Volume 1 of 2 Anastasios M. Ioannides and Amar Deshini · Volume 1 of 2 Anastasios M. Ioannides and...
Transcript of Volume 1 of 2 Anastasios M. Ioannides and Amar Deshini · Volume 1 of 2 Anastasios M. Ioannides and...
Fineness of Densified Microsilica and Dispersion in Concrete Mixes
Volume 1 of 2
Anastasios M. Ioannides and Amar Deshini
for the Ohio Department of Transportation
Office of Research and Development
State Job Number 148000
June 2006
Fineness of Densified Microsilica and Dispersion in Concrete Mixes
State Job No.: 14800(0) FINAL REPORT
Prepared in cooperation with the Ohio Department of Transportation and the
U.S. Department of Transportation, Federal Highway Administration.
by
University of Cincinnati Cincinnati Infrastructure Institute
Department of Civil and Environmental Engineering Cincinnati, OH
August 2006
Research Team: Anastasios M. Ioannides and Richard A. Miller (co-PIs) Amarendranath Deshini, Jeff C. Mills, Kristina M. Walsh (Research Assistants)
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DISCLAIMER
The contents of this report reflect the views of the authors who are
responsible for the facts and the accuracy of the data presented
herein. The contents do not necessarily reflect the official views or
policies of the Ohio Department of Transportation or the Federal
Highway Administration. This report does not constitute a
standard, specification or regulation.
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FOREWORD
The investigation described in this Report was sponsored by the Ohio Department
of Transportation (ODOT) and by the Federal Highway Administration (FHWA) as Ohio
State Job No.: 14800(0); PID No.: 11340, under project AFineness of Densified
Microsilica and Dispersion in Concrete Mixes.@ The Principal Investigators were Drs
Anastasios M. Ioannides and Richard A. Miller, Department of Civil and Environmental
Engineering, University of Cincinnati. The ODOT Technical Liaison was Mr Bryan
Struble, the Research Manager was Mr Lloyd Welker, the Administrator for the Office of
Research and Development at ODOT was Ms Monique Evans, and the FHWA liaison in
Columbus, OH was Mr Herman Rodrigo. The assistance, cooperation and friendship of
these individuals was a major contributor to the success of the study, and their support is
gratefully acknowledged. Special thanks are also extended to Tim Jones, ODOT
laboratory technician, who conducted the tests on microsilica. The sand and both kinds
of coarse aggregates were supplied free of charge by Martin Marietta Materials, through
Mr Jim Martin. The cement was donated by CEMEX, through Mr Steve Reibold, and the
microsilica by ELKEM Materials, through Mr Tony N. Kojundic. The MB-AE 90 air
entrainer and the Rheobuild 1000 plasticizer were supplied at no cost by Master Builders,
Inc., through Mr Greg Wirthlin. The authors also acknowledge the contributions to the
project of graduate students Kristy M. Walsh and Jeff C. Mills. This Report will be
submitted by Amarendranath Deshini to the Division of Research and Advanced Studies
of the University of Cincinnati in partial fulfillment of the requirements for the degree of
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Master of Science in the Department of Civil and Environmental Engineering, in
December 2006.
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ABSTRACT
This study explores the effect of densification of microsilica on the mechanical
and other engineering properties of concrete used on Ohio Department of Transportation
(ODOT) projects. American Society for Testing and Materials (ASTM) C 1240 requires
wet-sieved microsilica to pass a No. 325 sieve with no more than 10% retained.
Densified microsilica samples submitted to ODOT sometimes do not meet this
specification, since the sieving process may not be able to break the bonds formed due to
densification. During this study, No. 325 sieve tests on three microsilica types
(undensified, densified, and abused by prolonged exposure to moisture) were performed
at the ODOT laboratory, but none of the materials tested were found to conform to the
ASTM fineness specification. This calls into question the application of this procedure to
assessing the suitability of densified microsilica for use in concrete. In contrast, the
compressive and flexural strengths of concretes mixed with each of the three microsilica
types exceeded those envisaged by ODOT Item 499.03 Concrete-General:
Proportioning. As expected, undensified microsilica concrete yielded higher values than
its densified and abused microsilica counterparts at all ages, but this advantage was rather
limited. This was true for both natural and crushed coarse aggregate mixes. With very
few exceptions attributable to material and testing variability, trends observed with regard
to the effects of microsilica and coarse aggregate types, age and specimen size on the
development of strength were also as anticipated. Therefore, it is concluded that
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densified microsilica can be used on ODOT projects for the construction of pavements
and bridges.
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ACKNOWLEDGEMENTS
I would like to thank my graduate advisor Dr. Anastasios M. Ioannides and co-
advisor Dr. Richard A. Miller, without whom my thesis would not have happened. I
really appreciate the constant support I received from them. Their assistance not only
helped me to complete my Masters degree successfully, but also helped me shape my
professional career. I would also like to thank Dr. Sam M. Salem and Dr. Issam A.
Minkarah for readily accepting my request to be on my thesis committee.
I am ever grateful to my parents and to my sister for being with me when I am
low, and for the encouragement that I received from them from time to time. My special
thanks to Mr. Vamshidhar Thakkalapalli for his support, and for suggesting University of
Cincinnati for my graduate studies. The encouragement and valuable suggestions from
my roommates and friends (Sita, Ravi, Sharat, Karuna, Raju, Preethi, Pavan, etc., to name
but a few) can never be forgotten.
Lastly, I would like to express my gratitude to the Department of Civil and
Environmental Engineering for giving me the opportunity to pursue my Master of
Science in Construction Engineering and Management at University of Cincinnati.
During my studies at the University, I received financial assistance in the form of
Research and Teaching Assistantships (April 2002 to December 2003), and a University
Graduate Scholarship (September 2001 to April 2004).
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TABLE OF CONTENTS
Page
FOREWORD iii
ABSTRACT v
ACKNOWLEDGEMENTS vii
TABLE OF CONTENTS viii
LIST OF TABLES xiv
LIST OF FIGURES xvi
LIST OF SYMBOLS AND ABBREVIATIONS xviii
LIST OF SPECIFICATIONS CITED xxiii
SI* (MODERN METRIC) CONVERSION FACTORS xxv
1 INTRODUCTION 1
1.1 Problem Statement 1
1.2 Objectives 2
1.3 Technical Background 3
1.4 Report Organization 5
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2 LITERATURE REVIEW 7
2.1 Introduction 7
2.2 Production of Microsilica 8
2.3 Properties of Microsilica 9
2.4 Effect of Microsilica on Physical Properties of 11
Concrete
2.4.1 Water Demand 11
2.4.2 Cohesiveness 12
2.4.3 Slump and Workability 12
2.4.4 Air Content 13
2.4.5 Setting Time 13
2.4.6 Shrinkage and Cracking 14
2.4.7 Heat of Hydration 17
2.5 Effect of Microsilica on Mechanical Properties of 17
Concrete
2.5.1 Compressive Strength 17
2.5.2 Flexural Strength 18
2.5.3 Modulus of Elasticity 19
2.5.4 Bond Strength 19
2.5.5 Strength Development 20
2.6 Field Tests 22
x
2.7 Do Undispersed Agglomerates Matter? 24
3 MATERIALS AND PROCEDURES 27
3.1 Introduction 27
3.2 Materials Used 27
3.3 Tests on Microsilica 29
3.3.1 Preparation of Abused Microsilica 29
3.3.2 Fineness Tests 30
3.3.3 Gradation Tests 31
3.4 Tests on Aggregates 34
3.4.1 Specific Gravity and Absorption of Coarse Aggregate 34
3.4.2 Specific Gravity and Absorption of Fine Aggregate 35
3.4.3 Bulk Density of Coarse Aggregate 36
3.4.4 Sieve Analysis on Fine and Coarse Aggregates 37
3.4.5 Moisture Content of Fine and Coarse Aggregates 38
3.5 Mix Design 38
3.5.1 Constants and Variables 39
3.5.2 Ingredients 39
3.6 Mixing, Casting, and Curing Methods 41
3.6.1 Mixing Concrete 41
3.6.2 Casting Specimens 42
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3.6.3 Curing 43
3.7 Tests on Plastic Concrete 44
3.8 Strength Test Procedures on Hardened Concrete 45
3.8.1 Compressive Strength 45
3.8.2 Flexural Strength 46
4 TEST RESULTS 49
4.1 Introduction 49
4.2 Microsilica 49
4.2.1 Microsilica Fineness 49
4.2.2 Microsilica Gradation 50
4.3 Aggregates 50
4.4 Concrete Mixes 50
4.5 Mechanical Properties 51
5 DISCUSSION OF RESULTS 72
5.1 Introduction 72
5.2 Microsilica Fineness 72
5.3 Microsilica Gradation 74
5.4 Variability of Mechanical Tests 74
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5.4.1 Compressive Strength 75
5.4.2 Modulus of Rupture 76
5.5 Data Interpretation 76
5.5.1 Compressive Strength 77
5.5.2 Modulus of Rupture 79
5.6 Effect of Microsilica Type on Mechanical 79
Properties of Concrete
5.6.1 Compressive Strength 79
5.6.2 Modulus of Rupture 81
5.7 Effect of Coarse Aggregate Type on Mechanical 82
Properties of Concrete
5.7.1 Compressive Strength 82
5.7.2 Modulus of Rupture 83
5.8 Effect of Specimen Size on Mechanical Properties of 84
Concrete
6 CONCLUSIONS AND RECOMMENDATIONS 110
6.1 Summary 110
6.2 Conclusions 112
6.3 Recommendations 114
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6.4 Implementation Plan 115
REFERENCES 117
xiv
LIST OF TABLES
Page
4.1 Results of Tests Conducted on Microsilica Types at ODOT 52
Laboratory
4.2 Hydrometer Test on Undensified Microsilica 53
4.3 Hydrometer Test on Densified Microsilica 54
4.4 Hydrometer Test on Abused Microsilica 55
4.5 Dry Sieve Analysis of Undensified Microsilica 56
4.6 Dry Sieve Analysis of Densified Microsilica 57
4.7 Dry Sieve Analysis of Abused Microsilica 58
4.8 (a) Aggregate Sieve Analysis 59
4.8 (b) Physical Aggregate Properties 59
4.9 Ingredients by Mix (per yd3 of concrete) 60
4.10 Specimens Cast by Batch 61
4.11 Physical Properties by Batch 62
4.12 Compressive Strength for Large Cylinders, f′c 63
4.13 Compressive Strength for Small Cylinders, f′c 65
4.14 Modulus of Rupture for Large Beams, MR 67
4.15 Modulus of Rupture for Small Beams, MR 69
5.1 Coefficients of Variation, COV (%), in Laboratory Test Results 86
5.2 Average Compressive Strength for Large Cylinders (psi) 87
5.3 Average Compressive Strength for Small Cylinders (psi) 87
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5.4 Relative Compressive StrengthValues for Large Cylinders (%) 88
5.5 Relative Compressive Strength Values for Small Cylinders (%) 88
5.6 Best-Fit Compressive Strength Values for Large Cylinders (psi) 89
5.7 Best-Fit Compressive Strength Values for Small Cylinders (psi) 89
5.8 Average Modulus of Rupture Values for Beams (psi) 90
5.9 Relative Modulus of Rupture Values for Beams (%) 90
5.10 Best-Fit Modulus of Rupture for Small Beams (psi) 90
5.11 Cylinder Size Factors (%) 91
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LIST OF FIGURES
Page
4.1 Grain Size Distribution of Undensified, Densified, and Abused
Microsilica 71
5.1 Trend Line Curves for Large Cylinders 92
5.2 Trend Line Curves for Small Cylinders 93
5.3 Trend Line Curves for Small Beams 94
5.4 Effect of Microsilica Type on Large Cylinders with Natural 95
Aggregate
5.5 Effect of Microsilica Type on Small Cylinders with Natural 96
Aggregate
5.6 Effect of Microsilica Type on Large Cylinders with Crushed 97
Aggregate
5.7 Effect of Microsilica Type on Small Cylinders with Crushed 98
Aggregate
5.8 Effect of Microsilica Type on Small Beams with Natural 99
Aggregate
5.9 Effect of Microsilica Type on Small Beams with Crushed 100
Aggregate
5.10 Effect of Aggregate Type on Large Cylinders with Undensified 101
Microsilica
5.11 Effect of Aggregate Type on Small Cylinders with Undensified 102
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Microsilica
5.12 Effect of Aggregate Type on Large Cylinders with Densified 103
Microsilica
5.13 Effect of Aggregate Type on Small Cylinders with Densified 104
Microsilica
5.14 Effect of Aggregate Type on Large Cylinders with Abused 105
Microsilica
5.15 Effect of Aggregate Type on Small Cylinders with Abused 106
Microsilica
5.16 Effect of Aggregate Type on Small Beams with Undensified 107
Microsilica
5.17 Effect of Aggregate Type on Small Beams with Densified 108
Microsilica
5.18 Effect of Aggregate Type on Small Beams with Abused 109
Microsilica
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LIST OF SYMBOLS AND ABBREVIATIONS
°C: degree celcius
°F: degree Fahrenheit
µ: micro
γw: unit weight of water
%: percentage
A: % absorption
A: weight of oven-dry sample
AASHTO: American Association of State Highway and Transportation Officials
AC: abused microsilica concrete with crushed aggregate
ACI: American Concrete Institute
Al2O3: aluminum oxide
AN: abused microsilica concrete with crushed aggregate
ASG: apparent specific gravity
ASR: alkali silica reactivity
ASTM: American Society for Testing and Materials
b: average width
B: weight of pycnometer with water
B: weight of saturated surface dry sample in air
BSGSSD: bulk specific gravity at saturated surface dry condition
C: cement
C: weight of pycnometer with water
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C: weight of saturated sample in water
CaO: calcium oxide
C+P: cement + pozzolan
CA: coarse aggregate
COV: coefficient of variation
d: average depth
D: weight of oven-dry sample
D: diameter of particle
DC: densified microsilica with crushed aggregate
DN: densified microsilica with crushed aggregate
f ′: compressive strength
FA: fine aggregate
Fe2O3: ferric oxide
FM: fineness modulus
ft: feet
G: grams
G: mass of aggregate and measure
G1: specific gravity of liquid in which the sample was suspended
Gs: specific gravity of sample
Hrs: hours
in.: inch
K2O: potassium oxide
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kg: kilogram
km: kilometer
l: effective span
L: Distance from the surface of the suspension to the level at which the density of the
suspension is being measured
L: liter
Lb: pound
LOI: loss on ignition
m: meter
MgO: magnesium oxide
Min.: minutes
Mm: millimeter
MnO: manganese oxide
MR: modulus of rupture
MSSD: bulk density of aggregate at ssd condition
MW: mass of water
n: coefficient of viscosity of water
NA: not applicable
NA: not available
Na2O: sodium oxide
NCHRP: National Cooperative Highway Research Program
No.: number
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NT: not tested
ODOT: Ohio Department of Transportation
oz: ounce
P: pozzolan
P: load at failure
PCC: Portland Cement Concrete
pcf: pounds per cubic feet
psi: pound per square inch
P2O2: phosphorus oxide
r: rate of application of load
Ractual: actual hydrometer reading
Rc: corrected hydrometer reading
S: weight of ssd sample
SEM: scanning electron microscopy
SiO: silica oxide
SiO2: silicon-di-oxide
SO3: sulfur trioxide
Sq: square
SSD: surface dry condition
T: Interval of time from beginning of sedimentation to the taking of the reading
T: mass of measure
TEM: transmission electron microscopy
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TiO2: titanium dioxide
UC: undensified microsilica with crushed aggregate
UN: undensified microsilica with natural aggregate
US: United States of America
V: volume
Vair: volume of air
VSSD: volume at saturated surface condition
W: weight
W: density of water
w/c: water cement ratio
WCEM: weight of cement
WMS: weight of microsilica
WMS (SSD): weight of microsilica at ssd
WW (SSD): weight of water at ssd
yd: yard
µ: micro
γw: unit weight of water
No.: number
%: percentage
xxiii
LIST OF SPECIFICATIONS CITED
ASTM C 1240 – 01 Standard Specification for Use of Silica Fume as a Mineral Admixture in Hydraulic-Cement Concrete, Mortar and Grout ASTM C 430 – 96 Standard Test Method for Fineness of Hydraulic Cement by the 45-µm (No. 325) Sieve ASTM D 422 – 63 Standard Test Method for Particle-Size Analysis of Soils ASTM D 421 – 85 Standard Practice for Dry Preparation of Soil Samples for Particle-Size Analysis and Determination of Soil Constants ASTM D 854 – 06 Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer ASTM C 128 – 97 Standard Test Method for Specific Gravity and Absorption of Fine Aggregate ASTM C 29/C 29M – 97 Standard Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate ASTM C 136 – 96a Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates ODOT Supplemental Specification 848 Bridge Deck Repair and Overlay with Concrete Using Hydro-Demolition ODOT Item 499.03 Concrete-General: Proportioning ODOT Item 499.03 Concrete-General: Proportioning; Slump ASTM C 192/C 192M – 00 Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory ASTM C 143/C 143M – 00 Standard Test Method for Slump of Hydraulic-Cement Concrete ASTM C 231 – 97 Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method
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ASTM C 39/C 39M – 01 Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens ASTM C 78 – 02 Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading) ODOT Item 703.01 Aggregate-General: Size ODOT 703.02 Aggregate for Portland Cement Concrete: Fine Aggregate ASTM C 127 – 01 Standard Test Method for Density, Relative Density (Specific Gravity), and Absorption of Coarse Aggregate AASHTO T 22-03 Compressive Strength of Cylindrical Concrete Specimens ASTM C 260 – 01 Standard Specification for Air-Entraining Admixtures for Concrete AASHTO M 154 – 05 Standard Specification for Air-Entraining Admixtures for Concrete U.S. Army Corps of Engineers CRD-C 13 Standard Specification for Air-Entraining Admixtures for Concrete ASTM C 566 – 89 Standard Test Method for Total Moisture Content of Aggregate by Drying ODOT 2002 Construction and Material Specifications
xxv
1
1 INTRODUCTION
1.1 Problem Statement
Microsilica has proven to be an excellent admixture for Portland cement concrete.
Addition of microsilica to a concrete mix usually results in significant improvements in
strength, durability and permeability. Some of the improvements to the concrete
properties occur because microsilica is a pozzolan. Pozzolans are finely divided silica
that combine with free lime (calcium hydroxide) to create more calcium silicate hydrate.
When conventional Portland cement hydrates, it produces both calcium silicate hydrate,
the chemical glue that makes the cement hard, and free lime, which is weak and highly
soluble. This strengthens significantly the cement matrix and decreases its permeability.
