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UTILIZATION OF MUNICIPAL SOLID WASTE INCINERATOR BOTTOM ASH AS A SUSTAINABLE CONSTRUCTION MATERIAL: ISSUES CONCERNING MATERIAL
LEACHING AND DURABILITY
By
MATTHEW L. SCHAFER
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ENGINEERING
UNIVERSITY OF FLORIDA
2017
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ACKNOWLEDGMENTS
I would like to extend my genuine gratitude to the faculty members of my
graduate supervisory committee; Dr. Jean-Claude Bonzongo, Dr. Christopher Ferraro,
and Dr. Timothy Townsend, for allowing me the opportunity to perform this novel
research. The continuous support, direction, and technical guidance offered by these
individuals was vital to the successful and timely completion of this project. I’d like to
extend distinct appreciation to Dr. Tim Townsend for his professional mentorship, and
for the role he played in facilitating my personal and professional growth throughout
graduate school.
I would also like to thank the Solid Waste Authority of Palm Beach County,
Florida for providing me with the unique opportunity to perform this study, and supplying
the financial means required to accommodate such research. Furthermore, I would like
to acknowledge the innovation which was displayed by the Authority in their pursuit of
developing a waste-to-energy ash recycling program in Florida. The opportunity to work
in conjunction with the knowledgeable and experienced staff at the Authority was a true
pleasure. Additional thanks is extended to the Hinkley Center for Solid and Hazardous
Waste Management in Gainesville, FL for supplementary funding which accommodated
this research.
I would also like to recognize the numerous individuals who assisted me in a
variety of ways throughout the duration of this project; on matters ranging from technical
discussions and troubleshooting to heavy lifting and field sampling. Thank you to my
research colleagues Kyle Clavier, Justin Roessler, Linda Monroy Sarmiento, Chad
Spreadbury, and Stephen Townsend for all your help. Thank you to the graduate
students and faculty in the UF Civil Engineering department for helping me to better
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understand the fundamentals of concrete as a material: Danielle Kennedy, Taylor
Humbarger, Jerry Paris, Caitlin Tibbets, and Ben Watts. Thank you to the
undergraduate research assistants who assisted with the extensive field and laboratory
work involved in this study: Rachel Cohen, Sara Fox, Ryan Hundersmarck, and Jarrod
Petrohvich.
Finally, I’m most thankful for the constant love and support provided by my family
and friends throughout my years at the University of Florida, especially during graduate
school. I can’t thank you enough for the steady affirmation and motivational backing
you’ve all imparted on me, whether it came during the trivial times of my education, or
during the challenging ones. This effort would not have been possible without your
endless support. Thank you all so much.
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TABLE OF CONTENTS page
ACKNOWLEDGMENTS .................................................................................................. 3
LIST OF FIGURES .......................................................................................................... 9
LIST OF ABBREVIATIONS ........................................................................................... 11
ABSTRACT ................................................................................................................... 12
CHAPTER
1 INTRODUCTION .................................................................................................... 13
Background ............................................................................................................. 13 Motivation and Objective ......................................................................................... 14
Outline of Thesis ..................................................................................................... 15
2 LEACHING OF METALS FROM MUNICIPAL SOLID WASTE INCINERATOR BOTTOM ASH AND NATURAL AGGREGATE BLENDS: IMPLICATIONS FOR BENEFICIAL USE AS A GRANULAR ROAD BASE ............................................... 16
Background ............................................................................................................. 16
Methods .................................................................................................................. 19
Risk Assessment of Waste Materials ............................................................... 19
Experimental Approach .................................................................................... 20 Materials ................................................................................................................. 21
MSWI Bottom Ash ............................................................................................ 21
Natural and Recycled Aggregates .................................................................... 22 Leaching Procedures .............................................................................................. 23
Synthetic Precipitation Leaching Procedure ..................................................... 23 Leaching as a Function of Liquid-to-Solid Ratio ............................................... 23
Analytical Procedures ............................................................................................. 23
Results and Discussion........................................................................................... 24 Direct Exposure Pathway ................................................................................. 24
MSWI bottom ash ...................................................................................... 24
Natural and recycled aggregates ............................................................... 25
Blended products ....................................................................................... 25 Leaching to Groundwater Pathway .................................................................. 26
MSWI bottom ash ...................................................................................... 26 Natural and recycled aggregates ............................................................... 28 Blended products ....................................................................................... 28
Implications for Reuse as Road Base ..................................................................... 30 Summary of Findings .............................................................................................. 32 Figures and Tables ................................................................................................. 33
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3 CHARACTERIZATION AND MITIGATION OF ALKALI-AGGREGATE REACTIVITY IN MORTARS CONTAINING MUNICIPAL SOLID WASTE INCINERATION ASH AS AN AGGREGATE COMPONENT .................................. 41
Background ............................................................................................................. 41 Materials and Methods............................................................................................ 44
Bottom Ash Collection and Material Description ............................................... 44 Cementitious Materials ..................................................................................... 45 Experimental Approach .................................................................................... 45
Preparation of Mortar and Experimental Procedure ......................................... 46 Results and Discussion........................................................................................... 48
AMBT Expansion .............................................................................................. 48
Summary of Findings .............................................................................................. 49 Figures and Tables ................................................................................................. 50
4 CONCLUSIONS ..................................................................................................... 57
Summary of Research ............................................................................................ 57 Major Findings and Observations ........................................................................... 57
Recommendations for Future Work ........................................................................ 58
APPENDIX
A CHAPTER 2 SUPPLEMENTARY MATERIALS ...................................................... 59
B CHAPTER 3 SUPPLEMENTARY MATERIALS ...................................................... 63
LIST OF REFERENCES ............................................................................................... 66
BIOGRAPHICAL SKETCH ............................................................................................ 73
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LIST OF TABLES Table page 2-1 Total environmentally available concentrations (mg/kg-dry) of MSWI bottom
ash and natural/recycled aggregate materials. Total concentrations exceeding the residential Florida Soil Cleanup Target Levels are identified as COPC for the direct exposure risk pathway and have been shaded accordingly. ........................................................................................................ 33
2-2 Theoretical total environmentally available concentrations (mg/kg-dry) of blended products containing 15% MSWI bottom ash and 85% natural or recycled aggregates. Elemental concentrations exceeding the Florida Residential Soil Cleanup Target levels are identified as COPC and are shaded accordingly. ............................................................................................ 34
2-3 Average leachate concentrations of EPA Method 1312 (SPLP) performed in triplicate on MSWI bottom ashes and natural/recycled aggregates individually. Elemental concentrations exceeding the respective MCL are identified as COPC for the leaching to groundwater risk pathway and have been shaded accordingly. ................................................................................... 35
2-4 Average leachate concentrations of EPA Method 1312 (SPLP) performed in triplicate on blends of MSWI bottom ash and natural/recycled aggregates at a mass ratio of 15:85. Elemental concentrations of contaminants which exceed the respective MCL are identified as COPC for the leaching to groundwater risk pathway and have been shaded accordingly. .............................................. 36
3-1 Oxide composition (% weight) of materials obtained using X-ray fluorescence (XRF) spectroscopy. ........................................................................................... 50
3-2 Proportions of mortar materials for ASTM C160 mixes containing 15%, 30%, and 50% MSWI BA aggregate replacement. ...................................................... 51
3-3 Proportions of mortar materials for ASTM C1567 mixes containing portland cement, 20% pozzolan (ground glass or class F fly ash), and 30% MSWI BA aggregate replacement. ...................................................................................... 52
3-4 Length change data and performance classification of ASTM C160 and ASTM C1567 mortar mixes containing MSWI BA aggregate replacements. ...... 53
B-1 Aggregate properties of coarse fraction of MSWI bottom ash (3.5mm-19mm) used as aggregate replacements in accelerated mortar bar tests (ASTM C1260 and ASTM C1567) .................................................................................. 63
B-2 Individual length change measurements of ash-amended mortar bar specimens used in ASTM C1260 (portland cement only) ................................... 64
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B-3 Individual length change measurements of ash-amended mortar bar specimens used in ASTM C1567 (pozzolans included as portland cement replacement)....................................................................................................... 65
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LIST OF FIGURES
Figure page 2-1 Concentrations of aluminum in SPLP leachates for blends of Facility A MSWI
bottom ash and natural or recycled aggregates as a function of the bottom ash contained in the blended product. The risk-derived US EPA Regional Screening Level for aluminum (residential tap water) is displayed as dashed reference line. ..................................................................................................... 37
2-2 Ratio of aluminum leachate concentrations in the control bottom ashes to aluminum leachate concentrations in blended products containing lime rock and bottom ash at percentages of 0%, 15%, 30% and 50%, and 100% ash (SPLP batch leaching test). ................................................................................ 38
2-3 Concentrations of antimony in SPLP leachates for blends containing weathered MSWI bottom ash and four different aggregates. Antimony leachate concentrations are plotted as a function of bottom ash contained in the blended product. The US EPA National Primary Drinking Water Standard MCL for antimony is displayed as a dashed reference line. ............................... 39
2-4 Leaching of Antimony as a function of LS ratio (EPA Method 1316) in blended products containing 15% weathered MSWI bottom ash and 85% RCA and LR aggregates. ................................................................................... 40
3-1 ASTM C160 average length change of mortars containing 100% portland cement and 15%, 30%, and 50% aggregate replacement by MSWI BA1. ......... 54
3-2 ASTM C160 average length change of mortars containing 100% portland cement and 15%, 30%, and 50% aggregate replacement by MSWI BA2. ......... 54
3-3 ASTM C160 average length change of mortars containing 100% portland cement and 15%, 30%, and 50% aggregate replacement by MSWI BA3. ......... 55
3-4 ASTM C1567 length change of mortars containing 20% pozzolan (ground glass or class F fly ash) and 30% aggregate replacement by MSWI BA1 .......... 55
3-5 ASTM C1567 length change of mortars containing 20% pozzolan (ground glass or class F fly ash), and 30% aggregate replacement by MSWI BA2. ........ 56
3-6 ASTM C1567 length change of mortars containing 20% pozzolan (ground glass or class F fly ash), and 30% aggregate replacement by MSWI BA3. ........ 56
A-1 ASTM C136 particle size distribution of weathered MSWI bottom ashes used for EPA Method 1312/1316 batch leaching tests and EPA Method 3015A total metals analysis. .......................................................................................... 59
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A-2 EPA LEAF Method 1313 lead leaching as a function of eluent pH performed on fresh MSWI bottom ashes. ............................................................................ 60
A-3 EPA LEAF Method 1313 antimony leaching as a function of eluent pH performed on fresh MSWI bottom ashes ............................................................ 61
A-4 EPA LEAF Method 1316 antimony leaching as a function of liquid-to-solid ratio performed on weathered MSWI bottom ashes ........................................... 62
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LIST OF ABBREVIATIONS
AAR Alkali-Aggregate Reaction
AMBT Accelerated Mortar Bar Test
ASR Alkali-Silica Reaction
ASTM American Society for Testing and Materials
BA Bottom Ash
COPC Contaminant of Potential Concern
LEAF Leaching Environmental Assessment Framework
MSW Municipal Solid Waste
MSWI Municipal Solid Waste Incineration
PC Portland Cement
PCC Portland Cement Concrete
RAP Reclaimed Asphalt Pavement
RCA Recycled Concrete Aggregate
RSL Regional Screening Level
SCM Supplementary Cementitious Material
SCTL Soil Cleanup Target Level
SPLP Synthetic Precipitation Leaching Procedure
TCLP Toxicity Characteristic Leaching Procedure
TEA Total Environmentally Available
US EPA United States Environmental Protection Agency
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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering
UTILIZATION OF MUNICIPAL SOLID WASTE INCINERATOR BOTTOM ASH AS A SUSTAINABLE CONSTRUCTION MATERIAL: ISSUES CONCERNING MATERIAL
LEACHING AND DURABILITY
By
Matthew L. Schafer
May 2017
Chair: Timothy G. Townsend Major: Environmental Engineering Sciences
In this thesis, the beneficial reuse of municipal solid waste incinerator bottom ash
is explored with a focus on increasing the use of bottom ash as a construction material.
