Changes of asphalt fumes in hot-mix asphalt pavement recycling

Hot-mix asphalt pavement recycling is widely practiced for its economic and environmental benefits. Existing studies are mainly focused on the engineering properties of reclaimed asphalt pavement (RAP) materials, without considering their impacts on the generated asphalt fumes—a widely recognized environmental hazard. The effects of using RAP on asphalt fumes are systematically studied in this research. Asphalt binders from different sources were used to create RAP materials in three aging conditions. Asphalt fumes were generated and collected from non-aged asphalt materials as well as RAP materials, followed by gravimetric and chemical analysis of the collected asphalt fumes. RAP materials were found to generate greater amount of particulates in asphalt fumes as compared with non-aged ones. RAP materials are also associated with increase in the types and concentrations of polycyclic aromatic hydrocarbons (PAHs) in asphalt fumes, especially those PAHs with more than three aromatic rings. PAHs increase in asphalt fumes is particularly noticeable for RAP created in the natural aging condition. It is reasonable to conclude that asphalt fumes generated from RAP become more hazardous, hence deserving more attention from researchers and practitioners. The mechanisms of the increase in PAHs are discussed, in addition to field exposure studies and mitigation measures.