Effect of Thermal Aging on the Self-Healing Properties of High-Content Crumb Rubber–SBS Composite Modified Asphalt

High-content crumb rubber composite modified asphalt (HRCMA), which combines crumb rubber with a styrene–butadiene–styrene (SBS) modifier, offers excellent mechanical performance and environmental benefits, yet its high viscosity requires elevated production and construction temperatures that may accelerate thermo-oxidative aging and impair its durability and self-healing capability. In this study, the self-healing behavior of HRCMA under virgin, Thin Film Oven Test (TFOT)-aged, and Pressure Aging Vessel (PAV)-aged conditions was systematically investigated and compared with that of conventional SBS modified asphalt (SBSMA) using fatigue–healing–fatigue tests. The effects of damage degree, healing interval time, and healing temperature were evaluated, and a comprehensive self-healing index (HI) integrating the recovery of initial mechanical properties and the recovery of damage evolution characteristics was proposed. The results show that increasing the damage degree significantly reduces the self-healing capability of both binders, and thermal aging further intensifies this deterioration; two-way analysis of variance (ANOVA) confirmed that these effects are statistically significant. Extending the healing interval time and raising the healing temperature improve the self-healing performance, although the enhancement weakens after severe aging owing to the reduction in molecular mobility. Compared with SBSMA, HRCMA exhibits higher self-healing capability under all aging conditions, indicating stronger resistance to aging-induced damage. The proposed HI provides a more comprehensive evaluation of asphalt self-healing behavior, and the findings provide theoretical support for the durability assessment and engineering application of highly modified asphalt materials.