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Fly Ash Applicability in Pervious Concrete

Thesis

Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in

the Graduate School of The Ohio State University

By

Na Jin, B. E.

Graduate Program in Civil Engineering

The Ohio State University

2010

Thesis Committee

William E. Wolfe, Advisor

Fabian Hadipriono TanTarunjit Singh Butalia


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Copyright by

Na Jin

2010


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ABSTRACT

Pervious concrete has been used in the United State for over 30 years. Because of

its high porosity, the most common usages have been in the area of stormwater

management, but have been limited to use in pavements with low volume traffic because

of its low compressive strength compared to conventional concrete. Fly ash has been

shown in numerous post studies to increase the strength and durability of conventional

concrete. In this study, six batches of pervious concrete with different amounts of

aggregate, cement, and fly ash were prepared to find the mix that generated high

compressive strength and study the effect of fly ash on the compressive strength and

permeability of pervious concrete.

Materials used in this study were selected based on literature reviews and

recommendations from local sources. Unconfined compressive strength tests were carried

out on pervious concrete specimens with fly ash contents of 0%, 2%, 9%, 30%, 32% by

weight of the total cementitious materials. Falling head permeability tests were carried

out on specimens having 2% and 32% fly ash.

The results indicated the pervious concrete containing 2% fly ash can achieve

compressive strength greater than 3,000 psi at void content of 12%, and a compressive

strength 2,300 psi with a permeability of 0.13 cm/s at a void content of 15%. The

pervious concrete with 32% fly ash had a compressive strength of 2,000 psi and the

permeability of 0.21 cm/s at a void content of 15.8%. The failure surfaces of specimens


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with 2% fly ash developed through the coarse aggregates, indicating the high strength of

cement bonds. The failure of specimens containing 32% fly ash was observed to be along

the coarse aggregates surfaces, indicating a lower strength of the paste. Although it was

expected for pervious concrete with 32% fly ash to reach a higher compressive strength at

lower void content, the failure mode indicated that it may not reach the value as high as

that of pervious concrete with 2% fly ash at the same void content.


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DEDICATION

Dedicated to my dear parents and husband.


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ACKNOWLEDGEMENTS

I would like to express my sincere appreciation to my advisor, Dr. William E.

Wolfe, for his guidance, patience, kindness, and encouragement throughout this work. I

would also like to thank Dr. Fabian Hadipriono Tan for his suggestions and endless

support to me during my study. Without their help, the fulfillment of my master degree

would have been impossible.

I would also like to thank Dr. Tarunjit Singh Butalia for his suggestions and help

in facilitating the purchase of experimental equipments in this study. I am also grateful to

all of the professionals for their expertise, support, and kindness: Mr. Mark Pardi, is of

Ohio Concrete, gave me valuable suggestions and guidance on pervious concrete; Mr.

Dan Hunt, is of Buckeye Ready-Mix, carried out one example mix test on pervious

concrete and shared his valuable experience; Mr. Michael Adams, is of Euclid Chemical

Corp., provided with pervious concrete admixtures; Mr. Thomas J. Wissinger, is of the

Olen Corp., provided and delivered coarse aggregates even in bad weather; Mr. Dan Jahn,

is of Anderson Concrete, arranged a visit to the concrete company and provided with

portions of perivous concrete components.


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Table of Contents

ABSTRACTii

DEDICATIONiv

ACKNOWLDEGEMENTS.v

VITA...vi

List of Figures..x

List of Tables........xiii

CHAPTER 1: INSTRODUCTION...............................................................................1

1.1 Background............................................................................................................11.2 Objectives..............................................................................................................2

1.3 Organization ..........................................................................................................3

CHAPTER 2: LITERATURE REVIEW OF PORTLAND CEMENT PERVIOUS

CONCRETE ..................................................................................................................5

2.1 Introduction ...........................................................................................................5

2.2 Benefits and Problems ...........................................................................................62.2.1 Benefits...........................................................................................................6

2.2.2 Problems .........................................................................................................82.3 Components of Pervious Concrete .......................................................................11

2.3.1 Coarse Aggregate..........................................................................................112.3.2 Fine Aggregate..............................................................................................12

2.3.3 Cement..........................................................................................................122.3.4 Fly Ash .........................................................................................................13

2.3.5 Water ............................................................................................................132.3.6 Admixtures ...................................................................................................14

2.4 Important Properties of Pervious Concrete ...........................................................162.4.1 Permeability ..................................................................................................16

2.4.2 Compressive Strength....................................................................................202.4.3 Freeze-thaw Durability..................................................................................21

2.4.4 Modulus of Elasticity ....................................................................................24


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2.5 Factors Affect Compressive Strength and Permeability of Pervious Concrete.......242.5.1 Effect of Void Content ..................................................................................25

2.5.2 Effect of Aggregate.......................................................................................272.5.3 Effect of Aggregate/Cement Material Ratio...................................................28

2.5.4 Effect of Water/Cement Ratio .......................................................................28

2.5.5 Effect of fly ash.............................................................................................292.5.6 Effect of Compaction Energy ........................................................................292.5.7 Effect of Fibers .............................................................................................31

2.5.8 Effect of Other Factors ..................................................................................322.6 Standard Test Methods.........................................................................................33

2.7 Pervious Concrete Design ....................................................................................342.7.1 Pervious Concrete Mix Design ......................................................................34

2.7.2 Pervious Concrete Pavement Hydraulic Design.............................................362.7.3 Pervious Concrete Pavement Structural Design .............................................37

CHAPTER 3: LITERATURE REVIEW OF FLY ASH............................................44

3.1 Introduction of Coal Combustion Products (CCPs) ..............................................44

3.2 Introduction of Fly Ash........................................................................................473.2.1 Properties of Fly Ash.....................................................................................48

3.2.2 Class C and Class F Fly Ash..........................................................................483.2.3 Utilization of Fly Ash in Concrete .................................................................48

3.2.4 Environmental Benefits of Fly Ash Use.........................................................503.3 Effect of Fly Ash on Concrete..............................................................................51

3.3.1 Thermal Cracking .........................................................................................513.3.2 Compressive Strength....................................................................................51

3.3.3 Durability......................................................................................................533.3.4 Permeability ..................................................................................................54

3.3.5 Sulfate Attack ...............................................................................................553.4 Fly Ash in Pervious Concrete...............................................................................56

3.5 Summary .............................................................................................................56

CHAPTER 4: LABORATORY MIX AND TEST .....................................................59

4.1 Introduction .........................................................................................................594.2 Mix Preparation ...................................................................................................59

4.2.1 Mix Materials................................................................................................594.2.2 Mix Design ...................................................................................................65

4.2.3 Mixing Equipment ........................................................................................714.2.4 Specimen Mold .............................................................................................74

4.3 Mixing Procedure ................................................................................................744.4 Compaction Method.............................................................................................75

4.5 Curing Method.....................................................................................................764.6 Laboratory Tests ..................................................................................................77

4.6.1 Unit Weight and Void Content ......................................................................77


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4.6.2 Compressive Strength....................................................................................794.6.3 Permeability ..................................................................................................80

4.7 Summary of Test Procedure.................................................................................83

CHAPTER 5: DISCUSSION ON TEST RESULTS ................................ ..................86

5.1 Introduction .........................................................................................................865.2 Void Content vs. Unit Weight ..............................................................................86

