Chemical Characterization of Leachate Produced from RCA

The proposed NPDES regulations in the State of Washington, requiring a pH below 8.5 at the point of discharge from recycled concrete aggregate (RCA), may have the unintended consequence of prohibiting the use of recycled concrete materials in commonly accepted concrete recycling applications; e.g., as unbound base course or fill material or aggregate in ready-mix concrete. A more appropriate method to determine compliance with pH regulations would be to determine a “point of compliance” and enforce pH regulations at that point. However, selection of an appropriate point of compliance is hindered by disagreement in previous studies on the pH of leachate as well as its acid neutralizing capacity (alkalinity). Most laboratory studies and many field studies suggest that the leachate pH should be very high (e.g., >9) for extended periods of time; however, the NAICS data presented in Figure 1 and results of our own field studies (Chen et al., 2012; Chen et al., 2013) suggest that leachate pH values above 8.5 are actually infrequent.   Here we propose to couple laboratory leaching studies, utilizing representative saturation and geochemical conditions, with results from a forensic examination of an RCA base course located at the MnROAD test facility to determine mechanisms that may limit the production of high pH of leachate.

For more information:

RMRC Proposal – RCA Leachate pH

US Hwy 12/18/151 at Verona Road-Beltline: Recycled Materials Case Study

The eastbound Beltline Highway (US 12/18) from Whitney Way to Seminole Highway, a 1.5 mile stretch, is undergoing a reconstruction and expansion three lanes from fall 2014 to spring 2016. The RMRC research team proposes to use this project to better determine a methodology for gathering the data needed for the inputs of the life cycle assessment (LCA) and life cycle cost analysis (LCCA) tool, PaLATE, as well as assess the benefits of using recycled materials in the project. The project will be used in preparation for more analyses of member-state roads. Examples of user inputs include material volumes, road dimensions, equipment used, etc. During past research, the research team has been unable to utilize LCA and LCCA technology without making significant assumptions for the inputs. The Beltline project offers an opportunity to develop a method for data collection that could eliminate assumptions from the analyses.

For more information:

RMRC SOW – Beltline

SCMT4 Beltline Conference Paper

I-94 Recycled Materials Case Study

The Recycled Materials Resource Center (RMRC) analyzed the environmental benefits of incorporating recycled material in the reconstruction of Interstate 94 (I-94) in Kenosha County, WI, using BE2ST-in-Highways. BE2ST-in-Highways integrates various supporting databases and uses life cycle assessment (LCA) and life cycle cost analysis (LCCA) techniques to evaluate the overall impact of highway construction projects. An alternative construction project that contains recycled materials is typically analyzed in comparison to a reference project that contains virgin materials. With the goal of quantitatively determining the environmental benefits of using recycled materials, the RMRC targeted a one-mile stretch of the Kenosha County portion of the I-94 North-South Freeway Project because it incorporates recycled materials in its reconstruction. Recycled materials used in the project include fly ash, bottom ash, foundry sand, recycled concrete aggregate (RCA), and recycled asphalt pavement (RAP). Preliminary results of the BE2ST-in-Highways analysis of the I-94 mainline reconstruction show that the use of recycled materials reduces the environmental impact of the highway construction in all criteria over its lifetime. 

For more information:

I-94 SOW

GeoChicago Conference Paper – I-94 and Beltline LCA

Recycled Materials Network: Connecting Producers to Consumers Website

Over half a billion tons of recyclable material such as foundry sand, coal combustion products and construction and demolition debris, are produced each year in the United States. Many of these materials have beneficial use in transportation construction projects. Unfortunately, the widespread use of these materials is hindered by a lack of information; either an understanding of the beneficial use of the recycled material or simply finding an adequate source of the recycled material.

Providing potential consumers of recycled materials an on-line location-based information Network that includes recycled material sources, past projects that used recycled material, and regulations pertaining to the use of recycled material in construction projects is needed. Information about recycled material including: type(s) of material, availability, producer throughput, cost, and material characteristics should be included in the site. In addition to the map of recycled material sources, two additional map layers: case studies and regulations, need to be available on the site. The case study layer will focus on past projects that employed recycled material in the design and construction. The regulations layer will display state regulations pertaining to the beneficial use of recycled material. By providing locations and quantities of available recycled materials, examples of past case studies, and regulations governing recycled material, a single Recycled Materials Network to promote the use of recycled material will be created.

To access the Network, please visit:

Use of Recycled Materials Behind MSE Walls

To ensure long-term integrity of MSE walls, reinforced backfills consisting predominantly of coarse-grained materials have been recommended and used. This limitation on material type can significantly increase the cost of construction on some projects because of the cost of transporting select material to the construction site when local select fill is not available. At the same time, industrial operations and construction activities create coarse-grained materials that must be disposed. Again, producers of such materials must pay transportation costs, as well as disposal fees, to discard these materials. One solution is to recycle these materials and use them as alternative reinforced backfill.

Throughout the U.S., substantial amounts of recycled asphalt pavement (RAP) and recycled concrete aggregate (RCA) are being produced through reconstruction activities as well as granular industrial byproducts such as foundry sand/slag, bottom ash, and iron/steel slag. If these materials were used as reinforced backfill for MSE walls, transportation and disposal costs for these materials could be greatly reduced, translating into significant savings for state departments of transportation. Furthermore, such activities would promote sustainable construction, preserve natural resources, and reduce carbon footprint and landfill disposal in highway construction. There are reports of the use of these materials as reinforced backfill as well as research on their properties relevant to reinforced backfill requirements. Further focused research of recycled materials needs to be done to determine if their use as MSE wall reinforced backfill is considered suitable for a more sustainable and potentially economical design and develop design and construction recommendations.

