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dissertation entitled

RECYCLING OF REACTIVE AND REINFORCING BY—PRODUCTS IN
CONCRETE CONSTRUCTION: NEW DEVELOPMENTS AND
ASSESSMENT OF LONG—TERM PERFORMANCE

presented by

Abdulrahman M. Alhozaimy

has been accepted towards fulﬁllment
of the requirements for

PhAI )- _ degree in MAJ-lmnm'l“ l
6S) ”01“)

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Wampum-9.1

 

 

 

RECYCLING OF REACTIVE AND REINFORCIN G BY-PRODUCTS IN
CONCRETE CONSTRUCTION: NEW DEVELOPMENTS AND
ASSESSMENT OF LONG-TERM PERFORMANCE

By

Abdulrahman M. Alhozaimy

A DISSERTATION

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Civil and Environmental Engineering

1993

 

ABSTRACT

RECYCLING OF REACTIVE AND REINFORCING BY—PRODUCTS 1N
CONCRETE CONSTRUCTION: NEW DEVELOPMENTS AND
ASSESSMENT OF LON G~TERM PERFORMANCE

By

Abdulrahman Alhozaimy

The main thrust of this research was to enhance concrete performance through
judicious utilization of solid wastes. Coal ﬂy ash was used to react with cement
hydration products in order to enhance the pore system characteristics and chemical
stability of the concrete structure. Plastics and tire were considered as reinforcing
inclusions and light-weight aggregates for improving the toughness characteristics and
cracking resistance of concrete. Statistical methods of experimental design and analysis
were employed in order to derive reliable conclusions.

Fly ash was shown to be highly effective in enhancing the capillary pore structure
and chemical stability of concrete under sulfate attack and alkali—aggregate reaction.
These improvements are strongly dependent on ﬂy ash quality and content; the optimum
replacement level of cement with ﬂy ash was observed to depend on the ﬂy ash qualities.
Permeability of concrete was found to be more sensitive to ﬂy ash actions in concrete
than strength. Methods were suggested to evaluate ﬂy ash qualities in order to assess its
potential for enhancing concrete impermeability and resistance to chemical causes of

deterioration.

The capabilities of recycled plastic particles to bridge across cracks in brittle
concrete matrices and enhance their toughness characteristics and cracking resistance
were conﬁrmed experimentally. In light—weight concrete, partial replacement of ﬁne
aggregate with recycled plastics led to improved toughness characteristics and impact
resistance. In normal—weight concrete, small addition of recycled plastic particles led to
enhanced shrinkage crack control and desirable ductility characteristics, with other
mechanical and durability characteristics maintained at desirable levels. Mixed plastic
waste was found to perform well in concrete. In the case of tire inclusions, the
dimensional instability of tire particles was found to be a problem, and it was overcome
through application of polymeric coatings. The reinforcing action of tire inclusions in
normal-weight concrete was conﬁrmed through measurement of restrained shrinkage

crack widths and toughness characteristics.

 

 

 

IN THE NAME OF GOD
THE COMPASSIONATE THE MERCIFUL

 

 

DEDICATED TO

THE MEMORY OF MY FATHER,

 

MY MOTHER, BROTHERS, SISTERS,

MY WIFE (NORA) AND DAUGHTERS (NADA & SARAH)

 

iv

 

 

 

 

ACKNOWLEDGEMENTS

All praise and thanks are due to Allah, Lord of the Universe, for his merciful
divine direction throughout my studies.

I would like to thank professor Dr. Parviz Soroushian for his intellectual
inspiration, guidance, and encouragement. My thanks are also to members of the guidance
committee: Dr. Nicholas Altiero, Dr. Ronald Harichandran, and Dr. Gerald Ludden.

The ﬁnancial support of King Saud University, Riyadh, Saudi Arabia, for my
graduate study is sincerely appreciated. Financial support of this research was provided
by the US. EPA, Coalition Technologies Ltd. , and the Research Excellence Fund of the
State of Michigan. I would also like to express my appreciation to Mr. Charles H. Lee
for his sincere help and interest in performing some of the experimental work.

I would like to express my thanks to my friends Dr. Faiz Mirza, Dr. Abdulaziz
Alhamad, Dr. Hussain Alghtani and Dr. Atef Tlili for being there whenever I needed
them during my MS. and Ph. D. studies at Michigan State University.

My thanks and deep appreciation go to my family members in Saudi Arabia,
especially, my mother, brothers and sisters for their prayers, love and continuous
encouragement. Last but not least, I would like to express my special appreciation and
gratitude to my wife Nora for her care, patience, emotional support, and constant

encouragement. I am also grateful to my daughters Nada and Sarah.

 

 

 

 

 

TABLE OF CONTENTS
LIST OF TABLES ...................................... xii
LIST OF FIGURES ...................................... xiv
CHAPTER ONE
INTRODUCTION ....................................... 1
1.1 OBJECTIVES ................................ 3
1.2 ORGANIZATION OF THE THESIS .................. 5
CHAPTER TWO
EFFECTS OF CURING CONDITIONS AND AGE ON FLY ASH
MORTAR PERMEABILITY ................................ 6
2.1 INTRODUCTION .............................. 6
2.2 BACKGROUND ............................... 7
2. 3 EXPERIMENTAL PROGRAM ...................... 13
2.4 MATERIALS, MIX PROPORTION S AND TEST
PROCEDURES ............................... 13
2.5 TEST RESULTS AND DISCUSSION ................. 16
2.6 SUMMARY AND CONCLUSIONS ................... 27
CHAPTER THREE
COMPRESSIVE STRENGTH OF FLY ASH CONCRETE MATERIALS
AND CORRELATION WITH PERMEABILITY .................... 29
3.1 INTRODUCTION .............................. 29
3.2 BACKGROUND ............................... 30
3.2.1 Compressive Strength ................... 30
3.2.2 Drying Effects on Concrete Strength and Permeability . . . 32
3. 3 EXPERIMENTAL PROGRAM ...................... 33
vi

 

 

 

 

 

3.4 TEST RESULTS AND DISCUSSION ................. 35
3.4.1 Compressive Strength ................... 35
3.4.2 Relationship Between the Permeability and Compressive
Strength ................................ 43
3.5 SUMMARY AND CONCLUSIONS ................... 48
CHAPTER FOUR
EFFECTS OF FLY ASH ON SULFATE RESISTANCE OF CONCRETE AND
CORRELATION WITH PERMEABILITY ....................... 51
4.1 INTRODUCTION ............................. . 51
4.2 BACKGROUND ............................... 53
4.2.1 Mechanisms of Sulfate Attack .................. 53
4.2.2 Fly Ash Effects on Sulfate Attack ................ 54
4.3 EXPERIMENTAL PROGRAM ...................... 56
4.4 TEST PROCEDURES ........................... 58
4.5 TEST RESULTS AND DISCUSSION ................. 59
4.5.1 Test Results ............................. 59
4.5.2 Statistical Analysis and Discussion ............... 64
4.5.3 Correlation Studies ......................... 66
4.6 SUMMARY AND CONCLUSIONS .............. 71
CHAPTER FIVE
FLY ASH EFFECTS ON ALKALI-SILICA REACTION ............... 73
5.1 INTRODUCTION .............................. 73
5.2 BACKGROUND ON ALKALI—SILICA REACTION ........ 76
5.2.1 General ................................ 76
5.2.2 Mechanism of Expansion ..................... 78
5.2.3 Pessismum Behavior ....................... 79
5.2.4 Fly Ash Effects on ASR ...................... 80
5.3 EXPERIMENTAL PROGRAM ...................... 84
5.4 MATERIALS ................................ 84
5.4.1 Portland Cement .......................... 84
5.4.2 Fly Ash ................................ 86
5.4.3 Aggregates .............................. 87
5.4.4 Water ................................. 88
5.5 MIX PROPORTIONS ........................... 88
5.6 TEST PROCEDURES ........................... 88
5.7 TEST RESULTS AND DISCUSSION ................. 90
5.7.1 Test Results ............................. 90
5.7.2 Statistical Analysis and Discussion ............... 101

 

vii

 

 

5.7.3 Correlation Studies ......................... 105

5.8 SUMMARY AND CONCLUSIONS ................... 112
CHAPTER SIX

PLASTICS AND THEIR RECYCLING IN CONSTRUCTION ........... 114

6.1 INTRODUCTION .............................. 114

6.2 THERMOPLASTICS ............................ 115

6.3 THERMOSETIING ............................ 115

6.4 RECYCLING OF PLASTICS ...................... 117

6.5 RECYCLING OF PLASTICS IN CONSTRUCTION ........ 120

6.6 PLASTIC TYPES .............................. 122

6.6.1 Polyethylene ............................. 122

6.6.2 Polyethylene Terephthalate (PET) ................ 124

6.6.3 Polyvinyl Chloride (PVC) ..................... 124

6.6.4 Polypropylene (PP) ......................... 125

6.6.5 Polystyrene (PS) .......................... 126

6.6.6 Acrylonitrile—Butadiene-Styrene (ABS) ............. 127

CHAPTER SEVEN
MIX PROPORTIONS AND MECHANICAL PROPERTIES OF CONCRETE

INCORPORATING RECYCLED PLASTICS ..................... 128
7. 1 INTRODUCTION .............................. 128
7.2 SULFONATION CONCEPT ....................... 129
7.3 HYPOTHESES OF PLASTIC-CONCRETE INTERACTION . . . 131

7.4

PART I: RECYCLED PLASTICS AS PARTIAL
REPLACEMENT FOR LIGHT-WEIGHT

AGGREGATE ....................... 134

7.4.1 Background on Light-Weight Concrete ............. 134
7.4.2 Experimental Program ....................... 136
7.4.3 Materials .............................. 137
7.4.4 Mix Proportions and Optimization ................ 141
7.4.5 Test Procedures ........................... 143
7.4.6 Test Results and Discussion ................... 146
7.4.6.1 Hardened Unit Weight .............. 146
7.4.6.2 Flexural Performance .............. 147
7.4.6.3 Compressive Strength .............. 149
7.4.6.4 Impact Resistance ................. 151
7.4.6.5 Effects of Sulfonation .............. 152
7.4.6.6 Microstructural Observations .......... 152

viii

7.5 PART II: RECYCLED PLASTICS AS SECONDARY REINFORCING

INCLUSIONS IN NORMAL-WEIGHT CONCRETE . . . . 154

7.5.1 Introduction ............................. 154

7.5.2 Experimental Program ....................... 155

7.5.3 Test Procedures ........................... 156

7.5.4 Materials and Mix Proportions .................. 156

7.5.5 Test results and Discussion ................... 158

7.5.5.1 Flexural Strength ................. 158

7.5.5.2 Compressive Strength .............. 159

7.6 SUMMARY AND CONCLUSIONS ................... 160

CHAPTER EIGHT

DURABILITY CHARACTERISTICS OF RECYCLED

PLASTIC—CONCRETE COMPOSITES .......................... 162

8.1 INTRODUCTION .............................. 162

8.2 BACKGROUND AND TEST PROCEDURES ............ 163

8.2.1 Permeability ............................. 163

8.2.2 Acid Resistance ........................... 164

8.2.3 Corrosion Resistance ........................ 165

8.2.4 Hot Water Durability ....................... 170

8.3 EXPERIMENTAL PROGRAM ...................... 170

8.4 MATERIALS AND MIX PROPORTIONS ............... 171

8.5 TEST RESULTS AND DISCUSSION .............. 172

8.5.1 Permeability ............................. 172

8.5. 1. 1 Light-Weight Concrete .............. 172

8 . 5. 1.2 N ormal—Weight Concrete ............ 174

8.5.2 Acid Resistance (Light-Weight Concrete) ........... 175

8.5.3 Corrosion Resistance ....................... 175

8.5.3. 1 Light—Weight Concrete .............. 175

8.5.3.2 Normal-Weight Concrete ............ 177

8.5.4 Hot-Water Durability ....................... 178

8.5 .4. 1 Light—Weight Concrete .............. 178

8.5.4.2 Normal-Weight Concrete ............ 179

8.6 SUMMARY AND CONCLUSIONS ................... 182

CHAPTER NINE

RECYCLING OF TIRES IN CONCRETE MATERIALS ............... 184
9.1 INTRODUCTION .............................. 184
9.2 BACKGROUND ............................... 185

9.2.1 General ................................ 185
9.2.2 Production and Disposal ...................... 186
9.2.2.1 Volume of Production .............. 186
9.2.2.2 Disposal Problems ................ 188
9.2.3 Properties Of Tire ......................... 190
9.2.3.1 Chemical Composition .............. 190
9.2.3.2 Physical Properties ................ 192
9.3 RESOLVING OF POP-OUT OF TIRE PARTICLES ........ 194
9.3.1 Objective ............................... 194
9.3.2 Approach ............................... 194
9.4 TIRES AS REINFORCDIG INCLUSION IN CONCRETE ..... 198
9.4.1 Objective ............................... 198
9.4.2 Materials and Mix Proportions .................. 198
9.4.3 Test Procedures ........................... 199
9.4.4 Test Results and Discussion ................... 200
9.4.4.1 Flexural Strength and Toughness ....... 200
9.4.4.2 Compressive Strength .............. 202
9.4.4.3 Impact Resistance ................. 204
9.4.4.4 Restrained Drying Shrinkage .......... 205
9.4.4.5 Permeability .................... 206
9.5 SUMMARY AND CONCLUSIONS ................... 207
CHAPTER TEN
SUMMARY AND CONCLUSIONS ............................ 209
10.1 FLY ASH ................................... 210
10.1.1 Effects of Curing Conditions and Age on Fly Ash
Mortar Permeability .................... 210
10.1.2 Compressive Strength of Fly Ash Concrete
Materials and Correlation with permeability ..... 211
10.1.3 Effects of Fly Ash on Sulfate Resistance of
Concrete and Correlation with Permeability ..... 213
10.1.4 Fly Ash Effects on Alkali-Silica Reaction ....... 215
10.2 PLASTICS .................................. 216
10.2.1 Mix Proportions and Mechanical Properties of
Concrete Incorporating Recycled Plastics ....... 216
10.2.3 Durability Characteristics of Recycled Plastic-
Concrete Composites ................... 218
10.3 TIRE (Recycling of Tires in Concrete Materials) ........... 220
10.4 PRACTICAL RECOMMENDATIONS ................. 221
10.4.1 Fly Ash ........................... 221
10.4.2 Plastic and Tire ...................... 222

 

10.5 RESEARCH NEEDS ................................ 3%:
10.5.1 Fly Ash ........................... 223
10.5.2 Plastic and Tire ......................
...... 225
LIST OF REFERENCES .............................
xi

 

Table 2.1
Table 2.2
Table 2.3
Table 2.4
Table 3.1
Table 3.2

Table 3.3

‘ Table 3.4

Table 3.5

Table 4.1
Table 4.2
Table 4.3

Table 4.4

Table 4.5
Table 5 .1
Table 5.2
Table 5 .3
Table 5 .4

able 5 .5

 

 

LIST OF TABLES
Relative Permeability of Concretes With and Without Fly Ash. . . 10
Properties of Cement and Fly Ashes (percent by weight). ..... 14
Chloride Permeability classiﬁcations. .................. l6
Chloride Permeability Test Results (coulombs) . ............ 18
Compressive Strength Test Results (psi). ................ 36

Percent Change in Permeability and Strength with l4-Day Moist

Curing compared to 7-Day Moist Curing (positive change

corresponds to increase in strength and decrease in

permeability): All Results at 28 Days of Age. ............. 44
Percent Change in 28—Day Permeability and Strength After Air-

Drying Up to 90 Days (positive change corresponds to increase

in strength and decrease in permeability): All Results For 7 -Day

Moist Cure. .................................. 45
Correlation Coefﬁcients Between Compressive Strength and

Chloride Permeability for Each Fly Ash Type and Different Fly

Ash Contents. ................................ 46
Correlation Coefﬁcients Between Compressive Strength and

Chloride Permeability for Constant Fly Ash Content and

Different Fly Ash mes. ......................... 46
Factorial Design of Experiments. ..................... 57
Fly Ashes and Cement Properties (percent by weight). ....... 57
Test Ages (weeks) at Which the Effect of Fly Ash Content Was
Conﬁrmed at 99 % Level of Conﬁdence. ................ 64
Test Ages (weeks) at Which the Effect of Fly Ash Type Was
Conﬁrmed at 99% Level of Conﬁdence. ................ 65
Chloride Permeability Test Results (coulombs). ............ 68
Factorial Design of Experiments. ..................... 85
Cements Pr0perties (Percent by weight). .............. 86
Fly Ashes Properties (percent by weight). ............... 87
Test Ages (months) at Which the Effects of Alkali Content of

Cement Were Conﬁrmed at 99% Level of Conﬁdence ........ 102
Test Ages (months) at Which the Effects of Fly Ash Type Were
Conﬁrmed at 99% Level of Conﬁdence. ................ 103

xii

 

 

 

 

 

 

 

Table 5.6
Table 5 .7
Table 6.1
Table 6.2
Table 7.1
Table 7.2
Table 7.3
Table 7 .4
Table 7 .5
Table 7. 6

Table 7.7
Table 8.1

Table 9.1
Table 9.2
Table 9.3

Test Ages (months) at Which the Effects of Fly Ash Content

Were Conﬁrmed at 99% Level of Conﬁdence. ............ 104
Correlation Coefﬁcients between ASR Expansion and Fly Ash
Properties. .................................. 107
primary application and typical use after recycling for some

major thermoplastic. ............................ 1 16
primary application and typical use after recycling for some

major thermosetting. ............................ 1 18
Experimental Program For Light-Weight Concrete Incorporating
Recycled Plastics. ............................. .137
Light-Weight Aggregate Gradations. ................... 138
Types and Percentages of Different Plastics, by Weight. ...... 139

Average Thickness of the Different types of Recycled Plastics. . . 140
Optimized Mix Proportions for Light-Weight Concrete (lb/yd3) . 142
Experimental Program For normal-Weight Concrete

Incorporating Recycled Plastics. ..................... 15 6
Mix Proportions for Normal-Weight Concrete (lb/yd3) . ....... 157
Experimental Program For Light- and Normal-Weight Concrete

Incorporating Recycled Plastics. ..................... 171
Typical Chemical Composition of Tire Rubber (Fader, 1990) . . . 191
Physical Properties of Reinforcement Structures in Tires. ...... 193
Typical Properties of Cross-Linked Rubber Compounds Used in

Tires. ..................................... 193

xiii

 

 

 

 

 

 

Figure 2.1
Figure 2.2
Figure 2.3
Figure 2.4

Figure 2.5
Figure 2.6
Figure 2.7
Figure 2.8
Figure 2.9
Figure 3.1

Figure 3.2
Figure 3.3

Figure 3.4

Figure 3.5
Figure 3.6

 

Figure 4.1
Figure 4.2

Figure 4.3
Figure 4.4
Figure 4.5
igure 4.6
igure 4.7

   
    
 
 

igure 4.8

igure 4.9

 

 

LIST OF FIGURES

Continuity of Capillary Pores and Interface Microcracks. ......
Structure of Hardened Cement Paste Vs. Fly Ash-Cement Paste.
Chloride Permeability Test Set-Up.
Effects of Different Fly Ash Types and Contents on Water
Requirement for Constant Workability. .................
Chloride Permeability Vs. Fly Ash Content. ..............
Effects of Moist Curing Duration on Permeability.
Effects of Air-Drying Period on Permeability. .............
Effect of ﬂy ash type on Chloride Permeability .............
Interaction Diagrams (14-day moist curing). ..............
Effects of Capillary Porosity (space ratio) on Compressive

Strength and Permeability .........................
Compressive Strength Vs. Fly Ash Content. ..............
Effects of Moist Curing Duration on Compressive Strength
Development ..................................
Effects of Air-Drying Period on Compressive Strength
Development ..................................
Permeability Vs. Compressive Strength.
28-Day Permeability Vs. Strength (Typical Test Results and
Regression Lines). ..............................
Damage to Concrete Structures Resulting from Sulfate Attack. . . .
Effects of Different Fly Ash Types and Contents on Water
Requirement for Constant Workability. .................
Percent Expansion Vs. Time for Fly Ash F(l) .............
Percent Expansion Vs. Time for Fly Ash F(2) .............
Percent Expansion Vs. Time for Fly Ash C(1).
Percent Expansion Vs. Time for Fly Ash C(2).
Specimens After Deterioration due to Cracking Under Sulfate
Attack. .....................................
Relationships Between Sulfate Resistance and Permeability at
Different Ages.
Relationship Between 42—Day Expansion and 2—Month
Permeability. .................................

OOOOOOOOOOOOOOOO

ooooooooooooooooooooooooooooooo

xiv

8
10
15

17
19
21
22
24
26

32
38

40

42
43

47
52

59
61
61
62
62
63
69

70

Figure 5 .1
Figure 5.2
Figure 5.3
Figure 5 .4

Figure 5 .5
Figure 5.6
Figure 5.7
Figure 5.8
Figure 5.9
Figure 5.10

Figure 5.11

Figure 5.12

Figure 7.1

Figure 7 .2
Figure 7.3
Figure 7 .4
Figure 7.5
Figure 7 .6
Figure 7 .7
Figure 7.8
Figure 7.9
Figure 7.10

 

Figure 7.11

   
  
  

Figure 7.12

igure 7.13
igure 7.14
igure 7.15
igure 7.16
igure 7.17

 

 

Concrete Deterioration Caused by Alkali-Silica Reaction. ...... 75
Relationship Between Expansion and Reactive Silica Content . . . . 79

Alkali-Silica Reaction Test Set-Up. ................... 89
Class F Fly Ash Effects on ASR Expansions with Low-Alkali

Cement. .................................... 92
Class F Fly Ash Effects on ASR Expansions with Moderate-Alkali
Cement. .................................... 93
Class F Fly Ash Effects on ASR Expansions with High-Alkali

Cement. .................................... 94
Class C Fly Ash Effects on ASR Expansions with Low-Alkali

Cement. .................................... 95
Class C Fly Ash Effects on ASR Expansions with Moderate-Alkali
Cement. .................................... 96
Class C Fly Ash Effects on ASR Expansions with High-Alkali

Cement. .................................... 97

Six Months Expansions Vs. Fly Ash Content For Different Fly Ash
Types and Cement Alkali-Contents. ................... 99
Relationship Between 6 Months Expansions and the NaZO-
equivalent-to—Si02 Ratio of Fly Ash at Different Fly Ash

Content (Regression Lines and 95 % Conﬁdence Intervals). ..... 108
Relationship Between 12 Months Expansions and the Na20-
equivalent-to-SiOz Ratio of Fly Ash at Different Fly Ash Content
(Regression Lines and 95% Conﬁdence Intervals). .......... 110
Chemical Bonding of Sulfonated Plastic Surfaces to the Cement-

Based Matrix. ................................ 131
Concrete Microcracks. ........................... 133
Mechanism of Action of Plastic Inclusions in Concrete. ....... 133
Lightweight Aggregate Spectrum. .................... 136
Gradation of Plastic-Fine Aggregate Combinations ........... 140
Flexural Test Set-Up. ............................ 144
Impact Resistance Test Set—Up. ...................... 145
Hardened Unit Weight (Means and 95% Conﬁdence Intervals). . . 146
Typical Flexural Load-Deﬂection Curves at 28 Days. ........ 147
Flexural Strength Test Results (Means and 95 % Conﬁdence

Intervals). ................................... 148
Flexural Toughness Test Results (Means Values and 95%

Conﬁdence Intervals). ........................... 148
Compressive Strength Test Results (Means and 95% Conﬁdence
Intervals). ................................... 150
Impact Resistance Test Results . ..................... 151
SEM Micrographs of Plastic-Concrete Composite. .......... 153
Crack Width Vs. Drying Time. ...................... 155
Flexural Strength Test Results. ...................... 158
Compressive Strength Test Results. ................... 159

XV

 

 

 

 

Figure 8.1
Figure 8.2
Figure 8.3
Figure 8.4
Figure 8.5
Figure 8.6

Figure 87

Figure 8.8
Figure 9.1
Figure 9.2
Figure 9.3
Figure 9.4
Figure 9.5

Figure 9.6
Figure 9.7

Figure 9.8
Figure 9.9

Figure 9.10

 

 

 

The Electra-Chemical Process of Corrosion. .............. 168
Light-Weight Concrete Permeability Test Results. .......... 173
Normal-Weight Concrete Permeability Test Results. ......... 174
Change in Weight with Time. ....................... 176
Corrosion Potential Measurements. ................... 176
Flexural Strength of Light-Weight Concrete After Hot water
Immersion. .................................. 180
Flexural Toughness of Light-Weight Concrete After Hot Water
Immersion. .................................. 180
Flexural Strength of Normal-Weight Concrete After Hot-Water
Immersion. .................................. 181
Flow Diagram Showing Estimated Destination of Scrap Tires in

1990 (In Millions of Tires and Percent). ................ 187
Destination of Waste Tires in 1990. ................... 188
Volume Change of Tire Particles. .................... 196
Epoxy Coating Effects on Pop—Out in Hot Water ............ 197
Flexural Strength Test Results (Means and 95% Conﬁdence

Intervals). ................................... 201
Flexural Toughness Test Results. ..................... 201
Compressive Strength Test Results (Means and 95 % Conﬁdence
Intervals). ................................... 203
Impact Resistance Test Results. ...................... 204
Restrained Drying Shrinkage Vs. Time .................. 205
Permeability Test Results. ........................ 206

xvi

 

 

 

 

 

 

 

CHAPTER ONE

INTRODUCTION

Portland cement concrete is a composite material which generally consists of
aggregates and a binder of Portland Cement paste. The hydrated cement paste is the
continuous matrix phase in which aggregate particles are embedded. Aggregates
typically occupy about 70 to 80 % of the volume of concrete. Portland cement concrete
is the most widely used of all construction materials; currently close to one ton of
concrete is used annually for every human being in the world. No other material except
water is consumed in such tremendous quantities.

The successful use of concrete depends upon intelligent selection of materials, mix
proportions and construction procedures for speciﬁc service conditions. Concrete has
emerged as the most widely used engineering material because: (1) it possesses excellent
resistance to water; (2) structural concrete elements can be easily formed into a variety
of shapes and sizes; (3) concrete is usually the cheapest and most readily available
material on the job site; (4) compared to most other engineering materials, the production
of concrete requires considerably less energy input; and (5) large amounts of many
industrial wastes can be recycled as substitutes for various virgin materials in concrete.

However, concrete suffers from a major shortcoming, that is low tensile stress

and strain capacities; it cracks and fails in a brittle manner under tensile stresses caused

 

 

 

 

 

 

 

2

by external loading or environment effects. Rapid increase in the number of cases of
concrete deterioration due to chemical and physical attack throughout the world
underscores the urgent need for engineering solutions to these degradation processes.
The durability of concrete is affected by both surface reactions and reactions occurring
in the bulk of the construction material. The major causes of concrete deterioration are:
(1) chemical attack (for example, sulfate attack, acid attack, and alkali-aggregate
reactions); (2) corrosion of steel in concrete; and (3) freezing and thawing cycles.

It is generally possible to provide adequate strength, but strength is of little value
if the structure is not durable. Durability has to be deﬁned with reference to the loading
and environmental conditions because a concrete material may perform well under one
set of conditions while not lasting long under another set of conditions. To help
overcome various durability problems and brittleness, nowadays concrete is made with
several types of cement and also contains mineral and chemical admixtures, polymers,
ﬁbers, and so on.

The use of industrial by-products (e. g. ﬂy ash) and recycled waste materials (e. g.
plastic and tire) in concrete present the potentials to overcome various shortcomings of
concrete for developing a more durable concrete-based infrastructure, and can make
contributions toward the conservation of natural resources, saving of energy and
preservation of landﬁll space by reducing the demand for virgin raw materials. Judicious
introduction of waste products into concrete can help achieve cost savings while
Providing a product that is superior to conventional concrete made with virgin materials.

This research concerns beneﬁcial use of three major constituents of the solid

 

 

 

 

3

waste stream in concrete-ﬂy ash, plastic and tire; the main focus of research is on ﬂy
ash. Fly ash is a by-product of the combustion of pulverized coal in thermal power
plants. It is removed by the dust collection system as a ﬁne particulate residue from the
combustion gases before they are discharged into the atmosphere. In 1989, the total ﬂy
ash production in the world was on the order of 400 million tons annually.1 It is
considered a major solid waste, about 70 to 80% of the ﬂy ash goes to landﬁlls. Among
solid wastes, plastics have received a lot of attention because they are generally
considered to be non-biodegradable. There are about 11 million tons of plastic wastes
generated per year, about 7% by weight of all solid wastes. However, because plastic
wastes are very low in density, they constitute about 30% , by volume, of the total solid
waste stream.2 One major problem in plastic recycling is that various plastics are quite

different in nature, and their mixing in the waste stream complicates conventional

  
  
  
  
  
  

recycling activities. Annually about 240 million scrap tires are generated in the United

States. It is estimated that 78 % of the scrap tires are landﬁlled, stockpiled or illegally

 

dumped. Tires are prevalent municipal solid waste problems; tire stockpiles and landﬁlls

are ﬁre hazards, and ﬂoatation of tires to landﬁll surfaces also causes damage to landﬁll

covers.3

W
The research reported herein has been concerned with the use of recycled coal ﬂy

sh and plastics/ tire in concrete for achieving improved technical performance. Fly ash

used as a chemically reactive product while plastics/ tire act as reinforcing inclusions

 

 

 

 

 

 

 

and light-weight ﬁllers.

Fly ash is used in concrete as partial replacement for cement. This research has
relied on the chemical reactions between ﬂy ash and some cement hydration products to
produce a dense and chemically stable microstructure for improved permeability and
resistance to sulfate attack and alkali-aggregate reaction. The fundamental mechanisms
of ﬂy ash action in concrete were investigated.

Plastic particles are used in this research as light-weight aggregates and
reinforcing ﬁbers to provide light-weight and normal-weight concrete with enhanced
toughness characteristics, impact resistance and shrinkage cracking characteristics at
reduced unit weight.

Recycled tires are treated in this research as reinforcing inclusions (additives) in
normal-weight concrete, where tire particles are added to conventional concrete matrices
in order to overcome the problems with brittleness and low resistance to impact loads and
restrained shrinkage cracking. Successful use of tire particles in concrete requires
mitigation of moisture movements through sealing of tires against moisture access.

The concrete products developed in this research with recycled ﬂy ash, plastics
and tire present improved technical qualities at generally reduced cost, with positive
impacts on energy consumption, conservation of natural resources and preservation of

the environment.

 

 

 

 

 

 

 

l._2_ R ATI F THE

The research is divided into two parts, dealing with " ﬂy ash " and "plastics and
tire". Chapters two to ﬁve describe the work on recycling of ﬂy ash in concrete for
improved durability, and Chapters six to nine concern the recycling of plastics and tire
in concrete for achieving enhanced toughness, impact resistance, shrinkage cracking and
unit weight, with desirable durability characteristics.

Chapters two and three concern ﬂy ash effects on concrete permeability and
strength, and the correlation between the two. Chapters four and ﬁve deal with the
effectiveness of ﬂy ash in improving the sulfate resistance and alkali-aggregate reactions
in concrete, and discuss the fundamental mechanisms responsible for these effects.

Chapter six presents a literature review on plastics and their recycling in
construction. Chapter seven discusses the mix design and the mechanical properties of
light- and normal-weight concrete materials incorporating recycled plastics, and Chapter
eight presents the durability characteristics of recycled plastic-concrete composites.

Chapter nine concerns the use of recycled titre in concrete; the focus in this
chapter is on resolving adverse interactions between tire and cement-based matrices; the
reinforcing action of tire in concrete is also investigated.

A summary of the research and the conclusions are presented in Chapter ten.

 

 

 

 

 

CHAPTER TWO

EFFECTS OF CURING CONDITIONS AND AGE ON FLY ASH

MORTAR PERIVIEABILITY

L1 INTRODUCTION

Permeability is an important factor affecting concrete durability. It controls the
rate of entry of moisture that may contain aggressive chemicals. Concrete permeability
depends largely on the volume and size of the interconnected capillary pores in cement
paste, and also on the intensity of microcracks at aggregate-paste interfaces. Low
permeability of concrete can improve the resistance to the movement of water, sulfate
ions, chloride ions, alkali ions, and other causes of chemical attack.

Fly ash, a by—product of the combustion of pulverized coal in thermal power
plants, is commonly used in concrete as a partial replacement for Portland cement. In
cement and concrete applications, ﬂy ash provides far major reductions in permeability.
However, the effects of ﬂy ash depend on its composition and physical properties.
ASTM C-618 categorizes the ﬂy ashes suitable for concrete application into two groups:
Class F and Class C. The most notable chemical difference between these two classes
of ash is that the class C ashes contain relatively high levels of calcium oxide. Fly ash
's capable of reacting with the calcium hydroxide (CH) produced during cement hydration

0 form calcium silicate hydrate (CSH), which ﬁlls large capillary voids and disrupts

 

 

 

— —-Vm T‘F‘ ._ -__ I. .9.“‘—.” “'

7
their continuity. The blocldng of capillary voids reduces the permeability of concrete.

Class C fly ash, with relatively large calcium hydroxide content, exhibits both pozzolanic
and cementitious qualities; hence, the blocking of capillary pores is done more efﬁciently
with Class F ﬂy ash (dominantly a pozzolan) than with Class C ﬂy ash.

Microcracks appear at the coarse aggregate-paste interfaces in concrete materials
prior to any external loading due to the incompatible shrinkage movements, settlement

of aggregates inside the paste, and accumulation of bleeding water under aggregates.

 

These microcracks have dominant effects on concrete permeability. Fly ash could also
possibly inﬂuence microcracking process at the aggregate-paste interfaces by altering the

volume and shrinkage characteristics of the paste, and also by changing the bleeding

 

properties of cement paste and the microstructure of interface zones. These factors have
complex combined effects on interface microcracking, and the end result at this point is

a matter of speculation.