Microsilica is estimated to be about a hundred times finer than cement, giving it the
ability to plug voids between cement particles, and helping it increase the density of the
cement matrix (Malhotra, et al., 1987).
In its natural state, microsilica is extremely fine, having a particle size about the
same as that of cigarette smoke, and this makes it difficult to handle. Microsilica had
originally been used as a slurry, but this form was also found to be inconvenient for
ready-mix plants. The solution to this problem is densification. The microsilica is
bonded into larger particles that are far easier to handle (Malhotra, et al., 1987). There is
some concern, however, as to the effect of densification on the quality control process.
The American Society for Testing and Materials (ASTM) C 1240 – 01 Standard
Specification for Use of Silica Fume as a Mineral Admixture in Hydraulic-Cement
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Concrete, Mortar and Grout requires in its Table 2 that wet-sieved microsilica pass the
No. 325 sieve (45 µm) with no more than 10% retained, and advises that care be
exercised “to avoid retaining agglomerations of extremely fine material.” In its
Appendix X2, however, ASTM 1240 – 01 also states: “The 45-µm (No. 325) sieve
specification is to be used to determine the amount of foreign material present…; good
judgment must be exercised to differentiate between easily dispersible agglomerates and
foreign materials.” The Ohio Department of Transportation (ODOT) has found that
densified microsilica samples submitted sometimes do not meet this specification,
apparently because wet-sieving is not capable of breaking the bonds formed during the
densification process. On the other hand, it may be argued that densification bonds are
temporary and are easily overcome during concrete mixing itself. It is also possible that
densified microsilica will still have adequate field performance even if a certain
percentage of its particles do not pass the No. 325 sieve.
1.2 Objectives
In this study, two important questions that arise out of the processes involved in
packaging and subsequent mixing microsilica into fresh concrete are explored. The first
pertains to increased particle size that results during densification. The second issue is
related to the possible repercussions of densification into larger particle sizes on the
mechanical and other engineering properties of microsilica concrete. Because this type
of concrete is produced and utilized around the world in increasing amounts (Helland, et
al., 1988), and because these two questions have not been answered conclusively yet in
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the published literature, research reported herein assumes considerable significance, with
direct financial and engineering consequences. Whether densification increases the
amount retained on the No. 325 sieve to more than 10%, and whether such an increase is
detrimental to the engineering properties of microsilica concrete are issues that need to be
investigated using a well-designed factorial of experiments.
1.3 Technical Background
Microsilica is obtained as a by-product in the manufacture of silicon and
ferrosilicon, from a procedure that involves the reduction of high purity quartz with coal
at a temperature of 3300°F in an electric arc furnace. Consisting in excess of 85% of
amorphous non-crystalline silica (SiO2), microsilica is collected as the tiny particulate
matter present in the emissions from this combustion process, a material that would
otherwise have to be landfilled. Individual microsilica particles are spherical in shape
and measure about 0.1 µm in diameter, i.e., they are about 100 to 150 times smaller than
Portland cement particles. The bulk density of microsilica is in the range of 10 to 15 pcf
(150 to 250 kg/m3), and its specific surface area is on the order of 10,000 to 13,000 yd2/lb
(20,000 to 23,000 m2/kg) (Malhotra, et al., 1987).
Microsilica added to fresh concrete reacts with the calcium hydroxide produced
during the hydration of Portland cement to produce increased amounts of calcium silicate
hydrate. This results in a much stronger bond between the cement paste and the coarse
aggregate, thereby leading to increased compressive strength. Moreover, the additional
calcium silicate hydrates produced are much more resistant to chemical attack than the
4
weaker calcium hydroxide. Another beneficial mechanism operative when microsilica is
used derives from the fineness of its particles and is referred to as the micro-filler effect.
Filling of voids in the matrix leads to a much denser pore structure, and “reduces the
number and size of capillaries that would enable contaminants to infiltrate the concrete”
(www.norchem.com/appl-works.html; accessed: 07/21/05).
The combined action of microsilica as a pozzolan and as a filler, results in
concrete that can be of very high strength and durability. No more than thirty years ago,
6,000 psi concrete was considered to be high strength; using microsilica, compressive
strengths of up to 20,000 psi are reported in the literature. Similarly, the modulus of
elasticity and the flexural strength at 28 days are also higher than in ordinary Portland
cement concrete (Helland, et al., 1988). Improvements in durability and in scaling
resistance result from greatly reduced fluid permeability and ionic diffusivity and the
concomitant increased resistance to penetration by chloride ions, most notably present in
deicing or marine salts. Microsilica concrete can also exhibit very good freeze-thaw
durability provided the air entrained is controlled. Reduction in the alkalinity of the pore
solution and in the diffusion of alkali ions and water lead to a decrease in expansion and
in alkali-aggregate reactivity. High early strengths and resistance to abrasion are
additional benefits (Malhotra, et al., 1987).
Microsilica used in concrete is available in three forms: water slurry, dry
uncompacted powder, and dry densified (compacted) powder. The microsilica content of
the slurry form is about 50% by weight, the remainder being water. While used
commercially in this from, slurried microsilica can be difficult to handle in ready-mix
5
plants without special equipment. On the other hand, handling of the uncompacted
powder poses a potential health risk, since it may be breathed in by construction
personnel. Because of handling problems with both uncompacted and slurried
microsilica, compacted or densified microsilica is preferred. Dry compacted microsilica
is believed to have the same performance characteristics as the uncompacted material. At
typical densities of 40 pcf, its handling qualities approach those of Portland cement,
whose density is usually around 94 pcf. The bulk density of uncompacted microsilica is
typically 15 pcf. Compacted microsilica is virtually free of dust and lumps, flows readily
in pneumatic lines or along bucket elevators, and can be stored in ordinary cement silos
or transported in bulk cement tankers (Malhotra, et al., 1987).
1.4 Report Organization
This report is divided into six chapters. The first chapter provides a definition of
the problem explored, identifies the objectives of the study, and outlines the technical
background of the research. Chapter 2 presents a literature review into the use of
microsilica in concrete mixes, and the resulting effects on the physical, mechanical, and
durability properties of concrete. The third chapter offers a detailed description of the
mixing, casting, curing and testing procedures adopted during this project. Results from
the tests conducted are presented in Chapter 4, which is subdivided into three sections,
one for each of the microsilica types used, viz., densified, undensified and microsilica
abused in the laboratory by wetting and drying. The discussion of these results in the
fifth chapter involves a further subdivision, this time depending on the coarse aggregate
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type employed, i.e., natural or crushed. In addition, the effects of specimen age and size
on the compressive and flexural strengths of microsilica concrete are examined. On the
basis of these tests, a number of recommendations to ODOT are formulated regarding the
future application of microsilica in concrete pavements and bridges. These
recommendations along with summary and conclusions are presented in Chapter 6.
A companion report, detailing the results of rapid chloride permeability testing on
specimens prepared during this project, has also been prepared under separate cover.
7
2 LITERATURE REVIEW
2.1 Introduction
This chapter summarizes the literature on the use of microsilica as a concrete
admixture, and describes its effect on the physical, mechanical and durability properties
of the resulting mix. In general, the properties of concrete depend on a number of
variables, making it hard to identify the exact cause of a particular behavior change. The
best available information from previous investigations and case histories is presented in
this chapter.
Microsilica was first introduced on an experimental basis as a concrete additive in
the Scandinavian countries in the 1950s (Helland, et al., 1988). The development of high
range water reducers in Europe and Japan in the early 1970s led to a reduction in the
water/cement ratio of microsilica concrete, while ensuring acceptable workability, and
contributed to the more widespread use of the product. Microsilica concrete highway
applications in the United States did not begin until the mid-1980s, with trial placements
of full-depth decks and overlays in the state of Ohio (Whiting and Detwiler, 1998).
By the early 1990s, microsilica was being used by nearly 30 state agencies to
varying degrees. Today, states like Ohio and New York place microsilica concrete
overlays every year, while others explore the use of microsilica on an experimental basis.
Microsilica contents have ranged from 5 to 12%, and typical water-to-cementitious
material ratios have been between 0.3 and 0.4. There is no consensus yet on the optimum
values of these percentages (Whiting and Detwiler, 1998).
8
2.2 Production of Microsilica
As already noted in Chapter 1, microsilica is a by-product of the ferro-silicon
alloy and silicon metal industries. Silicon, ferro-silicon, and other alloys of silicon are
produced in electric arc furnaces, where quartz is reduced by carbon at very high
temperatures. In the process, the silica oxide (SiO) vapors produced, oxidize and
condense to form very tiny spheres of noncrystalline silica (silicon dioxide or SiO2). The
latter is highly pozzolanic, and is recovered by passing the outgoing flue gas through a
baghouse filter (Malhotra, et al., 1987). It seems that microsilica containing more than
78% SiO2 in amorphous form can be used in cement and concrete. Malhotra and Mehta
(1996) maintain that “the current world production of microsilica appears to be about one
million tons per year” with Norway and the United States numbering among the major
producers. Nonetheless, they also note that “in spite of several technical advantages, only
a small percentage of the current supply of microsilica is being used as a mineral
admixture in the cement and concrete industries,” attributing this to the high cost of the
material, as well as handling difficulties.
Microsilica particles are extremely fine and have low bulk density, which makes
handling and transportation of the material difficult. Therefore, microsilica is generally
transported and used in the form of slurry or pellets, or as a densified powder
(www.silicafume.org/general-concrete.html; accessed: 07/22/05). Undensified
microsilica, harvested directly from the baghouse filters, is not commonly used. This
form would be very useful as an admixture in concrete, but it is very difficult to handle
because of its very low loose bulk density. Sometimes, undensified microsilica is
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blended with cement to reduce handling and transportation costs. In order to make
microsilica easier to handle and transport, it is usually densified. Densification doubles
the loose bulk density of microsilica, and reduces the amount of dust created while
handling it. Densified microsilica is less costly than the undensified form, and is,
therefore, more economically attractive. The slurry form of microsilica contains 50%
water. Slurried microsilica has a number of advantages over undensified microsilica.
These advantages include lower transportation costs and the ability to be dispensed more
accurately. Its main disadvantage is that slurried microsilica must be protected from
freezing and from evaporation.
2.3 Properties of Microsilica
Microsilica particles are smooth, spherical, and have on average a particle
diameter between of 0.1 and 0.2 µm. This diameter is about a hundred times smaller than
that of Portland cement particles. The specific surface area of microsilica is measured by
nitrogen adsorption techniques. Most types of microsilica have an average specific
surface area of 1.07 × 105 ft2/lb (22 m2/g), although this parameter can vary between 6.34
× 104 (13) and 1.37 × 105 ft2/lb (28 m2/g). Undensified microsilica has an average bulk
density of 16 pcf (256 kg/m3), although this can vary between 5 (80) and 27 pcf (432
kg/m3). Densified forms of microsilica have bulk densities between 30 and 45 pcf. The
typical range for microsilica specific gravity is 2.2 to 2.3 (Luther and Smith, 1991).
When ordinary Portland cement hydrates, it produces calcium silicate hydrate, the
chemical glue that makes the cement hard, as well as lime (calcium hydroxide), which is
10
very weak and dissolves easily. When microsilica is added, the silica combines with the
free lime to create more calcium silicate hydrate. The primary active ingredient in
microsilica is silicon dioxide. Most types of microsilica have SiO2 contents above 85%.
Loss on Ignition (LOI) is used to infer the carbon content; most types of microsilica have
LOI values below 3% (Luther and Smith, 1991). Other chemical compounds like Al2O3,
SO3, Fe2O3, MnO, TiO2, CaO, K2O, P2O2, MgO, Na2O make up the other percentages in
microsilica.
Wolsiefer, et al. (1995) tested mixtures of concrete containing sixteen different
samples of microsilica. These samples differed with regard to the microsilica form
employed, as well as its silicon dioxide content. Their tests involved undensified,
densified, slurry, and a pelletized form of microsilica. The investigators found that using
different forms of microsilica had no significant effect on mechanical properties of
concrete, such as compressive and tensile strength. They also concluded that the shearing
forces applied during mixing were sufficient to break up agglomerations of microsilica
particles, even in pelletized form.
2.4 Effect of Microsilica on Physical Properties of Concrete
Due to its pozzolanic character, microsilica influences many of the physical
properties of concrete, including water demand, cohesiveness, bleeding, plastic
shrinkage, etc., as discussed below.
11
2.4.1 Water Demand
Microsilica particles tend to fill the void space between cement particles. This
void space is typically filled with so-called free water. Particle packing allows free water
to become available for hydration, thereby decreasing water demand in a microsilica
concrete mix. On the other hand, since microsilica particles have a relatively high
surface area, more water is adsorbed by the particles, and this tends to increase water
demand. Usually, such increases more than offset the water demand decreases stemming
from improved particle size distribution, so that the net effect is an increase in water
demand. Consequently, high range water reducers and superplasticizers are generally
added in microsilica concrete mixes to compensate the water demanding characteristic of
microsilica and maintain the required workability (Malhotra, et al., 1987).
The net effect of microsilica on the physical properties of concrete depends on a
number of factors, including the water-to-cementitious material ratio of the concrete,
microsilica content, and the presence of water reducers or superplasticizers. Typically,
when its concentrations are kept small, the overall effect of microsilica on water demand
is negligible. When the microsilica content is increased, however, the water demand will
also increase. Consequently, unless a superplasticizer is used, water must be added to
maintain workability (Malhotra, et al., 1987). Jacobsen and Sellevold (1997) tested the
frost resistance of microsilica concrete, and noted that one L/m3 of water should be used
for every kg/m3 of microsilica added in order to maintain a consistent level of
workability.
12
2.4.2 Cohesiveness
When microsilica is added to concrete of high cement content or low water-to-
cementitious material ratio, the concrete appears to be more cohesive (i.e., sticky and
gluey), making it more difficult to place and to consolidate. High cohesiveness often
results in a reduction in surface bleeding, i.e., in the development of a layer of water at
the top surface of freshly placed concrete,. Bleeding occurs due to excess water in the
concrete. Addition of microsilica reduces bleeding in concrete because of the high
affinity of condensed microsilica to water, thereby resulting in less water remaining
available for bleeding. Bleeding has mostly undesirable effects on concrete properties,
e.g., low strength, yet it helps protect against plastic shrinkage cracking, i.e., cracking of
the freshly placed concrete due to insufficient surface moisture. Consequently, it is
important for contractors to cure the concrete properly (Malhotra, et al., 1987).
Moreover, the addition of microsilica increases the concrete’s viscosity (i.e., its
resistance to flow). Consequently, a concrete containing microsilica is less prone to
segregation (i.e., the separation of its ingredients) than a mix without it. This effect
ensures a more uniform mixture and, therefore, results in higher strength, especially in
the presence of a superplasticizer (Malhotra, et al., 1987).
2.4.3 Slump and Workability
The addition of microsilica as a concrete admixture has been shown to decrease
both the slump and the workability of fresh concrete. In order to maintain a minimum
level of workability, a contractor must either add more water or use a water reducing
agent. In fact, it is generally considered that a somewhat higher slump must be achieved
13
with microsilica concrete in order to retain the same workability as ordinary Portland
cement concrete. Yet, at a low water/cement ratio, and if proper amounts of
superplasticizer are used, the workability of microsilica concrete may in fact be higher,
on account of the small particles displacing some of the water present in the matrix
(Malhotra, et al., 1987).
2.4.4 Air Content
It is generally possible to ensure the same amount of air in a mix containing
microsilica as in ordinary Portland cement concrete, even though the amount of an air
entraining admixture may need to be increased slightly. If a constant dosage of air
entrainer is used, the addition of microsilica can reduce the air volume in the mix. To
retain constant air content, the demand for an air entraining agent is higher in concrete
with microsilica than without it. This higher demand is caused by the high surface area
of the microsilica, and possibly by its carbon content (Malhotra, et al., 1987).
2.4.5 Setting Time
There is currently no consensus regarding how setting time of concrete is affected
by microsilica. Pinto and Hover (1997) conducted an extensive experiment to answer
this question. Their study consisted of two series of tests. In the first, the curing
temperature was held constant and nine separate high-strength mortar mixtures were
tested. In the second, the temperature was varied and six mixtures were examined. The
water-to-cementitious material ratio varied from 0.27 to 0.33. Three levels of microsilica
content were used: 0, 5, and 10%. Two levels of superplasticizer were also employed:
14
0.8 and 1.6%. The experiments showed that the presence of microsilica accelerated the
setting behavior.
On the other hand, during their experiments on the freeze-thaw durability of
concrete, Soeda, et al. (1999) noticed that the inclusion of microsilica increases setting
time by alleviating excessive viscosity stemming from a low water-binder ratio.
Investigations by Malhotra and Mehta (1996) have shown that ordinary concrete
mixtures incorporating small amounts of microsilica, i.e., up to 10% by weight of cement,
exhibit no significant difference in setting time compared to conventional mixes. Since
microsilica is typically used in combination with water reducers and superplasticizers, the
effects of microsilica on setting time of concrete tend to be masked.
For their part, Khayat and Aϊtcin (1992) reported that concretes with microsilica
take longer to set and achieve a given strength level than mixes without it. Moreover, the
addition of microsilica to concrete without the use of a water reducer or superplasticizer
delays setting time, especially when the microsilica content is high. Plasticizers are also
known to increase the setting time of concrete, so the combination of microsilica and
superplasticizers magnify the retarding effects of microsilica and make it difficult to
determine how much of the increased setting time is due to each of the microsilica and
the superplasticizer.
2.4.6 Shrinkage and Cracking
As concrete containing microsilica shows little to no surface bleeding, the risk of
plastic shrinkage is high. This can be a very serious problem under curing conditions of
elevated temperature, low humidity, and high wind, all of which contribute to rapid
15
evaporation of water from freshly placed concrete. Crack formation can begin soon after
casting, and can continue until the concrete starts to set (Malhotra, et al., 1987). To
overcome plastic shrinkage, the surface of concrete should be protected from evaporation
by covering it with plastic sheets or wet burlap, or by adding curing compounds and
evaporation retarders (Mehta and Monteiro, 1993).
Drying shrinkage depends heavily on the amount of microsilica used, the water-
to-cementitious material ratio, and the length, as well as method of curing. Generally, the
higher the amount of microsilica, the more prone a concrete becomes to drying shrinkage
and cracking. Microsilica concretes with a low water-to-cementitious material ratio
exhibit similar levels of shrinkage cracking as ordinary mixes. Microsilica concretes
moist cured for fewer than seven days exhibit higher shrinkage cracking levels than
mixes cured for at least seven days (Malhotra, et al., 1987).
