Insights into thermo-oxidative aging properties and mechanisms of high-content desulfurized rubber modified asphalt: A macro-rheological and micro-chemical perspective

To maximize the resource utilization of waste tires, this study systematically investigates the rheological degradation, phase stability, and micro-evolution mechanisms of high-content (30 wt%-50 wt%) desulfurized rubber modified asphalt (HDRA) under short-term and long-term thermo-oxidative aging by rotating film oven test and pressure aging vessel test (RTFOT and PAV). Through multi-scale approaches including DSR, BBR, TD-GC-MS, FTIR, and microscopic morphology characterizations (SEM/FM), the macroscopic rheology, full-lifecycle volatile organic compound (VOC) emissions, and morphological responses were quantitatively evaluated. The results reveal that the 50% HDRA exhibits a unique "aging self-adaptive" characteristic: thermo-oxidative exposure triggers deep swelling and cross-linking of the dense rubber network, which substantially reinforces high-temperature elasticity while restricting particle migration, thereby completely reversing the initial high-temperature segregation susceptibility. However, the hyper-dense skeleton introduces a low-temperature "rheological trade-off"; long-term aging restricts the internal free volume, significantly diminishing the stress relaxation capacity under sub-zero conditions. Furthermore, gaseous molecule tracking and chemical index analysis confirm a microscopic "sacrificial protection" mechanism. The early-stage intensive depolymerization and devulcanization of the rubber network consume thermo-oxidative energy and physically and chemically shield the base asphalt from profound hardening. Consequently, as aging deepens, the full-lifecycle failure mode transitions from conventional matrix embrittlement to severe polymer-asphalt interfacial debonding and phase homogenization. This study provides a novel theoretical foundation for the precise design and eco-friendly application of ultra-high content solid-waste rubber in long-life pavement materials.