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Sustainable concrete design and accounting in highway infrastructures

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Sustainable concrete design and accounting in highway infrastructures
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Rudzeviciute, Kristina
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Fly ash ( lcsh )
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Fly ash ( fast )
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theses ( marcgt )
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Includes bibliographical references.
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College of Engineering and Applied Science
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by Kristina Rudzeviciute.

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Full Text
SUSTAINABLE CONCRETE DESIGN AND
ACCOUNTING IN HIGHWAY INFRASTRUCTURES
by
Kristina Rudzeviciute
Bachelor of Science, Civil Engineering, University of Colorado at Denver 2007
A thesis submitted to the
University of Colorado Denver
in partial fulfillment
of the requirements for the degree of
Master of Science
College of Engineering and Applied Sciences
July 2009


This thesis for the Master of Civil Engineering
degree by
Kristina Rudzeviciute
has been approved
by
Stephan A. Durham
Cheng Yu Li
/*, c%oo9
Date


Rudzeviciute, Kristina (M.S., College of Engineering and Applied Sciences)
Sustainable concrete design and accounting in highway infrastructures
Thesis directed by Assistant Professor Stephan A. Durham.
ABSTRACT
Fly ash use as a supplementary cementitiuos material in concrete mixtures has
become an everyday practice. Research has demonstrated that replacing a portion of
the cement content with fly ash improves the workability of fresh concrete, increases
later age compressive strength and improves long-term durability,.
This thesis examined the current Colorado Department of Transportation (CDOT)
Class P and determine whether the percentage of fly ash could be increased from 30%
to 50% by weight of the cement. The current CDOT Class P (30% fly ash) and a
modified Class P (50% fly ash) were produced and tested for compressive strength,
flexural strength, and permeability. A 20% increase in cement replacement with fly
ash would result in a cost savings of $4.40 per cubic yard. In addition, the Class P
Modified mixture provides for a more sustainable concrete mixture by reducing the
amount of cement required for concrete production and consequently reducing C02
release into the atmosphere.
This thesis showed that the Class P Modified mixture containing 50% fly ash
exceeded the CDOT performance criteria for the current Class P concrete.


This abstract accurately represents the content of the candidates thesis. I recommend
its publication.
Signed
Stephan A. Durham


DEDICATION
I dedicate this thesis to my parents, who gave me an opportunity to grow, leam and
explore the world. I also dedicate this thesis to my fiance, Karolis, for his incredible
support and encouragement while I was working and at the same time preparing this
thesis.


ACKNOWLEDGEMENT
I would like to give special thanks to my advisor, Dr. Stephan A. Durham, for his
support and his time he was able to provide in helping me out with this research.
Many thanks for ability to help me with laboratory work during this research period.
In addition, I would like to thank Dr. Durham for all the comments and advice he
gave me during this research.
I also would like to thank Dr. Rens and Dr. Li for their time and participation on my
research committee.


TABLE OF CONTENTS
List of Figures.............................................................xiv
List of Tables..............................................................xvi
Chapter
1. Introduction...........................................................1
1.1 What Is Sustainability?................................................1
1.2 Importance of Highway Sustainability...................................1
1.3 Material Evaluation....................................................3
1.4 Objectives.............................................................5
1.5 Scope..................................................................5
2. Literature Review......................................................6
2.1 High Volume Fly Ash (HVFA).............................................6
2.2 HVFA Affect on Concrete Properties.....................................9
2.2.1 Overview...............................................................9
2.2.2 Fresh Concrete Properties.............................................11
2.2.3 Hardened Concrete Properties..........................................11
2.3 Sustainability and Highways...........................................13
2.3.1 Overview..............................................................13
2.3.2 Recycling in Colorado.................................................15
3. Problem Statement.....................................................1?
x


.19
.19
.19
.20
.21
.22
.22
.23
.25
.26
.26
.28
.30
.32
.32
.32
.32
.33
.35
.35
37
Experimental Procedures and Research Program.................
General......................................................
Scope of Work................................................
Specifications from CDOT Class P concrete and Modified Concrete
Materials....................................................
Portland Cement..............................................
Fine Aggregate...............................................
Coarse Aggregate.............................................
Fly Ash......................................................
Experimental Procedures......................................
Mixing and Batching..........................................
Fresh and Flardened Concrete Tests...........................
Curing.......................................................
Experimental Test Results....................................
Concept.......................................;..............
Slump Test...................................................
Slump Concept................................................
Slump Test Results...........................................
Air Content and Unit Weight..................................
Air Content and Unit Weight Concept..........................
Air Content and Unit Weight Results..........................
xi


5.4 Fresh Concrete Temperature Test......................................39
5.5 Compressive Strength Test............................................40
5.5.1 Compressive Strength Purpose.........................................40
5.5.2 Compressive Strength Test Results....................................42
5.6 Flexure Strength Test................................................47
5.6.1 Flexure Test Scope...................................................47
5.6.2 Flexure Test Results.................................................49
5.7 Permeability Test....................................................51
5.7.1 Permeability Test Purpose............................................51
5.7.2 Permeability Test Results............................................52
5.8 Experimental Test Results............................................54
6. Sustainability of Concrete Mixtures in Highway Construction..........55
6.1 Sustainable Highways.................................................55
6.2 CO2 Emission.........................................................56
6.3 Fly Ash..............................................................57
6.4 CO2 Reduction........................................................59
7. Prescriptive Compared to Performance Specifications..................63
7.1 Prescriptive.........................................................63
7.2 Performance..........................................................64
8. Cost Analysis........................................................67
9. Conclusions and Recommendations......................................74
xii


9.1 Comparison of Study Findings to CDOT Specifications..................74
9.2 Conclusions..........................................................74
9.2.1 Fresh Concrete Properties............................................75
9.2.2 Hardened Concrete Properties.........................................76
9.3 Recommendations......................................................77
Appendices
References
xiii


LIST OF FIGURES
Figure:
1. Various Components of a Concrete Mixture.................... ....4
2. Scanning Electron Microscope Micrograph of HVFA (U.S. Department of
Energy, 2007).....................................................6
3. Compressive Strength Cylinders and Flexural Strength Beams...31
4. Concrete Curing Room and Tanks....................................31
5. Slump Measurements................................................33
6. Class P and Modified Class P Mixture Slump Measurements...........34
7. Air Pressure Meter Device.........................................35
8. Fresh concrete measuring in a container of known volume to determine unit
weight (PCA, 2002)...............................................37
9. Unit Weight and Air Content Measurements..........................38
10. Compressive Strength Assembly.....................................42
11. Compressive Strength Test Pictures................................44
12. Compressive Strength (psi) vs. Time (days)........................45
13. Rate of Compressive Strength Gain.................................46
14. ASTM C 78 Third- Point Loading (Dr. Durham, Class CE 3141,2006).48
15. Flexure Test Assembly.............................................48
16. Class P Modified Concrete Flexure Test Failure Beam...............50
xiv


17.
Flexure Test Failure
50
18. Permeability Testing cells.........................................52
19. Cost Comparison for Raw Materials..................................72
xv


LIST OF TABLES
Table:
1. Concrete Requirements (CDOT, 2005).................................20
2. Grading Requirements for Coarse Aggregate (ASTM C 33, 2003)........24
3. Mixture Design.....................................................26
4. Specific Gravity...................................................27
5. Batch Volumes per Cubic Foot (cubic meters)........................27
6. Aggregate Volume Based on Aggregate Weight.........................27
7. Fresh Concrete Tests...............................................29
8. Hardened Concrete Tests............................................29
9. Air Contents and Unit Weight Results...............................38
10. Temperature Measurement Results....................................40
11. Compressive Strength Maximum Loads in lbs (kg).....................43
12. Compressive Strength Values in psi (kg/m2).........................45
13. Flexure Strength Test Results in psi (kg/m2).......................49
14. Chloride Ion Permeability Based on Charge Passed...................53
15. Permeability Test Results..........................................53
16. Experimental Test Results..........................................54
17. Historical Data in Process-related C02 emission from U.S. Cement
Manufacturing (US Environmental protection Agency, 2007) (%).......57
xvi


18. Reduction of CO2 Emission in Past 4 Years using modified Class P concrete
mix.................................................................60
19. Energy efficiency improvement options for cement production processes
(Hendriks, 2004)....................................................62
20. CDOT Concrete Table (CDOT, 601-1, 2005).............................63
21. 2005 CDOT concrete Class P usages and pricing......................67
22. 2006 CDOT concrete Class P usages and pricing......................68
23. 2007 CDOT concrete Class P usages and pricing......................69
24. 2008 CDOT concrete Class P usages and pricing......................70
25. CDOT Class P Concrete Average Prices................................70
26. CDOT Concrete Costs (Bestway Concrete, 2009)........................71
27. Cost Comparison for Laboratory Mixtures Including Equipment and Labor
(Bestway Concrete, 2009)............................................72
28. CDOT savings with the Modified Class P Mixture......................73
29. Comparison to CDOT Requirements.....................................74
xvii


Chapter 1
Introduction
1.1 What Is Sustainability?
Todays society faces many challenges. Numerous government agencies and world
communities are seeking to become more sustainable. Currently, sustainability is a
major topic being discussed by many governmental and private organizations. The
Sustainability Leadership Institute (1987) describes sustainability as each person in a
society doing his or her part to build the kind of world economically,
environmentally and socially that everyone wants to live in. The type of
environment, one wants his or her children and grandchildren to inherit. In order to
become more sustainable, society must become aware of all interconnections visible
and invisible in which peoples day-to-day choices affect the intricate balance of
social, economic and ecological systems.
One of the most difficult aspects of an environmentally responsible design is to find
the most appropriate materials and available products that help prolong the earth and
human health. In addition, creating infrastructure that is sustainable examination of
methods currently used to design and build a societys infrastructure.
1.2 Importance of Highway Sustainability
In modem society, roadways are considered one of the most important forms of
infrastructure, as they allow a means for society to stay connected. The Colorado
1


transportation infrastructure allows access from suburban areas to major metropolitan
business and industrial regions of the state. Many technologies exist to reduce the
environmental impacts of highways. The Colorado Department of Transportation
(CDOT) incorporates in their design many advanced planning techniques, intelligent
construction developments and efficient maintenance to advance in sustainability.
Research completed by CDOT in 2002 indicated that concrete pavement design could
be optimized. The research showed that replacing 20% of cement with Class F fly ash
could lead to great results. The partial replacement of cement with fly ash did not
appear to pose any significant deleterious impact to the concrete durability (CDOT,
2002).
Currently, highways have enormous negative impact on the surrounding ecosystems
and the overall environmental quality. The first step to progress in the development of
highway infrastructure requires human participation to reduce the effects of highways
on environment and benefit the society by decreasing the traffic of the highway.
There are numerous methods to implement sustainability in the design and
construction of transportation infrastructure. For example, lifecycle energy reduction
standards stipulate that a highway will have a long-term life and will accommodate
traffic flows with minimal congestion impacts. It depends on how often highways
need to be reconstructed or even replaced. If the lifecycle of the concrete pavement
could be increased, the energy used to operate equipment on the construction sites
would decrease. Designing a highway in such a manner not only reduces the cost of
2


energy and maintenance, but also increases the capacity and long-term usage of the
highway and decreases emissions caused by automobiles delayed in congestion.
The objective of this thesis is to evaluate the CDOT specification for Class P concrete
mixture design and to create a more sustainable and durable design for highway
infrastructures. The design proposed in this thesis will produce a concrete mixture
with equal or superior performance, reduce the CO2 emission caused by cement
production, and ultimately reduce the overall cost of the concrete used in Colorado
highways. In addition, the purpose is to evaluate CDOT concrete class P usage,
recycling, and cost. Furthermore, differences between prescriptive and performance
based specifications will be examined. It is expected that concrete mixtures designed
utilizing performance-based specifications can produce higher quality concrete
mixtures at lower overall costs.
1.3 Material Evaluation
The majority of transportation infrastructure is composed of concrete. This includes
roadway pavements, bridge super and sub-structures, box culverts, retaining walls,
etc. Concrete is more durable and requires less maintenance than other leading
paving materials. The Portland Cement Association (PCA) describes a concrete
mixture composed of five basic ingredients: portland cement, water, coarse aggregate,
fine aggregate, and air. See Figure 1 (PCA, 2009).
3


