Chemistry of RCA Leachate in Base Course Applications

Uncertainty regarding the high pH, high alkalinity leachate from recycled concrete aggregate (RCA) leachate limits the use of RCA as a substitute for virgin aggregate in pavement base course. The purpose of this work is to understand the time-dependent behavior of leachate chemistry from RCA in pavement base course applications and the persistence of high pH leachate in the environment. A state-of-the-art review of the existing laboratory and field investigations of RCA leachate chemistry identifies discrepancies in field and laboratory measurements of RCA leachate pH. Critical evaluation of the existing investigations indicates that conventional laboratory methodology, which employs abrasive, closed system batch reactors, is not representative of field conditions. In order to understand the physicochemical factors that control RCA leachate pH and alkalinity the physical properties, solid phase chemistry, and time-dependent leachate chemistry were integrated into a geochemical model. The model illustrates that RCA leachate chemistry can be described by two parameters: portlandite content of RCA available for dissolution, and the availability of carbon dioxide. The fundamental understanding of time-dependent behavior of RCA leachate chemistry was extended to applications in pavement base course using RCA-leachate contact times according to AASHTO base course drainage quality standards. Contact time experiments indicate that longer contact times do not increase peak pH associated with RCA leachate pH, such that using RCA in base course applications poses no additional concern regarding drainage quality, and that RCA leachate pH will equilibrate to a near-neutral value, pH 7.7 and pH 8.5 given sufficient exposure to atmospheric carbon dioxide or soil acidity.  The findings of this study can be used to provide guidelines for practice to ensure safe and wise use of RCA base course.


The full thesis may be found in the following file:

Sanger_M.S. Thesis

Suitability Of Cement Kiln Dust For Reconstruction Of Bituminous Roads

Most of the highways in the United States were built in 1950s and 1960s and have deteriorated significantly to date. More than 96% of the current highways and most surface streets are paved with asphalt. Asphaltic pavement that is removed during road reconstruction or rehabilitation is often landfilled with significant costs and environmental issues. Quarrying virgin aggregate for road reconstruction also results in environmental problems and energy consumption. There is an increased trend to recycle existing asphalt pavement in situ as base course for the new pavement surface. However, the load carrying capacity of such a base course is of concern due to the inclusion of asphalt and possibly fine-grained materials. Reuse of existing material in place would reduce material, transportation, and disposal costs and save energy. Much CKD is reintroduced to the Portland cement manufacturing process as kiln feed, but amounts are limited by alkalinity requirements for Portland cement and kiln operation issues. Too much CKD can clog parts of the system. Other options for reuse include soil stabilization, soil amendment for agriculture, and wastewater treatment. Cement kiln dust stabilization for rehabilitation of roads would provide another option to DOTs and municipalities depending on location and availability of suitable material.

The full thesis may be found in the following file:

Jeremy Baugh Master Thesis 2007

Leaching from Roadways Stabilized with Additive Coal Combustion Products (CCPs): Data Assessment and Synthesis

Approximately 37% of the electrical power used in the United States is generated by coal-fired power plants. Air pollution control systems installed on coal-fired power plants collect solid byproducts of coal combustion, which are commonly referred to as coal combustion products (CCPs). Common CCPs include fly ash, bottom ash, boiler slag, and flue gas desulfurization (FGD) residuals. Disposing CCPs in landfills or similar waste containment facilities is costly and land intensive, and many CCPs have useful engineering properties. Consequently, CCPs are often used beneficially in other products or applications, most notably as construction materials. Beneficial use of CCPs has many positive benefits in the context of sustainability including an annual reduction in greenhouse gas emissions by 11 million tons, fossil fuel consumption by 17 TJ, and water consumption by 121 GL, amounting to more than $11 billion (US) in total economic benefits.
Field water quality data collected from roadways where fly ash or bottom ash was used as embankment fill or as a stabilizing agent in the base or subgrade was assessed for any potential risk of ground water and surface water trace element contamination. Trace element concentrations (e.g. As, Cd, etc.) were obtained for seven roadways in Minnesota, Wisconsin, Indiana, and Georgia, spanning the applications of fly ash base and subgrade stabilization, fly ash fill, and bottom ash fill.

