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Examining the influence of post-mercury-control on properties of fly ash concrete

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Examining the influence of post-mercury-control on properties of fly ash concrete
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Liu, Rui
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xiii, 147 leaves : ; 28 cm.

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Fly ash ( lcsh )
Concrete ( lcsh )
Mercury wastes ( lcsh )
Concrete ( fast )
Fly ash ( fast )
Mercury wastes ( fast )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

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Thesis:
Thesis (Ph. D.)--University of Colorado Denver, 2010.
Bibliography:
Includes bibliographical references (leaves 141-147).
Statement of Responsibility:
by Rui Liu.

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Full Text
EXAMINING THE INFLUENCE OF POST-MERCURY-CONTROL ON
PROPERTIES OF FLY ASH CONCRETE
by
Rui Liu
B.S., Northeast Forestry University, Harbin, China, 2004
M.S., Northeast Forestry University, Harbin, China, 2007
A dissertation submitted to the
University of Colorado Denver
in partial fulfillment
of the requirements for the degree of
Doctor of Philosophy
Civil Engineering
2010


2010 by Rui Liu
All rights reserved.


This dissertation for the Doctor of Philosophy
degree by
Rui Liu
has been approved
by
Stephan A. Durham
Anu Ramaswami
-1 /£ / Xq/q
Date
Chengyu Li


Liu, Rui (Ph.D., Civil Engineering)
Examining the Influence of Post-Mercury-Control on Properties of Fly Ash
Concrete
Dissertation directed by Assistant Professor Stephan A. Durham
ABSTRACT
Activated carbon injections are the most mature technologies for mercury capture
at coal-fired power plants. However the increased carbon content and concentrated
toxic heavy metal elements (i.e. mercury, arsenic, lead etc.) in the fly ash may
reduce the suitability of fly ash for use in concrete and call into question the safety
of using this fly ash.
This study examined the reuse potential of post-mercury-control fly ash in concrete.
Specifically, the structural strength, durability, and environmental leaching of post-
mercury-control fly ash concrete were tested.
Thirteen concrete mixtures containing post-mercury-control fly ashes derived from
different technologies were designed and batched. This study confirmed the
influence of the carbon on the air content of the concrete. However there was no
difficulty in entraining air in activated carbon injection fly ash concretes within the
recommended dosage range of air-entraining admixture. All air-entrained fly ash
concretes exhibited excellent characteristics in compressive strength (> 32.0 MPa
at 28 days), resistance to chloride-ion penetration (moderate to low at 28 days) and
freeze-thaw (>90 average durability factor after 300 cycles).
One fly ash was selected based on the structural performance of the fly ash
concrete for the optimization phase of this study. Laboratory testing was completed
to optimize the cementitious material and fly ash contents in the concrete. The
cementitious materials content and the maximum possible cement replacement
percentage by the fly ash can be selected to be 338 kg/m3 (570 lbs/cy) and 50%
respectively to yield a 28-day strength and a durability greater than that required by
the Colorado Department of Transportation Class D structural concrete.
The possible leaching of heavy metal elements was evaluated using the U.S.
Environmental Protection Agencys Toxicity Characteristic Leaching Procedure for
the selected fly ash and the optimized fly ash concrete mixture. The test results


indicate that the leaching of only two toxic elements was higher than the reporting
limits, but much lower than the maximum contamination level.
The environmental impact of post-mercury-control fly ash concrete infrastructure
in the Metropolitan-Denver Area was evaluated by calculating the embodied
energy and GHG emission associated with one cubic meter fly ash concrete using a
Cradle-to-Grave LCA model. The optimized concrete mixture has the lower
embodied energy (2708 MJ/m3) and GHG emission (0.3696 MTCChE/m3) than
other mixtures (control mixture: embodied energy 3936 MJ/m3; GHG 0.5562
MTC02E/m3).
This abstract accurately represents the content of the candidates dissertation. I
recommend its publication.
Signed
itephan A. Durham


ACKNOWLEDGMENT
The post mercury fly ash samples were provided by Boral Material Technologies
Ceramatec Inc, URS Corporation and ADA-ES Inc. This investigation was funded
in part by Colorado Department of Higher Education. Grateful acknowledgement is
made to Mr. David Neel, Boral Material Technologies, for his helpful comments
during the investigation.
Grateful acknowledgement is also made to Assistant Professor Stephan A. Durham
and Professor Kevin L. Rens, for their assistance during the research. I would like
to thank Dr. Anu Ramaswami, Dr. Yunping Xi, Dr. John O. Dow, and Dr. Chengyu
Li for participating on my dissertation committee.
Additionally, I would like to thank Tom Thuis, Logan Young and other staff for
their technical support and guidance on the equipment used in the University of
Colorado Denver, Civil Engineering Department laboratory.


TABLE OF CONTENTS
Figures...................................................................x
Tables....................................................................xii
Chapter
1. Introduction........................................................1
1.1 Sustainable Urban Infrastructure....................................1
1.2 Federal and State Air Emission Regulations..........................2
1.3 Objectives of the Study.............................................5
2. Background of Fly Ash and Fly Ash Concrete..........................9
2.1 Physical and Chemical Properties of Fly ash........................10
2.2 Comprehensive Utilization of Fly Ash in the United States..........11
2.3 Mercury Control Technologies.......................................17
2.3.1 Removing Mercury from Coal prior to Combustion.....................21
2.3.2 Sorbents Injection.................................................22
2.3.3 Enhanced Wet Scrubbing.............................................27
2.3.4 Other technologies.................................................28
2.4 Concerns of Utilization of Post Mercury Control Fly ash............29
2.4.1 Influence on Concrete Durability...................................29
2.4.1.1 Air Entrainment Interfered by Regular Fly Ash.....................30
2.4.1.2 Air Entrainment Interfered by Post-Mercury-Control Fly Ash........32
2.4.2 Influence on Concrete Other Properties............................35
2.4.3 Influence on the Environment......................................36
2.4.3.1 Gaseous Mercury from Fly Ash and Curing Fly ash Concretes.........37
2.4.3.2 Mercury Leaching from Fly Ash and Fly Ash Concrete................38
2.5 Summary from Literature Review.....................................42
3. Experimental Plan: Laboratory Testing of Post Mercury Control
Fly Ash Concrete.................................................45
3.1 Concrete Materials ................................................47
3.1.1 Fly Ash ...........................................................47
3.1.2 Portland Cement....................................................49
3.1.3 Aggregate..........................................................51
3.1.4 Chemical Admixture.................................................52
3.2 Mixture Design.....................................................52
3.3 Test Method........................................................53
3.4 Data Analysis......................................................54
vii


4 Phase I: Reuse Potential of Sorbent Injection Ashes in Concrete....55
4.1 Concrete Mix Proportions...........................................55
4.2 Test Results.......................................................57
4.2.1 Fresh Concrete Properties Test Results.............................57
4.2.1.1 Phase I: Slump and Superplasticizer................................57
4.2.1.2 Phase I: Air Content and Unit Weight...............................60
4.2.2 Phase I: Compressive Strength Characteristics......................64
4.2.2.1 Effect of Sorbent Injection Fly Ash Content........................68
4.2.2.2 Effect of Air Content..............................................68
4.2.3 Phase I: Resistance to Chloride-Ion Penetration....................70
4.2.4 Phase I: Resistance to Freeze/Thaw Cycling.........................73
4.2.5 Phase I: Resistance to Sulfate Attack..............................75
4.3 Conclusion of Phase I Laboratory Testing...........................78
5 Phase II: Optimization of Cementitious Material and Fly Ash Content ..81
5.1 Phase II: Mixture Proportions......................................81
5.2 Test Results.......................................................83
5.2.1 Fresh Concrete Properties Test Results.............................83
5.2.1.1 Phase II: Slump and Superplasticizer...............................83
5.2.1.2 Phase II: Air Content and Unit Weight..............................85
5.2.2 Phase II: Compressive Strength Results.............................86
5.2.3 Phase II: Resistance to Chloride-Ion Penetration...................93
5.2.4 Phase II: Resistance to Freeze/Thaw Cycling........................99
5.2.5 Phase II: Resistance to Sulfate Attack............................101
5.3 Leaching of ACI Fly Ash Concrete..................................102
5.4 Conclusion of Phase II Laboratory Testing.........................104
5.5 Evaluating Post Mercury Control Fly Ash Concrete with
Environmental Life Cycle Assessment..............................106
5.5.1 Background: Types of LCA..........................................107
5.5.2 LCA Methodology...................................................108
5.5.3 LCA of Fly Ash Concrete Infrastructure in Denver, Colorado.......111
5.5.3.1 LCA Infrastructure Comparison Matrix.............................112
5.5.3.2 Concrete flows in Metro-Denver, CO...............................113
5.5.3.3 Cradle-to-Grave Concrete LCA model..............................114
5.5.4 LCA Analysis......................................................119
5.5.4.1 Theoretical and Actual LCA Results................................120
5.5.4.2 LCA Results Analysis..............................................121
5.5.5 LCA Analysis Conclusion...........................................125
6 Conclusions and Recommendations...................................126
6.1 Conclusions.......................................................126
6.2 Recommendations...................................................130
viii


Appendix
A. Photographs of Nine Sorbent Injection Fly Ashes.....................132
B. Cement Certification Report.........................................133
C. Laboratory Test Report for the Coarse Aggregate.....................134
D. Laboratory Test Report for the Fine Aggregate......................135
E. Matlab Codes for Optimization.......................................136
Bibliography ...........................................................141
ix


FIGURES
Figure
2-1 The Production, Beneficial Use Totals and Beneficial Use Rate of Fly
Ash in U.S. in Recent Years (ACAA, 1995-2006)...................... 12
2-2 Utilization of Fly Ash in Civil Engineering Infrastructure versus Other
Utilizations in 2001 in the United States (ACAA, 2001).............15
2-3 Utilization of Fly Ash in Civil Engineering Infrastructure versus Other
Utilizations in 2006 in the United States (ACAA, 2006)..............16
2-4 Process Flow Diagram for WRIs Mercury Removal Technology............21
2-5 Typical Activated Carbon Injection System (Dombrowski, 2007)........26
2-6 TOXECON II (Dombrowski,2007).........................................26
2-7 Mer-Cure (Kang et al.,2007)..........................................27
2-8 Enhanced Wet Scrubbing system.........................................28
4-la Phase I: Slump and Superplasticizer (Mixtures 1-8)..................58
4-lb Phase I: Slump and Superplasticizer (Mixtures 1, 2, 9-13)...........59
4-2a Phase I: Unit Weight and Air Content (Mixtures 1-8).................60
4-2b Phase I: Unit Weight and Air content (Mixtures 1, 2, 9-13)..........61
4-3 Phase I: Unit Weight vs. Air Content................................64
4-4a Phase I: Compressive Strength Development (Mixtures 1-8)............67
4-4b Phase I: Compressive Strength Development (Mixtures 1, 2, 9-13) ....67
4-5 Phase I: Compressive Strength vs. Air Content.......................69
4-6 Phase I: Rapid Chloride Ion Penetrability Tests Results.............72
4-7 Phase I: Coulombs vs. Air Content...................................72
4-8 Phase I: Durability Factors.........................................74
4- 9 Phase I: Length Change Percentage of Mortar Bars....................78
5- 1 Phase II: Slump and Superplasticizer................................84
5-2 Phase II: Unit Weight and Air Content...............................86
5-3 Phase II: Compressive Strength Development..........................89
5-4a Iso-strength lines of ACI1 fly ash concrete (MPa)....................90
5-4b Iso-strength lines of ACI1 fly ash concrete (psi)....................91
5-5 Phase II: Rapid Chloride Ion Penetrability Tests Results............95
5-6 Iso-total Charge Passed Contour Lines of ACI1 Fly Ash Concrete.......98
5-7 Phase II: Durability Factors.......................................100
5-8 Phase II: Length change percentage of mortar bars..................102
5-9 Embodied Energy vs. GHG emission......................................122
5-10 Iso-embodied Energy and Iso-GHG Emission Contour Lines for
x


ACI1 fly ash concrete.............................................123
A. 1 Photographs of Sorbent Injection Fly Ash Samples...................132
XI


TABLES
Table
1 -1 Outline of Chapters and Objectives...................................7
2-1 Typical Bulk Analyses of Fly Ash and Other Pozzolans (wt %).........11
2-2 Different Sorbent Types.............................................23
2- 3 Summary of Post-Mercury-Control Fly Ash Concrete from Literature
Review 44
3- 1 Sorbent and Provider of Each Sorbent Injection Ash..................47
3-2 Chemical Analysis of Fly Ashes......................................49
3-3 Chemical Properties of the Cement...................................50
3-4 Physical Properties of the Cement...................................50
3-5 Coarse and Fine Aggregates Properties...............................51
3- 6 Fresh and Hardened Concrete Tests..................................54
4- la Phase I: Mixture Proportions (SI)..................................56
4-lb Phase I: Mix Proportions (U.S. Customary)..........................57
4-2 Phase I: Fresh Concrete Properties Tests Results...................58
4-3a Phase I: Compressive Strength Data (SI)............................65
4-3b Phase I: Compressive Strength Data (U.S. Customary)................65
4-4 Phase I: Resistance to Chloride-ion Penetrability..................71
4-5 Phase I: Freeze/Thaw Durability Factors............................74
4- 6 Phase I: Sulfate Expansion of Fly Ash Mortar Bars with 15% ACI Ash... 76
5- la Phase II: Mixture Proportions (SI).................................82
5-lb Phase II: Mixture Proportions (U.S. Customary).....................83
5-2 Phase II: Fresh Concrete Properties Test Results ..................84
5-3a Phase II: Compressive Strength (SI)................................87
5-3b Phase II: Compressive Strength (U.S. Customary)....................87
5-4 Phase II: Rapid Chloride Ion Penetrability ........................94
5-5 Phase II: Durability Factors......................................100
5-6 Phase II: Length Changes (Expansion %) of Mortar Bars.............101
5-7 Phase II: Leaching Test Results...................................104
5-8 Identification of Scenarios in LCA Analysis........................113
5-9 Concrete Flows in Denver, CO......................................114
5-10 EIOLCA Inputs for 1-tonne Concrete Debris and Avoidance Landfill
Impact for Fly Ash................................................118
5-11 Cradle-to-Grave LCA model for Fly Ash Concrete in Denver, CO....119
5-12 Sources of Materials and Transportation Modes......................120
xii


5-13 Summary of LCA Analysis (theoretical)...........................................120
5-14 Summary of LCA Analysis (actual)................................................121
xiii