Whiting and Detwiler (1998) conducted experiments to assess the effects of
microsilica on drying shrinkage and on cracking of bridge decks. Two classes of
concrete mixtures were included in their study: full-depth mixtures, containing 620 lb/yd3
of cementitious material with a maximum aggregate size of ¾ in.; and overlay mixtures
containing 700 lb/yd3 of cementitious material with a maximum aggregate size of 3/8 in.
For each mix design, separate test mixtures were prepared over a range of water-to-
cementitious material ratios and microsilica contents. The microsilica content ranged
from 0 to 12% for both mixture classes, whereas the water-to-cementitous material ratio
ranged from 0.35 to 0.45, and from 0.30 to 0.40 for full-depth and overlay mixtures,
16
respectively. Specimens from full-depth mixtures were moist cured for seven days
before testing, while overlay mixtures were moist cured for only three days.
Drying shrinkage was measured on beam specimens after 4, 7, 14, and 28 days,
and after 8, 16, 44, and 64 weeks. Cracking tendency was measured according to a
restrained-ring method developed under National Cooperative Highway Research
Program (NCHRP) Project 12-37 (Krauss and Rogalla, 1996). In the first phase of the
investigations, tests were carried out on both full-depth and overlay mixtures. In the
second, more comprehensive series of tests were performed on the full-depth mixtures
only, during which the more significant variables were examined using more replicates.
Chloride ion penetration was measured by exposing the concrete to a chloride solution
for 180 days, and measuring the chloride content close to the surface. This information
was used to develop chloride diffusivity coefficients for each mixture. Compressive
strength was measured on moist-cured cylinders after 7, 28, 56, and 90 days. The
researchers stressed the importance of proper moist curing techniques on drying
shrinkage. At early ages, inadequate curing, a high water-to-cementitious material ratio,
and/or a high cement factor can increase shrinkage cracking by up to 40% in microsilica
concretes used for bridge deck placement. Drying shrinkage increases with decreasing
water-to-cementitious material ratio, but this effect is more pronounced as microsilica
content increases. Specimens cured for only one day and containing between 6 and 9%
microsilica showed a high tendency for cracking. In specimens water-cured for seven
days, no significant correlation between microsilica content and cracking was observed.
17
2.4.7 Heat of Hydration
The addition of microsilica can cause a rise in the mix temperature in the first
couple of days, but will also lead to a significant overall decrease in temperature at later
ages. The initial temperature rise can be attributed to the acceleration of the cement
hydration reaction (Helland, et al., 1988).
2.5 Effect of Microsilica on Mechanical Properties of Concrete
2.5.1 Compressive Strength
Addition of microsilica increases the compressive strength of concrete. The main
reasons for the increase are the strong cement matrix formed due to the micro-filler effect
and the pozzolanic characteristics of microsilica. Various factors contribute to this
strength increase, including percentage of microsilica added to the mix, water-to-
cementitious material ratio, cementitious material content, dosage of superplasticizer,
temperature, humidity, and length as well as method of curing (Malhotra and Mehta,
1996).
Usually, the water demand of microsilica is very high. If slump is to be
maintained constant without using a superplasticizer, the water demand is directly
proportional to the percentage of microsilica replacement of cement. In this instance, the
increase in strength development due to the microsilica is offset by the loss of strength
that comes from a high water-to-cementitious material ratio (Malhotra, et al., 1987).
Malhotra and Mehta (1996) note that “in general, the use of superplasticizers is a
prerequisite to achieve the proper contribution of microsilica to concrete compressive
18
strength. In fact, many important applications of microsilica in concrete depend strictly
upon its utilization in conjunction with super plasticizing admixtures.” The effect of
microsilica on compressive strength is small when compared to that of a lower water-to-
cementitious material ratio. This effect on compressive strength is most pronounced
when 0 to 6% of cement is replaced by microsilica, but beyond 6% the strength increases
are minimal (Malhotra and Mehta, 1996).
The extent of compressive strength gain due to the microsilica addition depends
on the age of the concrete, the cement content, and the microsilica content. The age at
which microsilica starts to contribute to strength gain depends on the cement content and
the water-to-cementitious material ratio of the concrete. Generally, in concretes with
high water-to-cementitious material ratios, the microsilica takes a longer time to
contribute to compressive strength (Helland, et al., 1988). Prussack, et al. (2001)
observed that most of the contribution of microsilica to compressive strength
development occurs in the first 7 days under steam curing and in the first 28 days for
moist-cured concrete.
2.5.2 Flexural Strength
In general, the development of flexural strength in microsilica concrete is similar
to that in ordinary Portland cement concrete, but the contribution of drying is more
significant in the former. Moist cured concrete specimens show higher flexural strengths
than air-dried specimens. With or without microsilica, concretes cured with water will
have similar flexural-to-compressive strength ratios. When air cured, concrete containing
19
microsilica will generally have a lower flexural-to-compressive strength ratio (Malhotra,
et al., 1987).
2.5.3 Modulus of Elasticity
In general, the increase in compressive strength of concrete is accompanied by a
small increase in the Young’s modulus of elasticity. The addition of microsilica reduces
the porosity of the transition zone between the aggregate and the cement paste, allowing
the stiffness of the aggregate to contribute more to the overall stiffness of the concrete
(Helland, et al., 1988).
2.5.4 Bond Strength
Internal bleeding in concrete can cause free water to accumulate around coarse
aggregate and steel reinforcement. A high water content in a concrete mix can also
reduce the adhesion between the cement and the aggregates, or between the cement and
the reinforcing steel. As noted earlier, microsilica reduces the amount of bleeding,
thereby strengthening the bond between concrete and reinforcing steel. This effect is
attributable to a less porous transition zone between the cement and the aggregate. As a
result, pullout strength increases as the amount of microsilica increases (Malhotra and
Mehta, 1996).
Fitch and Abdulshafi (1998) tested a total of 62 bridge deck overlay specimens
for bond strength. After curing for 28 days, cylinders made with Portland cement
concrete were cut in half and one circular face was sandblasted to simulate the surface of
a bridge deck. The specimens were then placed at the bottom of a cylinder mold and
material from various batches made with microsilica concrete was placed over them. Six
20
different batches of microsilica concrete were prepared: three had natural gravel, whereas
the other three contained crushed limestone. Three different moisture conditions, viz.,
dry, saturated surface dry, and wet, were used for the Portland cement concrete base. The
specimens were then subjected to tensile loading to see whether failure occurred at the
overlay interface or within the Portland cement or the microsilica concrete matrix itself.
All of the specimens with a dry surface condition showed higher overlay bond
than concrete matrix strength. A majority of the specimens in the saturated surface dry
condition exhibited higher bond than concrete matrix strength. Specimens with a wet
surface condition generally had weaker bond than concrete matrix strength. These
findings show that microsilica concrete overlays achieve their highest bond strengths
when the Portland cement concrete base is dry.
2.5.5 Strength Development
Malhotra and Mehta (1996) state that “the main contribution of microsilica to
concrete strength development at normal room [curing] temperatures takes place between
the ages of about 3 and 28 days.” The overall strength development patterns in
microsilica concretes can vary according to concrete proportions and composition, and
are also affected by the curing conditions. High curing temperatures have a greater
strength accelerating effect on microsilica concretes than on comparable Portland cement
concrete mixes (Malhotra and Mehta, 1996).
As noted in previous paragraphs, curing conditions have a significant effect on a
number of properties of both fresh and hardened concrete. The inclusion of microsilica
as an admixture seems to magnify this effect, especially as far as strength development is
21
concerned. Microsilica concretes that are continuously moist cured show superior
mechanical properties than air cured ones (Malhotra, et al., 1987). In fact, Carette and
Malhotra (1992) found that air cured concrete containing microsilica may even show a
slight decrease in compressive strength after 100 days or more. Typically, seven days of
moist curing is sufficient to prevent this.
Sasatani, et al. (1995) performed tests for a period of five years, in which they
exposed concrete containing various admixtures to different weather conditions.
Concrete mixtures containing fly ash, blast-furnace slag, and microsilica were prepared.
Water-to-cementitious material ratios of 0.45, 0.55, and 0.65 were used for the control
concretes containing only ordinary Portland cement; for concretes containing admixtures
this ratio was fixed at 0.55. Replacement levels of ordinary Portland cement by fly ash,
blast-furnace slag, and microsilica were 30, 50 and 10%, respectively. Specimens were
cured in two different ways. In the first, specimens were cured in 20°C-water for 28
days, whereas in the second they were cured in 20°C-water for 7 days and then kept in a
dry environment for another 21 days. After curing, the specimens were exposed to four
separate environmental conditions: indoors, in 20°C-water; indoors, at 20°C and 60%
relative humidity; on the roof of a building at Kanazawa University located 15 km from
the sea; and at Matsuto Beach, facing the Sea of Japan. Chloride permeability and pore
size distribution were measured after 28 days of environmental exposure. Following
exposure times of 1, 3, and 5 years, compressive strength, pulse velocity, depth of
carbonation, and chloride ion penetration were also measured.
22
Air-dried 10% microsilica concrete showed a decrease in compressive strength
with exposure time over the first twelve months since casting. This may be ascribed to
internal stress built up due to uneven drying between the surface and concrete matrix.
Uneven drying probably results from the dense and discontinuous pore structure of
microsilica concrete. The effects of curing conditions were not as pronounced for
concrete exposed to outdoor conditions. This is because the concrete can absorb the
water needed for hydration from the environment.
2.6 Field Tests
Fitch and Abdulshafi (1998) conducted brief visual inspections on 145 microsilica
overlaid concrete decks. Of these, 27 decks showed noticeable cracks in the overlay
surface. The undersides of 84 of the decks were also visually inspected. Of these, 29
showed several transverse full-depth cracks, and evinced flow of water through the deck
resulting in deep chloride penetration. In-depth condition surveys were also performed
on 28 microsilica overlaid concrete decks. These surveys included manual sounding to
detect horizontal cracking, and core samples to be tested in the laboratory.
Approximately 39% of the concrete decks inspected exhibited cracking over more than
10% of their surface. Seven of the 28 decks showed maximum crack widths exceeding
0.20 mm.
Aϊtcin (1990) conducted three field experiments testing various properties of
concrete containing microsilica. In the first test, 50 m3 of microsilica concrete were used
for part of the three-lane Highway 25 in Montreal, Quebec, Canada. A reference mix of
23
concrete not containing microsilica was used nearby. The second field experiment
consisted of two sidewalks built in Sherbrooke, Quebec. Each sidewalk had sections of
microsilica, as well as of ordinary concrete. These sidewalks were chosen because of the
high amount of deicing salts they were routinely exposed to. In the third field
experiment, two experimental columns were cast during the construction of La
Laurentienne, a 26-story building in Montreal. Both columns contained microsilica, but
only one column was part of the building. The other was used as a mock column to study
the creep of the concrete.
Compressive strength and chloride ion permeability tests were performed on both
concrete cast during the experiment, and on cores drilled from the field for the first two
experiments. In the third, cores were drilled from the mock column two and four years
after casting. In the Highway 25 experiment, all the specimens had approximately the
same compressive strength after one year, but the reference concrete experienced a
greater strength increase between 28 days and one year. The chloride ion permeability
was much lower in the microsilica concrete than in the reference concrete. In the second
experiment, microsilica specimens cured in the laboratory had higher compressive
strengths than those from ordinary concrete, but in the field the situation was reversed.
After two years, no significant differences in compressive strength between the two sets
of specimens were found. Again, the microsilica concrete had much lower chloride
permeability. In the third experiment, the 28-day compressive strengths of the mock
column and the lab specimens were nearly identical, while the long-term strength gain in
the lab specimens was greater than that in the mock column. The chloride ion
24
permeability was extremely low. The combined results showed that microsilica concrete
exposed to outdoor conditions performed just as well as ordinary concrete. Yet, it
appeared that microsilica concrete suffered more from poor curing conditions. The
chloride-ion permeability was extremely low in microsilica concrete even after four to six
years.
2.7 Do Undispersed Agglomerates Matter?
The conventional wisdom on the repercussions of unbroken clusters in densified
microsilica is represented by the study conducted by Wolsiefer, et al. (1995), who tested
mixtures of concrete containing sixteen different samples of microsilica. These samples
differed with regard to the microsilica form employed as well as silicon dioxide content.
Thus, tests involved undensified, densified, slurry, and pelletized form of microsilica.
The investigators found that using different forms of microsilica had no significant effect
on the mechanical properties of concrete, such as compressive and tensile strengths, etc.
They also concluded that the shearing forces applied during mixing are sufficient to break
up agglomerations of microsilica particles, even in pelletized form.
On the other hand, in a “deliberately provocative” paper, Diamond and Sahu
(2003) set out to redress “the perceived failure of many respected sources of information
in the industry to properly convey a clear picture of the nature and particulate
characteristics of densified [microsilica].” They note with evident frustration, for
example, that “nowhere in the current [American Concrete Institute] ACI ‘Guide for the
Use of Silica Fume in Concrete’ is there mention of the fact that the actual size of the
25
densified silica fume, as supplied to the customer, is always in the range of hundreds of
µm...until and unless the fume is physically broken up by some process.” Although the
tone of this paper is unlike most in the professional literature, being rather aggressive and
almost personal, the issues it raises are worth considering seriously. Diamond and Sahu
(2003) insist that “it is extremely unlikely that complete dispersion ever takes place in
concrete mixing” analogous to that achieved using an “extremely powerful ultrasonic
system.” They cite a number of transmission and scanning electron microscopy (TEM
and SEM) studies, that suggest that clusters were noticed not only in densified microsilica
but also in undensified microsilica. This would be an indication that that these clusters
are not formed during the process of densification of commercial densified microsilica,
but would pose the same level of difficulty to break in the undensified material, as well.
The study by Diamond and Sahu (2003) is motivated by “two separate concerns
stemming from the failure of agglomerates of densified silica fume to be completely
dispersed in concrete mixing.” The first is that “to the degree that [undispersed]
agglomerates remain in concrete the expected fine particle packing benefit is lost,” since
such agglomerates are “often much coarser than cement.” The second concern is
potentially more important: “agglomerates can clearly act as extremely aggressive alkali-
silica reactive (ASR) aggregates,” despite the fact that microsilica “is ordinarily
considered as mitigating the effects of possible ASR when reactive sand or coarse
aggregate is components are present.”
The implications of the assertions by Diamond and Sahu (2003) are far reaching,
but only a few of their facets can be explored within the scope of this study. For
26
example, it is not feasible to conduct TEM or SEM measurements, but more conventional
means of establishing the gradation curves for the materials used herein can be employed.
The repercussions of agglomerates on fine particle packing can be examined using unit
weight determinations of the concrete prepared, as well as strength comparisons.
Regrettably, the potential for ASR deterioration cannot be reliably assessed in a study as
brief as the present one.
27
3 MATERIALS AND PROCEDURES
3.1 Introduction
The materials employed in this project are first enumerated in this chapter; they
include primarily the microsilica and the coarse aggregate types. Tests conducted on
these materials are outlined next, to illustrate conformity with the prescriptions by the
American Society for Testing and Materials (ASTM), by the Ohio Department of
Transportation (ODOT), or by the American Association of State Highway and
Transportation Officials (AASHTO). The derivation of the mix design for each of the
specimen lots cast is then described, emphasizing again adherence to the pertinent
governing specifications. The most arduous and time-consuming aspect of the project
was mixing, casting and curing the test specimens, the procedures for which are
discussed next. Finally, the tests conducted on the plastic and cured concrete samples are
described.
3.2 Materials Used
Sand, coarse aggregate, Type I-II Portland cement, water (www.cincinnati-
oh.gov/water; accessed: 07/22/05) from greater Cincinnati water works, microsilica,
superplasticizer, and air entrainer are the materials used in this project. The sand and
coarse aggregate were supplied free of charge by Martin Marietta Materials, a leading
supplier in the Cincinnati area. The sand was natural and came from their sand and
28
gravel facility in Ross, OH. Coarse aggregate was of two kinds, both in the No. 8
gradation with a nominal maximum aggregate size of 3/8 in.: natural river gravel, or
crushed limestone. The gravel was obtained from their gravel facility in Fairfield, OH,
whereas the stone was produced at their Phillipsburg quarry in Brookville, OH (Jim R.
Martin: personal communication, 10/14/02; www.martinmarietta.com; accessed:
12/02/02). The natural aggregate had a rounded shape and a smooth surface, whereas the
crushed aggregate had a more angular shape and a rougher surface. At given
water/cement ratio, concrete made with crushed aggregate is usually expected to have
higher compressive strength than concrete made with natural aggregate, as crushed
aggregate creates a stronger bond with cement mortar due to its rough texture (Mehta and
Monteiro, 1993).
The Portland cement Type I-II was donated by CEMEX from their operation in
Fairborn, OH (Steve Reibold: personal communication, 09/11/02; www.cemexusa.com;
accessed: 08/14/02), and the microsilica by ELKEM Materials from their location in
Alloy, WV (Tony N. Kojundic: personal communication, 08/07/02; www.materials.
elkem.com; accessed: 07/24/02). The other admixtures were supplied at no cost by
Master Builders, Inc. (Greg Wirthlin: personal communication, 08/07/02; www.
masterbuilders.com; accessed: 07/24/02). These were: MB-AE 90 air entrainer, meeting
the requirements of ASTM C 260, AASHTO M 154 and CRD-C 13, and recommended
for obtaining “adequate freeze-thaw durability in a properly proportioned concrete
mixture, if standard industry practices are followed;” and Rheobuild 1000 “high range,
water reducing admixture, formulated to produce rheoplastic concrete that flows easily,
29
maintaining high plasticity for time periods longer than conventional superplasticized
concrete,” and that “meets ASTM C 494 requirements for Type A, water reducing, and
Type F, high range water reducing, admixtures.” The research laboratory facilities on the
University of Cincinnati campus were used, except as noted.
3.3 Tests on Microsilica
Testing was performed on four types of microsilica, viz., undensified, densified,
and two types of abused microsilica. Undensified and densified forms are readily
available on the market, and were procured commercially. Abused microsilica was
prepared by the research team so as to represent a worst case scenario for the handling
and storage of commercially available material, particularly with regard to its exposure to
ambient moisture.
3.3.1 Preparation of Abused Microsilica
Two different abused microsilica samples were prepared. For the first sample of
abused microsilica (A), 9 kg of densified microsilica was weighed and soaked in a water
tub. The microsilica was stirred rigorously at the beginning, and the water level was
maintained to at least 3 in. above the surface of the settling solids. After a period of three
days, the microsilica had settled and the water above it was clean enough to be removed
using small plastic buckets. The wet sample was spread evenly onto plastic lined trays,
placed on a flat horizontal surface, and was left to dry at room temperature for nearly
three weeks. The second sample of abused microsilica (B) resulted from exposing
30
densified microsilica to high humidity in the curing room for two weeks before allowing
it to air-dry. In both cases, any clumps forming during drying were broken from time to
time using a small trowel. When completely dry, the microsilica was collected into
plastic bags, which were sealed and stored in a cool and dry place, until the time of
testing.
