc-tion and traffic.

203

Chapter 11 ◆ Placing and Finishing Concrete

Fig. 11-20. Brooming provides a slip-resistant surfacemainly used on exterior concrete. (69943)

Fig. 11-21. (top) This machine is tining the surface of freshconcrete. (bottom) Tining of pavements improves tire trac-tion and reduces hydroplaning. (69944, 69945)

ularly true with high rates of placement. Also, theencasing formwork prevents the escape of moisture fromthe fresh concrete. While formwork provides adequatecuring as long as it remains in place, the top surface wherethere is no encasing formwork may dry out too rapidly;this may result in a weak porous layer unless protectionand curing are provided.

Preparing Hardened Concrete

When freshly mixed concrete is placed on recently hard-ened concrete, certain precautions must be taken to securea well-bonded, watertight joint. The hardened concretemust be clean, sound, and reasonably rough with somecoarse aggregate particles exposed. Any laitance, softmortar, dirt, wood chips, form oil, or other foreign mate-rials must be removed since they could interfere withproper bonding of the subsequent placement.

The surface of old concrete upon which fresh concreteis to be placed must be thoroughly roughened and cleanedof all dust, surface films, deposits, loose particles, grease,oil, and other foreign material. In most cases it will be nec-essary to remove the entire surface down to sound con-crete. Roughening and cleaning with lightweight chippinghammers, waterblasting, scarifiers, sandblasting (Fig.11-23), shotblasting and hydrojetting are some of the satis-factory methods for exposing sound concrete. Care mustbe taken to avoid contamination of the clean surface beforea bonding grout and overlay concrete are placed.

Partially set or recently hardened concrete may onlyrequire stiff-wire brushing. In some types of construction

PLACING ON HARDENED CONCRETE

Bonded Construction Joints in Structural Concrete

A bonded construction joint is needed between two struc-tural concrete placements. When freshly mixed concrete isplaced in contact with existing hardened concrete, a high-quality bond and watertight joint are required. Poorlybonded construction joints are usually the result of (1) lackof bond between old and new concrete, or (2) a weakporous layer in the hardened concrete at the joint. Thequality of a bonded joint therefore depends on the qualityof the hardened concrete and preparation of its surface.

In columns and walls, the concrete near the top sur-face of a lift is often of inferior quality to the concretebelow. This may be due to poor consolidation or use ofbadly proportioned or high-slump mixtures that causeexcessive laitance, bleeding, and segregation. Even inwell-proportioned and carefully consolidated mixtures,some aggregate particle settlement and water gain(bleeding) at the top surface is unavoidable; this is partic-

204


Fig. 11-22. An excellent method of wet curing is tocompletely cover the surface with wet burlap and keep itcontinuously wet during the curing period. (69946)

Fig. 11-23. Sandblasting can clean any size or shape sur-face – horizontal, vertical or overhead. Consult local envi-ronmental regulations regarding sandblasting. (55805)

Curing should begin immediately after finishing (Fig.11-22). Curing is needed to ensure continued hydration ofthe cement, strength gain of the concrete, and a minimumof early drying shrinkage.

Special precautions are necessary when concrete workcontinues during periods of adverse weather. In coldweather, arrangements should be made in advance forheating, covering, insulating, or enclosing the concrete.Hot-weather work may require special precautions againstrapid evaporation and drying and high temperatures.

such as dams, the surface of each concrete lift is cut with ahigh-velocity air-water jet to expose clean, sound concretejust before final set. This is usually done 4 to 12 hours afterplacing. The surface must then be protected and continu-ously cured until concreting is resumed for the next lift.

For two-course floors, the top surface of the base slabcan be roughened just before it sets with a steel or stifffiber broom. The surface should be level, heavily scored,and free of laitance; then it should be protected until it isthoroughly cleaned just before the grout coat and toppingmix are placed. When placing a bonded topping on a floorslab, the base slab should be cleaned of all laitance, dust,debris, grease or other foreign substances by using one ofthe following methods:

a. Wet- or dry-grit sandblastingb. High-pressure water blastingc. Mechanical removal by scabblers, or grinding wheelsd. Power brooming and vacuuming

Hardened concrete may be left dry or be moistenedbefore new concrete is placed on it; however, the surfaceshould not be wet or have any free-standing water. Labor-atory studies indicate a slightly better bond is obtained ona dry surface than on a damp surface; however, theincreased moisture level in the hardened concrete and inthe environment around the concrete reduces water lossfrom the concrete mixture. This can be very beneficial,especially on hot, dry days.

For making a horizontal construction joint in rein-forced concrete wall construction, good results have beenobtained by constructing the forms to the level of the joint,overfilling the forms a few centimeters (inches), and then

removing the excess concrete just before hardening occurs;the top surface then can be manually roughened with stiffbrushes. The procedure is illustrated in Fig. 11-24.

In the case of vertical construction joints cast against abulkhead, the concrete surface generally is too smooth topermit proper bonding. So, particular care should be givento removal of the smooth surface finish before reerectingthe forms for placing freshly mixed concrete against thejoint. Stiff-wire brushing may be sufficient if the concrete isless than three days old; otherwise, bushhammering orsandblasting may be needed, followed by washing withclean water to remove all dust and loose particles.

Bonding New to Previously Hardened Concrete

Care must be used when making horizontal constructionjoints in wall sections where freshly-mixed concrete is tobe placed on hardened concrete. A good bond can beobtained by placing a rich concrete (higher cement andsand content than normal) in the bottom 150 mm (6 in.) ofthe new lift and thoroughly vibrating the joint interface.Alternatively, a cement-sand grout can be scrubbed into aclean surface immediately ahead of concreting.

A topping concrete mix for slabs can be bonded tothe previously prepared base slab by one of the followingprocedures:

1. Portland cement-sand grouting: A 1 to 1 cement-sandgrout having a water-cement ratio of not greater than0.45, mixed to a creamlike consistency, is scrubbedinto the prepared dry or damp (no free water) baseslab surface.

205


Lap overhardenedconcrete notmore than25 mm (1")50 mm (2")

100 mm(4") max.

Tierod not over150 mm (6")above joint.

25 mm(1") strip

16 mm (5/8") threaded boltgreased for easy removal.Bolt to hold forms tight against hardened concrete

Place concrete to level of broken line.Allow to settle and strike off to bottomof strip. Remove strip, clean and curejoint as specified.

50 mm (2")

Fig. 11-24. A straight, horizontal construction joint can be built using this detail.

(1⁄2-in.) material is commonly used. Care should be takento ensure that all the edges for the full depth of the slab areisolated from adjoining construction; otherwise crackingcan occur.

Columns on separate footings are isolated from thefloor slab either with a circular or square-shaped isolationjoint. The square shape should be rotated to align its cor-ners with control and construction joints.

Contraction Joints

Contraction joints (Fig. 11-27) provide for movement inthe plane of a slab or wall and induce controlled crackingcaused by drying and thermal shrinkage at preselectedlocations. Contraction joints (also sometimes called con-

2. Latex. A latex-bonding agent is added to the cement-sand grout and is spread in accordance with the latexmanufacturer’s direction.

3. Epoxy. An approved epoxy-bonding agent placed onthe base concrete, prepared in accordance with theepoxy manufacturer’s direction.

The bonding procedure should produce tensile bondstrength with the base concrete in excess of 1.0 MPa(150 psi).

Grout is placed just a short distance ahead of theoverlay or top-course concrete (Fig. 11-25). This methodmay also be applicable to horizontal joints in walls. Thegrout should not be allowed to dry out prior to the overlayplacement; otherwise, the dry grout may act as a poor sur-face for bonding. The surface of the base slab should havebeen prepared by one of the methods discussed pre-viously. Overlays are discussed further under “Patching,Cleaning, and Finishing” later in this chapter.

206


Fig. 11-25. Application of a bonding grout just ahead of theoverlay concrete. The grout must not dry out before theconcrete is placed. (51995)

Expansionjoint material

Joint sealing compound

Isolation Joint

Fig. 11-26. Isolation joints permit horizontal and verticalmovements between abutting faces of a slab and fixedparts of a structure.

Sawcut

Plastic or hardboardpreformed strip

1/4 D min.

1/4 D min.

Induced crack D

D

Sawed contraction joint

Premolded insert contraction joint

Fig. 11-27. Contraction joints provide for horizontalmovement in the plane of a slab or wall and induce controlledcracking caused by drying and thermal shrinkage.

MAKING JOINTS IN FLOORS AND WALLS

The following three types of joints are common in concreteconstruction: isolation joints, contraction joints, and con-struction joints.

Isolation Joints

Isolation joints (Fig. 11-26) permit both horizontal and ver-tical differential movements at adjoining parts of a struc-ture. They are used, for example, around the perimeter ofa floor on ground, around columns, and around machinefoundations to separate the slab from the more rigid partsof the structure.

Isolation-joint material (often called expansion-jointmaterial) can be as thin as 6 mm (1⁄4 in.) or less, but 13-mm

trol joints) should be constructed to permit transfer ofloads perpendicular to the plane of a slab or wall. If nocontraction joints are used, or if they are too widelyspaced in slabs on ground or in lightly reinforced walls,random cracks may occur; cracks are most likely whendrying and thermal shrinkage produce tensile stresses inexcess of the concrete’s tensile strength.

Contraction joints in slabs on ground can be made inseveral ways. One of the most common methods is to sawa continuous straight slot in the top of the slab (Fig. 11-28).This creates a plane of weakness in which a crack willform. Vertical loads are transmitted across a contractionjoint by aggregate interlock between the opposite faces ofthe crack providing the crack is not too wide and thespacing between joints is not too great. Crack widths atsaw-cut contraction joints that exceed 0.9 mm (0.035 in.) donot reliably transfer loads. The effectiveness of loadtransfer by aggregate interlock depends on more thancrack width. Other factors include: slab thickness, sub-grade support, load magnitude, repetitions of load, andaggregate angularity. Steel dowels (Figs. 11-6 and 11-29b)may be used to increase load transfer at contraction jointswhen heavy wheel loads are anticipated. Sizes and spacingof dowels, which are placed at the center of the slab depth,are shown in Farny (2001). See ACI Committee 302 andPCA (1982) for further discussions on doweled joints.

Sawing must be coordinated with the setting time ofthe concrete. It should be started as soon as the concretehas hardened sufficiently to prevent aggregates frombeing dislodged by the saw (usually within 4 to 12 hoursafter the concrete hardens); sawing should be completedbefore drying shrinkage stresses become large enough toproduce cracking. The timing depends on factors such asmix proportions, ambient conditions, and type and hard-ness of aggregates. New dry-cut sawing techniques allow

saw cutting to take place shortly after final finishing iscompleted. Generally, the slab should be cut before theconcrete cools, when the concrete sets enough to preventraveling or tearing while saw cutting, and before drying-shrinkage cracks start to develop.

Contraction joints also can be formed in the fresh con-crete with hand groovers or by placing strips of wood,metal, or preformed joint material at the joint locations.The top of the strips should be flush with the concrete sur-face. Contraction joints, whether sawed, grooved, or pre-formed, should extend into the slab to a depth of at leastone-fourth the slab thickness or a minimum of 25 mm (1in.) deep. It is recommended that the joint depth notexceed one-third the slab thickness if load transfer fromaggregate interlock is important.

Contraction joints in walls are also planes of weaknessthat permit differential movements in the plane of thewall. The thickness of the wall at a contraction joint shouldbe reduced by 25%, preferably 30%. Under the guidance ofthe design engineer, in lightly reinforced walls, half of thehorizontal steel rebars should be cut at the joint. Care mustbe taken to cut alternate bars precisely at the joint. At thecorners of openings in walls where contraction joints arelocated, extra diagonal or vertical and horizontal rein-forcement should be provided to control cracking.Contraction joints in walls should be spaced not morethan about 6 meters (20 ft) apart. In addition, contractionjoints should be placed where abrupt changes in wallthickness or height occur, and near corners—if possible,within 3 to 4 meters (10 to 15 ft). Depending on the struc-ture, these joints may need to be caulked to prevent thepassage of water through the wall. Instead of caulking, awaterstop (or both) can be used to prevent water fromleaking through the crack that occurs in the joint.

The spacing of contraction joints in floors on grounddepends on (1) slab thickness, (2) shrinkage potential ofthe concrete, (3) subgrade friction, (4) environment, and(5) the absence or presence of steel reinforcement. Unlessreliable data indicate that more widely spaced joints arefeasible, the suggested intervals given in Table 11-2 shouldbe used for well-proportioned concrete with aggregateshaving normal shrinkage characteristics. Joint spacingshould be decreased for concrete suspected of having highshrinkage characteristics. The panels created by contrac-tion joints should be approximately square. Panels withexcessive length-to-width ratio (more than 11⁄2 to 1) arelikely to crack at an intermediate location. In joint layoutdesign it is also important to remember that contraction(control) joints should only terminate at a free edge or atan isolation joint. Contraction joints should never termi-nate at another contraction joint as cracking will beinduced from the end of the terminated joint into the adja-cent panel. This is sometimes referred to as sympatheticcracking. Refer to Fig. 11-31, which illustrates one possiblejoint layout solution to eliminate the potential for inducedsympathetic cracking.

207


Fig. 11-28. Sawing a continuous cut in the top of a slab isone of the most economical methods for making acontraction joint. (69947)

Construction Joints

Construction joints (Fig. 11-29) are stopping places in theprocess of construction. A true construction joint shouldbond new concrete to existing concrete and permit nomovement. Deformed tiebars are often used in construc-tion joints to restrict movement. Because extra care isneeded to make a true construction joint, they are usuallydesigned and built to function as contraction or isolationjoints. For example, in a floor on ground the constructionjoints align with columns and function as contractionjoints and therefore are purposely made unbonded. Thestructural designer of suspended slabs should decide thelocation of construction joints. Oils, form-release agents,and paints are used as debonding materials. In thick,

heavily-loaded floors, unbonded doweled constructionjoints are commonly used. For thin slabs, the flat-facedbutt-type joint will suffice.

On most structures it is desirable to have wall jointsthat will not detract from appearance. When properlymade, wall joints can become inconspicuous or hidden byrustication strips. They thus can become an architecturalas well as a functional feature of the structure. However, ifrustication strips are used in structures that may beexposed to deicing salts, such as bridge columns and abut-ments, care should be taken to ensure that the reinforcingsteel has the required depth of concrete cover to preventcorrosion.

Horizontal joints in walls should be made straight,exactly horizontal, and should be placed at suitable loca-tions. A straight horizontal construction joint can be madeby nailing a 25 mm (1 in.) wood strip to the inside face ofthe form near the top (see Fig. 11-24). Concrete shouldthen be placed to a level slightly above the bottom of thestrip. After the concrete has settled and before it becomestoo hard, any laitance that has formed on the top surface

208


Table 11-2 (Metric). Spacing of Contraction Jointsin Meters*

Slab Maximum-size Maximum-sizethickness, aggregate aggregate

mm less than 19 mm 19 mm and larger

100 2.4 3.0

125 3.0 3.75

150 3.75 4.5

175 4.25 5.25**

200 5.0** 6.0**

225 5.5** 6.75**

250 6.0** 7.5**

* Spacings are appropriate for slumps between 100 mm and 150mm. If concrete cools at an early age, shorter spacings may beneeded to control random cracking. (A temperature difference ofonly 6°C may be critical.) For slumps less than 100 mm, jointspacing can be increased by 20%.

** When spacings exceed 4.5 m, load transfer by aggregate interlockdecreases markedly.

Table 11-2 (Inch-Pound Units). Spacing ofContraction Joints in Feet*

Slab Maximum-size Maximum-sizethickness, aggregate aggregate

in. less than 3⁄4 in. 3⁄4 in. and larger

4 8 10

5 10 13

6 12 15

7 14 18**

8 16** 20**

9 18** 23**

10 20** 25**

* Spacings are appropriate for slumps between 4 in. and 6 in. If con-crete cools at an early age, shorter spacings may be needed to con-trol random cracking. (A temperature difference of only 10°F maybe critical.) For slumps less than 4 in., joint spacing can beincreased by 20%.

** When spacings exceed 15 ft, load transfer by aggregate interlockdecreases markedly.

Edge each side with3-mm (1/8-in.) radius



Smooth dowelbar coated toprevent bond

Prevent bond

Deformed tie bar

D

Butt-type construction joint

D

Butt-type construction joint with dowels

D

Butt-type construction joint with tie bars(not a contraction joint)

(a)

(b)

(c)

Fig. 11-29. Construction joints are stopping places in theprocess of construction. Construction-joint types (a) and(b) are also used as contraction joints.

of the V. If rectangular or beveled, the joint should bemade at the top edge of the inner face of the strip.

JOINT LAYOUT FOR FLOORS

A typical joint layout for all three joint types—isolation,contraction, and construction—is illustrated in Fig. 11-31.Isolation joints are provided around the perimeter of thefloor where it abuts the walls and around all fixed ele-ments that may restrain movement of the slab. Thisincludes columns and machinery bases that penetrate thefloor slab. With the slab isolated from other building ele-ments, the remaining task is to locate and correctly spacecontraction joints to eliminate random cracking. Con-struction joint locations are coordinated with the floorcontractor to accommodate work schedules and crewsize. Unbonded construction joints should coincide withthe contraction joint pattern and act as contraction joints.Construction joints should be planned to provide long-strips for each placement rather than a checker-board pat-tern. Contraction joints are then placed to divide thelong-strips into relatively square panels, with panellength not exceeding 1.5 times the width. Contractionjoints should stop at free edges or isolation joints. For

more information on joints, see ACI Committee 302(1996), PCA (1982), and Farny (2001). For joints in walls,see PCA (1982), PCA (1982a), PCA (1984), PCA (1984a),and PCA (1984b).

FILLING FLOOR JOINTS

There are three options for treating joints: they can befilled, sealed, or left open. The movement at contractionjoints in a floor is generally very small. For some indus-trial and commercial uses, these joints can be left unfilledor unsealed. Where there are wet conditions, hygienic anddust-control requirements, or considerable traffic bysmall, hard-wheel vehicles, joint filling is necessary.

The difference between a filler and a sealer is thehardness of the material; fillers are more rigid than sealersand provide support to joint edges. In many places wheretraffic loading is light, a resilient material such as apolyurethane elastomeric sealant is satisfactory. However,heavy-traffic areas require support for joint edges to pre-vent spalling at saw-cuts; in such cases a good quality,semi-rigid epoxy or polyurea filler with a Shore Hardnessof A-80 or D-50 (ASTM D 2240) should be used. The mate-

209


30 mm (11/4 in.) 40 mm(11/2 in.)

50 mm (2 in.)

DimensionvariesDimension

varies Constructionjoint here

Constructionjoint here

20 mm (3/4 in.) – Varies withwall thickness 20 mm (3/4 in.) – Varies with

wall thickness

(a) (b)

Fig. 11-30. Horizontal construction joints in walls withV-shaped (a) and beveled (b) rustication strips.

9.0 m (30 ft)

3.0 m(10 ft)

2.75

m(9

ft)

3.0

m(1

0 ft)

8.5

m (2

8 ft)

8.5

m (2

8 ft)

4.25

m(1

4 ft)

4.25

m(1

4 ft)3.0 x 3.0 m

(10 x 10 ft)Machine

base

100-mm to 150-mm (4-in. to 6-in.) slump 19-mm (3/4-in.) aggregate150-mm (6-in.) thick slab

Isolation jointsContraction (control) jointsUnbonded construction joint

Column

Column

Fig. 11-31. Typical joint layout for a 150-mm (6-in.) thickconcrete floor on ground.

should be removed. The strip can then be removed andany irregularities in the joint leveled off. The forms areremoved and then reerected above the construction jointfor the next lift of concrete. To prevent concrete leakagefrom staining the wall below, gaskets should be usedwhere forms contact previously placed hardened concrete.

A variation of this procedure makes use of a rustica-tion strip instead of the 25 mm (1 in.) wood strip to form agroove in the concrete for architectural effect (Fig. 11-30).Rustication strips can be V-shaped, rectangular, or slightlybeveled. If V-shaped, the joint should be made at the point

eral, for concrete temperatures above 10°C (50°F), the sideforms of reasonably thick, supported sections can beremoved 24 hours after concreting. Beam and floor slabforms and supports (shoring) may be removed between 3and 21 days, depending on the size of the member and thestrength gain of the concrete. For most conditions, it isbetter to rely on the strength of the concrete as determinedby in situ or field-cured specimen testing rather than arbi-trarily selecting an age at which forms may be removed.Advice on reshoring is provided by ACI Committee 347.

For form removal, the designer should specify theminimum strength requirements for various members. Theage-strength relationship should be determined from rep-resentative samples of concrete used in the structure andfield-cured under job conditions. It should be remembered,however, that strengths are affected by the materials used,temperature, and other conditions. The time required forform removal, therefore, will vary from job to job.

A pinch bar or other metal tool should not be placedagainst the concrete to wedge forms loose. If it is necessaryto wedge between the concrete and the form, onlywooden wedges should be used. Stripping should bestarted some distance away from and move toward a pro-jection. This relieves pressure against projecting cornersand reduces the chance of edges breaking off.

Recessed forms require special attention. Woodenwedges should be gradually driven behind the form andthe form should be tapped lightly to break it away fromthe concrete. Forms should not be pulled off rapidly afterwedging has been started at one end; this is almost certainto break the edges of the concrete.

PATCHING, CLEANING, AND FINISHING

After forms are removed, all bulges, fins, and small pro-jections can be removed by chipping or tooling. Undesiredbolts, nails, ties, or other embedded metal can be removedor cut back to a depth of 13 mm (1⁄2 in.) from the concretesurface. When required, the surface can be rubbed orground to provide a uniform appearance. Any cavitiessuch as tierod holes should be filled unless they areintended for decorative purposes. Honeycombed areasmust be repaired and stains removed to present a concretesurface that is uniform in color. All of these operations canbe minimized by exercising care in constructing the form-work and placing the concrete. In general, repairs areeasier to make and more successful if they are made assoon as practical, preferably as soon as the forms areremoved. However, the procedures discussed belowapply to both new and old hardened concrete.

Holes, Defects, and Overlays

Patches usually appear darker than the surrounding con-crete; therefore, some white cement should be used inmortar or concrete for patching where appearance is

rial should be installed full depth in the saw cut, withouta backer rod, and flush with the floor surface.

Isolation joints are intended to accommodate move-ment; thus a flexible, elastomeric sealant should be used tokeep foreign materials out of the joint.

UNJOINTED FLOORS

An unjointed floor, or one with a limited number of joints,can be constructed when joints are unacceptable. Threeunjointed floor methods are suggested:

1. A prestressed floor can be built through the use ofpost-tensioning. With this method, steel strands inducts are tensioned after the concrete hardens to pro-duce compressive stress in the concrete. This com-pressive stress will counteract the development oftensile stresses in the concrete and provide a crack-free floor. Large areas, 1000 m2 (10,000 ft2) and more,can be constructed in this manner without inter-mediate joints.

2. Large areas—a single day of slab placement, usually800 to 1000 m2 (8000 to 10,000 ft2)—can be cast with-out contraction joints when the amount of distributedsteel in the floor is about one-half of one percent of thecross-sectional area of the slab. Special effort shouldbe made to reduce subgrade friction in floors withoutcontraction joints. Farny (2001) discusses use of dis-tributed steel in floors.

3. Concrete made with expansive cement can be used tooffset the amount of drying shrinkage to be antici-pated after curing. Contraction joints are not neededwhen construction joints are used at intervals of 10 to35 meters (40 to 120 ft). Large areas, up to 2000 m2

(20,000 ft2), have been cast in this manner withoutjoints. Steel reinforcement is needed in order to pro-duce compressive stresses during and after the expan-sion period—this is a form of prestressing.

REMOVING FORMS

It is advantageous to leave forms in place as long as pos-sible to continue the curing period. However, there aretimes when it is necessary to remove forms as soon as pos-sible. For example, where a rubbed finish is specified,forms must be removed early to permit the first rubbingbefore the concrete becomes too hard. Furthermore, it isoften necessary to remove forms quickly to permit theirimmediate reuse.

In any case, shoring should not be removed until theconcrete is strong enough to satisfactorily carry thestresses from both the dead load of the structure and anyimposed construction loads. The concrete should be hardenough so that the surfaces will not be injured in any waywhen reasonable care is used in removing forms. In gen-

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important. Samples should be applied and cured in aninconspicuous location, perhaps a basement wall, severaldays in advance of patching operations to determine themost suitable proportions of white and gray cements. Steeltroweling should be avoided since this darkens the patch.

Bolt holes, tierod holes, and other cavities that aresmall in area but relatively deep should be filled with adry-pack mortar. The mortar should be mixed as stiff as ispractical: use 1 part cement, 21⁄2 parts sand passing a 1.25mm (No. 16) sieve, and just enough water to form a ballwhen the mortar is squeezed gently in the hand. Thecavity should be clean with no oil or loose material andkept damp with water for several hours. A neat-cementpaste should be scrubbed onto the void surfaces, but notallowed to dry before the mortar is placed. The mortarshould be tamped into place in layers about 13 mm (1⁄2 in.)thick. Vigorous tamping and adequate curing will ensuregood bond and minimum shrinkage of the patch.

Concrete used to fill large patches and thin-bondedoverlays should have a low water-cement ratio, often witha cement content equal to or greater than the concrete tobe repaired. Cement contents range from 360 to 500 kg percubic meter (600 to 850 lb per cubic yard) and the water-cement ratio is usually 0.45 or less. The aggregate sizeshould be no more than 1⁄3 the patch or overlay thickness.A 9.5-mm (3⁄8-in.) nominal maximum size coarse aggregateis commonly used. The sand proportion can be higherthan usual, often equal to the amount of coarse aggregate,depending on the desired properties and application.

Before the patching concrete is applied, the sur-rounding concrete should be clean and sound (Fig. 11-32).Abrasive methods of cleaning (sandblasting, hydrojetting,waterblasting, scarification, or shotblasting) are usuallyrequired. For overlays, a cement-sand grout, a cement-sand-latex grout, or an epoxy bonding agent should beapplied to the prepared surface with a brush or broom (see

the earlier section “Bonding New to Previously HardenedConcrete”). Typical grout mix proportions are 1 partcement and 1 part fine sand and latex or epoxy admix-tures. The grout should be applied immediately before thenew concrete is placed. The grout should not be allowedto dry before the freshly mixed concrete is placed; other-wise bond may be impaired. The concrete may be dry ordamp when the grout is applied but not wet with free-standing water. The minimum thickness for most patchesand overlays is 20 mm (3⁄4 in.). Some structures, like bridgedecks, should have a minimum repair thickness of 40 mm(11⁄2 in.). A superplasticizer is one of many admixturesoften added to overlay or repair concrete to reduce the

of consolidation (Kosmatka 1985a).water-cement ratio and to improve workability and ease

Honeycombed and other defective concrete should becut out to expose sound material. If defective concrete isleft adjacent to a patch, moisture may get into the voids; intime, weathering action will cause the patch to spall. Theedges of the defective area should be cut or chippedstraight and at right angles to the surface, or slightlyundercut to provide a key at the edge of the patch. Nofeatheredges should be permitted (Fig. 11-33). Based onthe size of the patch, either a mortar or a concrete patchingmixture should be used.

Shallow patches can be filled with a dry-pack mortaras described earlier. This should be placed in layers notmore than 13 mm (1⁄2 in.) thick, with each layer given ascratch finish to improve bond with the subsequent layer.The final layer can be finished to match the surroundingconcrete by floating, rubbing, or tooling, or on formed sur-faces by pressing a section of form material against thepatch while still plastic.

Deep patches can be filled with concrete held in placeby forms. Such patches should be reinforced and doweledto the hardened concrete (Concrete Manual 1981). Large,

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Fig. 11-32. Concrete prepared for patch installation. (69972)

(a) Incorrectly installed patch. The feathered edges can break down under traffic or weather away.

(b) Correctly installed patch. The chipped area should be at least 20 mm (3/4 in.) deep with the edges at right angles or undercut to the surface.

Fig. 11-33. Patch installation.

and not harmful. If possible, identify the characteristics ofthe discoloration because some treatments are more effec-tive than others in removing certain materials.

Water cleaning methods include low-pressure washes,moderate-to-high-pressure waterblasting, and steam.Low-pressure washing is the simplest, requiring only thatwater run gently down the concrete surface for a day ortwo. The softened dirt then is flushed off with a slightlyhigher pressure rinse. Stubborn areas can be scrubbed witha nonmetallic-bristle brush and rinsed again. High-pres-sure waterblasting is used effectively by experienced oper-ators. Steam cleaning must be performed by skilledoperators using special equipment. Water methods are theleast harmful to concrete, but they are not without poten-tial problems. Serious damage may occur if the concretesurface is subjected to freezing temperatures while it is stillwet; and water can bring soluble salts to the surface,forming a chalky, white deposit called efflorescence.

Chemical cleaning is usually done with water-basedmixtures formulated for specific materials such as brick,stone, and concrete. An organic compound called a surfac-tant (surface-active agent), which acts as a detergent to wetthe surface more readily, is included in most chemicalcleaners. A small amount of acid or alkali is included toseparate the dirt from the surface. For example,hydrochloric (muriatic) acid is commonly used to cleanmasonry walls and remove efflorescence. There can beproblems related to the use of chemical cleaners. Their acidor alkaline properties can lead to reaction between cleanerand concrete as well as mortar, painted surfaces, glass,metals, and other building materials. Since chemicalcleaners are used in the form of water-diluted solutions,they too can liberate soluble salts from within the concreteto form efflorescence. Some chemicals can also expose theaggregate in concrete. Chemicals commonly used to cleanconcrete surfaces and remove discoloration include weaksolutions (1% to 10% concentration) of hydrochloric, acetic,or phosphoric acid. Diammonium citrate (20% to 30%water solution) is especially useful in removing discol-oration stains and efflorescence on formed and flatworksurfaces. Chemical cleaners should be used by skilledoperators taking suitable safety precautions. See Greening(1966) and PCA (1988) for more information.

Mechanical cleaning includes sandblasting, shot-blasting, scarification, power chipping, and grinding.These methods wear the dirt off the surface rather thanseparate it from the surface. They, in fact, wear away boththe dirt and some of the concrete surface; it is inevitablethat there will be some loss of decorative detail, increasedsurface roughness, and rounding of sharp corners.Abrasive methods may also reveal defects (voids) hiddenjust beneath the formed surface.

Chemical and mechanical cleaning can each have anabrading effect on the concrete surface that may changethe appearance of a surface compared to that of an adja-cent uncleaned surface.

shallow vertical or overhead repairs may best be accom-plished by shotcreting. Several proprietary low-shrinkagecementitious repair products are also available.

Curing Patches

Following patching, good curing is essential (Fig. 11-34).Curing should be started immediately to avoid earlydrying. Wet burlap, wet sand, plastic sheets, curing paper,tarpaulins, or a combination of these can be used. In loca-tions where it is difficult to hold these materials in place,an application of two coats of membrane-curing com-pound is often the most convenient method.

Cleaning Concrete Surfaces

Concrete surfaces are not always uniform in color whenforms are removed; they may have a somewhat blotchyappearance and there may be a slight film of form-releaseagent in certain areas. There may be mortar stains fromleaky forms or there may be rust stains. Flatwork can alsobecome discolored during construction. Where appear-ance is important, all surfaces should be cleaned after con-struction has progressed to the stage where there will beno discoloration from subsequent construction activities.

There are three techniques for cleaning concrete sur-faces: water, chemical, and mechanical (abrasion). Waterdissolves dirt and rinses it from the surface. Chemicalcleaners, usually mixed with water, react with dirt to sep-arate it from the surface, and then the dirt and chemicalsare rinsed off with clean water. Mechanical methods—sandblasting is most common—remove dirt by abrasion.

Before selecting a cleaning method, it should be testedon an inconspicuous area to be certain it will be helpful

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Fig. 11-34. Good curing is essential to successful patching.This patch is covered with polyethylene sheeting plus rigidinsulation to retain moisture and heat for rapid hydrationand strength gain. (40434)

Finishing Formed Surfaces

Many off-the-form concrete surfaces require little or noadditional treatment when they are carefully constructedwith the proper forming materials. These surfaces aredivided into two general classes: smooth and textured orpatterned. Smooth surfaces are produced with plastic-coated forms, steel forms, fiberglass-reinforced plasticforms, formica forms, or tempered-hardboard forms. Tex-tured or patterned surfaces are achieved with form liners,rough-sawn lumber, special grades and textures of ply-wood, or by fracturing the projections of a striated surface.

Rough-form finishes require patching of all tieholesand defects, unless tieholes are left open for architecturaleffect. Otherwise, these surfaces need no further worksince texture and finish are imparted by the forms.

For a smooth off-the-form finish, it is important toarrange the smooth-facing forming material and tierods ina symmetrical pattern. Studs and wales that are capable ofpreventing excessive deflections must support smooth-finish forms that are somewhat lightweight.

A smooth, rubbed finish is produced on a newly hard-ened concrete surface no later than the day following formremoval. The forms are removed and necessary patchingcompleted as soon as possible. The surface is then wettedand rubbed with a carborundum brick or other abrasiveuntil a satisfactory uniform color and texture are produced.

A sand-floated finish can also be produced on newlyhardened concrete surfaces. No later than 5 to 6 hours fol-lowing form removal, the surface should be thoroughlywetted and rubbed with a wood float in a circular motion,working fine sand into the surface until the resultingfinish is even and uniform in texture and color.

A grout cleandown (sack-rubbed finish) can be usedto impart a uniform color and appearance to a smooth sur-face. After defects have been repaired, the surface shouldbe saturated thoroughly with water and kept wet at leastone hour before finishing operations begin. Next a groutof 1 part cement, 11⁄2 to 2 parts of fine sand passing a600 µm (No. 30) sieve, and sufficient water for a thick,creamy consistency should be prepared. It should bepreshrunk by mixing at least one hour before use and thenremixed without the addition of water and applied uni-formly by brush, plasterer’s trowel, or rubber float to com-pletely fill all air bubbles and holes.

The surface should be vigorously floated with a wood,sponge rubber, or cork float immediately after applying thegrout to fill any small air holes (bugholes) that are left; anyremaining excess grout should be scraped off with asponge-rubber float. If the float pulls grout from the holes,a sawing motion of the tool should correct the difficulty;any grout remaining on the surface should be allowed tostand undisturbed until it loses some of its plasticity but notits damp appearance. Then the surface should be rubbedwith clean, dry burlap to remove all excess grout. All airholes should remain filled, but no visible film of groutshould remain after the rubbing. Any section being cleaned

with grout must be completed in one day, since groutremaining on the surface overnight is difficult to remove.

If possible, work should be done in the shade andpreferably during cool, damp weather. During hot ordry weather, the concrete can be kept moist with a finefog spray.

The completed surface should be moist-cured bykeeping the area wet for 36 hours following the cleandown. When completely dry, the surface should have auniform color and texture.

SPECIAL SURFACE FINISHES

Patterns and Textures

A variety of patterns and textures can be used to producedecorative finishes. Patterns can be formed with dividerstrips or by scoring or stamping the surface just before theconcrete hardens. Textures can be produced with littleeffort and expense with floats, trowels, and brooms; moreelaborate textures can be achieved with special techniques(Fig. 11-35). See Kosmatka (1991).

Exposed-Aggregate Concrete

An exposed-aggregate finish provides a rugged, attractivesurface in a wide range of textures and colors. Select aggre-gates are carefully chosen to avoid deleterious substances;they are usually of uniform size such as 9.5 to 12.5 mm (3⁄8to 1⁄2 in.) or larger. They should be washed thoroughlybefore use to assure satisfactory bond. Flat or elongatedaggregate particles should not be used since they are easilydislodged when the aggregate is exposed. Caution shouldbe exercised when using crushed stone; it not only has agreater tendency to stack during the seeding operation(requiring more labor), but it also may be undesirable insome applications (pool decks, for example).

The aggregate should be evenly distributed or seededin one layer onto the concrete surface immediately afterthe slab has been bullfloated or darbied. The particlesmust be completely embedded in the concrete. This can bedone by lightly tapping with a wooden hand float, adarby, or the broad side of a piece of lumber; then, whenthe concrete can support a finisher on kneeboards, the sur-face should be hand-floated with a magnesium float ordarby until the mortar completely surrounds and slightlycovers all the aggregate particles.

Methods of exposing the aggregate usually includewashing and brushing, using retarders, and scrubbing.When the concrete has hardened sufficiently, simultane-ously brushing and flushing with water should exposethe aggregate. In washing and brushing, the surfacelayer of mortar should be carefully washed away with alight spray of water and brushed until the desired expo-sure is achieved.

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Waterblasting can also be used to texture the surfaceof hardened concrete, especially where local ordinancesprohibit the use of sandblasting for environmental rea-sons. High-pressure water jets are used on surfaces thathave or have not been treated with retarders.

In tooling or bushhammering, a layer of hardenedconcrete is removed and the aggregate is fractured at thesurface. The surfaces attained can vary from a light scalingto a deep, bold texture obtained by jackhammering with asingle-pointed chisel. Combs and multiple points can beused to produce finishes similar to some finishes used oncut stone.

Grinding and polishing will produce an exposed-aggregate concrete such as terrazzo, which is primarilyused indoors. This technique is done in several successivesteps using either a stone grinder or diamond-diskgrinder. Each successive step uses finer grit than the pre-ceding one. A polishing compound and buffer can then beused for a honed finish.

Regardless of the method employed, it is wise for thecontractor to make a preconstruction mock-up (fieldsample) for each finish to determine the timing and stepsinvolved; in addition, the mock-up is used to obtainaesthetic approval from the architect and owner. Formore information see Kosmatka (1991), PCA (1972), andPCA (1995).

Since timing is important, test panels should be madeto determine the correct time for exposing the aggregatewithout dislodging the particles. On large jobs, a water-insoluble retarder can be sprayed or brushed on the sur-face immediately after floating, but on small jobs this maynot be necessary. When the concrete becomes too hard toproduce the required finish with normal washing andbrushing, a dilute hydrochloric acid can be used. Surfacepreparation should be minimized and applicable localenvironmental laws should be followed.

Two other methods for obtaining an exposed aggre-gate surface are: (1) the monolithic technique where aselect aggregate, usually gap-graded, is mixed throughoutthe batch of concrete, and (2) the topping technique inwhich the select exposed-aggregate is mixed into a toppingthat is placed over a base slab of conventional concrete.

The aggregate in exposed-aggregate concrete can alsobe exposed by methods other than those already dis-cussed. The following techniques expose the aggregateafter the concrete has hardened to a compressive strengthof around 28 MPa (4000 psi):

Abrasive blasting is best applied to a gap-gradedaggregate concrete. The nozzle should be held per-pendicular to the surface and the concrete removed to amaximum depth of about one-third the diameter of thecoarse aggregate.

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Fig. 11-35. Patterned, textured, and colored concretes are very attractive. (59031, 53598, 59003, 47835, 44898)

Colored Finishes

Colored concrete finishes for decorative effects in bothinterior and exterior applications can be achieved by fourdifferent methods: (1) the one-course or integral method,(2) the two-course method, (3) the dry-shake method, and(4) stains and paints (discussed below).

Color pigments added to the concrete in the mixer toproduce a uniform color is the basis for the one-coursemethod. Both natural and synthetic pigments are satisfac-tory if they are: (1) insoluble in water, (2) free from solublesalts and acids, (3) fast to sunlight, (4) fast to alkali andweak acids, (5) limited to small amounts of calcium sul-phate, and (6) ground fine enough so that 90% passes a45 micron screen. Use only the minimum amount necessaryto produce the desired color and not more than 10% byweight of the cement.

In the two-course method, a base slab is placed andleft with a rough texture to bond better to a colored top-ping layer. As soon as the base slab can support a cementmason’s weight, the topping course can be placed. If thebase slab has hardened, prepare a bonding grout for thebase slab prior to placing the topping mix. The toppingmix is normally 13 mm (1⁄2 in.) to 25 mm (1 in.) thick, witha ratio of cement to sand of 1:3 or 1:4. The mix is floatedand troweled in the prescribed manner. The two-coursemethod is more commonly used because it is more eco-nomical than the one-course method.

In the dry-shake method, a prepackaged dry-colormaterial is cast onto the surface of a concrete slab. The dry-shake material is applied after the concrete has beenscreeded and darbied or bullfloated, excess moisture hasevaporated from the surface, and preliminary floating hasbeen done. Two-thirds of the dry material is shaken evenlyby hand over the surface and thoroughly floated into thesurface in a manner that evenly distributes the material.Immediately, the rest of the material is cast onto the surfaceand floated as before. The surface can then be troweled atthe same time as a typical slab. For exterior surfaces thatwill be exposed to freezing and thawing, little or no trow-eling followed by brooming with a soft bristle concretebroom is usually sufficient.

Stains, Paints, and Clear Coatings

Many types of stains, paints and clear coatings can beapplied to concrete surfaces. Among the principal paintsused are portland cement base, latex-modified portlandcement, and latex (acrylic and polyvinyl acetate) paints(PCA 1992). However, stains and paints are used onlywhen it is necessary to color existing concrete. It is difficultto obtain a uniform color with dyes or stains; therefore, themanufacturer’s directions should be closely followed.

Portland cement based paints can be used on eitherinterior or exterior exposures. The surface of the concreteshould be damp at the time of application and each coat

should be dampened as soon as possible without dis-turbing the paint. Damp curing of conventional portlandcement paint is essential. On open-textured surfaces, suchas concrete masonry, the paint should be applied withstiff-bristle brushes (scrub brushes). Paint should beworked well into the surface. For concrete with a smoothor sandy finish, whitewash or Dutch-type calciminebrushes are best.

The latex materials used in latex-modified portlandcement paints retard evaporation, thereby retaining the nec-essary water for hydration of the portland cement. Whenusing latex-modified paints, moist curing is not required.

Most latex paints are resistant to alkali and can beapplied to new concrete after 10 days of good dryingweather. The preferred method of application is by long-fiber, tapered nylon brushes 100 to 150 mm (4 to 6 in.) wide;however, roller or spray methods can also be used. Thepaints may be applied to damp, but not wet surfaces. If thesurface is moderately porous, or if extremely dry condi-tions prevail, prewetting the surface is advisable.

Clear coatings are frequently used on concrete sur-faces to (1) prevent soiling or discoloration of the concreteby air pollution, (2) to facilitate cleaning the surface if itdoes become dirty, (3) to brighten the color of the aggre-gates, and (4) to render the surface water-repellent andthus prevent color change due to rain and water absorp-tion. The better coatings often consist of methyl methacry-late forms of acrylic resin, as indicated by a laboratoryevaluation of commercial clear coatings (Litvin 1968). Themethyl methacrylate coatings should have a higher vis-cosity and solids content when used on smooth concrete,since the original appearance of smooth concrete is moredifficult to maintain than the original appearance ofexposed-aggregate concrete.

Other materials, such as silane and siloxane pene-trating sealers, are commonly used as water repellents formany exterior concrete applications.

PRECAUTIONS

Protect Your Head and Eyes. Construction equipment andtools represent constant potential hazards to busy construc-tion personnel. That’s why hard hats are required on con-struction projects. It is therefore recommended that somesort of head protection, such as a hard hat or safety hat, beworn when working any construction job, large or small.

Proper eye protection is essential when working withcement or concrete. Eyes are particularly vulnerable toblowing dust, splattering concrete, and other foreign objects.On some jobs it may be advisable to wear full-cover gog-gles or safety glasses with side shields. Actions that causedust to become airborne should be avoided. Local or gen-eral ventilation can control exposures below applicableexposure limits; respirators may be used in poorly venti-lated areas, where exposure limits are exceeded, or whendust causes discomfort or irritation.

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REFERENCES

ACI Committee 207, Roller Compacted Mass Concrete, ACI207.5R-99, American Concrete Institute, Farmington Hills,Michigan, 1999, 47 pages.

ACI Committee 301, Specifications for Structural Concrete,ACI 301-99, American Concrete Institute, FarmingtonHills, Michigan, 1999, 49 pages.

ACI Committee 302, Guide for Concrete Floor and SlabConstruction, ACI 302.1R-96, American Concrete Institute,Farmington Hills, Michigan, 1996, 65 pages.

ACI Committee 304, Guide for Measuring, Mixing,Transporting and Placing Concrete, ACI 304R-00, AmericanConcrete Institute, Farmington Hills, Michigan, 2000, 41pages.

ACI Committee 309, Guide for Consolidation of Concrete,ACI 309R-96, American Concrete Institute, FarmingtonHills, Michigan, 1996, 39 pages.

ACI Committee 347, Guide to Formwork for Concrete, ACI347R-94, reapproved 1999, American Concrete Institute,Farmington Hills, Michigan, 1999, 34 pages.

ACI, “Vapor Retarder Location,” Concrete International,American Concrete Institute, Farmington Hills, Michigan,April 2001, pages 72 and 73.

Colley, B. E., and Humphrey, H. A., Aggregate Interlock atJoints in Concrete Pavements, Development DepartmentBulletin DX124, Portland Cement Association, http://www.portcement.org/pdf_files/DX124.pdf, 1967.

Concrete Manual, 8th ed., U.S. Bureau of Reclamation,Denver, revised 1981.

Protect Your Back. All materials used to make concrete—portland cement, sand, coarse aggregate, and water—canbe quite heavy, even in small quantities. When liftingheavy materials, the back should be straight, legs bent,and the weight between the legs as close to the body aspossible. Mechanical equipment should be used to placeconcrete as close as possible to its final position. After theconcrete is deposited in the desired area by chute, pump,or wheelbarrow, it should be pushed—not lifted—intofinal position with a shovel; a short-handled, square-endshovel is an effective tool for spreading concrete, but spe-cial concrete rakes or come-alongs also can be used.Excessive horizontal movement of the concrete should beavoided; it not only requires extra effort, but may also leadto segregation of the concrete ingredients.

Protect Your Skin. When working with fresh concrete,care should be taken to avoid skin irritation or chemicalburns (see warning statement in the box). Prolonged con-tact between fresh concrete and skin surfaces, eyes, andclothing may result in burns that are quite severe,including third-degree burns. Eyes and skin that come incontact with fresh concrete should be flushed thoroughlywith clean water. If irritation persists, consult a physician.For deep burns or large affected skin areas, seek medicalattention immediately.

The A-B-Cs of fresh concrete’s effect on skin are:

Abrasive Sand contained in fresh concrete is abrasiveto bare skin.

Basic & Portland cement is alkaline in nature, so wetCaustic concrete and other cement mixtures are

strongly basic (pH of 12 to 13). Strong bases—like strong acids—are harmful, or causticto skin.

Drying Portland cement is hygroscopic—it absorbswater. In fact, portland cement needs waterto harden. It will draw water away from anymaterial it contacts—including skin.

Clothing worn as protection from fresh concreteshould not be allowed to become saturated with moisturefrom fresh concrete because saturated clothing cantransmit alkaline or hygroscopic effects to the skin.Clothing that becomes saturated from contact with freshconcrete should be rinsed out promptly with clear waterto prevent continued contact with skin surfaces.Waterproof gloves, a long-sleeved shirt, and long pantsshould be worn. If you must stand in fresh concrete whileit is being placed, screeded, or floated, wear rubber bootshigh enough to prevent concrete from getting into them(PCA 1998).

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WARNING: Contact with wet (unhardened) concrete,mortar, cement, or cement mixtures can cause SKIN IRRI-TATION, SEVERE CHEMICAL BURNS (THIRD-DEGREE), or SERIOUS EYE DAMAGE. Frequentexposure may be associated with irritant and/or allergiccontact dermatitis. Wear waterproof gloves, a long-sleeved shirt, full-length trousers, and proper eye protec-tion when working with these materials. If you have tostand in wet concrete, use waterproof boots that are highenough to keep concrete from flowing into them. Washwet concrete, mortar, cement, or cement mixtures fromyour skin immediately. Flush eyes with clean waterimmediately after contact. Indirect contact throughclothing can be as serious as direct contact, so promptlyrinse out wet concrete, mortar, cement, or cement mix-tures from clothing. Seek immediate medical attention ifyou have persistent or severe discomfort.

Farny, James A., Concrete Floors on Ground, EB075, PortlandCement Association, 2001, 136 pages.

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PCA, Working Safely with Concrete, MS271, PortlandCement Association, 1998, 6 pages.

Stark, David C., Effect of Vibration on the Air-Void Systemand Freeze-Thaw Durability of Concrete, Research and Devel-opment Bulletin RD092, Portland Cement Association,http://www.portcement.org/pdf_files/RD092.pdf, 1986.

Suprenant, Bruce A., “Free Fall of Concrete,” ConcreteInternational, American Concrete Institute, FarmingtonHills, Michigan, June 2001, pages 44 and 45.

Turner, C. D., “Unconfined Free-Fall of Concrete,” Journalof the American Concrete Institute, American Concrete Insti-tute, Detroit, December 1970, pages 975 to 976.

217


Curing is the maintenance of a satisfactory moisture con-tent and temperature in concrete for a period of time imme-diately following placing and finishing so that the desiredproperties may develop (Fig. 12-1). The need for adequatecuring of concrete cannot be overemphasized. Curing has astrong influence on the properties of hardened concrete;proper curing will increase durability, strength, watertight-ness, abrasion resistance, volume stability, and resistance tofreezing and thawing and deicers. Exposed slab surfacesare especially sensitive to curing as strength developmentand freeze-thaw resistance of the top surface of a slab canbe reduced significantly when curing is defective.

When portland cement is mixed with water, a chemicalreaction called hydration takes place. The extent to whichthis reaction is completed influences the strength and dura-bility of the concrete. Freshly mixed concrete normally con-

tains more water than is required for hydration of the ce-ment; however, excessive loss of water by evaporation candelay or prevent adequate hydration. The surface is partic-ularly susceptible to insufficient hydration because it driesfirst. If temperatures are favorable, hydration is relativelyrapid the first few days after concrete is placed; however, itis important for water to be retained in the concrete duringthis period, that is, for evaporation to be prevented or sub-stantially reduced.

With proper curing, concrete becomes stronger, moreimpermeable, and more resistant to stress, abrasion, andfreezing and thawing. The improvement is rapid at earlyages but continues more slowly thereafter for an indefiniteperiod. Fig. 12-2 shows the strength gain of concrete withage for different moist curing periods and Fig. 12-3 showsthe relative strength gain of concrete cured at differenttemperatures.

CHAPTER 12

Curing Concrete

Fig. 12-1. Curing should begin as soon as the concretestiffens enough to prevent marring or erosion of the sur-face. Burlap sprayed with water is an effective method formoist curing. (69973)

60

50

40

30

20

10

00 7 28 90 365

8

6

4

2

0

Age at test, days

Moist-cured entire time



In laboratory air entire time

Com

pres

sive

stre

ngth

, MP

a

Com

pres

sive

stre

ngth

, 100

0 ps

i

Fig. 12-2. Effect of moist curing time on strength gain ofconcrete (Gonnerman and Shuman 1928).

219

The most effective method for curing concretedepends on the materials used, method of construction,and the intended use of the hardened concrete. For mostjobs, curing generally involves applying curing com-pounds, or covering the freshly placed and finished con-crete with impermeable sheets or wet burlap. In somecases, such as in hot and cold weather, special care usingother precautions is needed.

Concrete mixtures with high cement contents and lowwater-cement ratios (less than 0.40) may require specialcuring needs. As cement hydrates (chemically combiningwith water) the internal relative humidity decreases caus-ing the paste to self-desiccate (dry out) if no external wateris provided. The paste can self-desiccate to a level wherehydration stops. This may influence desired concreteproperties, especially if the internal relative humiditydrops below 80% within the first seven days. In view of

220


this, membrane-forming curing compounds may notretain enough water in the concrete. Therefore, foggingand wet curing become necessary to maximize hydration(Copeland and Bragg 1955). Fogging during and afterplacing and finishing also helps minimize plastic crackingin concretes with very low water-cement ratios (especiallyaround 0.30 or less).

When moist curing is interrupted, the development ofstrength continues for a short period and then stops afterthe concrete’s internal relative humidity drops to about80%. However, if moist curing is resumed, strength devel-opment will be reactivated, but the original potentialstrength may not be achieved. Although it can be done ina laboratory, it is difficult to resaturate concrete in thefield. Thus, it is best to moist-cure the concrete continu-ously from the time it is placed and finished until it hasgained sufficient strength, impermeability, and durability.

Loss of water will also cause the concrete to shrink,thus creating tensile stresses within the concrete. If thesestresses develop before the concrete has attained adequatetensile strength, surface cracking can result. All exposedsurfaces, including exposed edges and joints, must be pro-tected against moisture evaporation.

Hydration proceeds at a much slower rate when theconcrete temperature is low. Temperatures below 10°C(50°F) are unfavorable for the development of earlystrength; below 4°C (40°F) the development of earlystrength is greatly retarded; and at or below freezingtemperatures, down to -10°C (14°F), little or no strengthdevelops.

In recent years, a maturity concept has been introducedto evaluate the development of strength when there is vari-ation in the curing temperature of the concrete. Maturity isthe product of the age of the concrete and its average curingtemperature above a certain base temperature. Refer toChapter 14 for more information on the maturity concept. Itfollows that concrete should be protected so that its tem-perature remains favorable for hydration and moisture isnot lost during the early hardening period.

CURING METHODS AND MATERIALS

Concrete can be kept moist (and in some cases at a favor-able temperature) by three curing methods:

1. Methods that maintain the presence of mixing waterin the concrete during the early hardening period.These include ponding or immersion, spraying orfogging, and saturated wet coverings. These methodsafford some cooling through evaporation, which isbeneficial in hot weather.

2. Methods that reduce the loss of mixing water fromthe surface of the concrete. This can be done by cov-ering the concrete with impervious paper or plasticsheets, or by applying membrane-forming curingcompounds.

Casting/curing temperature, °C (°F)

125

105

85

65

45

250 20 40 60

Age, days

Com

pres

sive

stre

ngth

, % 2

8-da

y st

reng

th

23/23 (73/73)32/32 (90/90)10/10 (50/50)23/10 (73/50)

Casting/curing temperature, °C (°F)

120

100

80

600 20 40 60

Age, days

Com

pres

sive

stre

ngth

, % 2

3°C

(73°

F)

23/23 (73/73)32/32 (90/90)10/10 (50/50)23/10 (73/50)

Fig. 12-3. Effect of curing temperature on strength gain(top) relative to 28-day strength and (bottom) relative to thestrength of concrete at 23°C (73°F) (Burg 1996).

221

Chapter 12 � Curing Concrete

3. Methods that accelerate strength gain by supplyingheat and additional moisture to the concrete. This isusually accomplished with live steam, heating coils,or electrically heated forms or pads.

The method or combination of methods chosendepends on factors such as availability of curing materials,size, shape, and age of concrete, production facilities (inplace or in a plant), esthetic appearance, and economics.As a result, curing often involves a series of proceduresused at a particular time as the concrete ages. For example,fog spraying or plastic covered wet burlap can precedeapplication of a curing compound. The timing of eachprocedure depends on the degree of hardening of the con-crete needed to prevent the particular procedure fromdamaging the concrete surface (ACI 308 1997).

Ponding and Immersion

On flat surfaces, such as pavements and floors, concretecan be cured by ponding. Earth or sand dikes around theperimeter of the concrete surface can retain a pond ofwater. Ponding is an ideal method for preventing loss ofmoisture from the concrete; it is also effective for main-taining a uniform temperature in the concrete. The curingwater should not be more than about 11°C (20°F) coolerthan the concrete to prevent thermal stresses that couldresult in cracking. Since ponding requires considerablelabor and supervision, the method is generally used onlyfor small jobs.

The most thorough method of curing with water con-sists of total immersion of the finished concrete element.This method is commonly used in the laboratory forcuring concrete test specimens. Where appearance of theconcrete is important, the water used for curing by pond-ing or immersion must be free of substances that will stainor discolor the concrete. The material used for dikes mayalso discolor the concrete.

Fogging and Sprinkling

Fogging (Fig. 12-4) and sprinkling with water are excellentmethods of curing when the ambient temperature is wellabove freezing and the humidity is low. A fine fog mist isfrequently applied through a system of nozzles orsprayers to raise the relative humidity of the air over flat-work, thus slowing evaporation from the surface. Foggingis applied to minimize plastic shrinkage cracking until fin-ishing operations are complete. Once the concrete has setsufficiently to prevent water erosion, ordinary lawn sprin-klers are effective if good coverage is provided and waterrunoff is of no concern. Soaker hoses are useful on surfacesthat are vertical or nearly so.

The cost of sprinkling may be a disadvantage. Themethod requires an ample water supply and carefulsupervision. If sprinkling is done at intervals, the concretemust be prevented from drying between applications of

water by using burlap or similar materials; otherwisealternate cycles of wetting and drying can cause surfacecrazing or cracking.

Wet Coverings

Fabric coverings saturated with water, such as burlap,cotton mats, rugs, or other moisture-retaining fabrics, arecommonly used for curing (Fig. 12-5). Treated burlaps thatreflect light and are resistant to rot and fire are available.The requirements for burlap are described in the Specifica-tion for Burlap Cloths Made from Jute or Kenaf (AASHTO M182), and those for white burlap-polyethylene sheeting aredescribed in ASTM C 171 (AASHTO M 171).

Fig. 12-4. Fogging minimizes moisture loss during and afterplacing and finishing of concrete. (69974)

Fig. 12-5. Lawn sprinklers saturating burlap with water keepthe concrete continuously moist. Intermittent sprinkling isacceptable if no drying of the concrete surface occurs.(50177)

curing-paper patches. When the condition of the paper isquestionable, additional use can be obtained by using it indouble thickness.

In addition to curing, impervious paper providessome protection to the concrete against damage from sub-sequent construction activity as well as protection fromthe direct sun. It should be light in color and nonstainingto the concrete. Paper with a white upper surface is prefer-able for curing exterior concrete during hot weather.

Plastic Sheets

Plastic sheet materials, such as polyethylene film, can beused to cure concrete (Fig. 12-7). Polyethylene film is alightweight, effective moisture retarder and is easilyapplied to complex as well as simple shapes. Its applica-tion is the same as described for impervious paper.

Curing with polyethylene film (or impervious paper)can cause patchy discoloration, especially if the concretecontains calcium chloride and has been finished by hard-steel troweling. This discoloration is more pronouncedwhen the film becomes wrinkled, but it is difficult andtime consuming on a large project to place sheet materialswithout wrinkles. Flooding the surface under the coveringmay prevent discoloration, but other means of curingshould be used when uniform color is important.

Polyethylene film should conform to ASTM C 171(AASHTO M 171), which specifies a 0.10-mm (4-mil)thickness for curing concrete, but lists only clear and whiteopaque film. However, black film is available and is satis-factory under some conditions. White film should be usedfor curing exterior concrete during hot weather to reflectthe sun’s rays. Black film can be used during cool weather

Burlap must be free of any substance that is harmfulto concrete or causes discoloration. New burlap should bethoroughly rinsed in water to remove soluble substancesand to make the burlap more absorbent.

Wet, moisture-retaining fabric coverings should beplaced as soon as the concrete has hardened sufficiently toprevent surface damage. During the waiting period othercuring methods are used, such as fogging or the use ofmembrane forming finishing aids. Care should be taken tocover the entire surface with wet fabric, including theedges of slabs. The coverings should be kept continuouslymoist so that a film of water remains on the concrete sur-face throughout the curing period. Use of polyethylenefilm over wet burlap is a good practice; it will eliminatethe need for continuous watering of the covering.Periodically rewetting the fabric under the plastic before itdries out should be sufficient. Alternate cycles of wettingand drying during the early curing period may causecrazing of the surface.

Wet coverings of earth, sand, or sawdust are effectivefor curing and are often useful on small jobs. Sawdust frommost woods is acceptable, but oak and other woods thatcontain tannic acid should not be used since deteriorationof the concrete may occur. A layer about 50 mm (2 in.) thickshould be evenly distributed over the previously mois-tened surface of the concrete and kept continuously wet.

Wet hay or straw can be used to cure flat surfaces. Ifused, it should be placed in a layer at least 150 mm (6 in.)thick and held down with wire screen, burlap, or tarpau-lins to prevent its being blown off by wind.

A major disadvantage of moist earth, sand, sawdust,hay, or straw coverings is the possibility of discoloringthe concrete.

Impervious Paper

Impervious paper for curing concrete consists of twosheets of kraft paper cemented together by a bituminousadhesive with fiber reinforcement. Such paper, con-forming to ASTM C 171 (AASHTO M 171), is an efficientmeans of curing horizontal surfaces and structural con-crete of relatively simple shapes. An important advantageof this method is that periodic additions of water are notrequired. Curing with impervious paper enhances thehydration of cement by preventing loss of moisture fromthe concrete (Fig. 12-6).

As soon as the concrete has hardened sufficiently toprevent surface damage, it should be thoroughly wettedand the widest paper available applied. Edges of adjacentsheets should be overlapped about 150 mm (6 in.) andtightly sealed with sand, wood planks, pressure-sensitivetape, mastic, or glue. The sheets must be weighted tomaintain close contact with the concrete surface duringthe entire curing period.

Impervious paper can be reused if it effectively retainsmoisture. Tears and holes can easily be repaired with

222


Fig.12-6. Impervious curing paper is an efficient means ofcuring horizontal surfaces. (69994)

or for interior locations. Clear film has little effect on heatabsorption.

ASTM C 171 (AASHTO M 171) also includes a sheetmaterial consisting of burlap impregnated on one sidewith white opaque polyethylene film. Combinations ofpolyethylene film bonded to an absorbent fabric such asburlap help retain moisture on the concrete surface.

Polyethylene film may also be placed over wet burlapor other wet covering materials to retain the water in thewet covering material. This procedure eliminates thelabor-intensive need for continuous watering of wet cov-ering materials.

Membrane-Forming Curing Compounds

Liquid membrane-forming compounds consisting ofwaxes, resins, chlorinated rubber, and other materials canbe used to retard or reduce evaporation of moisture fromconcrete. They are the most practical and most widelyused method for curing not only freshly placed concretebut also for extending curing of concrete after removal offorms or after initial moist curing. However, the mosteffective methods of curing concrete are wet coverings orwater spraying that keeps the concrete continually damp.Curing compounds should be able to maintain the relativehumidity of the concrete surface above 80% for seven daysto sustain cement hydration.

Membrane-forming curing compounds are of twogeneral types: clear, or translucent; and white pigmented.Clear or translucent compounds may contain a fugitivedye that makes it easier to check visually for completecoverage of the concrete surface when the compound isapplied. The dye fades away soon after application. Onhot, sunny days, use of white-pigmented compounds are

recommended; they reduce solar-heat gain, thus reducingthe concrete temperature. Pigmented compounds shouldbe kept agitated in the container to prevent pigment fromsettling out.

Curing compounds should be applied by hand-oper-ated or power-driven spray equipment immediately afterfinal finishing of the concrete (Fig. 12-8). The concrete sur-face should be damp when the coating is applied. On dry,windy days, or during periods when adverse weatherconditions could result in plastic shrinkage cracking,application of a curing compound immediately after finalfinishing and before all free water on the surface hasevaporated will help prevent the formation of cracks.Power-driven spray equipment is recommended for uni-form application of curing compounds on large pavingprojects. Spray nozzles and windshields on such equip-ment should be arranged to prevent wind-blown loss ofcuring compound.

Normally only one smooth, even coat is applied at atypical rate of 3 to 4 m2 per liter (150 to 200 sq ft per gallon);but products may vary, so manufacturer’s recommendedapplication rates should be followed. If two coats are nec-essary to ensure complete coverage, for effective protectionthe second coat should be applied at right angles to thefirst. Complete coverage of the surface must be attainedbecause even small pinholes in the membrane will increasethe evaporation of moisture from the concrete.

Curing compounds might prevent bonding betweenhardened concrete and a freshly placed concrete overlay.And, most curing compounds are not compatible with ad-hesives used with floor covering materials. Consequently,they should either be tested for compatibility, or not usedwhen bonding of overlying materials is necessary. Forexample, a curing compound should not be applied to the

223


Fig. 12-7. Polyethylene film is an effective moisture barrierfor curing concrete and easily applied to complex as well assimple shapes. To minimize discoloration, the film shouldbe kept as flat as possible on the concrete surface. (70014)

Fig. 12-8. Liquid membrane-forming curing compoundsshould be applied with uniform and adequate coverageover the entire surface and edges for effective, extendedcuring of concrete. (69975)

Steam Curing

Steam curing is advantageous where early strength gainin concrete is important or where additional heat is re-quired to accomplish hydration, as in cold weather.

Two methods of steam curing are used: live steam atatmospheric pressure (for enclosed cast-in-place structuresand large precast concrete units) and high-pressure steamin autoclaves (for small manufactured units). Only livesteam at atmospheric pressure will be discussed here.

A typical steam-curing cycle consists of (1) an initialdelay prior to steaming, (2) a period for increasing thetemperature, (3) a period for holding the maximum tem-perature constant, and (4) a period for decreasing thetemperature. A typical atmospheric steam-curing cycle isshown in Fig. 12-9.

Steam curing at atmospheric pressure is generallydone in an enclosure to minimize moisture and heat losses.Tarpaulins are frequently used to form the enclosure.Application of steam to the enclosure should be delayeduntil initial set occurs or delayed at least 3 hours after finalplacement of concrete to allow for some hardening of theconcrete. However, a 3- to 5- hour delay period prior tosteaming will achieve maximum early strength, as shownin Fig. 12-10.

Steam temperature in the enclosure should be kept atabout 60°C (140°F) until the desired concrete strength hasdeveloped. Strength will not increase significantly if themaximum steam temperature is raised from 60°C to 70°C(140°F to 160°F). Steam-curing temperatures above 70°C(160°F) should be avoided; they are uneconomical and

base slab of a two-course floor. Similarly, some curingcompounds may affect the adhesion of paint to concretefloors. Curing compound manufacturers should be con-sulted to determine if their product is suitable for theintended application.

Curing compounds should be uniform and easy tomaintain in a thoroughly mixed solution. They should notsag, run off peaks, or collect in grooves. They should forma tough film to withstand early construction trafficwithout damage, be nonyellowing, and have good mois-ture-retention properties.

Caution is necessary when using curing compoundscontaining solvents of high volatility in confined spaces ornear sensitive occupied spaces such as hospitals becauseevaporating volatiles may cause respiratory problems.Applicable local environmental laws concerning volatileorganic compound (VOC) emissions should be followed.

Curing compounds should conform to ASTM C 309(AASHTO M 148). A method for determining the efficiencyof curing compounds, waterproof paper, and plastic sheetsis described in ASTM C 156 (AASHTO T 155). ASTM C1151, discontinued in 2000, also evaluates the effectivenessof curing compounds. Curing compounds with sealingproperties are specified under ASTM C 1315.