1 Introduction
1.1 Sustainable Urban Infrastructure
Currently, more than 50% of the worlds population resides in urban areas (U.N.,
2003). By 2030 this percentage is expected to increase to 60% (U.N., 2007). In the
United States and Europe, more than 75% of the nations population lives in cities,
with many areas of Western-Southwestern USA expecting steep increases in
population over then next few decades (Reiner, 2007).
Urban infrastructure refers to natural and engineered systems that provide water,
energy, transport, sanitation, information, recreation and built environment services
to more than half of the worlds population living in cities today(Ramaswami,
2005). Given these trends, in order to provide and maintain urban infrastructure,
intelligent design and materials selection become critical for economic and
resource sustainability.
Concrete is the dominate material used in construction, both in terms of gross mass
of material used as well as the energy consumed and the pollution released from
1


cement manufacture. Global carbon dioxide (CO2) emissions from cement
production were approximately 829 million metric tons of CO2 in 2000, about 3.4%
of global CO2 emissions from fossil fuel combustion and cement production
(Marland et al, 2003). Use of fly ash in cement and concrete avoids the landfill
dumping, reduces the use of natural raw materials and therefore contributes to
industrial sustainability. Blended cements and concrete containing large
proportions of fly ash offer the benefit of CO2 emissions avoidance.
1.2 Federal and State Air Emission Regulations
The fly ash and other coal combustion products will most likely be unusable under
the Clean Air Interstate Rule (CAIR) and the Clean Air Mercury Rule (CAMR).
The Clean Air Act Amendment of 1990 required large reduction in emissions of
nitrogen oxide (NOx) and sulfur dioxide (SO2) from coal-fired power plants. Based
on 1999 estimates, U.S. coal-fired power plants emit approximately 43.5 metric
tons (48 U.S. short tons) of mercury (Hg) per year (Kilgroe et al, 2002). The U.S.
Environmental Protection Agency (EPA) announced the following clean air
regulations that further reduce emissions of NOx and SO2 and require limits on Hg
emissions from coal-fired power plants:
2


(1) The CAIR calls for 28 eastern states and Washington D.C. to have a 70%
reduction of SO2 emissions and a 60% reduction of NOx emissions compared to
2003 levels by the year 2015.
(2) The CAMR consists of two phases and applies to both existing and new plants.
The first phase of control was scheduled to begin in 2010 with a 38 ton Hg
emission cap based largely on co-benefit reductions achieved through further
SO2 and NOx emission controls required under EPAs CAIR. The second phase
of control requires a 15 ton Hg emissions cap beginning in 2018.
These regulations seek to lower levels using cap-and-trade mechanism by which
power plants are signed emission limits but can exceed those limits by purchasing
credits from companies whose emissions are below their assigned limits. In
addition to federal regulations, several states are proposing their own regulations
that would require additional cuts in SO2, NOx, and Hg emissions over a shorter
time period than required under federal rules. However, on Feb 8, 2008 and July 11,
2008, the United States Court of Appeals in the District of Columbia vacated the
CAMR and CAIR regulations for both new and existing electric generating units,
which are believed less stringent and unfair by some from various environmental
organizations. CAMR will be discussed in Chapter 2.3. The U.S. EPA is
developing more strict regulations regarding Hg emissions.
3


Several concerns brought forth by industry related to the impact of the federal and
state air emission regulations on the beneficial use of fly ash include:
(1) Fly ash may no longer be able to be used in cement manufacture, which is
derived from sorbent injection for mercury control. Sorbent injection is a type
of mercury control technology. This technology is discussed in detail in
Chapter 2. Fly ash collected at coal-fired units that employ sorbent injection for
mercury control is banned from serving as a feedstock at cement kilns
following a December 2006 final rule issued by the EPA (U.S.EPA, 2006).
(2) The leading technology for mercury control is activated carbon injection (ACI).
ACI may lead to increased concentrations of mercury-containing sorbents and
higher carbon contents in fly ash. Fly ash containing high levels of carbon will
likely no longer be used in concrete due to carbons impact on air entraining
agents (AEA). Increased concentrations of mercury in fly ash called into
question the safety of using this fly ash.
(3) NOx control technologies result in the production of fly ash with a noticeable
decline in quality, namely, the presence of unbumed carbon at varying levels.
Some fly ashes containing carbon are no longer suitable for use in concrete but
can be sold as a raw material for cement manufacture.
Numerous technologies have been developed to address the second concern
regarding the beneficial use of the post mercury control fly ash in concrete by
4


separating the carbon and fly ash physically and chemically. But insufficient data
are available to demonstrate the reuse potential of post-mercury-control fly ash in
concrete.
1.3 Objectives of the Study
The focus of this study is to examine the reuse potential of post-mercury-control fly
ash in concrete. Specifically, the structural strength, durability, and environmental
leaching of post-mercury-control fly ash concrete were tested. In addition, its life
cycle potential for Greenhouse Gas (GHG) mitigation was researched. The
following objectives were examined in this study:
Utilization: Evaluate the barriers and perceived risks for incorporating post-
mercury-control fly ash into concrete.
Lab examination: Compare the influences of post-mercury-control fly ash
derived from different technologies on properties of concrete; The specific
objectives include:
Design and batch concrete mixtures containing post-mercury-control fly
ash.
Test fresh properties of the concrete mixtures.
5


Test and analyze the hardened concrete properties. Specifically examine
the compressive strength, freeze-thaw resistance, permeability, and
sulfate resistance of fly ash concrete mixtures.
Recommendation: Optimize the cementitious material and post-mercury-
control fly ash contents in concrete. Conduct leaching test for post-mercury-
control fly ash concrete and evaluate the safety of using this fly ash.
LCA investigation: Determine the life cycle potential for Greenhouse Gas
reduction in the Denver Metropolitan area.
The dissertation contains six chapters. An outline of the chapters and the objectives
addressed by each chapter are presented in Table 1.1.
Chapter l provides the background information and brings forward the objectives
of this research. Chapter 2 contains the background on the fly ash and its utilization
in the United States. This chapter also contains the literature review on the mercury
control technologies and discussion on the concerns of utilization of post-mercury-
control fly ash concrete. The barriers and perceived risks for incorporating post-
mercury-control fly ash in concrete were evaluated through literature review in this
chapter.
S


Table 1-1 Outline of Chapters and Objectives
Chapters Objectives Note
1. Introduction NA NA
2. Background of Fly Ash and Fly ash Concrete Utilization Background/Literature review
3. Experimental Plan: Laboratory Testing of Post Mercury Control Fly Ash Concrete Experimental Plan and Testing Procedures Material and Testing Description
4 Phase I: Reuse Potential of Sorbent Injection Ashes in Concrete Reuse Potential of Post CAMR fly ash Nine Mercury Control Fly Ash Tested
5 Phase II: Optimization of Cementitious Material and Fly Ash Contents Mixture Optimization & LCA Investigation Cementitious and Fly Ash Content Optimized Based on Lab Testing and LCA
6. Conclusions and Recommendations Summary of Results NA
Chapter 3-5 contain the methodology and results for laboratory testing and LCA
investigation of post-mercury-control fly ash concrete. Chapter 3 provides the
experimental plan. The reuse potential of post-mercury-control fly ash was
examined by lab testing (e.g. compressive strength, resistance to chloride ion
penetration, freeze thaw and sulfate attack) in Chapter 4 for fly ash concrete
mixtures with 15% of fly ash replacement for portland cement. The fly ash with
best structural performance was selected to perform the optimization phase testing
and LCA investigation, which is included in Chapter 5. The optimum fly ash
content and cementitious material content were determined to meet CDOT Class D
structural concrete requirements. The U.S. EPAs Toxicity Characteristic Leaching
Procedure (TCLP) was utilized for the optimized concrete mixture to examine the
7


safety of utilization of the post-mercury-control fly ash. Chapter 5 also provides a
Cradle-to-Grave LCA model of fly ash concrete infrastructures in Denver
Metropolitan area, Colorado. Based on this LCA model, the embodied energy and
GHG emission per cubic meter fly ash concrete were determined. The
environmental impacts of the optimized concrete mixture were evaluated by the
LCA methodology. Hence, the objectives of the lab examination, recommendation
and LCA investigation were addressed in Chapter 3-5.
Chapter 6 contains the conclusions and recommendations of the research.
Supplementary information is provided in the appendices. Appendix A contains the
photographs of fly ashes derived from different technologies. Appendix B contains
the cement certification report including the chemical and physical properties of the
ASTM Type I cement used in this study. The lab analyses of the coarse and fine
aggregate are provided in Appendix C and D. Appendix E includes the Matlab
codes to draw the iso-strength contour lines, iso-durability (charges passed) contour
lines, iso-embodied energy and iso-GHG emission contour lines.
3


2 Backgrounds of Fly Ash and Fly Ash Concrete
The major structural building material today is concrete being a composite material
made of cement, aggregates, admixtures, and water. The aggregates are sand and
rock. Cement is manufactured from burning ground limestone and clay into clinker
followed by blending with a small percentage of gypsum. Admixtures for concrete
are materials other than cement, water, and aggregates added to the mixture either
before or during the mixing process. The admixtures can be in chemical form with
the most important utilized to accelerate or retard the setting and hardening process,
reduce the amount of water required to obtain a given workability, and to enhance
air entrainment in concrete. In addition, admixtures can also be in the form of
mineral admixtures or pozzolans, which are siliceous or siliceous and aluminous
materials that together with water and calcium hydroxide form cementitous
products at ambient temperature. Fly ash from pulverized coal combustion is
categorized as a pozzolan (Ramachandran, 1984; Wesche,199l;Taylor, 1997).


2.1 Physical and Chemical Properties of Fly ash
Fly ash particles from pulverized coal combustion have gone through a molten
stage at high temperatures and are generally spherical in shape with diameters
ranging from below 1pm to above 150pm, specific surfaces 300 m2/kg to 500
m2/kg, and specific gravities in the range of 2.2-2.8.
Fly ashes are subdivided into two classes, class F and class C, which reflect the
composition of the inorganic fractions. Burning high rank coal such as anthracite or
bituminous coal produces ashes with a high content of silica and alumina and a low
concentration of lime. Burning subbituminous coal or lignite, which is lower in
rank, results in an ash with a higher content of lime. The latter not only
demonstrates pozzolanic properties, but do possess at some levels cementitous
properties due to their high content of lime. Class F fly ashes are produced from
coals that are typically found in states east of the Mississippi river, and class C fly
ashes from coals of western states, principally Wyoming and Montana. According
to the American Society for Testing Materials (ASTM C618), the ashes containing
more than 70 weight percentage (wt %) of SiO? + AI2O3 + Fe2C>3 and being low in
lime are defined as class F, while those with a SiC>2 + AI2O3 + Fe2(>3 content
between 50 and 70 wt% and high in lime are define as class C. The typical bulk
10


analyses of fly ash are shown in Table 2-1 compared with other pozzolan materials
(Mindness et al, 2002).
Table 2-1 Typical Bulk Analyses of Fly Ash and Other Pozzolans (wt %) (Adapted
from Mindness et al, 2002)
Material Si02 Al203 Fe203 CaO Na20 K,0 Carbon
Fly Ash-Class F >50 20-30 <20 <5 Variable <5
Fly Ash-Class C >30 15-25 <10 20-30 Variable <1
Silica Fume 85-98 <2 <10 Variable, low <2
Rice Husk Ash 85 <1 1-4 3-10 3-18
Calcined clay ~55 35-45 <10 <1 <1
2.2 Comprehensive Utilization of Fly Ash in the United States
More than 50% of the United States electricity comes from coal-fired power plants
(Goss, 2005). Demand for electricity has resulted in the burning of large quantities
of coal to produce a portion of the electricity needed. Recently, more than 65
million metric tons (72 million U.S. short tons) of coal fly ash is generated annually
in the United States (ACAA 1995-2006).
Figure 2-1 shows that the beneficial use rate of fly ash in the United States
continues to increase from 2000, but falls short of a 45% beneficial use rate in 2006.
In 2006, 36.27 million metric tons (39.98 million U.S. short tons) fly ash went to
landfills or equivalent repositories, which leaves great room for improvement and
re-utilization effort for the United States in the future.
11


1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Production Total i i Beneficial Use Total * Beneficail Use Rate
Figure 2-1 The Production, Beneficial Use Totals and Beneficial Use Rate of Fly
Ash in U.S. in Recent Years (ACAA, 1995-2006)
The current studies and the applications of fly ash in civil engineering
infrastructure in the United States include (Liu et al, 2008):
Cement and concrete products & construction materials utilizing light weight
aggregate;
Structural fill and cover material;
Roadway and pavement utilization.
12
Beneficial Use Rate (%)


Fly ash is used in cement production mainly for its alumina in cement kilns but also
contributes silica, iron, and calcium to the raw materials. Low alkali content and
high fineness of fly ash can improve clinker quality. Great quantities of fly ash can
be used in blended cement, typically substituting approximately 5-40 wt% of the
Portland cement clinker. However some future mercury control rules in the United
States will most likely limit the utilization of fly ash in cement production due to its
high content of carbon and concentrated mercury.
Fly ash contains silica which can react with the existing calcium hydroxide in the
cement paste produced during cement hydration. This chemical reaction referred to
as the pozzolanic reaction, produces additional calcium-silicate-hydrate, the main
strength contributor in hardened concrete. Its rounded particle shape helps reduce
the water demand. Fly ash used as a supplementary cementitious material (SCM)
has a number of positive effects on the resulting concrete. It can lower the material
construction costs, improve concrete workability, enhance the ultimate strength of
concrete, and improve its durability. Other advantages include lower permeability,
and better resistance to alkali, sulfate, chloride and carbon dioxide ingress.
Utilization of fly ash as a by-product aggregate in the manufacture of light weight
construction products includes fly ash brick products, the manufacture of roofing
products such as rigid roofing tiles and wallboard. The main advantage of this
13


beneficial use is the economic savings to the manufacturer associated with the
reduced freight costs of shipping the finished product, as compared to the non-light
weight product (Scheetz et al, 1998).
Currently, the greatest utilization is as an additive to cement and concrete. In 2001,
60.9% of all re-utilized fly ash was used for this purpose in the United States as
compared to 59.2% in 2006 (ACAA 1995-2006). Although construction materials
utilizing light weight aggregate in the United States accounted for less than 0.5% of
the reused ash in 2001 and 2006, fly ash use as a filler material in some drywalls
could have extensive potential due to its under utilization in this product area
(Scheetz et al, 1998).
Fly ash used alone as a structural fill or cover material presents itself as a very
logical way to utilize and dispose large volumes of fly ash. The ash can be utilized
as backfill materials for walls and used in retaining structures such as bridge
abutments. In addition fly ash grout can be used to fill abandoned rock quarries.
Use of fly ash as a fill material in the United States accounted for the reuse of over
3.64 million metric tons (4.01 million U.S. short tons) or about 18.2% of the total
fly ash utilized in 2001 and 6.61 million metric tons (7.29 million U.S. short tons)
or about 22.5% in 2006(ACAA, 1995- 2006).
14