The research reported herein contributes to the body of knowledge needed to
determine the optimum levels of cement substitution with speciﬁc types of ﬂy ash and
the effective curing conditions which yield impervious ﬂy ash concretes with desirable

durability characteristics.

2.; BACKGROUND
The permeability of concrete is controlled by the pore structure of concrete, the
microcracks that are present at the aggregate-paste interfaces, and possibly the pore

system characteristics of aggregates. The permeability of hydrated cement paste (without

 

 

8
aggregates) is most inﬂuenced by the larger capillary pores. When aggregates are added

to cement paste ( i.e., in concrete), the interface microcracks as well as the porosity of
interface zones seem to play an important role in establishing the interconnection between
capillary cavities (Figure 2.1) and increasing the permeability of concrete. Fly ash
reduces concrete permeability through reﬁning the capillary pore system and possibly

improving the aggregate—paste interface conditions.

pores

ace
crack

   
 

Framework of
hydration products

tggregate

lure 2.1 Continuity of Capillary Pores and Interface Microcracks.

 

 

9

Figure 2.2(a) schematically shows the structure of hydrated cement paste (no ﬂy
ash used). The structure consists of "A" which represents aggregation of Calcium
Silicate Hydrate (C-S-H) particles (a stable cement hydration product with desirable
strength development and durability properties); “H“ which consists of products such as
Calcium Hydroxide (CH) forming large crystals which are not stable in the presence of
water especially when some aggressive chemicals are present; and "C" representing the
capillary void system, that is basically the space originally occupied by water which did
not get ﬁlled completely with the cement hydration products. It is through the capillary
void system that water, which possibly carries some aggressive chemicals, enters
concrete and causes the durability problems.

The structure of ﬂy ash-cement paste is presented in Figure 2.2(b). The major
change is that crystal products (CH), as a result of the ﬂy ash pozzolanic reactions,
change to C—S-H particles of low density which ﬁll the large capillary voids and reduce
the continuity of the capillary void system. The blocking of capillary voids reduces
concrete permeability.

A number of investigations have been performed on the inﬂuence of ﬂy ash on
the relative permeability of concrete pipes. Davis (1954)5 examined the permeability of
concrete pipes incorporating ﬂy ash substituted for cement in amounts of 30 to 60%.
Permeability tests were made on 150 x 150 mm (6 x 6 in.) cylinders at ages 28 days and

6 months. The results of these tests are shown in Table 2.1.

 

 

 

 

 

 

 

 

 

 

 

 

10
, A

//

’ .. - H _ -

’0&.. .
c .

. c

[pm

(a) Cement Paste (b) Fly Ash-Cement Paste

Iigure 2.2 Structure of Hardened Cement Paste Vs. Fly Ash-Cement Paste.4

Relative Permeability of Concretes With and Without Fly Ash.5

 

 

W/(C+F) Relative Permeability
By Weight 28 Days 6 Mo.
0.75 100 26
0.70 220 5
0.65 1410 2

 

 

11

It is clear from these data that the permeability of concrete related directly to the
quantity of hydrated cementitious material at any given time. After 28 days of curing,
at which time little pozzolanic activity would have occurred, the ﬂy ash concretes were
more permeable than the control concrete for the speciﬁc mix proportions used by Davis
(1954)5. After 6 months, however, this tendency was reversed. Considerable
imperviousness had developed in ﬂy ash concretes, presumably due to the pozzolanic
inﬂuence of ﬂy ash. This seems to conﬁrm the view that the transformation of large
pores to ﬁne pores, as a consequence of the pozzolanic reaction between Portland cement
paste and ﬂy ash, substantially reduces the interconnection of pores and thus the
permeability of cementitious systems.6

Roy et a1 (1987)7 studied the effects of curing temperature, water-to-binder ratio,
and ﬂy ash type and content on the permeability of paste and mortar. The level of
cement substitution with ﬂy ash (Class F and C) ranged from 20 to 35% and permeability
was represented by chloride ion diffusivity. Specimens were subjected to two 28-day
curing regime with temperatures of 23 °C (73 °F) and 38 °C (100 °F), and > 95 % relative
humidity. It was found that Class F ﬂy ash at any replacement, and class C ﬂy ash at
higher replacement levels increase the resistance against chloride ion migration. This is
possibly due to the strong interactions between Class F ﬂay ash or its reaction products

ith cement and ionic species in pore ﬂuids. Also, increased curing temperature was
ound to enhance the resistance of blend to chloride ion penetration, possibly due to the
ore advanced degree of reaction of ﬂy ash and the greater proportion of C-S-H.

arsh et a1 (1986)8 concluded that the acceleration of pozzolanic reaction of ﬂy ash in

.; 42/ _,/,// a

 

12

cement is greater than the acceleration of Portland cement for a given curing
temperature, and the acceleration increases with increasing curing temperature.

Whiting and Kuhlman (1987)9 studied the effect of curing condition on chloride
permeability, and concluded that permeability of concrete generally decrease with time,
the largest decrease occurring within the ﬁrst two months of curing. Thomas et a1
(1989)10 carried out tests on the effects of curing on the strength and permeability of ﬂy
ash concrete. Different levels (15, 30 and 50%) of cement were substituted with Class
F ﬂy ash in these tests; permeability was assessed through oxygen and water permeability
tests at 28 days of age with different initial moist curing periods. They concluded that
as the initial moist curing period increases, ﬂy ash concretes become considerably more
impermeable than normal concretes. Results also showed that longer curing periods are
required for ﬂy ash concrete to achieve strength parity with normal concrete. However,
an extended initial moist curing period is not necessary in order for ﬂy ash concrete to
achieve lower permeability than normal concrete.

Kawamyra et a1 (1989)11 studied the effects of curing condition on chloride
permeability of concrete at various replacement levels of Portland cement with ﬂy ash.
The curing conditions were various combinations of the initial curing time of 7 to 90
days in water at 20 °C (68 °F) and the subsequent cure in a dry environment (60% RH,
20 °C, 68 °F) for various time periods. It was concluded that the chloride permeability

f concrete containing ﬂy ash is more sensitive to the duration of dry curing in the curing
egime than the chloride permeability of concrete without ﬂy ash which is affected

ainly by the drastic changes in curing environment from cure in water to in air rather

 

 

 

13

than by duration of dry curing. Also, it was noted that the addition of ﬂy ash is effective
in decreasing chloride permeability even in concretes cured in air for relatively long time
periods. The pozzolanic reaction and hydration seem to continue to some extent even

in a relatively dry environment.

2_.3, EXPERIMENTAL PROGRAM

The key variables of the experimental program were the ﬂy ash type, ﬂy ash
content, moist curing period, and age of testing. Experiments were conducted following
a 3x3x2x2 (3 ﬂy ash types x 3 ﬂy ash contents x 2 moist curing periods x 2 ages of
testing) factorial design with 3 replications. Control tests with no ﬂy ash were also
performed. Two Class F and one Class C ﬂy ashes were considered. The three
replacement levels of cement with ﬂy ash were 10, 20, and 30% by weight of cement.
The moist curing periods were 7 days and 14 days at 32 °C (90 °F). The ages of testing
were 28 days and 90 days. The specimens were stored in the laboratory (23 °C, 73 °F,
and 45 i 5 % Relative Humidity) after the period of initial moist curing until the age of

testing.

2+4 MATERIALS MIX PROPORTIONS AND TEST PROCEDURES

The materials used in this experimental study were Ottawa sand (ASTM C-109)
with a maximum particle size of 0.6 mm (0.024 in.), type I Portland cement, and three
fly ash types (two Class F and one Class C). Table 1 presents the chemical composition,

ﬁneness and speciﬁc gravity of the cement and ﬂy ashes used.

\s‘
K»

14

 

 

 

 

 

 

 

 

 

 

 

Table 2.2 Properties of Cement and Fly Ashes (percent by weight).

Property Cement Class—F (1) Class-F(2) Class-C

Silicon dioxide (S102) 20.49 49.30 51.41 31.8

Aluminum oxide (A120,) 5.39 26.70 28.75 20.7
Ferric oxide (FezO3) 2.55 8.95 8.43 6.45
Calcium oxide (CaO) 62.42 1.70 1.76 19.60
Magnesium oxide (MgO) 3.63 1.50 1.60 4.82
Sulfur trioxide (S03) 3.19 0.52 0.35 4.50
Total Alkalies (as NaZO) 0.80 3.70 2.80 7.25
Loss on ignition 2.00 5.50 3.66 0.60
Speciﬁc gravity 3.15 2.13 2.17 2.58

Fineness (% retained 10.7 19.60 34.70 16.0

on # 325 sieve)

 

 

 

 

 

 

 

The mortar mixtures considered in this investigation had a sand-binder ratio of
2.75 by weight. Mixing was carried out according to ASTM C-305. Water content was
adjusted to give a ﬂow (ASTM C-109) of 100-110%.

The chloride permeability tests were conducted following ASTM C-1202 or
AASHTO T—277 (Rapid Determination of the Chloride Permeability of Concrete).12 The
test procedure can be summarized as follows: (1) after the curing age, the perimeter of
the cylindrical specimen is covered with epoxy; (2) after the epoxy is dried, the concrete
specimen is placed into a vacuum desiccator and vacuum is maintained for 3 hours; (3)
while the vacuum pump is still running, the desiccator is ﬁlled with de—aerated water to
cover the specimen, vacuum is maintained for another hour and then it is shut off and

'he specimen soaks for 18 hours; (5) the specimen is then removed from water and

 

 

15

connected to an applied voltage cell where one side is in contact with sodium hydroxide
solution (see Figure 2.3).

Permeability is then represented by the amount of charge passed through a
concrete specimen subjected to permeation of chloride ions at 60 VDC for 6 hours. The
I total charge passed (in Coulombs) is related to chloride ion permeability. The more
permeable the concrete, the higher would be the Coulombs (see Table 2.3). A
cylindrical specimen 102 mm (4 in.) in diameter by 51 mm (2 in.) in thickness is used

for this test.

 

0.3M NaOH
solution

3% NaCl
' solution

 

 

 

concrete specimen

 

(a) Vacuum Saturation Apparatus (b) Test Setup

Figure 2.3 Chloride Permeability Test Set-Up.

 

 

 

16
Table 2.3 Chloride Permeability classiﬁcations.9

 

 

Charge Passed Chloride .

(Coulombs) Permeability Typical Of
> 4,000 High High water—cement ratio ( 20.6), conventional PCC.

2,000—4,000 Moderate Moderate water-cement ratio (0.4-0.5), conventional

PCC.

LOGO-2,000 Low Low water-cement ratio (<0.4), conventional PCC.

100—1,000 Very Low Latex—modiﬁed concrete, internally sealed concrete.
< 100 Negligible Polymer impregnated concrete, polymer concrete.

 

 

 

 

 

A; TEST RESULTS AND DISCUSSION

Different mixes considered in this investigation all had comparable levels of
workability, i.e. a ﬂow (ASTM C-109) of 100-110%. As shown in Figure 2.4, the
addition of Class C ﬂy ash reduced water requirements considerably, whereas the
addition of Class F ﬂy ashes did not change the ﬂow (and thus water requirement)
substantially.

The permeability test results for 3x3x2x2 factorial design and the control mixture
(with 3 replications) are presented in Table 2.4. It should be noted that the temperature
in the cell was measured periodically during the test. Following the AASHTO
recommendations, the test was discontinued if temperature exceeded 88 °C (190 °F) in
rder to avoid damage to the cell. For specimens of 10% Class F(2) ﬂy ash, which were

oist cured for 7 days and tested at 90 days, and control specimens as well as those with

0 and 20% Class C ﬂy ash, moist cured for 7 days and tested at both 28 and 90 days

.5:

 

 

 

 

17

_________ C lass-F(2)

(Cement+ Fly Ash)

O
01
O
0

Water/

  

.0 .o
A A
01 \I
O 01

   

0.0 10.0 20.0 30.0 40.0
FLY ASH CONTENT (%)

Figure 2.4 Effects of Different Fly Ash Types and Contents on Water Requirement
for Constant Workability.

of age or moist cured for 14 days and tested at 90 days, the amount of current passing
through concrete was sufﬁcient to increase the temperature above 88°C. In these cases,
the experiment had to be discontinued after about 4 to 5 hours. The total charge passed
in the recommended 6-hour duration of test was then estimated by extrapolation. A
comprehensive statistical analysis using the analysis of variance technique was performed
n order to analyze the effects of various factors involved. This analysis, at 99% level
If conﬁdence, conﬁrmed that all the variables of this investigation (ﬂy ash type, ﬂy ash
Ontent, moist curing period, and the age of testing) as well as their paired interactions,
“apt for the interaction of ﬂy ash content with age of testing, inﬂuenced the

ermeability of concrete.

'Tabk:2.4

 

18

Chloride Permeability Test Results (coulombs).

 

Iﬂy.Ash'Type

 

(Ha&e(F1)

(Hass4F2)

(ﬂass43

 

Blond caning

hdohniiurhu;

Moist Curing

 

Fly Ash

7Lday

14-day

7Lday

14~day

7Lday

14-day

 

(knnent

IkstrAge

Thetrkge

Tketrsge

1k5trsge

Teﬂ.Age

TeﬂuAge

 

28-
day

90-
day

23—
day

90.
day

28-
day

90-
day

28—
day

90-
day

28-
day

90-
day

28-
day

90-
day

 

1096

7630
7109
7920

10500

8950

9150

5124
5199
5432

5798
5470
6609

l 5222

 

10150
11300
10500

14632
15021

6658
7823
5714

7050
6840
8079

1405518454
1517018603
1404018360

10500
10900
12500

15029
15988
16135

 

2096

6470
6401
7833

8265
8647
7179

2462
2104
2148

2120
2008
2723

9478
8623
7650

11660
11320
10800

3520
3292
3482

3569
2678
3495

1230017330
1350016926
1325016230

4869
5915
6359

13811
14141
13396

 

3096

4443
4505
3900

5438
5573
5021

1730
1686
1425

1271
1565
1701

5326
5968
5710

 

6313
7106
7725

 

2675
2360
2779

 

2281
2073
2454

 

5399
6738
5146

 

11824
11460
12332

2888
2875
2611

 

 

7213
6859
6844

 

Connol
(0%)

1441818711
1506018512
18232

1403

 

 

 

 

 

9593
10220
9860

 

14009
15010
14400

 

 

 

Figures 2.5(a) and 2.5(b) present the effects of ﬂy ash content, for different ﬂy
ash types at 28- and 90—day testing, on the permeability of concrete materials with 7 and
14 days of moist curing, respectively. Class F ﬂy ash is observed in these Figures to
reduce permeability even at relatively low levels of cement substitution (10% by weight).

[n the case of class C ﬂy ash, however, relatively high cement substitution levels (20 to

30% by weight) were required to produce any signiﬁcant reduction of permeability.

 

 

 

   

 

 

 

 

 

 

 

 

 

19
20000
' """"""" X‘- - ~ - \ FLYASH—Fi
18°00 \\ ‘\.\ ——-— FLYASH—FZ
$15000 \‘\ x\- _ — FL ASH—c
CD \ \
2 . - 0 TEST AGE=28 DAYS
0 14000 ' - . - x TESTAGE=90 DAYS
_1
8 12000
t.)
v
a: 10000
(1:33 8000
:25 $000
0:
31' 4000 r
.
2000 L
L
o L l l
0 10 20 30 4o
FLY ASH CONTENT (Z)
(a) 7—Day Moist Curing
20000
__ —— FLYASH—F1
18000 — — —- — FLYASH-FZ
V) 16000
02:1 TEST AGE=28 DAYS
0 14000 TESTAGE=90 DAYS
_J
D i‘
0 12000
0 -
\_l
t 10000
:1
55 5000
g 6000
33
o_ 4000
2000
o - j l l
0 1o 20 30 40
FLY ASH CONTENT (7.)
(b) 14-Day Moist Curing

gure 2.5 Chloride Permeability Vs. Fly Ash Content.

 

20
Figures 2.6(a) and 2.6(b) compare the 28-day and 90-day chloride permeabilities,

ectively, of concrete materials (with different ﬂy ash types and contents) when
ected to 7 and 14 days of moist curing. Four—way analysis of variance and
nation of means conﬁrmed, at 99 % level of conﬁdence, that extended moist curing
ods lead to reduced concrete permeability for each of the ﬂy ash types and contents
sidered and also for the control mixture. The average ratios of 28—day permeabilities
the l4-day to 7-day moist-cured materials were 0.68 and 0.45 for cases with 0% and
5 ﬂy ash-binder ratios, respectively; the corresponding ratios were 0.78 and 0.44 for
lay permeabilities. This conﬁrms that extended moist curing is more beneﬁcial to
tsh concrete permeability when compared to conventional concrete permeability.
The effect of air-drying in labartory (up to 28 and 90 days of age) on the chloride
reability with different ﬂy ash types and contents are shown in ﬁgure 2.7 (a) for 7-
initial moist curing and Figure 2.7 (b) for l4-day initial moist curing. The
ption of moist curing followed by air drying caused an increase in permeability
t for the Class F ﬂy ashes after the longer moist curing duration (14 days) for
permeability stayed almost constant. The increase in permeability between 28 and
ys for each ﬂy ash type and content, including the control mixture (0%
itution), was conﬁrmed statistically (using the separation of mean technique) at 99 %
of conﬁdence, except for the Class F ﬂy ashes at all contents in the case of 14-day
curing. One may attribute this effect of air drying to the formation of shrinkage
craks with particularly adverse effects on permeability, which more than

mate for any positive effects of the slow progress of hydration 0r pozzolanic

 

 

 

 

21

PERMEABILITY (Thousand Coulombs)

 

    
  

' " 7’—‘Déy' MOIST Curing W7'14'4'D'éymM’0i’sIMCUT'I'DEW "I

,_ . , , I”~95%'~Oon-tldeﬂce'I-nter‘vaI

 

 

controI 10% 20% 80% 10% 20% 30% 10% 20% 80%
Class-C CIassTIZ) Class—F(I)

 

 

  

(a) 28—Day age of testing

PERMEABILITY (Thousand Coulombs)

 

' 5:55-1:55? 7—Day'Mols'i Curing ' \1‘4—DayM'olst Curing " ”

    

. I 95% Oonf-IdencelntervaI

 

        
   

 

. '1':‘:::’::\ l sisiziaésisih Teeth :stéssaA
30% 10% 20%

CIass-O Class-F(2) Class—F(I)

(b) 90—Day Age of Testing

Effects of Moist Curing Duration on Permeability.

 

 

I: i l .
. .

1

I

22

PERMEABILITY (Thousand Coulombs)

 

 

go 28 Days '\'Test Ag’eé'QO'DaS/s' '

 

ODGDOM
111

 

 

 

Class-C Class-F(2) Class—F(I)

1 (a) 7-Day Moist Curing

PERMEABILITY (Thousand Coulombs)

 

   
  

 

Test ’A’g'e'=28 Days” "\ TesthgeEQO' Days”

 

- I95%Con-tidance-Interval»

 

 

 

control 10% 20% (30% 10% 20% 30% 10% 20% 80%
Class-C Class-F(2) Class-F(I)
(b) l4-Day Moist Curing

 

 
 

Effects of Air-Drying Period on Permeability.

 

23

reaction in an environment with low humidity.

It may be observed in Figures 2.7(a) and 2.7(b) that continued air drying from
28 to 90 days affected chloride permeability more signiﬁcantly in the control and Class
C ﬂy ash mixtures. This suggests that, in the case of Class F ﬂy ash with stronger
potentials for pozzolanic reaction, the continuation of pozzolanic reaction (after 14 days
of moist curing) in low-humidity conditions tends to compensate for any adverse effects
of shrinkage cracking on permeability.

Different ﬂy ash types, with different chemical compositions and particle sizes,
are expected to have different effects on concrete permeability. Comparisons between
the chloride permeability of concretes incorporating different ﬂy ash types, at similar ﬂy
ash—binder ratios and two different testing ages (28 and 90 days) are presented in Figures
2.8(a) and 2.8(b) for cases with 7 and 14 days of moist curing, respectively. Statistical
Signiﬁcance of ﬂy ash type effects on concrete permeability, at each ﬂy ash content (10-
30%) was conﬁrmed at 99% level of conﬁdence except for: 1) control (no ﬂy ash) and
10% ﬂy ash C at both ages in 7-day moist curing; 2) 30% ﬂy ashes C and F(2) at 28—day
testing in both 7- and 14—day moist curing; and 3) 30% ﬂy ashes F(l) and F(2) at 90-day
testing in 14-day moist curing. The presence of ﬂy ash had statistically signiﬁcant
effects on (reducing) permeability in all cases except for the Class C ﬂy ash at 10%

substitution level (at both 28— and 90-day testing ages).

 

 

24
’ERMEABILITY (Thousand Coulombs)
Test Age=28 Days <—-—> Test Age=90 Days
I—9596‘Gonfldence Interval . - ~77 - . »

 

   
    

 

 

 

 

0.0 0.0 10 20 30
FLY ASH CONTENT (96)

 

 

 

' CL ASS-C 2323333233235 CL ASS—F(2) CLASS—F(l) 1

 

(a) 7-Day Moist Curing

DERMEABILTY (Thousand Coulombs)

 

 

‘7 ' Test Age=278 Days : : TeétAge=90 Days '
I 95% Confidence-Intervalm' > .

 

   
     

 

 

 

I
1 I 1

0.0 10.0 20.0 80.00 0.0
FLY ASH CONTENT (96)

 

 

i iii‘iii CLASS-C 2:212:42? CLASS-H 2)

 

(b) 14-Day Moist Curing

Effect of ﬂy ash type on Chloride Permeability.

 

24
PERMEABILITY (Thousand Coulombs)

 

— I 95%-Confidence Interval Tr

UlV-PUJUJUNbUJCDON
llllIlIll I

Test Age=28 Days ——> Test Age=90 Days 7

  

 

 

 

 

 

 

0.0 10.0 20.0 30.00 0.0 10 20 80
FLY ASH CONTENT (%)

 

 

 

CLASS—C -CLASS—F(2) -CLASS-F(1) '
(a) 7-Day Moist Curing

PERMEABILTY (Thousand Coulombs)

 

‘ I 95% Contidencelnlerval '7 -

-...V.v-oau1wol\3
lllll ll

7 Te“ Age=28 Days <——> Test Age=90 Days " '

  

 

 

 

0.0 10.0 20.0 30.00 0.0 10 20 ' 80
FLY ASH CONTENT (%)

 

i 5551551???CLAss-c -CLASS-F(2) -CLASS-F(1) '

 

(b) l4—Day Moist Curing

2.8 Effect of ﬂy ash type on Chloride Permeability.

25

As it has been mentioned, all the variables (ﬂy ash type, ﬂy ash content, moist
curing period, and age of testing) as well as their paired interactions have statistically
signiﬁcant effects on permeability. The signiﬁcance of interactions means that some or
all of the variables are not acting independently from one another (i.e. the response to
changes in one variable is conditioned by the level of the other). In order to see these
interaction more clearly, some of them are shown in Figures 2.9(a) and 2.9(b).

In general, the Class C ﬂy ash used in this investigation gave higher
permeabilities than Class F ﬂy ashes (except for 30% substitution level at 28-day testing
age); this occurred in spite of the fact that Class C ﬂy ash was particularly effective in
reducing water requirements for achieving desirable levels of workability. It should be
noted that the F(l) ﬂy ash reduced permeability less than the F(2) ﬂy ash. This can be
attributed to particle size; ﬁneness (% retained on # 325 sieve) of ﬂy ash F(l) is 19.6
while that of ﬂy ash F(2) is 34.7. A coarser gradation can result in reduced role of

>ozzolanic reaction.

 

26

 

 

 

 

 

 

 

 

 

O)

1 0
g [as Test Age=28 Days + Test Age=90 Days]
8 s
3
O
D
C .\
ES 6
U)
3
E
g 4
2
:D
g 2 \
a Nit
J.
O l |
30% Fly Ash 0 30% Fly Ash F(1)
(a) Interaction of Fly Ash Type and Age
1 2
g ale Fly Ash C + Fly Ash (F2)
5 1 0
3
D
D
2 8
3
O
3
2

I:

 

1 0% 30%
FLY ASH CONTENT

(b) Interaction of Fly Ash Content and Fly Ash Type at 28 Days

Interaction Diagrams (14-day moist curing)-

 

27

Z._6 SUMMARY AND CONCLUSIONS

An experimental study was conducted in order to assess the effects of ﬂy ash
ype, ﬂy ash content, period of moist curing, and age on concrete permeability. Three
ifferent ﬂy ash types (two Class F and one Class C), three different ﬂy ash contents (in
:ldition to the control), two different moist curing periods (7 and 14 days), and two
ifferent ages of testing (28 and 90 days) were investigated. The test data were analyzed
atistically. The following conclusions could be derived from the generated test results:

All factors considered in this investigation (ﬂy ash type, ﬂy ash content, moist

curing period, and age) had important effects on concrete permeability at 99%

level of conﬁdence.

Class F ﬂy ash reduced permeability even at relatively low levels of cement

substitution (10% by weight). In case of Class C ﬂy ash, however, relatively

high cement substitution levels (20 to 30% by weight) were required to produce
any signiﬁcant reduction in permeability.

In spite of the fact that Class C ﬂy ash was effective in reducing water demand,

it gave higher permeabilities than Class F ﬂy ashes except for 30% substitution

level at 28-day testing age.

Extended moist curing periods led to reduced concrete permeability. The effect

of moist curing period on concrete permeability was more pronounced in the

presence of ﬂy ash, particularly at higher replacement levels (20 to 30% by

weight).

 

28

Longer air-drying periods were observed to increase permeability, possibly due
to shrinkage microcracking, except for the Class F ﬂy ashes after longer initial
moist curing durations for which permeability stayed almost constant.

The evaluation of concrete permeability with or without ﬂy ash at the age of 28
days (after an initial moist curing period) can be misleading (except for Class F
ﬂy ash with longer of initial moist curing) due to the continuing adverse effects
of shrinkage microcracks on permeability beyond 28 days of age in air curing
condition, which more than compensate for any positive effects of the slow
progress of hydration and pozzolanic reaction in an environment with low

humidity.

 

CHAPTER THREE

COMPRESSIVE STRENGTH OF FLY ASH CONCRETE MATERIALS

AND CORRELATION WITH PERNIEABILITY

3_._l INTRODUCTION

Fly ash is used in concrete to improve, beside the impermeability and durability
characteristics of concrete, its strength particularly at later ages. Fly ash is capable of
reacting with the calcium hydroxide (CH) produced during cement hydration to form
calcium silicate hydrate (CSH), which ﬁlls large capillary voids and disrupts their
continuity.

The ultimate strength and the rate of strength gain in ﬂy ash concrete depend on
he type and amount of the ﬂy ash used, the curing conditions (temperature and
iumidity), and the concrete mixture composition (cement content and type, water/ cement

Ltio, and the presence of admixtures). This research intends to produce statistically

 

eliable conclusions regarding the effects and interactions of the ﬂy ash type and content
1d curing/exposure conditions in deciding the development of compressive strength in
made. The research reported herein contributes to the understanding of the strength
:velopment characteristics of concrete materials under exposure conditions expected in
my ﬁeld applications. The issue of permeability characteristics in different curing

vironments and the relationship to strength are also discussed; the results can help

29

 

30

better understand limitations of strength in representing concrete permeability and thus

durability characteristics.

L2 BACKGROUND
3.2.1 Compressive Strength

Several investigators have studied the ﬂy ash effects on the compressive strength
of concrete. Sivasundaram et al (1989)13 have studied the properties of concrete
materials incorporating relatively high volumes of low-calcium ﬂy ash. They concluded
that air-curing of test specimens, preceded by 7 days of initial moist curing, does not
appear to have severe effects on strength development up to the age of 91 days. Up to
28 days, strength development of the ﬂy ash and control concretes under air-curing
:onditions is comparable to that under moist-curing conditions. However, under long—

erm air—curing, ﬂy ash concrete and control concretes show a marked reduction in

ength when compared to moist-cured specimens.

Rome (1989) 1“ carried out tests on the effect of condensed silica fume and ﬂy ash
Class F) on the compressive strength development of concrete, and concluded that
)ncrete cured continuously in water at 20 °C (68 °F) showed increasing strength at all
:es. Concretes exposed to 50% RH showed lower strength after 28 days of curing
hen compared with those cured in water. Concretes cured in water for 3 days before
posure to 50% RH showed higher initial strengths; however, their strength decreased

er 2-4 months when compared with those continuously cured in water.

 

 

31
Steven et a1 (1986)” studied the effects of ﬂy ash on some physical properties of

concrete, and concluded that concrete containing Class F ﬂy ash required more initial
moist curing for long-term air-cured compressive strength development than did concrete
with Class C ﬂy ash or that without any ﬂy ash. At early ages, compressive strength of
concretes with ﬂy ash, regardless of class, was essentially unaffected by moisture
availability during curing relative to the control concretes. These compressive strength
data illustrate the importance of proper curing for strength development of concrete with
or without ﬂy ash. In general, concretes without ﬂy ash were less sensitive to moisture
inavailability at later ages than concrete mixes with ﬂy ash.

Thomas et a1 ( 1989)10 conﬁrmed that the strength of ﬂy ash concrete appears to
1e more sensitive to poor curing than that of conventional concrete. Marsh et a1 (1986)5
uggest that the calcium hydroxide (CH) content of ﬂy ash and control pastes does not
irectly relate to strength development. Instead, the increases and decreases in strength
rhich occurred during curing were mirrored by corresponding changes an the porosity
fmaterials.

Tikalsky et a1 (1988)16 indicate that concrete with Class C ﬂy ash showed lower
Impressive strength than similar concrete with Class F ﬂy ash under the same curing
nditions. Concretes containing Class F ﬂy ash showed similar or higher compressive
ength than the concrete containing no ﬂy ash for all curing conditions. In general, it
3 concluded that ﬂy ash slightly reduces the early age strength and improves long-term

npressive strength.

 

 

 

 

 

 

32
.2 Drying Effects on Concrete Strength and Permeability

Strength and permeability are both closely related to capillary porosity. However,
neability is more affected by changes in the capillary porosity. Figure 3.1 shows the
st of capillary porosity (space ratio) on compressive strength and permeability. The

led area shows the typical capillary porosity range in hydrated cement paste.4

 

  

 

 

~ EA
1 '9
) 30 - —- 120 3
_ Q)
< Q
T E
I 8
i’ 20 80 ...~
T pmeability g;
.. o
2‘
IO 40 E
.Q
C
Q)
E
O . .;.;. .- 0 (19
1.0 0.9 0.8 0.7 0.6 0.5 0.4
Solid/ Space Ratio (I-P)
3.1 Effects of Capillary Porosity (space ratio) on Compressive Strength

and Permeability.4

 

 

 

33
As shown in the ﬁgure, when solid/capillary porosity drops from 0.7 to 0.6 (i.e.

capillary porosity increases) the compressive strength drops by about 140% while
permeability increases by 500%. The large inﬂuence of segmenting of capillaries
resulting from reduced porosity on permeability suggests that permeability is not a simple
function of porosity. It is possible for two porous bodies to have similar porosities but
different permeabilities. Only one large passage connecting capillary pores will result
in a large permeability, while the porosity will remain virtually unchanged.17

It is generally believed that the higher the strength of the paste the lower would

be its permeability. Drying of the cement paste increases its permeability, probably

 

)ecause shrinkage may rupture some of the gel between capillaries and thus open new
)assages of water.18 If pastes are allowed to dry and then rewetted, the ﬁnal
lermeability coefﬁcient would be higher. This may be due to changes in pore-size
istributions that occur upon shrinkage and which allow capillary pores to become
artially interconnected. The effect is even more marked in concrete, since cracking at

e paste aggregate interfaces will create further opportunities for water to ﬂow.19

1 EXPERIMENTAL PROGRAM

The effects of ﬂy ash type and content on the compressive strengths of concretes
ljected to different curing conditions were investigated. Two Class F and one Class
ly ashes and three replacement levels of cement with ﬂy ash (10, 20 and 30% by
ght of cement) were considered. Two batches were prepared for each mix

position; 16 specimens were made from each batch, which were subjected to

 

34

different initial moist curing periods (7 and 14 days) after which they were subjected to
internal laboratory conditions at 23 °C (73 °F) and 45 i5 % Relative Humidity up to two
different test ages of 28 and 90 days. Specimens for the two moist curing durations and
the two ages of testing were taken from the same batch; this represents a split-plot design
of experiments based on 3x3x2x2 factorial design (3 ﬂy ash types x 3 ﬂy ash contents
x 2 moist curing periods x 2 ages of testing). The factors ﬂy ash type and ﬂy ash
content were considered to be whole plots (from different batches), and the factors moist
curing period and testing age were considered to be subplots within the whole plots (i.e. ,

from the same batch). Statistical analysis of results based on this design provides greater

 

)recision in the sense that it distinguishes between within—batch and between—batch
1ariations in assessing the effects of different factors.20

It should be noted that materials and mix proportions were the same as introduced
1 Section 2.4. Compressive strength tests were conducted using 50.8 mm (2 in.) cubes
ASTM C—109).

Permeability test results reported in Chapter 2 were used to investigate the

Irrelation between strength and permeability of ﬂy ash concrete.

 

35
TEST RESULTS AND DISCUSSION

.1 Compressive Strength

Different mixes considered in this investigation all had comparable levels of
'kability, i.e. a ﬂow (ASTM C-109) of 100-110%. As mentioned in Chapter 2 (see
are 2.4), the addition of Class C ﬂy ash reduced water requirements considerably,
:reas the addition of Class F ﬂy ashes did not change the ﬂow (and thus water
nirement) substantially.