The full thesis may be found in the following file:

Brigitte Brown Master Thesis 2015

Life Cycle Benefits of Recycled Materials in Highway Construction

The use of recycled materials in highway construction has the potential to achieve significant benefits affecting the triple-bottom line (environment, prosperity, and society). Although state departments of transportation (DOTs) have been in the forefront of introducing recycled materials infrastructure projects, it has been challenging to clearly convey the benefits in a quantitative and transparent manner using easily understood metrics. What is lacking is direct information on sustainability assessment characteristics, i.e. greenhouse gas emissions, energy, water consumption, and waste generation.
To determine the benefits of using recycled materials for DOTs, the Recycled Materials Resource Center (RMRC) conducted life cycle assessments (LCA) and cost analyses using recycled material quantities provided by six-member state DOTs; Georgia (GDOT), Illinois(IDOT), Minnesota (MnDOT), Pennsylvania (PennDOT), Virginia (VDOT) and Wisconsin(WisDOT). PaLATE was used as the LCA analysis tool, after researching other publicly available tools to find an optimal analysis. Four environmental parameters (energy use, water consumption, carbon dioxide emissions, and hazardous waste generation) showed significant reductions when states used recycled industrial byproducts such as fly ash, and recycled roadway materials such as recycled concrete aggregate (RCA) and recycled asphalt pavement (RAP). The cost analysis indicated potential savings of up to 60 million dollars.

Life Cycle Benefits of Recycled Materials in Highway Construction TRB



Beneficial Reuse Of Foundry Sands In Controlled Low Strength Material

The objective of this study was to characterize how properties of foundry sands affect the characteristics of flowable fill.  To meet this objective, tests were performed to evaluate flow, setting time, strength, and environmental degradation of flowable fills containing various foundry sands.  The results were used to develop general guidelines for successfully incorporating foundry sands into flowable fill.

The full thesis may be found in the following files:

Jefferey Dingrando Master Thesis 1999

Assessing the Life Cycle Benefits of Recycled Material In Road Construction

There is interest in determining and validating the environmental and economic benefits of incorporating recycled materials into road construction using life cycle assessments (LCA) and life cycle cost analysis (LCCA) tools. However, the process of collecting the necessary data for LCAs and LCCAs from departments of transportations (DOTs) and road construction contractors is not well defined. This thesis provides a study of real-time data collection to compare with the results of pre-construction estimated LCA data. The goal of this comparison is to determine a data collection precedent for environmental analyses of future transportation projects. Additionally, two prominent LCA tools were used in conducting the assessment and the results were compared to validate the predicted impacts

The full thesis may be found in the following file:

Eleanor Bloom Master Thesis 2016

Strength And Stiffness Of Recycled Base Materials Blended With Fly Ash

The objectives of this study were to assess the engineering properties of two recycled materials. Laboratory experiments were conducted in which a recycled pavement material (RPM) and a road surface gravel (RSG) were tested to determine the California bearing ratio (CBR), resilient modulus (Mr), and unconfined compressive strength (UCS). Results of these tests were compared to the properties of a conventional base material (Class 5 base). The recycled materials were blended with two fly ash contents (10 and 15%) and three curing times (7, 28, and 56 d). Resilient modulus and unconfined compression strength tests were also conducted after 5 cycles of freezing and thawing to asses the impact of freeze-thaw cycling.

The full thesis may be found in the following file:

Felipe Filizzola Camargo Master Thesis 2008


Beneficial Use of Dredged Materials in Great Lakes Commercial Ports for Transportation Projects

This project focuses on beneficial use of DM as an alternative material for earthwork construction applications in the transportation sector (e.g., embankments, pavement base, etc.). The long term objective of the effort is to contribute to sustainable construction by facilitating use of DM instead of natural mined materials. The immediate objective, as described here and summarized in Figure 1.1, is to produce a set of guidelines that explicitly links together: 1) applications for the use of DM as construction materials in transportation-related earthwork projects, 2) required geotechnical properties of materials for specific construction applications, 3) geotechnical laboratory and field test methods available to determine these properties, 4) specifications (values) of these properties required for specific transportation-related projects, and 5) locations within the Great Lakes from which dredged materials having properties meeting these specifications may be sourced. The project is intended to build upon existing and more general frameworks for beneficial use of DM from the Great Lakes region (Great Lakes Commission, 2004) but within the specific context of using DM in the transportation construction sector. Emphasis is placed entirely on suitability in terms of physical characteristics. Suitability in terms of toxicity or environmental characteristics of the material is assumed.