Re-utilization of fly ash as a material in the construction of roadways and
associated peripheral projects has been a significant outlet for ash during the 1990s.
Fly ash has been used in embankment soil stabilization, sub-grade base course
material, as aggregate filler, a bituminous pavement additive and as mineral filler
for bituminous concrete. The combination of all of these uses in the United States
in 2001 accounted for the re-utilization of approximately 8.5% of the total fly ash
utilized as compared to 3.2% in 2006(ACAA, 2001- 2006). The decrease is
probably due to the less roadway construction projects in 2006.
Figures 2-2 and 2-3 show the comprehensive utilizations of fly ash in Civil
Engineering infrastructure versus other utilizations in the United States in 2001 and
2006.
18.2%
Cement, Concrete &
Construction Materials
Structural Fill & Cover
Meterial
Roadway and
Pavement Utilization
Other Utilizations
Figure 2-2 Utilization of Fly Ash in Civil Engineering Infrastructure versus Other
Utilizations in 2001 in the United States (ACAA, 2001)
15


Cement, Concrete &
Construction Materials
Structural Fin & Cover
Meterial
Roadway and
Pavement Utilization
Other Utilizations
Figure 2-3 Utilization of Fly Ash in Civil Engineering Infrastructure versus Other
Utilizations in 2006 in the United States (ACAA, 2006)
These figures clearly show the large volumes of fly ash utilization alternatives that
exist in civil engineering infrastructures, especially in the application of cement,
concrete, and construction materials in the United States.
Although the total amount of fly ash being utilized on a yearly basis has been
increasing over the last decade in the United States, the amount utilized in
comparison to production has remained relative constant at 45%. Utilizations of fly
ash in cement and concrete account for a large percentage in re-using the coal
combustion by-product, however mercury regulations in the United States might
affect the beneficial use in this area.
16


2.3 Mercury Control Technologies
Mercury is a naturally occurring element that is found in air, water, soil, and rocks.
Coal is a type of rock that stores mercury. When coal is burned, mercury is released
into the environment. In the United States, coal-fired power plants are the largest
human-caused source of mercury emissions to the air (U.S. EPA, 2010). Eventually,
the mercury in the air settles into water or onto land. Certain microorganisms can
change the deposited mercury into methylmercury, a highly toxic form found in
fish, shellfish and animals that eat fish. Fish and shellfish are the main sources of
methylmercury exposure to humans. Another less common exposure to mercury is
breathing mercury vapor. Mercury exposure at high levels can harm the heart, brain,
kidneys, and immune system of people of all ages. High levels of methylmercury in
the bloodstream of unborn babies and young children may harm the developing
nervous system, making the children less able to think and learn (U.S. EPA, 2010).
EPA issues regulations that require coal- fired power plants to reduce mercury
releases to air and water. The Clean Air Act (CAA) amendment of 1990 required
the EPA to conduct a study of hazardous air pollutant emissions. Standards of
control were to be issued if a positive finding was made. In 2000, the EPA
administrator found it was appropriate and necessary to regulate the hazardous air
pollutants including mercury from coal- and oil-fired power plants under CAA
Section 112 and listed these electric utility steam generating units (EGUs) as
17


sources of hazardous air pollutants regulated under that section. Section 112
requires the EPA to regulate emission of hazardous air pollutants because they
could cause, or contribute to, an increase in mortality or an increase in serious
irreversible or incapacitating reversible illness. However, in 2005, after
reconsidering its previous determination, the EPA purported to remove these EGUs
from the section 112 list. On March 15, 2005, the EPA issued the final CAMR to
reduce mercury emissions from coal-fired power plants. The CAMR builds on
CAIR, both of which will reduce mercury emission by up to 70%. But the EPA
promulgated CAMR under section 111. Section 111 requires the EPAs
Administrator to establish standards of performance for pollutants from new
sources that in the Administrator's judgment, which cause or contribute
significantly to, air pollution which may reasonably be anticipated to endanger
public health or welfare. Obviously, more stringent requirements exist under
section 112 than the section 111. The EPA's removal of these EGUs from the
section 112 list violates the CAA because it never made specific findings before
removing a source listed under section 112 as required by section 112(c) (9). The
CAMRs regulatory approach was effectively invalidated because coal-fired EGUs
are listed sources under section 112, regulation of existing coal-fired EGUs'
mercury emissions under section 111 is prohibited (U.S. Court of Appeals in the
District of Columbia, 2008).
18


The EPA is developing air toxics emissions standards for power plants under the
Clean Air Act (Section 112) regarding the Clean Air Mercury Rule. The standards
will be proposed by March 10, 2011 and the rule will be finalized by November 16,
2011(U.S. EPA, 2010).
Fly ash used as a SCM in concrete by replacing a portion of the cement content is
the greatest utilization of the coal by-product in the United States. Proposed
mercury regulations (e.g. CAMR) have caused power plants to change their
processes to reduce toxic gases and consequently produce a fly ash that contains
higher concentrations of mercury and carbon. This may reduce the suitability of fly
ash for use in concrete and call into question the safety of using this fly ash
(Thomeloe, 2006).
Under the leadership of the U.S. Department of Energys National Energy
Technology Laboratory (DOE/NETL) and through a successful public-private
partnership, technologies have been developed to remove mercury from coal prior
to combustion (Bland, 2008) or capture mercury in the coal combustion flue gas
through a series of physical or chemical process (Dombrowski, 2007; Kang et
al.,2007, Feeley III et al, 2008).
19


Sampling and data analysis have indicated that technologies to capture mercury in
the coal combustion flue gas is cost-effective. The trace amount of mercury
present in coal is volatized during combustion and converted to gaseous elemental
mercury (Hg). A portion of Hg is converted to gaseous oxidized forms of mercury
(Hg2+) and particulate-bound mercury (Hgp) in two processes. One is the
subsequent cooling of coal combustion flue gas and the other is the interaction of
the gaseous Hg with other flue gas constituents, such as chlorine and unbumed
carbon. As a result, coal combustion flue gas contains varying percentages of Hg,
Hg2+, and Hgp. The Hgp fraction is typically removed by a particulate control
device such as an electrostatic precipitator (ESP) or fabric filter (FF). The Hg2+
portion is water-soluble and therefore, a relatively high percent can be captured in
wet flue gas desulfurization (FGD) systems. Both Hgp and Hg2+ can be removed by
existing air pollution control device (APCD) configurations. However the Hg
fraction cannot be captured by existing APCD.
The primary focus of DOE/NETL's current mercury control program is the full-
scale testing of two advanced technologies -- sorbent injection and enhanced wet
scrubbing. NETL also sponsored the pilot-scale development of several novel
mercury control concepts, as well as numerous laboratory and bench-scale efforts
to better understand the emission and control of mercury from coal-based power
systems. These methods are discussed below.
20


2.3.1 Removing Mercury from Coal prior to Combustion
A DOE-funded process has been patented by the Western Research Institute (WRI)
that removes mercury from the coal prior to combustion (Bland, 2008). This novel
process is based on a two-stage thermal pretreatment of the raw coal to remove
both moisture and mercury. In this process, the coal is heated to remove the
moisture and then heated to a higher temperature in a separated zone to evolve the
mercury. The process flow diagram is shown in Figure 2-4.
Coal
crushing/
Grinding
Gas, Water
Vapor
Heater
and Dryer
Hot Gas
Mercury .
Remover
Cyclone
Filter
Mercury-Free
Gas to Recycle
jl or to Vent
Mercury Removal
from Gas Phase
Dry Adsorption
Figure 2-4 Process Flow Diagram for WRIs Mercury Removal Technology
Results from the testing indicate that the removal goal of 50 % is achievable for the
range of subbituminous and lignite coals and that the mercury removal ranges from
21


50 % to 87 %. The removal of mercury prior to combustion obviously allows for
continued sales and use of the ash, since no sorbents end up in the ash from the
combustion of the treated coal.
The co-benefits of this treatment process include the reduced emissions of SOx,
CO2 and NOx. The reduced emissions of SOx and CO2 are due to increased
efficiency gains by 3.5% and 4% and by up to 30% respectively.
2.3.2 Sorbents Injection
Sorbent injection requires the right type of sorbent, the right injection point to
maximize the time the sorbent has to work, and the right injection system to ensure
effective distribution and use. This technology can be classified based on the
sorbent type and injection system (Liu et al, 2008). Table 2-2 shows different
sorbent types. Injection systems include typical activated carbon injection system
(ACI) (Dombrowski,2007), TOXECON II (Dombrowski,2007), Mer-Cure
(Kang et aJ.,2007) etc. Injection systems are shown in Figures 2-5 to 2-7.
22


Table 2-2 Different Sorbent Types
Sorbent Type Concrete friendly sorbent Carbon Based e. g. C-PAC Sorbent Technologies
Non-carbon Based e.g. Mineral based sorbent, BASF Catalysts, LLC
Concrete unfriendly Sorbent Traditional carbon-based sorbent e.g. DARCO Hg Norit Americas B-PAC Sorbent Technologies
Some researchers found mercury captured by untreated ACI varies 50 to 86% with
sorbent injection rates ranging from 4.5 to 9.5 Ib/MMacf (pounds per million actual
cubic feet, where the "actual" condition refers to the actual ESP outlet condition)
(0.072 to 0.153g/m3) (Dombrowski et al, 2005; ADA-ES, 2005); Chemically
treated ACI can remove 85 to 93% mercury with sorbent injection rates ranging
from 0.14-3.3 lb/MMacf (0.0023 to 0.053 g/m3) (ADA-ES, 2005). The outstanding
performances of these chemically treated sorbents has accelerated the
commercialization of mercury control technologies and drastically reduced the
estimated cost of mercury control due to a reduction in the sorbent injection rate
required to achieve a given level of control, which offsets the higher cost of these
sorbents. However both untreated ACI and chemically treated ACI use the typical
ACI system (Figure 2-5). This mercury control strategy leads to commingling of
the activated carbon powder and fly ash that may prohibit the beneficial reuse of fly
ash
23


Sorbent Injection
System
Coil
Fly Ash + Spent stacK
Sorbent
Figure 2-5 Typical Activated Carbon Injection System (Dombrowski,2007)
Boiler
-
Most Fly Ash CaJ^Ash
Unaffected by ACI waste
Figure 2-6 TOXECON II (Dombrowski,2007)
24


In order to minimize the impact of ACI on fly ash utilization, non-carbon/
concrete-friendly sorbent injection and TOXECON configurations were
invented.
In one of URS corporations field tests, the injection of the concrete-friendly C-
PAC sorbent at approximately 1.5 lb/MMacf (0.024 g/m3) resulted in
approximately 73% ACI mercury removal (Dombrowski et al, 2007). Higher
mercury removal is expected with higher sorbent injection rates.
The TOXECON configuration has achieved approximately 90% total mercury
removal with untreated DARCO Hg and brominated DARCO Hg-LH injection at
approximately 3 and 2 lb/MMacf (0.048 to 0.032 g/m3), respectively. The installed
capital cost of this system is approximately $128 per kilowatt for the retrofit fabric
filter (FF) (Derenne et al, 2007). EPRIs TOXECON II(Figure 2-6) requires
minimal capital investment compared to the TOXECON configuration, because
a retrofit FF is not required. This technology injects sorbents directly into the
downstream collecting fields of an Electrostatic Precipitator (ESP). The majority of
fly ash (-90%) is collected in the upstream ESP fields. ADA-ESs new TOXECON
II design achieved 90% total mercury removal with DARCO Hg-LH injection at
5.5 lb/MMacf ( 0.088 g/m3) (Campbell et al, 2007).
25


The Mer-Cure process, another chemically-treated ACI technology invented by
ALSTOM Power, Inc.-U.S. Power Plant Laboratories (Fig. 2-7) is unique in that
injection takes place in the high-temperature region upstream of the air preheater
(APH) and the process employs a proprietary processor to prevent chemically-
treated Mer-Clean sorbents agglomeration and ensure uniform sorbent dispersion.
Mer-Cure achieved an average total mercury removal of 90-92% with
chemically-treated Mer-Clean 8 injection rate of 0.63 to 1.4 lb/MMacf (0.010 to
0.022 g/m3). ALSTOM-PPL evaluated three sorbents (eSorb 11, eSorb 13, and
eSorb 18) designed to preserve fly ash quality, along with Mer-Clean 8.
Preliminary results indicate that fly ash remains marketable with eSorb 13 at
about 0.5 lb/MMacf(0.008 g/m3) (85% ACI Hg capture) (Kang et al, 2007).
26


Patent pending
Figure 2-7 Mer-Cure (Kang et al.,2007)
2.3.3 Enhanced Wet Scrubbing
Oxidizing elemental mercury with catalysts makes mercury water-soluble such that
it can be captured in wet Flue Gas Desulfurization (FGD) systems that are already
installed in power plants for sulfur dioxide control. The advantage is no impact on
by-product disposal or usage, but oxidized mercury can convert back into elemental
mercury inside a wet FGD absorber, impeding mercury removal. Figure 2-8 shows
the wet FGD systems. Tests conducted by URS indicated the total mercury capture
across a pilot-scale wet FGD ranged from 76%-87% (Blythe, 2006)
27


Wet FGD System
(SO^Hg Removal)
Figure 2-8 Enhanced Wet Scrubbing system
2.3.4 Other Technologies
There are pilot-scale developments of several novel mercury control concepts such
as unbumed carbon as a mercury sorbent (Johnson et al, 2007; Samuelson et al,
2007) and ultraviolet light to convert elemental mercury into an oxidized form.
Information about whether the fly ash produced by these two novel concepts can be
used in the concrete is not available.
Sorbent injection is an effective and power plants affordable mercury removal
technology; however, sufficient data is not available to prove the reuse potential of
post-mercury-control fly ash in concrete even derived from concrete friendly
sorbents. This subject matter is discussed in the next section.
28


2.4 Concerns of Utilization of Post Mercury Control Fly ash
Fly ash derived from coal-fired power plants by sorbent injection is banned from
service as a feedstock at cement kilns. Currently the use of fly ash derived from
sorbent injection as a substitute of portland cement in concrete production has been
called into question. The utilization of fly ash in concrete production is particularly
sensitive to carbon content as well as the surface area of the carbon present in the
fly ash. Activated carbon used in mercury removal has a high surface area that is
ideal for mercury capture, but also promotes the adsorption of surfactants known as
air entraining agents (AEAs) that is added to the fresh concrete to stabilize an
optimum amount of air in the concrete, thus improving its workability and
resistance to freeze thaw cycles. Furthermore, the post-mercury-control fly ash may
influence marketability simply due to a perceived connection with the hazards of
mercury.
2.4.1 Influence on Concrete Durability
The inclusion of air as small, sub-millimeter air bubbles (less than 250 pm) makes
the concrete more resistant to damage from freezing and thawing and improves its
workability and cohesion (Bruere, 1971; Rixom et al, 1986). The residual carbon in
fly ash may interfere with AEAs and affect concretes workability and durability
towards freezing and thawing conditions.
29