In Chapter 2, the environmental mobility of metal contaminants in a road base
reuse scenario is investigated using laboratory batch leaching tests. Blended products
containing bottom ash and natural aggregates are also considered for leaching.
Antimony and aluminum leachates exceeded risk-based thresholds by factors of
approximately 5-6, but blending of bottom ash with natural aggregates significantly
reduced the concentrations of leached aluminum. Antimony release from bottom ash
was found to be governed by solubility and pH.
In Chapter 3, the durability of concrete made with bottom ash as an aggregate
replacement is evaluated using an accelerated test method. The expansion of mortar
specimens is used as an indicator of the alkali-aggregate reactivity of bottom ash.
Mortars containing 15% bottom ash expanded beyond the innocuous limit of 0.1%. Two
pozzolans were found to reduce expansion in the mortars by up to 90%, and allowed for
increased amounts of bottom ash to be used (at least 30% replacement).
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CHAPTER 1
INTRODUCTION
Background
An expanding global population has resulted in an increase in the quantity of raw
materials and resources exhausted by consumers, and subsequent generation of
municipal solid waste. The strategic management of municipal solid waste (MSW) is of
growing importance as municipal resource consumption rates climb and spatial
availability for landfill disposal becomes increasingly limited, especially in developing
countries [1] . As a result, numerous strategies and processes have been developed to
more effectively manage MSW and decrease reliance on landfill disposal.
The incineration of MSW with energy recovery, or MSW incineration (MSWI) is a
popular strategy for solid waste management due to the volumetric reduction of waste
achieved by combustion (up to 90%), as well as the ability to simultaneously recover
heat and generate steam or electricity. While MSWI drastically reduces the initial
quantity of incoming waste, a large portion of residual bottom ash (BA) is produced as a
byproduct of the incineration process (in addition to fly ash). Bottom ashes represent the
non-combusted fraction of MSW which is discharged from the incinerator furnace
grating, and generally make up 15-20% of the original mass of MSW incinerated [2].
The high volume of bottom ash produced by MSW incinerators in addition to its
physical characteristics create the potential for the material to be beneficially reused,
primarily as a secondary building material in construction applications. While beneficial
reuse of MSWI BA has been highly successful in some areas [3]–[5], additional
research regarding the behavior of the material could promote higher recycling rates in
certain regions, such as the United States. The goal of the research presented in this
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thesis is to supplement the existing knowledge surrounding the beneficial reuse of
MSWI BA as an alternative construction material, and to provide a technical
investigation into two specific constraints which currently limit the reuse of bottom ash
as a construction aggregate.
Motivation and Objective
Recycling of MSWI BA as an alternative construction material is common
practice in many areas, primarily in Europe and parts of Asia, and numerous reuse
applications have been identified for BA produced in these regions [6], [7]. In the United
States, however, recycling of MSWI BA is highly underutilized and current practice is to
dispose of the vast majority of BA in lined ash monofills [8]. The lack of BA recycling in
the US can be attributed to a plethora of domestic factors, but two specific issues have
been identified which limit current BA recycling rates in the US:
1. The presence of trace amounts of inorganic contaminants (primarily metals and salts) contained in MSWI BA often hinders beneficial reuse as a construction aggregate, due to the potential risks these contaminants may pose to human or environmental health if they become mobile in the environment. These risks are particularly prohibitive in the scenario of MSWI BA being reused as a granular material in pavement base or subbase applications.
2. A gap in comprehensive research regarding the reuse of MSWI BA as an aggregate replacement in Portland cement concrete, particularly regarding a series of potential chemical reactions between MSWI BA and Portland cement, which may jeopardize the long-term durability and performance of concretes amended with MSWI BA.
The objective of this research is to investigate these two issues individually as
they relate to MSWI BA recycling, and to produce peer-reviewed data and
recommendations that can be used by decision makers and end users to facilitate an
increase in current MSWI BA recycling rates in the U.S.
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Outline of Thesis
Chapters 2 and 3 in this document address issues 1 and 2 listed in the Research
Motivation and Objectives section of this document, respectively. Chapter 2 examines
the leaching of select metals from MSWI BA intended for reuse as a granular material in
a road base, and presents an engineered approach to mitigate the environmental risk
presented by such contaminants. Chapter 3 investigates the durability of MSWI BA as a
prospective aggregate replacement concrete, with a focus on dimensional expansion
induced by reactivity of the ash. Chapter 4 provides conclusions, synthesis of the two
studies, and recommendations for future work. Each chapter is organized such that all
figures and tables appear at the end of each respective chapter. References to all cited
literature and methodology appear after the conclusion of Chapter 4.
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CHAPTER 2 LEACHING OF METALS FROM MUNICIPAL SOLID WASTE INCINERATOR BOTTOM ASH AND NATURAL AGGREGATE BLENDS: IMPLICATIONS FOR BENEFICIAL USE
AS A GRANULAR ROAD BASE
Background
Municipal solid waste incineration (MSWI) with energy recovery is an effective
solid waste management practice resulting in the production of significant amounts of
bottom ash (BA) as a residual byproduct (about 20% of the initial mass of MSW). In
2014, approximately 30 x 106 Mg of MSW was incinerated in the US (13% of the total
domestic MSW produced) at some 80 operational incineration facilities, generating over
5 x 106 Mg of residual BA. The vast majority of BA produced in the US is comingled with
fly ash (in order to create a nonhazardous waste product) and ultimately disposed of in
an ash monofill, with current recycling/reuse rates lower than 5% (US EPA, 2016a).
Comprehensive research has been performed to identify beneficial reuse options
for MSWI BA [6], [10]–[12]. The recycling of MSWI BA as a secondary aggregate
material in roadway applications has been carried out in Europe [13], Asia [14], and is
slowly gaining attention in the US [8]. MSWI bottom ashes exhibit similar mineralogy
and physical properties to some natural aggregates [15]–[17] and thus may prove
economically and environmentally advantageous if natural aggregates can be
supplemented or replaced in roadways (especially when factoring in the avoided cost of
landfilling the ash). Furthermore, a sustainable aggregate source used as granular road
base decreases reliance on naturally-mined minerals and offsets greenhouse gas
emissions from mining. In 2014, 59.2 x 106 Mg of crushed stone (primarily lime rock and
dolomite) was mined in the US with usage designation as a graded aggregate in road
base and subbase applications [18]. The mining of crushed stone could be reduced if
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the available tonnage of MSWI BA were utilized to help meet the aggregate demand for
granular road base.
One concern that must be addressed concerning the use of MSWI BA as a road
base material is the risk of human or environmental harm as a result of exposure to
contaminants of potential concern (COPC) present in the ash. While MSWI BA is
predominantly classified as a nonhazardous waste in the US by the Toxicity
Characteristic Leaching Procedure, research has demonstrated that BA contains small
amounts of metals and salts that may pose a risk to environmental and ecological
health [2], [19], [20]. While the risk posed by direct contact to COPC in MSWI BA is low
when the material is placed beneath a compacted pavement layer, the potential for
contaminant leaching to groundwater must still be considered. Much of the risk posed
by COPC in BA can be mitigated by use of certain engineering controls (e.g. natural
weathering, physical encapsulation, ash washing) and institutional controls (e.g.
scenario-specific approval, leaching criteria, etc.). Other engineering controls are still
being explored to reduce any risks posed by the use of MSWI BA. To date, little
laboratory or field research has been conducted to investigate road base products
containing a combination of MSWI BA and a more conventional aggregate source (e.g.,
lime rock). The idea of blending incinerator bottom ash with common granular materials
is one engineering control for risk reduction which has yet to be targeted in laboratory or
pilot studies. While blending the materials should reduce the total concentrations of
metals in the ash, leaching of certain species may not always be directly proportional to
the original mass of ash present. Other factors, including pH, solubility, redox, and
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surface complexation play a role in leaching [19], [21]–[23], thus materials-specific
testing is necessary to best assess risk.
Previous pilot studies conducted on bottom ashes assessed the leaching risk
posed by metals, but only when ash was the sole component in the base or subbase
material [4], [24]–[27]. Other research has investigated stabilizing bottom with cement
ash to enhance the mechanical properties of the material as a base, but the treatment
did not reduce heavy metals leachability [28]. In areas where reuse of MSWI BA is
approved by regulation, reuse as a road base may be hindered by a limited supply of
bottom ash. Road base and subbase projects require substantial amounts of aggregate,
often of such magnitude that MSWI bottom ash alone cannot sufficiently accommodate,
and thus diminish industry-wide acceptance. Combining MSWI BA with natural
aggregates may produce a blended aggregate product that provides some of the
economic and environmental benefits of materials recovery, but also offers contractors
a consistent and sustainable aggregate source. The practice of blending aggregates
may not only reduce dependency on natural resources, but could also reduce the
amount of environmental risk posed by the use of MSWI ash alone.
This research investigates the behavior of MSWI BA ash blended with a variety
of natural and recycled aggregates with a focus on leaching of trace metals (As, Mo, Pb,
Sb) and macro elements (Al). The study aims to assess the blending effect on bottom
ash leaching, and to examine if total metals and those leached can be reduced to an
acceptable level of risk for a road base. To examine this hypothesis, aggregate fractions
of two MSWI bottom ashes were blended with two natural aggregates and two recycled
aggregates in varying percentages, and a leaching analysis was performed using
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standard protocols. A total concentrations analysis of metals in the materials was also
performed.
Methods
Risk Assessment of Waste Materials
When assessing the risks to human health associated with the beneficial reuse of
a nonhazardous solid waste material, two exposure pathways are typically considered
[29]:
1. Leaching of aqueous COPC to water supplies (groundwater or surface water)
2. Direct exposure (DE) to COPC through direct human contact (e.g. inhalation, ingestion, dermal contact)
The risk of COPC leaching to water supplies is often measured using batch
leaching tests (concentration results in mg/L), while direct exposure (DE) risk is
relatable to the total metals content of the material (mg metal/kg material). COPC
concentrations obtained from batch leaching tests and total metals analyses are
typically compared to appropriate regulatory benchmarks or screening levels to assess
the potential risk posed to a specific exposure pathway. In the US, state regulatory
agencies set their own risk-based thresholds to characterize DE risk; these thresholds
vary depending on assumed exposure and risk criteria, as well as background soil
concentrations. For this analysis, we compare total metal concentration results to the
DE risk thresholds applicable to the location where the ash was generated (Florida Soil
Cleanup Target Levels (SCTLs; [30] and in some cases, the US EPA’s Regional
Screening Levels (RSLs) are compared to provide additional context [31]. Leach test
results were compared to the US EPA National Primary Drinking Water Standards
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(NPDWS) [32], and in some cases to residential tap water RSLs [31] (for constituents
with no health-based NPDWS).
