Fractional viscoelastic and GSCS micromechanical modeling of RAP bituminous mastics

This study investigates the viscoelastic and micromechanical behavior of bituminous mastics incorporating fine fractions of reclaimed asphalt pavement (RAP), with emphasis on its binder activation and mobilization. Mastics were prepared with varying RAP filler contents, warm-mix additives, and rejuvenators, and characterized by time–temperature frequency sweep tests. The experimental data was shifted into master curves using the Christensen-Anderson (CA) model and subsequently analyzed with the fractional derivative model (FDM-4) and the generalized self-consistent scheme (GSCS). Master curve analysis indicated that stiffness evolution in mastics was primarily driven by RAP binder activation rather than filler reinforcement. This observation was reproduced by FDM-4 modelling, which further highlighted the crystalline stiffening effect of Fischer-Tropsch (FT) wax. GSCS results revealed that immobilized binder volume increased with RAP content but decreased with rejuvenator addition, while FT wax counteracted the rejuvenator-induced reduction in stiffness. Comparing the blending frameworks showed that the black rock assumption oversimplifies mastic behavior, while the total blending tends to overestimate binder availability. Overall, these findings demonstrate that binder availability in RAP mastics is governed by RAP content and temperature and can be engineered by incorporating rejuvenators and warm mix additives.