Internal Moist Curing

Internal moist curing refers to methods of providing mois-ture from within the concrete as opposed to outside theconcrete. This water should not effect the initial water tocement ratio of the fresh concrete. Lightweight (low-den-sity) fine aggregate or absorbent polymer particles with anability to retain a significant amount of water may provideadditional moisture for concretes prone to self desiccation.When more complete hydration is needed for concreteswith low water to cement ratios (around 0.30 or less),60 kg/m3 to 180 kg/m3 (100 lb/yd3 to 300 lb/yd3) of satu-rated lightweight fine aggregate can provide additionalmoisture to extend hydration, resulting in increasedstrength and durability. All of the fine aggregate in a mix-ture can be replaced with saturated lightweight fineaggregate to maximize internal moist curing. Internalmoist curing must be accompanied by external curingmethods.

Forms Left in Place

Forms provide satisfactory protection against loss of mois-ture if the top exposed concrete surfaces are kept wet. Asoaker hose is excellent for this. The forms should be lefton the concrete as long as practical.

Wood forms left in place should be kept moist bysprinkling, especially during hot, dry weather. If thiscannot be done, they should be removed as soon as prac-tical and another curing method started without delay.Color variations may occur from formwork and unevenwater curing of walls.

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60

40

20

00 5 10 15 20 24

140

160

120

100

80

60

40

1 2

3 4

Temp. reduced at20°C (40°F)/hr untilwithin 10°C (20°F)of outside air

Steam applied to enclosure at rate of10 to 20°C (20 to 40°F)/hr

Outside airat 10°C(50°F)

Steam temp. in enclosure held to 60°C (140°F),until desired concrete strength is developed

Time after placing, hours

Initial concrete temp. = 21°C (70°F)

Tem

pera

ture

with

in s

team

enc

losu

re, °

C

Tem

pera

ture

with

in s

team

enc

losu

re, °

F

1

2

3

4

Initial delay prior to steaming 3 to 5 hoursTemperature increase period 21/2 hoursConstant temperature period 6 to 12 hours*Temperature decrease period 2 hours

*Type III or high-early-strength cement, longer for other types

Fig. 12-9. A typical atmospheric steam-curing cycle.

may result in damage. It is recommended that the internaltemperature of concrete not exceed 70°C (160°F) to avoidheat induced delayed expansion and undue reduction inultimate strength. Use of concrete temperatures above70°C (160°F) should be demonstrated to be safe by test orhistoric field data.

Concrete temperatures are commonly monitored atthe exposed ends of the concrete element. Monitoring airtemperatures alone is not sufficient because the heat ofhydration may cause the internal temperature of the con-crete to exceed 70°C (160°F). Besides early strength gain,there are other advantages of curing concrete at tempera-tures of around 60°C (140°F); for example, there is reduceddrying shrinkage and creep as compared to concrete curedat 23°C (73°F) for 28 days (Klieger 1960 and Tepponen andEriksson 1987).

Excessive rates of heating and cooling should beavoided to prevent damaging volume changes. Tempera-tures in the enclosure surrounding the concrete should notbe increased or decreased more than 22°C to 33°C (40°F to60°F) per hour depending on the size and shape of theconcrete element.

The curing temperature in the enclosure should beheld until the concrete has reached the desired strength.The time required will depend on the concrete mixture

and steam temperature in the enclosure (ACI Committee517 1992).

Insulating Blankets or Covers

Layers of dry, porous material such as straw or hay can beused to provide insulation against freezing of concretewhen temperatures fall below 0°C (32°F).

Formwork can be economically insulated with com-mercial blanket or batt insulation that has a tough mois-tureproof covering. Suitable insulating blankets aremanufactured of fiberglass, sponge rubber, cellulosefibers, mineral wool, vinyl foam, and open-cell poly-urethane foam. When insulated formwork is used, careshould be taken to ensure that concrete temperatures donot become excessive.

Framed enclosures of canvas tarpaulins, reinforcedpolyethylene film, or other materials can be placed aroundthe structure and heated by space heaters or steam.Portable hydronic heaters are used to thaw subgrades aswell as heat concrete without the use of an enclosure

Curing concrete in cold weather should follow therecommendations in Chapter 14 and ACI 306 (1997), Cold-Weather Concreting. Recommendations for curing concretein hot weather can be found in Chapter 13 and ACI 305,Hot-Weather Concreting.

Electrical, Oil, Microwave, and Infrared Curing

Electrical, hot oil, microwave and infrared curing methodshave been available for accelerated and normal curing ofconcrete for many years. Electrical curing methodsinclude a variety of techniques: (1) use of the concreteitself as the electrical conductor, (2) use of reinforcing steelas the heating element, (3) use of a special wire as theheating element, (4) electric blankets, and (5) the use ofelectrically heated steel forms (presently the most popularmethod). Electrical heating is especially useful in cold-weather concreting. Hot oil may be circulated throughsteel forms to heat the concrete. Infrared rays andmicrowave have had limited use in accelerated curing ofconcrete. Concrete that is cured by infrared methods isusually under a covering or enclosed in steel forms.Electrical, oil, and infrared curing methods are used pri-marily in the precast concrete industry.

CURING PERIOD AND TEMPERATURE

The period of time that concrete should be protected fromfreezing, abnormally high temperatures, and against lossof moisture depends upon a number of factors: the type ofcementing materials used; mixture proportions; requiredstrength, size and shape of the concrete member; ambientweather; and future exposure conditions. The curing

225


80

60

40

20

01 3 5 7 9 11 13 15

17 15 13 11 9 7 5 3

Delay period prior to steaming, hours

Steaming period, hours

80°C (175°F) max steam temperature

65°C (150°F)

52°C (125°F)

Note: Steam temperature increased22°C (40°F)/hr up to maximumType I cement

Com

pres

sive

stre

ngth

at 1

8 ho

urs,

% o

f 28-

day

moi

st-c

ured

stre

ngth

Fig. 12-10. Relationship between strength at 18 hours anddelay period prior to steaming. In each case, the delayperiod plus the steaming period totaled 18 hours (Hanson1963).

cylinders or beams should be fabricated in the field, keptadjacent to the structure or pavement they represent, andcured by the same methods. Equipment is available thatcan monitor internal concrete temperatures and matchthat temperature in the concrete cylinder curing box; thisis the most accurate means of representing in-place con-crete strengths. Cores, cast-in-place removable cylinders,and nondestructive testing methods may also be used todetermine the strength of a concrete member.

Since the rate of hydration is influenced by cementtype and the presence of supplementary cementing mate-rials, the curing period should be prolonged for concretesmade with cementing materials possessing slow-strength-gain characteristics. For mass concrete (large piers, locks,abutments, dams, heavy footings, and massive columnsand transfer girders) in which no pozzolan is used as partof the cementitious material, curing of unreinforced sec-tions should continue for at least 2 weeks. If the mass con-crete contains a pozzolan, minimum curing time forunreinforced sections should be extended to 3 weeks.Heavily-reinforced mass concrete sections should becured for a minimum of 7 days.

During cold weather, additional heat is often requiredto maintain favorable curing temperatures of 10°C to 20°C(50°F to 70°F). Vented gas or oil-fired heaters, heatingcoils, portable hydronic heaters, or live steam can be usedto supply the required heat. In all cases, care must be takento avoid loss of moisture from the concrete. Exposure offresh concrete to heater or engine exhaust gases must beavoided as this can result in surface deterioration anddusting (rapid carbonation).

High-early-strength concrete can be used in coldweather to speed-up setting time and strength develop-ment. This can reduce the curing period, but a minimumtemperature of 10°C (50°F) must be maintained.

For adequate deicer scale resistance of concrete, theminimum curing period generally corresponds to the timerequired to develop the design strength of the concrete atthe surface. A period of air-drying after curing willenhance resistance to scaling. This drying period shouldbe at least 1 month of relatively dry weather before theapplication of deicing salts.

SEALING COMPOUNDS

Sealing compounds (sealers) are liquids applied to thesurface of hardened concrete to reduce the penetration ofliquids or gases such as water, deicing solutions, andcarbon dioxide that cause freeze-thaw damage, corrosionof reinforcing steel, and acid attack. In addition, sealingcompounds used on interior floor slabs reduce dustingand the absorption of spills while making the surfaceeasier to clean.

Sealing compounds differ in purpose from curingcompounds; they should not be confused as being thesame. The primary purpose of a curing compound is to re-

period may be 3 weeks or longer for lean concrete mix-tures used in massive structures such as dams; conversely,it may be only a few days for rich mixes, especially if TypeIII or HE cement is used. Steam-curing periods are nor-mally much shorter, ranging from a few hours to 3 days;but generally 24-hour cycles are used. Since all the desir-able properties of concrete are improved by curing, thecuring period should be as long as necessary.

For concrete slabs on ground (floors, pavements, canallinings, parking lots, driveways, sidewalks) and for struc-tural concrete (cast-in-place walls, columns, slabs, beams,small footings, piers, retaining walls, bridge decks), thelength of the curing period for ambient temperaturesabove 5°C (40°F) should be a minimum of 7 days; addi-tional time may be needed to attain 70% of the specifiedcompressive or flexural strength. When the daily meanambient temperature is 5°C (40°F) or lower, ACICommittee 306 recommendations for curing should befollowed to prevent damage by freezing.

A higher curing temperature provides earlier strengthgain in concrete than a lower temperature but it maydecrease 28-day strength as shown in Fig. 12-11. If strengthtests are made to establish the time when curing can ceaseor forms can be removed, representative concrete test

226


6

5

4

3

2

1

0

40

30

20

10

Com

pres

sive

stre

ngth

, MP

a

Com

pres

sive

stre

ngth

, 100

0 ps

i

40 60 80 100 120

10 20 30 40 50

At 28 days

At 1 day

Curing temperature, °F

Curing temperature, °C

Fig. 12-11. One-day strength increases with increasingcuring temperature, but 28-day strength decreases withincreasing curing temperature (Verbeck and Helmuth 1968).

tard the loss of water from newly placed concrete and it isapplied immediately after finishing. Surface sealing com-pounds on the other hand retard the penetration ofharmful substances into hardened concrete and are typi-cally not applied until the concrete is 28 days old. Surfacesealers are generally classified as either film-forming orpenetrating.

Sealing exterior concrete is an optional proceduregenerally performed to help protect concrete from freeze-thaw damage and chloride penetration from deicers.Curing is not optional when using a sealer; curing is nec-essary to produce properties needed for concrete to per-form adequately for its intended purpose. Satisfactoryperformance of exterior concrete still primarily dependson an adequate air-void system, sufficient strength, andthe use of proper placing, finishing and curing tech-niques. However, not all concrete placed meets those cri-teria; surface sealers can help improve the durability ofthese concretes.

Film-forming sealing compounds remain mostly onthe surface with only a slight amount of the material pen-etrating the concrete. The relatively large molecular struc-ture of these compounds limits their ability to penetratethe surface. Thinning them with solvents will not improvetheir penetrating capability. These materials not onlyreduce the penetration of water, they also protect againstmild chemicals; furthermore, they prevent the absorptionof grease and oil as well as reduce dusting under pedes-trian traffic.

Surface sealers consist of acrylic resins, chlorinatedrubber, urethanes, epoxies, and alpha methyl styrene. Theeffectiveness of film-forming sealers depends on the con-tinuity of the layer formed. Abrasive grit and heavy trafficcan damage the layer requiring the reapplication of thematerial. Consult manufacturers’ application recommen-dations because some of these materials are intended forinterior use only and may yellow and deteriorate underexposure to ultraviolet light.

The penetrating sealer that has been used most exten-sively for many years is a mixture of 50 percent boiled lin-seed oil and 50 percent mineral spirits (AASHTO M 233).Although this mixture is an effective sealer, it has twomain disadvantages: it darkens the concrete, and periodicreapplication is necessary for long-term protection.

A new generation of water-repellent penetratingsealers have a very small molecular size that allows pen-etration and saturation of the concrete as deep as 3 mm(1⁄8 in.). The two most common are silane and siloxane,compounds which are derived from the silicone family.These sealers allow the concrete to breath, thus pre-venting a buildup of vapor pressure between the concreteand sealer that can occur with some film-forming mate-rials. Because the sealer is embedded within the concrete,making it more durable to abrasive forces or ultravioletdeterioration, it can provide longer lasting protection

than film-forming sealers. However, periodic retreatmentis recommended. In northern states and coastal areassilanes and siloxanes are popular for protecting bridgedecks and other exterior structures from corrosion of rein-forcing steel caused by chloride infiltration from deicingchemicals or sea spray (Fig 12-12).

Application of any sealer should only be done onconcrete that is clean and allowed to dry for at least24 hours at temperatures above 16°C (60°F). At least28 days should be allowed to elapse before applyingsealers to new concrete. Penetrating sealers cannot fillsurface voids if they are filled with water. Some surfacepreparation may be necessary if the concrete is old anddirty. Concrete placed in the late fall should not be sealeduntil spring because the sealer may cause the concrete toretain water that may exacerbate freeze-thaw damage.

The precautions outlined earlier regarding volatile sol-vents in curing compounds also apply to sealing com-pounds. The effectiveness of water-based surface sealers isstill being determined. The scale resistance provided byconcrete sealers should be evaluated based on criteriaestablished in ASTM C 672. For more information on sur-face sealing compounds, see AASHTO M 224, ACI Com-mittee 330 and ACI Committee 362.

227


Fig 12-12. Penetrating sealers help protect reinforcing steelin bridge decks from corrosion due to chloride infiltrationwithout reducing surface friction. (69976)

Hanson, J. A., Optimum Steam Curing Procedure in Pre-casting Plants, with discussion, Development DepartmentBulletins DX062 and DX062A, Portland Cement Associa-tion, http://www.portcement.org/pdf_files/DX062.pdfand http://www.portcement.org/pdf_files/DX062A.pdf,1963, 28 pages and 19 pages, respectively.

Hanson, J. A., Optimum Steam Curing Procedures for Struc-tural Lightweight Concrete, Development DepartmentBulletin DX092, Portland Cement Association, http://www.portcement.org/pdf_files/DX092.pdf, 1965.

Highway Research Board, Curing of Concrete Pavements,Current Road Problems No. 1-2R, Highway ResearchBoard, Washington, D.C., May 1963.

Klieger, Paul, Curing Requirements for Scale Resistance ofConcrete, Research Department Bulletin RX082, PortlandCement Association, http://www.portcement.org/pdf_files/RX082.pdf, 1957, 17 pages.

Klieger, Paul, Some Aspects of Durability and Volume Changeof Concrete for Prestressing, Research Department BulletinRX118, Portland Cement Association, http://www.portcement.org/pdf_files/RX118.pdf, 1960, 15 pages.

Klieger, Paul, and Perenchio, William, Silicone Influence onConcrete to Freeze-Thaw and De-icer Damage, Research De-partment Bulletin RX169, Portland Cement Association,http://www.portcement.org/pdf_files/RX169.pdf, 1963,15 pages.

Lerch, William, Plastic Shrinkage, Research DepartmentBulletin RX081, Portland Cement Association, http://www.portcement.org/pdf_files/RX081.pdf, 1957, 7 pages.

Pierce, James S., “Mixing and Curing Water for Concrete,”Significance of Tests and Properties of Concrete and Concrete-Making Materials, STP 169C, American Society for Testingand Materials, West Conshohocken, Pennsylvania, 1994,pages 473 to 477.

Powers, T. C., A Discussion of Cement Hydration in Relationto the Curing of Concrete, Research Department BulletinRX025, Portland Cement Association, http://www.portcement.org/pdf_files/RX025.pdf, 1948, 15 pages.

Senbetta, Ephraim, “Curing and Curing Materials,” Signi-ficance of Tests and Properties of Concrete and Concrete-MakingMaterials, STP 169C, American Society for Testing andMaterials, West Conshohocken, Pennsylvania, 1994, pages478 to 483.

Tepponen, Pirjo, and Eriksson, Bo-Erik, “Damages inConcrete Railway Sleepers in Finland,” Nordic ConcreteResearch, Publication No. 6, The Nordic Concrete Federa-tion, Oslo, 1987.

Verbeck, George J., and Helmuth, R. A., “Structures andPhysical Properties of Cement Pastes,” Proceedings, FifthInternational Symposium on the Chemistry of Cement, vol. III,The Cement Association of Japan, Tokyo, 1968, page 9.

REFERENCES

ACI Committee 305, Hot-Weather Concreting, ACI 305R-99,American Concrete Institute, Farmington Hills, Michigan,1999, 17 pages.

ACI Committee 306, Cold-Weather Concreting, ACI 306R-88,Reapproved 1997, American Concrete Institute, Farming-ton Hills, Michigan, 1997, 23 pages.

ACI Committee 308, Standard Practice for Curing Concrete,ACI 308-92, Reapproved 1997, American Concrete Insti-tute, Farmington Hills, Michigan, 1997, 11 pages.

ACI Committee 330, Guide for Design and Construction ofConcrete Parking Lots, ACI 330R-92, Reapproved 1997,American Concrete Institute, Farmington Hills, Michigan,1997, 27 pages.

ACI Committee 362, Guide for the Design of Durable ParkingStructures, ACI 362.1R-97, American Concrete Institute,Farmington Hills, Michigan, 1997, 40 pages.

ACI Committee 516, “High Pressure Steam Curing:Modern Practice and Properties of Autoclaved Products,”Proceedings of the American Concrete Institute, AmericanConcrete Institute, Farmington Hills, Michigan, August1965, pages 869 to 908.

ACI Committee 517, Accelerated Curing of Concrete atAtmospheric Pressure, ACI 517.2R-87, revised 1992,American Concrete Institute, Farmington Hills, Michigan,1992, 17 pages.


Copeland, L. E., and Bragg, R. H., Self Desiccation inPortland Cement Pastes, Research Department BulletinRX052, Portland Cement Association, http://www.portcement.org/pdf_files/RX052.pdf, 1955, 13 pages.

German Committee for Reinforced Concrete, Recommenda-tion on the Heat Treatment of Concrete, Deutscher Ausschussfuer Stahlbeton, Deutsches Institut fuer Normung (DIN),Berlin, September 1989, 13 pages.

Gonnerman, H. F. and Shuman, E. C., “Flexure andTension Tests of Plain Concrete,” Major Series 171, 209,and 210, Report of the Director of Research, Portland CementAssociation, November 1928, pages 149 and 163.

Greening, N. R., and Landgren, R., Surface Discoloration ofConcrete Flatwork, Research Department Bulletin RX203,Portland Cement Association, http://www.portcement.org/pdf_files/RX203.pdf, 1966, 19 pages.

228


Weather conditions at a jobsite—hot or cold, windy orcalm, dry or humid—may be vastly different from theoptimum conditions assumed at the time a concrete mix isspecified, designed, or selected, or from laboratory condi-tions in which concrete specimens are stored and tested.Hot weather conditions adversely influence concretequality primarily by accelerating the rate of moisture lossand rate of cement hydration that occur at higher temper-atures. Detrimental hot weather conditions include:

• high ambient temperature• high concrete temperature• low relative humidity• high wind speed• solar radiation

Hot weather conditions can create difficulties in freshconcrete, such as:

• increased water demand• accelerated slump loss leading to the addition of

water on the jobsite• increased rate of setting resulting in placing and fin-

ishing difficulties• increased tendency for plastic cracking• critical need for prompt early curing • difficulties in controlling entrained air • increased concrete temperature resulting in long-term

strength loss• increased potential for thermal cracking

Adding water to the concrete at the jobsite canadversely affect properties and serviceability of the hard-ened concrete, resulting in:

• decreased strength from higher water to cement ratio• decreased durability due to cracking• increased permeability• nonuniform surface appearance • increased tendency for drying shrinkage• reduced abrasion resistance from tendency to

sprinkle water during finishing

Only by taking precautions to alleviate these difficul-ties in anticipation of hot-weather conditions can concretework proceed smoothly. For more information on theabove topics, see ACI Committee 305 (1999).

WHEN TO TAKE PRECAUTIONS

During hot weather the most favorable temperature forachieving high quality freshly mixed concrete is usuallylower than can be obtained without artificial cooling. Aconcrete temperature of 10°C to 15°C (50°F to 60°F) isdesirable to maximize beneficial mix properties, but suchtemperature are not always practical. Many specificationsrequire only that concrete when placed should have a tem-perature of less than 29°C to 32°C (85°F to 90°F). TheASTM C 94 (AASHTO M 157) specifications for ready

CHAPTER 13

Hot-Weather Concreting

Fig. 13-1. Liquid nitrogen added directly into a truck mixerat the ready mix plant is an effective method of reducingconcrete temperature for mass concrete placements orduring hot-weather concreting. (69954)

229

• consider methods to limit moisture loss duringplacing and finishing, such as sunshades, wind-screens, fogging, or spraying

• apply temporary moisture-retaining films afterscreeding

• organize a preconstruction conference to discuss theprecautions required for the project

The above precautions are discussed in further detailthroughout this chapter.

EFFECTS OF HIGH CONCRETE TEMPERATURES

As concrete temperature increases there is a loss in slumpthat is often unadvisedly compensated for by addingwater to the concrete at the jobsite. At higher temperaturesa greater amount of water is required to hold slump con-stant than is needed at lower temperatures. Adding waterwithout adding cement results in a higher water-cementratio, thereby lowering the strength at all ages andadversely affecting other desirable properties of the hard-ened concrete. This is in addition to the adverse effect onstrength at later ages due to the higher temperature, evenwithout the addition of water. Adding cement to compen-sate for the use of additional mix water may not beenough to achieve the desired concrete properties becauseadditional cement will further increase the concrete tem-perature and water demand.

As shown in Fig. 13-2, if the temperature of freshlymixed concrete is increased from 10°C to 38°C (50°F to100°F), about 20 kg/m3 (33 lb/yd3) of additional water isneeded to maintain the same 75-mm (3-in.) slump. Thisadditional water could reduce strength by 12% to 15% and

mixed concrete notes in some situations difficulty may beencountered when concrete temperatures approach 32°C(90°F). However, this specification does not mandate amaximum concrete temperature unless heated aggregatesor heated water are used.

Precautions should be planned in advance to counterthe effects of a high concrete temperature when the con-crete placed is somewhere between 25°C and 35°C (77°Fand 95°F). Last-minute attempts to prevent hot-weatherdamage are rarely performed soon enough. If acceptablefield data is not available, the maximum temperature limitshould be established for conditions at the jobsite; thisshould be based on trial-batch tests at the temperature andfor the typical concrete section thickness anticipated,rather than on ideal temperatures of 20°C to 30°C (68°F to86°F) cited in ASTM C 192 (AASHTO T 126). If possible,large batches should be made to measure mix propertiesat time intervals to establish the relationship for the prop-erty of interest as a function of time at various batch tem-peratures of interest. This process will establish themaximum allowable time to discharge concrete afterbatching for various concrete temperatures.

More than controlling the maximum temperature isrequired to determine when to employ precautions to pro-duce concrete with the required strength and durability.For most work it is too complex to simply limit only themaximum temperature of concrete as placed; circum-stances and concrete requirements vary too widely. Forexample, a temperature limit that would serve successfullyat one jobsite could be highly restrictive at another.Atmospheric conditions, including air temperature, rela-tive humidity and wind speed, in conjunction with siteconditions influence the precautions needed. For example,flatwork done under a roof that blocks solar radiation withexterior walls in place that screen the wind could be com-pleted using a high temperature concrete; this concretewould cause difficulty if placed outdoors on the same daywhere it would be exposed to direct sun and wind.

Which precautions to use and when to use them willdepend on: the type of construction; characteristics of thematerials being used; and the experience of the placingand finishing crew in dealing with the atmospheric con-ditions on the site. The following list of precautions willreduce or avoid the potential problems of hot-weatherconcreting:

• use materials and mix proportions that have a goodrecord in hot-weather conditions

• cool the concrete or one or more of its ingredients(Fig. 13-1)

• use a concrete consistency that allows rapid place-ment and consolidation

• reduce the time of transport, placing and finishing asmuch as possible

• schedule concrete placements to limit exposure toatmospheric conditions, such as at night or duringfavorable weather conditions

230


0 10 20 30 40

40 60 80 100310

300

290

280

270

180

170

160

Concrete temperature, °C

Wat

er c

onte

nt, k

g/m

3

Wat

er c

onte

nt, l

b/yd

3

Concrete temperature, °F

Slump: 75 mm (3 in.)Max. size agg: 37.5 mm (11/2 in.)

Fig. 13-2. The water requirement of a concrete mixtureincreases with an increase in concrete temperature Bureauof Reclamation (1981).

231

Chapter 13 � Hot-Weather Concreting

produce a compressive strength cylinder test result thatmay not comply with specifications.

High temperatures of freshly mixed concrete increasethe rate of setting and shorten the length of time withinwhich the concrete can be transported, placed, and fin-ished. Setting time can be reduced by 2 or more hourswith a 10°C (18°F) increase in concrete temperature (Fig.13-3). Concrete should remain plastic long enough so thateach layer can be placed without development of coldjoints or discontinuities in the concrete. Retarding admix-tures, ASTM C 494 (AASHTO M 194) Type B, and hydra-tion control admixtures can be beneficial in offsetting theaccelerating effects of high temperature.

In hot weather, there is an increased tendency forcracks to form both before and after hardening. Rapidevaporation of water from freshly placed concrete cancause plastic-shrinkage cracks before the surface has hard-ened (discussed in more detail later in this chapter).Cracks may also develop in the hardened concretebecause of increased drying shrinkage due to higher watercontents or thermal volume changes as the concrete cools.

Air entrainment is also affected in hot weather. Atelevated temperatures, an increase in the amount ofair-entraining admixture is required to produce a givenair content.

Fig. 13-4 shows the effect of high initial concrete tem-peratures on compressive strength. The concrete tempera-tures at the time of mixing, casting, and curing were 23°C(73°F), 32°C (90°F), 41°C (105°F), and 49°C (120°F). After28 days, the specimens were all moist-cured at 23°C (73°F)until the 90-day and one-year test ages. The tests, usingidentical concretes of the same water-cement ratio, showthat while higher concrete temperatures give higher earlystrength than concrete at 23°C (73°F), at later ages concretestrengths are lower. If the water content had beenincreased to maintain the same slump (without increasing

cement content), the reduction in strength would havebeen even greater than shown.

The proper fabrication, curing, and testing of com-pression test specimens during hot weather is critical.Steps should be taken to make sure ASTM C 31 (AASHTOT 23) procedures are followed regarding initial curing ofstrength specimens for acceptance or quality controltesting at 16ºC to 27ºC (60ºF to 80ºF). If the initial 24 hourcuring is at 38ºC (100ºF), the 28-day compressive strengthof the test specimens may be 10% to 15% lower than ifcured at the required ASTM C 31 (AASHTO T 23) curingtemperatures (Gaynor 1985).

Because of the detrimental effects of high concrete tem-peratures, all operations in hot weather should be directedtoward keeping the concrete as cool as possible.

COOLING CONCRETE MATERIALS

The usual method of cooling concrete is to lower the tem-perature of the concrete materials before mixing. One ormore of the ingredients should be cooled. In hot weatherthe aggregates and mixing water should be kept as cool aspracticable; these materials have a greater influence onconcrete temperature after mixing than other ingredients.

The contribution of each ingredient in a concrete mix-ture to the temperature of the freshly mixed concrete isrelated to the temperature, specific heat, and quantity ofeach material. Fig. 13-5 shows graphically the effect oftemperature of materials on the temperature of fresh con-crete. It is evident that although concrete temperature is

1 3 7 28 90 365

140

120

100

80

60

40

20

0

23°C(73°F)

32°C(90°F)

41°C(105°F)

49°C(120°F)

Mix data:w/c ratio: 0.45Slump: 25 to 75 mm (1 to 3 in.)Air content: 4.5%Cement: Type I, Normal

Curing: specimens castand moist-cured attemperature indicatedfor first 28 days. Allmoist-cured at 23°C(73°F) thereafter.

Com

pres

sive

stre

ngth

, per

cent

of 2

8 da

y 23

°C (7

3°F)

cur

ed c

oncr

ete

Age of test, days

Fig. 13-4. Effect of high concrete temperatures on com-pressive strength at various ages (Klieger 1958).

10°C (50°F) 23°C (73°F) 32°C (90°F)0

3

6

9

12

15Mix proportions held constant.

Casting temperature

Tim

e, h

ours

Initial set

Final set

Initial set

Final set

Cement A

Cement B

ASTM C 403(AASHTO T 197)

Fig. 13-3. Effect of concrete temperature on setting time(Burg 1996).

Initial concrete temperature = 79,9172515 = 31.8°C

To achieve 1°C reduction in initial concrete temperature:

Cement temperature must be lowered = 2515308 = 8.2°C

Or water temperature dropped = 2515515 = 4.9°C

Or aggregate temperature cooled = 25151692 = 1.5°C

Of all the materials in concrete, water is the easiest tocool. Even though it is used in smaller quantities than theother ingredients, cold water will produce a moderatereduction in the concrete temperature. Mixing water froma cool source should be used. It should be stored in tanksthat are not exposed to the direct rays of the sun. Tanksand pipelines carrying mixing water should be buried,insulated, shaded, or painted white to keep water as coolas practical. Water can be cooled by refrigeration, liquidnitrogen, or ice. Cooling the mix water temperature 2.0°Cto 2.2°C (3.5°F to 4°F) will usually lower the concrete tem-perature about 0.5°C (1°F). However, because mix water issuch a small percentage of the total mixture, it is difficultto lower concrete temperatures more than about 4.5°C(8°F) by cooling the water alone.

Ice can be used as part of the mixing water providedit is completely melted by the time mixing is completed.

primarily dependent upon the aggregate temperature,cooling the mixing water can be effective.

The approximate temperature of concrete can be cal-culated from the temperatures of its ingredients by usingthe following equation (NRMCA 1962):

0.22(TaMa + TcMc) + TwMw + TwaMwaT =0.22(Ma + Mc) + Mw + Mwa

where

T = temperature of the freshly mixed concrete, °C (°F)

Ta , Tc, Tw, and Twa = temperature in °C (°F) of aggre-gates, cement, added mixing water, and free water onaggregates, respectively

Ma , Mc, Mw, and Mwa = mass, kg (lb), of aggregates,cementing materials, added mixing water, and free wateron aggregates, respectively

Example calculations for initial concrete temperatureare shown in Table 13-1A.

232


Table 13-1A (Metric). Effect of Temperature of Materials on Initial Concrete Temperatures

InitialSpecific heat Joules to vary temperature of Total joules

Material Mass, M, kg kJ/kg • K temperature, 1°C material, T, °C in material

(1) (2) (3) (4) (5)Col.1 x Col. 2 Col. 3 x Col. 4

Cement 335 (Mc) 0.92 308 66 (Tc) 20,328Water 123 (Mw) 4.184 515 27 (Tw) 13,905Total aggregate 1839 (Ma) 0.92 1692 27 (Ta) 45,684

2515 79,917

Initial concrete temperature = 95,7201088 = 88.0°F.

To achieve 1°F reduction in initial concrete temperature:

Cement temperature must be lowered = 1088124 = 8.8°F

Or water temperature dropped = 1088282 = 3.9°F

Or aggregate temperature cooled = 1088682 = 1.6°F

Table 13-1A (Inch-Pound Units). Effect of Temperature of Materials on Initial Concrete Temperatures

InitialBtu to vary temperature of Total Btu’s

Material Mass, M, lb Specific heat temperature, 1°F material, T, °F in material

(1) (2) (3) (4) (5)Col.1 x Col. 2 Col. 3 x Col. 4

Cement 564 (Mc) 0.22 124 150 (Tc) 18,600Water 282 (Mw) 1.00 282 80 (Tw) 22,560Total aggregate 3100 (Ma) 0.22 682 80 (Ta) 54,560

1088 95,720

When using crushed ice, care must be taken to store it at atemperature that will prevent the formation of lumps.

When ice is added as part of the mixing water, theeffect of the heat of fusion of the ice must be considered;so the equation for temperature of fresh concrete is modi-fied as follows:

0.22(TaMa + TcMc) + TwMw + TwaMwa –80MiT (C°) =0.22(Ma + Mc) + Mw + Mwa + Mi

0.22(TaMa + TcMc) + TwMw + TwaMwa –112MiT (F°) =0.22(Ma + Mc) + Mw + Mwa + Mi

where Mi is the mass in kg (lb) of ice (NRMCA 1962 andMindess and Young 1981).

The heat of fusion of ice in metric units is 335 kJ perkg (in British thermal units, 144 Btu per pound). Calcu-lations in Table 13-1B show the effect of 44 kg (75 lb) of icein reducing the temperature of concrete. Crushed orflaked ice is more effective than chilled water in reducingconcrete temperature. The amount of water and ice mustnot exceed the total mixing-water requirements.

Fig. 13-6 shows crushed ice being charged into atruck mixer prior to the addition of other materials.Mixing time should be long enough to completely melt

the ice. The volume of ice should not replace more thanapproximately 75% of the total batch water. The max-imum temperature reduction from the use of ice is limitedto about 11°C (20°F).

If a greater temperature reduction is required, the in-jection of liquid nitrogen into the mixer may be the bestalternative method.

The liquid nitrogen can be added directly into a cen-tral mixer drum or the drum of a truck mixer to lower con-crete temperature. Fig. 13-1 shows liquid nitrogen addeddirectly into a truck mixer near a ready mix plant. Careshould be taken to prevent the liquid nitrogen from con-tacting the metal drum; the super cold liquid nitrogenmay crack the drum. The addition of liquid nitrogen doesnot in itself influence the amount of mix water requiredexcept that lowering the concrete temperature can reducewater demand.

Aggregates have a pronounced effect on the freshconcrete temperature because they represent 70% to 85%of the total mass of concrete. To lower the temperature ofconcrete 0.5°C (1°F) requires only a 0.8°C to 1.1°C (1.5°F to2°F) reduction in the temperature of the coarse aggregate.

There are several simple methods of keeping aggre-gates cool. Stockpiles should be shaded from the sun and

233


Concrete temperature =65,1772699 = 24.1°C

Table 13-1B (Metric). Effect of Ice (44 kg) on Temperature of Concrete

Specific heat Joules to vary Initial temperature Total joulesMaterial Mass, M, kg kJ/kg • K temperature, 1°C of material, T, °C in material

(1) (2) (3) (4) (5)Col.1 x Col. 2 Col. 3 x Col. 4

Cement 335 (Mc) 0.92 308 66 (Tc) 20,328Water 123 (Mw) 4.184 515 27 (Tw) 13,905Total aggregate 1839 (Ma) 0.92 1692 27 (Ta) 45,684Ice 44 (M i ) 4.184 184 0 (Ti ) 0

2699minus 44 (M i ) x heat of fusion, (335 kJ/kg) = –14,740

65,177

Concrete temperature =81,3201088 = 74.7°F

*32 Mi – 144 Mi = –112 Mi

Table 13-1B (Inch-Pound Units). Effect of Ice (75 lb) on Temperature of Concrete

Btu to vary Initial temperature Total Btu’sMaterial Mass, M, lb Specific heat temperature, 1°F of material, T, °F in material

(1) (2) (3) (4) (5)Col.1 x Col. 2 Col. 3 x Col. 4

Cement 564 (Mc) 0.22 124 150 (Tc) 18,600Water 207 (Mw) 1.00 207 80 (Tw) 16,560Total aggregate 3100 (Ma) 0.22 682 80 (Ta) 54,560Ice* 75 (M i ) 1.00 75 32 (Ti ) 2,400

1088minus 75 (M i ) x heat of fusion, (144 Btu/lb) = –10,800

81,320

kept moist by sprinkling. Do not spray salt water on ag-gregate stockpiles. Since evaporation is a cooling process,sprinkling provides effective cooling, especially when therelative humidity is low.

Sprinkling of coarse aggregates should be adjusted toavoid producing excessive variations in the surface mois-ture content and thereby causing a loss of slump unifor-mity. Refrigeration is another method of cooling materials.Aggregates can be immersed in cold-water tanks, orcooled air can be circulated through storage bins. Vacuumcooling can reduce aggregate temperatures to as low as1°C (34°F).

Cement temperature has only a minor effect on thetemperature of the freshly mixed concrete because ofcement’s low specific heat and the relatively smallamount of cement in a concrete mixture. A cement tem-perature change of 5°C (9°F) generally will change theconcrete temperature by only 0.5°C (1°F). Because cementloses heat slowly during storage, it may still be warmwhen delivered. (This heat is produced in grinding thecement clinker during manufacture.) Since the tempera-ture of cement does affect the temperature of the freshconcrete to some extent, some specifications place a limiton its temperature at the time of use. This limit variesfrom 66°C to 82°C (150°F to 180°F) (ACI Committee 305).However, it is preferable to specify a maximum tempera-ture for freshly mixed concrete rather than place a tem-perature limit on individual ingredients (Lerch 1955).

SUPPLEMENTARY CEMENTITIOUS MATERIALS

Many concrete producers consider the use of supplemen-tary cementitious materials to be essential in hot weatherconditions. The materials of choice are fly ash and otherpozzolans (ASTM C 618 or AASHTO M 295) and groundgranulated blast-furnace slag (ASTM C 989 or AASHTOM 302). These materials generally slow both the rate of set-ting as well as the rate of slump loss. However, some cau-tion regarding finishing is needed; because the rate ofbleeding can be slower than the rate of evaporation,plastic shrinkage cracking or crazing may result. This isdiscussed in greater detail under “Plastic ShrinkageCracking” below.

PREPARATION BEFORE CONCRETING

Before concrete is placed, certain precautions should betaken during hot weather to maintain or reduce concretetemperature. Mixers, chutes, conveyor belts, hoppers,pump lines, and other equipment for handling concreteshould be shaded, painted white, or covered with wetburlap to reduce solar heat.

Forms, reinforcing steel, and subgrade should befogged or sprinkled with cool water just before the con-

234


20 30 40

70 80 90 100 110

30

20

10

0

90

80

70

60

50

40

32

Concrete temperature:

35°C(95°F)32°C

(90°F)29°C(85°F)27°C

(80°F)24°C(75°F)

Aggregate temperature, °C

Aggregate temperature, °FM

ixin

g-w

ater

tem

pera

ture

, °C

Mix

ing-

wat

er te

mpe

ratu

re, °

F

Fig. 13-5. Temperature of freshly mixed concrete asaffected by temperature of its ingredients. Although thechart is based on the following mixture, it is reasonablyaccurate for other typical mixtures:

Aggregate 1360 kg (3000 lb)Moisture in aggregate 27 kg (60 lb)Added mixing water 109 kg (240 lb)Cement at 66°C (150°F) 256 kg (564 lb)

Fig. 13-6. Substituting ice for part of the mixing water willsubstantially lower concrete temperature. A crusherdelivers finely crushed ice to a truck mixer reliably andquickly. (44236)

crete is placed. Fogging the area during placing and fin-ishing operations not only cools the contact surfaces andsurrounding air but also increases its relative humidity.This reduces the temperature rise of the concrete and min-imizes the rate of evaporation of water from the concreteafter placement. For slabs on ground, it is a good practiceto moisten the subgrade the evening before concreting.There should be no standing water or puddles on forms orsubgrade at the time concrete is placed.

During extremely hot periods, improved results canbe obtained by restricting concrete placement to earlymorning, evening, or nighttime hours, especially in aridclimates. This practice has resulted in less thermalshrinkage and cracking of thick slabs and pavements.

TRANSPORTING, PLACING, FINISHING

Transporting and placing concrete should be done asquickly as practical during hot weather. Delays contri-bute to loss of slump and an increase in concrete temper-ature. Sufficient labor and equipment must be available atthe jobsite to handle and place concrete immediatelyupon delivery.

Prolonged mixing, even at agitating speed, should beavoided. If delays occur, stopping the mixer and then agi-tating intermittently can minimize the heat generated bymixing. ASTM C 94 (AASHTO M 157) requires that dis-charge of concrete be completed within 11⁄2 hours or beforethe drum has revolved 300 times, whichever occurs first.During hot weather the time limit can be reasonably re-duced to 1 hour or even 45 minutes. If specific time limita-tions on the completion of discharge of the concrete aredesired, they should be included in the project specifica-tions. It is also reasonable to obtain test data from a trialbatch simulating the time, mixing, and anticipated con-crete temperature to document, if necessary, a reduction inthe time limit.

Since the setting of concrete is more rapid in hotweather, extra care must be taken with placement tech-niques to avoid cold joints. For placement of walls, shal-lower layers can be specified to assure enough time forconsolidation with the previous lift. Temporary sunshadesand windbreaks help to minimize cold joints.

Floating of slabs should be done promptly after thewater sheen disappears from the surface or when the con-crete can support the weight of a finisher with no morethan a 5-mm (1⁄4-in.) indentation. Finishing on dry andwindy days requires extra care. Rapid drying of the con-crete at the surface may cause plastic shrinkage cracking.

PLASTIC SHRINKAGE CRACKING

Plastic shrinkage cracks sometimes occur in the surface offreshly mixed concrete soon after it has been placed, whileit is being finished or shortly thereafter (Fig. 13-7). These

cracks which appear mostly on horizontal surfaces can besubstantially eliminated if preventive measures are taken.

Plastic shrinkage cracking is usually associated withhot-weather concreting; however, it can occur any timeambient conditions produce rapid evaporation of mois-ture from the concrete surface. These cracks occur whenwater evaporates from the surface faster than it can travelto the surface during the bleeding process. This createsrapid drying shrinkage and tensile stresses in the surfacethat often result in short, irregular cracks. The followingconditions, singly or collectively, increase evaporation ofsurface moisture and increase the possibility of plasticshrinkage cracking:

1. Low air temperature 2. High concrete temperature 3. Low humidity 4. High wind speed

The crack length is generally 50 to 1000 mm (a few inchesto 3 ft) in length and they are usually spaced in an irreg-ular pattern from 50 to 700 mm (a few inches to 2 ft) apart.Fig. 13-8 is useful for determining when precautionarymeasures should be taken. There is no way to predict withcertainty when plastic shrinkage cracking will occur.

When the rate of evaporation exceeds 1 kg/m2 (0.2lb/ft2) per hour, precautionary measures such as wind-screens are almost mandatory. With some concrete mix-tures, such as those containing pozzolans, cracking ispossible if the rate of evaporation exceeds 0.5 kg/m2 (0.1lb/ft2) per hour. Concrete containing silica fume is partic-ularly prone to plastic shrinkage because bleeding ratesare commonly only 0.25 kg/m2 (0.05 lb/ft2) per hour.Therefore, protection from premature drying is essentialat lower evaporation rates. At some point in the processof setting, bleeding goes to zero and the surface begins todry at evaporation rates much lower than the typicallyspecified 1.0 kg/m2 (0.2 lb/ft2) per hour; in such cases,further protection becomes necessary regardless of thetype of concrete mixture.

235


Fig. 13-7. Typical plastic shrinkage cracks. (1311)

236


4

3

2

1

0

Rat

e of

eva

pora

tion,

kg

(m2 /h

r)

5 10 15 20 25 30 35Air temperature, °C

Relative humidity, percent Concrete temperature, °C

Wind velocity, km/h

100

90

80

70

60

50

40

30

20

10

40

35

30

25

20

15

10

5

0

5

10

15

20

25

30

35

40

0.8

0.6

0.4

0.2

0

Rat

e of

eva

pora

tion,

lb (f

t2 /hr

)

Relative humidity, percent Concrete temperature, °F

Wind velocity, mph40 60 80

Air temperature, °F100

100

80

60

40

20

40

50

60

70

80

90

100

25

20

15

10

5

20

Fig. 13-8. Effect of concrete and air temperatures, relative humidity, and wind velocity on rate of evaporation of surfacemoisture from concrete. Wind speed is the average horizontal air or wind speed in km/h (mph) measured at 500 mm (20 in.)above the evaporating surface. Air temperature and relative humidity should be measured at a level approximately 1.2 to1.8 m (4 to 6 ft) above the evaporating surface and on the windward side shielded from the sun’s rays (Menzel 1954).

To use these charts:

1. Enter with air temperature, moveup to relative humidity.

2. Move right to concrete temperature.

3. Move down to wind velocity.

4. Move left: read approximate rate ofevaporation.

Metric

Inch-Pound Units

One or more of the precautions listedbelow can minimize the occurrence ofplastic shrinkage cracking. They should beconsidered while planning for hot-weatherconcrete construction or while dealing withthe problem after construction has started.They are listed in the order in which theyshould be done during construction.

1. Moisten concrete aggregates that aredry and absorptive.

2. Keep the concrete temperature low bycooling aggregates and mixing water.

3. Dampen the subgrade (Fig. 13-9) andfog forms prior to placing concrete.

4. Erect temporary windbreaks to reducewind velocity over the concrete surface.

5. Erect temporary sunshades to reduceconcrete surface temperatures.

6. Protect the concrete with temporary coverings, suchas polyethylene sheeting, during any appreciabledelay between placing and finishing.

7. Fog the slab immediately after placing and before fin-ishing, taking care to prevent the accumulation ofwater that may reduce the quality of the cement pastein the slab surface.

8. Add plastic fibers to the concrete mixture to helpreduce plastic shrinkage crack formation.

Fogging the concrete before and after final finishing isthe most effective way to minimize evaporation andreduce plastic shrinkage cracking. Use of a fog spray willraise the relative humidity of the ambient air over the slab,thus reducing evaporation from the concrete. Fog nozzlesatomize water using air pressure (Figs. 13-10 and 13-11) tocreate a fog blanket. They should not be confused withgarden-hose nozzles, which leave an excess amount ofwater on the slab. Fogging should be continued until asuitable curing material such as a curing compound, wetburlap, or curing paper can be applied.

Other methods to prevent the rapid loss of moisturefrom the concrete surface include:

• Spray application of temporary moisture-retainingfilms (usually polymers); these compounds can beapplied immediately after screeding to reduce waterevaporation before final finishing operations andcuring commence. These materials are floated andtroweled into the surface during finishing and shouldhave no adverse effect on the concrete or inhibit theadhesion of membrane-curing compounds.

• Reduction of time between placing and the start ofcuring by eliminating delays during construction.

If plastic shrinkage cracks should appear during fin-ishing, striking each side of the crack with a float andrefinishing can close the cracks. However, the crackingmay reoccur unless the causes are corrected.

CURING AND PROTECTION

Curing and protection are more critical in hot weather thanin temperate periods. Retaining forms in place cannot beconsidered a satisfactory substitute for curing in hotweather; they should be loosened as soon as practicalwithout damage to the concrete. Water should then beapplied at the top exposed concrete surfaces—for example,

237


Fig. 13-9. Dampening the subgrade, yet keeping it free ofstanding water will lessen drying of the concrete andreduce problems from hot weather conditions. (69955)

Fig. 13-10. Fog nozzle. (9853)

Fig. 13-11. Fogging cools the air and raises the relativehumidity above flatwork to lessen rapid evaporation fromthe concrete surface, thus reducing cracking and im-proving surface durability. (69956)

the concrete. As a general rule a 5°C to 9°C (10°F to 15°F)temperature rise per 45 kg (100 lb) of portland cement canbe expected from the heat of hydration (ACI Committee211 1997). There may be instances in hot-weather-concretework and massive concrete placements when measuresmust be taken to cope with the generation of heat fromcement hydration and attendant thermal volume changesto control cracking (see Chapters 15 and 18).

REFERENCES

ACI Committee 211, Standard Practice for SelectingProportions for Normal, Heavyweight, and Mass Concrete, ACI211.1-91, reapproved 1997, American Concrete Institute,Farmington Hills, Michigan, 1997, 38 pages.

ACI Committee 305, Hot-Weather Concreting, ACI 305R-99,American Concrete Institute, Farmington Hills, Michigan,1999, 17 pages.

ACI Committee 308, Standard Specification for CuringConcrete, ACI 308.1-98, American Concrete Institute,Farmington Hills, Michigan, 1998, 9 pages.


Bureau of Reclamation, Concrete Manual, 8th ed., Denver,revised 1981.

Gaynor, Richard D.; Meininger, Richard C.; and Khan,Tarek S., Effect of Temperature and Delivery Time on ConcreteProportions, NRMCA Publication No. 171, National ReadyMixed Concrete Association, Silver Spring, Maryland,June 1985.

Klieger, Paul, Effect of Mixing and Curing Temperature onConcrete Strength, Research Department Bulletin RX103,Portland Cement Association, http://www.portcement.org/pdf_files/RX103.pdf, 1958.

Lerch, William, Hot Cement and Hot Weather Concrete Tests,IS015, Portland Cement Association, http://www.portcement.org/pdf_files/IS015.pdf, 1955.

Menzel, Carl A., “Causes and Prevention of CrackDevelopment in Plastic Concrete,” Proceedings of thePortland Cement Association, 1954, pages 130 to 136.

Mindess, Sidney, and Young, J. Francis, Concrete, PrenticeHall, Englewood Cliffs, New Jersey, 1981.

NRMCA, Cooling Ready Mixed Concrete, NRMCAPublication No. 106, National Ready Mixed ConcreteAssociation, Silver Spring, Maryland, 1962.

with a soil-soaker hose—and allowed to run down insidethe forms. On hardened concrete and on flat concrete sur-faces in particular, curing water should not be more thanabout 11°C (20°F) cooler than the concrete. This will mini-mize cracking caused by thermal stresses due to tempera-ture differentials between the concrete and curing water.

The need for moist curing is greatest during the firstfew hours after finishing. To prevent the drying of exposedconcrete surfaces, moist curing should commence as soonas the surfaces are finished and continue for at least 24hours. In hot weather, continuous moist curing for theentire curing period is preferred. However, if moist curingcannot be continued beyond 24 hours, while the surfacesare still damp, the concrete should be protected fromdrying with curing paper, heat-reflecting plastic sheets, ormembrane-forming curing compounds.

White-pigmented curing compounds can be used onhorizontal surfaces. Application of a curing compoundduring hot weather should be preceded by 24 hours ofmoist curing. If this is not practical, the compound shouldbe applied immediately after final finishing. The concretesurfaces should be moist.

Moist-cured surfaces should dry out slowly after thecuring period to reduce the possibility of surface crazingand cracking. Crazing, a network pattern of fine cracksthat do not penetrate much below the surface, is caused byminor surface shrinkage. Crazing cracks are very fine andbarely visible except when the concrete is drying after thesurface has been wet. The cracks encompass small con-crete areas less than 50 mm (2 in.) in dimension, forming achicken-wire like pattern.

ADMIXTURES

For unusual cases in hot weather and where careful in-spection is maintained, a retarding admixture may be ben-eficial in delaying the setting time, despite the somewhatincreased rate of slump loss resulting from their use. Ahydration control admixture can be used to stop cementhydration and setting. Hydration is resumed, when de-sired, with the addition of a special accelerator (reactivator).

Retarding admixtures should conform to the require-ments of ASTM C 494 (AASHTO M 194) Type B. Ad-mixtures should be tested with job materials under jobconditions before construction begins; this will determinetheir compatibility with the basic concrete ingredients andtheir ability under the particular conditions to produce thedesired results.

HEAT OF HYDRATION

Heat generated during cement hydration raises the tem-perature of concrete to a greater or lesser extent de-pending on the size of the concrete placement, itssurrounding environment, and the amount of cement in

238


CHAPTER 14

Cold-Weather Concreting

Concrete can be placed safely without damage fromfreezing throughout the winter months in cold climates ifcertain precautions are taken. Cold weather is defined byACI Committee 306 as a period when for more than 3 suc-cessive days the average daily air temperature dropsbelow 5°C (40°F) and stays below 10°C (50°F) for morethan one-half of any 24 hour period. Under these circum-stances, all materials and equipment needed for adequateprotection and curing must be on hand and ready for usebefore concrete placement is started. Normal concretingpractices can be resumed once the ambient temperature isabove 10°C (50°F) for more than half a day.

During cold weather, the concrete mixture and itstemperature should be adapted to the construction proce-dure and ambient weather conditions. Preparations shouldbe made to protect the concrete; enclosures, windbreaks,portable heaters, insulated forms, and blankets should beready to maintain the concrete temperature (Fig. 14-1).

Forms, reinforcingsteel, and embeddedfixtures must beclear of snow andice at the time

concrete is placed. Thermometers and proper storagefacilities for test cylinders should be available to verify thatprecautions are adequate.

EFFECT OF FREEZING FRESHCONCRETE

Concrete gains very little strength at low temperatures.Freshly mixed concrete must be protected against the dis-ruptive effects of freezing (Fig.14-2) until the degree of sat-uration of the concrete has been sufficiently reduced bythe process of hydration. The time at which this reductionis accomplished corresponds roughly to the time requiredfor the concrete to attain a compressive strength of 3.5MPa (500 psi) (Powers 1962). At normal temperatures andwater-cement ratios less than 0.60, this occurs within thefirst 24 hours after placement. Significant ultimatestrength reductions, up to about 50%, can occur if concreteis frozen within a few hours after placement or before itattains a compressive strength of 3.5 MPa (500 psi)(McNeese 1952). Concrete to be exposed to deicers shouldattain a strength of 28 MPa (4,000 psi) prior to repeatedcycles of freezing and thawing (Klieger 1957).

Concrete that hasbeen frozen just onceat an early age canbe restored to nearlynormal strength byproviding favorablesubsequent curing con-ditions. Such concrete,however, will not be asresistant to weatheringnor as watertight asconcrete that had notbeen frozen. The crit-ical period after whichconcrete is not seri-ously damaged by oneor two freezing cyclesFig. 14-1. When suitable preparations to build enclosures and insulate equipment have been made,

cold weather is no obstacle to concrete construction. (69876, 43464)

239

is dependent upon the concrete ingredients and con-ditions of mixing, placing, curing, and subsequent drying.For example, air-entrained concrete is less susceptibleto damage by early freezing than non-air-entrainedconcrete. See Chapter 8, “Air-Entrained Concrete,” formore information.

STRENGTH GAIN OF CONCRETEAT LOW TEMPERATURES

Temperature affects the rate at which hydration of cementoccurs—low temperatures retard hydration and con-sequently retard the hardening and strength gain ofconcrete.

If concrete is frozen and kept frozen above aboutminus 10°C (14°F), it will gain strength slowly. Below thattemperature, cement hydration and concrete strengthgain cease. Fig. 14-3 illustrates the effect of cool tempera-tures on setting time. Fig. 14-4 illustrates the effects ofcasting temperature on slump. Figs. 14-5 and 14-6 showthe age-compressive strength relationship for concretethat has been cast and cured at various temperatures.Note in Fig. 14-6 that concrete cast and cured at 4°C (40°F)and 13°C (55°F) had relatively low strengths for the firstweek; but after 28 days—when all specimens were moist-cured at 23°C (73°F)—strengths for the 4°C (40°F) and13°C (55°F) concretes grew faster than the 23°C (73°F)concrete and at one year they were slightly higher.

240


Fig. 14-2. Closeup view of ice impressions in paste offrozen fresh concrete. The ice crystal formations occur asunhardened concrete freezes. They do not occur inadequately hardened concrete. The disruption of the pastematrix by freezing can cause reduced strength gain andincreased porosity. (44047)

0 10 20 30 40

32 52 72 92200

150

100

50

0

Per

cent

initi

al s

et a

t 23°

C (

73°F

)



Cement A Cement B

Mix proportionsheld constant.

0 10 20 30 40

32 52 72 92200

150

100

50

0

Per

cent

fina

l set

at 2

3°C

(73

°F)



Cement A Cement B


Fig. 14-3. Initial set characteristics as a function of castingtemperature (top), and final set characteristics as a functionof casting temperature (bottom) (Burg 1996).

0 10 20 30 40

32 52 72 92250

150

200

100

50

0

Per

cent

slu

mp

at 2

3°C

(73

°F)



Cement A Cement B


Fig. 14-4 Slump characteristics as a function of castingtemperature (Burg 1996).

Higher-early strengths can be achieved through use ofType III high-early-strength cement as illustrated in Fig.14-7. Principal advantages occur during the first 7 days. Ata 4°C (40°F) curing temperature, the advantages of TypeIII cement are more pronounced and persist longer than atthe higher temperature.

HEAT OF HYDRATION

Concrete generates heat during hardening as a result ofthe chemical process by which cement reacts with water toform a hard, stable paste. The heat generated is called heatof hydration; it varies in amount and rate for differentcements. Dimensions of the concrete placement, ambientair temperature, initial concrete temperature, water-cement ratio, admixtures, and the composition, fineness,and amount of cementitious material all affect heat gener-ation and buildup.

Heat of hydration is useful in winter concreting as itcontributes to the heat needed to provide a satisfactorycuring temperature; often without other temporary heatsources, particularly in more massive elements.

Concrete must be delivered at the proper temperatureand account must be taken of the temperature of forms,reinforcing steel, the ground, or other concrete on whichthe fresh concrete is cast. Concrete should not be cast onfrozen concrete or on frozen ground.

Fig. 14-8 shows a concrete pedestal being coveredwith a tarpaulin just after the concrete was placed.Tarpaulins and insulated blankets are often necessary toretain the heat of hydration more efficiently and keep theconcrete as warm as possible. Thermometer readings of

241

Chapter 14 � Cold-Weather Concreting

140

120

100

80

60

40

20

01 3 7 28 90 365

Age at test, days

Com

pres

sive

str

engt

h, p

erce

nt o

f28

-day

23°

C c

ured

con

cret

e

23°C

(73°

F)

4°C

(40°

F)

13°C

(55°

F)

Mix data:Water to cement ratio = 0.43Air content: 4 to 5%Cement: Type I, 310 kg/m3 (517 lb/yd3)

Curing:Specimens cast and moist-curedat temperature indicated for first28 days. All moist-cured at23°C (73°F) thereafter.

Fig. 14-6. Effect of low temperatures on concrete compres-sive strength at various ages. Note that for this particularmixture made with Type I cement, the best temperature forlong-term strength (1 year) was 13°C (55°F) (Klieger 1958).

40

30

6

5

4

3

2

1

0

20

10

01 3 7 28 90 365

Age at test, days

Com

pres

sive

str

engt

h, M

Pa

Com

pres

sive

str

engt

h, 1

000

psi

23°C

(73°

F)

23°C

(73°F

)

-4°C (25°F)

100%

RH

50%

RH

100% RH

50% RHWater to cement ratio = 0.43Air content: 4 to 5%Cement: Type I, 310 kg/m3 (517 lb/yd3)

Fig. 14-5. Effect of temperature conditions on the strengthdevelopment of concrete. Concrete for the lower curve wascast at 4°C (40°F) and placed immediately in a curing roomat -4°C (25°F). Both concretes received 100% relative-humidity curing for first 28 days followed by 50% relative-humidity curing (Klieger 1958).

50

40

30

20

10

01 3 7 28

Mix data:Water to cement ratio = 0.43, Type I cement = 0.45, Type III cementAir content: 4 to 5%Cement content: 310 kg/m3 (517 lb/yd3)

Com

pres

sive

stre

ngth

, MP

a

Com

pres

sive

stre

ngth

, 100

0 ps

i

7

6

5

4

3

2

1

Type III, mixed and cured at 23°C (73°F)Type I, mixed and cured at 23°C (73°F)Type III, mixed and cured at 4°C (40°F)Type I, mixed and cured at 4°C (40°F)

Age of test, days

Fig. 14-7. Early-age compressive-strength relationships forType I and Type III portland cement concretes mixed andcured at 4°C (40°F) compared to 23°C (73°F) (Klieger 1958).

Chlorides are not recommended for concretes exposed tosoil or water containing sulfates or for concretes suscepti-ble to alkali-aggregate reaction.

Accelerators must not be used as a substitute forproper curing and frost protection. Specially designedaccelerating admixtures allow concrete to be placed attemperatures down to -7°C (20°F). The purpose of theseadmixtures is to reduce the time of initial setting, but notnecessarily to speed up strength gain. Covering concreteto keep out moisture and to retain heat of hydration is stillnecessary. Furthermore, traditional antifreeze solutions, asused in automobiles, should never be used; the quantity ofthese materials needed to appreciably lower the freezingpoint of concrete is so great that strength and other prop-erties can be seriously affected.

Since the goal of using special mixtures during coldweather concreting is to reduce the time of setting, a lowwater-cement ratio, low-slump concrete is particularlydesirable, especially for cold-weather flatwork; concretemixtures with higher slumps usually take longer to set. Inaddition, evaporation is minimized so that finishing canbe accomplished quicker (Fig. 14-9).

AIR-ENTRAINED CONCRETE

Entrained air is particularly desirable in any concreteplaced during freezing weather. Concrete that is not airentrained can suffer strength loss and internal as well assurface damage as a result of freezing and thawing (Fig.14-10). Air entrainment provides the capacity to absorbstresses due to ice formation within the concrete. SeeChapter 8, “Air-Entrained Concrete.”

the concrete’s temperature will tell whether the coveringis adequate. The heat liberated during hydration willoffset to a considerable degree the loss of heat duringplacing, finishing, and early curing operations. As the heatof hydration slows down, the need to cover the concretebecomes more important.

SPECIAL CONCRETE MIXTURES

High strength at an early age is desirable in winter con-struction to reduce the length of time temporary protec-tion is required. The additional cost of high-early-strengthconcrete is often offset by earlier reuse of forms andshores, savings in the shorter duration of temporaryheating, earlier setting times that allows the finishing offlatwork to begin sooner, and earlier use of the structure.High-early-strength concrete can be obtained by using oneor a combination of the following:

1. Type III or HE high-early-strength cement2. Additional portland cement (60 to 120 kg/m3 or 100

to 200 lb/yd3)3. Chemical accelerators

Small amounts of an accelerator such as calcium chlo-ride (at a maximum dosage of 2% by weight of portlandcement) can be used to accelerate the setting and early-agestrength development of concrete in cold weather.Accelerators containing chlorides should not be usedwhere there is an in-service potential for corrosion, such asin concrete members containing steel reinforcement orwhere aluminum or galvanized inserts will be used.

242


Fig. 14-8. Concrete footing pedestal being covered with atarpaulin to retain the heat of hydration. (69870)

Fig. 14-9. Finishing this concrete flatwork can proceedbecause a windbreak has been provided, there is adequateheat under the slab, and the concrete has low slump.(43465)

400

300

200

100

00 10 20 30 40 50 60

Cured normally(never frozen)

Frozen dry

Frozen wet

Per

cent

age

of th

e st

reng

th a

t 7 d

ays

Number of cycles of freezing and thawing

Fig. 14-10. Effect of freezing and thawing on strength ofconcrete that does not contain entrained air (cured 7 daysbefore first freeze) (Powers 1956).

Fig. 14-11. Example of a concrete floor that was saturatedwith rain, snow, or water and then frozen, showing the needfor air entrainment. (69869)

Thickness of sections, mm (in.)Less than 300 to 900 900 to 1800 Over

Line Condition 300 (12) (12 to 36) (36 to 72) 1800 (72)1 Minimum temperature Above -1°C (30°F) 16°C (60°F) 13°C (55°F) 10°C (50°F) 7°C (45°F)

of fresh concrete as2 mixed for weather -18°C to -1°C (0°F to 30°F) 18°C (65°F) 16°C (60°F) 13°C (55°F) 10°C (50°F)

indicated.3 Below -18°C (0°F) 21°C (70°F) 18°C (65°F) 16°C (60°F) 13°C (55°F)

4 Minimum temperature of fresh concrete as placedand maintained.**

13°C (55°F) 10°C (50°F) 7°C (45°F) 5°C (40°F)

Table 14-1. Recommended Concrete Temperature for Cold-Weather Construction—Air-Entrained Concrete*

* Adapted from Table 3.1 of ACI 306R-88.** Placement temperatures listed are for normal-weight concrete. Lower temperatures can be used for lightweight concrete if justified by tests.

For recommended duration of temperatures in Line 4, see Table 14-3.

Air entrainment should always be used for construc-tion during the freezing months. The exception is concretework done under roof where there is no chance that rain,snow, or water from other sources can saturate the concreteand where there is no chance of freezing.

The likelihood of water saturating a concrete floorduring construction is very real. Fig. 14-11 shows con-ditions in the upper story of an apartment building duringwinter construction. Snow fell on the top deck. Whenheaters were used below to warm the deck, the snowmelted. Water ran through floor openings down to a levelthat was not being heated. The water-saturated concretefroze, which caused a strength loss, particularly at the

floor surface. This could also result in greater deflection ofthe floor and a surface that is less wear-resistant than itmight have been.

TEMPERATURE OF CONCRETE

Temperature of Concrete as Mixed

The temperature of fresh concrete as mixed should not beless than shown in Lines 1, 2, or 3 of Table 14-1 for therespective thickness of section. Note that lower concretetemperatures are recommended for more massiveconcrete sections because heat generated during hydra-tion is dissipated less rapidly in heavier sections. Alsonote that at lower ambient air temperatures more heat islost from concrete during transporting and placing; hence,the recommended concrete temperatures as mixed arehigher for colder weather.

243


material) can be assumed as 0.925 kJ (0.22 Btu) comparedto 4.187 kJ (1.0 Btu) for water.

Fig. 14-12 shows the effect of temperature of materialson temperature of fresh concrete. The chart is based on theequation

where

temperature in degrees Celsius (Fahrenheit) ofthe fresh concrete

temperature in degrees Celsius(Fahrenheit) of the aggregates, cement, added mixingwater, and free moisture on aggregates, respectively;generally =

mass in kilograms(pounds) of the aggregates, cement, free moisture onaggregates, and mixing water, respectively

If the weighted average temperature of aggregatesand cement is above 0°C (32°F), the proper mixing-watertemperature for the required concrete temperature can beselected from Fig. 14-12. The range of concrete tempera-tures in the chart corresponds with the recommendedvalues given in Lines 1, 2, and 3 of Table 14-1.

M M M Ma c w wa, , , and =

TwaTa

T ,T ,T , Ta c w waand =

T =

T = 0.22 T M T M T M T M

. M M M Ma a c c w w wa wa

a c w wa

+( ) + ++( ) + +0 22

There is little advantage in using fresh concrete at atemperature much above 21°C (70°F). Higher concretetemperatures do not afford proportionately longer protec-tion from freezing because the rate of heat loss is greater.Also, high concrete temperatures are undesirable sincethey increase thermal shrinkage after hardening, requiremore mixing water for the same slump, and contribute tothe possibility of plastic-shrinkage cracking (caused byrapid moisture loss through evaporation). Therefore, thetemperature of the concrete as mixed should not be morethan 5°C (10°F) above the minimums recommended inTable 14-1.

Aggregate Temperature. The temperature of aggregatesvaries with weather and type of storage. Aggregates usu-ally contain frozen lumps and ice when the temperature isbelow freezing. Frozen aggregates must be thawed toavoid pockets of aggregate in the concrete after batching,mixing, and placing. If thawing takes place in the mixer,excessively high water contents in conjunction with thecooling effect due to the ice melting must be avoided.

At temperatures above freezing it is seldom necessaryto heat aggregates, the desired concrete temperature canusually be obtained by heating only the mixing water. Attemperatures below freezing, in addition to heating themixing water, often only the fine aggregate needs to beheated to produce concrete of the required temperature,provided the coarse aggregate is free of frozen lumps.