2.4.1.1 Air Entrainment Interfered by Regular Fly Ash
The utilization of fly ash in concrete has been reported to affect the required dosage
of AEAs to entrain the proper amount of air in concrete mixtures (Wesche, 1991;
Bouzoubaa et al, 2000; Dhir et al, 1999; Lane, 1991). The AEAs are strongly
adsorbed by some fractions of the fly ash instead of stabilizing the air-water/cement
interface, reducing the amount of AEAs to stabilize entrained air (Hachmann et al,
1998; Hill et al, 1997). The adsorption loss can be compensated by an increased
dosage of AEA, but normal variations in ash properties give rise to large and
unacceptable variations in entrained air (Hachmann et al, 1998; Freeman et al,
1997). A study indicated even in ashes acquired from the same power plant,
variations in several properties of fly ash existed (Helmuth, 1987). These variations
can emerge from fluctuating load conditions (Clendenning et al, 1963). In addition,
air entrained fly ash concrete has been reported to lose its air over mixing time
(Zhang, 1996; Gebler et al, 1983; Lane et al, 1991). The increased AEA
requirements in fly ash result in higher air loss tendency (Gebler et al, 1983).
However, laboratory data have shown that air loss may be due to the type of AEA
used (Zhang, 1996) and loss of air with time in 100% portland cement concrete has
been reported as well (Dodson, 1990; Dhir et al, 1999).
30


The unbumed carbon, and not the inorganic fraction of the fly ash, appears to be
responsible for the adsorption of AEAs (Gao et al, 1997; Gebler et al, 1983;
Clendenning et al, 1963; Hachmann et al, 1998; Hill et al, 1997; Freeman et al,
1997). A large part of the carbon surface is non-polar which provides active
adsorption sites for the hydrophobic part of the surfactants. Recent work
concerning fly ash interference with air entrainment in concrete by some scholars
(Kulaots et al, 2004; Gao et al, 1997; Hachmann et al, 1998; Freeman et al, 1997;
Yu et al, 2000; Gao et al, 2002) argued that the following properties of unbumed
carbon contribute to the AEA adsorption: (1) the amount, (2) the specific surface
area, (3) the accessibility of the surface area, and (4) the chemical nature of the
surface.
Other compounds of fly ash, which may influence the air entrainment in concrete,
have been reported by Gebler and Klieger (1983). Increased SO3 or total alkalis
(N2O or K2O) content has led to reduced air loss or decreased AEA requirements in
freshly mixed concrete respectively. The latter observation is noted to be in
agreement with work by others (Greening, 1967; Kulaots et al, 2003) showing that
less AEA was required in portland cement mortars with increased alkalis. Finally,
higher fineness of fly ash has been argued to lead to increased required dosage of
AEA (Dodson, 1990; Bouzoubaa et al, 2000), but has been stated by others to be of
minor importance (Clendenning et al, 1963; Dhir et al, 1999).
31


2.4.1.2 Air Entrainment Interfered by Post-Mercury-Control Fly Ash
The post mercury control fly ash derived from ACI contains a higher carbon
content than standard ash. To what extent a given fly ash interferes with air
entrainment in concrete is commonly determined by the foam index test (Kulaots et
al, 2004).
This test is a simple laboratory titration method and a proposed procedure is
outlined by Dodson (Dodson, 1990). A diluted commercial AEA is added in small
aliquots to a suspension of cement (cement / fly ash) and water. The bottle
containing the suspension is capped and shaken for 15s after each addition. The
surfactant behavior of the AEA results in foam formation, which is visually
observed for stability. Further addition of AEA increases the foam stability, and the
test is continued until no bursting of bubbles is observed in a period of 15s. The
amount of AEA added to produce the stable foam corresponds to the foam index
value of the cement (cement / fly ash). Usually, the foam index value of a pure
cement sample is used as blank and subtracted from the value of the cement / fly
ash sample in order to eliminate any variations in the foam index value caused by
the cement.
32


Senior et al (2004) completed full-scale demonstration of sorbent injection for
mercury control on WE Energiess Pleasant Prairie Power Plant, Unit 2 that burned
western subbituminous coal. An ESP is installed in that unit. The long-term tests
were divided into three 5-day periods of continuous injection rates of 1, 3, and 10
lb/MMacf (0.016, 0.048, and 0.161 g/m3) with a traditional carbon based sorbent
provided by Norit Americas. The average mercury removal efficiencies for the
three injection rates were 40-50%, 50-60% and 60-70%, respectively. Increasing
injection concentration above 10 lb/MMacf (0.161 g/m3) did not increase mercury
removal. Fly ash from the long-term tests met the nominal ASTM C-618 limits,
however fly ash samples containing any amount of activated carbon failed the foam
index test.
Foam index tests conducted by Lockert et al (2005) indicates that using pure fly ash
with no added carbon, Concrete-Friendly C-PAC in both 1 wt% and 3 wt%
levels had no measurable affect on AEA requirements. Typical carbon based
sorbent, B-PAC, however, required almost 10 times as much AEA to achieve the
6% air entrainment goal at 1 wt% and nearly 30 times as much at 3 wt%. During
the long-term test (Nelson Jr. et al, 2007), foam index values of the fly ash samples
containing the C-PAC sorbents at 4.6 lb/MMacf (0.074 g/m3) indicated that
concretes made with the fly ash and slightly elevated AEA additions had the same
wet and dry air entrainment characteristics and bubble stability.
33


Foam index tests for Mer-Cure Technology (Kang et al, 2007) indicates that for
Mer-Clean 8 sorbent, reduction of 72% of baseline mercury or 87% of input
rw
mercury can be achieved while still allowing continued ash sales. For eSorb 13
sorbent, reduction of 85% of baseline mercury or 92% of input mercury can be
achieved while allowing continued ash sales.
The foam index test is not a standardized method and is carried out in various
modified ways by different research groups. Factors which make the test difficult to
standardize include AEAs, the individual user criterion of stable foam endpoint,
and test times (Kiilaots et al, 2003; Freeman et at, 1997; Baltrus et al, 2001; Yu et
al, 2000). Commercial AEAs show different chemical nature. The age of the AEA
and the individual user criterion of the stable foam endpoint influence the foam
index results. Experiments have shown that adsorption of surfactants still occurs up
to 20 minutes (Baltrus et al, 2001) and more than 60 minutes (Yu et al, 2000) after
being added, which is longer than the total test time of 10 minutes often used in the
foam index test. However, this may be due to the presence of CO? in the
atmosphere which reacts with the surfactants to form insoluble acids (Kiilaots et al,
2003; Baltrus et al, 2001). Thus the influence of the discussed parameters makes it
difficult to compare results between different laboratories and research groups.
34


The inclusion of air makes the concrete more durable to freezing and thawing, but
many factors make the foam index test difficult to standardize. The foam index test
cannot give a true measure of the resistance of post-mercury-control fly ash
concrete to damage from freezing and thawing. Therefore, the direct freezing and
thawing test should be completed. In addition, the durability of concrete requires
the concrete is excellent in resistance to sulfate attack and chloride ion penetration.
However, there is no data available to show the influence of post-mercury-control
fly ash on the durability of concrete from the direct freeze-thaw resistance test,
sulfate resistance test and permeability test.
2.4.2 Influence on Concrete Other Properties
The effect of residual carbon in fly ash concrete, besides poor air entrainment
behavior, is increased water requirement to obtain normal consistency in the
concrete paste (Wesche, 1991), mixture segregation (Freeman, 1997), and
discoloration (Freeman, 1997). The latter is aesthetically unacceptable in certain
applications.
Locked et al (2005) found that addition of C-PAC at both 1 wt% and 3 wt%
concentrations had no measurable effect on 7, 14, or 28 days of age compressive
strength. During the long term test (Nelson Jr. et al, 2007), concretes made with fly
ash containing C-PAC sorbents could meet the strength requirement. Dombrowski
35


(2007) found that fly ash concrete passed all criteria including slump 15 cm 25
mm(6 in. 1 in.) and strength requirement. This fly ash was derived from a plant
burning Texas Lignite with Darco Hg-LH (traditional carbon based sorbent)
injection at the upstream of ESP with 2 lb/MMacf (0.032 g/m3). The mercury
removal goal was 50-70%. This indicates that the low Darco Hg-LH injection rate
will not prohibit fly ash reuse.
2.4.3 Influence on the Environment
An estimated 68 metric tons (75 U.S. short tons) of mercury are contained in the
fuel burned annually at coal-fired power plants. Currently approximately 60% is
released to the atmosphere and the remaining 40% is removed by particulate and
sulfur dioxide control devices and managed with the coal combustion by-products
(Gustin et al, 2004). Mercury in coal combustion by-products is present in
relatively low concentrations (<500 ng/g) and is stable with little evidence of
leaching or volatilization (EPRJ, 1999, 2001; Chu et al 1999). Enhanced mercury
removal technologies will result in an increase of the mercu^ in the coal
combustion by-products. Another concern of the utilization of the post mercury
control fly ash in concrete is its influence on the environment. Volatilization and
leaching appear to be the most likely pathway for liberation of mercury from fly
ash concrete.
36


2.4.3.1 Gaseous Mercury from Fly Asb and Curing Fly ash Concretes
Volatilization is the primary pathway for mercury if fly ash is used as a raw
material in cement kilns. A December 2006 final rule issued by EPA has banned
the fly ash collected at coal-fired units that employ sorbent injection for mercury
control serving as a feedstock at cement kilns (U.S.EPA, 2006).
The exchange of mercury between fly ash and the atmosphere was measured in the
laboratory and in situ at a fly ash landfill by Gustin et al (2004). All samples of fly
ash, with the exception of that derived from lignite-type coal, can absorb
atmospheric mercury, which includes samples collected from two demonstration
projects using carbon injection for enhanced mercury capture.
Gaseous mercury was measured by Golightly and co-workers (2005) in the
laboratory from cured concretes that contain ordinary portland cement (OPC) and
three concretes in which class F fly ash substituted for a fraction of the cement: (a)
33% fly ash (FA33), (b) 55% fly ash (FA55), and (c) 33% fly ash plus 0.5%
mercury-loaded powered activated carbon (HgPAC). Release of mercury was
confirmed for the four concretes, and mean rates of mercuiy release (0.10-0.43
ng/day per kg of concrete, which is equal to 0.1-0.43xl0'l2lb/day per lb of concrete)
over the standard first 28 days of the curing followed the order OPC < FA33 =
37


FA55 < HgPAC. The mercury flux from exposed surfaces of these concretes
ranged from 1.9 0.5 to 8.1 2.0 ng/m2/h (0.39 0.1 xlO12 to 1.7 0.4 xlO'12
lb/f^/h), values similar to the average flux for multiple natural substrates in Nevada,
4.2 1.4 ng/m2/h (0.86 0.29 xio12 lb/tf/h) (Zehner et al, 2002). Mercury
release rates for FA55 and HgPAC beyond the initial 28 days maturation may
ultimately diminish to levels exhibited by OPC concrete. The release of mercury
from all samples was less than 0.1% of total mercury content over the initial curing
period, implying that nearly all of the mercury was retained in the concrete.
2.4.3.2 Mercury Leaching from Fly Ash and Fly Ash Concrete
When considering leaching of mercury from the fly ash, whether it takes place in
landfills or in concrete, it is difficult to specify one single condition in terms of pH
and temperature that will apply in each case. A variety of different leaching
procedures have been used to characterize the stability of sorbent-containing fly ash
in the environment.
Toxicity Characteristic Leaching Procedure (TCLP) TCLP was designed to
simulate leaching in an unlined, sanitary landfill, based on a co-disposal scenario of
95% municipal waste and 5% industrial waste. The method is an agitated extraction
test using leaching fluid that is a function of the alkalinity of the phase of the waste.
Typically, an acetic acid solution having a pH of 2.88 is used for this procedure.
33


The leachate is analyzed for mercury using cold vapor atomic adsorption
spectroscopy (zCV-AAS) (U.S. EPA, 1990).
Synthetic Ground Water Leaching Procedure (SGLP) SGLP was developed at
the University of North Dakota Energy and Environmental Research Center and
was designed to simulate the leaching of coal utilization by-products under likely
environmental conditions. The SGLP was designed primarily for use with materials
that undergo hydration reactions upon contact with water. Test conditions are end-
over-end agitation, a 20:1 liquid-to-solid ratio and a 18-h equilibrium time (Hassett,
1987).
ASTM Water Leaching Procedure (ASTM D-3987) This method is a procedure
for rapidly generating a leachate from solid waste that can be used to estimate the
mobility of inorganic constituents from the waste under the specified test
conditions. This procedure is an agitated extraction method that uses reagent water
as the leaching fluid. The procedure involves an 18-hour contact time between a
solid waste and reagent water with rotary agitation. The method calls for testing a
representative sample of the waste, and as a result, it does not require particle size
reduction. The method has been tested to determine its applicability to inorganic
constituents, but it has not been tested for application to organic constituents.
39


EPA Method 1312, Synthetic Precipitation Leaching Procedure (SPLP) The
extraction fluid is comprised of 60:40 sulfuric acid : nitric acid by weight that is
added to deionized water to adjust the pH to between 4.2 and 5. Samples are
agitated for 182 hr at 302 rpm using a rotary agitation apparatus. Aliquots of the
leach solutions are filtered using a stainless-steel zero-head-space extractor using
pre-purified nitrogen gas. Three 100 mL aliquots are taken for total Hg analysis.
Total Hg in the extraction fluid was determined using bromine monochloride
oxidation and tin chloride reduction (U.S. EPA, 2003).
An Integrated Framework for Evaluating Leaching in Waste Management
and Utilization of Secondary Materials (Kosson et al, 2002) This procedure
provides a tiered, flexible framework capable of incorporating a range of site
conditions that affect waste leaching and can estimate leaching potential under
conditions more representative of actual waste management. The integrated
framework evaluates inorganic constituent leaching from wastes which is based on
the measurement of intrinsic leaching properties to estimate release under field
management scenarios. Detailed test methodologies includes a titration pre-test, an
availability test at pH 7.5, a teachability test at 11 different pHs, and a long term
leachability test at various liquid to solid ratios.
40