5.3 Effect of Compaction Energy...............................................................................875.4 Effect of W/C Ratio, A/C Ratio and Fly Ash on Void Content .............................90

5.5 Compressive Strength ..........................................................................................905.5.1 Compressive Strength vs. Curing Period........................................................91

5.5.2 Compressive Strength vs. Void Content ........................................................925.5.3 Compressive Strength vs. Unit Weight ..........................................................94

5.5.4 Compressive Stress-strain Curves vs. Void Content.......................................945.5.5 Compressive Failure vs. Curing Period..........................................................98

5.5.6 Failure Modes ...............................................................................................995.6 Permeability.......................................................................................................103

CHAPTER 6: SUMMARY, CONCLUSION, AND RECOMMENDATIONS.......107

6.1 Summary ...........................................................................................................107

6.2 Conclusion.........................................................................................................1096.3 Recommendations for Future Work....................................................................111

REFERENCES..........................................................................................................113

APPENDIX A: EXAMPLES OF PERVIOUS CONCRETEEXPERIMENTS FROM

LITERATURE REVIEWS .......................................................................................121

APPENDIX B: PROPERTIES OF PERVIUOS CONCRETE COMPONENTS ...125

APPENDIX C: LABORATORY TEST RESULT ................................ ................... 137

APPENDIX D: PERVIOUS CONCRETE MIX DESIGN PROGRAM CODE .....168


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List of Figures

Figure 2.1. Model Resulting from the Nonlinear Fitting of the Saturated Hydraulic

Conductivity and Total Porosity Data to the Carman-Kozeny Equation .........................18Figure 2.2. Plot of the Ergun Equation and Values Calculated Using the Falling Head

Experimental Data from Samples Calculated withDp= 0.1,Dp= 0.3, andDp=0.6.(adapted from Montes and Haselbach

).....................................................................19

Figure 2.3. Relationship between Strength, Void Content and Permeability for SeveralTrial Mixes of Portland Cement Pervious Concrete........................................................26

Figure 2.4. Nomograph to Determine Structural Number (Pavement Strength) .............38

Figure 3.1. Uses of Coal Combustion Products in 2008(AACA adapted from U. SEnvironmental Protection Agency (EPA)) .....................................................................45Figure 3.2. 1966-2007 CCP Beneficial Use vs. Production (AACA) ..............................46

Figure 3.3. Coal Combustion Products Generation and Use (Short Tons) (AACA adaptedfrom EPA) .....................................................................................................................47

Figure 3.4. Top Uses of Coal Fly Ash 2003 (AACA adapted from)................................49Figure 3.5. Comparison between Ash Concrete Compressive Strength and Plain Cement

Concrete Compressive Strength. ....................................................................................52Figure 3.6. Effect of Fly Ash on Permeability of Concrete (adapted from) .....................55

Figure 4.1. Grain Distribution Curve of Size Number 8 River Gravel(Olen Corp.)........61Figure 4.2. Pervious Concrete Mix Calculation Program................................................68

Figure 4.3. 20 quart Blakeslee Mixer .............................................................................72Figure 4.4. Specimen Mixed Using 20 Quart Blakeslee Mixer .......................................72

Figure 4.5. 3.4ft3capacity Gilson 39555 (drum speed speed 22 ~ 25 RPM) ...................73

Figure 4.6. INSTRON-5585 Compressive Strength Testing Machine.............................80

Figure 4.7. Falling Head Permeability Test for Pervious Concrete Specimen .................82Figure 4.8. Pervious Concrete Specimen for Permeability Test ......................................82

Figure 5.1. Relationship between Void Content (%) and Unit Weight (lb/ft3).................87Figure 5.2. Void Contents of Specimens Compacted by Different Methods ...................88

Figure 5.3. The Specimen Compacted by Proctor Hammer ............................................89Figure 5.4. Pervious Concrete Mix #3~#6 Compressive Strength vs. Curing Period.......92

Figure 5.5. Relaiton between 28-day Compressive Strength and Void Content ..............93

Figure 5.6. Relationship between 28-day Compressive Strength and Unit Weight..........94Figure 5.7. Stress-strain Curves Tested on Specimens with Different Void Content at 28-day Curing Period, Mix #5.............................................................................................96

Figure 5.8. Stress-strain Curves Tested on Specimens with Different Void Content at 28-day Curing Period, Mix #6.............................................................................................97

Figure 5.9. Stress-strain Curves Tested on Specimens with Void Content 18% at 7-day,21-day, and 28-day Curing Periods, Mix #6 ...................................................................99


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Figure 5.10. Failure Mode I of Pervious Concrete Samples..........................................100Figure 5.11. Failure Mode II of Pervious Concrete Samples.........................................100

Figure 5.12. Failure of Specimen Compacted by Standard Proctor Hammer (Mix #6)..101Figure 5.13. Failure Surface Comparison between Specimen from Mix #5 and Mix #6102

Figure 5.14. Relationship between Void Content and Permeability of Pervious Concrete

Specimens ...................................................................................................................103Figure 5.15. Comparison of Permeability Test Results with Previous Studies ..............106Figure 6.1. Permeability and 28-day Compressive Strength vs. Void Content ..............109

Figure B.1. Properties of Coarse Aggregates................................................................126Figure B.2. Properties of Cement (St. Marys) ..............................................................127

Figure B.3. Properties of High Range Water Reducer (Euclid Chemical Company) .....128Figure B.4. Properties of Mid-Range Water Reducer (Euclid Chemical Company) ......130

Figure B.5. Properties of Mid-Range Water Reducer (Euclid Chemical Company) ......132Figure B.6. Properties of Viscosity Modifying Admixture (Euclid Chemical Company)

....................................................................................................................................134Figure B.7. Properties of Fiber (Euclid Chemical Company)........................................135

Figure C.1. 11-day Compressive Stress-strain Curve of Specimen with Void Contend of31% from Mix #3 ........................................................................................................147















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Figure C.17. 28-day Compressive Stress-strain Curve of Specimen with Void Contend of

14% from Mix #5 ........................................................................................................155Figure C.18. 28-day Compressive Stress-strain Curve of Specimen with Void Contend of14% from Mix #5 ........................................................................................................155








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List of Tables

Table 2.1. NMCRA Classification of Regions and Recommendation of Precautions ofUtilizing pervious concrete ...........................................................................................22

Table 2.2. Compaction Method Conducted by Rizvi et al...............................................31Table 2.3. Recommended Typical Mix Design by National Ready Mixed Concrete

Association....................................................................................................................35Table 2.4. Recommended Typical Mix Design by the Southern California Ready Mix

Concrete Association (adapted from) ............................................................................35Table 2.5. Recommended Typical Mix Design by the Euclid Chemical Company .........35

Table 4.1. Physical Properties of #8 River Gravel (Olen Corp.) .....................................61

Table 4.2. Coarse Aggregate Distribution (Olen Corp.)..................................................61Table 4.3. Chemical Properties of St. Marys Type I Cement (St. Marys, Inc.)................63Table 4.4. Physical Properties of fly ash ........................................................................64

Table 4.5. Admixtures from Euclid Chemical Company ................................................65Table 4.6. Pervious Concrete Mix Design ......................................................................66

