RECYCLED TIRES AS COARSE AGGREGATE IN CONCRETE PAVEMENT MIXTURES by YANG ZHOU B.S., Northeast Forestry University, 2012 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirements for the degree of Master of Science Civil Engineering 2014
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RECYCLED TIRES AS COARSE AGGREGATE
IN CONCRETE PAVEMENT MIXTURES
by
YANG ZHOU
B.S., Northeast Forestry University, 2012
A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado in partial fulfillment
of the requirements for the degree of
Master of Science
Civil Engineering
2014
ii
This thesis for the Master of Science degree by
Yang Zhou
has been approved for the
Master of Science
by
Kevin L. Rens, Chair
Chengyu Li
Frederick Rutz
4/29/2014
iii
Zhou, Yang (M.S., Civil Engineering)
Recycled Tires as Coarse Aggregate in Concrete Pavement Mixtures
Thesis directed by Professor Kevin L. Rens.
ABSTRACT
This research evaluated the reuse potential of recycled tire chips as coarse
aggregates in pavement concrete. Experimental investigation of modified pavement
concrete, using different volume coarse aggregate replaced by tire chips, was completed
to check the fresh and hardened concrete properties. One control mixture was designed
for comparison. The coarse aggregate component of rubberized concrete was replaced by
volumes of 100%, 50%, 30%, 20%, and 10% using tire-chips particles. The cementitious
materials was changed from 660 lbs/cy to 570 lbs/cy to evaluate the performance. Two
mixtures with 10% coarse aggregate replaced by tire chips had the best performance
among all the mixtures and exceeded the 28-day compressive strength and flexural
strength requirement of Colorado Department of Transportation Class P pavement
concrete. The two mixtures showed high freeze/thaw durability in moderate chloride-ion
penetration tests. Effects of using high-range water reducer and low-range water reducer
were examined for mixtures with 10% coarse aggregate replacement. The rubberized
concrete mixtures investigated in this study demonstrated ductile failure in compressive,
flexural, and splitting tests instead of brittle failure as a control mixture.
The form and content of this abstract are approved. I recommend its publication.
Approved: Kevin L. Rens
iv
DEDICATION
I dedicate this work to the persons who have believed in me and supported me the
most. Through their endless love, encouragement, understanding, and support throughout
all the years of my educational pursuits, I owe my deepest gratitude to my father, Guojun
Zhou, and my mother, Ruomin Sun.
v
ACKNOWLEDGMENTS
I express my sincere gratitude to my advisor, Dr. Kevin Rens, for his invaluable
instruction, encouragement, and guidance throughout the study of “Recycled Tires as
Coarse Aggregate in Concrete Pavement Mixtures.” In addition, I thank Dr. Chengyu Li
and Dr. Frederick Rutz for participating on my thesis committee.
I also thank my previous professor and current friend, Dr. Rui Liu, for
recognizing my potential and giving me the opportunity to do this study and for his
endless help and encouragement throughout the experimental program.
I also express my appreciation for the technical support provided by the
Laboratory at University of Colorado at Denver, including Dr. Nien-Yin Chang and Tom
Thuis. Additionally, I thank Mr. Dan Bentz from Bestway Concrete for the donation of
coarse aggregates and Mr. Steve Calhoun from Sika for the donation of water reducers.
Finally, I thank all the faculty and staff of University of Colorado at Denver, Civil
Engineering Department, for their help and guidance throughout my educational career.
vi
TABLE OF CONTENTS
CHAPTER
I. INTRODUCTION ....................................................................................................... 1
Objectives of this Research ..................................................................................... 3
Scope ....................................................................................................................... 4
Thesis Outline ......................................................................................................... 5
II. LITERATURE REVIEW ............................................................................................ 6
Uses of Waste Tires ................................................................................................ 6
Classification of Recycled Waste Tire Particles ..................................................... 7
Fresh Concrete Properties of Rubberized Concrete ................................................ 8
Hardened Concrete Properties of Rubberized Concrete ....................................... 12
Modulus of Elasticity of Rubberized Concrete ..................................................... 16
III. PROBLEM STATEMENT ........................................................................................ 19
IV. EXPERIMENTAL PROGRAM ................................................................................ 21
Materials for Test Specimens................................................................................ 21
Concrete Materials .................................................................................... 21
Recycled Tire Particles ............................................................................. 21
Recycled Waste Tire Specific Gravity Experimental Testing and
Results ........................................................................................... 26
Admixtures ................................................................................................ 26
Type I Portland Cement ............................................................................ 27
Mixture Proportions .............................................................................................. 27
Batching of Concrete Mixture .............................................................................. 29
vii
Preparation Before Batching Concrete Mixture ....................................... 29
Mixing Process.......................................................................................... 30
Curing of Specimen .............................................................................................. 31
Testing of Concrete ............................................................................................... 32
Testing for Fresh Concrete Properties ...................................................... 32
Testing for Hardened Concrete Properties ................................................ 32
V. EXPERIMENTAL RESULTS AND DISCUSSIONS PHASE I .............................. 34
Batching of Trial Mixtures.................................................................................... 34
Fresh Concrete Properties ..................................................................................... 34
Temperature of Freshly Mixed Hydraulic Cement Concrete, ASTM C-
1064........................................................................................................... 36
Slump of Hydraulic-Cement Concrete, ASTM C-143 ............................. 38
Unit Weight ............................................................................................... 40
Air Content................................................................................................ 40
Hardened Concrete Properties .............................................................................. 42
Compressive Strength of Concrete Specimens, ASTM C-39 ................... 44
Flexural Strength or Modulus of Rupture, ASTM C-78 ........................... 51
Splitting Tensile Test, ASTM C-496 ........................................................ 54
Rapid Chloride-ion Permeability, ASTM C-1202 .................................... 56
Freeze-thaw Durability, ASTM C-666 ..................................................... 60
VI. EXPERIMENTAL RESULTS AND DISCUSSIONS PHASE II ............................. 67
Fresh Concrete Properties ..................................................................................... 67
Temperature of Freshly Mixed Hydraulic-Cement Concrete, ASTM C-
1064........................................................................................................... 68
viii
Slump of Hydraulic-Cement Concrete, ASTM C-143 ............................. 68
Unit Weight, ASTM C-138....................................................................... 69
Air Content of Freshly Mixed Concrete ASTM C-231 ............................ 70
Hardened Concrete Properties .............................................................................. 70
Compressive Strength of Cylinder Specimens, ASTM C-39 ................... 71
Modulus of Elasticity of Concrete in Compression, ASTM C-469 .......... 73
VII. CONCLUSIONS ....................................................................................................... 76
Results ................................................................................................................... 76
Summary of Fresh Concrete Properties ................................................................ 77
Slump ........................................................................................................ 77
Air Content................................................................................................ 77
Unit Weight ............................................................................................... 77
Temperature .............................................................................................. 77
Summary of Hardened Concrete Properties ......................................................... 78
Compressive Strength ............................................................................... 78
Splitting Tensile Strength ......................................................................... 78
Flexural Strength ....................................................................................... 78
Durability .................................................................................................. 78
Modulus of Elasticity ................................................................................ 79
The Effects Caused by Water Reducer ................................................................. 79
Recommendations ................................................................................................. 80
REFERENCES ................................................................................................................. 81
ix
APPENDIX ........................................................................................................................84
A. Product Specification Sheet...................................................................................84
B. CDOT Class P Concrete Requirement...................................................................92
C. Concrete Mixtures..................................................................................................94
x
LIST OF TABLES
TABLE
2.1 ASTM D-6270 Terminology for Recycled Waste Tire Particles ................................. 8
4.1 Sieve Analysis for Sand, Rocks, and Tire Chips ........................................................ 24
4.2 Research Design Mixtures Proportions ...................................................................... 28
4.3 Fresh Concrete Tests ................................................................................................... 32
4.4 Hardened Concrete Tests for Phase I .......................................................................... 33
4.5 Hardened Concrete Tests for Phase II ........................................................................ 33
5.1 Trial Mixtures Proportion after Water Adjustment .................................................... 35
5.2 Water Reducer Dosage After Adjustment .................................................................. 36
5.3 Concrete Temperatures ............................................................................................... 37
5.4 Air Content by Pressure Meter, ASTM-C231 ............................................................ 41
5.5 Air Content by Rolloer Meter, ASTM-C173 .............................................................. 41
5.6 Compressive Strength, ASTM C-39 ........................................................................... 46
5.7 Permeability Rating Classification ............................................................................. 58
5.8 Rapid Chloride-ion Penetration Testing Results......................................................... 59
5.9 Duribility Factor.......................................................................................................... 65
5.10 Resistance to Freeze/Thaw Cycling .......................................................................... 66
xi
LIST OF FIGURES
FIGURE
1.1 Annual Waste Tires Added to Stockpiles in Colorado ................................................. 2
2.1 Typical Size and Shape of Refinements ...................................................................... 7
2.2 Rubber Content by Total Aggregate Volume (%) ..................................................... 10
2.3 Relationship between Unit Weight With Rubber Content ......................................... 11
2.4 Compressive Strength for Rubberized Concrete ........................................................ 14
2.5 Durability Factor vs. Cycle Count ............................................................................. 17
2.6 Modulus of Elasticity with Time ............................................................................... 17
4.1 Rocks-Coarse Aggregates ........................................................................................... 22
4.2 Sand- Fine Aggregates ................................................................................................ 23
4.3 Rubber Chips Sample ................................................................................................. 23
4.4 ASTM C-33 Grading Limits and Values for Coarse Aggregates ............................... 25
5.1 Temperatures Measuring ............................................................................................ 37
5.2 Zero Slump for Mixture #2 ......................................................................................... 38
5.3 Concrete Slump and WRA.......................................................................................... 39
5.4 Unit Weight of Concrete Mixture ............................................................................... 42
5.5 Air Content and AEA.................................................................................................. 43
5.6 Compressive Strength for Each Mixture..................................................................... 47
5.7 % Strength Loss of Mixtures to the Control (high cementitious content) .................. 48
5. 8 % Strength Loss of Mixtures to the Control (low cementitious content) .................. 48
5.9 Rate Gain of Compressive Strength at 28 Days.......................................................... 49
5.10 Residual Strength Characteristic ............................................................................... 50
xii
5.11 Compressive Failure of Concrete Cylinder............................................................... 51
5.12 Flexural Failure of Mixture #6 .................................................................................. 52
5.13 Flexural Strength for Each Mixture .......................................................................... 53
5.14 Splitting Tensile Test Setup ...................................................................................... 54
5.15 Splitting Tensile Strength for Each Mixture ............................................................. 55
5.16 Splitting Tensile Test Specimen Failure ................................................................... 56
5.17 Cell Preparation ........................................................................................................ 57
5.18 Cell Preparation ........................................................................................................ 57
5.19 Air Content (Roller Meter) vs. Coulombs ................................................................ 60
5.20 Chloride-ion Permeability vs Air Content ................................................................ 61
5.21 Transverse Resonant Testing Setup .......................................................................... 64
6.1 Concrete Temperatures for Phase II ........................................................................... 68
6.2 Concrete Slump for Phase II ....................................................................................... 69
6.3 Unit Weight of Concrete Mixture for Phase II ........................................................... 69
6.4 Air Content in Concrete Mixtures for Phase II ........................................................... 70
6.5 Compressive strength for Phase II .............................................................................. 71
6.6 Rate Gain of Compressive Strength for Phase II ........................................................ 72
6.7 Concrete Failure for Mixture #10 ............................................................................... 73
6.8 MOE Test Results and MOE Calculated From ACI Equation ................................... 74
6.9 Modulus of Elasticity Test Setup ................................................................................ 75
1
CHAPTER I
INTRODUCTION
Concrete is one of the most popular building materials used for modern
constructions, such as highways, buildings, and skyscrapers. The demand for concrete
will increase to about 18 billion tons a year by 2050 (Mehta 2002). At the same time,
solid waste disposal is one of the major environmental issues in almost every city around
the world. Roughly 4.6 billion tons of nonhazardous solid waste materials are generated
every year in the United States (Amirkhanian 1994). Domestic and industrial wastes
constitute almost 600 million tons of this total (Khatib and Bayomy 1999).