Three of the most common methods for heatingaggregates are: (1) storing in bins or weigh hoppers heatedby steam coils or live steam; (2) storing in silos heated byhot air or steam coils; and (3) stockpiling over heatedslabs, stem vents or pipes. Although heating aggregatesstored in bins or weigh hoppers is most commonly used,the volume of aggregate that can be heated is often limitedand quickly consumed during production. Circulatingsteam through pipes over which aggregates are stockpiledis a recommended method for heating aggregates.Stockpiles can be covered with tarpaulins to retain anddistribute heat and to prevent formation of ice. Livesteam, preferably at pressures of 500 to 900 kPa (75 to 125psi), can be injected directly into the aggregate pile to heatit, but the resultant variable moisture content in aggre-gates might result in erratic mixing-water control.

On small jobs aggregates can be heated by stockpilingover metal culvert pipes in which fires are maintained.Care should be taken to prevent scorching the aggregates.

Mixing-Water Temperature. Of the ingredients used tomake concrete, mixing water is the easiest and most prac-tical to heat. The mass of aggregates and cement in con-crete is much greater than the mass of water; however,water can store about five times as much heat as cancement and aggregate of the same weight. For cement andaggregates, the average specific heat (that is, heat unitsrequired to raise the temperature 1°C (1°F) per kg (lb) of

244


78

70

62

54

46

38

30

0 4 8 12 16 20 24

Mix

ing

wat

er te

mpe

ratu

re, °

C

Mix

ing

wat

er te

mpe

ratu

re, °

F

Weighted average temperature ofaggregates and cement, °C

Weighted average temperature ofaggregates and cement, °F

40 50 60 70180

160

140

120

100

80

8°C(46°F)

12°C(54°F)

16°C(61°F)

20°C(68°F)

24°C(75°F)

Concrete temperature

Mix data:Aggregate = 1360 kg (3000 lb)Moisture in aggregate = 27 kg (60 lb)Added mixing water = 108 kg (240 lb)Portland cement = 256 kg (564 lb)

Fig. 14-12. Temperature of mixing water needed to produceheated concrete of required temperature. Temperatures arebased on the mixture shown but are reasonably accuratefor other typical mixtures.

Section size, minimum dimensions, mm (in.)Less than 300 to 900 900 to 1800 Over300 (12) (12 to 36) (36 to 72) 1800 (72)

28°C (50°F) 22°C (40°F) 17°C (30°F) 11°C (20°F)

Table 14-2. Maximum Allowable Temperature DropDuring First 24 Hours After End of Protection Period*

Fig. 14-13. A bimetallic pocket thermometer with a metalsensor suitable for checking fresh concrete temperatures.(69881, 69882)

Thermometer

Gasket stopper

Water oralcohol

Drilled orpreformedhole

Surface of concrete

Fig. 14-14. Scheme for measuring concrete temperaturesbelow the surface with a glass thermometer.* Adapted from Table 5.5 of ACI 306R-88.

To avoid the possibility of a quick or flash set of theconcrete when either water or aggregates are heated toabove 38°C (100°F), they should be combined in the mixerfirst before the cement is added. If this mixer-loadingsequence is followed, water temperatures up to the boil-ing point can be used, provided the aggregates are coldenough to reduce the final temperature of the aggregatesand water mixture to appreciably less than 38°C (100°F).

Fluctuations in mixing-water temperature from batchto batch should be avoided. The temperature of the mix-ing water can be adjusted by blending hot and cold water.

Temperature of Concrete as Placed and Maintained

There will be some temperature loss after mixing whilethe truck mixer is traveling to the construction site andwaiting to discharge its load. The concrete should beplaced in the forms before its temperature drops belowthat given on Line 4 of Table 14-1; that concrete tempera-ture should be maintained for the duration of the protec-tion period given in Chapter 12 under “Curing Period andTemperature.”

Cooling After Protection

To avoid cracking of the concrete due to sudden tempera-ture change near the end of the curing period, ACICommittee 306 requires that the source of heat and coverprotection be slowly removed. The maximum allowabletemperature drop during the first 24 hours after the end ofthe protection is given in Table 14-2. The temperaturedrops apply to surface temperatures. Notice that the cool-ing rates for surfaces of mass concrete (thick sections) arelower than for thinner members.

CONTROL TESTS

Thermometers are needed to check the concrete tempera-tures as delivered, as placed, and as maintained. An inex-pensive pocket thermometer is shown in Fig. 14-13.

After the concrete has hardened, temperatures can bechecked with special surface thermometers or with anordinary thermometer that is kept covered with insulatingblankets. A simple way to check temperature below the

concrete surface is shown in Fig. 14-14. Instead of fillingthe hole shown in Fig. 14-14 with a fluid, it can be fittedwith insulation except at the bulb.

Concrete test cylinders must be maintained at atemperature between 16°C (60°F) and 27°C (80°F) at thejobsite for up to 48 hours until they are taken to a labora-tory for curing (ASTM C 31 or AASHTO T 23). For con-crete mixtures with a specified strength of 40 MPa (6,000psi) or greater, the initial curing temperature shall be be-tween 20°C and 26°C (68°F and 78°F). During this period,cylinders should be kept in a curing box and covered witha nonabsorptive, nonreactive plate or impervious plasticbag; the temperature in the box should be accurately con-

245


CONCRETING ON GROUND

Concreting on ground during cold weather involves someextra effort and expense, but many contractors find that itmore than pays for itself. In winter, the site around thestructure may be frozen rather than a morass of mud. Theconcrete will furnish some if not all of the heat needed forproper curing. Internal concrete temperatures should bemonitored. Insulated blankets or simple enclosures areeasily provided. Embankments are frozen and require lessbracing. With a good start during the winter months,construction gets above the ground before warmerweather arrives.

Placing concrete on the ground involves different pro-cedures from those used at an upper level: (1) the groundmust be thawed before placing concrete; (2) cementhydration will furnish some of the curing heat; (3) con-struction of enclosures is much simpler and use of insu-lating blankets may be sufficient; (4) in the case of a floorslab, a vented heater is required if the area is enclosed; and(5) hydronic heaters can be used to thaw subgrades usinginsulated blankets or to heat enclosures without concernfor carbonation. For more on hydronic heaters, see“Heaters” later in this chapter.

Once cast, footings should be backfilled as soon aspossible with unfrozen fill. Concrete should never beplaced on a frozen subgrade or backfilled with frozen fill;otherwise once they thaw, uneven settlements may occurcausing cracking.

ACI Committee 306 requires that concrete not beplaced on any surface that would lower the temperature ofthe concrete in place below the minimum values shown onLine 4 in Table 14-1. In addition, concrete placement tem-peratures should not be higher than these minimum valuesby more than 11°C (20°F) to reduce rapid moisture loss andthe potential development of plastic shrinkage cracks.

When the subgrade is frozen to a depth of approxi-mately 80 mm (3 inches), the surface region can be thawedby (1) steaming; (2) spreading a layer of hot sand, gravel,or other granular material where the grade elevationsallow it; (3) removing and replacing with unfrozen fill;(4) covering the subgrade with insulation for a few days;or (5) using hydronic heaters under insulated blanketswhich can thaw frozen ground at a rate of 0.3 m (1 ft) per24 hours to a depth up to 3 m (10 ft) (Grochoski 2000).Placing concrete for floor slabs and exposed footingsshould be delayed until the ground thaws and warmssufficiently to ensure that it will not freeze again duringthe protection and curing period.

Slabs can be cast on ground at ambient temperatures aslow as 2°C (35°F) as long as the minimum concrete temper-ature as placed is not less than shown on Line 4 of Table14-1. Although surface temperatures need not be higherthan a few degrees above freezing, they also should prefer-ably not be more than 5°C (10°F) higher than the minimumplacement temperature either. The duration of curingshould not be less than that described in Chapter 12 for the

trolled by a thermostat (Fig. 14-15). When stored in aninsulated curing box outdoors, cylinders are less likelyto be jostled by vibrations than if left on the floor of atrailer. If kept in a trailer where the heat may be turnedoff at night or over a weekend or holiday, the cylinderswould not be at the prescribed curing temperaturesduring this critical period.

In addition to laboratory-cured cylinders, it is usefulto field-cure some test cylinders in order to monitor actualcuring conditions on the job in cold weather. It is some-times difficult to find the right locations for field curing.Differences in the surface to volume ratios between cylin-ders and the structure, in conjunction with differences inmass, make correlating field-cured cylinder strengths toin-place strengths difficult. A preferred location is in aboxout in a floor slab or wall with thermal insulation forcover. When placed on a formwork ledge just below aheated, suspended floor, possible high temperatures therewill not duplicate the average temperature in the slab, northe lowest temperature on top of the slab. Still, field-curedcylinders are more indicative of actual concrete strengththan laboratory-cured cylinders. Particular care should betaken to protect compressive strength test cylinders fromfreezing; their small mass may not generate enough heatof hydration to protect them.

Molds stripped from cylinders after the first 24 ± 8hours must be wrapped tightly in plastic bags or labora-tory curing started immediately. When cylinders arepicked up for delivery to the laboratory, they must bemaintained at a temperature of 16°C (60°F) to 27°C (80°F)until they are placed in the laboratory curing room.

Cast-in-place cylinders (ASTM C 873) and non-destructive testing methods discussed in Chapter 16, aswell as maturity techniques discussed later in this chapter,are helpful in monitoring in-place concrete strength.

246


Fig. 14-15. Insulated curing box with thermostat for curingtest cylinders. Heat is supplied by electric rubber heatingmats on the bottom. A wide variety of designs are possiblefor curing boxes. (43463)

appropriate exposure classification. Because of the risk ofsurface imperfections that might occur on exterior concreteplaced in late fall and winter, many concrete contractorschoose to delay concrete placement until spring. By waitinguntil spring, temperatures will be more favorable for ce-ment hydration; this will help generate adequate strengthsalong with sufficient drying so the concrete can resistfreeze-thaw damage.

CONCRETING ABOVEGROUND

Working aboveground in cold weather usually involvesseveral different approaches compared to working atground level:

1. The concrete mixture need not be changed to generatemore heat because portable heaters can be used toheat the undersides of floor and roof slabs.Nevertheless, there are advantages to having a mixthat will produce a high strength at an early age; forexample, artificial heat can be cut off sooner (see Table14-3), and forms can be recycled faster.

2. Enclosures must be constructed to retain the heatunder floor and roof slabs.

3. Portable heaters used to warm the underside offormed concrete can be direct-fired heating units(without venting).

Before placing concrete, the heaters under a formeddeck should be turned on to preheat the forms and meltany snow or ice remaining on top. Temperature require-ments for surfaces in contact with fresh concrete are thesame as those outlined in the previous section “Concretingon Ground.” Metallic embedments at temperatures belowthe freezing point may result in local freezing thatdecreases the bond between concrete and steel reinforce-ment. ACI Committee 306 suggests that a reinforcing barhaving a cross-sectional area of about 650 mm2 (1 in.2)should have a temperature of at least -12°C (10°F) immedi-ately before being surrounded by fresh concrete at a tem-perature of at least 13°C (55°F). Caution and additionalstudy are required before definitive recommendations canbe formulated. See ACI 306 for additional information.

When slab finishing is completed, insulating blanketsor other insulation must be placed on top of the slab toensure that proper curing temperatures are maintained.The insulation value (R) necessary to maintain theconcrete surface temperature of walls and slabs above-ground at 10°C (50°F) or above for 7 days may be esti-mated from Fig. 14-16. To maintain a temperature forlonger periods, more insulation is required. ACI 306 hasadditional graphs and tables for slabs placed on ground at

247


Protection from early-age freezing For safe stripping strengthConventional High-early strength Conventional High-early-strength

Service category concrete,** days concrete,† days concrete,** days concrete,† daysNo load, not exposed‡favorable moist-curing

2 1 2 1

No load, exposed, but laterhas favorable moist-curing

3 23 2

Partial load, exposed 6 4Fully stressed, exposed See Table B below

Required percentage of Days at 10°C (50°F) Days at 21°C (70°F)

standard-cured 28-day Type of portland cement Type of portland cementstrength I or GU II or MS III or HE I or GU II or MS III or HE

50 6 9 3 4 6 365 11 14 5 8 10 485 21 28 16 16 18 1295 29 35 26 23 24 20

Table 14-3.A. Recommended Duration of Concrete Temperature in Cold Weather–Air-Entrained Concrete*

B. Recommended Duration of Concrete Temperature for Fully Stressed, Exposed, Air-Entrained Concrete

* Adapted from Tables 5.1 and 5.3 of ACI 306. Cold weather is defined as that in which average daily temperature is less than 4°C (40°F) for 3successive days except that if temperatures above 10°C (50°F) occur during at least 12 hours in any day, the concrete should no longer beregarded as winter concrete and normal curing practice should apply. For recommended concrete temperatures, see Table 14-1. For concretethat is not air entrained, ACI Committee 306 states that protection for durability should be at least twice the number of days listed in Table A.

Part B was adapted from Table 6.8 of ACI 306R-88. The values shown are approximations and will vary according to the thickness of con-crete, mix proportions, etc. They are intended to represent the ages at which supporting forms can be removed. For recommended concretetemperatures, see Table 14-1.

** Made with ASTM Type I, II, GU, or MS portland cement.† Made with ASTM Type III or HE cement, or an accelerator, or an extra 60 kg/m3 (100 lb/yd3) of cement.‡ “Exposed” means subject to freezing and thawing.

Corners and edges are particularly vulnerable duringcold weather. As a result, the thickness of insulation forthese areas, especially on columns, should be about threetimes the thickness that is required to maintain the samefor walls or slabs. On the other hand, if the ambienttemperature rises much above the temperature assumedin selecting insulation values, the temperature of theconcrete may become excessive. This increases the proba-bility of thermal shock and cracking when forms areremoved. Temperature readings of insulated concreteshould therefore be taken at regular intervals and shouldnot vary from ambient air temperatures by more than thevalues given in ACI 306. In addition, insulated concretetemperatures should not be allowed to rise much above27°C (80°F). In case of a sudden increase in concrete tem-perature, up to say 35°C (95°F), it may be necessary toremove some of the insulation or loosen the formwork.The maximum temperature differential between the con-crete interior and the concrete surface should be about20°C (35°F) to minimize cracking. The weather forecast

a temperature of 2°C (35°F). Insulation can be selectedbased on R values provided by insulation manufacturersor by using the information in Table 14-4.

When concrete strength development is not deter-mined, a conservative estimate can be made if adequateprotection at the recommended temperature is providedfor the duration of time found in Table 14-3. However, theactual amount of insulation and length of the protectionperiod should be determined from the monitored in-placeconcrete temperature and the desired strength. A correla-tion between curing temperature, curing time, and com-pressive strength can be determined from laboratorytesting of the particular concrete mix used in the field (see“Maturity Concept” discussed later in this chapter). ACI306 states that with a compressive strength of 3.5 MPa (500psi), concrete will normally have sufficient strength toresist early frost damage. If the concrete will be in a satu-rated condition when frozen, the concrete should be prop-erly air entrained and must have developed a compressivestrength of 28 MPa (4000 psi).

248


0 12 24 0 12 24 0 12 24

6005004003002001000

50

40

30

20

10

0

-10

-20

-30

-40

-50

-60

R = 0.35 (2)R = 0.35 (2)

R = 0.35 (2)R = 0.70 (4)

R = 0.70 (4)

R = 0.70 (4)

R = 1.06 (6)

R = 1.06 (6)

R = 1.06 (6)

R = 1.41 (8)

R = 1.41 (8)

R = 1.41 (8)

Cement content237 kg/m3

(400 lb/yd3)


(500 lb/yd3)


(600 lb/yd3)

10

5

0

-5

-10

-15

-20

-25

-30

-35

-40

-45

-50

Wall or slab thickness, in.

Wall or slab thickness, mm

Min

imum

am

bien

t tem

pera

ture

, °C

Min

imum

am

bien

t tem

pera

ture

, °F

6005004003002001000 6005004003002001000

Fig. 14-16. Thermal resistance (R) of insulation required to maintain the concrete surface temperature of walls and slabsaboveground at 10°C (50°F) or above for 7 days. Concrete temperature as placed: 10°C (50°F). Maximum wind velocity:24 km/h (15 mph). Note that in order to maintain a certain minimum temperature for a longer period of time, more insulationor a higher R value is required (adapted from ACI 306).

should be checked and appropriate action taken forexpected temperature changes.

Columns and walls should not be cast on foundationsat temperatures below 0°C (32°F) because chilling of con-crete in the bottom of the column or wall will retardstrength development. Concrete should not be placed onany surface that would lower the temperature of the as-placed concrete below the minimum values shown on Line4 in Table 14-1.

ENCLOSURES

Heated enclosures are very effective for protectingconcrete in cold weather, but are probably the most expen-sive too (Fig. 14-17). Enclosures can be of wood, canvastarpaulins, or polyethylene film (Fig. 14-18). Prefabricated,rigid-plastic enclosures are also available. Plastic enclo-

249


Table 14-4. Insulation Values of Various Materials

Thermal resistance, R, for10-mm (1-in.) thicknessof material,* (m2 · K)/W

Material Density kg/m3 (lb/ft3) ([°F · hr · ft2]/Btu)Board and SlabsExpanded polyurethane 24 (1.5) 0.438 (6.25)Expanded polystyrene, extruded smooth-skin surface 29 to 56 (1.8 to 3.5) 0.347 (5.0)Expanded polystyrene, extruded cut-cell surface 29 (1.8) 0.277 (4.0)Glass fiber, organic bonded 64 to 144 (4 to 9) 0.277 (4.0)Expanded polystyrene, molded beads 16 (1) 0.247 (3.85)Mineral fiber with resin binder 240 (15) 0.239 (3.45)Mineral fiberboard, wet felted 256 to 272 (16 to 17) 0.204 (2.94)Vegetable fiberboard sheathing 288 (18) 0.182 (2.64)Cellular glass 136 (8.5) 0.201 (2.86)Laminated paperboard 480 (30) 0.139 (2.00)Particle board (low density) 590 (37) 0.128 (1.85)Plywood 545 (34) 0.087 (1.24)

Loose fillWood fiber, soft woods 32 to 56 (2.0 to 3.5) 0.231 (3.33)Perlite (expanded) 80 to 128 (5.0 to 8.0) 0.187 (2.70)Vermiculite (exfoliated) 64 to 96 (4.0 to 6.0) 0.157 (2.27)Vermiculite (exfoliated) 112 to 131 (7.0 to 8.2) 0.148 (2.13)Sawdust or shavings 128 to 240 (8.0 to 15.0) 0.154 (2.22)

Thermal resistance, R, forMaterial thickness thickness of material,*

Material mm (in.) (m2 · K)/W ([°F · hr · ft2]/Btu)Mineral fiber blanket, fibrous form (rock, slag, or glass) 50 to 70 (2 to 2.75) 1.23 (7)

5 to 32 kg/m3 (0.3 to 2 lb/ft3) 75 to 85 (3 to 3.5) 1.90 (11)90 to 165 (5.5 to 6.5) 3.34 (19)

Mineral fiber loose fill (rock, slag, or glass) 95 to 125 (3.75 to 5) 1.90 (11)10 to 32 kg/m3 (0.6 to 2 lb/ft3) 165 to 220 (6.5 to 8.75) 3.34 (19)

190 to 250 (7.5 to 10) 3.87 (22)260 to 350 (10.25 to 13.75) 5.28 (30)

Fig. 14-17. Even in the winter, an outdoor swimming poolcan be constructed if a heated enclosure is used. (43453)

* Values are from ASHRAE Handbook of Fundamentals, American Society of Heating, Refrigerating, and Air-conditioning Engineers, Inc., NewYork, 1977 and 1981.R values are the reciprocal of U values (conductivity).

the minimum required on Line 4 in Table 14-1, additionalinsulating material, or material with a higher R value,should be applied. Corners and edges of concrete are mostvulnerable to freezing. In view of this, temperatures atthese locations should be checked often.

The thermal resistance (R) values for common insu-lating materials are given in Table 14-4. For maximum effi-ciency, insulating materials should be kept dry and inclose contact with concrete or formwork.

Concrete pavements can be protected from coldweather by spreading 300 mm (1 ft) or more of dry strawor hay on the surface for insulation. Tarpaulins, polyeth-ylene film, or waterproof paper should be used as aprotective cover over the straw or hay to make the insula-tion more effective and prevent it from blowing away. Thestraw or hay should be kept dry or its insulation value willdrop considerably.

Stay-in-place insulating concrete forms becamepopular for cold-weather construction in the 1990s (Fig.

sures that admit daylight are the most popular but tempo-rary heat in these enclosures can be an expensive option.

When enclosures are being constructed below a deck,the framework can be extended above the deck to serve asa windbreak. Typically, a height of 2 m (6 ft) will protectconcrete and construction personnel against biting windsthat cause temperature drops and excessive evaporation.Wind breaks could be taller or shorter depending on antic-ipated wind velocities, ambient temperatures, relativehumidity, and concrete placement temperatures.

Enclosures can be made to be moved with flying forms;more often, though, they must be removed so that the windwill not interfere with maneuvering the forms into position.Similarly, enclosures can be built in large panels like gangforms with the windbreak included (Fig. 14-1).

INSULATING MATERIALS

Heat and moisture can be retained in the concrete bycovering it with commercial insulating blankets or battinsulation (Fig. 14-19). The effectiveness of insulation canbe determined by placing a thermometer under it and incontact with the concrete. If the temperature falls below

250


Fig. 14-18. (top) Tarpaulin heated enclosure maintains anadequate temperature for proper curing and protection dur-ing severe and prolonged winter weather. (bottom) Poly-ethylene plastic sheets admitting daylight are used to fullyenclose a building frame. The temperature inside is main-tained at 10°C (50°F) with space heaters. (69877, 69878)

Fig. 14-19. Stack of insulating blankets. These blankets trapheat and moisture in the concrete, providing beneficialcuring. (43460)

Fig. 14-20. Insulating concrete forms (ICF) permit con-creting in cold weather. (69699)

14-20). Forms built for repeated use often can be econom-ically insulated with commercial blanket or batt insula-tion. The insulation should have a tough moisture-proofcovering to withstand handling abuse and exposure tothe weather. Rigid insulation can also be used (Fig. 14-21).

Insulating blankets for construction are made of fiber-glass, sponge rubber, open-cell polyurethane foam, vinylfoam, mineral wool, or cellulose fibers. The outer coversare made of canvas, woven polyethylene, or other toughfabrics that will withstand rough handling. The R value fora typical insulating blanket is about 1.2 m2 · °C/W for 50 to70 mm thickness, 7(°F · hr · ft2)/Btu, but since R values arenot marked on the blankets, their effectiveness should bechecked with a thermometer. If necessary, they can be usedin two or three layers to attain the desired insulation.

HEATERS

Three types of heaters are used in cold-weather concreteconstruction: direct fired, indirect fired, and hydronicsystems (Figs. 14-22 to 14-25). Indirect-fired heaters arevented to remove the products of combustion. Where heatis to be supplied to the top of fresh concrete— for example,a floor slab—vented heaters are required. Carbon dioxide

251


Fig. 14-21. With air temperatures down to -23°C (-10°F),concrete was cast in this insulated column form made of19-mm (3⁄4-in.) high-density plywood inside, 25-mm (1-in.)rigid polystyrene in the middle, and 13-mm (1⁄2-in.) roughplywood outside. R value: 1.0 m2 · °C/W (5.6 [°F · hr · ft2]/Btu). (43461)

Air,CO,CO2,

Air,CO,CO2,

Airsupply

FlameFan

Air

Air

FlameFan

Air

Air

b) Indirect-fired heater

a) Direct-fired heater

Airsupply

Cleanheated

aironly

Stove pipe vent

Enclosure

Fig. 14-22. Two types of air heaters.

Fig. 14-23. An indirect-fired heater. Notice vent pipe thatcarries combustion gases outside the enclosure. (43459)

(Kauer and Freeman 1955). The result is a soft, chalkysurface that will dust under traffic. Depth and degree ofcarbonation depend on concentration of CO2, curingtemperature, humidity, porosity of the concrete, length ofexposure, and method of curing. Direct-fired heaters,therefore, should not be permitted to heat the air overconcreting operations—at least until 24 hours haveelapsed. In addition, the use of gasoline-powered con-struction equipment should be restricted in enclosuresduring that time. If unvented heaters are used, immediatewet curing or the use of a curing compound will minimizecarbonation.

Carbon monoxide (CO), another product of combus-tion, is not usually a problem unless the heater is usingrecirculated air. Four hours of exposure to 200 parts permillion of CO will produce headaches and nausea. Threehours of exposure to 600 ppm can be fatal. The AmericanNational Standard Safety Requirements for Temporaryand Portable Space Heating Devices and EquipmentUsed in the Construction Industry (ANSI A10.10) limitsconcentrations of CO to 50 ppm at worker breathinglevels. The standard also establishes safety rules for venti-lation and the stability, operation, fueling, and mainte-nance of heaters.

(CO2) in the exhaust must be vented to the outside andprevented from reacting with the fresh concrete(Fig. 14-23). Direct-fired units can be used to heat theenclosed space beneath concrete placed for a floor or aroof deck (Fig. 14-24).

Hydronic systems transfer heat by circulating aglycol/water solution in a closed system of pipes or hoses(see Fig. 14-25). These systems transfer heat more effi-ciently than forced air systems without the negative effectsof exhaust gases and drying of the concrete from air move-ment. The specific heat of water/glycol solutions is morethan six times greater than air. As a result, hydronic heaterscan deliver very large quantities of heat at low temperaturedifferentials of 5°C (10°F) or less between the heat transferhose and the concrete. Cracking and curling induced bytemperature gradients within the concrete are almost elim-inated along with the danger of accidentally overheatingthe concrete and damaging long-term strength gain.

Typical applications for hydronic systems includethawing and preheating subgrades. They are also used tocure elevated and on-grade slabs, walls, foundations, andcolumns. To heat a concrete element, hydronic heatinghoses are usually laid on or hung adjacent to the structureand covered with insulated blankets and sometimes plas-tic sheets. Usually, construction of temporary enclosuresis not necessary. Hydronic systems can be used over areasmuch larger than would be practical to enclose. If aheated enclosure is necessary for other work, hydronichoses can be sacrificed (left under a slab on grade) tomake the slab a radiant heater for the structure builtabove (Grochoski 2000).

Any heater burning a fossil fuel produces carbondioxide (CO2); this gas will combine with calcium hydrox-ide on the surface of fresh concrete to form a weak layer ofcalcium carbonate that interferes with cement hydration

252


Fig. 14-24. A direct-fired heater installed through theenclosure, thus using a fresh air supply. (69875)

Fig. 14-25. Hydronic system showing hoses (top) laying onsoil to defrost subgrade and (bottom) warming the formswhile fresh concrete is pumped in. (68345, 68344)

A salamander is an inexpensive combustion heaterwithout a fan that discharges its combustion products intothe surrounding air; heating is accomplished by radiationfrom its metal casing. Salamanders are fueled by coke, oil,wood, or liquid propane. They are but one form of adirect-fired heater. A primary disadvantage of salaman-ders is the high temperature of their metal casing, a defi-nite fire hazard. Salamanders should be placed so thatthey will not overheat formwork or enclosure materials.When placed on floor slabs, they should be elevated toavoid scorching the concrete.

Some heaters burn more than one type of fuel. Theapproximate heat values of fuels are as follows:

No. 1 fuel oil 37,700 kJ/L (135,000 Btu/gal) Kerosene 37,400 kJ/L (134,000 Btu/gal)Gasoline 35,725 kJ/L (128,000 Btu/gal)Liquid-propane gas 25,500 kJ/L (91,500 Btu/gal) Natural gas 37,200 kJ/m3 (1,000 Btu/ft3)

The output rating of a portable heater is usually the heatcontent of the fuel consumed per hour. A rule of thumb isthat about 134,000 kJ are required for each 100 m3 (36,000Btu for 10,000 ft3) of air to develop a 10°C (20°F) tempera-ture rise.

Electricity can also be used to cure concrete in winter.The use of large electric blankets equipped with thermo-stats is one method. The blankets can also be used to thawsubgrades or concrete foundations.

Use of electrical resistance wires that are cast into theconcrete is another method. The power supplied is under50 volts, and from 7.0 to 23.5 MJ (1.5 to 5 kilowatt-hours)of electricity per cubic meter (cubic yard) of concrete isrequired, depending on the circumstances. The methodhas been used in the Montreal, Quebec, area for manyyears. Where electrical resistance wires are used, insula-tion should be included during the initial setting period. Ifinsulation is removed before the recommended time, theconcrete should be covered with an impervious sheet andthe power continued for the required time.

Steam is another source of heat for winter concreting.Live steam can be piped into an enclosure or suppliedthrough radiant heating units. In choosing a heat source, itmust be remembered that the concrete itself supplies heatthrough hydration of cement; this is often enough forcuring needs if the heat can be retained within theconcrete with insulation.

DURATION OF HEATING

After concrete is in place, it should be protected and keptat the recommended temperatures listed on Line 4 ofTable 14-1. These curing temperatures should be main-tained until sufficient strength is gained to withstandexposure to low temperatures, anticipated environment,and construction and service loads. The length of protec-tion required to accomplish this will depend on the

cement type and amount, whether accelerating admix-tures were used, and the loads that must be carried.Recommended minimum periods of protection are givenin Table 14-3. The duration of heating structural concretethat requires the attainment of full service loading beforeforms and shores are removed should be based on theadequacy of in-place compressive strengths rather than anarbitrary time period. If no data are available, a conserva-tive estimate of the length of time for heating and protec-tion can be made using Table 14-3.

Moist Curing

Strength gain stops when moisture required for curing isno longer available. Concrete retained in forms or coveredwith insulation seldom loses enough moisture at 5°C to15°C (40°F to 55°F) to impair curing. However, a positivemeans of providing moist curing is needed to offsetdrying from low wintertime humidities and heaters usedin enclosures during cold weather.

Live steam exhausted into an enclosure around theconcrete is an excellent method of curing because itprovides both heat and moisture. Steam is especially prac-tical in extremely cold weather because the moistureprovided offsets the rapid drying that occurs when verycold air is heated.

Liquid membrane-forming compounds can be usedfor early curing of concrete surfaces within heatedenclosures.

Terminating the Heating Period

Rapid cooling of concrete at the end of the heating periodshould be avoided. Sudden cooling of the concrete surfacewhile the interior is still warm may cause thermal crack-ing, especially in massive sections such as bridge piers,abutments, dams, and large structural members; thuscooling should be gradual. A safe temperature differentialbetween a concrete wall and the ambient air temperaturecan be obtained from ACI 306R-88. The maximum uni-form drop in temperature throughout the first 24 hoursafter the end of protection should not be more than theamounts given in Table 14-2. Gradual cooling can beaccomplished by lowering the heat or by simply shuttingoff the heat and allowing the enclosure to cool to outsideambient air temperature.

FORM REMOVAL AND RESHORING

It is good practice in cold weather to leave forms in placeas long as possible. Even within heated enclosures, formsserve to distribute heat more evenly and help preventdrying and local overheating.

If the curing temperatures listed on Line 4 of Table14-1 are maintained, Table 14-3A can be used to determinethe minimum time in days that vertical support for forms

253


With these limitations in mind, the maturity concept hasgained greater acceptance for representing the compres-sive strength of the concrete for removal of shoring oropening a pavement to traffic; but it is no substitute forquality control and proper concreting practices (Malhotra1974 and ACI Committee 347).

To monitor the strength development of concrete inplace using the maturity concept, the following informa-tion must be available:

1. The strength-maturity relationship of the concrete usedin the structure. The results of compressive strengthtests at various ages on a series of cylinders made ofa concrete similar to that used in the structure; thismust be done to develop a strength-maturity curve.These cylinders are cured in a laboratory at 23°C ± 2°C(73°F ± 3°F).

2. A time-temperature record of the concrete in place.Temperature readings are obtained by placing expend-able thermistors or thermocouples at varying depths inthe concrete. The location giving the lowest values pro-vides the series of temperature readings to be used inthe computation (Fig. 14-26).

See ACI 306R-88 for sample calculations using thematurity concept.

should be left in place. Before shores and forms areremoved, fully stressed structural concrete should betested to determine if in-place strengths are adequate,rather than waiting an arbitrary time period. In-placestrengths can be monitored using one of the following:(1) field-cured cylinders (ASTM C 31 or AASHTO T 23);(2) probe penetration tests (ASTM C 803); (3) cast-in-placecylinders (ASTM C 873); (4) pullout testing (ASTM C 900);or (5) maturity testing (ASTM C 1074). Many of these testsare indirect methods of measuring compressive strength;they require correlation in advance with standard cylin-ders before estimates of in-place strengths can be made.

If in-place compressive strengths are not documented,Table 14-3B lists conservative time periods in days toachieve various percentages of the standard laboratory-cured 28-day strength. The engineer issuing project draw-ings and specifications in cooperation with the formworkcontractor must determine what percentage of the designstrength is required (see ACI Committee 306). Side formscan be removed sooner than shoring and temporary false-work (ACI Committee 347).

MATURITY CONCEPT

The maturity concept is based on the principle thatstrength gain in concrete is a function of curing time andtemperature. The maturity concept, as described in ACI306R-88 and ASTM C 1074 can be used to evaluatestrength development when the prescribed curingtemperatures have not been maintained for the requiredtime or when curing temperatures have fluctuated. Theconcept is expressed by the equation:

Metric: M = ∑ (C + 10) ∆t

Inch-Pound Units: M = ∑ (F – 14) ∆twhere

M = maturity factor ∑ = summation C = concrete temperature, degrees CelsiusF = concrete temperature, degrees Fahrenheit∆t = duration of curing at temperature C (F), usually

in hours

The equation is based on the premise that concretegains strength (that is, cement continues to hydrate) attemperatures as low as -10°C (14°F).

Before construction begins, a calibration curve isdrawn plotting the relationship between compressivestrength and the maturity factor for a series of test cylin-ders (of the particular concrete mixture proportions) curedin a laboratory and tested for strength at successive ages.

The maturity concept is not precise and has somelimitations. But, the concept is useful in checking thecuring of concrete and estimating strength in relation totime and temperature. It presumes that all other factorsaffecting concrete strength have been properly controlled.

254


REFERENCES

ACI Committee 306, Cold-Weather Concreting, ACI 306R-88, reapproved 1997, American Concrete Institute, Farm-ington Hills, Michigan, 1997, 23 pages.

ACI Committee 347, Guide to Formwork for Concrete, ACI347R-94, reapproved 1999, American Concrete Institute,Farmington Hills, Michigan, 1999, 34 pages.

Brewer, Harold W., General Relation of Heat Flow Factors tothe Unit Weight of Concrete, Development DepartmentBulletin DX114, Portland Cement Association, http://www.portcement.org/pdf_files/DX114.pdf, 1967.

Burg, Ronald G., The Influence of Casting and CuringTemperature on the Properties of Fresh and Hardened Concrete,Research and Development Bulletin RD113, Portland Ce-ment Association, 1996, 20 pages.

Copeland, L. E.; Kantro, D. L.; and Verbeck, George,Chemistry of Hydration of Portland Cement, ResearchDepartment Bulletin RX153, Portland Cement Associa-tion, http://www.portcement.org/pdf_files/RX153.pdf,1960.

Grochoski, Chet, “Cold-Weather Concreting with Hy-dronic Heaters,” Concrete International, American ConcreteInstitute, Farmington Hills, Michigan, April 2000, pages 51to 55.

Kauer, J. A., and Freeman, R. L., “Effect of Carbon Dioxideon Fresh Concrete,” Journal of the American ConcreteInstitute Proceedings, vol. 52, December 1955, pages 447 to454. Discussion: December 1955, Part II, pages 1299 to1304, American Concrete Institute, Farmington Hills,Michigan.

Klieger, Paul, Curing Requirements for Scale Resistance ofConcrete, Research Department Bulletin RX082, PortlandCement Association, http://www.portcement.org/pdf_files/RX082.pdf, 1957.

Klieger, Paul, Effect of Mixing and Curing Temperature onConcrete Strength, Research Department Bulletin RX103,Portland Cement Association, http://www.portcement.org/pdf_files/RX103.pdf, 1958.

Malhotra, V. M., “Maturity Concept and the Estimation ofConcrete Strength: A Review,” Parts I and II, IndianConcrete Journal, vol. 48, Associated Cement Companies,Ltd., Bombay, April and May 1974.

McNeese, D. C., “Early Freezing of Non-Air-EntrainedConcrete,” Journal of the American Concrete InstituteProceedings, vol. 49, American Concrete Institute, Farm-ington Hills, Michigan, December 1952, pages 293 to 300.

NRMCA, Cold Weather Ready Mixed Concrete, PublicationNo. 130, National Ready Mixed Concrete Association,Silver Spring, Maryland, 1968.

255


Fig. 14-26. (top) Automatic temperature recorder. (bottom)Thermocouples and wiring at various depths in a caisson.(57368, 57366)

Powers, T. C., Resistance of Concrete to Frost at Early Ages,Research Department Bulletin RX071, Portland CementAssociation, http://www.portcement.org/pdf_files/RX071.pdf, 1956.

Powers, T. C., Prevention of Frost Damage to Green Concrete,Research Department Bulletin RX148, Portland CementAssociation, http://www.portcement.org/pdf_files/RX148.pdf, 1962, 18 pages.

U.S. Bureau of Reclamation, Concrete Manual, 8th ed., U.S.Bureau of Reclamation, Denver, 1981.

256


Concrete changes slightly in volume for various reasons,and understanding the nature of these changes is useful inplanning or analyzing concrete work. If concrete were freeof any restraints to deform, normal volume changeswould be of little consequence; but since concrete inservice is usually restrained by foundations, subgrades,reinforcement, or connecting members, significantstresses can develop. This is particularly true of tensilestresses.

Cracks develop because concrete is relatively weak intension but quite strong in compression. Controlling thevariables that affect volume changes can minimize highstresses and cracking. Tolerable crack widths should beconsidered in the structural design.

Volume change is defined merely as an increase ordecrease in volume. Most commonly, the subject of con-crete volume changes deals with linear expansion andcontraction due to temperature and moisture cycles. Butchemical effects such as carbonation shrinkage, sulfateattack, and the disruptive expansion of alkali-aggregatereactions also cause volume changes. Also, creep is avolume change or deformation caused by sustained stressor load. Equally important is the elastic or inelastic changein dimensions or shape that occurs instantaneously underapplied load.

For convenience, the magnitude of volume changes isgenerally stated in linear rather than volumetric units.Changes in length are often expressed as a coefficient oflength in parts per million, or simply as millionths. It isapplicable to any length unit (for example, m/m or ft/ft);one millionth is 0.000001 m/m (0.000001 in./in.) and 600millionths is 0.000600 m/m (0.000600 in./in.). Change oflength can also be expressed as a percentage; thus 0.06% isthe same as 0.000600, which incidentally is approximatelythe same as 6 mm per 10 m (3⁄4 in. per 100 ft). The volumechanges that ordinarily occur in concrete are small,ranging in length change from perhaps 10 millionths up toabout 1000 millionths.

EARLY AGE VOLUME CHANGES

The volume of concrete begins to change shortly after it iscast. Early volume changes, within 24 hours, can influencethe volume changes (such as drying shrinkage) and crackformation in hardened concrete, especially for low waterto cement ratio concrete. Following are discussions onvarious forms of early volume change:

Chemical Shrinkage

Chemical shrinkage refers to the reduction in absolutevolume of solids and liquids in paste resulting fromcement hydration. The absolute volume of hydratedcement products is less than the absolute volume ofcement and water before hydration. This change involume of cement paste during the plastic state is illus-trated by the first two bars in Fig. 15-1. This does notinclude air bubbles from mixing. Chemical shrinkagecontinues to occur at a microscopic scale as long ascement hydrates. After initial set, the paste cannotdeform as much as when it was in a plastic state.

CHAPTER 15

Volume Changes of Concrete

Unhydratedcement

andwater

Chemicalshrinkage

Autogenousshrinkage(pre set)

Autogenousshrinkage(apparentvolumereduction)

Autogenousshrinkage(after set)

Chemicalshrinkage(absolutevolumereduction)

Void

s ge

nera

ted

by h

ydra

tion

Pasteas cast

Paste atinitial set

Paste afterfinal set

Paste afterfinal set

Cumulatedvoids

Fig. 15-1. Chemical shrinkage and autogenous shrinkagevolume changes of fresh and hardened paste. Not to scale.

257

Therefore, further hydration and chemical shrinkage iscompensated by the formation of voids in the microstruc-ture (Fig. 15-1). Most of this volume change is internaland does not significantly change the visible externaldimensions of a concrete element.

The amount of volume change due to chemicalshrinkage can be estimated from the hydrated cementphases and their crystal densities or it can be determinedby physical test as illustrated in Fig. 15-2. The JapanConcrete Institute has a test method for chemicalshrinkage of cement paste (Tazawa 1999). An example oflong-term chemical shrinkage for portland cement paste isillustrated in Fig. 15-3. Early researchers sometimesreferred to chemical shrinkage as the absorption of water

258


during hydration (Powers 1935). Le Chatelier (1900) wasthe first to study chemical shrinkage of cement pastes.

Autogenous Shrinkage

Autogenous shrinkage is the macroscopic volume reduc-tion (visible dimensional change) of cement paste, mortar,or concrete caused by cement hydration. The macroscopicvolume reduction of autogenous shrinkage is much lessthan the absolute volume reduction of chemical shrinkagebecause of the rigidity of the hardened paste structure.Chemical shrinkage is the driving force behind autogenousshrinkage. The relationship between autogenous shrink-age and chemical shrinkage is illustrated in Figs. 15-1, 15-4,and 15-5. Some researchers and organizations consider that

Chemicalshrinkagevolume attime n

Waterlevel attime n

Limesaturatedwater

Cementpaste

Water levelat timezero

Fig. 15-2. Test for chemical shrinkage of cement pasteshowing flask for cement paste and pipet for absorbedwater measurement.

00 1 10 100 1000

Age, hours

2

4

6

8

Che

mic

al s

hrin

kage

, %

w/c = 0.50

Ordinary portland cement

Fig. 15-3. Chemical shrinkage of cement paste (Tazawa1999).

1.2

1

0.8

0.6

0.4

0.2

00 2 4 6 8 10

Autogenous shrinkageChemical shrinkage

Start ofsetting

Time after mixing, hours

Shr

inka

ge, c

m3 /1

00 g

cem

ent

Fig. 15-4. Relationship between autogenous shrinkage andchemical shrinkage of cement paste at early ages (Hammer1999).

Chemicalshrinkage

Chemical shrinkageSubsidence

Water

Cement

Water

Bleed waterAutogenous shrinkage

Cement

Hydratedcement

Cement

At casting At initial setting After hardening

Water

Hydratedcement

Cumulativehydration voids

Fig. 15-5. Volumetric relationship between subsidence,bleed water, chemical shrinkage, and autogenous shrink-age. Only autogenous shrinkage after initial set is shown.Not to scale.

259

Chapter 15 � Volume Changes of Concrete

autogenous shrinkage starts at initial set while others eval-uate autogenous shrinkage from time of placement.

When external water is available, autogenous shrink-age cannot occur. When external water is not available,cement hydration consumes pore water resulting in selfdesiccation of the paste and a uniform reduction of volume(Copeland and Bragg 1955). Autogenous shrinkageincreases with a decrease in water to cement ratio and withan increase in the amount of cement paste. Normal con-crete has negligible autogenous shrinkage; however, au-togenous shrinkage is most prominent in concrete with awater to cement ratio under 0.42 (Holt 2001). High-strength, low water to cement ratio (0.30) concrete canexperience 200 to 400 millionths of autogenous shrinkage.Autogenous shrinkage can be half that of drying shrinkagefor concretes with a water to cement ratio of 0.30.

Recent use of high performance, low water to cementratio concrete in bridges and other structures has renewedinterest in autogenous shrinkage to control crack develop-ment. Concretes susceptible to large amounts of autoge-nous shrinkage should be cured with external water for atleast 7 days to help control crack development. Foggingshould be provided as soon as the concrete is cast. Thehydration of supplementary cementing materials alsocontributes to autogenous shrinkage, although at differentlevels than portland cement. In addition to adjusting pastecontent and water to cement ratios, autogenous shrinkagecan be reduced by using shrinkage reducing admixturesor internal curing techniques. Some cementitious systemsmay experience autogenous expansion. Tazawa (1999)and Holt (2001) review techniques to control autogenousshrinkage.

Test methods for autogenous shrinkage and expan-sion of cement paste, mortar, and concrete and tests forautogenous shrinkage stress of concrete are presented byTazawa (1999).

Subsidence

Subsidence refers to the vertical shrinkage of fresh cemen-titious materials before initial set. It is caused by bleeding(settlement of solids relative to liquids), air voids rising tothe surface, and chemical shrinkage. Subsidence is alsocalled settlement shrinkage. Subsidence of well-consoli-dated concrete with minimal bleed water is insignificant.The relationship between subsidence and other shrinkagemechanisms is illustrated in Fig. 15-5. Excessive subsi-dence is often caused by a lack of consolidation of freshconcrete. Excessive subsidence over embedded items,such as supported steel reinforcement, can result incracking over embedded items. Concretes made with airentrainment, sufficient fine materials, and low water con-tents will minimize subsidence cracking. Also, plasticfibers have been reported to reduce subsidence cracking(Suprenant and Malisch 1999).

Plastic Shrinkage

Plastic shrinkage refers to volume change occurring whilethe concrete is still fresh, before hardening. It is usuallyobserved in the form of plastic shrinkage cracks occurringbefore or during finishing (Fig. 15-6). The cracks oftenresemble tears in the surface. Plastic shrinkage results froma combination of chemical and autogenous shrinkage andrapid evaporation of moisture from the surface thatexceeds the bleeding rate. Plastic shrinkage cracking can becontrolled by minimizing surface evaporation through useof fogging, wind breaks, shading, plastic sheet covers, wetburlap, spray-on finishing aids (evaporation retarders),and plastic fibers.

Fig. 15-6. Plastic shrinkage cracks resemble tears in freshconcrete. (1312)

Swelling

Concrete, mortar, and cement paste swell in the presenceof external water. When water drained from capillaries bychemical shrinkage is replaced by external water, thevolume of the concrete mass increases. As there is no selfdesiccation, there is no autogenous shrinkage. Externalwater can come from wet curing or submersion. Swellingoccurs due to a combination of crystal growth, absorptionof water, and osmotic pressure. The swelling is not large,only about 50 millionths at early ages (Fig. 15-7). When the

100

75

50

25

00 24 48

Age, hours

Swel

ling,

1 x

10–6

0.30

0.45

w/c = 0.35

Demolding

Fig. 15-7. Early age swelling of 100 x 100 x 375-mm (4 x 4 x15-in.) concrete specimens cured under water (Aítcin 1999).

to air drying. Autogenous shrinkage reduces the volumeof the sealed concretes to a level about equal to theamount of swelling at 7 days. Note that the concretes wetcured for 7 days had less shrinkage due to drying andautogenous effects than the concrete that had no watercuring. This illustrates the importance of early, wet curingto minimize shrinkage (Aítcin 1999).

Tests indicate that the drying shrinkage of small, plainconcrete specimens (without reinforcement) ranges fromabout 400 to 800 millionths when exposed to air at 50%humidity. Concrete with a unit drying shrinkage of 550millionths shortens about the same amount as the thermalcontraction caused by a decrease in temperature of 55°C(100°F). Preplaced aggregate concrete has a dryingshrinkage of 200 to 400 millionths; this is considerably lessthan normal concrete due to point-to-point contact ofaggregate particles in preplaced aggregate concrete. Thedrying shrinkage of structural lightweight concrete rangesfrom slightly less than to 30 percent more than that ofnormal-density concrete, depending on the type of aggre-gate used.

The drying shrinkage of reinforced concrete is less thanthat for plain concrete, the difference depending on theamount of reinforcement. Steel reinforcement restricts butdoes not prevent drying shrinkage. In reinforced concretestructures with normal amounts of reinforcement, dryingshrinkage is assumed to be 200 to 300 millionths. Similarvalues are found for slabs on ground restrained by subgrade.

For many outdoor applications, concrete reachesits maximum moisture content in winter; so in winterthe volume changes due to increase in moisture contentand the decrease in average temperature tend to offseteach other.

The amount of moisture in concrete is affected by therelative humidity of the ambient air. The free moisturecontent of concrete elements after drying in air at relative

external water source is removed, autogenous shrinkageand drying shrinkage reverse the volume change.

Early Thermal Expansion

As cement hydrates, the exothermic reaction provides asignificant amount of heat. In large elements the heat isretained, rather than dissipated as happens with thin ele-ments. This temperature rise, occurring over the first fewhours and days, can induce a small amount of expansionthat counteracts autogenous and chemical shrinkage(Holt 2001).

MOISTURE CHANGES (DRYINGSHRINKAGE) OF HARDENED CONCRETE

Hardened concrete expands slightly with a gain in mois-ture and contracts with a loss in moisture. The effects ofthese moisture cycles are illustrated schematically in Fig.15-8. Specimen A represents concrete stored continuouslyin water from time of casting. Specimen B represents thesame concrete exposed first to drying in air and then toalternate cycles of wetting and drying. For comparativepurposes, it should be noted that the swelling that occursduring continuous wet storage over a period of severalyears is usually less than 150 millionths; this is about one-fourth of the shrinkage of air-dried concrete for the sameperiod. Fig. 15-9 illustrates swelling of concretes wet curedfor 7 days following by shrinkage when sealed or exposed

260


Stored in water

Stored in air

Specimen A

Specimen B

Drying Alternate wetting and drying

Time

Shr

inka

geS

wel

ling

Fig. 15-8. Schematic illustration of moisture movements inconcrete. If concrete is kept continuously wet, a slight ex-pansion occurs. However, drying usually takes place, caus-ing shrinkage. Further wetting and drying causes alternatecycles of swelling and shrinkage (Roper 1960).

100

0

-100

-200

-300

-400

7 14 21 28

Sealed

Drying

No water curing

Watercuring

Age, days

Shr

inka

ge (

x 10

-6)

Sw

ellin

g (x

10-

6 )

0.35

0.30

0.45

0.35

0.30

w/c = 0.45

Fig. 15-9. Length change of concrete samples exposed todifferent curing regimes (Aítcin 1999).

humidities of 50% to 90% for several months is about 1%to 2% by weight of the concrete; the actual amountdepends on the concrete’s constituents, original watercontent, drying conditions, and the size and shape of theconcrete element.

After concrete has dried to a constant moisture con-tent at one relative humidity condition, a decrease inhumidity causes it to lose moisture while an increasecauses it to gain moisture. The concrete shrinks or swellswith each such change in moisture content due primarilyto responses of the cement paste to moisture changes.Most aggregates show little response to changes in mois-ture content, although there are a few aggregates thatswell or shrink in response to such changes.

As drying takes place, concrete shrinks. Where thereis no restraint, movement occurs freely and no stresses orcracks develop (Fig. 15-10a top). If the tensile stress thatresults from restrained drying shrinkage exceeds the ten-sile strength of the concrete, cracks can develop (Fig.15-10a bottom). Random cracks may develop if joints arenot properly provided and the concrete element isrestrained from shortening (Fig. 15-10b). Contractionjoints for slabs on ground should be spaced at distances of

24 to 36 times the slab thickness to control random cracks(Fig. 15-10c). Joints in walls are equally important forcrack control (Fig. 15-10d). Fig. 15-11 illustrates the rela-tionship between drying rate at different depths, dryingshrinkage, and mass loss for normal-density concrete(Hanson 1968).

Shrinkage may continue for a number of years,depending on the size and shape of the concrete mass. Therate and ultimate amount of shrinkage are usually smallerfor large masses of concrete than for small masses; on theother hand, shrinkage continues longer for large masses.Higher volume-to-surface ratios (larger elements) experi-ence lower shrinkage as shown in Fig. 15-12.

The rate and amount of drying shrinkage for smallconcrete specimens made with various cements are shownin Fig. 15-13. Specimens were initially moist-cured for 14days at 21°C (70°F), then stored for 38 months in air at thesame temperature and 50% relative humidity. Shrinkagerecorded at the age of 38 months ranged from 600 to 790millionths. An average of 34% of this shrinkage occurredwithin the first month. At the end of 11 months an averageof 90% of the 38-month shrinkage had taken place.

261


Shrinkage + freedom to move = no cracks

Slab Granular fill

Shrinkage + subbase restraint = cracks

Shrinkage and cracking

Slab Rollers

Fig. 15-10. (a) Illustration showing no crack development in concrete that is free to shrink (slab on rollers); however, inreality a slab on ground is restrained by the subbase (or other elements) creating tensile stresses and cracks. (b) Typicalshrinkage cracks in a slab on ground. (c) A properly functioning contraction joint controls the location of shrinkagecracking. (d) Contraction joints in the slabs and walls shown will minimize the formation of cracks. (A-5271, 4434, 1144)

b

a

d

c

262


50

60

70

80

90

100R

elat

ive

hum

idity

, per

cent

0

200

400

600

800

Shr

inka

ge, m

illio

nths

0

0.1

0.2

0.3

0.4

0.5

0.6

0 75 150 225 300 375

Mas

s lo

ss, k

g

Time of drying, days



Cement content: 270 kg/m3 3(454 lb/yd )Normal-density concrete

w/c ratio: 0.66

75 mm (3 in.) depth

45 (13/4)

6 (1/4)

20 (3/4)

Fig. 15-11. Relative humidity distribution at various depths,drying shrinkage, and mass loss of 150 � 300-mm (6 � 12-in.) cylinders moist-cured for 7 days followed by drying inlaboratory air at 23°C (73°F) and 50% RH (Hanson 1968).

100 mm (4 in.) diameter specimens in air

150 mm (6 in.)

200 mm (8 in.)

300 mm (12 in.)

400 mm (16 in.)

500 mm (20 in.)

600 mm (24 in.)

150 mm (6 in.) diameter sealed specimens

Environment:Air-dry specimens at 21°C (70°F), 50% RHSpecimens sealed in rubber tubes and storedin a fog room (bottom curve only)

Shr

inka

ge s

train

, mill

iont

hs

1200

1000

800

600

400

200

00 200 400 600

Time, days

Fig. 15-12. Drying shrinkage of various sizes of cylindricalspecimens made of Elgin, Illinois gravel concrete (Hansenand Mattock 1966).

I II III IV V

Type of cement

1000

1200

800

600

400

200

0

38 mo.28 mo.11 mo. 1 mo.

Specimens: 100 x 100 x 1000 mm (4 x 4 x 40 in.) concrete beamsCement content: 335 kg/m3 (564 lb/yd3)Curing: 14 days moist at 21°C (70°C), then in air at 50% RH and 21°C (70°C)

Dry

ing

shrin

kage

, mill

iont

hs

Fig. 15-13. Results of long-term drying shrinkage tests bythe U.S. Bureau of Reclamation. Shrinkage ranged from 600to 790 millionths after 38 months of drying. The shrinkageof concretes made with air-entraining cements was similarto that for non-air-entrained concretes in this study (Bureauof Reclamation 1947 and Jackson 1955).

Effect of Concrete Ingredients on Drying Shrinkage

The most important controllable factor affecting dryingshrinkage is the amount of water per unit volume of con-crete. The results of tests illustrating the water content toshrinkage relationship are shown in Fig. 15-14. Shrinkagecan be minimized by keeping the water content of con-crete as low as possible. This is achieved by keeping thetotal coarse aggregate content of the concrete as high aspossible (minimizing paste content). Use of low slumpsand placing methods that minimize water requirementsare thus major factors in controlling concrete shrinkage.Any practice that increases the water requirement of thecement paste, such as the use of high slumps (withoutsuperplasticizers), excessively high freshly mixed concretetemperatures, high fine-aggregate contents, or use of small-size coarse aggregate, will increase shrinkage. A smallamount of water can be added to ready mixed concrete atthe jobsite without affecting drying shrinkage propertiesas long as the additions are within mix specifications(Suprenant and Malisch 2000).

The general uniformity of shrinkage of concreteswith different types of cement at different ages is illus-trated in Fig. 15-13. However, this does not mean that allcements or cementing materials have similar shrinkage.

Supplementary cementing materials usually have littleeffect on shrinkage at normal dosages. Fig. 15-15 showsthat concretes with normal dosages of selected fly ashesperformed similar to the control concrete made with onlyportland cement as the cementing material.

Aggregates in concrete, especially coarse aggregate,physically restrain the shrinkage of hydrating cementpaste. Paste content affects the drying shrinkage of mortarmore than that of concrete. Drying shrinkage is alsodependent on the type of aggregate. Hard, rigid aggre-gates are difficult to compress and provide more restraintto shrinkage than softer, less rigid aggregates. As anextreme example, if steel balls were substituted for ordi-nary coarse aggregate, shrinkage would be reduced 30%or more. Drying shrinkage can also be reduced byavoiding aggregates that have high drying shrinkageproperties and aggregates containing excessive amountsof clay. Quartz, granite, feldspar, limestone, and dolomiteaggregates generally produce concretes with low dryingshrinkages (ACI Committee 224). Steam curing will alsoreduce drying shrinkage.

Most chemical admixtures have little effect onshrinkage. The use of accelerators such as calcium chloridewill increase drying shrinkage of concrete. Despite reduc-tions in water content, some water-reducing admixturescan increase drying shrinkage, particularly those that con-tain an accelerator to counteract the retarding effect of theadmixture. Air entrainment has little or no effect on dryingshrinkage. High-range water reducers usually have littleeffect on drying shrinkage (Fig. 15-16). Drying shrinkagecan be evaluated in accordance with ASTM C 157(AASHTO T 160).

263


1400

1200

1000

800

600

400

200

0125 150 175 200 225 250 275

210 250 290 340 380 420 460

Water, lb/yd3

Water, kg/m3

Dry

ing,

shr

inka

ge, m

illio

nths

Fig. 15-14. Relationship between total water content anddrying shrinkage. A large number of mixtures with variousproportions is represented within the shaded area of thecurves. Drying shrinkage increases with increasing watercontents.

0.1

0.08

0.06

0.04

0.02

00 7 14 21 28 35 42 49 56 63

Age, weeks

Dry

ing

shrin

kage

, %

Control

Class C Class F

Fig. 15-15. Drying shrinkage of fly ash concretes comparedto a control mixture. The graphs represent the average offour Class C ashes and six Class F ashes, with the range indrying shrinkage rarely exceeding 0.01 percentage points.Fly ash dosage was 25% of the cementing material (Geblerand Klieger 1986).

ASTM C 157

Steam curing will also reduce drying shrinkage.Computer software is available to predict the effect ofcuring and environmental conditions on shrinkage andcracking (FHWA and Transtec 2001). Hedenblad (1997)provides tools to predict the drying of concrete as effectedby different curing methods and type of construction.

TEMPERATURE CHANGES OF HARDENED CONCRETE

Concrete expands slightly as temperature rises and con-tracts as temperature falls, although it can expand slightlyas free water in the concrete freezes. Temperature changesmay be caused by environmental conditions or by cementhydration. An average value for the coefficient of thermalexpansion of concrete is about 10 millionths per degreeCelsius (5.5 millionths per degree Fahrenheit), althoughvalues ranging from 6 to 13 millionths per degree Celsius(3.2 to 7.0 millionths per degree Fahrenheit) have beenobserved. This amounts to a length change of 5 mm for 10m of concrete (2⁄3 in. for 100 ft of concrete) subjected to arise or fall of 50°C (100°F). The coefficient of thermalexpansion for structural low-density (lightweight) con-crete varies from 7 to 11 millionths per degree Celsius (3.6to 6.1 millionths per degree Fahrenheit). The coefficient ofthermal expansion of concrete can be determined byAASHTO TP 60.

Thermal expansion and contraction of concrete varieswith factors such as aggregate type, cement content,water-cement ratio, temperature range, concrete age, andrelative humidity. Of these, aggregate type has the greatestinfluence.

Table 15-1 shows some experimental values of thethermal coefficient of expansion of concretes made withaggregates of various types. These data were obtainedfrom tests on small concrete specimens in which all factorswere the same except aggregate type. In each case, the fineaggregate was of the same material as the coarse aggregate.

The thermal coefficient of expansion for steel is about12 millionths per degree Celsius (6.5 millionths per degreeFahrenheit), which is comparable to that for concrete. Thecoefficient for reinforced concrete can be assumed as 11millionths per degree Celsius (6 millionths per degreeFahrenheit), the average for concrete and steel.

Temperature changes that result in shortening cancrack concrete members that are highly restrained byanother part of the structure or by ground friction. Considera long restrained concrete member cast without joints that,after moist curing, is allowed to drop in temperature. As thetemperature drops, the concrete wants to shorten, butcannot because it is restrained longitudinally. The resultingtensile stresses cause the concrete to crack. Tensile strengthand modulus of elasticity of concrete both may be assumedproportional to the square root of concrete compressivestrength. And calculations show that a large enough tem-

Effect of Curing on Drying Shrinkage

The amount and type of curing can effect the rate and ulti-mate amount of drying shrinkage. Curing compounds,sealers, and coatings can trap free moisture in the concretefor long periods of time, resulting in delayed shrinkage.Wet curing methods, such as fogging or wet burlap, holdoff shrinkage until curing is terminated, after which theconcrete dries and shrinks at a normal rate. Cooler initialcuring temperatures can reduce shrinkage (Fig. 15-17).

264


0

0.01

0.02

0.03

0.04

0.05

0.06

0 8 16 24 32

Dry

ing

shrin

kage

, %

Age, weeks

C

N

M

X

Cement content = 323 kg/m3 (545 lb/yd3) ASTM C 157

Fig. 15-16. Drying shrinkage of concretes made withselected high-range water reducers (N,M, and X) comparedto a control mixture (C) (Whiting and Dziedzic 1992).

0

0.02

0.04

0.06

0.08

0.1

Dry

ing

shrin

kage

, %

0 8 16 24 32 40 48 56 64Age, weeks

23

°C(73°F)

4°C(40°F)

ASTM C 157

Cement content= 307 kg/m3 (517 lb/yd3)

Fig. 15-17. Effect of initial curing on drying shrinkage ofportland cement concrete prisms. Concrete with an initial 7-day moist cure at 4°C (40°F) had less shrinkage thanconcrete with an initial 7-day moist cure at 23°C (73°F).Similar results were found with concretes containing 25%fly ash as part of the cementing material (Gebler andKlieger 1986).

perature drop will crack concrete regardless of its age orstrength, provided the coefficient of expansion does notvary with temperature and the concrete is fully restrained(FHWA and Transtec 2001 and PCA 1982).

Precast wall panels and slabs and pavements onground are susceptible to bending and curling caused bytemperature gradients that develop when concrete is coolon one side and warm on the other. The calculated amountof curling in a wall panel is illustrated in Fig. 15-18.

For the effect of temperature changes in mass concretedue to heat of hydration, see Chapter 18.

Low Temperatures

Concrete continues to contract as the temperature isreduced below freezing. The amount of volume change atsubfreezing temperatures is greatly influenced by themoisture content, behavior of the water (physical state—ice or liquid), and type of aggregate in the concrete. In onestudy, the coefficient of thermal expansion for a tempera-ture range of 24°C to -157°C (75°F to –250°F) varied from6 x 10-6 per °C (3.3 x 10-6 per °F) for a low density (light-weight) aggregate concrete to 8.2 x 10-6 per °C (4.5 x 10-6

per °F) for a sand and gravel mixture. Subfreezing tem-peratures can significantly increase the compressive andtensile strength and modulus of elasticity of moist con-crete. Dry concrete properties are not as affected by lowtemperatures. In the same study, moist concrete with anoriginal compressive strength of 35 MPa at 24°C (5000 psiat 75°F) achieved over 117 MPa (17,000 psi) at –100°C(–150°F). The same concrete tested ovendry or at a 50%internal relative humidity had strength increases of onlyabout 20%. The modulus of elasticity for sand and gravelconcrete with 50% relative humidity was only 8% higherat –157°C than at 24°C (–250°F than at 75°F), whereas themoist concrete had a 50% increase in modulus of elasticity.Going from 24°C to –157°C (75°F to –250°F), the thermalconductivity of normal-weight concrete also increased,especially for moist concrete. The thermal conductivity oflightweight aggregate concrete is little affected (Monforeand Lentz 1962 and Lentz and Monfore 1966).

High Temperatures

Temperatures greater than 95°C (200°F) that are sustainedfor several months or even several hours can have signifi-cant effects on concrete. The total amount of volumechange of concrete is the sum of volume changes of thecement paste and aggregate. At high temperatures, thepaste shrinks due to dehydration while the aggregateexpands. For normal-aggregate concrete, the expansion ofthe aggregate exceeds the paste shrinkage resulting in anoverall expansion of the concrete. Some aggregates such asexpanded shale, andesite, or pumice with low coefficientsof expansion can produce a very volume-stable concrete inhigh-temperature environments (Fig. 15-19). On the otherhand, some aggregates undergo extensive and abruptvolume changes at a particular temperature, causing dis-ruption in the concrete. For example, in one study adolomitic limestone aggregate contained an iron sulfideimpurity caused severe expansion, cracking, and disinte-gration in concrete exposed to a temperature of 150°C(302°F) for four months; at temperatures above and below150°C (302°F) there was no detrimental expansion (Carette,Painter, and Malhotra 1982). The coefficient of thermalexpansion tends to increase with temperature rise.

Besides volume change, sustained high temperaturescan also have other, usually irreversible, effects such as a

265


Table 15-1. Effect of Aggregate Type on ThermalCoefficient of Expansion of Concrete

Aggregate Coefficient Coefficienttype (from of expansion, of expansion,

one source) millionths per °C millionths per °F

Quartz 11.9 6.6Sandstone 11.7 6.5Gravel 10.8 6.0Granite 9.5 5.3Basalt 8.6 4.8Limestone 6.8 3.8

Coefficients of concretes made with aggregates from differentsources may vary widely from these values, especially those forgravels, granites, and limestones (Davis 1930).

Cold sideT2 = -6°C

Warm sideT1 = 20°C

Concrete thicknesst = 150 mm

� = 2 mm

� = 2 mm

� =(T1 – T2)�L2

8t

� =(20 + 6) x 0.00001 x 30002

8 x 150

� = Coefficient of expansion per °Ct = Panel thickness

When � = 0.00001 per °C

L =

3 m

= 3

000

mm

Fig. 15-18. Curling of a plain concrete wall panel due totemperature that varies uniformly from inside to outside.