Experimental Approach
Bottom ash samples collected from two MSW incinerators in Florida, US, were
characterized individually for total metals and leaching, and then blended with two
naturally-mined aggregates (lime rock, cemented coquina) and two recycled aggregates
(reclaimed asphalt pavement, recycled concrete) in different mass-based proportions.
Batch leaching concentrations for each ash and aggregate (derived using EPA
Method 1312, the Synthetic Precipitation Leaching Procedure (SPLP) [33] were used to
identify leaching COPC, and then blends of ash and aggregate were similarly leached.
COPC concentrations in the blended samples were compared to the predicted leachate
concentrations (mathematically weighting the leaching results on individual materials).
The leaching data were supplemented by conducting EPA Method 1316 [34] on the ash
samples and on select blends of ash and conventional aggregates. The data obtained
from Method 1316 were used to examine the release of metals over a range of liquid-to-
solid (LS) ratios, and to investigate the leaching behavior of solubility-controlled species
(As, Pb, Sb).
Total environmentally available (TEA) concentrations were used to identify
COPC which present a risk to the direct exposure pathway. After obtaining the TEA
concentrations of COPC in each material individually, concentrations in the blended
products were estimated empirically by multiplying the concentration of COPC in each
ash and aggregate by its prospective mass-based ratio in a blended product.
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Materials
MSWI Bottom Ash
Bottom ash generated at two Florida MSWI facilities (hereafter Facilities A and B)
was collected for this study. Facility A is a 62-megawatt refuse-derived fuel (RDF)
facility with a nominal bottom ash production of 400 Mg per day, and Facility B is a 95-
megawatt mass burn facility producing up to 700 Mg of bottom ash per day. Each
facility’s feedstock consists primarily of MSW along with small amounts of construction
and demolition debris. Following combustion and water quenching, bottom ash from
both facilities undergoes ferrous and nonferrous metal recovery as it exits the furnace.
Composite samples of bottom ash were collected from each facility during a 7-
day collection event following an EPA sampling protocol [35]. Approximately 10 Mg of
freshly quenched bottom ash was obtained daily from each facility’s ash bunker and
transferred to an on-site staging area over the course of one week. The samples were
obtained in a manner to ensure that only bottom ash was included. At the conclusion of
the 7-day sampling period, the seven individual piles of bottom ash were uniformly
mixed, and a 70 Mg composite stockpile was created for each facility. The stockpile was
representative of one week of routine ash production at each MSWI unit.
Each composite stockpile was left undisturbed for approximately 4 months to
allow for natural weathering (aging). Temporary weathering of MSWI BA has been
shown to immobilize various heavy metals by allowing for atmospheric carbonation and
the formation of insoluble metal hydroxides and carbonates, thus creating a more
environmentally inert material for reuse [19], [36]–[38]. After weathering, the stockpiles
were screened to obtain a desired particle size using an industrial aggregate vibratory
screen. The screening operation produced a bottom ash fraction containing particles 38
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mm in size and less (with many particles as small as 50 microns). A particle size
distribution of the two bottom ashes collected for this study can be found in the
supplemental materials accompanying this paper. The less than 38 mm in size fraction
of bottom ash was targeted under the assumption that it possesses the optimum
structural and geotechnical properties for reuse as a road base coarse (e.g., gradation,
optimum compaction, bearing strength). Several 20 kg composite samples of the
weathered, screened MSWI BA were collected from various locations on a circular
sampling pad in accordance with ASTM D75 [39] and sealed in 20L HDPE containers to
retain moisture and limit additional carbonation.
Natural and Recycled Aggregates
Two natural aggregate materials, Florida lime rock (LR) and cemented coquina (CC),
were used as components in blended products containing MSWI BA. CC aggregates
are naturally occurring deposits formed of broken mollusk shell, corals and the skeletal
remains of other marine invertebrates cemented together by carbonates or other natural
cementing agents [40]. LR aggregate consists of natural minerals, primarily calcium and
magnesium carbonates. Both materials have been approved by the Florida Department
of Transportation (FDOT) as graded aggregate road base and are produced at
aggregate mines in proximity to the MSWI facilities. Several 20 kg bagged samples of
the LR and CC aggregates were obtained directly from stockpiles at the aggregate
mines.
The recycled aggregates included reclaimed asphalt pavement (RAP) and recycled
concrete aggregate (RCA). Both materials were also collected in 20 kg bags from
aggregate stockpiles at a recycling facility in Florida. The RCA stockpile was pre-
approved as a graded aggregate road base material in Florida.
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Leaching Procedures
Synthetic Precipitation Leaching Procedure
For the SPLP, homogeneous samples of the weathered, screened MSWI BA
were size reduced to less than 9.5 mm using an industrial-grade blender, and mixed
with the natural and recycled aggregates in mass-based ratios of 0:100, 15:75, 30:70,
50:50, and 100:0 in a nonreactive HDPE vessel. The vessels were then filled with a
diluted 60:40 nitric and sulfuric acid extraction fluid (pH = 4.2 ± 0.05) at a LS ratio of
20:1. The solutions were placed on a standard rotary agitator at room temperature and
rotated for 18 hours. The resulting eluent was extracted by vacuum filtration through a
0.7-micron glass microfiber filter, and a 50-mL aliquot of the leachate was preserved for
elemental analysis. SPLP extractions were performed in triplicate for all materials and
blended proportions.
Leaching as a Function of Liquid-to-Solid Ratio
EPA Method 1316 was performed in duplicate on the two ash samples and on
blended samples containing 15% bottom ash and 85% of either RCA or LR. The
necessary mass of the size reduced (< 2 mm) materials was added to a volume of
reagent water to obtain 5 target LS ratios: 0.5, 1, 2, 5, and 10 L/kg. The samples were
agitated in an end-over-end fashion for 48 hours and the eluent was vacuum-filtered
through a 0.45-micron polypropylene filter and preserved for elemental analysis.
Analytical Procedures
For TEA characterization, several 2-g samples of MSWI BA and aggregate
samples were size reduced to < 2 mm, then digested using a microwave-assisted
HCl/HNO3 acid digestion following EPA Method 3051A [41]. Leachates obtained from
the batch leaching tests were prepared for elemental analysis using an automated hot
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block HCl/HNO3 acid digestion in accordance with EPA Method 3010A [42]. Following
each digestion procedure, both the leachate and solid samples were analyzed for 23
inorganic elements (Al, As, B, Ba, Be, Ca, Cd, Cr (total), Cu, Fe, K, Mg, Mn, Mo, Na, Ni,
Pb, Sb, Se, Sn, Sr, V, and Z) using inductively coupled plasma atomic emission
spectrometry (ICP–AES) in accordance with EPA Method 6010D [43] . TEA
concentrations were reported as the average of five replicates analyzed for each
material. Concentrations were reported on a dry-mass basis. Leachate concentrations
were reported as averages of the triplicate SPLPs performed on each material and each
blend of materials. Standard quality control and quality assurance measures including
method blanks, blank spikes, matrix spikes (75% - 125% recovery), certified metal
standard solutions, and duplicate spectrometer exposures were applied during the
analysis.
Results and Discussion
Direct Exposure Pathway
MSWI bottom ash
The TEA concentrations results of the two bottom ashes found six inorganic
elements to exceed the residential SCTL: As, Ba, Cr, Cu, Pb, and Sb. The total
concentrations of these elements were above the SCTL in both of the ashes analyzed,
with the exception of Cr (only exceeded for facility A ash). These six elements are
considered COPC to DE in terms of the bottom ash itself. The measured total
concentrations of these elements were similar to the range of concentrations of other
incinerator bottom ashes [2], [8], [44]–[46]. Of the 6 metals that exceeded the residential
SCTL, none exceeded the corresponding commercial thresholds. Table 2-1 displays the
total concentrations of the six COPC in comparison to the residential and commercial
25
SCTLs. As, Ba, Cr, Pb and Sb marginally exceeded the residential limit (concentrations
of these elements were within three times of the benchmark). The total concentration of
Cu in both bottom ashes (3400 mg/kg and 1900 mg/kg) exceeded the residential SCTL
by an order of magnitude. Total Cu was well below the commercial SCTL of 89,000
mg/kg.
Natural and recycled aggregates
The four natural and recycled aggregates were found to be relatively low in total
metal concentrations in comparison with risk-based DE thresholds. Only As exceeded
the residential SCTL, with a total concentration of 3.5 mg/kg in the lime rock and 6.4
mg/kg in the RCA. Thus, As is considered a COPC to the DE pathway in limerock and
RCA. These concentrations were comparable to the total As concentrations in both
MSWI ashes (5.17 mg/kg and 7.68 mg/kg). Previous research has reported background
soil As concentrations in the same geological area to be above the residential SCTL
[47]. RAP and CC aggregates produced no elements with total concentrations above
the Florida residential SCTL.
Blended products
The TEA concentrations of metals calculated in the blended products suggests
that DE risk to bottom ash is reduced a with the addition of other aggregates.
Concentrations of all bottom ash COPC declined as ash was substituted with any of the
four other aggregates. At a mass-based ratio of 15:85 BA to aggregate, the estimated
total concentrations of four of the original six bottom ash COPC (Ba, Cr, Pb, Sb) fell
beneath the residential SCTL. The theoretically calculated TEA concentrations of the
blended products containing 15% bottom ash can be seen in Table 2-2. As and Cu were
estimated to exceed the residential SCTL at all of the blended proportions considered,
26
however, blends containing CC and RAP were within 10% of the residential SCTL for
these elements. Again, as the arsenic concentration in BA is similar to lime rock and
RCA, which are major construction materials of common use, this element was not
viewed as problematic to the DE risk pathway.
The estimated values of total Cu exceed the residential target level in all four
blended products, even at low ash percentages. This is partly due to the fact that the
Florida residential SCTL for Cu (150 mg/kg) is significantly more stringent than the
commercial limit (89,000 mg/kg), as compared to the limits for the other COPCs. The
larger discrepancy between the residential and commercial benchmarks for Cu can be
explained by the methodology in which they were developed, where an acute exposure
scenario rather than chronic exposure was assumed [48]. The use of acute toxicity data
as reference dose for Cu implied that a child might ingest a relatively large quantity of
soil (>10 g) at one time (this is unlikely for BA placed beneath a pavement). Additionally,
if the US EPA RSL for total Cu (residential setting) of 3,100 mg/kg were applied, Cu
would not be considered a residential COPC to DE in any of the reported blended
proportions, including BA itself. If it is assumed that the current SCTLs for Cu and As
are overly conservative, BA could be introduced to the blends at more than 30% by
mass until total concentrations of other COPC (primarily Pb) would approach their
respective SCTLs and begin to present a DE concern.
Leaching to Groundwater Pathway
MSWI bottom ash
The SPLP leaching tests conducted on the two bottom ashes identified four
COPC that might possibly present a leaching risk to water supplies: Al, As, Pb, and Sb.
