Composite rejuvenation of aged SBS‑modified asphalt using epoxidized soybean oil and reactive compounds: performance recovery and physicochemical mechanism

This study proposed a composite rejuvenation strategy to simultaneously restore asphalt components and repair SBS polymers in aged SBS-modified asphalt (SBSMA). Four formulations were developed using epoxidized soybean oil (ESO), 4,4′-dicyclohexylmethane diisocyanate (HMDI) and cardanol glycidyl ether (CGE), and their effects and underlying mechanisms were systematically investigated through physical, rheological, adhesion and chemical analyses. Results indicated that ESO restored low-temperature flexibility of aged SBSMA by supplementing light components without chemical reactions. ESO&HMDI enhanced high-temperature performance, increasing softening point and complex modulus while decreasing phase angle; amidation and esterification formed new amide and ester linkages to reconnect fractured SBS structures, raising molecular weight and densifying SBS distribution. ESO&CGE delivered better low-temperature recovery than pure ESO, boosting penetration, ductility and phase angle and reducing complex modulus via epoxy ring-opening and esterification, generating flexible ether and ester groups with increased molecular weight and denser SBS distribution. The rejuvenated SBSMA by the blend of ESO, HMDI and CGE achieved optimal balanced high and low-temperature performance via physicochemical synergy, with the most complete SBS structure restoration and adhesion recovered to a level comparable to unaged SBSMA. These findings provide guidance for rejuvenator selection and systematic design for aged SBSMA.