Table 4.7. Mix No. Corresponding to Mix ID. ...............................................................67Table 4.8 Compaction Method ID Explanation ..............................................................75

Table 4.9. Pervious Concrete Mixes Compacted Using Different Methods Mix .............76Table 4.10. Specific Gravities of Materials in Portland Cement Pervious Concrete Mix.79

Table A.1: Examples of Laboratory Tests on Pervious Concrete. .................................122Table A.2. Examples of Field Projects of Pervious Concrete........................................124

Table C.1. Mix Design of Pervious Concrete Mix #1 ...................................................138Table C.2. Unit Weight and Void Content of 4in x 8in Samples from Pervious Concrete

Mix #1.........................................................................................................................138Table C.3. Mix Design of Pervious Concrete Mix #2 ...................................................139

Table C.4. Unit Weight and Void Content of 4in x 8in Samples from Pervious ConcreteMix #2.........................................................................................................................139

Table C.5. Mix Design of Pervious Concrete Mix #3 ...................................................140Table C.6. Unit Weight and Void Content of 4in x 8in Samples from Pervious Concrete

Mix #3.........................................................................................................................140Table C.7. Mix Design of Pervious Concrete Mix #4 ...................................................141

Table C.8. Unit Weight and Void Content of 4in x 8in Samples from Pervious Concrete

Mix #4.........................................................................................................................141Table C.9. Mix Design of Pervious Concrete Mix #5 ...................................................142Table C.10. Unit Weight and Void Content of 4in x 8in Samples from Pervious Concrete

Mix #5.........................................................................................................................142Table C.11. Unit Weight and Void Content of 3in x 6in Samples from Pervious Concrete

Mix #5.........................................................................................................................143Table C.12. Mix Design of Pervious Concrete Mix #6 .................................................143


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Table C.15. Compressive Strength of Specimens from Mix #1~#6 at 7, 21, and 28 Days

Curing Periods.............................................................................................................145Table C.16. 28-day Compressive Strength of Specimens from Mix #1~#6 with VariousVoid Content ...............................................................................................................146

Table C.17. Measured and Calculated Permeability of Pervious Concrete Specimens fromLiterature Review ........................................................................................................159

Table C.18. Permeability Calculation Parameters in Falling Head Permeability Test ...161Table C.19. Permeability Test Data for Specimen with Void Content of 19.5% from Mix

#5 ................................................................................................................................162Table C.20. Permeability Test Data for Specimen with Void Content of 19.5% from Mix









#6 ................................................................................................................................166Table C.29. Void Contents of Specimens Compacted at Different Compaction Methods

....................................................................................................................................167


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CHAPTER 1

INTRODUCTION

1.1 Background

According to National Ready Mixed Concrete Association (NRMCA)1

,

pervious concrete is a special type of concrete with a high porosity used for concrete

flatwork applications that allows water from precipitation and other sources to pass

through it, thereby reducing the runoff from a site and recharging ground water

levels. It is also known as no-fines concrete and is composed of Portland cement,

coarse aggregate, water, admixtures, and little or no sand. In the past 30 years,

pervious concrete has been increasingly used in the United States, and is among the

Best Management Practices (BMPs) recommended by the Environmental Protection

Agency (EPA)2. By capturing stormwater and allowing it to seep into the ground,

pervious concrete is instrumental in recharging groundwater, reducing stormwater

runoff, and meeting U.S. EPA stormwater regulations. Other benefits of using

pervious concrete are: reduction of downstream flows, erosion and sediment;

reduction of large volumes of surface pollution flowing into rivers; decrease of urban

heat island effect; eliminating traffic noise; and enhancing safety of driving during

raining. The use of pervious concrete in building site design can also aid in the


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process of qualifying the building for Leadership in Energy and Environmental

Design (LEED) Green Building Rating System credits2.

Due to the advantages of pervious concrete, the utilization and construction

properties of pervious concrete have been studied by many researchers3,4,5,6. The

characteristic of high permeability of pervious concrete contributes to its advantage in

storm water management. However, the mechanical properties such as compressive

strength are reduced due to this character, limiting the application of pervious

concrete to the roads that have light volume traffic.

The advantage of pervious concrete can be enhanced by substituting some of

the cement with other materials, such as fly ash. Fly ash is one of the by-products of

coal combustion in power generation plants. Large amount of fly ash are discarded

each year, increasing costs for disposal. On the other hand, fly ash has been shown to

improve the overall performance of concrete, when substituted for a portion of the

cement7. Hence, when fly ash is used in pervious concrete, the occupation of landfill

space can be reduced and CO2 emissions generated during cement production can be

decreased, improving the sustainability of pervious concrete.

1.2 Objectives

The objective of this research is to investigate the effects on the important

engineering properties of pervious concrete with the use of fly ash. The physical

properties examined include compressive strength and permeability of pervious

concrete. The parameters that affect the strength and the hydraulic conductivity of


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pervious concrete will be analyzed. The potential use of pervious concrete containing

a large portion of fly ash will also be discussed.

1.3 Organization

This thesis consists of six chapters and four appendices. Chapter 1 is an

introduction of pervious concrete background and the study objectives. Chapter 2

presents literature reviews of pervious concrete, including benefits and problems, mix

designs, and properties of pervious concrete. Chapter 3 contains a brief literature

review of fly ash, introducing the application and effect of fly ash on concrete

properties. Chapter 4 introduces the laboratory mixing and laboratory tests, including

the selection of materials, mixing equipment, mix design, compaction method, and

test equipments. Chapter 5 elaborates on the test results, including void content,

compressive strength, and permeability of pervious concrete specimens. Chapter 6

summarizes the conclusions of the study, discusses the applicability of pervious

concrete that contains large amounts of fly ash, and provides with recommendations

for future work. Appendix A presents examples of pervious concrete experiments

taken from literature reviews. Appendix B illustrates the properties of pervious

concrete components used in this research. Appendix C presents the laboratory test

results. Appendix D shows codes of a program developed for pervious concrete mix

design.

1NRMCA CIP 38 pervious concrete brochure of National Ready Mixed

Concrete Association (NRMCA),

(Feb. 01, 2010).


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2National Ready Mixed Concrete Association (NRMCA),

(May 24, 2010).

3

Offenberg, M. (2008). Is pervious concrete ready for structural applications?Structure Magazine, February,p. 48.

4Johnston, K. (2009). Pervious concrete: past, present and future. Green

Building, Concrete Contractor,

(April. 24, 2010).

5Schaefer, V. R., Suleiman, M. T., Wang, K., Kevern, J. T., and Wiegand, P.

(2006). An overview of pervious concrete applications in stormwatermanagement and pavement systems. < http://www.rmc-

foundation.org/images/PCRC%20Files/Hydrological%20&%20Environmental%20Design/An%20Overview%20of%20Pervious%20Concrete%20Applications%20

in%20Stormwater%20Management%20and%20Pavement%20Systems.pdf> (Jun.16, 2010).

6Yang, J., and Jiang. G. (2003). Experimental study on properties of pervious

concrete pavement materials. Cement and Concrete Research, vol. 33, pp. 381-386.

7Headwaters Resources (2005). Fly ash in pervious concrete. Bulletin No. 29,

(May 21, 2010).