3.3.2 Fineness Tests
Samples of all types of microsilica used in this project were transported to the
ODOT laboratory in Columbus, OH on 05/14/03, for fineness testing by the agency’s
personnel, Mr. Tim Jones, who is responsible for checking conformance with ASTM C
430 – 96 Standard Test Method for Fineness of Hydraulic Cement by the 45-µm (No.
325) Sieve. The following equipment was used: small dessicator bowl with pouring lip,
2 in. dia., 3/4 in. tall; twelve No. 325 sieves, 1 ½ in. dia., 2 ¼ in. tall, each with 3 ½ in.
legs, each with its own calibration factor from the Cement and Concrete Reference
Laboratory (CCRL); electronic scale (Mettler Model PC 180), calibrated to 1/1000 g
precision; small paint brush; hot plate, 250-350°F temperature range; city water faucet;
pressure stabilizer; and temperature compensated pressure gage to 30 psi, 0.1 psi
precision. The ambient temperature in the laboratory was 78°F, and the humidity was
53%.
For each type of microsilica, three 1.000-g samples were weighed in the
dessicator bowl, and then pour into each sieve with the help of the brush and light tapping
of the bowl. First, each sieve was quickly rinsed with de-ionized water from a plastic
spray bottle with a narrow tip. Next, each sieve was subjected to a 10-psi stream of tap
31
water for a period of one minute. A constant stream of tap water was ensured by
connecting both the pressure stabilizer and the pressure gage to the end of the faucet,
which allowed easy control of the water pressure. The sieve was moved in a circular
motion to ensure that the entire sieve was irrigated evenly. The sieve was rotated at
approximately one rotation per second. For one sample from each type of microsilica, a
small paint brush was used in addition to the stream of water. In such cases, the sieve
remained stationary, but the brush was moved in a circular motion. Finally, each sieve
was rinsed again with de-ionized water, and the bottom of the sieve was blotted dry using
a towel. The sieves were then placed on a hot plate set to a temperature between 250 and
350°F. The samples were left here approximately for an hour and a half, or until all of
the moisture had evaporated. Once dry, the samples were allowed to cool off for another
hour, before the microsilica was removed from the sieves and was weighed in the
dessicator bowl again. The weight was recorded as the weight retained, and the sieve
correction factor was applied according to the specification.
3.3.2 Gradation Tests
The gradation of each of the three microsilica types was also determined using
ASTM D 422 – 63 Standard Test Method for Particle-Size Analysis of Soils (Hydrometer
Test), conducted in conjunction with ASTM D 421 – 85 Standard Practice for Dry
Preparation of Soil Samples for Particle-Size Analysis and Determination of Soil
Constants, and ASTM D 854 – 06 Standard Test Methods for Specific Gravity of Soil
Solids by Water Pycnometer. In each case, 15 g of oven dry microsilica material
previously washed through the No. 200 sieve, was mixed with 125 mL of 4% sodium
32
metaphosphate (NaPO3) solution, in a 250 mL beaker. The solution, whose trade name is
Calgon and whose function is that of a deflocculant or dispersant, had just been been
prepared by mixing 40 g of dry chemical with enough water to make 1000 mL. The
beaker was then covered with wet paper towels to minimize evaporation, and the contents
were left to stand for an hour. The mixture was subsequently transferred to a dispersion
cup, which was filled to about 2/3 of its volume with water, and was stirred for about 2
min. The suspension was then transferred into a sedimentation cylinder, more water was
added up to the 1000 mL mark, and the cylinder was capped and agitated for 1 min. Two
minutes after setting the cylinder down, the first reading was taken on the hydrometer,
which had been inserted into the cylinder about 20 s before the measurement.
Subsequent readings were taken at elapsed times of 4, 8, 16, 30, 60, 120, 240, 480, 960,
1920, 3840, and 5760 min. The temperature was also noted each time, and was used to
determine the viscosity of the water in the cylinder. The hydrometer readings were taken
to the top of the meniscus, and were later corrected as follows:
Tactualc CCRR +−= 0 (3.1)
where: Rc = corrected hydrometer reading; Ractual = actual hydrometer reading; C0 = “zero
correction” for impurities in tap water and for the use of a disperasal agent; CT =
temperature correction factor (Bowles, 1992).
The hydrometer percent finer, Fh, was then computed using:
%100×=s
ch M
RaF (3.2)
in which:
33
)1(65.265.1
−×
=s
s
GG
a (3.3)
Ms = mass of oven dry material previously washed through the No. 200 sieve used in the
test = 15 g (from above); and Gs = specific gravity of the solid particles in the sample.
This percentage is adjusted in proportion to the material that had been retained on the No.
200 sieve, F200, using the following expression:
200FFF hadjh ×= (3.4)
For each elapsed time, t, and depending on Rc, the effective sedimentation depth, L, is
read from Table 2 in the specification, whereupon the particle diameter, D, can be
obtained from Stokes’ formula, as follows:
tL
GGD
ws )(98030
−=
η (3.5)
with Gw = specific gravity of water in which the sample was suspended (=1.0); and η =
absolute viscosity of the suspension water, adjusted for temperature per the specification.
Prior to the hydrometer tests, a 200-g of oven dried sample of each microsilica
type was sieved mechanically through a stack of the following sieves: No. 10, 20, 40, 60,
140 and 200, following the procedures detailed by Bowles (1992). Moreover, the
specific gravity of the microsilica solids was determined for each type using the
procedure of ASTM D 854 – 06 Standard Test Methods for Specific Gravity of Soil
Solids by Water Pycnometer. ODOT Supplemental Specification 848 Bridge Deck
Repair and Overlay with Concrete Using Hydro-Demolition assumes that for microsilica
solids, Gs = 2.2.
34
3.4 Tests on Aggregates
3.4.1 Specific Gravity and Absorption of Coarse Aggregate
ASTM C 127 – 01 Standard Test Method for Density, Relative Density (Specific
Gravity), and Absorption of Coarse Aggregate was followed in conducting this test.
Coarse aggregate was taken in sufficient quantity and was immersed in water at room
temperature. After 24 ± 4 hours of soaking, it was removed from the water and was
rolled on a large absorbent towel, until all visible moisture was blotted from the surface
of the aggregate. The aggregate was then considered to be in the saturated surface dry
(SSD) condition. The test sample was weighed in air, before being placed in a container
and immersed in water at 73.4 ± 3°F, where its submerged weight was also determined.
The sample was then placed in an oven at 230 ± 9°F for a period of 24 ± 4 hours, after
which its oven-dried weight was measured. Three types of specific gravities were
determined, viz., bulk specific gravity for the oven-dried sample, bulk specific gravity for
the saturated surface dry sample, and the apparent specific gravity of the sample. In
addition, the absorption value for the aggregate was calculated. The following formulae
were used:
CBABSG−
= Dry),(Oven Gravity SpecificBulk (3.6)
CBBBSGSSD −
= Dry), Surface Saturated (Gravity SpecificBulk (3.7)
CAAASG−
= Gravity, SpecificApparent (3.8)
35
100)(% ,Absorption ×
−
=A
ABAbsorption (3.9)
where: A = weight of oven dry sample in air, g; B = weight of saturated surface dry
sample in air, g; and C = weight of saturated sample in water, g.
3.4.2 Specific Gravity and Absorption of Fine Aggregate
ASTM C 128 – 97 Standard Test Method for Specific Gravity and Absorption of
Fine Aggregate was followed in conducting this test. A 1000-g sample of sand was
immersed in water at room temperature for 24 ± 4 hours. The excess water was drained
and the sand was then spread over a flat nonabsorbent surface exposed to a gently
blowing current of air. The material was stirred frequently to ensure even drying. This
process was continued until the specimen no longer stood on its own when subjected to
the specified cone test, at which point the sand was considered to be in the saturated
surface dry condition. A pycnometer was filled partially with water and 500 g of this
saturated surface dry sample was added to it. The remaining volume of the pycnometer
was filled with water, up to the calibration mark. The mixture was agitated slightly in
order to remove the air bubbles. The total weight of the pycnometer with the sample and
water was then recorded. The pycnometer was emptied and the sample was dried in an
oven at 230 ± 9°F for 24 ± 4 hours. The sample was taken out of the oven and its weight
noted. The pycnometer was then filled only with water up to the calibration mark and its
weight was recorded again. The following calculations were performed to determine the
three specific gravities and the absorption value for the fine aggregate:
CSBABSG−+
= Dry),(Oven Gravity SpecificBulk (3.10)
36
CSBBBSGSSD −+
= Dry), Surface Saturated (Gravity SpecificBulk (3.11)
CABAASG−+
= Gravity, SpecificApparent (3.12)
100)(% ,Absorption ×
−
=A
ASAbsorption (3.13)
where: A = weight of oven dry sample in air, g; B = weight of pycnometer filled with
water, g; S = weight of saturated surface dry sample, g; and C = weight of pycnometer
with water, g.
3.4.3 Bulk Density of Coarse Aggregate
ASTM C 29/C 29M – 97 Standard Test Method for Bulk Density (“Unit Weight”)
and Voids in Aggregate was followed in performing this test. A sufficient amount of
aggregate was oven-dried for 24 ± 4 hours. The bucket measure was calibrated by filling
it with water and determining the weight of water in it. The unit weight of the water was
read off Table 3 (Density of Water) in the specification, as a function of its temperature.
The volume was determined using the formula:
w
wWV
γ= (3.14)
where: Ww = weight of water (lb); and γw = unit weight of water, pcf.
The effort to be expended in placing the aggregate in the bucket measure was
decided based on the size of aggregate. If the nominal maximum aggregate size was 1½
in. or less, a rodding procedure was used. This involved filling the measure in three
layers and rodding each one with a tamping rod 25 times. If the nominal maximum
37
aggregate size was greater than 1½ in., a jigging procedure was used. This involved
filling the measure in three layers, raising one side of the measure approximately 2 in.,
and allowing it to drop to the ground 25 times. After tamping the aggregate, the surface
of the measure was leveled so that no aggregates protruded over the top of the measure.
The mass of the measure plus contents, and mass of the measure alone were determined.
The following formulae were used:
VTGM )( Dry),(Oven Density Bulk −
= (3.15)
+=
1001 Dry), Surface (SaturatedDensity Bulk AMM SSD (3.16)
×−×
×=WS
MWSVoids )(100% Content, Void (3.17)
where: MSSD = bulk density of aggregate at SSD condition, pcf; G = mass of measure
plus aggregate, lb; T = mass of measure, lb; V = volume of measure, ft3; A = %
absorption; S = bulk specific gravity; and W = density of water (=62.4 pcf).
3.4.4 Sieve Analysis of Fine and Coarse Aggregate
This test was conducted in accordance with ASTM C 136 – 96a Standard Test
Method for Sieve Analysis of Fine and Coarse Aggregates. For the fine aggregates,
sieves No. 4, 8, 16, 30, 50, 100, and a pan were weighed and stacked in a column, and
between 300 and 1000 g of each sample were placed on the No. 4 sieve. The sieves were
locked on to a mechanical shaker and the shaker was run for 5 min. The sieves were then
released and they were weighed along with the material, and the readings noted. The
fineness modulus, FM, of the fine aggregate was calculated using the formula:
38
100RetainedsPercentageCumulative∑=FM (3.18)
The procedure for sieve analysis of coarse aggregates was the same as that for
fine, except that five additional sieves were used, viz., 3/8, 3/4, 1/2, 1, and 1½ in. sieves.
The fineness modulus was not calculated for coarse aggregates.
3.4.5 Moisture Content of Fine and Coarse Aggregates
ASTM C 566 – 89 Standard Test Method for Total Moisture Content of
Aggregate by Drying was followed in this case. The weight of a moisture tin was
recorded and an appropriate quantity of aggregate was placed in it. The weight of the
moisture tin plus moist sample was also recorded. The specimen was then kept in an
oven at a temperature of 230 ± 9°F for 24 ± 4 hours. The material was weighed again
after taking it out of the oven. The moisture content, w, was calculated using the
formula:
100×
−
=D
DWw (3.19)
where: W = weight of moist sample, g; and D = weight of oven-dried sample, g.
3.5 Mix Design
Concrete mix designs used in this project were prepared in accordance with
pertinent ODOT specifications, viz., ODOT Item 499.03 Concrete-General:
Proportioning of the ODOT 2002 Construction and Material Specifications; and ODOT
848.
39
3.5.1 Constants and Variables
Cement content of 700 lb/yd3, water/cement ratio of 0.36 and microsilica content
of 8% replacement of cement were maintained constant for all mixes. The amount of
water was variable, however, since it depends on the physical properties of the aggregate
used in any mix. The amount of MB-AE 90 air entrainer for each mix was set at 1.5
oz/100 lb (44.36 mL/100 kg) of cementitious materials, per manufacturer
recommendations (1/4 to 4 fl. oz/cwt, or 16 to 260 mL/100 kg), in order to maintain an
air content of 8 ± 2%, as specified by the ODOT specification cited. The Rheobuild 1000
plasticizer was taken as 650 mL/100 kg of cementitious materials for all mixes,
conforming to the manufacturer’s recommendations of 10 to 25 fl. oz/cwt, or 650 to 1000
mL/100 kg . Proper workability did not require the use of another water reducer.
Different properties of aggregate influence the water/cement ratio to a great
extent. Therefore, in order to maintain a constant water/cement ratio for all mixes, the
weights of the coarse aggregate (CA) and fine aggregate (FA) have to be adjusted for
each mix, based on their respective properties so as to maintain the specified proportion
of coarse to fine aggregate, CA:FA.
3.5.2 Ingredients
All determinations below are for the saturated surface dry condition, as indicated
by the subscript SSD in the equations presented. ODOT 499 assumes SSD bulk specific
gravity values of 2.62 for natural sand and gravel, and 2.65 for crushed limestone; the dry
values of 2.20 for microsilica and 3.15 are also used, per ODOT 848 and 499.03. The
mix design per cubic yard of concrete was adjusted after determining the actual BSGSSD
40
values for the aggregates. The saturated surface dry (SSD) volumes for CA and FA were
retained per the specification, and new SSD weights for CA and FA were backcalculated
using the lab BSGSSD values. The mix design was further modified in order to achieve
the desired percentage of cement-plus-pozzolan and air percentages % (c + p) and % air,
respectively. The weight of microsilica for determinations at SSD condition was first
calculated using the formula:
100)(%1
100)(%
)(
)( pc
pcWW
SSDCEM
SSDMS +−
+×
= (3.20)
where: WMS(SSD) = weight of microsilica for determinations at SSD condition; and
WCEM(SSD) = weight of cement for determinations at SSD condition = 700 lb/yd3, in
accordance with ODOT 848. As noted, both these weights are dry weights.
The weight of water and the volume of air were then calculated using the
formulae:
)()/()( MSCEMSSDW WWcwW +×= (3.21)
100%27 3 airftVAir
×= (3.22)
where: Ww(SSD) = weight of water for determinations at SSD condition; (w/c) =
water/cement ratio = 0.36, per the specification; and Vair = volume of air.
The volumes of cement, microsilica, and water were then calculated using for
each the formula:
41
wSSD
SSDSSD BSG
WV
γ×=
)( (3.23)
where: VSSD = volume at SSD condition; WSSD = weight at SSD condition; BSGSSD = bulk
specific gravity at SSD condition; and γw = unit weight of water = 62.4 pcf (assumed).
The sum of the volumes of cement, water, microsilica, and air were then
subtracted from a cubic yard (=27 ft3) to obtain the available volume for CA plus FA.
The proportions for CA and FA given by the specification were retained, and used to split
the available volume between CA and FA. Finally, the SSD weights for CA and FA were
backcalculated. The mix design charts are appended at the end of this report.
3.6 Mixing, Casting, and Curing Methods
ASTM C 192/C 192M – 00 Standard Practice for Making and Curing Concrete
Test Specimens in the Laboratory, and AASHTO T 126-86 Standard Method of Test for
Making and Curing Concrete Test Specimens in the Laboratory were adopted for mixing,
casting, and curing the concrete specimens, as described below.
3.6.1 Mixing Concrete
The ingredients used for the mixing process were weighed according to the mix
design. The concrete was mixed in a mechanical mixer of 5 ft3 capacity. The coarse
aggregate and about 20% of the mixing water into which the air entrainer and
superplasticizer had been dissolved were added in the mixer prior to turning it on. After
the mixer was started, the fine aggregate, the cement with the microsilica, and the
remaining water were added. After letting the mixer run for 3 min., it was rested for 3
42
min. It was then restarted, rotated for 2 more min., after which the concrete was poured
into a clean pan placed on a smooth rigid surface.
In order to cast the required number of specimens, nearly 4 ft3 of concrete needed
to be mixed. For densified microsilica concrete, 7 to 8 ft3 were used, as several large
specimens were cast for those mixes. The concrete mixer used by the research team had
a yield of just 2.5 ft3, and consequently the material had to be mixed in 4 batches. To
reduce the amount of concrete required, the investigators subsequently obtained ODOT’s
permission to cast smaller specimens for undensified and abused microsilica. This made
the mixing process more efficient and consistent. Thus, two batches were mixed for
concrete made from undensified and abused microsilica, while three to four batches were
made for mixes including densified microsilica.
3.6.2 Casting Specimens
Four different kinds of specimens were cast from the concrete mixed, viz., small
cylinders (4 × 8 in.), large cylinders (6 × 12 in.), large beams (6 × 6 × 21 in.), and small
beams (3½ × 4½ × 16 in.). The cylinders were tested to determine compressive strength,
and the beams were used for the calculation of flexural strength. The concrete was
placed in two layers in the molds for small cylinders, small beams and large beams, using
a scoop, and consolidated using a standard rod. For large cylinders, the concrete was
placed in three layers, and was rodded in the same way. Care was taken to avoid
segregation and to ensure that the concrete placed in each mold was representative of the
entire batch mixed. After the specimens were cast, they were transferred to rigid
43
horizontal surface, and were cured in air overnight. A plastic cover was placed over the
specimens to prevent undue moisture loss during this initial 24-hour period.
A total of six mixes of concrete were made with three kinds of microsilica
(densified, undensified, and abused) and two types of aggregate (natural and crushed).