In Table 2-3, the SPLP leachate concentrations from both bottom ashes are compared
27
to risked-based drinking water standards. Average leachate concentrations of Al, As,
Pb, and Sb were greater than or equal to the NPDWS in at least one of the two leached
bottom ashes. The elevated leaching of these four COPC is consistent with other batch
leaching tests performed on weathered bottom ashes under similar laboratory
conditions [46], [49]. Arsenic leached from Facility B ash at the same concentration as
the NPDWS, and below the method detection limit for Facility A ash. Pb leachate
concentrations narrowly exceeded the NPDWS by 5 ± 1 µg/L in one bottom ash, and
was below detection limit in the other. The low concentrations of Pb and As with respect
to the NPDWS suggests that these COPC do not pose a significant health risk at a
groundwater point of compliance, where leachate concentrations are expected to be
much lower after being reduced by natural dilution and attenuation factors in the
subsurface environment [50], [51]. Furthermore, the weathering of fresh MSWI BA is
effective in controlling the mobility of Pb by reducing the natural bottom ash pH to levels
at which amphoteric Pb species become insoluble [37], thus allowing the risk of Pb
leaching from road base to be accurately predicted and controlled.
Al and Sb leached to the greatest extent in both ashes, exceeding risk-based
MCL’s by factors of approximately five and six, respectively. Sb likely poses a greater
leaching risk than Al in an unencapsulated road base scenario, given its classification
as a primary drinking water contaminant in the US and its behavior as a blood irritant at
low reference doses [32]. The data provided in Table 2-3 suggests that Al and Sb are
the two primary metals in the MSWI BA leachates that should be monitored for a
reduction in the blended products.
28
Natural and recycled aggregates
The four natural and recycled aggregates investigated were relatively inert in
regard to metals leaching, as expected. Compared to the BA, these aggregates leached
much less in terms of COPC. Molybdenum, a natural lime rock impurity, appeared in the
lime rock aggregate (0.064mg/L) and RCA (0.049 mg/L) at concentrations higher than
both bottom ashes (0.024 mg/L), but below the EPA RSL of 0.1 mg/L. The presence of
Mo in the leachate of both of these materials is unsurprising, as lime rock is a commonly
used aggregate in the production of portland cement concrete, and in turn is likely to be
present in recycled concrete. Any risk posed by Mo leaching is considered marginal as
batch test concentrations are well below the EPA RSL of 0.1 mg/L, and concentrations
of Mo are known decrease with increasing time and L/S ratios [52].
In the RAP samples, the average Ni, and Pb leachate concentrations were
elevated in comparison to drinking water standards, however, the standard deviation of
Ni concentrations in the batch leaching test was greater than the arithmetic mean, and 2
of the 3 triplicate samples were below the method detection limit for Ni. Ni is not known
to be a leaching COPC in RAP according to data from other studies on the material [53].
Pb leached from the RAP in this study at a concentration equal to the NPDWS.
Elevated Pb leaching from RAP has been reported in column leaching experiments [54],
but the peak concentrations decreased sharply with elapsed time, and were below 0.1
µg/L at the end of the 40-day column extraction.
Blended products
The SPLP leaching tests performed on blended proportions of MSWI BA and the four
aggregates showed a reduction in leachate concentrations of some elements initially
identified as COPC in the ash itself. At all blended proportions tested, the introduction of
29
other aggregates to the MSWI BA showed a reduction in concentration of most COPCs.
Mixtures containing 15% MSWI BA and 85% aggregate were the most environmentally
inert products in respect to leaching. Table 2-4 presents the SPLP leaching data from
the blends containing 15% bottom ash. As can be seen in Table 2-4, several of the ash
COPC initially identified in Table 2-3 were no longer in exceedance of drinking water
standards when the ash was blended with other aggregates. Leaching of aluminum was
clearly dependent on the mass of bottom ash present in the blend. This can be seen in
Figure 2-1, where Al leached below the RSL of 20 mg/L for blends containing 15% and
30% bottom ash. In fact, leaching of Al displayed a near linear relationship between the
measured leachate concentration and the mass of bottom ash included in the blend.
This linear relationship for Al leaching can be observed in Figure 2-2.
Unlike Al, the leaching of Sb from the bottom ashes remained elevated above the
NPDWS, and was relatively unaffected by the addition of three of the four tested
aggregates (LR, RAP, CC). This suggests that leaching of Sb species is primarily
controlled by solubility and is unaffected by the mass of bottom ash contained in a
sample. Other research has found that solubility to be the primary mechanism affecting
the leaching behavior of oxyanion-forming elements such as Sb [55]. However, in
blends containing RCA, the observed leachates steadily decreased in Sb concentration
as ash was substituted with RCA. At a mixture of 15% ash and 85% RCA, leaching of
Sb was at or within 1 µg/L of the NPDWS. The pH-dependent leaching behavior of Sb
can be observed in data from a pH static leaching procedure (EPA Method 1313) [56]
performed on MSWI BA in the supplemental materials of this paper. MSWI BA displays
a leaching minima for Sb in the 10.8 -11.0 pH range of mildly weathered MSWI BA, and
30
dissolution increases at pH > 11, while over-carbonation of fresh bottom ash to pH < 9
increases leaching of Sb due to equilibrium with calcium antimonite [36]. The eluent pH
of the SPLP on the blend of 15% BA and 85% RCA (10.97) was in the leaching minima
range for Sb, thus these blends leached less Sb compared to the other three aggregate
blends. The leaching behavior of Sb in the SPLP on the 15% ash blends can be seen in
Figure 2-3, in which RCA clearly shows a lower Sb release as compared to the other
blends. In Method 1316, however, the 15/85 blends of ash and RCA leached below the
NPDWS for Sb at all LS ratios, even at equilibrium pH values > 11, where MSWI BA
should release more Sb according to the pH dependence observed from Method 1313.
The leaching of Sb in Method 1316 can be seen in Figure 2-4, where Sb leached much
less from RCA blends compared to lime rock blends containing the same percentage of
bottom ash.
Arsenic leaching was relatively unaffected by the addition of other aggregate
sources, and remained below the method detection limit or within 2 µg/L of the NPDWS.
Iron and nickel leaching was below target levels for all materials at all blended
percentages.
Implications for Reuse as Road Base
Two pathways of human health and environmental risk posed by MSWI bottom
ash used as road base were assessed: DE and leaching to groundwater. The DE risk
pathway for BA is not a major concern during the use phase of a road base due to a low
likelihood of direct human contact while the bottom is confined underneath an asphalt or
concrete pavement coarse of varying thickness. The total metals results demonstrated
that blending should reduce DE risk to a point where the blended product the complied
with most COPC regulated by residential SCTLs (the most stringent category of soil
31
benchmarks in Florida, and a conservative benchmark for a granular base or subbase
layer). Cu persisted in the blended products at levels higher than residential SCTL of
150 mg/kg, but below the EPA RSL for residential soils. The latter set of contaminant
benchmarks are developed using tools such as the EPA's Integrated Risk
Information System (IRIS) and The Agency for Toxic Substances and Disease
Registry (ATSDR) to provide the most up to date and accurate toxicity data inputs.
Total concentrations of Cu in US bottom ashes should decline in the future as
incinerator operators explore increased nonferrous metal recovery technologies [57].
From a DE perspective, the blending of aggregates with MSWI BA showed that the risk
posed by COPC is low and should not be prohibitive to the inclusion of bottom ash into
the stream of road construction aggregates.
When assessing the leaching pathway, the SPLP demonstrated that Al and Sb
were the most likely elements to exceed risked-based concentrations for groundwater.
For Al, leaching was reduced by the amount of bottom ash contained in the sample, but
the actual aggregate which was blended with the bottom ash did not compound an
additional reduction in metals leaching. Given the mass-dependent leaching
relationship, the anticipated increase of nonferrous metal recovery from incinerator
ashes should certainly reduce the environmental burden presented by Al leachates [58].
Sb presented to be the most prominent leaching risk, but immobilization of Sb seems to
achievable by blending ash with a calcium-bearing aggregate material such as RCA,
having an alkaline pH and mineralogy with an adsorption affinity for Sb. The reduced Sb
leachate concentrations in RCA blends at a high equilibrium pH suggests that other
interactions between with calcium-bearing minerals (portlandite and ettringite) could be
32
responsible for the Sb immobilization observed in the RCA blends, and pH is not the
sole mechanism controlling dissolution. The higher abundance of the portlandite and
ettringite mineral phases in RCA as compared to the other three aggregates and MSWI
BA itself may allow for a higher rate of adsorption and corresponding reduction in
leaching.
Summary of Findings
In this study, the blending of conventional road base aggregates with MSWI BA
reduced the relative direct exposure and groundwater contamination risks posed by
metals inherent to the bottom ash. For most of the blends of materials considered, the
total and leached concentrations of COPC declined as bottom ash was replaced with
the cleaner aggregates. Sb leached at elevated concentrations in blends containing
even small proportions of bottom ash, but RCA was found to mitigate Sb leaching in
these blends to levels comparable to drinking water standards. The analysis of the
leaching data suggests that the environmental risk posed by most bottom ash COPC
decreases when the ash is combined with a cleaner road base aggregate, and blending
of such aggregates presents a unique opportunity for the generation a sustainable
construction product to be used in road base infrastructure.
33
Figures and Tables
Table 2-1. Total environmentally available concentrations (mg/kg-dry material) of MSWI bottom ash and natural/recycled aggregate materials. Total concentrations exceeding the residential Florida Soil Cleanup Target Levels are identified as COPC for the direct exposure risk pathway and have been shaded accordingly.
MSWI Bottom Ash Natural Aggregates Recycled Aggregates Soil Benchmarks
Facility A
< 38 mm,
weathered
Facility B
< 38 mm,
weathered
LR CC RCA RAP Florida SCTL
(Residential)
Florida
SCTL
(Commercial)
US EPA
RSL
(Residential)
As 5.17 ± 2.99 7.68 ± 1.82 3.50 ± 0.268 1.37 ± 0.445 6.38 ± 0.693 1.27 ± 0.586 2.1 12 0.68
Ba 307 ± 69.7 245 ± 27.6 25.6 ± 2.94 4.73 ± 0.563 39.4 ± 3.30 10.2 ± 0.837 120 130,000 150,000
Cr (total) 305 ± 198 205 ± 87.7 40.8 ± 4.95 79.6 ± 38.7 55.1 ± 2.01 70.4 ± 9.35 210 470 -
Cu 3400 ± 1290 1920 ± 1780 2.43 ± 0.374 2.26 ± 1.11 45.1 ± 3.26 6.02 ± 0.619 150 89,000 3100
Pb 446 ± 111 981 ± 352 0.826 ± 0.00 0.816 ± 0.00 12.1 ± 1.54 7.90 ± 3.88 400 1,400 400
Sb 39.4 ± 14.5 39.6 ± 12.1 2.24 ± 0.541 1.98 ± 1.27 2.27 ± 0.560 2.15 ± 0.466 27 370 31
34
Table 2-2. Theoretical total environmentally available concentrations (mg/kg-dry) of blended products containing 15% MSWI bottom ash and 85% natural or recycled aggregates. Elemental concentrations exceeding the Florida Residential Soil Cleanup Target levels are identified as COPC and are shaded accordingly.