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CHAPTER 2

LITERATURE REVIEW OF PORTLAND CEMENT PERVIOUS CONCRETE

2.1 Introduction

Offenberg3stated that the first popular usage of pervious concrete was in post-

World War II England where it was used in two-story homes known as the Wimpey

Houses. During World War II, nearly two third of Britains houses had been

destroyed; and no new buildings had been constructed since 1939. Consequently, the

demand for housing was very high, causing a shortage of bricks. In this situation,

people were seeking alternate construction materials that were economical, reliable

and efficient. No-fine concrete was then used in some parts of the walls by Wimpey 8

architects and engineers to decrease the cost.

In the United States, pervious concrete has been used for almost 30 years

since it was first introduced in California4. In order to study the factors influencing

the performance of pervious concrete, researchers have conducted experiments varing

mix proportions of cement, water, coarse aggregate, sand, fly ash, and admixtures.

According to experimental studies6,7,9,10,11,12,13

, researchers have found that factors

that affect the mechanical properties of pervious concrete are void content, aggregate

to cement ratio, fine aggregate amount, coarse aggregate size, coarse aggregate type,

compaction energy, and curing period.


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2.2 Benefits and Problems

Due to the absence of fine aggregate, pervious concrete has high porosity,

which brings both benefits and drawbacks to construction.

2.2.1 Benefits

Since the pervious concrete pavement is permeable, water can be captured and

flow through the pavement during rainfall. In the mean time, free air is stored in the

pavement and allows the communication between the subsurface and the air. These

properties offer many advantages for pervious concrete.

2.2.1.1 Storm-water Management

One of the primary uses of pervious concrete is in storm water management.

Due to its high porosity, pervious concrete can capture stormwater and provide a path

for water to flow into the subsoil, helping to naturally adjust the ground water level.

Furthermore, instead of being carried into rivers and lakes by rain water, the residues

on pavement roads will be absorbed by pervious concrete or underneath soils, and

then degraded by microorganisms in soils2. Consequently, the pollution of water

resources could be decreased substantially, dramatically saving expense of storm

water management.

2.2.1.2 Heat Island Effect

Pervious concrete is much cooler than asphalt and conventional concrete. First

of all, the light color reflects more ultraviolet rays from sun and absorbs less heat than


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asphalt. Secondly, the voids in pervious concrete allow it to store less heat than

conventional concrete does. This character benefits the districts in hot weather

climates. For instances, the group of National Center of Excellence for Sustainable

Materials and Renewable Technology at Arizona State University recommended the

utilization of pervious concrete for minimizing the urban heat-island effect14

. Houston

Advanced Research Center (HARC)15

published a report titled Cool Houston! A

Plan for Cooling the Region, in which the benefits of reducing heat island effect in

high density urban areas by using pervious concrete has been introduced.

2.2.1.3 Traffic Benefits

Pervious concrete shows several advantages on traffic. Firstly, the large

amounts of voids in pervious concrete are beneficial to reducing traffic noise. As

stated by Kim and Lee16

, pervious concrete is applied for sound barriers or

pavements to absorb traffic (tire) noise and reduce sound wave reflection. To

investigate this property of absorption, Kim and Lee16

created a model to study the

acoustic absorption ability of pervious concrete, considering the gradation and shape

of aggregates and void content on pervious concrete pavement. The results calculated

by the modeling were compared with experimental and statistical results from

previous studies. All results illustrated that the maximum acoustic absorption ability

was increased with void content and was hardly affected by the shape of aggregate

when pervious concrete was compacted well. Secondly, pervious concrete enhances

the safety of driving during raining because of the elimination of ponding.


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2.2.1.4 LEED

The usage of pervious concrete in building site design can also aid in the

process of qualifying for Leadership in Energy and Environmental Design (LEED)

Green Building Rating System credits. LEED was developed by the U.S. Green

Building Concil (USGBC). It provides a concise framework for identifying and

implementing practical and measurable green building design, and construction.

LEED for New Construction and Major Renovations version 2.2 has maximum total

of 69 points, in which concrete can earn up to 25 points. In addition, with the usage of

fly ash or other recycled materials in pervious concrete, up to 5 more credits could be

earned2.

2.2.2 Problems

High porosity is the necessary condition that makes pervious concrete

permeable, and is the main beneficial characteristic of pervious concrete. However it

can cause problems that limit the utilization of pervious concrete.

2.2.2.1 Compressive Strength

The bearing capacity of pervious concrete is decreased because of the

existence of large amounts of air voids. The low strength limits the utilization of

pervious concrete to parking-lots, side walks, and other low-volume traffic roadways.

Obviously, high porosity and strength are two incompatible features of pervious

concrete. This disadvantage initiates the study on pervious concrete aim to improve

its compressive strength while maintaining the relative high porosity.


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2.2.2.2 Freeze-thaw Durability

The usage of pervious concrete in a freeze-thaw environment is also a concern,

especially in the northern area of the United States, which are districts experiencing

cold weather. The pervious concrete is more vulnerable to be destroyed under freeze-

thaw weather. Research has been done to study the suitability of pervious concrete in

this type of climate. Regulations have been made to ensure the applicability of the

pervious concrete. For example ASTM C 666M-0317

Standard Test Method for

Resistance of Concrete to Rapid Freezing and Thawing specifies the standard test

method to determine the resistance of concrete specimens to rapidly repeated cycles

of freezing and thawing in the laboratory following procedure A,Rapid Freezing and

Thawing in Water, and procedure B,Rapid Freezing in Air and Thawing in Water.

2.2.2.3 Abrasion

Abrasion of pervious concrete may limit its utilization. Raveling may happen

if aggregate is not sufficiently coated with cement paste. Other factors such as low

Water/Cement (W/C) ratio, dry weather, especially the rough surface also make

aggregate vulnerable to the abrasion. Theoretically, the abrasion of surface may make

surface more uneven and worsen abrasion over time. However, Hein and Schindler18

studied field projects constructed on the Auburn University campus, and found that

after curing of pervious concrete, about only 10% of surface aggregates were

displaced. But remaining surface was smooth enough as for a sidewalk and had

performed very well for three years.


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2.2.2.4 Clogging Maintenance

Clogging is an unavoidable problem due to the existence of voids in pervious

concrete. The open voids are highly prone to be clogged during the utilization of

pervious concrete pavement over time. The U. S. EPA recommends that cleaning

need to be done regularly to prevent clogging2. Two methods of cleaning are

currently used: vacuum sweeping and high pressure washing. Even though cleaning is

performed regularly, not all contaminants are removed and the performance of

pervious concrete may lessen over the years. Moreover, the residues may cause

contamination of the water that runs through the pervious concrete. Hence,

stormwater testing is recommended in critical situations to preserve the quality of

ground water and inspect the permeability of pervious concrete.

2.2.2.5 Cost

Typically, the initial cost of pervious concrete is greater than that of

conventional concrete. However, because the lifespan of pervious concrete is longer

than that of the regular concrete2, some of the added cost is offset. The high initial

cost of pervious concrete is partly caused by the construction of the subgrade. A thick

layer of open gravel subgrade is usually installed under the pavement to provide the

storage and drainage of water. With such subgrade, pervious concrete normally can

perform very well even when built on clay soils. An example is presented by Dietz19

,

who tested a subgrade of 10-in. thick layer of open graded gravel with undrained

system below. The subgrade showed good storage and drainage conditions. In general,

a thick layer of coarse aggregate provides greater storage capacity and a longer time


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11

allows water to exfiltrate to the native soils before underdarin flow would begin19

.

