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

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