Figure 1: Various Components of a Concrete Mixture
Concrete is a composite material, which is made of filler and a binder (PCA, 2003).
The binder (cement paste) "glues" the filler together to form a synthetic
conglomerate. The constituents used for the binder are cement and water, while the
filler is composed of fine or coarse aggregate. Portland cement is the main ingredient
of the concrete mix design. In many cases, recycled materials, or by-products of
various manufacturing processes, may be used as a partial cement replacement.
These materials are referred to as supplementary cementitious materials. This thesis
examines the CDOT concrete Class P mixture compared with a modified more
sustainable mixture design. CDOT specifications indicate that concrete Class P is
used for pavement design.
4


1.4 Objectives
The first objective of this thesis is to investigate the CDOT Class P concrete and
modified concrete mixtures such that a 50% replacement of cement with fly ash is
incorporated with the modified mixture. Performance tests were conducted to
compare the compressive strength, tensile strength, and permeability of both
mixtures. The modified mixture will be compared to both the CDOT Class P
concrete mixture and the CDOT Class P specification to determine whether the
modified mixture can be used based on the mixture performance. Second, in this
thesis the cost differences for both mixtures are examined. In addition, the thesis
demonstrates that using a 50% replacement of cement with Class F fly ash provides
for a more sustainable mixture design. Finally, the differences between prescriptive
and performance based specifications will be discussed.
1.5 Scope
This study examines two types of concrete: the CDOT Class P and modified Class P
concretes. The Class P and modified Class P concretes are used for the design and
construction of highway pavements. The primary difference between the CDOT
specified Class P concrete mixture and the UCD Class P Modified mixture is a
replacement of 20% of cement with fly ash. The total cement replacement with fly
ash for the modified Class P mixture is 50%.
5


Chapter 2
Literature Review
2.1 High Volume Fly Ash (HVFA)
Fly Ash is a by-product generated by coal burning power plants. Typically, fly ash is
landfilled or, where lack of regulations permit, it allowed to be emitted into the
atmosphere. Fly Ash is well accepted as a pozzolanic material that may be used either
as a component of mixed portland cements or as a mineral admixture in concrete. A
microscopic image of fly ash particles is shown in Figure 2.
Figure 2: Scanning Electron Microscope Micrograph of HVFA (U.S.
Department of Energy, 2007)
Fly ash is commonly used in concrete as a partial cement replacement. Typically, the
replacement rate ranges from 0 to 30 % by mass of the total cementitiuos material
(Midness, et. al., 2005). However, past researches has shown that using 50% or even
greater replacement of fly ash can have an extensive range of benefits (Midness, et.
al., 2005). The difference between fly ash and HVFA is particle size. Federal
6


Highway Administration indicates that HVFA concrete contains more than 30% of
fly ash. Research has demonstrated that fly ash is a by-product and therefore less
expensive than portland cement. In addition, it is known to improve workability and
reduce internal temperatures. HVFA has a wide range of benefits with durability
being one of the most significant factors. The improvements in durability are the
result of the reduction in calcium hydroxide, which is the most soluble of the
hydration products and from changes in the pore structure (Midness, et. al., 2005).
Pozzolanic reaction occurs between dissolved elements from silica and calcium
hydroxide. CSH paste is formed when hydroxyl ions break down the silica in the
glass, which react with the calcium in the portlandite. This type of reaction enlarges
the bond strength between the cement paste and aggregate. Silica and alumina species
broken from the silica framework reach with Ca(OH)2 and forms CSH phases and
minerals (Byard, 2007). Cement reaction: SiC>2 + AI2O3 + Fe2C>3 (from fly ash) +
CaOH2 (from cement hydration) = CSH (calcium silicate hydrate which is a
compound in cement paste)
Some research indicated that HVFA concrete is more crack-resistant than
conventional concrete, due to the decreased shrinkage (Green Recourse Center,
2004). This may result from the decreased mixing water, decreased water to
cementitious material (w/cm) ratio, as well as the decrease in the total volume of
cement paste that is required in HVFA.
7


In 2004, the Green Resource Center examined the differences between HVFA
concrete and Conventional concrete. Their findings are listed below:
a) High Volume Fly Ash Concrete:
Less energy intensive manufacture
Higher ultimate strength
More durable
Requires less water
Uses a waste by-product
Creates fewer global warming gases
b) Conventional Concrete:
Energy intensive manufacture
Lower ultimate strength
Less durable
Requires more water
Uses virgin materials only
Creates more global warming gases
In conventional concrete, cement is the main component. Cement is primarily
composed of lime and silica (sourced from limestone, clay, and sand) and is fired in a
rotary kiln at 2700 F (1482C), consuming massive quantities of fossil fuels and
thereby producing high amounts of CO2 (Green Resource Center, 2004). By replacing
8


a large percentage of the cement in concrete with fly ash, the associated
environmental impacts of CO2 production and air pollution are significantly reduced.
Mark Reiner, a PhD student at the University of Colorado, in 2008 in his research
paper found that high performance green concrete with fly ash and recycled aggregate
could reduce pollution (Reiner, Dissertation on technology, Environment, Resource
and Polity Assessment of Sustainable Concrete in Urban Infrastructure 2007).
2.2 HVFA Affect on Concrete Properties
2.2.1 Overview
With HVFA concrete mixtures, depending on the quality of fly ash and the amount of
cement replaced, up to 20% reduction in water could be reduced (Kaur, 2004). This
means that good fly ash could act as a super plasticizing admixture when used in
high-volume. The water reducing property of fly ash could be advantageously used
for achieving a considerable reduction in the drying shrinkage of concrete mixtures
(Kaur, 2004). Due to a significant reduction in the water requirement, the total
volume of the cement paste in the HVFA concrete is only 25% as compared to 29.6%
for the conventional portland-cement concrete, which represents a 30% reduction in
the cement-paste -to aggregate volume ratio (Kosior-Kazberuk, 2007). For non-
reinforced concrete construction, several methods are incorporated to prevent thermal
cracking. Some of these methods could be successfully used for mitigation of
thermal cracks in reinforced-concrete structures. With a HVFA concrete mixture
9


containing 50% cement replacement with a Class F fly ash, the adiabatic temperature
rise is expected to be 86- 95F (30-35C). As a rule of thumb, the maximum
temperature difference between the interior and exterior concrete should not exceed
77F (25C) to avoid thermal cracking. This is because higher temperature
differentials are accomplished by rapid cooling rates that usually result in cracking.
The Journal of Civil Engineering and Management in 2007 performed a study on the
fly ash concrete strength development (The Journal of Civil Engineering and
Management in 2007). The test results demonstrated that all mixtures containing fly
ash were able to develop a higher flexural strength than the control mixtures. In
addition, the results obtained demonstrated that the fly ash has an advantageous effect
on compressive strength of all cements used in this research. When the rate of
strength of fly ash concrete is much slower and sustains for longer periods, the
concretes consisting of fly ash are able to develop higher strengths than comparable
concrete mixtures containing only portland cement. Another aspect of this research is
that after 180 days of curing concrete that contains 20% of fly ash, the compressive
strength increased approximately 25% more than concrete mixtures that containing no
fly ash. The journal indicates that statistical methods could be used to examine the
selected range of combinations (fly ash and cement) and have a big affect on selected
performance distinctiveness of concrete material. In addition, the statistical methods
could be used to evaluate and verify statistical models that could serve as an
10


instrument for estimating the compressive strength development of concrete with fly
ash content as well as to identify the best possible cementitious content.
2.2.2 Fresh Concrete Properties
The use of fly ash increases the absolute volume of cementitious materials compared
to concrete without fly ash. In this case, the paste volume is increased, leading to a
decrease in aggregate particle interruption and development in concrete workability.
Thus, the uses of fly ash in concrete mixtures increase concrete workability (Midness,
et. al., 2005).
The fly ash in air-entrained and non-air-entrained concrete mixtures typically
decrease bleeding potential by providing a higher volume of fines and lower water
content for a given workability. Though increased fineness typically increases the
water requirement as well, the spherical partial shape of the fly ash decreases element
friction and offsets such effects. Concretes with high fly ash content (about 30-50%
of fly ash) will require less water than concrete without fly ash to achieve an equal
slump.
2.2.3 Hardened Concrete Properties
All Class F Fly ash increase the time of setting of concrete (FHWA Materials Group,
1999). Time of setting of fly ash concrete is influenced by the amount of fly ash used
in concrete. For highway construction, changes in time of setting of fly ash concrete
11


from concrete without fly ash using similar materials will not typically initiate a
requirement for any modifications in construction methods used.
Strength of fly ash concrete is influenced by what kind of cement is used, also the
quality of fly ash, as well as curing temperature compared to concrete without fly ash
balanced for corresponding 28-day compressive strength. Concrete containing Class F
fly ash develops lower strength at 3 and 7 days of age when compared to 100%
Portland cement concrete mixtures. Fly ash concretes typically have higher later-day
strengths than 100% portland cement concrete mixtures due to the continued
formation of C-S-H from the pozzolanic reaction. The slow strength gain is the
consequence of the relatively slow pozzolanic reaction of fly ash.
The addition of fly ash has no major effect on the freeze-thaw resistance of concrete
if the strength and air content are kept constant (FHWA Materials Group, 1999).
However, in many cases fly ash will increase the long-term strength and decrease
permeability, thereby improving overall durability. The use of fly ash in air-entrained
concrete will typically require an increase in the amount of the air-entraining
admixture to keep constant air. Air-entraining admixture dosage rates depend on
carbon content, loss of ignition, fineness, and amount of organic material in the fly
ash.
12


2.3 Sustainability and Highways
2.3.1 Overview
Research conducted in 2008 at the University of Washington explained the proposed
standard for quantifying sustainable practices connected with roadway design and its
construction (University of Washington, 2008). Sustainability was defined as having
three major mechanisms: environmental, economic, and social. A sustainable
roadway is defined as one that balanced these three mechanisms and searched for the
best results. This research indicated that, green roads were a straightforward rating
system that would create more sustainable highway system. The University of
Washington demonstrated that to have green roads there are several aspects that need
to be addressed. The first aspect was to use understandable system. Another aspect
was to make an improvement in the public awareness of roadway sustainability. In
addition, sustainable innovations should be encouraged throughout the country.
Sustainability has become an important topic in engineering and the construction
industry, of which highway work is a substantial part. Green roadways can provide a
common metric for considering sustainability in highway design and construction.
Fundamentally, such a metric will assist engineers in constructing more sustainable
highway systems.
The Assistant Secretary of Energy Efficiency and Renewable Energy of the U.S.
Department of Energy, Climate Protection Division, Office of Air and Radiation, and
the U.S. Environmental Protection Agency analyzed the historic trends for energy
13


efficiency in U.S. cement industry in 1999. In addition, this group analyzed the cost-
effective energy and carbon dioxide savings that could possibly be achieved in the
future. The focus of this research was detailed analysis of energy use and carbon
dioxide emissions. In addition, this research analyzed the specific energy efficiency
technologies and measures to decrease energy use and carbon dioxide emissions.
Furthermore, the energy efficiency and carbon dioxide emissions reduction potential
for cement production in the U.S. was determined. This study group determined that
cement production has changed very little in past years; however, the composition of
production has changed significantly. As highway demand significantly increased
over the years, the production of blended cement in the U.S. increased significantly.
This demonstrated that blended cement manufacturing could be the key to a cost-
effective strategy for energy efficiency improvement and carbon dioxide emission
reductions in the U.S. cement and highway industry.
The University of Colorado Denver evaluated the sustainability of High Performance
Green Concrete (HPGC) that incorporated fly ash and recycled aggregate into
concrete mixture designs (Reiner, 2007). Reiner evaluated the structural strength and
durability, flow analysis, environmental impact analysis, and economical effects of
utilizing HPGC. Reiner found that the average compressive strength of mixtures with
recycled aggregate (RA) compared to virgin coarse aggregate mixtures, would have
the 30%FA 30%FA/50%RA and 40%FA 40%FA/50%RA were slightly outside
of the 95% confidence level (above the 90% confidence level) at 28-days curing. This
14


means that compressive strength is almost equal. However, the 7-day average
compressive strengths for 40%FA and 40%/50%RA did not differ too much (within
the 95% confidence level), indicating that strength increases at later day testing
(Reiner, 2007). In addition, Reiner determined that the average cost of 1-tons of
concrete debris disposal at a recycling facility is $5.95 and the average cost of 1-ton
of concrete debris disposal at a landfill is $15.28. Based on this data, the concrete
debris that is submitted to a recycling facility is economically beneficial.
2.3.2 Recycling in Colorado
In 2007, CDOT began using recycled concrete on new projects. In addition, CDOT
began sending their concrete from demolitions to recycling facilities (CDOT, 2007).
Concrete is recycled by concrete crushing plants to produce road base, backfill,
aggregate, and other materials. Additional applications of recycled concrete consist of
retaining walls, erosion, off-site mud-tracking control, and flood control projects. Old
concrete pavements can be included into new pavement sections through the use of
construction techniques such as rubblization and crack/break and seat. The use of
these methods help to reduce the amount of old concrete pavements being landfilled
(CDOT, 2007).
Recycled concrete aggregate can be used as coarse aggregate in portland cement
concrete for:
Highway pavements
15