But the construction of subgrade increases the total cost of the pervious concrete

pavement. Another reason is the increased maintenance cost for pervious concrete

pavement after construction. As stated before, clogging problems need to be solved to

ensure the serviceability of pervious concrete.

2.3 Components of Pervious Concrete

Pervious concrete is mainly composed by coarse aggregate, cement, and water.

Small amount of fine aggregate may be added to obtain higher compressive strength.

Other admixtures such as High/Middle Range Water Reducer (HRWR, MRWR),

water retarder, viscosity modifying admixtures, and fibers are usually used. In some

cases, fly ash is used as a substitute for Portland cement to enhance the environmental

friendliness of pervious concrete.

2.3.1 Coarse Aggregate

Coarse aggregate is the main component of pervious concrete. The gradation,

size, and type of coarse aggregate have been found to affect the character of pervious

concrete6,9,10,11. In practice, river gravels that have size number of 8 (ASTM C 33 20)

are widely used in construction. Other sizes of river gravels and limestone have been

used in laboratory tests to study the effect of coarse aggregate11

.


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2.3.2 Fine Aggregate

A fine aggregate is sometimes used in pervious concrete to improve the

mechanical capabilities of pervious concrete. On the other hand, the permeability will

typically decrease when fine aggregate is added. Wang et al.10

studied pervious

concrete with a fine aggregate amount of 7% of total aggregate by weight. Wangs

tests illustrated that the compressive strength and freeze-thaw ability of pervious

concrete were significantly improved with addition of fine aggregate while

maintaining adequate water permeability. However, the amount of fine aggregate is

recommended to be limited within 7% of the total aggregate by weight so that

permeability is satisfied10

.

According to the ASTM C 3320

, the fine aggregate shall consist of natural or,

subject to approval, other inert materials with similar characteristics, or combinations

having hard, strong, durable particles. The amount substances such as clay lumps coal

and lignite, shale, and other deleterious substance should be limited within a range

individually, and the total amount should be less than 2% by dry weight. Soundness

loss should be less than 10% by weight. The fine aggregate should be free from

organic impurities.

2.3.3 Cement

Portland cement is another main component of pervious concrete. Type I/II

cement is normally used in pervious concrete9,10,11,12

. The content of cement is

dependent on the amount and size of coarse aggregate and the water content. Various


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13

amounts of cement are recommended by different agencies and will be introduced in

section 2.7.1.

2.3.4 Fly Ash

Fly ash can be used in pervious concrete as a substitute for a portion of the

cement. Two types of fly ash which are Class C and Class F fly ash are both able to

used in pervious concrete. Currently, fly ash can replace 5-65% of the Portland

cement2 in conventional concrete. However, according to the publication from

Headwaters Resources7

, California Ready Mix Concrete Association (SCRMC)

recommended amount of ASTM C-618 fly ash is only 50-116lb/yd3

in pervious

concrete. The advantage of using fly ash is obvious: fly ash is a by-product of coal

burning in power plants, its utilization saves the energy required to produce the

cement. In addition, fly ash improves the flowability and workability of concrete.

2.3.5 Water

Water is a crucial component in pervious concrete. Wanielista and Chopra11

discussed the importance of adding appropriate amount of water in pervious concrete

mix. Enough water should be added so that cement hydration is thoroughly developed.

However, too much water will settle the paste at the base of the pavement and clog

the pores. Meanwhile, too much water increases the distance between particles,

causing higher porosity and lower strength. Wanielista and Chopra11

stated that the

correct amount of water will maximize the strength without compromising the

permeability characteristics of the pervious concrete.


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2.3.6 Admixtures

Admixtures are sometime necessary for pervious concrete to obtain good

properties. Typical admixtures used in pervious concrete include HRWR, MRWR,

water retarder, viscosity modifying admixtures, air-entraining and fibers. The

admixtures should follow standards of ASTM C 49421

(chemical admixtures) and

ASTM C 26022(Air-entraining admixtures).

2.3.6.1 High/Middle Range Water Reducer

Based on experimental results, less water is used in pervious concrete than in

regular concrete2,9,18

. One of the reasons is too much water causes settlement of

cement at the bottom resulting in clogging. To decrease the water content, a HRWR

or MRWR is often used. The dosages of water reducer used in pervious concrete are

various and should closely follow manufacturers recommendation.

2.3.6.2 Water Retarder

The National Ready Mixed Concrete Association reports that because of the

rapid setting time associated with pervious concrete, retarders or hydration-stabilizing

admixtures are commonly used2. Water retarder can extend setting time so that the

hydration of cement is fully developed.

2.3.6.3 Viscosity Modifying Admixtures

Compared to regular concrete, pervious concrete is very dry and hard to cast.

However with the usage of viscosity modifying admixtures, the workability can be

highly improved, and pervious concrete can be more manageable18. In a field project,


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Hein and Schindler18

found that The use of water reducing admixtures in

combination with viscosity modifying admixtures significantly reduced or eliminated

most of the previous difficulties experienced placing pervious concrete pavements.

Since the usage of viscosity eliminated hard physical labor and improved the

smoothness and quality of pavement, Hein and Schindler claimed it as a major

milestone in facilitating successful placement of quality pervious concrete

pavements.

2.3.6.4 Air-entraining Admixtures

Air-entraining admixtures can be used in pervious concrete to improve its

freeze-thaw durability. Air-entraining admixtures can produce micro-closed air holes,

which can flexibly respond to the forces generated by freeze-thaw cycles. These

micro air bubbles are different from the voids in pervious concrete, which are open

holes and do not functional to sustain freeze-thaw forces.

2.3.6.5 Fibers

Fibers can be used in pervious concrete if higher compressive strength is

required. Experiments by Schaefer et al.23showed that adding latex fibers increases

strength of pervious concrete; Yang and Jiang6used organic polymer fibers and found

that they enhanced the strength of pervious concrete greatly. However, they typically

also cause a decrease in hydraulic conductivity.


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2.4 Important Properties of Pervious Concrete

Permeability, compressive strength, freeze-thaw durability are important

properties of pervious concrete. They are affected by many factors such as water

content, void content, aggregate gradations, W/C ratio, and A/C ratio. Research has

been carried out to study the effect of different factors. In this research W/C ratio

stands for Water/total Cementitious Material ratio for simplification. A/C ratio stands

for total Aggregate/total Cementitious Materials ratio.

2.4.1 Permeability

High permeability is the primary characteristic of pervious concrete. Based on

previous studies24,25,26,27

two permeability tests, the falling head tests and constant

head tests were both used to measure the hydraulic conductivity of pervious concrete

samples taken from sites or made in labs. Some lab testing also simulated the

conditions of pervious concrete in actual applications. Experimental and field tests

found that the typical permeability is larger than 0.1cm/sec or 140in/hour10

, which is

considered as the lower limit of pervious concrete permeability.

