Mechanistic Insights into the Aging and Regeneration of SBS-Modified Asphalt Under Coastal Humid–Hot Environmental Conditions

The deterioration of SBS-modified asphalt under coupled temperature–ultraviolet (UV)–coastal humidity conditions is significantly accelerated in coastal regions because of seawater evaporation, leading to severe durability degradation of pavement materials. However, the performance evaluation laws and underlying regeneration mechanisms under such coupled environmental aging conditions remain insufficiently understood. Therefore, taking Shanghai as a representative coastal city, a temperature–UV–coastal humidity coupled aging system was established to simulate the saline and humid environment of coastal regions. Industrial animal oil and waste engine oil were selected as regeneration materials, and a multi-scale experimental approach was adopted to evaluate the performance recovery of aged asphalt. The results indicate that both regeneration materials effectively restore ductility and improve rheological behavior, while reducing viscosity but cause a measurable decrease in softening point, indicating a reduction in high-temperature stability. Industrial animal oil shows superior improvement in ductility, whereas waste engine oil exhibits stronger effects on viscosity reduction and microstructural regulation. A content of approximately 6% was recommended as a practical content to balance performance recovery and high-temperature stability under the tested coupled-aging condition. Microstructural analysis confirms that the regeneration mechanism is dominated by light component replenishment and colloidal structure reconstruction rather than chemical modification of SBS chains.