The compressive strength test results for 3x3x2x2 split-plot design of experiments
th 2 replications from different batches and each replication consisting of 4 specimens)
presented in Table 3.1(a); the control test results (with no ﬂy ash) are given in Table
(b). A comprehensive statistical analysis using split-plot analysis of variance was

ormed to assess the effects of various factors involved. This analysis of test results

  
  
  
  
  
  
  
  

ﬁrmed, at 99% level of conﬁdence, that all variables of this investigation (ﬂy ash
:, ﬂy ash content, moist curing period, and age of testing) as well as their paired
ractions (except for the interaction of ﬂy ash type with content and ﬂy ash content

moist curing) inﬂuenced the compressive strength of concrete.

 

The variation in compressive strength for the 7- and 14-day moist curing
itions are shown in Figures 3.2(a) and 3.2(b), respectively, for different ﬂy ash

, contents, and ages of testing.

k:3.l

36

Compressive Strength Test Results (psi).

(a) Fly Ash Concrete

 

lAmh
ntent

Iﬂy.Ash'Type

 

(Ilass-]?(l)'

Class-F(2)'

(ZhuxFCT

 

hdohu Chuing

Moist Curing

blah“ (ﬁning

 

7Lday

14—day

7-day

14-day

7Lday

14—day

 

'Teﬂ.Age

Teﬂ.Age

Tem:Age

Test Age

1kx¢.Age

'Teu.Age

 

28- 90-
day day

28— 90-
day day

28- 90-
day day

28— 90-
day day

28— 90-
day day

28- 90-
day day

 

.096

5122 6517
5536 6622
5282 5875
5224 6478

5701
5611
5447
5689

6274
5859
6091
6617

5269 6754
5429 6680
6363 6580
5155 6765

6401
5482
6000
5870

6854
6943
6237
7041

5603 5982
5296 6599
5860 6358
5408 6108

5318
5267
5169
5706

6308
5791
5827
6431

5758 6277
5516 6382
5887 6161
5753 6843

5794
5857
5560
6064

6701
6494
6934
6853

4790 6185
4917 6242
5166 6324
5007 5853

5066
4589
4767
5034

6140
5878
6075
5823

5469 6420
5011 6380
5293 6090
5415 6094

5393
4916
5246
5033

6307
6213
6523
5826

 

196

5146
5419
5619
5781

5890
5649
5558
5687

5300
4951
5331
5459

5400
5566
5729
5614

5447
5464
5920
6061

7000
6142
6871
6334

5882
5388
5724
5435

6781
6618
6197
6393

5309
5245
5225
5531

5483
5359
5594
6091

5260
4732
4998
5215

5425
5898
5368
5183

5652
5572
5722
5019

6105
5848
6471
5819

5822
5795
5219
5430

7350
6269
6509
6517

4198
4956
4600
4970

5735
6064
5424
5305

4665
4485
4475
4283

5671
5990
5865
5634

4440
4884
4798
4878

6060
5621
5783
5929

4287
4316
4604
4634

5496
5888
5917
5818

 

%>

 

5153
4853
4997
5184

5533
6032
6961
5084

4966
4793
4668

53031
5487
5159

 

 

5114 5640

5619
5261
5246
5515

6240
6115
6214
5960

5009
5502
5094
5021

6191
6021
6240
5525

 

 

 

4391
4473
4669
4516

4982
5470
5164
5398

4629
4888
4897
4773

5405
5499
5612
5404

 

 

4759
5078
4878
5104

5777
5718
5618
5899

5203
4677
5292
4981

5896
5812
5693
5728

 

 

4575
4625
4160
4512

5475
5266
5537
5150

4875
4580
4700
4102

5473
5692
5118
5801

 

5258
4688
4798
4184

5737
5556
5358
5401

4977
4460
4356
4592

5634
5487
5565
5486

 

 

 

 

- ‘ l
l
l

37
Is 1.1 (cont’d).

(b) Control Concrete

 

Control'
Moist Curing
7-day 14-day
Test Age Test Age
28-day 90-day 28-day 90-day

4872 5820 575 8 6286
5350 5928 4951 6352
5209 6188 5585 6366
5633 5848 5497 6193

 

 

 

 

 

 

5200 5737 5708 6203
5514 6139 5863 6311
5478 5982 5747 6588
5703 6150 6039 6502

 

 

 

 

 

 

or each ﬂy ash type and content in addition to control, specimens for different moist
ng periods and test ages were prepared from the same batch (and a replicated batch
replicated tests).

 

 

 

   

38
7000
—— FLY ASE—Fl
c — — — - FLYAS — 2
3 6500 ~— - —— FLYASH—C
v 0 TEST AGE=28 DAYS
TEST AGE=90 DAYS
6000

5500

5000

COMPRESSIVE STRENGTH

A
01
O
O

 

 

 

4000 .
o 20 4o
FDYASFICONTENT(Z)

(a) 7—Day Moist Curing

 

 

 

 

 

7000
FLYASH—Fl
FLYASH—FZ
HSﬁgagewws

6500 TEST AGE=90 DAYS

6000

5500

5000

4500

4000 1 , ‘ ' t ' T

O 10 20 30 4O

FUYASFICONTENT(Z)

(b) 14—Day Moist Curing

3.2 Compressive Strength Vs. Fly Ash Content.

 

39
The two Class F ﬂy ash types at the 10% and 20% substitution levels showed similar or

higher 28- and 90-day compressive strengths when compared with the control concrete
containing no ﬂy ash (0% substitution), except for the 20% substitution-level at-90 day
testing in the case of 7-day moist curing. The Class C ﬂy ash at all replacement levels
(except for the 10% substitution level at 90—day testing in the case of 7-day moist curing)
and the Class F ﬂy ash at the 30% substitution level reduced the compressive strength
compared to the concrete containing no ﬂy ash (0% substitution). This was in spite of
the fact that Class C ﬂy ash was effective in reducing water requirement for achieving
desirable workability. The relatively high alkali content of the Class C ﬂy ash could be
ldversary inﬂuencing the development of strength in concrete materials (Rose et a1,
1989 .21
A comprehensive analysis of test data presented in Figure 3.2 is given below.
e effects of moist curing duration on the 28- and 90-day compressive strength are
own in Figures 3.3(a) and 3.3(b), respectively. As expected, longer moist curing
ration causes an increase in compressive strength. Concretes incorporating Class C
ash at all replacement levels (10, 20, and 30%), however, were not greatly effected
extending moist curing except for the 28-day compressive strength at 10% substitution
e1. The increase in compressive strength with longer moist curing duration was
ﬁrmed statistically (using the separation of means technique) at 99% level of
ﬁdence. The 90-day compressive strength of concretes containing any of the two
ss F ﬂy ashes was more sensitive to the increased moist curing duration when

pared to control concrete with no ﬂy ash. This can be attributed to the pozzolanic

 

 

 

 

————+;
T'.

40

9 Compressive Strength (ksl)

 

 

 

 

Class-O Class-F(2) Class~F(l)

(a) 28-Day age of testing

Compressive Strength (ksl)

 

9
8 ... ._.L ....... ,. .. .. .. 7-Day Molst Ourln m 14 Da Mlsl Curin

 

 

ooooooo 10% 20% 80% 10% 20% 80% 10% 20% 80%

Class—C Class-F(2) Class-F(l)
(6) 90—Day Age of Testing

3 Effects of Moist Curing Duration on Compressive Strength Development.

 

41

reaction which generally takes place at a slower rate than typical hydration of Portland
cement; longer moist curing and testing at later ages seem to beneﬁt pozzolanic reaction
in the presence of Class F ﬂy ash.

Figures 3.4(a) and 3.4(b) show the effects of testing age (air-drying duration) for
he 7- and 14-day initial moist curing durations, respectively. In both ﬁgures, strength
Ievelopment is observed to continue in concretes with or without ﬂy ash in spite of the
iterruption in moist curing (and storage at 23 °C and 45_-l;5% RH). Therefore, exposure
)low-humidity environment can promote compressive strength development. Statistical
ralyses of results conﬁrmed, at 99% level of conﬁdence, that air-curing for 28 to 90
lys contributes to strength developments in all mixtures considered in this investigation,
respective of the ﬂy ash type and content.

On the average, the increase in compressive strength with continued air-curing
cm 28 days to 90 days) was 20 to 25% in the case of Class C ﬂy ash, and 11 to 17%
the case of Class F ﬂy ash and control mixtures (no ﬂy ash), except for the 20%
stitution level of Class F ﬂy ash which showed a small increase (6%) in compressive
ngth with extended air~curing. It should be noted that in the case of Class F ﬂy ash
er moist curing helped pronounce the effects of extended air-curing on compressive
gth. This further conﬁrms that Class F ﬂy ash concrete, when compared to Class
y ash concretes and control mixtures, required longer moist curing durations to

e its strength development potentials.

 

 

—: 1 .
1 .

42

 

g Compressive Strength (ksl)

 

 

Class-C Class-F(2) Class-F(1)

(a) 7-Day Moist Curing

 

) Compressive Strength (ksl)

 

 

Class-C Class-F(2) Class-F(i)

(b) 14—Day Moist Curing

- Effects of Air-Drying Period on Compressive Strength Development.

ll

 

 

43
3.4.2 Relationship Between the Permeability and Compressive Strength

Permeability test results were produced in chapter 2 with similar moist curing
condition and age of testing. This section is concerned with the correlation between
permeability and strength of ﬂy ash concrete. Figure 3.5 shows the correlation between
permeability and compressive strength for all test results. Correlation coefﬁcient (which
provides a measure of the interrelationship between strength and permeability) was 0.16,
Indicating no strong correlation between permeability and compressive strength which is
generally applicable irrespective of ﬂy ash type and content, curing condition, and age
a strong positive correlation would have resulted in a correlation coefﬁcient greater than
1.40). The fact that moist curing duration and air drying do not affect strength and
lermeability similarly is partly responsible for the lack of any strong correlation between
1e tow. As shown in Tables 3.2 and 3.3, extended moist curing and longer periods of
Ir drying, respectively, cause changes in strength and permeability which are, at 99%
vol of conﬁdence based on statistical analysis of results, quite different in magnitude

nd actually in opposite directions in the case of longer air-drying effects).

 

 

 

44

 

Permeability

XX

>K>leK 9K 9K

x * ¥>K x

 

 

 

4000

4500

5000 5500 6000 6500

Compressive Strength (psi)

7000

 

 

 

ure 3.5 Permeability Vs. Compressive Strength.

le 3.2 Percent Change in Permeability and Strength with l4-Day Moist Curing
compared to 7-Day Moist Curing (positive change corresponds to increase
in strength and decrease in permeability): All Results at 28 Days of Age.

Ash Fly Ash Content

rpe 10 % 20 % 30%

>ck

F ) Permeability Strength Permeability Strength Permeability Strength

'1) 31 5 67 5 62 6

2) 37 6 6O 7 54 4

T 22 6 66 1 51 1

 

 

 

 

 

 

‘.~....~..

 

 

 

Table 3.3

 

45

Percent Change in 28-Day Permeability and Strength After Air-Drying Up
to 90 Days (positive change corresponds to increase in strength and
decrease in permeability): All Results For 7 «Day Moist Cure.

-
4—

l]

 

 

 

 

 

 

 

 

 

 

 

 

 

Fly Ash Content
10% 20% 30 %
Permeability Strength Permeability Strength Permeability Strength
F(1) -27 13 -16 5 -25 11
F(2) -41 13 ~32 6 -24 8
23 24 -106 20

In order to provide more insight into the relationship between strength and
termeability, correlation studies were also conducted on subsets of the conditions
onsidered in this investigation. Tables 3.4 and 3.5 show the correlation coefﬁcients
etween permeability and compressive strength for different subsets of the test data.
able 3 .4 indicates a very strong positive correlation (i.e. correlation coefﬁcient
:ceeding 0.7) between strength and permeability for each ﬂy ash type at different ﬂy
h contents (see full lines in Figure 3.6 for a typical condition), indicating that an
:rease in strength leads to an unexpected increase in permeability for each ﬂy ash type
hen ﬂy ash content is a variable). Table 3.5 indicates a very strong negative
relation (i.e. correlation coefﬁcient less than —O.7), except for the 7-day moist curing
e at 90 days of age for 20 and 30% ﬂy ash contents (see dashed lines in Figure 3.6
a typical condition). Hence, permeability generally decreases as strength increases

expected) for a constant ﬂy ash content and variable ﬂy ash types.

 

 

46

‘able 3.4 Correlation Coefﬁcients Between Compressive Strength and Chloride
Permeability for Each Fly Ash Type and Different Fly Ash Contents.

 

ble 3.5 Correlation Coefﬁcients Between Compressive Strength and Chloride
Permeability for Constant Fly Ash Content and Different Fly Ash Types.

 

Moist Curing
Ply Ash 7-Day 14-Day
Content Test Age Test Age

I 28-Day 90-Day 28-Day 90—Day
M ' -O.891 -0.752 -0.962 -0.985
20% I -o.999 0.491 -0.973 -O.898
30% 1 -O.972 -O.465 -O.874 -O.897

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

47

 

18000 T T V

16000 -

   

14000 -

10% Fly Ash Content
12000 — x

10000 -

i

8000

 

6000 -

Permeability (Coulombs)

 

 

 

4000 -

2000

O J . . .

4000 4500 5000 5500 6000

 

Comp. Strength (psi)

:ure 3.6 28—Day Permeability Vs. Strength (Typical Test Results and Regression
Lines). .

 

 

 

48

It seems that increased ﬂy ash content has particularly positive effects on reducing
permeability while it may damage strength at earlier ages. This may result from the
overshadowing beneﬁts of the blocking of capillary pores by pozzolanic reaction on
permeability; in the case of compressive strength it seems that the adverse effects of the
relatively slow rate of pozzolanic reaction (compared to cement hydration) is not
compensated for by the blocking of capillary pores. Any shrinkage microcracks
developed in concrete under air drying would also have more pronounced effects on

permeability than on compressive strength.

 

The above correlation study suggests that the measurement of strength alone may

produce misleading results as far as the permeability of ﬂy ash concrete is concerned.

 

The higher ﬂy ash contents are generally beneﬁcial to permeability while strength at
earlier ages may be reduced. This has important practical implications in applications,

where permeability is a prime concern.

345 SUMMARY AND CONCLUSIONS

The effects of ﬂy ash type and content on compressive strength development of
concrete processed in two different curing conditions and tested at two different ages
were investigated. Three different ﬂy ash types (two Class F and one Class C) and three
different ﬂy ash contents in addition to the control (0% substitution) were considered.
Split-plot analysis of variance with repeated measurements was used to analyze the data

statistically. It was concluded that:

 

 

 

 

49

1. All variables of this investigation (ﬂy ash type, ﬂy ash content, moist curing
period, and age of testing) as well as their paired interactions (except for the
interaction of ﬂy ash type with content and ﬂy ash content with moist curing)
inﬂuenced the compressive strength of concrete.

2. The two Class F ﬂy ashes at 10% and 20% replacement levels generally showed
similar or higher 28- and 90-day compressive strengths when compared with the
control concrete containing no ﬂy ash; the reverse was generally true for Class

C ﬂy ash at all replacement levels and Class F ﬂy ash at 30% replacement level.

 

This was in spite of the fact that Class C ﬂy ash was effective in reducing water

demand. The relatively high alkali content of the Class C ﬂy ash may illustrate

 

its adverse effects on strength.

As the moist curing duration increased, the ﬂy ash concrete became stronger;
Class C ﬂy ash was generally an exception to this rule. It should be noted that
the 90-day compressive strength of concretes containing any of the two Class F
ﬂy ashes was more sensitive to the increased moist curing period than control
concretes with no ﬂy ash.

The interruption of moist curing and exposure to a low-humidity (interior)
environment led to continued increase in strength irrespective of ﬂy ash type and
content. The low-humidity environment, however, damaged permeability
possibly by introducing shrinkage microcracks the effects of which on
permeability could not be compensated for the slow progress of hydration and

pozzolanic reaction in a low—humidity environment.

 

 

 

 

50

No strong correlation could be drawn between strength and permeability in ﬂy
ash concrete. Depending on the speciﬁc subset of the ﬂy ash concrete mixtures
selected, the correlation could vary from positive to negative, indicating that
reliance on strength test results for the evaluation of ﬂy ash concrete permeability

can be misleading.

 

 

CHAPTER FOUR

EFFECTS OF FLY ASH ON SULFATE RESISTANCE OF CONCRETE AND

CORRELATION WITH PERMEABILITY

$1 INTRODUCTION
One of the most widespread and common causes of concrete deterioration is due

to the action of sulfates on cement paste. Sulfates are often present in groundwater,

 

particularly when high proportions of clay are present in the soil, and in seawater, of

which they are a major constituent. In groundwater there may be very high

 

concentrations of sulfates in the vicinity of industrial wastes such as mine tailings, slag
heaps, and rubble ﬁlls. Sulfates are also present in acid rainfall caused by air pollution,
or can be produced by biological sources. ‘9 Structural deterioration and damage due to

sulfate attack are shown in Figures 4.1-a and 4.1-bf“22

 

Concretes exposed to sulfates tend to deteriorate gradually with age through
undergoing cracking, spalling and loss of strength due to the formation of hydrates of
calcium sulphate (gypsum) and calcium sulphoaluminate (ettringite). The reason for this
deterioration is that both these compounds occupy a greater volume than the compounds
which they replace so that expansion and disruption of concrete would take place.
Recommended methods of testing the potentials for sulfate attack are based on evaluation

of the change in mechanical strength (compressive or particularly ﬂexural strength) or

51

 

 

52

 

(b) Dam

Ire 4.1 Damage to Concrete Structures Resulting from Sulfate Attack."22

 

 

 

53

expansion when immersed in sulfate solutions (e. g. ASTM 01012).

The main thrust of this study was to assess the effects of ﬂy ash type and content
on the sulfate resistance of concrete. Correlations between permeability and sulfate
resistance of ﬂy ash concrete were investigated in order to check the hypothesis that ﬂy

ashes produce physical effects on the capillary pore system, thus inﬂuencing

permeability and eventually sulfate resistance.

1,; BAKR

 

4.2.1 Mechanisms of Sulfate Attack

Calcium hydroxide and alumina-bearing phases of hydrated Portland cement are
more susceptible to attack by sulfate ions.4 The hydration of tricalcium aluminate (CA)

in Portland cement involves reactions with sulfate ions which are supplied by the

dissolution of gypsum (calcium sulfate).

C3A + 3CSH2 + 26H ---> C6AS3H32
tricalcium aluminate + gypsum + wate --- > ettringite

At this stage, the formation of ettringite (calcium sulfoaluminate hydrate) is harmless

because the concrete is still in a semi-plastic state. If the sulfate is fully consumed before

the CA has completely hydrated, ettringite is transformed into monosufoaluminate.19
Soluble sulfate attack on concrete is generally believed to take place in either or

both of the following ways:

1. Sulfate ions, except for the case of calcium sulfate attack, react with calcium

 

 

 

 

54

hydroxide to produce gypsum which causes expansion and cracking or softening
of concrete.

2. Sulfate ions react with the hydration products of C3A (like hydrated calcium
aluminate and monosulfoaluminate) to produce ettringite which can also cause

expansion and cracking.

Sulfate ions can come from either calcium, sodium or magnesium sulfate.
Magnesium sulfate exerts a more damaging effect than other sulfates because it leads to
the decomposition of the hydrated calcium silicates (C-S-H) as well as the Ca(OH)2 and
of hydrated C3A; eventually, hydrated magnesium silicate is formed which has no
cementing properties. 17

Both the physical and chemical properties of concrete are important to sulfate
attack. In general, the diffusion of sulfate ions into the pores of concrete is controlled by
the porosity and permeability of concrete. As internal cracking occurs, the effective

permeability coefﬁcient of concrete tends to increase, accelerating further sulfate attack.

4.2.2 Fly Ash Effects on Sulfate Attack
The use of ﬂy ash as a Portland cement replacement in concrete improves its

chemical resistance, including the resistance to sulfate attack, through pozzolanic

  
   
 

eaction. The effectiveness of a ﬂy ash in improving sulfate resistance may depend on
e degree of pozzolanic reaction and therefore on the physical and chemical properties

f the ﬂy ash; these properties vary with ﬂy ash type and source, and all ﬂy ashes are

 

 

 

 

55

not equally effective in improving sulfate resistance.23
As it has been mentioned earlier, the major factors contributing to the expansion
mechanisms under sulfate attack are those reactions involving calcium hydroxide and the
hydration products of C3A. When the ﬂy ash is used as a cement replacement, the C3A
content of cement is diluted; the extent of this dilution, however, may be reduced by
using high calcium ﬂy ashes containing measurable amounts of (15A.24 The pozzolanic
reaction of ﬂy ash reduces the amount of calcium hydroxide in the hardened concrete;
this effect is less pronounced with ﬂy ashes which have high calcium oxide contents.”
Reduced permeability of concretes in the presence of ﬂy ash also helps in controlling
sulfate attack; the conversion of calcium hydroxide through pozzolanic reaction to low-
density calcium silicate hydrate leads to partial blocking of capillary pores and thus

reduced permeability of concrete containing ﬂy ash.

  
  
  
  
  
  
  
  
  
  
  

Mehta (1981)26 suggests that ﬂy ash inﬂuences the sulfate resistance of concrete
dominantly by reﬁning capillary pore size distribution rather than modifying the chemical
composition. Also Mehta (1986)27 concludes that, rather than chemical composition or
the R—factor of ﬂy ash (R=(%CaO - 5)/ %Fe203), it is the mineralogical composition of
the cement-ﬂy ash interaction product that controls the sulfate resistance. Tikalsky and
Carrasquillo (1992)28 have studied the inﬂuence of ﬂy ash on the sulphate resistance of
concrete, and through correlating the chemical or mineralogical composition of ﬂy ash
ith the sulphate resistance of concrete concluded that ﬂy ashes with high amounts of
cium oxide and amorphous calcium aluminate increase the susceptibility of concrete

5 o sulphate attack; however, ﬂy ashes with low amounts of calcium oxide decrease the

 

 

 

 

 

56
susceptibility of concrete to sulphate attack.

In short, the improvements in the sulfate resistance of ﬂy ash concrete can be
attributed to two factors: (1) reduction in the free lime content due to the chemical
pozzolanic reaction; and (2) reduction in permeability due to pore reﬁnement by the extra

hydration products deposited by the ﬂy ash.29

1.; EXPERIMENTAL PROGRAM

The effects of ﬂy ash type and content on the sulfate resistance of concrete were
investigated, and the relationship between sulfate resistance and 28-day permeability was
established. The experimental design was based on a replicated 4 x 3 (4 ﬂy ash types
x 3 ﬂy ash contents) factorial design (see Table 4.1). Control tests with no ﬂy ash (two
replications) were also performed. The replacement levels of cement with ﬂy ash were
10, 20 and 30 % by weight of cement. One replication in this investigation refers to the
mean value of test results on at least four specimens from two different mixtures.

The materials used in this experimental study were Ottawa sand (ASTM 0109)
with a maximum particle size of 0.6 mm (0.024 in.), type I Portland cement, and four
ﬂy ash types (two Class F and two Class C). Table 4.2 presents the chemical
composition, ﬁneness and speciﬁc gravity of the cement and ﬂy ashes used. The mortar
mixtures considered in this investigation had a sand-binder ratio of 2.75 by weight.

Mixing was carried out according to ASTM 0305. Water content was adjusted to give

 

a ﬂow (ASTM C-109) of IOU-110%.

 

 

 

 

 

 

 

 

 

 

57
Table 4.1 Factorial Design of Experiments.
FLY ASH TYPE
FLY ASH
CONTENT F(l) F(2) (3(1) (3(2)
10% I i I I
20% : : : :
30% : : : :
, ____________L___________J________J___._____J_________.i,

 

 

 

 

- Average of at least four specimens from the same batch

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 4.2 Fly Ashes and Cement Properties (percent by weight).
g— m
Property Cement Class-F(l) Class-F(2) Class-C(l) Class-C(2) ll
Silicon dioxide (SiOz) 20.49 49.30 51.41 31.8 32.2
Aluminum oxide (A1203) 5.39 26.70 28.75 20.7 20.5“
Ferric oxide (Fe/203) 2.55 8.95 8.43 6.45 6.58
Calcium oxide (CaO) 62.42 1.70 1.76 19.60 26.20
Magnesium oxide (MgO) 3.63 1.50 1.60 4.82 7.06
Sulfur trioxide (803) 3.19 0.52 0.35 4.50 1.78
Total Alkalies (as NaQO) 0.80 3.70 2.80 7.25 2.50
Loss on ignition 2.00 5.50 3.66 0.60 0.50
Speciﬁc gravity 3.15 2.13 2.17 2.58 2.62
Fineness (% retained 10.7 19.60 34.70 16.00 21.30
on # 325 sieve)

 

 

 

 

 

 

 

 

ﬁ
ﬁ

 

 

J9

 

58

$4 TEST PROCEDURES
Test procedures mostly followed ASTM C-1012. Sulfate resistance tests were
conducted on 25.4 x 25.4 x 285.8 mm (1 x 1 x 11 in.) mortar bars. 50.8 mm (2 in.)
cubes were used to monitor the development of compressive strength. Mixing was carried
out according to ASTM C-305. Two batches were prepared for each mixture
composition; six mortar bars in addition to the cubes were made from each mix. A total
of 156 bars were prepared. After molding, the specimens were covered with a sheet of
plexiglass and sealed. They were then placed in a curing tank containing water at 35 i
3 °C (95 _~l_— 5 °F ) for 24 hours and then removed from molds. The bars and cubes were
cured in saturated lime water at a temperature of 22 °C (74 °F) until a compressive
strength of at least 2850 psi (20 War) was reached. Thereafter, the initial and

subsequent length measurements were made.

 
 
  
   
 
  
  
  
  

Mortar bars were subsequently immersed in a water bath containing 5% (0.35
molar) sodium sulfate (Na2S04) solution in distilled water. The sulfate solution in the
bath was circulated to eliminate any sedimentation. The proportion of sulfate solution
to mortar bars in the water bath was 4 volume of solution to 1 volume of mortar bars.

The mortar bars were tested for length variation after 1, 2, 3, 4, 5, 6, 7 ........ 50
eeks (until all the samples disintegrated). In the ﬁrst 28 days, the sulfate solution was
eplaced once every 7 days with a fresh solution having a pH of 7 to 8; after the ﬁrst 28
ys, the sulfate solution was replaced with a fresh solution once every 4 weeks. It
ould be noted that when the bars were immersed in a fresh solution the pH increased

about 9—11 in less than 24 hours. This can be attributed to the formation of NaOH

 

 

h

 

59

and the decrease in the amount of 804' as the sulfate attack proceeded. The solution was

not adjusted for a constant pH between changing solutions.

4L5 JET mULTS AND DISCUSSION
4.5.1 Test Results

Different mixtures considered in this investigation all had comparable levels of
workability, i.e. a ﬂow (ASTM C-109) of 100-110%. As shown in Figure 4.2, the
addition of Class C ﬂy ash reduces water requirements considerably, whereas the

addition of Class F ﬂy ash does not change the ﬂow (and thus water requirements)

 

 

 

 

 

 

 

 

 

 

substantially.
0.600
0.575 e ------------------------------------
5:, Class F(2)
<3:
2 _________________
u. .
:1: " \Claes F(1)
g _____________________
E
a)
Q
t: ___________________________________
g Class 0(2)
0.475 - ———————————————————————————— gasaguin
0.450 n r r
0.0 10.0 20.0 30.0 40.0

FLY ASH CONTENT (%)

  
 

gure 4.2 Effects of Different Fly Ash Types and Contents on Water Requirement
for Constant Workability.

 

 

 

 

60

Average expansions at different ﬂy ash contents are shown in Figures 4.3, 4.4,
4.5 and 4.6 for ﬂy ash types F(l), F(2), C(1) and C(2), respectively. The disintegration
point shown in these ﬁgures indicates excess cracking, deformation or softening in most
of the replicated specimens for each test condition. The two Class F ﬂy ashes at the
20% and 30% replacement levels, and the Class C(l) ﬂy ash at the 30% replacement
level, are effective in delaying the disintegration caused by sulfate attack. In general, the
Class F ﬂy ashes were superior in increasing sulfate resistance when compared with
Class C ﬂy ashes. Typical pictures of the specimens damaged through expansion and
cracking under sulfate attack are presented in Figure 4.7 . It should be noted that
expansion and cracking alone may not reﬂect the level of sulfate attack; softening of
specimens may prevent expansion under sulfate attack while the specimens are actually
disintegrating. Fly ash C(2) showed a high degree of softening, partly because it

produced concretes with the highest permeability.

 

 

 

61

0.5

 

B B B: Disintegration * 0%
+ 10% _
* 20%
B + 30%

.0
A
r
~o

 

% Expanson
O O
N 00
MN
\o\

 

 

 

 

  

 

 

 

“ "'i"'|"'i"'l"'i'"i"‘i"'l"'i"‘
O 4 81216202428323640444852

 

 

 

 

 

 

Time (Weeks)
Figure 4.3 Percent Expansion Vs. Time for Fly Ash F(l).
0.5
Br 8: Disintegration * 04’
o4 BA +404
* 20%
8 13 7s + 30%
g 0.3 # f
8 B
”)5, 0.2 f
0.1
O i r

 

 

 

I l i l i l I i l I
O481216202428323640444852
Time (Weeks)

Figure 4.4 Percent Expansion Vs. Time for Fly Ash F(2).

 

0.5

.0
rs

% Expanson
O
to

.0
m

0.1

62

 

 

 

 

 

 

 

 

 

ﬂ
B: Disintegration 1““ 0%
—— BA +10%
[ *20%
+30%
71
8%? ./B
r
r'1" l"'l"'i"'i"'l"'i"'l"'l"‘i"'l"
O 4 81216202428323640444852

Time (Weeks)

 

 

 

 

 

 

 

 

 

 

Figure 4.5 Percent Expansion Vs. Time for Fly Ash C(1).
0.5
B: Disintegration 1‘5 0%
B o
Q4 .. +101.
[ 420%
C + 30%
.3 0.3
C B
(U
8 7I
°\o 0.2
B
0.1 B
O T'i"'l'1'l"'l"'l"'l"'l"'|"'|"'l"'l"'l"'l
O 4 81216202428323640444852
Time (Weeks)
Figure 4.6 Percent Expansion Vs. Time for Fly Ash C(2).

63

 

 

(b) 10X Magniﬁcation

Figure 4.7 Specimens After Deterioration due to Cracking Under Sulfate Attack.

 

64
4.5.2 Statistical Analysis and Discussion

Split-plot analysis of variance with repeated measurements was used to analyze
the data statistically. This analysis of test results conﬁrmed, at 99 % level of conﬁdence,
that all the variables of this investigation (ﬂy ash type, ﬂy ash content, and the duration
of exposure to sulfate solution) as well as their interactions inﬂuenced the expansion of
concrete materials under sulfate attack.

The separation of means technique was used to identify the ages at which there

were signiﬁcant effects exerted by the ﬂy ash type and content on expansion at 99 % level

of conﬁdence (see Tables 4.3 and 4.4).

 

 

 

 

 

 

 

 

 

 

 

 

Table 4. 3 Test Ages (weeks) at Which the Effect of Fly Ash Content Was
Conﬁrmed at 99 % Level of Conﬁdence.
Fly Ash Fly Ash Type
C
”m Fa) F(2) ca) C(2)
0% Vs. 10% a a a a
10% Vs. 20% 11 9 a a
20% Vs. 30% 27 10 9 a
IH—“i—W

a: Statistically Comparable at All Ages Considered.

Tal

 

 

65

Table 4.4 Test Ages (weeks) at Which the Effect of Fly Ash Type Was Conﬁrmed
at 99% Level of Conﬁdence.

 

 

 

 

Fly Ash Fly Ash Content

Type 10% 20% 30%
F1 Vs. F2 9 10 15
F1 Vs. C1 7 10 19
F2 Vs. C2 6 8 9
F2 Vs. C1 7 10 23
F2 Vs. C2 6 8 10
C1 Vs. C2 a a 9

 

 

 

 

 

: Statistically Comparable at All Ages Considered.

n analysis of these tables suggests that:
At 10% replacement level, regardless of ﬂy ash type, the sulfate resistance of ﬂy
ash concrete was comparable to that of the control concrete without ﬂy ash (see
Figures 4.3, 4.4, 4.5, 4.6 and Table 4.3).
The two Class C ﬂy ashes at any replacement level, except for Class C(l) at
30% , did not produce any substantial change in sulfate resistance when compared
with the control concrete (see Figures 4.5, 4.6 and Table 4.4).

The two Class C ﬂy ashes behaved similarly except at 30% replacement level (see

Table 4.4).

 

66

4. There were differences in the response of the two Class F ashes to sulfate attack
(see Table 4.4).
S. The two Class C ﬂy ashes at any replacement level produced faster cracking than

the Class F ﬂy ashes (see Table 4.4).

4.5.3 Correlation Studies

In order to determine the underlying reasons for ﬂy ash effects on the sulfate
resistance of concrete, attempts were made to establish correlations between sulfate
resistance and permeability of concrete, and also between sulfate resistance and ﬂy ash
:haracteristics.

Fly ash reduces concrete permeability by reﬁning the capillary pore system. For
he concrete mixes considered in this investigation, rapid chloride permeability
:xperiments (ASTM C-1202 or AASHTO T-277) were conducted on continuously moist-
:ured specimens at different ages (28 days, and 2, 3 and 6 months); the permeability test
esults are presented in Table 4.5.

The relationships between disintegration time under sulfate attack and permeability
t different ages are presented in Figures 4. 8(a) through 4. 8(d) for concrete mixtures
rith different percentages of various types of ﬂy ash. Permeability, particularly after
inger periods of moist-curing, is ob served to correlate well (in a non-linear fashion)
ith sulfate resistance, irrespective of the speciﬁc ﬂy ash type and content. Reduced
=rmeability mitigates sulfate attack by reducing the diffusion of sulfate ions into

increte; also, reduced permeability may indicate increased pozzolanic reaction and

 

 

67

consequently reduced calcium hydroxide content in concrete (a factor which also reduces
sulfate attack). In any case, Figures 4.8(a) through 4.8(d) suggest that one may use
permeability test results to rank ﬂy ash concretes with different ﬂy ash types and contents
based on resistance against sulfate attack. It should be noted that correlation studies
indicate that the calcium and silicon oxide content of ﬂy ash are key factors in
inﬂuencing permeability and thus sulfate resistance of ﬂy ash concrete; the higher
calcium oxide and lower silicon oxide contents resulted in higher permeability and lower
sulfate resistance of concrete.