The mixes were named Densified Natural (DN), Densified Crushed (DC), Undensified
Natural (UN), Undensified Crushed (UC), Abused Natural (AN), and Abused Crushed
(AC). The number of specimens cast in each mix will be reported in Chapter 4. Large
size specimens were more numerous than small ones in mixes DN and DC, whereas
smaller specimens outnumbered the larger ones in mixes UN, UC, AN, and AC. The
main motivation for switching to smaller specimens was the researchers’ desire to make
the mixing and casting process more efficient. This change was implemented following
ODOT staff consent. It is noted that ASTM C 192 / C 192 M specifies that “the diameter
of a cylindrical specimen or minimum cross-sectional dimension of a rectangular section
shall be at least three times the nominal maximum size of the coarse aggregate in the
concrete.” The maximum aggregate size used in this project is 3/8 in., so small cylinders
(4 × 8 in.) and small beams (3½ × 4½ × 16 in.) are also permissible.
3.6.3 Curing
Upon casting, the specimens were immediately covered using a plastic sheet in
order to avoid evaporation from the fresh concrete. After 24 hours, the specimens were
extruded from the molds. Air pressure was used to demold the cylinders. The specimens
were then cured submerged in water tubs in the University of Cincinnati moist room,
44
until the day and time of testing, 7 to 90 days later. Calcium hydroxide (lime) was added
to saturation in these tubs, so as to avoid leaching.
3.7 Tests on Plastic Concrete
Immediately after mixing each batch of concrete, slump, air content, and unit
weight determinations were conducted. Concrete slump is measured in inches, and is
used as a measure of workability and of consistency from batch to batch. The procedure
followed was as prescribed by ASTM C 143/C 143M – 00 Standard Test Method for
Slump of Hydraulic-Cement Concrete. The mold was first dampened and placed on a flat
surface. The concrete was then placed in three layers, each occupying approximately a
third of the total volume of the mold. The concrete placed in each layer was rodded 25
times with a standard rod. The excess concrete from the top layer was removed using a
rolling action of the rod, and the mold was immediately raised off the specimen. The
slump was measured by determining the vertical distance between the top surface of the
mold and the displaced original center of the top surface of the concrete specimen.
The air content of concrete was measured as stipulated in ASTM C 231 – 97
Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure
Method. The measuring bowl was placed on a level surface after the inner sides had been
dampened. The concrete was then placed in three equal layers, consolidating each layer
by 25 strokes of the standard rod. The extra concrete from the top layer was stricken off,
the rim of the bowl was thoroughly cleaned, and the bowl was sealed using the covering
lid. The air valve located between the air chamber and the measuring bowl was closed.
45
The petcocks were opened and water was injected into one of them, until water came out
from the other, which was then closed. Water was pumped into the other petcock, which
was closed when the water overflowed out of it. Air was pumped into the air chamber,
until the gage hand reached the initial pressure line. After a few seconds, the air valve
was opened, and the percentage of air was read on the dial.
The unit weight of concrete was calculated by dividing the weight into the
corresponding known volume of concrete. The concrete was first weighed in a container
of known volume after properly compacting it in three layers following the ASTM
standard procedure. The weight of the container was also noted after filling it completely
with water. The weight of the water alone was then calculated by subtracting the weight
of container from the weight of the container plus water. Dividing the weight of water by
its unit weight gives the volume of the container. The unit weight of concrete was then
determined by dividing the weight of concrete by the volume of the container.
3.8 Strength Test Procedures on Hardened Concrete
3.8.1 Compressive Strength
The procedure followed was as specified by ASTM C 39/C 39M – 01 Standard
Test Method for Compressive Strength of Cylindrical Concrete Specimens and by
AASHTO T 22-03 Compressive Strength of Cylindrical Concrete Specimens. The
diameter was measured twice at 90° to each other, and the average diameter was
calculated, from which the average cross sectional area was also determined. With the
hand finished surface at the top, the cylinder to be tested was placed on the loading table
46
of a 400-kip Tinius Olsen universal testing machine (http://www.tiniusolsen.com/
products/hydraulic/hydraulic-2000kn.html; accessed: 07/21/05). The cylinder was placed
such that its axis was aligned exactly with the center of thrust of the spherically seated
upper block of the loading head. After adjusting the initial reading to zero, the upper
block of the loading machine was brought down so that it just touched the top of the
cylinder. Load was applied at a uniform rate of 60,000 ± 25,000 lb/min. for large
cylinders, and 27,000 ± 12,000 lb/min. for small cylinders, until the specimen failed
completely. These rates conformed with ASTM C39/C 39 M, which specifies the rate of
load application as between 20 and 50 psi/s. Therefore, the lower limit is 20×60×π×d2/4
= 33,929 lb/min. for large cylinders (diameter, d = 6 in.), and 15,080 lb/min. for small
cylinders (d = 4 in.). Similarly, the upper limit is calculated as 84,823 and 37,699
lb/min., respectively. The compressive strength, f′c, of the concrete specimens was
calculated by dividing the maximum load at failure by the average cross sectional area of
the cylinder.
3.8.2 Flexural Strength
ASTM C 78 – 02 Standard Test Method for Flexural Strength of Concrete (Using
Simple Beam with Third-Point Loading) and AASHTO T 97 were adhered to. The beams
were simply supported on each end, so that the effective span for large beams was 18 in.
for large beams, and 13.5 in. for small beams. The specification requires that the
effective span should be three times the depth, which was 6 and 4.5 in., respectively.
After recording the dimensions of each beam on two opposite sides, the average
dimensions were calculated. Two load-applying blocks were placed on the top side of
47
the beam so that they were in contact with the surface of the beam at the third points
between the bottom supports. Load was applied at a rate of 1800 ± 300 lb/min. for large
beams and 775 ± 125 lb/min. for small beams, until the specimens failed completely,
whereupon the failure pattern was recorded. These rates conform to ASTM C 78 – 02,
which requires that the load be applied “at a rate that constantly increases the extreme
fiber stress between 125 and 175 psi/min. until rupture occurs.” To calculate such a rate,
the specification provides the following equation:
LdbSr
2
= (3.24)
in which: r = loading rate, lb/min.; S = rate of increase in extreme fiber stress, e.g., 125 or
175 psi/min.; b = average beam width, in.; d = average beam depth, in.; and L = effective
beam span, in.
Thus, from the lower limit of S = 125 psi/in., r is found to be 125×6×36/18 =
1500 lb/min. for large beams, and 125×3.5×20.25/13.5 = 656 lb/min. for small beams.
The values corresponding to the upper limit of S = 175 psi/min. are 2100 and 919 lb/min.,
respectively. The rates adopted are convenient rounded off values based on these
calculation results.
According to ASTM C 78 – 02, the modulus of rupture, MR, must be calculated
using one of the formulae below, depending on the location of the failure plane:
2dbLPM R = (3.25)
or:
48
2
3db
aPM R = (3.26)
where: P = ultimate load, lb; and a = average distance between the line of fracture and
the nearest support, in.
Equation (3.25) is to be used when failure occurs inside the middle third of the
span, whereas Equation (3.26) applies when failure occurs outside this region. None of
the specimens tested necessitated the latter equation.
49
4 TEST RESULTS
4.1 Introduction
The main purpose of this chapter is to present the data collected during this
project, including all information recorded, as well as any observations made while
performing the experiments. The raw data are tabulated along with derivative values
calculated from them. The information provided in this chapter will form the database
for the discussions to follow in Chapter 5, concerning the effect such parameters as age,
specimen size, microsilica type, and aggregate type.
4.2 Microsilica
4.2.1 Microsilica Fineness
The results of the fineness tests conducted on the four microsilica types
(undensified, densified, abused-A and abused-B) are presented in Table 4.1. These tests
were performed at the laboratory of the Ohio Department of Transportation (ODOT), and
some involved brushing the sample even though this is not prescribed by the American
Society for Testing and Materials (ASTM) in ASTM C 430 – 96 Standard Test Method
for Fineness of Hydraulic Cement by the 45-µm (No. 325) Sieve.
50
4.2.2 Microsilica Gradation
The calculations for the grain size distributions of undensified, densified and
abused microsilica are tabulated in Tables 4.2 through 4.7. The gradation curves plotted
in Fig. 4.1 represent the results of both the sieve and hydormeter tests.
4.3 Aggregates
The results of sieve analysis for the fine and coarse aggregate types are tabulated
in Table 4.8(a), which also includes the required percentages passing according to Ohio
Department of Transportation (ODOT) Items 703.01 Aggregate-General: Size and
703.02 Aggregate for Portland Cement Concrete: Fine Aggregate. Item 703.01 is
identical with the American Association of State Highway and Transportation Officials
(AASHTO) M 43. It can be seen that amounts passing are within the prescribed limits.
Each aggregate test was conducted three times by independent researchers, from
which average values and other statistics were determined. These results are tabulated in
Table 4.8(b), in which the coefficients of variation (COV) are also given. It is observed
that the COV did not exceed approximately 5% for most of the aggregate properties,
except for the absorption values. It can be said, therefore, that the values obtained by the
researchers are reliable from a statistical point of view.
4.4 Concrete Mixes
The amounts of each ingredient, used per cubic yard of concrete of each mix, are
given in Table 4.9. The mixes were named after the microsilica type and the nature of
51
the coarse aggregate used, as Densified Natural (DN), Densified Crushed (DC),
Undensified Natural (UN), Undensified Crushed (UC), Abused Natural (AN), and
Abused Crushed (AC).
A number of batches were prepared in order to obtain the required volume of each
mix. Table 4.10 enumerates the number of specimens cast from each batch, while Table
4.11 presents the physical properties of each batch, from which average values for each
mix were calculated.
4.5 Mechanical Properties
The results of the compressive strength tests are tabulated in Table 4.12 for large
cylinders, and in Table 4.13 for small cylinders. At each age, a minimum of three
cylinders were tested. All specimens gained a significant amount of strength by the age
of 28 days, but explosive failures (typical of high strength concrete) occurred at almost
all ages. Shearing of aggregate was observed in all specimens tested, and the ratio of the
frequency of this failure mode to that by aggregate pullout was 4:1 in most cases.
Modulus of rupture results can be found in Table 4.14 for large beams, and in
Table 4.15 for small beams. All beams failed with a vertical failure plane near the center
of the beam, between the two points of load application. In most of the beams, a crack
was observed to originate at the bottom of the beam and to propagate up. Examining the
specimens after failure, revealed that the failure mode was similar to that under
compressive strength testing, i.e., there was much more shearing in the aggregate itself
than aggregate pullout, typically in the ratio of 4:1.
52
Table 4.1 Results of Tests Conducted on Microsilica Types at ODOT Laboratory
Microsilica Type Sample No. Weight
Retained (g) Correction Factor (%)
Corrected % Retained
1 0.358 32.9 47.58 4 0.334 26.77 42.34 Undensified
Microsilica 9* 0.023 24.85 2.87 6 0.83 32.9 110.31 7 0.828 26.77 104.97 Densified
Microsilica 8* 0.767 44.56 110.88 3 0.596 84.14 109.75 5 0.606 52.59 92.47 Abused
Microsilica A 10* 0.506 35.03 68.33 2 0.836 30.79 109.34 11 0.832 24.85 103.88 Abused
Microsilica B 12* 0.766 44.56 110.73
Note: *Third replicate of each microsilica type pertains to a brushed specimen. specimen.
53
Table 4.2 Hydrometer Test on Undensified Microsilica
Calculated Gs = 2.060; a = 1.21; Percent finer than No. 200 sieve (wet sieving) = 87.80%
Elapsed Time (Min.)
Elapsed Time, t
(s)
Tempe-rature (°C)
Viscosity (Poise)
Act. Hyd. Rdg, R a
Corr. Hyd. Rdg, R c
Actual %
Finer
Adjusted % Finer
Hyd. Corr. Only for
Meniscus, R
L (cm) L/t D
(µm)
2 120 24 0.00914 20 18 145.2 127.5 21 12.9 0.1075 41.241
4 240 24 0.00914 18 16 129.1 113.3 19 13.2 0.055 29.499
8 480 24 0.00914 17 15 121 106.2 18 13.3 0.027708 20.938
16 960 24 0.00914 16 14 112.9 99.2 17 13.5 0.014063 14.916
30 1800 24 0.00914 14 12 96.8 85 15 13.8 0.007667 11.013
60 3600 24 0.00936 13 10.7 86.3 75.8 14 14 0.003889 7.938
120 7200 24 0.00914 12 10 80.7 70.8 13 13 0.001972 5.586
240 14400 23 0.00936 12 9.7 78.2 68.7 13 13 0.000986 3.997
480 28800 23 0.00936 11 8.7 70.2 61.6 12 12 0.000497 2.836
960 57600 23 0.00936 11 8.7 70.2 61.6 12 12 0.000248 2.006
1920 115200 23 0.00936 11 8.7 70.2 61.6 12 12 0.000124 1.418
3840 230400 23 0.00936 11 8.7 70.2 61.6 12 12 0.000062 1.003
5760 345600 23 0.00936 10 7.7 62.1 54.5 11 11 0.000042 0.824
54
Table 4.3 Hydrometer Test on Densified Microsilica
Calculated Gs = 1.970; a = 1.26; Percent finer than No. 200 sieve (wet sieving) = 24.93%
Elapsed Time (Min.)
Elapsed Time, t
(s)
Tempe-rature (°C)
Viscosity (Poise)
Act. Hyd. Rdg, R a
Corr. Hyd. Rdg, R c
Actual %
Finer
Adjusted % Finer
Hyd. Corr. Only for
Meniscus, R
L (cm) L/t D
(µm)
2 120 24 0.00914 16 14 118 29.4 17 13.5 0.1125 44.103
4 240 24 0.00914 13 11 92.7 23.1 14 14 0.05833 31.758
8 480 24 0.00914 9 7 59 14.7 10 14.7 0.03063 23.011
16 960 24 0.00914 9 7 59 14.7 10 14.7 0.01531 16.271
30 1800 24 0.00914 8 6 50.6 12.6 9 14.8 0.00822 11.923
60 3600 24 0.00936 7 5 42.2 10.5 8 15 0.00417 8.488
120 7200 24 0.00914 7 5 42.2 10.5 8 15 0.00208 6.002
240 14400 23 0.00936 7 4.7 39.6 9.9 8 15 0.00104 4.295
480 28800 23 0.00936 7 4.7 39.6 9.9 8 15 0.00052 3.037
960 57600 23 0.00936 7 4.7 31.2 9.9 8 15 0.00026 2.147
1920 115200 23 0.00936 6 3.7 31.2 7.8 7 15.2 0.00013 1.528
3840 230400 23 0.00936 6 3.7 31.2 7.8 7 15.2 0.00007 1.081
5760 345600 23 0.00936 6 3.7 31.2 7.8 7 15.2 0.00004 0.882
55
Table 4.4 Hydrometer Test on Abused Microsilica
Elapsed Time (Min.)
Elapsed Time, t
(s)
Tempe-rature (°C)
Viscosity (Poise)
Act. Hyd. Rdg, R a
Corr. Hyd. Rdg, R c
Actual %
Finer
Adjusted % Finer
Hyd. Corr. Only for
Meniscus, R
L (cm) L/t D
(µm)
2 120 24 0.00914 18 16 140.5 34.2 19 13.2 0.11 45.35
4 240 24 0.00914 15 13 114.1 27.8 16 13.7 0.057083 32.669
8 480 24 0.00914 10 8 70.2 17.1 11 14.5 0.030208 23.765
16 960 24 0.00914 9 7 61.4 15 10 14.7 0.015313 16.92
30 1800 24 0.00914 9 7 61.4 15 10 14.7 0.008167 12.357
60 3600 23 0.00936 9 7 61.4 15 10 14.7 0.004083 8.737
120 7200 24 0.00914 9 7 61.4 15 10 14.7 0.002042 6.178
240 14400 23 0.00936 9 6.7 58.8 14.3 10 14.7 0.001021 4.421
480 28800 23 0.00936 9 6.7 58.8 14.3 10 14.7 0.00051 3.126
960 57600 23 0.00936 9 6.7 58.8 14.3 10 14.7 0.000255 2.211
1920 115200 23 0.00936 8 5.7 50 12.2 9 14.8 0.000128 1.568
3840 230400 23 0.00936 9 6.7 58.8 14.3 10 14.7 0.000064 1.105
5760 345600 23 0.00936 9 6.7 58.8 14.3 10 14.7 0.000043 0.902
Calculated Gs = 1.897; a = 1.32; Percent finer than No. 200 sieve (wet sieving) = 24.34%
56
Table 4.5 Dry Sieve Analysis of Undensified Microsilica
Sieve Number
Sieve Size
(mm)
Tare (g)
Tare + Material
(g)
Weight of
Material Retained
(g)
% Retained
% Cumulative
Retained
% Passing
10 2 1250 1285 35 18.421 18.42 81.58 20 0.85 1155 1190 35 18.421 36.84 63.16 40 0.425 1120 1135 15 7.895 44.74 55.26 60 0.25 1125 1135 10 5.263 50.00 50.00 140 0.106 1110 1180 70 36.842 86.84 13.16 200 0.075 1070 1090 20 10.526 97.37 2.63 270 0.053 1130 1135 5 2.632 100.00 0.00 325 0.045 1035 1035 0 0 100.00 0.00 Pan 1140 1140 0 0 100.00 0.00
SUM 190 100
57
Table 4.6 Dry Sieve Analysis of Densified Microsilica
Sieve Number
Sieve Size
(mm)
Tare (g)
Tare + Material
(g)
Weight of
Material Retained
(g)
% Retained
% Cumulative
Retained
% Passing
10 2 1250 1250 0 0 0.00 100.00 20 0.85 1155 1190 35 11.111 11.11 88.89 40 0.425 1120 1225 105 33.333 44.44 55.56 60 0.25 1125 1170 45 14.286 58.73 41.27 140 0.106 1110 1195 85 26.984 85.71 14.29 200 0.075 1070 1105 35 11.111 96.83 3.18 270 0.053 1130 1140 10 3.175 100.00 0.00 325 0.045 1035 1035 0 0 100.00 0.00 Pan 1140 1140 0 0 100.00 0.00
SUM 315 100
58
Table 4.7 Dry Sieve Analysis of Abused Microsilica
Sieve Number
Sieve Size
(mm)
Tare (g)
Tare + Material
(g)
Weight of
Material Retained
(g)
% Retained
% Cumulative
Retained
% Passing
10 2 1250 1250 0 0 0.00 100.00 20 0.85 1155 1190 35 13.208 13.21 86.79 40 0.425 1120 1210 90 33.962 47.17 52.83 60 0.25 1125 1170 45 16.981 64.15 35.85 140 0.106 1110 1170 60 22.642 86.79 13.21 200 0.075 1070 1095 25 9.434 96.23 3.77 270 0.053 1130 1140 10 3.774 100.00 0.00 325 0.045 1035 1035 0 0 100.00 0.00 Pan 1140 1140 0 0 100.00 0.00
SUM 265 100.001
59
Table 4.8 (a) Aggregate Sieve Analysis
Sieve Size or Number
% Passing for No. 8 per Specification
% Passing for
Crushed No. 8
% Passing for Natural
No. 8
% Passing for Natural Sand Per
Specification
% Passing Average for
Natural Sand
1 ½ in. 100 100 100 100 100 1 in. 100 100 100 100 100 ¾ in. 100 100 100 100 100 ½ in. 100 100 100 100 100
3/8 in. 85-100 86 94 100 100 No. 4 10-30 11 20 95-100 100 No. 8 0-10 2 1 70-100 94 No. 16 0-5 1 0 38-80 72 No. 30 0 0 0 18-60 43 No. 50 0 0 0 5-30 14 No. 100 0 0 0 1-10 2
Pan 0 0 0 0-5 0
Table 4.8 (b) Physical Aggregate Properties
Natural Sand No. 8 Natural No. 8 Crushed Type of Test
Average COV (%) Average COV
(%) Average COV (%)
Apparent Specific Gravity 2.72 3.7 2.77 1.21 2.8 1.52
Bulk Specific Gravity
(Saturated Surface Dry)
2.62 6.1 2.61 3.04 2.59 1.45
Bulk Specific Gravity
(Oven Dry) 2.57 7.79 2.52 4.69 2.47 1.29
% Absorption 3.21 50.22 3.7 52.51 4.78 0.67 Fineness Modulus 3.11 17.94
Dry Unit Weight (pcf) 108.21 4.8 94 5.87
60
Table 4.9 Ingredients by Mix (per yd3 of concrete)
Mix
Ingredient UN UC DN DC AN AC
CEMEX Type 1/II cement (lb) 700 700 700 700 700 700
Martin Marietta Materials air-dry coarse aggregate (lb)
1339 1319 1339 1319 1339 1319
Martin Marietta Materials air-dry fine aggregate (lb)
1344 1355 1344 1355 1344 1355
ELKEM microsilica (lb) 61 61 61 61 61 61
City of Cincinnati water above air-dry (lb)
361 374 361 374 361 374
MB-AE 90 air entrainer (mL) 337.6 337.6 337.6 337.6 337.6 337.6
Rheobuild 1000 plasticizer (mL) 2070 2070 2070 2070 2070 2070
61
Table 4.10 Specimens Cast by Batch
Batch No. 1 2 3 4 5† Total Undensified Natural (UN)
Volume (ft3) 2.0 2.0 1.0 5.0 Small Cylinders 9 6 7 22 Large Cylinders 1 1 0 2
Small Beams 5 4 0 9 Large Beams 0 1 0 1
Undensified Crushed (UC) Volume (ft3) 2.0 2.0 1.0 5.0
Small Cylinders 10 7 8 25 Large Cylinders 1 1 0 2
Small Beams 5 4 0 9 Large Beams 0 1 0 1
Densified Natural (DN) Volume (ft3) 2.0 2.0 2.0 2.0 1.0 9.0
Small Cylinders 4 0 0 1 7 12 Large Cylinders 7 0 2 4 0 13
Small Beams 0 0 0 0 0 0 Large Beams 0 4 3 2 0 9
Densified Crushed (DC) Volume (ft3) 2.5 2.5 2.5 1.0 8.5
Small Cylinders 3 3 0 7 13 Large Cylinders 3 3 4 1 11
Small Beams 0 0 0 0 0 Large Beams 3 3 3 0 9
Abused Natural (AN) Volume (ft3) 1.8 1.8 1.0 4.6
Small Cylinders 8 9 8 25 Large Cylinders 1 2 1 4
Small Beams 5 4 0 9 Large Beams 0 0 0 0
Abused Crushed (AC) Volume (ft3) 1.8 1.8 1.0 4.6
Small Cylinders 8 9 7 24 Large Cylinders 1 2 1 4
Small Beams 5 4 0 9 Large Beams 0 0 0 0
Notes: †-Specimens cast in 2004; remainder cast in 2003.
