Hardening mechanism and crystallization characteristics of polymer-modified asphalt binder under thermoreversible aging

The hardened crystallization of asphalt binder due to thermoreversible aging in cold regions directly impacts its resistance to low-temperature cracking. The thermoreversible aging mechanism of a polymer-modified asphalt binder (PMA, including styrene-butadiene-styrene-modified asphalt binder (SBSMA) and crumb rubber-modified asphalt binder (CRMA)) was investigated using molecular dynamics (MD) methods. The fracture characteristics and crystallization properties of the PMAs were analyzed through single-edge notched beam (SENB) tests and crystallization kinetics. The results show that in the process of thermoreversible aging of PMA, the mobility of the asphalt molecular segment gradually decreases, the free volume of PMA continuously decreases, and the molecules gradually gather. Asphaltene plays a crucial role in the thermoreversible aging of PMA. It is suggested to evaluate the low-temperature properties of the PMA by measuring the fracture energy from the SENB tests after a 24-hour conditioning time. The relative crystallinity of PMA follows an exponential distribution pattern over time and a normal distribution trend with decreasing temperature. The crystal nucleation and growth modes of PMA exhibit one-dimensional rod-shaped instantaneous growth, characterized by high restriction and disorder. CRMA is recommended as the preferred asphalt binder for highway engineering projects in cold regions.