Senior et al (2004) conducted the mercury leaching tests for fly ash derived from
sorbent injection for mercury control on coal-fired power plants using TCLP,
SGLP and ASTM D-3987 methods. These power plants burned low sulfur
bituminous, Powder River Basin or subbituminous coals and the mercury removal
rate ranged between 40-70% with an injection rate of 1-10 lb/MMacf (0.016 -0.161
g/m3) of traditional carbon-based sorbents. All tests show the amount of mercury
leached from the sorbent/ash mixtures is low and generally below the detection
limit of the method.
Research completed by Gustin et al (2004) indicates that mercury concentrations of
extracts derived using SPLP methods for fly ash samples from two demonstration
projects using carbon injection for mercury capture were less than 14.4 ng/L
(8.99* 10'10 lb/fit3), compared with the Safe Drinking Water Act concentration of
2000 ng/L (1.25*1 O'7 lb/ft3) and the EPA Goldbook Criterion of 1400 ng/L
(8.74*10 lb/ft3).
Sanchez et als study (2006) focused on facilities that use sorbent injection for
mercury control, which includes four facilities with activated carbon injection (AC1)
and two facilities with brominated ACI. Fly ash was obtained from each facility
with and without the addition of enhanced mercury control technology. Each fly
41


ash sampled was evaluated in the laboratory for leaching as a function of pH and
liquid to solid ratio using Kossons integrated framework for evaluating leaching.
Results indicate that mercury is strongly retained by the resulting coal combustion
residuals (OCRs) and unlikely to be leached at levels of environmental concern.
Arsenic and selenium may be leached at levels of potential concern from CCRs
generated at some facilities both with and without enhanced mercury control
technology.
Currently, a research study evaluating mercury leaching from fly ash concrete is
being conducted by the U.S. Electrical Power Research Institute (EPRI) (Ladwig,
K., Personal Communication, August 22, 2008). However there is still no published
data available at this time.
2.5 Summary from Literature Review
Table 2-3 summarizes researches of influence of post-mercury-control fly ash on
fresh and hardened properties of concrete from literature review. Activated carbon
injections are the most mature technologies for mercury capture. These
technologies have great potential for significant use in coal-fired power plants. The
increased carbon content in the fly ash might interfere with AEAs and prohibit the
reutilization of fly ash. However, the influence of carbon on the durability of fly
ash concrete is just indicated from the in-direct Foam Index Tests. There is no data
42


available to show the influence from the freeze-thaw resistance test, sulfate
resistance test, and permeability test all of which are important tests for concrete
durability. As previously discussed, it is difficult to compare the foam index results
from different research groups. Some studies indicate that it is not a concern
regarding the volatilization and leaching of mercury from fly ash and fly ash
concrete. But there is not enough data to indicate the leaching of other toxic
elements besides mercury, such as arsenic, lead, selenium, etc from fly ash concrete.
Therefore a comprehensive study on the influences of different mercury controls on
fresh and hardened properties of fly ash concrete is needed to examine the reuse
potential of post mercury control fly ash derived from sorbent injection. In addition,
the safety concerns regarding the use of fly ash containing mercury must be
examined.
43


Table 2-3 Summary of Post-Mercurv-Control Fly Ash Concrete from Literature Review
Mercury Control Technologies Fresh Concrete Properties (Air Entrainment) Compressive Strength (ASTM C 39) Freeze-Thaw (ASTM C 666) Sulfate Resistance (ASTM C 1012) Chloride Ion Penefrabsty (ASTM C 1202) Leaching
Sorbent Injection Typical ACI with Concrete Unfriendly Sorbent Senior et al. 2004, Lockert et al, 2005 Dombrowski, 2007 X X X Senior et al, 2004 Gustm et al, 2004 Sanchez et al. 2006
Typical ACI with Concrete friendly Sorbent Lockett et al, 2005; Nelson Jr et al, 2007 Lockert ct al, 2005 Nelson Jr. et al, 2007 X X X X
TOXECON n X X X X X X
Mer-Cure Kang et al, 2007 X X X X X
Enhanced Wet Scrubbing X X X X X X
x indicates no published data available


3 Experimental Plan: Laboratory Testing of Post Mercury Control Fly Ash
Concrete
Chapter 3,4 and 5 examine the reuse potential of post-mercury-control fly ash
derived from sorbent injection in concrete. As discussed in the Chapter 2, due to its
low cost and high efficiency, sorbent injection, particularly ACI, has potential for
significant use in the coal fired power plants. However, two concerns may affect
these fly ashes from use in concrete. The first concern is the influence on the
concrete properties due to the increased carbon content, e.g. air content, durability,
etc. The second concern is the environmental and safety issue as a result of the
mercury concentration. In order to examine the reuse potential of the post-mercury-
control fly ash in concrete, two phases of investigation were completed in this
dissertation.
Phase I Concrete mixtures containing nine different sorbent injection fly
ashes with 15% cement replacement were designed and batched. The fresh and
hardened concrete properties were tested and analyzed. The reuse potential of
45


the sorbent injection ashes was examined. The fly ash with the best
performance was selected for Phase II testing.
Phase II The cementitious material and fly ash contents in the concrete were
optimized based on the fresh and hardened concrete properties testing and
LCA investigation. Concrete mixtures with ACI fly ash contents ranging from
15%-60% and cementitious material contents from 338 391 kg/m3 (570 -705
lb/cy) were investigated. In addition, tests were completed to examine the
leaching potential for the mercury and other toxic elements (i.e. arsenic, lead,
selenium, etc) from the optimized ACI fly ash concrete mixture.
Phase I of this research study examined nine fly ashes obtained from Boral Material
Technologies, URS Corporation, Cerametec Inc., and ADA-ES. These fly ash
samples were investigated through a comprehensive concrete testing program. The
fresh and hardened concrete properties were researched to determine the effects
each fly ash and their mercury control technologies had on concrete performance.
The best performing fly ash was selected for Phase II of this study. During Phase II,
the cementitious content and percent replacement of portland cement with fly ash
were changed in order to develop an optimized mixture. The optimized fly ash and
cementitious content was decided through strength and durability tests. In addition,
iso-strength and iso-durability (charge passed) contour lines were developed to aid
46


in the determination of the optimized fly ash and cementitious contents. The
leaching potential of mercury and other toxic elements from the optimized concrete
mixture was performed.
3.1 Concrete Materials
3.1.1 Fly Ash
Nine sorbent injection fly ashes from four different sources in the U.S. were used in
phase I. As shown in Table 3-1. Two samples (ACI1&2) were provided by Boral
Material Technologies. Five (ACI 5-9) were from URS Corporation, and the
remaining two (ACI3&4) came from Cerametec Inc. and ADA-ES respectively.
Table 3-1 Sorbent and Provider of Each Sorbent Injection Ash
ACI1 ACI2 ACI3 ACM ACI5 ACM ACI7 ACI8 ACI9
Sorbent CPAC Calgon Unknown Calgon CPAC CPAC BASF* BASF* Darco Hg
Provider Boral Boral Cerametec ADA- ES URS URS URS URS URS
a. Type 7 and 8 fly ash were named ACI7 and ACI8 for convenience, but they contain a non-
carbon based sorbent BASF.
Five samples (ACU, ACI5, ACI6, ACI7, and ACI8) contain concrete-friendly
sorbents which do not interfere with AEAs ability to entrain air. ACI1 contained a
carbon based sorbent CPAC. But the injection rate of the sorbent was not available.
ACI5-8 samples were from the same power plant. ACI5 and ACI6 contained CPAC
with 0.5 Ib/MMacf (0.008 g/m3) and 1.5 Ib/MMacf (0.024 g/m3) of injection rates
47


respectively, while ACI7 and ACI8 had non-carbon based sorbent BASF with 12
lb/MMacf (0.193 g/m3) and 8 lb/MMacf (0.128 g/m3) of injection rates respectively.
Three samples (ACI2, ACM and ACI9) contained concrete-unfriendly sorbents
Calgon and Darco-Hg (Table 3-1), which do absorb AEAs. The sorbent type in the
third ash (ACI3) is unknown. The sorbent injection rate of ACI9 was 1.0 lb/MMacf
(0.016 g/m3), but the injection rates for ACI 2, 3, &4 were not available.
The chemistry analysis of ACI1, 2, &3 is shown in Table 3-2. The sum of SiC>2,
AI2O3 and Fe2C>3 of the three ashes are 55.93, 55.34 and 58.59 % for ACU, ACI2
and ACI3, respectively. The three fly ashes had high CaO content, 28.60, 28.74 and
24.69 %for ACI1, ACI2 and ACI3, respectively. According to ASTM C 618, the
fly ashes with a SiC>2 + AI2O3 + Fe2C>3 content between 50 and 70 wt% and high in
lime (20 30 wt%) are defined as class C. The losses on ignitions of the three are
under 6%. Loss on ignition represents the carbon content in the fly ash. ACI3 has
higher carbon content than ACI1 and ACI2. The higher carbon injection rate for
ACI3 is expected. The outstanding performances of these chemically treated
sorbents have accelerated the commercialization of mercury control technologies
and drastically reduced the estimated cost of mercury control due to a reduction in
the carbon injection rate required to achieve a given level of control. This offsets
the higher cost of these sorbents. In addition, the low injection rates guarantee the
43


carbon does not darken the fly ash derived from ACI. The chemistries of the three
fly ashes met ASTM C 618 class C specification.
Table 3-2 Chemical Analysis of Fly Ashes
CHEMICAL TESTS ACI1 ACI2 ACI3 ASTM C 618 CLASS F/C
Silicon Dioxide (Si02), % 33.14 32.73 33.28
Aluminum Oxide (A1203), % 15.65 15.55 18.82
Iron Oxide (Fe203), % 7.14 7.06 6.49
Sum of Si02, A1203, Fe203, % 55.93 55.34 58.59 70.0/50.0 min.
Calcium Oxide (CaO), % 28.60 28.74 24.60
Magnesium Oxide (MgO), % 6.81 6.99 5.59
Sulfur Trioxide (S03), % 2.47 2.62 1.50 5.0 max.
Sodium Oxide (Na20), % 1.95 1.99 1.74
Potassium Oxide (K20), % 0.32 0.29 0.60
Loss on ignition, % 0.89 0.95 3.52 6.0 max
The chemistries of the other fly ash samples are not available. Low carbon injection
rates are expected in other fly ash samples because the carbon did not darken these
fly ashes. Appendix A shows photographs of the nine sorbent injection fly ashes.
3.1.2 Portland Cement
An ASTM Type I portland cement provided from Holcim, Inc. The specific gravity
of this cement was 3.15 and the Blain fineness was 398 m2/kg. The complete
chemical and physical properties of the cement are shown in Table 3-3 and 3-4.
The material certification report was attached at Appendix B.
49


Table 3-3 Chemical Properties of the Cement
Item Result ASTM C 150 Limits
Si02 (%) 19.7
Ai203 (%) 4.6 6.0 max
Fe20, (%) 3.2 6.0 max
CaO (%) 63.8
MgO (%) 1.3 6.0 max
S03 (%) 3.2 3.0 max
Loss on Ignition (%) 2 3.0 max
Insoluble Residue 0.53 0.75 max
C02 (%) 1.1
Limestone (%) 2.9 5.0 max
CaC03 in Limestone(%) 83 70 min
Inorganic Processing Addition 0 5.0 max
C3S (%) 62
C2S(%) 9
C3A (%) 7 8 max
C4AF(%) 10
C3S + 4.75 C3A (%) 95 100 max
Table 3-4 Physical Properties of the Cement
Item Result ASTM C 150 Limits
Air Content(%) 7 12 max
Blaine Fineness (m2/kg) 398 260 min
430 max
Autoclave Expansion (%) (C151) 0.01 0.80 max (C 151)

Compressive Strength Mpa (psi) C 150
3 days 31.4 (4450) 10.0(1450) min
7 days 38.7(5620) 17.0 (2470) min

Initial Vicat (minutes) 134 45-375
Mortar Bar Expansion (%) (C 1038) 0.003
Heat of Hydration: 7 days, kJ/kg (cal/g) 343(82)
50


3.1.3 Aggregates
Coarse and fine aggregate were obtained from a representative source within
Colorado. The UCD Materials Testing Laboratory acquired both the coarse and
fine aggregate conforming to the ASTM C33 standard. Bestway Aggregate
provided material properties and gradation reports for the aggregates.
The coarse aggregate meets the ASTM C33 Size Number 57 and 67 gradation
requirements. The graded coarse aggregate had a maximum aggregate size (MAS)
of 25.4mm (l.Oin.) and a nominal maximum aggregate size (NMAS) of 19mm
(0.75 in.).
The fine aggregate meets the ASTM C33 gradation requirement for concrete fine
aggregate. Based upon laboratory tests performed by WesTest of Denver, Colorado,
this aggregate has a low potential for deleterious alkali-silica behavior. The
material properties data for both coarse and fine aggregate are included in
Appendix C and D. The properties of the coarse and fine aggregate are shown in
Table 3-5.
Table 3-5 Coarse and Fine Aggregate Properties
Material BSGSSd ASG AC (%) DRUW (lb/cf) FM
Coarse Aggregate 2.61 2.64 0.8 103 -
Fine Aggregate 2.63 2.66 0.7 - 2.74
51


3.1.4 Chemical Admixtures
A commercially available sulfonated, naphthalene formaldehyde condensate high
range water reducer admixture (HRWRA) was supplied by W.R. Grace. The
product instruction recommended that addition rates of the HRWRA range from 6
to 20 fl oz/cw (390-1300 mL/ 100kg) of cementitious material.
The AEA used in all the fly ash concrete mixtures contained a blend of high-grade
saponified rosin and organic acid salts. Typical addition rates ranged from 1/4 to 3
fl oz/cw (15 to 200 mL/lOOkg) of cementitious material.
3.2 Mixture Designs
The absolute volume method as described in the Portland Cement Association
document Design and Control of Concrete Mixtures was used for the design of
the concrete mixtures. The phase I study examined a total of thirteen mixtures with
a water-to-cementitious ratio (w/cm) of 0.40 and a cementitious content of 377
kg/m3 (6351b/cy). Two of the thirteen mixtures did not contain fly ash and acted as
the control mixtures for the study phase. The remaining eleven mixtures contained
a 15% replacement of cement with fly ash. The AEA dosage rate ranged from 0 to
2.5 fl oz/cwt (0 to 163 mL/100 kg). Phase II consisted of the design and batching
of eight concrete mixtures containing the Boral CPAC mercury control fly ash. The
52


w/cm remained constant at 0.40 for all the mixtures. The cementitious content
ranged from 338 391 kg/m3 (570-705 lb/cy) and the percent fly ash from 30-60%.
3.3 Test Methods
The batching followed ASTM C 192 Standard Practice for Making and Curing
Concrete Test Specimens in the Laboratory. Both fresh and hardened concrete
properties were examined for each mixture batched. The fresh concrete properties
that were examined at the time of batching included slump (ASTM C 143), unit
weight (ASTM C 138), air content (ASTM C 231).
Hardened concrete properties that were evaluated in this study included
compressive strength at 1, 3, 7, 28, 56, and 90 days of age, using for each test three
4x8 cylinders, rapid chloride ion penetrability (ASTM C 1202) at 28, 56 and 90
days of age and resistance to freezing and thawing (ASTM C 666). DK-4000
Dynamic Resonance Frequency Tester and E-METER Resonant Frequency Tester
were used to measure the resonant frequency of concrete prisms. Both of the two
equipments comply with ASTM C 215. The length changes of mortar bars were
measured by ASTM C 1012.
53