The fact that expansion alone, disregarding softening, cannot fully represent the
.evel of sulfate attack is partly reﬂected in Figure 4.9. While the time to disintegration
:measured based on visual observation of specimens) correlated well to permeability (see
2igure 4. 8), the measured value of expansion under sulfate attack did not correlate well
vith permeability (Figure 4. 8) because some specimens (particularly those with ﬂy ash

3(2)) softened without excess expansion.

 

 

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4. 8 Relationships Between Sulfate Resistance and Permeability at Different Ages.

 

70

 

._.L
O)

_.L
.b
l
N

 

-—L
[\D
i

_L

O
I
N
9K

 

 

PERMEABILITY (Thousand Coulombs)

 

 

 

 

8 — a
o

6 0 a 9K [X Class-C(2) \

4 — .k 9K Class-0(1)

2 ﬂ oi" a Class-F(2)
0 Class-F(i)

0 a i i w T

0 0.02 0.04 0.06 0.08 0.1 0.12

 

% EXPANSION

e 4.9 Relationship Between 42-Day Expansion and 2-Month Permeability.

 

 

71
4,5 srmanv m QQNQLysIQNs

The effects of the ﬂy ash type (two Class F and two Class C) and content (10,

20 and 30 % by weight of cement) on the sulfate resistance of concrete were investigated.

Correlations were drawn between the sulfate resistance and permeability of concrete

materials. It was concluded that:

1. Fly ash type and replacement level both inﬂuence the sulfate resistance of
concrete at 99 % level of conﬁdence; their interaction was also signiﬁcant.

2. The two class F ﬂy ashes at 20% and 30% replacement levels, and one of the
Class C ﬂy ashes (ﬂy ash C(1)) at 30 % replacement level are effective in
resisting sulfate attack (delaying disintegration time). There were also differences
between the two class F ﬂy ashes

At lower replacement levels (10%), regardless of ﬂy ash type, the sulfate

 

resistance of ﬂy ash concrete was comparable to that of the control concrete
without ﬂy ash.

The two Class C ﬂy ashes at any replacement level, except for ﬂy ash C(l) at
30 % , did not produce any substantial change in sulfate resistance when compared
with the control concrete.

The Class F ﬂy ashes were superior in increasing sulfate resistance when
compared with the Class C ﬂy ashes (i.e. the two Class C ﬂy ashes at any
replacement level produced faster degradation than the Class F ﬂy ashes).
Strong correlations were found between disintegration time under sulfate attack

and permeability for all concrete materials (irrespective of the ﬂy ash type and

 

 

 

72

content). Concrete permeability seems to be fundamental to its sulfate resistance,
and ﬂy ash effects on permeability seem to be largely responsible for the
corresponding effects on sulfate resistance of concrete. The signiﬁcance of
permeability may partly reﬂect the fact that it also represents the level of
pozzolanic reaction which causes favorable chemical effects in concrete through
the consumption of calcium hydroxide.

The calcium and silicon oxide contents of ﬂy ash were the key factors inﬂuencing
permeability and thus sulfate resistance of ﬂy ash concrete; higher calcium oxide
and lower silicon oxide contents increased the permeability and lowered the
sulfate resistance.

Expansion alone, disregarding softening, cannot fully represent the level of sulfate
attack. The reliance on expansion test results for evaluating sulfate resistance of

ﬂy ash concrete can be misleading.

 

 

CHAPTER FIVE

FLY ASH EFFECTS ON ALKALI—SILICA REACTION

L1 w

Prior to 1940, it was generally assumed that aggregates are innocuous and inert
constituents of Portland cement concrete. It is now recognized that all natural rocks react
with the alkaline pore solution in concrete to a greater or lesser degree. These alkaline
components in pore water are derived mainly from the Portland cement component of
concrete; other concrete constituents as well as the migration of alkalies from external
sources can contribute to the alkalinity of concrete pore water. While in most cases the
alkali—aggregate reactivity is not harmful, in some instances it can result in deleterious
expansion and cracking, leading to concrete deterioration. 3°

It is believed that there are three types of alkali—aggregate reaction which can lead
to cracking of concrete:

(a) alkali-silicate reaction

(b) alkali-carbonate reaction

(c) alkali-silica reaction, which is more common and is considered in this

study.

In spite of the differing mechanisms of expansion in each type of reaction, the

73

74

common factor is the alkaline pore solution. The alkali-silicate reaction is believed to
be a reaction between the metal alkalis in the pore water of concrete and an interlayer
precipitate in phyllosillicates. Alkali-silica reaction is a reaction between the hydroxyl
ions in the pore water of a concrete and certain forms of silica which occasionally occur
in aggregate. The alkali-silicate reaction is slower than the alkali-silica reaction.
Cracking of structures damaged by alkali silica reaction is usually observed in about 10
years after construction, while damage from alkali-silicate reaction is observed in about
20 years. Alkali-carbonate reaction takes place between certain dolomitic limestones and
the metal hydroxides in the pore water of concrete. Problems associated with dolomitic
limestones are rare and most limestone aggregates used in concrete have good
performance records and are innocuous. However, in North America, alkali-carbonate
reactions involving some dolomitic limestones have led to map cracking in concretes
, exposed to external moisture and frost attack. Cracking may be observed within 5 years
of construction.“’32
In the recent years concrete deterioration caused by alkali-silica reaction has
received considerable attention and publicity. Deterioration due to the alkali-silica
reaction is more common than deterioration due to either the alkali-silicate or the alkali-
carbonate reactions. These latter reactions and their effects are less understood than the
alkali-silica reaction. Examples of map cracking caused by alkali silica reaction are
shown in Figures 5.1—a and 5.1-b.31
The main thrust of this phase of research was to produce a comprehensive study

if the effects of ﬂy ash characteristics and replacement level on alkali—silica reaction in

 

 

75

 

(a) Wall Structure

"I; i (fl—7",?- .
. {3mg- -,-

ii‘_

' ‘*-. M Imuuqrug:
. up ..

 

(0) Beam Element

5.1 Concrete Deterioration Caused by Alkali-Silica Reaction.31

 

76

 

concrete materials made with cements having different total alkali contents (low,
moderate, and high). Three different ﬂy ash contents, four ﬂy ash types and three
ortland cements (with different alkali contents) were considered and sufﬁcient
eplications of tests were conducted in order to provide data for deriving statistically
eliable conclusions. Correlation studies were conducted in order to identify the key ﬂy

h characteristics inﬂuencing the alkali—silica reactions in ﬂy ash concrete.

.2.1 General

1 2 BACKGROUND ON ALKALI-SILICA REACTION

 

Alkali-silica reaction (ASR) is a chemical reaction between the hydroxyl ion in
.e pore water of concrete and certain forms of silica which occasionally occur in
gniﬁcant quantities in aggregates. It is not primarily a reaction between sodium and
itassium ions and reactive silica.“33
The alkalis in cement occur mainly as the readily soluble sodium and potassium
fates, as a mixed sodium/potassium sulphate and also in solid solution in the cement
ierals. When water is added to cement these alkali sulfates, together with calcium and
)hate ions from the gypsum and calcium hydroxide from the initial hydration reactions
he cement minerals produce the early pore solution in which potassium, sodium,
ium, hydroxyl and sulphate ions are all present in major proportion. The sulphate
calcium ions then begin to react with the hydrated tricalcium aluminate to precipitate
igite, lowering the sulphate and calcium concentrations and leaving the pore solution

iosed mainly of sodium, potassium and hydroxyl ions. Continuing dissolution of

 

 

77

sodium and potassium ions and reduction in the unbound water as the cement continues
0 hydrate enhances the hydroxyl ion concentration still further.34
The concentration of sodium, potassium and hydroxyl ions is dependent on the
uality of sodium and potassium compounds in the anhydrous Portland cement. The
ydroxyl ion concentration in a saturated solution of calcium hydroxide is 0.04 molar
or pH= 12.6; the pH of an aqueous solution is the logarithm of the reciprocal of the
ydrogen ion concentration. The pH of the pore solution in a concrete made with a low
' cement ranges from 12.7 to 13.1 and in the case of a high alkali cement from 13.5
13.9. The hydroxyl ion concentration in the pore solution of a concrete made with
high alkali cement can be ten times as high as that made with a low alkali cement. It
only in pore solutions of high hydroxyl ion concentration that signiﬁcant attack on the
lica occurs.31
It is known that alkali silica reaction (ASR) can be avoided by limiting the alkali
ntent in cement or by using non-reactive aggregates. However, there are some trends
rich increase the occurrence of ASR; the most important of these trends are: 1)
pletion of good aggregate sources; as a result some aggregates formerly considered
be of marginal quality are being used in concrete; 2) Increase in cement alkalis in
re areas due to changes in the manufacturing process; these changes have been
ught about by the national need to conserve energy and, at the same time, to reduce
ironmental pollution; and 3) The application of alkaline salts to concrete, due to the
of deicing chemicals.32

The hydroxyl ion concentration in the pores within concretes or mortars is a

 

F_i—7

78

function of the sodium and potassium contents of the cements used and the water/cement
ratio. It has been found that the induced expansion is more closely correlated with the
total alkali content expressed as equivalent percentage of NaZO than with the individual

contents of sodium and potassium oxides.31

 

Na20)mwm, = NaZO + 0.658(K20)
Equivalent sodium = sodium oxide + 0.658 x potassium oxide
ixide content content

In general, the induced expansion is dependent upon the quantity of reactive
ggregate present in the concrete (the content of reactive silica), the particle size of

:active aggregate, the alkali content of the cement, water/cement ratio, and temperature.

2.2 Mechanism of Expansion

The alkali metal hydroxides present in the pore water of cement paste attack the
active forms of silica to produce a gel of alkali silicates of variable composition. Gel
1ction products absorb water, thus growing in volume and causing a swelling pressure
develop within the concrete. As more water is absorbed the gel becomes more ﬂuid
1 able to ﬂow into cracks and voids within the aggregate and concrete.22 Continued
ilability of water to the concrete causes enlargement and expansion of microcracks,
ch eventually reach outer surfaces of concrete. The crack pattern is irregular and it
alled map cracking.4

ASR can be summarized as a result of two steps:

 

79
1. Hydroxyl ion (OH') + reactive silica = gel reaction product
2. Gel reaction product + moisture = expansion

.2.3 Pessismum Behavior

For the faster reacting forms of reactive siliceous constituents it has been found
at there is a proportion of reactive material in an aggregate which leads to a maximum
rpansion. The proportion of reactive material, or reactive aggregate, corresponding to
ie peak expansion is called the "pessimum content". A typical relationship between
rpansion and reactive material content is shown in Figure 5.2. The pessimum reactive

lica content in this case is approximately 2.5% by mass of total aggregate.

 

 

1.5 -
Expansion
M)

1.0 _

0.5 _

0 r I r I

ll 1 2 3 4 5
Opaline silica content ( % by mass)

 

re 5 .2 Relationship Between Expansion and Reactive Silica Content.31

 

 

80

The reactive silica/alkali ratio corresponding to the peak expansions lies in the
range 3.5-5.5. The behavior of mortars and concretes at this most critical silica/alkali
ratio is of particular practical signiﬁcance because if concretes do not crack at this
critical silica/alkali ratio, similar concretes containing higher or lower reactive aggregate

contents or higher aggregate/cement ratios will not crack.31

5.2.4 Fly Ash Effects on ASR

The main factors inﬂuencing the effectiveness of ﬂy ash in reducing hydroxyl ion
concentration include: the alkali level of the ﬂy ash, the ﬁneness/pozzolanicity of the ﬂy
ash, and the alkali level of the Portland cement; the alkali level is generally believed to
be the most important. A ﬁne, highly pozzolanic ﬂy ash with a low alkali level
substituting for a high-alkali cement will be most effective whereas a coarse, high-alkali
ﬂy ash substituting for a very low-alkali cement may increase the hydroxyl ion
concentration. The level of cement substitution with the ﬂy ash also inﬂuences the total
available hydroxyl ion content which is the main cause of ASR.31

Hobbs (1988)31 has concluded that all the alkalies in the cement and one-sixth of
the total alkalies in the ﬂy ash are available for reaction when the ﬂy ash content is
greater than 20% by weight. Nixon et a1. (1987)35 have suggested that the above
conclusions may only be valid for concretes containing aggregates with fast reacting
forms of silica such as opal which produce a conventional pessimum behavior.

The ﬂy ash contributes alkali metal and hydroxyl ion to the pore water but also

removes/reduces them possibly through incorporation into the CSH gel, the latter process

 

 

81

becoming predominant as the pozzolanic reaction begins to make a major contribution
after 28 days.

Lee (1989)36 has studied the effects of alkalies in class C ﬂy ash on alkali-
aggregate reaction. Pyrex glass was used as a reactive aggregate. Two type I cements
(with total alkalies of 0.49 and 0.85%) were used. Three class C ﬂy ashes (with total
alkali contents of 2.26, 3.39, and 7.37%) were used. Results obtained indicate that
replacement of high or low—alkali cement with class C ﬂy ash may negatively inﬂuence
concretes containing reactive aggregates if ﬂy ash is used arbitrarily. He concluded also
that replacement of small amounts of high-alkali cement and up to 40% of low-alkali
cement with the class C ﬂy ashes considered in his research produced greater amounts
of mortar bar expansions when compared with concrete without ﬂy ash. Effects of ﬂy
ash on mortar bar expansion seem to be dependent not only upon the percentage
replacement but also upon the composition of the cementitious materials. Maximum
expansions may be observed when the total equivalent Na20/8102 mole ratio of the
cementitious materials is at a critical value. This critical N/ S mole ratio seems to vary
from ﬂy ash to ﬂy ash. Fly ashes with higher alkali contents tended to have lager critical
N/S mole ratios’.

Kobayshi et al (1989)37 carried out a study on the effect of the quality of ﬂy ash
on controlling alkali-aggregate reaction. Fourteen ﬂy ashes were used with CaO contents
ranging between 1.7 to 9.0%. Total alkalies ranged from 0.4 to 3.22%. Type I Portland
cement with 1.2% total alkalies (considered high alkali) was used. The relationship

between expansion after 6 months and ﬂy ash composition was tested in the case of 10%

 

 

82

replacement, where the controlling effect depends on the type of ﬂy ash. Correlation
with SiOz, CaO, MgO, and equivalent NaZO contents were found to be -0.62, 0.5, 0.7
and 0.84, respectively. It was concluded that equivalent NaZO in ﬂy ash tends to
accelerate ASR, while SiO2 in ﬂy ash tends to prevent ASR. The quantity of alkali in
cement determines the effective amount of ﬂy ash substitution.

Carrasquillo and Snow (1987)38 have studied the effects of ﬂy ash on alkali-
aggregate reaction in concrete with different ﬂy ash types (two class F and two class C
having available alkali contents ranging from 0.57 to 4.35 %). Two type I cements (with
total alkalies of 0.43 and 0.66%) and type 1P cement with total alkali of 0.5% were
considered. Three sources of aggregate were used: highly reactive, medium reactive,
and pyrex glass as the control aggregate. It was found that replacing cement with ﬂy ash
generally tends to reduce expansions caused by alkali-aggregate reaction. The calcium
oxide content of ﬂy ash does not seem to have a signiﬁcant effect on alkali-aggregate
reactions in concrete.

Carrasquillo and Snow concluded that: (1) when the available alkali content of ﬂy
ash is less than 1.5 %, the effect of ﬂy ash on preventing expansions caused by alkali-
aggregate reactions increases as the level of replacing cement with ﬂy ash increases,
egardless of the of ﬂy ash type, its alkali content, the alkali content of cement, and
ggregate reactivity; (2) When the available alkali content of ﬂy ash is greater than

.5 % , there is a minimum replacement of ﬂy ash with cement below which the ﬂy ash
uses expansions larger than those of a mixture without ﬂy ash, and above which the

y ash causes smaller expansions. This minimum is referred to as pessimum limit.

 

 

 

L “th—

 

 

83

It should be noted that the effect of SiOz has not been considered in this study on
expansions caused by alkali-aggregate reaction. It has been mentioned that SiO2 has a
correlation coefﬁcient of -0.623 with the mortar bar expansion. Also, the results
obtained from the above study conﬂict with conclusions made by Lee (1989)36 who
studied the effects of alkalies in class C ﬂy ash on alkali-aggregate reaction. He
concluded that replacement of small amounts of high-alkali cement and up to 40% of
low-alkali cement with class C ﬂy ash produce greater amounts of mortar bar expansions
than expansions produced when ﬂy ash was not used.

According to Perry et a1 (1986)”, the amount of ﬂy ash required for limiting the
expansion of concrete due to ASR depends on the source and type of ﬂy ash (physical
and chemical properties of ﬂy ash), and can vary from 10% to more than 40% by weight
of Portland cement. Acid-soluble alkali content, lime content and speciﬁc surface area
(Blaine) were found most critical ﬂy ash properties which have important roles in
determining effectiveness against alkali-silica reaction .

The inﬂuence of ﬂy ash on the expansion of mortar bars containing either Pyrex
glass or Beltane opal has been studied by Robert (1986).40 The results show signiﬁcant
behavioral differences between Pyrex glass and Beltane opal. When Pyrex glass was
used, the ﬂy ash reduced the expansions of the mortar bars; all mixes were found to be
expansive in the absence of ﬂy ash. When Beltane opal was used, ﬂy ash increased the
expansion in all cases except at the pessimum. In practice, the reactive aggregates are
usually mildly reactive in comparison to the two aggregates.

Alasali (1989)41 concluded that there are pessimum alkali contents for particular

 

 

 

84

ﬂy ash replacement and alkali levels, at which point an alkali " counteraction " occurs;
below this point, the ﬂy ash contributes its alkalies to the reaction but no contribution

occurs above this point.

5_.3 EXPERIMENTAL PROGRAM

A comprehensive experimental study was conducted to investigate the effects of
the following key variables in ﬂy ash concrete mixtures on alkali-silica reactivity: ﬂy ash
type (alkali content), ﬂy ash content, and the total alkali content of cement. A factorial
design of experiments (4 ﬂy ash types x 3 ﬂy ash contents x 3 different alkali content of
Type I Portland cement) was devised for this study (see Table 5.1). Control tests

without ﬂy ash were also conducted.

.544 MELIALS.
The basic mortar mix constituents were cement, ﬂy ashes, aggregate, and water.

A brief description of all the materials used in this research is given below:

5.4.1 Portland Cement
Three different sources of Type I Portland cement were used. They were selected
based on total alkali contents: 0.53% (low alkali), 0.8% (moderate alkali), and 1.21%

(high alkali). Table 5 .2 presents properties of the cements used.

 

 

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86

Table 5.2 Cements Properties (Percent by weight).

 

 

 

 

 

 

 

 

 

 

 

Low-alkali Moderate-alkali High—alkali

Property cement Cement cement

Silicon dioxide (SiOz) 20.61 20.49 20.56
Aluminum oxide (A1203) 4.77 5.39 5.88
Ferric oxide (FeZO3) 2.20 2.55 2.41
Calcium oxide (CaO) 63.44 62.42 63.18
Magnesium oxide (MgO) 4.19 3.63 3.16
Sulfur trioxide (S03) 2.55 3.19 3.21
Total Alkalies (as NaZO) 0.53 0.80 1.21
Loss on ignition 1.18 2.00 1.63
Speciﬁc Gravity 3.15 3.15 3.15
F‘f:§;g§?sri:g‘ed 11.0 10.7 10.80

 

 

 

 

 

 

 

5.4.2 Fly Ash
Four ﬂy ashes were used, two class F and two class C. The chemical
. composition, ﬁneness and speciﬁc gravity of these ﬂy ashes are given in Table 5.3. The
1 major difference between the two class F (F(l) and F(2)) ﬂy ashes is in total alkali
content (3.8% and 2.9%) and ﬁneness(19.6% and 34.7% retained on #325 sieve). The
two class C ﬂy ashes can also be distinguished based on alkali content; ﬂy ash C(1) had

‘a high alkali content of 7.98%, and ﬂy ash C(2) had a low alkali content of 2.38%.

 

 

 

 

 

 

 

 

 

 

 

 

 

87
Table 5 .3 Fly Ashes Preperties (percent by weight).
Pmpe‘ty Class-F(l) ClasseF(2) Class-C(1) Class-C(2)
Silicon dioxide (3102) 49.30 51.41 31.8 32.2
Aluminum oxide (A1203) 26.70 28.75 20.7 20.55
Ferric oxide (FeZO3) 8.95 8.43 6.45 6.58
Calcium oxide (CaO) 1.70 1.76 19.60 26.20
Magnesium oxide (MgO) 1.50 1.60 4.82 7.06
Sulfur trioxide (803) 0.52 0.35 4.50 1.78
Total Alkalies (as NazO) 3.70 2.80 7 .25 2.50 h
Loss on ignition 5.50 3.66 0.60 0.50
Speciﬁc gravity 2.13 2.17 2.58 2.62"
Fineness (% retained 19.60 34.70 16.00 21.30"
on # 325 sieve)

 

 

 

 

 

 

 

5.4.3 Aggregates

Pyrex glass recommended by ASTM C-441 and opal have been used in most
published literature on alkali-silica reactivity, particularly in the presence of ﬂy ash.
Pyrex glass and opal, however are not representative of most alkali-reactive aggregates
and generally give rapid early expansion but do not represent the longer-term expansion
normally encountered with real aggregates. Therefore, a natural reactive aggregate was
selected for use in this study to better represent the longer-term expansion. This
aggregate was quarried limestone containing 4% microscopic Chalcedony from Spratt’s
Quarry near Ottawa, Ontario (Canada). Concrete made with this aggregate has shown

xpansion and cracking at the age of nine years. This aggregate was crushed and graded

 

 

88
according to the requirements of ASTM C-227.

5.4.4 Water

Distilled water with a PH of 7 was used in all mixes.

5.5 MIX PROPORTIONS

The mortar mixtures considered in this investigation had a ﬁne aggregate-binder
ratio of 2.25 by weight. A water/binder ratio of 0.55 was used in all mixes. Mixing
was carried out according to ASTM C-305. The range of ﬂow (following ASTM C-277)
was between 90 and 110%; control and class F ﬂy ashes had higher ﬂow than class C

ﬂy ashes.

M TEST PRQCEDCLES

Alkali-silica reaction tests were conducted on 25.4 x 25 .4 x 285.8 mm (1 x 1 x
11 in) mortar bars. Thirty nine different mixes were considered; four mortar bars were
made from each mix. A total of 156 bars were prepared. After molding, the specimens
were placed in moist cabinet for 24 hours and then removed from molds at which time
the initial length was measured.

Thereafter, the mortar bars were stored in four metallic containers. The bars
were placed randomly in cabinets, as they were rotated between different cabinets after
each measurement. These containers (Figures 5.3(a) and 5.3(b)) were designed following

ASTM C-227 requirements, except that they had a larger capacity (about 50 bars), and

 

 

 

cover

Al

N water-tight

""""""""" \\ stainless steel grid to
position mortar bars

mortar bar

  
 
  
 

/stainless steel grid

 

water

 

(a) Schematic of Set-Up

 

 

(b) The Actual Set-Up

ure 5.3 Alkali-Silica Reaction Test Set-Up.

 

 

9O

icking lines (absorbent materials) were placed inside the containers. Rogers and
ton (1989)42 suggest that the use of mortar bar containers with efﬁcient wicks is
essful in promoting expansion in Pyrex glass mortars. However, these containers
wick systems are not successful in promoting expansion with the majority of alkali-

reactive aggregates. It appears that successful testing requires removing the wicks
containers or sealing the bars in plastic bags.

The four containers were placed in a curing tank containing water in the bottom
°C (100 °F). The concept of placing the containers in a curing tank (having water
3 bottom) is based on the principle of a double regulation system of R.H..

The mortar bars were tested for length variation after 14 days, and 1, 2, 3, 4, 5,

8, 9, 10, 11, 12, 13, 14 and 15 months.

TEST RESULTS AND DISCUSSICN
Test Results

The expansion test results presented here are the average values of expansion in

ortar bars cast from each mixture; the individual test results satisﬁed the ASTM

precision limits.

Average expansions at different ﬂy ash contents, for ﬂy ashes F( 1) and F(2), are

in Figures 5.4 through 5 .6 for three cements having different alkali contents. The
ss F ﬂy ashes at any replacement level, regardless of their alkali content, reduced
ansions caused by alkali-silica reaction, particularly with high- and moderate-alkali

(1.21% and 0.8%). Figures 5.7 through 5.9 show the average expansions at

 

 

 

 

 

91

ifferent ﬂy ash contents for ﬂy ashes C(1) and C(2) and three cements having 0.53, 0.8
id 1.21% alkali contents. The high-alkali Class C ﬂy ash is observed to generally

crease ASR expansions, particularly at lower replacement levels and with low alkali

 

ment. The low-alkali Class C ﬂy ash, however, produced ASR expansions which were
3 than or similar to that of control.

While the alkali content of Class F ﬂy ash did not substantially inﬂuence alkali—
ica reactivity, the alkali content of Class C ﬂy ash turned out to be a signiﬁcant factor.
e high-alkali Class C ﬂy ash, particularly at lower replacement levels, produced more
)ansions than control mixtures with no ﬂy ash. It should be noted that the difference
alkali contents of the Class C ﬂy ashes considered in this study was more than that of

Class F ﬂy ashes.

The effect of ﬂy ash (particularly Class F) on reducing ASR expansions can be

  
  
  
  
  
  
  

'buted to two important factors: (1) the pozzolanic reaction of ﬂy ash in concrete,
ch reﬁnes and blocks the capillary pores, reduces the mobility and availability of the
' and hydroxyl ions and the pore solution (i.e. reduction in ionic diffusivity and
eability); and (2) calcium silicate hydrate (CSH), produced by reacting ﬂy ash with
alcium hydroxide (CH) produced during cement hydration, is able to incorporate and
p large amounts of the alkali ions; this is more pronounced with Class F than Class

ash.

_‘C—U_£ 40>“ \5

0.35

0.3
Cement Total Alkalies =O.53%
0.25

  
 

 

.0
N

% EXPANSION
.0
a

Q
—L

0.05

O

O 1 2 8 4 5 6 7 8 9 10111218141516
AGE (MONTHS)

(a) Fly Ash F(l)

Cement Total Alkalies =o,53%

 

O 1 2 8 4 5 6 7 8 9 10111213141516
AGE(MONTHS)

(b) Fly Ash F(2)

gure 5.4 Class F Fly Ash Effects on ASR Expansions with Low-Alkali Cement.

 

 

+ 0%

"9“ 1 0%
“*‘ 20%
“‘ 30%

 

 

 

+ 0%

‘9'“ 1 0%
“*‘ 20%
—" 30%

 

 

 

 

.1C7U_¢<aL\IL a

93

Cement Total Alkalies =0.80%

 

0.05

 

0
2 3 4 5 6 7 8 910111213141516

AGE (MONTHS)

O 1

(a) Fly Ash F(l)

Cement Total Alkalies =o_ao%

 

0 1 2 3 4 5 6 7 8 910111213141516
AGE (MONTHS)

(b) Fly Ash F(2)

 

 

 

‘°‘ 0%

* 1 0%
‘*‘ 20%
“" 30%

 

 

 

 

+ 0%

* 1 0%
4“ 20%
"' 30%

 

 

 

re 5 .5 Class F Fly Ash Effects on ASR Expansions with Moderate-Alkali Cement.

_/_C_U./_ <0)”. \0

94

0.35

Cement Total Alkalies =1 .2196

0.25

0.2

0.15

 

3.05

 

O 1 2 3 4 5 6 7 8 910111213141516
AGE (MONTHS)

(a) Fly Ash F(l)

Cement Total Alkalies =1,21%

 

   

0 1 2 3 4 5 6 7 8 910111213141516
AGE(MONTHS)

(b) Fly Ash F(2)

re 5.6 Class F Fly Ash Effects on ASR Expansions with High-Alkali Cement.

95

Cement Total Alkalies =o_53%

 

+ 0%

+ 1 0%
+ 20%
—°— 30%

 

 

 

 

O 1 2 3 4 5 6 7 8 910111218141516
AGE(MONTHS)

(a) Fly Ash C(1)

Cement Total Alkalies =0.53%

      
   
   

+ 0%
+ 1 0%
+ 20%
"‘ 30%

 

 

O 1 2 3 4 5 6 7 8 910111213141516
AGE(MONTHS)

(b) Fly Ash C(2)

Ire 5 .7 Class C Fly Ash Effects on ASR Expansions with Low-Alkali Cement.

 

96

 

 

 

 

 

 

3.35
Cement Total Alkalies
0.3
3.25
+ 0%
0.2
+ 1 0%
3.1 5 + 20%
~— 0
0.1 30 ’6
3.05
O
O 1 2 3 4 5 6 7 8 9 10111213141516
AGE (MONTHS)
(a) Fly Ash C(1)
Cement Total Alkalies =O.80%
+ 0%
* 1 0%
+ 20%
* 30%

 

 

 

 

O 1 2 3 4 5 6 7 8 9 10111213141516
AGE (MONTHS)

(b) Fly Ash C(2)

ire 5.8 Class C Fly Ash Effects on ASR Expansions with Moderate-Alkali Cement.

 

 

97

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.35
Cement Total Alkalies =1 21%
0.3 ———————————————————— _ __
0.25 ——————— — _____________________ .1
+ 0%
0.2 ’37.,— _
+ 10%
0.15 ———————————————————— + 20%
_.... o
0.1 __________________________ 304.
0.05 7 ______________________________
O l 1 l l T l— T T— j l— j r I T—_l
O 1 2 3 4 5 6 7 8 910111213141516
AGE (MONTHS)
(a) Fly Ash C(1)
0.35 _
3
0.3: __________________________________
? Cement Total Alkalies =1 .21%
0.25: ————————————————————————————————— .l
0.2,: _____________________ _ _. _ __
I * 10%
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O F 7*! l l l l l l

O 1 2 3 4 5 6 7 8 9 10111213141516
AGE (MONTHS)

(b) Fly Ash C(2)

gre 5.9 Class C Fly Ash Effects on ASR Expansions with High-Alkali Cement.

 

 

 

98

The six-month expansion test results with different ﬂy ash types and contents are
presented in Figures 5.10 a, b and c for low, medium and high-alkali cements,
respectively. It should be noted that six-month expansions exceeding 0.1% are generally
assumed to be deleterious. The two Class F ﬂy ashes at any replacement level as well
as the low-alkali Class C ﬂy ash at 30% replacement level reduced ASR expansions
below this 0.1% limit. Figure 5.10 suggests that the increase in replacement level with
the two Class F ﬂy ashes and the low-alkali Class C ﬂy ash consistently leads to reduced
expansions; in the case of high-alkali Class C ﬂy ash, increase in ﬂy ash content ﬁrst
increases and then decreases ASR expansion. Hence, the concept of pessimum limit
applies only to the high-alkali Class C ﬂy ash within the range of ﬂy ash replacement
levels and characteristics considered in this investigation; this may be due to speciﬁc
alkali/reactive silica ratios reached with the aggregates and binders used in this study, or

ossibly the pessimum behavior may not be generally applicable to slow reacting forms
f silica.

All the ﬂy ashes used in this investigation had relatively high total alkali contents.
n Spite of this, the class F ﬂy ashes were highly effective in controlling ASR expansions.
t seems that evaluating ﬂy ash for effectiveness in the control of ASR expansion based
n alkali content while disregarding other aspects of chemical and physical properties is

ot warranted.

 

 

99

 

 

 

 

 

 

 

0.35
Cement Total Alkalles =0.53%
g 0.8 --------------------------
(:9 .
E 0.25 ************************
C53 0 2 ________________________ y + Fly Ash (C1)
:‘3 + Fly Ash (C2)
<1: ________________________
CZ) 0'15 ASTM c-277 lelt ﬁt ‘* Fly ASh (F1)
(2’3 0,1 _________________________ 1 + Fly Ash (F2)
at
35 0.05 —————————————————— L
N gas- \‘f
0 LL 1
O 1 O 20 30
FLY ASH CONTENT (%)
(a) Low-Alkali Cement
0.35

3 Cement Total Alkalies =0.8%

8‘9 O3" ——————————————————————————

+ Fly Ash (C1)
+ Fly Ash (02)
+ Fly Ash (F1)
+ Fly Ash (F2)

 

  

EXPANSION AT 6 MONTHS
o E?
.3. 0‘

.0

O

01
Law

 

 

 

O

1 O 20 80
FLY ASH CONTENT (%)

O

(b) Medium-Alkali Cement

lre 5.10 Six Months Expansions Vs. Fly Ash Content For Different Fly Ash
Types and Cement Alkali—Contents.

 

 

100

 

1 Cement Total Alkalies =1.21%

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(c) High-Alkali Cement

ure 5.10 (cont’d).

+ Fly Ash (01)
+ Fly Ash (02)
+ Fly Ash (F1)
+ Fly Ash (F2)

 

 

 

101
5.7.2 Statistical Analysis and Discussion

Split-plot analysis of variance with repeated measurements was performed to
analyze the data statistically. This analysis of test results conﬁrmed, at 99% level of
conﬁdence, that all the variables of this investigation (ﬂy ash type, ﬂy ash content, total
alkali content of cement, and the duration of exposure to ASR), as well as their paired
interactions, had statistically signiﬁcant effects on the expansions caused by ASR.

The separation of means technique was used to identify the ages at which there
were signiﬁcant effects exerted by the ﬂy ash type, ﬂy ash content, and total alkali
content of cement on expansion at 99% level of conﬁdence (see Tables 5 .4, 5 .5 and 5 .6).

