Diffusion Behavior of Rejuvenator and Its Influences on the Interfacial Properties of Recycled Asphalt Mixtures by Molecular Dynamics Simulations and Experiments

In hot in-place recycled (HIR) technology, the in-place mixing paving construction method suffers from the problems of low mixing temperature and short mixing time, which lead to incomplete rejuvenator diffusion in waste asphalt binder. Quantitative evaluation of rejuvenator diffusion degree and the corresponding microscopic characteristics are beneficial in guiding HIR construction technology. In this study, the interface model of virgin asphalt, rejuvenator, and aged asphalt was established through molecular dynamics (MD) simulations. Rejuvenator diffusion rates at the virgin–aged asphalt interface (VAAI) at different temperatures were investigated. The results showed that temperature increased rejuvenator diffusion rate. Relative concentrations at different diffusion times were used to quantitatively evaluate rejuvenator diffusion degrees at the interface. The results showed that diffusion degree and uniformity of rejuvenators could be improved by the passage of time. At the same time, the modulus and stress–strain curves of various VAAI models with different diffusion degrees were drawn. The results showed that increase of diffusion degree increased modulus and maximum tensile stress and strain of VAAI; that is, stability at high temperature and crack resistance at low temperature were improved. At low rejuvenator diffusion degrees, rejuvenators accumulated at VAAI, which had a negative effect on reclaimed asphalt performance. According to MD simulation results and site conditions, it was suggested that the HIR technology construction temperature had to remain above 428 K. At the same time, it was suggested that rejuvenator diffusion degree had to be increased to improve road performance.