The fresh and hardened concrete tests in this study are shown in Table 3-6. The
properties of concretes incorporated with sorbent injection fly ash were compared
with control mixtures in both phases of this study.
Table 3-6 Fresh and Hardened Concrete tests
Fresh Concrete Tests Standard Time of Test
Slump A STM C 143 At Batching
Unit Weight ASTM C 138 At Batching
Air Content ASTMC231 At Batching
Hardened Concrete Tests Standard Time of Test
Compressive Strength ASTM C 39 1,3,7,28,56,90 days
Freeze-thaw Resistance ASTM C 666 28 and Subsequent days
Rapid Chloride Ion Penetrability ASTM C 1202 28, 56,90days
Sulfate Attack Resistance ASTM C1012 7 days and Subsequent days
3.4 Data Analysis
Chapter 4 provides the mixture design and test results for the Phase I study.
Chapter 5 provides the mixture design and test results for the Phase II optimization
study. Based on the fresh and hardened concrete properties data measured in this
research and the leaching test results, life cycle analyses were completed on phase
II concrete mixtures. Thus recommendations are made for the use of post-mercury-
control fly ash in concrete.
54


4 Phase I: Reuse Potential of Sorbent Injection Ashes in Concrete
Fly ash use in concrete is practiced and accepted at low replacement levels. The
majority of engineering, architects, and contractors are not comfortable with
specifying higher percent replacement of portland cement with fly ash, e.g. 20% or
greater, without incentive or mandate (Reiner, 2007). The reuse potential of the
sorbent injection fly ashes was examined by incorporating 15% fly ash
(replacement of portland cement) into the concrete and testing the fresh and
hardened concrete properties.
4.1 Concrete Mix Proportions
Thirteen concrete mixtures were designed, batched, and tested for Phase I. The
mixture characteristics of the concrete mixtures 1 through 13 are summarized in
Table 4-la (SI Units) and Table 4-lb (U.S. Customary). The cementitious material
content in all mixtures except Mixture 2 was 377 kg/m3 (635 Ib/cy). Mixtures 1 and
2 were control mixtures without fly ash. Mixture 1 was included an AEA dosage of
163 mL/lOOkg cementitious material (2.5 fl oz/cwt), while Mixture 2 did not
include AEA. Mixture 2 was created in order to examine the influence of the
HRWRA on the air content of the concrete. Sorbent injection fly ashes replaced
55


15% of cement by weight in Mixtures 3-5 with a 163 mL/100kg cementitious
material (2.5 fl oz/cwt) dosage rate of AEA. Sorbent injection fly ashes replaced
15% of cement in Mixtures 6-13 respectively with a 98 mL/100 kg cementitious
material (1.5 fl oz/cwt) dosage rate of AEA.
The target slump for all mixtures was 102 25 mm( 4 1 in). A HRWRA was
used to meet the slump requirements.
Table 4-la Phase I: Mixture Proportions (SI)
Mixture Identification W/(C+FA) Water Cement Fly Ash Coarse Aggregate Fine Aggregate AEA
kg/m3 kg/m3 kg/m3 kg/m3 kg/m3 mL/ 100kg
1 0Ash_2.5 0.4 151 377 0 1032 720 163
2 OAsh 0 0.47 151 320 0 1032 711 0
3 15ACI12.5 0.4 151 377 57 1032 711 163
4 15ACI2 2.5 0.4 151 377 57 1032 711 163
5 15ACI3 2.5 0.4 151 377 57 1032 711 163
6 15ACI1 1.5 0.4 151 377 57 1032 711 98
7 15ACI2 1.5 0.4 151 377 57 1032 711 98
8 15ACI41.5 0.4 151 377 56 1032 711 98
9 15ACI51.5 0.4 151 377 56 1032 711 98
10 15ACI6 1.5 0.4 151 377 56 1032 711 98
11 15ACI7 1.5 0.4 151 377 56 1032 711 98
12 15ACI8 1.5 0.4 151 377 56 1032 711 98
13 15ACI9 1.5 0.4 151 377 56 1032 711 98
56


Table 4-lb Phase I: Mix Proportions (U.S. Customary)
Mixture Identification W/(C+FA) Water Cement Fly Ash Coarse Aggregate Fine Aggregate AEA
lb/cy lb/cy lb/cy lb/cy lb/cy fl oz/cwt
1 OAsh 2.5 0.4 254 635 0 1740 1214 2.5
2 OAsh 0 0.47 254 540 0 1740 1199 0
3 15ACI1 2.5 0.4 254 635 95 1740 1199 2.5
4 15AC12 2.5 0.4 254 635 95 1740 1199 2.5
5 15ACI3 2.5 0.4 254 635 95 1740 1199 2.5
6 15ACI1 1.5 0.4 254 635 95 1740 1199 1.5
7 15ACI 1.5 0.4 254 635 95 1740 1199 1.5
8 15 ACM 1.5 0.4 254 635 95 1740 1199 1.5
9 15ACI5 1.5 0.4 254 635 95 1740 1199 1.5
10 15ACI6 1.5 0.4 254 635 95 1740 1199 1.5
11 15ACI7 1.5 0.4 254 635 95 1740 1199 1.5
12 15ACI8 1.5 0.4 254 635 95 1740 1199 1.5
13 15ACI9 1.5 0.4 254 635 95 1740 1199 1.5
4.2 Test Results
4.2.1 Fresh Concrete Properties Test Results
The fresh concrete properties tests included slump, unit weight, and air content.
The results of these tests are summarized in Table 4-2.
4.2.1.1 Phase I: Slump and Superplasticizer
The slumps of the thirteen mixtures and the amounts of superplasticizer added are
shown in Table 4-2 and plotted in Fig. 4-la (Mixtures 1-8) and Fig. 4-lb (Mixtures
1,2, 9-13).
57


Table 4-2 Phase I: Fresh Concrete Properties Tests Results
Mixture Identification Slump Unit Weight Air Content HRWR
mm in. kg/m3 Ib/cf % L/100kg fl oz/cw
1 0Ash_2.5 13.3 5.25 2195 137.0 11.0 1.35 20.7
2 0Ash_0 7.6 3.00 2371 148.0 2.8 0.91 14.0
3 15ACI1_2.5 8.9 3.50 2223 138.8 9.0 0.67 10.3
4 15ACI2_2.5 7.6 3.00 2249 140.4 9.0 0.86 13.2
5 15ACI3_2.5 8.3 3.25 2339 146.0 5.0 1.04 16.0
6 15ACI1_1.5 10.2 4.00 2291 143.0 7.0 1.25 19.2
7 15ACI2_1.5 13.3 5.25 2217 138.4 9.5 0.91 14.0
8 15ACI4_1.5 8.9 3.50 2316 144.6 5.4 2.74 42.0
9 15ACI5_1.5 9.5 3.75 2284 142.6 8.0 1.14 17.5
10 15ACI6_1.5 8.9 3.50 2268 141.6 8.5 1.02 15.7
11 15AC17_1.5 7.0 2.75 2255 140.8 8.0 0.68 10.5
12 15ACI8_1.5 11.4 4.50 2236 139.6 10.0 1.14 17.5
13 15ACI9J.5 7.0 2.75 2236 139.6 8.5 0.74 11.4
16.0
14.0
12.0
I 10.0
| 8.0
3 6.0
w
4.0
2.0
0.0
o>
o
o
13
tc
X
H Slump HRWR
Figure 4-la Phase I: Slump and Superplasticizer (Mixtures 1-8)
58


16.0 ----------------------------------------------------------------- 1.60
i Slump HRWR
Figure 4-lb Phase I: Slump and Superplasticizer (Mixtures 1,2, 9-13)
Different dosage rates of the superplasticizer were used to obtain the targeted
slump of 100mm 25mm (4 lin). Fly ash is beneficial to workability. Its
particles are generally spherical in shape, which can act as small ball bearings to
reduce interparticle friction. The 0Ash_2.5 and 15ACI2_1.5 had the highest slump
13.3mm (5.25 in.) with 1.35L/100kg (20.7 fl oz/cw) and 0.91L/100kg (14.0 fl
oz/cw) of HRWRA, respectively. The reduction of the dosage in 15ACI21.5 is
most likely due to the 15% cement replacement by fly ash. The improvement of the
slump due to the fly ash is not obvious by comparing other fly ash concrete
mixtures with the control mixtures. However, all the fly ash concrete mixtures
59
HRWR(L/100kg)


reached the targeted slump by adding HRWRA. The dosage rates of which were all
within the manufactures recommended range.
4.2.1.2 Phase I: Air Content and Unit Weight
The air contents and unit weights of the various concrete mixtures are given in
Table 4-2 and plotted in Fig 4-2a (Mixtures 1-8), and Fig 4-2b (Mixtures 1,2,9-13).
2400
£2350
^ 2300
1,2250
§ 2200
g 2150
2100
H Unit Weight Air Content
Figure 4-2a Phase I: Unit Weight and Air Content (Mixtures 1-8)
SO
Air Content (%)


2400
12.0
10.0
8.0 g.
C
(D
6.0 H
o
<
2.0
2100
0.0
Unit Weight Air Content
Figure 4-2b Phase I: Unit Weight and Air content (Mixtures 1,2, 9-13)
The air content of the non-air entrained OAsh O was only 2.8%, while other air-
entrained mixtures ranged between 7.0% and 11.0% with different dosages of AEA.
In Figure 4-2a, 15AC11_2.5, 15ACI2_2.5, 15ACI3 2.5 and the control mixture
0Ash_2.5 had 9.0%, 9.0%, 5.0% and 11.0% air content respectively with 163
mL/100 kg cementitious material (2.5 fl oz/cwt) of AEA. The difference in the air
content is most likely due to the interaction of different factors affecting the AEA
requirements, i.e., carbon ,alkali contents, and the fly ash fineness. The finenesses
of the three fly ashes were not tested. They have similar alkali contents (Table 3-2).
The concrete made with ACI3 had a lower air content when compared to those
incorporated with ACI1 and ACI2, which had a lower air content compared to the
61


control mixture. This is probably due to the higher carbon content in the ACF fly
ash.
In Figure 4-2a, 15ACI 1_1.5, 15ACI2_1.5 were batched with 98 mL/100 kg
cementitious material (1.5 fl oz/cwt), a lower AEA dosage rate. The air content of
the concrete made with ACI1 was reduced to 7.0%; however the mixture made
with ACI2 was not reduced. The influence of the HRWRA on the air content was
investigated by the batching of 0Ash_0, which had a 0.91L/ 100kg (14.0 fl oz/cwt)
dosage of HRWRA and 2.8% air content. Thus, the HRWRA did not aid in
entraining air in the concrete. The 15ACI2_1.5 had a higher air content than the
15ACI22.5. This is due to the inconsistent carbon content in the fly ash, which is
a concern for the activated carbon injection.
In Figure 4-2b, 15ACI5_1.5, 15ACI6J.5, 15ACI7J.5, 15ACI8J.5 and
15ACI91.5 had 8.0%, 8.5%, 8.0%, 10.0% and 8.5% air content respectively.
ACI5-9 fly ashes were from the same coal fired power plants, but were derived
using different sorbents with different injection rates. ACI5 and ACI6 contain
CPAC with 0.5 lb/Macf (0.008g/mJ) and 1.5 lb/Macf (0.024 g/mJ) injection rates
respectively, while ACI7 and ACI8 have non-carbon based sorbent BASF with 12
lb/Macf (0.193 g/m3) and 8 Ib/Macf(0.128 g/m3) injection rates respectively. ACI9
contains carbon based concrete unfriendly sorbent Darco-Hg, the sorbent injection
62


rate of which is 1.0 lb/Macf (0.016 g/m3). 15ACI91.5 had 8.5% air content,
indicating the fly ash mixed with the Darco-Hg with 1.0 lb/Macf (0.016 g/m3)
injection rate did not affect air content in the concrete. The air contents of the other
four mixtures range between 8%~10%, confirming that the sorbents used are
concrete friendly and do not absorb AEAs..
Figure 4-2a and b show the unit weights of the concrete incorporated with 15% fly
ash derived from sorbent injection range between 2217.0 kg/m3 and 2338.8kg/m3
(138.4 lb/cf and 146 lb/cf)- From the data, mixtures with high air contents produce
low unit weights. The relationship between unit weight and air content can be
regressed into a linear function, which was plotted in Figure 4-3. The point of
0Ash_0 is close to the line, which also means the low air content was not due to the
error from the measurement. For the normal weight aggregate concrete, the air
content can be predicted by the unit weight, vice versa.
63


2400
_ 2350
n
E
* 2300
£
g>
2250
c
3 2200
2150
0.0 2.0 4.0 6.0 8.0 10.0 12.0
Air Content (%)
Figure 4-3 Phase I: Unit Weight vs. Air Content
4.2.2 Phase I: Compressive Strength Characteristics
The compressive strength data for the thirteen concrete mixtures are listed in Table
4-3a (SI) and Table 4-3b (U.S. Customary) and illustrated in Figures 4-4a and b.
Compressive strength was tested at 1, 3, 7, 28, 56, and 90 days of age. Fly ash
concrete mixtures gain a considerable amount of strength beyond 28 days of age.
Thus, testing beyond 28 days of age was warranted. The compressive strength data
reported in Tables 4-3a,b and Figures 4-4a, b are the average of three 10.2 cm><20.3
cm (4in x 8in) cylinders.
64


Table 4-3a Phase I: Compressive Strength Data (SI)
Mixture Identification 1-day 3-day 7-day 28-day 56-day 90-day
MPa MPa MPa MPa MPa MPa
1 0Ash_2.5 23.9 29.2 32.9 39.0 41.5 42.6
2 0Ash_0 22.3 34.9 39.7 48.3 52.3 53.5
3 15ACI1_2.5 14.9 22.6 26.5 32.4 33.5 35.8
4 15AC12_2.5 18.9 28.4 29.9 34.7 37.7 39.9
5 15AC13_2.5 23.2 35.9 39.8 47.9 48.8 54.3
6 15AC11_1.5 24.0 32.3 36.7 43.1 42.3 48.2
7 15ACI2_1.5 17.8 25.1 27.1 34.2 36.2 39.3
8 15ACI41.5 12.5 35.3 42.0 48.7 54.1 56.2
9 15ACI5_1.5 22.0 30.7 34.2 42.4 46.1 47.5
10 15ACI6_1.5 19.3 29.5 32.0 39.7 43.6 45.0
11 15AC17_1.5 14.8 23.2 27.4 32.2 37.8 39.4
12 15AC18_1.5 20.0 28.3 32.9 38.9 42.7 45.0
13 15ACI9_1.5 17.3 22.1 25.8 32.0 34.3 37.2
Table 4-3b Phase I: Compressive Strength Data (U.S. Customary)
Mixture Identification 1-day 3-day 7-day 28-day 56-day 90-day
psi psi psi psi psi psi
1 0Ash_2.5 3472 4228 4766 5655 6025 6179
2 0Ash_0 3228 5066 5760 7003 7582 7765
3 15AC11_2.5 2154 3284 3846 4696 4854 5198
4 15ACI2_2.5 2746 4115 4332 5026 5468 5784
5 15ACI3_2.5 3368 5203 5771 6949 7074 7869
6 15ACI1J.5 3485 4688 5330 6257 6142 6994
7 15ACI2J.5 2580 3643 3931 4956 5252 5706
8 15AC14J.5 1807 5122 6091 7068 7851 8150
9 15ACI5J.5 3189 4448 4955 6154 6689 6885
10 15ACI6J.5 2792 4272 4645 5760 6328 6533
11 15ACI7J.5 2142 3365 3975 4673 5487 5721
12 15ACI8J.5 2900 4099 4768 5647 6200 6530
13 15ACI9J.5 2516 3207 3745 4637 4977 5389
65