The full thesis may be found in the following file:

Hua Yu Master Thesis 2014

Evaluating The Sustainability Of Construction With Recycled Materials

A lack of data on quantified benefits that can be achieved through the
application of sustainability strategies acts as a barrier to the promotion of sustainable
movement. For this reason, two frameworks were developed to provide a quantitative
methodology for evaluating the benefits of sustainable construction and to rate the
relative benefits of construction projects compared to projects using conventional
construction concepts: a pairing method of comparative environmental and economic
life-cycle analyses for assessing construction; a rating system, the Building
Environmentally and Economically Sustainable Transportation Infrastructure-
A pairing method was used to quantify the benefits of using recycled materials
in highway pavements by conducting life-cycle assessment and life-cycle cost analysis
on pavements consisting of conventional and recycled materials for a highway
construction project in Wisconsin. Results of the analysis indicate that using recycled
materials in the base and subbase layers of a pavement can result in reductions in
global warming potential, energy and water consumption, and hazardous waste
generation while also extending the service life of the pavement. In addition, using
recycled materials in the base and subbase layers can result in a life-cycle cost savings.

The full thesis may be found in the following file:

Jin Cheol Lee Dissertation 2010

The Beneficial Reuse Of Asphalt Shingles In Roadway Construction

Approximately 11 million tons of reclaimed asphalt shingles (RAS) are disposed in landfills every year. Research has demonstrated that these materials can be recycled into a variety of products. A widespread, large-scale recycling and reuse application would utilize an otherwise wasted resource while clearing landfill space and creating new business opportunities. One potential reuse application is the utilization of RAS in the aggregate base (AB) and subbase (ASB) layers of roadway pavements and as working platforms for pavement construction over soft subgrades, and as embankment fills. RAS has the potential to act as an additive or substitute for the earth materials typically utilized in these applications. Like any recycling activity, the proper regulatory and permitting requirements for the reuse of RAS must be addressed. The purpose of this study was to determine the technical specifications of RAS, the effect of fly ash stabilization on RAS strength, and the practicality of the widespread implementation of RAS in roadway applications. RAS, fly ash stabilized RAS (S-RAS), RAS-aggregate mixtures, and RAS silt mixtures were evaluated for particle size characteristics, compaction characteristics, California Bearing Ratio (CBR), unconfined compressive strength, and resilient modulus. In summary, RAS is a granular material with particle size characteristics similar to that of well-graded sand, however, with very different particle shape and strength. RAS stiffness, in general, increases with increasing dry unit weight, and RAS dry unit weight increases with decreasing maximum particle size and increasing fines percentage; although the nature of RAS particles also play a role. The localized penetrative resistance, or CBR, of RAS is small.

The full thesis may be found in the following file:

Justin Warner Master Thesis 2007

Leaching From Soil Stabilized With Fly Ash: Behavior And Mechanisms

In situ stabilizing soil with fly ash has become a practical and economical solution for construction on soft ground. However, leaching of trace elements from stabilized soil can be a concern. Understanding the pH-dependent leaching behavior and mechanisms controlling release of elements from soil-fly ash mixture is important for assessing the environmental impacts associated with using fly ash in soil stabilization. In this study, pH-dependent leaching tests were conducted to investigate the leaching behavior of soilfly ash mixtures used in roadway construction. The soils included organic clay, silt, clay, and sand. The fly ashes included Class C and off-specification high-carbon fly ashes. Four leaching patterns as a function of pH were observed: (i) leaching of Ca, Cd, Mg, and Sr follows a cationic pattern; (ii) leaching of Al, Fe, Cr, Cu, and Zn follows an amphoteric pattern; (iii) leaching of As and Se follows an oxyanionic pattern for some mixtures and anomalous leaching patterns for other mixtures; and (iv) leaching of Ba presents amphoteric-like pattern but less pH-dependent. Modeling results from MINTEQA2 indicated that release of the elements, except As and Se are solubility-controlled. For a given element, the solubility-controlling solids were found to be very consistent. Oxide and hydroxide minerals control leaching of Al, Fe, Cr, and Zn, whereas carbonate minerals control leaching of Mg and Cd. Leaching of Cu is controlled by oxide and/or carbonate minerals. Both carbonate and sulfate minerals are controlling solids for Ca, Ba, and Sr depending on pH of the leachate. The difference and inconsistency between the release behavior for As and Se and the other elements are probably due to different controlling mechanisms, such as sorption, or solid-solution formation.