62
Table 4.11 Physical Properties by Batch
Batch # 1 2 3 4 5† Average COV (%)
Undensified Natural (UN) Slump
(in.) 5.75 5.50 5.50 5.58 2.59
% Air 7.40 7.00 7.00 7.13 3.24 Unit
weight (pcf)
139.10 141.40 141.00 140.51 0.89
Undensified Crushed (UC) Slump
(in.) 5.75 5.25 4.00 5.00 18.03
% Air 8.70 7.10 7.80 7.87 10.20 Unit
weight (pcf)
139.40 141.60 138.60 139.86 1.11
Densified Natural (DN) Slump
(in.) 4.25 6.00 4.75 5.75 6.00 5.35 15.00
% Air 7.90 9.00 8.20 7.80 9.00 8.38 6.98 Unit
weight (pcf)
138.00 137.70 138.60 140.50 138.40 138.62 0.80
Densified Crushed (DC) Slump
(in.) 4.75 4.00 6.00 6.00 5.19 19.02
% Air 7.20 8.00 7.70 9.50 8.10 12.22 Unit
weight (pcf)
141.40 139.40 140.90 138.10 139.95 1.06
Abused Natural (AN) Slump
(in.) 7.50 6.50 5.50 6.5 15.38
% Air 9.00 9.50 8.00 8.83 8.65 Unit
weight (pcf)
137.30 135.50 138.30 137.04 1.02
Abused Crushed (AC) Slump
(in.) 6.50 7.00 6.50 6.67 4.33
% Air 10.50 10.00 10.00 10.17 2.84 Unit
weight (pcf)
134.80 134.60 135.80 135.08 0.46
Note: †-Specimens cast in 2004; remainder cast in 2002-2003.
63
Table 4.12 Compressive Strength of Large Cylinders, f′c
Mix/Age 7 days 28 days
UN C1 P (lb) 189958
Mean A (in.2) 27.69 f′c (psi) 6861
Mean f′c (psi, COV) 6861,
UC D1 P (lb) 186277
Mean A (in.2) 27.98 f′c (psi) 6657
Mean f′c (psi, COV) 6657,
DN A1 A3 A4 A1a A1b A4 P (lb) 122993 120727 127698 152968 152723 156605
Mean A (in.2) 28.57 28.57 28.57 28.27 27.98 27.98 f′c (psi) 4305 4226 4470 5410 5458 5597
Mean f′c (psi, COV) 4333, 2.87% 5488, 1.77%
DC B1 B2 B3 B1 B2 B3 P (lb) 137483 130945 124667 157817 162724 181443
Mean A (in.2) 28.87 28.27 28.27 28.27 28.28 28.28 f′c (psi) 4762 4631 4409 5582 5755 6417
Mean f′c (psi, COV) 4601, 3.88% 5918, 7.45%
AN G2 G1 P (lb) 102490 154065
Mean A (in.2) 27.98 27.98 f′c (psi) 3663 5506
Mean f′c (psi, COV) 3663, 5506,
AC I2 I2 P (lb) 108070 145031
Mean A (in.2) 28.28 28.87 f′c (psi) 3822 5024
Mean f′c (psi, COV) 3822, 5024,
64
Table 4.12 Compressive Strength of Large Cylinders, f′c (Cont’d)
Mix/Age 56 days 90 days
UN C2
P (lb) 205818 Mean A (in.2) 28.87
f′c (psi) 7129 Mean f′c
(psi, COV) 7129,
UC D2
P (lb) 210985 Mean A (in.2) 28.57
f′c (psi) 7385 Mean f′c
(psi, COV) 7385,
DN A1 A3 A4 A1 A1 A4 A1
P (lb) 175569 172942 171845 182309 175511 180865 183160 Mean A (in.2) 28.27 28.27 27.98 28.57 28.57 28.57 28.57
f′c (psi) 6209 6117 6141 6381 6143 6331 6411 Mean f′c
(psi, COV) 6156, 0.78% 6316, 1.90%
DC B1 B2 B3 B3 B6
P (lb) 205544 171138 169421 207146 190636 Mean A (in.2) 27.98 28.57 28.87 28.58 27.98
f′c (psi) 7346 5990 5869 7249 6813 Mean f′c
(psi, COV) 6401, 12.81% 7031, 4.38%
AN G2 G9
P (lb) 169969 181544 Mean A (in.2) 27.98 28.27
f′c (psi) 6074 6421 Mean f′c
(psi, COV) 6074, 6421,
AC I8 I8
P (lb) 175482 172221 Mean A (in.2) 28.57 28.28
f′c (psi) 6142 6090 Mean f′c
(psi, COV) 6142, 6090,
65
Table 4.13 Compressive Strength of Small Cylinders, f′c
Mix/Age 7 days 28 days
UN C1a C1b C2 C1a C1b C2 C6 C4
P (lb) 68791 62941 68063 85307 89279 90923 92999 86071
Mean A (in.2) 12.57 12.57 12.57 12.76 12.96 12.76 12.57 12.57 f′c (psi) 5473 5009 5416 6683 6888 7123 7401 6849
Mean f′c (psi, COV) 5299, 4.78% 6989, 3.99% UC D1a D1b D2 D1a D1b D2 D6 D4
P (lb) 70561 68308 71941 104065 95699 98017 89780 92015 Mean A (in.2) 12.57 12.57 12.57 12.18 12.37 12.57 12.76 12.37
f′c (psi) 5615 5436 5725 8546 7735 7800 7034 7438 Mean f′c (psi, COV) 5592, 2.61% 7711, 7.22%
DN A1 A1 A4 A5 P (lb) 57494 71430 61596 67457
Mean A (in.2) 12.76 12.37 12.76 12.76 f′c (psi) 4504 5774 4826 5285
Mean f′c (psi, COV) 4504, 5295, 8.95% DC B1 B2 B4 B5
P (lb) 65536 81796 74832 69245 Mean A (in.2) 12.76 12.18 12.76 12.57
f′c (psi) 5134 6717 5863 5510 Mean f′c (psi, COV) 5134, 6030, 10.29%
AN G1A G1B G2 G1 G2a G2b G4 G6 P (lb) 46014 51886 48793 65132 66524 63525 75059 75445
Mean A (in.2) 12.37 12.37 12.57 12.37 12.18 12.37 12.97 12.18 f′c (psi) 3719 4194 3883 5265 5463 5135 5789 6196
Mean f′c (psi, COV) 3932, 6.13% 5570, 7.69% AC I1 I2a I2b I1a I1b I2 I6 I4
P (lb) 51251 56157 52718 69133 65139 78617 65377 70121 Mean A (in.2) 12.57 12.37 12.37 12.57 12.57 12.57 12.57 12.57
f′c (psi) 4078 4539 4261 5501 5184 6256 5203 5580 Mean f′c (psi, COV) 4293, 5.40% 5545, 7.84%
66
Table 4.13 Compressive Strength of Small Cylinders, f′c (Cont’d)
Mix/Age 56 days 90 days
UN C1 C2a C2b C3 C5 C1 C2a C2b C7
P (lb) 99235 99923 92891 89557 88843 97717 96315 95778 91053
Mean A (in.2)
12.57 12.37 12.97 12.57 12.37 12.77 12.57 12.37 12.37
f′c (psi) 7897 8077 7165 7127 7181 7652 7665 7742 7360
Mean f′c (psi, COV) 7489, 6.16% 7604, 2.21%
UC D1a D1b D2 D3 D5 D1 D2a D2b D2c D2d D1 D7
P (lb) 94369 96110 109109 96845 94783 102908 89939 103200 107421 102850 91528 95652
Mean A (in.2)
12.57 12.57 12.57 12.57 12.57 12.37 12.76 12.37 12.37 12.37 12.37 12.76
f′c (psi) 7508 7646 8680 7707 7541 8318 7046 8342 8683 8313 7398 7494
Mean f′c (psi, COV) 7816, 6.26% 7942, 7.77%
DN A3 A6 A1h A1h A7
P (lb) 67126 72457 80545 84950 75330
Mean A (in.2)
12.57 12.56 12.37 12.76 12.37
f′c (psi) 5342 5766 6510 6655 6089
Mean f′c (psi, COV) 5554, 5.40% 6418, 4.58%
DC B2 B1h B1 B3 B1h B8
P (lb) 93327 96488 78415 74933 92455 80484
Mean A (in.2)
12.37 12.57 12.57 12.57 12.77 12.37
f′c (psi) 7544 7678 6240 5963 7241 6506
Mean f′c (psi, COV) 6856, 12.84% 6873, 7.55%
AN G1 G2a G2b G1 G5 G1a G1b G2 G2b G7 G8
P (lb) 75416 72367 76508 76771 73841 77445 72096 80855 69912 80913 82982
Mean A (in.2)
12.57 12.57 12.57 12.97 12.57 12.76 12.76 12.57 12.57 12.37 12.76
f′c (psi) 6001 5759 6088 5921 5876 6067 5648 6434 5563 6540 6501
Mean f′c (psi, COV) 5929, 2.11% 6126, 7.14%
AC I1 I2a I2b I1 I5 I1a I1b I2 I3
P (lb) 72096 79327 71501 67273 72201 77802 91983 83566 71992
Mean A (in.2)
12.37 12.57 12.57 12.57 12.57 12.57 12.76 12.76 12.37
f′c (psi) 5828 6313 5690 5353 5746 6191 7206 6547 5819
Mean f′c (psi, COV) 5786, 5.97% 6441, 9.17%
67
Table 4.14 Modulus of Rupture for Large Beams, MR
Mix 7 days 28 days UN
P (lb) bAVG (in.) dAVG (in.) MR (psi)
Mean MR (psi), COV
UC P (lb)
bAVG (in.) dAVG (in.) MR (psi)
Mean MR (psi), COV
DN A2 A3 A4 A2a A2b A3 P (lb) 8068.50 6446.30 7967.20 11086.00 8304.00 7567.30
bAVG (in.) 6.00 6.00 6.00 6.00 6.00 6.06 dAVG (in.) 6.00 6.00 6.00 6.00 6.00 6.00 MR (psi) 672 537 664 924 692 624
Mean MR (psi), COV 625, 12.13% 747, 21.05%
DC B1 B2 B3 B1 B2 B3 P (lb) 10874 7755.5 7158.4 7952.7 8623.1 9061
bAVG (in.) 6.00 6.13 6.00 6.06 6.06 6.06 dAVG (in.) 6.13 6.00 6.00 6.00 6.00 6.00 MR (psi) 870 633 597 656 704 747
Mean MR (psi) 700, 21.18% 702, 6.51% AN
P (lb) bAVG (in.) dAVG (in.) MR (psi)
Mean MR (psi), COV
AC P (lb)
bAVG (in.) dAVG (in.) MR (psi)
Mean MR (psi), COV
68
Table 4.14 Modulus of Rupture for Large Beams, MR (cont’d)
Mix 56 days 90 days UN
P (lb) bAVG (in.) dAVG (in.) MR (psi) Mean MR (psi, COV)
UC P (lb)
bAVG (in.) dAVG (in.) MR (psi) Mean MR (psi, COV)
DN A2 A3 A4 P (lb) 10246 8746.2 8436.8
bAVG (in.) 6.00 6.00 5.94 dAVG (in.) 6.00 6.09 6.03 MR (psi) 854 707 703 Mean MR (psi, COV) 755, 11.40%
DC B1 B2 B3 P (lb) 9221.2 7906.6 8226.9
bAVG (in.) 6.00 6.00 6.03 dAVG (in.) 6.06 6.16 6.00 MR (psi) 753 626 678 Mean MR (psi, COV) 686, 9.29%
AN P (lb)
bAVG (in.) dAVG (in.) MR (psi) Mean MR (psi, COV)
AC P (lb)
bAVG (in.) dAVG (in.) MR (psi) Mean MR (psi, COV)
69
Table 4.15 Modulus of Rupture of Small Beams, MR
Mix 7 days 28 days UN C1a C1b C2 C1 C2a C2b
P (lb) 4077.70 3724.80 3794.50 4333.70 4964.30 4427.80 bAVG (in.) 4.50 4.47 4.44 4.59 4.56 4.56 dAVG (in.) 3.53 3.53 3.5 3.66 3.53 3.75 MR (psi) 981 902 942 953 1178 932 Mean MR (psi, COV) 942, 4.17% 1021, 13.38%
UC D1a D1b D2 D1 D2a D2b P (lb) 3733.90 3295.10 3113.20 5127.20 4014.50 4551.80
bAVG (in.) 4.59 4.56 4.56 4.59 4.56 4.69 dAVG (in.) 3.88 3.63 3.56 3.75 3.66 3.56 MR (psi) 731 742 726 1071 889 1033 Mean MR (psi, COV) 733, 1.13% 998, 9.66%
DN
P (lb) bAVG (in.) dAVG (in.) MR (psi) Mean MR (psi, COV)
DC
P (lb) bAVG (in.) dAVG (in.) MR (psi) Mean MR (psi, COV)
AN G1a G1b G2 G1 G2a G2b P (lb) 3017.30 2935.00 3339.40 3945.60 4359.00 3988.10
bAVG (in.) 4.50 4.47 4.06 4.47 4.50 4.63 dAVG (in.) 3.53 3.50 3.63 3.56 3.56 3.50 MR (psi) 726 724 844 939 1030 950 Mean MR (psi, COV) 765, 9.03% 973, 5.11%
AC I1a I1b I2 I1 I2a I2b P (lb) 3154.80 3718.50 3296.10 3653.30 4093.10 4442.30
bAVG (in.) 4.50 4.50 4.53 4.56 4.56 4.56 dAVG (in.) 3.53 3.5 3.5 3.53 3.56 3.69 MR (psi) 759 911 802 867 954 1018 Mean MR (psi, COV) 824, 9.49% 946, 8.01%
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Table 4.15 Modulus of Rupture of Small Beams, MR (Cont’d)
Mix 56 days 90 days UN C1a C1b C2
P (lb) 3995.30 4341.90 3734.80 bAVG (in.) 4.56 4.72 4.53 dAVG (in.) 3.66 3.63 3.56 MR (psi) 884 945 877 Mean MR (psi, COV) 902, 4.17%
UC D1a D1b D2 P (lb) 3852.40 3753.80 3219.10
bAVG (in.) 4.56 4.50 4.63 dAVG (in.) 3.59 3.56 3.63 MR (psi) 883 887 715 Mean MR (psi, COV) 828, 11.85%
DN P (lb)
bAVG (in.) dAVG (in.) MR (psi) Mean MR (psi, COV)
DC P (lb)
bAVG (in.) dAVG (in.) MR (psi) Mean MR (psi, COV)
AN G1a G1b G2 P (lb) 4366.30 3742.00 3844.20
bAVG (in.) 4.63 4.53 4.59 dAVG (in.) 3.56 3.59 3.56 MR (psi) 1004 863 890 Mean MR (psi, COV) 919, 8.14%
AC I1a I1b I2 P (lb) 4314.70 4160.00 3951.00
bAVG (in.) 4.66 4.59 4.59 dAVG (in.) 3.56 3.63 3.59 MR (psi) 986 930 899 Mean MR (psi, COV) 938, 4.68%
71
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
0.0001000.0010000.0100000.1000001.000000
Particle Diameter, mm
Perc
ent F
iner
Abused (Hydrometer)Densified (Hydrometer)Undensified (Hydrometer)Densified (Sieve) Abused (Sieve)Undensified (Sieve)
Fig 4.1 Grain Size Distribution of Undensified, Densified, and Abused Microsilica
72
5 DISCUSSION OF RESULTS
5.1 Introduction
The interpretation and discussion of the data collected in this project are presented in
this chapter. The main problems encountered in this task are identified first: the questionable
validity of results from the American Society for Testing and Materials (ASTM) C 430 – 96
Standard Test Method for Fineness of Hydraulic Cement by the 45-µm (No. 325) Sieve) as
performed by Ohio Department of Transportation (ODOT) personnel; and, the significant
variability of the results of the mechanical tests conducted at the University of Cincinnati. In
order to deal with the latter, an innovative approach to statistical data interpretation is
proposed, which can lead to a number of meaningful conclusions by imposing a set of
engineering boundary conditions, i.e., that strength increases with age at a decreasing rate.