McCain and Dewoolkar26

published a study on pervious concrete, in which

falling head permeability tests were carried out on three sets of specimens with

diameter 3 inches, 4 inches, and 6 inches, respectively. The falling head permeability

tests also simulated the situation of winter surface, which was covered by sand-salt

mixture. The results showed that the hydraulic conductivity ranged from 0.68cm/s to

0.98cm/s. One significant and special contribution of this article was the study on the


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17

decrease of permeability by simulating the winter surface. The results illustrated 15%

average reduction on hydraulic conductivity. However, the permeability was still in

the allowable range (greater than 0.1cm/s).

Crouch et al.27 used a triaxial flexible-wall constant head permeameter to

measure the permeability of pervious concrete in the range of 1 to 14,000 inches/hour

(0.001 to 10 cm/sec). Crouch et al. found the constant head permeability was a

function of three factors: effective air void content, effective void size, and drain

down, where drain down is a result of too much paste for the applied compactive

effort or the paste being too fluid, sealing the lower surface of pervious concrete

sample27

.

Montes and Haselbach25

compared the hydraulic conductivity of pervious

concrete samples taken from three different field-placed slabs using a falling head

permeameter system. To investigate the factors affecting permeability of pervious

concrete, samples were collected with different W/C ratios and A/C ratios. Based on

previous studies7,24,25,26, the average porosity of the samples range from 15% to 30%

is typical for pervious concrete. The results indicated that the hydraulic conductivity

is dependent on the porosity. By comparing experimental results with the calculated

values from the equation, Montes and Haselbach25

studied the relationship between

porosity and hydraulic conductivity and found most fitted value of =17.9 2.3

(Figure 2.1) in the Carman-Kozeny equation: ks = [p3/(1-p)

2], where: ks = the

saturated hydraulic conductivity, p = porosity of pervious concrete (adapted from

Montes and Haselbach25). The effect of cementitious material and the non-spherical

shape of particles had been considered in this equation.


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Figure 2.1. Model Resulting from the Nonlinear Fitting of the Saturated HydraulicConductivity and Total Porosity Data to the Carman-Kozeny Equation

25


used the Ergun equation to analyze the flow

condition inside the pervious concrete samples. The Ergun equation has the form: f =

150/Re+ 7/4, where f is a dimensionless friction factor, Re is a modified Reynolds

number which indicates the particular fluid porous media flow situation. The results

of Ergun model calculation presented for pervious concrete samples with various

porosities and saturated hydraulic conductivities were presented by Montes and

Haselbach25(Figure 2.1). The trial results indicated that most of the samples were in


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the laminar flow region. However, the flow regime may fall into the transition region

for higher porosity samples impacted by higher hydraulic head25

.

Figure 2.2. Plot of the Ergun Equation and Values Calculated Using the Falling HeadExperimental Data from Samples Calculated with Dp = 0.1, Dp = 0.3, and Dp =

0.6.(adapted from Montes and Haselbach25

)Note: Dp=0.1, 0.3, and 0.6cm can be interpreted as particles with different average

diameters and sphericities so that Dp would be equal to 0.1, 0.3, or 0.6 cm.


established the equation between hydraulic

conductivity and porosity of pervious concrete sample as kS= 18 p3

/ (1-p)2

, which

show a high coefficient value between experiment and calculated results. However,

they also claimed the validation of the equation was for the pervious concrete samples

in that specific study, in which the size of aggregate was 3/8 inches ~ 5/8 inches, and


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the porosity ranged from 15% to 32%. Although the application of equation is limited,

the study showed the flow regime in pervious concrete is in the laminar flow region,

in which Darcys law can be applied. This study is significant because it verified the

validation of Darcys law, which is assumed to be valid in most study of pervious

concrete permeability.

All articles stated above considered the permeability of pervious concrete in

freshly cast condition. Researchers rarely discussed the performance of pervious

concrete that had been used for a while or had become partially clogged. Haselbach et

al.

24

studied the permeability of pervious concrete in partially clogged condition.

Considering the in-situ pervious concrete pavement, clogging is one of the important

concerns because it will decrease the porosity of pervious concrete, decreasing

permeability. In order to study the effect of clogging, Haselbach et al.24

started with

predicting the permeability of pervious concrete with formulas based on empirical

statistics and theoretical analysis. Then experiments were conducted to simulate the

rainfall and clogging situation, and the results were used to compare with predicted

values. The comparison showed good agreement between experimental results and

calculated values, verifying the validity of the prediction. The specialty of this

research is that it proposed models to predict the permeability of pervious concrete

under the worst condition of clogging, which is usually ignored in most research.

2.4.2 Compressive Strength

According to ASTM C 3928

, a minimum compressive strength of 300psi is

required for pervious concrete. According to field and laboratory tests, pervious


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concrete compressive strength regularly falls in a range of 400psi ~ 4,000psi (2.8MPa

~ 28MPa). But the common strength is from 600psi to 1,500psi (4MPa to 10MPa).

Laboratory studies have found compressive strength ranges from 600 psi to 3,600 psi

(4 MPa to 25 MPa)9,10,11.

Wanielista and Chopra11

summarized previous studies on compressive

strength of pervious concrete and stated that researchers agreed that factors affect

pervious concrete compressive strength included: A/C ratio, W/C ratio, coarse

aggregate size, compaction, and curing. Researchers disagree as to whether pervious

concrete can consistently attain compressive strengths equal to conventional

concrete.

2.4.3 Freeze-thaw Durability

Freeze-thaw durability is a crucial property to evaluate the suitability of

pervious concrete in cold weather. Freeze-thaw deterioration happens when concrete

is more than 91% saturated, which is generally true for concrete surfaces. When water

freezes, its volume will increase. The expansion of volume generates large pressures,

which act on concrete. When the pressure is in excess of the tensile strength of

concrete or mortar layer at a surface, cracking and scaling will occur.

Although some field projects indicated that pervious concrete performed well

in freeze-thaw situations, it must be used carefully in cold weather regions. The

NRMCA29

recommends the utilization of pervious concrete in different areas that

have various weather conditions. Table 2.1 shows the classification of different

districts and the suitability of using pervious concrete:


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a thick layer of 8 to 24 inches (200 to 600mm) of open graded stone base, saturation

can be effectively avoided23

.

In order to test the freeze-thaw resistance of pervious concrete, some

researchers did tests on saturated pervious concrete following procedure A, Rapid

Freezing and Thawing in Waterof ASTM C 66617

, requiring less than 5% mass loss

after 300 freeze-thaw cycles10

. However, the fully saturated condition in procedure A

is very severe and not representative of field conditions29

. Theoretically, partially

saturated pervious concrete performs well in freeze thaw region because the voids in

concrete can provide sufficient space for water to move. However, a fully saturated

condition may exist; and pervious concrete should be avoided in regions where this

situation is most likely to happen.

Schaefer et al.23

stated the failure mechanism of pervious concrete when

subjected to freeze-thaw cycles is either a result of aggregate deterioration or cement

paste matrix failure. Aggregate failure is seen by the deterioration or splitting of the

aggregate where a portion (usually 15%) of an aggregate particle becomes separated

from the concrete. Cement paste failure is observed by the raveling of entire pieces of

aggregate from the concrete. According to the experimental results presented by

Schaefer et al., in general, mixes containing limestone (i.e. Mix 3/8-LS) failed by the

deterioration of the aggregate; however, mixes containing the smaller size No. 4 river

gravel failed due to aggregate deterioration and splitting23

.


