Performance restoration of aged SBS-modified asphalt in RAP via dry-process SBS modifier diffusion at the interface of aggregate-aged asphalt-virgin asphalt

To address and recycle more RAP (Reclaimed Asphalt Pavement), dry-process SBS(Styrene-Butadiene-Styrene) modifier was applied in hot in-place recycling. Molecular simulation and laboratory experiments were conducted to investigate the diffusion behavior of dry-process SBS modifier on RAP surfaces and its effects on the properties of recycled asphalt and recycled asphalt mixtures (RAM). Molecular simulation results revealed that after the diffusion of dry-process SBS on RAP surfaces, the fractured and aged SBS molecules in the aged asphalt were replenished, leading to a 59.49 % enhancement in the interface energy between aged asphalt and aggregates. Dry-process SBS exhibited bidirectional diffusion between RAP and virgin asphalt, with a preference for the intact SARA components of Virgin asphalt. The diffusion coefficient of the dry-process recycling system was significantly higher compared to conventional wet-process recycling, achieving a higher degree of fusion (DOB) between virgin and aged asphalt. Laboratory experiments demonstrated that dry-process recycling was more effective in restoring the performance of aged SBS-modified asphalt compared to wet-process recycling. At high RAP contents (80 %, 100 %), the asphalt mixtures from wet-process recycling failed to meet specifications for high-temperature permanent deformation resistance, low-temperature cracking resistance, and resistance to water damage. However, using 10 % dry-process SBS modifier by mass of aged asphalt in RAP enabled 100 % RAP content asphalt mixtures to meet specifications.