The full thesis may be found in the following file:

Kanokwan Komonweeraket Dissertation 2010

Large Scale Model Experiments Of Recycled Base Course Materials Stabilized With Cement And Cement Kiln Dust

The objectives of this study were to determine the resilient modulus of two recycled roadway materials: recycled pavement material (RPM) and road surface gravel (RSG) with and without cement and cement kiln dust (CKD) stabilization. The resilient modulus was determined by conducting Large Scale Model Experiments (LSME) designed to replicate field conditions, and compared with the resilient modulus determined from the laboratory test method described by NCHRP 1-28A. Results of wet-dry and freeze-thaw durability tests were used to select a portland cement content of 4% by weight and a CKD content of 10% by weight to chemically stabilize RPM and RSG. The stiffness at curing times of 7 and 28 days was evaluated, and the summary resilient modulus (SMR) corresponding to a bulk stress of 208 kPa was used to calculate AASHTO base layer coefficients for use in pavement layer thickness design. A conventional base course material specified as a Class 5 material gradation employed in Minnesota, and similar to AASHTO grading C, was used as a reference material. This study has shown that the addition of cement or CKD can significantly improve the stiffness of RPM and RSG, having the potential to allow greater use of recycled roadway materials in the reconstruction of roads, minimizing construction costs and environmental impacts. However, the low durability of materials mixed with CKD should be investigated further, because the expansion may be damaging to pavement structures.

The full thesis may be found in the following file:

Brian Kootstra Master Thesis 2011


Effect of Freeze and Thaw Cycling on Soils Stabilized using Fly Ash

The objective of this research was to study how the resilient modulus and unconfined compressive strength of soils stabilized with fly ash change after freeze-thaw cycling.  To reach this objective, resilient modulus and unconfined compression tests were conducted on a range of fly ash stabilized materials after freeze-thaw cycling (0, 1, 3, 5, 10, and 12 cycles).  The stabilized materials tested included fine-grained soil, coarse-grained soil, and recycled pavement material.  Five different flyashes were used [Columbia and Riverside 7 (classified as Class C); Dewey, King and Riverside 8 (classified as off-specification)] at different percentages (10%, 12%,14% and 20%) and at three different water contents (7% wet of optimum, optimum,and at field water content).  Tests were also conducted on soil alone (0% fly ash)without freeze-thaw cycling to define the reference condition.

The full thesis may be found in the following files:

Maria Rosa Master Abstract 2007Maria Rosa Master Thesis 2007

Leaching Of Trace Elements From Roadway Materials Stabilized With Fly Ash

This study evaluated the leaching of trace elements from roadway materials physically stabilized with fly ash from coal combustion. Five field sites with stabilized materials and three sites with control materials used as base course or subgrade were constructed with pan lysimeters to collect leachate discharging from the bottom of the roadway layers. Pore volumes of flow from the layers was calculated from the volume of leachate collected, pH and Eh of the leachate was measured, and samples were collected for chemical analysis. Laboratory column leach tests (CLTs) and water leach tests (WLTs) were also conducted on specimens of some fly ash and base course/subgrade materials collected in the field. The type, concentration, and pattern of elemental leaching from field and laboratory specimens were determined, and concentrations were compared to those from control materials and relevant groundwater maximum contaminant levels (MCLs). The laboratory tests were compared for their utility in predicting field leaching behavior. The elements As, Cd, Cr, Mo, Ni, Pb, Se, and V exceeded MCLs and were elevated relative to control concentrations, with B, Mo, and V concentrations the most elevated from the controls, and exceeding the MCL for the longest time. Both CLTs and WLTs were similar in their utility for estimating peak field concentrations, especially when peak field concentrations were >500 μg/L.