For more information:

RMRC RFP3 – Recycled Matls as MSE Wall Fill

Statewide Materials Use Study

RMRC and various governmental agencies have developed fact sheets on various recycled materials and industrial byproducts for their use in highway construction applications. However, these fact sheets often lack direct information on sustainability assessment characteristics, i.e., greenhouse emissions, energy and water consumption and life cycle cost benefits. Although state transportation departments have been in the forefront of introducing recycled materials, they have not been able to clearly convey the benefits in a quantitative and transparent manner using easily understood metrics.

The first objective of this study is to develop/update factsheets on various recycled materials and industrial byproducts that are being used in highway construction. New information generated in recent years relative to their engineering properties and environmental impact questions will be added as well as relevant life cycle assessment data. The second objective of this study is to develop a tool by which the state system-wide material use quantities can be used to calculate the life cycle benefits associated with the incorporation of recycled materials and industrial byproducts to highway pavement construction.

For more information:

RMRC SOW – Systemwide Life Cycle Benefits of Recycled Materials

Preliminary report for GeoChicago Conference: GeoChi Statewide


Project 68

Specifications and Recommendations for Recycled Materials Used as Unbound Base Course

Project 68 provides recommendations and specifications for recycled asphalt pavement and recycled concrete aggregate that can be used as unbound base course.

Project 67

Update of WiscLEACH Roadway Environmental Assessment Software

This project, in partnership with Jackson State University, updates on the development of a software program.  WiscLEACH, a web-based computing tool, is used to evaluate groundwater impacts from beneficial use of industrial byproducts in roadway stabilization and embankment.structural fill applications.

Project 66

Design System for HMA Containing a High Percentage of RAS Material

The primary objective of this research is to develop and validate a simple design system for hot mix asphalt (HMA) containing a high percentage of reclaimed asphalt shingles (RAS).

Project 61

Large Scale Model Experiments of Recycled Base Course Materials Stabilized with Cement and Cement Kiln Dust

The objectives of this study was to determine the resilient modulus of two recycled roadway materials: recycled pavement material and road surface gravel with and without cement and cement kiln dust stabilization. In order to replicate field conditions,  Large Scale Model Experiments were conducted.

Project 55

Evaluation of Recycled Asphalt Shingles as Structural Fill

In this research, possible reuse of discarded asphalt shingles as structural fill was investigated. The engineering properties that were evaluated include: compaction characteristics, hydraulic conductivity, compressability shear strength, and coefficient of lateral earth pressure at rest.

Project 54

Synthesis of Use of Crumb Rubber in Hot Mix Asphalt

Ground tire rubber (GTR) is a unique recycled material and it is not clear what the optimum method for incorporating GTR in the asphalt is. This project focused on developing optimum methods of processing and blending GTR, reacting time between GTR and asphalt binders while blending, and the designing of GTR modified binders to yield superior performance.

Project 53

Reconstruction of Railroads and Highways with in-situ Reclamation Materials

This project focuses on sustainable construction of highways and railways for increasing freight capacity of the transportation systems in the US.


Project 52

Evaluation of the Environmental Performance of CCPs in Roadway Applications

This project focuses on two theses:

1. The Leaching of Trace Elements from Roadway Materials Stabilized with Fly Ash

2. Leaching from Soil Stabilized with Fly Ash: Behavior and Mechanisms

Project 50

Evaluation of Testing Protocols for the Environmental Assessment of Fly Ash Stabilized Soils

This project is in partnership with the University of Maryland, was a comprehensive laboratory study to evaluate the trace metal leaching from fly ash stabilized soils.

Project 48

Utilize Cementitious High Carbon Fly Ash (CHCFA) to Stabilize Cold In-Place Recycled (CIR) Asphalt Pavement as Base Course

This project evaluate the performance of cementitous high carbon fly ash stabilized recycled asphalt pavement as a base course material in a real world setting. Three test road cells were built in partnership with MnROAD in Minnesota.

Project 47

Stabilization of Reclaimed Pavement Material and Road Surface Gravel with Coal Combustion Project

Conducted by UW, this project is sponsored by the Minnesota Local Roads Research Board (LRRB), with support from the RMRC. This project is evaluating the stabilization of reclaimed pavement material (RPM) and RAP with CCPs.

Project 45

Modulus and CBR Values for Construction and Demolition Debris (UNH)

This project will be conducted by UNH with a budget of $77,203 to be funded by the RMRC Pooled Fund. Additional funds $42,820 were provided in the form of a tuition and a stipend. This project addresses the need for additional information on coarse and fine aggregate obtained from C&D debris.

Project 44

Assessment of leaching in Embankments constructed with Coal Fly Ash (Colebrook, NH) and C&D Debris (Epping, NH)


This project will be conducted by UNH with a budget of $22,000 funded by US EPA IAG. Monitoring of leachate from a full-scale coal fly ash embankment in Colebrook, NH will continue until the ground freezes in the winter, and will resume in the spring. Additional leaching and hydrogen sulfide monitoring will be conducted at a full-scale embankment constructed of construction and demolition debris fines.