Urban roadway pavements
Sidewalks
Driveways
Temporary pavement interchange ramps and shoulders
Concrete barriers
Curbs and gutters
Concrete is one of the largest construction material quantities processed on CDOT
highway projects. Recycling 100% of this material would drastically increase the
quantity percentages of materials recycled on CDOT projects. This amount would
vary year-to-year depending on the number and size of construction projects.
However, 35,000 to 200,000 tons (38570 to 220400 metric tons) would be recycled
compared to the 1,000 tons (1,102 metric tons) currently recycled (CDOT, 2007).
This difference could have a significant impact on the aggregate and concrete
industries in the State of Colorado.
16


Chapter 3
Problem Statement
Governments throughout the world have been pressured by societies to discuss
environmental issues and global sustainability. Global warming is one of the most
controversial debates. The CDOT provides major roadway infrastructures for
highways in Colorado, which have segments that contain concrete pavement.
Concrete pavements provide higher strength and are more durable in high volume
traffic areas. CDOT not only maintains the existing concrete pavements as well as
other structures such as concrete barriers, bridge decks, and many other concrete
structures, but also constructs new structures providing access to some newly
developed urban areas. This thesis examines the sustainable nature of CDOT
concrete pavements based on the material design. Specifically, the CDOT structural
concrete Class P mixture is evaluated.
Concrete is the leading material used in Colorado highways infrastructure. Each year,
approximately one ton of concrete is produced for each human on the planet,
generating CO2 (carbon dioxide) emission that contributes to the greenhouse effect
(Mehta, 2001). Concrete and cement producers are working with scientist to minimize
this negative environmental impact. Environmental issues, mostly greenhouse gas
mitigation, will have an economic impact on the cement industry. Today, there are
economically acceptable alternatives for manufacturing an environmentally friendly
Portland cement, e.g. sustainable materials and alternative fuels.
17


The possibility of making a profit with CO2 emission is also a parameter that may
impact the competitiveness of the cement industry. At the turn of the 21st century,
worldwide, cement production accounted for more than 1.6 billion tons of CO2
released as emissions, approximately 7% of total CO2 emissions from all human
activities (Mehta, 2001).
Typically, CO2 emissions mirror energy consumption; however, the production of
cement involves the release of additional CO2 during pyroprocessing, or the
calcinations process (conversion of calcium carbonate to calcium oxide), which
results in approximately twice the CO2 that would be produced from energy
consumption alone (CEMBUREAU, 1998).
The materials used in Colorado pavements, particularly concrete, impact the
environment and sustainable design of the Colorado infrastructure design and
development.
The purpose of this thesis is to analyze the structural performance and economic
impact a 20% increase cement replacement with fly ash for the CDOT Class P
concrete would have. In addition, this thesis will develop a more sustainable concrete
mixture to reduce CO2 emission. Fly ash plays a major role in this thesis. This
research evaluated the CDOT Class P concrete mixture design to minimize
economical and environmental costs. A mixture containing 50% Class F fly ash was
used for Class P modified concrete mixture. By increasing the fly ash volume in the
mixture, the material cost for the CDOT Class P concrete was decreased.
18


Chapter 4
Experimental Procedures and Research Program
4.1 General
This experimental study was performed to evaluate whether a modified concrete
mixture was able to replace the current CDOT Class P concrete mixture. Most
notably, an increase in the percentage of cement replacement with fly ash (30% to
50%) was examined. The fresh and hardened concrete properties of the current Class
P mixture design and the modified Class P design were compared in order to
determine whether the modified mixture exhibited equal or superior results. In
addition to the experimental evaluation, a cost comparison was made between the
current and modified Class P designs. To aid in the cost comparison, CDOT
construction records were analyzed and the total amount of Class P concrete used
over the previous four years was reviewed. Furthermore, this thesis details the
quantity of cement that could have been reduced during this four year period had the
modified Class P mixture been used.
4.2 Scope of Work
The scope of the experiment is to examine the fresh and hardened concrete properties
of the CDOT Class P and modified Class P concrete mixtures. The control mixture
(current Class P mixture) followed the current CDOT specifications, which consisted
19


of 70% portland cement and 30% Class F fly ash. The modified Class P mixture
consisted of 50% portland cement and 50% Class F fly ash. Fresh concrete properties
including slump, air content, unit weight, and temperature were examined for both
mixtures. In addition, the hardened concrete properties were examined in this study.
Hardened concrete property testing included compressive strength, flexure strength
(Modulus of Rupture), and permeability. The compressive strength of the concrete
mixtures were determined at 3, 7, 14, 28, and 56 days of age. The flexure strength test
was determined at 28 day of age. The permeability of the mixtures was performed at
28 day of age.
4,3 Specifications from CDOT Class P concrete and Modified Concrete
In accordance with the CDOT Structural Concrete Standard Specifications, the
control mixture (Mixture 1) was designed, batched, and tested. The prescriptive
specifications for Class P concrete are provided in Table 1 and discussed thereafter.
Table 1: Concrete Requirements (CDOT, 2005)
Concrete Class Required Field Compressive Strength Cement Content: Minimum or Range Air Content: % Range (Total) Water Cement Ratio: Maximum or Range
P 4200 psi (428 kg/m2) at 28 days 660 lbs/yd3 390 (kg/m3) 4-8 0.44
20


Additional requirements for Class P concrete include (CDOT, 2005):
a) Concrete must contain a minimum of 55 percent AASHTO M 43 size No. 357
or No. 467 coarse aggregate by weight of aggregate. If all transverse joints
are doweled, then Class P concrete may contain a minimum of 55 percent
AASHTO M 43 sizes No. 57, No. 67, No. 357, or No. 467 coarse aggregate.
b) Laboratory experimental mix for Class P concrete must generate an average
28-day flexural strength of at least 650 psi (66 kg/m2). Class P concrete must
contain 70 percent to 90 percent portland cement and minimum 10 percent to
a maximum of 20 percent Class C or minimum 10 percent to a maximum of
30 percent Class F fly ash in the total weight of cementitious materials.
c) If acceptance is based on flexural strength, the total weight of cement plus fly
ash shall not be less than 520 lbs/yd3 (307 kg/m3).
d) Portland cement shall follow ASTM C 150 Type II requirements.
4.4 Materials
The primary materials used in this experimental study include ASTM C 150 Type II
Portland cement, Class F fly ash, fine aggregate (sand), and coarse aggregate (rock).
Material specifications for these materials are shown in Appendix A.
21


4.4.1 Portland Cement
ASTM C 150 describes portland cement as a hydraulic cement formed by pulverizing
clinkers consisting of hydraulic calcium silicates, typically containing one or more
forms of calcium sulfate as an inter ground addition. Clinker has a diameter of 0.2-1.0
inch of a sintered material that is formed when a raw mixture of predetermined
composition is heated to high temperature (ASTM C 150, 2007). In addition, the
maximum percent of equivalent alkalis (Na20 + 0.658 K2O) shall not exceed 0.90
percent. Where Type II portland cement is required, blended hydraulic cement
conforming to ASTM C 595 Type IP or Type IP (MS) may be used, except that the
blended cement shall consist of no less than 70 percent portland cement. The Type II
portland cement utilized in this study conforms to the ASTM C 150 requirements.
4.4.2 Fine Aggregate
Fine aggregate is described as material that passes a No. 4 sieve and will, for the
most part, be retained on a No. 200 sieve. Fine aggregate with a rounded shape
provides increased workability and a more economical mixture. The primary function
of the fine aggregate is to fill voids in the coarse aggregate and to act as a workability
agent. Section 703.01 of CDOT Structural Concrete Specifications states that fine
aggregate used for Class P concrete shall conform to the requirements of AASHTO
M 6. Several additional criteria is listed in the CDOT specification section (CDOT,
2005):
22


a) The amount of material finer than 75 pm (No. 200) sieve shall not exceed
three percent by dry weight of fine aggregate, when tested in accordance with
AASHTO T 11 or Colorado Procedure 31, Method D, unless otherwise
specified.
b) The minimum sand equivalent, as tested in accordance with AASHTO T 176
shall be 80 unless otherwise specified.
c) The fineness modulus, as determined by AASHTO T 27, shall not be less than
2.50 or greater than 3.50 unless otherwise approved.
Sieve analysis data used for this research is provided in Appendix A.
4.4.3 Coarse Aggregate
Typically, aggregates are inert granular materials such as gravel, or crushed stone.
CDOT specifications indicate that coarse aggregate for concrete shall conform to the
requirements of AASHTO M 80, except that the percentage of wear shall not exceed
45 when tested in accordance with AASHTO T 96. Coarse aggregate shall conform to
the grading in Table 2. Sizes 357 and 467 shall each be furnished in two separate
sizes and combined in the plant in the proportions necessary to conform to the
grading requirements. Compliance with grading requirements will be based on the
combination and not on each individual stockpile (CDOT Specifications, 2005).
23


Table 2: Grading Requirements for Coarse Aggregate (ASTM C 33, 2003)
Size Number Nominal size, sieves with square opening 100 mm 90 mm 75 mm 63 mm 50 mm 37.5 mm
4 in 3 Vz in 3 in 2 Vz in 2 in 1 Vz in
1 90 to 37.5 mm 3 Vz to 1 Vzin 100 90 to 100 - 25 to 60 - Oto 15
2 63 to 37.5 mm 2 Vz to 1 Vz in - - 100 90 to 100 - Oto 15
3 50 to 25 mm 2 to 1 in - - - 100 35 to 70 35 to 70
357 50 to 4.75 mm 2 in to No. 4 - - - 100 90 to 100 -
4 37.5 to 19 mm 1 Vz to % in - - - - 95 to 100 90 to 100
467 37.5 to 4.75 mm 1 Vz in to No. 4 - - - - 100 95 to 100
5 25 to 12.5 mm 1 to Vz in - - - - 100 100
56 25 to 9.5 mm 1 to % in - - - - - 100
57 25 to 4.75 mm 1 in to No. 4 - - - - - 100
6 19 to 9.5 mm % to V% in - - - - - -
67 19 to 4.75 mm % in to No. 4 - - - - - -
7 12.5 to 4.75 mm Vz in to No 4 - - - - - -
8 9.5 to 2.36 mm Vt in to No. 8 - - - - - -
Size Number Nominal size, sieves with square opening 25 mm 19 mm 12.5 mm 9.5 mm 4.75 mm 2.36 mm 1.18 mm
lin % in Vz in V% in (No.4) (No. 8) (No. 16)
1 90 to 37.5 mm 3 Vz to 1 Vzin - 0 to 5 - - - - -
2 63 to 37.5 mm 2 Vz to 1 Vz in - 0 to 5 - - - - -
3 50 to 25 mm 2 to 1 in Oto 15 - 0 to 5 - - - -
357 50 to 4.75 mm 2 in to No. 4 35 to 70 - 10 to 30 - 0 to 5 - -
4 37.5 to 19 mm 1 Vz to % in 20 to 55 Oto 15 - 0 to 5 - - -
467 37.5 to 4.75 mm 1 Vz in to No. 4 - 35 to 70 - 10 to 30 0 to 5 - -
5 25 to 12.5 mm 1 to Vz in 90 to 100 20 to 55 Oto 10 0 to 5 - - -
56 25 to 9.5 mm 1 to Vs in 90 to 100 40 to 85 10 to 40 Oto 15 0 to 5 - -
57 25 to 4.75 mm 1 in to No. 4 95 to 100 - 25 to 60 - Oto 10 0 to 5 -
6 19 to 9.5 mm % to V* in 100 90 to 100 20 to 55 Oto 15 0 to 5 - -
67 19 to 4.75 mm % in to No. 4 100 90 to 100 - 25 to 55 Oto 10 0 to 5 -
7 12.5 to 4.75 mm Vz in to No 4 - 100 90 to 100 40 to 70 Oto 15 0 to 5 -
8 9.5 to 2.36 mm V% in to No. 8 - - 100 85 to 100 0 to 30 Oto 10 0 to 5
24


