LAUSR

Despite the merits of using polyphosphoric acid (PPA) in modification of bitumen, its desirable stiffening effect on bitumen is totally composition-dependent. While asphaltenes and resins are correctly introduced as the immediate components affected by PPA, our laboratory rheological investigations show that bitumen’s wax content could be a potential interference for PPA’s modification function. As evidenced by the complex viscosity test, PPA is very effective in low-wax bitumen, but its effect on high-wax bitumen is quite negligible. In a high-wax medium, the trend of interaction energy improvement with the number of wax chains suggests that the crystalline networks of wax can interfere in interactions of PPA with either asphaltene or resin through concealing interaction sites of asphaltene and resin. This in turn leads to the reduction of their accessible active sites for interacting with PPA. To study the working mechanism of PPA on bitumen constituents, the density functional theory (DFT) approach and...