If stable aggregates are used and strength reductionand the effects on other properties are accounted for in themix design, high quality concrete can be exposed to tem-peratures of 90°C to 200°C (200°F to 400°F) for longperiods. Some concrete elements have been exposed totemperatures up to 250°C (500°F) for long periods of time;however, special steps should be taken or special materials(such as heat-resistant calcium aluminate cement) shouldbe considered for exposure temperatures greater than200°C (400°F). Before any structural concrete is exposed tohigh temperatures (greater than 90°C or 200°F), laboratorytesting should be performed to determine the particularconcrete’s thermal properties. This will avoid any unex-pected distress.

CURLING (WARPING)

In addition to horizontal movement caused by changes inmoisture and temperature, curling of slabs on ground canbe a problem; this is caused by differences in moisture con-tent and temperature between the top and bottom of slabs(Fig. 15-21).

The edges of slabs at the joints tend to curl upwardwhen the surface of a slab is drier or cooler than thebottom. A slab will assume a reverse curl when the surfaceis wetter or warmer than the bottom. However, enclosedslabs, such as floors on ground, curl only upward. Whenthe edges of an industrial floor slab are curled upwardthey lose support from the subbase and become a can-tilever. Lift-truck traffic passing over joints causes a repet-itive vertical deflection that creates a great potential forfatigue cracking in the slab. The amount of verticalupward curl (curling) is small for a short, thick slab.

reduction in strength, modulus of elasticity, and thermalconductivity. Creep increases with temperature. Above100°C (212°F), the paste begins to dehydrate (lose chemi-cally combined water of hydration) resulting in significantstrength losses. Strength decreases with increases in tem-perature until the concrete loses essentially all its strength.The effect of high-temperature exposure on compressivestrength of concretes made with various types of aggre-gate is illustrated in Fig. 15-20. Several factors includingconcrete moisture content, aggregate type and stability,cement content, exposure time, rate of temperature rise,age of concrete, restraint, and existing stress all influencethe behavior of concrete at high temperatures.

266


0 400 800 1200

0 200 400 600

0.008

0.004

0

Exp

ansi

on, m

m/m

m (

in./i

n.)

Carbonate

Siliceous

Sandedexpanded shale

Temperature, °F

Temperature, °C

Fig. 15-19. Thermal expansion of concretes containingvarious types of aggregate (Abrams 1977).

20 200 400 600 800

70 400 800 1200100

75

50

25

0

Sanded expanded shale aggregate

Siliceous aggregateCarbonateaggregate

Heated unstressed, then stored7 days at 21°C (70°F)

Avg. original strength = 27 MPa (3900 psi)Com

pres

sive

stre

ngth

, per

cent

of o

rigin

al

Temperature, °C

Temperature, °F

Fig. 15-20. Effect of high temperatures on the residualcompressive strength of concretes containing varioustypes of aggregate (Abrams 1973).

Fig. 15-21. Illustration of curling of a concrete slab onground. The edge of the slab at a joint or free end lifts offthe subbase creating a cantilevered section of concretethat can break off under heavy wheel loading.

Curling can be reduced or eliminated by using designand construction techniques that minimize shrinkage dif-ferentials and by using techniques described earlier toreduce temperature and moisture-related volume changes.Thickened edges, shorter joint spacings, permanent vapor-impermeable sealers, and large amounts of reinforcingsteel placed 50 mm (2 in.) below the surface all help reducecurling (Ytterberg 1987).

ELASTIC AND INELASTIC DEFORMATION

Compression Strain

The series of curves in Fig. 15-22 illustrate the amount ofcompressive stress and strain that results instantaneouslydue to loading of unreinforced concrete. With water-cementratios of 0.50 or less and strains up to 1500 millionths, theupper three curves show that strain is closely proportionalto stress; in other words, the concrete is almost elastic. Theupper portions of the curves and beyond show that the con-crete is inelastic. The curves for high-strength concrete havesharp peaks, whereas those for lower-strength concreteshave long and relatively flat peaks. Fig. 15-22 also showsthe sudden failure characteristics of higher strength, lowwater to cement ratio, concrete cylinders.

When load is removed from concrete in the inelasticzone, the recovery line usually is not parallel to the orig-inal line for the first load application. Therefore, theamount of permanent set may differ from the amount ofinelastic deformation (Fig. 15-23).

The term “elastic” is not favored for general discus-sion of concrete behavior because frequently the strainmay be in the inelastic range. For this reason, the term“instantaneous strain” is often used.

Modulus of Elasticity

The ratio of stress to strain in the elastic range of a stress-strain curve for concrete defines the modulus of elasticity(E) of that concrete (Fig. 15-23). Normal-density concretehas a modulus of elasticity of 14,000 to 41,000 MPa

267


60

50

40

30

20

10

0 1000 2000 3000 4000 5000

8

6

4

2

Con

cret

e st

ress

, MP

a

Con

cret

e st

ress

, 100

0 ps

i

Strain-concentric compression tests, millionths

150 mm(6 in.)

300

mm

(12

in.)

P

Water-to-cement ratio:

0.33

0.40

0.50

0.67

1.00

Fig. 15-22. Stress-strain curves for compression tests on 150 � 300-mm (6 � 12-in.) concrete cylinders at an age of 28 days(Hognestad, Hanson, and McHenry 1955).

Elas

tic ra

nge

Reco

very

line

Load

line

f

�

Inelasticdeformation

Permanent set�Strain,

fS

tress

,

f�

Modulus of elasticity = E =

Fig. 15-23. Generalized stress-strain curve for concrete.

Shear Strain

Concrete, like other materials, deforms under shear forces.The shear strain produced is important in determining theload paths or distribution of forces in indeterminate struc-tures—for example where shear-walls and columns bothparticipate in resisting horizontal forces in a concretebuilding frame. The amount of movement, while notlarge, is significant in short, stubby members; in largermembers it is overshadowed by flexural strains.Calculation of the shear modulus (modulus of rigidity), G,is shown in Fig. 15-25; G varies with the strength andtemperature of the concrete.

(2,000,000 psi to 6,000,000 psi), depending on factors suchas compressive strength and aggregate type. For normal-density concrete with compressive strengths (¯) between20 MPa and 35 MPa (3000 psi and 5000 psi), the modulusof elasticity can be estimated as 5000 times the square rootof ¯ (57,000 times the square root of ¯ in psi). The mod-ulus of elasticity for structural lightweight concrete isbetween 7000 MPa and 17,000 MPa (1,000,000 psi and2,500,000 psi). E for any particular concrete can be deter-mined in accordance with ASTM C 469.

Deflection

Deflection of concrete beams and slabs is one of the morecommon and obvious building movements. The deflec-tions are the result of flexural strains that develop underdead and live loads and that may result in cracking in thetensile zone of concrete members. Reinforced concretestructural design anticipates these tension cracks. Concretemembers are often cambered, that is, built with an upwardbow, to compensate for the expected later deflection.

Poisson’s Ratio

When a block of concrete is loaded in uniaxial compres-sion, as in Fig. 15-24, it will shorten and at the same timedevelop a lateral strain or bulging. The ratio of lateral toaxial strain is called Poisson’s ratio, µ. A common valueused is 0.20 to 0.21, but the value may vary from 0.15 to0.25 depending upon the aggregate, moisture content, con-crete age, and compressive strength. Poisson’s ratio (ASTMC 469) is generally of no concern to the structural designer;it is used in advanced structural analysis of flat-platefloors, shell roofs, arch dams, and mat foundations.

268


��

��

�

�

��

�µ =

Fig. 15-24. Ratio of lateral to axial strain is Poisson’s ratio, µµ.

Torsional Strain

Plain rectangular concrete members can also fail in tor-sion, that is, a twisting action caused by bending about anaxis parallel to the wider face and inclined at an angle ofabout 45 degrees to the longitudinal axis of a member.Microcracks develop at low torque; however, concretebehaves reasonably elastic up to the maximum limit of theelastic torque (Hsu 1968).

CREEP

When concrete is loaded, the deformation caused by theload can be divided into two parts: a deformation thatoccurs immediately (elastic strain) and a time-dependentdeformation that begins immediately but continues at adecreasing rate for as long as the concrete is loaded. Thislatter deformation is called creep.

The amount of creep is dependent upon (1) the mag-nitude of stress, (2) the age and strength of the concrete

Area = A

w h

G =E

2(1 + µ)

Displacement

� = 6wh2

10GA

Fig. 15-25. Strain that results from shear forces on a body.G = shear modulus. µµ = Poisson’s ratio. Strain resultingfrom flexure is not shown.

when stress is applied, and (3) the length of time the con-crete is stressed. It is also affected by other factors relatedto the quality of the concrete and conditions of exposure,such as: (1) type, amount, and maximum size of aggre-gate; (2) type of cementing materials; (3) amount ofcement paste; (4) size and shape of the concrete element;(5) volume to surface ratio of the concrete element;(6) amount of steel reinforcement; (7) prior curing condi-tions; and (8) the ambient temperature and humidity.

Within normal stress ranges, creep is proportional tostress. In relatively young concrete, the change in volumeor length due to creep is largely unrecoverable; in older ordrier concrete it is largely recoverable.

The creep curves shown in Fig. 15-26 are based ontests conducted under laboratory conditions in accor-dance with ASTM C 512. Cylinders were loaded to almost40% of their compressive strength. Companion cylindersnot subject to load were used to measure dryingshrinkage; this was then deducted from the total deforma-tion of the loaded specimens to determine creep.Cylinders were allowed to dry while under load exceptfor those marked “sealed.” The two 28-day curves for eachconcrete strength in Fig. 15-26 show that creep of concreteloaded under drying conditions is greater than creep ofconcrete sealed against drying. Concrete specimensloaded at a late age will creep less than those loaded at anearly age. It can be seen that as concrete strength

decreases, creep increases. Fig. 15-27 illustrates recoveryfrom the elastic and creep strains after load removal.

A combination of strains occurring in a reinforcedcolumn is illustrated in Fig. 15-28. The curves representdeformations and volume changes in a 14th-story columnof a 76-story reinforced concrete building while underconstruction. The 400 x 1200-mm (16 x 48-in.) column con-tained 2.08% vertical reinforcement and was designed for60-MPa (9000-psi) concrete.

269


10

5

0

1.5

1.0

0.5

0

5

7.51.0

0.5

00

Concrete strength, 28 MPa (4000 psi)

Age of loading28 days

90

28 (sealed)180

Concrete strength, 41 MPa (6000 psi)

Age of loading28 days

9028 (sealed)360

250 500 750 1000 1250

Cre

ep s

train

, mill

iont

hs p

er k

Pa

Cre

ep s

train

, mill

iont

hs p

er p

si

Age, days

Fig. 15-26. Relationship of time and age of loading to creepof two different strength concretes. Specimens wereallowed to dry during loading, except for those labeled assealed (Russell and Corley 1977).

Creep strain

Elastic strain

Irrecoverable creep

Instantaneous recovery

Creep recovery

Permanent set

Load removed

0.01250.08

0.06

0.04

0.02

0.0100

0.0075

0.0050

0.0025

0 400 800 1200 1600

Stra

in p

er 1

000

psi o

f stre

ss, p

erce

nt

Stra

in p

er M

Pa

of s

tress

, per

cent

Time, days

Fig. 15-27. Combined curve of elastic and creep strainsshowing amount of recovery. Specimens (cylinders) wereloaded at 8 days immediately after removal from fog curingroom and then stored at 21°C (70°F) and 50% RH. Theapplied stress was 25% of the compressive strength at 8days (Hansen and Mattock 1966).

00

300

600

900

1200

1500

500 1000 1500

Com

pres

sive

stra

in, m

illio

nths

Total

Creep

Drying shrinkage

Instantaneous deformation

Age, days

Fig. 15-28. Summation of strains in a reinforced concretecolumn during construction of a tall building (Russell andCorley 1977).

in-place concrete is insignificant and does not have to beconsidered in engineering practice.

Carbonation of paste proceeds slowly and produceslittle direct shrinkage at relative humidities of 100% and25%. Maximum carbonation and carbonation shrinkageoccurs at about 50% relative humidity. Irreversibleshrinkage and weight gain occurs during carbonation.And the carbonated product may show improved volumestability to subsequent moisture change and reduced per-meability (Verbeck 1958).

During manufacture some concrete masonry units aredeliberately exposed to carbon dioxide after reaching 80%of their rated strength; this introduction to carbonationshrinkage makes the units more dimensionally stable.Future drying shrinkage is reduced 30% or more(Toennies and Shideler 1963).

One of the causes of surface crazing of concrete is theshrinkage that accompanies natural air carbonation ofyoung concrete. More research is needed on the effect ofearly carbonation on deicer scaling resistance.

Carbonation of another kind also can occur in freshlyplaced, unhardened concrete. This carbonation causes asoft, chalky surface called dusting; it usually takes placeduring cold-weather concreting when there is an unusualamount of carbon dioxide in the air due to unventedheaters or gasoline-powered equipment operating in anenclosure.

Sulfate Attack

Sulfate attack of concrete can occur where soil andgroundwater have a high sulfate content and measures toreduce sulfate attack, such as use of a low water tocementing materials ratio, have not been taken. The attackis greater in concrete that is exposed to wetting anddrying, such as foundation walls and posts. Sulfate attackusually results in an expansion of the concrete because ofthe formation of solids from the chemical action or saltcrystallization. The amount of expansion in severe cir-cumstances has been significantly higher than 0.1%, andthe disruptive effect within the concrete can result inextensive cracking and disintegration. The amount ofexpansion cannot be accurately predicted.

Alkali-Aggregate Reactions

Certain aggregates can react with alkali hydroxides inconcrete, causing expansion and cracking over a period ofyears. The reaction is greater in those parts of a structureexposed to moisture. A knowledge of the characteristics oflocal aggregates is essential. There are two types of alkali-reactive aggregates, siliceous and carbonate. Alkali-aggre-gate reaction expansion may exceed 0.5% in concrete andcan cause the concrete to fracture and break apart.

Structural design techniques cannot counter theeffects of alkali-aggregate expansion, nor can the expan-

The method of curing prior to loading has a markedeffect on the amount of creep in concrete. The effects oncreep of three different methods of curing are shown inFig. 15-29. Note that very little creep occurs in concretethat is cured by high-pressure steam (autoclaving). Notealso that atmospheric steam-cured concrete has consider-ably less creep than 7-day moist-cured concrete. The twomethods of steam curing shown in Fig. 15-29 reducedrying shrinkage of concrete about half as much as theyreduce creep.

CHEMICAL CHANGES AND EFFECTS

Some volume changes of concrete result from chemicalreactions; these may take place shortly after placing andfinishing or later due to reactions within the hardenedconcrete in the presence of water or moisture.

Carbonation

Hardened concrete containing some moisture reacts withcarbon dioxide present in air, a reaction that results in aslight shrinkage of the surface paste of the concrete. Theeffect, known as carbonation, is not destructive but actu-ally increases the chemical stability and strength of theconcrete. However, carbonation also reduces the pH ofconcrete. If steel is present in the carbonated area, steelcorrosion can occur due to the absence of the protectiveoxide film provided by concrete’s high pH. Rust is anexpansive reaction and results in cracking and spalling ofthe concrete. The depth of carbonation is very shallow indense, high-quality concrete, but can penetrate deeply inporous, poor-quality concrete. Because so little of a con-crete element carbonates, carbonation shrinkage of cast-

270


7 days moist-cured

Atmospheric steam-cured

High-pressure steam-cured

0 50 100 150 200 250 300 350

Cre

ep d

efor

mat

ion

Note: Same concrete strength at time of loading in all cases

Time after loading, days

Fig. 15-29. Effect of curing method on magnitude of creepfor typical normal-density concrete (Hanson 1964).

sion be controlled by jointing. In areas where deleteriouslyreactive aggregates are known to exist, special measuresmust be taken to prevent the occurrence of alkali-aggre-gate reaction.

REFERENCES

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Abrams, M. S., Performance of Concrete Structures Exposedto Fire, Research and Development Bulletin RD060, Port-land Cement Association, http://www.portcement.org/pdf_files/RD060.pdf, 1977.

Abrams, M. S., Behavior of Inorganic Materials in Fire,Research and Development Bulletin RD067, Portland Ce-ment Association, http://www.portcement.org/pdf_files/RD067.pdf, 1979.

Abrams, M. S., and Orals, D. L., Concrete Drying Methodsand Their Effects on Fire Resistance, Research DepartmentBulletin RX181, Portland Cement Association, http://www.portcement.org/pdf_files/RX181.pdf, 1965.

ACI Committee 209, Prediction of Creep, Shrinkage, andTemperature Effects in Concrete Structures, ACI 209R-92,reapproved 1997, American Concrete Institute, Farming-ton Hills, Michigan, 1997, 47 pages.

ACI Committee 224, Control of Cracking in ConcreteStructures, ACI 224R-01, American Concrete Institute,Farmington Hills, Michigan, 2001, 43 pages.

ACI Committee 224, Causes, Evaluation, and Repair of Cracksin Concrete Structures, ACI 224.1R-93, reapproved 1998,American Concrete Institute, Farmington Hills, Michigan,1998, 22 pages.

Aítcin, Pierre-Claude, “Does Concrete Shrink or Does itSwell?,” Concrete International, American Concrete Insti-tute, Farmington Hills, Michigan, December 1999, pages77 to 80.

Brewer, H. W., Moisture Migration—Concrete Slab-on-Ground Construction, Development Department BulletinDX089, Portland Cement Association, http://www.portcement.org/pdf_files/DX089.pdf, 1965.


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Carette, G. G.; Painter, K. E.; and Malhotra, V. M., “Sus-tained High Temperature Effect on Concretes Made withNormal Portland Cement, Normal Portland Cement andSlag, or Normal Portland Cement and Fly Ash,” ConcreteInternational, American Concrete Institute, FarmingtonHills, Michigan, July 1982.

Carlson, Roy W., “Drying Shrinkage of Concrete asAffected by Many Factors,” Proceedings of the Forty-FirstAnnual Meeting of the American Society for Testing andMaterials, vol. 38, part II, Technical Papers, AmericanSociety for Testing and Materials, West Conshohocken,Pennsylvania, 1938, pages 419 to 440.

Copeland, L. E., and Bragg, R. H., Self Desiccation inPortland Cement Pastes, Research Department BulletinRX052, Portland Cement Association, http://www.portcement.org/pdf_files/RX052.pdf, 1955.

Cruz, Carlos R., Elastic Properties of Concrete at HighTemperatures, Research Department Bulletin RX191, Port-land Cement Association, http://www.portcement.org/pdf_files/RX191.pdf, 1966.

Cruz, C. R., and Gillen, M., Thermal Expansion of PortlandCement Paste, Mortar, and Concrete at High Temperatures,Research and Development Bulletin RD074, PortlandCement Association, http://www.portcement.org/pdf_files/RD074.pdf, 1980.

Davis, R. E., “A Summary of the Results of InvestigationsHaving to Do with Volumetric Changes in Cements,Mortars, and Concretes Due to Causes Other Than Stress,”Proceedings of the American Concrete Institute, AmericanConcrete Institute, Farmington Hills, Michigan, vol. 26,1930, pages 407 to 443.

FHWA and Transtec, HIPERPAV, http://www.hiperpav.com, 2001.

Gebler, Steven H., and Klieger, Paul, Effect of Fly Ash onSome of the Physical Properties of Concrete, Research and De-velopment Bulletin RD089, Portland Cement Association,http://www.portcement.org/pdf_files/RD089.pdf, 1986.

Hammer, T. A., “Test Methods for Linear Measurement ofAutogenous Shrinkage Before Setting,” AutogenousShrinkage of Concrete, edited by E. Tazawa, E&FN Sponand Routledge, New York, 1999, pages 143 to 154. Alsoavailable through PCA as LT245.

Hanson, J. A., Prestress Loss As Affected by Type of Curing,Development Department Bulletin DX075, PortlandCement Association, http://www.portcement.org/pdf_files/DX075.pdf, 1964.

271


Kosmatka, Steven H., “Floor-Covering Materials andMoisture in Concrete,” Concrete Technology Today, PL853,Portland Cement Association, http://www.portcement.org/pdf_files/PL853.pdf, 1985.

Le Chatelier, H., “Sur les Changements de Volume quiAccompagent le durcissement des Ciments,” BulletinSociete de l‘Encouragement pour l‘Industrie Nationale,5eme serie, tome 5, Paris, 1900.

Lentz, A. E., and Monfore, G. E., Thermal Conductivities ofPortland Cement Paste, Aggregate, and Concrete Down to VeryLow Temperatures, Research Department Bulletin RX207,Portland Cement Association, http://www.portcement.org/pdf_files/RX207.pdf, 1966.

Lerch, William, Studies of Some Methods of Avoiding theExpansion and Pattern Cracking Associated with the Alkali-Aggregate Reaction, Research Department Bulletin RX031,Portland Cement Association, http://www.portcement.org/pdf_files/RX031.pdf, 1950.

Malhotra, M. L., “The Effect of Temperature on theCompressive Strength of Concrete,” Magazine of ConcreteResearch, vol. 8., no. 23, Cement and Concrete Association,Wexham Springs, Slough, England, August 1956, pages85 to 94.

Monfore, G. E., A Small Probe-Type Gage for Measuring Rela-tive Humidity, Research Department Bulletin RX160,Portland Cement Association, http://www.portcement.org/pdf_files/RX160.pdf, 1963.

Monfore, G. E., and Lentz, A. E., Physical Properties ofConcrete at Very Low Temperatures, Research DepartmentBulletin RX145, Portland Cement Association, http://www.portcement.org/pdf_files/RX145.pdf, 1962.

Nawy, Edward G.; Barth, Florian G.; and Frosch, Robert J.,Design and Construction Practices to Mitigate Cracking,SP-204, American Concrete Institute, Farmington Hills,Michigan, 2001, 284 pages.

PCA, Effect of Long Exposure of Concrete to High Temperature,ST32, Portland Cement Association, 1969.

PCA, Building Movements and Joints, EB086, Portland Ce-ment Association, http://www.portcement.org/pdf_files/EB086.pdf, 1982.

PCA, Concrete Slab Surface Defects: Causes, Prevention,Repair, IS177, Portland Cement Association, 2001.

Philleo, Robert, Some Physical Properties of Concrete at HighTemperatures, Research Department Bulletin RX097, Port-land Cement Association, http://www.portcement.org/pdf_files/RX097.pdf, 1958.

Hanson, J. A., Effects of Curing and Drying Environments onSplitting Tensile Strength of Concrete, Development Depart-ment Bulletin DX141, Portland Cement Association,http://www.portcement.org/pdf_files/DX141.pdf, 1968.

Hansen, Torben C., and Mattock, Alan H., Influence of Sizeand Shape of Member on the Shrinkage and Creep of Concrete,Development Department Bulletin DX103, PortlandCement Association, http://www.portcement.org/pdf_files/DX103.pdf, 1966.

Hedenblad, Göran, “Concrete Drying Time,” PL982, Con-crete Technology Today, Portland Cement Association, http://www.portcement.org/pdf_files/PL982.pdf, July 1998.

Hedenblad, Göran, Drying of Construction Water inConcrete, Byggforskningsradet, The Swedish Council forBuilding Research, Stockholm, 1997 [PCA LT229].

Helmuth, Richard A., and Turk, Danica H., The Reversibleand Irreversible Drying Shrinkage of Hardened PortlandCement and Tricalcium Silicate Pastes, Research DepartmentBulletin RX215, Portland Cement Association, http://www.portcement.org/pdf_files/RX215.pdf, 1967.

Holt, Erika E., Early Age Autogenous Shrinkage of Concrete,VTT Publication 446, Technical Research Center ofFinland, Espoo, 2001, 194 pages. Also available throughPCA as LT257.

Holt, Erika E., and Janssen, Donald J., “Influence of EarlyAge Volume Changes on Long-Term Concrete Shrinkage,”Transportation Research Record 1610, Transportation Re-search Board, National Research Council, Washington,D.C., 1998, pages 28 to 32.

Hognestad, E.; Hanson, N. W.; and McHenry, D., ConcreteStress Distribution in Ultimate Strength Design, DevelopmentDepartment Bulletin DX006, Portland Cement Association,http://www.portcement.org/pdf_files/DX006.pdf, 1955.

Hsu, Thomas T. C., Torsion of Structural Concrete—PlainConcrete Rectangular Sections, Development DepartmentBulletin DX134, Portland Cement Association, http://www.portcement.org/pdf_files/DX134.pdf, 1968.

Jackson, F. H., Long-Time Study of Cement Performance inConcrete—Chapter 9. Correlation of the Results of LaboratoryTests with Field Performance Under Natural Freezing andThawing Conditions, Research Department Bulletin RX060,Portland Cement Association, http://www.portcement.org/pdf_files/RX060.pdf, 1955.

Kaar, P. H.; Hanson, N. W.; and Capell, H. T., Stress-StrainCharacteristics of High-Strength Concrete, Research and De-velopment Bulletin RD051, Portland Cement Association,http://www.portcement.org/pdf_files/RD051.pdf, 1977.

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Pickett, Gerald, The Effect of Change in Moisture Content onthe Creep of Concrete Under a Sustained Load, Research De-partment Bulletin RX020, Portland Cement Association,http://www.portcement.org/pdf_files/RX020.pdf, 1947.

Powers, T. C., “Absorption of Water by Portland CementPaste during the Hardening Process,” Industrial andEngineering Chemistry, Vol. 27, No. 7, July 1935, pages790 to 794.

Powers, Treval C., “Causes and Control of VolumeChange,” Volume 1, Number 1, Journal of the PCA Researchand Development Laboratories, Portland Cement Asso-ciation, January 1959.

Roper, Harold, Volume Changes of Concrete Affected byAggregate Type, Research Department Bulletin RX123,Portland Cement Association, http://www.portcement.org/pdf_files/RX123.pdf, 1960.

Russell, H. G., and Corley, W. G., Time-Dependent Behaviorof Columns in Water Tower Place, Research and DevelopmentBulletin RD052, Portland Cement Association, http://www.portcement.org/pdf_files/RD052.pdf, 1977.

Steinour, Harold H., “Some Effects of Carbon Dioxide onMortars and Concrete—Discussion,” Proceedings of theAmerican Concrete Institute, vol. 55, American Concrete In-stitute, Farmington Hills, Michigan, 1959, pages 905 to 907.

Suprenant, Bruce A., and Malisch, Ward R., “The FiberFactor,” Concrete Construction, Addison, Illinois, October1999, pages 43 to 46.

Suprenant, Bruce A., and Malisch, Ward R., “A New Lookat Water, Slump, and Shrinkage,” Concrete Construction,Addison, Illinois, April 2000, pages 48 to 53.

Tazawa, Ei-ichi, Autogenous Shrinkage of Concrete, E & FNSpon and Routledge, New York, 1999, 428 pages [PCALT245].

Toennies, H. T., and Shideler, J. J., Plant Drying andCarbonation of Concrete Block—NCMA-PCA Cooperative Pro-gram, Development Department Bulletin DX064, PortlandCement Association, http://www.portcement.org/pdf_files/DX064.pdf, 1963.

Tremper, Bailey, and Spellman, D. L., “Shrinkage ofConcrete—Comparison of Laboratory and FieldPerformance,” Highway Research Record Number 3,Properties of Concrete, Transportation Research Board,National Research Council, Washington, D.C., 1963.

Verbeck, G. J., Carbonation of Hydrated Portland Cement,Research Department Bulletin RX087, Portland CementAssociation, http://www.portcement.org/pdf_files/RX087.pdf, 1958.

Whiting, David A.; Detwiler, Rachel J.; and Lagergren, EricS., “Cracking Tendency and Drying Shrinkage of SilicaFume Concrete for Bridge Deck Applications,” ACI Mate-rials Journal, American Concrete Institute, FarmingtonHills, Michigan, January–February, 2000, pages 71 to 77.

Whiting, D., and Dziedzic, W., Effects of Conventional andHigh-Range Water Reducers on Concrete Properties, Researchand Development Bulletin RD107, Portland Cement Asso-ciation, 1992.

Ytterberg, Robert F., “Shrinkage and Curling of Slabs onGrade, Part I—Drying Shrinkage, Part II—Warping andCurling, and Part III— Additional Suggestions,” ConcreteInternational, American Concrete Institute, FarmingtonHills, Michigan, April 1987, pages 22 to 31; May 1987,pages 54 to 61; and June 1987, pages 72 to 81.

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CHAPTER 16

Control Tests for Concrete

Satisfactory concrete construction and performance re-quires concrete with specific properties. To assure thatthese properties are obtained, quality control and accept-ance testing are indispensable parts of the constructionprocess. Test results provide important feedback used tobase decisions regarding mix adjustments. However, pastexperience and sound judgment must be relied on in eval-uating tests and assessing their significance in controllingthe design, batching and placement processes that influ-ence the ultimate performance of the concrete.

Specifiers are moving toward performance-basedspecifications (also called end-result or end-property spe-cifications) that require the final performance of concretebe achieved independent of the process used to achievethe performance. Physical tests and concrete propertiesare used to measure acceptance. Such specifications maynot have acceptance limits for process control tests suchas slump or limits on the quantities of concrete ingredi-ents as do prescriptive specifications. The end result ofcompressive strength, low permeability, documenteddurability, and a minimal number of cracks, for example,would be the primary measure of acceptance. Of course,even though process control tests may not be specified,the wise concrete producer would use them to guide theproduct to a successful end result. However, most speci-fications today are still a combination of prescriptive andperformance requirements (Parry 2000).

CLASSES OF TESTS

Project specifications may affect (1) characteristics of themixture, such as maximum size of aggregate, aggregateproportions, or minimum cement content; (2) characteris-tics of the cement, water, aggregates, and admixtures; and(3) characteristics of the freshly mixed and hardenedconcrete, such as temperature, slump, air content, andcompressive or flexural strengths.

Cementitious materials are tested for their compliancewith ASTM or AASHTO standards to avoid any abnormalperformance such as early stiffening, delayed setting, orlow strengths in concrete. More details regarding cementi-tious materials can be found in Chapters 2 and 3.

Tests of aggregates have two major purposes: (1) todetermine the suitability of the material itself for use inconcrete, including tests for abrasion, soundness againstsaturated freeze-thaw cycles, harmful materials by petro-graphic examination, and potential alkali-aggregate reac-tivity; and (2) to assure uniformity, such as tests formoisture control, relative density (specific gravity), andgradation of aggregates. Some tests are used for bothpurposes. Testing aggregates to determine their potentialalkali-aggregate reactivity is discussed in Chapter 5,“Aggregates for Concrete.” Tests of concrete to evaluatethe performance of available materials, to establishmixture proportions, and to control concrete qualityduring construction include slump, air content, tempera-ture, density (unit weight), and strength. Slump, aircontent, and strength tests are usually required in projectspecifications for concrete quality control, whereasdensity is more useful in mixture proportioning. Never-theless, ASTM C 94 (AASHTO M 157) specifies thatslump, air-content, density, and temperature tests shouldbe made when strength specimens are made.

Following is a discussion of frequency of testing anddescriptions of the major control tests to ensure unifor-mity of materials, desired properties of freshly mixedconcrete, and required strength of hardened concrete.Special tests are also described.

ASTM (2000) and Klieger and Lamond (1994)provide extensive discussions of test methods for con-crete and concrete ingredients.Computational Software. In order to make computationof test data easier, NRMCA (2001) provides a CD withspread sheets for a variety of concrete and aggregate tests.

FREQUENCY OF TESTING

Frequency of testing is a significant factor in the effective-ness of quality control of concrete. Specified test frequen-cies are intended for acceptance of the material or one ofits components at a random location within the quantityor time period represented by the test. Such frequenciesmay not occur often enough to control the material within

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Specimens should be laboratory cured when tested foracceptance or ultimate performance of the concrete.However, laboratory-cured specimens should not be usedas an indication of in-place concrete strengths (ACICommittee 318, 1999).

In-place concrete strengths are typically documentedby casting specimens that are field-cured (as nearly aspractical) in the same manner as concrete in the structure.Field-cured specimens are commonly used to decidewhen forms and shores might be removed under a struc-tural slab or to determine when traffic will be allowed onnew pavement. ASTM C 31 (AASHTO T 23) containsadditional instructions regarding the handling of field-cured cylinders. Although field-cured specimens may betested at any age, 7-day tests are often made for compar-ison with laboratory tests at the same age; these are usefulto judge if curing and protection during cold weatherconcreting is adequate.

TESTING AGGREGATES

Sampling Aggregates

Methods for obtaining representative samples of aggre-gates are given in ASTM D 75 (AASHTO T 2). Accuratesampling is important. The location in the productionprocess where samples will be obtained must be carefullyplanned. Sampling from a conveyor belt, stockpile, oraggregate bin may require special sampling equipment.Caution must be exercised to obtain a sample away fromstockpile segregation and the sample must be largeenough to meet ASTM minimum sample size require-ments. In addition, samples obtained for moisture contenttesting should be placed in a sealed container or plasticbag as soon as possible to retain moisture until testing.

Reducing large field samples to small quantities forindividual tests must be done with care so that thefinal samples will be truly representative ASTM C 702(AASHTO T 248). For coarse aggregate, this is done by thequartering method: The sample, thoroughly mixed, isspread on a piece of canvas in an even layer 75 or 100 mm(3 or 4 in.) thick. It is divided into four equal parts. Twoopposite parts are then discarded. This process is repeateduntil the desired size of sample remains. A similar proce-dure is sometimes used for moist, fine aggregate. Samplesplitters are desirable for dry aggregate (Fig. 16-1) butshould not be used for samples that are more than satu-rated surface dry.

Organic Impurities

Organic impurities in fine aggregate should be deter-mined in accordance with ASTM C 40 (AASHTO T 21). Asample of fine aggregate is placed in a sodium hydroxidesolution and shaken. The following day the color of thesodium hydroxide solution is compared with a glass color

specified limits during production. Process control testsare nonrandom tests performed more often than specifiedto document trends that allow adjustments to be madebefore acceptance tests are performed.

The frequency of testing aggregates and concrete fortypical batch-plant procedures depends largely upon theuniformity of materials, including the moisture content ofaggregates, and the production process. Initially it is ad-visable to make process control tests several times a day,but as work progresses and the material becomes morepredictable, the frequency often can be reduced. ASTM C1451 provides a standard practice for determining theuniformity of cementitious materials, aggregates, andchemical admixtures used in concrete.

Usually, aggregate moisture tests are made once ortwice a day. The first batch of fine aggregate in themorning is often overly wet since moisture will migrateovernight to the bottom of the storage bin. As fine aggre-gate is drawn from the bottom of the bin and additionalaggregate is added, the moisture content should stabilizeat a lower level and the first moisture test can be made.Obtaining moisture samples representative of the aggre-gates being batched is important; a one percent change inmoisture content of fine aggregate will change the amountof mix water needed by approximately eight kilogramsper cubic meter (13 lb/yd3).

Slump tests should be made for the first batch ofconcrete each day, whenever consistency of concreteappears to vary, and whenever strength-test cylinders aremade at the jobsite.

Air-content tests should be made often enough at thepoint of delivery to ensure proper air content, particularlyif temperature and aggregate grading change. An air-content test should be performed for each sample ofconcrete from which cylinders are made; a record of thetemperature of each sample of concrete should also be kept.

The number of strength tests made will depend on thejob specifications and the occurrence of variations. TheACI 318 building code and ASTM C 94 require thatstrength tests of each class of concrete placed each dayshould be taken not less than once a day, nor less thanonce for each 115 cubic meters (150 cu yd) of concrete. Inaddition, ACI 318 recommends not less than once for each500 square meters (5000 sq ft) of surface area for slabs orwalls placed each day. The average strength of two 28-daycylinders is required for each test used for evaluatingconcrete. A 7-day test cylinder, along with the two 28-daytest cylinders, is often made and tested to provide an earlyindication of strength development. As a rule of thumb,the 7-day strength is about 60% to 75% of the 28-daycompressive strength, depending upon the type andamount of cementitious materials, water-cement ratio,curing temperature, and other variables. Additional spec-imens may be required when high-strength concrete isinvolved or where structural requirements are critical.

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standard or standard color solution. If the color of thesolution containing the sample is darker than the standardcolor solution or Organic Glass Plate No. 3, the fine aggre-gate should not be used for important concrete workwithout further investigation.

Some fine aggregates contain small quantities of coalor lignite that give the liquid a dark color. The quantitymay be insufficient to reduce the strength of the concreteappreciably. If surface appearance of the concrete is notimportant, ASTM C 33 (AASHTO M 6) states that fineaggregate is acceptable if the amount of coal and lignitedoes not exceed 1.0% of the total fine aggregate mass. Afine aggregate failing this ASTM C 33 (AASHTO M 6) limitmay be used if, when tested in accordance with ASTM C 87(AASHTO T 71), the 7-day strengths of mortar cubes madewith the sand (ASTM C 109 or AASHTO T 106) are at least95% of the 7-day strengths of mortar made with the samesand, but washed in a 3% solution of sodium hydroxideand then thoroughly rinsed in water. It should be realizedthat appreciable quantities of coal or lignite in aggregatescan cause popouts and staining of the concrete and canreduce durability when concrete is exposed to weathering.Local experience is often the best indication of the durabil-ity of concrete made with such aggregates.

Objectionable Fine Material

Large amounts of clay and silt in aggregates can adverselyaffect durability, increase water requirements, and in-crease shrinkage. Specifications usually limit the amountof material passing the 75 µm (No. 200) sieve to 2% or 3%in fine aggregate and to 1% or less in coarse aggregate.Testing for material finer than the 75 µm (No. 200) sieveshould be done in accordance with ASTM C 117(AASHTO T 11). Testing for clay lumps should be inaccordance with ASTM C 142 (AASHTO T 112).

Grading

Gradation of aggregates significantly affects concrete mix-ture proportioning and workability. Hence, gradationtests are an important element in the assurance of concretequality. The grading or particle size distribution of anaggregate is determined by a sieve analysis test in whichthe particles are divided into their various sizes by stan-dard sieves. The analysis should be made in accordancewith ASTM C 136 (AASHTO T 27).

Results of sieve analyses are used in three ways: (1) todetermine whether or not the materials meet specifica-tions; (2) to select the most suitable material if severalaggregates are available; and (3) to detect variations ingrading that are sufficient to warrant blending selectedsizes or an adjustment of concrete mix proportions.

The grading requirements for concrete aggregate areshown in Chapter 5 and ASTM C 33 (AASHTO M 6/M80). Materials containing too much or too little of any onesize should be avoided. Some specifications require thatmixture proportions be adjusted if the average finenessmodulus of fine aggregate changes by more than 0.20.Other specifications require an adjustment in mixtureproportions if the amount retained on any two consecu-tive sieves changes by more than 10% by mass of the totalfine-aggregate sample. A small quantity of clean particlesthat pass a 150 µm (No. 100) sieve but are retained on a 75µm (No. 200) sieve is desirable for workability. For thisreason, most specifications permit up to 10% of this mate-rial in fine aggregate.

Well-graded aggregates contain particles on each sievesize. Well-graded aggregates enhance numerous factorsthat result in greater workability and durability. The morewell-graded an aggregate is, the more it will pack togetherefficiently, thus reducing the volume between aggregateparticles that must be filled by paste. On the other hand,gap-graded aggregates—those having either a large quan-tity or a deficiency of one or more sieve sizes—can result inreduced workability during mixing, pumping, placing,consolidation and finishing. Durability can suffer too as aresult of using more fine aggregate and water to produce aworkable mix. See Chapter 5 and Galloway (1994) for addi-tional information on aggregate grading.

Moisture Content of Aggregates

Several methods are used for determining the amount ofmoisture in aggregate samples. The total moisture con-tent for fine or coarse aggregate can be tested in accor-dance with ASTM C 566 (AASHTO T 255). In thismethod a measured sample of damp aggregate is driedeither in a ventilated conventional oven, microwaveoven, or over an electric or gas hotplate. From the massbefore and after drying, the total moisture content can becalculated as follows:

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Chapter 16 ◆ Control Tests for Concrete

Fig. 16-1. Sample splitter commonly used to reduce coarseaggregate samples. (70012)


the sample is dry; (5) after burning, the sample is cooledfor a few minutes and weighed; and (6) the percentage ofmoisture is then calculated.

When drying equipment is not available a field orplant determination of surface (free) moisture in fineaggregate can be made in accordance with ASTM C 70.The same procedure can be used for coarse aggregate withappropriate changes in the size of sample and dimensionsof the container. This test depends on displacement ofwater by a known mass of moist aggregate; therefore, therelative density (specific gravity) of the aggregate must beknown accurately.

Electric moisture meters are used in many concretebatching plants primarily to monitor the moisture contentof fine aggregates, but some plants also use them to checkcoarse aggregates. They operate on the principle that theelectrical resistance of damp aggregate decreases as mois-ture content increases, within the range of dampnessnormally encountered. The meters measure the electricalresistance of the aggregate between electrodes protrudinginto the batch hopper or bin. Moisture meters using themicrowave-absorption method are gaining popularitybecause they are more accurate than the electric meters.However, both methods measure moisture contents accu-rately and rapidly, but only at the level of the probes.These meters require frequent calibration and must bemaintained properly. The variable nature of moisturecontents in aggregates cause difficulty in obtaining repre-sentative samples for comparison to electric moisturemeters. Several oven-dried moisture content tests shouldbe performed to verify the calibration of these metersbefore trends in accuracy can be established.

Table 16-1 illustrates a method of adjusting batchweights for moisture in aggregates.

P = 100(M – D)/D

where

P = moisture content of sample, percent M = mass of original sample D = mass of dried sample

The surface (free) moisture can be calculated if thepercentage of absorbed moisture in the aggregate isknown. The surface moisture content is equal to the totalmoisture content minus the absorbed moisture. Historicinformation for an aggregate source can be used to obtainabsorbed moisture content data if the mineral compositionof the pit or quarry has not changed significantly. How-ever, if recent data is not available, they can be determinedusing methods outlined in ASTM C 127 (AASHTO T 85)for coarse aggregate and ASTM C 128 (AASHTO T 84) forfine aggregate.

Only the surface moisture, not the absorbed moisture,becomes part of the mixing water in concrete. Surfacemoisture percentages are used to calculate the amount ofwater in the aggregates to reduce the amount of mix waterused for batching. In addition, the batch weight of aggre-gates should be increased by the percentage of surfacemoisture present in each type of aggregate. If adjustmentsare not made during batching, surface water will replace aportion of the aggregate mass and the mix will not yieldproperly.

Another method to determine moisture content,which is not as accurate, is to evaporate the moisture byburning alcohol. In this method: (1) a measured sample ofdamp fine aggregate is placed in a shallow pan; (2) about310 ml of alcohol for each kilogram (5 oz for each pound)is poured over the sample; (3) the mixture is stirred with arod and spread in a thin layer over the bottom of the pan;(4) the alcohol is then ignited and allowed to burn until

278

Aggregate mass Aggregate mass Mix water correction forMix design mass (SSD condition),** (in moist condition), surface moisture in

(aggregates in dry kg/m3 (lb/yd3) kg/m3 (lb/yd3) aggregates, kg/m3 (lb/yd3) AdjustedConcrete BOD condition),* BOD •

(Absorbed %) BOD •(Moisture %) BOD •

(Moist%-Absorb%) batch weight, ingredients kg/m3 (lb/yd3) 100 100 100 kg/m3 (lb/yd3)

Cement 355 (598) 355 (598)Fine aggregate 695 (1171) 703 (1185) 735 (1239) 32 (54) 735 (1239)Coarse aggregate 1060 (1787) 1064 (1793) 1068 (1800) 4 (7) 1068 (1800)Water 200 (337) 164 (276)

Total 2310 (3893) 36 (61) 2322 (3913)†

* An aggregate in a bulk-oven dry (BOD) condition is one with its permeable voids completely dry so that it is fully absorbent.** An aggregate in a saturated, surface-dry (SSD) condition is one with its permeable voids filled with water and with no surface moisture on

it. Concrete suppliers often request mix design proportions on a SSD basis because of batching software requirements.† Total adjusted batch weight is higher than total mix design weight by the amount of water absorbed in the aggregate.

Table 16-1. Example of Adjustment in Batch Weights for Moisture in Aggregates

Aggregate data Absorption, % Moisture content, %

Fine aggregate 1.2 5.8Coarse aggregate 0.4 0.8


TESTING FRESHLY MIXED CONCRETE

Sampling Freshly Mixed Concrete

The importance of obtaining truly representative samplesof freshly mixed concrete for control tests must be empha-sized. Unless the sample is representative, test results willbe misleading. Samples should be obtained and handled inaccordance with ASTM C 172 (AASHTO T 141). Except forroutine slump and air-content tests performed for processcontrol, ASTM C 172 (AASHTO T 141) requires that samplesize used for acceptance purposes be at least 28 liter (1 cu ft)and be obtained within 15 minutes between the first andfinal portions of the sample. The composite sample, madeof two or more portions, should not be taken from the veryfirst or last portion of the batch discharge. The sampleshould be protected from sunlight, wind, and other sourcesof rapid evaporation during sampling and testing.

Consistency

The slump test, ASTM C 143 (AASHTO T 119), is the mostgenerally accepted method used to measure the consis-tency of concrete (Fig. 16-2). The test equipment consists ofa slump cone (a metal conical mold 300 mm [12 in.] high,with a 200-mm [8-in.] diameter base and 100-mm [4-in.]diameter top) and a steel rod 16 mm (5⁄8 in.) in diameter and600 mm (24 in.) long with a hemispherically shaped tip.The dampened slump cone, placed upright on a flat,nonabsorbent rigid surface, should be filled in three layersof approximately equal volume. Therefore, the coneshould be filled to a depth of about 70 mm (21⁄2 in.) for thefirst layer, a depth of about 160 mm (6 in.) for the second

layer, and overfilled for the third layer. Each layer isrodded 25 times. Following rodding, the last layer is struckoff and the cone is slowly raised vertically 300 mm (12 in.)in 5 ± 2 seconds. As the concrete subsides or settles to anew height, the empty slump cone is then inverted andgently placed next to the settled concrete. The slump is thevertical distance the concrete settles, measured to the near-est 5 mm (1⁄4 in.); a ruler is used to measure from the top ofthe slump cone (mold) to the displaced original center ofthe subsided concrete (see Fig. 16-2).

A higher slump value is indicative of a more fluidconcrete. The entire test through removal of the coneshould be completed in 21⁄2 minutes, as concrete losesslump with time. If a falling away or shearing off occursfrom a portion of the concrete, another test should be runon a different portion of the sample.

Another test method for flow of fresh concreteinvolves the use of the K-Slump Tester (ASTM C 1362).This is a probe-type instrument that is thrust into theconcrete in any location where there is a minimum depthof 175 mm (7 in.) of concrete a 75-mm (3-in.) radius ofconcrete around the tester. The amount of mortar flowinginto openings in the tester is reported as a measure of flow.

Additional consistency tests include: the FHWAvibrating slope apparatus (Wong and others 2001 andSaucier 1966); British compacting factor test (BS 1881);Powers remolding test (Powers 1932); German flow tabletest (DIN 1048-1); Vebe consistometer for roller-compactedconcrete (ASTM C 1170); Kelly ball penetration test (ASTMC 360-92 now discontinued); Thaulow tester; the invertedslump cone for fiber-reinforced concrete (ASTM C 995);Powers and Wiler plastometer (Powers and Wiler 1941);

279

Fig. 16-2. Slump test for consistency of concrete. Figure A illustrates a lower slump, Figure B a higher slump. (69786, 69787)

A B

sample and container is required. For example, a 7-liter(0.25-ft3) density container requires a scale sensitive to 50g (0.1 lb). The size of the container used to determinedensity and yield varies with the size of aggregate; if ingood condition, the 7-liter (0.25-ft3) air meter container iscommonly used with aggregates up to 25 mm (1 in.); a14-liter (0.5-ft3) container is used with aggregates up to50 mm (2 in.). The container should be calibrated at leastannually (ASTM C 1077). Care is needed to consolidatethe concrete adequately by either rodding or internalvibration. Strike off the top surface using a flat plate sothat the container is filled to a flat smooth finish. Thedensity is expressed in kilograms per cubic meter (poundsper cubic foot) and the yield in cubic meters (cubic feet).

The density of unhardened as well as hardenedconcrete can also be determined by nuclear methods,ASTM C 1040 (AASHTO T 271).

Air Content

A number of methods for measuring air content of freshlymixed concrete can be used. ASTM standards include thepressure method (C 231) (AASHTO T 152), the volumetricmethod (C 173) (AASHTO T 196), and the gravimetricmethod (C 138) (AASHTO T 121).

The pressure method (Fig. 16-5) is based on Boyle’slaw, which relates pressure to volume. Many commercialair meters of this type are calibrated to read air contentdirectly when a predetermined pressure is applied. Theapplied pressure compresses the air within the concretesample, including the air in the pores of aggregates. For thisreason, tests by this method are not suitable for determin-ing the air content of concretes made with some lightweightaggregates or other very porous materials. Aggregatecorrection factors that compensate for air trapped in

Tattersall (1971) workability device; Colebrand test; BMLviscometer (Wallevik 1996); BTRHEOM rheometer forfluid concrete (de Larrard, Szitkar, Hu, and Joly 1993); free-orifice rheometer (Bartos 1978); delivery chute torquemeter (US patent 4,332,158 [1982]); delivery-chute vane(US patent 4,578,989 [1986]); Angles flow box (Angles1974); ring penetration test (Teranishs and others 1994);and the Wigmore (1948) consistometer. The Vebe test andthe Thaulow test are especially applicable to stiff andextremely dry mixes while the flow table is especiallyapplicable to flowing concrete (Scanlon 1994).

Temperature Measurement

Because of the important influence concrete temperaturehas on the properties of freshly mixed and hardenedconcrete, many specifications place limits on the tempera-ture of fresh concrete. Glass or armored thermometers areavailable (Figs. 16-3). The thermometer should be accurateto plus or minus 0.5°C (±1°F) and should remain in a repre-sentative sample of concrete for a minimum of 2 minutesor until the reading stabilizes. A minimum of 75 mm (3 in.)of concrete should surround the sensing portion of thethermometer. Electronic temperature meters with precisedigital readouts are also available. The temperature meas-urement (ASTM C 1064 or AASHTO T 309) should becompleted within 5 minutes after obtaining the sample.

Density and Yield

The density (unit weight) and yield of freshly mixedconcrete (Fig. 16-4) are determined in accordance withASTM C 138 (AASHTO T 121). The results should be suf-ficiently accurate to determine the volumetric quantity(yield) of concrete produced per batch (see Chapter 9). Thetest also can give indications of air content provided therelative densities of the ingredients are known. A balanceor scale sensitive to 0.3% of the anticipated mass of the

280


Fig. 16-4. Fresh concrete is measured in a container ofknown volume to determine density (unit weight). (69785)

Fig. 16-3. A thermometer is used to take the temperature offresh concrete. (69885A)

normal-weight aggregates are relatively constant and,though small, should be subtracted from the pressure metergauge reading to obtain the correct air content. The instru-ment should be calibrated for various elevations above sealevel if it is to be used in localities having considerabledifferences in elevation. Some meters utilize change in pres-sure of a known volume of air and are not affected bychanges in elevation. Pressure meters are widely usedbecause the mix proportions and specific gravities of theconcrete ingredients need not be known. Also, a test can beconducted in less time than is required for other methods.

The volumetric method (Fig. 16-6) outlined in ASTMC 173 (AASHTO T 196) requires removal of air from aknown volume of concrete by agitating the concrete in anexcess of water. This method can be used for concrete con-taining any type of aggregate, including lightweight orporous materials. An aggregate correction factor is notnecessary with this test. The volumetric test is not affectedby atmospheric pressure, and specific gravity of theconcrete ingredients need not be known. Care must betaken to agitate the sample sufficiently to remove all air.The addition of 500 mL (1 pt) of alcohol accelerates theremoval of air, thus shortening test times; it also dispelsmost of the foam and increases the precision of the test,including those performed on high-air-content or high-cement-content concretes.

The gravimetric method utilizes the same test equip-ment used for determining the density (unit weight) ofconcrete. The measured density of concrete is subtractedfrom the theoretical density as determined from the abso-lute volumes of the ingredients, assuming no air is present(see ASTM C 138 or AASHTO T 121). This difference,

expressed as a percentage of the theoretical density, is theair content. Mixture proportions and specific gravities ofthe ingredients must be accurately known; otherwiseresults may be in error. Consequently, this method is suit-able only where laboratory-type control is exercised.Significant changes in density can be a convenient way todetect variability in air content.

A pocket-size air indicator (AASHTO T 199) can beused as a quick check for the presence of low, medium, orhigh levels of air in concrete, but it is not a substitute forthe other more accurate methods. A representative sampleof mortar from the concrete is placed in the container. Thecontainer is then filled with alcohol and rolled with thethumb over the open end to remove the air from themortar. The indicated air content is determined bycomparing the drop in the level of the alcohol with a cali-bration chart. The test can be performed in a few minutes.It is especially useful in checking for the presence of air inconcrete near the surface that may have suffered reduc-tions in air because of faulty finishing procedures.

With any of the above methods, air-content testsshould be started within 5 minutes after the final portion ofthe composite sample has been obtained.

Studies into the effect of fly ash on the air-void stabilityof concrete have resulted in the development of the foam-index test. The test can be used to measure the relative air-entraining admixture requirements for concrete mixturescontaining fly ash. The fly ash to be tested is placed in awide mouth jar along with the air-entraining admixtureand shaken vigorously. Following a waiting period of 45seconds, a visual determination of the stability of the foamor bubbles is made (Gebler and Klieger 1983).

281


Fig. 16-5. Pressure-type meter for determining air content.(69766)

Fig. 16-6. Volumetric air meter. (69886)


Strength Specimens

Specimens molded for strength tests should be made andcured in accordance with ASTM C 31 or AASHTO T 23(field-molded specimens) or ASTM C 192 or AASHTO T126 (laboratory-molded specimens). Molding of strengthspecimens should be started within 15 minutes after thecomposite sample is obtained.

The standard test specimen for compressive strengthof concrete with a maximum aggregate size of 50 mm(2 in.) or smaller is a cylinder 150 mm (6 in.) in diameterby 300 mm (12 in.) high (Fig. 16-7). For larger aggregates,the diameter of the cylinder should be at least three timesthe maximum-size aggregate, and the height should betwice the diameter. While rigid metal molds are preferred,parafined cardboard, plastic, or other types of disposablemolds conforming to ASTM C 470 can be used. Theyshould be placed on a smooth, level, rigid surface andfilled carefully to avoid distortion of their shape.

A 100-mm (4-in.) diameter by 200-mm (8-in.) highcylinder mold has been commonly used with high strengthconcrete containing up to 19 mm (3⁄4 in.) maximum-sizeaggregate (Burg and Ost 1994, Forstie and Schnormeier1981, and Date and Schnormeier 1984). The 100 x 200-mmcylinder is easier to cast, requires less sample, weighs con-siderably less than a 150 x 300-mm (6 x 12-in.) concretecylinder; it is therefore easier to handle and requires lessmoist-curing storage space. In addition, the smaller cross-sectional area allows higher compressive strengths to bereached by a testing machine that has a smaller load capac-ity. The difference in indicated strength between the twocylinder sizes is insignificant as illustrated in Fig. 16-8. Thestandard deviation and coefficient of variation of 100-mm

cylinders is slightly higher orsimilar to that for 150-mmcylinders (Burg and others 1999and Pistilli and Willems 1993).The predominant size used inCanada is the 100-mm diametercylinder. Consult job specifica-tions for allowable cylinder sizes.

Beams for the flexuralstrength test should be 150 x 150mm (6 x 6 in.) in cross section foraggregates up to 50 mm (2 in.).For larger aggregates, the mini-mum cross-sectional dimensionshould be not less than threetimes the maximum size ofaggregate. The length of beamsshould be at least three timesthe depth of the beam plus 50mm (2 in.), or a total length ofnot less than 500 mm (20 in.) fora 6 x 6-in. beam.

Test cylinders to be rodded(slump of 25 mm [1 in.] or more)should be filled in three approx-imately equal layers with each

282

25,000

20,000

15,000

10,000

5,000

0

0 5,000 10,000 15,000 20,000 25,000

160

120

80

40

0

6x12-in. cylinder strength, psi

150x300 mm cylinder strength, MPa

4x8-

in. c

ylin

der

stre

ngth

, psi

100x

200-

mm

cyl

inde

r st

reng

th, M

Pa

40 80 120 1600

Moist curedAir curedBest fit line

Fig. 16-8. Comparison of 100 x 200-mm (4 x 8-in.) and 150 x 300-mm (6 x 12-in.) cylinderstrengths (Burg and Ost 1994).

Fig. 16-7. Preparing standard test specimens forcompressive strength of concrete. (69790)

layer rodded 25 times for 150-mm (6-in.) diameter cylinders;beam specimens up to 200 mm (8 in.) deep should be filled intwo equal layers with each layer rodded once with a 16-mm(5⁄8-in.) rod for each 1400 mm2 (2 in.2) of the specimen’s topsurface area. If the rodding leaves holes, the sides of the moldshould be lightly tapped with a mallet or open hand. Cylin-ders to be vibrated should be filled in two layers with one in-sertion per layer for 100-mm (4-in.) diameter cylinders andtwo insertions per layer for 150-mm (6-in.) cylinders.

Beams over 200 mm (8 in.) deep and cylinders 300 to450 mm (12 to 18 in.) deep to be vibrated (slump of 75mm[3 in.] or less) should be filled in two layers; beams 150 to200 mm (6 to 8 in.) deep to be vibrated can be filled in onelayer. Internal vibrators should have a maximum width ofno more than 1⁄3 the width of beams or 1⁄4 the diameter ofcylinders. Immediately after casting, the tops of the speci-mens should be (1) covered with an oiled glass or steelplate, (2) sealed with a plastic bag, or (3) sealed with aplastic cap.

The strength of a test specimen can be greatly affectedby jostling, changes in temperature, and exposure todrying, particularly within the first 24 hours after casting.Thus, test specimens should be cast in locations where sub-sequent movement is unnecessary and where protection ispossible. Cylinders and test beams should be protectedfrom rough handling at all ages. Remember to identifyspecimens on the exterior of the mold to prevent confusionand errors in reporting. Do not etch identification numbersinto the surface of fresh concrete test specimens. Use tapeor identification tags that do not damage the sample.

Standard testing procedures require that specimensbe cured under controlled conditions, either in the labora-tory (Fig. 16-9) or in the field. Controlled laboratory curing

in a moist roomor in a limewaterstorage tank givesan accurate in-dication of thequality of the con-crete as delivered.Limewater mustbe saturated withhydrated lime,not agriculturallime, in accor-dance with ASTMC 511 (AASHTOM 201) to preventleaching of limefrom concrete spe-cimens.

Specimenscured in the fieldin the same man-ner as the struc-ture more closelyrepresent the ac-

tual strength of concrete in the structure at the time oftesting; however, they give little indication of whether adeficiency is due to the quality of the concrete as deliveredor to improper handling and curing. On some projects,field-cured specimens are made in addition to those des-tined for controlled laboratory curing; these are especiallyuseful when the weather is unfavorable, to determinewhen forms can be removed, or when the structure can beput into use. For more information see “Strength Tests ofHardened Concrete” in this chapter and ASTM (2000).

In-place concrete strength development can also beevaluated by maturity testing (ACI Committee 306 andASTM C 1074), which was discussed in Chapter 14.

Time of SettingTest method ASTM C 403 (AASHTO T 197) is used todetermine the time of setting of concrete by means of pene-tration resistance measurements made at regular timeintervals on mortar sieved from the concrete mixture (Fig.

283


Fig. 16-9. Controlled moist curing in thelaboratory for standard test specimensat a relative humidity of 95% to 100%and temperature of 23±2°C (73±3°F)(ASTM C 511 or AASHTO M 201). (8974)

35

28

21

14

7

0

5

4

3

2

1

0180 210 240 270 300 330 360 390 420

Final setting

Initial setting

Elapsed time, min.

Pen

etra

tion

resi

stan

ce, M

Pa

Pen

etra

tion

resi

stan

ce, 1

000

psi

Fig. 16-10. (top) Time of setting equipment. (bottom) Plot oftest results. (69788)

Portland Cement Content,Water Content, and Water-Cement Ratio

Test methods are available for estimating the portlandcement and water content of freshly mixed concrete.These test results can assist in determining the strengthand durability potential of concrete prior to setting andhardening and can indicate whether or not the desiredcement and water contents were obtained. ASTM testmethods C 1078-87 and C 1079-87 (discontinued in 1998),based on the Kelly-Vail method, can be used to determinecement content and water content, respectively. Exper-imental methods using microwave absorption have beendeveloped to estimate water to cement ratio. The disad-vantage of these test methods is they require sophisticatedequipment and special operator skills, which may not bereadily available.

Other tests for determining cement or water contentscan be classified into four categories: chemical determina-tion, separation by settling and decanting, nuclear related,and electrical. The Rapid Analysis Machine and nuclearcement gage have been used to measure cement contents(Forester, Black, and Lees 1974 and PCA 1983). The micro-wave oven (AASHTO T 23) and neutron-scattering meth-ods have been used to measure water contents. For anoverview of these and other tests from all four categories,see Lawrence (1994). A combination of these tests can berun independently of each other to determine eithercement content or water content to calculate the water-cement ratio.

Supplementary Cementitious Materials Content

Standard test methods are not available for determiningthe supplementary cementitious materials content offreshly mixed concrete. However, the presence of certainsupplementary cementitious materials, such as fly ash,can be determined by washing a sample of the concrete’smortar over a 45 µm (No. 325) sieve and viewing theresidue retained with a stereo microscope (150 to 250X)(Fig. 16-11). Fly ash particles appear as spheres of variouscolors. Sieving the mortar through a 150 or 75 µm (No. 100or 200) sieve is helpful in removing sand grains.

Bleeding of Concrete

The bleeding properties of fresh concrete can be deter-mined by two methods described in ASTM C 232(AASHTO T 158). One method consolidates the specimenby tamping without further disturbance; the other methodconsolidates the specimen by vibration after which thespecimen is vibrated intermittently throughout the test.The amount of bleed water at the surface is expressed asthe volume of bleed water per unit area of exposedconcrete, or as a percentage of the net mixing water in thetest specimen. Typical values range from 0.01 to 0.08

16-10). The initial and final time of setting is determined asthe time when the penetration resistance equals 3.4 MPa(500 psi) and 27.6 MPa (4000 psi), respectively. Typically,initial set occurs between 2 and 6 hours after batching andfinal set occurs between 4 and 12 hours. The rate of hard-ening of concrete greatly influences the rate of which con-struction progresses. Temperature, water-cementing mate-rials ratio, and admixtures all affect setting time.

Accelerated Compression Teststo Project Later-Age Strength

The need to assess the quality of concrete at early ages incomparison to traditional 28-day tests has received muchattention due to the quickening pace of today’s construc-tion. ASTM has developed two methods for estimatinglater-age strengths of concrete specimens based uponearly-age tests.

ASTM C 684 uses accelerated strength tests to expe-dite quality control of concrete. Cylinder strength tests areaccelerated using one of four curing procedures: warmwater at 35°C ± 3°C (95°F ± 5°F), boiling water, autogenous(insulated), and high temperature at 150°C ± 3°C (300°F ±5°F). Accelerated strength tests are performed at agesranging between 5 and 49 hours, depending on the curingprocedure used. Later-age strengths are estimated usingpreviously established relationships between acceleratedstrength and standard 28-day compressive strength tests.

ASTM C 918 uses the maturity method of monitoringtemperature of cylinders cured in accordance with stan-dard methods outlined in ASTM C 31 (AASHTO T 23).Cylinders are tested at early ages beyond 24 hours, andthe concrete temperature history is used to compute thematurity index at the time of test. Using historic data, aprediction equation is developed to project the strength atlater ages based on the maturity index and early-agestrength tests. See Carino (1994).

Chloride Content

The chloride content of concrete and its ingredientsshould be checked to make sure it is below the limit nec-essary to avoid corrosion of reinforcing steel. An approxi-mation of the water-soluble chloride content of freshlymixed concrete, aggregates, and admixtures can be madeusing a method initiated by the National Ready MixedConcrete Association (NRMCA 1986). A determination ofthe total chloride content of freshly mixed concrete may bemade by summing up the chloride contents of all of theindividual constituents of the mix. The NRMCA methodgives a quick approximation and should not be used todetermine compliance. See Chapter 9 for chloride-ionlimitations for concrete.

284


mL/cm2 or 0.1% to 2.5% of mix water. The bleeding test israrely used in the field (Fig. 16-12). Bleeding was alsodiscussed in Chapter 1.

TESTING HARDENED CONCRETE

Premolded specimens described in the previous section“Strength Specimens” (ASTM C 31 [AASHTO T 23], ASTMC 192 [AASHTO T 126], or ASTM C 873), or samples ofhardened concrete obtained from construction or labora-tory work (ASTM C 42 [AASHTO T 24], ASTM C 823, orASTM C 873) can be used in tests on hardened concrete.Separate specimens should be obtained for each testperformed because specimen preconditioning for certaintests can make the specimen unusable for other tests.

Strength Tests of Hardened Concrete

Strength tests of hardened concrete can be performed onthe following: (1) cured specimens molded in accordancewith ASTM C 31 or C 192 (AASHTO T 23 and T 126) fromsamples of freshly mixed concrete; (2) in-situ specimenscored or sawed from hardened concrete in accordance withASTM C 42 (AASHTO T 24); or (3) specimens made fromcast-in-place cylinder molds, ASTM C 873 (Fig. 16-13).

Cast-in-place cylinders can be used in concrete that is125 to 300 mm (5 to 12 in.) in depth. The mold is filled inthe normal course of concrete placement. The specimen isthen cured in place and in the same manner as the rest ofthe concrete section. The specimen is removed from theconcrete and mold immediately prior to testing to deter-mine the in-place concrete strength. This method is par-ticularly applicable in cold-weather concreting, post-tensioning work, slabs, or any concrete work where aminimum in-place strength must be achieved before con-struction can continue.

For all methods, cylindrical samples should have adiameter at least three times the maximum size of coarseaggregate in the concrete and a length as close to twice thediameter as possible. Correction factors are available inASTM C 42 (AASHTO T 24) for samples with lengths of 1to 2 times the diameter. Cores and cylinders with a heightof less than 95% of the diameter before or after cappingshould not be tested. Use of a minimum core diameter of95 mm (3.75 in.) is suggested where a length to diameter(L/D) ratio greater than one is possible.