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2.4.4 Modulus of Elasticity

Dynamic modulus of elasticity is another important mechanical characteristic

of pervious concrete. The elastic modulus shows the resistance performance of

pervious concrete to fatigue, and is significant for evaluating the durability of

pavements, which is one of the most important indices to evaluate the pervious-

concrete lifespan.

Crouch et al.9 tested the static moduli of four different pervious concrete

mixes with various aggregate sizes and gradations. The results showed that the static

elastic modulus was inversely proportional to the void content. And the optimum void

range which is from 23% to 31% happened in the mix with uniform gradation.

Crouch et al.9 found that the static elastic modulus decreased with increasing

aggregate and decreasing paste. No effect of aggregate sizes on static elastic modulus

has been shown.

2.5 Factors Affect Compressive Strength and Permeability of

Pervious Concrete

The compressive strength and permeability of pervious concrete have been

investigated and their relationships to void content were found. Higher void content

usually leads to higher permeability and lower compressive strength. Other factors

have also been found through experiments. These factors include aggregate, W/C

ratio, A/C ratio, fly ash, compaction energy9,23,27

.


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2.5.1 Effect of Void Content

Schaefer et al.23

studied effects of different proportions of mixture on the

properties of pervious concrete, and provided results to show the relationship between

strength, void content and permeability for several trial mixes of pervious concrete.

The experimental results showed that the permeability increased and compressive

strength decreased with increasing void content. The relationship is illustrated in

Figure 2.3. As shown, when the void content increased from 15% to 32%, the 7-day

compressive strength of pervious concrete decreased from 3,200psi to 1,300psi, while

the permeability increases from 50in/hour to 2,000in/hour. As can be seen in the

figure, the effect of void content on the measured permeability increased when the

void content increased from about 25% to 32%. Their tests showed that the increase

of permeability became more apparent when the void content was relatively large,

while the compressive strength as a function of void content remains linear.


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Figure 2.3. Relationship between Strength, Void Content and Permeability for

Several Trial Mixes of Portland Cement Pervious Concrete23

Crouch et al.27 also studied the correlation between void content and

permeability in both laboratory and field cored specimens. The results showed

agreement with those from Schaefer et al.23

. The average values illustrated high

strength of bond between void content and permeability with correlation coefficient

0.9737. In addition by comparing the laboratory results with experimental results

from prior studies, Crouch et al.27 found that the permeability at low void content

showed high consistency with the previous experimental results30,31

than those at high

void content. This indicated compressive strength values might be more consistent at

low void content.

Void content has been found as the primary factor that determines the

properties of pervious concrete. It was found to be determined from the concrete mix,

including amount of aggregate, cementitious materials, and water2.


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2.5.2 Effect of Aggregate

The effect of aggregate on compressive strength and permeability of pervious

concrete comes from the coarse aggregate size, type, gradation, and the percentage of

fine aggregate.

2.5.2.1 Effect of Coarse Aggregate Type, Size and Gradation

Mulligan32

stated that since cement bond is limited in pervious concrete and

the aggregate rely on the contact surfaces between one another, the aggregate with

higher stiffness such as granite or quartz would have higher compressive strength

than a softer aggregate such as limestone.

Besides the effect of aggregate type, the size of aggregate is another important

factor for compressive strength and permeability of pervious concrete. Yang and

Jiang6 conducted experiments on pervious concrete mixes having various aggregate

sizes. The results showed that the compressive strength was improved by decreasing

the aggregate size. Yang and Jiang analyzed that the reason that smaller aggregate

size generated higher compressive strength might because it enlarged the bond area

between aggregates. However, decreasing aggregate size also resulted in a decreasing

in the permeability.

The gradation of aggregate also affects the properties of pervious concrete.

Crouch et al.9

found that a more uniform gradation deduced to slightly higher

effective void content. Furthermore, the compressive strength was higher at the same

void content in mix that having uniform gradation. The effect of gradation on

compressive strength and permeability was also studied by Wang et al.10. They


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29

0.22 and 0.27, and suggested using the lower value, if workability could be

maintained. In contrast, in an actual applicaiton published by NRMCA29

W/C ratio up

to 0.55 was used.

W/C should be large enough so that hydration of cementitious materials can

fully develop. Yang and Jiang6pointed out that the cement bond should provide good

connection between aggregate so that the failure is by splitting of the aggregate, in

which way the mixture most effectively works. However, too much water may

decrease the strength, which is known to be the case in conventional concrete.

Furthermore, excessive water will result in settlement of paste, sealing the bottom of

pervious concrete.

2.5.5 Effect of fly ash

Generally, fly ash is realized to be able to decrease the permeability of

conventional concrete, increase freeze-thaw durability of concrete, and improve the

later-age strength of concrete. The effect of fly ash will be thoroughly discussed in

Chapter 3.

2.5.6 Effect of Compaction Energy

Compaction energy has been shown by several researchers12,13,23,27

to affect

the compressive strength, freeze-thaw durability, and permeability.

Suleiman et al.12

found the significant effect of compaction energy on freeze-

thaw durability and compaction failure mode of pervious concrete based on the

experiments conducted by Schaefer et al.23

. The specimens compacted at lower


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energy sustained less cycles of freeze-thaw (110 cycles) at failure than those (failed at

153 cycles and 196 cycles) compacted at higher energy. Suleiman et al.23

also found

an interesting phenomenon that samples compacted at regular compaction energy

failed through the aggregate, while samples compacted at lower energy failed through

both aggregate and paste.

Crouch et al.27

studied the effect of compaction energy on permeability by

comparing the experimental results of specimens with the same mixture design while

compacted at six different compaction efforts. By investigating the effective air void

content and the permeability of both in field and laboratory pervious concrete

mixtures, Crouch et al. found that larger compaction effort resulted in less effective

void content of pervious concrete.

To further study the effect of compaction energy, various compaction methods

were used and compared by Rizvi et al.13

. The compaction method is determined

from the compaction equipment, compaction cycles, and compaction forces. Widely

used compaction equipment includes standard tamping rod, standard Proctor hammer

in laboratory and compact roller in field.

In the research reported by Rizvi et al.13

, five different consolidation

techniques as illustrated in Table 2.2were used to cast identical 6in x 12in cylinders.

For each consolidation technique, samples were prepared for 7, 14 and 28 day

compressive strength testing, permeability, and air void testing. The results revealed

the optimum compaction technique was a standard Proctor hammer 10times/layer for

2 layers. Samples compacted by this method achieve both relatively high compressive

strength and high permeability. In addition, the cylinders compacted by this method


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31

also achieved the most consistent results with the least variance for compressive

strength and relatively low standard deviations for permeability and air void13

.

Method Layers

Drops

/Tamping

rod/layer

Voids

(%)

28Days

Compressive

Strength (MPa)

Permeability

(cm/s)

Rod 3 25 18.5 18.3 0.719

Rod 3 15 21.2 21 1.03

Rod 3 5 21.8 15.7 1.027

ProctorHammer

2 10 19.9 17.5 0.584

Proctor

Hammer 2 20 17.2 20.7 1.041Table 2.2. Compaction Method Conducted by Rizvi et al.