The one-day compressive strengths of the thirteen mixtures range between 12.5
MPa (1807 psi) and 24 MPa (3485 psi). The 15ACI11.5 had the highest strength
and 15ACI4_1.5 had the lowest strength at 1 day respectively. Thel5ACI9_1.5 had
the lowest strength at 28 days of age with 32.0 MPa (4637psi) and the 15ACI41.5
had the highest, 48.7 MPa (7068psi) at 28 days of age. The 15ACI12.5 had the
lowest at 90 days with 35.8 MPa (5198psi) and the 15ACI4_1.5 had the highest
strength, 56.2 MPa (8150 psi) at 90 days. The interaction of different factors (i.e.
cementitious material content, fly ash content and air content) influenced the
strength development of the concrete. The mixture 0Ash_0 had 320 kg/m3 (540
lb/cy) cement, which is less than other mixtures with 377 kg/m3 (635 lb/cy)
cementitious material, but it had pretty high 28-day and 90-day strength. This
probably is due to its low air content (2.8%). The focus of this study is to
investigate the effect of the sorbent fly ash content and air content on the
compressive strength development.
ss


Compressive Strength (Mpa) I-. Compressive Strength (Mpa)
0Ash_2.5 -....0Ash_0 --A-- 15ACI1_2.5 X 15ACt2_2.5
15ACI3_2.5 ------ 15ACI1J.5 +- 15ACI2_1.5-------15ACI4J.5
Figure 4-4a Phase I: Compressive Strength Development (Mixtures 1-8)
0Ash_2.5 0Ash_0 - - 15ACI5_1.5 X 15ACI6_1 5
--X-- 15ACI7_1.5*15ACI8_1.515ACI9_1.5
Figure 4-4b Phase I: Compressive Strength Development (Mixtures 1, 2, 9-13)
07


4.2.2.1 Effect of Sorbent Injection Fly Ash Content
Figure 4-4a shows the strengths of 15ACI1_2.5, 15ACI22.5 and 15ACI21.5 at
different ages were lower than the control mixture, 0Ash_2.5, while Figure 4-4b
shows the strengths of 15ACI81.5 were lower than the 0Ash_2.5 at 1, 3, 7 and 28
days, but higher than the 0Ash_2.5 at 56 and 90 days. These mixtures are
comparable because the fly ash concrete mixtures have slightly lower air contents
than the 0Ash_2.5. The effect of air content will be discussed in the next section.
At the early ages, the strength of 0Ash_2.5 developed much faster than the fly ash
concrete mixtures. The strength gain of the 0Ash_2.5 from 0 to 7 days is faster than
15ACI12.5, 15ACI2 2.5 and 15ACI2J.5 in Figure 4-4a and 15ACI8_1.5 in
Figure 4-4b. The cement hydration governs the early strength development of the
concrete. At later ages, the strength increase of the control concrete mixture
0Ash_2.5 was slower than that of 15ACI1_2.5, 15ACI2 2.5, 15ACI2_1.5 and
15ACI81.5. The increased strength gain at later ages can be attributed to the
pozzolanic nature of the fly ash.
4.2.2.2 Effect of Air Content
The strengths of 15ACI32.5, 15ACI1_1.5 and 15ACI41.5 (except 1 day strength)
at all ages were similar or higher than the control concrete mixtures because they
had lower air contents, 5%, 7% and 5.4% respectively. However, the fly ash
concretes with higher air content (^9%) i.e. 15ACI12.5, I5ACI2 2.5,
68


15ACI2_1.5, had lower strength compared to the control concrete mixture,
0Ash_2.5, which has even higher air content. The compressive strength versus the
air content of the concrete is illustrated in Figure 4-5. This figure demonstrates that
the concretes with 5%~7% air contents had better performance than that with 9% of
air content. The concrete mixtures, 15ACI5_1.5, 15ACI6_1.5, 15ACI7_1.5,
15ACI8J.5, 15ACI9_1.5, with 8.0%, 8.5%, 8.0%, 10.0% and 8.5% of air
respectively, had lower early strength than the control mixture 0Ash_2.5, but
higher later strength (except 15ACI7_1.5 and 15ACI9_1.5) than the control
mixture.
Air Content (%)
1-day 3-day 7-day x 28-day x 56-day 90-day
Figure 4-5 Phase I: Compressive Strength vs. Air Content
69


In Figure 4-5, line 1-6 connected 1-day to 90-day strength points of the sorbent
injection fly ash concrete with air content less than 7%, respectively (in the dashed
rectangle). The slopes (absolute value) of these lines increase as the ages of the
concrete increase. This shows the influence of air content on the early age strength
is less effective than the later ages. This is probably because the cement hydration
governs the strength increase at the early age. After the cementitious material
hydration becomes stable at later ages, the air content becomes an important factor
affecting the ultimate compressive strength.
4.2.3 Phase I: Resistance to Chloride-Ion Penetration
The data in Table 4-4 show that all sorbent injection fly ash concretes exhibited
high resistance to chloride-ion penetration, specifically at later ages. This data is
further illustrated in Figure 4-6.
The total charge passed for the sorbent injection fly ash concretes ranges from 1424
to 2215 and from 874 to 1413 coulombs at 28 and 90 days of age, respectively. The
improvement in the resistance to chloride-ion penetration as the testing age
increased is due to the reduction in the porosity of the concretes as a result
continued cement hydration and the pozzolanic reaction. Figure 4-6 shows the total
charge passed for the sorbent injection fly ash concretes at all ages is higher than
70


the control concrete 0Ash_2.5 (except 15ACI32.5 at 56 days, 15ACI51.5 at 28
and 90 days, and 15ACI8_1.5 at 90 days).
Table 4-4 Phase I: Resistance to Chloride-ion Penetrability
Mixture Identification 28-day 56-day 90-day
Coulombs Coulombs Coulombs
1 0Ash_2.5 1418(Low) 1171 (Low) 990 (Very Low)
2 0Ash_0 3045 (Moderate) 2758 (Moderate) 2117 (Moderate)
3 15ACI1_2.5 1906(Low) 1497(Low) 1214 (Low)
4 15ACI2_2.5 1649(Low) 1351(Low) 995 (Very Low)
5 15AC13_2.5 1424(Low) 1100 (Low) 1085(Low)
6 15ACI1J.5 1650(Low) 1330(Low) 1104 (Low)
7 15ACI2J.5 2142 (Moderate) 1725(Low) 1413(Low)
8 15ACI4_1.5 2215 (Moderate) 1682(Low) 1267(Low)
9 15ACI5_1.5 1645(Low) 1078(Low) 874 (Very Low)
10 15ACI6J.5 1734 (Low) 1354(Low) 1029(Low)
11 15ACI7J.5 2056 (Moderate) 1293(Low) 1042 (Low)
12 15ACI8_1.5 1804 (Low) 1249(Low) 901 (Very Low)
13 15AC19J.5 1948(Low) 1478(Low) 1196 (Low)
The air content might influence the total charge passed for the concrete mixtures.
The mixtures with higher air content were expected to have an increased
permeability. However the control concrete mixture, 0Ash_2.5, had the highest air
content among the thirteen mixtures. Thus, the 15% replacement of cement with
ACI fly ash increases the porosity of the hardened cement paste when compared to
a mixture with 100% portland cement. At 90 days of age, all but one mixture
exhibited either low or very low permeability. The data also shows that the
71


concretes made with 635 lb/cy (377 kg/m3) of cementitious material had a better
resistance to chloride-ion penetration than the 0Ash_0 with 320 kg/m3 (540 lb/cy)
cement only. This is illustrated in Figure 4-6 and Figure 4-7. In addition, Figure 4-7
shows that the cementitious material content plays a more important role in
influencing the permeability of the concrete than air content. This is best illustrated
in Figure 4-7 as the chloride-ion penetrability values do not fluctuate significantly
as air content increases.
28-day 56-day 90-day
Figure 4-6 Phase I: Rapid Chloride Ion Penetrability Tests Results
72


3500
3000
2500
E 2000
o
3
o
O
g 1500
0Ash_0 with 320 kg/m3 (540 Ib/cy) cement
i ! l H | Mixtures with 377 kg/m3 (635 Ib/cy) CM
L*J : : ill-; i 1

0.0 2.0 4.0 6.0 8.0
Air Content(%)
10.0
12.0
28-day 56-day a 90-day
Figure 4-7 Phase I: Coulombs vs. Air Content
4.2.4 Phase I: Resistance to Freeze/Thaw Cycling
The resistance of the concrete mixtures to freezing and thawing cycles was
measured by subjecting concrete beams to rapid freezing and thawing (ASTM C
666). The transverse resonant frequency was measured periodically and the
durability factors were calculated. The durability factors are listed in Table 4-5. All
the air-entrained concrete mixtures (1,3-13) resulted in durability factors greater
than 88 and excellent resistance to freeze/thaw regardless of sorbent injection fly
ash. See Figure 4-8. These mixtures reached 300 freeeze/thaw cycles. As expected,
Mixture OAsh O with 320 kg/m3 (540 lb/cy) cement and 2.8% air content had poor
freeze/thaw resistance. The surface deterioration of all concrete beams except two
73


beams of the mixture OAshO (due to freezing and thawing cycling was observed
after 300 cycles, but it did not cause significant weight loss. The concretes had
excellent resistance to freezing and thawing when air content was greater than 5%.
Table 4-5 Phase I: Freeze/Thaw Durability Factors
Mixture Identification Resonant frequency Durability Factor
DK-4000(HZ) E-METER(HZ)
Initial Final Initial Final DK-4000 E-METER
1 0Ash_2.5 2041 1982 1989 1962 94 97
2 OAshO 2148 1191 2118 1175* 4 b 4
3 15AC11_2.5 1973 1895 1956 1830 92 88
4 15ACI2_2.5 2021 1904 1959 1912 89 95
5 15ACI3_2.5 2148 2061 2138 2040 92 91
6 15ACI 1_1.5 2100 2070 2050 2064 97 101
7 15ACI2J.5 2021 1973 2018 1944 95 93
8 15ACI41.5 2070 2012 2052 2002 94 95
9 15ACI5_1.5 2080 2051 2091 2064 97 97
10 15ACI6J.5 2061 2041 2089 2021 98 94
11 15ACI7J.5 2061 2041 1990 2019 98 103
12 15ACI8J.5 2119 2090 2097 2047 97 95
13 15ACI9_1.5 2031 1992 2032 1955 96 93
Note: a. The frequency was measured at 42 cycles.
b. The durability factor was calculated based on the transverse frequency at 42 cycles.
74


120
5 100
80
L.
§ 60
2 40
20
0

<5

0?
<$r GNN' &' <$>' £>' &' &' <$?' &' $' <$>' ^ V
S'
DK-4000 E-METER
Figure 4-8 Phase I: Durability Factors
4.2.5 Phase I: Resistance to Sulfate Attack
Four levels of sulfate exposure are presented in the ACI 318-08 Table 4.2.1 based
on the concentration of water soluble sulfate in the soil by weight or in water (ppm)
anticipated to be in contact with the concrete. For the ASTM C 1012 testing, a S3
exposure (very severe) was used to evaluate the sulfate resistance of the fly ash
mortar mixtures compared to the control mixtures. The cement types for severe
exposure condition recommended by ACI 318-08 R4.3 include blended (IP) cement
and a pozzolan addition to Type V. ACI 201 standard requires the use of Type V
cement for exposure S3 with a blend of fly ash at a replacement by mass of 25% to
35%. For this test, the samples used Type I cement in order to better evaluate the
effect of the presence of post-mercury-control fly ashes. The performance option
75


requires an expansion <0.1% at 18 months to qualify as sulfate resistant in such
exposure.
The data in Table 4-6 shows expansions of different mortar mixtures due to sodium
sulfate from 7 days to 6 months. Two control mixtures were created (OAshO and
0Ash_1.5). The mixture 0Ash_0 was made with 100% portland cement without
AEA addition. The water/cement ratio was 0.485. In addition, the 0Ash_1.5 mortar
mixture consisted of 100% portland cement and a 98 mL/lOOkg (1.5 fl oz/cwt)
AEA dosage. Other mortar mixtures were made with 75% cement and 15% fly ash
by weight for the cementitious material and a 98 mL/lOOkg (1.5 fl oz/cwt) dosage
of AEA. The water/cementitious material ratio of all the air entrained mortar
mixtures was 0.46.
Table 4-6 Phase I: Sulfate Expansion of Fly Ash Mortar Bars with 15% ACI Ash
Mix 1 week 2 week 3 week 4 week 8 week 13 week 15 week 4 month 6 month
OAsh 0 -0.0013 0.0017 0.0068 0.0056 0.0190 0.0234 0.0308 0.0320 0.0448
OAsh 1.5 -0.0007 -0.0030 0.0056 0.0077 0.0113 0.0144 0.0234 0.0227 0.0351
15ACI1 1.5 0.0024 0.0001 0.0063 0.0091 0.0114 0.0211 0.020^ 0.0246 0.0319
15ACI2 1.5 0.0051 0.0044 0.0080 0.0077 0.0231 0.0318 0.0294 0.0352 0.0484
15ACI3 1.5 -0.0006 0.0083 0.0082 0.0098 0.0146 0.0160 0.0234 0.0231 0.0225
15AC14 1.5 0.0201 0.0515 0.1130 0.1757 0.3598 0.0725 0.1544 0.2051 0.3181
15ACI5 1.5 0.0049 0.0066 0.0087 0.0090 0.0146 0.0234 0.0262 0.0250 0.0320
15AC16 1.5 0.0069 0.0094 0.0100 0.0143 0.0245 0.0339 0.0376 0.0440 0.0468
15AC17 1.5 0.0060 0.0055 0.0102 0.0098 0.0184 0.0282 0.0278 0.0335
15ACI8 1.5 0.0035 0.0025 0.0093 0.0097 0.0217 0.0213 0.0260 0.0258
15ACI9 1.5 0.0032 0.0107 0.0107 0.0135 0.0258 0.0297 0.0357 0.0381
76