The full thesis may be found in the following file:

Jonathan O’Donnell Master Thesis 2009

Evaluation of Recycled Materials as Backfill for Geosynthetically Reinforced Mechanically Stabilized Earth (MSE) Walls

Recycled asphalt pavement (RAP) also satisfies general criteria for use in MSE backfill applications (e.g., grain size distribution, shear strength), but displays significant potential for deviatoric creep and thermal sensitivity due to its asphalt content. These issues require more attention for use of RAP in long-term applications. Similarly, foundry sand/slag, bottom ash, andiron/steel slag have suitable frictional and drainage properties. All of these materials, when compacted, display adequate friction angle required for MSE reinforced backfill. However,secondary issues such as compatibility with geosynthetic reinforcement, drainage, creep potential,and interface frictional behavior require more consideration.
The overall goal of this research is to facilitate use of RAP and RCA in reinforced backfills for MSE retaining wall construction. This thesis consists of five Chapters. In Chapter 1, the engineering properties of different types of recycled materials for potential use as backfill material are summarized from the literature. The design procedures for MSE walls, selection of backfill and geosynthetics, and current specifications are also summarized in Chapter 1. Chapter 2 summarizes issues related to responses of different types of recycled materials, as well as failure modes of MSE walls. The materials selected to conduct this research (including different types of geosynthetics and RAP and RCA samples) and testing procedures are described in Chapter 3. The experimental testing program includes index property tests, interface direct shear tests, pull-out tests and triaxial compression tests. Chapter 4 describes the test results and interpretation of the results. Chapter 5 summarizes the conclusions and recommendations from this research

The full thesis may be found in the following file:

Paulo Florio Master Thesis 2016

The Effects Of Climatic Conditions And Brick Content On Recycled Asphalt Pavement And Recycled Concrete Aggregate As Unbound Road Base

This study evaluates the use of recycled concrete aggregate (RCA) and recycled asphalt pavement (RAP) as an unbound road base. This investigation looked at the climatic behavior (i.e., temperature effects, wet/dry cycling) of RAP and RCA and the effects of brick content on the resilient modulus and plastic strain (as an index) of RCA. The two chapters of this thesis individually discuss each one of these studies. The recycled materials used in this study came from a large geographical area covering eight U.S. states including California, Colorado, Michigan, Minnesota, New Jersey, Ohio, Texas and Wisconsin. Basalt and a quartz/granite/limestone blend meeting Minnesota Department of Transportation’s Class 5 gradation standard were used as control materials.

The full thesis may be found in the following file:

Ryan Shedivy Master Thesis 2012

Evaluation Of Metals Leaching From Gray Iron Foundry And Coal Combustion Byproducts

This report is summarizes the results of two separate studies on the leaching ofmetals from industrial byproducts.  The first section of the report describes acomparative study on the leaching of metals from field and laboratory tests on industrialbyproducts used as highway construction materials.  The second section describes astudy on the leaching of metals from high-carbon fly ashes used to stabilize organicsoils.

The full thesis may be found in the following file:

Jacob Sauer Master Thesis 2006

Geotechnical Evaluation of Recycled Asphalt Shingles as Structural Fill

To evaluate the effect of seasonal temperature on engineering properties of RAS mixtures, a thermo-mechanical system and the related testing procedures were developed. Systematic tests to evaluate engineering properties including hydraulic conductivity, one-dimensional compression, triaxial compression and deviatoric creep tests were conducted at constant and varying temperatures (between 5 oC and 35 oC). Results show that at room temperature, RAS mixtures are favorable lightweight materials with sufficient shear strength and drainage capacity for use in structural fills. Up to 50% RAS in granular materials and between 10 to 20% fly ash content in the stabilized RAS reduced the compressibility to meet the settlement criteria for roadway design. The secondary compression index increased as a power function with stress level. As the temperature increases the shear strength decreased due to reduction in viscosity of the asphalt binder in RAS particles. However the shear strength of the mixture with RAS content up to 50% remained higher than 30o . The hydraulic conductivity increased with ii increasing temperature due to reduction of viscosity of permeating water. The compressibility of the compacted RAS mixtures exponentially increased with temperature. Since the viscosity of RAS particles is reduced with temperature, if the embankment containing RAS mixture is constructed during warm season of the year the majority of the compression occurs during construction and the RAS embankment settlement during the rest of the year will be negligible. RAS mixtures were also susceptible to creep rupture under the applied deviatoric stress. When designing side slopes of the embankments containing RAS, the applied stress should be reduced to 80% of the maximum deviatoric stress to ensure no creep rupture will occur. Design graphs and analytical models were developed to predict shear strength and compressibility of RAS mixtures at constant and varying temperatures under the stress levels typical to highway embankments. The results of this research contribute to testing and design procedures associated with the use of recycled materials in geotechnical applications and help provide more sustainable roadway infrastructure.

