Evaluation of asphalt effect on water quality using leaching test and molecular simulation

The contact of water and asphalt in roadway pavement can lead to the leaching of components from asphalt and cause water contamination. In order to study influencing factors affecting water contamination caused by asphalt materials, leaching tests were performed on asphalt mixture specimens with different mix designs. Chemical oxygen demand (COD), pH value, and total hardness are used to evaluate the leachability of asphalt mixture. The thin film leaching tests were carried out using a self-developed pressurized device. The effects of asphalt type, pH value of water, and submersion time on the concentration of ten metal ions leached from asphalt film were investigated. Finally, molecular dynamics simulations were performed to investigate the molecular diffusion between asphalt components and water. Results indicate that the concentration of metallic elements was affected by the pH value of water and submersion time. Compared with aged and SBS (Styrene-Butadiene-Styrene)–modified asphalt, virgin asphalt has the higher leaching potential for water contamination. The light fractions of aromatic and saturate molecules are more likely to diffuse at high temperature and high pressure. The study results can help better understand the environmental impact of asphalt in the framework of life-cycle assessment.