13

Compared to the lab testing, the field compaction methods have been less

studied. However, Hein and Schindler18

, when reviewing the projects on Auburn

University campus, mentioned the different compaction results of using vibrating

roller and hand roller in field. By observing these field projects, he stated that

vibrating roller appeared to seal the surface and collapse the pores, providing too

great a compactive effort. The hand roller guided by side forms seemed to provide the

smoothest finish.

2.5.7 Effect of Fibers

The positive effect of fibers has been shown in many studies. Yang and Jiang6

added polymer fibers into the pervious concrete and obtained increased compressive


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strength. The increase of compressive strength might because the fiber enhanced the

binder6. In addition, the permeability was unaffected, which differed to the effects of

other factors and therefore enhanced the advantage of adding fibers in pervious

concrete.

2.5.8 Effect of Other Factors

Some factors such as specimen size and testing method have also been studied

in a few cases. Although these factors are not critical to determine pervious concrete

properties, they were discussed and may be considered in some situations.

The size of specimen is not usually considered because they are generally

compacted to the standard size defined by national codes. For example, 4in x 8in

cylinders are normally used in the United States for compressive strength test; 6in x

12in cylinders were cast in the University of Waterloo in Canada, while rectangular

cylinders were used in China. To study the impact of diameter on cylinder samples,

McCain and Dewoolkar26tested the compressive strength on three sets of specimens

with diameter of 3 inches, 4 inches, and 6 inches. For each set, three identical

specimens were tested. The compressive strength drawn from these experiments

ranged between 650psi (4.5MPa) and 1,100psi (7.6MPa). Even for specimens that

were the same size, the compressive strengths were different with 150 to 260psi. The

experimental results showed that the effect of specimen size was unpredictable.

However, the specimens with 4 inches diameters showed higher average compressive

strength compared to the 3 inches and 6 inches diameters specimens. However, the


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effect of specimen size could not be distinguished from the effect of inconsistent

casting of specimens due to the limited experimental results.

Another factor that affects the compressive strength of pervious concrete is

capping. Capping is sometimes used in compressive strength test to smooth the

surface of pervious concrete specimen, reducing the effect of stress concentration

consequently. The studies on pervious concrete conducted by Kevern33

showed that

the specimens with sulfur capping compound has higher compressive strength than

those without capping.

2.6 Standard Test Methods

Some tests methods that are required for regular concrete may be unnecessary

for pervious concrete. For example, since pervious concrete has low water content

and lower fluidity, the slump test is not informative.

Currently, standard test methods for field permeability, compressive strength,

hardened concrete density and porosity, and flexural strength of pervious concrete are

under development by ASTM C 09/4934

. Only ASTM C 1688 with title of Fresh

concrete Density (Unit Weight) and Void Contenthas been published35

. Obviously,

the progress of developing standard test methods for pervious concrete is only at

beginning. No standard ASTM test procedure has been suggested to measure the

entrained air content for pervious concrete. In fact, before the finalization of

testing/mixing methods for pervious concrete, people are using those designed for

conventional concrete, even those methods may not be appropriate in many situations.


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2.7 Pervious Concrete Design

This section introduces pervious concrete mix design, pervious concrete

pavement structure and hydraulic design. The mix design of pervious concrete is

concerned with the properties of pervious concrete used in the pavement; while the

pervious concrete pavement design is the process of designing the whole system of

pavement including the pavement surface and the subgrade layer.

2.7.1 Pervious Concrete Mix Design

Pervious concrete mix design should generate batches that satisfy compressive

strength and permeability requirements. Typical mix designs of pervious concrete

have been recommended by different agencies such as National Ready Mixed

concrete Association, the Southern California Ready Mix concrete Association, and

the Euclid Chemical Company. The recommended mix designs are shown in Table

2.3, Table 2.4, and Table 2.5. The examples of mix design in laboratory experiments

and in field projects have been done and are listed in Appendix I.


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Material Amount

(pcy)

Cementitious Materials 450 700 lbs

Aggregate 2000 2500 lbs

W/C by Mass 0.27 0.34

A/C by Mass 4 4.5 : 1

Table 2.3. Recommended Typical Mix Design by National Ready Mixed Concrete

Association36

Material Amount (pcy)

Compacted Voids 10%

Cement 580lbs

ASTM C-618 fly ash 50 116 lbs

Total Cementitious Materials 630 696 lbs

Aggregate 27 ft3

Table 2.4. Recommended Typical Mix Design by the Southern California Ready MixConcrete Association (adapted from

1)

Material Amount (pcy)

Cement 600lbs

Coarse Aggregate 3/8 Limestone 2600 lbs

Water 160 lbs

W/C by Mass 0.27

Table 2.5. Recommended Typical Mix Design by the Euclid Chemical Company37


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As shown, there is no single accepted mix design for pervious concrete. Since

less water is used than typical for conventional concrete, pervious concrete appears

drier and more sensitive to the actual water content. Water reducer and water retarder

are used in most cases. In addition, the amount of water and other materials are varied

with the mixing condition and may need to be adjusted during mixing process. Hence,

the mixing of pervious concrete should be done by a crew who has been trained in a

certification program.

2.7.2 Pervious Concrete Pavement Hydraulic Design

The purpose of hydraulic design is to provide a pavement system in which

water can easily pass through the top layer, be temporarily stored in the subgrade

layer and freely enter a shallow groundwater.

North Carolina Department of Environment and Natural Resources

(NCDENR)38

introduced process of hydraulic design for permeable pavement as

illustrated below:

(1) Select Design Storm

(2) Determine Water Storage Capacity of Pavement

(3) Select Exfiltration Time

(4) Calculate Drawdown (Exfiltration) Time

(5) Compare Actual Drawndown with Design Exfiltration

Following this process, designer can calculate the desirable pavement open

space, which can produce the required drainage at a certain rainfall rate. The

pavement is then designed to have this open space.


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In addition, Malcolm et al.39

developed a program to do the hydraulic design

based on the pervious concrete hydrological analysis program. Input parameters of

the program contains trial thickness of pervious concrete and gravel base, porosity of

pervious concrete and gravel base, local rainfall information, and adjacent areas

which will drain onto pervious concrete. After analyzing the input parameters, the

software can generate a chart to model the flowing situation of rainfall with elapsed

time. Hence, a satisfactory thickness of the pavement and subgrade layers can be

determined by examining the flowing situation.

2.7.3 Pervious Concrete Pavement Structural Design

NCDENR also developed a structural design worksheet for permeable

pavements40

. According to the worksheet, the structural design of pervious concrete

includes four elements: total traffic, in-situ soil strength, environmental elements, and

actual layer design. The primary purpose of the structural design is to examine and

finalize the thickness of subgrade layer. The top layer of pavement is set to the

pervious concrete block, which is usually 6 inches or more. The thickness of pervious

concrete pavement is greater than those of regular concrete that is 4 inches in

normal11

because pervious concrete has lower compressive strength than regular

concrete.

Before beginning the structural design, the thickness of each layer has been

determined from the hydraulic design. Only the thickness of subgrade layer will be

checked in the structural design to determine whether or not the pavement is strong

enough. A formula is given to determine a calculated Structural Number (SNcalc),

7/23/2019 FLY ASH FLY ASHFLY ASHFLY ASH

FLY ASH FLY ASHFLY ASHFLY ASHFLY ASHFLY ASHFLY ASH

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