An analysis of these tables suggests that:

Moderate and high alkali cements in mixtures incorporating ﬂy ash at any

replacement level behave similarly as far as ASR is concerned (see Table 5.4).

At 20% and 30% replacement levels of Class F ﬂy ash, the effects of cement

alkali content on ASR diminishes. This is also true for Class C ﬂy ashes at 30%

replacement level, noting that even at this high replacement the high-alkali Class

C ﬂy ash is not effective in reducing ASR expansion (see Table 5 .4).

The two Class F ﬂy ashes performed similarly irrespective of the cement alkali

content and the ﬂy ash content. It should be noted that the Class F ﬂy ash with

higher alkali content was ﬁner which could pronounce pozzolanic reaction and

compensate for the effects of high alkali content (see Table 5 .5 and Figure 5 . 10).

The two Class C ﬂy ashes behaved differently in all conditions (see Table 5 .5 and

Figure 5.10).

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105
The Class F ﬂy ash was always superior to Class C ﬂy ash in controlling ASR,

in particular with moderate—and high—alkali cements even though one of the Class

C ﬂy ashes had lower alkali content than Class F ﬂy ashes (see Table 5.5 and

Figure 5.10).

Class F ﬂy ashes at 20% and 30% replacement levels produced comparable

results in controlling ASR expansion irrespective of the cement alkali content (see
Table 5.6).

The effects of fly ash on ASR expansion tends to be more pronounced as the
alkali content of cement increases; it should, however, be noted that the damaging
effects of high-alkali Class C ﬂy ash tend to be more pronounced in the case of

low—alkali cement (see Table 5.6).

5.7.3 Correlation Studies
Correlation studies were conducted in order to identify the key ﬂy ash
characteristics inﬂuencing the alkali-silica reactions in ﬂy ash concrete. Expansions at
6 and 12 months were used to represent the extent of alkali—silica reactions. Correlation
studies were conducted following “ interactive multiple-linear—regression technique" which
accounts for all inter-relations between independent variables; this approach adopts a
stepwise procedure to determine the most important independent variables (among
different fly ash characteristics) inﬂuencing the dependent variable (expansion caused by
alkali-silica reaction). This stepwise procedure permits reexamination, at every step,

of the variables incorporated in the model in previous steps.

 

 

 

106

Previous analyses in this research indicated that in the presence of ﬂy ash the
effect of cement alkali content on expansion is not, in general, statistically signiﬁcant.
Hence, the correlation study was conducted on all mixtures incorporating a speciﬁc ﬂy
ash content (10% , 20% , or 30%) irrespective of the cement alkali content (low, medium
or high).

Results of the analysis suggested that those ﬂy ash characteristics which have
strong statistical as well as logical relationships to alkali-silica expansion are the total
alkali (N a20-equivalent) content and the silicon dioxide (SiOz) content. Coefﬁcient of
multiple correlation (which is a measure of the success of ﬁtted regression model in
explaining the variation in the data) between both 6- and lZ-month expansions and the
combination of alkali and silicon dioxide contents of ﬂy ash ranged from 0.91 to 0.96
for each of the three ﬂy ash contents considered (i.e. the ﬁtted model has explained 91
to 96% of the variation observed in the dependent variables). It should be noted that
multiple correlation analysis occasionally showed statistical relationship of expansion with
factors such as SO, and Fe203, which do not logically correlate strongly to alkali-silica
reactions; such statistical relationships were judged to simply result from the fact that
limited number of ﬂy ash types were used in this investigation.

In multiple-linear-regression analysis, the NaZO-equivalent and Si02 coefﬁcients
were found to be positive and negative, respectively, indicating opposite effects of the
two variables on alkali-silica expansion. The ratio of Na20-equiva1ent content to $102
content of ﬂy ash was thus considered as a single variable potentially capable of

representing the ﬂy ash effects on alkali-silica reaction. The correlation coefﬁcients

 

107

(which show the validity of linear relations between the expansions under ASR and each
variable) between N aZO-equivalent content, SiO2 content and N aZO-equivalent/ SiO, ratio
of ﬂy ash, and the 6— and 12-month expansions shown in Table 5.7 suggest that the ratio
of NazO-equivalent content to SiO2 content of ﬂy ash has the strongest correlation to
alkali-silica expansion (correlation coefﬁcient ranging from 0.917 to 0.977). This
conﬁrms that the effectiveness of ﬂy ash in controlling alkali-silica reaction may be best
represented by the NaZO—equivalent-to-Sioz ratio. Figures 5.11 a, b and c, and 5.12 a,
b and c show the relationship between 6- and 12-months expansions, respectively, and
the NaZO-equivalent-to-Sioz ratio of ﬂy ash at each ﬂy ash content considered (regardless
of the alkali content of cement). More test data with a boarder range of ﬂy ash
chemistries is needed to conﬁrm this relationship because, as shown in Figures 5.11 and
5.12, the NaZO/SiO2 ratios for ﬂy ashes considered in this study happen to fall within two

narrow ranges.

 

 

 

 

 

 

 

 

Table 5 .7 Correlation Coefﬁcients between ASR Expansion and Fly Ash Properties.
Fly Ash Test Age Fly Ash Content
Properties (Months) 10 % 20% 30%

Na,o,q. 6 0.850 0.910 0.886

12 0.872 0.883 0.888

SiO2 6 -0.750 -O.737 -0.762

12 -0.791 -0.788 -O.781

NaZOq/SiOz 6 0.930 0.997 0.963

12 0.919 0.968 0.969

 

 

 

 

 

 

 

 

 

 

 

 

 

 

108
0.85 n l L n l
0.80 - it? _.
32?

0.25 4 e
Z ”i?
g 020 a -—
Z
<1:
%
N

0.10 J _

0.05 n _.

000 l 1* a l m

000 0.05 0.10 0.15 0.20 0.25 0.30

Na20/SI02

(a) 10% Fly Ash Content

Figure 5.11 Relationship Between 6 Months Expansions and the N aZO-equivalent-to-
SiOz Ratio of Fly Ash at Different Fly Ash Content (Regression Lines and
95 % Conﬁdence Intervals).

% EXPANSION

 

0.35

0.30

0.25

0.20

0.05

0.00

109

 

 

 

 

0.00

 

% EXPANSION

0.35

0.30

0.25

0.20

0.05

0.00

0.00

Figure 5.11 (cont’d).

NaZO/SIOZ

(b) 20% Fly Ash Content

0.15

0.80

 

 

/

 

 

010

NaZO/SiOZ

(c) 30% Fly Ash Content

0.15

0.30

 

 

110

.—

035 ' I I I

 

0.80 _ _

0.25 — sﬁr _

0.20 — _

0.15 - _

% EXPANSION
23%

0.10 - _

0.05 — _

 

 

 

0.00 I I I I I
0.00 0.05 0.10 0.15 0.20 0.25 0.30

N320/8i02

(a) 10% Fly Ash Content

Figure 5.12 Relationship Between 12 Months Expansions and the NaZO-equivalent-to-
SiO2 Ratio of Fly Ash at Different Fly Ash Content (Regression Lines

and 95 % Conﬁdence Intervals).

 

111

% EXPANSION

0.1 0
0.05
0.00

0.00 0.05 0.1 O O. 1 5 0.20 0.25 0.30
NaZO/SIOZ

(b) 20% Fly Ash Content

0.35

0.30

% EXPANSION

I l
0.00 0.05 0.10 0.1 5 0.20 0.25 0.30
NaZO/SIOZ

(c) 30% Fly Ash Content

Figure 5.12 (cont’d).

iﬁ

1 12
SUNINIARY AND CONCLUSIONS

The effects of the ﬂy ash type (two class F and two class C with different alkali

contents), ﬂy ash content (10, 20 and 30% by weight of cement), and total alkali content

of cement (0.53. O. 80 and 1.21%) on alkali—silica reaction were investigated. Correlation

studies were performed to identify the most important variables among ﬂy ash

characteristics inﬂuencing the alkali-silica reaction. The following conclusions could be

derived based on statistical analysis of the generated test results:

1.

Class F ﬂy ash is highly effective in reducing ASR expansions regardless of ﬂy
ash content used (10, 20, and 30 %), particularly with high— and moderate-alkali
cements (1.21% and 0.8% total alkali content).

Alkali content of Class F ﬂy ash is not necessarily representative of its
effectiveness in controlling ASR expansions. However, the alkali content of
Class C ﬂy ash turned out to be a significant factor. The high-alkali Class C ﬂy
ash, particularly at lower replacement levels, produced more expansion than
control mixtures with no ﬂy ash.

The Class F ﬂy ash was always superior to Class C ﬂy ash in controlling ASR,
in particular with moderate and high-alkali cements even though one of the Class
C ﬂy ashes had lower alkali content than Class F ﬂy ashes.

When sufficient replacement level of Class F ﬂy ash is used, the alkali content
of cement loses its signiﬁcance in determining ASR expansions. This does not
apply to Class C ﬂy ash, particularly if its alkali content is high.

Evaluating ﬂy ash for the control of alkali—silica reaction in concrete based on

 

 

113

alkali content while disregarding other aspects of chemical and physical properties
is not warranted.

Interactive multiple-linear-regression analysis test data showed that the total alkali
content (NaZO-equivalent) and the silicon dioxide (SiOz) content were the most
important properties of ﬂy ash inﬂuencing alkali silica reaction.

The ratio of NaZO—equivalent to Si02 content of ﬂy ash was found to be the most
inﬂuential single variable in determining effectiveness in controlling alkali-silica
reaction. The Si02 content may reﬂect pozzolanic reactivity which controls ASR
through consuming alkalies and reducing concrete permeability. More test data

covering various ﬂy ash chemistries are needed to conﬁrm this conclusion.

 

 

 

CHAPTER SIX

PLASTICS AND THEIR RECYCLING IN CONSTRUCTION

_6_,_1_ INTRODUCTION

Plastics are formed by chemically taking apart ingredients or raw materials such
as coal, water, air, petroleum, limestone, salt, etc. , and putting them together in different
more desirable combinations. Plastics can be deﬁned as high molecular weight synthetic
products which will ﬂow into a given form, usually under the effects of heat and
pressure.

Before manufactured products called plastics are made into ﬁnished products, they
are called polymers or resins. The term polymer may be deﬁned as a chemical
compound or mixture of compounds formed by polymerization. The raw materials used
in plastics contain two or more of six chemical elements that go into the building of a
polymer (carbon, hydrogen, oxygen, nitrogen, chlorine, and ﬂuorine). Carbon is
considered the backbone of polymers as it usually links elements to form a polymer. The
elements sulfur and silicon are sometimes used in the preparation of few special
polymers. Polymers may be classiﬁed into two groups, thermoplastic and thermosetting;
they are distinguished by the way in which the monomer is polymerized. Monomer

means "one part" and refers to a material made of small molecules all of the same size."'3

114

 

 

 

 

115
$2 W

Thermoplastics represent about 90 % of the total plastic production. The
molecular structure of thermoplastics allows them to be heated and reprocessed with only
minor damage to their properties.

Thermoplastic polymers are characterized by softening upon heating and
hardening by cooling. Since the giant molecules of these materials have no strong bonds
between the individual molecules, they can be softened by heat and remolded over and
over again. This is an advantage in molding processes such as extrusion or injection
where scrap products can be reground and molded again. Some of the thermoplastic
materials will burn freely when exposed to an open ﬂame while others of this group will
not support combustion.43 Table 6.1 presents a general view of some major

thermoplastics, their primary applications, and typical uses after recycling.“4

ii THERMQSETTLNQ

Thermosets represent 10 % of the total plastics production. Unlike thermoplastics,
the molecular structure of thermosets do not allow them to be heated and reprocessed
without damaging their properties.

The group of thermosetting polymers, numbering less than the thermoplastic
group, possesses quite different characteristics. Thermosetting materials differ from
thermOplastics in many ways. Basically the differences are due to the chemical
condensation polymerization process through which the thermosetting materials are

produced. Because of the irreversible reaction by which thermosets polymerize, they

116

 

 

 

 

 

 

 

Table 6.1 Primary application and typical use after recycling for some major
thermoplastic.“
Plastic type Primary applications Typical use after recycling
high density Bottles, especially for food Industrial bags, detergent
polyethylene products, detergents and bottles, pipes, containers and
(HDPE) cosmetics, containers, toys, wood substitutes e. g. animal
housewares, fuel tanks and ﬂooring and fencing. A
industrial wrapping and ﬁlm, method has been developed
sheets, gas and waste pipes. to incorporate recycled
HDPE with virgin polymers.
low density Cling film, bags, bin liners, Waste disposal bags,
polyethylene toys, coatings, ﬂexible industrial bags, ﬂexible
(LDPE) containers, irrigation pipes and bottles, pipes, containers,
general ﬁlm. waterproof membranes,
agricultural ﬁlm and wood
substitutes e.g. animal
ﬂooring and fencing.
polyethylene Bottles, food packaging, Textiles for bags, webbing
terephlthalate carpets, cords for vehicle tires. and sails, jackets, pillows,
(PET) cushions, sleeping bags,
rope, string, carpets.
polypropylyne Packaging such as yogurt and Milk crates, timber
(PP) margarine pots, sweet and snack substitutes, automotive
wrappers, vehicle battery cases, components, tool boxes, auto
cereal packet linings, batteries, chairs and textiles.
microwave—proof containers,
medical packaging, milk crates.
Automotive parts, carpets and
ﬁbers and electrical
components.
polystyrene Packaging, dairy product Thermal insulation, trays,
containers, electrical appliances, ofﬁce accessories, rubbish
thermal insulation, cassette bins.
tapes, cups and plates.
polyvinyl Window frames, ridged pipes, Pipe ﬁttings, conduits, ﬂoor
chloride (PVC) ﬂooring, wallpaper, bottles, tiles, fencing, rails,
packaging ﬁlm, cable insulation, containers, footwear, garden
credit cards, medical products furniture.
including plasma bags.

 

 

 

 

 

 

 

 

117

form a rigid, hard and often brittle, infusible mass. The cross—linking molecular
structure with strong chemical bonds between the polymer chains causes these materials
to be rigid and hard as no slippage can occur between the polymer chains. Since all the
bonds are strong, when the material is heated no chain ﬂow or softening can occur.
Intensive heating of a therrnoset will cause breakage of the chemical bonds resulting in
a charring of the material. Thermosets are not ﬂammable. In general, thermosetting
plastics can be described as being hard, strong, and rigid, with good heat resistance.43
Table 6.2 presents a general view of the primary applications and typical uses after

recycling of some major thermosetting plastics.44

M RECYCLING OF PLASTICS

The solid waste crisis is important from both the economic and environmental
point of view. As landﬁll areas are rapidly depleting, the cost of solid waste disposal
is increasing. Among solid wastes, plastics have received a lot of attention because they
are generally considered to be non-biodegradable. There are about 11 million tons of
plastic wastes generated per year; about 7 % , by weight, of all solid wastes. However,
because plastic wastes are very low in density, they consume about 30%, by volume, of
the total solid waste stream.2

The types of plastic wastes, by use, are post-consumer or public waste (90-95 %),
and manufacturing waste (5-10 %). Because plastic manufacturers internally recycle more
than 75 % of their own wastes, manufacturing waste represents a low percentage. In their

case, recycling is generally cheaper than disposal. The fact that manufacturing waste is

 

 

118

Table 6.2 Primary application and typical use after recycling for some major
thermosetting.“

 

 

Plastic Type Primary applications Typical use after recycling

 

polyurethane Coatings, ﬁnishes, additives to Carpet underlay and shoe
(PU) improve rubber’s resistance to soles.

chemicals and ozone. As
elastomers they form bumpers,
gears, diaphragms, gaskets and
seals. PU forms are found in
cushions, mattresses and vehicle
seats.

 

EPOXY Adhesives, automotive Most recycling of thermoset
components. electrical/electronic is at laboratory or pilot plant
components, sports equipment, stage. There has been some
boats. success by chemists who
have demonstrated that they
can break down mixtures of
thermoset salvaged from old
cars into simple chemicals.

 

PHENOLIC Adhesives, bonding wood Most recycling of thermoset
laminates, ovens, toasters, is at laboratory or pilot plant
plugs, handles for pots and stage.

cutlery. Automotive parts such
as water pumps, intake
manifolds, pistons and engine
blocks. Electrical components
such as circuit boards.

 

 

 

 

 

 

 

 

 

119

uncontaminated and easily collectible also helps. Conversely, most post-consumer waste
ends up in the municipal waste stream; it is contaminated, poses a collection problem,
and is therefore difﬁcult to recycle. Plastics in packaging are the major source of post-
consumer waste with more than 50%, by weight, of the total. Packaging has life of less
than one year; hence, it quickly falls into the waste stream.2

Recycling of plastic discards is one method of reducing municipal solid waste.
They are beginning to join glass, steel, aluminum and paper as waste stream components
that have been accepted into recycling programs across the country. It is difﬁcult,
however, to expand plastics recycling because of the variety of plastic wastes, the
difﬁculty of sorting different types of plastics, the low density of post-consumer plastic
wastes in comparison to other recyclable and the limited history of plastics recycling.
Because of its heterogeneous nature and the amount of contaminants present, separation
of post-consumer mixed plastic waste is the most difﬁcult. Waste plastics from industrial
operations are cleaner and more homogeneous in resin type and scrap form. The term
" mixed plastics, " a mixture of plastic types or a mixture of package/product types which
may or may not be the same plastic type or color category, has been used to describe
broad scale processing of post-consumer plastic waste. Mixed plastics also includes
products which may be the same resin type but which have been fabricated using
differing manufacturing techniques.“

A successful recycling program not only includes the creation of an infrastructure
to help collect post-consumer plastic wastes before they enter the municipal waste stream,

but also the establishment of markets where recycled products can be cost-effectively

 

 

 

120

used. The construction industry is one example of a market where recycled plastic
products can ﬁnd useful applications. Efforts in recycling have concentrated on the
thermoplastics HDPE, LDPE, PP, PS, PVC and PET because thermoplastics can be
repeatedly softened by temperature increase and hardened by temperature decrease.
The performance of recycled resins is not as good as virgin resins. Reprocessing
and environmental exposure degrades some of the beneﬁcial properties of some plastics,
such as durability and dimensional stability. Therefore, recycled plastics usually are used
in products with less demanding applications than the original products. Degradation of

some properties can be overcome with the use of additives.

15:5 RECYCLING QF PLASTICS 1N CONSTRUCTION

There are many incentives to look for plastics recycling markets in the
conStruction industry. First, it is the single largest industry in the country, therefore
providing a huge potential market for recycled plastic products, especially at a time when
pavements and bridges are in urgent need of repair. According to the Federal Highway
Agency, more than 25 % of existing pavements in the US. are either in deteriorating
condition, and more than 40% of the 574,000 bridges in the US. are either structurally
deﬁcient or functionally obsolete. The cost of rebuilding the nation’s roads is estimated
to be about $1.6 trillion.2

Also, recycled plastics used in many construction applications may not need to
be puriﬁed to the same extent as recycled plastics used in other applications such as

packaging, thus simplifying the recycling process. Finally, the long life of construction

 

 

121

products (more than 30 years) would provide for a long-term disposal of the plastics
wastes, which is an important consideration in recycling operations.

There are different methods which can be used to recycle plastics for construction
applications. One method is thermal reprocessing for thermoplastics; this method can
not be applied to thermosets. Thermoplastics can be heated and reprocessed into bridge
or building panels, fence posts, or reinforcing ﬁbers for various concrete structures.
This method usually requires the separation of various plastic waste components by type.
Second method is depolymerization, or chemical modiﬁcation of the plastic wastes, to
recover their basic chemicals. For example, recent ﬁndings show that recycled PET can
be chemically modiﬁed to produce unsaturated polyester resin, 3 thermoset polyester.
The unsaturated polyester resin is a liquid component that can be mixed with inorganic
aggregates such as gravel, sand, and ﬂy ash (a waste material generated by the burning
of coal or waste) to produce polymer concrete. The resulting material is much stronger,
more durable, and cures faster than conventional Portland cement concrete. A third
method is to use plastic wastes as fillers with virgin resins or other materials like
concretes.2 This procedure is an easy way to recycle thermoset or contaminated plastics.
This approach was adopted in this research project, where plastics were used not only

as light-weight ﬁllers but also as reinforcing inclusions in concrete.

 

 

 

122

g: PLASTIC TYPES

This section introduces the key plastic types present in the solid waste stream.
6.6.1 Polyethylene

Polyethylene is one of the most widely used polymers among the thermoplastic
materials. It has one of the simplest molecular structures; more has probably been
written about polyethylene than any other polymer. Polyethylene was produced on a
commercial scale as early as 1939. It is one of the most chemically resistant materials
at ordinary temperatures. Its simplicity of manufacture and high chemical resistivity
make it one of the most important industrial plastics. In general, polyethylene may be
considered as a very high molecular weight parafﬁn.“3"“"47

There are three basic polyethylene types: low-density polyethylene (LDPE),
medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). LDPE
and MDPE are produced with a relatively short chain molecular structure and a high
degree of side branching. This structure provides a polymer with approximately 65%
crystallinity. On the other hand, HDPE is polymerized to form much longer linear
chains with few side branches. This results in a greater density and a crystallinity range
of 85%. In general, as the density increases, the stiffness, hardness, strength, and
impermeability increase. As density decreases, impact strength and stress crack
resistance tend to increase.
Some of the general properties of polyethylene arez43’46'47’“

1. low speciﬁc gravity (0.91 to 0.96): LDPE (0.91 - 0.93) and HDPE (0.94 - 0.96)

2. low water absorption (practically zero)

 

 

123

very tough at low temperatures.

ﬂexibility is good to excellent, even to 38 °C (100 °F).

softening or melting range for LDPE 102-112 °C (216-234 °F) and for HDPE
125-135 °C (257—275 °F).

excellent electrical insulating properties.

impermeable to water vapor and alcohol vapor, but permeable to hydrocarbons
(petrol, benzene and particularly chlorinated hydrocarbons).

excellent chemical resistance, it is relatively unaffected by common polar organic
solvents (alcohol, acetone), water, concentrated acids, alkalies, and ozone (in the
absence of UV light). It can be decomposed by hot concentrated nitric acid and

hot concentrated sulfuric acid. It can be swollen by chlorinated hydrocarbons.

luris (1988)49 studied polyethylene resins for geomembrane applications. Long-

term durability is one of the main technical reasons why polyethylene is used. It is used
for geomembrane applications such as municipal garbage dumps, sewage ponds,
hazardous waste landﬁlls, industrial holding pond, irrigation canals and reservoirs. He
concluded that medium density polyethylene has become the preferred material because
of its excellent balance between chemical resistance and environmental stress crack
resistance. The chemical resistance of a polyethylene is determined to a great extent by

its crystallinity/ natural density.

Doyle and Baker (1988)50 conducted weathering tests on geomembranes using

HDPE. The materials were exposed on a laboratory roof, which is considered an

 

 

 

124

industrial atmosphere. HDPE showed no signs of degradation. None of the parameters
(hardness, breaking strength, elongation, and appearance) showed any signiﬁcant change

after one— and two-year exposures. There was only a slight change in appearance.

6.6.2 Polyethylene Terephthalate (PET)
PET is a young plastic resin created in 1973. While industrial PET scrap has
always been reused, post—consumer PET recycling only began in the early 1980’s.
Recently in the U.S., PET has been one of the most recycled plastics especially soft

drink bottles.51

The speciﬁc gravity of PET is 1.3—1.4 and softening or melting range is 255-265
°C (491-509 °F). The characteristics that distinguish PET are its high strength, high
modulus, toughness, dimensional stability, low shrinkage and heat stability, low moisture
regain and quick drying ability, thermal stability, and resistance to stretching and
shrinkage, weather and most chemicals. PET is highly resistant to most acids. In
contrast to excellent acid resistance, PET has somewhat limited resistance to alkalies.

These include ammonia media and caustic solutions of relatively high concentration .43-52

6.6.3 Polyvinyl Chloride (PVC)
PVC is the largest polymer in the vinyl group. Approximately one-half of the
PVC produced is used for rigid pipes and ﬁttings. Other uses range from grade
packaging to wire insulation.

The speciﬁc gravity of PVC is 1.30-1.35, and softening or melting range is 150—

 

 

 

125
200 °C (302-392 °F). The general characteristics of all members of the vinyl group are

similar, such as good strength, excellent water and chemical resistance, good weather
resistance, electrical properties, and abrasion resistance. It can be swollen by aromatic
and chlorinated hydrocarbons, nitroparafﬁns, acetone, acetic anhydride, and aniline. It
can be decomposed by concentrated oxidizing acids (HZSO4, I-INOs). Zinc and iron, as
metals or compounds, should be excluded. Two factors that make PVC uniquely

different from other plastics are its wide range of properties and being self-extinguishing

(PVC products will melt but will not burn)“48

6.6.4 Polypropylene (PP)

Polypropylene resins are made from propylene gas by addition polymerization.
The process is similar to the production of I-HDPE. The improved properties of PP over
the same properties of polyethylene are: rigidity, heat distortion, tensile strength and

stress crack resistance. The increase in these properties is due to higher crystallinity and
the large methal group.“3

The major properties of polypropylene are:

1. It is one of the lightest plastic available with a density range of 0.8900905.
2. Excellent dimensional stability.
3. It does not present stress cracking problems.
4. Excellent electrical properties even at high temperature.
5. Its permeability is as good or better than HDPE.
6.

Softening or melting range is 160-165 °C (320-329 °F).

 

6.6.5

 

126
Tough at temperatures from 41-46 °C (105-115 °F), but brittle below -18 °C (0

°F).

Some hydrocarbons will soften and swell the polymers.

Good chemical resistance; it offers excellent chemical resistance at higher
temperatures, it is not effected by water solutions of inorganic salts, mineral acids
or bases, it can package concentrated HCL, and 80% solution of sulfuric acid up

to 60 °C (140 °F).

Polystyrene (PS)

Polystyrene is prepared from ethylene and benzene. Ethylene is made from

natural gas or petroleum. PS materials are easily identiﬁed from all other plastic

materials by the distinct metallic sound produced when they are struck or dropped.

The wide melting range of 70-115 °C (158-239 °F) gives it versatility and ease of

molding at various temperatures and pressures. However, there are two major

disadvantages to PS; its brittleness and poor chemical resistance. This can be overcome

by the physical addition of synthetic rubber, butadiene. This material is then known as

high impact styrene and its strength is improved tremendously, making it a much more

versatile plastic.‘3'45

The important properties of PS are as follows:
Speciﬁc gravity of l.04-1.1.
Softening or melting range is 70-115 °C (158—239 °F).

High degree of hardness.

 

IIIIA

 

 

127
4. Low cost.
5 . Brittle, except when modiﬁed.
6. Excellent electrical pr0perties.
7. Low moisture absorption.
8. Excellent organic acid, alkali, salts, and lower alcohol resistance. Deterioration

or softening occurs when used with hydrocarbons, esters, and essential oils.

6.6 .6 Acrylonitrile-Butadiene—Styrene (ABS)

Three chemicals, acrylonitrile, butadiene and styrene are combined to make the
ABS plastics. It is one of the few thermoplastics which combines both hardness and
toughness. Typical applications for ABS compounds include business machine and
camera housings, telephone handsets, electrical hand tools such as drill housings, knobs,
handles, blowers, bearings, wheels, gears, pump impellers, grilles, deﬂectors,
automotive trims and hardware, pipe and pipe ﬁttings.

The major properties of ABS are: resistance to most common chemicals and some
hydrocarbons (ABS materials are little affected by water, alkalies, weak acids and
inorganic salts). Alcohol and hydrocarbon solvents may affect the surfaces and cause
swelling if the exposure is extended), limited heat resistance (withstand temperature up
to 104 °C (220 °F), remains tough at ~40 °C (-40 °F), good electrical properties, but

ﬂammable, good wear and scratch resistance, and low coefﬁcient of friction.53

 

 

CHAPTER SEVEN

lVIIX PROPORTIONS AND MECHANICAL PROPERTIES OF CONCRETE

INCORPORATING RECYCLED PLASTICS

7_.1_ INTRODUCTION

There are some key advantages associated with recycling in concrete construction:
(1) potentials for the development of large-volume markets for waste products; (2)
reduced need for puriﬁcation of waste; and (3)10ng-term removal of recycled materials
from the waste stream, noting that concrete products typically have a service life
exceeding 40 years.

Improvements in some key aspects of concrete performance can make important
contributions toward developing a more reliable infrastructure. Recycling of plastics in
concrete construction can help overcome problems with the brittleness and relatively high
unit weight of concrete. Plastics can also help control shrinkage cracking of concrete.
Reduced weight would also have positive implications for the thermal insulation qualities
of concrete products.

Many applications of light-weight concrete, including masonry units, ﬂoor and
roof slabs, bridges and insulating components as well as many precast products can take
advantage of the enhanced toughness, impact resistance and deformation capacity

imparted by plastic inclusions. Partial replacement of ﬁne light-weight aggregate with

128

 

 

 

129

plastics in concrete construction presents the potentials for utilizing up to 10 % of all
plastic wastes in light-weight concrete alone. In normal-weight concrete, the desirable
shrinkage crack control characteristics of plastics can be fully utilized in a variety of
applications, including slabs on grade (walkways, industrial ﬂoors, etc.), parking
garages, bridge decks and pavements. While small volume percentages of plastics are
needed in those applications, the practicality and economy of this approach and the
tremendous volumes of normal-weight concrete used annually present promises for
beneﬁcial use of close to half of the plastic wastes generated annually.

The work performed on recycling of plastic in concrete is presented here in two
parts; part I concerns the recycling of plastics as partial substitutes for light-weigh
aggregates in light-weigh concrete materials where plastics are also expected to enhance
the toughness characteristics of light-weight concrete. Part II deals with the use of
recycled plastics as secondary reinforcing inclusions (additives) in normal-weight

concrete for shrinkage crack control

L2 SULFONATION CONCEPT

The objective of sulfonation is to provide a process for the generation of sulfur
trioxide (803) in a carrier, and for using the $03 in a carrier to sulfonate the surfaces of
polymeric resin materials. Sulfonation is typically carried out by using gaseous mixtures
of dry air containing from 2 to 8 % 803 which are then reacted with polymeric materials.
803 can be produced by different systems; for example, oleum (concentrated sulfuric acid

containing sulfur trioxide) (1-12S3010) has been used as a source of S03 gas. In this

 

 

130
system, dry air is passed through the oleum to facilitate S03 stripping of the oleum by

mass transfer?4

Sulfur trioxide has been used as the surface treatment of a variety of polymeric
resins to chemically modify their surfaces by sulfonation reaction. For example, such
surface sulfonated polymers are useful as substrates for painting and metal coating and
are also useful as enclosure members for containing hydrocarbons such as gasoline and
the like. These uses include ﬁbrous materials for use in carpets, clothing and other
fabrics, and containers such as fuel tanks, fuel barrels and drums; the surfaces of medical
devices are also required to be wettable to prevent air bubbles from sticking to a surface
and ending up in a patient’s blood. Sulfonation of plastic resins utilized in medical
devices is necessary to modify the surface pr0perties of such resins to make those
surfaces hydrophilic instead of hydrophobic.”

Sulfonation of plastics is used in this investigation to make the plastic surfaces
wettable and provide for chemical bonding of the cement-based matrix to plastic surfaces

(see Figure 7 . 1).

 

 

 

131

I | I I Sizzgsfzijpfgg . .
'SI'O-ca-
I it?

  
  

  

    
  

 

. .‘.

Plastic 0

Cement-Based Matrix

  

Sulfonation-Bridge

Figure 7.1 Chemical Bonding of Sulfonated Plastic Surfaces to the Cement-Based
Matrix.

Li W
It is now well known that even before the application of external loads
microcracks already exist in the transition zone between the mortar matrix and coarse
aggregates in concrete as shown in Figure 7.2-a.SS The number and width of these cracks
in concrete would depend, among other factors, on bleeding characteristics, strength of

the transition zone, and the curing history of concrete. Under ordinary curing conditions

 

 

 

 

132

(when a concrete element is subjected to drying shrinkage or thermal strains), due to the
differences of dimensional movements and elastic moduli, differential strains will be set
up between the matrix and coarse aggregates, generating microcracks in the transition
zone. Under load and environmental effects, the transition zone microcracks begin to
increase in length, width and number, initially within the transition zone and later into
the matrix and (in the case of light-weight aggregates) through the aggregates (Figure

7 .2—b). The relatively low fracture energies required for the propagation of cracks in
brittle concrete matrices result in relatively low toughness, impact resistance and tensile
strength of concrete.
In plastic-concrete composites, the encounter of propagating microcracks with the
tough and well-bonded plastics leads to relaxed intensity of stresses at the crack tips, a
phenomenon which increases the fracture energy and thus the toughness and impact
resistance of the composite as well as its resistance to shrinkage cracking. Delayed
pr0pagation of microcracks encountering the plastic inclusions would take place mainly
within the transition zone rather than through the plastic inclusions (Figure 7 .3-a).
Eventually, when increased load levels lead to interconnection and rapid growth of
microcracks, the bridging of plastic inclusions across the resulting cracks (Figure 7 .3-b)
helps maintain the integrity of the composite at large post-peak deformations and control

the crack widths (e.g. under restrained shrinkage movements).

 

"\

 

 

 

 

 

 

 

 

 

..
o

2

n

n

r

Mic

(a) Prior to Load/Environment Effects (b) UnderLoad/Environment Effects

Figure 7.2 Concrete Microcracks.”

 

 

 

 

 

 

(a) Arrest and Deﬂection of Microcracks (b) Bridging of Cracks

Figure 7.3 Mechanism of Action of Plastic Inclusions in Concrete.

 

 

 

134

The main thrust of this study is to validate these hypotheses regarding microcrack
arrest and deﬂection, and bridging of cracks by plastic inclusions in concrete (and the
consequent improvements in toughness and shrinkage crack control). In the work
reported herein, these hypotheses are validated for light-weight concrete (toughening

effects) and normal—weight concrete (shrinkage crack control).

