Effect of phenol-carbamate bonds on the repair performance of polyurethane-modified asphalt and repair mechanism analysis

To enhance the self-healing ability of polyurethane-modified asphalt (PUA), we prepared selfhealing PUAs containing reversible phenol-carbamate bonds using cashew phenol phenolic resin (CPPR) and 4,4 '-dihydroxy diphenyl sulfone (BPS) as chain extenders, denoted as CPPR-PUA and BPS-PUA, respectively. Additionally, maleic anhydride (MA)-modified polyurethane asphalt (MA-PUA) was synthesized by grafting MA and hydroxy-terminated polybutadiene (HTPB) onto the base asphalt. The phenolic hydroxyl groups on CPPR and BPS reacted with isocyanate groups to form reversible phenol-carbamate bonds, while MA facilitated the ring-opening reaction with -OH in the base asphalt, introducing unsaturated bonds and free carboxyl groups. These carboxyl groups further esterified with HTPB, extending the asphalt molecular chain and creating a crosslinking network structure in MA-PUA. Our results demonstrate that MA-PUA, despite its low PU content (5 %-15 %), exhibited superior high-temperature deformation resistance due to its MA-PU-asphalt cross-linking network. Notably, the recovery rates of the PUAs followed the order: MA-PUA > BPS-PUA > CPPR-PUA. MA-PUA10 % achieving an excellent complex shear modulus recovery of 88.55 %. Microscopic analysis revealed that cracks in the PUA underwent rapid and dynamic exchange of phenol-carbamate bonds at elevated temperatures (50-80 degrees C), leading to effective self-healing upon cooling. This study provides valuable insights into the repair mechanisms of PUAs, highlighting the potential of phenol-carbamate bonds in improving the performance and longevity of asphalt pavements, reducing maintenance costs, and ensuring road safety.