In the United States, over 270 million disposal tires are scraped every year
(Siddique and Naik 2004). Research estimates that about 4,595.7 thousand tons of waste
tires were produced in 2007, and 89.3% of them by weight were consumed in end-use
markets (Rubber Manufacturers Association 2009). However, about 489.9 thousand tons
of scrapped tires were still added to the existing stock piles throughout the U.S. each year.
In 2009, Colorado had about 45 million tires stored, roughly one-third of the stockpiled
tires in the country, and the number of stockpiled tires is rising each year (Ayers 2009).
In 2011, a total of 5,097,944 Colorado-generated tires were processed in Colorado
waster-tire processors and a Utah-based waste tire processing facility. Colorado
Department of Public Health and Environment (CDPHE) reported the annual waste tires
added to stockpiles in Colorado. Figure 1.1 shows decline trends in the number of waste
tires added to existing stockpiles in Colorado (CDPHE 2011). In 2011, there were only
69,452 additional waste tires stockpiled compared to 604,151 tires and 572,121 tires in
2010 and 2009, respectively.
2
Figure 1.1: Waste Tires Added to Stockpiles in Colorado (Adapted from CDPHE, 2011)
The classification of waste tires defined by federal regulations is of non-
hazardous waste. However, the stockpiles are occupying the land resources and also are
easily catching fire. The product of combustion of tires is heavy metals, oil, and other
hazardous compounds. Also, the stockpiles provide breeding grounds for rats, mosquitoes,
and other vermin (Siddique and Naik 2004).
Some innovative solutions have been developed to solve the problems associated
with stockpiling tires. For example, tire bales are used as road foundation and retaining
wall construction, and tire shreds are useful as back fill for walls and bridge abutments.
Due to the light weight of tire shreds, the horizontal pressure is reduced, allowing for
thinner and less expensive construction. Also, grounded waste tires can be used in asphalt
concrete as part of asphalt binders. Plus, tire chips can be used for thermal insulation and
potentially can be used as an alternative to aggregate materials in civil engineering
applications.
1,500,000
830,000 783,000
572,121 604,151
69,452
0
200,000
400,000
600,000
800,000
1,000,000
1,200,000
1,400,000
1,600,000
2006 2007 2008 2009 2010 2011
Num
ber
of
Tir
es
Year
3
In the early 1990s, the use of recycled waste-tire particles expanded into a
relatively new product called rubberized concrete, which uses Portland cement as its
binder (Kaloush et al. 2005; Ellis and Gandhi 2009). Research has shown that rubberized
concrete has a very positive outlook for inception into select markets, such as pavement
applications (Kardos 2011). A recent research study completed by the University of
Colorado at Denver, for the Colorado Department of Public Health and Environment,
indicated that processed crumb rubber can be used as a partial replacement for fine
aggregate in Colorado Department of Transportation (CDOT) Class P pavement concrete
mix (Kardos 2011). From 10% to 50% replacements of sands by volume were tested for
both fresh and hardened concrete properties. The results showed that 20% and 30%
replacement mixtures meet CDOT Class P concrete requirements. Leaching tests were
performed to evaluate the environmental sustainability of the concrete mixtures and
indicated that this material would pose no threat to human health. As a potential solution
to help eliminate waste tires in Colorado, the reuse potential of waste-tire chips as part of
coarse aggregate in concrete mixture was examined in this study.
Objectives of this Research
The primary objectives of this research study were to:
Examine the effects of increasing the coarse aggregate replacement
percentage with recycled tire chips on concrete compressive strength, split-
tension strength, flexural strength, modulus of elasticity, permeability, and
freeze/thaw resistance; and determine an optimum replacement percentage of
coarse aggregate with recycled tire chips for pavement concrete mixtures.
4
Develop a concrete mixture that will incorporate waste-stream materials as
partial replacement for cement, rock, and sand.
Test tire-chip concrete mixtures for fresh concrete properties (slump, air
content, unit weight).
Test tire-chips concrete for hardened concrete properties.
Provide recommendations for the use of recycled tire chips as a coarse
aggregate replacement in a concrete mixture designed for field
implementation.
Examine the effects of changing the Plastocrete 161 (low-range water reducer)
to Viscocrete 210 (high-range water reducer) for 10% coarse aggregate
replacement concrete.
Scope
This study evaluated the reuse potential of waste-tire chips as coarse aggregate in
pavement concrete mixtures. Two phases of experimental investigations were performed.
The purpose of the first experimental investigation (phase I) was to observe the effects of
increasing the coarse aggregate replacement percentage with recycled tire chips on both
fresh and hardened concrete properties. Ten mixtures were batched; and 150 cylinders
and more than 40 beams were tested for the results, including compressive strength,
splitting tensile strength, flexural strength, and permeability. The goal was to determine
which replacement percentage would meet the requirements specified by CDOT Class P
concrete.
The purpose of the second experimental investigation (phase II) was to evaluate
the modulus of elasticity of the mixtures that met the CDOT requirements. Additionally,
5
to evaluate the effect of changing water reducer on both fresh and hardened concrete
properties, the water reducer was changed from low-range water reducer to high-range
water reducer. All tests were completed based on ASTM standards.
Thesis Outline
Chapter I is the thesis introduction. Chapter II presents the literature reviewed
regarding previous research on usages of waste tires and rubberized concrete properties,
including fresh and hardened concrete properties. Chapter III provides the problem
statement. Chapter IV provides a detailed description of the experimental program;
including the materials for test specimens, admixtures, batching process, curing and
testing for both fresh and hardened concrete properties. Chapter V presents the results of
the experimental investigation for phase I and the effects of various percentages of tire
chips replacement on concrete properties and cementitious materials content. Chapter VI
discusses the modulus of elasticity of the concrete mixture with 10% coarse aggregates
with tire chips and the influence of changing water reducer. Chapter VII presents the
conclusions of this study and provides recommendations for further research.
6
CHAPTER II
LITERATURE REVIEW
This literature review covers the various topics researchers have investigated.
Previous research conducted on rubberized concrete and utilization of scrap tires in civil
engineering applications is briefly discussed.
Uses of Waste Tires
Waste tires that are no longer suitable for use on vehicles due to wear or
irreparable damage can be recycled, as aggregates in Portland cement concrete or
recycled into other tires (Nehdi and Khan 2001). Shredded tires can be chosen as the
filling material in school playgrounds. Some states—Alabama, Florida, Georgia, South
Carolina, Virginia—allow tire shreds to be used in construction of drain fields for septic
systems (Environmental Protection Agency 2011).Tires can even be cut up into tire chips
and used in garden beds to hold in water; also, tires placed in garden beds can prevent
weeds from growing.
Stockpiled tires create a huge health and safety risk to our lives. They easily catch
fire, burning for months and creating substantial pollution in the air and ground. Tire
piles also offer dwelling places for mosquitoes, which carry diseases.
A new use for waste tires involves refining them. Refinements are generated in
different sizes for use in a variety of applications. Figure 2.1 shows the different sizes of
crumb/shredded rubber (Eldin and Senouci 1993, with permission from ASCE). In the
early 1990s, shredded tires/crumb rubber’s usage expanded into a relatively new product
called rubberized concrete (Kaloush et al. 2005). Li et al. (1998) wrote, “They might be
suitable
7
for applications such as driveways, sidewalks or road construction where strength is not a
high priority but greater toughness is preferred.” It also has been found that the use of
rubber particles improves the engineering characteristics of concrete (Goulias et al. 1997);
research indicates that rubberized concrete has a highly potential usage in light-duty
applications, such as surface pavement materials and light-duty structures.
Figure 2.1: Typical Size and Shape of Refinements (With permission from ASCE)
Classification of Recycled Waste Tire Particles
Various ways to reuse recycled waste tires particles have been developed in recent
years. American Society for Testing Material (ASTM) gives a classification of recycled
waste-tire particles. Table 2.1 shows the terminology for recycled waste tire particles as
defined by the ASTM D-6270 Standard Practice for Use of Scrap Tires in Civil
Engineering Applications.
8
Table 2.1: ASTM D-6270 Terminology for Recycled Waste Tire Particles
Classification Lower Limit, in(mm) Upper Limit, in(mm)
Chopped Tire Unspecified dimensions
Rough Shred 1.97×1.97×1.97(50×50×50) 30×1.97×3.94(762×50×100)
Tire Derived Aggregate 0.47(12) 12(305)
Tire Shred 1.97(50) 12(305)
Tire Chips 0.47(12) 1.96(50)
Granulated Rubber 0.017(0.425) 0.47(12)
Ground Rubber - <0.017(0.425)
Powered Rubber - <0.017(0.425)
Chopped-tires dimensions are not specified in the standard; they were cut by a
cutting machine into very large pieces. The primary shredding process can produce scrap
tires with a size as large as 12”–18” long by 2”–9” wide (Siddique and Naik 2004). After
secondary shredding, the rough shreds, tire derived aggregate, tire shreds and tire chips
are cut down to 0.5”–to 3”. Granulated rubber, powered rubber, and ground rubber are
processed by the cracker-mill process, granular process, or micro-mill process, two stages
of magnetic separation and screening (Heitzman 1992).