Particle shape and surface texture influence the properties of freshly mixed concrete.
Larger size aggregate and improved grading decrease the void content of the concrete
mixture. The CDOT specification for Class P concretes requires the use of No. 67
coarse aggregate, following section 703.02. A coarse aggregate size 67 is used as
pavement bed, and it was the only time of aggregate available in the laboratory. It is
crushed, washed and screened to a size less then 3/4" (19mm) to #4 with no fines
aggregate. There is an optimum size for the coarse aggregate that will yield the
greatest compressive strength per unit mass of cement. A smaller size aggregate will
result in a higher compressive strength concrete. Larger aggregates increase tensile
strength as they can bridge the stress across cracks. Since aggregate size 67 is not a
large size aggregate that would increase tensile strength, it is a conservative choice
for pavement design. A coarse aggregate size 67 was used for both mixtures.
4.4,4 Fly Ash
Fly ash was the major variable for this study. CDOT specifications indicate that fly
ash for concrete shall conform to the requirements of ASTM C 618, Class F. In
CDOT standard specifications, it is indicated that for Class P concrete design, 20% to
30% Class F fly ash should be used. For chemical requirements of fly ash, see ASTM
C 618 in Appendix A.
25


4.5 Experimental Procedures
4.5.1 Mixing and Batching
This research included two mixture designs. The fresh and hardened concrete
properties of both mixtures must meet the requirements for Class P concrete.
Specifically, the 28-day compressive and flexural strength of the concrete were of
importance. The mixture proportions for the Class P and Class P Modified mixtures
are listed in Table 3.
Table 3: Mixture Design
Mixture CDOT Class P CDOT Class P Modified Class P Modified Class P
Material Weight (lb/cy) Weight (kg/m3) Weight (lb/cy) Weight (kg/m3)
Cement 462 273 330 195
Fly Ash Class F 198 117 330 195
Coarse Aggregate 1766 1042 1766 1042
Fine Aggregate 1064 628 1027 606
Water 264 156 264 156
Air 0.065 0.065 0.065 0.065
The w/cm for both mixtures was set constant at 0.40. This w/cm meets the CDOT
requirement, which states a maximum w/cm of 0.44. In addition, the Class P concrete
should contain a minimum of 55 percent AASHTO M 43 sizes No. 57, No. 67, No.
357, or No coarse aggregate by weight of total aggregate. In this study, an AASHTO
M43 size No 67 size aggregate was used as the coarse aggregate.
The specific gravity of each material is shown in a table below.
26


Table 4: Specific Gravity
Material Specific Gravity
Cement 3.15
Fly Ash Class F 2.37
Coarse Aggregate 2.61
Fine Aggregate 2.63
Water 1.00
The mixture proportion calculations for both concrete mixtures are shown in
Appendix A. The volumes of the materials used are shown in Table 5.
Table 5: Batch Volumes per Cubic Foot (cubic meters)
Mix CDOT Class P CDOT Class P Modified Class P Modified Class P
Material Weight (cu ft) Weight (m3) Weight (cu ft) Weight (m3)
Cement 2.35 0.066 1.68 0.047
Fly Ash Class F 1.34 0.038 2.23 0.062
Coarse Aggregate 10.84 0.304 10.84 0.304
Fine Aggregate 6.48 0.181 6.26 0.175
Water 4.23 0.118 4.23 0.118
Air 1.76 0.049 1.76 0.049
Table 6 shows that both mixtures meet CDOT criteria with at least 55%
minimum required aggregate. In this study, both mixtures exceed this requirement.
Table 6: Aggregate Volume Based on Aggregate Weight
Mix CDOT Class P Modified Class P
Aggregate Volume 64.17% 63.35%
27


The CDOT specification for Class P concrete states that the mixture shall
contain 70 to 90 percent portland cement. The 10 30% remaining cementitious
materials is fly ash. In this study, 70 percent and 50 percent portland cement was
used for the standard Class P mixture and the modified Class P respectively. An
increase in cement replacement with fly ash, up to 50%, was incorporated into the
modified mixture in an effort to produce a more sustainable design.
Currently, the CDOT Structural Concrete Specification for Class P concrete allows a
minimum of 10 percent to a maximum of 30 percent Class F fly ash in the total
weight of cementitious materials. A cement replacement of 30 percent with Class F
fly ash was used during this study for the standard Class P mixture.
4.5.2 Fresh and Hardened Concrete Tests
In order to determine whether each mixture met or exceeded the CDOT Structural
Concrete Specifications, fresh and hardened concrete properties were performed.
Table 7 provides a list of fresh concrete tests performed during this study. ASTM
(American Society for Testing and Materials) testing procedures were followed for
each test.
28


Table 7: Fresh Concrete Tests
Test Standard Time of testing
Slump ASTM C 143 AASHTOT 119 During batching
Air content (Pressure Method) ASTM C 231 AASHTOT 152 During batching
Unit Weight ASTM C 138 AASHTOT 121 During batching
Temperature ASTM C 1064 AASHTO T 309 During batching
The compressive strength, flexural strength (Modulus of Rupture), and permeability
were measured for each mixture. These tests and the time of testing for each is
included in Table 8.
Table 8: Hardened Concrete Tests
Test Standard Time of Testing
Compressive Strength ASTM C 39 AASHTO T 22 3, 7, 14, 28, 56 days
Flexure Strength ASTM C 78 28 day
Permeability ASTM C 1202 28 day
Compressive strength test requires several days of testing in order to determine
concretes strength increase over a period of time. Testing of the concrete
compressive strength at 3, 7, 14, 28, and 56 days of age allows for the determination
of rate of strength gain at early and late ages. It was expected in this study that the
29


Class P Modified mixture would have less strength at early ages; however, would
gain greater strength at later ages (28 and 56 days of age) due to the increased fly ash
content. At batching, sixteen 4in. x 8 in. cylinders and two 3in. x 4in. x 16in.
beams for each of the mixtures. The beams were batch to test flexure strength at 28-
day, because of the CDOT requirements. The permeability test was performed at 28-
day, because CDOT requires. Figure 3 shows the compressive strength cylinders and
flexural strength beams used for the standard Class P mixture batched for this study.
4.5.3 Curing
The initial curing period is defined as the period between placing the concrete and
application of final curing. Curing has a major influence on the properties of hardened
concrete. Adequate curing will increase durability and strength. When the samples
were prepared, they were placed in a curing room with a temperature that remained
constant at 733F (232C). In the curing room, the samples were submerged in
water meeting these temperature requirements until time of testing. Figure 4 shows
the curing room and tanks used in this research.
30


Figure 3: Compressive Strength Cylinders and Flexural Strength Beams
31


Chapter 5
Experimental Test Results
5.1 Concept
Concrete performance is very important for the design. The growing demand for
more sustainable infrastructure design requires a variety of mixtures of concrete for
the various uses. To obtain desired concrete mixture design several tests needs to be
performed. Those tests would determine its usage. When concrete is fresh, four main
tests were performed: slump, air entrainment, unit weight, and temperature. In
addition, hardened concrete tests were performed from 3 to 56 days of age to
determine whether the mixtures met the CDOT Structural Concrete Specifications for
Class P concrete. Specifically, compressive strength, flexural strength, and
permeability tests were performed.
5.2 Slump
5.2.1 Slump Concept
Slump is described as a measurement of uniformity of freshly mixed concrete, equal
to the immediate subsidence of a specimen molded with a standards slump cone
(PCA, 2003). A Slump test, ASTM C 143 (ASSHTO T 119), is usually standard
technique used to measure the consistency and workability of concrete. See Figure 5.
32


Figure 5: Slump Measurements
The purpose of the concrete slump test is to measure workability, which provides a
range on how easy is it to compact and handle the concrete, as well as the suitablility
for job conditions. Workability is frequently considered as a measure of the work
needed to compact the wet concrete, but it is also used to measure the effortlessness
with which concrete can be placed. Consistency is very important. Consistency is the
capability of freshly mixed concrete to flow. Plasticity determines concretes ability
to be molded. Increasing or decreasing the w/cm, water, or admixtures alters the
slump workability of the concrete.
5.2.2 Slump Test Results
The slump test was performed on the CDOT Class P and modified Class P concrete
mixtures. The slump results are presented in Figure 6.
33


CDOT Class P Modified Class P
Mixture Identification
Figure 6: Class P and Modified Class P Mixture Slump Measurements
The average slump for CDOT is required from 3 to 6 in (7.62 to 15.2cm). The
experimental mixtures slump was 6 in (15.2 cm) for CDOT Class P and 6.5 (16.5
cm) for Modified Class P mixture. These values are indicative of a more fluid
concrete. This test shows that in both mixtures of concrete are workable and easy to
place. A difference of 0.5 inches (1.3 cm) was measured between the Class P and
modified Class P mixtures, indicating there is negligible difference between the two
mixtures; therefore, the modified Class P mixture has adequate slump.
34


5.3 Air Content and Unit Weight
5.3.1 Air Content and Unit Weight Concept
The Air Pressure Meter (ASTM C 231) was used to determine the air content of the
two mixtures produced in this study. Figure 7 shows a typical pressure meter device.
The pressure test method covers the determination of air content of freshly mixed
concrete from observation of the change in volume of concrete with a change in
pressure. Entrained air is essential to the long-term durability of concrete pavements
that are subject to freezing and thawing. Air content is a commonly specified
parameter in paving specifications. This test device is easy to use, and has worked
very well for years as a quality control tool. The fresh concrete is fully consolidated
in an airtight container, and pressure from a fixed-volume cell is applied to the
Figure 7: Air Pressure Meter Device
35


sample in the container. Air in the sample is compressed including the air in the
pores of aggregates, and the decrease in pressure in the cell is directly connected to
the volume of air in the sample. The air content of the sample is thus read directly
from the gauge of a calibrated meter. Pressure meters are widely used because the
mixture proportions and specific gravities of concrete ingredients need to be known.
Also, a test can be conducted in less time than is required for other methods (PCA,
2003). The unit weight (density) of concrete varies, depending on the amount and
density of the aggregate, the amount of air that is entrapped, and the water and
cementitious contents, which in turn are influenced by the maximum size of the
aggregate. The unit weight measurement will provide an indication of air content
given that the relative densities of the ingredients are known. To perform this test,
fresh concrete was placed in a container of known volume and weighed on a scale.
See Figure 8. It was important to not overfill the container and take off any excess,
because this can push the aggregates down in the sample, squeezing out the mortar,
and result in an inaccurate measurement.
36


Figure 8: Fresh concrete measuring in a container of known volume to
determine unit weight (PCA, 2003)
5.3.2 Air Content and Unit Weight Results
The unit weight was determined by first weighing a concrete right away before
conducting the air content test. The air content and unit weight results are presented
in Table 9 and Figure 9.
From the results in Table 9, the difference in unit weight can be due to the change in
air content. Higher air contents provide lower calculated unit weights. The measured
unit weights were 144.4 pcf (85 kg/m3) for CDOT Class P and 146.0pcf (86 kg/m3)
for modified Class P mixture. Air content was determined to be 4.5% for CDOT
Class P and 3.6 % for modified Class P mix. In addition, the modified Class P had a
higher unit weight because of the higher fly ash content due to the difference in
specific gravity between fly ash and cement.
37


