Laboratory Study and Molecular Dynamics Simulation of High- and Low-Temperature Properties of Polyurethane-Modified Asphalt

This study investigated the modification mechanism of polyurethane (PU) on the high- and low-temperature properties of asphalt based on experimental and molecular dynamics (MD) simulations. PU-modified asphalt was prepared using an in situ polymerization method. The high- and low-temperature properties of asphalt containing various PU contents were investigated via a series of laboratory tests. The asphalt molecular model, the PU molecular model, and the PU-asphalt mixes system were modeled using software. Based on reasonable models, the influence of PU content on the physical modulus and molecular motion of asphalt at high temperatures was researched using MD simulations. The glass transition temperature of PU-modified asphalt with different contents was obtained using software, and the free volume theory and molecular diffusion movement were used to interpret the improvement mechanism of PU content on the low-temperature performance of asphalt. The results indicate that PU effectively can improve the high- and low-temperature properties of asphalt. PU has a significant positive effect on the physical modulus of asphalt, and the effect becomes more significant with the increase of PU content. In addition, PU can form a tight structure with asphalt and increase the stability of the asphalt system. The free volume ensures the free movement of PU molecules in the asphalt, allowing PU to be dispersed homogeneously in the asphalt. However, the free volume decreases when the PU content exceeds 15% by weight, which limits the improvement of the low-temperature performance of asphalt. The results of molecular simulation can explain the enhancement mechanism of PU, providing a reference for the performance enhancement of PU-modified asphalt.