Fresh Concrete Properties of Rubberized Concrete
The fresh concrete properties usually evaluated for freshly mixed concrete are
temperature, slump, air content, and unit weight. All properties and testing methods are
defined by:
9
Slump of Hydraulic-Cement Concrete: ASTM C-143
Temperature of Freshly Mixed Hydraulic-Cement Concrete: ASTM C-1064
Unit Weight and Air Content of Concrete: ASTM C-138
Air Content of Freshly Mixed Concrete by the Pressure Method: ASTM C-
231
Air Content of Freshly Mixed Concrete by the Volumetric Method: ASTM C-
173.
Slump is a property that shows how flowable the concrete is. The higher the
slump, the better the workability. Superplasticizer, also known as high-range water
reducer, can increase slump of concrete mixtures by comparison of the same concrete
mixture with low-range water reducer. High-slump concrete is usually used for slim slabs
or highly reinforced structures. For heavily reinforced sections, self-consolidating
concrete is selected. In rubberized concrete, the fresh concrete properties are effected by
the rubber particle size and quantity. Khatib and Bayomy (1999) found that with rubber
contents of 80% or higher (about 40% by total aggregate volume), the slump is near zero
and the mix is not workable by hand mixing. In their research, the specimens were
divided into three groups: Group A, Group B, and Group C. In Group A, only fine
aggregates were replaced by crumb rubber; in Group B, only the coarse aggregates were
replaced by tire chips; in Group C, both fine aggregates and coarse aggregates were
replaced by crumb rubber and tire chips, respectively. The results of a research completed
by Aiello and Leuzzi (2010) were quite different, however; showing that the workability
of fresh concrete is slightly improved by the partial substitution of aggregate with rubber
particles.
10
Figure 2.2 (Adapted from Khatib, 1999) shows the relationship between slump
and rubber content for all groups.
Figure 2.2: Slump vs Rubber Content (Adapted from Khatib, 1999)
Kaloush et al. (2005) found that with an increasing rubber content in concrete, the
unit weight decreases. With the use of recycled tire particles, a notable effect in the unit
weight begins to occur when the percentage of replacement is higher than 20% by the
volume of total aggregate used in the concrete mixture (Siddique and Naik 2004). The
research indicates that when 33% by volume of sand is replaced by crumb rubber, the
unit weight of rubberized concrete is reduced by approximately 10% (Li et al. 1998).
Khatib found that the unit weight has a linear relation with the decreasing of rubber
content. Figure 2.3 (Adapted from Li et al. 1998) shows the decreasing relationship
between unit weight and rubber content incorporated in the concrete mixtures.
11
Figure 2.3: Unit Weight vs Rubber Content (Adapted from Li et al., 1998)
In general, with the air content increasing, the unit weight of rubberized concrete
decreases uniformly. In Khatib and Bayomy’s (1999) research, the rate of increase in air
contents was very similar for all three testing groups: only fine aggregates were replaced
by crumb rubber, only coarse aggregates were replaced by tire chips, both fine aggregates
and coarse aggregate were replaced by crumb rubber and tire chips, respectively; while
the rubber content was less than 30% of total aggregate volume.
Fedroff et al. (1996) reported that the air content in rubberized concrete mixtures
is higher than in traditional concrete mixtures. This is because rubber has a hydrophobic
property, which repels the surrounding water and traps more air attached to the surface of
the rubber. For traditional concrete mixtures, more air content in concrete mixture
increases its durability, up to approximately 9% of air content.
After this literature review about rubberized concrete, the effects of temperature
on rubberized concrete are not thoroughly discussed. However, this would be a
noteworthy topic because temperature has a significant impact on practical concrete
12
placement. Aggregate warehouses usually store the aggregate in the open air without the
protection of shade, and a tremendous amount of heat can build up due to the black color
of tires. Excessive heat results in rapid hydration of the cement paste in rubberized
concrete mixtures and leads to some difficulties for concrete placement.
Generally, these are the properties of freshly mixed concrete:
With the rubber content increasing, the slump and unit weight decrease.
Air content increases with the increasing of rubber content.
Hydrophobic tendencies of waste tire particles increases the air content.
High temperature due to the storage of recycled tires can result in placement
difficulty.
Hardened Concrete Properties of Rubberized Concrete
The hardened property of rubberized concrete testing includes compressive
strength, flexural strength, splitting tensile strength, rapid chloride permeability test, and
resistance of concrete to rapid freezing and thawing test. These tests are defined by:
Compressive Strength of Concrete: ASTM C-39
Flexural Strength of Concrete: ASTM C-78
Splitting Tensile Strength: ASTM C-496
Rapid Chloride Permeability Test: ASTM C-1202
Resistance of Concrete to Rapid Freezing and Thawing: ASTM C-666.
The research literature on rubberized concrete indicates a consensus regarding tire
chips as the singularity in concrete mixtures, and that the compressive strength of
rubberized concrete mixtures is directly affected by the amount of recycled tire chips
used in a matrix. Plus, the particle size, surface treatment, and content are reported to
13
have significant effects on both compressive and tensile strength. Xi (2004) used 0.073”–
0.162” (1.85-4.12 mm) recycled rubber particles. Zhang and Li (2012) used 0.039”–0.093”
(1-2.36 mm) particles. Kaloush et al. (2005) used recycled tires with sizes ranging
0.039”–0.78” (1-20 mm) waste tire particles. Aiello and Leuzzi (2010) tested rubberized
concrete with the tire particle sizes 0.39”–0.88” (10-25 mm). All the studies evaluated the
compressive, tensile, and flexural strength with certain percentages of the aggregate
replaced by recycled rubber, and the mentioned conclusions were developed.
Strength loss was due to the poor adhesion between the rubber particles and the
surface of cement paste. Xi (2004) found that using the 8% silica fume pretreatment on
the surface of rubber particles can improve the properties of rubber-modified mortars
(RMM). On the other hand, directly using silica fume to replace equal amount (weight) of
cement in concrete mix has the same effect. The interfacial transition zone (ITZ) has
direct influence on the performance of rubberized concrete mixtures.
Research of pretreatments of rubber particles shows that several chemical
treatment methods could enhance the bond between rubber particles and concrete: PAAM
(polyacrylamide) pretreatment, PVA (pressure ageing vessel) pretreatment and silane
pretreatment (Xi 2004). The PAAM, PVA, and silane chemical treatments could enhance
the performance for ITZ. The PAAM is quite effective to improve the performance of
ITZ but has an adverse effect on the rubberized concrete workability when more than 10%
of total aggregate is replaced by rubber particles by volume; yet, there is no such adverse
effect on the workability of rubberized concrete by using PVA and silane pretreatment
method. It has been proven that PVA is more effective than silane pretreatment (Xi 2004).
The compressive strength decreased as the rubber content increased: 60% of the 28 day
14
strength was achieved at 3 days, and 80% was achieved at 7 days (Kaloush et al. 2005).
In Eldin and Senouci’s (1993) study, when coarse aggregate was 100% replaced by tire
chips, there was approximately 85% compressive strength reduction and 50% splitting
tensile strength reduction. Previous research also shows that rubberized concrete can be
used for the low-strength and lightweight requirements of civil engineering applications.
Figure 2.4 (With permission from ASCE) shows the relationship between
compressive strength at the age of 7 days and 28 days and rubber content. The
compressive strength with aggregates 100% replaced by rubber partical is less than 17%
of the original concrete mixture which has no rubber particle incorporated. (Eldin and
Senouci 1993)
Figure 2.4: Compressive Strength (With permission from ASCE)
Compared to traditional brittle concrete mixture, rubberized concrete experiences
non-brittle failure during compressive, flexural, and splitting tensile strength testing.
Because the rubber pieces are flexible and have a low modulus of elasticity, when
15
concrete begins to crack during flexural tests, the rubber particles act as reinforcement
and keep two pieces of concrete from sudden failure. In the Kaloush et al. (2005) study,
the modulus of elasticity decreased slightly for mixtures with a low crumb-rubber content.
For mixtures with a high crumb-rubber content, the modulus of elasticity was drastically
reduced. To predict the compressive strength of rubberized concrete block with different
rubber content, Ling (2011) proposed the following prediction equation, which is
applicable within 0%–50% for rubber content and 0.45%–0.55% for water cement ratio:
𝑅𝐶𝑆 = (𝑆𝑟
𝑆𝑐)(
𝑤
𝑐)(𝑟)
𝑅28𝑑𝐶𝑆 = 0.0274𝐿𝑛(𝑟) + 0.0169
Where 𝑅𝐶𝑆= strength reduction factor for general, 𝑅28𝑑𝐶𝑆= strength reduction factor for
28 days, 𝑆𝑟= compressive strength of rubberized concrete block (MPa), 𝑆𝑐=compressive
strength of control concrete block (Mpa), r=rubber content by volume, 𝑤
𝑐=water cement
ratio.
For this study, in order to constitute the durability of rubberized concrete, the
abilities to withstand both the recycling freeze/thawing temperature change (ASTM C-
666) and chemical permeability (ASTM C-1202) were tested to give the simulation and
evaluation. The durability factor of freezing/thawing was determined by the dynamic
modulus of elasticity of the concrete at 300 cycles of freezing/thawing cycles, or when
the dynamic modulus of elasticity reached 60% of initial, whichever came first. The
permeability of concrete was based on the amount of electrical current passing through
the concrete slices sample; usually, it measured at 28 days. According to Kosmatka and
Panarese (2002), a concrete sample with a durability factor larger than 95 is considered
16
high freezing/thawing resistant, and a concrete sample with 1000-2000 coulombs passing
through it is treated as low permeability. Kardos’ (2011) study indicated that for concrete
with crumb rubber, the best durability is 10% replacement of sand for the highest, which
is 0.91, followed by 20% replacement of sand.
Modulus of Elasticity of Rubberized Concrete
The modulus of elasticity of concrete reveals the capability of deformation under
loads. Fedroff et al. (1996) found that for higher strength concretes, the stress-strain
curves become more linear. Güneyisi et al. (2004) found that with increasing the rubber
content to 50% of the total aggregate volume, the modulus of elasticity reduced to about
6.5 and 8.0 gpa, for water cement ratios of 0.6 and 0.4, respectively; and that the modulus
of elasticity slightly increases with the use of silica fume.
