Study on the compatibility between polyurethane and asphalt based on experiment and molecular dynamics simulation

Compatibility between asphalt and polyurethane (PU) additives is the most challenging issue affecting the performance of PU modified asphalt. This study aims to investigate the influence of shearing temperature and PU content on compatibility between PU and asphalt via experiments and molecular dynamics (MD) simulation. Herein, the molecular models of base asphalt, PU molecules, and PU/asphalt blends were first constructed in Materials Studio (MS) software. Based on a reasonable model, the influence of shearing temperature on the storage stability of PU modified asphalt was measured by calculating the solubility parameters (δ) and diffusion coefficient. In addition, the effect of PU content on the compatibility of PU and asphalt was evaluated through cohesive energy density (CED), hydrogen bonding, and radial distribution function (RDF). Finally, the simulation results were compared with results from the segregation test and fluorescence microscope (FM). The simulation results indicate that PU and asphalt obtain optimal compatibility when the temperature is 135 °C, at which the diffusion coefficient of PU modified asphalt is enhanced significantly. The CED of modified asphalt is enhanced with the increase of PU content. Meanwhile, PU shows a significant effect on the RDF of each asphalt component. All these changes in asphalt molecules demonstrate that PU plays a positive role in improving the tightness of asphalt molecular structure, and the optimal content is 15 wt%. The simulation results are consistent with experimental results.