Table 9: Air Contents and Unit Weight Results
Mixture CDOT Class P Modified Class P
Air Entrainment 4.5% 3.6%
Unit Weight 144.4 pcf (85 kg/m3) 146.0 pcf (86 kg/m3)
Figure 9: Unit Weight and Air Content Measurements
CDOT requires air content within the range of 4% to 8% by volume for Class P
concrete. In the laboratory experiments air content value was within this range for
CDOT Class P mix but modified Class P mix had little bit lower air content. In
comparing the two mixtures, there is no significant difference in the air content as
well as unit weight. With a slight adjustment in the air-entraining admixture, the
38


modified Class P mixture would meet the CDOT required 4 8% air content
specification.
5.4 Fresh Concrete Temperature Test
Concrete temperature is one of the most important factors influencing the quality,
time of set and strength of concrete. Without control of concrete temperature,
predicting the concretes performance is very difficult, if not impossible. Concrete
with a high initial temperature will have higher than normal early strength and lower
than normal ultimate strength (Snell, 2006). In addition, the overall quality of the
concrete will be lowered. Conversely, concrete placed and cured at low temperatures
less than 50F (10C) the optimum concrete temperature should be in the range of 50
to 60F (10 to 16C) (Mindess et. al., 2003)) will develop strength at a slower rate, but
ultimately will have higher strength and be of a higher quality. The temperatures of
concrete and of the air are used to determine the type of curing and protection needed,
as well as the length of curing time. Controlling concrete temperature and limiting
placement to certain air temperatures will reduce or eliminate many problems,
including those associated with strength development and durability.
Temperature of concrete at the time of placement is important to control and to avoid
many possible difficulties. In hot climates, it is important to measure temperature of
the fresh concrete to ensure it is not too hot, which may cause a rapid reduction in
39


workability. The ambient and concrete temperatures for the mixtures produced in this
study are listed in Table 10.
Table 10: Temperature Measurement Results
Mixture CDOT Class P Modified Class P
Room Temperature 70F (21C) 69F (20C)
Concrete Temperature 65F (18C) 66F (19C)
The ambient temperature is different for both mixtures. This is a result of the
mixtures being batched on different days. However, neither the ambient nor the
concrete temperatures for the two mixtures are significantly different.
5.5 Compressive Strength Test
5.5.1 Compressive Strength Purpose
Compressive strength is defined as the measured maximum axial load a concrete
specimen can be subjected to prior to failure. Compressive strength of the Class P and
modified Class P mixtures was determined at 3, 7, 14, 28 and 56 days of age. The
relationship between the 28-day strength and other test age strengths are very
important. Typically, seven-day strengths are estimated to be approximately 66% -
75% of the 28-day strengths. Depending on the cementitious materials utilized in the
mixtures, compressive strength gain beyond 28 days of age can increase by as much
as 10% to 15%.
40


The compressive strength that a concrete achieves fc results from the water -
cement ratio, the extent to which hydration has progressed, the curing and
environmental conditions, and the age of concrete (PCA, 2003). In addition, the
cementitious content, supplementary cementitious materials content, and air content
will influence compressive strength.
Compressive strength was determined on 4in. (10.16 cm) x 8in. (20.32cm) cylindrical
specimens fabricated during the batching process. The strength at each of the days
tested was determined by placing three cylinders, each at a time, in the compression
machine and testing until failure. Figure 10 shows the concrete compression machine
apparatus and testing of a cylinder. The compressive strength was calculated by
dividing the failure load by the cross-sectional area resisting the load and reporting
the measurements in pounds per square inch (psi). See Equation 2.
Load
CompressiveStrenght = ------;--------- ,
CrossSectionalArea Equation 2
The CDOT Structural Concrete Specifications requires a minimum of 4200psi (428
kg/m2) at 28 days of age for Class P concrete.
41


Figure 10: Compressive Strength Assembly
5.5.2 Compressive Strength Test Results
Three cylinders were tested for each the Class P and Class P Modified mixtures. The
maximum loads required prior to failure are reported in Table 11.
42


Table ll:Compressive Strength Maximum Loads in lbs (kg)
CDOT Class P Mix
Day Test Schedule Cylinder 1 Cylinder 2 Cylinder 3
lbs kg lbs kg lbs kg
Day 3 2/2/2009 35,755 16,233 38,540 17,497 40,025 18,171
Day 7 2/6/2009 49,895 22,652 49,575 22,507 49,435 22,443
Day 14 2/13/2009 53,005 24,064 47,745 21,676 43,995 19,974
Day 28 2/27/2009 63,470 28,815 62,240 28,257 63,975 29,045
Day 56 3/27/2009 73,150 33,210 78,710 35,734 - -
Modified Class P Mix
Day Test Schedule Cylinder 1 Cylinder 2 Cylinder 3
lbs kg lbs kg lbs kg
Day 3 2/9/2009 23,875 10,839 23,975 10,885 23,525 10,680
Day 7 2/13/2009 41,920 19,032 43,960 19,958 44,380 20,149
Day 14 2/20/2009 51,895 23,560 49,400 22,428 53,275 24,187
Day 28 3/6/2009 63,665 28,904 64,695 29,372 65,535 29,753
Day 56 4/3/2009 74,230 33,700 78,950 35,843 - -
Test results shown above do not have some values for cylinder 3 for both mixtures at
56-day. It is because there were no cylinders left to test.
Figure 11 shows compressive strength test in the machine after the load reach peak
value and the specimens have cracked.
43


Table 12 and Figure 12 shows average compressive strength values for each mixture
on their respective days of age.
At day 14, CDOT Class P value of cylinder 3 was significantly lower; therefore this
value was subtracted from the averaging in this table. This may be caused by poor
consolidation of specimen. Consolidation is the process of inducing a closer
arrangement of the solid particles in freshly mixed concrete or mortar during
placement by the reduction of voids, usually by vibration, centrifugation (spinning),
rodding, spading, tamping, or some combination of these actions. It is possible that
44


this particular cylinder was poorly mixed and this caused much lower values than
other cylinders.
Table 12: Compressive Strength Values in psi (kg/m2)
Day CDOT Class P Modified Class P
psi kg/m2 psi kg/m2
Day 3 3,049 1,799 1,903 1,123
Day 7 3,971 2,343 3,474 2,050
Day 14 4,030 2,378 4,122 2,432
Day 28 5,058 2,984 5,171 3,051
Day 56 6,074 3,584 6,127 3,615
Figure 12: Compressive Strength (psi) vs. Time (days)
45


Figure 12 indicates that the 3-day strength is significantly different between the Class
P and Class P Modified concrete mixtures. This is because of the higher fly ash
content in modified CDOT Class P concrete mixture. Another consequence of
decreasing cement content in the mixture is slower hydration and the pozzolanic
reaction. However, the compressive strengths of the CDOT Class P and modified
Class P mixtures are more comparable by 7 days of age, 3,971 psi and 3,474 psi
respectively. A negligible difference in compressive strength was found at 14 days
of age. The modified Class P mixtures surpassed the Class P mixture by 28 days of
age. Furthermore, the Class P Modified mixture has a slightly higher compressive
strength at 56 days of age when compared to the Class P Standard mixture. Figure 13
shows the percentage of each mixtures 56-day compressive strength at 3,7,14, 28 and
56 days for each mixture.
£
Vi
u
a

U
a>
a u
O
Cl
a
HH
a
v
u
s-
a>
Oh
100% -I
90% -
80% -
70% -
60% -
50% -
40% -
30% -
20% -
10% -
0% -
Day 3
Day 7
II Day 14
0 Day 28
D Day 56
CDOT Class P Modified Class P
Figure 13: Rate of Compressive Strength Gain
46


Figure 13 indicates that the modified Class P mixture develops its ultimate strength
more grater than CDOT Class P Standard mixture. Fly ash typically reduces early
age compressive strength; however, later age strength gain is typically higher for fly
ash concrete mixtures. CDOT specifications requires that the compressive strength at
28-day should be 4,200 psi (428 kg/m2). However, both mixtures meet the required
CDOT specifications. Modified Class P mixture exceeds the current Class P
specification with a compressive strength of 5,171 psi (527 kg/m2) strength at 28-day.
5.6 Flexure Strength Test
5.6.1 Flexure Test Scope
The Flexure strength is expressed as Modulus of Rupture (MOR) and is determined
by standard test methods ASTM C 78 (third-point loading). See Figure 14. The MOR
is about 10 to 20 % of the compressive strength depending on the type, size and
volume of coarse aggregate used in the mixture. CDOT standard specifications
require flexure strength of 650psi (66 kg/m2) at 28 days of age. Figure 15 shows a
beam being tested during this study.
47


Figure 15: Flexure Test Assembly
48


5.6.2 Flexure Test Results
Two beam specimens were tested for each mixture. Each beam was fabricated during
batching and measured 3in. (7.62cm) x 4in. (10.16 cm) x 16in. (40.64cm) Equation 3
was used to obtain the MOR values for each mixture.
PL
MOR - Equation 3
Table 13 lists the results from the modulus of rupture tests performed on the Class P
and modified Class P mixtures. Because CDOT requires 650 psi (66 kg/m2) flexural
strength at 28 days of age, the beams tested in this study were tested at 28 days of age
to determine whether they meet the specification.
Table 13: Flexure Strength Test Results in psi (kg/m2 )
Mix CDOT Class P Modil led Class P
psi kg/m2 psi kg/m2
Beam 1 783 86 773 85
Beam 2 977 108 412 45
Average 880 97 773 85
Beam 2 of the modified Class P mixture was significantly different than the other
samples. It was determined that this difference was a result of Beam 2 being poorly
consolidated. See Figure 16. Since the Beam 2 of the modified Class P concrete
mixture was much lower than the other measurements it was eliminated from the
results. CDOT requirements for Class P concrete are 650 psi (66 kg/m2) at 28 days of
age. Experimental test results for both samples exceeded that requirement. Though
49


the modified concrete mixture had lower flexure strength when compared to the Class
P Standard mixture, it still met this requirement. A beam failure is shown in Figure
17.
Because of the low reading observed in Beam 2 of the Class P Modified mixture
testing, it is recommended that a minimum of three beams be tested in future studies.
Figure 17: Flexure Test Failure
50


5.7 Permeability Test
5.7.1 Permeability Test Purpose
Concrete permeability was measured at 28 days of age. The permeability test was
used to measure the concretes ability to resist chloride ion penetration in accordance
with ASTM C 1202 standard. This test was performed when an electrical current
passed through a 2 in. (5.08 cm) thick by 4 in. (10.16 cm) diameter concrete sample
for 6 hours. According to ASTM C 1202, the standard voltage was 60V and was
maintained across the ends of the sample, one of which was immersed in a sodium
chloride and sodium hydroxide solutions. The total charge passed, in Coulombs, was
then compared to standard permeability classifications found in ASTM C 1202. Two
specimens were tested for each mixture at 28 days of age. Figure 18 shows the set
up for the rapid chloride penetrability test.
51


5.7.2 Permeability Test Results
ASTM C 1202 provides permeability classifications based on the number of
Coulombs passed during a six-hour period. Table 14 provides a list of the Coulombs
for each permeability classification. After each of the mixtures was tested at 28 days
of age, the permeability classification was determined for the Class P and Class P
Modified mixtures.
52


Table 14: Chloride Ion Permeability Based on Charge Passed
Coulombs Chloride Ion Permeability Typical of
>4000 High High w/c ratio (>0.60)
4000-2000 Moderate Moderate w/c ratio (0.40-0.50
2000-1000 Low Low w/c ratio (<0.40)
1000-100 Very Low Latex- modified concrete or internally sealed concrete
<100 Negligible Polymer impregnated concrete, Polymer concrete
The permeability reading Coulombs of the modified Class P concrete mixture was
1% higher than the CDOT Class P concrete mixture. Thus, there is a negligible
difference between the two mixtures in regards to permeability. Though permeability
testing is not required per the CDOT Class P specification, this test can provide an
indication of the concrete performance and durability. Table 15 provides the
permeability test data for both mixtures.
Table 15: Permeability Test Results
CDOT Class P Mixture Modified Class P Mixture
Cylinder 1 Cylinder 2 Cylinder 1 Cylinder 2
Voltage Actual 60 60 60 60
Current Actual 56.4 55.5 59.8 64.1
Elapsed Time 6 hrs 6 hrs 6 hrs 6 hrs
Predicted Coulombs 1173 1132 1257 1340
Testing Time 6 hrs 6 hrs 6 hrs 6 hrs
Specimen Diameter 100 mm 100 mm 100 mm 100 mm
Coulombs 1171 1130 1256 1338
Permeability Classification Low Low Low Low
53