Figure 2.5 (With permission from ProQuest) shows the relationship between
durability factor versus cycle count for rubberized concrete with different amount crumb
rubber incorporated. Rubber content reduces the durability of concrete subjected to
freeze/thaw cycling condition. The concrete mixtures with less than or equal to 20% fine
aggregate replaced by crumb rubber and without recycled coarse aggregate show
excellent freeze/thaw resistance. (Kardos 2011)
The gain rate of rubberized concrete modulus of elasticity with different rubber
content incorporated is shown in Figure 2.6 (With permission from TRB). The modulus
of elasticity reduces rapidly as the rubber particle increases. (Fedroff et al. 1996).
17
Figure 2.5: Durability Factor vs. Cycle Count
Figure 2.6: Modulus of Elasticity with Time (With permission from TRB)
18
The Structural Concrete Building Code (ACI 318-11) section 8.5.1 provides a prediction
equation for modulus of elasticity of concrete:
𝑀𝑜𝑑𝑢𝑙𝑢𝑠 𝑜𝑓 𝑒𝑙𝑎𝑠𝑡𝑖𝑐𝑖𝑡𝑦 = 𝑤𝑐1.5 ∗ 33 ∗ √𝑓𝑐
′
𝑤𝑐 is the unit weight of concrete, ranging from 90 to 160 𝑙𝑏
𝑓𝑡3 and 𝑓𝑐′ is the compressive
strength of concrete.
19
CHAPTER III
PROBLEM STATEMENT
Colorado has about 45 million stockpiled tires, and that number is rising each
year. Eastern Colorado lacks virgin coarse aggregates for pavement concrete mixtures.
Virgin aggregates usually are shipped from Front Range quarries to Eastern Colorado
projects, which has resulted in significant transportation costs as well as a larger carbon-
footprint due to the mining and trucking.
A recent study completed by University of Colorado at Denver (UCD) for the
Colorado Department of Public Health and Environment indicates the potential use of
commercially processed crumb rubber as an alternative replacement for fine aggregate in
CDOT Class P paving concrete mixtures. In this study, five mixtures with 10%–50%
replacements of sand by volume were tested for both fresh and hardened concrete
properties. From five replacement values, the 20% and 30% replacement mixtures met
the requirements of CDOT Class P concrete. The recycled rubber particles did not exhibit
an unusual rate of strength-gain behaviors with different replacement quantities. The
leaching tests were performed to examine the environmental sustainability of rubberized
concrete. The results showed that rubberized concrete poses no threat to human health.
The processing of crumb rubber increases cost of concrete to $300 to $400 per
ton. The expense of replacing the fine aggregates that are available in Eastern Colorado
with crumb rubber is high. An alternative way is to use recycled tire chips to supplement/
replace coarse aggregate in concrete mixtures. The less effort required, the less will be
the associated costs. This study examined the reuse potential of recycled tire chips as
coarse aggregates in paving concrete mixtures. The use of recycled tire chips would
20
replace the more expensive virgin coarse aggregate on the eastern plains of Colorado.
This study will help to eliminate Colorado’s stockpiled waste tires.
21
CHAPTER IV
EXPERIMENTAL PROGRAM
The primary objective of this research study was to create a sustainable concrete
mixture using recycled tire chips as partial replacements for coarse aggregates. The new
concrete mixture was developed and examined to meet the requirement of CDOT Class P
pavement concrete. This study consisted of two phases. In phase I, nine mixtures were
batched to examine the performance of both fresh and hardened concrete properties. The
cementitious material content was also changed to test the effect. In phase II, the mixtures
that fulfill the CDOT Class P concrete requirement were modified with different types of
water reducer to examine the effects. The modulus of elasticity was also investigated and
compared with the results calculated by the equations provided by ACI 318-11.
Materials for Test Specimens
Concrete Materials
Concrete mixture consists of coarse aggregates, fine aggregates, cementitious
materials, admixtures, and water. The design method used to proportion the concrete
mixture was the absolute volume method. In this study, the increments of coarse
aggregate volume were replaced with recycled tire chips. Figure 4.1 shows the coarse
aggregates provided by Bestway Concrete were in compliance with ASTM C-33
requirements. Coarse aggregates usually are any particles greater than 0.19”, generally
range between 3/8” and 1.5” in diameter. Fine aggregate usually consist of natural sand
with majority particles passing through 3/8” sieve. Figure 4.2 shows the fine aggregates
that were used in this study.
22
Recycled Tire Particles
Three different sizes of recycled tire chips were used in this research: 1/4”, 1/2”,
3/4” as shown in figure 4.3. They were purchased from Front Range Tire Recycle Inc.
with the price of $0.18 per pound, $360 per ton. Recycled tire chips do not have any
economic advantages when compared to conventional aggregates. But as discussed in
chapter II, recycled tire chips have economic advantages when compared to crumb rubber
particles. The sieve analysis for traditional coarse aggregates, fine aggregates, and
recycled tire chips were performed for each size. None of the single type of tire chips met
the ASTM C-33 grading requirement. In order to meet the requirement of ASTM-C33, a
designed mix of recycled tire chips with 40% of 3/4” and 60% of 1/2" was used as
replacement coarse aggregate for the proportioning concrete mixture based on the sieve
analysis.
Figure 4.1: Rocks-Coarse Aggregates
23
Figure 4.2: Sand- Fine Aggregates
Figure 4.3: Rubber Chips Sample, 3/4”, 1/4”, 1/2”, from Left to Right, Respectively
According to ASTM C-33, the sieve analysis was done for all aggregates used in
this study. Table 4.1 shows the sieve analysis results for both conventional aggregates
and recycled tire particles. Figure 4.4 shows the ASTM C-33 grading limits and the sieve
analysis results for coarse aggregates.
24
Table 4.1: Sieve Analysis for Sand, Rocks, and Tire Chips
25
Figure 4.4: ASTM C-33 Grading Limits and Values for Coarse Aggregates
26
Recycled Waste Tire Specific Gravity Experimental Testing and Results
It was important to determine the specific gravity value of the recycled tire chips
in order to adjust the proportion in the concrete mixture containing recycled waste tire
particles. The specific gravity of rubber chips was measured according to ASTC C-127
Standard Test Method for Density, Relative Density (Specific Gravity), and Absorption of
Coarse Aggregate. The literature reviewed indicates that tires would float on top of water
instead of submerge into the water. The solution was to use a de-airing chemical
admixture to control the air bubbles beneath the tire chips. In this study, the tire chips did
not float when submerged initially in water. No de-airing chemical admixture was used
through the entire specific gravity experimental testing. The specific gravity of tire chips
used in this study was measured to be 1.1.
Admixtures
The chemical admixtures used for this study were high-range water reducer
(HRWR), low-range water reducer (LRWR), and air-entraining admixture (AEA). The
AEA used was Sika Air in order to maintain the specified 4%–8% air content in the
rubberized concrete mixture; it contained a blend of high-grade saponified rosin and
organic acid salts. Typical amounts used in a concrete mixture range from 0.5–3 fl. oz.
per 100 lbs. of cementitious material. In this study, a dosage of 0.5 fl. oz. per 100 lbs. was
chosen to be used in each mixture.
Sika Plastocrete 161, a kind of low-range water reducer (LRWR), was used for
determining the proportion that met the requirement of CDOT Class P pavement
concrete. Sika Viscocrete 2100, a kind of high-range water reducer (HRWR), was used
for all the proportions that met the requirement to examine the effect of using different
27
types of water reducers. According to the manufacturer’s recommendation, the dosage
ranges 2–6 fl. oz. per 100 lbs. of cementitious materials. The target slump is 2”. Due to
the high volume of tire chips used in some mixtures, the slump of zero was observed in
some mixtures even with excessive water reducer incorporated.
Type I Portland Cement
An ASTM Type I Portland cement was used in this study. The specific gravity of
this cement was 3.15 and the blaine fineness was 217 yd2/lb.
Mixture Proportions
The mixture design identification (mix ID in Table 4.2) shows the detail
proportion for each mixture. For example, the first number (0.4/660/100S/100R/0TC/P)
represents that the water cement ratio of the mixture design was 0.4. The second number
(0.4/660/100S/100R/0TC/P) represents the content of cementitious materials in pounds.
The third number (0.4/660/100S/100R/0TC/P) represents the percentage of sand used for
the mixture by volume. The set of values in the fourth and fifth slots represent the
percentage of coarse aggregate (native rock) and the percentage of recycled tire chips,
respectively. Lastly, the final number in the design identification
(0.4/660/100S/100R/0TC/P) represents the type of water reducer used in the mixture, P
for Plastocrete161 (low-range water reducer) and V for Viscocrete 2100 (high-range
water reducer). All trial mixtures proportions details were shown in table 4.2.
28
Table 4.2: Research Design Mixtures Proportions
29
Batching of Concrete Mixture
During 2013, batching of concrete that contained different tire chips as coarse
aggregate with two kinds of water reducer was completed for testing. The procedures of
batching concrete were set by ASTM C-192 Making and Curing Concrete Test
Specimens in the Laboratory and all processes were performed accordingly.
Preparation Before Batching Concrete Mixture
Coarse aggregates and fine aggregates are stored in the open air. For this study,
they were spread on the ground under the sun for drying when it had rained the day
before. After that, about five days before batching they were placed in the laboratory by
using wheel carts so the extra water content in the aggregates would have enough time to
evaporate. This allowed the aggregates to balance out to room temperature during this
time. The components of each mixture were weighed and placed in five-gallon buckets.
This included the coarse aggregates, fine aggregates, tire chips, cement, and water.
Before batching, samples of coarse aggregates and fine aggregates were taken and
microwave-dried. Using the microwave, the samples were heated three minutes each time
and the weights of samples were recorded. The procedure was repeated until the weight
loss was less than 0.1 gram than the previous measure. The water content in both fine
aggregates and coarse aggregates was calculated by using this equation:
30
𝑤 =(𝑤0 − 𝑤𝑐) − (𝑤𝑑 − 𝑤𝑐)
𝑤𝑑 − 𝑤𝑐∗ 100
Where
w: water content in aggregates
𝑤0: weight of original sample aggregates and container
𝑤𝑑: weight of dried sample aggregates and container
𝑤𝑐: weight of container
After determining the water content in the aggregates, the water portion of the concrete
mixture could be adjusted. Admixtures—such as air-entrained admixture, low-range
water reducer and high-range water reducer—were measured and placed in test tubes.
The batching area consisted of all the necessary tools and equipment to test fresh concrete
properties. In addition, the cylinder molds and beam molds were adequately cleaned and
set in the batching area for casting the concrete specimens.