The data in Table 4-6 indicate that the expansion of 15ACI41.5 exceeded 0.1% at
3 weeks and then decreased between 8 weeks and 13 weeks. When the mixture was
batched, it set too fast to finish all 6 mortar bars. All 6 bars were not completely
consolidated and resulted in large voids to the outside of the bars. The ACM fly ash
was believed to consist of a high lime (CaO) content. This results in decreased
setting time. The voids on the bar surface provided an easier path for the sulfate
solution to penetrate the mortar bars. Gypsum corrosion governed the sulfate attack,
which can be described by the reaction between sulfate ions and calcium hydroxide:
CH + SOl'(aq) CSH2 + 20H (aq). This reaction can cause an expansion in solid
volume of approximatly 120%. The high permeability of the mortar surface (honey
combed) increased the reaction speed. In addition, a bar was broken when the
length change was tested at 8 weeks. The shortening of the bars at 8 weeks is a
result of the broken bar, which was more severely attacked by the sulfate solution.
The expansions of different mortar mixtures are plotted in the Figure 4-9 without
the mixture 15ACI41.5. The control mixture 0Ash_1.5 had less length change
than the other control mixture OAshO, which is a result of the air entrainment in
the mixture. The length changes of all nine fly ash mortar mixtures were larger than
the control 0Ash_1.5. Four mixtures (15ACI41.5 excluded) were produced
expansion values larger than the control OAsh O at 4 months, for which the air and
77


the CaO contents in these mixtures are responsible. The same dosage of AEA was
added to the fly ash mortar mixtures. The carbon and fly ash are responsible for the
less air contents in the mortar mixtures containing sorbent injection fly ashes than
the 0Ash_1.5. All the fly ashes are expected to be Class C fly ash, thus higher CaO
contents were expected in the mortar mixtures containing sorbent injection ashes.
The low air contents and gypsum corrosion caused all the mortar mixtures
containing sorbent injection fly ashes to experience larger length change.
Furthermore, this test indicates that the use of Class C fly ash did not improve the
sulfate resistance of concrete.
0Ash_0 0Ash_1.5 15ACI1J.5*15ACI2_1.5
*15ACI3_1.5 -H-- 15ACI5J.5------15ACI6_1.5-----15ACI7_1.5
15ACI8_1.5 15ACI9J.5
Figure 4-9 Phase I: Length Change Percentage of Mortar Bars
78


4.3 Conclusion of Phase I Laboratory Testing
All air-entrained ACI fly ash concretes exhibited excellent characteristics in
compressive strength, resistance to chloride-ion penetration and freezing and
thawing cycling tests.
The chemistries of the fly ash derived from ACI still meet the ASTM C 618
specification although the carbon content is high. This study confirmed the
influence of the carbon on the air content of the concrete, but there was no
difficulty in entraining air in ACI fly ash concretes within the recommended dosage
range of AEA. However the consistency of the carbon content in the fly ash was a
concern for the ACI technology.
The compressive strengths of the sorbent injection fly ash concretes with -5=9% air
content were lower than the control concrete mixture, but high enough for
structural application purposes with greater than 1807 psi (12.5 MPa) at 1 day and
greater than 4637 psi (32.0 MPa) at 28 days. This paper also confirmed the
increased strength gain at later ages for ACI fly ash concretes. The air content
influences the strength of the ACI fly ash concrete particularly at later ages.
79


All sorbent injection fly ash concretes demonstrated excellent resistance to
chloride-ion penetration with values of less than 1413 coulombs after 90 days of
moist-curing. But the data showed the 15% replacement of cement by fly ash
increased the porosity of the hardened cement pastes when compared to the 100%
Portland cement concrete mixture. The durability factors of the sorbent injection fly
ash concrete prisms after 300 cycles of freezing and thawing in ASTM C 666 were
excellent.
The sulfate attack tests indicated that all sorbent injection fly ash did not improve
the sulfate resistance of the mortar mixtures when compared to the control mixture.
The amount of all these fly ashes to be used in S3 exposure environment shall be
determined by sulfate resistance tests when mixed with Type V cement.
Among the thirteen concrete mixtures, 15ACI11.5 had excellent performance:
7.0% air content with 98 ml/lOOkg (1.5 fl oz/cwt) of AEA; 24 MPa (3485 psi) 1-
day strength and 43.1 MPa (6257 psi) 28-day strength; 1650 coulombs passed at 28
days of age; and 97 and 101 durability factors tested by the DK-4000 and E-
METER devices respectively. This concrete mixture included the ACI1 fly ash
mixed with the CPAC sorbent. Boral Materials Technology supplied this mercury
control fly ash. Based on the performance of this fly ash in the concrete during
Phase I, ACI1 was selected for the Phase II optimization laboratory testing.
80


5 Phase II: Optimization of Cementitious Material and Fly Ash Content
The objective of Phase II was to determine the optimum amount of ACI1 fly ash in
concrete yielding a similar 28-day compressive strength to that of Colorado
Department of Transportation Class D structural concrete. Class D concrete is a
widely used dense medium strength structural concrete. Required field compressive
strength is 31 MPa (4500 psi) at 28 days of age; the cementitious material content
ranges between 365 to 392kg/m3 (615 to 660 lbs/cy); air content ranges between 5-
8% and the maximum water/cementitious material ratio is 0.44. The concrete
mixture, 15ACI1_1.5, met these requirements. For the fly ash concrete in Phase II,
the cement replacement range with fly ash was 30% to 60% of the total weight of
the cementitious materials. The cementitious material content was kept at 338 to
418 kg/m3 (570 to 705 lbs/cy). The AEAs and HRWR were used to obtain 5-8% air
content and a 102 25 mm( 4 I in) slump.
5.1 Phase II: Mixture Proportions
To develop an optimized mixture, eight concrete mixtures were designed and tested
in this phase. Two concrete mixtures were made with a cementitious material
81


content of 392 kg/m3 (660 lbs/cy) and a fly ash content of 30% and 50%, two
concrete mixtures with a cementitious material content of 338 kg/m3 (570 lbs/cy)
and a fly ash content of 30% and 50%. In addition, three concrete mixtures with a
cementitious material content of 365 kg/m3 (615 lbs/cy) and a fly ash content of
40% were produced to verify the repeatability of the test results. One concrete
mixture was made with a cementitious material content of 418 kg/m3 (705 lbs/cy)
and a fly ash content of 60% to examine the performance of high volume ACI1 fly
ash concrete. The proportions of the concrete mixtures are summarized in Table 5-
la (SI) and Table 5-lb (U.S. Customary).
Table 5-la Phase II: Mixture Proportions (SI)
Mixture Identification W/(C+FA) Water Cement Fly Ash Coarse Aggregate Fine Aggregate AEA
kg/m3 kg/m3 kg/m3 kg/m3 kg/m3 mL/ 100kg
1 40ACI1 615 0.4 146 219 146 1032 720 98
2 30ACI1 660 0.4 157 274 117 1032 674 98
3 40ACI1 615 0.4 146 219 146 1032 720 98
4 30ACI1 570 0.4 135 237 101 1032 111 98
5 40ACI1 615 0.4 146 219 146 1032 720 98
6 50AC11 660 0.4 157 196 196 1032 662 98
7 50ACI1 570 0.4 135 169 169 1032 767 98
8 60ACI1705 0.4 167 167 251 1032 603 98
82


Table 5-lb Phase II: Mixture Proportions (U.S. Customary)
Mixture Identification W/(C+FA) Water Cement Fly Ash Coarse Aggregate Fine Aggregate AEA
lb/cy lb/cy lb/cy lb/cy lb/cy fl oz/ewt
1 40AC11 615 0.4 246 369 246 1740 1214 1.5
2 30ACI1 660 0.4 264 462 198 1740 1136 1.5
3 40ACI1 615 0.4 246 369 246 1740 1214 1.5
4 30ACI1_570 0.4 228 399 171 1740 1310 1.5
5 40ACI1 615 0.4 246 369 246 1740 1214 1.5
6 50ACI1 660 0.4 264 330 330 1740 1116 1.5
7 50ACI1570 0.4 228 285 285 1740 1292 1.5
8 60 AC 11 705 0.4 282 282 423 1740 1016 1.5
Phase II included the same testing program utilized in Phase I. For a description of
these fresh and hardened concrete tests see Chapter 3.3 and Table 3-4.
5.2 Test Results
5.2.1 Fresh Concrete Properties Test Results
The fresh concrete properties tests included slump, unit weight, and air content.
The results of these tests are summarized in Table 5-2.
5.2.1.1 Phase II: Slump and Superplasticizer
The slumps of the nine mixtures and the amounts of superplasticizer added are
shown in Table 5-2 and plotted in Figure 5-1.
83


Table 5-2 Phase II: Fresh Concrete Properties Test Results
Mixture Identification Slump Unit Weight Air Content HRWR
cm in. kg/m5 Ib/cf % L/100kg fl oz/cwt
Control 15ACIl 635 10.2 4.00 2291 143 7.0 1.25 19.2
2 40ACI1_615A 9.5 3.75 2265 141.4 8.0 0.47 7.2
3 30ACI1_660 10.2 4.00 2239 139.8 9.0 0.44 6.7
4 40ACI1_615B 9.5 3.75 2262 141.2 9.0 0.47 7.2
5 30ACI1_570 8.3 3.25 2278 142.2 8.0 1.14 17.5
6 40ACI1_615C 7.6 3.00 2275 142 7.4 0.47 7.2
7 50ACI1_660 9.5 3.75 2214 138.2 9.0 0.00 0.0
8 50ACI1J70 7.6 3.00 2294 143.2 7.0 0.51 7.8
9 60ACI1_705 19.1 7.50 2220 138.6 8.0 0.00 0.0
25.0 ------------------------------------------------------- 1.40
O)
o
o
2]
a:
x
Slump HRWR
Figure 5-1 Phase II: Slump and Superplasticizer
The slump of the control mixture 15ACI1635 from Phase I was 10.2 cm (4 in.)
with 1.25 L/100 kg cementitious materials (19.2 fl oz/cwt) of HRWRA. The slumps
of ACIl fly ash concrete ranged from 7.6 to 19.1 cm (3 to 7.5 in.) The mixture
84


30ACI1 660 had a slump of 10.2 cm (4 in.) with 0.44 L/100 kg (6.7 fl oz/cwt) of
HRWRA, while the mixture 30 ACI1_570 had a slump of 8.3 cm (3.25 in.) with
1.14 L/100kg (17.5 fl oz/cwt). Thus, as the cementitious material content decreases,
the slump of the concrete decreases. The same conclusion is made when comparing
the 50ACI1_660 and 50ACI1_570 mixtures. The concrete mixture 50ACI1660
had a slump of 9.5 cm (3.75 in.) without incorporating HRWRA. From comparing
mixtures 30ACI1 660 and 50ACI1_660, the data shows that as the fly ash content
increases, the slump of the concrete increases. Unsurprisingly, the concrete mixture
60%ACI1_705 had the largest slump with the highest cementitious material content
and fly ash content without incorporating HRWRA. The three mixtures
40ACI1_615A, B, and C had similar slumps with the same amount of HRWRA.
5.2.1.2 Phase II: Air Content and Unit Weight
The air contents and unit weights of the nine concrete batches are given in Table
Table 5-2 and plotted in Figure 5-2.
The control mixture 15ACI1 635 had an air content of 7% with a unit weight of
2291 kg/m3 (143 lb/cf) and other mixtures ranged between 7.0 and 9.0% with unit
weights ranging between 2214 and 2294 kg/m3 (138.2 Ib/cy to 143.2 lb/cy). The air
contents of three mixtures, 30ACI1 660, 40ACI1615, and 50ACI1 660, exceeded
8% required by the CDOT Class D concrete. But the air content can be reduced
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with increased mixing time and/or adjustment in AEA dosage. The air contents of
the three mixtures 40ACI1615A, B and C were 8%, 9% and 7.4% respectively.
The difference among each was likely a result of human error. The similarity of the
three mixtures proves the repeatability of the air content testing.
2300
cT-2280
"9)2260
~ 2240
2220
^ 2200
5 2180
2160

& #
is'
' &

mm Unit Weight
Air Content
Figure 5-2 Phase II: Unit Weight and Air Content
5.2.2 Phase II: Compressive Strength Results
The data on compressive strength of the Phase 11 testing are listed in Table 5-3a (SI)
and Table 5-3b (U.S. Customary) and illustrated in Figure 5-3.
36


Table 5-3a Phase II: Compressive Strength (SI)
Mixture Identification 1-day 3-day 7-day 28-day 56-day 90-day
MPa MPa MPa MPa MPa MPa
1 15ACI1_635 24.0 32.3 36.7 43.1 42.3 48.2
2 40ACI1_615A 12.6 20.5 24.6 30.4 34.0 35.9
3 30ACI1_660 12.9 21.1 23.9 30.9 33.4 35.4
4 40AC11_615B 10.4 21.7 26.2 32.7 34.1 35.8
5 30ACI1_570 16.4 29.8 35.1 41.4 45.0 47.7
6 40ACI1_615C 13.0 24.4 28.0 35.4 39.8 40.2
7 50ACI1_660 5.4 18.0 21.0 29.6 31.0 34.5
8 50ACI1_570 6.3 20.3 24.5 32.0 35.5 39.2
9 60ACI1_705 2.5 14.3 18.6 24.9 29.4 32.4
Table 5-3b Phase II: compressive strength (U.S. Customary)
Batches 1-day 3-day 7-day 28-day 56-day 90-day
psi psi psi psi psi psi
1 15ACI1_635 3485 4688 5330 6257 6142 6994
2 40ACI1_615A 1827 2969 3563 4414 4932 5211
3 30ACI1_660 1869 3064 3460 4479 4850 5140
4 40ACI1_615B 1503 3141 3793 4744 4942 5186
5 30ACI1_570 2374 4318 5095 6001 6529 6914
6 40ACI1_615C 1886 3537 4065 5137 5774 5829
7 50ACI1660 789 2606 3039 4294 4489 4999
8 50ACI 1_570 909 2950 3553 4635 5146 5681
9 60ACI1_705 362 2068 2693 3618 4266 4704
The one-day compressive strength of the control mixture 15ACI1_615 was 24.0
MPa (3485 psi). The eight mixtures batched during Phase II ranged between 2.5
MPa (362 psi) and 16.4 MPa (2374 psi) at one day of age. The 28-day strength of
the 15ACI1615 reference mixture was 43.1 MPa (6157 psi) and the Phase II
mixtures ranged between 24.9 MPa (3618 psi) and 41.4 MPa (6001 psi). The
87