Targeted design of polyurethane modified asphalt based on Click reaction: Application for enhancing interfacial bonding properties of ultra-thin overlays

To alleviate the common issues of poor high-temperature workability and insufficient interfacial bonding with the lower layer during service of binder materials in maintenance scenarios such as ultra-thin overlays, this study designed and prepared a polyurethane modified asphalt (PUA) containing dynamic disulfide (S-S) bonds and its mixture based on the Click reaction principle. The adhesion between PUA and aggregates, as well as the high-temperature flow characteristics of PUA mixture, were evaluated respectively through contact angle test at the nanoscopic scale, bond strength test, oblique shear test and self-developed variable speed mixing test at the macroscopic scale. Additionally, the interfacial interaction between PUA and aggregates was simulated at the molecular scale. The results indicated that the Click reaction proceeded smoothly in PUA, increasing its macromolecular proportion and contributing to partial crosslinking, which significantly enhanced its cohesive strength. PUA containing dynamic S-S bonds exhibited superior spreading and wetting properties in liquids. Compared with commonly used high-viscosity SBS modified asphalt and its mixture, it demonstrated higher bonding strength and interlayer shear resistance. This PUA mixture was capable of reducing production and mixing temperatures by more than 11°C, while maintaining its pavement performance under various environmental temperatures and water conditions. This contributes to energy conservation and emission reduction. Molecular simulation results revealed that the addition of S-S bonds or water molecules in the environment would reduce the diffusion rate of PUA components toward the aggregate interface, weaken the self-aggregation tendency of asphaltene, and slightly decrease its adhesion work. The findings provide a scientific basis for the targeted design of polyurethane modified asphalt and its sustainable application in high-performance ultra-thin overlays. • A thermoplastic polyurethane asphalt (PUA) mixture suitable for ultra-thin overlays was prepared based on Click reaction principle. • The bonding strength of PUA at room temperature was enhanced through addition reaction and dynamic exchange effects of S-S bonds. • Variable speed mixing test evaluated that the high-temperature workability of PUA mixture was superior to SBS modified asphalt mixture. • Effects of moisture on movement and diffusion behavior of PUA on the aggregate surface were revealed through MD simulation.