Facility A Blended Products 15%
MSWI Bottom Ash
< 38 mm, weathered
Facility B Blended Products 15% MSWI Bottom Ash
< 38 mm, weathered
Soil Benchmarks
85%
LR
85%
CC 85% RCA
85% RAP
85% LR
85% CC
85% RCA
85% RAP
Florida SCTL
(Residential)
Florida
SCTL
(Commercial)
US EPA
RSL
(Residential)
As 3.74 1.92 6.20 1.84 4.10 2.27 6.57 2.21 2.1 12 0.68
Ba 66.8 48.6 79.3 54.2 57.5 39.3 69.8 44.7 120 130,000 150,000
Cr (total) 79.5 112 92.4 105 64.6 97.6 77.2 90.0 210 470 -
Cu 500 495 545 507 281 287 322 287 150 89,000 3100
Pb 65.9 65.3 76.7 72.7 143 150 155 150 400 1,400 400
Sb 7.68 7.41 7.80 7.66 7.66 7.64 7.78 7.64 27 370 31
35
Table 2-3. Average leachate concentrations of EPA Method 1312 (SPLP) performed in triplicate on MSWI bottom ashes and natural/recycled aggregates individually. Elemental concentrations exceeding the respective MCL are identified as COPC for the leaching to groundwater risk pathway and have been shaded accordingly.
MSWI Bottom Ash Natural Aggregates Recycled Aggregates Groundwater Benchmark
Facility A < 38 mm,
Weathered
Facility B < 38 mm,
Weathered
Cemented Coquina
Florida Lime rock
Recycled Concrete
Aggregate
Reclaimed Asphalt
Pavement
Maximum Contaminant Level
Element mg/L ± std
dev mg/L ± std
dev mg/L ± std
dev mg/L ± std
dev mg/L ± std
dev mg/L ± std
dev mg/L
Al 112 ± 2.07 52.6 ± 8.75 0.116 ± 0.049
0.154 ± 0.061 2.86 ± 0.008 0.240 ± 0.077 20***
As < 0.004 0.010 ± 0.002 < 0.008 < 0.008 < 0.008 < 0.008 0.01*
Fe 0.009 ± 0.004 < 0.004 < 0.004 < 0.004 < 0.004 0.399 ± 0.684 14**
Mo 0.024 ± 0.000 0.024 ± 0.001 < 0.006 0.064 ± 0.009 0.049 ± 0.004 < 0.006 0.10**
Ni < 0.004 0.008 ± 0.006 < 0.002 < 0.002 < 0.002 0.326 ± 0.562 0.2**
Pb 0.020 ± 0.001 < 0.008 < 0.008 < 0.008 < 0.008 0.015 ± 0.012 0.015*
Sb 0.043 ± 0.006 0.037 ± 0.004 < 0.006 < 0.006 < 0.006 < 0.006 0.006*
Eluent pH
10.7 ± 0.04 10.2 ± 0.04 8.13 ± 0.40 8.64 ± 0.13 10.97 ± 0.44 7.83 ± 1.10 -
*US EPA National Primary Drinking Water Standard **US EPA Regional Screening levels (RSL) for residential tap water was applied in the absence of a NPDWS for a given pollutant. RSLs for carcinogens are based on a target cancer risk = 1 in 1,000,000. RSLs for non-carcinogens are based on a hazard quotient =1. ***The National Secondary Drinking Water Standard for aluminum of 0.2 mg/L was established to meet certain aesthetic conditions for drinking water and is not toxicity-based. The health-risk based RSL of 20 mg/L was substituted to accurately quantify the risk Al poses to human health.
36
Table 2-4. Average leachate concentrations of EPA Method 1312 (SPLP) performed in triplicate on blends of MSWI bottom ash and natural/recycled aggregates at a mass ratio of 15:85. Elemental concentrations of contaminants which exceed the respective MCL are identified as COPC for the leaching to groundwater risk pathway and have been shaded accordingly.
Facility A Blended Products
15% MSWI Bottom Ash, < 38 mm, weathered
Facility B Blended Products
15% MSWI Bottom Ash, < 38 mm, weathered
Groundwater
Benchmark
85%
LR
85%
CC
85%
RCA
85%
RAP
85%
LR
85%
CC
85%
RCA
85%
RAP
Maximum
Contaminant
Level
Element mg/L ± std
dev
mg/L ± std
dev
mg/L ± std
dev
mg/L ± std
dev
mg/L ± std
dev
mg/L ± std
dev
mg/L ± std
dev
mg/L ± std
dev mg/L
Al 22.7 ± 0.77 23.6 ± 0.76 7.89 ± 0.79 12.6 ± 0.14 8.93 ± 0.24 10.8 ± 1.93 5.56 ± 1.00 8.34 ± 2.54 20***
As < 0.004 < 0.004 < 0.004 < 0.004 0.009 ± 0.002 0.010 ± 0.003 0.010 ± 0.002 0.012 ± 0.003 0.010*
Fe 0.009 ± 0.004 0.011 ± 0.006 0.018 ± 0.002 0.031 ± 0.014 < 0.004 < 0.004 < 0.004 < 0.004 14**
Mo 0.086 ± 0.002 < 0.006 0.063 ± 0.001 < 0.006 0.081 ± 0.002 < 0.006 0.057 ± 0.002 < 0.006 0.10**
Ni < 0.004 0.004 ± 0.003 0.005 ± 0.002 0.015 ± 0.012 < 0.002 < 0.002 < 0.002 < 0.002 0.2**
Pb < 0.004 < 0.004 0.017 ± 0.007 < 0.004 < 0.004 < 0.004 < 0.004 < 0.004 0.015*
Sb 0.036 ± 0.001 0.034 ± 0.002 0.006 ± 0.002 0.040 ± 0.003 0.029 ± 0.000 0.026 ± 0.000 0.007 ± 0.001 0.027 ± 0.002 0.006*
Eluent
pH 10.46 ± 0.03 10.67 ± 0.06 11.33 ± 0.03 10.32 ± 0.03 9.92 ± 0.02 9.90 ± 0.06 11.04 ± 0.16 9.88 ± 0.65 -
*US EPA National Primary Drinking Water Standard **US EPA Regional Screening levels (RSL) for residential tap water was applied in the absence of a NPDWS for a given pollutant. RSLs for carcinogens are based on a target cancer risk = 1 in 1,000,000. RSLs for non-carcinogens are based on a hazard quotient =1 ***The National Secondary Drinking Water Standard for aluminum of 0.2 mg/L was established to meet certain aesthetic conditions for drinking water and is not toxicity-based. The health-risk based RSL of 20 mg/L was substituted to accurately quantify the risk Al poses to human health.
37
Figure 2-1. Concentrations of aluminum in SPLP leachates for blends of Facility A
MSWI bottom ash and natural or recycled aggregates as a function of the bottom ash contained in the blended product. The risk-derived US EPA Regional Screening Level for aluminum (residential tap water) is displayed as dashed reference line.
38
Figure 2-2. Ratio of aluminum leachate concentrations in the control bottom ashes to
aluminum leachate concentrations in blended products containing lime rock and bottom ash at percentages of 0%, 15%, 30% and 50%, and 100% ash (SPLP batch leaching test).
39
Figure 2-3. Concentrations of antimony in SPLP leachates for blends containing
weathered MSWI bottom ash and four different aggregates. Antimony leachate concentrations are plotted as a function of bottom ash contained in the blended product. The US EPA National Primary Drinking Water Standard for antimony is displayed as a dashed reference line.
40
Figure 2-4. Leaching of Antimony as a function of LS ratio (EPA Method 1316) in
blended products containing 15% weathered MSWI bottom ash and 85% RCA and LR aggregates.
41
CHAPTER 3 CHARACTERIZATION AND MITIGATION OF ALKALI-AGGREGATE REACTIVITY IN MORTARS CONTAINING MUNICIPAL SOLID WASTE INCINERATION ASH AS AN
AGGREGATE COMPONENT
Background
The practice of incorporating solid waste products into the manufacture of
construction materials such as portland cement (PC) and PC concrete is gaining
popularity due to a growing awareness into the sustainable management of materials
[59]–[61]. Bottom ash (BA) residues produced from municipal solid waste incineration
(MSWI) possess physical properties similar to common natural aggregates [6], and
reuse of MSWI BA as a coarse aggregate in hardened concrete is a prospective second
life application for the waste material [11], [16], [49], [62]. In densely populated countries
where incineration is a common waste management technique [3], [63], [64] , thousands
of tons of MSWI BA are generated annually. The availability of such quantities of MSWI
BA could offset the mining of natural concrete aggregates if recycling rates of ash are
increased.
In portland cement concrete (PCC), a number of deleterious alkali-aggregate
reactions (AAR) can occur between interaction of the alkali hydroxides found in cement
paste and reactive minerals present in certain aggregates. One particular form of AAR,
the alkali-silica reaction (ASR), is a common reaction between the amorphous silica of
certain aggregates and the alkali species (KOH, NaOH) in cement paste [65] . ASR is
well known to produce deleterious effects to concrete when reactive, siliceous minerals
are used as aggregates [66]. The dimensional expansion produced by the swelling of
silica-based gels in the presence of moisture can propagate cracking and result in an
overall reduction in the integrity and serviceability of the affected concrete. It has also
42
been documented that fine particles of aluminum in MSWI BA may produce similar
expansive reactions [67]. The high content of amorphous silica and metallic aluminum in
MSWI BA present an AAR risk. It is critical that the potential for any AAR in MSWI BA is
evaluated in order to ensure that ash-amended concrete will maintain suitable durability
during its service life.
To date, the potential for AAR to occur in MSWI BA as an aggregate replacement
in concrete has not been comprehensively examined throughout research. Müller and
Rübner [68] identified three types of AAR in specimens of field and laboratory concretes
containing MSWI bottom ash as a partial aggregate replacement:
1. Alkali-silica reaction of bottle glass fragments and glassy compounds of other siliceous components of the bottom ash
2. Reaction of elemental aluminum to form aluminum hydroxide and calcium aluminate hydrate (CAH) and
3. Reaction of aluminate with calcium sulfate to form ettringite and monosulphate
Damage as a result of the aluminum hydroxide reaction was reported to be more
severe than that caused by ASR. Deleterious cracking, spalling, and longitudinal voids
were attributed to the reaction of aluminum and the evolution of hydrogen gas. It should
be noted that this study used petrographic techniques to characterize AAR; dimensional
length changes of the concrete specimens were not reported; information which is
pertinent to accurately quantify the presence of reactive aggregates and the magnitude
of relative degradation caused by AAR. Van den Heede et al., [69] observed the
expansion of concrete blocks made with bottom ash as a full aggregate replacement
(100% coarse and fine), and found expansion to be more than double that of the
reference concrete, indicating that an AAR had occurred. However, both the ash-
43
amended and reference concretes in the study expanded by more than 0.1% over 14
days; the industry expansion limit indicative of innocuous field performance per ASTM
C160 [70]. This anomaly indicates the possibility that a reactive material was present in
the reference concrete, or that the testing conditions were overly aggressive for proper
characterization of the MSWI BA under investigation. Chemical methods have been
utilized to provide a rapid indication of the AAR potential of aggregates [71]; Forteza et
al. [6] performed a chemical analysis as part of a geotechnical assessment of
incinerator ashes in Spain using the Spanish method UNE 146507-1:1999 [72]. This
study reported the BA as nonreactive after a granular fraction of ash was immersed in a
1N solution of NaOH at 80° C for 24 hours, and the corresponding leachate was
measured for levels of dissolved silica and alkalinity.
