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 self-healing 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 cross-linking 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 ℃), 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. • Three polyurethane-modified asphalts based on phenol–carbamate bonds were prepared. • The chemical structure of different polyurethane-modified asphalts was investigated. • Fracture and repair mechanisms of polyurethane-modified asphalt containing phenol–carbamate bonds were constructed.