Investigation on the Diffusion Behavior of Dry Modified SBS at the Asphalt-Aggregate Interface: Molecular Simulation and Experiments

Dry modified Styrene-Butadiene-Styrene block copolymer (SBS) is an innovative method of modifying asphalt mixture that has gained attention due to its convenience, low carbon footprint, and high efficiency. To understand the diffusion behavior and micromechanism of dry modified SBS at the asphalt-aggregate interface, molecular dynamic simulation technology was employed to investigate its behavior at various temperatures. The mean square displacement, diffusion coefficient, statistical relative concentration distribution, and interfacial energy were used to calculate the diffusion and migration mechanism of dry modified SBS at the asphalt-aggregate interface. Additionally, the water-boiling test and Fourier transform infrared spectroscopy (FTIR) test were conducted to analyze the interfacial stripping form and SBS dispersion in the asphalt film. The results indicated that at high temperatures, dry modified SBS exhibited the highest mean square displacement and diffusion coefficient, suggesting that higher temperatures promoted its diffusion toward the asphalt layer. Dry modified SBS clusters and asphalt displayed opposite migration diffusion tendencies, with the migration of dry modified SBS toward the asphalt film becoming more pronounced over time. The introduction of SBS altered the distribution of asphalt components on the aggregate surface, increasing the interfacial energy and adhesion strength between asphalt and aggregate. Laboratory experiments supported these findings, confirming that dry modified SBS enhanced diffusion distribution and interfacial strength. The diffusion distribution of dry modification was found to be similar to that of wet-process SBS modified asphalt under sufficient temperature and time. Therefore, in engineering applications, raising the mixing temperature can improve the diffusion distribution of dry modified SBS, further enhancing its modification efficiency and effectiveness.