Rheological Property Evaluation and Microreaction Mechanism of Rubber Asphalt, Desulfurized Rubber Asphalt, and Their Composites

Desulfurized rubber asphalt (DRA) is a good environmentally friendly road construction material, but its high-temperature performance is relatively insufficient compared to ordinary rubber asphalt (RA). Therefore, in order to make full use of its environmental protection features and overcome its shortcomings in high-temperature performance, polyphosphoric acid (PPA) was used to modify DRA to prepare composite modified asphalt (PPA-DRA). First, RA, DRA, and PPA-DRA were prepared in this study, and their high-temperature performance and fatigue properties were compared and analyzed by a temperature scanning test and multistress creep recovery test (MSCR). Then, their low-temperature performance was also compared and analyzed by using a bending beam rheological test (BBR). Finally, the modified mechanism of PPA-DRA was revealed by the FTIR test, thermogravimetric analysis (TGA), and microswelling model. Results show that compared to RA and DRA, PPA-DRA performed better both at high and low temperatures but worse at fatigue resistance, and it can be applied to a wider range of traffic grades. However, PPA-DRA and DRA are more susceptible to aging than RA, and the elastic component in PPA-DRA increases greatly due to aging. According to the strategic highway research program (SHRP) specification, PPA-DRA, DRA, and RA can be graded as PG82-34, PG76-28, and PG76-28, respectively. Also, the FTIR test in conjunction with TGA proves that PPA-DRA exhibits better high-temperature performance than DRA and RA from the microscopic perspective, and its modification process is of chemical modification; the swelling model shows that compared to RA and DRA, PPA-DRA shows the largest number of micelles and the best combination between modifier and asphalt molecules, which promotes the formation of a dense spatial network structure and makes the asphalt structure more stable.