Design, Performance and Mechanisms of Asphalt Modified with Polyurethane and Hydroxylated Crumb Rubber

Under long-term heavy load and complex service environments, polyurethane-modified asphalt (PUMA) struggles to simultaneously satisfy the requirements of rutting and cracking resistance of asphalt pavements, as cyclic stress loading reduces the elastic recovery and low-temperature toughness of polyurethane (PU). To address this issue, this study employed hydroxylated crumb rubber (HCR), which is obtained by activating the surface of crumb rubber (CR) and can chemically crosslink with PU in asphalt to form a crosslinked network structure. The aim was to enhance the rutting and cracking resistance of PUMA by utilizing the elasticity and low-temperature toughness of CR. An orthogonal design was employed to systematically design a modified asphalt formulation with PU and HCR (PU/HCRMA) by controlling the isocyanate index and the contents of PU and HCR. The basic properties, rheological properties, and viscoelastic properties of PU/HCRMA were systematically investigated. The results demonstrate that the rutting and cracking resistance of PU/HCRMA are substantially enhanced, with an improvement of 28.91% in the rutting factor at 64 °C compared to PUMA and a reduction of 49.93 MPa in the stiffness modulus at −24 °C. Simultaneously, incorporating HCR in PUMA enhances its viscosity and flow resistance while reducing temperature susceptibility. Furthermore, by providing load-bearing sites, HCR endows PU/HCRMA with exceptional elastic recovery and deformation resistance. Results from FTIR and FM confirm the reaction between isocyanate groups in the PU prepolymer and the hydroxyl groups on the surface of HCR and the formation of HCR-PU crosslinked networks. Finally, PU/HCRMA asphalt mixtures demonstrate significant improvements in both rutting and cracking resistance. This research outcome provides a new direction for the development of high-performance road asphalt materials.