The conclusions on AAR in MSWI BA obtained from a small sample size of
research suggests the need for rapid and conclusive information on the issue of AAR in
concrete or mortar containing BA as an aggregate, and a quantification as to the
amount of damage that can be attributed to inclusion of the BA. The limited amount of
comprehensive data summarizing the expansion of bottom ash-amended specimens
was the main motivation in performing this study. Due to the significant amount of time
required to test the expansion induced by reactive aggregates in actual concrete
specimens (minimum of 64 weeks), the accelerated mortar bar test (AMBT) was
adopted for use in this study [70] . The AMBT can be used to rapidly quantify the AAR
of aggregates (in as little as 16 days) by immersing small mortar bars in a highly
alkaline solution at elevated temperatures and monitoring periodic length change of the
specimens. Expansion results obtained from the short term AMBT are known to
44
correlate well with those obtained in the 15-month concrete prism test, and yield an
accurate indication of reactivity. [73], [74].
In this study, three different sources of MSWI BA were used as partial aggregate
replacements in the AMBT to determine the maximum amount of BA that could be
introduced to mortars before deleterious expansion was observed. Furthermore, two
supplementary cementitious materials (class F coal fly ash and a ground glass powder)
were investigated as mineral admixtures to mitigate AAR in the ash-amended mortars,
as many SCM’s are known to reduce the deleterious reactions caused by reactive
aggregates [73], [75], [76].
Materials and Methods
Bottom Ash Collection and Material Description
Three bottom ashes (hereafter referred to as BA1, BA2, and BA3) were collected
from different municipal waste incinerators in the southeastern United States.
Composite samples of the freshly quenched ashes were obtained over a 7-day period,
and immediately transported to outdoor stockpiles where they were weathered or aged
for approximately 90 days to facilitate atmospheric carbonation and allow the formation
of stable metal hydroxides and carbonates. Research indicates that aging limits the
environmental mobility of select heavy metals contained in the ash [37], [77]. BA3 was
sampled as a combined ash stream (containing bottom and fly ash), then processed to
remove any material finer than 6 mm, effectively removing all fly ash content from the
sample. The weathered bottom ashes were sieved in the field using a large double-deck
vibratory screening conveyor to obtain an aggregate particle size range of 6.35 mm -19
45
mm. The stockpiles of screened bottom ash were then sampled in accordance with
ASTM D75 [39].
Physically, the weathered bottom ash samples comprised of a heterogeneous
mixture of mineral components (primarily silicates), ceramics, and some incompletely
combusted organics and deleterious materials (textiles, fibers, food scraps). Fragments
of ferrous and nonferrous metals (primarily aluminum, copper, and zinc) were visible in
the ash, which had not extracted by the ferrous magnets and eddy current separators
installed at each incinerator. A chemical composition of each bottom ash analyzed using
X-ray fluorescence spectroscopy is presented in Table 3-1. The high alkali content of
the MSWI BA (> 5%) in comparison to the cementitious components of the mortars is
noteworthy, as portland cement is typically the main source of alkalis in the material
system which contribute to AAR. As aggregates typically account for 50-70% of the total
volume of concrete, it is expected that the inclusion of MSWI BA will result in a higher
total alkali load to the system.
Cementitious Materials
The cement used in the AMBT was classified as a type I/II PC as per ASTM
C150 [78]. Two pozzolans were used in an attempt to mitigate the expected expansion
in the ash-amended mortars. A class F (low calcium) fly ash was obtained from an
electrostatic precipitator at a coal-fired power station in Jacksonville, FL and met the
specifications for class F fly ash per ASTM C618 [79]. A low-alkali ground glass powder
was obtained from a local glass recycling facility.
Experimental Approach
A total of 16 mortar mixes were created and used in two variations of the AMBT
to quantify length change of specimens containing BA as a partial aggregate. An initial
46
series of 10 mixes were cast based on ASTM C1260 [70], with each BA replacing a
nonreactive natural sand in mass-based percentages of 0% (control), 15%, 30%, and
50%. The mortar used in this series of bars contained only Type I/II PC as the binder.
Length change of these specimens was measured to quantify the maximum allowable
BA content that could be introduced while maintaining innocuous expansion. Then, an
additional set of 6 mixes were cast according to ASTM C1567 [80]. Each of these
mortars contained an aggregate content of 30% MSWI BA, and a binary cementitious
matrix comprised of 80% PC and 20% SCM (ground glass or class F fly ash). The
expansions of this set of bars was compared to the initial ASTM C1260 mortars to
identify any reduction in expansion achieved by the addition of a pozzolan. Scanning
electron microscopy (SEM) was performed on several post-mortem specimens to
observe the specific AAR products that had evolved in the ash-amended mortars.
Preparation of Mortar and Experimental Procedure
Specimens cast to measure the expansion of mortar containing MSWI BA
aggregates in the AMBT were prepared following the guidelines specified in ASTM
C1260 [70]. The three BA’s and a nonreactive sand were dried in an oven at 100°C,
then size reduced using a benchtop jaw crusher with tungsten carbide plates to produce
the fine aggregate gradation specified in ASTM C1260 [70]. All materials were
proportioned using a Mettler-Toledo PB3002-S scale with a 0.01 g precision. The
mixtures were batched with the prescribed fine aggregate:binder:water ratio of
2.25:1:0.47. In the event that the fine aggregates (bottom ash and sand) resulted in an
average weighted specific gravity of less than 2.45, the aggregates were proportioned
according to the equation denoted in ASTM C1260 Part 8.4.3 “Proportioning of Mortar”
47
[70]. Each aggregate replacement was proportioned as a percentage of the total
aggregate content. Mortar proportions for specimens containing only BA, cement, and
the nonreactive sand are presented in Table 3-2. The two pozzolans used were
introduced as a percentage of the total cementitious content. Mortar mixes containing
combinations of PC, fly ash, ground glass, BA, and natural sand were prepared in
accordance with ASTM C1567 [80]. The specific mortar proportions for the binary mixes
can be seen in Table 3-3.
Mortars were mixed using a stainless steel mixing bowl and paddle stirrer
following the mixing sequence listed in ASTM C305 [81]. After being mixed, the mortar
was placed into steel double-gang molds of dimension 25.4 mm x 25.4 mm x 254 mm
with steel gage studs embedded at a fixed length. The molded mortar specimens were
allowed to cure in air for 24 ± 2 hr (while preventing any loss of moisture), then
demolded, measured for initial dimensions, and placed in cylindrical HDPE containers,
where they were completely submerged in a tap water bath at 80°C for an additional 24
± 2 hr period. Following removal from the water bath, initial zero readings of the
specimens were taken using a dial gauge comparator with precision of 0.0025 mm and
a fixed-length invar calibration bar. After the zero reading, the bars were reintroduced to
the containers and immersed in a 1N NaOH solution at 80° C. The containers remained
in the NaOH bath for 14 days and expansion measurements were taken using the dial
gage comparator at ages of 4, 7, 10, and 14 days. The average 14-day length change
readings of the four replicate bars for each mortar mix was reported.
48
Results and Discussion
AMBT Expansion
The length change measurements of the ash-amended mortar specimens are
presented in Table 3-4. Mortars which expand more than 0.10% during the AMBT are
considered to be potentially deleterious, and those exceeding 0.20% are considered
deleterious, as per ASTM’s C1260 [70] and C1567 [80]. The 30% BA and 50% BA
mortars containing only portland cement expanded beyond the deleterious limit of
0.20%. At 15% aggregate replacement, BA1 and BA2 mortars exceeded 0.10%
expansion, but did not reach the deleterious threshold (Figures 3-1 and 3-2). BA3
performed innocuously at 15% aggregate replacement (Figure 3-3). The length change
data from this evaluation indicates that MSWI BA could replace 15% of the nonreactive
sand before deleterious effects would be expected in field concretes or mortars using
the same mix proportions (if Type I/II portland cement is the sole binder used).
For the binary mortars containing 20% pozzolan, all specimens were classified
as innocuous at an aggregate replacement of 30% BA (Figures 3-4, 3-5, and 3-6). Both
fly ash and ground glass were effective in reducing reactivity during the AMBT, and
limited total of expansion all specimens to under 0.05% - less than half of the innocuous
limit. Neither pozzolan appeared to outperform the other in terms of relative reduction in
expansion. Both pozzolans reduced the expansion of the ash-amended specimens by
approximately 90% for each of the three MSWI BA studied in the AMBT.
49
Summary of Findings
The following conclusions were made regarding mortars made with MSWI BA as
an aggregate replacement in the AMBT:
1. MSWI BA is abundant in amorphous silica, which facilitated the alkali-silica reaction and produced expansive reaction products when MSWI BA was in the presence of alkalis and water.
2. The alkali-silica reaction was the dominant expansive reaction observed in the ash-amended mortars, more so than the alkali-aluminum reaction. The latter of which was not correlated with expansive reactions, only instances of spalling and hydrogen gas evolution.
3. Inclusion of MSWI BA as an aggregate at replacements greater than 15% resulted in deleterious expansion of mortar specimens containing only portland cement.
4. The introduction of pozzolanic ground glass or class F fly ash to the cementitious matrix reduced the expansion associated with AAR of the MSWI BA by approximately 90%, and increased the achievable percentages of MSWI BA as an aggregate replacement to levels of at least 30%.
50
Figures and Tables
Table 3-1. Oxide composition (% weight) of materials obtained using X-ray fluorescence (XRF) spectroscopy.
Aggregates Cementitious Materials1
Analyte BA1 BA2 BA3 Type I/II
PC Class F Fly Ash
Ground Glass
SiO₂ 43.6 45.8 41.9 18.7 57.8 61.2
Al₂O₃ 10.1 6.75 9.28 5.36 21.4 14.0
Fe₂O₃ 11.7 11.2 10.8 4.44 11.8 0.28
CaO 14.5 15.9 16.1 63.5 1.29 17.2
MgO 1.58 1.78 1.68 0.94 1.32 2.6
SO₃ 2.15 1.69 2.78 3.27 0.24 <0.01
Na₂O 4.89 4.69 5.83 0.14 0.90 2.64
K₂O 1.02 0.87 0.98 0.40 2.52 0.05
TiO₂ 0.86 0.62 0.91 0.27 0.99 0.69
P₂O₅ 0.83 0.75 0.90 0.64 0.19 0.05
Mn₂O₃ 0.13 0.11 0.12 0.07 0.04 <0.01
SrO 0.04 0.11 0.04 0.07 0.05 0.07
Cr₂O₃ 0.18 0.18 0.17 0.07 0.02 0.02
ZnO 0.37 0.34 0.44 0.08 0.02 <0.01
BaO 0.11 0.16 0.12 <0.01 0.07 <0.01
L.O.I. (950°C) 7.18 8.19 6.09 1.78 0.90 0.27
Total 99.2 99.2 98.1 99.7 99.6 99.1
Alkali Eq. (Na₂O + 0.658K₂O)
5.57 5.26 6.47 0.41 2.56 2.68
1Adopted from Paris, et al., 2016 “Evaluation of Alternative Pozzolanic Materials for Partial Replacement of Portland Cement in Concrete”.