5.2 Microsilica Fineness
It is anticipated that the smaller the particle size, the lower the percentage of material
retained, and the higher the fineness value. The undensified microsilica, as expected, had the
lowest amount of material retained. The abused samples were expected to have higher
amounts of material retained, but this was not the case. Abused microsilica A had the next
lowest amount, while abused microsilica B and densified microsilica had almost identical
amounts of material retained. It was also found that brushing the samples caused more
material to pass through the sieves.
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Looking at Table 4.1, it can be seen that many of the % Retained values exceed 100.
Obviously, such values are not reasonable. Thus, for the purposes of this project, any %
Retained amounts above 100 will be assumed to be 100%, indicating that none of the
material passed through the sieves. The corrected results show that only the undensified
microsilica and two of the abused microsilica A specimens were able to pass through the No.
325 sieve to any significant degree. The densified, as well as the abused microsilica B
specimens failed to pass through the sieves. According to ASTM C 1240 – 01 Standard
Specification for Use of Silica Fume as a Mineral Admixture in Hydraulic-Cement Concrete,
Mortar and Grout, microsilica used in concrete should have a fineness value greater than
90%, i.e., the % Retained should be below 90%. Therefore, it can be concluded that even the
undensified microsilica is not suitable for use in concrete, as 90% of the sample could only
pass through the sieve when, deviating from the specification, the sample was brushed
thoroughly. The results of testing by the water pressure method, as well as by using a brush,
do not seem to produce any useful information other than that all of the microsilica samples
failed this test.
Looking solely at the weight retained, it can be seen in addition that the two abused
samples of microsilica do not have the desired particle size. These samples were abused so
that they would have a larger particle size than both the undensified and densified samples.
The abused sample B had nearly identical results as the densified sample, while abused
sample A was actually finer than the densified sample. It is concluded that this test provides
no meaningful information for the purpose of assessing the engineering properties of
densified (or even of abused) microsilica, and should be dropped as a means of quality
assurance. decreasing rate.
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5.3 Microsilica Gradation
The hydrometer method in conjunction with dry sieve analysis is not the ideal manner
to explore microsilica gradation, but it was the only approach feasible during this limited
project. Nonetheless, the data obtained and presented in Fig. 4.1 corroborate some of the
concerns expressed by Diamond and Sahu (2003), who point out that “the actual size of the
densified silica fume, as supplied to the customer, is always in the range of hundreds of µm.”
In contrast, the data obtained in this study create no reasons for concern regarding “clusters”
even in the undensified microsilica itself, as Diamond and Sahu (2003) suggest. Although
dry sieving of undensified microsilica may lead to the impression that this type is hardly
different from the densified and abused varieties, the superiority of the former is clearly
visible in the hydrometer test results. For their part, the hydrometer gradations of the
densified and abused microsilica in Fig. 4.1 are practically indistinguishable, indicating that
abuse does not create agglomerations that survive the rigor of the hydrometer test
methodology. This observation reinforces the conclusion reached above concenring the
inadequacy of the microsilica test to distinguish among the microsilica types considered, yet
by itself sheds no light on the suitability of using densified microsilica in construction. The
latter question needs to be answered through additional testing, as discussed below.
5.4 Variability of Mechanical Tests
The coefficients of variation (COV) of the compressive strength and modulus of
rupture test data are discussed in this section. Even though the researchers had taken great
care during mixing, casting and curing procedures to ensure consistency, considerable
variation in the test results was observed ascribed mainly to the nature of concrete. From
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prior experience, the following COV values may be expected: 0-5%: uncommonly low; 5-
10%: excellent engineering work; 10-15%: good engineering work; > 15%: questionable
reliability. The uniformity of the mixing processes employed is reflected in the low COV
statistics obtained for the physical properties of each batch prepared. According to ODOT
Item 499.03 Concrete-General: Proportioning; Slump, the slump may vary between 4 and 8
in. for concrete in which chemical admixtures are used. It can be seen from Table 4.11 that
the average slump of all the mixes ranged between these values. Therefore, it can be said
that the concrete used in this project meets the ODOT slump specification, even though
slump was not a property that was controlled in itself. Similarly, the expected air content
was 8 ± 2%, according to ODOT Supplemental Specification 848 Bridge Deck Repair and
Overlay with Concrete Using Hydro-Demolition. Consequently, the average air content
values in Table 4.11 also met the ODOT specification, falling within the range specified,
except for a small deviation in a single batch.
5.4.1 Compressive Strength
The coefficients of variation for various mixes at ages of 7, 28, 56 and 90 days are
tabulated in Table 5.1. As noted in Chapter 4, a two letter designation is used to identify the
mixes, in terms of the microsilica and coarse aggregate types used, viz., Densified Natural
(DN), Densified Crushed (DC), Undensified Natural (UN), Undensified Crushed (UC),
Abused Natural (AN), and Abused Crushed (AC). Moreover, compressive test results are
designated as pertaining to large or to small cylinders, LC or SC, respectively. Low values
were obtained in the compressive strength, f′c, tests at almost all ages. From Table 5.1, it can
be seen that the average coefficients of variation for the compressive strength tests varied
mostly between 2 and 10% for all mixes, representing excellent engineering work. The
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actual values of f′c obtained can be found in Tables 4.12 and 4.13 for large and small
cylinders, respectively.
5.4.2 Modulus of Rupture
Coefficients of variation obtained for the modulus of rupture, MR, tests are also
tabulated in Table 5.1, in which they are designated as pertaining to large or to small beams,
LB or SB, respectively. It can be seen that COV values were higher for modulus of rupture
than for compressive strength testing. This is because beams are sensitive to even minor
changes in mixing, casting or testing methods. Similar variability has been reported in the
literature. The average coefficients of variation for MR varied between 7 and 15%, which
represent excellent to good engineering work. The actual values of MR obtained can be
found in Tables 4.14 and 4.15for large and small beams, respectively.
5.5 Data Interpretation
Despite the researchers’ efforts to ensure uniformity and consistency in the results
obtained, which are reflected in COV values representing excellent to good engineering
work, the data collected pose a difficult interpretation problem since the small number of
specimens tested does not permit an exclusively statistical analysis. Consequently, it has
been found useful to appeal in addition to a set of engineering boundary conditions to ensure
that strength increases with age at a decreasing rate. This approach has been found to
reinforce the statistical analyses performed, leading to a number of meaningful conclusions,
as described below.
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5.5.1 Compressive Strength
The average compressive strength of the various mixes at each age is tabulated in
Tables 5.2 and 5.3, pertaining to large and small cylinder specimens, respectively. From
these data, relative strength values at each age with respect to the corresponding 28-day
average strength were calculated, as found in Tables 5.4 and 5.5. For example, in Table 5.5,
the 7-day strength for the small cylinder mix with densified microsilica and natural aggregate
(DN) is 85% of its 28-day strength, while the 56-day strength for the same mix is 105% of
the corresponding 28-day strength. These values are calculated by dividing the strength at a
particular age by the strength at 28 days; e.g., from Table 5.3, the compressive strength for
small cylinders at 7 days for mix DN is 4504 psi; similarly, the strength at 28 days for the
same mix is 5295 psi. Therefore, the relative strength at 7 days with respect to the 28-day
strength is calculated as follows: (4504 / 5295) × 100 = 85%.
All relative strengths thus calculated were plotted against age, as shown in Figures
5.1 and 5.2, from the data for large and small cylinders, respectively. In each case, the
researchers then fitted a trend curve through the points, by adjusting slightly the line
predicted statistically, so as to conform to the boundary conditions that the slope should
decrease and the strength should increase with increasing age. It can be noted from Figures
5.1 and 5.2 that the trend curve is only slightly different from the unadjusted statistical lines.
The enforcement of boundary conditions results in a smooth curve that reproduces the
expected trends. From the trend line thus obtained, adjusted relative strength values at each
age were read. For example, in Fig. 5.1, the trend line indicates 75% strength at 7 days, and
98%, 112% and 117% at 28, 56 and 90 days of age, respectively. Thus, the strength gain
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between two ages can be determined; e.g., the strength gain between ages 28 and 90 from
Fig. 5.1 can be calculated as (117-98)/98 = 19%.
In this manner, a set of best-fit compressive strength values were obtained for each
mix, as presented in Tables 5.6 and 5.7, for large and small cylinder specimens, respectively,
and will be used below in the interpretation of the test results. The entire procedure leading
to the derivation of these best-fit strength values may be summarized as follows, for a
particular specimen size:
1. Obtain the laboratory data pertaining to each mix at every age.
2. Calculate the average strength value of each mix at every age.
3. Normalize these average values with respect to the corresponding 28-day strength, to
obtain the relative strengths for each mix at every age.
4. Plot the relative strengths for all mixes against age, and obtain a statistically predicted
line through these points.
5. Impose the engineering boundary conditions of strength increase at a decreasing rate
with time, to adjust the statistical line and thus obtain a smooth trend curve.
6. From the adjusted trend curve, read off the percentage strength gain with each age
increment.
7. Return to the laboratory data, and inspect them to identify the optimum age for each
mix, to be used in the best-fit strength derivation. One way to do this, is to select the age, for
which the coefficient of variation is the lowest.
8. Use the incremental strength gains from Step 6 in conjunction with the laboratory
strength at the optimum age for each mix from Step 7, in order to derive the best-fit strength
values for each mix at every age. For example, if laboratory 90-day compressive strength of
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mix DC is equal to 6873 psi (Table 5.3) and the lowest coefficient of variation occurs at this
point as shown in Table 5.1, then the best-fit 7-day strength is 6873 multiplied by strength
gain from 7 days to 90 days i.e., 6873 × (72/110) = 4499. Note that 72% and 110% are
obtained from the trend line from Fig. 5.2 at 7 days and 90 days, respectively.
5.5.2 Modulus of Rupture
The procedure followed in obtaining the best-fit modulus of rupture values is
analogous to that for compressive strength. Because of the small number of large and small
specimens tested, the analysis considered the two types of specimens collectively. The
average values of actual test data obtained for each mix at each age tested are presented in
Table 5.8, from which the corresponding values relative to the corresponding 28-day strength
are obtained, as shown in Table 5.9. The trend line for the modulus of rupture can be seen in
Fig. 5.3, from which the best-fit values in Table 5.10 are determined.
5.6 Effect of Microsilica Type on Mechanical Properties of Concrete
5.6.1 Compressive Strength
Natural Coarse Aggregate
Mixes DN, UN, and AN were made using natural aggregate, each with one of the
three types of microsilica, viz., densified, undensified and abused, respectively. The
compressive strength comparisons based on the type of microsilica are plotted in Figures 5.4
and 5.5 for large and small cylinders, respectively. It can be observed that the compressive
strength of undensified microsilica was greater than the other two microsilica concretes at all
ages, for both large and small cylinders. At 28 days, large cylinders made with undensified
microsilica concrete had nearly 576 psi (10%) and 923 (17%) psi higher compressive
80
strength than densified and abused microsilica concretes, respectively. In the compressive
strength results of small cylinders, the strength of undensified microsilica concrete was 1025
psi (18.5%) and 1137 psi (15%) psi greater than densified and abused microsilica concretes,
respectively.
The compressive strength of densified microsilica exceeded 5000 psi at 28 days for
both large and small specimens. In comparison, for mixes typically used in pavement
construction, ODOT 499.03 requires “an average compressive strength at 28 days of 4000 psi
for Class C, 3000 psi for Class F and 4500 psi for Class S.” Therefore, even though
densified microsilica had lower compressive strengths than the undensified material, it can
still be used on Ohio Department of Transportation (ODOT) projects, since it has adequate
strength to meet the requirements of this agency. In fact, even the abused microsilica results
appear adequate.
Crushed Coarse Aggregate
The effect of aggregate on concrete made with crushed aggregate and undensified
microsilica can be found in Figures 5.6 and 5.7, respectively, for large and small cylinders.
As was the case for concrete made with natural aggregate, the compressive strength of
concrete made with undensified microsilica and crushed aggregate, showed higher strengths
than densified and abused microsilica concretes. The abused microsilica exhibited in all
cases lower strengths compared to the other two types, as expected.
At 28 days, the compressive strength of large cylinders made with undensified
microsilica had 544 (9%) and 1088 (20%) psi higher strength than densified and abused
microsilica concretes, respectively. Similarly, the small cylinders made with undensified
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microsilica had 1442 (24%) and 1714 (30%) psi greater strength than densified and abused
microsilica concretes, respectively.
Once again, the densified microsilica with crushed aggregate showed higher strengths
than those prescribed by ODOT 499.03 at 28 days of curing in all cases. Therefore, densified
microsilica meets the ODOT specifications in all cases and can be used in the construction of
pavements and bridges.
5.6.2 Modulus of Rupture
Natural Coarse Aggregate
The effect of microsilica type on the modulus of rupture of concrete made with
natural aggregate can be found in Fig. 5.8. The beams made with undensified microsilica
showed somewhat higher strengths compared to densified and abused microsilica concretes.
Surprisingly, abused microsilica concrete had higher modulus of rupture than densified
microsilica concrete and was comparable to undensified microsilica concrete. At 28 days,
for example, the beams made with undensified microsilica had 22 psi (3%) and 73 psi (11%)
higher strengths than densified and abused microsilica concretes, respectively.
Crushed Coarse aggregate
Figure 5.9 shows the effect of microsilica type on concrete with crushed aggregate.
The results for modulus of rupture of concrete with crushed aggregate also showed some
surprising trends. Densified microsilica concrete exhibited lower values than undensified
and abused microsilica concretes at all ages. Comparing Figures 5.8 and 5.9, it is observed
that at 28 days concrete made with crushed aggregate showed slightly higher modulus of
rupture values than concrete with natural aggregate, as expected.
82
5.7 Effect of Coarse Aggregate Type on Mechanical Properties of
Concrete
5.7.1 Compressive Strength
Undensified Microsilica
As expected, the compressive strength of large cylinders made with crushed
aggregate showed higher strengths than the concrete made with natural aggregate for large
and small cylinders at all ages and for all mixes. The effect of aggregate type on the
compressive strength of concrete made with undensified microsilica can be found in Figures
5.10 and 5.11, for large and small cylinders, respectively. Concrete made with undensified
microsilica and crushed aggregate showed higher strengths than the concrete made with same
microsilica type and natural aggregate. As expected, at 28 days of age, the compressive
strength of large cylinders from mix UC had 224 (4%) psi higher strength than large
cylinders from mix UN. When the compressive strengths of small cylinders made with
undensified microsilica are observed at 28 days, the concrete made with crushed aggregate
shows an increase of 810 (12%) psi over the concrete made with natural aggregate.
Densified Microsilica
Similarly, large and small cylinders made with densified microsilica and crushed
aggregate showed greater strengths at all ages than the concrete made from the same
microsilica and natural aggregate. The effect of aggregate type on compressive strength of
large and small cylinders made with densified microsilica is plotted in Fig. 5.12 and Fig.
5.13. Moreover, the difference in strengths due to aggregate type is higher for small than for
large cylinders. This trend was also observed for undensified microsilica concrete. At 28
days, large cylinders made with crushed aggregate had 256 (5%) psi higher strength than
83
natural aggregate concrete, whereas for small cylinders, the difference in the strengths of
crushed aggregate concrete and natural aggregate concrete was 393 (7%) psi.
Abused Microsilica
Abused microsilica concrete showed the same trends as undensified and densified
microsilica concretes. Figures 5.14 and 5.15 show the effect of aggregate type on the
compressive strength of abused microsilica concrete for large and small cylinders,
respectively. Concrete made with crushed aggregate had higher strengths than the concrete
made with natural aggregate at all ages, as expected. At 28 days, large cylinders made with
crushed aggregate had 59 (1%) psi higher strength than the ones made with natural
aggregate. In contrast, for small cylinders, the difference in strengths of crushed and natural
aggregate was 300 (6%) psi.
5.7.2 Modulus of Rupture
The modulus of rupture values showed similar trends as compressive strength results,
values being higher when crushed aggregate was used. The effects of aggregate type on the
three types of microsilica are explained in the following sections.
Undensified Microsilica
The effect of aggregate type on undensified microsilica concrete beams is plotted in
Fig. 5.16. At 28 days, the beams made with crushed aggregate had 13 psi (2 %) higher
flexural strength than beams made with natural aggregate.
Densified Microsilica
Rather surprisingly, beams made from densified microsilica concrete with natural
aggregate showed greater strength than those made with crushed aggregate at all ages.
Figure 5.17 shows the effect of aggregate type on densified microsilica concrete beams. It
84
can be seen that, at 28 days, beams made with natural aggregate had nearly 10 psi (1%)
higher flexural strength than beams made with crushed aggregate.
Abused Microsilica
The effect of aggregate type on abused microsilica concrete beams can be seen in Fig.
5.18. at 28 days, the modulus of rupture of beams with natural aggregate was surprisingly
somewhat higher when compared to beams with crushed aggregate. At other ages, however,
the beams with crushed aggregate exhibited greater values than the ones with natural
aggregate, as expected. In all cases, the variability in the values calculated far exceeds any
intrinsic differences due to aggregate type.