Mixing Process
The mixing process began by thoroughly dampening the concrete mixer with
water; when finished, all excessive water was dumped. This prevented the wall of the
concrete mixer from absorbing the water from the concrete mix. After all the excessive
water was dumped, the coarse aggregates, tire chips and fine aggregates were placed into
the concrete mixer. After all the aggregates were added into the mixer, the mixture was
allowed to blend for three to five minutes so that all of the different kinds of aggregates
were mixed evenly. The purpose of this was to prevent the various types of aggregates
from sticking together. When all of the blending procedures were completed, cement was
added into the mixer and blended with the aggregates for a few minutes. This was
performed to prevent clumping of the cement onto the wall of the mixer. The air-
31
entrained admixture was added into the measured water in the bucket. Then the whole
bucket of water was poured into the mixer slowly. After all the aggregates, cement,
water, and air-entrained admixtures were placed into the mixer, the water reducer was
added into the batch. Once all of the constituents had been added to the mixer, another
five minutes mixing time was allowed to mix the concrete thoroughly.
After the mixing was complete, all the concrete inside the mixer was placed onto
a dampened wheel cart, and a big cover was put on top of the wheel cart to prevent fast
evaporation. Fresh concrete tests were performed as soon as possible, in addition to
casting the concrete into cylinders and beams by using the molds prepared before the
batching.
Curing of Specimen
All the specimens, including cylinders and beams, were moved to the curing room
immediately after being cast for initial curing. The curing room was dedicated entirely to
concrete specimen storage and curing. The temperature in the curing room was
maintained at 23.0±4.0℃. The humidity controller of the curing room would increase the
room humidity when the relative humidity dropped below 50%.
The water tanks in the curing room were equipped with heaters and an analog
chart recorder with a digital temperature display. The temperature of the water in the
water tank was maintained at 23.0±2.0℃ in accordance, with ASTM C-511.
The specimens were placed in the curing storage room for the 24 hours initial
curing. After the initial curing, the cylinders and beams were de-molded.
Then concrete cylinders and beams were put into the water tank immediately for 100%
32
water curing. Cylinder tests were scheduled after the curing time of the 3rd day, 14th day,
and 28th day. Beams were tested when the curing time hit 28 days.
Testing of Concrete
Two phases of testing took place for each concrete mixture: freshly mixed
concrete properties and hardened concrete properties. The fresh concrete properties
included temperature, slump, unit weight, and air content; the hardened concrete
properties included compressive strength, splitting tensile strength, modulus of rapture,
rapid chloride-ion permeability, freeze/thaw resistance, and modulus of elasticity. The
fresh concrete tests took place during the batching of the mixture, and the hardened
concrete tests were performed at the scheduled days.
Testing for Fresh Concrete Properties
Freshly mixed concrete property tests were performed immediately after the
mixing procedure. Freshly mixed concrete properties of concrete are often used to
evaluate the behavior of components that are in the concrete matrix. All the tests were
performed in accordance with ASTM standards. Table 4.3 shows the standard procedure
and the testing time for the concrete mixtures.
Table 4.3: Fresh Concrete Tests
Fresh Concrete Tests Standard Time of Test
Slump ASTM C 143 At Batching
Unit Weight ASTM C 138 At Batching
Air Content ASTM C 231 At Batching
Temperature ASTM C 1064 At Batching
Testing for Hardened Concrete Properties
Tests performed on hardened concrete for trial mixtures are compressive strength,
splitting tensile strength, modulus of rupture, rapid chloride-ion permeability, and
33
freeze/thaw resistance. The hardened concrete properties testing on phase II included
compressive strength and modulus of elasticity. All the tests were completed in
accordance with ASTM standard. Table 4.4 and Table 4.5 indicate the standard
procedures, in addition to the time the tests were completed for the concrete mixtures.
Table 4.4: Hardened Concrete Tests for Phase I
Table 4.5: Hardened Concrete Tests for Phase II
Hardened Concrete Tests Standard Time of Test
Compressive Strength ASTM C 39 3,14,28 days
Modulus of Rupture ASTM C 78 28 days (Class P)
Freeze-Thaw Resistance ASTM C 666 28 and Subsequent days
Rapid Chloride Ion Penetrability ASTM C 1202 28days
Splitting Tensile ASTM C 496 28 days
Hardened Concrete Tests Standard Time of Test
Compressive Strength ASTM C 39 3,14,28 days
Modulus of Elasticity ASTM C 469 28 days
34
CHAPTER V
EXPERIMENTAL RESULTS AND DISCUSSIONS PHASE I
Batching of Trial Mixtures
The design plan was set. For phase I tests, mixture #1 through mixture #9 were
trial mixtures that aimed to determine the coarse aggregates replacement percentage to
satisfy CDOT Class P pavement concrete requirements. The batching of trial mixtures
was completed using 100%, 50%, 30%, 20%, 10% replacements of conventional coarse
aggregates. A control mixture, which had no tire chip, was batched for comparison.
Water content adjustment was performed before the batching. The final proportions for
both phase I and phase II are shown in Table 5.1.
Fresh Concrete Properties
Fresh concrete properties performed at the time of batching included temperature,
slump, unit weight, and air content for each mixture. When all of the materials were
being mixed in the mixer, it was observed that the higher tire-chips content that had been
incorporated, the lower the flow ability that showed in the mix. The amount of water
reducer used in each mixture was adjusted individually during the mixing procedure in an
effort to get the slump of 1 to 2 inches. The amount of water reducer used in each mixture
was recorded as shown in Table 5.2.The fresh concrete property results, in both metric
units and U.S. units, are summarized in the following sections.
35
Table 5.1: Trial Mixtures Proportion after Water Adjustment
36
Table 5.2: Water Reducer Dosage After Adjustment
Mix# Mix ID
WRA
L/100kg
(fl oz/cwt)
1 0.4/660/100S/100R/0TC/P 0.326(5)
2 0.4/660/100S/0R/100TC/P 2.169(33.27)
3 0.4/660/100S/50R/50TC/P 0.508(7.79)
4 0.4/660/100S/70R/30TC/P 0.474(7.27)
5 0.4/660/100S/80R/20TC/P 1.17(17.99)
6 0.4/660/100S/90R/10TC/P_1 0.326(5)
7 0.4/660/100S/90R/10TC/P_2 0.326(5)
8 0.4/570/100S/70R/30TC/P 1.884(28.90)
9 0.4/570/100S/90R/10TC/P 1.71(26.24)
10 0.4/660/100S/90R/10TC/V 0.326(5)
11 0.4/660/100S/90R/10TC/P 0.326(5)
Temperature of Freshly Mixed Hydraulic Cement Concrete, ASTM C-1064
The ideal temperature to place concrete is between 50° and 60°F (10°–16°C), but
should not exceed 85°F (29°C) (Mindess and Darwin 2003). A temperature over 85°F
will cause an increase of the water evaporation in the concrete. This undesirable
increased rate of evaporation is the cause of plastic shrinkage and results in internal
stresses that cause cracking (Kardos 2011). To avoid the exceeded maximum
recommended temperature, the concrete mixtures were batched outside during good
weathers and batched inside of lab during extreme weathers. Direct sunshine should be
avoid to protect the temperature of the surface of freshly mixed concrete going over the
limit. None of the mixture temperatures in this study exceeded the maximum
recommended temperature. The temperatures recorded for all the mixtures are
summarized in Table 5.3.
37
Table 5.3: Concrete Temperatures
Mixture# Mixture Name Temperature in Concrete Environment Temperature
Fahrenheit Fahrenheit
1 0.4/660/100S/100R/0TC/P 52 49
2 0.4/660/100S/0R/100TC/P 50 55
3 0.4/660/100S/50R/50TC/P 50 57.5
4 0.4/660/100S/70R/30TC/P 47 48
5 0.4/660/100S/80R/20TC/P 75 84
6 0.4/660/100S/90R/10TC/P_1 45 47
7 0.4/660/100S/90R/10TC/P_2 55 57
8 0.4/570/100S/70R/30TC/P 72 75
9 0.4/570/100S/90R/10TC/P 72 75
According to ASTM C 1064 Standard Test Method for Temperature of Freshly
Mixed Hydraulic-Cement Concrete, the container should be large enough to provide at least
3” in all directions around the sensor of the temperature measureing device as shown in
figure 5.1.
Figure 5.1 Temperatures Measuring
38
Slump of Hydraulic-Cement Concrete, ASTM C-143
The slump values of all trial mixtures and the water reducer usage for each
mixture are shown in Figure 5.3. The slump of concrete represents the workability of the
mixture. The tire chips resulted in a less workable mixture by comparison to normal
concrete (Liu 2013). It was observed that the slump for mixture #2 was zero even though
the water reducer had been added excessively (figure 5.2). Mixtures that had lower
cementitious materials experienced low slump and the workability was very poor.
Figure 5.2: Zero Slump for Mixture #2
39
Figure 5.3: Concrete Slump and WRA
40
Unit Weight
Unit weights were tested for each mixture in accordance with ASTM C-138. The
results ranged from 93 𝑙𝑏/𝑓𝑡3 to 145 𝑙𝑏/𝑓𝑡3 depending on the tire chips’ content
incorporated in the mixture and the air content. A unit weight of mixtures descends as
tire-chip contents increase; this trend was evident. The control mixture, which had no tire
chips replacement, had the unit weight of 145 𝑙𝑏/𝑓𝑡3. When the tire-chips content went
up to 30% of coarse aggregate volume, the unit weight decreased to 87% of the control
mixture. Once the tire chips had replaced all the coarse aggregates in the concrete
mixture, the unit weight went down to 64% of the control mixture. Only when the coarse
aggregates content were replaced by tire chips over 30% did the unit weight change
dramatically. Figure 5.4 shows the unit weight of each mixture design.
Air Content
Air-entrained admixture was used for all nine trial mixtures. The air content was
measured by pressure-meter method in accordance with ASTM C-231. The same amount
(0.5 fl oz/cwt) of air-entrained admixture was used for each mixture but the air content
varied. Using different types of water reducer affected the air content in the concrete in
the second phase of tests. High-range water reducer increased the air content in the
concrete mixtures. Figure 5.5 shows the air content and AEA used in each mixture. As
discussed in the literature review, rubber has the property of holding the air around; and
an 18% air content was found in mixture #2 (0.4/660/100S/0R/100TC/P).
