Effect of synthesized warm mix additive and rejuvenator on performance of recycled warm asphalt mixtures

In this study, a warm mix additive (composed of diamine and fatty acid amine) and a rejuvenator (consisting of styrene-butadiene-styrene and aromatic elements) were synthesized to facilitate the incorporation of 50% recycled asphalt pavement (RAP) in warm mix asphalt for the surface layer and 100% RAP in cold asphalt mixtures for the base layer. The effect of WMA and rejuvenator-modified asphalt binder was performed through rotation viscosity, dynamic shear rheometer, and bending beam rheometer. Simultaneously, the performances of RAP-modified asphalt mixtures were assessed using dynamic modulus, overlay test, and flow number test. Constructing two testbed roads provided a real-world evaluation of two surface mixtures and two base mixtures. The results indicated that modifying asphalt binder PG 64–22 with 2.0% warm mix additive (WMA) and 5.0% rejuvenator upgraded the performance grade to PG 76–22, significantly improving rutting resistance, and reducing 40% creep stiffness. The asphalt mixture with 50% RAP, modified with WMA and rejuvenator, demonstrated a better resistance to rutting and low-temperature cracking compared to the original mixture. Both surface and base mixtures met field application specifications, exhibiting excellent performance after a year of service, as confirmed by pavement condition surveys, and falling weight deflectometer tests, thus highlighting the potential for sustainable and high-performance recycled asphalt solutions in road construction.