5.8 Experimental Test Results
Table 16 provides a summary of the CDOT requirements
Table 16: Experimental Test Results
CDOT Class P Requirements CDOT Class P Modifiec Class P
Minimum of 55 percent AASHTO M 43 sizes No. 67coarse aggregate 64.17% 64.17% 63.35% 63.35%
Slump is required form 3 to 6 in (7.62 to 15.24 cm) 6 in 15.24 cm 6.5 in 16.51 cm
Average 28 day flexural strength of at least 650 psi (66 kg/m2) 880 psi 90 kg/m2 773 psi 85 kg/m2
Average 28 day compressive strength of 4200psi (428 kg/m2) 5,058 psi 516 kg/m2 5,171 psi 570 kg/m2
Class F fly ash used 30% 30% 50% 50%
Air Content: Range 4-8% 4.50% 4.50% 3.60% 3.60%
Water Cement Ratio: Maximum of 0.44 0.4 0.4 0.4 0.4
The results in this table meet CDOT requirements, except air content for the modified
Class P mix, which is lower; however, it could be increased with additional air
entraining admixture. This table also shows that modified Class P concrete mixture
performed as well as CDOT Class P mixture. Looking at the experimental results
CDOT class P could be replaced with more sustainable modified Class P mixture.
54


Chapter 6
Sustainability of Concrete Mixtures in Highway Construction
6.1 Sustainable Highways
Green highway development includes designing highways in a manner that improves
the quality of the nations infrastructure. Such highway development would include
cement usage reductions, and instead of using cement, incorporating more sustainable
admixtures. The Department of Transportation (DOT) chooses a lifecycle energy
reduction standard according to which highway will have a long-term life and
accommodate traffic flows with minimal congestion. Designing a highway in such a
way not only reduces energy cost and maintenance, but also increases the capacity of
the highways and reduces emissions caused by vehicles in congestion.
Concrete pavements offer some inherent features and benefits that are well suited for
sustainability goals and objectives. The long life of concrete pavements not only
provides important economic advantages in terms of life-cycle costs, but also
contributes directly to the systems sustainability in several important ways. A long-
lasting concrete pavement does not require rehabilitation or reconstruction as often as
asphalt pavements, and therefore consumes fewer raw materials in the long-term
(Naik et al, 2004). The long life benefits the environment in other ways as well.
Energy savings are realized, since rehabilitation and reconstruction efforts consume
energy. Additionally overcrowding highways could be reduced drastically with
55


associated energy savings and decrease in automobile pollutants by utilizing long-
lasting concrete pavements. This could be performed because of less construction
zones obstructing traffic flow.
6.2 CO2 Emission
Cement is often considered a key contributor to the release of CO2 into the
atmosphere, and it is an essential input into the production of concrete. The
importance of cement for various construction-related activities such as highways,
tunnels, and dams, have tendency to reflect to general economic activities.
Furthermore, because of the large demand for cement, there is a relatively high costs
associated with transportation of this product, considering the wide geographic
distribution of limestone, the principal raw material used to produce cement. Cement
manufacturing is a key contributor of CO^ emissions due to the significant reliance on
coal and petroleum to fuel the kilns for clinker production.
Cement production is not only a source of combustion-related CC>2 emissions, but it is
also one of the largest sources of industrial process-related emissions in the United
States. Between 1990 and 2001, U.S. process-related emissions increased 24%.
CC>2 emissions from cement manufacture differ depending on the specific type of
cement produced. In the United States, masonry cement accounts for approximately
4-5% of total production, the remainder is portland cement.
56


Table 17 illustrates the total C02 emissions from cement manufacturing in the United
States during the past eight years. The table also illustrates the breakdown between
combustion and process-related emissions. For each ton of cement produced,
approximately 54% of total emissions are process-related and 46% are combustion-
related.
Table 17: Historical Data in Process-related C02 emission from U.S. Cement
Manufacturing (US Environmental protection Agency, 2007) (%)
Year Combustion- related CO 2 Process-related C02 (inch CKD) Total CO 2
1994 30.6 36.1 66.7
1995 31.3 36.8 68.1
1996 31.6 37.1 68.7
1997 32.1 38.3 70.4
1998 32.9 39.2 72.1
1999 36.1 40.0 76.1
2000 36.5 41.2 77.7
2001 35.5 41.4 76.9
2005 40.4 45.9 86.3
2006 41.1 46.6 87.7
2007 39.0 44.5 83.5
6.3 Fly Ash
Research on fly ash has indicated that fly ash reacts with the calcium hydroxide
formed during cement hydration and water to form calcium-silicate-hydrate (C-S-H).
This formation of C-S-H increases the compressive strength at early and late ages.
57


The fine particle size and spherical shape of fly ash provides 7-9% water reduction,
and contributes to higher strengths.
Replacing energy-consuming portland cement with recycled material fly ash offers
two distinct benefits to the environmentit significantly reduces the amount of CO2
released into the atmosphere, and it minimizes the massive landfill disposal. In
addition, the use of fly ash as a partial cement replacement reduces the depletion of
virgin raw materials used in cement production.
Green concrete such as high-volume fly ash concrete provides a level of increased
sustainability to concrete infrastructure. Fly ash is a by-product of coal-burning
power plants, with as much as 75% of fly ash produced landfilled in the past. Today,
the beneficial use of this waste-stream material has become more common such that
most concrete mixtures, particularly CDOT concrete mixtures, include fly ash to
some degree fly ash within them.
Recycled fly ash, when mixed with calcium hydroxide and water, forms a
hydration product, C-S-H. This product is extremely strong and durable.
High-volume fly ash concrete displaces more than 25% of the cement used in
traditional concrete, reducing the amount of emissions needed to make the
concrete mixture.
Fly ash concrete was somewhat difficult to source in the past. Due to a significant
increase in demand, there are more producers and distributors working to steadily
increase the supply of fly ash.
58


The primary objective of this research was to examine a greater cement replacement
with fly ash for the CDOT Class P concrete mixture. Specifically, this study examines
the replacement of 50% cement with fly ash. Furthermore, this thesis examines the
structural performance of a modified Class P and the economic effects of such a
mixture for the Colorado Department of Transportation.
6.4 CO2 Reduction
Carbon dioxide reduction is an important aspect to sustainability. By replacing one
ton of cement, one ton of CO2 emission could be reduced. U.S. Environment
Protection agency provides with average annual emission and fuel consumption of
passenger cars and light trunks. Thus, passenger car release 5.7 tons per year of CO2
and light truck release 8 tons of CO2. Therefore, if the Colorado Department of
Transportations increased their replacement of cement with Class F fly ash to 50%
(from 30% replacement) during the past 4 years, the CDOT could have reduced about
390 passenger cars or 278 light trucks from the highway.
CDOT could have reduced the amount of cement used and increased the reduction in
CO2. CDOT could have used 2,220 fewer tons of cement, which translates into 2,220
fewer tons of CO2 emissions, see table 18 for more details.
59


Table 18: Reduction of CO2 Emission in Past 4 Years using modified Class P
concrete mix.
Year CDOT Class P Concrete Mix with 70% of cement and 30% of fly ash Modified Class P with 50% of cement and 50% of fly ash Reduction in cement Cement saved using 50 % of Fly ash CO2 emission reduction
cu yd m3 cu yd M3 cu yd m3 ton Metric ton ton Metric ton
2008 28,482 21,776 20,297 15,518 8,185 6,258 804 730 804 730
2007 16,622 12,708 11,846 9,057 4,776 3,652 469 426 469 426
2006 25,554 19,537 18,211 13,923 7,343 5,614 721 654 721 654
2005 7,962 6,087 5,674 4,338 2,288 1,749 225 204 225 204
TOTAL 78,620 60,109 56,028 42,836 22,592 17,273 2,220 2,014 2,220 2,014
CDOT could have possibly reduced the CO2 by 2,220 tons (2,014 metric tons), equal
to taking approximately 390 passenger cars or 278 light trucks off the highway.
Emission of carbon dioxide can be reduced by other methods:
Improvement of the energy efficiency of the process of cement
manufacturing.
Shifting to a more energy efficient process (e.g. from (semi) wet to (semi) dry
process).
Replacing high carbon fuels with low carbon fuels.
60


Applying lower clinker/cement ratio (increasing the ratio additives/cement):
blended cements.
Application of alternative cements (blended cements).
Removal of CO2 from the flue gases.
Table 19 shows the important options to improve the energy efficiency of cement
production facilities.
61


Table 19: Energy efficiency improvement options for cement production processes
(Hendriks, 2004)
Technique Description Emission reduction/ energy improvement Economics
Process Control and Management Systems Automated computer control may help to optimise the combustion process and conditions Typically 2.5-5% Economics of advanced processes very' good (pay back time as short as 3 months)
Raw Meal Use of gravity-type Reduction power use No information available
Conversion from Wet to Semi-Dry Process Moisture content of raw material reduced through thermal drying system Estimated at 2 GJ/t clinker. Small increase of powrer consumption No capital information available for this study
Conversion from Wet to Dry Process Complex operation, leaving only the structural parts mtact Estimated at 2.2 GJ/t (increase of power by about 10 kWh/t) High costs (133 US$/t annual capacity), but vary across the world. May be economically feasible
Conversion from dry to multi-stage preheater kiln Four or five stage preheating reduces heat losses, and sometimes reduces pressure drop Depending on original process. In one example reduction from 3.9 to 3.4 GJ/t Estimated at 30-40 US$/t annual capacity
Conversion from dry to precalciner kiln Increase of capacity, and lowering specific fuel consumption Depending on original process. Estimated at 12% (0.44 GJ/t) Estimated at 28 USS/t annual capacity
Conversion from Cooler to Grate Cooler Large capacity and efficient heat recovery. Reduction of 0.1-0.3 GJ/t (increase in power by 3 kWh/t) Probably only attractive when installing a precalciner simultaneously
Efficient Kiln Technology (China) size and shape, insulation and computer control. for the 1990 mix (10- 30%) 230 Yuan/t annual capacity. Pay back time of less than 2 years.
Fluidised bed Kiln Rotary kiln replaced by stationary kiln leading to lower capital costs, wider variety of fuel use and lower energy use Fuel use of 2.9 to 3.35 GJ/t clinker (also lower NOx emissions) Lower investment and maintenance costs expected
Advance Comminution Technologies Non-mechanical milling technologies as ultrasound. Not commercially available m coining decades Expected (theoretical) savings are large No information available due to preliminary stage of development
Mineral Polymers Mineral polymers are made from alumino-silicates leaving calcium oxide as the binding agent. Preliminary estimates suggests 5 to 10 times lower energy' use and emissions No specific cost information was available for this study.
62


Chapter 7
Prescriptive Compared to Performance Specifications
7.1 Prescriptive
Prescriptive is defined as being established by rules and regulations by some
governmental organization or State Department of Transportation (DOT) for
transportation related projects. All of the Departments of Transportation within the
United States have prescriptive specifications for concrete mixtures and use them for
their concrete design. The Colorado Department of Transportation (CDOT) is one of
them. CDOT concrete design uses several prescriptive standard specifications for
concrete design, see Table 20.
Table 20: CDOT Concrete Table (CDOT, 601-1, 2005).
Concrete Class Required Field Compressive Strength (psi) Cement Content: Minimum or Range (lbs/yd3) Air Content: % Range (Total) Water Cement Ratio: Maximum or Range
B 3500 at 28 days 565 5-8 0.50
BZ 4000 at 28 days 610 N/A 0.50
D 4500 at 28 days 615 to 660 00 1 0.44
DT 4500 at 28 days 700 5-8 0.44
E 4200 at 28 days 660 00 1 0.44
H 4500 at 56 days 580 to 640 5-8 0.38 0.42
HT 4500 at 56 days 580 to 640 5-8 0.38 0.42
P 4200 at 28 days 660 i 00 0.44
S35 5000 at 28 days 615 to 720 5-8 0.42
S40 5800 at 28 days 615 to 760 5-8 0.40
S50 7250 at 28 days 615 to 800 5-8 0.38
63


