Research on the interfacial degradation mechanism of field-aged SBS-modified asphalt binder under freeze–thaw effects based on molecular dynamics simulations

Aging and freeze–thaw effects significantly reduce the lifespan of asphalt pavements, necessitating an understanding of the microscopic mechanisms behind these processes for improved material development and durability prediction. This study investigates the nanoscale interfacial behavior of long-term aged Styrene–Butadiene–Styrene (SBS) modified asphalt binder under freeze–thaw effects by using molecular dynamics (MD) simulations. The aged asphalt binder models were refined and optimized using field-aged samples from three highways with service years ranging from 6 to 15. An asphalt–aggregate interface model was further constructed to examine changes in component distribution and interfacial adhesion strength. The results showed a loss of approximately 11.4% in adhesion performance with aging in dry conditions. Under wet conditions, the work of adhesion decreased to 20–25% of dry conditions. Findings reveal that interfacial adhesion is significantly more sensitive to moisture damage than to aging due to the lack of electrostatic interaction energy on the quartz surface. Compared to water, the ice interface alters the asphalt binder's concentration distribution, resulting in component retreat from the surface and more severe adhesion damage due to reduced intermolecular interactions. These insights enhance the understanding of pavement aging factors, guiding predictions of asphalt pavement performance in freeze–thaw environments. © 2026 Elsevier B.V.