Drilled cores should not be taken until the concretecan be sampled without disturbing the bond between themortar and the coarse aggregate. For horizontal surfaces,cores should be taken vertically and not near formed jointsor edges. For vertical or sloped faces, cores should betaken perpendicular to the central portion of the concreteelement. Although diamond-studded coring bits can cutthrough reinforcing steel, it should be avoided if possible

285


Fig. 16-11. Fly ash particles retained on a 45 µµm sieve afterwashing, as viewed through a microscope at 200X. (58949)

Fig. 16-12. ASTM C 232 (AASHTO T 158) test for bleeding ofconcrete; Method A without vibration. The container has aninside diameter of about 255 mm (10 in.) and height ofabout 280 mm (11 in.). The container is filled to a height ofabout 255 mm and covered to prevent evaporation of thebleed water. (69780)

Fig. 16-13. Concrete cylinders cast in place in cylindricalmolds provide a means for determining the in-place com-pressive strength of concrete. (69781)

pad. A cap is placed on one or both ends of the cylinder; thespecimen is then tested in accordance with ASTM C 39(AASHTO T 22) with the added step to stop the test at 10%of the anticipated load to check that the axis of the cylinderis vertical within a tolerance of 0.5°. If either the perpendic-ularity of the cylinder end, or the vertical alignment duringloading are not met, the load applied to the cylinder may beconcentrated on one side of the specimen. This can cause ashort shear fracture in which the failure plane intersects theend of the cylinder. This type of fracture usually indicatesthe cylinder failed prematurely, yielding results lower thanthe actual strength of the concrete. If perpendicularityrequirements are not met, the cylinder can be saw-cut,ground, or capped with a sulfur mortar compound inaccordance with ASTM C 617 (AASHTO T 231).

Short shear fractures can also be reduced by: dustingthe pad and end of cylinder with corn starch or talcumpowder, preventing excess water from cylinders or burlapfrom draining into the retainer and below the pad, andchecking bearing surfaces of retainers for planeness andindentations. In addition, annually clean and lubricate thespherically seated block and adjacent socket on thecompression machine.

Testing of specimens (Fig. 16-15) should be done inaccordance with (1) ASTM C 39 (AASHTO T 22) forcompressive strength, (2) ASTM C 78 (AASHTO T 97) forflexural strength using third-point loading, (3) ASTM C 293(AASHTO T 177) for flexural strength using center-pointloading, and (4) ASTM C 496 (AASHTO T 198) for splittingtensile strength. Fig. 16-16 shows the correlation betweencompressive strength and flexural strength test results.

For both pavement thickness design and pavementmixture proportioning, the modulus of rupture (flexuralstrength) should be determined by the third-point loadingtest (ASTM C 78 or AASHTO T 97). However, modulus ofrupture by center-point loading (ASTM C 293 or AASHTOT 177) or cantilever loading can be used for job control ifempirical relationships to third-point loading test resultsare determined before construction starts.

when obtaining compression test specimens. A cover-meter (electromagnetic device) or a surveyor’s magneticlocator can be used to locate reinforcing steel. Cores takenfrom structures should be tested in a moisture conditionas near as that of the in-place concrete as possible.Conditioning options for preparing specimens aredescribed in ASTM C 42 (AASHTO T 24) and ACI 318.

Fig. 16-14 shows the effects of core conditioning onthe strength of drilled core samples. Forty-eight hourwater immersion of the specimens prior to testing yieldssignificantly lower test results than air-drying specimensfor seven days prior to testing. Measured strengths variedby up to 25%, depending upon the time and type of condi-tioning prior to testing.

Flexure test specimens that are saw-cut from in-placeconcrete are always immersed in lime-saturated water at23.0°C ± 2.0°C (73.5°F ± 3.5°F) for at least 40 hours imme-diately prior to testing.

Test results are greatly influenced by the condition ofthe ends of cylinders and cores. For compression testing,specimens should be ground or capped in accordancewith the requirements of ASTM C 617 (AASHTO T 231) orASTM C 1231. Various commercially available materialscan be used to cap compressive test specimens. ASTM C617 (AASHTO T 231) outlines methods for using sulfurmortar capping. Caps must be allowed to harden at leasttwo hours before the specimens are tested. Unbondedneoprene caps can be used to test molded cylinders ifquick results are needed. Sulfur mortar caps should bemade as thin as is practical to avoid a cap failure thatmight reduce test results.

ASTM C 1231 describes the use of unbonded neoprenecaps that are not adhered or bonded to the ends of the spec-imen. This method of capping uses a disk-shaped 13 ± 2-mm (1⁄2 ± 1⁄16-in.) thick neoprene pad that is approximatelythe diameter of the specimen. The pad is placed in a cylin-drical steel retainer with a cavity approximately 25 mm(1 in.) deep and slightly smaller than the diameter of the

286


40

35

30

25

20

5900

5400

4900

4400

3900

3400

2900

Soak48 hr

Soak7 days

Air dry7 day

In bags1 day

In bags7 day

Str

engt

h, M

Pa

Str

engt

h, p

si

Fig. 16-14. Effect of core conditioning on strength of drilledcores (Fiorato, Burg and Gaynor 2000).

Fig. 16-15. Testing hardened concrete specimens: (left) cyl-inder, (right) beam (44178, 69684).

The moisture content of the specimen has considerableeffect on the resulting strength (Fig. 16-15). Beams for flex-ural tests are especially vulnerable to moisture gradienteffects. A saturated specimen will show lower compressivestrength and higher flexural strength than those forcompanion specimens tested dry. This is important toconsider when cores taken from hardened concrete in serv-ice are compared with molded specimens tested as takenfrom the moist-curing room or water storage tank.Cylinders used for acceptance testing for a specifiedstrength must be cured in accordance with ASTM C 31 andC 511 (AASHTO T 23 and M 201) to accurately representthe quality of the concrete. However, cores are subject toworkmanship, variable environmental site conditions, andvariable conditioning after extraction. Cores are tested ineither a dry or moist condition, but rarely in a saturatedcondition similar to lab-cured cylinders. Because cores andcylinders are handled in very different ways, they cannotbe expected to yield the same results.

The amount of variation in compressive-strengthtesting is far less than for flexural-strength testing. To avoidthe extreme care needed in field flexural-strength testing,compressive-strength tests can be used to monitor concretequality; however, a laboratory-determined empirical rela-tionship (Fig. 16-16) must be developed between the com-pressive and flexural strength of the concrete used(Kosmatka 1985a). Because of this empirical relationshipand the economics of testing cylinders instead of beams,most state departments of transportation are now utilizingcompression tests of cylinders to monitor concrete qualityfor their pavement and bridge projects.

Evaluation of Compression Test Results. The ACI 318building code states that the compressive strength ofconcrete can be considered satisfactory if the following

conditions are met: the averages of all sets of three consecu-tive strength tests equal or exceed the specified 28-daystrength ˘ and no individual strength test (average of twocylinders) is more than 3.5 MPa (500 psi) below the specifiedstrength. If the results of the cylinder tests do not meet thiscriteria, the strength of the in-place concrete should be eval-uated by drilled cores.

In addition to the two 28-day cylinders, job specifica-tions often require one or two 7-day cylinders and one ormore “hold” cylinders. The 7-day cylinders monitor earlystrength gain. Hold cylinders are commonly used toprovide additional information in case the 28-day cylin-ders are damaged or do not meet the required compres-sive strength. For low 28-day test results, the hold cylin-ders are typically tested at 56 days in age.

Protection and curing procedures should also be eval-uated to judge if they are adequate when field-cured cylin-ders have a strength of less than 85% of that of companionlaboratory-cured cylinders. The 85% requirement may bewaived if the field-cured strength exceeds ˘ by more than3.5 MPa (500 psi).

When necessary, the in-place concrete strength shouldbe determined by testing three cores for each strength testtaken in the portion of the structure where the laboratory-cured cylinders did not meet acceptance criteria. Moistureconditioning of cores prior to compression testing shouldfollow the guidelines in ASTM C 42 (AASHTO T 24) orACI 318.

Nondestructive test methods are not a substitute forcore tests (ASTM C 42 or AASHTO T 24). If the averagestrength of three cores is at least 85% of ˘, and if no singlecore is less than 75% of ˘, the concrete in the area repre-sented by the cores is considered structurally adequate. Ifthe results of properly made core tests are so low as toleave structural integrity in doubt, load tests as outlined inChapter 20 of ACI 318 may be performed. Refer toChapter 9 and NRMCA (1979), ACI Committee 214 (1997),and ACI Committee 318 (1999).

Air Content

The air-content and air-void-system parameters of hard-ened concrete can be determined by ASTM C 457. Thehardened air-content test is performed to assure that theair-void system is adequate to resist damage from a freeze-thaw environment. The test is also used to determine theeffect different admixtures and methods of placement andconsolidation have on the air-void system. The test can beperformed on premolded specimens or samples removedfrom the structure. Using a polished section of a concretesample, the air-void system is documented by makingmeasurements using a microscope. The informationobtained from this test includes the volume of entrainedand entrapped air, its specific surface (surface area of theair voids), the spacing factor, and the number of voids per

287


Square root of compressive strength, MPa

Square root of compressive strength, psiM

odul

us o

f rup

ture

, MP

a

Mod

ulus

of r

uptu

re, p

si

Standard moist-cured cylinders,150 x 300 mm (6 x 12 in.) nominalAges from 1 day to 5 years

200 40 8060 120100

6

1000

900

800

700

600

500

400

300

200

100

0

5

4

3

2

1

00 1 2 3 4 5 6 7 8 9 10

Fig. 16-16. Long-term data show that compressive strengthis proportional to the square root of flexural strength(measured by third-point loading) over a wide range ofstrength levels (Wood 1992).

should be noted that the boiling procedure in ASTM C 642can render the specimens useless for certain additionaltests, especially strength tests. The density can be obtainedby multiplying the relative density (specific gravity) bythe density of water (1000 kg/m3 or 62.4 lb/ft3).

Saturated, surface-dry density (SSD) is often requiredfor specimens to be used in other tests. In this case, thedensity can be determined by soaking the specimen inwater for 48 hours and then determining its weight in air(when SSD) and immersed in water. The SSD density isthen calculated as follows:

where

is density in the SSD condition

is the SSD mass in air, kg (lb)

is the apparent mass immersed in water, kg (lb)

is the density of water, 1000 kg/m3 (62.4 lb/ft3)

The SSD density provides a close indication of thefreshly mixed density of concrete. The density of hard-ened concrete can also be determined by nuclear methods(ASTM C 1040 or AASHTO T 271).

� M2

M1

DSSD

D

MM M

SSD =1

1 2

�

−

lineal distance (Fig. 16-17). See Chapter 8 “Air-EntrainedConcrete,” for more information.

Density, Relative Density (SpecificGravity), Absorption, and VoidsThe density, relative density (specific gravity), absorption,and voids content of hardened concrete can be determinedin accordance with ASTM C 642 procedures (Table 16-2). It

288


Fig. 16-17. View of concrete air-void system under a micro-scope. (67840)

Permeability AbsorptionCompressive Vol. of Absorption after im-

Cement, strength at 90 days Por- permeable after im- mersionMix kg/m3 90 days, RCPT, ponding, Water, Air, osity, voids, mersion, andNo. (lb/yd3) w/cm MPa (psi) coulombs % Cl m/s** m/s** %† % % boiling, %

ASTM ASTMC 39 C 1202

(AASHTO (AASHTO AASHTO API API ASTM ASTM ASTMT 22) T 277) T 259 RP 27 RP 27 C 642 C 642 C 642

1445

0.26*104.1

65 0.013 — 2.81 x 10-10 7.5 6.2 2.43 2.56(750) (15100)

2445

0.29*76.7

852 0.022 — 3.19 x 10-10 8.8 8.0 3.13 3.27(750) (11130)

3381

0.40*46.1

3242 0.058 2.61 x 10-13 1.16 x 10-9 11.3 12.2 4.96 5.19(642) (6690)

4327

0.5038.2

4315 0.076 1.94 x 10-12 1.65 x 10-9 12.5 12.7 5.45 5.56(550) (5540)

5297

0.6039.0

4526 0.077 2.23 x 10-12 1.45 x 10-9 12.7 12.5 5.37 5.49(500) (5660)

6245

0.7528.4

5915 0.085 8.32 x 10-12 1.45 x 10-9 13.0 13.3 5.81 5.90(413) (4120)

Table 16-2. Permeability and Absorption of Concretes Moist Cured 7 Days and Tested After 90 Days.

* Admixtures: 59.4 kg/m3 (100 lb/yd3) silica fume and 25.4 ml/kg of cement (30 fl.oz/cwt) HRWR (Mix 1); 13.0 ml/kg (20 fl.oz/cwt) HRWR(Mix 2); 2.2 ml/kg (3.4 fl. oz/cwt) WR (Mix 3).

** To convert from m/s to Darcy, multiply by 1.03 x 105, from m/s to m2, multiply by 1.02 x 10-7.† Measured with helium porosimetrie.

Adapted from Whiting (1988).

Portland Cement Content

The portland cement content of hardened concrete can bedetermined by ASTM C 1084 (AASHTO T 178) standardmethods. Although not frequently performed, the cementcontent tests are valuable in determining the cause of lackof strength gain or poor durability of concrete. Aggregatecontent can also be determined by these tests. However,the user of these test methods should be aware of certainadmixtures and aggregate types that can alter test results.The presence of supplementary cementitious materialswould be reflected in the test results.

Supplementary Cementitious Material and Organic Admixture Content

The presence and amount of certain supplementarycementitious materials, such as fly ash, can be determinedby petrographic techniques (ASTM C 856). A sample ofthe supplementary cementitious material used in the con-crete is usually necessary as a reference to determine thetype and amount of the supplementary cementitiousmaterial present. The presence and possibly the amount ofan organic admixture (such as a water reducer) can bedetermined by infrared spectrophotometry (Hime,Mivelaz, and Connolly 1966).

Chloride Content

Concern with chloride-induced corrosion of reinforcingsteel has led to the need to monitor and limit the chloridecontent of reinforced concrete. Limits on the water-solu-ble chloride-ion content of hardened reinforced concreteare given in ACI 318. The water-soluble chloride-ioncontent of hardened concrete can be determined in accor-dance with procedures outlined in ASTM C 1218. In addi-tion, ASTM C 1152 can be used to determine theacid-soluble chloride content of concrete which in mostcases is equivalent to total chloride.

Many of the above tests for chloride-ion content alsoextract chloride-ions from the fine and coarse aggregatesthat generally do not contribute to corrosion of reinforcingsteel. ASTM PS 118 (to be redesignated as ASTM C 1500) isa standard for the analysis of aggregate for water-extractable chloride (Soxhlet method). It is used whenchloride contents have been found to be significantly highin aggregates, concretes, or mortars when tested by eitherASTM C 1152 or C 1218. Because ASTM PS 118 does notpulverize the aggregates as other tests do, it theoreticallymeasures more closely the chloride-ions available for cor-rosion. ACI 222.1 is also a Soxhlet procedure that testschunks of concrete for water-extractable chloride. The truemeaning of results from the Soxhlet procedures is stillbeing debated.

Petrographic Analysis

Petrographic analysis uses microscopic techniquesdescribed in ASTM C 856 to determine the constituents ofconcrete, concrete quality, and the causes of inferior per-formance, distress, or deterioration. Estimating future per-formance and structural safety of concrete elements can befacilitated. Some of the items that can be reviewed by apetrographic examination include paste, aggregate, flyash, and air content; frost and sulfate attack; alkali-aggre-gate reactivity; degree of hydration and carbonation;water-cement ratio; bleeding characteristics; fire damage;scaling; popouts; effect of admixture; and several otheraspects. Almost any kind of concrete failure can be ana-lyzed by petrography (St. John, Poole, and Sims 1998).However, a standard petrographic analysis is sometimesaccompanied by “wet” chemical analyses, infrared spec-troscopy, X-ray diffractometry, scanning electronmicroscopy with attendant elemental analysis, differentialthermal analysis, and other analytical tools.

The Annex to ASTM C 856 (AASHTO T 299) describesa technique for field and laboratory detection of alkali-silica gel. Using this method, a uranyl-acetate solution isapplied to a broken or roughened concrete surface that hasbeen dampened with distilled or deionized water. Afterone minute, the solution is rinsed off and the treated sur-face is viewed under ultraviolet light. Areas of gel fluo-resce bright yellow-green. It must be recognized, however,that several materials not related to ASR in concrete canfluoresce and interfere with an accurate indication of ASRgel. Materials that fluoresce like gel include: naturally flu-orescent minerals, carbonated paste, opal, and some otherrock ingredients, and reactions from fly ash, silica fume,and other pozzolans. ASTM C 856 includes a prescreeningprocedure that gives a visual impression to compensatefor the effects of these materials. However, this test is con-sidered ancillary to more definitive petrographic examin-ations and other tests. In addition, the toxicity andradioactivity of uranyl acetate warrants special handlingand disposal procedures regarding the solution andtreated concrete. Caution regarding potential eye damagefrom ultraviolet light also merits attention.

The Los Alamos method is a staining technique thatdoes not require ultraviolet light or uranyl-acetate solu-tion. Instead, solutions of sodium cobaltinitrite and rho-damine B are used to condition the specimen and producea dark pink stain that corresponds to calcium-rich ASR gel.It should be noted that these methods can produce evi-dence of ASR gel without causing damage to concrete. ASRgel can be present when other mechanisms such asfreeze-thaw action, sulfate attack, and other deteriorationmechanisms have caused the damage. These rapid meth-ods for detecting the presence of ASR gel are useful buttheir limitations must be understood. Neither of the rapidprocedures is a viable substitute for petrographic examina-tion coupled with proper field inspection (Powers 1999).

289



Alkali-Silica Reactivity. Alkali-silica reaction is best con-trolled at the design stage when selecting materials for usein a specific concrete mixture. Aggregate can be tested forpotential alkali-silica reactivity by using the ASTM C 227mortar bar test (for moderate to highly reactive aggre-gate), ASTM C 289 chemical method (for highly reactiveaggregate), ASTM C 295 (petrographic analysis), ASTM C1260 (AASHTO T 303) rapid mortar bar, and ASTM C 1263concrete prism test. Materials, such as fly ash and slag, areoften used to control alkali-silica reaction; they should beevaluated by tests such as ASTM C 227, ASTM C 441,modified C 1260 (PCA 1998), or C 1293 to determine theireffectiveness. An alternate to testing aggregate separatelyfor potential reactivity is to test the concrete mixture to beused on the job; here one would use ASTM C 1260 (modi-fied) or C 1293. A rapid 13-week version of ASTM C 1293is being developed by the University of Texas at Austinthrough the International Center for Aggregate Research(Touma, Fowler, Folliard, and Nelson 2001). Existing con-crete structures can be evaluated for alkali-silica reactionusing ASTM C 856.

Alkali-Carbonate Reactivity. Alkali-carbonate reactivityis more rare than alkali-silica reactivity. Potential reactivityof aggregates can be evaluated by using ASTM C 295,ASTM C 586 rock cylinder, and ASTM C 1105. Existingconcrete structures can be evaluated for alkali-carbonatereaction using ASTM C 856.

Corrosion Resistance. The corrosion resistance of rein-forced concrete is rarely tested unless unusual materialsare used, concrete will be used in a very severe environ-ment, or there is a need to evaluate the potential for in-place corrosion. Corrosion activity can be evaluated usingASTM C 876.

Abrasion Resistance. Abrasion resistance can be deter-mined by using ASTM C 418 (sandblasting), ASTM C 779(revolving disk, dressing wheel, and ball bearingmethods), ASTM C 944 (rotating cutter), and ASTM C 1138(underwater test).

Volume and Length Change

Volume or length change limits are sometimes specifiedfor certain concrete applications. Volume change is also ofconcern when a new ingredient is added to concrete tomake sure there are no significant adverse effects. ASTM C157 (AASHTO T 160) (water and air storage methods)determines length change in concrete due to drying shrink-age, chemical reactivity, and forces other than those inten-tionally applied. Determination of early volume change ofconcrete before hardening can be performed using ASTMC 827. Creep can be determined in accordance with ASTMC 512. The static modulus of elasticity and Poisson’s ratioof concrete in compression can be determined by methodsoutlined in ASTM C 469 and dynamic values of theseparameters can be determined by using ASTM C 215.

Durability

Durability refers to the ability of concrete to resist deterio-ration from the environment or from the service in whichit is placed. Properly designed concrete should endurewithout significant distress throughout its service life. Inaddition to tests for air content and chloride contentdescribed previously, the following tests are used to meas-ure the durability of concrete:

Frost Resistance. The freeze-thaw resistance of concreteis usually determined in accordance with ASTM C 666(AASHTO T 161). Samples are monitored for changes indynamic modulus, mass, and volume over a period of 300or more cycles of freezing and thawing. ASTM C 617(AASHTO T 231) and ASTM C 682 are also available toevaluate frost resistance. Concrete that will be exposed todeicers as well as saturated freezing should be testedaccording to ASTM C 672 for deicer-scaling resistance.Although ASTM C 672 requires that only surface scalingbe monitored, many practitioners also measure mass loss,as is done in Canada (Fig. 16-18). Concrete mixtures thatperform well in ASTM C 666 (AASHTO T 161) do notalways perform well in ASTM C 672. ASTM C 666(AASHTO T 161) and ASTM C 672 are often used to eval-uate innovative mix designs, or new materials such aschemical admixtures, supplementary cementitious mate-rials, and aggregates to determine their effect on frost anddeicer resistance.

Sulfate Resistance. The sulfate resistance of concretematerials can be evaluated by using a saturated mortar bartest, ASTM C 1012. This test is valuable in assessing the sul-fate resistance of concrete that will be continuously wet,but it does not evaluate the more aggressive wet-drycycling environment. The test can be modified to includewet-dry cycling or the U.S. Bureau of Reclamation’s wet-dry concrete prism test for sulfate attack can be used.ASTM D 516 (AASHTO T 290) or the Bureau’s method(U.S. Bureau of Reclamation 1975) can be used to test soiland water for sulfate ion content to determine the severityof the sulfate exposure (ASTM is currently developing anew test).

290

0

1

2

3

4

5

0.01 0.10 1.00 10.00

Vis

ual r

atin

g

Mass loss (kg/m2)

y = –1.06 + 4.68 x 0.31

r2 = – 0.86

Fig. 16-18. Correlation between mass loss and visual ratingfor each specimen tested according to ASTM C 672 (Pintoand Hover 2001).

Moisture Testing

The in-place moisture content, water vapor emission rate,and relative humidity of hardened concrete are usefulindicators in determining if concrete is dry enough forapplication of floor-covering materials and coatings. Themoisture content of concrete should be low enough toavoid spalling when exposed to temperatures above theboiling point of water. Moisture related test methods fallinto two general categories: either qualitative or quantita-tive. Qualitative tests provide an indication of the pres-ence or absence of moisture while quantitative testsmeasure the amount of moisture. Qualitative tests maygive a strong indication that excessive moisture is presentand the floor is not ready for floor-covering materials.Quantitative tests are performed to assure that the floor isdry enough for these materials.

Qualitative moisture tests include: plastic sheet, matbond, electrical resistance, electrical impedance, andnuclear moisture gauge tests. The plastic sheet test (ASTMD 4263) uses a square sheet of clear plastic film that istaped to the slab surface and left for 24 hours to see ifmoisture develops under it. The plastic sheet test is unre-liable. In the mat bond test, a 1-m2 (9-ft2) sheet of floor cov-ering is glued to the floor with the edges taped to theconcrete for 72 hours. The force needed to remove theflooring is an indication of the slab moisture condition.Electrical resistance is measured using a moisture meterthrough two probes placed in contact with the concrete.Electrical impedance uses an electronic signal that is influ-enced by the moisture in the concrete. Nuclear moisturegauges contain high-speed neutrons that are slowed bythe hydrogen atoms in water. The affect of these encoun-ters is a measure of the moisture content of the concrete.Although the last three tests each yield a numeric testresult, their value is quite limited. Experience and skill areneeded to judge the trustworthiness of the devices and thetest results produced by them.

Quantitative test methods include: gravimetric mois-ture content, moisture vapor emission rate, and relativehumidity probe tests. The most direct method for deter-mining moisture content is to dry cut a specimen from theconcrete element in question, place it in a moisture proofcontainer, and transport it to a laboratory for testing. Afterobtaining the specimen’s initial mass, dry the specimen inan oven at about 105°C (220°F) for 24 hours or until con-stant mass is achieved. The difference between the twomasses divided by the dry mass, times 100, is the moisturecontent in percent. The moisture vapor emission rate(ASTM F 1869) is the most commonly used test in theUnited States for measuring the readiness of concrete forapplication of floor coverings. The emission rate isexpressed as kilograms (pounds) of moisture emittedfrom 93 m2 (1000 ft2) in 24 hours. See Kosmatka (1985), andPCA (2000) for more information.

Relative humidity tests are used in several countriesoutside the United States for measuring moisture in con-

crete slabs. Two British standards, BS 5325: 1996 andBS 8203: 1996 use a hygrometer or relative humidity probesealed under an insulated, impermeable box to trap mois-ture in an air pocket above the floor. The probe is allowedto equilibrate for at least 72 hours or until two consecutivereadings at 24 hours intervals are within the precision ofthe instrument (typically ± 3% RH). Acceptable relativehumidity limits for the installation of floor coverings rangefrom a maximum of 60% to 90%. It can require severalmonths of air-drying to achieve the desired relativehumidity. A method for estimating drying time to reach aspecified relative humidity based on water-cement ratio,thickness of structure, number of exposed sides, relativehumidity, temperature and curing conditions can be foundin Hedenblad (1997), Hedenblad (1998), and Farny (2001).

Carbonation

The depth or degree of carbonation can be determined bypetrographic techniques (ASTM C 856) through the obser-vation of calcium carbonate—the primary chemical prod-uct of carbonation. In addition, a phenolphthalein colortest can be used to estimate the depth of carbonation bytesting the pH of concrete (carbonation reduces pH). Uponapplication of the phenolphthalein solution to a freshlyfractured or freshly cut surface of concrete, noncarbonatedareas turn red or purple while carbonated areas remaincolorless. (Fig. 16-19). The phenolphthalein indicatorwhen observed against hardened paste changes color at apH of 9.0 to 9.5. The pH of good quality noncarbonatedconcrete without admixtures is usually greater than 12.5.For more information, see “pH Testing Methods” below,and see Verbeck (1958), Steinour (1964), and Campbell,Sturm, and Kosmatka (1991).

291


Fig. 16-19. The depth of carbonation is determined byspraying phenolphthalein solution on a freshly broken con-crete surface. Noncarbonated areas turn red or purple, car-bonated areas stay colorless. (69804)

Each method has limitations and caution should be exer-cised against acceptance of nondestructive test results ashaving a constant correlation to the traditional compres-sion test; for example, empirical correlations must bedeveloped prior to use (Malhotra 1976, NRMCA 1979,Malhotra 1984, Clifton 1985, Malhotra and Carino 1991).

An NDT program may be undertaken for a variety ofpurposes regarding the strength or condition of hardenedconcrete, including:

• Determination of in-place concrete strength• Monitoring rate of concrete strength gain• Location of nonhomogeneity, such as voids or honey-

combing in concrete• Determination of relative strength of comparable

members• Evaluation of concrete cracking and delaminations• Evaluation of damage from mechanical or chemical

forces• Steel reinforcement location, size, and corrosion activity• Member dimensions

Irrespective of the type of NDT test used, adequateand reliable correlation data with standard 28-day com-pressive strength data is usually necessary to evaluate theaccuracy of the NDT method. In addition, correlation toin-place compressive strengths using drilled cores fromone or two locations can provide guidance in interpretingNDT test results; these can then be used to survey largerportions of the structure. Care should be taken to considerthe influence that varying sizes and locations of structuralelements can have on the NDT test being used.

Rebound Hammer Tests. The Schmidt rebound hammer(Fig. 16-20) is essentially a surface-hardness tester thatprovides a quick, simple means of checking concreteuniformity. It measures the rebound of a spring-loaded

pH Testing Methods

There are three practical methods for measuring the pH ofhardened concrete in the field. The first uses litmus paperdesigned for the alkaline range of pH readings. Place a fewdrops of distilled water on the concrete, wait 60 ± 5 sec-onds and immerse an indicator strip (litmus paper) in thewater for 2 to 3 seconds. After removing the strip, compareit to the standard pH color scale supplied with the indi-cator strips. A second method uses a pH “pencil.” Thepencil is used to make a 25 mm (1 in.) long mark afterwhich 2 to 3 drops of distilled water are placed on themark. After waiting 20 seconds, the color is compared to astandard color chart to judge the pH of the concrete.Finally, the third method uses a wide-range liquid pH indi-cator on a freshly fractured surface of the concrete or a coreobtained from the concrete. After several minutes, theresulting color is compared to a color chart to determinethe pH of the concrete. This method is also effective formeasuring the depth of carbonation present on theconcrete surface. See PCA (2000) for more information.

Permeability

Both direct and indirect methods of determining perme-ability are used. Table 16-2 shows typical concrete perme-abilities. Resistance to chloride-ion penetration, forexample, can be determined by ponding chloride solutionon a concrete surface and, at a later age, determining thechloride content of the concrete at particular depths(AASHTO T 259). The rapid chloride permeability test(RCPT) (ASTM C 1202 and AASHTO T 277), also calledthe Coulomb or electrical resistance test, is often specifiedfor concrete bridge decks. Various absorption methods,including ASTM C 642, are used. Direct water perme-ability data can be obtained by using the Army Corp ofEngineers CRC C 163-92 test method for water perme-ability of concrete using a triaxial cell. A test method rec-ommended by the American Petroleum Institute fordetermining the permeability of rock is also available.ASTM is in the process of developing a standard methodfor hydraulic permeability of concrete. All the above testmethods have limitations. For more information, seeAmerican Petroleum Institute (1956), Tyler and Erlin(1961), Whiting (1981), Pfeifer and Scali (1981), andWhiting (1988).

Nondestructive Test Methods

Nondestructive tests (NDT) can be used to evaluate therelative strength and other properties of hardened con-crete. The most widely used are the rebound hammer,penetration, pullout, and dynamic or vibration tests.Other techniques for testing the strength and other prop-erties of hardened concrete include X-rays, gamma radi-ography, neutron moisture gages, magnetic cover meters,electricity, microwave absorption, and acoustic emissions.

292


Fig. 16-20. The rebound hammer gives an indication of thecompressive strength of concrete. (69782)

plunger after it has struck a smooth concrete surface. Therebound number reading gives an indication of the com-pressive strength and stiffness of the concrete. Two dif-ferent concrete mixtures having the same strength butdifferent stiffnesses will yield different readings. In viewof this, an understanding of the factors influencing theaccuracy of the test is required.

The results of a Schmidt rebound hammer test (ASTMC 805) are affected by surface smoothness, size, shape, andrigidity of the specimen; age and moisture condition of theconcrete; type of coarse aggregate; and degree of carbona-tion of the concrete surface. When these limitations arerecognized; and the hammer is calibrated for the partic-ular materials used in the concrete (Fig. 16-21) by compar-ison with cores or cast specimens, then this instrument canbe useful for determining the relative compressivestrength and uniformity of concrete in the structure.

Penetration Tests. The Windsor probe (ASTM C 803),like the rebound hammer, is basically a hardness testerthat provides a quick means of determining the relativestrength of the concrete. The equipment consists of apowder-actuated gun that drives a hardened alloy probeinto the concrete (Fig. 16-22). The exposed length of theprobe is measured and related by a calibration table to thecompressive strength of the concrete.

The results of the Windsor-probe test will be influ-enced by surface smoothness of the concrete and the typeand hardness of aggregate used. Therefore, to improveaccuracy, a calibration table or curve for the particularconcrete to be tested should be made, usually from coresor cast specimens.

Both the rebound hammer and the probe damage theconcrete surface to some extent. The rebound hammerleaves a small indentation on the surface; the probe leavesa small hole and may cause minor cracking and smallcraters similar to popouts.

Maturity Tests. The maturity principle is that strengthgain is a function of time and temperature. ASTM C 1074generates a maturity index that is based on temperatureand time factors. The estimated strength depends onproperly determining the strength-maturity function for aparticular concrete mixture. The device uses thermocou-ples or thermistors placed in the concrete and connectedto strip-chart recorders or digital data-loggers that recordconcrete temperature as a function of time. The tempera-ture in relation to time data is correlated to compressiontests performed on cylindrical specimens to generate atemperature-time versus strength curve that is used toestimate in-place concrete strength.

Pullout Tests. A pullout test (ASTM C 900) involvescasting the enlarged end of a steel rod in the concrete to betested and then measuring the force required to pull it out(Fig. 16-23). The test measures the direct shear strength ofthe concrete. This in turn is correlated with the compres-sive strength; thus a measurement of the in-placecompressive strength is made.

Break-Off Tests. The break-off test (ASTM C 1150) deter-mines the in-place strength of the concrete by breaking offan in situ cylindrical concrete specimen at a failure planeparallel to the finished surface of the concrete element. Abreak-off number is generated and assessed in relation tothe strength of the concrete. Similar to pullout tests, therelationship between break-off test numbers and compres-

293


Fig. 16-22. The Windsor-probetechnique for determining therelative compressive strengthof concrete.(top) Powder-actuated gundrives hardened alloy probeinto concrete. (69783)(left) Exposed length of probeis measured and relative com-pressive strength of theconcrete then determined froma calibration table. (69784)

40

5000

4000

3000

2000

1000

30

20

10

0 0

Horizontal positionConcrete: saturated surface dryLimestone aggregate

10 15 20 25 30 35 40Rebound reading

Com

pres

sive

str

engt

h, M

Pa

Com

pres

sive

str

engt

h, p

si

Fig. 16-21. Example of a calibration chart for an impact(rebound) test hammer.

C 1040 (AASHTO T 271) procedures use gamma radiationto determine the density of unhardened and hardenedconcrete in place.

Battery-operated magnetic detection devices, like thepachometer or covermeter, are available to measure thedepth of reinforcement in concrete and to detect the positionof rebars. Electrical-resistivity equipment is being developedto estimate the thickness of concrete pavement slabs.

A microwave-absorption method has been developedto determine the moisture content of porous buildingmaterials such as concrete. Acoustic-emission techniquesshow promise for studying load levels in structures andfor locating the origin of cracking.

Ground-penetrating (short-pulse) radar is a rapidtechnique for nondestructive detection of delaminationsand other types of defects in overlaid reinforced concretedecks. It also shows potential for monitoring strengthdevelopment in concrete, measuring the thickness ofconcrete members, and locating reinforcement.

Infrared thermographic techniques are used to detectand show, both large and small, internal voids, delamina-tions and cracks in bridges, highway pavements, garagedecks, buildings and other structural elements exposed todirect sunlight. For more information, see Malhotra andCarino (1991). ACI Committee 228 (1998) presents addi-tional information on these and other nondestructivetest methods.

Finally, acoustic impact methods also employ simplehammer and chain drag soundings that are low-cost accu-rate tests used to identify delaminated areas of concrete.Hammer soundings can be used on either vertical or hor-izontal surfaces, but are usually limited to small areas ofdelaminations. These areas are identified by striking thesurface of the concrete with a hammer while listening foreither a ringing or hollow sound. Dragging either a singlechain, in small areas, or for larger areas, a T-bar with orwithout wheels having four or more chains attached arealso used to identify delaminated concrete (ASTM D4580). Approximately one meter (3 ft) of chain is in contactwith the concrete during chain drag soundings. Thesound emitted indicates whether the concrete is delami-nated or not. Chain drag soundings are usually limited tohorizontal surfaces that have a relatively rough texture.Smooth concrete may not bounce the chain links enoughto generate adequate sound to detect delaminated areas.Note that corrosion of reinforcing bars in the area ofdelaminated concrete will probably extend beyond theboundary identified as delaminated.

Table 16-3 lists several nondestructive test methodsalong with main applications.

sion tests must also be developed prior to obtaining finaltest results.

For more information on test methods used to estimatein-place concrete strengths, see ACI Committee 228 (1995).

Dynamic or Vibration Tests. A dynamic or vibration(ultrasonic pulse velocity) test (ASTM C 597) is based on theprinciple that velocity of sound in a solid can be measuredby (1) determining the resonant frequency of a specimen, or(2) recording the travel time of short pulses of vibrationsthrough a sample. High velocities are indicative of goodconcrete and low velocities are indicative of poor concrete.

Resonant frequency methods employ low-frequencyvibration to impart mechanical energy used to detect,locate, and record discontinuities within solids. Resonantfrequency is a function of the dynamic modulus of elas-ticity, poisson ratio, density, and geometry of the structuralelement. The presence and orientation of surface andinternal cracking can be determined. In addition, funda-mental transverse, longitudinal, and torsional frequenciesof concrete specimens can also be determined by ASTM C215, a method frequently used in laboratory durabilitytests such as freezing and thawing (ASTM C 666 orAASHTO T 161).

Stress wave propagation methods using impact-echotests are employed in ASTM C 1383 to measure P-wavespeeds and the thickness of concrete elements such asslabs, pavements, bridge decks and walls. The advantageof the test is that its not only nondestructive, but alsoaccess is only required to one side of the structure. Otherstress-wave methods not yet mentioned include: ultra-sonic-echo and spectral analysis of surface waves.

Other Tests. The use of X-rays for testing concrete prop-erties is limited due to the costly and dangerous high-voltage equipment required as well as radiation hazards.

Gamma-radiography equipment can be used in thefield to determine the location of reinforcement, density, andperhaps honeycombing in structural concrete units. ASTM

294


Fig. 16-23. Pullout test equipment being used to measurethe in-place strength of concrete. (44217)

REFERENCES

ACI Committee 214, Recommended Practice for Evaluation ofStrength Test Results of Concrete, ACI 214-77, reapproved1997, American Concrete Institute, Farmington Hills,Michigan, 1997, 14 pages.

ACI Committee 222, Provisional Standard Test Method forWater Soluble Chloride Available for Corrosion of EmbeddedSteel in Mortar and Concrete Using the Soxhlet Extractor, ACI222.1-96, American Concrete Institute, Farmington Hills,Michigan, 1996, 3 pages.

ACI Committee 228, In-Place Methods to Estimate ConcreteStrength, ACI 228.1R-95, American Concrete Institute,Farmington Hills, Michigan, 1995, 41 pages.

ACI Committee 228, Nondestructive Test Methods forEvaluation of Concrete in Structures, ACI 228.2R-98,American Concrete Institute, Farmington Hills, Michigan,1998, 62 pages.

ACI Committee 306, Cold-Weather Concreting, ACI 306R-88,reapproved 1997, American Concrete Institute, FarmingtonHills, Michigan, 1997, 23 pages.

ACI Committee 318, Building Code Requirements for Struc-tural Concrete and Commentary, ACI 318-02, American Con-crete Institute, Farmington Hills, Michigan, 2002, 369 pages.

ACI Committee 364, Guide for Evaluation of Concrete Struc-tures Prior to Rehabilitation, ACI 364.1 R-94, American Con-crete Institute, Farmington Hills, Michigan, 1994, 22 pages.

American Petroleum Institute, Recommended Practice forDetermining Permeability of Porous Media, API RP 27,American Petroleum Institute, Washington, D.C., 1956.

Angles, J., “Measuring Workability,” 8(12), Concrete, 1974,page 26.

ASTM, Manual of Aggregate and Concrete Testing, AmericanSociety for Testing and Materials, West Conshohocken,Pennsylvania, 2000.

Bartos, P., “Workability of Flowing Concrete—Assessmentby a Free Orifice Rheometer,” 12(10), Concrete, 1978, pages28 to 30.

Bois, Karl J.; Mubarak, Khalid; and Zoughi, Reza, ASimple, Robust and On-Site Microwave Inspection Techniquefor Determining Water-to-Cement-Based Materials, PCA R&DSerial No. 2405, Portland Cement Association, 1999,46 pages.

295


Concrete properties Recommended NDT methods Possible NDT methods

Strength Penetration probeRebound hammerPullout methodsBreak off

General quality and uniformity Penetration probe Ultrasonic pulse echoRebound hammer Visual examinationUltrasonic pulse velocityGamma radiography

Thickness RadarGamma radiographyUltrasonic pulse echo

Stiffness Ultrasonic pulse velocity Proof loading (load-deflection)

Density Gamma radiography Neutron density gageUltrasonic pulse velocity

Rebar size and location Covermeter (pachometer) X-ray radiographyGamma radiography Ultrasonic pulse echo

Radar

Corrosion state of Electrical potentialreinforcing steel measurement

Presence of Acoustic impact Infrared thermographysubsurface voids Gamma radiography X-ray radiography

Ultrasonic pulse velocity Ultrasonic pulse echoRadarResonant frequency testing

Structural integrity of concrete Proof loading (load-deflection) Proof testing using acoustic emissionstructures

Table 16-3. Nondestructive Test Methods for Concrete

Adapted from ACI Subcommittee 364 (1994) and Clifton (1985).

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Forester, J. A.; Black, B. F.; and Lees, T. P., An Apparatus forRapid Analysis Machine, Technical Report, Cement andConcrete Association, Wexham Springs, Slough, England,April 1974

Forstie, Douglas A., and Schnormeier, Russell, “Develop-ment and Use of 4 by 8 Inch Concrete Cylinders inArizona,” Concrete International, American ConcreteInstitute, Farmington Hills, Michigan, July 1981, pages42 to 45.

Galloway, Joseph E., “Grading, Shape, and SurfaceProperties,” Significance of Tests and Properties of Concreteand Concrete-Making Materials, STP 169C, AmericanSociety for Testing and Materials, West Conshohocken,Pennsylvania, 1994, pages 401 to 410

Gebler, S. H., and Klieger, P., Effects of Fly Ash on the Air-Void Stability of Concrete, Research and DevelopmentBulletin RD085T, Portland Cement Association, http://www.portcement.org/pdf_files/RD085.pdf, 1983.

Hedenblad, Göran, Drying of Construction Water inConcrete—Drying Times and Moisture Measurement, T9,Swedish Council for Building Research, Stockholm, 1997,54 pages. [Available from Portland Cement Association asLT229]

Hedenblad, Göran, “Concrete Drying Time,” ConcreteTechnology Today, PL982, Portland Cement Association,http://www.portcement.org/pdf_files/PL982.pdf, 1998,pages 4 and 5.

Hime, W. G.; Mivelaz, W. F.; and Connolly, J. D., Use ofInfrared Spectrophotometry for the Detection and Identificationof Organic Additions in Cement and Admixtures in HardenedConcrete, Research Department Bulletin RX194, PortlandCement Association, http://www.portcement.org/pdf_files/RX194.pdf, 1966, 22 pages.

Kelly, R. T., and Vail, J. W., “Rapid Analysis of FreshConcrete,” Concrete, The Concrete Society, Palladian Pub-lications, Ltd., London, Volume 2, No. 4, April 1968, pages140-145; Volume 2, No. 5, May 1968, pages 206 to 210.

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Kosmatka, Steven H., “Compressive versus FlexuralStrength for Quality Control of Pavements,” Concrete Tech-nology Today, PL854, Portland Cement Association,http://www.portcement.org/pdf_files/PL854.pdf, 1985a,pages 4 and 5.

Burg, R. G.; Caldarone, M. A.; Detwiler, G.; Jansen, D. C.;and Willems, T. J., “Compression Testing of HSC: LatestTechnology.” Concrete International, American ConcreteInstitute, Farmington Hills, Michigan, August 1999, pages67 to 76.

Burg, Ron G., and Ost, Borje W., Engineering Properties ofCommercially Available High-Strength Concrete (IncludingThree-Year Data), Research and Development BulletinRD104, Portland Cement Association, 1994, 58 pages

Campbell, D. H.; Sturm, R. D.; and Kosmatka, S. H.,“Detecting Carbonation,” Concrete Technology Today,PL911, http://www.portcement.org/pdf_files/PL911.pdf,Portland Cement Association, March 1991, pages 1 to 5.

Carino, Nicholas J., “Prediction of Potential ConcreteStrength at Later Ages,” Significance of Tests and Propertiesof Concrete and Concrete-Making Materials, STP 169C,American Society for Testing and Materials, WestConshohocken, Pennsylvania, 1994, pages 140 to 152.

Clear, K. C., and Harrigan, E. T., Sampling and Testing forChloride Ion in Concrete, FHWA-RD-77-85, Federal High-way Administration, Washington, D.C., August 1977.

Clemena, Gerardo G., Determination of the Cement Contentof Hardened Concrete by Selective Solution, PB-213 855, Vir-ginia Highway Research Council, Federal Highway Ad-ministration, National Technical Information Service, U.S.Department of Commerce, Springfield, Virginia, 1972.

Clifton, James R., “Nondestructive Evaluation in Rehabil-itation and Preservation of Concrete and MasonryMaterials,” SP-85-2, Rehabilitation, Renovation, and Preser-vation of Concrete and Masonry Structures, SP-85, AmericanConcrete Institute, Farmington Hills, Michigan, 1985,pages 19 to 29.

The Concrete Society, Permeability of Concrete and ItsControl, The Concrete Society, London, 1985.

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de Larrard, F.; Szitkar, J.; Hu, C.; and Joly, M., “Design andRheometer for Fluid Concretes,” Proceedings, InternationalRILEM Workshop, Paisley, Scotland, March 2 to 3, 1993,pages 201 to 208.

Farny, James A., Concrete Floors on Ground, EB075, PortlandCement Association, 2001, 140 pages.

296


Kosmatka, Steven H., “Floor-Covering Materials andMoisture in Concrete,” Concrete Technology Today, PL853,Portland Cement Association, http://www.portcement.org/pdf_files/PL853.pdf, September 1985, pages 4 and 5.

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298


CHAPTER 17

High-Performance Concrete

• High modulus of elasticity• High abrasion resistance• High durability and long life in severe environments• Low permeability and diffusion• Resistance to chemical attack• High resistance to frost and deicer scaling damage• Toughness and impact resistance• Volume stability• Ease of placement• Compaction without segregation• Inhibition of bacterial and mold growth

High-performance concretes are made with carefullyselected high-quality ingredients and optimized mixturedesigns; these are batched, mixed, placed, compacted andcured to the highest industry standards. Typically, suchconcretes will have a low water-cementing materials ratioof 0.20 to 0.45. Plasticizers are usually used to make

these concretes fluid andworkable.

High-performanceconcrete almost alwayshas a higher strengththan normal concrete.However, strength is notalways the primary re-quired property. For ex-ample, a normal strengthconcrete with very highdurability and very lowpermeability is consid-ered to have high-performance properties.Bickley and Fung (2001)demonstrated that 40MPa (6,000 psi) high-performance concrete forbridges could be eco-nomically made whileFig. 17-1. High-performance concrete is often

used in bridges (left) and tall buildings (right).(70017, 70023)

High-performance concrete (HPC) exceeds the propertiesand constructability of normal concrete. Normal and spe-cial materials are used to make these specially designedconcretes that must meet a combination of performancerequirements. Special mixing, placing, and curing prac-tices may be needed to produce and handle high-perform-ance concrete. Extensive performance tests are usuallyrequired to demonstrate compliance with specific projectneeds (ASCE 1993, Russell 1999, and Bickley and Mitchell2001). High-performance concrete has been primarily usedin tunnels, bridges, and tall buildings for its strength, dura-bility, and high modulus of elasticity (Fig. 17-1). It has alsobeen used in shotcrete repair, poles, parking garages, andagricultural applications.

High-performance concrete characteristics are devel-oped for particular applications and environments; someof the properties that may be required include:

• High strength• High early strength

299

meeting durability factors for air-void sys-tem and resistance to chloride penetration.

Table 17-1 lists materials often used inhigh-performance concrete and why theyare selected. Table 17-2 lists properties thatcan be selected for high-performance con-crete. Not all properties can be achieved atthe same time. High-performance concretespecifications ideally should be perform-ance oriented. Unfortunately, many speci-fications are a combination of performancerequirements (such as permeability orstrength limits) and prescriptive require-ments (such as air content limits or dosageof supplementary cementing material(Ferraris and Lobo 1998). Table 17-3 pro-vides examples of high-performance con-crete mixtures used in a variety ofstructures. Selected high-performance con-cretes are presented in this chapter.

HIGH-EARLY-STRENGTHCONCRETE

High-early-strength concrete, also called fast-trackconcrete, achieves its specified strength at an earlier agethan normal concrete. The time period in which a speci-fied strength should be achieved may range from a few

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Table 17-1. Materials Used in High-Performance Concrete

Material Primary contribution/Desired propertyPortland cement Cementing material/durabilityBlended cement Cementing material/durability/high strengthFly ash Cementing material/durability/high strengthSlag Cementing material/durability/high strengthSilica fume Cementing material/durability/high strengthCalcined clay Cementing material/durability/high strengthMetakaolin Cementing material/durability/high strengthCalcined shale Cementing material/durability/high strengthSuperplasticizers FlowabilityHigh-range water reducers Reduce water to cement ratioHydration control admixtures Control settingRetarders Control settingAccelerators Accelerate settingCorrosion inhibitors Control steel corrosionWater reducers Reduce cement and water contentShrinkage reducers Reduce shrinkageASR inhibitors Control alkali-silica reactivityPolymer/latex modifiers DurabilityOptimally graded aggregate Improve workability and reduce paste demand

Table 17-2. Selected Properties of High-Performance Concrete

Property Test method Criteria that may be specifiedHigh strength ASTM C 39 (AASHTO T 22) 70 to 140 MPa (10,000 to 20,000 psi) at 28 to 91 daysHigh-early compressive strength ASTM C 39 (AASHTO T 22) 20 to 28 MPa (3000 to 4000 psi) at 3 to 12 hours or

1 to 3 days High-early flexural strength ASTM C 78 (AASHTO T 97) 2 to 4 MPa (300 to 600 psi) at 3 to 12 hours or 1 to

3 daysAbrasion resistance ASTM C 944 0 to 1 mm depth of wearLow permeability ASTM C 1202 (AASHTO T 277) 500 to 2000 coulombsChloride penetration AASHTO T 259 & T 260 Less than 0.07% Cl at 6 monthsHigh resistivity ASTM G 59Low absorption ASTM C 642 2% to 5%Low diffusion coefficient Wood, Wilson and Leek (1989) 1000 x 10–13 m/s

Test under development by ASTMResistance to chemical attack Expose concrete to saturated No deterioration after 1 year

solution in wet/dry environmentSulfate attack ASTM C 1012 0.10% max. expansion at 6 months for moderate sulfate

exposures or 0.5% max. expansion at 6 months forsevere sulfate exposure

High modulus of elasticity ASTM C 469 More than 40 GPa (5.8 million psi) (Aitcin 1998)High resistance to freezing and ASTM C 666, Procedure A Durability factor of 95 to 100 at 300 to thawing damage 1000 cycles (max. mass loss or expansion can

also be specified)High resistance to deicer scaling ASTM C 672 Scale rating of 0 to 1 or mass loss of 0 to 0.5 kg/m3 after

50 to 300 cyclesLow shrinkage ASTM C 157 Less than 400 millionths (Aitcin 1998)Low creep ASTM C 512 Less than normal concrete

hours (or even minutes) to several days. High-early-strength can be attained by using traditional concreteingredients and concreting practices, although sometimesspecial materials or techniques are needed.

High-early-strength can be obtained by using one or acombination of the following, depending on the age at

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Chapter 17 � High-Performance Concrete

which the specified strength must be achieved and on jobconditions:

1. Type III or HE high-early-strength cement2. High cement content (400 to 600 kg/m3 or 675 to 1000

lb/yd3)

Table 17-3 (Metric). Typical High-Performance Concretes Used in Structures

Mixture number 1 2 3 4 5 6Water, kg/m3 151 145 135 145 130 130Cement, kg/m3 311 398* 500 335* 513 315Fly ash, kg/m3 31 45 — — — 40Slag, kg/m3 47 — — 125 — —Silica fume, kg/m3 16 32* 30 40* 43 23Coarse aggregate, kg/m3 1068 1030 1100 1130 1080 1140Fine aggregate, kg/m3 676 705 700 695 685 710Water reducer, L/m3 1.6 1.7 — 1.0 — 1.5Retarder, L/m3 — 1.8 — — —Air, % 7 ± 1.5 5 – 8 — — — 5.5HRWR or plasticizer, L/m3 2.1 3 14 6.5 15.7 5.0Water to cementing materials ratio 0.37 0.30 0.27 0.29 0.25 0.34Comp. strength at 28 days, MPa 59 — 93 99 119 —Comp. strength at 91 days, MPa — 60 107 104 145 —

1. Wacker Drive bi-level roadway, Chicago, 2001.2. Confederation Bridge, Northumberland Strait, Prince Edward Island/New Brunswick, 1997.3. La Laurentienne Building, Montreal, 1984.4. BCE Place Phase 2, Toronto, 1993.5. Two Union Square, Seattle, 1988.6. Great Belt Link, East Bridge, Denmark, 1996.* Originally used a blended cement containing silica fume. Portland cement and silica fume quantities have been separated for comparison

purposes.

Table 17-3 (Inch-Pound Units). Typical High-Performance Concretes Used in Structures

Mixture number 1 2 3 4 5 6Water, lb/yd3 254 244 227 244 219 219Cement, lb/yd3 525 671* 843 565* 865 531Fly ash, lb/yd3 53 76 — — — 67Slag, lb/yd3 79 — — 211 — —Silica fume, lb/yd3 27 54* 51 67* 72 39Coarse aggregate, lb/yd3 1800 1736 1854 1905 1820 1921Fine aggregate, lb/yd3 1140 1188 1180 1171 1155 1197Water reducer, oz/yd3 41 47 — 27 — 38Retarder, oz/yd3 — — 48 — — —Air, % 7 ± 1.5 5 – 8 — — — 5.5HRWR or plasticizer, oz/yd3 55 83 375 175 420 131Water to cementing materials ratio 0.37 0.30 0.27 0.29 0.25 0.34Comp. strength at 28 days, psi 8,590 — 13,500 14,360 17,250 —Comp. strength at 91 days, psi — 8700 15,300 15,080 21,000 —

1. Wacker Drive bi-level roadway, Chicago, 2001.2. Confederation Bridge, Northumberland Strait, Prince Edward Island/New Brunswick, 1997.3. La Laurentienne Building, Montreal, 1984.4. BCE Place Phase 2, Toronto, 1993.5. Two Union Square, Seattle, 1988.6. Great Belt Link, East Bridge, Denmark, 1996.* Originally used a blended cement containing silica fume. Portland cement and silica fume quantities have been separated for comparison

purposes.

3. Low water-cementing materials ratio (0.20 to 0.45 bymass)

4. Higher freshly mixed concrete temperature5. Higher curing temperature6. Chemical admixtures7. Silica fume (or other supplementary cementing mate-

rials)8. Steam or autoclave curing9. Insulation to retain heat of hydration

10. Special rapid hardening cements.

High-early-strength concrete is used for prestressedconcrete to allow for early stressing; precast concrete forrapid production of elements; high-speed cast-in-placeconstruction; rapid form reuse; cold-weather construction;rapid repair of pavements to reduce traffic downtime;fast-track paving; and several other uses.

In fast-track paving, use of high-early-strength mix-tures allows traffic to open within a few hours after con-crete is placed. An example of a fast-track concretemixture used for a bonded concrete highway overlay con-sisted of 380 kg (640 lb) of Type III cement, 42 kg (70 lb) ofType C fly ash, 61⁄2% air, a water reducer, and a water-to-cementing materials ratio of 0.4. Strength data for this 40-mm (11⁄2-in.) slump concrete are given in Table 17-4. Figs.17-2 and 17-3 illustrate early strength development of con-cretes designed to open to traffic within 4 hours afterplacement. Fig. 17-4 illustrates the benefits of blanketcuring to develop early strength for patching or fast-trackapplications.

When designing early-strength mixtures, strengthdevelopment is not the only criteria that should be evalu-ated; durability, early stiffening, autogenous shrinkage,drying shrinkage, temperature rise, and other propertiesalso should be evaluated for compatibility with theproject. Special curing procedures, such as fogging, maybe needed to control plastic shrinkage cracking.

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Table 17-4. Strength Data for Fast-Track Bonded Overlay

Compressive strength, Flexural strength, Bond strength,Age MPa (psi) MPa (psi) MPa (psi)

4 hours 1.7 (252) 0.9 (126) 0.9 (120)

6 hours 7.0 (1020) 2.0 (287) 1.1 (160)

8 hours 13.0 (1883) 2.7 (393) 1.4 (200)

12 hours 17.6 (2546) 3.4 (494) 1.6 (225)

18 hours 20.1 (2920) 4.0 (574) 1.7 (250)

24 hours 23.9 (3467) 4.2 (604) 2.1 (302)

7 days 34.2 (4960) 5.0 (722) 2.1 (309)

14 days 36.5 (5295) 5.7 (825) 2.3 (328)

28 days 40.7 (5900) 5.7 (830) 2.5 (359)

Adapted from Knutson and Riley 1987

0

1

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3

4

5

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engt

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3 hours 4 hours 28 daysTime

Fig. 17-2. Strength development of a high-early strengthconcrete mixture using 390 kg/m3 (657 lb/yd3) of rapidhardening cement, 676 kg/m3 (1140 lb/yd3) of sand, 1115kg/m3 (1879 lb/yd3) of 25 mm (1 in.) nominal max. sizecoarse aggregate, a water to cement ratio of 0.46, a slumpof 100 to 200 mm (4 to 8 in.), and a plasticizer and retarder.Initial set was at one hour (Pyle 2001).

Type III

Type II/III

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Fig. 17-3. Strength development of high-early strengthconcrete mixtures made with 504 to 528 kg/m3 (850 to 890lb/yd3) of Type III or Type II/III cement, a nominal maximumsize coarse aggregate of 25 mm (1 in.), a water to cementratio of 0.30, a plasticizer, a hydration control admixture,and an accelerator. Initial set was at one hour (Pyle 2001).

HIGH-STRENGTH CONCRETE

The definition of high strength changes over the years asconcrete strength used in the field increases. This publica-tion considers high-strength concrete (HSC) to have astrength significantly beyond what is used in normal prac-tice. For example, today about 90% of ready mixed con-crete has a 28-day specified compressive strength rangingfrom 20 MPa (3000 psi) to 40 MPa (6000 psi), with most ofit between 28 MPa (4000 psi) and 35 MPa (5000 psi).Therefore, HSC considered here has a design strength of atleast 70 MPa (10,000 psi).

Most high-strength concrete applications are designedfor compressive strengths of 70 MPa (10,000 psi) or greateras shown in Tables 17-3 and 17-5. For strengths of 70 MPa(10,000 psi) and higher, stringent application of the bestpractices is required. Compliance with the guidelines and

303


Standard cure

Insulating Blanket

0

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700F

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Fig. 17-4. Effect of blanket insulation on fast-track concrete.The concrete had a Type I cement content of 421kg/m3 (710lb/yd3) and a water to cement ratio of 0.30 (Grove 1989).

Mix numberUnits per m3 1 2 3 4 5 6

Cement, Type I, kg 564 475 487 564 475 327Silica fume, kg — 24 47 89 74 27Fly ash, kg — 59 — — 104 87Coarse aggregate SSD (12.5 mm

crushed limestone), kg 1068 1068 1068 1068 1068 1121

Fine aggregate SSD, kg 647 659 676 593 593 742HRWR Type F, liters 11.6 11.6 11.22 20.11 16.44 6.3HRWR Type G, liters — — — — — 3.24Retarder, Type D, liters 1.12 1.05 0.97 1.46 1.5 —Water to cementing materials ratio 0.28 0.29 0.29 0.22 0.23 0.32

Fresh concrete propertiesSlump, mm 197 248 216 254 235 203Density, kg/ m3 2451 2453 2433 2486 2459 2454Air content, % 1.6 0.7 1.3 1.1 1.4 1.2Concrete temp., °C 24 24 18 17 17 23

Compressive strength, 100 x 200-mm moist-cured cylinders3 days, MPa 57 54 55 72 53 437 days, MPa 67 71 71 92 77 6328 days, MPa 79 92 90 117 100 8556 days, MPa 84 94 95 122 116 —91 days, MPa 88 105 96 124 120 92182 days, MPa 97 105 97 128 120 —426 days, MPa 103 118 100 133 119 —1085 days, MPa 115 122 115 150 132 —

Modulus of elasticity in compression, 100 x 200-mm moist-cured cylinders91 days, GPa 50.6 49.9 50.1 56.5 53.4 47.9

Drying shrinkage, 75 by 75 x 285-mm prisms7 days, millionths 193 123 100 87 137 —28 days, millionths 400 287 240 203 233 —90 days, millionths 573 447 383 320 340 —369 days, millionths 690 577 520 453 467 —1075 days, millionths 753 677 603 527 523 —

Table 17-5 (Metric). Mixture Proportions and Properties of Commercially Available High-Strength Concrete(Burg and Ost 1994)

cementing materials are usually incorporated into the con-crete mixture. This produces additional benefits in theform of reduced heat generation during hydration.

With use of low-slump or no-slump mixes, high-compressive-strength concrete is produced routinelyunder careful control in precast and prestressed concreteplants. These stiff mixes are placed in ruggedly-builtforms and consolidated by prolonged vibration or shockmethods. However, cast-in-place concrete uses morefragile forms that do not permit the same compactionprocedures, hence more workable concretes are necessaryto achieve the required compaction and to avoid segrega-

recommendations for preconstruction laboratory andfield-testing procedures described in ACI 363.2 are essen-tial. Concrete with a design strength of 131 MPa (19,000psi) has been used in buildings (Fig. 17-5).

Traditionally, the specified strength of concrete hasbeen based on 28-day test results. However, in high-riseconcrete structures, the process of construction is such thatthe structural elements in lower floors are not fully loadedfor periods of a year or more. For this reason, compressivestrengths based on 56- or 91-day test results are commonlyspecified in order to achieve significant economy in mate-rial costs. When later ages are specified, supplementary

304


Mix numberUnits per yd3 1 2 3 4 5 6

Cement, Type I, lb 950 800 820 950 800 551

Silica fume, lb — 40 80 150 125 45

Fly ash, lb — 100 — — 175 147

Coarse aggregate SSD (1⁄2 in. crushed limestone), lb 1800 1800 1800 1800 1800 1890

Fine aggregate SSD, lb 1090 1110 1140 1000 1000 1251

HRWR Type F, fl oz 300 300 290 520 425 163

HRWR Type G, fl oz — — — — — 84

Retarder, Type D, fl oz 29 27 25 38 39 —

Water to cementing materials ratio 0.28 0.29 0.29 0.22 0.23 0.32

Fresh concrete properties

Slump, in. 73⁄4 93⁄4 81⁄2 10 91⁄4 8

Density, lb/ft3 153.0 153.1 151.9 155.2 153.5 153.2

Air content, % 1.6 0.7 1.3 1.1 1.4 1.2

Concrete temp., °F 75 75 65 63 62 74

Compressive strength, 4 x 8-in. moist-cured cylinders

3 days, psi 8,220 7,900 7,970 10,430 7,630 6,170

7 days, psi 9,660 10,230 10,360 13,280 11,150 9,170

28 days, psi 11,460 13,300 13,070 17,000 14,530 12,270

56 days, psi 12,230 13,660 13,840 17,630 16,760 —

91 days, psi 12,800 15,170 13,950 18,030 17,350 13,310

182 days, psi 14,110 15,160 14,140 18,590 17,400 —

426 days, psi 14,910 17,100 14,560 19,230 17,290 —

1085 days, psi 16,720 17,730 16,650 21,750 19,190 —

Modulus of elasticity in compression, 4 x 8-in. moist-cured cylinders

91 days, million psi 7.34 7.24 7.27 8.20 7.75 6.95

Drying shrinkage, 3 x 3 by 11.5-in. prisms

7 days, millionths 193 123 100 87 137 —

28 days, millionths 400 287 240 203 233 —

90 days, millionths 573 447 383 320 340 —

369 days, millionths 690 577 520 453 467 —

1075 days, millionths 753 677 603 527 523 —

Table 17-5 (Inch-Pound Units). Mixture Proportions and Properties of Commercially Available High-StrengthConcrete (Burg and Ost 1994)

tion and honeycomb. Superplasticizing admixtures areinvariably added to HPC mixtures to produce workableand often flowable mixtures.

Production of high-strength concrete may or may notrequire the purchase of special materials. The producermust know the factors affecting compressive strength andknow how to vary those factors for best results. Eachvariable should be analyzed separately in developing amix design. When an optimum or near optimum is estab-lished for each variable, it should be incorporated as theremaining variables are studied. An optimum mix designis then developed keeping in mind the economic advan-tages of using locally available materials. Many of theitems discussed below also apply to most high-perform-ance concretes.

Cement

Selection of cement for high-strength concrete should notbe based only on mortar-cube tests but should alsoinclude tests of comparative strengths of concrete at 28, 56,and 91 days. A cement that yields the highest concretecompressive strength at extended ages (91 days) is prefer-able. For high-strength concrete, a cement should producea minimum 7-day mortar-cube strength of approximately30 MPa (4350 psi).

Trial mixtures with cement contents between 400 and550 kg/m3 (675 to 930 lb/yd3) should be made for each

cement being considered for the project. Amounts willvary depending on target strengths. Other than decreasesin sand content as cement content increases, the trialmixtures should be as nearly identical as possible.

Supplementary Cementing Materials

Fly ash, silica fume, or slag are often mandatory in the pro-duction of high-strength concrete; the strength gainobtained with these supplementary cementing materialscannot be attained by using additional cement alone. Thesesupplementary cementing materials are usually added atdosage rates of 5% to 20% or higher by mass of cementingmaterial. Some specifications only permit use of up to 10%silica fume, unless evidence is available indicating thatconcrete produced with a larger dosage rate will have sat-isfactory strength, durability, and volume stability. Thewater-to-cementing materials ratio should be adjusted sothat equal workability becomes the basis of comparisonbetween trial mixtures. For each set of materials, there willbe an optimum cement-plus-supplementary cementingmaterials content at which strength does not continue toincrease with greater amounts and the mixture becomestoo sticky to handle properly. Blended cements containingfly ash, silica fume, slag, or calcined clay can be used tomake high-strength concrete with or without the additionof supplementary cementing materials.

Aggregates

In high-strength concrete, careful attention must be givento aggregate size, shape, surface texture, mineralogy, andcleanness. For each source of aggregate and concretestrength level there is an optimum-size aggregate thatwill yield the most compressive strength per unit ofcement. To find the optimum size, trial batches should bemade with 19 mm (3⁄4 in.) and smaller coarse aggregatesand varying cement contents. Many studies have foundthat 9.5 mm to 12.5 mm (3⁄8 in. to 1⁄2 in.) nominalmaximum-size aggregates give optimum strength.

In high-strength concretes, the strength of the aggre-gate itself and the bond or adhesion between the paste andaggregate become important factors. Tests have shown thatcrushed-stone aggregates produce higher compressivestrength in concrete than gravel aggregate using the samesize aggregate and the same cementing materials content;this is probably due to a superior aggregate-to-paste bondwhen using rough, angular, crushed material. For specifiedconcrete strengths of 70 MPa (10,000 psi) or higher, thepotential of the aggregates to meet design requirementsmust be established prior to use.