41
Table 5.4: Air Content by Pressure Meter, ASTM-C231
Mixture Name Air Content
%
0.4/660/100S/100R/0TC/P 5
0.4/660/100S/0R/100TC/P 18
0.4/660/100S/50R/50TC/P 11
0.4/660/100S/70R/30TC/P 10
0.4/660/100S/80R/20TC/P 3.25
0.4/660/100S/90R/10TC/P_1 6
0.4/660/100S/90R/10TC/P_2 6
0.4/570/100S/70R/30TC/P 6
0.4/570/100S/90R/10TC/P 4.75
The roller meter method was also used for part of trial mixtures to determine the
air content and the results are summarized in table 5.5.
Table 5.5: Air Content by Roller Meter, ASTM-C173
Mixture Name Air Content
%
0.4/660/100S/0R/100TC/P 3.5
0.4/660/100S/50R/50TC/P 10.75
0.4/660/100S/70R/30TC/P 7.25
0.4/660/100S/90R/10TC/P_1 5.75
0.4/660/100S/90R/10TC/P_2 5.25
42
Figure 5.4: Unit Weight of Concrete Mixture
43
Figure 5.5: Air Content and AEA
44
Hardened Concrete Properties
Hardened concrete properties of rubberized concrete mixtures were performed in
accordance with ASTM standards. There were 14 cylinder specimens, in addition to at
least 4 prismatic beams that were cast for the tests for each mixture. A total number of
126 cylinders and 36 beams were cast for phase I tests. The tests performed on the
hardened concrete were:
Compressive Strength: 3 cylinders at 3, 14, 28 days
Modulus of Rupture: 2 beams at 28 days
Rapid Chloride-ion Permeability: 2 cylinders at 28 days
Splitting Tensile Strength: 3 cylinders at 28 days
Freeze/thaw Resistance: 2 beams at 28 days.
Compressive Strength of Concrete Specimens, ASTM C-39
The compressive strength of concrete is an important component in concrete
design. Three cylinders were tested for each mixture on the respective day of age.
Cylinders are 4” in diameter by 8” in length. The strength is determined by the failure
uniaxial load (lb.) divided by the cylinder surface area (𝑖𝑛2). According to current CDOT
Class P specifications, the requirement of compressive strength is 4200 psi at the age of
28 days. An average of three cylinder compressive testing results was obtained to
represent the performance of concrete at a certain age.
Compressive strength of each mixture at each designed age is summarized in Table 5.6
and Figure 5.6. Figure 5.7 and Figure 5.8 indicate the compressive strength loss by
comparison of control mixture at each testing day for 660 lb/cy cementitious materials
mixtures and 570 lb/cy cementitious materials mixtures, respectively. The compressive
45
strength gain rage for each mixture at 3 days, 14days, and 28 days were shown in
Figure5.9. The compressive values were obtained with the average of three specimens
and the coefficient of variation was calculated for each mixture. The coefficient of
variations for all mixtures lower than 2.9%, which is the precision requirement specified
by ASTM C39 except mixture #2, the mixture with 100% coarse aggregate replaced by
tire chips.
46
Table 5.6: Compressive Strength, ASTM C-39
47
Figure 5.6: Compressive Strength for Each Mixture
4200psi
48
Figure 5.7: % Strength Loss of Mixtures to the Control (high cementitious content)
Figure 5. 8: % Strength Loss of Mixtures to the Control (low cementitious content)
49
Figure 5.9: Rate Gain of Compressive Strength at 28 Days
4200psi
50
It was observed that the 10% replacement mixture #6 (0.4/660/100S/90R/10TC/P_1)
met the CDOT structural performance requirement. Mixture #7
(0.4/660/100S/90R/10TC/P_2) with the same proportion was batched and examined to meet
the requirement. The repeatability was approved. Figure 5.10 demonstrates the failure
mechanism of the cylinder under compression. Figure 5.11 is a concrete cylinder after
compressive failure.
Figure 5.10: Residual Strength Characteristic
0
10000
20000
30000
40000
50000
60000
70000
0 20 40 60 80 100 120 140 160
Lo
ad (
lbs)
Time (sec)
Load (lbs)
51
(a) Mixture #6, 10% Tire Chips (b) Mixture #2, Control Mixture
Figure 5.11: Compressive Failure of Concrete Cylinder
Flexural Strength or Modulus of Rupture, ASTM C-78
A minimum flexural strength of 650 psi is required by CDOT Class P pavement
specifications. This is a very important parameter for pavement applications, because
pavement concrete slabs will deform under the service load and the bottom of the
concrete slab tends to rupture. Sufficient flexural strength prevents the rupture happening
under the design load. This study’s results show that mixtures #6, #7, #8, and #9 met the
requirement of flexural strength. Mixtures #6 and #7, which had 10% coarse aggregates
replaced by tire chips, reached 924 psi and 991 psi at the age of 28 days, respectively.
They showed even better flexural strength than the control mixture, which had the
flexural strength 907 psi at the age of 28 days. Thus, it is concluded that the flexural
strength of concrete mixtures can be increased by replacing a certain level (~10%) of
coarse aggregate. Mixtures #8 and #9 showed good flexural strength behavior, too.
52
However, they did not meet the requirement of compressive strength at the age of 28
days, proving them inapplicable in this particular case; though high flexural strength
made them applicable for other cases where lower compressive strength is required, such
as sidewalks. Figure 5.12 demonstrates flexural failure.
Figure 5.12: Flexural Failure of Mixture #6
Figure 5.13 shows the flexural strength for each mixture. For all of the mixtures
with tire chips that had been incorporated, visual observations during the tests indicated
that all of the beams had ductile deformations instead of brittle failure. This demonstrated
that the tire chips acted as fiber reinforcement in the concrete and would not be crushed if
the concrete failed at the bottom. Instead, once the cracking began to form, the tire chips
held the two pieces of concrete and kept deforming until total failure. The flexural
strength values were obtained with the average of two specimens for each mixture and
the coefficient of variation meets the precision requirement specified by ASTM C78.
53
Figure 5.13: Flexural Strength for Each Mixture
650 p
si
54
Splitting Tensile Test, ASTM C-496
Figure 5.14 demonstrates the splitting tensile test set up. The results of splitting
tensile tests shown in Figure 5.15 demonstrate a similar trend, like compressive strength.
As the recycled waste tire particle contents increased, the splitting tensile strength
decreased. Mixtures from #5 to #9 showed good splitting tensile strength. The control
mixture had the highest tensile strength. It was confirmed that the recycled tire particles
did not increase the tensile strength of concrete. The splitting tensile values were obtained
with the average of two specimens and the coefficient of variation meets the precision
requirement, which is 5% specified by ASTM C496.
Figure 5.14: Splitting Tensile Test Setup
Examples of splitting tensile specimen failure for mixture #7 and mixture #8 in
the test were shown in Figure 5.16.
55
Figure 5.15: Splitting Tensile Strength for Each Mixture
56
Figure 5.16: Splitting Tensile Test Specimen Failure
Rapid Chloride-ion Permeability, ASTM C-1202
Concrete experiences damage caused by infiltration of solutions due to high
permeability of concrete. So, rapid chloride ion permeability tests were performed on the
concrete in this study at 28 days. The ASTM C-1202 discusses procedures for monitoring
the amount of electrical current that passes through 2” thick by 4” diameter concrete
slices. For this study, the slices were cut by a wet-saw to get the 2” slices of the concrete
cylinders, then all the slices were put in a dry vacuum desiccator for approximately 2
hours. Figure 5.17 shows the vacuum desiccator setup.
Next, deionized water was introduced to the desiccator via a tube connected to the
desiccator. Once the slices were completely submerged, the tube was switched off. The
concrete slices were kept in the water for 18 hours before the sample slices were put into
the test cells. Figure 5.18 demonstrates the cell preparation.
57
Figure 5.17: Vacuum Desiccator
Figure 5.18: Cell Preparation
58
Two solutions are required for rapid chloride-ion permeability testing: sodium
chloride (𝑁𝑎𝐶𝑙) solution and sodium hydroxide (𝑁𝑎𝑂𝐻) solution; the sodium chloride
solution is 3% by mass in distilled water, and 0.3 molar sodium hydroxide solution is
required. So, for this study the sodium chloride solution was set at one side of the cell,
and the sodium hydroxide solution was set at the other end. The cell set was tightened,
and a 60-volt direct-current source was maintained across the two ends of the specimen
for 6 hours. Table 5.7 shows the classification used to determine the concrete’s
permeability based on the coulombs passed.
Table 5.7: Permeability Rating Classification
Charge Passed (Coulombs) Chloride Ion Penetrability
>4,000 High
2,000-4,000 Moderate
1,000-2,000 Low
100-1,000 Very Low
<100 Negligible
Two sample slices were tested for each mixture. Table 5.8 shows that the average
coulombs passed two samples, and all rubberized mixtures were subjected to moderate-
to-high chloride ion penetrability at the age of 28 days, except for mixture #8
(0.4/570/100S/70R/30TC/P); the total coulombs passed for each specimen for mixture #8
were 5661 and 2708, respectively. Cracks were found in the slice, which had 5661
coulombs passed for the test when the cell was being disassembled, because the cracks
might have been formed during the preparation of the sample. If only use the sample had
2708 coulombs to represent the permeability at the age of 28 days, the mixture #8 was
classified at the moderate level.
59
Table 5.8: Rapid Chloride-ion Penetration Testing Results
Mixture
# Mixture Name 28-day(coulombs) Classification
1 0.4/660/100S/100R/0TC/P 1785 Low
2 0.4/660/100S/0R/100TC/P 2183 Moderate
3 0.4/660/100S/50R/50TC/P 1356 Low
4 0.4/660/100S/70R/30TC/P 2889 Moderate
5 0.4/660/100S/80R/20TC/P 1516 Low
6 0.4/660/100S/90R/10TC/P_1 2257 Moderate
7 0.4/660/100S/90R/10TC/P_2 2146 Moderate
8 0.4/570/100S/70R/30TC/P 4185 High
9 0.4/570/100S/90R/10TC/P 1648 Low
Figure 5.19 indicates an increase in coulombs due to an increase in the air content
by using the roller-meter method. However, mixture #3 (0.4/660/100S/50R/50TC/P)
showed out of the trend range. So, more mixtures were recommended to be batched in
order to investigate the abnormal point formed by mixture #3. Generally, as tire-chip
particles content increases, the air content increases; and, the more air content that is
entrained, the more total charges are passed.
Figure 5.20 demonstrates the chloride-ion permeability versus the air content
entrained for each mixture. No obvious trend was found between the total charge passed
and the air content. The air-content readings from the pressure-meter method were high.
The roller-meter method was used to measure the air content for mixture #2
(0.4/660/100S/0R/100TC/P), #3 (0.4/660/100S/50R/50TC/P), #4
(0.4/660/100S/70R/30TC/P), #6(0.4/660/100S/90R/10TC/P_1), and
#7(0.4/660/100S/90R/10TC/P_2). The results are summarized in Table 5.5.
