Research Spotlight: Evaluation of Waste Concrete Road Materials for Use in Oyster Aquaculture

Dong Hee Kang, PhD, Lecturer, Civil Engineering, Morgan State University
Anastasia Chirnside, PhD, Assistant Professor, Entomology and Wildlife Ecology, University of Delaware
Mark Bundy, Assistant Research Professor, Patuxent Environmental and Aquatic Research Laboratory (PEARL), Morgan State University

State highway administrations have a problem. As they repair and rebuild transportation infrastructure and resurface roads and bridges, significant amounts of waste concrete road materials are generated. Often, this old concrete is simply discarded or it is crushed and milled into recycled concrete aggregate (RCA) that can be repurposed as base, sub-base, or fill material for embankments.

An additional use for RCA might be found within the oyster industry. Oyster shells have traditionally been used to condition the bottom of the Chesapeake Bay with a hard substrate, enabling baby oysters (spat-on-shell) to thrive and flourish. Yet oyster shells have become increasingly scarce. One way to use recycled materials in an environmentally responsible way could be to use RCA on the bottom of the Chesapeake Bay to support spat-on-shell aquaculture. For this to be an acceptable practice, it must be determined that RCA does not have any negative environmental impacts to the surrounding ecology. In addition, it must be compatible with traditional oyster harvesting and meet regulatory criteria.

In a 2013 Maryland State Highway Administration (SHA)-funded Phase 1 study, Dong Hee Kang, PhD, from Morgan State University, Mark Bundy, PhD, from the Patuxent Environmental and Aquatic Research Laboratory, and several other researchers conducted laboratory tests to determine the suitability of RCA from road projects as bottom conditioning material. The testing was designed to evaluate the impact on water chemistry from the introduction of RCA and evaluate the effect of RCA on the survivorship and growth of oyster spat. The results showed that, in the laboratory, oyster reefs made from RCA did not adversely affect oyster spat growth and survival, or the surrounding environment.

Phase 2 of the SHA study sought to implement the findings in test plots in the Chesapeake Bay to validate the laboratory test in situ. Completed in February 2015 by researchers at the Patuxent Environmental and Aquatic Research Laboratory, the study found that RCA was generally similar to natural oyster shell with regard to the ability of the oyster population to flourish.

The current MATS UTC-funded project is now tackling the issue, building upon the promising results of the two previous SHA-funded studies. Its goal is to evaluate the RCA for petroleum byproducts and to analyze the impact on water quality in the local marine ecosystem. Kang and Bundy have teamed up with Anastasia Chirnside, PhD, from the University of Delaware, an environmental engineer and a certified agronomist, to provide standardized specifications and guidelines for the safe use of recycled concrete for spat-on-shell aquaculture without detrimental environmental effects. They will also work with the Maryland Department of the Environment and nine related agencies (Department of Natural Resources, Department of the Environment, Department of Health, Board of Public Works, Department of Planning, State Highway Administration, Critical Area Commission, Aquaculture Review Board, Maryland Sport Fish Advisory Commission) to develop a mechanism for the acceptance of RCA for artificial reef construction.

Although the project just got underway this summer, multiple benefits to the natural environment and public interests are expected from this research. The team hopes to position RCA to support oyster aquaculture while addressing a waste and recycling issue for the transportation industry. Kang explained that, “by providing methodologies for state organizations and the SHA to evaluate recycled materials and establish consistent environmental quality standards, we hope to ultimately improve the health of the Chesapeake Bay.”

For more information about this project, contact Dong Hee Kang at