Coarse aggregates used in high-strength concreteshould be clean, that is, free from detrimental coatings ofdust and clay. Removing dust is important since it mayaffect the quantity of fines and consequently the waterdemand of a concrete mix. Clay may affect the aggregate-

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Fig. 17-5. The Two Union Square building in Seattle usedconcrete with a designed compressive strength of 131 MPa(19,000 psi) in its steel tube and concrete compositecolumns. High-strength concrete was used to meet a designcriteria of 41 GPa (6 million psi) modulus of elasticity.(59577)

these trial batches, it will be possible to determine theworkability, setting time, and amount of water reductionfor given admixture dosage rates and times of addition.

The use of air-entraining admixtures is not necessaryor desirable in high-strength concrete that is protectedfrom the weather, such as interior columns and shearwallsof high-rise buildings. However, for bridges, concrete piles,piers, or parking structures, where durability in a freeze-thaw environment is required, entrained air is mandatory.Because air entrainment decreases concrete strength of richmixtures, testing to establish optimum air contents andspacing factors may be required. Certain high-strengthconcretes may not need as much air as normal-strengthconcrete to be frost resistant. Pinto and Hover (2001) foundthat non-air-entrained, high-strength concretes had goodfrost and deicer-scaling resistance at a water to portlandcement ratio of 0.25. Burg and Ost (1994) found good frostresistance with non-air-entrained concrete containing silicafume at a water to cementing materials ratio of 0.22 (MixNo. 4 in Table 17-5); however, this was not the case withother mixtures, including a portland-only mixture with awater to cement ratio of 0.28.

Proportioning

The trial mixture approach is best for selecting propor-tions for high-strength concrete. To obtain high strength, itis necessary to use a low water to cementing materialsratio and a high portland cement content. The unitstrength obtained for each unit of cement used in a cubicmeter (yard) of concrete can be plotted as strength effi-ciency to assist with mix designs.

The water requirement of concrete increases as thefine aggregate content is increased for any given size ofcoarse aggregate. Because of the high cementing materialscontent of these concretes, the fine aggregate content canbe kept low. However, even with well-graded aggregates,a low water-cementing materials ratio may result in con-crete that is not sufficiently workable for the job. If asuperplasticizer is not already being used, this may bethe time to consider one. A slump of around 200 mm(8 in.) will provide adequate workability for most appli-cations. ACI Committee 211 (1998), Farny and Panarese(1994), and Nawy (2001) provide additional guidance onproportioning.

Mixing

High-strength concrete has been successfully mixed intransit mixers and central mixers; however, many of theseconcretes tend to be sticky and cause build-up in thesemixers. Where dry, uncompacted silica fume has beenbatched into a mix, “balling” of the mix has occurred andmixing has been less than complete. In such instances ithas been found necessary to experiment with thesequence in which solids and liquids are added, and the

paste bond. Washing of coarse aggregates may be neces-sary. Combining single sizes of aggregate to produce therequired grading is recommended for close control andreduced variability in the concrete.

The quantity of coarse aggregate in high-strengthconcrete should be the maximum consistent withrequired workability. Because of the high percentage ofcementitious material in high-strength concrete, an in-crease in coarse-aggregate content beyond values recom-mended in standards for normal-strength mixtures isnecessary and allowable.

In high-rise buildings and in bridges, the stiffness ofthe structure is of interest to structural designers. On cer-tain projects a minimum static modulus of elasticity hasbeen specified as a means of increasing the stiffness of astructure (Fig. 17-5). The modulus of elasticity is not neces-sarily proportional to the compressive strength of a con-crete. There are code formulas for normal-strengthconcrete and suggested formulas for high-strength con-crete. The modulus achievable is affected significantly bythe properties of the aggregate and also by the mixtureproportions (Baalbaki and others 1991). If an aggregate hasthe ability to produce a high modulus, then the optimummodulus in concrete can be obtained by using as much ofthis aggregate as practical, while still meeting workabilityand cohesiveness requirements. If the coarse aggregatebeing used is a crushed rock, and manufactured fine aggre-gate of good quality is available from the same source, thena combination of the two can be used to obtain the highestpossible modulus.

Due to the high amount of cementitious material inhigh-strength concrete, the role of the fine aggregate(sand) in providing workability and good finishing char-acteristics is not as crucial as in conventional strengthmixes. Sand with a fineness modulus (FM) of about 3.0—considered a coarse sand—has been found to be satisfac-tory for producing good workability and highcompressive strength. For specified strengths of 70 MPa(10,000 psi) or greater, FM should be between 2.8 and 3.2and not vary by more than 0.10 from the FM selected forthe duration of the project. Finer sand, say with a FM ofbetween 2.5 and 2.7, may produce lower-strength, stickymixtures.

Admixtures

The use of chemical admixtures such as water reducers,retarders, high-range water reducers or superplasticizersis necessary. They make more efficient use of the largeamount of cementitious material in high-strength concreteand help to obtain the lowest practical water to cementingmaterials ratio. Chemical admixture efficiency must beevaluated by comparing strengths of trial batches. Also,compatibility between cement and supplementary ce-menting materials, as well as water-reducing and otheradmixtures, must be investigated by trial batches. From

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percentage of each material added at each step in thebatching procedure. Batching and mixing sequencesshould be optimized during the trial mix phase. Wheretruck mixing is unavoidable, the best practice is to reduceloads to 90% of the rated capacity of the trucks.

Where there is no recent history of HSC or HPC mix-tures that meet specified requirements, it is essential tofirst make laboratory trial mixes to establish optimumproportions. At this stage, the properties of the mix, suchas workability, air content, density, strength and modulusof elasticity can be determined. Once laboratory mixtureproportions have been determined, field trials using fullloads of concrete are essential; they should be delivered tothe site or to a mock-up to establish and confirm the suit-ability of the batching, mixing, transporting and placingsystems to be used.

Prequalification of concrete suppliers for high-strength concrete projects is recommended (Bickley 1993).In a prequalification procedure, one or more loads of theproposed mixture is cast into a trial mock-up. The freshconcrete is tested for slump, air content, temperature, anddensity. Casting the mock-up provides the opportunity toassess the suitability of the mix for placing andcompaction. The mock-up can be instrumented to recordtemperatures and temperature gradients; it can also becored and tested to provide correlation with standardcylinder test results. The cores can be tested to provide thedesigner with in-place strength and modulus values forreference during construction. The heat characteristics ofthe mixture can also be determined using a computerinteractive program, and the data used to determine howcuring technology should be applied to the project.

Placing, Consolidation, and Curing

Close liaison between the contractor and the concrete pro-ducer allows concrete to be discharged rapidly afterarrival at the jobsite. Final adjustment of the concreteshould be supervised by the concrete producer’s techni-cians at the site, by a concrete laboratory, or by aconsultant familiar with the performance and use of high-strength concrete.

Delays in delivery and placing must be eliminated;sometimes it may be necessary to reduce batch sizes ifplacing procedures are slower than anticipated. Rigid sur-veillance must be exercised at the jobsite to prevent anyaddition of retempering water. Increases in workabilityshould only be achieved by the addition of a superplasti-cizer. This should be done by the supplier’s technician.The contractor must be prepared to receive the concreteand understand the consequences of exceeding the speci-fied slump and water-cementitious materials ratio.

Consolidation is very important in achieving the po-tential strengths of high-strength concrete. Concrete mustbe vibrated as quickly as possible after placement in theforms. High-frequency vibrators should be small enough

to allow sufficient clearance between the vibrating headand reinforcing steel. Over-vibration of workable normal-strength concrete often results in segregation, loss ofentrained air, or both. On the other hand, high-strengthconcrete without a superplasticizer, will be relatively stiffand contain little air. Consequently, inspectors should bemore concerned with under-vibration rather than over-vibration. Most high-strength concrete, particularly veryhigh-strength-concrete, is placed at slumps of 180 mm to220 mm (7 in. to 9 in.). Even at these slumps, some vibra-tion is required to ensure compaction. The amount ofcompaction should be determined by onsite trials.

High-strength concrete is often difficult to finishbecause of its sticky nature. High cementitious materialscontents, large dosages of admixtures, low water contents,and air entrainment all contribute to the difficulty offinishing these concretes. Because the concrete sticks to thetrowels and other finishing equipment, finishing activitiesshould be minimized. The finishing sequence should bemodified from that used for normal concrete.

Curing of high-strength concrete is even more impor-tant than curing normal-strength concrete. Providing ade-quate moisture and favorable temperature conditions isrecommended for a prolonged period, particularly when56- or 91-day concrete strengths are specified.

Additional curing considerations apply with HSCand HPC. Where very low water-cement ratios are used inflatwork (slabs and overlays), and particularly wheresilica fume is used in the mixture, there will be little if anybleeding before or after finishing. In these situations it isimperative that fog curing or evaporation retarders beapplied to the concrete immediately after the surface hasbeen struck off. This is necessary to avoid plasticshrinkage cracking of horizontal surfaces and to minimizecrusting. Fog curing, followed by 7 days of wet curing, hasproven to be very effective.

It is inevitable that some vertical surfaces, such ascolumns, may be difficult to cure effectively. Whereprojects are fast-tracked, columns are often stripped atan early age to allow raising of self-climbing form sys-tems. Concrete is thus exposed to early drying,sometimes within eleven hours after casting. Becauseof limited access, providing further curing is difficultand impractical.

Tests were conducted on column concrete to deter-mine if such early exposure and lack of curing have anyharmful effects. The tests showed that for a portlandcement-slag-silica fume mixture with a specifiedstrength of 70 MPa (10,000 psi), the matrix was soundand a very high degree of impermeability to water andchloride ions had been achieved (Bickley and others1994). Nevertheless, the best curing possible is recom-mended for all HPC.

The temperature history of HPC is an integral part ofits curing process. Advantage should also be taken ofrecent developments in curing technology. Temperature

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Confederation Bridge across the Northumberland Straitbetween Prince Edward Island and New Brunswick has a100-year design life (see Mix No. 2 in Table 17-3). Thisbridge contains HPC designed to efficiently protect theembedded reinforcement. The concrete had a diffusioncoefficient of 4.8 x 10-13 at six months (a value 10 to 30times lower than that of conventional concrete). The elec-trical resistivity was measured at 470 to 530 ohm-m,compared to 50 for conventional concrete. The designrequired that the concrete be rated at less than 1000coulombs. The high concrete resistivity in itself will resultin a rate of corrosion that is potentially less than 10 percentof the corrosion rate for conventional concrete (Dunaszegi1999). The following sections review durability issues thathigh-performance concrete can address.

Abrasion Resistance

Abrasion resistance is directly related to the strength ofconcrete. This makes high strength HPC ideal for abrasiveenvironments. The abrasion resistance of HPC incorpo-rating silica fume is especially high. This makes silica-fume concrete particularly useful for spillways andstilling basins, and concrete pavements or concrete pave-ment overlays subjected to heavy or abrasive traffic.

Holland and others (1986) describe how severe abra-sion-erosion had occurred in the stilling basin of a dam;repairs using fiber-reinforced concrete had not proven to bedurable. The new HPC mix used to repair the structure thesecond time contained 386 kg/m3 (650 lb/yd3) of cement,70 kg/m3 (118 lb/yd3) of silica fume, admixtures, and had awater to cementing materials ratio of 0.28, and a 90-daycompressive strength exceeding 103 MPa (15,000 psi).

Berra, Ferrara, and Tavano (1989) studied the additionof fibers to silica fume mortars to optimize abrasion resist-ance. The best results were obtained with a mix using slagcement, steel fibers, and silica fume. Mortar strengthsranged from 75 MPa to 100 MPa (11,000 psi to 14,500 psi).In addition to better erosion resistance, less dryingshrinkage, high freeze-thaw resistance, and good bond tothe substrate were achieved.

In Norway steel studs are allowed in tires; this causessevere abrasion wear on pavement surfaces, with resur-facing required within one to two years. Tests using anaccelerated road-wear simulator showed that in the rangeof 100 MPa to 120 MPa (14,500 psi to 17,000 psi), concretehad the same abrasion resistance as granite (Helland1990). Abrasion-resistant highway mixes usually containbetween 320 and 450 kg/m3 (539 and 758 lb/yd3) ofcement, plus silica fume or fly ash. They have water tocementing materials ratios of 0.22 to 0.36 and compressivestrengths in the range of 85 to 130 MPa (12,000 to 19,000psi). Applications have included new pavements andoverlays to existing pavements.

increases and gradients that will occur in a concrete place-ment can be predicted by procedures that provide data forthis purpose. With this technique, measures to heat, cool,or insulate a concrete placement can be determined andapplied to significantly reduce both micro- and macro-cracking of the structure and assure durability. Theincreasing use of these techniques will be required in moststructures using HPC to assure that the cover concreteprovides long term protection to the steel, and results inthe intended service life of the structure.

Quality Control

A comprehensive quality-control program is required atboth the concrete plant and onsite to guarantee consistentproduction and placement of high-strength concrete.Inspection of concreting operations from stockpiling ofaggregates through completion of curing is important.Closer production control than is normally obtained onmost projects is necessary. Also, routine sampling andtesting of all materials is particularly necessary to controluniformity of the concrete.

While tests on concrete should always be made instrict accordance with standard procedures, some addi-tional requirements are recommended, especially wherespecified strengths are 70 MPa (10,000 psi) or higher.In testing high-strength concrete, some changes andmore attention to detail are required. For example, card-board cylinder molds, which can cause lower strength-test results, should be replaced with reusable steel orplastic molds. Capping of cylinders must be done withgreat care using appropriate capping compounds.Lapping (grinding) the cylinder ends is an alternativeto capping. For specified strengths of 70 MPa (10,000 psi)or greater, end grinding to a flatness tolerance of0.04 mm is recommended.

The physical characteristics of a testing machine canhave a major impact on the result of a compression test. Itis recommended that testing machines be extremely stiff,both longitudinally and laterally.

The quality control necessary for the production ofhigh compressive strength concrete will, in most cases,lead to low variance in test results. Strict vigilance in allaspects of quality control on the part of the producer andquality testing on the part of the laboratory are necessaryon high-strength concrete projects. For concretes withspecified strengths of 70 MPa (10,000 psi), or greater, thecoefficient of variation is the preferred measure ofquality control.

HIGH-DURABILITY CONCRETE

Most of the attention in the 1970s and 1980s was directedtoward high strength HPC; today the focus is more onconcretes with high durability in severe environmentsresulting in structures with long life. For example, the

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Blast Resistance

High-performance concrete can be designed to have excel-lent blast resistance properties. These concretes often havea compressive strength exceeding 120 MPa (14,500 psi)and contain steel fibers. Blast-resistant concretes are oftenused in bank vaults and military applications.

Permeability

The durability and service life of concrete exposed toweather is related to the permeability of the cover concreteprotecting the reinforcement. HPC typically has very lowpermeability to air, water, and chloride ions. Low perme-ability is often specified through the use of a coulombvalue, such as a maximum of 1000 coulombs.

Test results obtained on specimens from a concretecolumn specified to be 70 MPa (10,000 psi) at 91 days andwhich had not been subjected to any wet curing were asfollows (Bickley and others):

Water permeability of vacuum-saturated specimens:Age at test: 7 yearsApplied water pressure: 0.69 MPaPermeability: 7.6 x 10-13 cm/s

Rapid chloride permeability (ASTM C 1202):Age at test, years Coulombs

1 3032 2587 417

The dense pore structure of high-performance con-crete, which makes it so impermeable, gives it charac-teristics that make it eminently suitable for uses where ahigh quality concrete would not normally be considered.Latex-modified HPC is able to achieve these same lowlevels of permeability at normal strength levels withoutthe use of supplementary cementing materials.

A large amount of concrete is used in farm structures.It typically is of low quality and often porous and with arough surface, either when placed or after attack by farm-yard wastes.

Gagne, Chagnon, and Parizeau (1994) provided a casehistory of the successful application of high performanceconcrete for agricultural purposes. In one case a farmerraising pigs on a large scale was losing about 1 kg per pigthrough diarrhea. This problem was resolved by recon-structing the pig pens with high performance concrete.Cited as beneficial properties in this application were:

• Surface smoothness that is compatible with the sensi-tive skin of a piglet

• Non-slip surface• Good thermal conductivity resulting in uniform

distribution of heat• Impermeable surface to resist the growth of bacteria

and viruses• Easy to place

• Resistant to attack by acid (farmyard) wastes• Price effective

The mix used had a water to portland cement ratio of0.33 and had a 7-day compressive strength of 50 MPa(7,250 psi).

Diffusion

Aggressive ions, such as chloride, in contact with thesurface of concrete will diffuse through the concrete untila state of equilibrium in ion concentration is achieved. Ifthe concentration of ions at the surface is high, diffusionmay result in corrosion-inducing concentrations at thelevel of the reinforcement.

The lower the water-cementing materials ratio thelower the diffusion coefficient will be for any given set ofmaterials. Supplementary cementing materials, particu-larly silica fume, further reduce the diffusion coefficient.Typical values for diffusion for HPC are as follows:

Type of Concrete Diffusion CoefficientPortland cement-fly-ash

silica fume mix: 1000 x 10-15 m2/sPortland cement-fly ash mix: 1600 x 10-15 m2/s

Carbonation

HPC has a very good resistance to carbonation due to itslow permeability. It was determined that after 17 years theconcrete in the CN Tower in Toronto had carbonated to anaverage depth of 6 mm (0.24 in.) (Bickley, Sarkar, andLanglois 1992). The concrete mixture in the CN Tower hada water-cement ratio of 0.42. For a cover to the reinforce-ment of 35 mm (1.4 in.), this concrete would providecorrosion protection for 500 years. For the lower water-cementing materials ratios common to HPC, significantlylonger times to corrosion would result, assuming a crackfree structure. In practical terms, uncracked HPC coverconcrete is immune to carbonation to a depth that wouldcause corrosion.

Temperature Control

The quality, strength, and durability of HPC is highlydependent on its temperature history from the time ofdelivery to the completion of curing. In principle, favor-able construction and placing methods will enable: (1) alow temperature at the time of delivery; (2) the smallestpossible maximum temperature after placing; (3) mini-mum temperature gradients after placing; and (4) agradual reduction to ambient temperature after maximumtemperature is reached. Excessively high temperaturesand gradients can cause excessively fast hydration andmicro- and macro-cracking of the concrete.

It has been a practice on major high-rise structuresincorporating concretes with specified strengths of 70 MPa

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crete (Mix 4) with a water to cementing materials ratio of0.22 was frost resistant.

Sidewalks constructed in Chicago in the 1920s used25-mm (1-in.) thick toppings made of no-slump dry-packmortar that had to be rammed into place. The concretecontained no air entrainment. Many of these sidewalks arestill in use today; they are in good condition (minus somesurface paste exposing fine aggregate) after 60 years ofexposure to frost and deicers. No documentation exists onthe water to cement ratio; however, it can be assumed thatthe water to cement ratio was comparable to that ofmodern HPCs.

While the above experiences prove the excellent dura-bility of certain high-performance concretes to freeze-thaw damage and salt scaling, it is considered prudent touse air-entrainment. No well-documented field experi-ments have been made to prove that air-entrainment is notneeded. Until such data are available, current practice forair-entrainment should be followed. It has been shownthat the prime requirement of an air-void system for HPCis a preponderance of air bubbles of 200 µm size andsmaller. If the correct air bubble size and spacing can beassured, then a moderate air content will ensure durabilityand minimize strength loss. The best measure of air-entrainment is the spacing factor.

Chemical Attack

For resistance to chemical attack on most structures, HPCoffers a much improved performance. Resistance tovarious sulfates is achieved primarily by the use of adense, strong concrete of very low permeability and lowwater-to-cementing materials ratio; these are all charac-teristics of HPC. Similarly, as discussed by Gagne andothers (1994), resistance to acid from wastes is alsomuch improved.

Alkali-Silica Reactivity

Reactivity between certain siliceous aggregates and alkalihydroxides can affect the long-term performance ofconcrete. Two characteristics of HPC that help combatalkali-silica reactivity are:

(1) HPC concretes at very low water to cement ratioscan self desiccate (dry out) to a level that does not allowASR to occur (relative humidity less than 80%). Burg andOst (1994) observed relative humidity values rangingfrom 62% to 72% for their six mixes in Table 17-5. The lowpermeability of HPC also minimizes external moisturefrom entering the concrete.

(2) HPC concretes can use significant amounts ofsupplementary cementing materials that may have theability to control alkali-silica reactivity. However, thismust be demonstrated by test. HPC concretes can also useASR inhibiting admixtures to control ASR.

HPC concretes are not immune to alkali-silica reac-tivity and appropriate precautions must be taken.

to 85 MPa (10,000 psi to 12,000 psi) to specify a maximumdelivery temperature of 18°C (64°F) (Ryell and Bickley1987). In summertime it is possible that this limit could onlybe met by using liquid nitrogen to cool the concrete.Experience with very-high-strength concrete suggests thata delivery temperature of no more than 25°C (77°F), prefer-ably 20°C (68°F), should be allowed. In addition to liquidnitrogen, measures to cool HPC in the summer may involveusing ice or chilled water as part of the mix water. The spec-ifier should state the required delivery temperature.

In HPC applications such as high-rise buildings,column sizes are large enough to be classed as mass con-crete. Normally, excessive heat generation in mass con-crete is controlled by using a low cement content. Whenhigh-cement-content HPC mixes are used under theseconditions, other methods of controlling maximum con-crete temperature must be employed. Burg and Ost (1994)recorded temperature rise for 1220-mm (4-ft) concretecubes using the mixtures in Table 17-5. A maximumtemperature rise of 9.4°C to 11.7°C for every 100 kg ofcement per cubic meter of concrete (1°F to 12.5°F for every100 lb of cement per cubic yard of concrete) was meas-ured. Burg and Fiorato (1999) monitored temperature risein high-strength concrete caissons; they determined thatin-place strength was not affected by temperature rise dueto heat of hydration.


Because of its very low water-cementing materials ratio(less than 0.25), it is widely believed that HPC should behighly resistant to both scaling and physical breakup dueto freezing and thawing. There is ample evidence thatproperly air-entrained high performance concretes arehighly resistant to freezing and thawing and to scaling.

Gagne, Pigeon, and Aítcin (1990) tested 27 mixes usingcement and silica fume with water-cementing materialsratios of 0.30, 0.26, and 0.23 and a wide range of quality inair-voids systems. All specimens performed exceptionallywell in salt-scaling tests, confirming the durability of high-performance concrete, and suggesting that air-entrainmentis not needed. Tachitana and others (1990) conductedASTM C 666 (Procedure A) tests on non-air-entrained highperformance concretes with water-cementing materialsratios between 0.22 and 0.31. All were found to beextremely resistant to freeze-thaw damage and again itwas suggested that air-entrainment is not needed.

Pinto and Hover (2001) found that non-air-entrainedconcrete with a water to portland cement ratio of 0.25 wasdeicer-scaling resistant with no supplementary cementingmaterials present. They found that higher strength port-land cement concretes needed less air than normalconcrete to be frost and scale resistant.

Burg and Ost (1994) found that of the six mixes testedin Table 17-5 using ASTM C 666, only the silica fume con-

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Resistivity

HPC, particularly that formulated with silica fume, hasvery high resistivity, up to 20 to 25 times that of normalconcrete. This increases resistance to the flow of electricalcurrent and reduces corrosion rates. Particularly if dry,HPC acts as an effective dielectric. Where cracking occursin HPC, the corrosion is localized and minor; this is due tothe high resistivity of the concrete which suppresses thedevelopment of a macro corrosion cell.

SELF-COMPACTING CONCRETE

Self-compacting concrete (SCC), also referred to as self-consolidating concrete, is able to flow and consolidateunder its own weight. At the same time it is cohesiveenough to fill spaces of almost any size and shape withoutsegregation or bleeding. This makes SCC particularlyuseful wherever placing is difficult, such as in heavily-reinforced concrete members or in complicated formwork.

This technology, developed in Japan in the 1980s, isbased on increasing the amount of fine material, forexample fly ash or limestone filler, without changing thewater content compared to common concrete. Thischanges the rheological behavior of the concrete. SCC hasto have a low yield value to ensure high flowability; a lowwater content ensures high viscosity, so the coarse aggre-gate can float in the mortar without segregating. To achievea balance between deformability and stability, the totalcontent of particles finer than the 150 µm (No. 100) sievehas to be high, usually about 520 to 560 kg/m3 (880 to 950lb/yd3). High-range water reducers based on polycarboxy-late ethers are typically used to plasticize the mixture. SCCis very sensitive to fluctuation in water content; therefore,stabilizers such as polysaccarides are used. Fig. 17-6 showsan example of mix proportions used in self-compactingconcrete as compared to a regular concrete mix.

In Japan, self-compacting concretes are divided intothree different types according to the composition of themortar:

• Powder type• Viscosity agent (stabilizer) type• Combination type

For the powder type, a high proportion of fines producesthe necessary mortar volume. In the stabilizer type, thefines content can be in the range admissible for vibratedconcrete. The viscosity required to inhibit segregation willthen be adjusted by using a stabilizer. The combinationtype is created by adding a small amount of stabilizer tothe powder type to balance the moisture fluctuations inthe manufacturing process.

Since SCC is characterized by special fresh concreteproperties, many new tests have been developed tomeasure flowability, viscosity, blocking tendency, self-lev-eling, and stability of the mixture (Skarendahl andPeterson 1999 and Ludwig and others 2001). A simple testto measure the stable and unblocked flow is the J-Ringtest, which is a modified slump test. The J-Ring—300 mm(12 in.) diameter with circular rods—is added to the slumptest (Fig. 17-7). The number of rods has to be adjusteddepending on the maximum size aggregate in the SCCmix. The SCC has to pass through the obstacles in theJ-Ring without separation of paste and coarse aggregates.The slump diameter of a well-proportioned SCC isapproximately the same with and without the J-Ring; it isusually about 750 mm (30 in.). Therefore, the test surfacehas to be at least 1000 mm (40 in.) in diameter.

Strength and durability of well-designed SCC arealmost similar to conventional concrete. Without propercuring, SCC tends to have higher plastic shrinkage

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Regular Mix

SCC

Cement Water Fine Aggregate Coarse AggregateAir

10% 18% 25%2% 45%

10% 18% 8% 26%2% 36%

Fines

Fig. 17-6. Examples of materials used in regular concreteand self-compacting concrete by absolute volume.

300 mm (12 in.)18 mm (0.7 in.)

Fig. 17-7. J-ring test. Photo courtesy of VDZ.

severe structural service. Table 17-6 compares hardenedconcrete properties of RPC with those of an 80-MPa(11,600-psi) concrete.

RPC has found some applications in pedestrianbridges (Fig. 17-9) (Bickley and Mitchell 2001 and Semioli2001). Also, the low porosity of RPC gives excellent dura-bility and transport properties, which makes it a suitablematerial for the storage of nuclear waste (Matte andMoranville 1999). A low-heat type of reactive-powderconcrete has been developed to meet needs for mass con-crete pours for nuclear reactor foundation mats andunderground containment of nuclear wastes (Gray andShelton 1998).

cracking than conventional concrete (Grube and Rickert2001). Research indicates greater tensile creep for SCC,resulting in a reduced tendency to crack (Bickley andMitchell 2001). The use of fly ash as a filler seems to beadvantageous compared to limestone filler; it results inhigher strength and higher chloride resistance (Bouzoubaaand Lachemi 2001 and Ludwig and others 2001).

The production of SCC is more expensive than reg-ular concrete and it is difficult to keep SCC in the desiredconsistency over a long period of time. However, con-struction time is shorter and production of SCC is envi-ronmentally friendly (no noise, no vibration).Furthermore, SCC produces a good surface finish. Theseadvantages make SCC particularly interesting for use inprecasting plants. SCC has been successfully used in anumber of rehabilitation projects in Canada (Bickley andMitchell 2001).

REACTIVE-POWDER CONCRETE

Reactive-powder concrete (RPC) was first patented by aFrench construction company in 1994. It is characterizedby high strength and very low porosity, which is obtainedby optimized particle packing and low water content.

The properties of RPC are achieved by: (1) eliminatingthe coarse aggregates; just very fine powders are usedsuch as sand, crushed quartz, and silica fume, all with par-ticle sizes between 0.02 and 300 µm; (2) optimizing thegrain size distribution to densify the mixture; (3) post-setheat-treatment to improve the microstructure; (4) additionof steel and synthetic fibers (about 2% by volume); and(5) use of superplasticizers to decrease the water to cementratio—usually to less than 0.2—while improving the rhe-ology of the paste. See Fig. 17-8 for a typical fresh RPC.

The compressive strength of reactive-powder con-crete is typically around 200 MPa (29,000 psi), but can beproduced with compressive strengths up to 810 MPa(118,000 psi) (Semioli 2001). However, the low compara-tive tensile strength requires prestressing reinforcement in

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Fig. 17-8. Freshly-mixed reactive-powder concrete.

Table 17-6. Typical Mechanical Properties of Reactive Powder Concrete (RPC)Compared to an 80-MPa Concrete (Perry 1998)

Property Unit 80 MPa RPC

Compressive strength MPa (psi) 80 (11,600) 200 (29,000)

Flexural strength MPa (psi) 7 (1000) 40 (5800)

Tensile strength MPa (psi) 8 (1160)

Modulus of Elasticity GPa (psi) 40 (5.8 x 106) 60 (8.7 x 106)

Fracture Toughness 103 J/m2 <1 30

Freeze-thaw, ASTM C 666 RDF 90 100

Carbonation depth: 36 days in CO2 mm 2 0

Abrasion 10-12 m2/s 275 1.2

REFERENCES

ACI Committee 211, Guide for Selecting Proportions for High-Strength Concrete with Portland Cement and Fly Ash, ACI 211.4-93, reapproved 1998, American Concrete Institute, Farm-ington Hills, Michigan, 1998, 13 pages.ACI Committee 363, Guide to Quality Control and Testing ofHigh-Strength Concrete, 363.2R-98, American ConcreteInstitute, Farmington Hills, Michigan, 1998, 18 pages.ACI Committee 363, State-of-the-Art Report on High-StrengthConcrete, 363R-92, reapproved 1997, American ConcreteInstitute, Farmington Hills, Michigan, 1997, 55 pages.ACPA, Fast-Track Concrete Pavements, TB004, American Con-crete Pavement Association, Skokie, Illinois, 1994, 32 pages.Aı tcin, P.-C., High-Performance Concrete, Modern ConcreteTechnology 5, E & FN Spon, London, 1998, 591 pages.Aı tcin, P.-C. and Richard, P., “The Pedestrian/BikewayBridge of Sherbrooke,” Proceedings of the 4th InternationalSymposium on Utilization of High-Strength/High-PerformanceConcrete, Paris, 1996, pages 1399 to 1406.ASCE, High-Performance Construction Materials and Systems,Technical Report 93-5011, American Society of CivilEngineers, New York, April 1993.Baalbaki, W.; Benmokrane, B.; Chaallal, O.; and Aítcin, P. C.,“Influence of Coarse Aggregate on Elastic Properties of High-Performance Concrete,” ACI Materials Journal, AmericanConcrete Institute, Farmington Hills, Michigan, September/October 1991, page 499.Bentz, Dale, CIKS for High Performance Concrete,http://ciks.cbt.nist.gov/bentz/welcome.html, National In- stitute of Standards and Technology, Gaithersburg, Mary-land, 2001.Bentz, Dale, Concrete Optimization Software Tool,http://ciks.cbt.nist.gov/bentz/welcome.html, National In- stitute of Standards and Technology, Gaithersburg, Mary-land, 2001.Berra, M.; Ferrara, G.; and Tavano, S., “Behaviour of high-erosion resistant silica fume: mortars for repair of hy-draulic structures,” Fly ash, silica fume, slag and natural

pozzolans in concrete: Proceedings, Third InternationalConference, Trondheim, Norway, (SP-114), vol. 2, AmericanConcrete Institute, Farmington Hills, Michigan, 1989,pages 827 to 847.Bickley, John A., and Fung, Rico, Optimizing the Economics ofHigh-Performance Concrete, A Concrete Canada and CanadianCement Industry Joint Research Project, Cement Associationof Canada, Ottawa, Ontario, 2001, 21 pages.Bickley, John A., and Mitchell, Denis, A State-of-the-Art Reviewof High Performance Concrete Structures Built in Canada: 1990—2000, Cement Association of Canada, Ottawa, Ontario, May2001, 122 pages. Bickley, J. A.; Ryell, J.; Rogers, C.; and Hooton, R. D., “SomeCharacteristics of High-Strength Structural Concrete: Part 2,”Canadian Journal for Civil Engineering, National ResearchCouncil of Canada, December 1994. Bickley, J. A., Prequalification Requirements for the Supplyand Testing of Very High Strength Concrete, Concrete Inter-national, American Concrete Institute, Farmington Hills,Michigan, February 1993, pages 62 to 64.Bickley, J. A.; Sarkar, S.; and Langlois, M., The CN Tower,Concrete International, American Concrete Institute, Farm-ington Hills, Michigan, August 1992, pages 51 to 55.Bonneau, O.; Poulin, C.; Dugat, J.; Richard, P.; and Aitcin, P.-C., “Reactive Powder Concrete: From Theory to Practice,”Concrete International, American Concrete Institute,Farmington Hills, Michigan, April 1996, pages 47 to 49.Bouzoubaa, N., and Lachemi, M., “Self-compacting concreteincorporating high volumes of class F fly ash. Preliminaryresults,” Vol. 31, Cement and Concrete Research, Pergamon-Elsevier Science, Oxford, 2001, pages 413 to 420.Burg, R. G., and Fiorato, A. E., High-Strength Concrete in Mas-sive Foundation Elements, Research and Development BulletinRD117, Portland Cement Association, 1999, 28 pages.Burg, R. G., and Ost, B. W., Engineering Properties of Commer-cially Available High-Strength Concretes (Including Three-YearData), Research and Development Bulletin RD104, PortlandCement Association, 1994, 62 pages.Dunaszegi, Laszlo, “HPC for Durability of the ConfederationBridge,” HPC Bridge Views, Federal Highway Administrationand National Concrete Bridge Council, Portland CementAssociation, September/October 1999, page 2.Farny, James A., and Panarese, William C., High-Strength Con-crete, EB114, Portland Cement Association, 1994, 60 pages.Ferraris, Chiara F., and Lobo, Colin L., “Processing of HPC,”Concrete International, American Concrete Institute, Farming-ton Hills, Michigan, April 1998, pages 61 to 64.Gagne, R.; Chagnon, D.; and Parizeau, R., “L’Utilization duBeton a Haute Performance dans l’Industrie Agricole,”Proceedings of Seminar at Concrete Canada Annual Meeting,Sherbrooke, Quebec, October 1994, pages 23 to 33.Gagne, R.; Pigeon, M.; and Aítcin, P. C., “Durabilite au gel desbetons de hautes performance mecaniques,” Materials andStructures, Vol. 23, 1990, pages 103 to 109.

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Chapter 17 ◆ High-Performance Concrete

Fig. 17-9. The Sherbrooke footbridge in Quebec, built in1997, is North America’s first reactive-powder concretestructure. (68300)

NIST, Partnership for High Performance Concrete Technology,http://ciks.cbt.nist.gov/phpct, National Institute ofStandards and Technology, Gaithersburg, Maryland, 2001.Okamura, H., and Ozawa, K., “Mix Design for Self-Compacting Concrete,” Concrete Library of JSCE No. 25,(Translation of Proceedings of JSCE, No. 496/V-24, 1994.8),Tokyo, June 1995, pages 107 to 120.

Okamura, H.; Ozawa, K.; and Ouchi, M., “Self-CompactingConcrete,” Structural Concrete 1, 2000, pages 3 to 17.Perenchio, W. F., An Evaluation of Some of the Factors Involvedin Producing Very-High-Strength Concrete, Research andDevelopment Bulletin RD014, Portland Cement Association,http://www.portcement.org/pdf_files/RD014.pdf, 1973.Perenchio, William F., and Klieger, Paul, Some Physical Prop-erties of High-Strength Concrete, Research and DevelopmentBulletin RD056, Portland Cement Association, http://www.portcement.org/pdf_files/RD056.pdf, 1978.Perry, V., “Industrialization of Ultra-High PerformanceDuctile Concrete,” Symposium on High-Strength/High-Perform-ance Concrete, University of Calgary, Alberta, November 1998.Pinto, Roberto C. A., and Hover, Kenneth C., Frost and ScalingResistance of High-Strength Concrete, Research and Devel-opment Bulletin RD122, Portland Cement Association, 2001,75 pages.Pyle, Tom, Caltrans, Personal communication on earlystrength concretes used in California, 2001.Russell, Henry G., “ACI Defines High-Performance Con-crete,” Concrete International, American Concrete Institute,Farmington Hills, Michigan, February 1999, pages 56 to 57.Ryell, J., and Bickley, J. A., “Scotia Plaza: High StrengthConcrete for Tall Buildings,” Proceedings International Con-ference on Utilization of High Strength Concrete, Stavanger,Norway, June 1987, pages 641 to 654.Saak, Aaron W.; Jennings, Hamlin M.; and Shah, Surendra P.,“New Methodology for Designing Self-CompactingConcrete,” ACI Materials Journal, American Concrete Insti-tute, Farmington Hills, Michigan, November-December2001, pages 429 to 439.

Semioli, William J., “The New Concrete Technology,”Concrete International, American Concrete Institute, Farm-ington Hills, Michigan, November 2001, pages 75 to 79.Skarendahl, Å., and Peterson, Ö., Self-compacting concrete —Proceedings of the first international RILEM-Symposium, Stock-holm, 1999, 786 pages.Tachitana, D.; Imai, M.; Yamazaki, N.; Kawai, T.; and Inada,Y., “High Strength Concrete Incorporating SeveralAdmixtures,” Proceedings of the Second International Sympo-sium on High Strength Concrete, SP-121, American Concrete In-stitute, Farmington Hills, Michigan, 1990, pages 309 to 330.Wood, J. G. M.; Wilson, J. R.; and Leek, D. S., “ImprovedTesting of Chloride Ingress Resistance of Concretes and Rela-tion of Results to Calculated Behaviour,” Proceedings of theThird International Conference on Deterioration and Repair ofReinforced Concrete in the Arabian Gulf, Bahrain Society ofEngineers and CIRIA, 1989.

Goodspeed, Charles H.; Vanikar, Suneel; and Cook,Raymond A., “High-Performance Concrete Defined forHighway Structures,” Concrete International, AmericanConcrete Institute, Farmington Hills, Michigan, February1996, pages 62 to 67.Gray, M. N., and Shelton, B. S., “Design and Development ofLow-Heat, High-Performance Reactive Powder Concrete,”Proceedings, International Symposium on High-Performance andReactive Powder Concretes, Sherbrooke, Quebec, August 1998,pages 203 to 230.Grove, James D., “Blanket Curing to Promote Early StrengthConcrete,” Concrete and Construction—New Developments andManagement, Transportation Research Record, 1234,Transportation Research Board, Washington, D.C., 1989.Grube, Horst, and Rickert, Joerg, “Self compacting con-crete—another stage in the development of the 5-componentsystem of concrete,” Betontechnische Berichte (ConcreteTechnology Reports), Verein Deutscher Zementwerke,Düsseldorf, 2001, pages 39 to 48.Helland, S., “High Strength Concrete Used in HighwayPavements,” Proceedings of the Second International Symposiumon High Strength Concrete, SP-121, American ConcreteInstitute, Farmington Hills, Michigan, 1990, pages 757 to 766.Holland, T. C.; Krysa, Anton; Luther, Mark D.; and Liu, TonyC., “Use of Silica-Fume Concrete to Repair Abrasion-ErosionDamage in the Kinzua Dam Stilling Basin,” Proceedings of theSecond International Conference on Fly Ash, Silica Fume, Slag andNatural Pozzolans in Concrete, SP-91, American ConcreteInstitute, Farmington Hills, Michigan, 1986, pages 841 to 864.Khayat, K. H.; Bickley, J. A.; and Lessard, M., “Performance ofSelf-Consolidating Concrete for Casting Basement andFoundation Walls,” ACI Materials Journal, American ConcreteInstitute, Farmington Hills, Michigan, May-June 2000, pages374 to 380.Knutson, Martin, and Riley, Randall, “Fast-Track ConcretePaving Opens Door to Industry Future,” Concrete Construc-tion, Addison, Illinois, January 1987, pages 4 to 13.Ludwig, Horst-Michael; Weise, Frank; Hemrich, Wolfgang;and Ehrlich, Norbert, “Self compacting concrete—principlesand practice,” Betonwerk- und Fertigteil-Technik (ConcretePlant+Precast Technology), Wiesbaden, Germany, June 2001,pages 58 to 67.Matte, V., and Moranville, M., ”Durability of ReactivePowder Composites: influence of silica fume on leachingproperties of very low water/binder pastes,” Cement andConcrete Composites 21, 1999, pages 1 to 9.McCullough, B. Frank, and Rasmussen, Robert Otto, Fast-Track Paving: Concrete Temperature Control and Traffic OpeningCriteria for Bonded Concrete Overlays, FHWA RD 98-167,Federal Highway Administration, Washington, D.C.,October 1999, 205 pages.Meschino, M., and Ryell, J., “Bottom-Up Construction of 31Meter High Reinforced Concrete-Filled Steel Columns for theGreater Toronto Airports Authority New Terminal Building,” pre-sented at the ACI Convention, Toronto, October 2000.Nawy, Edward G., Fundamentals of High-Performance Concrete,John Wiley and Sons, New York, 2001.NIST, Bridge LCC, http://www.bfrl.nist.gov/bridgelcc,National Institute of Standards and Technology, 2001.

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Special types of concrete are those with out-of-the-ordi-nary properties or those produced by unusual techniques.Concrete is by definition a composite material consistingessentially of a binding medium and aggregate particles,and it can take many forms. Table 18-1 lists many specialtypes of concrete made with portland cement and somemade with binders other than portland cement. In manycases the terminology of the listing describes the use,property, or condition of the concrete. Brand names arenot given. Some of the more common concretes are dis-cussed in this chapter.

STRUCTURAL LIGHTWEIGHT CONCRETE

Structural lightweight concrete is similar to normal-weight concrete except that it has a lower density. It ismade with lightweight aggregates (all-lightweight con-crete) or with a combination of lightweight and normal-weight aggregates. The term “sand lightweight” refers tolightweight concrete made with coarse lightweightaggregate and natural sand.

Structural lightweight concrete has an air-dry densityin the range of 1350 to 1850 kg/m3 (85 to 115 pcf) and a

CHAPTER 18

Special Types of Concrete

Table 18-1. Some Special Types of Concrete

Special types of concrete made with portland cement

Architectural concrete Heavyweight concrete Recycled concreteAutoclaved cellular concrete High-early-strength concrete Roller-compacted concreteCentrifugally cast concrete High-performance concrete Sawdust concreteColloidal concrete High-strength concrete Self-compacting concreteColored concrete Insulating concrete Shielding concreteControlled-density fill Latex-modified concrete ShotcreteCyclopean (rubble) concrete Low-density concrete Shrinkage-compensating concreteDry-packed concrete Mass concrete Silica-fume concreteEpoxy-modified concrete Moderate-strength lightweight concrete Soil-cementExposed-aggregate concrete Nailable concrete Stamped concreteFerrocement No-slump concrete Structural lightweight concreteFiber concrete Polymer-modified concrete Superplasticized concreteFill concrete Pervious (porous) concrete TerrazzoFlowable fill Pozzolan concrete Tremie concreteFlowing concrete Precast concrete Vacuum-treated concreteFly-ash concrete Prepacked concrete Vermiculite concreteGap-graded concrete Preplaced aggregate concrete White concreteGeopolymer concrete Reactive-powder concrete Zero-slump concrete

Special types of concrete not using portland cement

Acrylic concrete Furan concrete Polyester concreteAluminum phosphate concrete Gypsum concrete Polymer concreteAsphalt concrete Latex concrete Potassium silicate concreteCalcium aluminate concrete Magnesium phosphate concrete Sodium silicate concreteEpoxy concrete Methyl methacrylate (MMA) concrete Sulfur concrete

Most of the definitions of these types of concrete appear in Cement and Concrete Terminology, ACI 116.

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28-day compressive strength in excess of 17 MPa (2500psi). Some job specifications allow air-dry densities up to1920 kg/m3 (120 pcf). For comparison, normal-weightconcrete containing regular sand, gravel, or crushed stonehas a dry density in the range of 2080 to 2480 kg/m3 (130to 155 pcf). ASTM C 567 provides a test for density ofstructural lightweight concrete. Structural lightweightconcrete is used primarily to reduce the dead-load weightin concrete members, such as floors in high-rise buildings.

Structural Lightweight Aggregates

Structural lightweight aggregates are usually classifiedaccording to their production process because variousprocesses produce aggregates with somewhat differentproperties. Processed structural lightweight aggregatesshould meet the requirements of ASTM C 330, whichincludes:

• Rotary kiln expanded clays (Fig. 18-1), shales, andslates

• Sintering grate expanded shales and slates• Pelletized or extruded fly ash• Expanded slags

Structural lightweight aggregates can also be pro-duced by processing other types of material, such as nat-urally occurring pumice and scoria.

Structural lightweight aggregates have densities sig-nificantly lower than normal-weight aggregates, rangingfrom 560 to 1120 kg/m3 (35 to 70 pcf), compared to 1200 to1760 kg/m3 (75 to 110 pcf) for normal-weight aggregates.These aggregates may absorb 5% to 20% water by weightof dry material. To control the uniformity of structurallightweight concrete mixtures, the aggregates are pre-wetted (but not saturated) prior to batching.

CompressiveStrength

The compressive strengthof structural lightweightconcrete is usually relatedto the cement content at agiven slump and air con-tent, rather than to a water-to-cement ratio. This is dueto the difficulty in deter-mining how much of thetotal mix water is absorbedinto the aggregate and thusnot available for reactionwith the cement. ACI 211.2provides guidance on therelationship between com-pressive strength and ce-ment content. Typical

compressive strengths range from 20 to 35 MPa (3000 to5000 psi). High-strength concrete can also be made withstructural lightweight aggregates.

In well-proportioned mixtures, the cement contentand strength relationship is fairly constant for a particularsource of lightweight aggregate. However, the relation-ship will vary from one aggregate source or type toanother. When information on this relationship is notavailable from the aggregate manufacturer, trial mixtureswith varying cement contents are required to develop arange of compressive strengths, including the strengthspecified. Fig. 18-2 shows the relationship between cementcontent and compressive strength. An example of a28-MPa (4000-psi) structural lightweight concrete mixturewith an air-dry density of about 1800 kg/m3 (112 pcf), acombination of natural sand and gravel, and a lightweightrotary kiln expanded clay coarse aggregate follows:

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Fig. 18-1. Expanded clay. (69793)

20

30

40

20

30

40

4

3

5

6

4

3

5

6

200 300 400 500 200 300 400 500Cement content, kg/m3 Cement content, kg/m3

Cement content, lb/yd3

Com

pres

sive

stre

ngth

, MP

a

Com

pres

sive

stre

ngth

, MP

a

Com

pres

sive

stre

ngth

, 100

0 ps

i

Com

pres

sive

stre

ngth

, 100

0 ps

i

All low density Sanded low density

400 500 600 700 800Cement content, lb/yd3

400 500 600 700 800

Fig. 18-2. Relationship between compressive strength and cement content of field structurallightweight concrete using (left) lightweight fine aggregate and coarse aggregate or (right)lightweight coarse aggregate and normal-weight fine aggregate (data points represent actualproject strength results using a number of cement and aggregate sources) (ACI 211.2).

• 356 kg (600 lb) Type I portland cement • 534 kg (900 lb) sand, ovendry • 320 kg (540 lb) gravel (12.5 to 2.36 mm [1⁄2 in. to #8]),

ovendry • 356 kg (600 lb) lightweight aggregate (9.5 mm to 600

µm [3⁄8 in. to #30]), ovendry • 172 kg (290 lb) mix water added• 0.7 L (20 oz) water-reducing admixture• 0.09 L (2.5 oz) air-entraining admixture• 1 m3 (1 yd3) yield• Slump—75 mm (3 in.)• Air content—6%

Material proportions vary significantly for differentmaterials and strength requirements.

Entrained Air

As with normal-weight concrete, entrained air in structurallightweight concrete ensures resistance to freezing andthawing and to deicer applications. It also improves work-ability, reduces bleeding and segregation, and may com-pensate for minor grading deficiencies in the aggregate.

The amount of entrained air should be sufficient to pro-vide good workability to the plastic concrete and adequatefreeze-thaw resistance to the hardened concrete. Air con-tents are generally between 5% and 8%, depending on themaximum size of coarse aggregate (paste content) used andthe exposure conditions. Testing for air content should beperformed by the volumetric method (ASTM C 173 orAASHTO T 196). The freeze-thaw durability is also signifi-cantly improved if structural lightweight concrete is allowedto dry before exposure to a freeze-thaw environment.

Specifications

Many suppliers of lightweight aggregates for use in struc-tural lightweight concrete have information on suggestedspecifications and mixture proportions pertaining to theirproduct. The usual specifications for structural concretestate a minimum compressive strength, a maximum density,a maximum slump, and an acceptable range in air content.

The contractor should also be concerned with thebleeding, workability, and finishing properties of struc-tural lightweight concrete.

Mixing

In general, mixing procedures for structural lightweightconcrete are similar to those for normal-density concrete;however, some of the more absorptive aggregates mayrequire prewetting before use. Water added at the batch-ing plant should be sufficient to produce the specifiedslump at the jobsite. Measured slump at the batch plantwill generally be appreciably higher than the slump at thesite. Pumping can especially aggravate slump loss.

Workability and Finishability

Structural lightweight concrete mixtures can be propor-tioned to have the same workability, finishability, andgeneral appearance as a properly proportioned normal-density concrete mixture. Sufficient cement paste must bepresent to coat each particle, and coarse-aggregate parti-cles should not separate from the mortar. Enough fineaggregate is needed to keep the freshly mixed concretecohesive. If aggregate is deficient in minus 600 µm(No. 30) sieve material, finishability may be improved byusing a portion of natural sand, by increasing cementcontent, or by using satisfactory mineral fines. Sinceentrained air improves workability, it should be usedregardless of exposure.

Slump

Due to lower aggregate density, structural lightweightconcrete does not slump as much as normal-weight con-crete with the same workability. A lightweight air-entrained mixture with a slump of 50 to 75 mm (2 to 3 in.)can be placed under conditions that would require aslump of 75 to 125 mm (3 to 5 in.) for normal-weight con-crete. It is seldom necessary to exceed slumps of 125 mm(5 in.) for normal placement of structural lightweight con-crete. With higher slumps, the large aggregate particlestend to float to the surface, making finishing difficult.

Vibration

As with normal-weight concrete, vibration can be usedeffectively to consolidate lightweight concrete; the samefrequencies commonly used for normal-density concreteare recommended. The length of time for proper consoli-dation varies, depending on mix characteristics. Excessivevibration causes segregation by forcing large aggregateparticles to the surface.

Placing, Finishing, and Curing

Structural lightweight concrete is generally easier tohandle and place than normal-weight concrete. A slumpof 50 to 100 mm (2 to 4 in.) produces the best results forfinishing. Greater slumps may cause segregation, delayfinishing operations, and result in rough, uneven surfaces.

If pumped concrete is being considered, the specifier,suppliers, and contractor should all be consulted aboutperforming a field trial using the pump and mixtureplanned for the project. Adjustments to the mixture maybe necessary; pumping pressure causes the aggregate toabsorb more water, thus reducing the slump and in-creasing the density of the concrete.

Finishing operations should be started earlier thanfor comparable normal-weight concrete, but finishing tooearly may be harmful. A minimum amount of floating

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Chapter 18 � Special Types of Concrete

in both moderate-strength and structural lightweight con-crete (up to about 1900 kg/m3 or 120 pcf air-dry).

Group III concretes are made by incorporating into acement paste or cement-sand mortar a uniform cellularstructure of air voids that is obtained with preformedfoam (ASTM C 869), formed-in-place foam, or specialfoaming agents. Ovendry densities ranging between 240to 1900 kg/m3 (15 to 120 pcf) are obtained by substitutionof air voids for some or all of the aggregate particles; airvoids can consist of up to 80% of the volume. Cellular con-crete can be made to meet the requirements of both insu-lating and moderate strength lightweight concrete.

Aggregates used in Groups I and II should meet therequirements of ASTM C 332, Standard Specification forLightweight Aggregates for Insulating Concrete. These aggre-gates have dry densities in the range of from 96 to 1120kg/m3 (6 to 70 pcf) down to 16 kg/m3 (1 pcf) for expandedpolystyrene beads.

Mixture Proportions

Examples of mixture proportions for Group I and III con-cretes appear in Table 18-2. In Group I, air contents may beas high as 25% to 35%. The air-entraining agent can beprepackaged with the aggregate or added at the mixer.Because of the absorptive nature of the aggregate, the vol-umetric method (ASTM C 173 or AASHTO T 196) shouldbe used to measure air content.

Water requirements for insulating and fill concretesvary considerably, depending on aggregate characteris-tics, entrained air, and mixture proportions. An effortshould be made to avoid excessive amounts of water ininsulating concrete used in roof fills. Excessive watercauses high drying shrinkage and cracks that maydamage the waterproofing membrane. Accelerators con-taining calcium chloride should not be used where galva-nized steel will remain in permanent contact with theconcrete because of possible corrosion problems.

Mixture proportions for Group II concretes usuallyare based on volumes of dry, loose materials, even whenaggregates are moist as batched. Satisfactory proportionscan vary considerably for different aggregates or combi-nations of aggregates. Mixture proportions ranging from0.24 to 0.90 cubic meters of aggregate per 100 kg (4 to 14cu ft per 100 lb) of cement can be used in lightweight con-cretes that are made with pumice, expanded shale, andexpanded slag. Some mixtures, such as those for no-finesconcretes, are made without fine aggregate but with totalvoid contents of 20% to 35%. Cement contents for GroupII concretes range between 120 to 360 kg per cubic meter(200 and 600 lb per cubic yard) depending on air content,aggregate gradation, and mixture proportions.

No-fines concretes containing pumice, expanded slag,or expanded shale can be made with 150 to 170 kg of waterper cubic meter (250 to 290 lb of water per cubic yard), total

and troweling should be done; magnesium finishing toolsare preferred.

The same curing practices should be used for light-weight concrete as for normal-weight concrete. The twomethods commonly used in the field are water curing(ponding, sprinkling, or using wet coverings) and pre-venting loss of moisture from the exposed surfaces (cov-ering with waterproof paper, plastic sheets, or sealingwith liquid membrane-forming compounds). Generally,7 days of curing are adequate for ambient air tempera-tures above 10°C (50°F).

INSULATING AND MODERATE-STRENGTH LIGHTWEIGHT CONCRETES

Insulating concrete is a lightweight concrete with anovendry density of 800 kg/m3 (50 pcf) or less. It is madewith cementing materials, water, air, and with or withoutaggregate and chemical admixtures. The ovendry densityranges from 240 to 800 kg/m3 (15 to 50 pcf) and the 28-daycompressive strength is generally between 0.7 and 7 MPa(100 and 1000 psi). Cast-in-place insulating concrete isused primarily for thermal and sound insulation, roofdecks, fill for slab-on-grade subbases, leveling courses forfloors or roofs, firewalls, and underground thermal con-duit linings.

Moderate-strength lightweight concrete has a densityof 800 to 1900 kg/m3 (50 to 120 pcf) ovendry and has acompressive strength of approximately 7 to 15 MPa (1000to 2500 psi). It is made with cementing materials, water,air, and with or without aggregate and chemical admix-tures. At lower densities, it is used as fill for thermal andsound insulation of floors, walls, and roofs and is referredto as fill concrete. At higher densities it is used in cast-in-place walls, floors and roofs, and precast wall and floorpanels. See ACI documents for more information.

For discussion purposes, insulating and moderate-strength lightweight concretes can be grouped as follows:

Group I is made with expanded aggregates such as per-lite, vermiculite, or expanded polystyrene beads. Ovendryconcrete densities using these aggregates generally rangebetween 240 to 800 kg/m3 (15 and 50 pcf). This group isused primarily in insulating concrete. Some moderate-strength concretes can also be made from aggregates inthis group.

Group II is made with aggregates manufactured by ex-panding, calcining, or sintering materials such as blast-furnace slag, clay, diatomite, fly ash, shale, or slate, or byprocessing natural materials such as pumice, scoria, ortuff. Ovendry concrete densities using these aggregatescan range between 720 to 1440 kg/m3 (45 and 90 pcf).Aggregates in this group are used in moderate-strengthlightweight concrete and some of these materials(expanded slag, clay, fly ash, shale, and slate) are also used

318


air voids of 20% to 35%, and a cement content of about 280kg per cubic meter (470 lb per cubic yard).

Workability

Because of their high air content, lightweight concretesweighing less than 800 kg/m3 (50 pcf) generally haveexcellent workability. Slumps of up to 250 mm (10 in.) usu-ally are satisfactory for Group I and Group III concretes;appearance of the mix, however, may be a more reliableindication of consistency. Cellular concretes are handledas liquids; they are poured or pumped into place withoutfurther consolidation.

Mixing and Placing

All concrete should be mechanically mixed to produce auniform distribution of materials of proper consistencyand required density. In batch-mixing operations, varioussequences can be used for introducing the ingredients; the

preferred sequence is to first introduce the requiredamount of water into the mixer, then add the cement, air-entraining or foaming agent, aggregate, preformed foam,and any other ingredients.

Excessive mixing and handling should be avoidedbecause they tend to break up aggregate particles, therebychanging density and consistency. Segregation is not usuallya problem (though it could be for Group II) because of therelatively large amounts of entrained air in these mixtures.

Pumping is the most common method of placement,but other methods can be used. Finishing operationsshould be kept to a minimum; smoothing with a darby orbullfloat is usually sufficient. Placement of insulatingconcretes should be done by workers experienced withthese special concretes.

Periodic wet-density tests (ASTM C 138 or AASHTOT 121) at the jobsite can be performed to check the unifor-mity of the concrete. Variations in density generallyshould not exceed plus or minus 32 kg/m3 (2 pcf). A closeapproximation of the ovendry density can be determinedfrom the freshly mixed density.

319


Table 18-2. Examples of Lightweight Insulating Concrete Mixtures

28-day compressiveRatio: portland Ovendry Type I strength, MPa (psi),

cement to aggregate density, portland cement, Water-cement 150 x 300-mmType of concrete by volume kg/m3 (pcf) kg/m3 (Ib/yd3) ratio, by mass (6 x 12-in.) cylinders

1:4 480 to 608 (30 to 38) 362 (610) 0.94 2.75 (400)

Perlite* 1:5 416 to 576 (26 to 36) 306 (516) 1.12 2.24 (325)1:6 352 to 545 (22 to 34) 245 (414) 1.24 1.52 (220)1:8 320 to 512 (20 to 32) 234 (395) 1.72 1.38 (200)

1:4 496 to 593 (31 to 37) 380 (640) 0.98 2.07 (300)

Vermiculite* 1:5 448 to 496 (28 to 31) 295 (498) 1.30 1.17 (170)1:6 368 to 464 (23 to 29) 245 (414) 1.60 0.90 (130)1:8 320 to 336 (20 to 21) 178 (300) 2.08 0.55 (80)

Polystyrene:**sand:

0 kg/m3 (0 lb/yd3) 1:3.4 545 (34)‡ 445 (750) 0.40 2.24 (325)73 kg/m3 (124 lb/yd3) 1:3.1 625 (39)‡ 445 (750) 0.40 2.76 (400)

154 kg/m3 (261 lb/yd3) 1:2.9 725 (44)‡ 445 (750) 0.40 3.28 (475)200 kg/m3 (338 lb/yd3) 1:2.5 769 (48)‡ 474 (800) 0.40 3.79 (550)

Cellular* — 625 (39) 524 (884) 0.57 2.41 (350)(neat cement) — 545 (34) 468 (790) 0.56 1.45 (210)

— 448 (28) 396 (668) 0.57 0.90 (130)— 368 (23) 317 (535) 0.65 0.34 (50)

Cellular†(sanded)†† 1:1 929 (58) 429 (724) 0.40 3.17 (460)

1:2 1250 (78) 373 (630) 0.41 5.66 (820)1:3 1602 (100) 360 (602) 0.51 15.10 (2190)

* Reichard (1971).** Source: Hanna (1978). The mix also included air entrainment and a water-reducing agent.† Source: Gustaferro (1970).

†† Dry-rodded sand with a bulk density of 1600 kg/m3 (100 pcf).‡ Air-dry density at 28 days, 50% relative humidity.

Thermal Resistance

ASTM C 177, Test Method for Steady-State Heat FluxMeasurements and Thermal Transmission Properties by Meansof the Guarded-Hot-Plate Apparatus, is used to determinevalues of thermal conductivity. Fig. 18-3 shows an ap-proximate relationship between thermal resistance anddensity. The thermal conductivity of concrete increaseswith an increase in moisture content and density. SeeBrewer (1967) for additional density and conductivityrelationships.

320


6

4

0

2

800

1000

600

400

200

0160 480 800 1120

10 30 50 70

Density, ovendry, kg/m3

Com

pres

sive

str

engt

h at

28

days

, MP

a

Com

pres

sive

str

engt

h at

28

days

, psi

Density, ovendry, lb/ft3

Perlite, vermiculite, or neat cement (cellular)

Pumice, 1:5

Expanded shale, 1:5 – 1:14;Expanded slag, 1:5 – 1:9

Fig. 18-4. Approximate relationship between ovendry bulkdensity and compressive strength of 150 x 300-mm (6 x 12-in.) cylinders tested in an air-dry condition for some insulat-ing and fill concretes. For the perlite and vermiculite con-cretes, mix proportions range from 1:3 to 1:10 by volume.

3000 600 900 1200 1500 1800 2100

5

10

15

20

2520 40 60 80 100 120

3

2

1

w/cby mass

cementkg/m3

446390335

(lb/yd3)

(752)(658)(564)

0.450.500.60

Plastic density, kg/m3

Plastic density, lb/ft3

Com

pres

sive

stre

ngth

, MPa

Com

pres

sive

stre

ngth

, 100

0 ps

i

Fig. 18-5. Plastic density versus compressive strength forsanded cellular concretes. Compressive strength was deter-mined with 150 x 300-mm (6 x 12-in.) cylinders that werecured for 21 days in a 100% relative humidity moist roomfollowed by 7 days in air at 50% RH (McCormick 1967 andACI 523.3R).

Density, lb/ft3

Density, kg/m3

Normal-densitystructuralconcrete

Ther

mal

resi

stan

ce, h

• ft2 •

ºF/B

tu

Ther

mal

resi

stan

ce, K

• m

2 /W

0 30 60 90 120 150

0 400 800 1200 1600 2000 2400

0.25

0.2

0.15

0.1

0.05

0

1.4

1.2

1

0.8

0.6

0.4

0.2

0

Fig. 18-3. Thermal resistance of concrete versus density(PCA 1980).

Strength

Strength requirements depend on the intended use of theconcrete. For example, a compressive strength of 0.7 MPa(100 psi), or even less, may be satisfactory for insulation ofunderground steam lines. Roof-fill insulation requires suf-ficient early strength to withstand foot traffic. Compressivestrengths of 0.7 to 1.5 MPa (100 to 200 psi) are usually ade-quate for roof fills, but strengths up to 3.5 MPa (500 psi) aresometimes specified. In general, the strength of insulatingconcrete is of minor importance. Compressive strength oflightweight insulating concrete should be determined bythe methods specified in ASTM C 495 or C 513.

Table 18-2 and Fig. 18-4 give examples of the relation-ship between density and strength for lightweight insu-lating concretes. Fig. 18-5 shows examples for cellularconcrete containing sand. Mixtures with strengths outsidethe ranges shown can be made by varying the mixtureproportions. Strengths comparable to those at 28 days

would be obtained at 7 days with high-early-strengthcement. The relationships shown do not apply to auto-claved products.


Insulating and moderate-strength lightweight concretesnormally are not required to withstand freeze-thaw expo-sure in a saturated condition. In service they are normallyprotected from the weather; thus little research has beendone on their resistance to freezing and thawing.

Drying Shrinkage

The drying shrinkage of insulating or moderate-strengthlightweight concrete is not usually critical when it is usedfor insulation or fill; however, excessive shrinkage cancause curling. In structural use, shrinkage should be con-sidered. Moist-cured cellular concretes made withoutaggregates have high drying shrinkage. Moist-cured cel-lular concretes made with sand may shrink from 0.1% to0.6%, depending on the amount of sand used. Autoclavedcellular concretes shrink very little on drying. Insulatingconcretes made with perlite or pumice aggregates mayshrink 0.1% to 0.3% in six months of drying in air at 50%relative humidity; vermiculite concretes may shrink 0.2%to 0.45% during the same period. Drying shrinkage of insu-lating concretes made with expanded slag or expandedshale ranges from about 0.06% to 0.1% in six months.

Expansion Joints

Where insulating concrete is used on roof decks, a 25-mm(1-in.) expansion joint at the parapets and all roof projec-tions is often specified. Its purpose is to accommodateexpansion caused by the heat of the sun so that the insu-lating concrete can expand independently of the roofdeck. Transverse expansion joints should be placed at amaximum of 30 m (100 ft) in any direction for a thermalexpansion of 1 mm per meter (1 in. per 100 lin ft). A fiber-glass material that will compress to one-half its thicknessunder a stress of 0.17 MPa (25 psi) is generally used toform these joints.

AUTOCLAVED CELLULAR CONCRETE

Autoclaved cellular concrete (also called autoclaved aer-ated concrete) is a special type of lightweight buildingmaterial. It is manufactured from a mortar consisting ofpulverized siliceous material (sand, slag, or fly ash),cement and/or lime, and water; to this a gas forming ad-mixture, for example aluminum powder, is added. Thechemical reaction of aluminum with the alkaline waterforms hydrogen, which expands the mortar as macro-pores with a diameter of 0.5 mm to 1.5 mm (0.02 in. to 0.06

in.) form. The material is then pressure steam cured (auto-claved) over a period of 6 to 12 hours using a temperatureof 190ºC (374ºF) and a pressure of 1.2 MPa (174 psi). Thisforms a hardened mortar matrix, which essentially con-sists of calcium silicate hydrates.

This porous mineral building material has densitiesbetween 300 and 1000 kg/m3 (19 and 63 lb/ft3) andcompressive strengths between 2.5 and 10 MPa (300 and1500 lb/in2). Due to the high macropore content—up to80 percent by volume—autoclaved cellular concrete has athermal conductivity of only 0.15 to 0.20 W/(m•K) (1 to1.4 Btu•in./[h•ft2•ºF]).

Autoclaved cellular concrete is produced in block orpanel form for construction of residential or commercialbuildings (Fig. 18-6).

Additional information can be found in ACI 523.2R,Guide for Precast Cellular Concrete.

