Multi-dimensional analysis of the mechanism of the effects of rejuvenator and warm mixing agents on aged SBS modified asphalt

The microstructure of warm mix recycled asphalt and the interactions among its components play a crucial role in determining its rheological properties. This study investigates the effects of aging, rejuvenators, and warm mix agents on the resistance to permanent deformation, fatigue characteristics, and microstructure of SBS-modified asphalt. The interactions among asphalt, rejuvenators, warm mix agents, and SBS molecules were investigated using a combination of Dynamic Shear Rheology (DSR), Multi-Stress Creep Recovery (MSCR), and Linear Amplitude Scanning (LAS) tests, alongside Atomic Force Microscopy (AFM), Molecular Dynamics (MD) simulations, and Density Functional Theory (DFT). The results indicate that REJ adversely affects the high-temperature deformation resistance of aged asphalt (AA) but exerts a positive effect on its fatigue resistance; WMA can enhance the high-temperature deformation resistance of aged asphalt and prolong its fatigue life. Furthermore, polar rejuvenator molecules are more likely to be distributed in the SBS-containing phase or near the SBS–asphaltene interfacial region, whereas Fischer–Tropsch (FT) wax molecules exhibit a slight aggregation tendency because of their relatively weak interaction with SBS macromolecules. Molecular simulations suggest that REJ and WMA mainly regulate the SBS–asphalt interfacial region and the aggregate structure, rather than being uniformly dispersed inside SBS itself. DFT analysis further reveals that specific atoms within both the rejuvenator and warm mix agent exhibit strong electrostatic interactions with polar molecules present in aged asphalt—particularly with -CHO and -COOH groups found in SB- and BS-components. This paper explores the mechanisms underlying interactions between aged asphalt, rejuvenators, and warm mix agents from macro-, micro-, and molecular perspectives, thereby providing valuable insights for applications involving warm mix recycled asphalt.