Diffusion Mechanism of Reactive Warm-Mix Rejuvenator in Aging SBS-Modified Asphalt

Abstract To investigate the diffusion behavior of warm-mix rejuvenators in aged styrene-butadiene-styrene-modified asphalt (ASBSMA), the effects of rejuvenator type, diffusion time, and temperature on diffusion performance were studied using rotational viscosity tests, the Fickian diffusion model, infrared spectroscopy tracing techniques, and molecular dynamics simulations. Results indicate that the self-developed rejuvenator, self-developed warm mix rejuvenator (SWR), exhibits superior diffusion performance compared to commercial rejuvenators RA1 and RA2. Its diffusion coefficient increases with rising temperature but decreases with extended diffusion time. After 120 minutes of diffusion at 145°C, SWR’s diffusion coefficient reached 1.125 × 10 − 8 m 2 / s , approximately 1.45 times that of RA1. Infrared tracing revealed that the migration depth of the warm-mix rejuvenator within ASBSMA increased with both temperature and time. Compared to RA1 and RA2, SWR migrated to the innermost layer of the asphalt film within 90 minutes at 145°C. Molecular dynamics simulations revealed bidirectional diffusion behavior between SWR and ASBSMA, with SWR molecules exhibiting more vigorous motion. In summary, the suitable operating temperature for SWR is 140°C–150°C, with a diffusion time of no less than 90 min.