This thesis analyzed CDOT Class P, used for pavements. CDOT also specifies several
other requirements that Class P concrete mixture must meet:
Class P concrete shall contain a minimum of 55 percent AASHTO M 43 sizes
No. 57, No. 67, No. 357, or No. 467 coarse aggregate.
Laboratory trial mix for CDOT Class P concrete must produce an average 28-
day flexural strength of at least 650 psi (66 kg/m2).
CDOT Class P concrete must contain 70 percent to 90 percent portland
cement and minimum 10 percent to a maximum of 30 percent Class F fly ash.
Laboratory trial mixture for CDOT Class P concrete must produce an average
28-day compressive strength of at least 4,200 psi (428 kg/m2).
Slump must be between 3 and 6 in (7.62 and 15.24 cm).
All of those criteria must be met in order meet the requirements of the CDOT
structural concrete standards.
7.2 Performance
Performing tests and determining the results by using a few trial methods define the
performance method. Performance concrete design does not follow the prescriptive
concrete design requirements, but instead is defined by performance criteria
established by the government or specification agency. The focus of this thesis is to
determine if the modified Class P concrete mixture meets the performance criteria
provided under the Class P specification. This will enable CDOT to determine with a
64


performance based specification can be established to provide adequate Class P
concrete that performs equal or better than the current Class P, is more economical,
and sustainable. Several tests were performed in order to determine the adequacy of
the Class P modified mixture. The modified Class P concrete design mixture
consisted of:
50% of Class F fly ash and 50 % of portland cement.
After testing the fresh concrete the following results were obtained:
Slump for modified Class P was 6.5 (16.5 cm).
Air content was 3.6 %.
Testing of hardened concrete revealed these results:
Compressive strength average at 28-day was 5,171 psi (570
kg/m2).
Flexure strength average at 28-day was 773 psi (85 kg/m ).
These test performed in the laboratory met the performance criteria within the current
Prescriptive CDOT Class P mixture design specifications. Therefore, the Prescriptive
CDOT Class P mixture could be replaced with Performance modified Class P
mixture.
Several advantages were discovered by using a Performance Based design:
Same performance criteria (compressive and flexural strength) were met. In
fact, the 28-day compressive strength for the Class P Modified mixture was
65


greater than the current Class P mixture. Furthermore, the permeability of
both mixtures were similar.
Cost analysis indicated that the Prescriptive CDOT Class P concrete was
7.82% more expensive than the Performance modified Class P concrete
mixture.
CDOT could reduce price and reduce 2,220 tons (2,014 metric tons) of CO2
emissions by using Performance mixture.
In conclusion, using a Performance modified Class P concrete mixture is more
advantageous than the current Prescriptive CDOT Class P mixture.
66


Chapter 8
Cost Analysis
Since concrete is a major material in highway infrastructure, its prices have continued
to increase throughout the years. The quantity and cost of CDOT Class P concrete
placed between 2005 and 2008 is presented in Tables 21-25. These costs include:
concrete materials, formwork, equipment, and labor. CDOT does not provide an
itemized list of costs associated with concrete placement.
Table 21: 2005 CDOT concrete Class P usages and pricing
Item Number and Description from CDOT Total Quantity (Cu Yard) Total Cost ($) Average Price ($/ cu yd)
412-00600 Concrete Pavement (6 Inch) 5 1,936.00 60.5
412-00600 Concrete Pavement (6 Inch) 6,299 931,210.92 24.64
412-00800 Concrete Pavement (8 Inch) 931 275,582.00 65.77
412-00801 Concrete Pavement (8 Inch) (Special) 241 93,310.00 86
412-00900 Concrete Pavement (9 Inch) 1,476 350,368.00 59.35
412-00901 Concrete Pavement (9 Inch) (Special) 124 42,570.00 86
412-00950 Concrete Pavement (9-1/2 Inch) 2,823 631,064.00 59
412-01000 Concrete Pavement (10 Inch) 24,772 2,705,608.00 30.34
412-01001 Concrete Pavement (10 Inch) (Special) 95 31,978.00 93.23
412-01015 Concrete Pavement (10 Inch) (Reinforced) 261 60,008.00 63.77
412-01025 Concrete Pavement (10-1/4 Inch) 13,061 1,543,201.36 33.64
412-01150 Concrete Pavement (11-1/2 Inch) 270 53,298.00 63
412-01200 Concrete Pavement (12 Inch) 16,979 1,833,732.00 36
412-01215 Concrete Pavement (12 Inch) (Reinforced) 11 4,693.08 146.66
412-01300 Concrete Pavement (13 Inch) 318 69,520.00 79
412-01350 Concrete Pavement (13-1/2 Inch) 31,084 2,830,693.50 34.15
TOTAL 98,750 11,458,772.86
67


Table 22: 2006 CDOT concrete Class P usages and pricing
Item Number and Description from CDOT Total Quantity (Cu Yard) Total Cost ($) Average Price ($/ cu yd)
412-00400 Concrete Pavement (4 Inch) 5 4,100.00 100
412-00600 Concrete Pavement (6 Inch) 1,761 504,709.35 47.77
412-00800 Concrete Pavement (8 Inch) 2,623 583,983.00 49.47
412-00950 Concrete Pavement (9-1/2 Inch) 3,361 416,647.00 32.71
412-00975 Concrete Pavement (9-3/4 Inch) 190 108,500.00 155
412-01000 Concrete Pavement (10 Inch) 5,707 1,277,440.00 62.18
412-01050 Concrete Pavement (10-1/2 Inch) 1,762 256,803.90 42.52
412-01100 Concrete Pavement (11 Inch) 8,448 1,482,082.05 53.61
412-01150 Concrete Pavement (11-1/2 Inch) 1,590 303,658.00 61
412-01200 Concrete Pavement (12 Inch) 104,036 11,478,155.77 36.78
412-01250 Concrete Pavement (12-1/2 Inch) 62,079 6,568,671.12 36.74
412-01300 Concrete Pavement (13 Inch) 98,717 10,037,673.80 36.72
412-01350 Concrete Pavement (13-1/2 Inch) 3,450 660,100.00 71.75
TOTAL 293,728 33,682,523.99
68


Table 23: 2007 CDOT concrete Class P usages and pricing
Item Number and Description from CDOT Total Quantity (Cu Yard) Total Cost ($) Average Price ($/ cu yd)
412-00600 Concrete Pavement (6 Inch) 425 149,120.50 58.5
412-00715 Concrete Pavement (7 Inch) (Reinforced) 67 63,270.00 185
412-00800 Concrete Pavement (8 Inch) 232 62,760.00 60.11
412-00850 Concrete Pavement (8-1/2 Inch) 2,440 301,369.50 29.16
412-00925 Concrete Pavement (9-1/4 Inch) 121 65,940.00 140
412-01000 Concrete Pavement (10 Inch) 11,418 1,360,525.20 33.1
412-01015 Concrete Pavement (10 Inch) (Reinforced) 346 174,160.00 140
412-01025 Concrete Pavement (10-1/4 Inch) 56,108 6,667,683.60 33.84
412-01050 Concrete Pavement (10-1/2 Inch) 5,692 682,990.00 35
412-01100 Concrete Pavement (11 Inch) 8,715 2,219,600.50 77.82
412-01150 Concrete Pavement (11-1/2 Inch) 9,841 1,640,472.75 53.25
412-01200 Concrete Pavement (12 Inch) 11,844 1,696,104.00 47.73
412-01300 Concrete Pavement (13 Inch) 83,814 9,051,861.00 39
TOTAL 191,062 24,135,857.05
69


Table 24: 2008 CDOT concrete Class P usages and pricing
Item Number and Description from CDOT Total Quantity (Cu Yard) Total Cost ($) Average Price ($/ cu yd)
412-00600 Concrete Pavement (6 Inch) 1,042 362,088.20 57.9
412-00850 Concrete Pavement (8-1/2 Inch) 27,639 3,952,995.00 33.77
412-00900 Concrete Pavement (9 Inch) 49,723 4,816,248.36 24.22
412-00950 Concrete Pavement (9-1/2 Inch) 7,283 938,366.00 34
412-01000 Concrete Pavement (10 Inch) 3,962 660,171.00 46.29
412-01025 Concrete Pavement (10-1/4 Inch) 37,137 5,114,198.35 39.21
412-01050 Concrete Pavement (10-1/2 Inch) 23,680 3,333,534.99 41.06
412-01100 Concrete Pavement (11 Inch) 101,978 10,219,749.31 30.62
412-01125 Concrete Pavement (11-1/4 Inch) 16,818 2,433,111.78 45.21
412-01150 Concrete Pavement (11-1/2 Inch) 1,023 192,060.00 60
412-01200 Concrete Pavement (12 Inch) 20,860 2,380,438.84 38.04
412-01215 Concrete Pavement (12 Inch) (Reinforced) 225 37,180.00 5 55
412-01250 Concrete Pavement (12-1/2 Inch) 36,006 4,676,914.80 45.1
TOTAL 327,376 39,079,876.63
Table 25: CDOT Class P Concrete Average Prices
Year Total Used Average Cost
Cu Yard $ / Cu Yard
2008 327,376 42.3
2007 191,062 71.7
2006 293,728 60.5
2005 98,750 63.8
Since the CDOT costs in Tables 21-25 do not provide individual prices for the
concrete only, Bestway Concrete was contacted and provided prices for CDOT Class
70


P and modified Class P mixture designs. Bestway also provided the costs associated
with each concrete material based on a S/cy basis. These costs are shown in Table 26.
Table 26: CDOT Concrete Costs (Bestway Concrete, 2009)
Mix CDOT Class P Modified Class P
lb/cu yd cost ($/cu yd) lb/cu yd cost ($/cu yd)
Cement 462 32.05 330 22.9
Fly Ash Class F 198 8.05 330 13.41
Coarse Aggregate 1773 11.56 1754 11.44
Fine Aggregate 1108 3.84 1021 3.54
Water 213 0.01 283 0.01
AEA (oz) 1 0.04 1 0.04
HRWR (ml) 137 0.69 98 0.5
Total Cost 56.24 51.84
Based on the cost data provided by Bestway Concrete for raw materials, the CDOT
Class P mixture cost $56.24 per cubic yard and the Class P Modified mixture cost
$51.84 per cubic yard. This indicates that the Class P Modified mixture results in a
cost savings of $4.40 per cubic yard. This difference is illustrated in Figure 19.
71


CDOT Class P Modified Class P
Mixture Identification
Figure 19: Cost Comparison for Raw Materials
The cost comparison of the two mixtures clearly shows that modified Class P
concrete mix is 7.82% cheaper than the CDOT Class P mix. Additionally, Bestway
Concrete provided total prices for both mixtures, which included material, equipment,
and labor, see table 27.
Table 27: Cost Comparison for Laboratory Mixtures Including Equipment and
Labor (Bestway Concrete, 2009)
Mix CDOT Class P Modified Class P
$/ cu yd $/ cu yd
Cost 96.25 91.85
If CDOT utilized a 50% replacement of cement with Class F fly ash instead of the
maximum 30% replacement for the current Class P concrete mixture during the past 4
72


years, CDOT would have experienced a savings of at least $3 million. Table 28
provides a cost savings per year based on the Class P Modified mixture being used
from 2005-2008.
Table 28: CDOT savings with the Modified Class P Mixture
Class P Concrete Mix with70% of cement and 30% of fly ash Modified Class P with 50% of cement and 50% of fly ash Reduction in cost
$ $ S
2008 3,399,949 2,422,952 976,997
2007 2,099,820 1,496,423 603,397
2006 2,930,380 2,088,316 842,064
2005 996,913 710,444 286,469
TOTAL 9,427,062 6,718,135 2,708,927
Based on the cost analysis provided in this chapter, the use of the modified Class P
concrete mixture would provide a cost savings for the CDOT. Furthermore, the
increased use fly ash and reduction in cement provides for a more sustainable design.
73