321


Fig. 18-6. (top) Residential build-ing constructed with autoclavedcellular concrete blocks. (bottom)Autoclaved cellular concreteblock floating in water. (70025,44109)

HIGH-DENSITY CONCRETE

High-density (heavyweight) concrete and has a density ofup to about 6400 kg/m3 (400 pcf). Heavyweight concrete isused principally for radiation shielding but is also usedfor counterweights and other applications where high-density is important. As a shielding material, heavy-weight concrete protects against the harmful effects ofX-rays, gamma rays, and neutron radiation. Selection ofconcrete for radiation shielding is based on space require-ments and on the type and intensity of radiation. Wherespace requirements are not important, normal-weightconcrete will generally produce the most economicalshield; where space is limited, heavyweight concrete willallow for reductions in shield thickness without sacri-ficing shielding effectiveness.

Additions

Boron additions such as colemanite, boron frits, and boro-calcite are sometimes used to improve the neutronshielding properties of concrete. However, they may ad-versely affect setting and early strength of concrete; there-fore, trial mixes should be made with the addition underfield conditions to determine suitability. Admixtures suchas pressure-hydrated lime can be used with coarse-sandsizes to minimize any retarding effect.

Properties of High-Density Concrete

The properties of high-density concrete in both the freshlymixed and hardened states can be tailored to meet jobconditions and shielding requirements by proper selectionof materials and mixture proportions.

Except for density, the physical properties of heavy-weight concrete are similar to those of normal-weight con-crete. Strength is a function of water-cement ratio; thus,for any particular set of materials, strengths comparable tothose of normal-weight concretes can be achieved. Typicaldensities of concretes made with some commonly usedhigh-density aggregates are shown in Table 18-3. Becauseeach radiation shield has special requirements, trial mix-tures should be made with job materials and under jobconditions to determine suitable mixture proportions.

Proportioning, Mixing, and Placing

The procedures for selecting mix proportions for heavy-weight concrete are the same as those for normal-weightconcrete. However, additional mixture information andsample calculations are given in ACI 211.1. Following arethe most common methods of mixing and placing high-density concrete:

Conventional methods of mixing and placing often areused, but care must be taken to avoid overloading themixer, especially with very heavy aggregates such as steel

Type and intensity of radiation usually determine therequirements for density and water content of shieldingconcrete. Effectiveness of a concrete shield against gammarays is approximately proportional to the density of theconcrete; the heavier the concrete, the more effective theshield. On the other hand, an effective shield against neu-tron radiation requires both heavy and light elements. Thehydrogen in water provides an effective light element inconcrete shields. Some aggregates contain crystallizedwater, called fixed water, as part of their structure. For thisreason, heavyweight aggregates with high fixed-watercontents often are used if both gamma rays and neutronradiation are to be attenuated. Boron glass (boron frit) isalso added to attenuate neutrons.

High-Density Aggregates

High-density aggregates such as barite, ferrophosphorus,goethite, hematite, ilmenite, limonite, magnetite, and de-greased steel punchings and shot are used to producehigh-density concrete. Where high fixed-water content isdesirable, serpentine (which is slightly heavier thannormal-weight aggregate) or bauxite can be used (seeASTM C 637 and C 638).

Table 18-3 gives typical bulk density, relative density(specific gravity), and percentage of fixed water for some ofthese materials. The values are a compilation of data from awide variety of tests or projects reported in the literature.Steel punchings and shot are used where concrete with adensity of more than 4800 kg/m3 (300 pcf) is required.

In general, selection of an aggregate is determined byphysical properties, availability, and cost. Heavyweightaggregates should be reasonably free of fine material, oil,and foreign substances that may affect either the bond ofpaste to aggregate particle or the hydration of cement. Forgood workability, maximum density, and economy, aggre-gates should be roughly cubical in shape and free of exces-sive flat or elongated particles.

322


Table 18-3. Physical Properties of Typical High-Density Aggregates and Concrete

Fixed-water,* Aggregate Aggregate bulk Concrete density,Type of aggregate percent by weight relative density density, kg/m3 (pcf) kg/m3 (pcf)

Goethite 10–11 3.4–3.7 2080–2240 (130–140) 2880–3200 (180–200)

Limonite** 8–9 3.4–4.0 2080–2400 (130–150) 2880–3360 (180–210)

Barite 0 4.0–4.6 2320–2560 (145–160) 3360–3680 (210–230)

Ilmenite † 4.3–4.8 2560–2700 (160–170) 3520–3850 (220–240)

Hematite † 4.9–5.3 2880–3200 (180–200) 3850–4170 (240–260)

Magnetite † 4.2–5.2 2400–3040 (150–190) 3360–4170 (210–260)

Ferrophosphorus 0 5.8–6.8 3200–4160 (200–260) 4080–5290 (255–330)

Steel punchings or shot 0 6.2–7.8 3860–4650 (230–290) 4650–6090 (290–380)

* Water retained or chemically bound in aggregates.** Test data not available.† Aggregates may be combined with limonite to produce fixed-water contents varying from about 1⁄2% to 5%.

punchings. Batch sizes should be reduced to about 50% ofthe rated mixer capacity. Because some heavy aggregatesare quite friable, excessive mixing should be avoided toprevent aggregate breakup with resultant detrimentaleffects on workability and bleeding.

Preplaced aggregate methods can be used for placingnormal and high-density concrete in confined areas andaround embedded items; this will minimize segregation ofcoarse aggregate, especially steel punchings or shot. Themethod also reduces drying shrinkage and produces con-crete of uniform density and composition. With thismethod, the coarse aggregates are preplaced in the formsand grout made of cement, sand, and water is thenpumped through pipes to fill the voids in the aggregate.

Pumping of heavyweight concrete through pipelinesmay be advantageous in locations where space is limited.Heavyweight concretes cannot be pumped as far asnormal-weight concretes because of their higher densities.

Puddling is a method whereby a 50-mm (2-in.) layer ormore of mortar is placed in the forms and then coveredwith a layer of coarse aggregate that is rodded or internallyvibrated into the mortar. Care must be taken to ensure uni-form distribution of aggregate throughout the concrete.

MASS CONCRETE

Mass concrete is defined by ACI Committee 116 as “Anylarge volume of cast-in-place concrete with dimensionslarge enough to require that measures be taken to copewith the generation of heat and attendant volume changeto minimize cracking.” Mass concrete includes not onlylow-cement-content concrete used in dams and other mas-sive structures but also moderate- to high-cement-contentconcrete in structural members of bridges and buildings(Fig. 18-7). Mass concrete placements require special con-

siderations to reduce heat of hydration and the resultingtemperature rise to avoid damaging the concrete throughexcessive temperatures and temperature differences thatcan result in thermal cracking (Gajda and VanGeem, 2002).

In mass concrete, temperature rise (Fig. 18-8) resultsfrom the heat of hydration of cementitious materials. Asthe interior concrete increases in temperature andexpands, the surface concrete may be cooling and con-tracting. This causes tensile stresses that may result inthermal cracks at the surface if the temperature differen-

323

Chapter 18 ◆ Special Types of Concrete

Fig.18-7. Large foundation placements as shown requiremass-concrete precautions. (50918)

82

62

42

22

2

-18

150

200

50

0

100

0 100 200 300 400 500 600

Center Temperatures

Edge Temperatures

Level 1 – BottomLevel 2 – MiddleLevel 3 – Top

Cement, Type I = 328 kg (553 lb)Silica Fume = 27 kg (45 lb)Fly ash = 87 kg (147 lb)HRWR = 7.86 L (266 fl oz)w/cm = 0.281

Time from start of placement, hr

Tem

pera

ture

, °C

Tem

pera

ture

, °F

Fig. 18-8. (left) A drilled shaft (caisson), 3 m (10 ft) in diameter and 12.2 m (40 ft) in depth in which “low-heat” high-strengthconcrete is placed and (right) temperatures of this concrete measured at the center and edge and at three different levelsin the caisson (Burg and Fiorato 1999). (57361)

estimate of the adiabatic temperature rise can be madeusing equations in a PCA publication (PCA 1987).

Massive structural reinforced concrete members withhigh cement contents (300 to 600 kg per cubic meter or 500to 1000 lb per cu yard) cannot use many of the placing tech-niques and controlling factors mentioned above to maintainlow temperatures to control cracking. For these concretes(often used in bridges, foundations, and power plants), agood technique is to (1) avoid external restraint from adja-cent concrete elements, (2) reduce the size of the member byplacing the concrete in multiple smaller pours, or (3) controlinternal differential thermal strains by preventing the con-crete from experiencing an excessive temperature differen-tial between the surface and the center. The latter is done byproperly designing the concrete and either keeping the con-crete surface warm through use of insulation or reducingthe internal concrete temperature by precooling of the con-crete or postcooling with internal cooling pipes.

Studies and experience have shown that by limitingthe maximum temperature differential between the inte-rior and exterior surface of the concrete to less than about20°C (36°F), surface cracking can be minimized or avoided(FitzGibbon 1977 and Fintel and Ghosh 1978). Somesources indicate that the maximum temperature differen-tial (MTD) for concrete containing granite or limestone(low-thermal-coefficient aggregates) should be 25°C and31°C (45°F and 56°F), respectively (Bamforth 1981). Theactual MTD for a particular mass concrete placement andconcrete mix design can be determined using equations inACI 207 (1995).

In general, an MTD of 20°C (36°F) should be assumedunless a demonstration or calculations based on physicalproperties of the actual concrete mix the geometry of the con-crete member show that higher MTD values are allowable.

By limiting the temperature differential to 20°C (36°F)or less, the concrete will cool slowly to ambient tempera-ture with little or no surface cracking; however, this is trueonly if the member is not restrained by continuous rein-forcement crossing the interface of adjacent or oppositesections of hardened concrete. Restrained concrete willtend to crack due to eventual thermal contraction after thecool down. Unrestrained concrete should not crack ifproper procedures are followed and the temperature dif-ferential is monitored and controlled. If there is any con-cern over excess temperature differentials in a concretemember, the element should be considered as mass con-crete and appropriate precautions taken.

Fig. 18-10 illustrates the relationship between temper-ature rise, cooling, and temperature differentials for a sec-tion of mass concrete. As can be observed, if the forms(which are providing adequate insulation in this case) areremoved too early, cracking will occur once the differencebetween interior and surface concrete temperaturesexceeds the critical temperature differential of 20°C (36°F).If higher temperature differentials are permissible, theforms can be removed sooner. For large concrete place-ments, surface insulation may be need for an extendedperiod of time of up to several weeks or longer.

tial between the surface and center is too great. The widthand depth of cracks depends upon the temperature dif-ferential, physical properties of the concrete, and the rein-forcing steel.

A definite member size beyond which a concrete struc-ture should be classified as mass concrete is not readilyavailable. Many large structural elements may be massiveenough that heat generation should be considered; this isparticularly critical when the minimum cross-sectionaldimensions of a solid concrete member approach or exceed1 meter (3 feet) or when cement contents exceed 355 kg/m3

(600 lb per cubic yard). Temperature rise in mass concreteis related to the initial concrete temperature (Fig. 18-9),ambient temperature, size of the concrete element (volumeto surface ratio and minimum dimension), and type andquantity of cementitious materials. Smaller concrete mem-bers less than 0.3 meters (1 ft) thick with moderateamounts of cementitious materials are typically of littleconcern as the generated heat is rapidly dissipated.

To avoid cracking, the internal concrete temperaturefor dams and other nonreinforced mass concrete struc-tures of relatively low compressive strength should not beallowed to rise more than 11°C to 14°C (20°F to 25°F)above the mean annual ambient temperature (ACI 308).Internal concrete temperature gain can be controlled anumber of ways: (1) a low cement content—120 to 270kg/m3 (200 to 450 lb per cubic yard); (2) large aggregatesize—75 to 150 mm (3 to 6 in.); (3) high coarse aggregatecontent—up to 80% of total aggregate; (4) low-heat-of-hydration cement; (5) pozzolans—where heat of hydra-tion of a pozzolan can be 25% to 75% that of cement;(6) reductions in the initial concrete temperature to bycooling the concrete ingredients; (7) cooling the concretethrough the use of embedded cooling pipes; (8) steelforms for rapid heat dissipation; (9) water curing; and(10) low lifts—1.5 m (5 ft) or less during placement. Inmassive structures of high volume-to-surface ratio, an

324


0 1 2 3 4 7 14 28

40

35

30

25

20

15

10

5

0

70

60

50

40

30

20

10

0

Time, days

Adi

abat

ic te

mpe

ratu

re ri

se, °

F

Adi

abat

ic te

mpe

ratu

re ri

se, °

C 38

°C(100°F) placing temperature

32°C (90°F)

27°C (80°F)

21°C (70°F)

16°C (60°F)

10°C(50°F)

4°C(40°F)

Type I cement

Fig. 18-9. The effect of concrete-placing temperature ontemperature rise in mass concrete with 223 kg/m3 (376lb/yd3) of cement. Higher placing temperatures acceleratetemperature rise (ACI 207.2R).

The maximum temperature rise can be estimated byapproximation, if the concrete contains 300 to 600 kg ofcement per cubic meter (500 to 1000 lb of Type I/II cementper cubic yard) and the least dimension of the member is1.8 m (6 ft). This approximation (under normal, not adia-batic conditions) would be 12°C for every 100 kg ofcement per cubic meter (12.8°F for every 100 lb of cementper cubic yard). For example, the maximum temperatureof such an element made with concrete having 535 kg ofType I/II cement per cubic meter (900 lb of cement percubic yard) and cast at 16°C (60°F) would be about

16°C + (12°C x 535/100) or 80°C

(60°F + [12.8°F x 900/100] or 175°F)

Temperatures and temperature differences in mass con-crete can also be calculated by a method in ACI 207 (1996).

The slow rate of heat exchange between concrete andits surroundings is due to the concrete’s heat capacity. Heatescapes from concrete at a rate that is inversely propor-tional to the square of its least dimension. A 150-mm (6-in.)thick wall cooling from both sides will take approximately11⁄2 hours to dissipate 95% of its developed heat. A 1.5-m(5-ft) thick wall would take an entire week to dissipate thesame amount of heat (ACI 207). Inexpensive thermocou-ples can be used to monitor concrete temperature.

PREPLACED AGGREGATE CONCRETE

Preplaced aggregate concrete is produced by first placingcoarse aggregate in a form and later injecting a cement-sand grout, usually with admixtures, to fill the voids.Properties of the resulting concrete are similar to those ofcomparable concrete placed by conventional methods;however, considerably less thermal and drying shrinkagecan be expected because of the point-to-point contact ofaggregate particles.

Coarse aggregates should meet requirements ofASTM C 33 (AASHTO M 80). In addition, most specifica-tions limit both the maximum and minimum sizes; forexample, 75-mm (3-in.) maximum and 12.5-mm (1⁄2-in.)

minimum. Aggregates are generally graded to produce avoid content of 35% to 40%. Fine aggregate used in thegrout is generally graded to a fineness modulus ofbetween 1.2 and 2.0, with nearly all of the material passinga 1.25 mm (No. 16) sieve.

Although the preplaced aggregate method has beenused principally for restoration work and in the construc-tion of reactor shields, bridge piers, and underwater struc-tures, it has also been used in buildings to produceunusual architectural effects. Since the forms are com-pletely filled with coarse aggregate prior to grouting, adense and uniform exposed-aggregate facing is obtainedwhen the surface is sandblasted, tooled, or retarded andwire-brushed at an early age.

Tests for preplaced aggregate concrete are given inASTM C 937 through C 943. Preplaced aggregate concreteis discussed in more detail in ACI 304-00, Guide forMeasuring, Transporting, and Placing Concrete.

NO-SLUMP CONCRETE

No-slump concrete is defined as concrete with a consis-tency corresponding to a slump of 6 mm (1⁄4 in.) or less.Such concrete, while very dry, must be sufficiently work-able to be placed and consolidated with the equipment tobe used on the job. The methods referred to here do notnecessarily apply to mixtures for concrete masonry unitsor for compaction by spinning techniques.

Many of the basic laws governing the properties ofhigher-slump concretes are applicable to no-slump con-crete. For example, the properties of hardened concretedepend principally on the ratio of water to cement, pro-vided the mix is properly consolidated.

Measurement of the consistency of no-slump concretediffers from that for higher-slump concrete because theslump cone is impractical for use with the drier consisten-cies. ACI 211.3, Standard Practice for Selecting Proportions forNo-Slump Concrete, describes three methods for measuringthe consistency of no-slump concrete: (1) the Vebe appa-ratus; (2) the compacting-factor test; and (3) the Thaulowdrop table. In the absence of the above test equipment,workability can be adequately judged by a trial mixturethat is placed and compacted with the equipment andmethods to be used on the job.

Intentionally entrained air is recommended for no-slump concrete where durability is required. The amountof air-entraining admixture usually recommended forhigher-slump concretes will not produce air contents inno-slump concretes that are as high as those in the higher-slump concretes. The lower volume of entrained air, how-ever, generally provides adequate durability for no-slumpconcretes; while the volume of entrained air is not there,sufficient small air voids are present. This departure fromthe usual methods of designing and controlling entrainedair is necessary for no-slump concretes.

For a discussion of water requirements and computa-tion of trial mixtures, see ACI 211.3.

325

Chapter 18 ◆ Special Types of Concrete

0 1 2 3 4 5 6 7 8

50

40

30

20

10

0

80

100

40

60

0

20

Surfacetemperature

Inside temperature

Unprotectedsurface cools fast

Formremoval

Surfacecracking

Protectedsurfacecools slowly–no cracking

�t > 20°C (36°F)

�t < 20°C (36°F)

Days

Tem

pera

ture

rise

, °C

Tem

pera

ture

rise

, °F

Fig. 18-10. Potential for surface cracking after form re-moval, assuming a critical temperature differential, �t, of20°C (36°F). No cracking should occur if concrete is cooledslowly and �t is less than 20°C (36°F) (Fintel and Ghosh1978 and PCA 1987).

Other water control RCC applications include use asan emergency spillway or overtopping protection forembankment dams, low permeable liner for settling ponds,bank protection, and grade control structure for channelsand riverbeds.

Pavements

The uses for RCC paving range from pavements as thick asone meter (one yard) for the mining industry to city streets,paved surfaces for composting operations, logging, truckstagging areas, and warehouse floors.The procedures forconstruction of an RCC pavement require tighter controlthan for dam construction (Arnold and Zamensky 2000).Cement content is in the same range as conventional con-crete, 300 to 360 kg/m3 (500 to 600 lb/yd3), and compres-sive strength is of the same order, 30 to 40 MPa (4000 to6000 psi). The nominal maximum aggregate size is limitedto 19 mm (3⁄4 in.) to provide a smooth, dense surface. Foreven better surface textures, a 16 mm (5⁄8 in.) maximum sizeaggregate is recommended.

The zero slump mix is usually produced in a contin-uous flow pugmill mixer at production rates as high as 400tons per hour. It is possible to mix RCC in a central batchplant, but the plant must be dedicated to RCC productionexclusively, because the material tends to stick to the insidedrums. Specifications usually require that the mix betransported, placed, and compacted within 60 minutes ofthe start of mixing; although ambient weather conditionsmay increase or decrease that time window.

RCC is typically placed in layers 125 to 250 mm (5 to10 in.) in thickness using an asphalt-type paving machine.High-density paving equipment is preferred for layersthicker than 150 mm (6 in.) since the need for subsequentcompaction by rollers is reduced. Where a design calls forpavement thickness greater than 250 mm (10 in.), the RCCshould be placed in multiple layers. In this type of con-struction, it is important that there be a minimum timedelay in placing subsequent layers so that good bond isassured. Following placement by a paver, RCC can becompacted with a combination of vibratory steel-wheeledrollers and rubber-tired equipment.

Curing is vitally important in RCC pavement construc-tion. The very low water content at the initial mixing stagemeans that an RCC mix will dry out very quickly once it isin place. Continuous water curing is the recommendedmethod, although sprayed on asphaltic emulsion, plasticsheeting, and concrete curing compounds have been usedin some cases. Pavement projects have had design com-pressive strengths of about 35 MPa (5000 psi) with fieldstrengths in the range of 35 to 70 MPa (5000 to 10,000 psi)(Hansen 1987)

High-performance roller compacted concrete forareas subjected to high impact and abrasive loading weredeveloped in the mid-1990’s. These mixes are based on ob-taining the optimum packing of the various sizes of aggre-gate particles, and the addition of silica fume to the mix(Marchand and others 1997 and Reid and Marchand 1998).

ROLLER-COMPACTED CONCRETE

Roller-compacted concrete (RCC) is a lean, no-slump,almost dry concrete that is compacted in place by vibra-tory roller or plate compaction equipment (Fig. 18-11).RCC is a mixture of aggregate, cement, and water; sup-plementary cementing materials such as fly ash also havebeen used. Cement contents range from 60 to 360 kg percubic meter (100 to 600 lb per cubic yard). Mixing is donewith conventional batch mixers, continuous mixers, or insome instances tilting-drum truck mixers.

Applications for RCC fall into two distinct categories—water control structures (dams) and pavements. While thesame term is used to describe both types of concrete use, thedesign and construction processes are different.

Water Control Structures

RCC can be used for the entire dam structure, or as anovertopping protection on the upper section and on thedownstream face. The nominal maximum aggregate sizecan range up to 150 mm (6 in.). The zero slump mix isproduced in a high-capacity central-mixing plant near thesite and delivered by truck or by conveyor belt. Cementcontent is usually lower than that used in a conventionalconcrete mix, but similar to that of mass concrete. Com-pressive strengths ranging from 7 to 30 MPa (1000 to 4500psi) have been obtained from roller-compacted concrete indam projects. The RCC mix is transported by trucks andconveyor belts and spread by grader or bulldozer,followed by rolling with vibratory compactors. No formsare used. On some projects the upstream face is surfacedwith higher strength conventional air-entrained concreteor precast panels for improved durability.

RCC dams have the advantage of allowing muchsteeper slopes on both faces than an earth fill dam. In addi-tion to the advantage of using less material, the dam is com-pleted and placed in service earlier, usually at a significantsavings in overall cost compared to an earth fill structure.

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Fig. 18-11. Vibratory rollers are used to compact roller-compacted concrete. (64401)

ACI addresses roller-compacted concrete in twoguides—ACI 207.5, Roller Compacted Mass Concrete dealswith RCC for water control structures and ACI 325.10Roller Compacted Concrete Pavements, covers new develop-ments in RCC pavements. Holderbaum and Schweiger(2000) provide a guide for developing RCC specificationsand commentary.

SOIL-CEMENT

Soil-cement is a mixture of pulverized soil or granularmaterial, cement, and water. Some other terms applied tosoil-cement are “cement-treated base or subbase,”“cement stabilization,” “cement-modified soil,” and“cement-treated aggregate.” The mixture is compacted toa high density, and as the cement hydrates the materialbecomes hard and durable.

Soil-cement is primarily used as pavement basecourse for roads, streets, airports, and parking areas. Abituminous or portland cement concrete wearing course isusually placed over the base. Soil-cement is also used asslope protection for earth dams and embankments, reser-voir and ditch linings, deep-soil mixing, and foundationstabilization (Fig. 18-12).

The soil material in soil-cement can be almost anycombination of sand, silt, clay, and gravel or crushedstone. Local granular materials (such as slag, caliche, lime-rock, and scoria) plus a wide variety of waste materials(such as cinders, ash, and screenings from quarries andgravel pits) can be used to make soil-cement. Also, oldgranular-base roads, with or without their bituminoussurfaces, can be recycled to make soil-cement.

Soil-cement should contain sufficient portland cementto resist deterioration from freeze-thaw and wet-drycycling and sufficient moisture for maximum compaction.

Cement contents range from 80 to 255 kg per cubic meter(130 to 430 lb per cubic yard).

There are four steps in soil-cement construction:spreading cement, mixing, compaction, and curing. Theproper quantity of cement must be spread on the in-placesoil; the cement and soil material, and the necessaryamount of water are mixed thoroughly using any of sev-eral types of mixing machines; and finally, the mixture iscompacted with conventional road-building equipment to96% to 100% of maximum density. See ASTM D 558(AASHTO T 134) and PCA 1992.

A light coat of bituminous material is commonly usedto prevent moisture loss; it also helps bond and forms partof the bituminous surface. A common type of wearing sur-face for light traffic is a surface treatment of bituminousmaterial and chips 13 to 19 mm (1⁄2 to 3⁄4 in.) thick. Forheavy-duty use and in severe climates a 38-mm (11⁄2-in.)asphalt mat is used.

Depending on the soil used, the 7-day compressivestrengths of saturated specimens at the minimum cementcontent meeting soil-cement criteria are generally between2 to 5 MPa (300 and 800 psi). Like concrete, soil-cementcontinues to gain strength with age; compressivestrengths in excess of 17 MPa (2500 psi) have beenobtained after many years of service.

See ACI Committee 230 (1997) and PCA (1995) for de-tailed information on soil-cement construction.

SHOTCRETE

Shotcrete is mortar or small-aggregate concrete that ispneumatically projected onto a surface at high velocity(Fig. 18-13). Also known as “gunite” and “sprayed con-crete,” shotcrete was developed in 1911 and its concept isessentially unchanged even in today’s use. The relatively

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Fig. 18-12. A dozer places a plant-mixed soil-cement on aslope for construction a of wastewater lagoon. (59819)

Fig. 18-13. Shotcrete. (70018)

duces expansion during hardening and thereby offsets thecontraction occurring during drying (drying shrinkage).Shrinkage-compensating concrete is used in concreteslabs, pavements, structures, and repair work to minimizedrying shrinkage cracks. Expansion of concrete made withshrinkage-compensating cement should be determined bythe method specified in ASTM C 878.

Reinforcing steel in the structure restrains the con-crete and goes into tension as the shrinkage compensatingconcrete expands. Upon shrinking due to drying contrac-tion caused by moisture loss in hardened concrete, the ten-sion in the steel is relieved; as long as the resulting tensionin the concrete does not exceed the tensile strength of theconcrete, no cracking should result. Shrinkage-compen-sating concrete can be proportioned, batched, placed, andcured similarly to normal concrete with some precautions;for example, it is necessary to assure the expected expan-sion by using additional curing. More information can befound in Chapter 2 and in ACI 223-98, Standard Practice forthe Use of Shrinkage-Compensating Concrete.

PERVIOUS CONCRETE

Pervious (porous or no-fines) concrete contains a nar-rowly graded coarse aggregate, little to no fine aggregate,and insufficient cement paste to fill voids in the coarseaggregate. This low water-cement ratio, low-slump con-crete resembling popcorn is primarily held together bycement paste at the contact points of the coarse aggregateparticles; this produces a concrete with a high volume ofvoids (20% to 35%) and a high permeability that allowswater to flow through it easily.

Pervious concrete is used in hydraulic structures asdrainage media, and in parking lots, pavements, and airportrunways to reduce storm water run off. It also recharges thelocal groundwater supply by allowing water to penetratethe concrete to the ground below. Pervious concretes havealso been used in tennis courts and greenhouses.

As a paving material, porous concrete is raked or slip-formed into place with conventional paving equipmentand then roller compacted. Vibratory screeds or handrollers can be used for smaller jobs. In order to maintain itsporous properties, the surfaces of pervious concreteshould not be closed up or sealed; therefore, trowelingand finishing are not desired. The compressive strength ofdifferent mixes can range from 3.5 to 27.5 MPa (500 to 4000psi). Drainage rates commonly range from 100 to 900 litersper minute per square meter (2 to 18 gallons per minuteper square foot).

No-fines concrete is used in building construction(particularly walls) for its thermal insulating properties.For example, a 250-mm (10-in.) thick porous-concrete wallcan have an R value of 0.9 (5 using inch-pound units) com-pared to 0.125 (0.75) for normal concrete. No-fines con-crete is also lightweight, 1600 to 1900 kg/m3 (100 to 120pcf), and has low drying shrinkage properties (Malhotra1976 and Concrete Construction 1983).

dry mixture is consolidated by the impact force and can beplaced on vertical or horizontal surfaces without sagging.

Shotcrete is applied by a dry or wet process. In thedry process, a premixed blend of cement and dampaggregate is propelled through a hose by compressed airto a nozzle. Water is added to the cement and aggregatemixture at the nozzle and the intimately mixed ingredi-ents are projected onto the surface. In the wet process, allthe ingredients are premixed. The wet mixture is pumpedthrough a hose to the nozzle, where compressed air isadded to increase the velocity and propel the mixtureonto the surface.

As the shotcrete mixture hits the surface, some coarseraggregates ricochet off the surface until sufficient pastebuilds up, providing a bed into which the aggregate canstick. To reduce overspray (mortar that attaches to nearbysurfaces) and rebound (aggregate that ricochets off thereceiving surface) the nozzle should be held at a 90° angleto the surface. The appropriate distance between nozzleand surface is usually between 0.5 m and 1.5 m (1.5 ft and5 ft), depending on the velocity.

Shotcrete is used for both new construction and repairwork. It is especially suited for curved or thin concretestructures and shallow repairs, but can be used for thickmembers. The hardened properties of shotcrete are veryoperator dependent. Shotcrete has a density and compres-sive strength similar to normal- and high-strength con-crete. Aggregate sizes up to 19 mm (3⁄4 in.) can be used,however most mixtures contain aggregates only up to9.5 mm (3⁄8 in.); 25% to 30% pea gravel are commonly usedfor wet mixes (Austin and Robbins 1995).

Supplementary cementitious materials, such as flyash and silica fume, can also be used in shotcrete. Theyimprove workability, chemical resistance, and durability.The use of accelerating admixtures allows build-up ofthicker layers of shotcrete in a single pass. They alsoreduce the time of initial set. However, using rapid-setaccelerators often increases drying shrinkage and reduceslater-age strength (Gebler and others 1992).

Steel fibers are used in shotcrete to improve flexuralstrength, ductility, and toughness; they can be used as areplacement for wire mesh reinforcement in applicationslike rock slope stabilization and tunnel linings (ACI506.1R). Steel fibers can be added up to 2 percent byvolume of the total mix. Polypropylene fibers if used arenormally added to shotcrete at a rate of 0.9 to 2.7 kg/m3

(1.5 to 4.5 lb/yd3), but dosages up to 9 kg/m3 (15 lb/yd3)have also been used (The Aberdeen Group 1996).

Guidelines for the use of shotcrete are described inACI 506R, ASCE (1995), and Balck and others (2000).

SHRINKAGE-COMPENSATING CONCRETE

Shrinkage-compensating concrete is concrete containingexpansive cement or an expansive admixture, which pro-

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WHITE ANDCOLOREDCONCRETE

WhiteConcrete

White portland ce-ment is used to pro-duce white concrete,a widely used ar-chitectural material(Fig. 18-14). It is alsoused in mortar,plaster, stucco, ter-razzo, and portlandcement paint. Whiteportland cement ismanufactured fromraw materials of lowiron content; it con-forms to ASTM C

150 (AASHTO M 85) even though these specifications donot specifically mention white portland cement.

White concrete is made with aggregates and water thatcontain no materials that will discolor the concrete. Whiteor light-colored aggregates can be used. Oil that could stainconcrete should not be used on the forms. Care must betaken to avoid rust stains from tools and equipment. Curingmaterials that could cause stains must be avoided. Refer toFarny (2001) and http://www.portcement.org/white formore information.

Colored Concrete

Colored concrete can be produced by using colored aggre-gates or by adding color pigments (ASTM C 979) or both.When colored aggregates are used, they should beexposed at the surface of the concrete. This can be doneseveral ways; for example, casting against a form that hasbeen treated with a retarder. Unhydrated paste at the sur-face is later brushed or washed away. Other methodsinvolve removing the surface mortar by sandblasting,waterblasting, bushhammering, grinding, or acidwashing. If surfaces are to be washed with acid, a delay ofapproximately two weeks after casting is necessary.Colored aggregates may be natural rock such as quartz,marble, and granite, or they may be ceramic materials.

Pigments for coloring concrete should be pure min-eral oxides ground finer than cement; they should be in-soluble in water, free of soluble salts and acids, colorfast insunlight, resistant to alkalies and weak acids, and virtu-ally free of calcium sulfate. Mineral oxides occur in natureand are also produced synthetically; synthetic pigmentsgenerally give more uniform results.

The amount of color pigments added to a concretemixture should not be more than 10% of the mass of thecement. The amount required depends on the type of pig-ment and the color desired. For example, a dose of pig-ment equal to 1.5% by mass of cement may produce apleasing pastel color, but 7% may be needed to produce adeep color. Use of white portland cement with a pigmentwill produce cleaner, brighter colors and is recommendedin preference to gray cement, except for black or dark graycolors (Fig. 18-15).

To maintain uniform color, do not use calcium chloride,and batch all materials carefully by mass. To preventstreaking, the dry cement and color pigment must be thor-oughly blended before they are added to the mixer. Mixingtime should be longer than normal to ensure uniformity.

In air-entrained concrete, the addition of pigmentmay require an adjustment in the amount of air-entrainingadmixture to maintain the desired air content.

Dry-Shake Method. Slabs or precast panels that are casthorizontally can be colored by the dry-shake method.Prepackaged, dry coloring materials consisting of mineraloxide pigment, white portland cement, and speciallygraded silica sand or other fine aggregate are marketedready for use by various manufacturers.

After the slab has been bullfloated once, two-thirds ofthe dry coloring material should be broadcast evenly by

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Fig. 18-15. Colored concrete, used for a rapid transit plat-form. (67328)

Fig. 18-14. Office building con-structed with white cement con-crete. (55828)

REFERENCES

ACI Committee 116, Cement and Concrete Technology, ACI116R-00, ACI Committee 116 Report, American ConcreteInstitute, Farmington Hills, Michigan, 2000, 73 pages.

ACI Committee 207, Cooling and Insulating Systems forMass Concrete, ACI 207.4R-93, reapproved 1998, ACICommittee 207 Report, American Concrete Institute,Farmington Hills, Michigan, 1998, 22 pages.

ACI Committee 207, Effect of Restraint, Volume Change, andReinforcement on Cracking of Mass Concrete, ACI 207.2R-95,ACI Committee 207 Report, American Concrete Institute,Farmington Hills, Michigan, 1995, 26 pages.

ACI Committee 207, Mass Concrete, ACI 207.1R-96, ACICommittee 207 Report, American Concrete Institute,Farmington Hills, Michigan, 1996, 42 pages.

ACI Committee 207, Roller-Compacted Mass Concrete, ACI207.5R-99, ACI Committee 207 Report, American ConcreteInstitute, Farmington Hills, Michigan, 1999, 46 pages.

ACI Committee 211, Guide for Selecting Proportions forNo-Slump Concrete, ACI 211.3R-97, ACI Committee 211Report, American Concrete Institute, Farmington Hills,Michigan, 1997, 26 pages.

ACI Committee 211, Standard Practice for SelectingProportions for Structural Lightweight Concrete, ACI 211.2-98, ACI Committee 211 Report, American Concrete Insti-tute, Farmington Hills, Michigan, 1998, 18 pages.

ACI Committee 211, Standard Practice for SelectingProportions for Normal, Heavyweight, and Mass Concrete,ACI 211.1-91, reapproved 1997, ACI Committee 211Report, American Concrete Institute, Farmington Hills,Michigan, 1997, 38 pages.

ACI Committee 213, Guide for Structural LightweightAggregate Concrete, ACI 213R-87, reapproved 1999, ACICommittee 213 Report, American Concrete Institute,Farmington Hills, Michigan, 1999, 27 pages.

ACI Committee 223, Standard Practice for the Use ofShrinkage-Compensating Concrete, ACI 223-98, ACI Com-mittee 223 Report, American Concrete Institute, Farming-ton Hills, Michigan, 1998 28 pages.

ACI Committee 224, Control of Cracking in Concrete Struc-tures, ACI 224R-90, ACI Committee 224 Report, AmericanConcrete Institute, Farmington Hills, Michigan, 1990,43 pages.

ACI Committee 230, State-of-of-the-Art Report on SoilCement, ACI 230.1R-90, reapproved 1997, ACI Committee230 Report, American Concrete Institute, FarmingtonHills, Michigan, 1997, 23 pages. Also available throughPCA as LT120.

hand over the surface. The required amount of coloringmaterial can usually be determined from previously castsections. After the material has absorbed water from thefresh concrete, it should be floated into the surface. Thenthe rest of the material should be applied immediately atright angles to the initial application, so that a uniformcolor is obtained. The slab should again be floated to workthe remaining material into the surface.

Other finishing operations may follow dependingon the type of finish desired. Curing should beginimmediately after finishing; take precautions to preventdiscoloring the surface. See Kosmatka (1991) for moreinformation.

POLYMER-PORTLAND CEMENTCONCRETE

Polymer-portland cement concrete (PPCC), also calledpolymer-modified concrete, is basically normal portlandcement concrete to which a polymer or monomer has beenadded during mixing to improve durability and adhesion.Thermoplastic and elastomeric latexes are the most com-monly used polymers in PPCC, but epoxies and otherpolymers are also used. In general, latex improves duc-tility, durability, adhesive properties, resistance to chlo-ride-ion ingress, shear bond, and tensile and flexuralstrength of concrete and mortar. Latex-modified concretes(LMC) also have excellent freeze-thaw, abrasion, andimpact resistance. Some LMC materials can also resist cer-tain acids, alkalies, and organic solvents. Polymer-port-land cement concrete is primarily used in concretepatching and overlays, especially bridge decks. See ACI548.3R for more information on polymer-modified con-crete and ACI 548.4 for LMC overlays.

FERROCEMENT

Ferrocement is a special type of reinforced concrete com-posed of closely spaced layers of continuous relativelythin metallic or nonmetallic mesh or wire embedded inmortar. It is constructed by hand plastering, shotcreting,laminating (forcing the mesh into fresh mortar), or a com-bination of these methods.

The mortar mixture generally has a sand-cement ratioof 1.5 to 2.5 and a water-cement ratio of 0.35 to 0.50. Rein-forcement makes up about 5% to 6% of the ferrocementvolume. Fibers and admixtures may also be used to modifythe mortar properties. Polymers or cement-based coatingsare often applied to the finished surface to reduce porosity.

Ferrocement is considered easy to produce in avariety of shapes and sizes; however, it is labor intensive.Ferrocement is used to construct thin shell roofs, swim-ming pools, tunnel linings, silos, tanks, prefabricatedhouses, barges, boats, sculptures, and thin panels or sec-tions usually less than 25 mm (1 in.) thick (ACI 549R andACI 549.1R).

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ACI Committee 523, Guide for Cellular Concretes Above 50pcf and for Aggregate Concretes Above 50 pcf with CompressiveStrengths Less Than 2500 psi, ACI 523.3R-93, ACI Com-mittee 523 Report, American Concrete Institute, Farm-ington Hills, Michigan, 1993, 16 pages.

ACI Committee 544, Guide for Specifying, Proportioning,Mixing, Placing, and Finishing Steel Fiber Reinforced Concrete,ACI 544.3R-93, reapproved 1998, ACI Committee 544Report, American Concrete Institute, Farmington Hills,Michigan, 1998, 10 pages.

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“Porous Concrete Slabs and Pavement Drain Water,” Con-crete Construction, Concrete Construction Publications,Inc., Addison, Illinois, September 1983, pages 685 and 687to 688.

Reichard, T. W., “Mechanical Properties of InsulatingConcretes,” Lightweight Concrete, American Concrete Insti-tute, Farmington Hills, Michigan, 1971, pages 253 to 316.

Reid, E., and Marchand, J., “High-Performance RollerCompacted Concrete Pavements: Applications and RecentDevelopments”, Proceedings of the Canadian Society for CivilEngineering 1998 Annual Conference, Halifax, Nova Scotia,1998.

The Aberdeen Group, Shotcreting—Equipment, Materials,and Applications, Addison, Illinois, 1996, 46 pages.

Townsend, C. L., “Control of Cracking in Mass ConcreteStructures,” Engineering Monograph No. 34, U.S. Depart-ment of Interior, Bureau of Reclamation, Denver, 1965.

Tuthill, Lewis H., and Adams, Robert F., “CrackingControlled in Massive, Reinforced Structural Concrete byApplication of Mass Concrete Practices,” Journal of theAmerican Concrete Institute, American Concrete Institute,Farmington Hills, Michigan, August 1972, page 481.

Valore, R. C., Jr., “Cellular Concretes, Parts 1 and 2,” Pro-ceedings of the American Concrete Institute, vol. 50, AmericanConcrete Institute, Farmington Hills, Michigan, May 1954,pages 773 to 796 and June 1954, pages 817 to 836.

Valore, R. C., Jr., “Insulating Concrete,” Proceedings of theAmerican Concrete Institute, vol. 53, American ConcreteInstitute, Farmington Hills, Michigan, November 1956,pages 509 to 532.

VanGeem, Martha G.; Litvin, Albert; and Musser, DonaldW., Insulative Lightweight Concrete for Building Walls, pre-sented at the Annual Convention and Exposition of theAmerican Society of Civil Engineers in Detroit, October1985.

Walker, Stanton, and Bloem, Delmar L., “Effects ofAggregate Size on Properties of Concrete,” Proceedings ofthe American Concrete Institute, vol. 57, no. 3, AmericanConcrete Institute, Farmington Hills, Michigan, Sep-tember 1960, pages 283 to 298, and Discussion by N. G.Zoldner, March 1961, pages 1245 to 1248.

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AAbsorption—see Water absorption.Accelerating admixture—admixture that speeds therate of hydration of hydraulic cement, shortens thenormal time of setting, or increases the rate of harden-ing, of strength development, or both, of portlandcement, concrete, mortar, grout, or plaster.Addition—substance that is interground or blended inlimited amounts into a hydraulic cement during manu-facture—not at the jobsite—either as a “processingaddition” to aid in manufacture and handling of thecement or as a “functional addition” to modify theuseful properties of the cement. Admixture—material, other than water, aggregate, andhydraulic cement, used as an ingredient of concrete,mortar, grout, or plaster and added to the batch imme-diately before or during mixing.Aggregate—granular mineral material such as naturalsand, manufactured sand, gravel, crushed stone, air-cooled blast-furnace slag, vermiculite, or perlite.Air content—total volume of air voids, both entrainedand entrapped, in cement paste, mortar, or concrete.Entrained air adds to the durability of hardened mortaror concrete and the workability of fresh mixtures.Air entrainment—intentional introduction of air in theform of minute, disconnected bubbles (generallysmaller than 1 mm) during mixing of portland cementconcrete, mortar, grout, or plaster to improve desirablecharacteristics such as cohesion, workability, and dura-bility.Air-entraining admixture—admixture for concrete,mortar, or grout that will cause air to be incorporatedinto the mixture in the form of minute bubbles duringmixing, usually to increase the material’s workabilityand frost resistance.

Air-entraining portland cement—– portland cementcontaining an air-entraining addition added during itsmanufacture.Air void—entrapped air pocket or an entrained airbubble in concrete, mortar, or grout. Entrapped airvoids usually are larger than 1 mm in diameter;entrained air voids are smaller. Most of the entrappedair voids should be removed with internal vibration,power screeding, or rodding.Alkali-aggregate reactivity—production of expansivegel caused by a reaction between aggregates containingcertain forms of silica or carbonates and alkali hydrox-ides in concrete.Architectural concrete—concrete that will be perma-nently exposed to view and which therefore requiresspecial care in selection of concrete ingredients, form-ing, placing, consolidating, and finishing to obtain thedesired architectural appearance.Autoclaved cellular concrete—concrete containingvery high air content resulting in low density, and curedat high temperature and pressure in an autoclave.

BBatching—process of weighing or volumetricallymeasuring and introducing into the mixer the ingredi-ents for a batch of concrete, mortar, grout, or plaster.Blast-furnace slag—nonmetallic byproduct of steelmanufacturing, consisting essentially of silicates andaluminum silicates of calcium that are developed in amolten condition simultaneously with iron in a blastfurnace. Bleeding—flow of mixing water from a newly placedconcrete mixture caused by the settlement of the solidmaterials in the mixture.

The intent of this Glossary is to clarify terminology used in concrete construction, with special emphasis on thoseterms used in Design and Control of Concrete Mixtures. Additional terminology that may not be in this book isincluded in the Glossary for the convenience of our readers. Other sources for terms include ACI Committee 116,and ASTM standards.

Glossary

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Blended hydraulic cement—cement containingcombinations of portland cement, pozzolans, slag,and/or other hydraulic cement.Bulking—increase in volume of a quantity of sandwhen in a moist condition compared to its volumewhen in a dry state.

CCalcined clay—clay heated to high temperature toalter its physical properties for use as a pozzolan orcementing material in concrete.Calcined shale—shale heated to high temperature toalter its physical properties for use as a pozzolan orcementing material in concrete.Carbonation—reaction between carbon dioxide and ahydroxide or oxide to form a carbonate.Cellular concrete—–high air content or high voidratio concrete resulting in low density.Cement—see Portland cement and Hydraulic cement.Cement paste—constituent of concrete, mortar, grout,and plaster consisting of cement and water.Cementitious material (cementing material)—anymaterial having cementing properties or contributingto the formation of hydrated calcium silicatecompounds. When proportioning concrete, the follow-ing are considered cementitious materials: portland ce-ment, blended hydraulic cement, fly ash, groundgranulated blast-furnace slag, silica fume, calcined clay,metakaolin, calcined shale, and rice husk ash.Chemical admixture—see Admixture.Chemical bond—bond between materials resultingfrom cohesion and adhesion developed by chemicalreaction.Clinker—end product of a portland cement kiln; rawcementitious material prior to grindingChloride (attack)—chemical compounds containingchloride ions, which promote the corrosion of steelreinforcement. Chloride deicing chemicals are primarysources.Coarse aggregate—natural gravel, crushed stone, oriron blast-furnace slag, usually larger than 5 mm (0.2in.) and commonly ranging in size between 9.5 mm and37.5 mm (3⁄8 in. to 11⁄2 in.). Cohesion—mutual attraction by which elements of asubstance are held together.Colored concrete—concrete containing white cementand/or mineral oxide pigments to produce colors otherthan the normal gray hue of traditional gray cementconcrete.Compaction—process of inducing a closer arrange-ment of the solid particles in freshly mixed and placedconcrete, mortar, or grout by reduction of voids, usuallyby vibration, tamping, rodding, puddling, or a combi-nation of these techniques. Also called consolidation.

Compressive strength—maximum resistance that aconcrete, mortar, or grout specimen will sustain whenloaded axially in compression in a testing machine at aspecified rate; usually expressed as force per unit ofcross sectional area, such as megapascals (MPa) orpounds per square inch (psi).Concrete—mixture of binding materials and coarseand fine aggregates. Portland cement and water arecommonly used as the binding medium for normalconcrete mixtures, but may also contain pozzolans,slag, and/or chemical admixtures.Consistency—relative mobility or ability of freshlymixed concrete, mortar, or grout to flow. (See alsoSlump and Workability.)Construction joint—–a stopping place in the processof construction. A true construction joint allows forbond between new concrete and existing concrete andpermits no movement. In structural applications theirlocation must be determined by the structural engineer.In slab on grade applications, construction joints areoften located at contraction (control) joint locations andare constructed to allow movement and perform ascontraction joints.Contraction joint—weakened plane to control crack-ing due to volume change in a concrete structure. Jointmay be grooved, sawed, or formed. Also known as a“Control joint.”Corrosion—deterioration of metal by chemical, elec-trochemical, or electrolytic reaction.Creep—time-dependent deformation of concrete, or ofany material, due to a sustained load.Curing—process of maintaining freshly placed con-crete mortar, grout, or plaster moist and at a favorabletemperature for a suitable period of time during itsearly stages so that the desired properties of the mate-rial can develop. Curing assures satisfactory hydrationand hardening of the cementitious materials.

DDampproofing—treatment of concrete, mortar, grout,or plaster to retard the passage or absorption of water,or water vapor.Density—mass per unit volume; the weight per unitvolume in air, expressed, for example, in kg/m3

(lb/ft3).Durability—ability of portland cement concrete,mortar, grout, or plaster to resist weathering action andother conditions of service, such as chemical attack,freezing and thawing, and abrasion.

EEarly stiffening—rapidly developing rigidity infreshly mixed hydraulic cement paste, mortar, grout,plaster, or concrete.Entrapped air—irregularly shaped, unintentional airvoids in fresh or hardened concrete 1 mm or larger in

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Entrained air—spherical microscopic air bubbles—usually 10 µm to 1000 µm in diameter—intentionallyincorporated into concrete to provide freezing andthawing resistance and/or improve workability. Epoxy resin—class of organic chemical bondingsystems used in the preparation of special coatings oradhesives for concrete or masonry or as binders inepoxy-resin mortars and concretes. Ettringite—needle like crystalline compoundproduced by the reaction of C3A, gypsum, and waterwithin a portland cement concrete.Expansion joint—a separation provided between ad-joining parts of a structure to allow movement.

FFerrocement—one or more layers of steel or wire rein-forcement encased in portland cement mortar creatinga thin-section composite material.Fibers—thread or thread like material ranging from0.05 to 4 mm (0.002 to 0.16 in.) in diameter and from 10to 150 mm (0.5 to 6 in.) in length and made of steel,glass, synthetic (plastic), carbon, or natural materials.Fiber concrete—concrete containing randomly orientedfibers in 2 or 3 dimensions through out the concretematrix.Fine aggregate—aggregate that passes the 9.5-mm (3⁄8-in.) sieve, almost entirely passes the 4.75-mm (No. 4)sieve, and is predominantly retained on the 75-µm (No.200) sieve.Fineness modulus (FM)—factor obtained by addingthe cumulative percentages of material in a sample ofaggregate retained on each of a specified series ofsieves and dividing the sum by 100.Finishing—mechanical operations like screeding,consolidating, floating, troweling, or texturing thatestablish the final appearance of any concrete surface. Fire resistance—that property of a building material,element, or assembly to withstand fire or give protec-tion from fire; it is characterized by the ability toconfine a fire or to continue to perform a given struc-tural function during a fire, or both. Flexural strength—ability of solids to resist bending.Fly ash—residue from coal combustion, which iscarried in flue gases, and is used as a pozzolan or ce-menting material in concrete.Forms—temporary supports for keeping freshconcrete in place until it has hardened to such a degreeas to be self supporting (when the structure is able tosupport its dead load).Freeze-thaw resistance—ability of concrete to with-stand cycles of freezing and thawing. (See also Air en-trainment and Air-entraining admixture.)Fresh concrete—concrete that has been recentlymixed and is still workable and plastic.

GGrading—size distribution of aggregate particles,determined by separation with standard screen sieves.Grout—mixture of cementitious material with or with-out aggregate or admixtures to which sufficient wateris added to produce a pouring or pumping consistencywithout segregation of the constituent materials.

HHardened concrete—concrete that is in a solid stateand has developed a certain strength.High-density concrete (heavyweight concrete)—concrete of very high density; normally designed bythe use of heavyweight aggregates. High-strength concrete—concrete with a designstrength of at least 70 MPa (10,000 psi).Honeycomb—term that describes the failure of mortarto completely surround coarse aggregates in concrete,leaving empty spaces (voids) between them.Hydrated lime—dry powder obtained by treatingquicklime with sufficient water to satisfy its chemicalaffinity for water; consists essentially of calciumhydroxide or a mixture of calcium hydroxide andmagnesium oxide or magnesium hydroxide, or both.Hydration—in concrete, mortar, grout, and plaster, thechemical reaction between hydraulic cement and waterin which new compounds with strength-producingproperties are formed.Hydraulic cement—cement that sets and hardens bychemical reaction with water, and is capable of doingso under water. (See also Portland cement.)

IInch-pound units—units of length, area, volume,weight, and temperature commonly used in the UnitedStates during the 18th to 20th centuries. These include,but are not limited to: (1) length—inches, feet, yards,and miles; (2) area—square inches, square feet, squareyards, and square miles; (3) volume—cubic inches,cubic feet, cubic yards, gallons, and ounces;(4) weight—pounds and ounces; and (5) temperature—degrees Fahrenheit.Isolation Joint—separation that allows adjoining partsof a structure to move freely to one another, both hori-zontally and vertically.

JJoint—see Construction joint, Contraction joint, Isolationjoint, and Expansion joint.

KKiln—rotary furnace used in cement manufacture toheat and chemically combine raw inorganic materials,such as limestone, sand and clay, into calcium silicateclinker.

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LLightweight aggregate—low-density aggregate usedto produce lightweight (low-density) concrete. Couldbe expanded or sintered clay, slate, diatomaceous shale,perlite, vermiculite, or slag; natural pumice, scoria,volcanic cinders, tuff, or diatomite; sintered fly ash orindustrial cinders.Lightweight concrete—low-density concrete com-pared to normal-density concrete. Lime—general term that includes the various chemicaland physical forms of quicklime, hydrated lime, andhydraulic lime. It may be high-calcium, magnesian, ordolomitic.

MMasonry—concrete masonry units, clay brick, struc-tural clay tile, stone, terra cotta, and the like, or combi-nations thereof, bonded with mortar, dry-stacked, oranchored with metal connectors to form walls, buildingelements, pavements, and other structures.Masonry cement—hydraulic cement, primarily usedin masonry and plastering construction, consisting of amixture of portland or blended hydraulic cement andplasticizing materials (such as limestone, hydrated orhydraulic lime) together with other materials intro-duced to enhance one or more properties such assetting time, workability, water retention, and durabil-ity. Mass concrete—cast-in-place concrete in volumelarge enough to require measures to compensate forvolume change caused by temperature rise from heatof hydration in order to keep cracking to a minimum. Metakaolin—highly reactive pozzolan made fromkaolin clays. Metric units—also called System International (SI)Units. System of units adopted by most of the world bythe 21st Century. These include but are not limited to:(1) length—millimeters, meters, and kilometers;(2) area—square millimeters and square meters;(3) volume—cubic meters and liters; (4) mass—milli-grams, grams, kilograms, and megagrams; and (5)degrees Celsius.Mineral admixtures—see Supplementary cementitiousmaterials.Modulus of elasticity—ratio of normal stress to corre-sponding strain for tensile or compressive stress belowthe proportional limit of the material; also referred to aselastic modulus, Young’s modulus, and Young’s modu-lus of elasticity; denoted by the symbol E.Moist-air curing—curing with moist air (no less than95% relative humidity) at atmospheric pressure and atemperature of about 23ºC (73ºF).Mortar—mixture of cementitious materials, fine aggre-gate, and water, which may contain admixtures, and isusually used to bond masonry units.

Mortar cement—hydraulic cement, primarily used inmasonry construction, consisting of a mixture of port-land or blended hydraulic cement and plasticizingmaterials (such as limestone, hydrated or hydrauliclime) together with other materials introduced toenhance one or more properties such as setting time,workability, water retention, and durability. Mortarcement and masonry cement are similar in use andfunction. However, specifications for mortar cementusually require lower air contents and they include aflexural bond strength requirement.

NNormal weight concrete—class of concrete made withnormal density aggregates, usually crushed stone orgravel, having a density of approximately 2400 kg/m3

(150 lb/ft3). (See also Lightweight concrete and High-density concrete.)No-slump concrete—concrete having a slump of lessthan 6 mm (1⁄4 in.).

OOverlay—layer of concrete or mortar placed on orbonded to the surface of an existing pavement or slab.Normally done to repair a worn or cracked surface.Overlays are seldom less than 25 mm (1 in.) thick.

PPavement (concrete)—highway, road, street, path, orparking lot surfaced with concrete. Although typicallyapplied to surfaces that are used for travel, the termalso applies to storage areas and playgrounds.Permeability—property of allowing passage of fluidsor gases. Pervious concrete (no-fines or porous concrete)—concrete containing insufficient fines or no fines to fillthe voids between aggregate particles in a concretemixture. The coarse aggregate particles are coated witha cement and water paste to bond the particles at theircontact points. The resulting concrete contains an inter-connected pore system allowing storm water to drainthrough the concrete to the subbase below.pH—chemical symbol for the logarithm of the recipro-cal of hydrogen ion concentration in gram atoms perliter, used to express the acidity or alkalinity (base) of asolution on a scale of 0 to 14, where less than 7 repre-sents acidity, and more than 7 alkalinityPlastic cement—special hydraulic cement productmanufactured for plaster and stucco application. Oneor more inorganic plasticizing agents are intergroundor blended with the cement to increase the workabilityand molding characteristics of the resultant mortar,plaster, or stucco.Plasticity—that property of freshly mixed cementpaste, concrete, mortar, grout, or plaster that deter-mines its workability, resistance to deformation, or easeof molding.Plasticizer—admixture that increases the plasticity ofportland cement concrete, mortar, grout, or plaster.

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Polymer-portland cement concrete—fresh portlandcement concrete to which a polymer is added forimproved durability and adhesion characteristics,often used in overlays for bridge decks; also referred toas polymer-modified concrete and latex-modifiedconcrete.Popout—shallow depression in a concrete surfaceresulting from the breaking away of pieces of concretedue to internal pressure.Portland blast-furnace slag cement—hydrauliccement consisting of: (1) an intimately intergroundmixture of portland-cement clinker and granulatedblast-furnace slag; (2) an intimate and uniform blend ofportland cement and fine granulated blast-furnaceslag; or (3) finely ground blast-furnace slag with orwithout additions.Portland cement—Calcium silicate hydraulic cementproduced by pulverizing portland-cement clinker, andusually containing calcium sulfate and othercompounds. (See also Hydraulic cement.)Portland cement plaster—a combination of portlandcement-based cementitious material(s) and aggregatemixed with a suitable amount of water to form a plas-tic mass that will adhere to a surface and harden,preserving any form and texture imposed on it whileplastic. See also Stucco.Portland-pozzolan cement—hydraulic cement con-sisting of an intimate and uniform blend of portlandcement or portland blast-furnace slag cement and finepozzolan produced by intergrinding portland cementclinker and pozzolan, by blending portland cement orportland blast-furnace slag cement and finely dividedpozzolan, or a combination of intergrinding and blend-ing, in which the amount of the pozzolan constituent iswithin specified limits.Pozzolan—siliceous or siliceous and aluminous mate-rials, like fly ash or silica fume, which in itself possesslittle or no cementitious value but which will, in finelydivided form and in the presence of moisture, chemi-cally react with calcium hydroxide at ordinary temper-atures to form compounds possessing cementitiousproperties.Precast concrete—concrete cast in forms in acontrolled environment and allowed to achieve a spec-ified strength prior to placement on location.Prestressed concrete—concrete in which compres-sive stresses are induced by high-strength steel tendonsor bars in a concrete element before loads are applied tothe element which will balance the tensile stressesimposed in the element during service. This may beaccomplished by the following: Post-tensioning—amethod of prestressing in which the tendons/bars aretensioned after the concrete has hardened; or Pre-tensioning—a method of prestressing in which thetendons are tensioned before the concrete is placed.

QQuality control—actions taken by a producer orcontractor to provide control over what is being doneand what is being provided so that applicable stan-dards of good practice for the work are followed.

RReactive-powder concrete—high-strength, low-waterand low-porosity concrete with high silica content andaggregate particle sizes of less than 0.3 mm.Ready-mixed concrete—concrete manufactured fordelivery to a location in a fresh stateRecycled concrete—hardened concrete that has beenprocessed for reuse, usually as an aggregate.Reinforced concrete—concrete to which tensile bear-ing materials such as steel rods or metal wires areadded for tensile strength.Relative density—a ratio relating the mass of avolume of material to that of water; also called specificgravity.Relative humidity—The ratio of the quantity of watervapor actually present in the atmosphere to the amountof water vapor present in a saturated atmosphere at agiven temperature, expressed as a percentage.Retarder—an admixture that delays the setting andhardening of concrete.Roller-compacted concrete (RCC)—a zero slumpmix of aggregates, cementitious materials and waterthat is consolidated by rolling with vibratory com-pactors; typically used in the construction of dams, in-dustrial pavements, storage and composting areas, andas a component of composite pavements for highwaysand streets.

SScaling—disintegration and flaking of a hardenedconcrete surface, frequently due to repeated freeze-thaw cycles and application of deicing chemicals.Segregation—separation of the components (aggre-gates and mortar) of fresh concrete, resulting in anonuniform mixture.Self-compacting concrete—concrete of high worka-bility that require little or no vibration or othermechanical means of consolidation.Set—the degree to which fresh concrete has lost itsplasticity and hardened.Silica fume—very fine noncrystalline silica which is abyproduct from the production of silicon and ferrosili-con alloys in an electric arc furnace; used as a pozzolanin concrete.Shotcrete—mortar or small-aggregate concrete that isconveyed by compressed air through a hose andapplied at high velocity to a surface. Also known asgunite and sprayed concrete.Shrinkage—decrease in either length or volume of amaterial resulting from changes in moisture content,temperature, or chemical changes.

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Shrinkage-compensating concrete—concrete con-taining expansive cement, or an admixture, which pro-duces expansion during hardening and thereby offsetsthe contraction occurring later during drying (dryingshrinkage).Slag cement—hydraulic cement consisting mostly ofan intimate and uniform blend of ground, granulatedblast-furnace slag with or without portland cement orhydrated lime.Slump—measure of the consistency of freshly mixedconcrete, equal to the immediate subsidence of a spe-cimen molded with a standard slump cone.Slurry—thin mixture of an insoluble substance, such asportland cement, slag, or clay, with a liquid, such aswater.Soil cement—mixture of soil and measured amountsof portland cement and water compacted to a high den-sity; primarily used as a base material under pave-ments; also called cement-stabilized soil.Specific gravity—see Relative density.Stucco—portland cement plaster and stucco are thesame material. The term “stucco” is widely used todescribe the cement plaster used for coating exteriorsurfaces of buildings. However, in some geographicalareas, “stucco” refers only to the factory-preparedfinish coat mixtures. (See also Portland cement plaster.)Sulfate attack—most common form of chemical attackon concrete caused by sulfates in the groundwater orsoil manifested by expansion and disintegration of theconcrete. Superplasticizer (plasticizer)—admixture that in-creases the flowability of a fresh concrete mixture.Supplementary cementitious (cementing) mate-rials—Cementitious material other than portlandcement or blended cement. See also Cementitious material.

TTensile strength—stress up to which concrete is ableto resist cracking under axial tensile loading.

UUBC—Uniform Building Code, published by the Inter-national Conference of Building Officials, Whittier,California.Unit weight—density of fresh concrete or aggregate,normally determined by weighing a known volume ofconcrete or aggregate (bulk density of aggregates in-cludes voids between particles).

VVibration—high-frequency agitation of freshly mixedconcrete through mechanical devices, for the purposeof consolidation.Volume change—Either an increase or a decrease involume due to any cause, such as moisture changes,temperature changes, or chemical changes. (See alsoCreep.)

WWater absorption—(1) The process by which a liquid(water) is drawn into and tends to fill permeable poresin a porous solid. (2) The amount of water absorbed bya material under specified test conditions, commonlyexpressed as a percentage by mass of the test specimen.Water to cementing (cementitious) materials ratio—ratio of mass of water to mass of cementing materials inconcrete, including portland cement, blended cement,hydraulic cement, slag, fly ash, silica fume, calcinedclay, metakaolin, calcined shale, and rice husk ash.Water to cement ratio (water-cement ratio and w/c)—ratio of mass of water to mass of cement in concrete.Water reducer—admixture whose properties permit areduction of water required to produce a concrete mixof a certain slump, reduce water-cement ratio, reducecement content, or increase slump.White portland cement—cement manufactured fromraw materials of low iron content. Workability—That property of freshly mixed concrete,mortar, grout, or plaster that determines its workingcharacteristics, that is, the ease with which it can bemixed, placed, molded, and finished. (See also Slumpand Consistency.)

X

YYield—volume per batch of concrete expressed in cubicmeters (cubic feet).

ZZero-slump concrete—concrete without measurableslump (see also No-slump concrete).

1

ASTM Standards

A 820-96 Standard Specification for Steel Fibers forFiber Reinforced Concrete

C 29-97 Standard Test Method for Bulk Density(“Unit Weight”) and Voids in Aggregate

C 31-00 Standard Practice for Making and CuringConcrete Test Specimens in the Field

C 33-01 Standard Specification for ConcreteAggregates

C 39-01 Standard Test Method for CompressiveStrength of Cylindrical ConcreteSpecimens

C 40-99 Standard Test Method for OrganicImpurities in Fine Aggregates forConcrete

C 42-99 Standard Test Method for Obtaining andTesting Drilled Cores and Sawed Beamsof Concrete

C 70-01 Standard Test Method for SurfaceMoisture in Fine Aggregate

C 78-00 Standard Test Method for FlexuralStrength of Concrete (Using Simple Beamwith Third Point Loading)

C 85 Test Method for Cement Content ofHardened Portland Cement Concrete(Discontinued 1989–Replaced by C 1084)

C 87-83 (1995) Standard Test Method for Effect ofOrganic Impurities in Fine Aggregate onStrength of Mortar

C 88-99 Standard Test Method for Soundness ofAggregates by Use of Sodium Sulfate orMagnesium Sulfate

C 91-99 Standard Specification for MasonryCement

C 94-00 Standard Specification for Ready MixedConcrete

C 109-99 Standard Test Method for CompressiveStrength of Hydraulic Cement Mortars(using 50 mm [2 in.] Cube Specimens)

C 114-00 Standard Test Methods for ChemicalAnalysis of Hydraulic Cement

C 115-96 Standard Test Method for Fineness ofPortland Cement by the Turbidimeter

C 117-95 Standard Test Method for Materials Finerthan 75-µm (No. 200) Sieve in MineralAggregates by Washing

C 123-98 Standard Test Method for LightweightParticles in Aggregate

C 125-00 Standard Terminology Relating toConcrete and Concrete Aggregates

C 127-01 Standard Test Method for Density,Relative Density (Specific Gravity), andAbsorption of Coarse Aggregate

C 128-01 Standard Test Method for Density,Relative Density (Specific Gravity), andAbsorption of Fine Aggregate

C 131-96 Standard Test Method for Resistance toDegradation of Small Size CoarseAggregate by Abrasion and Impact in theLos Angeles Machine

C 136-01 Standard Test Method for Sieve Analysisof Fine and Coarse Aggregates

C 138-01 Standard Test Method for Density (UnitWeight), Yield, and Air Content(Gravimetric) of Concrete

C 141-97 Standard Specification for HydraulicHydrated Lime for Structural Purposes

C 142-97 Standard Test Method for Clay Lumpsand Friable Particles in Aggregates

C 143-00 Standard Test Method for Slump ofHydraulic Cement Concrete

C 150-00 Standard Specification for PortlandCement

C 151-00 Standard Test Method for AutoclaveExpansion of Portland Cement

C 156-98 Standard Test Method for WaterRetention by Concrete Curing Materials

C 157-99 Standard Test Method for Length Changeof Hardened Hydraulic Cement, Mortar,and Concrete

C 171-97 Standard Specification for Sheet Materialsfor Curing Concrete

C 172-99 Standard Practice for Sampling FreshlyMixed Concrete

C 173-01 Standard Test Method for Air Content ofFreshly Mixed Concrete by theVolumetric Method

C 174-97 Standard Test Method for MeasuringThickness of Concrete Elements UsingDrilled Concrete Cores

C 177-97 Standard Test Method for Steady-StateHeat Flux Measurements and ThermalTransmission Properties by Means of theGuarded-Hot-Plate Apparatus

C 183-97 Standard Practice for Sampling and theAmount of Testing of Hydraulic Cement

C 184-94 Standard Test Method for Fineness ofHydraulic Cement by the 150-µm (No.100) and 75-µm (No. 200) Sieves

C 185-01 Standard Test Method for Air Content ofHydraulic Cement Mortar

ASTM STANDARDSAmerican Society for Testing and Materials (ASTM) documents related to aggregates, cement, and concretethat are relevant to or referred to in the text are listed as follows and can be obtained at www.astm.org.