5.8 Effect of Specimen Size on Mechanical Properties of Concrete
Compressive Strength
Size factors pertaining to cylindrical specimens for mixes at various ages are
tabulated in Table 5.11. A size factor is calculated as the ratio of the compressive strength of
small cylinders to that of large cylinders, expressed as a percentage. Small cylinders, usually
have 5 to 8% higher strength than large cylinders (Mehta and Monteiro, 1993); therefore, size
factors are expected to be greater than 100%. From Table 5.11, it can be noticed that the size
factors obtained in this project do not follow any particular pattern. It can be seen that in for
mixes DN and AD, the compressive strength of the large cylinders was either higher than or
equal to that of the small cylinders at all ages.
85
Modulus of Rupture
Size factors for modulus of rupture results could not be calculated as either large
beams or small beams were tested at each age for all the mixes. Instead, a factor of 1.16 was
assumed based on past experience to convert the large beam values for mixes AN and DC to
the corresponding small beams values, so as to allow comparisons among aggregate and
microsilica types. Such comparisons suggest that the choice of the factor of 1.16 was
appropriate.
86
Table 5.1 Coefficients of Variation, COV (%), in Laboratory Test Results
Age (days) 7 28 56 90 Average Test
Mix: Undensified Natural (UN) f′c (LC) f′c (SC) 4.78 3.99 6.13 2.21 4.28
MR (LB) MR (SB) 4.17 13.38 4.17 7.24
Mix: Undensified Crushed (UC) f′c (LC) f′c (SC) 2.61 7.22 6.26 7.77 5.97
MR (LB) MR (SB) 1.13 9.66 11.85 7.55
Mix: Densified Natural (DN) f′c (LC) 2.87 1.77 0.78 1.90 1.83 f′c (SC) 8.95 5.40 4.58 6.31
MR (LB) 12.13 21.05 11.40 14.86 MR (SB)
Mix: Densified Crushed (DC) f′c (LC) 3.88 7.45 12.81 4.38 7.13 f′c (SC) 10.29 12.84 7.57 10.23
MR (LB) 21.18 6.51 9.29 12.33 MR (SB)
Mix: Abused Natural (AN) f′c (LC) f′c (SC) 6.13 7.69 2.11 7.14 5.77
MR (LB) MR (SB) 9.03 5.11 8.14 7.43
Mix: Abused Crushed (AC) f′c (LC) f′c (SC) 5.40 7.84 5.97 9.17 7.10
MR (LB) MR (SB) 9.49 8.01 4.68 7.39
87
Table 5.2 Average Compressive Strength for Large Cylinders (psi)
Age (days) UN UC DN DC AN AC
7 4333 4601 3663 3822 28 6861 6657 5488 5918 5506 5024 56 7129 7385 6156 6401 6074 6142 90 6316 7031 6421 6090
Note: The numbers in bold were used to calculate the best-fit values for each mix.
Table 5.3 Average Compressive Strength for Small Cylinders (psi)
Age (days) UN UC DN DC AN AC
7 5299 5592 4504 5134 3932 4293 28 6989 7711 5295 6030 5570 5545 56 7489 7816 5554 6856 5929 5786 90 7604 7942 6418 6873 6126 6441
Note: The numbers in bold were used to calculate the best-fit values for each mix.
88
Table 5.4 Relative Compressive Strength Values for Large Cylinders (%)
Mix Age (days) UN UC DN DC AN AC
7 79 78 67 76 28 100 100 100 100 100 100 56 104 111 112 108 110 122 90 115 119 117 121
Table 5.5 Relative Compressive Strength Values for Small Cylinders (%)
Mix Age (days) UN UC DN DC AN AC
7 76 73 85 85 71 77 28 100 100 100 100 100 100 56 107 101 105 114 106 104 90 109 103 121 114 110 116
89
Table 5.6 Best-Fit Compressive Strength Values for Large Cylinders (psi)
Age (days) UN UC DN DC AN AC
7 4774 4945 4333 4529 4068 4113 28 6238 6462 5662 5918 5315 5374 56 7129 7385 6471 6763 6074 6142 90 7448 7714 6760 7065 6346 6416
Note: The numbers in bold were used to calculate the best-fit values for each mix.
Table 5.7 Best-Fit Compressive Strength Values for Small Cylinders (psi)
Age (days) UN UC DN DC AN AC
7 4977 5592 4201 4499 4066 4293 28 6568 7378 5543 5936 5364 5664 56 7259 8155 6127 6561 5929 6261 90 7604 8543 6418 6873 6212 6559
Note: The numbers in bold were used to calculate the best-fit values for each mix.
90
Table 5.8 Average Modulus of Rupture Values for Beams (psi)
Age (days) UN UC DN DC AN AC
7 942 733 625 700 765 824 28 1021 988 747 702 973 946 56 902 828 755 686 919 938 90
Table 5.9 Relative Modulus of Rupture Values for Beams (%)
Age (days) UN UC DN DC AN AC
7 92 73 84 100 79 87 28 100 100 100 100 100 100 56 88 83 101 98 94 99 90
Table 5.10 Best-Fit Modulus of Rupture for Small Beams (psi)
Age (days) UN UC DN DC AN AC
7 722 733 700 691 735 751 28 851 864 825 815 867 885 56 902 916 875 864 919 938 90
Note: Large beams (6 × 6 × 21 in.) have been tested for Mixes DN and DC, whereas small beams (3½ × 4½ × 16 in.) have been tested for all other mixes. For mixes DN and DC, large beam lab data were converted to the small beam values in this Table through multiplication by a factor of 1.16, selected on the basis of past experience. The numbers in bold were used to calculate the best-fit values.
91
Table 5.11 Cylinder Size Factors (%)
Age (days) UN UC DN DC AN AC
7 104 113 97 99 100 104
28 105 114 98 100 101 105
56 102 110 95 97 98 102
90 102 111 95 97 98 102
Average by mix 104 112 96 98 99 103
Average by MS type
108 97 101
92
40
50
60
70
80
90
100
110
120
130
0 10 20 30 40 50 60 70 80 90 100
Age, days
Rel
ativ
e St
reng
th, %
Test Data
Trend Curve
Statistical Line
Fig. 5.1 Trend Line Curves for Large Cylinders
93
40
50
60
70
80
90
100
110
120
130
0 10 20 30 40 50 60 70 80 90 100
Age, days
Rel
ativ
e St
reng
th, %
Test Data
Trend Curve
Statistical Line
Fig. 5.2 Trend Line Curves for Small Cylinders
94
40
50
60
70
80
90
100
110
120
130
0 10 20 30 40 50 60 70 80 90 100Age, days
Rel
ativ
e St
reng
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Test Data
Trend Curve
Statistical Line
Fig. 5.3 Trend Line Curves for Small Beams
95
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
7 28 56 90Age, days
Com
pres
sive
Str
engt
h, p
si
UndensifiedDensifiedAbused
Fig. 5.4 Effect of Microsilica Type on Large Cylinders with Natural Aggregate
96
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4000
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7000
8000
9000
7 28 56 90Age, days
Com
pres
sive
Str
engt
h, p
si
UndensifiedDensifiedAbused
Fig. 5.5 Effect of Microsilica Type on Small Cylinders with Natural Aggregate
97
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
7 28 56 90
Age, days
Com
pres
sive
Str
engt
h, p
si
UndensifiedDensifiedAbused
Fig. 5.6 Effect of Microsilica Type on Large Cylinders with Crushed Aggregate
98
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
7 28 56 90
Age, days
Com
pres
sive
Str
engt
h, p
si
UndensifiedDensifiedAbused
Fig. 5.7 Effect of Microsilica Type on Small Cylinders with Crushed Aggregate
99
0
100
200
300
400
500
600
700
800
900
1000
7 28 56 90
Age, days
Mod
ulus
of R
uptu
re, p
si
UndensifiedDensifiedAbused
Fig. 5.8 Effect of Microsilica Type on Small Beams with Natural Aggregate
100
0
100
200
300
400
500
600
700
800
900
1000
7 28 56 90
Age, days
Mod
ulus
of R
uptu
re, p
si
UndensifiedDensifiedAbused
Fig. 5.9 Effect of Microsilica Type on Small Beams with Crushed Aggregate
101
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
7 28 56 90
Age, days
Com
pres
sive
Str
engt
h, p
si
NaturalCrushed
Fig. 5.10 Effect of Aggregate Type on Large Cylinders with Undensified Microsilica
102
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
7 28 56 90Age, days
Com
pres
sive
Str
engt
h, p
si
NaturalCrushed
Fig. 5.11 Effect of Aggregate Type on Small Cylinders with Undensified Microsilica
103
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
7 28 56 90
Age, days
Com
pres
sive
Str
engt
h, p
si
NaturalCrushed
Fig. 5.12 Effect of Aggregate Type on Large Cylinders with Densified Microsilica
104
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
7 28 56 90Age, days
Com
pres
sive
Str
engt
h, p
si
NaturalCrushed
Fig. 5.13 Effect of Aggregate Type on Small Cylinders with Densified Microsilica
105
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
7 28 56 90Age, days
Com
pres
sive
Str
engt
h, p
si
NaturalCrushed
Fig. 5.14 Effect of Aggregate Type on Large Cylinders with Abused Microsilica
106
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
7 28 56 90Age, days
Com
pres
sive
Str
engt
h, p
si
NaturalCrushed
Fig. 5.15 Effect of Aggregate Type on Small Cylinders with Abused Microsilica
107
0
100
200
300
400
500
600
700
800
900
1000
7 28 56 90Age, days
Mod
ulus
of R
uptu
re, p
si
NaturalCrushed
Fig. 5.16 Effect of Aggregate Type on Small Beams with Undensified Microsilica
108
0
100
200
300
400
500
600
700
800
900
1000
7 28 56 90
Age, days
Mod
ulus
of R
uptu
re, p
si
NaturalCrushed
Fig. 5.17 Effect of Aggregate Type on Small Beams with Densified Microsilica
109
0
100
200
300
400
500
600
700
800
900
1000
7 28 56 90
Age, days
Mod
ulus
of R
uptu
re, p
si
NaturalCrushed
Fig. 5.18 Effect of Aggregate Type on Small Beams with Abused Microsilica
110
6 CONCLUSIONS AND RECOMMENDATIONS
6.1 Summary
This project explored the use of densified microsilica in concrete used in the
construction of pavements and structures by Ohio Department of Transportation
(ODOT). Of the various kinds of microsilica that are commercially available in the
market, only two were considered by the research team: undensified microsilica and
densified microsilica. A third type of microsilica, viz., abused microsilica, was also
explored. It is usually assumed that undensified microsilica will result in higher strengths
than the densified material, which is the form most commonly used in practice. Wishing
to compare densified microsilica’s performance to a worst case scenario, the investigators
prepared a quantity of abused microsilica by soaking the densified material in water and
drying it, thereby encouraging the formation of clumps. Microsilica thus prepared was
expected to in the weakest concrete, assuming that the consequence of densification is
lower strength. Comparing the engineering performance of densified microsilica to
undensified and abused materials brackets the range of situations that may be
encountered in the field.
Undensified microsilica is expected to pass the requirement that it should have a
fineness value greater than 90% found in American Standard for Testing and Materials
(ASTM) C 1240 – 01 Standard Specification for Use of Silica Fume as a Mineral
Admixture in Hydraulic-Cement Concrete, Mortar and Grout when it is wet-sieved in
111
accordance with ASTM C 430 – 96 Standard Test Method for Fineness of Hydraulic
Cement by the 45-µm (No. 325) Sieve, whereas densified and abused microsilica may not
pass the sieve test. Abused microsilica was prepared by the research team in University
of Cincinnati concrete laboratory, while densified and undensified microsilica were
obtained free of charge from ELKEM chemicals. Cement, concrete admixtures, and
aggregate were provided free of charge by CEMEX, Master Builders, Inc., and Martin
Marietta Materials, respectively. The research team utilized the research facilities at
University of Cincinnati for performing the various tasks in this project.
After procuring all the materials needed for the project, the research team
conducted tests on the aggregates to determine their properties, and to formulate a mix
design for the concrete. Two kinds of coarse aggregate, viz., natural and crushed, with a
single gradation of No. 8 were used. ODOT Supplemental Specification 848 Bridge
Deck Repair and Overlay with Concrete Using Hydro-Demolition was used in preparing
the mix design, in conjunction with ODOT Item 499.03 Concrete-General:
Proportioning. Six concrete mixes were made with the three types of microsilica and the
two kinds of coarse aggregates.
Concrete specimens were tested to determine their compressive strength and
flexural strength. Cylinders and beams were cast for this purpose. Specimens were made
in two different sizes in each case, viz., small cylinders (4 × 8 in.), large cylinders (6 × 12
in.), small beams (3½ × 4½ × 16 in.), and large beams (6 × 6 × 21 in.). Cylinders were
tested to calculate compressive strength, whereas beams were used to determine flexural
strength. Three cylinders and three beams were tested at each age in most cases. Large-
112
sized specimens were used for mixes made from densified microsilica, whereas small
specimens were used for the other mixes. The decision to change the specimen size from
large to small was taken by the investigators as it helped achieve higher efficiency and
consistency, without deviating from the ASTM specification that requires the minimum
specimen dimension to exceed three times the nominal maximum size of the coarse
aggregate (ASTM C 192/C 192M – 00 Standard Practice for Making and Curing
Concrete Test Specimens in the Laboratory). The same mixing, casting and testing
procedures were followed for all six mixes in order to maintain consistency.
Tests were also conducted on the microsilica material itself to check if it passes
the sieve test. The facilities at ODOT laboratory were utilized in conducting these tests.
The effect of densification of microsilica on its properties was evaluated from the results
of the above tests.
6.2 Conclusions
During tests conducted at the ODOT laboratory on the three microsilica types
used in this project, it was observed that none of the materials could actually meet the
ASTM C 1240 – 01 requirement when subjected to the sieve test of ASTM C 430 – 96.
Test results were not meaningful, since negative fineness values were obtained for some
of the samples. Even undensified microsilica could only meet the specifcation when a
non-prescribed brush was used. Therefore, it can be concluded that the sieve test is not
effective in predicting the performance of microsilica concrete that is to be used for
113
ODOT projects, and that it is not appropriate for ODOT’s assessment of the suitability of
microsilica for use in concrete.
The tests conducted on the concrete specimens indicate that those made with
undensified microsilica show higher flexural and compressive strengths than concrete
made with densified microsilica and abused microsilica, for both natural and crushed
aggregate. The strengths of undensified microsilica concrete were followed by that of
densified and abused microsilica concretes in decreasing order. Trends observed in
almost all mixes with respect to increase in strength with age, microsilica type, aggregate
type and specimen size were as expected. The strength of concrete specimens from all
mixes increased with age; moreover, the strength increase was more rapid in the initial
ages than during later ages. Both large and small cylinders attained compressive
strengths in excess of those envisaged ODOT 499.03 at 28 days of curing. Even though
lower compressive strengths were obtained for densified and abused microsilica
concretes compared to undensified, they still had adequate strength as required for ODOT
projects. Therefore, densified microsilica can be used for construction of pavements and
bridges by ODOT even though it may fail the sieve test.
Just like compressive strength results, the modulus of rupture of undensified
microsilica concrete was greater than corresponding values of densified and abused
microsilica concretes, when natural aggregate was used. Yet, the modulus of rupture of
abused microsilica was nearly equal to that of undensified microsilica, and was greater
than that of densified microsilica concrete at all ages, for both types of aggregate.
114
Coefficients of variation were higher for the modulus of rupture than the compressive
strength results.
Concrete made with crushed aggregate showed higher compressive and flexural
strengths than concrete made with natural aggregate in most of the mixes. As noted
earlier, a combination of either three large cylinders with a small cylinder, or three small
cylinders with a single large cylinder, was used for any given mix to determine
compressive strength. It was observed that the small sized concrete specimens yielded
greater compressive strengths than large sized specimens.
As noted earlier, the compressive and flexural strengths of abused microsilica did
not differ much from that of densified microsilica. The abused microsilica was intended
to represent the worst possible situation that might arise in the field. The clumps formed
during the abusing process were broken using a trowel; therefore, it can be said that the
clusters of microsilica that are formed in the field due to moisture can easily broken
during the mixing process.
6.3 Recommendations
During the sieve tests conducted at ODOT, none of the three types of microsilica could
pass the ASTM C 1240 – 01 requirement. On the other hand, when results from
compressive and flexural strength tests are considered, all microsilica types achieved
strengths in excess of those envisaged by ODOT Item 499.03, irrespective of whether
they passed the No. 325 sieve test or not. Therefore, it is recommended that the No. 325
sieve test be abandoned as a consideration in assessing the suitability of microsilica for
115
use in concrete. This is not to imply that densification is no longer a concern for
microsilica users, nor that the No. 325 sieve test does not serve a useful purpose when
used by the manufacturers for quality assurance, as it was originally conceived to do The
recommendation simply asserts that as the No. 325 sieve is conducted by an agency such
as ODOT, it yields no meaningful information. It is also recommended that the
microsilica should be stored for limited time only, in areas of low humidity at room
temperatures, and that the mixing process should be careful and thorough, to limit the
amount of densification at mixing, and to permit any bonds to be broken.
6.4 Implementation Plan
IMPLEMENTATION STEPS & TIME FRAME: The recommendations above
can be implemented immediately by any ODOT District including microsilica in its
concrete mix design.
EXPECTED BENEFITS: The main benefits from this research will derive from
the use of densified microsilica from respected manufacturers in pavement and bridge
construction, if such use is justified based on the results from other, more specific and
expensive, studies. Another benefit will derive from the elimination of the No. 325 sieve
test at the ODOT laboratory for the purpose of assessing the suitability of microsilica for
use in concrete mixes.
EXPECTED RISKS, OBSTACLES, & STRATEGIES TO OVERCOME THEM:
It is anticipated that there may be a hesitation to abandon what may currently be the only
test conducted at the ODOT laboratory in order to assure the quality of densified
116
microsilica used in pavement and bridge construction. It is suggested that ODOT make
more stringent its microsilica procurement process, in order to ensure that material is
obtained from reliable manufacturers alone, whose declarations of suitability may be
accepted with confidence. The possibility of bonding the manufacturer to the
performance of the pavement or bridge concerned may also be considered.
OTHER ODOT OFFICES AFFECTED BY THE CHANGE: Any ODOT District
including microsilica in its concrete mix design.
PROGRESS REPORTING & TIME FRAME: To be determined by ODOT.
TECHNOLOGY TRANSFER METHODS TO BE USED: The Final Report from
this study will be made available to interested parties, either in hard copy, or in electronic
form, the latter to include either Word .doc format or pdf. At least one refereed journal
paper documenting this investigation will be prepared within a year from the completion
of this contract.
IMPLEMENTATION COST & SOURCE OF FUNDING: There are no costs
associated with implementing the findings of this study.
117
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