Investigation of the Physicochemical Interactions and Modification Effects of Polyurethane on Asphalt Binder

Polyurethane (PU) is a synthetic polymeric material with excellent mechanical properties and chemical designability. An in-depth understanding of the synergetic effect between polyurethane and asphalt binder is needed to produce durable PU-modified asphalt paving materials. This study focuses on the physicochemical changes, the states of in situ synthesized PU, and the modification effects of PU after PU prepolymers and chain extenders are added into asphalt binder. Investigation methods involve the Fourier transform infrared (FTIR) spectroscopy, partial Corbett separation, confocal fluorescence microscopy, particle size distribution test, rheological test, and theoretical calculation. It was found that the incorporation of PU has no obvious chemical influence on the asphalt binder and the main working principle of PU modification is its physical dispersion in asphalt binder. In situ synthesized PU is uniformly dispersed in asphalt binder and the size distribution of PU particles follows a log-normal distribution. As PU content exceeds 15%, the formed PU particles in asphalt binder are noticeably enlarged. Moreover, PU modification leads to significant improvements in asphalt binder properties, including high-temperature rutting resistance, elastic recovery, and deformation resistance. Rheological experiments and theoretical calculations under the framework of suspension rheology indicate that PU-modified asphalt binder can be reasonably modeled as a bimodal solid particle suspension, and the dynamic viscosity of PU-modified asphalt binder is predominantly determined by the dynamic viscosity of the maltenes and the volume fractions of PU and asphaltenes.