:74! PART I: RECYCLED PLASTICS AS PARTIAL REPLACEMENT FOR
LIQHT- ﬂ EIGHT AGGREGATE

1.11,; B ck un 11 Li t-Wei ht oncrete

Light-weight aggregate concrete is basically a normal concrete in every aspect
except that for reasons of overall cost reduction, the concrete is made with light-weight
cellular aggregates so that unit weight is reduced. It should be noted that light-weight
aggregates tend to reduce strength, when compared with normal-weight aggregates;
hence, reduced unit weight and the consequent improvements in thermal insulation
qualities are achieved at typically reduced strengths with light-weight concrete (under
circumstances comparable to those of normal-weight concrete). Some applications of
light-weight concrete include: masonry blocks, bridge deck overlays, ﬂoor systems in tall

buildings, precast elements and insulation products. Aggregates that weigh less than

 

 

 

 

135
1120 kg/m3 (70 lb/ft") are generally considered light—weight. The cellular and highly

porous microstructure of these aggregates is generally responsible for their light weight.
Natural light—weight aggregates are made by processing igneous volcanic rocks such as
pumice, scoria, or tuff. Synthetic light-weight aggregates can be manufactured by
thermal treatment from a variety of materials such as clays, shale, slate, diatomite,
perlite, vermiculite, blast furnace slag and ﬂy ash. Figure 7 .4 shows a whole spectrum
of light-weight aggregates weighing from 80 to 900 kg/rn3 (5 to 55 lb/ft3). Very porous
aggregates, which are at the lower end of the spectrum, are generally weak and are
therefore more suitable for making nonstructural insulating concretes. At the other end
of the spectrum are those light-weight aggregates that are relatively less porous; where
the pore structure consists of uniformly distributed ﬁne pores, the aggregate is usually
strong and capable of producing structural concrete.4

ASTM has separate speciﬁcations covering lightweight aggregates for use in
structural concrete (ASTM C-330), insulating concrete (ASTM C-332), and concrete for
production of masonry units (ASTM C-33l). These speciﬁcations contain requirements
for grading, undesirable substances, and unit weight of aggregate, as well as for unit

weight, strength, and drying shrinkage of concrete containing the aggregate.4

 

 

136

 

ATE —-—- UNIT N w
30

ABGREG

/.o

EIGHTS

   

 
  
 

80

FILL couc. AND
C- INSUL- CONC. 37‘
6 5°: 800-2000 034‘ 253””
5
9 «£1?— COMP- 371?: of 0
“Q WQ) .Q
”s
\< y IoocI = 16.02 Ito/m3

LOpﬂ=00069MPo

           

 

 

 

 

Figure 7 .4 Lightweight Aggregate Spectrum.4

1&2. Experimental Program

An experimental program has been designed based on the statistical concepts of
factorial analysis of variance (23 factorial design). This experimental program (Table
7.1) investigates the following three variables: plastic type (HDPE and MIXED), plastic
content (two different levels, 20 and 40% replacement of ﬁne light-weight aggregate by

volume corresponding to 7.5 % and 15% by total volume of concrete), and sulfonation

(sulfonated and unsolfonated).

 

 

 

 

 

 

 

 

137
Table 7. 1 Experimental Program For Light-Weight Concrete Incorporating Recycled
Plastics.
Plastic Sulfonation Replacement Level of Sand with Plastics, by volume
Type 20% 40%
HDPE Yes * *
No * *
MIXED Yes * *
No * *
L_____..______

 

 

 

 

 

 

CONTROL *

 

* Average 'of at least four specimens for ﬂexural and compressive strength, and ﬁve
specimens for impact resistance.

7.4. Mate 'als

The basic mix ingredients were Type I Portland cement, light-weight coarse
aggregate, light-weight ﬁne aggregate, recycled plastics (HDPE or MIXED), water, and
air-entraining agent (water-based). The chemical and physical properties of the cement
were introduced in Section 2.4.

The light-weight aggregate used in this investigation (Tufﬂite) was volcanic rock-
based with a maximum aggregate size of 12 mm (0.5 in.). Under petrographic
examination, Tufﬂite is revealed as a naturally occurring matrix of amorphous silica,
comprising millions of spherical voids. These voids are what contribute to the strength
(literally) and the acceptance of the aggregate while at the same time pose a strict quality

control challenge to ready-mix producers who use the material. This porosity gives

 

 

 

 

 

 

138
Tufﬂite an extremely high capacity for absorption. It can readily absorb 50 percent

moisture. As far as Tufﬂite aggregate has not absorbed about 50 percent moisture, it can
be a threat to the mix design--rubbing the mix of its calculated amount of water,
throwing off the water/cement ratio, reducing workability and producing under—strength
concrete.’6

Water absorption and speciﬁc gravity at saturation were tests performed for coarse
and ﬁne aggregates following ASTM C-127 and C-128, respectively. The speciﬁc
gravity of light-weight coarse and ﬁne aggregates were 1.2 and 1.5 , respectively. Water
absorption at saturation of light-weight coarse and ﬁne aggregates were 68 and 35 %,
respectively. Sieve analysis of ﬁne and coarse aggregate was conducted following ASTM
C—136. ASTM C-330 gives the grading requirements for light weight aggregate for
structural concrete. Table 7. 2 presents the gradation of coarse and ﬁne aggregates. The

gradation of coarse aggregate satisﬁes the grading requirements of ASTM C-330.

Table 7.2 Light-Weight Aggregate Gradations.

 

 

Sieve Size 19.0 12.5 9.5 4.75 2.36 1.18 600 pm 300 um 150 pm
mm (in.) (3/4) (1/2) (3/8) (No.4) (No.8) (No.16) (No.30) (No.50) (No.100)

Coarse 100 93 59.2 7.1 2.2 --- --- --- ---
Aggregate

Fine --- --- 100 99 -- 42.5 -— 4 2
Aggregate

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

139
Recycled "MIXED" plastic, as will be referred to in this study, is a combination

of high density polyethylene (HDPE) , polystyrene (PS), polypropylyne (PP), polyvinyl
chloride (PVC), polyethylene terephlthalate (PET) , and acrylonitrile butadiene styrene
(ABS). Table 7 .3 shows the percentages, by weight, of these plastics in municipal solid

waste and those used in this investigation.

Table 7.3 Types and Percentages of Different Plastics, by Weight.

 

 

 

 

 

 

 

 

Plastic Type MSW Used
HDPE 21 31
PP 16 24 I
PS ' 16 24
PVC 7 10
PET 4 6
ABS 3 5

 

 

 

 

* MSW: Municipal Solid Waste

Both recycled HDPE and "MIXED" plastic particles used in this investigation
were irregular (relatively ﬂat) in shape. The speciﬁc gravity of different types of plastics
ranged from 0.9 to l. 1. Both HDPE and "MIXED" plastics have a nominal planar
dimension of 10 mm (3/ 8 in.). The average thickness of the recycled HDPE and

"MIXED" plastic are shown in table 7 .4.

 

 

 

140
Table 7 .4 Average Thickness of the Different types of Recycled Plastics.

 

 

 

 

 

 

 

 

Plastic Type Thickness, in
HDPE 0.075
PS 0.095
PP 0.063
PVC 0.067
PET 0.041
ABS 0.091

 

 

 

 

Figure 7 .5 shows the gradation of plastic-ﬁne aggregate combinations at two

replacement levels (20 and 40% replacement of ﬁne aggregate by volume corresponding

 

to 7 .5 % and 15 % , respectively, of total volume of concrete).

 

 

 

 

1 _.___
OO / ’1’,
/ x’
/ -.
80 —P —————————————————————— /- —————————— a
/
/ /
E) 60— ———————————————————— 7/— {— ———————————— J
é: // //
(L
a. 40+————————* —————7 ,1 —————————————————
/ /
/ A
a / //
20* ——————————— 7 :74 ————————————————————— _I
o . . . .
No. 100 No. 50 No. 16 No. 4 8/8 in.

Seive Designation

 

I ‘1" Lower Limit *' 7.5% Plastic '9' 15% Plastic * Upper Limit I

 

Figure 7.5 Gradation of Plastic-Fine Aggregate Combinations.

 

 

 

141
7.4,4 Mix Proppﬁigms and Optimization

Proportioning procedures applied to normal-weight concrete mixtures are not
useful for designing lightweight concrete mixtures because: ( 1) the relation between
strength and water/cement ratio cannot be effectively employed since it is difﬁcult to
determine how much of the mixing water in concrete will be absorbed by the aggregate;
and (2) difﬁculty is caused not only by the large amounts of water absorption by porous
aggregate, but also by the fact that some aggregates continue to absorb water for several
weeks. Therefore, reliable estimates of moisture deviation from the saturated-surface dry
(SSD) condition and of the SSD bulk speciﬁc gravity are very difﬁcult.4

Workability considerations in freshly made lightweight aggregate concretes require
special attention because with high—consistency mixtures the aggregate tends to segregate
and ﬂoat on the surface. To combat this tendency, it is often necessary to limit the
maximum slump and to entrain air (irrespective of whether durability of concrete to frost
action is a consideration). Approximately 5 to 7 % air entrainment is generally required
to lower the mixing water requirement while maintaining the desired slump and reducing
the tendency for bleeding and segregation. For the purpose of mix design, the
compressive strength of lightweight aggregate concrete is usually related to cement
content at a given slump rather than to the water/ cement ratio. In most cases, the
compressive strength at a given cement and water content can be increased by reducing
the maximum size of coarse aggregate and/ or partial replacement of lightweight ﬁne
aggregate with a good-quality natural sand.4

Different trial mixtures were considered to optimize the cement content and the

 

 

 

142

ﬁne-to-coarse aggregate ratio, in order to achieve the maximum replacement level of ﬁne
aggregates with HDPE or "MDiED" plastics. The cement content and ﬁne
aggregate/ coarse aggregate ratio were 450 kg/m3 (750 lb/yd3) and 4 (by volume),
respectively. It should be noted that a relatively high ﬁne/ coarse aggregate ratio was
necessary in order to achieve desirable workability, compactability and ﬁnishability when
part of the light-weight ﬁne aggregate was replaced with HDPE or "MIXE " plastic.
Both the cement content and ﬁne-to—coarse aggregate ratio were kept constant in all
mixtures. The water content was adjusted to give comparable slumps of 38—51 mm (1.5—
2.0 in.). An air entraining agent (water based) was used at 0.06% by weight of cement.
It should be noted that plastic particles were well dispersed during mixing. Table 7.5

presents the optimized mix proportions.

Table 7 .5 Optimized Mix Proportions for Light-Weight Concrete (1b/yd3)*.

 

 

 

 

 

.3333... 3.3 3333“ w... A3“

Control 750 170 850 - 735 0.06
20% Plastic 750 180 719 120 698 0.06
40% plastic 750 193 579 258 638 0.06

 

 

 

 

 

 

 

 

a: 1 1b/yd3= 0594 kg/m"; AEA = Air Entraining Agent, by weight of cement

 

h

 

 

 

 

 

143
2A5 Test Prggednrg

Conventional mixing and curing procedures (ASTM C-94), were used to prepare
control mixtures and the plastic-concrete composites. External vibration was found to
be suitable for producing concretes incorporating recycled plastics. The Optimum
vibration time was found to be 25 _-_I; 5 seconds at a frequency of 80 Hz. All the
specimens were continuously moist-cured 23 °C (73 °F) up to the test age of 28 days.

The fresh mix workability was assessed by the slump test (ASTM C-143), and the
hardened unit weight was measured following the ASTM C-5 67 procedures.

For the hardened materials, the ﬂexural strength and toughness, compressive
strength and impact resistance were investigated experimentally in order to develop an
overall understanding of various aspects of material behavior.

The ﬂexural test specimens were 100x100x350 mm (4x4xl4 in.) and the
compressive strength test specimens were 75x15 mm (3x6 in.) cylinders. Flexural and
compression tests were conducted following ASTM C-78 and C-39 procedures,
respectively. The ﬂexural tests were conducted by four-point loading on a span of 12
in. (305 mm). Deﬂections were measured at the center of specimens with respect to the
loading points (Figure 7 .6). This method of displacement measurement eliminates any
errors associated with the rigid body movements of the specimen or penetration at

SUpport and loading points into the specimen.

 

 

144

 

E[IJ

r o o [-173

LVDT
F—

 

 

 

 

 

 

 

? 1.02 mm 102 mm I

Figure 7 .6 Flexural Test Set-Up.

Flexural loading was displacement-controlled at a quasi-static deﬂection rate of
1/ 1000 times the span length per minute. These ﬂexural tests produced load-deﬂection
curves which were characterized by ﬂexural strength (modulus of rupture), ﬂexural
toughness, and initial stiffness. The Japanese Concrete Institute speciﬁcation was
followed for calculating ﬂexural toughness, deﬁned as the area underneath the load-
deﬂection curve up to a deﬂection equal to the span length divided by 150.57

The impact test was conducted following the procedures recommended by ACI
Committee 544. This test measures the amount of impact energy (represented by the

number of blows) necessary to start a visible crack in the concrete incorporating recycled

 

I.

 

 

 

145

plastics and then to continue opening that crack until failure. The equipment for impact
test (Figure 7 .7) consists of a standard 4.55 Kg (lo-lb) compaction hammer with 460 mm
(18 in.) drop, a 63.5 mm (2.5 in.) diameter steel ball, and positioning ﬁxtures. The
impact test is performed by dropping the hammer repeatedly and recording the number
of blows required to cause the ﬁrst visible crack on the specimen top surface and then

failure.

2-1/2 In. Oia. Hardened Steel Ban

Note: Free In between
ball and pipe

   
  
  
 
 
 
 
  

(1 h..25.4 mm) 2412 In. Dia. Steel Pipe

2 x 114 In. Steel Ber
Typ.
2 I: 33/8 x 1/4 In. Bar

2321112In.8er

Typ.

   

1 114° :ms'—.I L——3-
12' DIa.

F

I;

Figure 7.7 Impact Resistance Test Set—Up.

 

 

146

7. .6 Test results and Discussion

It should be noted that sulfonated plastics gave results statistically comparable to
unsulfonated ones. Therefore, the effect of sulfonation was not included in the statistical

analysis; it is introduced in Section 7.4.6.5 separately.

7.4.6.1 Hardened Unit Weight

The hardened unit weight test results are presented in Figure 7.8. The addition
of recycled plastics tends to reduce the hardened unit weight, which adds value to
concrete properties. The reduction in hardened unit weight can be attributed to the fact
that the light-weight sand used in this investigation had a higher speciﬁc gravity than that
of the recycled plastics used.

120 HARDENED UNIT WEIGHT (lb/ft3)

 
 
  

80 "
60

40

 

 

 

 

 

 

 

 

CONTROL 7.5% HDPE 15% HDPE 7.5% MDIED 15% MDfED

Figure 7.8 Hardened Unit Weight (Means and 95% Conﬁdence Intervals).

 

 

147
7 .4.6.2 Flexural Performance

Typical 28-Day ﬂexural load-deﬂection curves for light-weight concrete and
plastic concretes incorporating 7.5 % and 15 % plastics (HDPE and ”MIXED" performed
almost similarly) are shown in Figure 7 .9. Figure 7.10 presents the ﬂexural strength test

results, and Figure 7.11 present the ﬂexural toughness test results.

 

 

 

 

3I
I [“ CONTROL 7.5% PLASTIC "“1596 PLASTIC]
I
1 E
24 J. _____________________________________
a I I
-_ 7 II:
9.9 ‘ ‘1
~ I I'.
“O J I I'.
8 - I I‘
—J j I“.
I :I“ "I.— ———————————————————————————————————
3 R
i 1 \\\
O IIIIIIIIIIIIIIIIIIIIIII m rrrrrrrrrrrrrrrrr W rrrrrrrrrrrrrrrrr

 

 

 

0 0.01 0.02 0.03 004 005 0.06 0.07
Displacement (in.)

Figure 7.9 Typical Flexural Load-Deﬂection Curves at 28 Days.

 

 

 

148

0'8 FLEXURAL STRENGTH (ksi)

 

 

I:I HDPE Plastic
06- I 95% Confidence'lnterval m MIXED Plastic

 

 

 

 

 

0.4 —

0.2 -

 

 

 

 

 

 

 

 

Control 7.5% Plastic 15% Plastic

Figure 7.10 Flexural Strength Test Results (Means and 95% Conﬁdence Intervals).

 

08 FLEXURAL TOUGHNESS (k.in.l

 

HDPE Plastic
0.06— . MIXED Plastic

 

 

 

   

0.04 . I ~95%-Confidence-~Inter-vale

I :1 i N

Control 7.5% Plastic 15% Plastic

0.02 ‘

  

 

 

 

 

Figure 7.11 Flexural Toughness Test Results (Means Values and 95% Conﬁdence
Intervals).

149

For the light-weight concrete mix composition used in this study, the addition of
plastics up to a certain level (7.5% of total volume) produced a ﬂexural strength
comparable to that of the control mixture without plastics. At 15% plastic content,
however, ﬂexural strength dropped by 6 and 12% for "MIXED" plastic and HDPE,
respectively, when compared with the control mixture. Two-way analysis of variance
and comparison of means of ﬂexural strength test results indicated that at 7.5 and 15%
plastic contents, ﬂexural strength was comparable at 95 % level of conﬁdence with that
of control concrete except for HDPE at 15 % plastic content.

Two-way analysis of variance conﬁrmed, at 95 % level of conﬁdence, that plastic
content inﬂuenced the ﬂexural toughness. The ﬂexural toughness increased with HDPE
and "MIXE " plastic to 4.5 and 8 times that of the control light-weight concrete at 7.5 %
and 15% plastic contents, respectively. This was conﬁrmed statistically (using the
separation of means technique between recycled plastics and control) at 99% level of
conﬁdence.

In general, the positive effects of plastics on ﬂexural toughness reﬂect their
capability to bridge the cracks and mitigate brittle modes of failure in concrete materials

by their pull-out resistance across cracks.

7.4.6.3 Compressive Strength
Figure 7.12 presents the 28-day compressive strength test results for light—weight
concrete. It was conﬁrmed statistically, at 95% level of conﬁdence, that plastics have

adverse effects on compressive strength. The situation would be improved if one

 

 

150

considers the compressive strength-to-weight ratio because plastics also reduce the unit
weight of concrete. The drop in compressive strength with the addition of plastics may
be attributed to the relatively low modulus of elasticity of plastics which leads to a
redistribution of stresses into the more rigid inorganic matrix. It should, however, be
noted that limits on load—carrying capacity and service life of concrete structures are
generally provided by the resistance of concrete to cracking and failure under tensile
stress systems. Concrete is fairly strong in compression, and concrete structures rarely

fail due to material failure in compression.

4 COMPRESSIVE STRENGTH (Ksi)

 

 

 

 

 

 

 

 

 

 

 

I 95% Confidence Interval E HDPE plastic
3 - E I\\\\\\\\N MIXED Plastic
2 _.
1 _
Control 7.5% Plastic 15% Plastic

Figure 7.12 Compressive Strength Test Results (Means and 95 % Conﬁdence Intervals).

 

 

 

 

15 1
7 .4.6.4 Impact Resistance

Figure 7.13 gives the mean values of the 28-day impact resistance test results for
light-weight concrete, presented as the number of blows to ﬁrst crack and failure.
Statistical analysis (comparison of means) showed, at 95 % level of conﬁdence, that
recycled plastics have a signiﬁcant positive effect on the impact resistance of concrete
beyond the initial crack up to failure.

The improvements in ultimate impact resistance in the presence of plastics further
validate the hypothesis that tough plastic inclusions help enhance the fracture energy and

toughness characteristics of concrete materials through bridging across cracks.

IMPACT RESISTANCE (# of Blows)

 

 

 

 

14

 

First Crack
1 2 ._..__...._-_......,.,..._...,.._,w...-.,....... ”W”... M..- Failure
10 3.--........._. . - . ._...._-_-_.-_s -. -,

 

 

 

 

 

 

 

 

 

 

..............

«a .....

 

 

 

 

 

 

 

 

.......... .‘.'
..................

. CONTROL 7.5% HDPE 15% HDPE 7.5% MIXED 15% MIXED

 

Figure 7.13 Impact Resistance Test Results.

 

152
7 .4.6.5 Effects of Sulfonation

The effects of sulfonated HDPE and MIXED recycled plastics incorporating 7.5
and 15 % plastic contents on compressive strength, ﬂexural behavior and impact
resistance were investigated. Sulfonated plastics performed essentially similar to
unsulfonated plastics. This can be attributed to the fact that rough plastic surfaces could
possibly develop mechanical bonding to the concrete matrix without sulfonation, and also
possibly the degree of sulfonation was not sufﬁcient to provide for chemical bonding of

the cement-based matrix to plastic surfaces.

7 .4.6.6 Microstructural Observations

In order to conﬁrm the crack arrest and bridging mechanisms of plastic inclusions
in concrete, fracture surfaces of ﬂexural specimens were observed under Scanning
Electron Microscope. A typical arrest of microcracks by plastics is shown in Figure
7.14-a (at 200x magniﬁcation), and Figure 7 . 14-b (at 50x magniﬁcation) presents a

typical condition of plastic inclusions bridging cracks. These observations further

validate the hypotheses of this investigation.

 

16KU x259

 

(a) Arrest of Microcrack

 

(b) Bridging of Cracks

Figure 7.14 SEM Micrographs of Plastic-Concrete Composite. ‘

 

154

1.; PART II' RECYCLED PLASTICS AS SECCNDARY REINFCRCLSC
INCLUSICNS IN NORMAL-WEICHT CONCRETE

 

7,5,1 Introduction

Volumetric changes in hardened concrete have a serious inﬂuence on the
performance and durability of concrete structures. Inadequate allowance for the effects
of shrinkage in concrete occasionally leads to cracking or warping of concrete slabs.

To lengthen the service life of a concrete structure, it is necessary to avoid the
formation of early age cracks as much as possible. The crack-arrest action of plastics
presents the potentials to delay the formation of shrinkage cracks and control the crack
widths.

The effects of the two variables (the width of plastic inclusion and plastic volume
fraction) in controlling the restrained drying shrinkage crack widths in normal weight
concrete were conducted by Eldarwish (1993)”. Figure 7 . 15 shows the crack width
versus time in restrained shrinkage tests. The addition of recycled plastics to concrete
helps control the drying shrinkage cracks. These valuable contributions of plastics to
concrete shrinkage cracking could be most beneﬁcial if other qualities of concrete
(including short-term mechanical properties) are not damaged (or are improved) in the
presence of plastics. Evaluation of plastic effects on mechanical properties is the major

purpose of the investigations reported in this chapter on recycling of plastics in concrete.

 

 

 

 

 

 

155
1.6“ +Control 00.257. HDPE Crackl
1 4 “ll-2.57. HDPE Crackl {—2.5% HDPE Crack2
' _ %57. HDPE Crackl £57.. HDPE Crack2
m1.2—
E -
E 1_
E _
:9
gOS-
6
p06- 0*
O
0.4—
O 2‘ In:
0 ”Tmm , ,m Hm , , mmm

 

1 9 I 7 25 33 41 49 57
Tlme (Days)

Figure 7.15 Total Crack Width Vs. Drying Time?8

7 .5 .2 Experimental Program
The experimental program conducted at this phase of the research (Table 7 .6) is

concerned with studying the effects of two variables (in a 22 factorial design): plastic

volume fraction (2.5 % and 5%) and plastic type (HDPE and MIXED).

 

156

Table 7. 6 Experimental Program For normal-Weight Concrete Incorporating
Recycled Plastics.

 

 

 

 

 

 

 

 

 

Plastic Volume Fraction Plastic Type
HDPE MIXED
2.5 % * *
5 % * *
Control *

 

 

* Average of at least four specimens for ﬂexural and compressive strength.

7 .5 . Tﬂ Procedurg

The test specimens were cured following the same procedure used with light-
weight concrete (part I). For each of the mixtures, the 28-day compressive strength
(ASTM C-39) and ﬂexural strength (ASTM C-78) tests were conducted. Details of test

specimens and the test procedures were introduced in Section 7 .4.5

7.5.4 Materials and Mix Propgrtions

The basic ingredients of the concrete materials used in this phase of research were
type I Portland cement, normal-weight aggregate (ﬁne and coarse with a maximum size
of 12 mm, 0.5 in.), water, recycled HDPE or "MIXED" plastics with maximum particle

size of 9.5 mm (3/ 8 in.), and air entraining agent (water-based). The gradation of coarse

and ﬁne aggregates met the ASTM C-33 requirements.

The concrete mixtures used in this phase had ﬁne aggregate/cement and coarse

 

157

aggregate/cement ratios of 2 and 2.5, respectively. Air entraining agent was used at
0.06% by weight of cement to produce resistance against frost attack. The water content
was adjusted for all mixtures to give similar slumps ( 44.5 to 57.2 mm, 1.75 in. to 2.25
in.). Water-cement ratio ranged from 0.39 to 0.43. Table 7.7 presents the mix

proportions.

Table 7.7 Mix Proportions for Normal-Weight Concrete (lb/yd3)*.

 

 

 

 

Volume Coarse Fine Air
Fraction Cement A A Water Entraining
gg. gg ' Agent ( %)
0.0 %
(Control) 637 1593 1274 248 0.06
2.5 %
Plastic 615 1538 1230 252 0.06
5 %
Plastic 593 1186 1322 255 0.06

 

 

 

 

 

 

 

 

* 1 lb/yd3 = 0.594 kg/m3

 

’0

 

 

158

_.5._5 Test Resulg and Discussion
7.5.5.1 Flexural Strength

Figure 7.16 shows the mean values of ﬂexural strength for different mixtures
incorporating recycled plastics as additives. Analysis of variance and comparison of
means showed that plastic-concrete with 2.5% plastics produced a ﬂexural strength
comparable to that of control. At 5% plastic content, however, ﬂexural strength was
11% less than that of control concrete with no plastics. This was conﬁrmed statistically
at 95% level of conﬁdence. It should be noted that the addition of recycled plastics

produced a ductile mode of failure rather than the conventionally brittle mode of failure

in concrete.

FLEXURAL STRENGTH (ksi)

 

HDPE Plastic

2.5% Plastic 5% Plastic

 

/

   
 

\\

%

  

 

    

 

 

 

Control

Figure 7.16 Flexural Strength Test Results.

159
7 .5.5 .2 Compressive Strength

The 28—day compressive strength test results for different concrete mixtures are
shown in Figure 7.17. Statistical analysis using analysis of variance and comparison of
means indicated that the addition of 2.5% of recycled plastics (HDPE or "MIXED"
plastic) showed comparable compressive strength to control. However, at 5% addition
of the plastics, strength dropped by 17% when compared to control normal-weight

concrete. This was conﬁrmed statistically at 95% level of conﬁdence.

9 COMPRESSIVE STRENGTH (ksi)

 

 

8‘ " ' - HDPE Plastic

7 ~ ~ P ' MIXED Plastic
6— ' ’ ' ' "
5-..
4..
3—
2‘

 

 

 

 

  

 

 

 

 

 

Control 2.5% Plastic 5% Plastic

 

 

 

Figure 7.17 Compressive Strength Test Results.

l“

160

SUMNIARY AND CONCLUSIONS

The effects of partial substitution of light-weight aggregate with recycled plastics

on concrete properties were investigated. Two plastic types (HDPE and "MlXED") and

two levels of replacement of ﬁne aggregate (7 .5 % and 15 % plastics by total volume of

concrete) were considered with sulfonated and unsulfonated plastics. Also the effects of

recycled plastics as secondary reinforcing inclusions (additives) in normal-weight

concrete were investigated.

The hardened material mechanical properties were assessed through ﬂexure,

impact and compression tests. The following conclusions were derived through analysis

of the generated test data:

1.

Relatively high ﬁne-to—coarse aggregate ratios were necessary in order to achieve
desirable dispersability, workability, compactability and ﬁnishability when part
of the light—weight ﬁne aggregate was replaced with HDPE or "MIXED" plastic.
Recycled plastics as partial replacement of light—weight aggregate at 7.5 and 15 %
volume fractions of light-weight concrete gave comparable ﬂexural strengths to
that of control concrete mix. However, ﬂexural toughness increased by 4.5 and
8 times, respectively. This was conﬁrmed statistically at 99% level of
conﬁdence.

Compressive strength test results of light-weight plastic concrete were indicative
of the adverse effects of recycled plastics. It should be noted that concrete is
fairly strong in compression, and rarely fails due to material failure in

compression. Furthermore, since the reduction in compressive strength 18

 

 

161

accompanied with the reduction in unit weight, the situation would be improved
if one looks at the compressive strength-to-unit weight ratio.

Recycled plastics have a signiﬁcant positive effect on the impact resistance of
concrete beyond the initial crack up to failure.

Sulfonated plastics gave similar results when compared with unsulfonated ones.
In normal-weight concrete, recycled plastics enhance the shrinkage cracking
characteristics of concrete without adversely inﬂuencing the short-term
mechanical properties of the material. More ductile modes of failure were

observed in normal-weight concrete materials incorporating recycled plastics.

 

 

 

 

CHAPTER EIGHT

DURABILITY CHARACTERISTICS OF RECYCLED

PLASTIC-CON CRETE COB/IPOSITES

L1 INTRODUCTION

Concrete materials incorporating recycled plastics as light-weight aggregates and
reinforcing ﬁbers for enhancing toughness characteristics, impact resistance and
shrinkage cracking characteristics at reduced unit weight present new developments in
concrete technology. In order to fully develop this class of materials it is important to
ensure their satisfactory long-term performance under severe environmental effects; this
was the main thrust of the work reported in this chapter.

The long-term durability tests performed on light-weight plastic-concrete
campsites include: permeability (ASTM C-1202 or AASHTO T-277), hot water durability
(ASTM C-1185), acid resistance, and corrosion resistance (ASTM C-876). The same
tests were conducted for normal-weight concretes incorporating recycled plastics as

secondary reinforcing inclusions (additives) except for acid resistance.

162

 

 

 

 

 

163
L; BACKGROUND AND TEST PROCEDURES

This section brieﬂy introduces the background and test procedures for the
assessment of various aspects of concrete durability (permeability, acid resistance,

protection against corrosion, and hot water durability).

8.2.1 Permeability

Permeability plays an important role in the long-term durability of concrete
materials; it is perhaps the most signiﬁcant durability-related parameter. Low
permeability of concrete can improve the resistance to the movement of water, sulfate
ions, chloride ions, alkali ions, and other causes of chemical attack.

The chloride permeability tests were conducted using ASTM 01202 or
AASHTO T-277 (Rapid Determination of the Chloride Permeability of Concrete).12 The
test procedure can be summarized as follows: (1) after the curing age (in this case it was
28—day moist curing), the perimeter of the cylindrical specimen is covered with epoxy;
(2) after the epoxy is dried, the concrete specimen is placed into a vacuum desiccator and
vacuum is maintained for 3 hours; (3) while the vacuum pump is still running, the
desiccator is ﬁlled with de—aerated water to cover the specimen, vacuum is maintained
for another hour and then it is shut off and the specimen soaks for 18 hours; (5) the
specimen is then removed from water and connected to an applied voltage cell where one
side is in contact with sodium hydroxide solution (see Figure 2.3 in Section 2.3).

Permeability is then represented by the amount of charge passed through a

concrete specimen subjected to permeation of chloride ions at 60 VDC for 6 hours. The

 

 

164
total charge passed (in Coulombs) is related to chloride ion permeability. The more

permeable the concrete, the higher would be the Coulombs (see Table 2.3 in Section
2.3). A cylindrical specimen 102 mm (4 in.) in diameter by 51 mm (2 in.) in thickness

is used for this test.

8.2.2 Acid Resistance

Acid attack in concrete is a process of structural change which starts at the surface
and progressively weakens the material by removal of the cementing constituents. Acids
such as HCl, HNO3 , and H2804 are highly corrosive to concrete. When permeability
is low, it is expected that decomposition by acid attack on concrete is limited to the
surface; otherwise, the process attacks the interior of concrete.

After the 28-day moist curing, concrete specimens were immersed in a 5%
solution of HCl (hydrochloric acid, pH value of 0.4). After one day of immersion, the
acid concentration changed (reaching a pH value of 2). The acid concentration was
checked regularly and the pH value of the solution was maintained at a range of pH=1
to 2. The weight change was measured at different time intervals. For this purpose, the
specimens were subjected to high air pressure to remove loose surface debris before
weight measurements. The compressive strength was then assessed and compared with

that of specimens which were moist cured for 28 days.

 

 

 

 

 

 

165

8.2.3 Corrosion Resistance

Cracking and spalling of concrete due to the corrosion of steel reinforcement are
the most common forms of deterioration in reinforced concrete structures subjected to
deicer salt application or marine environments. The formation of rust results in an
increase in volume compared with the original steel so that swelling pressure will cause
cracking and spalling of the concrete.

