Hydraulic and environmental impacts of using recycled asphalt pavement on highway shoulders

An experimental program was carried out to evaluate hydraulic and environmental behavior of recycled asphalt pavement (RAP) obtained from seven different roadways within the state of Maryland for their potential utilization in construction of highway shoulder edge drop-offs. Due to their common use in these edge drop-offs, graded aggregate base material, gravel, and topsoil were included as control materials in the testing program. Hydraulic conductivities of RAPs were evaluated through a series of constant-head tests, while their leaching potential was determined through batch and column leach tests. Laboratory test results indicated that the hydraulic conductivity of recycled asphalt pavement was comparable to that of natural aggregates with the gradation of a clean sand-gravel mixture. The stabilized concentrations of all metals released from the RAPs during the column leach tests were below the water quality limits. The numerical analysis results revealed that, with increasing distance from highway shoulder, the metal concentrations in nearby surface waters decreased further.