Leaching of Contaminants from Recycled Asphalt Pavement used in Highway Construction

Abstract

Recycled asphalt pavement (RAP) is a material resulting the removal and reprocessing of the existing asphalt pavement. Annually, more than 80 million tons of RAP is produced in the United States. Most of the RAP is landfilled, which constitutes a significant economic burden and a waste of landfill space. RAP has great potential in highway construction due to its good physical properties. However, concerns have been raised due to potential surface water and groundwater contamination by metals including some heavy metals and Polycyclic Aromatic Hydrocarbons (PAHs) present in RAP. A series of batch-level pH-dependent leaching tests and Toxicity Characteristics Leaching Procedure (TCLP) tests were conducted to investigate the leaching of metals from seven RAPs collected across the state of Maryland. The results of the pH-dependent leaching tests indicated As to be slightly above the U.S EPA Water Quality Limit (WQL). The results of a series of TCLP tests showed that two PAHs, chrysene and Indeno[1,2,3-cd]pyrene, may be present in the leachates, albeit, at concentrations very comparable to those leach from a new asphalt material. The results of the geochemical modeling indicated that the leached metals were solubility-controlled. Oxide and hydroxide minerals control the leaching of Al and Fe; whereas, leaching of Ba, Ca and Mg were controlled by carbonate and/or sulfate minerals.