Reinforcing bars which in theory are protected from rusting by the alkalinity of
the concrete (a pH of about 12 to 12.5 causes a passive oxide ﬁlm to form on the surface
of iron and prevents corrosion). This protection (known as passivity) is usually effective
for a very long time, but it is possible for the protection to be destroyed (when the pH
is reduced to about 11.0 or below) either as a result of the penetration into concrete of
acid gases which are present in the air (most often carbon dioxide, but in areas with
industrial pollution also sulphur dioxide), or by the penetration into the concrete of
chlorides from sea water in coastal environment; even inland structures, at some distance
from the sea, can be affected by salt-laden air carried in prevailing winds. The use of
chloride de-icing salts on concrete roads has also resulted in damage by frost scaling of
the surface or corrosion of reinforcement, particularly on bridge decks. Calcium
chloride, which was widely used in the past to accelerate the hardening of concrete, has
a similar effect. A critical reduction of pH occurs for example when calcium hydroxide,
which maintains the high PH in cement paste, is converted to calcium carbonate (calcite)
by atmospheric carbonation. 193259

Corrosion of steel occurs because of the electro—chemical action which is usually

 

 

 

166

encountered when two dissimilar metals are in electrical contact in the presence of
moisture and oxygen. However, the same process takes place in steel alone because of
differences in the electro-chemical potential on the surface which forms anodic and
cathodic regions, connected by the electrolyte in the form of the salt solution in the
hydrated cement. The positively charged ferrous ions Fe” + at the anode pass into
solution while the negatively charged free electrons e’ pass along the steel into the
cathode where they are absorbed by the constituents of the electrolyte and combine with
water and oxygen to form hydroxyl ions OH‘. These then combine with the ferrous ions
to form ferric hydroxide and this is converted by further oxidation to rust, the schematic

reactions are (see Figure 8.1-a):17

Fe ---> Fe++ + 2e‘ (anodic reaction)
4e’ + 02 + 2H20 --— > 4(0H)’ (cathodic reaction)
Fe++ + 2(OH)' --- > Fe(OH)2 (ferrous hydroxide)

4Fe(OH)2 + 2H20 + 02 --- > 4Fe(OH)3 (ferric hydroxide).

It should be noted that oxygen is consumed, but water is regenerated and is
needed only for the process to continue. Thus there is no corrosion in a completely dry
atmosphere, probably below a relative humidity of 40%; nor is there much corrosion in
concrete fully immersed in water, except when water can entrain air. It has been
suggested that the optimum relative humidity for corrosion is 70 to 80%. At higher

relative humidiﬁes, the diffusion of oxygen is considerably reduced and also the

 

 

 

 

167

environmental conditions are more uniform along the steel.

The presence of chloride ion in concentrations above some threshold level
destroys the passivity, and corrosion cells develop. The threshold chloride concentration
within the concrete at the level of the reinforcement necessary to initiate corrosion is
generally taken to be in the range 0.7 to 0.9 kg/m3 (0.42 to 0.53 lb/yd3) of concrete.
The surface of the steel then becomes activated locally to form the anode, with the
passive surface forming the cathode; the ensuing corrosion is in the form of localized

Pitting. In the presence of chlorides, the schematic reactions are (see Figure 8.1-b):17

Fe” + 2c1- ---> Feel,

FeC12 + 211,0 ---> mom, + 2HC1

The relative concentration of chloride and hydroxyl ions in pore solutions, and
the diffusivity of chloride ions are the two major parameters governing the risk of
chloride induced corrosion. The ratio of C1’ to OH' is thus important in determining
whether chloride induced corrosion will occur. In the presence of chloride ions,
depending on the Cl'/OH' ratio, it is reported that the protective ﬁlm may be destroyed
even at pH values considerably above 11.5. When Cl'IOH' molar ratios are higher than
0.6, steel seems to be no longer protected against corrosion, probably because the iron-

oxide ﬁlm becomes either permeable or unstable under these conditions.4

 

 

 

 

 

168
Concrete H20 102
Fe” (OH)‘

  
       

IIIIIIIIIIIA IIIIIIII’IIIIIIIIIIIII’IIIIIIIIIII

Steel
III/IIIIII/II/IIIIIIIIIIIII/IIIIIIIIIIIIIIIIIIIII/II

(a) The Electro-Chemical Process

 

 

 

 

' Concrete H20 1 02
Cl-
1 8 (01-1)“ Passivated layer
th + *' WfﬂlllllllllllllljlllllIll/[[14
W e Z /

7

Steel

WM/////////////////////////////////////////¢

(b) Effect of Chlorides

Figure 8.1 The Electra-Chemical Process of Corrosion. ‘7

 

 

 

169
The test procedures are designed to be a slightly modiﬁed version of the ASTM

C-876 speciﬁcation. The latter is generally used in ﬁeld applications to monitor
reinforcing steel bars in concrete structures. ASTM Standard test procedure was used
with some modiﬁcation so that it can be applied in laboratory. Nevertheless, the test
principles remain the same.

The test program consists of monitoring corrosion activity in 12.5 mm (0.5 in.)
diameter steel reinforcing bars that are cast inside 75x 150 mm (3x6 in.) concrete
cylinders; the cover thickness is uniform (32 mm, 1.25 in) all around and at the bottom
of cylinder. These cylinders (after 28-day moist curing) are partially immersed in 5%

sodium chloride solution and the level of solution is kept at twice the cover thickness.

 

The half-Cell Potential method is used to monitor corrosion activity in the reinforcing

 

steel at different ages. ASTM C-786 speciﬁes the signiﬁcance of the numerical values

of the measured potentials as follows:

if potential less than -350 mv ------- > greater than 90% probability of corrosion.
if potential greater than -200 mv -------- > less than 50% probability of corrosion.
if potential between -200mv and -350 mv -------- > probability of corrosion is uncertain.

The threshold potential is taken at -250 mv. Half cell potentials greater than this

value indicate that reinforcing steel corrosion is occurring.

 

 

 

:ﬁp’

 

 

 

 

170
8.2.4 Hot Water Durability

Hot water soak test investigates the long-term chemical interaction of constituent
materials. In this method of testing wet and elevated temperature conditions are used to
accelerate any chemical reactions. In this test, after 28-day moist curing of the
specimens, they are immersed in a hot water bath for 1 month at 60 °C (140 °F).
Specimens for flexural strength and flexural toughness, 100x100x350 mm (4x4x14in.),

are then tested in ﬂexure and compared to the 28-day moist cured specimens.

3g EXPERIMENTAL PROGRAM

An experimental program has been designed based on the statistical concepts of
factorial analysis of variance (22 factorial design). This experimental program (Table
8.1) investigates the following two variables: plastic type (HDPE and MIXED), plastic
content (two different levels, 20 and 40% replacement of ﬁne light-weight aggregate by
volume corresponding to 7 .5 % and 15 % by total volume of concrete) or plastic volume
fraction in the case of normal-weight concrete (2.5 % and 5 %). The sulfonation variable

was considered only in the case of light-weight concrete for permeability (for both HDPE

and MIXED plastics).

 

 

 

i—F'

 

 

 

171

Table 8.1 Experimental Program For Light- and Normal-Weight Concrete
Incorporating Recycled Plastics.

 

Replacement Level of Sand with Plastics, by volume Plastic Type
for light-weight concrete *

 

(Plastic Volume Fraction for normal-weight concrete) HDPE MIXED

 

20% (2.5%) - -
40% (5%) - -

 

 

 

 

 

 

I Control -

* 20% and 40% replacements of ﬁne aggregate correspond to 7.5% and 15% of total
volume.

- Average of at least six specimens for permeability, eight specimens for acid resistance,
ﬁve specimens for corrosion resistance and four specimens for hot water durability.

M MW

Details of materials and mix proportions of light- and normal-weight concrete
were introduced in Chapter seven.

The fresh materials were cast in molds and then consolidated through external
vibration. The specimens were demolded after 24 hours, during which they were
covered under wet burlap and plastic sheet, and stored at 23 °C (73 °F). Thereafter, All
the specimens were continuously moist-cured at 23 °C (73 °F) up to the test age of 28

days; then the speciﬁed durability tests were conducted according to the test procedures

mentioned in Section 8.2.

 

 

 

 

 

 

 

172
§._5_ flfLST RESULTS AND DISCUSSION

The durability test results of recycled plastics as partial substitutes for light-weigh
aggregates in light-weigh concrete materials and as secondary reinforcing inclusions in

normal-weight concrete (for shrinkage crack control) are discussed in the following:

8.5.1 Permeability
8.5.1.1 Light-Weight Concrete

The chloride permeability test results (means and 95 % conﬁdence intervals) for
light-weight concrete and plastic-concrete materials incorporating 7.5 % and 15 %
recycled HDPE and MIXED plastic contents by total volume are shown in Figure 8.2.
Two-way analysis of variance (22) conﬁrmed, at 99% level of conﬁdence, that the two
variables of this investigation (replacement level of sand with plastic and plastic type),
but not their paired interactions, inﬂuenced the permeability of light-weight concrete.
Separation of means of the test results conﬁrmed, at 95 % level of conﬁdence, that the
permeability of control concrete (no plastics) was statistically comparable to that of the
plastic-concrete composites with 7 .5 plastic content when HDPE was used. Increasing
the HDPE content to 15 % led to a slight increase in permeability. However, "MIXED“
plastic at 7.5 % and 15 % volume contents reduced permeability by 25% and 17% ,
respectively, when compared to control concrete. This was conﬁrmed at 95 % level of
conﬁdence. Hence, plastic-concrete presents permeability characteristics comparable or
superior to that obtained with conventional light-weight concrete materials.

In order to understand the effects of plastic on concrete permeability one should

 

 

173

consider that while plastics, as low-permeability inclusions which may also reduce
microcrack intensity, are expected to reduce permeability, porous or microcracked
plastic-cement interfaces may cause an increase in permeability. Hence, with improved
interface characteristics one may potentially reduce concrete permeability by the addition
of recycled plastics. It should be noted that sulfonation of plastics helped in reducing
permeability. The average ratios of 28-day permeabilities for the sulfonated to
unsulfonated HDPE plastic were 0.74 and 0.82 for cases ‘with 7.5% and 15% plastic
contents; the corresponding ratios were 0.68 and 0.77 for "MIXED“ plastics. This may
be due to the sensitivity of permeability to improvements in the bonding of plastic

surfaces to concrete.

16 PERMEABILITY (Thousand Coulombs)

 

 

14”“ ' " [:1 HDPE Plastic
12—7 [95%-Confidence Interval h\\\\\\\\) MIXED Plastic

 

 

 

 

 

 

 

 

 

 

 

 

Control 7.5% Plastic 15% Plastic

Figure 8.2 Light-Weight Concrete Permeability Test Results.

 

 

174
8.5.1.2 Normal-Weight Concrete

The chloride permeability test results (Figure 8.3) indicate that incorporating
2.5% recycled HDPE or "MIXE " plastic produced permeability levels comparable to
that of control. Although the addition of 5% recycled HDPE or "MIXED" plastic as
additives in normal-weight concrete increased permeability by an average of 14%, two-
way analysis of variance and separation of means showed that this increase was not

statistically signiﬁcant at 95% level of conﬁdence.

5 PERMEABILITY (Thousand Coulombs)

 

 

 

 

 

 

4_ HDPE Plastic
MIXED Plastic

3i

zl

1 _

 

 

 

 

 

 

 

 

Control 2.5% Plastic 5% Plastic

Figure 8.3 Normal-Weight Concrete Permeability Test Results.

 

 

 

 

175
8.5.2 Acid Resistance (Light-Weight Concrete)

Average percent change in weight of lightweight concrete and plastic—concrete
incorporating 7 .5 % and 15 % recycled HDPE and "MIXED" plastic contents by total
volume are presented in Figure 8.4. HDPE and "MIXE " plastics produced essentially
the same performance.

The split-plot analysis of variance with repeated measurement and separation of
means techniques were used to analyze the data statistically. The addition of plastics at
20% replacement of sand produced weight losses statistically comparable to that of
control mixtures without plastic. However, at 15 % plastic content, the plastic concrete
showed average weight loss increases of 16-19% more than the cases of 7.5 plastic
content and control. This was conﬁrmed statistically at 95 % level of conﬁdence. At
high plastic contents, acid attack on the cement-based matrix seemed to loosen plastic
particles on the surface, the separation of which from the mass caused the weight loss.

Acid attack did not have any signiﬁcant effect on the compressive strength of

plastic concrete composites at 7 .5% and 15 % volume contents of plastics.

8.5.3 Corrosion Resistance
8.5.3.1 Light-Weight Concrete

The half-cell corrosion potential measurements of light-weight concrete and
plastic-concretes incorporating 7 .5 % and 15 % recycled plastics are presented in Figure
8.5 . HDPE and "MIXED" plastics produced essentially similar performance. Each value

plotted is an average of ﬁve readings obtained on ﬁve specimens. The threshold

 

 

 

 

 

 

  
   

 

 

 

 

 

 

176
5 ,
4 ________________________ __ __ .—__.
8
E 3 ————————————— _ ——————————————————— 3
g) Occurnor.
g / tum PLASTIC
g / 906 15% PLASTIC
g; 2 ,/ ——————————————————————————————— j
0
_. 1
1 { —————————————————————————————————————— 1
1
O L ‘V l V T l l l l l
O 1 2 3 4 5 6 7 8 9 1 0
Time (Weeks)
Figure 8.4 Change in Weight with Time.
600 ‘
3. *CONTROL +15% PLASTIC * 15% PLASTIC
‘ J
A500 -------------------------------------
>
E
2
E5
E
O)
*5
a
C
.9
(I)
9
5
0

Figure 8.5

 

 

 

O l l l l f l '—r f . [—r r a
O 2 4 6 8 1O 12 14 16 18
Time (Weeks)

Corrosion Potential Measurements.

20

 

 

 

 

177

potential taken at -250 mv (indicating the starting of corrosion) is reached after nine
weeks in light—weight concrete and eleven weeks in plastic-concretes incorporating 7 .5 %
and 15 % plastics (concrete materials with 7.5 % and 15 % plastic contents by total volume
performed almost similarly). The corrosion potential measurements for control and
plastic concrete produced similar trends in the ﬁrst eight weeks (before the threshold
potential was reached); however, at later ages (8-19 weeks) plastic concrete at both 7.5 %
and 15 % volume contents and the control concrete started to behave differently, with the
situation of control concrete deteriorating more rapidly. Statistical analysis (using the
split-plot analysis of variance with repeated measurement and separation of means
techniques) of results between 8 and 19 weeks conﬁrmed the decrease in corrosion
potentials resulting from the incorporation of plastics (at 7.5 and 15 % by volume) at 95 %
level of conﬁdence. The electrical insulation qualities of plastics and somewhat reduced
permeability of concrete in the presence of plastics at least partly illustrate the positive

effects of plastic inclusions on corrosion resistance.

8.5.3.2 Normal-Weight Concrete

Corrosion potential tests on normal weight concretes incorporating 0% and 2.5 % HDPE
and "MIXE " plastics by volume were continued for approximately 5 months. At the
relatively low water-cement ratios used in this investigation (0.39 for control concrete
and 0,41 with plastics), the relatively small addition of plastic to normal-weight concrete

did not inﬂuence the excellent corrosion resistance of the material.

 

 

 

 

 

178
8.5 .4 Hot-Water Durability

8.5.4.1 Light-Weight Concrete

The ﬂexural strength and toughness test results for long-term immersion in hot

water bath of the light-weight concrete specimens incorporating recycled plastics (HDPE)
are shown in Figures 8.6 and 8.7, respectively. Hot water immersion led to generally
consistent damage to control specimens and those incorporating plastics of 7 .5 % and
15 % by total volume; the average strength drops of control specimen and those with
7.5% and 15% by volume of plastics were 33%, 42% and 49%, respectively. The
major drop in the strength of control concrete which was also reﬂected in plastic
concretes, is due to the weakness of the speciﬁc light-weight aggregate used in this
investigation.

Analysis of variance and comparison of means of the ﬂexural strength indicated
that all drops in strength after 30-day hot water immersion are statistically comparable
at 95 % level of conﬁdence, except for control concrete when compared with that
incorporating 15 % plastics by volume. The slightly increased average drop in ﬂexural
strength in the presence of plastics could result from the fact that tests were conducted
on hot specimens and the elastic modulus of plastics could have been lowered by the
elevated temperature. After 30 days of hot water immersion, the ﬂexural toughness
increased to about 8 times that of control at 7 .5 % and 15 % volume contents of plastics.
This was conﬁrmed statistically at 99 % level of conﬁdence. Hence, if the light-weight
aggregate type is selected to provide resistance to hot and humid environments, the

pronounced toughening mechanism of plastics could be highly advantageous in masonry

 

 

 

 

179

and other production processes where products are exposed to hot and humid

environments during accelerated (e. g. steam) curing.

8.5.4.2 N ormal-Weight Concrete

The hot-water durability test results for the ﬂexural strength of plain and plastic
concrete are presented in Figure 8.8. Long-term immersion in hot water bath had no
effects on control concrete and relatively small effects on the ﬂexural strength of plastic
concretes. The slight drOp in strength in the presence of plastics can be attributed to the
fact that the test was performed while the specimens were hot where elevated temperature
could lower the modulus of elasticity of plastic inclusions. More ductile modes of failure
were observed when plastic concretes were immersed in hot water.

Results of the analysis of variance of the test data indicated that the effects of
long-term immersion in hot water on ﬂexural strength of plain concrete or those

incorporating 2.5 % of recycled HDPE or "MIXED" plastics were not statistically

signiﬁcant at 95 % level of conﬁdence.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

182
8.6 UNIMARY AND ONCLU I N

The long-term durability of light-weight plastic-concrete campsites (incorporating
recycled HDPE and " MIXED " plastics as partial substitutes for light-weight aggregate
in light-weight concrete) were assessed through investigating: the permeability (ASTM
C-1202 or AASHTO T-277), hot water durability (ASTM C-1185), acid resistance, and
corrosion resistance (ASTM C-876) of the materials. The same tests (except for acid
resistance) were conducted for normal-weight concretes incorporating recycled HDPE
and "MIXE " plastics as secondary reinforcing inclusions (additives). Two different
levels, 20 and 40 % replacement of ﬁne light-weight aggregate by volume corresponding
to 7 .5 % and 15 % by total volume in the case of light-weight concrete, and 2.5 % and 5 %
plastic volume fraction in the case of normal-weight concrete, were considered.
Sulfonation was considered only in the case of permeability tests on light-weight concrete
(for both HDPE and MIXED plastics). It was concluded that:

In light-weight concrete: (1) chloride permeability test results showed that HDPE
produced results which were statistically comparable to those obtained with control
concrete. However, "MIXED" plastic reduced permeability at 7.5 and 15 % volume
fraction when compared with control concrete. Sulfonation helped in reducing
permeability, this may be due to the sensitivity of permeability to improvements in the
bonding of plastic surfaces to concrete; (2) In the case of acid resistance, the use of
plastics at 7 .5 % volume fraction produced weight losses statistically comparable to that
of control mixtures without plastic. However, at 15 % volume fraction, the plastic

concrete showed average weight loss increases 16-19% more than the cases of 7.5 %

 

 

 

 

 

 

183

plastic content and control. Acid attack did not have any signiﬁcant effect on the
compressive strength of plastic-concrete composites at 7 .5 % and 15 % volume contents;
(3) the corrosion potential measurement for control and plastic concretes produced similar
trends in the ﬁrst eight weeks (before the threshold potential was reached); however, at
later ages (8 — 19 weeks) plastic concrete for both 7 .5 % and 15 % volume fractions
provided better corrosion resistance than control concrete; (4) ﬂexural strength in the
presence of recycled plastics (compared to control) after immersion in hot water dropped
by about 9% and 16% at 7.5 % and 15 % plastic volume contents. However, the ﬂexural
toughness increased to about 8 times that of control at both plastic content. Accelerated
curing conditions involving exposure to hot and humid environments (e.g. steam curing
in masonry production) may help achieve this pronounced toughening effect of plastics.

In normal—weight concrete, recycled plastics can enhance the shrinkage cracking
characteristics of concrete without adversely inﬂuencing long-term performance
characteristics of the material under severe environmental effects (as measured by

permeability, corrosion resistance and hot water durability tests).

 

 

 

 

 

CHAPTERNINE

RECYCLING OF TIRES IN CONCRETE MATERIALS

2; INTRODUCTION

Approximately 240 million used vehicle tires are generated in the United States
each year. About 22 % of these tires are reused or processed. The remaining 78 % of
these tires are discarded in landﬁlls or illegal disposal sites, or stockpiled above ground.3

Tires usually contain a variety of rubber compositions as well as other constituents
such as carbon black, synthetic ﬁbers, steel wires, sulfur and zinc oxide, each
contributing certain pr0perties to the overall performance of tire. Rubber compounds
designed for a speciﬁc function will usually be similar but not identical in composition
and properties, although in some cases there can be signiﬁcant differences between
compounds in tires of various types. When coupled with cement and moisture, tire
constituents tend to swell inside concrete matrices; this eventually leads to pop-out at
outer surfaces of concrete and potentially increased dimensional movements of concrete.

Recycled tire inclusions can potentially relieve the stress intensity at sharp crack
tips in brittle concrete matrices, and thus produce a composite material with enhanced
resilience, toughness, energy absorption capacity, impact resistance and cracking
strength. The relatively low density of recycled tire inclusions would also improve the

thermal insulation properties of concrete. Many applications of recycled tires as

 

 

 

 

 

185

reinforcing inclusions such as slabs on grade can take advantage of the cracking

resistance and toughness characteristics of tire-concrete composites.

2; BACKQRO [1ND
9.2.1 General

About 240 million automotive, truck, and off-road tires are discarded in the
United States each year. This is approximately equal to one waste tire per person per
year. Additionally, there are 33.5 million tires that are retreated and an estimated 10
million that are reused each year as second-hand tires. It is estimated that 7% of the
discarded tires are currently being recycled into new products and 11% are converted to
energy. Nearly 78 % are being landﬁlled, stockpiled, or illegally dumped, with the
remainder being exported.

Tires are difﬁcult to landﬁll. Whole tires do not compact well, and they tend to
work their way up through the soil to the top. As a result, tire stockpiles, which cost
less than landﬁlls, have sprung up all over the country. It is estimated that between 2
and 3 billion tires are stockpiled in the U. S. at present, with at least one pile containing
over 30 million tires. Tire stockpiles are unsightly and are a threat to public health and
safety. Not only are tire piles excellent breeding grounds for mosquitoes, but they are
also ﬁre hazards.

Tire recycling activities include the use of whole tires or processed tires for useful
purposes. Whole tire applications include reefs and breakwaters, playground equipment,

erosion control, and highway crash barriers. Processed tire products include mats and

 

 

 

 

186
other rubber products, rubberized asphalt, playground gravel substitute, and bulking

agent for sludge composting.
Scrap tire combustion is practiced in power plants, tire manufacturing plants,

cement kilns, pulp and paper plants, and small package steam plants (EPA, 1990’.

9.2.2 Production and Disposal
9.2.2.1 Volume of Production

It is commonly accepted in the tire industry that about one tire per person per
year is discarded. Since there is no industry group or governmental agency that monitors
tire disposal in the United States, the best estimates that can be made are based on tire
production. The Rubber Manufacturers Association (RMA) records the number of
original equipment, replacement, and export tires that are shipped each year in the United
States. In 1990, a total of 264,262,000 tires were shipped. The RMA data include new
tire imports, but not imported used tires.

Figure 9.1 shows the estimated disposition of the 240 million scrap tires
generated in 1990. About 16.3 million were recycled, 26 million were recovered for
energy, and about 12 million were exported, leaving 188 million for landﬁlling,
stockpiling, or illegal dumping. Figure 9.2 shows that in 1990, 17.4% of the tires

scrapped were recycled or burned for energy (EPA, 1991).3

 

 

 

187

 

 

 

 

 

 

 

 

 

Reuse 10 7 Vehicles E 33-5 Retread I
1 10 . 33-5 1

L

 

 

 

 

 

242 100 %
ll

42.2 Waste Tire inventory ‘ .
17.4% 1r 1 5'0 %

 

 

12

 

 

 

 

 

 

 

187.8 77.6 °/o

i l l, ll

7 . ‘ Used
Illegal Dumplng Landllll Slockplle H
i 1. Whole 4 , EXP“

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2. Shredded
25.9 10.7 % 0.3 0.1 °/. 15-0 l 6.6 96
l:
Comb s i : Processed Tire Products
1, papa: Sights Whole Tire Applications 3 1. Processed rubber products
2. Tire plants 1. Reels and breakwaters l 2. Crumb rubber for pavements
2. Playground equipment 3- 3. Playground gravel
3. Cement plants i . . .
4. Pulp and paper mills 3. E_;o:ion contr: b i . substitute...
5. Small package boilers 4' H 9 way cras arr ers ; 4- S'Ud99 composting
5. Split lire products

 

 

Figure 9.1 Flow Diagram Showing Estimated Destination of Scrap Tires in 1990 (In
Millions of Tires and Percent).3

 

188

  
    

illegal Dumping

5%
Used
Expon

6. 7 %

Other

Recovery

10.7.y

O

Energy/Burning

Figure 9.2 Destination of Waste Tires in 1990.3

9.2.2.2 Disposal Problems

A wide range of scrape tire disposal technique are available or being investigated.
Numerous diverse schemes, such as artiﬁcial tire reefs, dock fenders, synthetic turf,
motor way crash barriers, ﬁllers for building and road materials, and ﬁlling in river
beds, railway cutting and marshlands have been contemplated, but inevitably have had
only minor impact on the total disposal problem.

Methods such as tire splitting, and reclaim and crumb recovery (most of which
is recycled to the tire industry) are carried out, but do not handle large truck tires and
produce by-product wastes with similar disposal problems.

An increasing majority of landﬁlls refuse to accept any tires because they do not

biochemically degrade when buried and can "ﬂoat" to the top, breaking thrOugh the cover

hi

 

 

 

189

causing damage which requires costly repairs. Tire piles provide excellent breeding
places for vermin and insets.

The recycling of rubber through size reduction, either by shredding and grinding
or by cryogenic fragmentation, would certainly attack a large market but is expensive.

In the United States, an oil and ground-tire mixture has been burned to produce
carbon black for re-use in new tires, while a stoker-ﬁred boiler has been operated using
a mixture of 10% shredded tire with coal. Biochemical degradation, by mixing steel-free
tire particles with yeast! fungi and certain chemicals, has also been reported for producing
a soil conditioner, although, without a market, the process is uneconomic.

Dumping is generally an expensive operation, is a waste of a valuable resource,
and is normally discouraged by local authorities because such sites are ﬁre risks as well
as being potentially unsightly. Where sites are not scarce, inaccessibility can be a
problem even when the normally low bulk—density of tires is more than doubled by
shredding. Several furnaces, operating worldwide, have been designed speciﬁcally for
burning tires. However, incineration of tires without heat recovery is disadvantageously
placed in an energy-conscious environment. The incorporation of a waste-heat recovery
system is attractive, provided economical operation is possible. The high caloriﬁc value
of a tire is troublesome, the air-fuel ratio must be maintained within close limits to
ensure the required fuel-vaporization rate and maintain the ignition temperature;
insufﬁcient quantities of air result in the production of explosive mixtures. Even so, the
combustion is violent and ﬂame extinction is always a possibility. The relatively high

sulfur content (up to 2%) results in sulfur dioxide formation and subsequent corrosion

 

 

 

190

problems. To comply with the requirements of the Clean Air Act, it is necessary to
install a sophisticated gas clean-up plant. The high temperature of operation, 1600 °C
(2912 °F) in some cases, necessitates temperature resistant construction materials with
associated additional costs. The high steel content of tires can cause major problems
with moving grate incinerators. For efﬁcient and acceptable treatment, specially
designed incinerators are therefore required, although tire-shredding and/ or mixing with
general waste materials can reduce this problem and allow the use of conventional units
(Fletcher, 1980).‘50

Fire is a particularly important problem, since tire ﬁres emit heavy black smoke
into the air, and release petroleum and other chemical contaminants into surface and
ground water. Once ignited, tire ﬁres are extremely difﬁcult to contain and extinguish,
requiring large amounts of manpower and equipment.

Anyone who has ever handled an old tire realizes the impossibility of dumping
all the water out of one. Such water creates a breeding habitat for mosquitoes, known

to carry yellow fever and many forms of encephalitis.

9.2.3 Properties Of Tire
9.2.3.1 Chemical Composition

Today’s tire is made to last under extremely severe physical, thermal, and
chemical conditions and is practically indestructible. Over years tires have developed to
be chemically complex, precision engineered and designed not to come apart. A tire

only becomes a scrap tire because the tread is worn off or it has been physically

 

 

 

191

damaged. The material out of which a tire is made, the fabric, ﬁber glass, wire and
rubber remain essentially as good as when they were introduced to make a new tire. The
most common tire rubber is styrene butadiene copolymer (SBR), containing about 25 %
by weight styrene. In combination with SBR, other elastromers such as natural rubber
(cis-polyisoprene), synthetic cis-ployisoprene, and cis-polybutadience are also used in
tires in varied amounts. A typical recipe for tire rubber is given in Table 9.1 ( Fader,

1990).61

Table 9.1 Typical Chemical Composition of Tire Rubber.61

 

 

 

 

 

 

 

 

Component Weight (%)
SBR 62.1
Carbon Black 31.0
Extender Oil 1.9
Zinc Oxide 1.9
Stearic Acid 1.2
Sulfur 1.1
Accelerator ‘ 0.7 A

 

 

 

 

A typical analysis of a scrap tire suggests that tire is a mixture of rubber, rayon,
nylon, polyester, carbon-black, and natural and synthetic rubbers. Steel (up to 17%),
non-ferrous metal (mainly as the vulcanizing agent, zinc oxide) and sulfur are also

present in signiﬁcant quantities in the whole tires.

 

 

 

 

 

192
9.2.3.2 Physical Properties

A pneumatic tire generally fulﬁlls the following functions: (1) Allows a
comparatively free and frictionless motion of the vehicle through rolling; (2) Distributes
vehicle weight over a substantial area of ground surface, thus avoiding excessive stress
on the latter and on the wheel; (3) Cushion the vehicle against road shocks; (4) Transmits
engine torque to the road surface with a low power consumption; (5) Permits, through
tire adhesion, the generation of substantial braking, driving and steering loads; and (6)
Ensures lateral and directional stability. N 0 other device exists today which can fulﬁll
these varied function in an efﬁcient manner as the pneumatic tire. To fulﬁll these
purposes, passenger-car radial ply tires are usually built of one to four radial plies of
rayon, nylon or polyester. The belt or breaker consists of either two layers of steel cords,
or four to six layers of textile cords. These are generally thicker than the cords used in
the radial portion of the casing and therefore have a considerably increased stiffness.
For truck and heavy-duty tires, it is useful to have a single layer of radial cords and two
or three layers in the belt, all of steel construction. Often, additional reinforcing strips
of cross-biased fabric extend a short way up the sidewalls of radial-ply tires. The
introduction of ﬁbrous glass as a substitute reinforcement for textiles in carcass design
deserves mention. Having received special chemical treatment, glass ﬁbers permit
greater adhesion to rubber and give increased stability in withstanding dynamic stress
when embedded in elastomeric material. Moisture and low elongation no longer appear
to be problems in using ﬁbers for rubber reinforcement. Table 9.2 (Moore, 1975)62

compares some of the physical properties of glass, rayon, nylon and polyester

 

 

 

 

reinforcement in tires, while Table 9.3 (Rodriguez, 1970)63 shows the typical pr0perties

 

193

of cross-linked rubber compounds of the most commonly used rubber tires.

Table 9.2

Physical Properties of Reinforcement Structures in Tires.62

 

 

 

 

 

 

 

 

 

 

 

Glass Rayon Nylon Polyester
Ultimate tensile strength
psi*1000 407 94 122 104
Ultimate Elongation, % 4.83 9.8 19.3 18.5
Toughness, psi 9,900 5,800 10,200 9,900
Modulus, 1000 psi 8,450 960 630 570
Breaking strength, lbf 79.0 39.1 33.2 32.1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 9.3 Typical Properties of Cross-Linked Rubber Compounds Used in Tires.‘53
Polyisoprene Polybutadine Styrene-butadine
(natural rubber, random copolymer
also made 25 wt% styrene

synthetically) SBR

Gum Stock (cross

-1inked, unﬁlled):

Density, gm/cm3 0.93 0.93 0.94

Tensile Str. , psi 300-2500 200-1000 200-400

Reinforced Stock:

Tensile Str. , psi 3000-4000 2000—3500 2000-3500

Elongation at 300-700 300—700 300-700

Break, %

Resistance To:

Acid Good Good Good

Alkali Good Good Good

Oxidation Good Good Good

 

 

 

 

 

 

 

 

 

194
2,3 grsgLvmg QF POP-QUE OF TIRE PARTICLE

9.3.1 Objective

Preliminary work on tire-concrete composites indicated that dimensional instability
of tire in the presence of moisture, particularly at elevated temperatures, is a problem;
surface pop-out is a result of the dimensional movements of tire particle.

Potential chemical and physical causes of dimensional instability of tires causing
pop-out were investigated in order to resolve the problem. For this purpose, concrete
specimens incorporating tire particles, subjected to different treatments (aimed at
controlling the chemical or physical causes of pop-out) were exposed to different

environments where pop-out could occur.

9.3.2 Approach

Based on alternative hypotheses regarding the pop-out mechanisms, different
treatments were considered for mitigating the pop-out problem. These treatments
included: immersion in lime solution, immersion in cold and hot water and other
chemicals, and coating with epoxy and acrylic latex. Immersion of tire particles in lime
solution for one week prior to mixing in concrete helped reduce the pop-out problem in
moist conditions at ambient temperature 23 °C (7 3 °F) , but when immersed in water at
high temperatures of approximately 60 °C (140 °F), it actually pronounced pop-out.

To further investigate the pop-out problem of tires in concrete at high
temperatures, different chemical pretreatments were investigated with limited success.

These treatments included immersion in solutions of coal ﬂy ash, coal ﬂy ash with lime,

 

 

 

 

 

195

cold and hot water, sodium hydroxide, aluminum oxide, Kaolin, calcium chloride,
sodium silicate, potassium hydroxide, aluminum sulfate, and silica fume slurry. These
treatments were supposed to remove different chemical causes of pop-out or physical
inhibit it. The lack of any considerable success led to the hypothesis that pop-out is a
physical problem caused by expansion of tire in the presence of moisture (and
particularly at high temperatures) rather than a chemical one.

Tires were subsequently immersed in cold/ hot water at different time intervals in
order to measure the volume change and water absorption. Figures 9.3-a and 9.3-b
shows the volume changes of the tire particles in cold and hot water, respectively. It
should be noted that the test method used to produce the results of Figure 9.3 is not a
standard test; hence, information on its prcision is not available.

