Leaching Characteristics of Recycled Asphalt Shingles Mixed with Industrial Byproducts as Structural Fills

Leaching characteristics of recycled asphalt shingles (RAS) mixed with self-cementing fly ash (FA) for use as structural fill materials were investigated. Long-term column leaching tests were conducted on the compacted RAS-FA mixture containing 10% and 20% self-cementing FA. Results showed that peak concentrations for all investigated elements occurred in the first 5 pore volumes of flow (PVFs). Only arsenic (As) and selenium (Se) exceed the maximum contamination levels (MCLs) of U.S. EPA drinking water standard. The peak concentrations of As and Se from RAS-FA (80-20) were 10.2 and 18.8 times higher than the corresponding MCLs (As_MCL = 10 ppb and Se_MCL = 50 ppb), while lower leached As and Se concentrations from the RAS-FA (90-10) were observed (7.1 and 1.8 times higher than the MCL values). WiscLEACH model was used to predict the environmental impact of RAS-FA mixtures as structural fills and calculate the reduction factors (RF) at a point of compliance (POC) 30 m away from the centerline of the roadway. The calculated RFs of As and Se were 14 and 18, respectively, and only concentration of Se leached from RAS-FA (80-20) were predicted higher than MCL at the POC. Based on mechanical and environmental evaluations, RAS-FA (90%-10%) is recommended for highway applications.