Dual self-repairing enhancement mechanisms of blocked dynamic isocyanate prepolymer on aging degradation and fatigue damages of high-content SBS-modified asphalt

High-content SBS-modified asphalt (HCSMA) was the primary binder material used in high-quality pavements. The aging degradation and fatigue damages of SBS cross-linked networks were the direct triggers of HCSMA properties deterioration. However, current main asphalt self-repairing enhancement technologies were unable to repair the damaged SBS structures, making it difficult to fully restore the properties of HCSMA. This study aimed to develop dual self-repairing techniques for actively repairing the SBS damages in HCSMA. To achieve this, the thermally initiated blocked dynamic isocyanate prepolymer (BDIP) was prepared as a modifier for HCSMA by introducing blocking agents and dynamic bonds into the isocyanate prepolymers. It showed that BDIP can react with asphalt components containing polar functional groups to improve the basic physical properties of HCSMA. Firstly, for the aging degradation of SBS networks, the isocyanate groups released from BDIP through deblocking reactions reacted with the active end groups in SBS degradation products to repair the aging degraded SBS, thereby constructing dynamic SBS cross-linked networks with dynamic covalent bonds. Analysis of molecular composition and fluorescence microscopy observation showed that BDIP repaired 64 % of the degraded networks in HCSMA during mild aging, resulting in the SBS networks being nearly intact. The biphasic reactions (asphalt and SBS phases) between BDIP and HCSMA enabled HCSMA/BDIP (HCSMA modified with BDIP) to exhibit excellent high-temperature deformation resistance both before and after aging. Secondly, for the fatigue damage of SBS networks, the reversible cleavage exchange reaction characteristic of dynamic bonds was used to repair the SBS fatigue damages under load. Linear amplitude sweep (LAS) test revealed that the reversible dynamic disulfide bonds in the SBS networks provided satisfactory fatigue life and excellent fatigue property stability with aging for HCSMA/BDIP. Additionally, the LAS-based healing test confirmed that the dynamic SBS cross-linked networks improved the fatigue repairing properties of aged HCSMA/BDIP, while maintaining excellent fatigue repairing property stability under aging conditions. Overall, the dual self-repairing enhancement mechanisms of BDIP were confirmed, HCSMA/BDIP demonstrated significant advantages over HCSMA without BDIP, most notably exhibiting at least a 50 % increase in shear viscosity and fatigue life.