It is observed in Figure 9. 3 that tire particles, when immersed in ambient
temperature water, tend to shrink and at longer periods of time start to expand, but
when immersed in hot water they expand from the beginning. The volume change of
tires at different water temperatures is partly due to thermal expansion. It should be
noted that the expansion of tires in moist/ hot condition is more severe than that in
moist/ cold condition. This further explains why tire particles at moist/ hot condition tend
to cause more severe pop-out than in moist/cold environments.

In order to prevent tire expansion upon exposure to moisture, tire particles were
coated with HydroEpoxy 1041 (water based), which is commercially available. This

resulted in eliminating the tire pop-out problem (see Figure 9.4). The combination of

 

lHydroEpoxy 104 is a commercially available Epoxy produced by ACME Chemicals Ltd, New York.

 

 

 

196

2 VOLUME CHANGE (%)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

AGE (WEEKS)

(a) Ambient Water Immersion

6 VOLUME CHANGE (7.)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

AGE (WEEKS)

(b) Hot Water Immersion

Figure 9.3 Volume Change of Tire Particles.

 

197

reducing the amount of water reaching the tire particles and providing an elastic layer
around the tire particles prevented the tire particles from causing pop—out in concrete
materials. This could be partly due to the fact that as tires particles tend to expand, the
thin elastic layer around the particles was able to withstand the pressure caused by the

tires and act as a "bumper" to prevent the tires from applying pressure on the thin

 

concrete surface which leads to pop-out. However, this method proved to be relatively
costly due to the high cost of Hydro Epoxy 104.

Acrylic latex, Synthemul 40401—002 which is water based and commercially
available, was then used to coat the tire particles. This method produced same results

as the Hydro Epoxy coating at reduced cost.

   

(a) Uncoated Tire Particles (b) Coated Tire Particles

Figure 9.4 Epoxy Coating Effects on Pop-Out in Hot Water.

 

2Synthemul 40401-00 is a commercially available Acrylic latex produced by Reichhold Chemicals,
Ltd. '

 

 

 

 

198
L4 TEES AS REINFORCIN G INCLUSION IN CONCRETE

9.4.1 Objective

Following the elimination of pop-out problem through coating of tire particles
with polymeric materials, the effectiveness of coated and uncoated tires as reinforcing
inclusions in concrete was demonstrated. The fact that coating increases the cost of
recycled tire particles encourages higher-value use of the coated particles (e. g. as
reinforcing inclusions rather than light-weight aggregates). Coated tire particles were
incorporated into concrete at 2.5 and 5 % volume fractions and uncoated tires at 5 %
volume fraction. Control mixtures without tire were also considered. The effects of
tire inclusions on the following properties of concrete were investigated: restrained
drying shrinkage, ﬂexural strength and toughness, compressive strength, impact

resistance and chloride permeability.

9.4.2 Materials and Mix Proportions

The basic ingredients of the concrete materials used in this phase of the research
were type I Portland cement, normal-weight aggregate (ﬁne and coarse with a maximum
size of 12 mm, 0.5 in.), water, recycled tires with maximum size of 12mm (0.5 in.), and
air entraining agent (water based). The gradation of coarse and ﬁne aggregates met the
ASTM C-33 requirements.

The concrete mixtures used in this phase had ﬁne aggregate/ cement and coarse
aggregate/cement ratios of 2 and 2.5, respectively. Air entraining agent was used at

0.06 % by weight of cement to produce resistance against frost attack. The water content

 

 

 

 

 

199
was adjusted for all mixtures to give similar slumps (44.5 to 57.2 mm, 1.75 to 2.25 in.).

Water-cement ratio ranged from 0.39 to 0.43. The mix proportions were the same as
used for plastics in Table 7 .7 Section 7.5 .4; number of hardened material test specimens
also were the same as the ones used in plastics.

For the normal-weight mortar mixtures, the cement: sandzwater ratio was

1:2.4:0.5. The ﬂow (ASTM C-230) ranged from 80 to 95 %.

9.4.3 Test Procedures

For the hardened materials, the ﬂexural strength and toughness, compressive
strength, impact resistance, restrained shrinkage cracking characteristics and chloride
permeability properties were investigated experimentally in order to develop an overall
understanding of various aspects of material behavior.

The ﬂexural test specimens were 100x100x350 mm (4x4xl4 in.) prisms, and the
compressive strength test specimens were 75x15 mm (3x6 in.) cylinders. Flexural and
compression tests were conducted following ASTM C-78 (four point loading) and C-39
procedures. Midspan deﬂection as well as loads were monitored in ﬂexure tests. The
impact test was conducted following the procedures recommended by AC1 Committee
544. This test measures the amount of impact energy (represented by the number of
blows) necessary to start a visible crack in concrete and then continue the opening of
crack until failure.

Ring type specimens are used for restrained drying shrinkage test on mortar. The

specimen is cast in two equal layers, leveled by trowel, and then covered with plastic

 

 

 

200

sheets for 6 hours. The specimens are then exposed to air at approximately 23 °C (73
°F and 40% R.H. Restraint of shrinkage movements by the steel ring inside the
specimen creates internal tangential tensile stresses which cause cracking.

Permeability tests were conducted using AASHTO T-277 (Rapid Determination
of the Chloride Permeability of Concrete). ‘2 This test measures the amount of charge
passed through a concrete specimen subjected to permeation of chloride ions at 60 VDC
for 6 hours. The total charge passed (in Coulombs) is related to chloride ion
permeability. The more permeable the concrete, the higher would be the Coulombs. A
cylindrical specimen 102 mm (4 in.) in diameter by 51 mm (2 in.) in thickness is used

for this test.

9.4.4 Test Results and Discussion
9.4.4.1 Flexural Strength and Toughness

Figures 9.5 and 9.6 show the ﬂexural strength and toughness test results of
normal-weight concrete incorporating recycled tires.

Although the ﬂexural strength of concrete incorporating recycled tires dropped
by 6, 35 and 9% at 2.5 and 5% coated, and 5% uncoated, respectively, when compared
to control mixtures (without tires), they were statistically comparable at 95 % level of
conﬁdence, except for 5 % treated tire. The drop in ﬂexural strength, particularly at 5 %
addition of coated tire can be attributed to the weak bond between coated tire inclusions

and cementitious matrices.

 

 

 

201

FLEXURAL STRENGTH (ksi)

 

1.4

1.2 —-«~~—EE—~---95%»~-—Oen~ilden-ee—-~ i enter-v23l-——-~-~-—~'~~--~-~--~ , --

 

 

1 ﬁg”...

 

 

 

 

 

0.8 1

 

 

 

0.6

 

0.4 - .. .-__._.._. 2

0.2 ‘r

     

   

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TIRE VOLUME FRACTION

Figure 9.5 Flexural Strength Test Results (Means and 95% Conﬁdence Intervals).

O 03 FLEXURAL TOUGHNESS (k.in.)

 

 

0.025 -...____. . .. ,. -..

 

 

 

 

 

 

 

 

 

 

0.01 -—-

0.005 4

 

 

 

 

   

 

 

 

 

 

 

 

352%?233 1 5:323:32: ?1:‘:?‘i‘::i Eiéﬁfi iii?
0
CONTROL(0%) 2.5% COATED 5% COATED 5% UNCOATED
TIRE VOLUME FRACTION

 

 

 

 

Figure 9.6 Flexural Toughness Test Results.

 

 

I",

 

 

 

202

Figure 9.6 is indicative of the positive effects of recycled tires on the post-peak
ductility and toughness of concrete materials in ﬂexure. The ﬂexural toughness of
concrete incorporating 2.5 and 5 % coated tire, and 5 % uncoated (as additives), improved
by about 3, 4 and 6.5 times, respectively, when compared to control mixture. The
signiﬁcant increase in ﬂexural toughness in the presence of recycled tires can be
attributed to the reinforcing action of the tough tire inclusions in the brittle cementitious
matrices. In spite of the potentially weak bonding of the tire particles to concrete matrix,
the fact that cracks can not go through tire inclusions but have to follow longer paths

around their interfaces seem to enhance the fracture properties of concrete.

9.4.4.2 Compressive Strength

The compressive strength test results are shown in Figure 9.7 The addition of tire
inclusions as additives in normal-weight concrete had an adverse effect on compressive
strength.

The compressive strength dropped by 18, 33 and 32% when 2.5 and 5% coated,
and 5 % uncoated tires were added to normal-weight concrete, respectively. The
reduction in compressive strength was conﬁrmed statistically at 95 % level of conﬁdence.
The drop in compressive strength was expected because of lower modulus of elasticity
of tire when compared to that of concrete (about 10 times less) leading to a redistribution
of stresses into concrete which is a more rigid matrix. It should, however be noted that
limits on load-carrying capacity and service life of concrete structures are generally

provided by the resistance of concrete to tensile stresses and impact loads. Concrete is

 

 

 

 

 

203

fairly strong in compression and concrete structures rarely fail in compression.

 

 

7 COMPRESSIVE STRENGTH (ksi)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I

0 E5553? Siféf ~S55 iiéigié 35;;
CONTROL (0%) 2.5% COATED 5% COATED 5% UNCOATED
TIRE VOLUME FRACTION

 

...............................

 

Figure 9.7 Compressive Strength Test Results (Means and 95 % Conﬁdence Intervals).

 

 

 

 

 

204
9.4.4.3 Impact Resistance

Figure 9. 8 shows the impact resistance test results measured as the number of
blows up to the initial crack and failure. The difference between the initial crack and
failure represent the post—cracking energy absorption capacity of the material.

One-way analysis of variance and comparison of means showed that, at 99% level
of conﬁdence, the recycled tires have a signiﬁcant positive effect on the impact resistance
of concrete beyond the initial crack up to failure. The improvements in impact resistance
between initial crack and failure in the presence of recycled tires in concrete materials
further validates the hypothesis that tough tire inclusions help enhance the fracture energy
and toughness characteristics of concrete materials through bridging of cracks by the tire

inclusions.

200 IMPACT RESISTANCE (# of Blows)

 

 

 

First Crack

 

 

 

 

 

 

150 ‘Iw FaiIUre
100 1---... ....
50

 

 

 

 

 

 

 

 

CONTROL(0%) 2.5% COATED 5% COATED 5% U COATED
TIRE VOLUME VRACTION

Figure 9.8 Impact Resistance Test Results.

 

 

 

 

 

205
9.4.4.4 Restrained Drying Shrinkage

Figure 9.9 shows the maximum crack width versus time in restrained shrinkage
test on normal—weight concrete. Each crack width reading is an average of two
specimens; it should be noted that the control mixtures produced one crack while the tire
concrete mixtures produced more than one crack at reduced width. The addition of
recycled tires to normal-weight concrete helps delay and control the drying shrinkage
cracks. This can be attributed to the fact that recycled tire particles act as reinforcing

inclusions that arrest microcracks and bridge across cracks to restrain their widening.

 

   
    
       

  
 

 

 

 

 

1.2
i
1 —1 Control
: 5% Crack2
E081.
E. I
ig O 6 — 2.5% Crack3
; 1 2.5% Crack2
f, i
<3 0.4 n
O : 2.5% Crack1 ______ _ -
'7 O
0.2— 5%0rack1 . >5" __
: \ ,.—<T:.’..’ .............. ,¢.-.-:-...-...L-u
1 /"'"7' _____ :-----.
O it?iii?r?ii?iiiiiiiiiiiiiiiiiiiirrrrrrrTrrrrllll
1 9 17 25 83 41 49
Time (Days)

Figure 9.9 Restrained Drying Shrinkage Vs. Time.

 

 

 

206
9.4.4.5 Permeability

The chloride permeability test results (Figure 9.10) indicate that incorporating
coated tire particles at 2.5 and 5 % volume fractions and uncoated tires at 5 % volume
fraction produced permeability levels comparable to that of control. Although the’
addition of 5 % coated tire as additive in normal-weight concrete increased permeability
by an average of 6% , one way analysis of variance and separation of means showed that
this increase was not statistically signiﬁcant at 95 % level of conﬁdence. In actual ﬁeld
conditions, control of restrained shrinkage cracking by tire inclusions could lead to

reduced permeability of tire-concrete composites.

PERMEABILITY (Coulombs)

 

3000

 

 

 

 

 

 

 

 

2500

2000

 

 

 

 

1500

 

 

 

 

 

1000

 

 

 

 

 

 

500

 

 

 

 

 

'1

 

 

 

 

 

 

 

 

 

 

 

.......................
................

................
................

COATED 5% UNCOATED
TIRE VOLUME FRACTION

 

 

 

Figure 9.10 Permeability Test Results.

 

 

207
_9._5 Y N L SION

The dimensional instability of tire particles in the presence of moisture, which is
pronounced at elevated temperatures and eventually leads to surface pop-out, was
investigated. Following the elimination of pop-out through coating of tire particles with
polymeric materials, the effects of tire inclusions on: restrained drying shrinkage,
ﬂexural strength and toughness, compressive strength, impact resistance and permeability
were investigated. The following conclusions were derived:

1. Coating of tire particles with polymeric materials proved to eliminate surface pop-
out of concrete particles even in extreme conditions of immersion in hot water.

2. The addition of recycled tires to normal-weight concrete helps delay restrained
drying shrinkage cracking and reduce the crack width.

3. Coated recycled tires at 2.5 % and uncoated recycled tire at 5 % volume fraction

 

produced ﬂexural strengths comparable to that of control concrete. However,
statistical analysis of variance showed that coated tire at 5 % volume fraction
reduced ﬂexural strength. This was conﬁrmed statistically at 95 % level of
conﬁdence.

4. The ﬂexural toughness of concrete incorporating 2.5 and 5 % coated tire, and 5 %
uncoated tire, increased by about 3, 4 and 6.5 times when compared to control
concrete mixtures. This was conﬁrmed statistically at 99 % level of conﬁdence.

5. Compressive strength test results were indicative of the adverse effects of

 

recycled tires on compressive strength. It should be noted that concrete is fairly

strong in compression, and brittle failure mode and low crack resistance are the

 

 

 

 

 

208

main problems which are targeted to be overcome through the use of soft
reinforcing inclusions.

Recycled tires have a signiﬁcant positive effect on impact resistance of concrete
beyond the initial crack up to failure.

Chloride permeability test results showed that coated tire and uncoated tire
produced results which were statistically comparable to those obtained with

control concrete.

 

 

 

 

 

CHAPTERTEN

SUMlWARY AND CONCLUSIONS

The potential for technically beneﬁcial use of some major constituents of the solid
waste stream in Portland cement concrete were investigated. Coal ﬂy ash was used to
react with cement hydration products and enhance the structure and durability of concrete
materials. Plastics and tires were used as tough and light-weight inclusions to enhance
the cracking resistance and toughness of light-weight and normal-weight concrete
materials. Statistical methods of experimental design and analysis were used in order to
derive reliable conclusions.

The work on ﬂy ash concrete concerned the following critical aspects relating to
ﬂy ash performance in concrete: (1) effects of curing conditions and age on permeability;
(2) correlation between strength and permeability; (3) sulfate resistance and correlation
with permeability; and (4) alkali-silica reactivity. The fundamental mechanisms of ﬂy
ash action in concrete were investigated.

Plastic particles were used in this research as light—weight aggregates and
reinforcing ﬁbers to provide light-weight and normal-weight concrete with enhanced
toughness characteristics, impact resistance and shrinkage cracking characteristics at
reduced unit weight. The part of research concerning plastics dealt with: (1) mix

proportioning and mechanical properties; and (2) durability characteristics. The focus

 

 

 

 

210

 

of work on tire-concrete composites was on the compatibility of tire inclusions with

concrete; the toughening action and shrinkage crack control properties of tires in concrete

were also conﬁrmed.
1M FLY ASH
10.1.1 Effects of Curing Conditions and Age on Fly Ash Mortar Permeability

An experimental study was conducted in order to assess the effects of ﬂy ash
type, ﬂy ash content, period of moist curing, and age on concrete permeability. Three
different ﬂy ash types (two Class F and one Class C), three different ﬂy ash contents (in

addition to the control), two different moist curing periods (7 and 14 days), and two
different ages of testing (28 and 90 days) were investigated. The test data were analyzed
statistically. The following conclusions could be derived from the generated test results:
0 All factors considered in this investigation (ﬂy ash type, ﬂy ash content, moist
curing period, and age) had important effects on concrete permeability at 99%
level of conﬁdence.

0 Class F ﬂy ash reduced permeability even at relatively low levels of cement
substitution (10% by weight). In case of Class C ﬂy ash, however, relatively
high cement substitution levels (20 to 30% by weight) were required to produce

any signiﬁcant reduction in permeability.
0 In spite of the fact that Class C ﬂy ash was effective in reducing water demand,
it gave higher permeabilities than Class F ﬂy ashes except for 30% substitution

level at 28—day testing age.

 

 

 

211

0 Extended moist curing periods led to reduced concrete permeability. The effect
of moist curing period on concrete permeability was more pronounced in the
presence of ﬂy ash, particularly at higher replacement levels (20 to 30% by
weight).

0 Longer air—drying periods were observed to increase permeability, possibly due
to shrinkage microcracking, except for the Class F ﬂy ashes after longer initial
moist curing durations for which permeability stayed almost constant.

0 The evaluation of concrete permeability with or without ﬂy ash at the age of 28
days (after an initial moist curing period) can be misleading (except for Class F
ﬂy ash with longer of initial moist curing) due to the continuing adverse effects

of shrinkage microcracks on permeability beyond 28 days of age in air curing

 

condition, which more than compensate for any positive effects of the slow
progress of hydration and pozzolanic reaction in an environment with low

humidity.

10.1.2 Compressive Strength of Fly Ash Concrete Materials and Correlation
with permeability

 

The effects of ﬂy ash type and content on compressive strength development of
concrete processed in two different curing conditions and tested at two different ages
were investigated. Three different ﬂy ash types (two Class F and one Class C) and three
different ﬂy ash contents in addition to the control (0 % substitution) were considered.

Split-plot analysis of variance with repeated measurements was used to analyze the data

 

 

 

 

212

statistically. It was concluded that:

All variables of this investigation (ﬂy ash type, ﬂy ash content, moist curing
period, and age of testing) as well as their paired interactions (except for the
interaction of ﬂy ash type with content and ﬂy ash content with moist curing)
inﬂuenced the compressive strength of concrete.

The two Class F ﬂy ashes at 10 % and 20 % replacement levels generally showed
similar or higher 28- and 90-day compressive strengths when compared with the
control concrete containing no ﬂy ash; the reverse was generally true for Class
C ﬂy ash at all replacement levels and Class F ﬂy ash at 30 % replacement level.
This was in spite of the fact that Class C ﬂy ash was effective in reducing water
demand. The relatively high alkali content of the Class C ﬂy ash may illustrate
its adverse effects on strength.

As the moist curing duration increased, the ﬂy ash concrete became stronger;
Class C ﬂy ash was generally an exception to this rule. It should be noted that
the 90-day compressive strength of concretes containing any of the two Class F
ﬂy ashes was more sensitive to the increased moist curing period than control
concretes with no ﬂy ash.

The interruption of moist curing and exposure to a low-humidity (interior)
environment led to continued increase in strength irrespective of ﬂy ash type and
content. The low-humidity environment, however, damaged permeability
possibly by introducing shrinkage microcracks the effects of which on

permeability could not be compensated for the slow progress of hydration and

 

 

 

 

 

 

 

 

213

pozzolanic reaction in a low-humidity environment.

0 No strong correlation could be drawn between strength and permeability in ﬂy
ash concrete. Depending on the speciﬁc subset of the ﬂy ash concrete mixtures
selected, the correlation could vary from positive to negative, indicating that
reliance on strength test results for the evaluation of ﬂy ash concrete permeability

can be misleading.

10.1.3 Effects of Fly Ash on Sulfate Resistance of Concrete and Correlation
with Permeability

The effects of the ﬂy ash type (two Class F and two Class C) and content (10,
20 and 30% by weight of cement) on the sulfate resistance of concrete were investigated.

Correlations were drawn between the sulfate resistance and permeability of concrete

 

materials. It was concluded that:

0 Fly ash type and replacement level both inﬂuence the sulfate resistance of
concrete at 99 % level of conﬁdence; their interaction was also signiﬁcant.

0 The two class F ﬂy ashes at 20% and 30% replacement levels, and one of the
Class C ﬂy ashes (ﬂy ash C( 1)) at 30 % replacement level are effective in
resisting sulfate attack (delaying disintegration time). There were also differences

between the two class F ﬂy ashes

 

0 At lower replacement levels (10%), regardless of ﬂy ash type, the sulfate

 

resistance of ﬂy ash concrete was comparable to that of the control concrete

without ﬂy ash.

0 The two Class C ﬂy ashes at any replacement level, except for ﬂy ash C( 1) at

 

 

 

 

214

30 % , did not produce any substantial change in sulfate resistance when compared
with the control concrete.

The Class F ﬂy ashes were superior in increasing sulfate resistance when
compared with the Class C ﬂy ashes (i.e. the two Class C ﬂy ashes at any
replacement level produced faster degradation than the Class F ﬂy ashes).
Strong correlations were found between disintegration time under sulfate attack
and permeability for all concrete materials (irrespective of the ﬂy ash type and
content). Concrete permeability seems to be fundamental to its sulfate resistance,
and ﬂy ash effects on permeability seem to be largely responsible for the
corresponding effects on sulfate resistance of concrete. The signiﬁcance of
permeability may partly reﬂect the fact that it also represents the level of
pozzolanic reaction which causes favorable chemical effects in concrete through
the consumption of calcium hydroxide.

The calcium and silicon oxide contents of ﬂy ash were the key factors inﬂuencing
permeability and thus sulfate resistance of ﬂy ash concrete; higher calcium oxide
and lower silicon oxide contents increased the permeability and lowered the
sulfate resistance.

Expansion alone, disregarding softening, cannot fully represent the level of sulfate
attack. The reliance on expansion test results for evaluating sulfate resistance of

ﬂy ash concrete can be misleading.

 

 

215
10.1.4 Fly Ash Effects on Alkali-Silica Reaction

The effects of the ﬂy ash type (two class F and two class C with different alkali
contents), ﬂy ash content (10, 20 and 30% by weight of cement), and total alkali content
of cement (0.5 3. 0. 80 and 1.21%) on alkali-silica reaction were investigated. Correlation

studies were performed to identify the most important variables among ﬂy ash

 

characteristics inﬂuencing the alkali-silica reaction. The following conclusions could be

derived based on statistical analysis of the generated test results:

0 Class F ﬂy ash is highly effective in reducing ASR expansions regardless of ﬂy
ash content used (10, 20, and 30 %), particularly with high— and moderate-alkali
cements (1.21% and 0.8 % total alkali content).

0 Alkali content of Class F ﬂy ash is not necessarily representative of its

 

effectiveness in controlling ASR expansions. However, the alkali content of
Class C ﬂy ash turned out to be a signiﬁcant factor. The high-alkali Class C ﬂy
ash, particularly at lower replacement levels, produced more expansion than
control mixtures with no ﬂy ash.

O The Class F ﬂy ash was always superior to Class C ﬂy ash in controlling ASR,
in particular with moderate and high-alkali cements even though one of the Class
C ﬂy ashes had lower alkali content than Class F ﬂy ashes.

0 When sufﬁcient replacement level of Class F ﬂy ash is used, the alkali content
of cement loses its signiﬁcance in determining ASR expansions. This does not

apply to Class C ﬂy ash, particularly if its alkali content is high.

 

0 Evaluating ﬂy ash for the control of alkali-silica reaction in concrete based on

 

216
alkali content while disregarding other aspects of chemical and physical properties
is not warranted.
Interactive multiple-linear—regression analysis test data showed that the total alkali
content (Nap—equivalent) and the silicon dioxide (SiOz) content were the most
important properties of ﬂy ash inﬂuencing alkali silica reaction.
The ratio of NaZO-equivalent to SiO2 content of ﬂy ash was found to be the most
inﬂuential single variable in determining effectiveness in controlling alkali-silica
reaction. The SiO2 content may reﬂect pozzolanic reactivity which controls ASR
through consuming alkalies and reducing concrete permeability. More test data

covering various ﬂy ash chemistries are needed to conﬁrm this conclusion.

10_.2 PLASTICS

10 .2.1 Mix Proportions and Mechanical Properties of Concrete Incorporating
Recycled Plastics

The effects of partial substitution of light-weight aggregate with recycled plastics
on concrete properties were investigated. Two plastic types (HDPE and "MIXED") and
two levels of replacement of ﬁne aggregate (7.5 % and 15% plastics by total volume of

concrete) were considered with sulfonated and unsulfonated plastics. Also the effects of
recycled plastics as secondary reinforcing inclusions (additives) in normal-weight
concrete were investigated.
The hardened material mechanical properties were assessed through ﬂexure,
impact and compression tests. The following conclusions were derived through analysis

of the generated test data:

 

217

Relatively high ﬁne-to-coarse aggregate ratios were necessary in order to achieve
desirable dispersability, workability, compactability and ﬁnishability when part
of the light-weight ﬁne aggregate was replaced with HDPE or "MIXED" plastic.

Recycled plastics as partial replacement of light-weight aggregate at 7 .5 and 15 %

volume fractions of light-weight concrete gave comparable ﬂexural strengths to

that of control concrete mix. However, ﬂexural toughness increased by 4.5 and

8 times, respectively. This was conﬁrmed statistically at 99 % level of

conﬁdence.

Compressive strength test results of light-weight plastic concrete were indicative

of the adverse effects of recycled plastics. It should be noted that concrete is

fairly strong in compression, and rarely fails due to material failure in

compression. Furthermore, since the reduction in compressive strength is

accompanied with the reduction in unit weight, the situation would be improved

if one looks at the compressive strength-to—unit weight ratio.

Recycled plastics have a signiﬁcant positive effect on the impact resistance of
concrete beyond the initial crack up to failure.

Sulfonated plastics gave similar results when compared with unsulfonated ones.

In normal-weight concrete, recycled plastics enhance the shrinkage cracking
characteristics of concrete without adversely inﬂuencing the short-term
mechanical properties of the material. More ductile modes of failure were

observed in normal-weight concrete materials incorporating recycled plastics.

 

 

 

 

218
10.2.3 Durability Characteristics of Recycled Plastic-Concrete Composites

The long-term durability of light-weight plastic-concrete campsites (incorporating
recycled HDPE and "MDIED" plastics as partial substitutes for light-weight aggregate
in light-weight concrete) were assessed through investigating: the permeability (ASTM

C- 1202 or AASHTO T-277), hot water durability (ASTM C-1185), acid resistance, and

 

corrosion resistance (ASTM C-876) of the materials. The same tests (except for acid
resistance) were conducted for normal-weight concretes incorporating recycled HDPE

and "MIXE " plastics as secondary reinforcing inclusions (additives). Two different

 

levels, 20 and 40% replacement of ﬁne light—weight aggregate by volume corresponding

to 7 .5 % and 15 % by total volume in the case of light-weight concrete, and 2.5 % and 5%

 

plastic volume fraction in the case of normal-weight concrete, were considered.

Sulfonation was considered only in the case of permeability tests on light-weight concrete

(for both HDPE and MIXED plastics). It was concluded that:

In light-weight concrete

0 Chloride permeability test results showed that HDPE produced results which were
statistically comparable to those obtained with control concrete. However,
"MIXED" plastic reduced permeability at 7 .5 and 15 % volume fraction when
compared with control concrete. Sulfonation helped in reducing permeability, this
may be due to the sensitivity of permeability to improvements in the bonding of
plastic surfaces to concrete.

0 In the case of acid resistance, the use of plastics at 7.5 % volume fraction

produced weight losses statistically comparable to that of control mixtures without

219

plastic. However, at 15 % volume fraction, the plastic concrete showed average
weight loss increases 16-19% more than the cases of 7 .5 % plastic content and
control. Acid attack did not have any signiﬁcant effect on the compressive
strength of plastic-concrete composites at 7 .5 % and 15 % volume contents.

0 The corrosion potential measurement for control and plastic concretes produced
similar trends in the ﬁrst eight weeks (before the threshold potential was
reached); however, at later ages (8-19 weeks) plastic concrete for both 7.5 % and
15 % volume fractions provided better corrosion resistance than control concrete.

0 Flexural strength in the presence of recycled plastics (compared to control) after
immersion in hot water dropped by about 9% and 16% at 7.5 % and 15% plastic
volume contents. However, the ﬂexural toughness increased to about 8 times that
of control at both plastic content. Accelerated curing conditions involving
exposure to hot and humid environments (e. g. steam curing in masonry
production) may help achieve this pronounced toughening effect of plastics.

In normal-weight concrete

0 Recycled plastics can enhance the shrinkage cracking characteristics of concrete
without adversely inﬂuencing long-term performance characteristics of the
material under severe environmental effects (as measured by permeability,

corrosion resistance and hot water durability tests).

 

220
1 .3 TIRE (Recycling of Tires in Concrete Materials)

The dimensional instability of tire particles in the presence of moisture, which is
pronounced at elevated temperatures and eventually leads to surface pop-out, was
investigated. Following the elimination of pop—out through coating of tire particles with

polymeric materials, the effects of tire inclusions on: restrained drying shrinkage,

 

ﬂexural strength and toughness, compressive strength, impact resistance and permeability

were investigated. The following conclusions were derived:

0 Coating of tire particles with polymeric materials proved to eliminate surface pop-
out of concrete particles even in extreme conditions of immersion in hot water.

0 The addition of recycled tires to normal-weight concrete helps delay restrained

drying shrinkage cracking and reduce the crack width.

 

0 Coated recycled tires at 2.5 % and uncoated recycled tire at 5 % volume fraction
produced ﬂexural strengths comparable to that of control concrete. However,
statistical analysis of variance showed that coated tire at 5 % volume fraction
reduced ﬂexural strength. This was conﬁrmed statistically at 95 % level of
conﬁdence.

0 The ﬂexural toughness of concrete incorporating 2.5 and 5 % coated tire, and 5 %
uncoated tire, increased by about 3, 4 and 6.5 times when compared to control
concrete mixtures. This was conﬁrmed statistically at 99 % level of conﬁdence.

0 Compressive strength test results were indicative of the adverse effects of

recycled tires on compressive strength. It should be noted that concrete is fairly

 

strong in compression, and brittle failure mode and low crack resistance are the

 

 

221

main problems which are targeted to be overcome through the use of soft
reinforcing inclusions.

O Recycled tires have a signiﬁcant positive effect on impact resistance of concrete
beyond the initial crack up to failure.

0 chloride permeability test results showed that coated tire and uncoated tire
produced results which were statistically comparable to those obtained with

control concrete.

1% W
10.4.1 Fly Ash

The Class F ﬂy ashes used in this investigation were highly effective in reducing
sulfate attack and alkali-silica reaction in concrete. Each speciﬁc ﬂy ash needs to be
evaluated in order to determine its effects in concrete; this is particularly true in the case
of Class C ﬂy ash.

The optimum replacement level of cement with ﬂy ash is strongly dependent on
the speciﬁc qualities of ﬂy ash. While the Class F ﬂy ashes used in this investigation at
replacement levels of 20 % and 30 % improved the resistance of concrete to sulfate attack
and alkali-silica reaction, the Class C ﬂy ashes should be used at higher replacement
level, and even then there is no guarantee of improved resistance to sulfate attack or
alkali aggregate reaction.

One may use simple permeability tests in order to achieve information about long-

term sulfate resistance of ﬂy ash concrete.

 

 

 

 

 

222

Strict reliance on expansion as a measure of damage due to sulfate attack can be
misleading because occasionally softening of the material is so extensive that prevents
expansion.

The ratio of NaZO equivalent to 8102 content of ﬂy ash seems to be the most
inﬂuential single variable determining the effectiveness of ﬂy ash in controlling alkali-
silica reactions.

When permeability is a key design criterion, strict reliance on compressive
strength as a measure of quality can be misleading. Fly ash (particularly Class F ﬂy ash)
is more effective in reducing permeability than in increasing compressive strength.
Drying shrinkage cracking also tends to be more damaging to concrete permeability than
compressive strength.

Initial moist curing for a sufﬁcient time period is essential for structural
developments in ﬂy ash concrete. Early air drying can lead to slow structural

development and shrinkage crack formation which damage permeability.

10.4.2 Plastic and Tire

Recycled plastics provide desirable reinforcement qualities for achieving improved
shrinkage crack control, toughness and impact resistance. The low density of plastic
inclusions also helps reduce the unit weight of concrete. Plastic-concrete composites
provide desirable durability characteristics. Accelerated curing conditions involving
exposure to hot and humid environments (e. g. steam curing in masonry production) can

help enhance the toughness characteristics of plastic-concrete composites.

 

 

 

 

 

223

Successful use of tires in concrete necessitates polymeric coating to inhibit their
dimensional movements caused by variations in humidity and temperature. Tire particles
present desirable reinforcement qualities; they can help overcome the problems with the
brittle nature of failure and low resistance of concrete to impact loads and restrained

shrinkage cracking.

.l_0_._5. W
10.5.1 Fly Ash
Research is needed to determine if concrete permeability can provide a
comprehensive representation of the physical and chemical effects of ﬂy ash in concrete.
Shrinkage microcracking was a key factor adversely inﬂuencing long-term
permeability of air-dried mortar; one needs to investigate the extent of this damage in
concrete.
Fundamental materials research is needed to determine the mechanisms through
which ﬂy ash improves the resistance of concrete to chemical causes of deterioration.
Improved test methods are needed to monitor both softening and expansive effects

of sulfate attack on concrete.

10.5.2 Plastic and Tire
The basic work conducted in this research needs to be followed with practical
research toward optimizing the use of plastics and tire in concrete and determining

practical implications of the resulting improvements in structural and non-structural

 

 

224
concrete applications.

Alternative approaches to enhancing the physical and chemical bonding of plastic

surface to concrete need to be developed.

As different plastics are used in concrete, one needs to investigate the durability

of inclusions in the highly alkaline environment of concrete.

 

Lower-cost methods of mitigating dimensional movements of tire particles need

to be developed.

 

 

 

 

 

 

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11.

 

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