51
Table 3-2. Proportions of mortar materials for ASTM C160 mixes containing 15%, 30%, and 50% MSWI BA aggregate replacement.
Control 15BA1 15BA2 15BA3 30BA1 30BA2 30BA3 50BA1 50BA2 50BA3
Type I/II portland cement (g)
523 515 511 510 508 522 521 524 522 520
MSWI BA (g) 0 174 173 172 343 326 323 538 517 511
Natural sand (g) 1176 985 978 976 800 760 754 538 517 511
Water (g) 246 242 240 240 239 245 245 246 245 245
Water:binder 0.47 0.47 0.47 0.47 0.47 0.47 0.47 0.47 0.47 0.47
Aggregate:binder 2.25 2.25 2.25 2.25 2.25 2.08 2.07 2.05 1.98 1.97
52
Table 3-3. Proportions of mortar materials for ASTM C1567 mixes containing portland cement, 20% pozzolan (ground glass or class F fly ash), and 30% MSWI BA aggregate replacement.
Control
30 BA1-F
30 BA1-G
30 BA2-F
30 BA2-G
30 BA3-F
30 BA3-G
Type I/II portland cement (g)
523 401 403 412 414 431 433
Class F fly ash (g) 0 100 0 103 0 108 0
Ground glass (g) 0 0 101 0 104 0 108
MSWI BA (g) 0 339 340 321 323 334 335
Natural sand (g) 1176 790 793 750 753 779 782
Water (g) 246 236 237 242 243 253 254
Water:Binder 0.47 0.47 0.47 0.47 0.47 0.47 0.47
Aggregate:Binder 2.25 2.25 2.25 2.08 2.08 2.07 2.07
Cementitious replacement (% mass)
0 20 20 20 20 20 20
53
Table 3-4. Length change data and performance classification of ASTM C160 and ASTM C1567 mortar mixes containing MSWI BA aggregate replacements.
Mix
Average 14-day Expansion1 (%)
Results Classification2
Portland Cement Mixes
Control (0 BA) 0.011 Innocuous
15BA1 0.171 Potentially Deleterious
15BA2 0.101 Potentially Deleterious
15BA3 0.077 Innocuous
30BA1 0.320 Deleterious
30BA2 0.309 Deleterious
30BA3 0.252 Deleterious
50BA1 0.410 Deleterious
50BA2 0.474 Deleterious
50BA3 0.400 Deleterious
Binary Mixes
30BA1-F 0.021 Innocuous
30BA2-F 0.038 Innocuous
30BA3-F 0.041 Innocuous
30BA1-G 0.031 Innocuous
30BA2-G 0.023 Innocuous
30BA3-G 0.032 Innocuous
1Length changes reported as an average of four specimens created for each mix.
2Expansion classification limits for listed in ASTM C1260/C1567 as indication of innocuous or
deleterious field performance of aggregates.
54
Figure 3-1. ASTM C160 average length change of mortars containing 100% portland cement and 15%, 30%, and 50% aggregate replacement by MSWI BA1.
Figure 3-2. ASTM C160 average length change of mortars containing 100% portland cement and 15%, 30%, and 50% aggregate replacement by MSWI BA2.
0.00%
0.10%
0.20%
0.30%
0.40%
0.50%
0 2 4 6 8 10 12 14 16
Len
gth
Ch
an
ge (
%)
Elapsed Time (days)
Control (0BA1) 15BA1 30BA1
50BA1 Innocuous Limit Deleterious Limit
BA1
0.00%
0.10%
0.20%
0.30%
0.40%
0.50%
0 2 4 6 8 10 12 14 16
Len
gth
Ch
an
ge (
%)
Elapsed Time (Days)
Control (0BA2) 15BA2 30BA2
50BA2 Innocuous Limit Deleterious Limit
BA2
55
Figure 3-3. ASTM C160 average length change of mortars containing 100% portland cement and 15%, 30%, and 50% aggregate replacement by MSWI BA3.
Figure 3-4. ASTM C1567 length change of mortars containing 20% pozzolan (ground glass or class F fly ash) and 30% aggregate replacement by MSWI BA1.
0.00%
0.10%
0.20%
0.30%
0.40%
0.50%
0 2 4 6 8 10 12 14 16
Len
gth
Ch
an
ge (
%)
Elapsed Time (Days)
Control (0BA3) 15BA3 30BA3
50BA3 Innocuous Limit Deleterious Limit
BA3
0.00%
0.10%
0.20%
0.30%
0.40%
0.50%
0 2 4 6 8 10 12 14 16
Len
gth
Ch
an
ge (
%)
Elapsed Time (Days)
Control (0BA1) 30BA1 30BA1-F
30BA1-G Innocuous Limit Deleterious Limit
BA1
56
Figure 3-5. ASTM C1567 length change of mortars containing 20% pozzolan (ground glass or class F fly ash), and 30% aggregate replacement by MSWI BA2.
Figure 3-6. ASTM C1567 length change of mortars containing 20% pozzolan (ground glass or class F fly ash), and 30% aggregate replacement by MSWI BA3.
0.00%
0.10%
0.20%
0.30%
0.40%
0.50%
0 2 4 6 8 10 12 14 16
Len
gth
Ch
an
ge (
%)
Elapsed Time (Days)
Control (0BA2) 30BA2 30BA2-F
30BA2-G Innocuous Limit Deleterious Limit
BA2
0.00%
0.10%
0.20%
0.30%
0.40%
0.50%
0 2 4 6 8 10 12 14 16
Len
gth
Ch
an
ge (
%)
Elapsed Time (Days)
Control (0BA3) 30BA3 30BA3-F
30BA3-G Innocuous Limit Deleterious Limit
BA3
57
CHAPTER 4 CONCLUSIONS
Summary of Research
In this thesis, two studies were conducted on bottom ash, a residual byproduct
created from the incineration of municipal solid waste. Both studies aimed to address
matters associated with the beneficial reuse of bottom ash as a secondary construction
material in the US. In the first study, a risk assessment of heavy metals was performed
using laboratory batch leaching tests, with a focus on recycling bottom ash as a road
base aggregate. In the second study, the expansive reactivity of bottom ash used was
investigated to characterize the durability of ash a replacement to natural aggregates
typically used in concrete. Both studies produced findings that could aid in the
development of bottom ash recycling programs in the US.
Major Findings and Observations
The following conclusions were made concerning the risk assessment of MSWI
bottom ash as a prospective road base material:
1. Six inorganic contaminants (As, Ba, Cr, Cu, Pb, and Sb) were detected in bottom ash at total concentrations higher than residential soil benchmarks in the state of Florida.
2. Four inorganic contaminants (Al, As, Pb, and Sb) were detected in the leachates of bottom ash at concentrations higher than or equal to risk-based drinking water benchmarks in the U.S.
3. The relative health risks associated with exposure to bottom ash COPC (direct and leaching) were reduced when the material was blended with a virgin or recycled aggregate source.
4. The leaching of antimony from bottom ash was reduced when recycled concrete was
used as a blended aggregate. The reduction in antimony leaching did not follow a typical solubility-controlled leaching behavior displayed by oxyanions in a high pH environment, suggesting that other mechanisms (e.g. sorption, complexation) associated with the recycled concrete contributed to the observed decline in antimony leaching.
58
The following conclusions were made concerning the reactivity of bottom ash as
a prospective coarse aggregate replacement in concrete:
1. The alkali-silica reaction was the dominant expansive reaction in ash-amended mortars. The large quantity of amorphous silica present in bottom ash was reactive during the accelerated mortar bar test, resulting in deleterious effects and volumetric expansion in specimens containing replacements higher than 15%.
2. Aluminum particles in bottom ash were reactive in an alkaline environment, and resulted in minor cracking and spalling of ash-amended mortar specimens, however, expansive reaction products/gels were not observed.
3. The replacement of ordinary portland cement with supplementary cementitious materials (coal fly ash and ground glass powder) greatly reduced the observed expansion in the bottom ash-amended mortar specimens.
Recommendations for Future Work
Based on this research, the following recommendations are suggested
concerning the use of MSWI bottom ash as a construction material:
1. The environmental mobility of COPC (particularly in groundwater) should be measured in pilot-scale in which bottom ash is utilized as a blended or exclusive road base aggregate.
2. The leaching of COPC should continue to be investigated through batch or pilot scale testing in road base products containing a combination of bottom ash and natural/recycled aggregates.
3. Additional batch leaching tests should be performed to observe the effect of recycled concrete on the leaching mechanisms of antimony.
4. The alkali-aggregate reactivity of bottom ash should be further investigated using
long-term test methods which evaluate actual concrete specimens cast with bottom ash as a coarse aggregate component.
5. The feasibility of increased ferrous and non-ferrous metal recovery from bottom ash
should be considered due to the benefits that could be gained in terms of increased material durability and reduction in leachability of certain elements identified as leaching COPC (e.g. aluminum, lead).
59
APPENDIX A CHAPTER 2 SUPPLEMENTARY MATERIALS
Figure A-1. ASTM C136 particle size distribution of weathered MSWI bottom ashes
used for EPA Method 1312/1316 batch leaching tests and EPA Method 3015A total metals analysis.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.01 0.1 1 10 100
Pe
rce
nt M
ass P
assin
g
Nominal Sieve Opening (mm)
MSWI BA1
MSWI BA2
60
Eluent pH
0 2 4 6 8 10 12 14
Le
ach
ed
Co
nce
ntr
atio
n (
mg/L
)
0.001
0.01
0.1
1
10
100
US EPA Primary Drinking Water Standard
Method Detection Limit
MSWI BA1
MSWI BA2
Pb
Figure A-2. EPA LEAF Method 1313 lead leaching as a function of eluent pH performed on fresh MSWI bottom ashes.
61
Eluent pH
0 2 4 6 8 10 12 14
Le
ach
ed
Co
nce
ntr
atio
n (
mg/L
)
0.001
0.01
0.1
1
Method Detection Limit
US EPA Primary Drinking Water Standard
MSWI BA 1
MSWI BA 2
Sb
Figure A-3. EPA LEAF Method 1313 antimony leaching as a function of eluent pH performed on fresh MSWI bottom ashes
62
Figure A-4. EPA LEAF Method 1316 antimony leaching as a function of liquid-to-solid ratio performed on weathered MSWI bottom ashes
LS Ratio (L/kg-dry)
0 2 4 6 8 10 12
Le
ached
Con
cen
tration
(m
g/L
)
0.001
0.01
0.1
Method Detection Limit
US EPA Primary Drinking Water Standard
MSWI BA1
MSWI BA2
Sb
63
APPENDIX B CHAPTER 3 SUPPLEMENTARY MATERIALS
Table B-1. Aggregate properties of coarse fraction of MSWI bottom ash (3.5mm-19mm)
used as aggregate replacements in accelerated mortar bar tests (ASTM C1260 and ASTM C1567).
