Study on the Rheological Properties of Aged SBS-Modified Asphalt Rejuvenated with Soybean Oil and Crumb Rubber

To address the issue that a single soybean oil rejuvenator weakens the high-temperature performance of aged SBS-modified asphalt, soybean oil and crumb rubber (CR) were used to construct a synergistic composite rejuvenation system for long-term aged SBS-modified asphalt (ASMA). Conventional property tests, dynamic shear rheometer (DSR) tests, bending beam rheometer (BBR) tests, and microstructural characterization were performed to investigate the macroscopic rheological properties and microscopic mechanisms of rejuvenated asphalt. The results indicate that soybean oil can restore the low-temperature performance of ASMA, yet it weakens its high-temperature deformation resistance. Incorporating CR into the 5 wt% soybean oil rejuvenated system effectively compensates for this drawback. As the CR content increases, the high-temperature deformation resistance, low-temperature crack resistance, fatigue life, and thixotropy of the rejuvenated asphalt improve significantly. Specifically, as the CR content increases from 0 wt% to 25 wt%, the rutting factor at 64 °C increases 14.7-fold, the fatigue life at 5% strain increases 13.7-fold, the low-temperature creep stiffness at −24 °C decreases by 17.1%, and the creep rate increases by 51.8%. The balanced optimization of high- and low-temperature rheological performance of the rejuvenated asphalt can be interpreted from multi-scale characterization results. On the one hand, weak interfacial chemical reactions occur during soybean oil rejuvenation, while CR mainly exerts physical swelling and filling effects. On the other hand, the system gradually evolves from dispersed-phase filling to a continuous network as the CR content increases. In addition, the likely competitive adsorption of soybean oil between CR and residual SBS modifiers promotes the formation of the continuous phase. This study provides a feasible technical reference for the synergistic rejuvenation of aged SBS-modified asphalt using bio-oil and CR.