The full thesis may be found in the following file:

Ali Soleimanbeigi Dissertation 2012

Stabilization Of Organic Soils Using Fly Ash

Chemical stabilization of soft soils involves blending a binder (e.g., cement, lime,or fly ash or combinations thereof) with the soil in sufficient quantities to increase thestrength and stiffness to acceptable levels.  Fly ash, a by product of coal combustionthat is produced in vast quantities, is a binder of significant interest because many flyashes are available at low cost.  Past research has shown that many fly ashes areeffective for stabilizing soft inorganic soils, but little is known about their effectivenessfor stabilizing soft organic soils.  The objectives of this study were (i) to determine iffly ashes can stabilize organic soils and, if so, (ii) to quantify the improvement in theunconfined compressive strength and resilient modulus of the organic soil asadmixed with fly ash and (iii) to investigate potentially important factors affecting thestabilization process such as fly ash and soil characteristics, fly ash percentage in themixture, and water content.

The full thesis may be found in the following file:

Erdem Onur Tastan Master Thesis 2005

Hydraulic Properties of Recycled Pavement Aggregates and Effect of Soil Suction on Resilient Modulus for Pavement Design

The successful incorporation of recycled aggregates in pavement design is important for achieving a higher level of sustainability in our transportation network. However, recycled aggregates are non-soil materials and have different unsaturated hydraulic and resilient modulus characteristics. This study investigated the unsaturated hydraulic properties and impact of soil suction on resilient modulus for compacted recycled aggregates used as unbound base course, including recycled asphalt pavement (RAP), recycled concrete aggregate (RCA), and recycled pavement material (RPM). Hydraulic properties and relationships including the soil-water characteristic curve (SWCC) and saturated and unsaturated hydraulic conductivity (Ks and K), were characterized using a hanging column test coupled with a large-scale testing cell. Regression of the hydraulic parameters from SWCC and K data for each type of recycled materials was completed. The effect of water repellency on hydraulic properties was evaluated. Development of testing equipment and procedures that incorporate the effect of soil suction during resilient modulus measurement is presented. A mathematical model to predict resilient modulus based on bulk stress, octahedrons shear stress, and soil suction is proposed. In addition, empirical relationships for predicting summary resilient modulus (SRM) via soil suction and SRM at optimum compaction for recycled aggregates are presented. Measured SRM and SWCCs for different types of recycled aggregate were used to evaluate flexible pavement performance according to the approach outlined in the Mechanistic-Empirical Pavement Design Guide (M-EPDG). The impact of environmental effects (including freeze-thaw cycles and changes in temperature) on the resilient modulus of recycled aggregates and subsequent pavement performance are evaluated and presented in this dissertation.

The full thesis may be found in the following file:

Kongrat Nokkaew Final Dissertation

Scaling and Equivalency of Bench-Scale Tests to Field Scale Conditions

The objectives of this study were to determine the resilient modulus for recycled materials using Large-Scale Model Experiments (LSME) to replicate field conditions.  Tests were conducted on two recycled materials; recycled asphaltpavement (RAP) and recycled concrete aggregate (RCA), as well as on one blended material consisting of 50% RCA and 50% conventional base material (Class 5).  The results of LSME testing were compared to the resilient modulus determined using laboratory methods in accordance with NCHRP 1-28a and field scale methods using falling weight deflectometer (FWD).  The scalability of the laboratory results to field conditions was addressed by adjusting the resilient modulus to reflect a comparable stress-state and strain level.  The plastic deformation of materials tested in theLSME was also assessed.  A conventional base course meeting the gradation standard of a Minnesota Department of Transportation Class 5 aggregate was used as a reference material in this study.

The full thesis may be found in the following file:

G. Scheartl Master Thesis 2010