60
Figure 5.19: Air Content (Roller Meter) vs. Coulombs
Freeze-thaw Durability, ASTM C-666
When water penetrates the holes inside of concrete and temperatures below 0°C
occur, the water freezes in the concrete. Because ice has a lower density than water, the
volume increases and expands against the internal surfaces of the small holes. This forms
internal stress, which causes micro-cracking because internal stress allows more water
infiltration and, finally, would cause failure of the concrete.
0.4/660/100S/50R/50TC/P
61
Figure 5.20: Chloride-ion Permeability vs Air Content
62
In accordance with ASTM C-666, the freeze/thaw durability of the concrete
mixtures in this study was determined by the transverse resonant frequency after 300
freeze/thaw cycles. Chemicals are used to modify the air content to enhance the durability
of a concrete mixture. In Colorado, the temperature varies 18°F–90°F (Denver Climate
Report 1981-2010). This region is subject to a large range of temperature gradients, and
the freeze/thaw durability of concrete pavement is a critical parameter.
For this study, two beams for each mixture were tested. They were put into the
freeze/thaw chamber, which runs the temperature from 0°F to 40°F, then backwards. At
the age of 28 days, the beams were moved from the curing water tank and immediately
placed in the beam holders with fresh water surrounding the beams. All beam holders
were put in the freeze/thaw chamber and run. The freeze/thaw chamber that is owned and
operated by the University of Colorado at Denver Materials Laboratory completes 36
cycles in approximately one week. The determination of one cycle is from 0°F to 40°F ,
then back to 0°F. ASTM C-666 states:
If, due to equipment breakdown or for other reasons, it becomes necessary to
interrupt the cycles for a protracted period, store the specimens in a frozen
condition in such a way as to prevent loss of moisture. For Procedure A, maintain
the specimens in the container and surround them by ice, if possible. If it is not
possible to store the specimens in their containers, wrap and seal them, in as wet a
condition as possible, in moisture-proof material to prevent dehydration and store
in a refrigerator or cold room maintained at 0±3°F (-18±2°C). Follow the latter
procedure when Procedure B is being used. In general, for specimens to remain in
a thawed condition for more than two cycles is undesirable, but a longer period
may be permissible if this occurs only once or twice during a complete test.
63
After 36 freeze/thaw cycles, all the beams were taken out and dried to SSD
condition. Next, the fundamental transverse frequency was tested, followed by placing
the beams back into the freeze/thaw chamber for another 36 cycles until the cycle number
hit 324. Per ASTM C-666, the relative dynamic modulus of elasticity and the durability
factor were calculated as follows:
𝑃𝑐 = (𝑛1
2
𝑛2) ∗ 100
Where:
𝑃𝑐= relative dynamic modulus of elasticity, after c cycles of freezing and
thawing, percent
𝑛1 = fundamental transverse frequency at 0 cycles of freezing and thawing
𝑛 = fundamental transverse frequency after c cycles of freezing and thawing
Durability factor (DF):
𝐷𝐹 = 𝑃𝑁/𝑀
Where:
DF= durability factor of the test specimen
P= relative dynamic modulus of elasticity at N cycles,%
N= number of cycles at which P reaches the specified minimum value for
discontinuing the test or the specified number of cycles at which the exposure is
to be terminated, whichever is less
M=specified number of cycles at which the exposure is to be terminated.
A photograph of the relative dynamic modulus of elasticity test process was
shown in Figure 5.21.
64
Figure 5.21: Transverse Resonant Testing Setup
65
As shown in Table 5.9, mixture #2 (0.4/660/100S/0R/100TC/P) had very low
durability-to-freeze/thaw cycling. The surface deterioration of all the concretes was
observed after 324 cycles of freezing and thawing, and no significant mass loss was
found except in mixture #2. However, the concrete mixture that had 10%–50% rubber
particles replaced by a volume of coarse aggregate did exhibit good resistance to freezing
and thawing. Generally, as the rubber content increased, the durability factor decreased.
Table 5.9: Duribility Factor
Mixture Name Initial (Hz) Final (Hz)
Durability
Factor
0.4/660/100S/100R/0TC/P 2177.74 2119.145 95
* 0.4/660/100S/0R/100TC/P 937.5 645 11
0.4/660/100S/50R/50TC/P 1572.27 1484.375 89
0.4/660/100S/70R/30TC/P 1767.58 1728.295 96
0.4/660/100S/80R/20TC/P 1855.47 1542.97 36
0.4/660/100S/90R/10TC/P_1 1972.66 1914.06 94
0.4/660/100S/90R/10TC/P_2 1972.66 1953.13 98
0.4/570/100S/70R/30TC/P 1425.78 947.27 44
0.4/570/100S/90R/10TC/P 1386.72 917.97 44
* Final Frequency was measured at 72 cycles
The testing results of transverse resonant frequencies after every 36 cycles of all mixtures
are shown in Table 5.10.
66
Table 5.10: Resistance to Freeze/Thaw Cycling
Mixtu
re#Mi
xture
Name
Befor
e Free
ze-
thaw(
0 cycl
e)
After
Freeze
-
thaw (
36cycl
es)
After
Freeze
-
thaw(
72cycl
es)
After
Freeze
-
thaw(
108cyc
les)
After
Freeze
-
thaw(
144cyc
les)
After
Freeze
-
thaw(
180cyc
les)
After
Freeze
-
thaw(
216cyc
les)
After
Freeze
-
thaw(
252cyc
les)
After
Freeze
-
thaw(
288cyc
les)
After
Freeze
-
thaw(
324cyc
les)
10.4
/660/1
00S/1
00R/0
TC/P
2177.7
4212
8.91
2099.6
1210
9.38
2089.8
45209
9.61
2080.0
75208
9.845
2080.0
75211
9.145
20.4
/660/1
00S/0
R/100
TC/P
937.5
859.38
644.53
644.53
644.53
1644
.531
585.93
8585
.938
664.06
3664
.063
30.4
/660/1
00S/5
0R/50
TC/P
1572.2
7156
2.48
1533.2
1155
2.74
1513.6
75152
3.44
1474.6
1147
4.61
1523.4
4148
4.375
40.4
/660/1
00S/7
0R/30
TC/P
1767.5
8176
7.58
1738.2
9174
8.05
1718.7
5173
8.28
1718.7
5170
8.765
1748.0
5172
8.295
50.4
/660/1
00S/8
0R/20
TC/P
1855.4
7179
6.88
1777.3
4175
7.81
1757.8
1167
7.22
1699.2
2164
0.63
1679.6
9154
2.97
60.4
/660/1
00S/9
0R/10
TC/P_
1202
1.49
1972.6
6191
4.06
1914.0
6191
4.06
1914.0
6191
4.06
1914.0
6191
4.06
1914.0
6
70.4
/660/1
00S/9
0R/10
TC/P_
2197
2.66
1962.9
1953.1
3195
3.13
1953.1
3195
3.13
1953.1
3195
3.13
1953.1
3195
3.13
80.4
/570/1
00S/7
0R/30
TC/P
1425.7
8127
9.295
1289.0
6110
3.52
1074.2
2110
3.515
1103.5
15966
.795
966.79
5947
.27
90.4
/570/1
00S/9
0R/10
TC/P
1386.7
2125
0121
0.94
1132.8
1957
.03976
.56976
.56917
.97866
.93917
.97
67
CHAPTER VI
EXPERIMENTAL RESULTS AND DISCUSSIONS PHASE II
As the result of the phase I study, the concrete mixture with 10% coarse
aggregate, which had been replaced by tire chips, satisfied all requirements specified by
CDOT Class P pavement concrete. Thus, phase II of this study examined the compressive
strength modulus of elasticity on rubberized concrete with 10% coarse aggregate replaced
by tire chips. Different types of water reducers were used to inspect the effects on
concrete. Repeatability of this rubberized concrete mixture design was again proven. The
mixtures were tested, by the standards and processes set by ASTM, for fresh concrete
properties, including slump, air content, unit weight, and temperature; and hardened
concrete properties, including compressive strength and modulus of elasticity. The value
of modulus of elasticity of this rubberized concrete was also compared with the results of
the prediction equation provided by ACI 318. Both mixture #10
(0.4/660/100S/90R/10TC/V) and mixture #11 (0.4/660/100S/90R/10TC/P) were batched
for phase II. The design mixture proportion and water reducer dosage adjustment were
summarized in Table 4.2 and Table 5.2, respectively.
Fresh Concrete Properties
Fresh concrete properties performed at the time of batching included temperature,
slump, unit weight, and air content for each mixture. Fresh concrete properties of mixture
#11 are similar with that of mixture #6 and mixture #7. Again, the repeatability was
approved. The results are summarized in the following sections.
68
Temperature of Freshly Mixed Hydraulic-Cement Concrete, ASTM C-1064
The temperatures of two mixtures are 70°F and 74°F, respectively. Neither mixture
temperature exceeded the maximum recommended temperature. The results of temperature
are shown in Figure 6.1.
Figure 6.1: Concrete Temperatures for Phase II
Slump of Hydraulic-Cement Concrete, ASTM C-143
The slump values of two mixtures are shown in Figure 6.2. The slump of concrete
represents the workability of the mixture. The tire chips resulted in a less workable
mixture by comparison to normal concrete. The workability of mixture #11 with high-
range water reducer was much higher than that of mixture #10 with low-range water
reducer.
7074
21 23
0
10
20
30
40
50
60
70
80
0.4/660/100S/90R/10TC/P 0.4/660/100S/90R/10TC/V
Fahrenheit Celsius
69
Figure 6.2: Concrete Slump for Phase II
Unit Weight, ASTM C-138
Unit weight was tested for each mixture in accordance with ASTM C-138. The
results were 142.4 𝑙𝑏/𝑓𝑡3 and 142.8 𝑙𝑏/𝑓𝑡3, respectively, and were consistent with the
results gained from phase I. Figure 6.3 shows the unit weight of each mixture design.
Figure 6.3: Unit Weight of Concrete Mixture for Phase II
1.25
4.75
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0.4/660/100S/90R/10TC/P 0.4/660/100S/90R/10TC/V
Slump (in.)
