Study on the Performance of SBS/Polyphosphoric Acid Composite Modified Asphalt

To address the issue of bad compatibility between a single polymer modifier and asphalt and high preparation cost, the composite modified asphalt with polyphosphoric acid (PPA) and SBS as a modifier was prepared. Basic properties, viscosity characteristics, high-temperature and low-temperature rheological performance, and aging-resistant performance of SBS/PPA composite modified asphalt were comprehensively evaluated, and the best content of PPA was obtained through the experimental results below. By performing an infrared spectrum test and a scanning electron microscope test, structural changes and modifying mechanisms of composite modified asphalt were analyzed. The results indicate the optimal PPA content is 0.75%. After adding PPA, the penetration and ductility of composite modified asphalt were reduced, while the softening point increased. At 135 °C, the viscosity was 1.2 times that of SBS modified asphalt. The average weight loss ratio was 0.163%. When the content of PPA was 0.75% and 1%, the rutting factor increased significantly. Therefore, PPA can not only improve the thermal oxidation aging resistance of asphalt, it can also improve the shear resistance, high-temperature performance, and temperature sensitivity of asphalt. Between 1027 and 1150 cm−1, the composite modified asphalt forms a new absorption peak, and from 1610 cm−1, the absorption peak presents an upward trend, suggesting that PPA reacts chemically with asphalt, produces the new substance, and also increases a large number of hydrocarbon components with chain structure. The surface appearance of the compound modified asphalt gradually presents a smooth wrinkle state due to the increase of PPA, so the issue of easy segregation of SBS in asphalt is improved.