Impact of Regulation of Wax-Based and Bio-Oil-Based Warm-Mix Additives on the Phase Behavior and Rheological Properties of Rubber-Modified Asphalt

Two warm-mix modification routes were examined to determine how additive chemistry affects the service-temperature rheology of rubber-modified asphalt. Wax-based and bio-oil-based additives were incorporated at 1–3%, and the resulting binders were characterized by FTIR, dynamic shear rheology, MSCR, LAS, and BBR testing. These measurements respectively provided physicochemical evidence and quantified the phase-related response, deformation recovery, fatigue-related damage tolerance, and low-temperature relaxation. The wax-based system developed a stiffness-oriented response: an intermediate dosage produced comparatively lower Jnr and higher R, but further addition impaired relaxation, with m(60) decreasing to 0.285 at −18 °C for the 3% formulation. In contrast, the bio-oil-based system favored relaxation; at a 3% dosage, the LAS-predicted Nf at 2% strain was 15,200 cycles, while m(60) reached 0.460 at −12 °C and 0.384 at −18 °C. The binder-level evidence therefore identifies different selection priorities: an intermediate wax dosage is advantageous when deformation recovery is emphasized, whereas the bio-oil-based route is more favorable for relaxation and low-temperature response. Additional mixture and workability testing is required before these binder findings are translated into construction-temperature or field-performance recommendations.