142.4 142.8
0
20
40
60
80
100
120
140
160
0.4/660/100S/90R/10TC/P 0.4/660/100S/90R/10TC/V
Unit Weight lb/cf
70
Air Content of Freshly Mixed Concrete ASTM C-231
Air-entrained admixture was used for both mixtures. The air content was
measured by pressure-meter method in accordance with ASTM C-231. The same amount
of air-entrained admixture was used for each mixture, but the air content varied. The use
of different types of water reducer affected the air content in the concrete. High-range
water reducer increased the air content in the concrete mixtures. Figure 6.4 shows the air
content of each mixture.
Figure 6.4: Air Content in Concrete Mixtures for Phase II
Hardened Concrete Properties
Tests for hardened concrete properties of rubberized concrete mixtures were
performed in accordance with ASTM. There were 20 cylinder specimens, in addition to 2
prismatic beams that were cast for the tests of each mixture. The tests performed on the
hardened concrete were:
Compressive Strength: 5 cylinders at 3, 14, 28 days
Modulus of Elasticity: 5 cylinders at 28 days.
3
6
0
1
2
3
4
5
6
7
0.4/660/100S/90R/10TC/P 0.4/660/100S/90R/10TC/V
Air Content %
71
Compressive Strength of Cylinder Specimens, ASTM C-39
For phase II of the study, five cylinders were tested for each mixture on the
respective day of age. The cylinders were 4” in diameter by 8” in length. According to
current CDOT Class P specifications, the requirement of compressive strength is 4200 psi
at the age of 28 days. An average of five cylinder compressive testing results was
obtained to represent the performance of concrete at a certain age. The compressive
strength of each mixture is shown in Figure 6.5.
Figure 6.5 Compressive strength for Phase II
The concrete mixture with low-range water reducer reached a compressive
strength of 3510 psi in its 3-days age. Not much compressive strength was gained from
the testing age of 3 days to the testing age of 14 days. A large compressive strength
increase was found between 14 days and 28 days for concrete mixture #10. Compared to
3510 3517
4506
3140
4025
4442
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
3 day 14 day 28 day
0.4/660/100S/90R/10TC/P 0.4/660/100S/90R/10TC/V
4200 psi
72
the other concrete mixture, mixture #11 had a lower compressive strength during the 3-
day test. It reached a much higher strength during 14-day test than mixture #10, and the
rate of increase for the strength slowed. Two concrete mixtures had similar compressive
strength that exceeded the Colorado Department of Transportation (CDOT) Concrete
Class P specification in their 28-day testing results. Figure 6.6 demonstrates the rate gain
of compressive strength for Phase II.
Figure 6.6: Rate Gain of Compressive Strength for Phase II
A compressive strength specimen failure from mixture #10 was shown in Figure
6.7. No brittle failure was found on all mixtures with tire chips incorporated.
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
0 3 day 14 day 28 day
0.4/660/100S/90R/10TC/P 0.4/660/100S/90R/10TC/V
73
Figure 6.7: Concrete Failure for Mixture #10
Modulus of Elasticity of Concrete in Compression, ASTM C-469
The modulus of elasticity (MOE) was used to inspect the response of the concrete
to load. The stiffness of the concrete was measured during this test. The MOE was
obtained by attaching a low-voltage displacement transducer (LVDT) to a
compressormeter. As the cylinder was tested in compression, the data acquisition system
recorded the vertical displacement and the compressive strength. The setup is shown in
Figure 6.9. The stress-strain curve was plotted, and the elastic modulus in compression
was calculated in accordance with ASTM C-469:
E = (𝑆2 − 𝑆1)/(𝜖2 − 0.000050)
74
Where: E= chord modulus of elasticity, psi; 𝑆2= stress corresponding to 40% of
ultimate load; 𝑆1= stress corresponding to a longitudinal strain of 50 millionths, psi; 𝜖2=
longitudinal strain produced by stress 𝑆2.
ACI 318 gives the equation for calculating the modulus of elasticity. The
comparison was made to examine whether the equation provided by ACI 318 was
suitable for this particular rubberized concrete mixture design. The modulus of elasticity
of 28 days for each mixture is shown in Figure 6.8.
Modulus of Elasticity, ACI 318-11 Section 8.5.1
𝐸𝐶 = 𝑤𝑐1.5 ∗ 33 ∗ √𝑓𝑐
′
Where,
𝐸𝐶= Modulus of elasticity of concrete, psi
𝑤𝑐. = Concrete unit weight, 𝑙𝑏 𝑓𝑡3⁄
𝑓𝑐′= Concrete compressive strength, psi
Figure 6.8: MOE Test Results and MOE Calculated From ACI Equation
384035603670 3590
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0.4/660/100S/90CA/10TC/LW 0.4/660/100S/90CA/10TC/HW
Test results ACI Equation Unit: ksi
75
Figure 6.9: Modulus of Elasticity Test Setup
76
CHAPTER VII
CONCLUSIONS
Results
This thesis evaluated the performance of concrete, using CDOT Class P pavement
concrete modified with recycled tire chips as partial coarse aggregates. The requirement
of CDOT Class P pavement concrete is attached in Appendix B. The replacement of
coarse aggregates by using tire chips ranged from 10% to 100%. The chemical admixture
dosage varied from the pre-approved CDOT Class P concrete for the mixtures
proportions, with more than 20% coarse aggregates replacement. For the mixture with
10% replacement, the dosages of chemical admixture remained consistent with the pre-
approved mixture proportion. Both phase I and II of this study showed that all mixtures
with 10% replacement (#6, #7, #10, #11) met the requirements of CDOT Class P
pavement concrete. All the hardened concrete property test results were obtained with the
average of testing specimens. The precision for all tests were checked, and met the
requirement of related ASTM standard. Thus, the modified concrete proportion
determined can be potentially used as concrete pavement and sidewalks in Colorado. In-
service monitoring would be necessary and evaluated to examine the practical
performance.
In total, eleven concrete mixtures were designed, batched, and tested for both
fresh concrete properties and hardened concrete properties. Fresh concrete properties
include slump, temperature, air content, and unit weight. Hardened concrete properties
include compressive strength, splitting tensile strength, flexural strength, rapid chloride-
77
ion penetration, freeze/thaw durability (in phase I), and compressive strength and
modulus of elasticity (in phase II).
Summary of Fresh Concrete Properties
Slump
Slump increased as the recycled tire chips decreased. The concrete mixtures with
replacement of coarse aggregate more than 10% have low workability even with
excessive low-range water reducer (Plastocrete161). Using high-range water reducer
could effectively improve the slump; however, rapid slump loss resulted in reduced
workability, allowing less time to place the concrete.
Air Content
The air content of each mixture was tested by the pressure-meter method and
some mixtures were also tested by the roller meter. The air content varied by using
consistent amounts of AEA. Generally, the air content goes up with the increase of tire
chips incorporated. However, a significant discrepancy of the air content measured from
the pressure meter and roller meter was observed for mixture #2
(0.4/660/100S/0R/100TC/P).
Unit Weight
The unit weights for all mixtures tested decreased as the tire-chips particle content
was increased. The unit weight decreased linearly regardless of the cement content.
Temperature
Temperatures for all of the concrete mixtures did not exceed the recommended
range. Temperature is not considered as an important role in the behavior in the concrete
for this study.
78
Summary of Hardened Concrete Properties
Compressive Strength
The compressive strength decreased as the tire-chips particle content increased.
Over 30% compressive strength loss was found, with 10% replacement of coarse
aggregate; and more strength loss was observed with higher replacement of coarse
aggregate. All the concrete mixtures with 660lb cementitious material per cubic yard and
10% tire chips by volume of coarse aggregate fulfilled the requirements of CDOT Class P
pavement concrete at the age of 28 days. Mixtures with lower cementitious material
incorporated had lower compressive strength.
Splitting Tensile Strength
It was observed that the splitting tensile strength of the mixtures with tire chips
was lower than that of the control mixture. The splitting tensile strength decreased by
more than 18%, with a 10% replacement of coarse aggregate with tire chips.
Flexural Strength
The flexural strength of the concrete mixtures with tire chips incorporated was
observed to be higher than the flexural strength of the control concrete mixtures. The
flexural strength of the mixture with 10% replacement coarse aggregate using tire chips
exceeded 900 psi at the age of 28 days. The failure of the beams were ductile instead of
brittle failure as a control mixture. With the tire-chips content increasing, the flexural
strength decreased.
Durability
An obvious trend of the durability factor decreasing, with increasing the tire chips
content, was observed. Freezing and thawing durability tests showed excellent durability
79
factor for the 10%. Mixture #2 (0.4/660/100S/0R/100TC/P) failed to complete 300 cycles
of the freeze/thaw test. After 72 cycles, the relative dynamic modulus of elasticity was
lower than the ASTM specified minimum value. An increase in mass loss was observed,
with increased percentages of tire-chips content.
Rapid chloride-ion penetration tests showed low to moderate classification on all
the mixtures, as discussed in chapter V. Mixtures with 10% replacement coarse
aggregates and higher cementitious materials showed good permeability. Concrete
mixtures with lower cementitious material content is not recommended.
Modulus of Elasticity
Modulus of elasticity was tested only on the mixture with 10% coarse aggregate
replaced by tire chips, which satisfied all CDOT Class P pavement concrete
requirements. The modulus of elasticity could be well-predicted by the equation provided
by ACI 318-11.
The Effects Caused by Water Reducer
Two mixtures with high-range water reducer (Viscocrete 2100) and low-range
water reducer (Plastocrete 161), respectively, were examined for this thesis. High-range
water reducer increased the slump and workability, obviously. However, the slump loss
was rapid and the concrete place time was less. For a concrete pavement mixture, the
recommended slump range is 1 to 3 inches, which could be obtained by increasing the
dosage of low-range water reducer. There was no significant difference in compressive
strength or in modulus of elasticity between two mixtures. The compressive strength
gained faster from the age of 3 days to the age of 14 days for the mixture with low-range
water reducer. At the 28 days age, two mixtures had very similar strength.
80
Recommendations
Following are the recommendations for designing CDOT Class P pavement
concrete modified with tire chips:
Tire chips can be used as partial replacement of coarse aggregate in concrete
pavement mixtures. Mixture with 10% coarse aggregate replaced
(0.4/660/100S/90R/10TC/P) had the best performance among all the tire-chips
incorporated mixtures.
The workability of all the mixtures was low. It is recommended to use low-
range water reducer and to adjust the dosage to improve the slump of
rubberized concrete. Additional tests are recommended to evaluate the
incorporation of fly ash to improve the slump of rubberized concrete.
All mixtures with 570 lbs/cy yard cementitious materials demonstrated low
strengths and stiffness. It is recommended to use 660 lbs/cy or more
cementitious materials instead of reducing the cementitious materials amount.
81
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APPENDIX A
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APPENDIX B
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APPENDIX C
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