Chapter 9
Conclusions and Recommendations
9.1 Comparison of Study Findings to CDOT Specifications
The performance of the Class P and Class P Modified concrete mixtures based on the
laboratory tests conducted in this study indicate that the Class P Modified mixture
meets or exceeds the CDOT requirements for Class P concrete mixtures. Table 29
provides a comparison between the two mixtures produced in this study.
Table 29: Comparison to CDOT Requirements
CDOT Class P Requirements CDOT Class P Modifiec Class P
Minimum of 55 percent AASHTO M 43 sizes No. 67 coarse aggregate 64.17% 64.17% 63.35% 63.35%
Slump is required form 3 to 6 in (7.62 to 15.24 cm) 6 in 15.24 cm 6.5 in 16.51 cm
Average 28 day flexural strength of at least 650 psi (66 kg/m2) 880 psi 90 kg/m2 773 psi 85 kg/m2
Average 28 day compressive strength of 4200psi (428 kg/m2) 5,058 psi 516 kg/m2 5,171 psi 570 kg/m2
Class F fly ash used 30% 30% 50% 50%
Air Content: Range 4-8% 4.50% 4.50% 3.60% 3.60%
Water Cement Ratio: Maximum of 0.44 0.4 0.4 0.4 0.4
9.2 Conclusions
This research evaluated both fresh and hardened concrete properties. Two different
concrete mixtures were examined. The CDOT Class P concrete mixture was
compared to a proposed modified Class P concrete mixture. The modified Class P
74


mixture included a 20% increase in fly ash content (50% total fly ash) when
compared to the standard Class P concrete mixture.
9.2.1 Fresh Concrete Properties
The slump values obtained during the batching of the Class P and Class P Modified
mixtures met the CDOT requirements. The modified Class P concrete mixture
produced a 0.5 in. greater slump than that the CDOT Class P mixture. This indicated
that the modified concrete mixture was more workable, and is most likely a result of
the increased percentage of fly ash in the concrete mixture.
Air content is specified by the CDOT as 4-8%. The Class P concrete mixture met this
requirement with an air content of 4.5%. The modified Class P mixture resulted in a
slightly lower air content of 3.6%, when compared to the control. It is probable that
the decrease in air content is a result of the increased percentage of cement
replacement with fly ash. By increasing air entraining agent in mixture, air content
could possibly be increased. The unit weight for CDOT Class P mixture was 144.4
pcf (85 kg/m3) and for modified Class P was 146.0 pcf (86 kg/m3). The difference
between the unit weights of the two mixtures is a result of the different air content
and the increased fly ash content in the modified Class P mixture. An increase in fly
ash content will result in a reduction in the unit weight.
The temperature of the concrete mixtures in this experiment ranged form 65F (18C)
to 66F (19C).
75


9.2.2 Hardened Concrete Properties
The modified mixture containing 50% fly ash proved that it had lower early day
strength than the CDOT Class P mixture containing 30% fly ash. As mixtures reached
28-day age, the modified mixture not only met the CDOT concrete requirements, but
also had a higher compressive strength than the CDOT Class P concrete mixture.
The permeability investigation indicated that there was not a significant difference
between the modified Class P and CDOT Class P mixture. Both mixtures resulted in a
low permeability classification per ASTM C 1202. Though the CDOT specification
for Class P concrete does not specify the permeability test being required, the results
from this study indicate that the modified Class P mixture performs similar to the
current CDOT Class P mixtures. It is expected that both mixtures would be durable
due to the low permeability.
CDOT requires flexural strength of 650 psi (66 kg/m2) for the Class P concrete at 28
days of age. Experimental test results for both samples exceeded that requirement
with average flexural strengths of 880 psi (90 kg/m2) for the Class P and 773 psi (85
kg/m ) for the Class P Modified mixture. Though the modified concrete mixture had
lower flexure strength when compared to the Class P Standard mixture, it still met the
CDOT requirement.
Based on the cost analysis, the modified Class P concrete mixture would provide a
7.82% of cost savings for the CDOT. Furthermore, the increased use of fly ash and
76


reduction in the cement required, provides for a more sustainable design, which, if
implemented CDOT would reduce CO2 emissions.
The performance of the modified Class P concrete mixture meets all of the CDOT
requirements, and therefore could replace the current prescriptive CDOT Class P
concrete mixture specification.
9.3 Recommendations
This thesis examines the potential to increase the cement replacement with fly ash
percentage for the CDOT Class P concrete mixture from 30% to 50%. This increase
has the potential to maintain or improve the overall concrete structural performance,
reduce the material cost to CDOT, and produce a more sustainable concrete mixture.
This research found that early day compressive strength was lower for concrete with
50% of fly ash. In this research a lower percentage of fly ash used in a Class P
mixture provided a higher compressive strength than the modified mixture at an early
age. In addition, this study proved that the mixture containing the higher percentage
of fly ash increased later day compressive strength. The major findings of this
experimental research are:
There was a negligible difference in slump values between the two mixtures
The increased fly ash content decreased the air content slightly
Less early-age strength was experienced for the modified mixture when
compared to the standard CDOT Class P mixture
77


The Class P Modified mixture had higher later-day compressive strength at 28
and 56 days of age, when compared to the CDOT Class P mixture
There was not a significant difference in permeability readings between the
Class P and Class P Modified mixtures
The cost of concrete for CDOT would be reduced by 7.82% if Class P
Modified mixture was used instead of the current Class P mixture
The CO2 emission could be reduced by approximately 2,220 tons (2,014
metric tons) of the Class P Modified mixture was used
78


APPENDIX A
CDOT Class P Concrete Mixture Design
Spreadsheet
Mix Proportion (SSD)
Material Weight (Ib/cy) Volume (cf) Volume Check
Cement 462 2.35 0.087
Fly Ash 198 1.34 0.050
BFS 0 0.00 0.000
Silica Fume 0 0.00 0.000
Rock 1766 10.84 0.402
Sand 1064 6.48 0.240
Water 264 4.23 0.157
Air 0.065 1.76 0.065
27.00 1.00
Material Properties
Material S.G. A.C
Cement 3.15 -
Fly Ash (F) 2.37 -
BFS 2.90 -
Silica Fume 2.20 -
Rock 2.61 0.80
Sand 2.63 0.70
Mix Characteristics
|w/c 0.40
Unit Weight (pcf) 139.0
Cementitious material (lb) 660
[Aggregate Volume (%) 64.17


CDOT Class P Concrete Mixture Design Spreadsheet
Suppl. Cementitious Mat. Percent (%) Weight (lb)
Fly Ash replacement (%) 30 198
BFS replacement (%) 0 0
SF replacement (%) 0 0
Moisture Content
sand pan 8.2 sand +pan wt. 250.1
rock pan 8.3 rock + pan wt. 241.1
dry wt. sand 238.8
dry wt. rock 238.4
sand me (%) 4.90 mc-ssd 0.042002602
rock me (%) 1.17 mc-ssd 0.003734029
Batch Weights (yd3)
Cement 462 b
Fly Ash 198 b
BFS 0 b
Silica Fume 0 b
Rock 1773 b
Sand 1108 b
Water 213 b
HRWR/AEA 1.0 fl oz./ewt
HRWR/AEA 137 ml
Testing Specimens Required
Compressive cylinders 12 0.70
RCIP cylinders 4 0.23
MOR 0 0.00
Unit weight 1 0.25
Permeameter slabs 0 0.00
Salt Ponding 0 0.00
MOE 0 0.00
Beam Molds 2 0.22
Split Cylinder 0 0.00


CDOT Class P Concrete Mixture
Design Spreadsheet
Total 1.40
x 1.1 1.54
Batch Weights (ft3)
Batch size 1.5 cf
Cement 26.4 b
Fly Ash 11.3 b
BFS 0.0 b
Silica Fume 0.0 b
Rock 101.3 b
Sand 63.4 lb
Water 12.2 lb
HRWR/AEA 7.8 ml
Mix done 1/30/2009 cylinder 1 (lb) cylinder 1 (psi) cylinder 2 (lb) cylinder 2 (psi) cylinder 3 (lb) cylinder 3 (psi)
3day 2/2/2009 35,755 2860 38,540 3083 40,025 3202
7day 2/6/2009 49,895 3992 49,575 3966 49,435 3955
14 day 2/13/2009 53,005 4240 47,745 3820 43,995 3520
28day 2/27/2009 63,470 5078 62,240 4979 63,975 5118
56day 3/27/2009 73,150 5852 78,710 6297 0
3,049
3,971
4,030
5,058
6,074
Target 4200


Class P Modified concrete Mixture
Design Spreadsheet
Mix Proportion (SSD)
Material Weight (Ib/cy) Volume (cf) Volume Check
Cement 330 1.68 0.062
Fly Ash 330 2.23 0.083
BFS 0 0.00 0.000
Silica Fume 0 0.00 0.000
Rock 1766 10.84 0.402
Sand 1027 6.26 0.232
Water 264 4.23 0.157
Air 0.065 1.76 0.065
27.00 1.00
Material Properties
Material S.G. A.C
Cement 3.15 -
Fly Ash (F) 2.37 -
BFS 2.90 -
Silica Fume 2.20 -
Rock 2.61 0.80
Sand 2.63 0.70
Mix Characteristics
w/c 0.40
Unit Weight (pcf) 137.7
Cementitious material (lb) 660
Aggregate Volume (%) 63.35
Suppl. Cementitious Mat. Percent (%) Weight (lb)
Fly Ash replacement (%) 50 330
BFS replacement (%) 0 0
SF replacement (%) 0 0


Class P Modified concrete Mixture
Design Spreadsheet
Moisture Content
sand pan 1072.2 sand +pan wt. 1910
rock pan 1027.7 rock + pan wt. 2178.2
dry wt. sand 1875
dry wt. rock 2149
Total 1.40
x 1.1 1.54


Class P Modified concrete Mixture
Design Spreadsheet
Batch Weights (ft3)
Batch size 1.5 cf
Cement 18.9 b
Fly Ash 18.9 b
BFS 0.0 b
Silica Fume 0.0 b
Rock 100.2 b
Sand 58.4 b
Water 16.1 b
HRWR/AEA 5.6 Til
Modified
Mix done 2/6/2009 cylinder 1 (lb) cylinder 1 (psi) cylinder 2 (lb) cylinder 2 (psi) cylinder 3 (lb) cylinder 3 (psi)
3day 2/9/2009 23,875 1,910 23,975 1,918 23,525 1,882
7day 2/13/2009 41,920 3,354 43,960 3,517 44,380 3,550
14day 2/20/2009 51,895 4,152 49,400 3,952 53,275 4,262
28day 3/6/2009 63,665 5,093 64,695 5,176 65,535 5,243
56day 4/3/2009 74,230 5,938 78,950 6,316 -
Average (psi
1,903
3,474
4,122
5,171
6,127
T arget 4200


LABORATORY TEST REPORT
CLIENT: Bestway Concrete WesTest PROJECT NO.: 202408
SOURCE: Brighton REPORT DATE: March 5, 2008
SAMPLED BY: Client t
PROJECT: Miscellaneous !
MATERIAL DESCRIPTION ASTM C 33 Size No. 57/67 Coarse Aggregate
DATE SAMPLED January 28. 2008
SAMPLE LOCATION Stockpile
Aggregate Physical Property and Quality Tests (ASfM C 33 Specifications)
ASTM C '117 8. C 136, AASHTO T 11 & T 27 ASTM C 127. AASHTO T 85, Bulk Specific Gravity = 2.59, Bulk Specific Gravity (SSD) = 2,61, Apparent Specific Gravity = 2.64, Absorption = 0.8% ASTM C 88, AASHTO T 104, Sodium Sulfate Soundness. 5 Cycles
SIEVE SIZE % Passing No. 57 Specification No. 67 Specification SIEVE SIZE GRADING or- ORIGINAL SAMPLE WEIGHT BEFORE TEST, g PERCENT PASSING AFTER TEST WEIGHTED PERCENT LOSS
2" ASTM C 131, AASHTO T 96, L.A. Abrasion Grading B, Loss = 40% Specification: 45% Max.
1-1/2 100 100
1 100 95 100 100 1-1/2" to 1" 0 1.6 0.1
3/4" 92 90- 100 ASTM C 142, AASHTO T 112, Clay Lumps & Friable Particles COARSE AGG = 0.2%, Specification: 3.0% MAX. r to 3M 5147
1/2 60 25-60 3/4 to 1/2 56 672.0 0.6 0.4
3/8 40 20 55 112 to 3/8" 331.4
it 4 7 0- 10 0-10 ASTM C 123, AASHTO T 113, Lightweight Particles in Aggregate 3/8. to No. 4 35 300.7 0.3 0.1
US 3 0-5 0 5 TOTAL 100 COARSE AGG. TOTAL 93% 1
U 16 2 SAMPLE WT. #30 2 \ ASTM C 29, AASHTO T 19, : Bulk Density and Voids in Aggregate i Rodding Method; Bulk Density = 103 pcf I Voids in Aggregate = 36%
#50 1 3188,7 ZnCI^.O 0.0% 0.5% Max.
#100 1 3188.7 ZnBrj/2.4 0.0% 3.0% Max.
#200 0.9 0-1.5 0-1.5
COMMENTS
Figure 1. Coarse Aggregate Data (ASTM C33)
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845 Navajo Street
Denver, CO 80204
303.975.9959, Fax 303.975.996S


Fl§ur 2. Fin* Ar*gt* Data {A8TM C33)