C 305-99 Standard Practice for Mechanical Mixingof Hydraulic Cement Pastes and Mortarsof Plastic Consistency

C 309-98 Standard Specification for LiquidMembrane

C 311-00 Standard Test Methods for Sampling andTesting Fly Ash or Natural Pozzolans forUse as a Mineral Admixture in Portland-Cement Concrete

C 330-00 Standard Specification for LightweightAggregates for Structural Concrete

C 332-99 Standard Specification for LightweightAggregates for Insulating Concrete

C 341-96 Standard Test Method for Length Changeof Drilled or Sawed Specimens ofHydraulic-Cement Mortar and Concrete

C 342-97 Standard Test Method for PotentialVolume Change of Cement-AggregateCombinations (Discontinued 2001)

C 348-97 Standard Test Method for FlexuralStrength of Hydraulic-Cement Mortars

C 359-99 Standard Test Method for Early Stiffeningof Portland Cement (Mortar Method)

C 360-92 Test Method for Ball Penetration in FreshPortland Cement Concrete (Discontinued1999)

C 384-98 Standard Test Method for Impedance andAbsorption of Acoustical Materials by theImpedance Tube Method

C 387-00 Standard Specification for Packaged, Dry,Combined Materials for Mortar andConcrete

C 403M-99 Standard Test Method for Time of Settingof Concrete Mixtures by PenetrationResistance

C 418-98 Standard Test Method for AbrasionResistance of Concrete by Sandblasting

C 430-96 Standard Test Method for Fineness ofHydraulic Cement by the 45-µm (No. 325)Sieve

C 441-97 Standard Test Method for Effectiveness ofMineral Admixtures or Ground Blast-Furnace Slag in Preventing ExcessiveExpansion of Concrete Due to the Alkali-Silica Reaction

C 451-99 Standard Test Method for Early Stiffeningof Hydraulic Cement (Paste Method)

C 452-95 Standard Test Method for PotentialExpansion of Portland-Cement MortarsExposed to Sulfate

C 457-98 Standard Test Method for MicroscopicalDetermination of Parameters of the Air-Void Content and Parameters of the Air-Void System in Hardened Concrete

C 465-99 Standard Specification for ProcessingAdditions for Use in the Manufacture ofHydraulic Cements

C 186-98 Standard Test Method for Heat ofHydration of Hydraulic Cement

C 187-98 Standard Test Method for NormalConsistency of Hydraulic Cement

C 188-95 Standard Test Method for Density ofHydraulic Cement

C 191-99 Standard Test Method for Time of Settingof Hydraulic Cement by Vicat Needle

C 192-00 Standard Practice for Making and CuringConcrete Test Specimens in theLaboratory

C 204-00 Standard Test Method for Fineness ofHydraulic Cement by Air PermeabilityApparatus

C 215-97 Standard Test Method for FundamentalTransverse, Longitudinal, and TorsionalFrequencies of Concrete Specimens

C 219-01 Standard Terminology Relating toHydraulic Cement

C 226-96 Standard Specification for Air-EntrainingAdditions for Use in the Manufacture ofAir-Entraining Hydraulic Cement

C 227-97 Standard Test Method for Potential AlkaliReactivity of Cement

C 230-98 Standard Specification for Flow Table forUse in Tests of Hydraulic Cement

C 231-97 Standard Test Method for Air Content ofFreshly Mixed Concrete by the PressureMethod

C 232-99 Standard Test Methods for Bleeding ofConcrete

C 233-01 Standard Test Method for Air-EntrainingAdmixtures for Concrete

C 235-68 Standard Method of Test for ScratchHardness of Coarse Aggregate Particles(Discontinued 1978)

C 243-99 Standard Test Method for Bleeding ofCement Pastes and Mortars

C 260-00 Standard Specification for Air-EntrainingAdmixtures for Concrete

C 265-99 Standard Test Method for Calcium Sulfatein Hydrated Portland Cement Mortar

C 266-99 Standard Test Method for Time of Settingof Hydraulic-Cement Paste by GillmoreNeedles

C 270-00 Standard Specification for Mortar for UnitMasonry

C 289-01 Standard Test Method for PotentialAlkali-Silica Reactivity of Aggregates(Chemical Method)

C 293-00 Standard Test Method for FlexuralStrength of Concrete (Using Simple BeamWith Center-Point Loading

C 294-98 Standard Descriptive Nomenclature forConstituents of Concrete Aggregates

C 295-98 Standard Guide for PetrographicExamination of Aggregates for Concrete

2


C 469-94 Standard Test Method for Static Modulusof Elasticity and Poisson’s Ratio ofConcrete in Compression

C 470-98 Standard Specification for Molds forForming Concrete Test CylindersVertically

C 490-00 Standard Practice for Use of Apparatusfor the Determination of Length Changeof Hardened Cement Paste, Mortar, andConcrete

C 494-99 Standard Specification for ChemicalAdmixtures for Concrete

C 495-99 Standard Test Method for CompressiveStrength of Lightweight InsulatingConcrete

C 496-96 Standard Test Method for Splitting TensileStrength of Cylindrical ConcreteSpecimens

C 511-98 Standard Specification for Moist Cabinets,Moist Rooms, and Water Storage TanksUsed in the Testing of Hydraulic Cementsand Concretes

C 512-87 (1994) Standard Test Method for Creep ofConcrete in Compression

C 513-89 (1995) Standard Test Method for Obtaining andTesting Specimens of HardenedLightweight Insulating Concrete forCompressive Strength

C 535-96 Standard Test Method for Resistance toDegradation of Large-Size CoarseAggregate by Abrasion and Impact in theLos Angeles Machine

C 566-97 Standard Test Method for TotalEvaporable Moisture Content ofAggregate by Drying

C 567-00 Standard Test Method for Density ofStructural Lightweight Concrete

C 586-99 Standard Test Method for Potential AlkaliReactivity of Carbonate Rocks forConcrete Aggregates (Rock CylinderMethod)

C 595-00 Standard Specification for BlendedHydraulic Cements

C 597-97 Standard Test Method for Pulse VelocityThrough Concrete

C 617-98 Standard Practice for Capping CylindricalConcrete Specimens

C 618-00 Standard Specification for Coal Fly Ashand Raw or Calcined Natural Pozzolanfor Use as a Mineral Admixture inConcrete

C 637-98 Standard Specification for Aggregates forRadiation-Shielding Concrete

C 638-92 (1997) Standard Descriptive Nomenclature ofConstituents of Aggregates for Radiation-Shielding Concrete

C 641-98 Standard Test Method for StainingMaterials in Lightweight ConcreteAggregates

C 642-97 Standard Test Method for Density,Absorption, and Voids in HardenedConcrete

C 666-97 Standard Test Method for Resistance ofConcrete to Rapid Freezing and Thawing

C 671-94 Standard Test Method for Critical Dilationof Concrete Specimens Subjected toFreezing

C 672-98 Standard Test Method for ScalingResistance of Concrete Surfaces Exposedto Deicing Chemicals

C 682-94 Standard Practice for Evaluation of FrostResistance of Coarse Aggregates in Air-Entrained Concrete by Critical DilationProcedures

C 684-99 Standard Test Method for Making,Accelerated Curing, and Testing ConcreteCompression Test Specimens

C 685-00a Standard Specification for Concrete MadeBy Volumetric Batching and ContinuousMixing

C 688-00 Standard Specification for FunctionalAdditions for Use in Hydraulic Cements

C 702-98 Standard Practice for Reducing Samplesof Aggregate to Testing Size

C 778-00 Standard Specification for Standard SandC 779-00 Standard Test Method for Abrasion

Resistance of Horizontal ConcreteSurfaces

C 786-96 Standard Test Method for Fineness ofHydraulic Cement and Raw Materials bythe 300-µm (No. 50), 150-µm (No. 100),and 75-µm (No. 200) Sieves by WetMethods

C 796-97 Standard Test Method for FoamingAgents for Use in Producing CellularConcrete Using Preformed Foam

C 801-98 Standard Test Method for Determiningthe Mechanical Properties of HardenedConcrete Under Triaxial Loads

C 803-97 Standard Test Method for PenetrationResistance of Hardened Concrete

C 805-97 Standard Test Method for ReboundNumber of Hardened Concrete

C 806-95 Standard Test Method for RestrainedExpansion of Expansive Cement Mortar

C 807-99 Standard Test Method for Time of Settingof Hydraulic Cement Mortar by ModifiedVicat Needle

C 823-00 Standard Practice for Examination andSampling of Hardened Concrete inConstructions

C 827-01 Standard Test Method for Change inHeight at Early Ages of CylindricalSpecimens of Cementitious Mixtures

C 845-96 Standard Specification for ExpansiveHydraulic Cement

3

ASTM Standards

C 979-99 Standard Specification for Pigments forIntegrally Colored Concrete

C 989-99 Standard Specification for GroundGranulated Blast-Furnace Slag for Use inConcrete and Mortars

C 995-94 Standard Test Method for Time of Flow ofFiber-Reinforced Concrete ThroughInverted Slump Cone

C 1012-95 Standard Test Method for Length Changeof Hydraulic-Cement Mortars Exposed toa Sulfate Solution

C 1017-98 Standard Specification for ChemicalAdmixtures for Use in Producing FlowingConcrete

C 1018-97 Standard Test Method for FlexuralToughness and First-Crack Strength ofFiber-Reinforced Concrete (Using BeamWith Third-Point Loading)

C 1038-95 Standard Test Method for Expansion ofPortland Cement Mortar Bars Stored inWater

C 1040-93 (2000) Standard Test Methods for Density ofUnhardened and Hardened Concrete InPlace By Nuclear Methods

C 1059-99 Standard Specification for Latex Agentsfor Bonding Fresh To Hardened Concrete

C 1064-99 Standard Test Method for Temperature ofFreshly Mixed Portland Cement Concrete

C 1073-97 Standard Test Method for HydraulicActivity of Ground Slag by Reaction withAlkali

C 1074-98 Standard Practice for Estimating ConcreteStrength by the Maturity Method

C 1077-00 Standard Practice for Laboratories TestingConcrete and Concrete Aggregates forUse in Construction and Criteria forLaboratory Evaluation

C 1078-87 (1992) Test Method for Determining CementContent of Freshly Mixed Concrete

C 1084-97 Standard Test Method for Portland-Cement Content of Hardened Hydraulic-Cement Concrete

C 1105-95 Standard Test Method for Length Changeof Concrete Due to Alkali-Carbonate RockReaction

C 1116-00 Standard Specification for Fiber-Reinforced Concrete and Shotcrete

C 1137-97 Standard Test Method for Degradation ofFine Aggregate Due to Attrition

C 1138-97 Standard Test Method for AbrasionResistance of Concrete (UnderwaterMethod)

C 1150-96 Standard Test Method for The Break-OffNumber of Concrete

C 1151-91 Standard Test Method for Evaluating theEffectiveness of Materials for CuringConcrete (Discontinued 2000)

C 856-95 Standard Practice for PetrographicExamination of Hardened Concrete

C 869-91 (1999) Standard Specification for FoamingAgents Used in Making Preformed Foamfor Cellular Concrete

C 873-99 Standard Test Method for CompressiveStrength of Concrete Cylinders Cast inPlace in Cylindrical Molds

C 876-91 (1999) Standard Test Method for Half-CellPotentials of Uncoated Reinforcing Steelin Concrete

C 878-95a Standard Test Method for RestrainedExpansion of Shrinkage-CompensatingConcrete

C 881-99 Standard Specification for Epoxy-Resin-Base Bonding Systems for Concrete

C 900-99 Standard Test Method for PulloutStrength of Hardened Concrete

C 917-98 Standard Test Method for Evaluation ofCement Strength Uniformity From aSingle Source

C 918-97 Standard Test Method for MeasuringEarly-Age Compressive Strength andProjecting Later-Age Strength

C 926-98 Standard Specification for Application ofPortland Cement-Based Plaster

C 928-00 Standard Specification for Packaged, Dry,Rapid-Hardening Cementitious Materialsfor Concrete Repairs

C 937-97 Standard Specification for GroutFluidifier for Preplaced-AggregateConcrete

C 938-97 Standard Practice for Proportioning GroutMixtures for Preplaced-AggregateConcrete

C 939-97 Standard Test Method for Flow of Groutfor Preplaced-Aggregate Concrete (FlowCone Method)

C 940-98 Standard Test Method for Expansion andBleeding of Freshly Mixed Grouts forPreplaced-Aggregate Concrete in theLaboratory

C 941-96 Standard Test Method for WaterRetentivity of Grout Mixtures forPreplaced-Aggregate Concrete in theLaboratory

C 942-99 Standard Test Method for CompressiveStrength of Grouts for Preplaced-Aggregate Concrete in the Laboratory

C 943-96 Standard Practice for Making TestCylinders and Prisms for DeterminingStrength and Density of Preplaced-Aggregate Concrete in the Laboratory

C 944-99 Standard Test Method for AbrasionResistance of Concrete or Mortar Surfacesby the Rotating-Cutter Method

C 953-87 (1997) Standard Test Method for Time of Settingof Grouts for Preplaced-AggregateConcrete in the Laboratory

4


C 1152-97 Standard Test Method for Acid-SolubleChloride in Mortar and Concrete

C 1157-00 Standard Performance Specification forHydraulic Cement

C 1170-91 (1998) Standard Test Methods for DeterminingConsistency and Density of Roller-Compacted Concrete Using a VibratingTable

C 1202-97 Standard Test Method for ElectricalIndication of Concrete’s Ability to ResistChloride Ion Penetration

C 1218-99 Standard Test Method for Water-SolubleChloride in Mortar and Concrete

C 1231-00 Standard Practice for Use of UnbondedCaps in Determination of CompressiveStrength of Hardened Concrete Cylinders

C 1240-01 Standard Specification for Use of SilicaFume for Use as a Mineral Admixture inHydraulic-Cement Concrete, Mortar, andGrout

C 1252-98 Standard Test Methods for UncompactedVoid Content of Fine Aggregate (asInfluenced by Particle Shape, SurfaceTexture, and Grading)

C 1260-94 Standard Test Method for Potential AlkaliReactivity of Aggregates (Mortar-BarMethod)

C 1263-95 (2000) Standard Test Method for ThermalIntegrity of Flexible Water VaporRetarders

C 1293-01 Standard Test Method for Determinationof Length Change of Concrete Due toAlkali-Silica Reaction

C 1315-00 Standard Specification for LiquidMembrane-Forming Compounds HavingSpecial Properties for Curing and SealingConcrete

C 1328-00 Standard Specification for Plastic (Stucco)Cement

C 1329-00 Standard Specification for Mortar CementC 1356-96 Standard Test Method for Quantitative

Determination of Phases in PortlandCement Clinker by Microscopical Point-Count Procedure

C 1362-97 Standard Test Method for Flow of FreshlyMixed Hydraulic Cement Concrete

C 1365-98 Standard Test Method for Determinationof the Proportion of Phases in PortlandCement and Portland-Cement ClinkerUsing X-Ray Powder Diffraction Analysis

C 1383-98 Standard Test Method for Measuring theP-Wave Speed and the Thickness ofConcrete Plates Using the Impact-EchoMethod

C 1437-99 Standard Test Method for Flow ofHydraulic Cement Mortar

C 1451-99 Standard Practice for DeterminingUniformity of Ingredients of ConcreteFrom a Single Source

C 1500 Standard Test Method for Water-Extractable Chloride in Aggregate(Soxhlet Method)

D 75-97 Standard Practice for SamplingAggregates

D 98-98 Standard Specification for CalciumChloride

D 345-97 Standard Test Method for Sampling andTesting Calcium Chloride for Roads andStructural Applications

D 448-98 Standard Classification for Sizes ofAggregate for Road and BridgeConstruction

D 512-89 (1999) Standard Test Methods for Chloride Ionin Water

D 516-90 (1995) Standard Test Method for Sulfate Ion inWater

D 558-96 Standard Test Methods for Moisture-Density Relations of Soil-CementMixtures

D 632-01 Standard Specification for SodiumChloride

D 2240-00 Standard Test Method for RubberProperty-Durometer Hardness

D 3042-97 Standard Test Method for InsolubleResidue in Carbonate Aggregates

D 3398-00 Standard Test Method for Index ofAggregate Particle Shape and Texture

D 3963-01 Standard Specification for Fabrication andJobsite Handling of Epoxy-Coated SteelReinforcing Bars

D 4263-83 (1999) Standard Test Method for IndicatingMoisture in Concrete by the Plastic SheetMethod

D 4580-86 (1997) Standard Practice for MeasuringDelaminations in Concrete Bridge Decksby Sounding

D 4791-99 Standard Test Method for Flat Particles,Elongated Particles, or Flat and ElongatedParticles in Coarse Aggregate

E 11-01 Standard Specification for Wire Cloth andSieves for Testing Purposes

F 1869-98 Standard Test Method for MeasuringMoisture Vapor Emission Rate ofConcrete Subfloor Using AnhydrousCalcium Chloride

G 59-97 Standard Test Method for ConductingPotentiodynamic Polarization ResistanceMeasurements

IEEE-ASTM-SI-10 Standard for Use of the InternationalSystem of Units (SI): The Modern MetricSystem

PS 118-99 Standard Test Method for Water-Extractable Chloride in Aggregate(Soxhlet Method)

5

ASTM Standards

6


T 11-91 (1996) Materials Finer than 75-µm (No. 200)Sieve in Mineral Aggregates by Washing

T 19-00 Bulk Density (“Unit Weight”) and Voidsin Aggregate

T 21-00 Organic Impurities in Fine Aggregate forConcrete

T 22-97 Compressive Strength of CylindricalConcrete Specimens

T 23-97 Making and Curing Concrete TestSpecimens

T 24-97 Obtaining and Testing Drilled Cores andSawed Beams of Concrete

T 26-79 (1996) Quality of Water to be Used in ConcreteT 27-99 Sieve Analysis of Fine and Coarse

AggregateT 71-93 (1997) Effect of Organic Impurities in Fine

Aggregate on Strength of MortarT 84-00 Specific Gravity and Absorption of Fine

AggregateT 85-91 (1996) Specific Gravity and Absorption of

Coarse AggregateT 96-99 Resistance to Degradation of Small-Size

Coarse Aggregate by Abrasion andImpact in the Los Angeles Machine

T 97-97 Flexural Strength of Concrete (UsingSimple Beam with Third Point Loading)

T 98-99 Fineness of Portland Cement by theTurbidimeter

T 103-91 (1996) Soundness of Aggregates by Freezingand Thawing

T 104-99 Soundness of Aggregate by Use ofSodium Sulfate or Magnesium Sulfate

T 105-00 Chemical Analysis of Hydraulic CementT 106-00 Compressive Strength of Hydraulic

Cement Mortar (Using 50-mm or 2-in.Cube Specimens)

T 107-00 Autoclave Expansion of PortlandCement

T 112-00 Clay Lumps and Friable Particles inAggregate

T 113-96 Lightweight Pieces in AggregateT 119-99 Slump of Hydraulic Cement ConcreteT 121-97 Mass per Cubic Meter (Cubic Foot),

Yield, and Air Content (Gravimetric) ofConcrete

T 126-97 Making and Cuing Concrete TestSpecimens in the Laboratory

T 127-00 Sampling and Amount of Testing byHydraulic Cement

M 6-93 (1997) Fine Aggregate for Portland CementConcrete

M 43-88 (1999) Sizes of Aggregate for Road and BridgeConstruction

M 80-87 (1999) Coarse Aggregate for Portland CementConcrete

M 85-00 Portland CementM 92-96 Wire-Cloth Sieves for Testing PurposesM 143-86 (1993) Sodium ChlorideM 144-86 (1996) Calcium ChlorideM 148-97 Liquid Membrane-Forming Compounds

for Curing ConcreteM 152-00 Flow Table for Use in Test of Hydraulic

CementsM 154-00 Air-Entraining Admixtures for ConcreteM 157-00 Ready-Mixed ConcreteM 171-00 Sheet Materials for Curing ConcreteM 182-91 (1996) Burlap Cloth Made From Jute or KenafM 194-00 Chemical Admixtures For ConcreteM 195-00 Lightweight Aggregate for Structural

ConcreteM 200-73 (1996) Epoxy Protective CoatingsM 201-00 Moist Cabinets, Moist Rooms, and Water

Storage Tanks Used in the Testing ofHydraulic Cements and Concretes

M 205-97 Molds for Forming Concrete TestCylinders Vertically

M 210-99 Use of Apparatus for the Determinationof Length Change of Hardened CementPaste, Mortar, and Concrete

M 224-91 (1996) Use of Protective Sealers for PortlandCement Concrete

M 231-95 (1999) Weighing Devices Used in the Testing ofMaterials

M 233-86 (1996) Boiled Linseed Oil Mixture forTreatment of Portland Cement Concrete

M 235-91 (1996) Epoxy Resin AdhesivesM 240-00 Blended Hydraulic CementsM 241-97 Concrete Made by Volumetric Batching

and Continuous MixingM 284-95 Epoxy Coated Reinforcing BarsM 295-00 Coal Fly Ash and Raw and Calcined

Natural Pozzolan for use as a MineralAdmixture in Concrete

M 302-00 Ground Granulated Blast-Furnace Slagfor Use in Concrete and Mortars

M 307-95 (1999) Microsilica for Use in Concrete andMortar

T 2-91 (1996) Sampling of Aggregates

AASHTO STANDARDSAmerican Association of State Highway and Transportation Officials (AASHTO) documents related to aggre-gates, cement, and concrete that are relevant to or referred to in the text are listed as follows and can beobtained at www.aashto.org.

T 128-97 Fineness of Hydraulic Cement by the150-µm (No. 100) and 75-µm (No. 200)Sieves

T 129-88 (1995) Normal Consistency of HydraulicCement

T 131-93 (1999) Time of Setting of Hydraulic Cement byVicat Needle

T 133-98 Density of Hydraulic CementT 134-95 Moisture-Density Relations of Soil-

Cement MixturesT 137-00 Air Content of Hydraulic Cement

MortarT 141-97 Sampling Freshly Mixed ConcreteT 152-97 Air Content of Freshly Mixed Concrete

by the Pressure MethodT 153-98 Fineness of Hydraulic Cement by Air

Permeability ApparatusT 154-91 (1996) Time of Setting of Hydraulic Cement by

Gillmore NeedlesT 155-91 (1996) Water Retention by Concrete Curing

MaterialsT 157-00 Air-Entraining Admixtures for ConcreteT 158-97 Bleeding of ConcreteT 160-97 Length Change of Hardened Hydraulic

Cement Mortar and ConcreteT 161-00 Resistance of Concrete to Rapid Freezing

and ThawingT 177-97 Flexural Strength of Concrete (Using

Simple Beam with Center-PointLoading)

T 178-98 Cement Content of Hardened PortlandCement Concrete

T 185-91 (1996) Early Stiffening of Portland Cement(Mortar Method)

T 186-97 Early Stiffening of Hydraulic Cement(Paste Method)

T 192-99 Fineness of Hydraulic Cement by the 45-µm (No. 325) Sieve

T 196-96 Air Content of Freshly Mixed Concreteby the Volumetric Method

T 197-00 Time of Setting of Concrete Mixtures ByPenetration Resistance

T 198 Splitting Tensile Strength of CylindricalConcrete Specimen

T 199-00 Air Content of Freshly Mixed Concreteby the Chace Indicator

T 210-96 Aggregate Durability IndexT 231-97 Capping Cylindrical Concrete SpecimenT 248-96 Reducing Samples of Aggregates to

Testing SizeT 255-00 Total Evaporable Moisture Content of

Aggregate by DryingT 259-80 Resistance of Concrete to Chloride Ion

PenetrationT 260-97 Sampling and Testing for Chloride Ion in

Concrete and Concrete Raw Materials

T 271-83 (1996) Density of Plastic and HardenedPortland Cement Concrete in-Place byNuclear Methods

T 276-97 Developing Early-Age Compression TestValues and Projecting Later-AgeStrength

T 277-96 Electrical Indication of Concrete’s Abilityto resist Chloride Ion Penetration

T 290 Determining Water-Soluble Sulfate IonContent in Soil

T 299-93 Rapid Identification of Alkali-SilicaReaction Products in Concrete

T 303-00 Accelerated Detection of PotentiallyDeleterious Expansion of Mortar BarsDue to Alkali-Silica Reaction

T 304-96 Uncompacted Void Content of FineAggregate

T 309-99 Temperature of Freshly Mixed PortlandCement Concrete

TP 23-93 (1996) Standard Test Method for Water Contentof Freshly Mixed Concrete UsingMicrowave Oven Drying

TP 60-00 Standard Test Method for the Coefficientof Thermal Expansion of HydraulicCement Concrete

7

AASHTO Standards

8


CEMENT AND CONCRETE RESOURCES

AASHTO American Association of State Highway andTransportation Officialshttp://www.transportation.orghttp://www.aashto.org

ACAA American Coal Ash Associationhttp://www.acaa-usa.org

ACBM Center for Advanced Cement Based Materials(Northwestern University)http://www.civil.northwestern.edu/ACBM

ACI American Concrete Institutehttp://www.aci-int.org

ACPA American Concrete Pavement Associationhttp://www.pavement.com

ACPA American Concrete Pipe Associationhttp://www.concrete-pipe.org

ACPA American Concrete Pumping Associationhttp://www.concretepumpers.com/

ACPPA American Concrete Pressure Pipe Associationhttp://www.acppa.org

ACS American Ceramic Societyhttp://www.acers.org

AIT International Ferrocement Societyhttp://www.ferrocement.org

APA Architectural Precast Associationhttp://www.archprecast.org

APCA American Portland Cement Alliancehttp://www.apca.org

API American Petroleum Institutehttp://www.api.org

ANSI American National Standards Institutehttp://www.ansi.org

ASCC American Society of Concrete Contractorshttp://www.assconc.org

ASCE American Society of Civil Engineershttp://www.asce.org

ASHRAE American Society of Heating, Refrigerating,and Air-Conditioning Engineers, Inc.http://www.ashrae.org

ASI American Shotcrete Associationhttp://www.shotcrete.org

ASTM American Society for Testing and Materialshttp://www.astm.org

BCA British Cement Associationhttp://www.bca.org.uk

BDZ Bundesverband der DeutschenZementindustrie e. V.http://www.bdzement.de

BFRL Building and Fire Research Laboratory(NIST)http://www.bfrl.nist.gov

BOCA Building Officials and Code AdministratorsInternationalhttp://www.bocai.org

BRE Building Research Establishment (UK)http://www.bre.co.uk

BSI British Standards Institutionhttp://www.bsi-global.com

CABO Council of American Building Officialshttp://www.cabo.org

CAC Cement Association of Canadahttp://www.cement.ca

CC Cement Careershttp://www.cementcareers.org

CCAA Cement and Concrete Association ofAustraliahttp://www.concrete.net.au

CCRI Concrete Corrosion Inhibitors Foundationhttp://www.corrosioninhibitors.org/

CERF Civil Engineering Research Foundationhttp://www.cerf.org

CFA Concrete Foundations Associationhttp://www.cfana.org

CH Concrete Homeshttp://www.concretehomes.com

CRSI Concrete Reinforcing Steel Institutehttp://www.crsi.org

CSA Canadian Standards Associationhttp://www.csa.ca

CSCE Canadian Society for Civil Engineeringhttp://www.csce.ca

CSDA Concrete Sawing and Drilling Associationhttp://www.csda.org

CSI Construction Specifications Institutehttp://www.csinet.org

CSI Cast Stone Institutehttp://www.caststone.org

DIN Deutsches Institut für Normung e.V. (GermanStandards Institution)http://www.din.de

ECCO Environmental Council of ConcreteOrganizationshttp://www.ecco.org

EPRI Electric Power Research Institutehttp://www.epri.com

ESCSI Expanded Shale, Clay and Slate Institutehttp://www.escsi.org

EUC European Concretehttp://www.europeanconcrete.com

FHWA Federal Highway Administrationhttp://www.fhwa.dot.gov/

9

Cement and Concrete Resources

FICEM Federacion Interamericana del Cementohttp://www.ficem.org

HPC-CAN High Performance Concrete Network ofCentres of Excellence (Canada)http://www.usherb.ca/concrete

IBC International Building Codehttp://www.intlcode.org

ICAR International Center for Aggregates Researchhttp://www.ce.utexas.edu/org/icar/

ICBO International Conference of Building Officialshttp://www.icbo.org

ICC International Code Councilhttp://www.intlcode.org

ICFA Insulating Concrete Forms Associationhttp://www.forms.org/

ICMA International Cement Microscopy Association http://www.cemmicro.org

ICPI Interlocking Concrete Pavement Institutehttp://www.icpi.org

ICRI International Concrete Repair Institutehttp://www.icri.org

IEEE Institute of Electrical & Electronics Engineershttp://www.ieee.org

IGGA International Grinding & GroovingAssociationhttp://www.igga.net

IMCYC Instituto Mexicano del Cemento y delConcreto A.C.http://www.imcyc.com

IPRF Innovative Pavement Research Foundationhttp://www.iprf.org

ISO International Standards Organizationhttp://www.iso.ch

JCI Japan Concrete Institutehttp://www.jci-net.or.jp/

LTPP Long Term Pavement Performancehttp://www.tfhrc.gov/pavement/ltpp/ltpp.htm

MERL U.S. Bureau of Reclamation Materials andEngineering Research Laboratory http://www.usbr.gov/merl

MRS Materials Research Societyhttp://www.mrs.org

NACE National Association of Corrosion Engineershttp://www.nace.org

NAHB National Association of Home Buildershttp://www.nahb.com

NCMA National Concrete Masonry Associationhttp://www.ncma.org

NIBS National Institute of Building Scienceshttp://www.nibs.org

NIST National Institute of Standards andTechnologyhttp://www.nist.gov

NPCA National Precast Concrete Associationhttp://www.precast.org

NRC National Research Councilhttp://www.nas.edu/nrc/

NRCC National Research Council of Canadahttp://www.nrc.ca/

NRMCA National Ready Mixed Concrete Associationhttp://www.nrmca.org

NSA National Slag Associationhttp://www.nationalslagassoc.org

NSSGA National Stone, Sand & Gravel Associationhttp://www.nssga.org

NTMA National Terrazzo & Mosaic Association Inc.http://www.ntma.com

OP&CMIA Operative Plasterers’ and Cement Masons’International Association http://www.opcmia.org

OSHA Occupational Safety and HealthAdministrationhttp://www.osha.gov

PCA Portland Cement Associationhttp://www.portcement.org

PCI Precast/Prestressed Concrete Institutehttp://www.pci.org

PI Perlite Institutehttp://www.perlite.org

PTI Post-Tensioning Institute http://www.post-tensioning.org/

REMR Repair, Evaluation, Maintenance, andRehabilitation Research Programhttp://www.wes.army.mil/REMR

RILEM International Union of Testing and ResearchLaboratories for Materials and Structureshttp://www.ens-cachan.fr/rilem.html

SCA Slag Cement AssociationSFA Silica Fume Association

http://www.silicafume.orgTAC Transportation Association of Canada

http://www.tac-atc.ca TCA Tilt-Up Concrete Association

http://www.tilt-up.orgTRB Transportation Research Board

http://www.nas.edu/trb/ TVA The Vermiculite Association

http://www.vermiculite.org/ USACE U.S. Army Corps of Engineers

http://www.usace.army.milVCCTL Virtual Cement and Concrete Testing

Laboratoryhttp://ciks.cbt.nist.gov/vcctl

VDZ Verein Deutscher Zementwerke (GermanCement Works Association)http://www.vdz-online.de

WES U.S. Army Engineer Waterways ExperimentStationhttp://www.wes.army.mil

WRI Wire Reinforcement Institutehttp://www.bright.net/~wwri

348


To convert from to multiply by

Mass (weight) per lengthkip per linear foot kilogram per meter 0.001488

(klf) (kg/m)pound per linear foot kilogram per meter 1.488

(plf) (kg/m)

Mass per volume (density)pound per cubic foot kilogram per cubic 16.01846

(lb/ft3) meter (kg/m3)pound per cubic yard kilogram per cubic 0.5933

(lb/yd3) meter (kg/m3)

Temperaturedegree Fahrenheit degree Celsius tC = (tF – 32)/1.8

(°F) (°C)degree Fahrenheit degree Kelvin tK = (tF + 459.7)/1.8

(°F) (°K)degree Kelvin (°K) degree Celsius tC = tK – 273.15

(°C )

Energy and heatBritish thermal unit joule (J) 1055.056

(Btu)calorie (cal) joule (J) 4.1868 EBtu/°F hr • ft2 W/m2 • °K 5.678263kilowatt-hour (kwh) joule (J) 3,600,000 EBritish thermal unit calories per 0.55556

per pound (Btu/lb) gram (cal/g)British thermal unit watt (W) 0.2930711

per hour (Btu/hr)

Permeabilitydarcy centimeter per second 0.000968

(cm/sec)feet per day (ft/day) centimeter per second 0.000352

(cm/sec)* E indicates that the factor given is exact.

** One U.S. gallon equals 0.8327 Canadian gallon.† A pascal equals 1.000 newton per square meter.

Note:One U.S. gallon of water weighs 8.34 pounds (U.S.) at 60°F.One cubic foot of water weighs 62.4 pounds (U.S.).One milliliter of water has a mass of 1 gram and has a volume ofone cubic centimeter.One U.S. bag of cement weighs 94 lb.The prefixes and symbols listed below are commonly used toform names and symbols of the decimal multiples and submulti-ples of the SI units.

Multiplication Factor Prefix Symbol1,000,000,000 = 109 giga G

1,000,000 = 106 mega M1,000 = 103 kilo k

1 = 1 — —0.01 = 10–2 centi c

0.001 = 10–3 milli m0.000001 = 10–6 micro µ

0.000000001 = 10–9 nano n

METRIC CONVERSION FACTORSThe following list provides the conversion relationshipbetween U.S. customary units and SI (International System)units. The proper conversion procedure is to multiply thespecified value on the left (primarily U.S. customary values)by the conversion factor exactly as given below and thenround to the appropriate number of significant digits desired.For example, to convert 11.4 ft to meters: 11.4 x 0.3048 =3.47472, which rounds to 3.47 meters. Do not round eithervalue before performing the multiplication, as accuracy wouldbe reduced. A complete guide to the SI system and its use canbe found in IEEE/ASTM SI-10, Metric Practice.To convert from to multiply by

Lengthinch (in.) micrometer (µm) 25,400 E*inch (in.) millimeter (mm) 25.4 Einch (in.) meter (m) 0.0254 Efoot (ft) meter (m) 0.3048 Eyard (yd) meter (m) 0.9144

Areasquare foot (ft2) square meter (m2) 0.09290304 Esquare inch (in.2) square millimeter 645.2 E

(mm2)square inch (in.2) square meter (m2) 0.00064516 Esquare yard (yd2) square meter (m2) 0.8361274

Volumecubic inch (in.3) cubic millimeter 16.387064

(mm3)cubic inch (in.3) cubic meter (m3) 0.00001639cubic foot (ft3) cubic meter (m3) 0.02831685cubic yard (yd3) cubic meter (m3) 0.7645549gallon (gal) U.S. liquid** liter (L) 3.7854118gallon (gal) U.S. liquid cubic meter (m3) 0.00378541fluid ounce (fl oz) milliliters (mL) 29.57353fluid ounce (fl oz) cubic meter (m3) 0.00002957

Forcekip (1000 lb) kilogram (kg) 453.6kip (1000 lb) newton (N) 4,448.222pound (lb) kilogram (kg) 0.4535924

avoirdupoispound (lb) newton (N) 4.448222

Pressure or stresspound per square kilogram per square 4.8824

foot (psf) meter (kg/m2)pound per square pascal (Pa)† 47.88

foot (psf)pound per square kilogram per square 0.07031

inch (psi) centimeter (kg/sq cm)pound per square pascal (Pa)† 6,894.757

inch (psi)pound per square megapascal (MPa) 0.00689476

inch (psi)

Mass (weight)pound (lb) kilogram (kg) 0.4535924

avoirdupoiston, 2000 lb kilogram (kg) 907.1848

Appendix ◆ Metric Conversion Factors

351

Index

Abrasion resistanceaggregate, 90-91concrete, 10-11, 65-66, 130, 290high-strength concrete, 308

Abrasive blasting, 212-214Absolute volume, 157, 159-166, 172-174Accelerated compression tests, 284Accelerated curing tests, 225Accelerating admixtures, 113, 242, 328Acid, 76, 91

cleaning, 212Admixtures, 105-120, 306

accelerating, 113, 242, 328air-detraining, 117, 137air-entraining, 107, 136-137, 142-144alkali-reactivity reducers, 115antiwashout, 117bonding, 116calcium chloride, 113-116carbon black, 116classified, 105-107coloring, 115-116compatibility, 117corrosion inhibiting, 114-115dampproofing, 116effect on air content, 63, 157fungicidal, 117gas-forming, 117grouting agents, 117high-range water reducing, 109hydration-controlling, 113mid-range water reducing, 109mix design, 172permeability-reducing, 116plasticizing, 110-112pumping aids, 116retarding (set-retarding), 113, 238shrinkage reducing, 115specifications, 106-107storing, 117-118superplasticizing, 110-112water-reducing, 107-109, 157

gap graded, 86-87grading, 80-87, 277handling, 98harmful, 92-93heating, 244heavy media separation, 98heavyweight, high-density, 80, 322impurities, 92, 276jigging, 98lightweight, low-density, 80, 316, 318lime-slurry stain test, 93maximum size, 81, 84-85, 138-139,

151-152, 305marine-dredged, 99metallic, 11minerals, 80moisture content, 88-89, 277-278mortar bar test, 96-97normal-weight, normal-density, 80objectionable fine material, 93, 277optimum size, 85-86, 305organic impurities, 92, 276-277ovendry, 88particle shape, 87, 100particle size, 80-87, 277, 312petrographic examination, 87, 98popouts, 89-90, 92-93recycled-concrete, 99-101relative density, 87-88rising-current classification, 98rock cylinder test, 98rocks, 79sampling, 276sand, 1, 79

also see finesaturated surface dry, 88segregation, 98-99selection, 105shrinkage, 86, 91, 100, 260-261, 263sieve analysis, 80, 84, 277size, 80-87, 277, 305size number, 81-82, 85skid resistance, 90-91

Age-strength relationships, 6, 7, 47, 48,64-65, 110, 112, 220, 231, 241

Aggregates, 79-104, 305-306abrasion resistance, 90-91absorption, 88, 100acid resistance, 91air dry, 88alkali-reactive, 98, 100, 270beneficiation, 98blast-furnace slag, 79, 80bond, 87, 92, 305bulk density, 87bulk volume, 152bulking of sand, 88-89cement requirements, 84, 87characteristics, 80-92, 151-152, 305-306chemical stability, 92-95, 98coarse, 84-86combined grading, 86compressive strength, 91consolidation, 80constituents, 80, 92-93contamination, 92-93content, 79-80, 151, 161, 163, 173cooling, 231-234corrosion resistance, 91damp, 88D-cracking, 89-90definitions, 79deleterious substances, 91-95, 98density, 8-9, 88

bulk, 87relative, 87-88

deterioration, 89-90, 92dispersion, 83drying, 277-278durability, 90effect on air content, 138exposed-aggregate concrete, 86, 213-214fine, 83-84fineness modulus, 84fire resistance, 92freeze-thaw resistance, 89-90

Index

352


slag, 79, 80soundness, 81specific gravity

see relative densityspecifications, 81staining, 93, 96-97stockpiling, 99-100storage, 99strength, 91sulfate test, 90surface moisture, 88surface texture, 87temperatures, 90, 92, 230, 232, 244tests, 81, 276-278thermal expansion, 264-266voids, 82-83, 87-89volume change, 81, 92volume in concrete, 1, 79-80washed, 99water requirements, 82, 92, 100, 155weather resistance, 89-91wetting and drying, 90

Air content, 1, 13, 62-63, 137-144, 145,152-154, 280-281, 287-288

Air detrainers, 117, 137Air-entraining cement, 30Air-entrained concrete, 1, 13, 129-148,

152-153admixture, 107, 136-137, 142-144admixture effects, 63, 137, 157age-strength relationship, 134-135air bubbles (air voids), 129air content tests, 280-281air drying, 134air indicator, 144, 281air-entraining materials, 30, 107, 136-137air-void spacing, 131-132air-void system, 131cement, 137-138coarse aggregate, 138cold-weather usage, 242-243coloring admixtures, 142-143deicer resistance, 132-134durability, 12-17, 129-134entrained air, 129, 131, 317entrapped air, 129factors affecting air content, 139-141field control, 131finishing, 144fine aggregate, 138freeze-thaw resistance, 129-132handling, 144hot weather, 231lightweight (low density) structural

concrete, 317-318mixing action, 143mixing water, 138, 139-141

Bonding admixtures, 116-117Bonding agents and grout, 205-206Break-off tests, 293-294Brooming, 203Buckets, 186Buggy, 185, 186Bulk density, 50, 87Bulking, 88Bullfloating, 201Burns, concrete, 216

Calcined clay, 133Calcined shale, 133Calcium aluminate, 17, 42Calcium aluminate cement, 37Calcium chloride, 113-114, 132, 157

effect on air entrainment, 143, 157in prestressed concrete, 75, 157

Calcium silicate hydrate, 40Canadian cement, 38-39Capillaries, 116, 130-131Carbon black, 142Carbonation, 14, 69, 270, 291, 309Cast-in-place tests, 285Cellular concrete, 318-321Cement, 21-56, 305

also see Portland cement and Specialcements

availability, 38blast-furnace slag, 33blended hydraulic, 31-32hot, 53hydraulic, 32-33packaging, 52particle size distribution, 44paste, 42-43shipment, 52slag, 32special, 33-37storage, 52strength, 47sulfate resistance, 27-28, 29thermal analysis, 50-51transportation, 52virtual testing, 51

Cement content, 160, 163, 169, 289effect on air entrainment, 137-138minimum, 132-133, 156

Cementitious (Cementing) materials,21-72

Chemical admixturessee Admixtures

Chemical changes of concrete, 270-271Chemical compounds of cement, 39-42Chemical resistance, 15, 69, 310Chemical shrinkage, 257-258Chloride

no-slump concrete, 325properties, 129-137proportioning, 1, 136-137, 152-153recommended air volume in concrete,

145-146recommended air volume in mortar

fraction, 131salt resistance, 132scaling, 133slump, 141-142spacing and size of air bubbles, 131-132,

138spacing factor, 131-132strength, 134-135sulfate resistance, 134superplasticizers, 142-143supplementary cementitious materials,

62, 142temperature, 142tests for air content

fresh concrete, 144-145hardened concrete, 145

transporting, 144vibration, 141-142water-cementing materials ratio, 134,

136workability, 136

Air-void analysis, 145Algae, 77Alite, 26, 39Alkali-aggregate reaction, 13-14, 68-69, 93,

270Alkali-carbonate reaction, 95, 98, 290Alkali-silica reaction, 93-95, 96-97, 101,

134, 290, 310inhibitors, 115

Alkaline waters, 76Aluminum, 188Antiwashout admixtures, 117Architectural concrete, 213, 329Auto-trimmer, 191Autoclave expansion soundness test, 45,

169Autoclaved cellular concrete, 321Autogenous shrinkage, 258-259

Batching, 179Belite, 26, 39Belt conveyors, 184, 187, 192Beneficiation of aggregates, 98Blaine test, 44Blankets, 225, 237, 239, 241-242, 247,

250-251Blast-furnace slag, 32, 59, 61-64, 133Blast resistance, 309Bleeding, 3, 62, 112Blended hydraulic cements, 31-32Bond, 204-205

353

Index

content, 75, 284, 289limits, 75, 157resistance, 14tests, 284

Chutes, 184Cleaning concrete surfaces, 211, 212

chemical, 212mechanical, 212-213water, 212

Clear coatings, 215Clinker, 25, 26Coarse aggregate

see AggregateCoatings, 215Coefficient of expansion, 92, 264-265Cold-weather concreting

aboveground, 247-249accelerators, 242aggregate temperature, 244air entrained, 242-243blankets, 239, 241-242, 247, 250-251concrete temperature, 243-245effect of low temperature, 240-241enclosures, 249-250freezing fresh concrete, 239-240frozen subgrade, 246heat of hydration, 241-242heaters, 251-252heating period, 253high-early strength, 242insulation materials and requirements,

249, 250-251maturity concept, 254mixing water heated, 244on ground, 246-247removal of forms, 253-254setting time, 240strength gain, 240tests, 245-246

Color, 30, 69, 70, 215Colored concrete, 329-330Colored finishes, 215Coloring admixtures, 115-116, 142-143Combined aggregate grading, 86Compacting factor test, 279Components of concrete, 1Compound transformations, 40Compression strain, 267Compressive strength, 7, 64-65

structural lightweight concrete, 316Consistency, 279-280

also see Slumpcement, 45effect on entrained air, 138-139slump test, 276, 279-280

Consolidation, 4also see Vibration

temperature, 225-226time, 225-226wet coverings, 221-222

Curling, 266-267Cylinders, 285-287

Dampproofing admixtures, 116Darbying, 201D-cracking, 89-90Dedolomitization, 98Defects, 211Deflection, 268Deformation of concrete, 267-268Deicing chemicals (deicers) and

scaling, 66-67Density

cement, 49-50concrete, 288aggregates, 88

Depositing concrete, 192-193Deterioration, 17-18, 87-88, 93-95Differential scanning calorimetry, 51Differential thermal analysis, 51Diffusion, 309Dropchutes, 184, 186Drying rate of concrete, 6Drying shrinkage, 67, 91, 260-264Dry-pack mortar, 211Durability, 12-18, 290Dusting, 6, 202, 270Dynamic tests, 294

Early stiffening, 46, 183Early strength, 6, 220, 224-225, 241, 302Early thermal expansion, 260Edging, 202Efflorescence, 212Elastic and inelastic deformation, 267-268Electric heat, 225Enclosures, 239, 249-250Epoxy, 15, 117, 206Equipment for placing concrete, 192-194Ettringite, 17Ettringite cements, 37European cement, 38Evaluation of compression tests, 287Evaporation rate, 235, 236Expansion joint, 321Expansion of concrete, 18Expansive cement, 36Exposed aggregate, 213-214Exposure conditions, 153

False set, 46Fast-track, 300-302Ferrocement, 330Fiber concrete, 121

Construction joints, 12, 204-205, 208-209Construction practices, 179-190Contraction joints, 12, 206-208Control joints

see Contraction jointControl tests, 275-298Conveying concrete, 192Cooling concrete, 231-234Cores, 285-287Corrosion, 14-15, 69

resistance, 290inhibitors, 114-115

Corrosive substances, 75, 91Cracking, 10

causes, 12D-cracking, 89-90

Cranes, 186, 187, 188Creep, 67, 268-270Curing, 5, 64, 203-204, 219-229, 317-318

autoclave, 224box, 245-246blankets, 225burlap, 221-222cold weather, 240-253compounds, 226-227drying shrinkage, 264duration, 225-226effect on creep, 270effect on hydration, 220electric, 225enclosures, 239-249fogging, 221forms left in place, 224high-strength, 307-308hot weather, 237-238impervious paper, 222infrared, 225internal moist, 224interrupted, 220materials and methods, 220-221maturity concept, 254membrane-forming compounds,

223-224microwave, 225minimum cure, 226oil, 225patches, 212plastic sheet, 222-223ponding or immersion, 221prolonged curing curve, 226rain protection, 200relative humidity, 220sealing compounds, 226-227slabs, 203-204spraying, 221steam, 224-225strength, effect on, 219, 220, 225, 226

Frozen subgrade, 246

Galvanized materials, 74, 144, 242, 318Gamma radiography, 294Gap-graded aggregates, 86-87Gas-forming admixtures, 117Geopolymer cements, 37Gillmore needle, 46Glass fibers, 124Grading of aggregates, 80-86Gravel

see AggregatesGrouting, 35, 36, 105, 203, 325Grouting Admixtures, 117Gunite

see ShotcreteGypsum, 24, 27, 39

Handling and placing equipment, 184-187Hardened concrete, 2, 5-12Hardening, 4Harmful materials, 92Haul time, 140, 144Heat induced delayed expansion, 17, 18Heat of hydration

see Hydration, heat ofHeaters, 246, 251-253Helicopter placement, 188-189Heavyweight aggregate

see High-density aggregateHeavyweight concrete

see High-density concreteHigh-density aggregates, 80, 322High-density concrete, 321-323High-durability concrete, 308-311

abrasion resistance, 308alkali-silica reactivity, 310blast resistance, 309carbonation, 309chemical attack, 310freeze-thaw resistance, 310diffusion, 309permeability, 309resistivity, 311temperature, 309-310

High-early-strength concrete, 300-302blanket, 303strength, 302

High-performance concrete, 299-314characteristics, 299fast-track, 300-302high-durability, 308-311high-early-strength, 300-302high-strength, 303-308reactive-powder, 312self-compacting, 311-312typical structures, 301

High-range water reducing admixtures,109-110

High-strength concrete, 303-308admixtures, 306aggregates, 305-306cement, 305consolidation, 307curing, 307-308mixing, 306-307placing, 307proportioning, 306quality control, 308supplementary cementitious materials,

305History

cement, 21, 24air-entrained concrete, 129

Holes, 210-211Honeycomb, 194, 211Hot cement, 53Hot-weather concreting, 229-238

admixtures, 238adverse effects, 229cement temperature, 234concrete temperature, 230-234cooling materials, 231-234crushed ice, 233curing, 237-238difficulties, 229hydration, 238nitrogen cooling, 229placing precautions, 234-235plastic shrinkage cracking, 235-237precautions, 229-230protection, 237-238setting time, 231strength, 231supplementary cementitious materials,

234water requirement, 229

Hydration, 4, 40-43concrete strength, 5heat of, 47-49, 63, 238, 241-242minimum relative humidity for, 5products of, 5, 21, 50rate, 5, 44

Hydration-control admixtures, 113Hydraulic cement, 32-33Hydraulic pressure, 12, 89, 130Hydraulic slag cements, 33

Ice, use in cooling concrete, 233Impact resistance, 65Impervious paper, 222Industrial wastewater, 76-77Infrared curing, 225Ingredients of concrete, 1

Fibers, 121-127glass, 124natural, 126properties, 123steel, 122-123systems, 126-127synthetic, 125-126

Fine aggregatesee Aggregate

Finely-ground cements, 35Fineness modulus, 84Fineness of portland cement, 43-44Finishes and finishing, 144, 317

brooming, 203bullfloating, 201bushhammering, 214darbying, 201defects, 211dry cement, 203edging, 202exposed-aggregate, 213-214floating, 202formed surfaces, 213grout cleandown, 213highway straightedging, 201jointing, 202paints and clear coatings, 215patterns and textures, 213-215precautions, 215-216premature, 203sandblasting, 204-205screeding, 200-201slabs, 198-204special surface finishes, 213-215striking off, 200-201troweling, 202-203

Fire resistance, 92Flash set, 46Flexural strength, 8, 286-287Floating, 202Floor covering, 199, 291Floors, 206-210Flow test, 279Flowable fill, 318

See Soil-cement and Cellular concreteFlowing concrete, 142, 280Fly ash, 58, 61-63, 64, 133Fogging, 221, 237Form removal, 210, 253-254Forms, 200Free lime, 43, 44Freeze-thaw resistance (frost resistance)

concrete, 12-13, 65-60, 129-132, 243, 290,310

aggregates, 89-90Freezing fresh concrete, 239-240Freshly mixed concrete, 2-5, 61-64

354


tests, 293Measuring concrete materials, 179Membrane-forming compounds, 223-224Microwave-absorption test, 278Mid-range water reducing admixtures,

109Minerals, 79-80Mineral admixtures

see Supplementary cementitious materialsMix characteristics, 149Mix design for concrete, 59-78, 149Mixers

central, 181continuous, 183mobile batcher, 183stationary, 180truck, 181

Mixing concrete, 3, 180agitating speedeffect on entrained air, 143Heavyweight (high-density) concrete,

321-323high-strength concrete, 306-307lightweight (low-density) concrete, 317mixing speed, 180remixing (retempering), 183sequence, 180

Mixing water, 13, 73, 78, 138, 139-141also see Water-cement ratioacid, 76algae, 77alkaline, 76amount and requirements, 138analyses, 73carbonates, 74chemical limits, 74chloride content, 74-75impurities, 73, 77iron salts, 75oils, 77questionable suitability, 73salts, 75seawater, 75sewage, 77silt, 77specifications, 75sugar, 77sulfates, 75temperaturestest methods, 74wash, 76waste, 76

Mixture proportioning, 70Mobile batcher, 184Moderate-strength lightweight concrete,

318Modified portland cements, 32

Modulus of elasticity, 8, 267Modulus of rupture, 8, 286Moist curing, 5, 219-220Moisture

changes, 260-262content, 291

Mortar cement, 33-35Mortar cubes, 47Multiple fiber systems, 126-127

Natural fibers, 126Natural pozzolans, 60-61Nitrogen cooling, 229No-fines concrete, 318, 323Nondestructive testing, 292-294No-slump concrete, 325Nuclear test, 199, 280, 291

Oils in mixing water, 77Oil-well cement, 36Ordering concrete, 179Organic admixture content, 289Organic impurities, 77Osmotic pressure, 130, 259Overlay, 211

Pachometer, 294Paints, 215Paper curing, 220Paste, 1, 4, 8-9Patching concrete, 210-211Patterned finishes, 213Penetration tests, 293Periclase, 44Perlite, 80, 318-319, 321Permeability, 9-10, 68, 292, 309Permeability-reducing admixtures, 116Pervious (porous) concrete, 328Petrographic examination, 289pH, 14, 292Pigments, 115-116Placement of concrete

cold weather, 239, 241, 245consolidation, 194-195depositing, 192-193dropchutes, 184, 186free fall, 193helicopter, 188-189high-strength, 307hot weather, 234-235layers, 192-193, 195, 198lifts, 187-188lightweight concrete, 317placement on hardened concrete, 204rain protection, 200underwater (tremie), 185, 188, 193-194vibration, 195-198

Inorganic salts, 75Insecticidal admixtures, 117Insulating blankets, 225Insulating concrete, 318-321

moderate strength lightweight concrete,318-321

Internal moist curing, 224Iron salts, 75Isolation joints, 12, 206

Joints, 12, 206-210bonded, 205-206cold, 192, 198construction, 12, 204-205, 208-209contraction (control), 12, 206-208expansion, 321filling, 209-210isolation, 12, 206layout, 209sawing, 207spacing, 208surface preparation, 204-205unjointed floors, 210walls, 206

Jointing, 202J-Ring test, 311

Kelly-Vail test (cement-content test),280-284

Kiln, 23, 24, 25, 26K-slump test, 279

Laser screed, 198Latex, 330Latex-modified concrete, 309, 315Length change, 257, 260, 264, 290Lightweight aggregates, 80, 316, 318Lightweight concretes, 315-321

insulating, 318moderate strength, 318structural, 315-317

Lime, 5, 21, 24, 31, 32, 36Lime-slurry stain test, 93Long-time study test plots, 16, 29, 131Loss on ignition, 49Low-density aggregate

see Lightweight aggregatesLow-density concrete

see Lightweight concrete

Magnesia, 44Magnesium phosphate cement, 37Manufacture of portland cement, 22-23,

24-25Masonry cement, 33-35Mass concrete, 323-325Maturity

concept, 254

355

Index

white, 30Pozzolans, 57-70Precautions, 215-216Preplaced aggregate concrete, 325Pressure method for air content, 144Proportioning mixtures, 1, 59-78, 149, 178,

306absolute volume method, 160-166,

172-174admixtures, 157aggregate, 151air content, 152-154arbitrary assignment, 159batching, 179calculations, 160-174cement type, 156characteristics of, 149density (unit weight), 159entrained air, 152-153examples of proportioning, 160, 163,

166, 168, 172field data, 157-158fineness modulus, 159flow chart, 176high-strength concrete, 303-308lightweight (low-density) insulating

concrete, 317-318measurements, 159-160slump, 153-155small jobs, 174-175strength, 149-151structural lightweight concrete, 317-318supplementary cementitious materials,

156-157, 172trial mixtures, 158-159, 166-172water-cement ratio, 149-151

method, 159water content, 155-156workability, 153yield, 159

Protection during curingsee Curing

Puddling, 323Pullout tests, 293Pulse velocity test, 294Pumice, 80, 316, 318Pumping, 64, 185, 187, 189Pumping aids, 116

Quality control, 308

Radiation shielding, 321Rain protection, 200Rapid analysis machine, 284Rapid hardening cement, 37Reactive powder concrete, 312Reactivity of aggregates, 13, 93, 95Ready mixed concrete, 180-183

Ready mix plant, 182Rebound hammer test, 292-293Recycled concrete, 100-101Recycled-concrete aggregate, 99-100References

see end of each chapterRegulated-set cement, 36Relative density

cement, 49-50concrete, 288aggregates, 87-88

Relative humidity, 59, 229-230, 236-237,260, 262, 291

Remixing concrete, 183Repair, 37, 117, 123, 210-212, 301, 328Reshoring, 210, 253Resistivity, 311Retarding admixtures, 113Revibration, 197-198Rock cylinder test, 98Rocks, 79Roller-compacted concrete, 326Rustication strip for joint, 208-209

Sack-rubbed finish, 213Salamander, 252-253Salts, 15-16, 66, 74-75, 91Sampling aggregate, 276Sampling fresh concrete, 279Sand, 1, 79Sandblasting, 204-205Saturated concrete, 5, 134Saturated surface-dry, 88Sawed joints, 207Scale-resistance, 67, 144, 227, 310Scanning electron microscope, 41Screeding, 200-201Screw spreader, 185, 188Sealing compounds, 226-227Seawater, 17, 27, 75Segregation, 184Self-compacting concrete, 311-312Setting time, 4, 45-46, 63Settlement, 3Sewage water, 77Shear strain, 268Shielding concreteShotcrete, 185, 327-328Shrinkage

autogenous, 258-259chemical, 257-258drying, 67, 91, 260-264plastic, 64, 235-237, 259

Shrinkage-compensating concrete, 328Shrinkage-reducing admixtures, 115Shrink-mixed concrete, 181Sieve analysis, 80, 84, 277

Plastic cement, 35Plastic concrete, 2Plastic sheet, 222-223Plastic shrinkage, 64, 235-237, 259Plasticity, 35, 46, 153Plasticizer, 110-112Poisson’s ratio, 268Polymer-portland cement concrete

(polymer modified concrete), 330Polypropylene fibers, 125Ponding, 221Popouts, 89-90, 92-93Pores, 130Porous (pervious) concrete, 328Portland cement, 21-30

also see Cement and Special cementsair-entraining, 30alkali content, 52blast-furnace slag, 31bulk density, 50chemical composition and

compounds, 39-42clinker, 25, 26compressive strength, 47consistency, 45expansive, 36false set, 46fineness, 43-44flow test, 45high-early-strength, 28, 30history, 21, 24hydration, 40-43invention, 21loss on ignition, 49low-heat of hydration, 29manufacture, 22-23, 24-25moderate sulfate resistant, 17, 27modified, 33normal, 27particle size distribution, 43-44paste, 1, 4, 8-9phase, 39pozzolan, 31pozzolan modified, 31-32properties, 27-30raw materials, 25relative density, 49-50setting time, 45-46shipment, 38, 52slag-modified, 32soundness, 44specifications, 37sulfate-resisting, 29surface area, 44types, 27-30water, 42-43waterproofed, 36

356


compressive, 7, 316curing, 219, 220, 225, 226cylinders, 286evaluation, 287fibers, 121-127flexural, 8high, 303-308high early, 242, 300-302penetration method of test, 293relationship between flexural, shear,

tensile, and compressive, 8specified compressive, 7specimen, 285tensile, 8tests, 285-287torsional, 8water-cement ratio relationship, 149-151

Strikeoff, 200-201Structural lightweight concrete, 315-318

aggregate, 316compressive strength, 316curing, 317-318entrained air, 317finishing, 317mixing, 317placing, 317slump, 317specifications, 317vibration, 317workability, 317

Subbase, 199Subgrade, 199Subsidence, 259Sugar, 77Sulfates, sulfate attack, 15-16, 17, 28, 69,

75, 134, 270, 290Sulfur cements, 37Superplasticizer

see PlasticizerSupplementary cementitious (cementing)

materials, 57-72, 142, 234, 289, 305calcined clay, 61calcined shale, 61effect on concrete, 61-70fly ash, 58, 61-63, 64, 133metakaolin, 61natural pozzolans, 60-61silica fume, 59-60slag, 31-32, 59, 61-64, 133specifications, 58

Surface moisture, 88, 237Surface treatment, 134Swelling, 259-260Synthetic fibers, 125-126

Temperature, 142calculations for fresh concrete, 232-234

curing, 225-226effects on air entrainment, 142effects on compressive strength,

230-231, 240-241effects on setting time, 231effects on volume changes, 17-18,

265-266effects on water requirements, 230effects on workability, 3high durability concrete, 309-310mass concrete, 323-324testing, 280

Tensile strength, 8Testing aggregates, 276-278Testing freshly mixed concrete, 279-285

accelerated curing, 225air content, 280-281bleeding, 284-285cement content, 284chloride content, 284consistency, 279-280density, 280fly ash content, 284frequency, 275-276sampling, 279slump, 279-280specimens, 282-283strength, 284supplementary cementitious materials

content, 284temperature, 245, 280time of set, 283-284water content, 284water-cement ratio, 284yield, 159, 280

Testing hardened concrete, 285-295absorption, 288air content, 287-288break-off test, 293-294carbonation, 291cement content, 289chloride content, 289coring, 285density, 288durability, 290dynamic test, 294evaluation of compression test results,

287length change, 290maturity test, 293moisture content (relative humidity),

291nondestructive test, 292organic admixture content, 289penetration (Windsor probe) test, 293permeability, 288, 292petrographic analysis, 289

Silica fume, 60, 307Silt, 77Skid resistance, 90-91Slab construction, 198-204Slag, 31-32, 59, 61-64, 133Slump, 108, 141-142, 153-155, 276, 279-280,

317also see Consistency

Sodium chloride, 132Sodium sulfate, 15-16, 75, 90Soil-cement, 327Soundness

portland cement, 44concrete, 69

Spacing factor, 131-132Spading, 194Special cements, 33-37

applications, 34calcium aluminate, 37finely ground (ultrafine), 35ettringite, 37expansive, 36geopolymer, 37magnesium phosphate, 37masonry, 33-35mortar, 33-35oil-well, 36plastic, 35rapid hardening, 37regulated-set, 36sulfur, 37water-repellent, 36

Special types of concrete, 315-334Specific gravity

see Relative densitySpecific heat, 234Spray cure, 221Sprayed concrete

see ShotcreteStandard deviation, 282Standards

ASTM, 345AASHTO, 350

Stationary mixing, 180Statistical analysis, quality control, 158Steam curing, 224-225Steel corrosion, 14-15, 69Steel fibers, 122-123Stone

see AggregateStorage of cement, 52Strain, 267-269Strength, 134-135

accelerated, 284age relationship, 6, 7, 47, 48, 64-65, 110,

112, 220, 231, 241aggregates, 91

357

Index

Volume changes, 257-273, 290also see Cracking and Shrinkagealkali-aggregate, 270carbonation, 270coefficient of expansion, 264-265compression strain, 267creep, 268-270curling, 266-267deflection, 268early age, 257-260early thermal expansion, 260effect of concrete ingredients, 263elastic and inelastic deformation,

267-270freeze-thaw, 264modulus of elasticity, 267moisture changes, 260-262Poisson’s ratio, 268shear strain, 268stability, 11-12subsidence, 259sulfate attack, 270swelling, 259-260temperature changes, 264-266torsional strain, 268wetting-drying, 260

Volumetric method for air content, 281

Walls, 206-207Warehouse pack, 53Warping, 266-267Wash water and wastewater, 76Waste concrete, 79Water curing, 224Water reducer, 107-109, 157Water to cement ratio, 12, 149-150

freeze-thaw resistance, 12-13minimum, 5maximum, 150proportioning of mixtures, 149-150strength, 149-151testing, 284trial mixture design, 149-150watertightness, 9

Water-reducing admixtures, 107-109, 157Water requirements

supplementary cementitious materials,61

cement, 45-46Water-repellent cement, 36Watertightness, 9Wheelbarrows, 185, 186, 192White concrete, 329White portland cement, 30Windsor probe test, 293Winter concreting, 241, 253Wood Fibers, 126

Workability, 3, 136, 317

X-ray diffraction, 41X-ray test, 294

Yield, 280

Zeolite cementsee Geopolymer cement

Zero-slump concrete, 325

pH test, 292pullout test, 293rebound test, 292-293relative density, 288sampling, 285strength, 285supplementary cementing materials

content, 289temperature, 245-246vibration test, 294voids, 288volume change, 290

Textured finishes, 214Thaulow drop table, 325Thermal analysis of cement, 50-51Thermal expansion, 92, 260, 266Thermal resistance, 248-249Thermal shrinkage, 206Thermogravimetric analysis, 51Thermometers, 245-280Thin-section examination, 39Time of setting, 283-284Tobermorite gel, 40Torsion and torsional strain, 268Transporting concrete, 183-187Tremie placement, 185Trial batch procedures, 158, 161, 164, 174Troweling, 202-203Truck agitators, 185Truck-mixed concrete, 181Truck mixers, 185Two-course floors, 205, 224

Ultrafine cements, 34Ultrasonic tests, 294, 295Underwater concrete, 106, 111, 156,

193-194, 325Uniformity, 47, 276Unjointed floors, 210Urea, 132

Vapor barrier, 199-200Vapor retarders, 199-200Vebe apparatus, 279, 280Vermiculite, 80, 249, 318, 319Vibration and vibrators, 141-142, 195-198,

317also see Consolidationtest, 294

Vibratory roller, 181Vibratory screed, 197Vicat apparatus, 45-46Virtual cement testing, 51Voids

aggregate, 82-83, 87-89concrete, 4, 129-131, 288

358


Design and Control of Concrete Mixtures, 14th Ed

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