A Novel Methodology for Assessing Environmental Impacts of Recycled and Waste Materials Used in Highway Construction

摘要

The use of recycled materials and industrial byproducts as transportation construction materials has caused concern about constituents released and their potential environmental impact on nearby surface and groundwater. To help transportation agencies, consultants, recycled materials suppliers, and health officials to properly screen waste materials and assess their environmental behavior, a novel methodology was developed and tested. The methodology includes steps to identify potential waste materials; evaluate short- and long-term leaching behavior of proposed wastes (leachate source strength); assess the effects of removal, reduction, and retardation (RRR) processes on constituents released to the nearby environment; and implement and validate the evaluation methodology using a combined chemical and biological approach. Selected test materials, which included coal fly ash, incinerator bottom ash, shingles, scrap tires, and foundry sand, are initially screened for potential aquatic impact in their raw (unamended) form, and then assessed in detail after amendment as either concrete or fill. Leaching source strength tests include both short- and long-term batch leaching tests, a flat-plate test to determine diffusion-controlled surface leaching, and a packed column test for subbase or fill materials. Environmental RRR tests include photolysis, which measures degradation under UV light exposure, and volatilization, which measures loss by aeration. Biodegradation is measured in a batch culture seeded with wastewater microorganisms. Soil sorption is determined using three representative soils at varying solid/liquid ratios. Short-term toxicity bioassays are used to directly measure the potential aquatic impact of derived leachates as a supplement to chemical analyses. For most materials, amendment with asphalt or aggregate largely reduced or eliminated impact on target aquatic organisms. Environmental impacts of waste-amended concrete or fill leachates were further reduced or eliminated after RRR processes. Soil sorption was the most effective contaminant removal mechanism. The evaluation methodology was shown to successfully assess environmental impacts of waste materials in highway construction applications.