MSWI BA1 MSWI BA2 MSWI BA3
Bulk SG (oven dry) 2.22 2.05 2.05
Bulk SG (saturated surface dry) 2.32 2.25 2.24
Apparent SG 2.49 2.56 2.54
Water Absorption 8.6% 9.7% 9.3%
64
Table B-2. Individual length change measurements of ash-amended mortar bar specimens used in ASTM C1260 (portland cement only).
Mortar Mix Date Expansion
(%) Expansion
(%) Expansion
(%) Expansion
(%)
Average Expansion
(%)
Control Specimen 1 Specimen 2 Specimen 3 Specimen 4
Demold/Water Bath 8-Nov-16 -- -- -- -- --
NaOH Day 1 9-Nov-16 -- -- -- -- --
Day 2 11-Nov-16 -0.0101 -0.0080 -0.0150 -0.0111 -0.0111
Day 6 15-Nov-16 0.0041 0.0050 -0.0020 0.0010 0.0020
Day 10 19-Nov-16 0.0051 0.0090 -0.0270 0.0484 0.0089
Day 14 23-Nov-16 0.0122 0.0151 0.0090 0.0091 0.0113
15 BA1
Demold – Water Bath 8-Nov-16 -- -- -- -- --
NaOH Day 1 9-Nov-16 -- -- -- -- --
Day 2 11-Nov-16 -0.0061 -0.0051 0.0111 -- 0.0000
Day 6 15-Nov-16 0.0203 0.0192 0.0332 -- 0.0242
Day 10 19-Nov-16 0.0813 0.0628 0.0653 -- 0.0698
Day 14 23-Nov-16 0.1555 0.1539 0.2021 -- 0.1705
15 BA2
Demold – Water Bath 8-Nov-16 -- -- -- -- --
NaOH Day 1 9-Nov-16 -- -- -- -- --
Day 2 11-Nov-16 -0.0020 0.0050 0.0040 0.0030 0.0025
Day 6 15-Nov-16 0.0121 0.0252 0.1348 0.0151 0.0468
Day 10 19-Nov-16 0.0556 0.2969 -- 0.2231 0.0932
Day 14 23-Nov-16 0.1344 0.1510 -- 0.1171 0.1006
15 BA3
Demold – Water Bath 8-Nov-16 -- -- -- -- --
NaOH Day 1 9-Nov-16 -- -- -- -- --
Day 2 11-Nov-16 0.0040 0.0051 0.0020 0.0010 0.0030
Day 6 15-Nov-16 0.0091 0.0081 0.0041 0.0111 0.0081
Day 10 19-Nov-16 0.0121 0.0670 0.0862 0.0755 0.0602
Day 14 23-Nov-16 0.0889 0.0792 0.0608 0.0785 0.0768
30 BA1
Demold – Water Bath 8-Nov-16 -- -- -- -- --
NaOH Day 1 9-Nov-16 -- -- -- -- --
Day 2 11-Nov-16 -0.0020 0.0081 0.0142 0.0010 0.0053
Day 6 15-Nov-16 0.0467 0.0333 0.0417 0.1606 0.0706
Day 10 19-Nov-16 0.1707 0.1546 0.2500 -- 0.1918
Day 14 23-Nov-16 0.3130 0.2748 0.3710 -- 0.3196
30 BA2
Demold – Water Bath 8-Nov-16 -- -- -- -- --
NaOH Day 1 9-Nov-16 -- -- -- -- --
Day 2 11-Nov-16 0.0060 0.0060 0.0010 0.0050 0.0045
Day 6 15-Nov-16 0.0603 0.0869 0.0559 0.0687 0.0679
Day 10 19-Nov-16 0.1648 0.0410 0.2774 0.2222 0.1763
Day 14 23-Nov-16 0.2854 0.3578 0.2814 0.3100 0.3087
30 BA3
Demold – Water Bath 8-Nov-16 -- -- -- -- --
NaOH Day 1 9-Nov-16 -- -- -- -- --
Day 2 11-Nov-16 0.0000 0.0000 0.0030 0.0020 0.0013
Day 6 15-Nov-16 0.0231 0.0243 0.0263 0.0173 0.0228
Day 10 19-Nov-16 0.1469 0.1449 0.2331 0.2182 0.1858
Day 14 23-Nov-16 0.2798 0.2604 0.2574 0.2101 0.2519
50 BA1
Demold – Water Bath 8-Nov-16 -- -- -- -- --
NaOH Day 1 9-Nov-16 -- -- -- -- --
Day 2 11-Nov-16 0.0151 0.0427 0.0121 0.0041 0.0185
Day 6 15-Nov-16 0.1199 0.1504 0.1112 0.1388 0.1301
Day 10 19-Nov-16 0.2851 0.3190 0.2759 0.3141 0.2986
Day 14 23-Nov-16 0.3919 0.4298 0.3921 0.4256 0.4099
50 BA2
Demold – Water Bath 8-Nov-16 -- -- -- -- --
NaOH Day 1 9-Nov-16 -- -- -- -- --
Day 2 11-Nov-16 0.0160 0.0111 0.0091 0.0183 0.0136
Day 6 15-Nov-16 0.2075 0.2101 0.1848 0.1778 0.1950
Day 10 19-Nov-16 0.1804 0.3317 0.3209 0.2946 0.2819
Day 14 23-Nov-16 0.5082 0.4945 0.4580 0.4338 0.4736
50 BA3
Demold – Water Bath 8-Nov-16 -- -- -- -- --
NaOH Day 1 9-Nov-16 -- -- -- -- --
Day 2 11-Nov-16 0.0010 0.0121 -0.0130 0.0000 0.0000
Day 6 15-Nov-16 0.0836 0.1121 0.0773 0.1600 0.1083
Day 10 19-Nov-16 0.3181 0.2878 0.1556 0.3697 0.2828
Day 14 23-Nov-16 0.3589 0.4201 0.3885 0.4335 0.4002
65
Table B-3. Individual length change measurements of ash-amended mortar bar specimens used in ASTM C1567 (pozzolans included as portland cement replacement).
Mortar Mix Date Expansion
(%) Expansion
(%) Expansion
(%) Expansion
(%)
Average Expansion
(%)
Control Specimen 1 Specimen 2 Specimen 3 Specimen 4
Demold/Water Bath 8-Nov-16 -- -- -- -- --
NaOH Day 1 9-Nov-16 -- -- -- -- --
Day 2 11-Nov-16 -0.0101 -0.0080 -0.0150 -0.0111 -0.0111
Day 6 15-Nov-16 0.0041 0.0050 -0.0020 0.0010 0.0020
Day 10 19-Nov-16 0.0051 0.0090 -0.0270 0.0484 0.0089
Day 14 23-Nov-16 0.0122 0.0151 0.0090 0.0091 0.0113
30BA1 – 20F
Demold/Water Bath 18-Jan-17 -- -- -- -- --
NaOH Day 1 19-Jan-17 -- -- -- -- --
Day 2 21-Jan-17 0.0171 0.0111 0.0172 0.0201 0.0164
Day 7 26-Jan-17 0.0161 0.0111 0.0192 0.0221 0.0171
Day 10 29-Jan-17 0.0181 0.0131 0.0192 0.0201 0.0176
Day 14 2-Feb-17 0.0272 0.0131 0.0202 0.0241 0.0212
30BA1 – 20G
Demold – Water Bath 18-Jan-17 -- -- -- -- --
NaOH Day 1 19-Jan-17 -- -- -- -- --
Day 2 21-Jan-17 0.0110 0.0140 0.0091 0.0101 0.0110
Day 7 26-Jan-17 0.0170 0.0220 0.0201 0.0212 0.0201
Day 10 29-Jan-17 0.0190 0.0230 0.0342 0.0192 0.0239
Day 14 2-Feb-17 0.0251 0.0260 0.0483 0.0242 0.0309
30BA2 – 20F
Demold – Water Bath 18-Jan-17 -- -- -- -- --
NaOH Day 1 19-Jan-17 -- -- -- -- --
Day 2 21-Jan-17 0.0191 0.0101 0.0162 0.0122 0.0144
Day 7 26-Jan-17 0.0242 0.0161 0.0345 0.0172 0.0230
Day 10 29-Jan-17 0.0221 0.0141 0.0345 0.0162 0.0217
Day 14 2-Feb-17 0.0372 0.0272 0.0456 0.0426 0.0382
30BA2 – 20G
Demold – Water Bath 18-Jan-17 -- -- -- -- --
NaOH Day 1 19-Jan-17 -- -- -- -- --
Day 2 21-Jan-17 0.0091 0.0050 0.0091 0.0080 0.0078
Day 7 26-Jan-17 0.0152 0.0131 0.0193 0.0161 0.0159
Day 10 29-Jan-17 0.0142 0.0121 0.0152 0.0101 0.0129
Day 14 2-Feb-17 0.0243 0.0202 0.0253 0.0211 0.0227
30BA3 -20F
Demold – Water Bath 18-Jan-17 -- -- -- -- --
NaOH Day 1 19-Jan-17 -- -- -- -- --
Day 2 21-Jan-17 0.0232 0.0211 0.0223 0.0231 0.0224
Day 7 26-Jan-17 0.0242 0.0271 0.0304 0.0292 0.0277
Day 10 29-Jan-17 0.0303 0.0291 0.0406 0.0332 0.0333
Day 14 2-Feb-17 0.0343 0.0381 0.0527 0.0372 0.0406
30BA3 – 20G
Demold – Water Bath 18-Jan-17 -- -- -- -- --
NaOH Day 1 19-Jan-17 -- -- -- -- --
Day 2 21-Jan-17 0.0223 0.0272 0.0194 0.0201 0.0222
Day 7 26-Jan-17 0.0243 0.0282 0.0234 0.0211 0.0243
Day 10 29-Jan-17 0.0304 0.0352 0.2987 0.0241 0.0299
Day 14 2-Feb-17 0.0334 0.0362 0.0296 0.0281 0.0318
66
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BIOGRAPHICAL SKETCH
Matthew L. Schafer was born in 1992 to Joseph and Donna Schafer in Utica, NY,
a small town in the northern portion of the state. At the age of five, Matthew and his
family relocated to Ocala, Florida, where he spent the remainder of his childhood
adolescence. Matthew was the youngest of three siblings, with a brother Joe and a
sister Amanda whom he shares close relationships with. Upon graduating from Forest
High School, Matthew enrolled at the University of Florida in the fall of 2011.
In December of 2015, Matthew received a Bachelor of Science degree in
Environmental Engineering Sciences, graduating Cum Laude. He immediately began
graduate school at the University of Florida in January 2016 under the advising of Dr.
Timothy Townsend, with a research focus on the sustainable management of solid
waste materials. During his tenure as a graduate student, Matthew conducted several
studies related to the beneficial reuse of incineration residues in the state of Florida, and
published two journal articles. In May 2017, Matthew completed his research thesis and
was awarded a Master of Engineering degree in Environmental Engineering. Upon the
completion of his graduate education, Matthew intends to begin his career in the private
consulting industry with HDR Engineering, Inc. in the south Florida area.
In his leisure time, Matthew enjoys recreational fishing and diving along the
Florida coastline and offshore waters, as well as spending time with his family and
friends.