Oxidative aging of bitumen: a structural and chemical investigation

The oxidative aging of bitumen was investigated chemically and structurally using SARA analysis, TOF-SIMS and AFM. Typical wax-containing and non-waxy bitumen samples were selected. Short- and long-term aging tests were conducted under standard conditions, and at prolonged aging times. For both the wax-containing and non-waxy bitumen, aging significantly decreases the aromatic fraction and at the same time increase the content of resins and asphaltenes. AFM shows bee-like structures on the wax-containing bitumen surface, and these structures change when the binder is aged. The bee structures are fewer but larger after a prolonged PAV. For the non-waxy bitumen, no structures were observed, even not after a severe PAV aging that increased the content of asphaltenes significantly. This implies that asphaltenes are most likely not responsible for the formation of bee structures. By TOF-SIMS, the non-waxy bitumen surface did not show structures, neither in the virgin state nor after the severe oxidative aging, further supporting that asphaltenes do not directly result in structure formation. For the wax-containing bitumen, TOF-SIMS shows aliphatics-enriched structures, which generally become larger after oxidative aging.