Rheological and aging performance of reclaimed asphalt binders modified by warm mix additive and recycling agent

Asphalt recycling promotes sustainable pavement construction but is limited by binder aging, stiffness, and decreased durability. Recycling agents (RAs) can improve ductility and low-temperature cracking resistance but often lower rutting resistance, whereas most warm-mix additives (WMAs) improve workability, rutting resistance, and aging durability while decreasing low-temperature flexibility. Despite these opposing effects, the combined use of high reclaimed asphalt binder (RAB) contents and their properties under aging has received little attention. This work assessed the rheological and aging properties of hot- and warm-mix asphalt binders containing 30% and 50% RAB, respectively, modified by an aromatic extract RA and Sasobit^® WMA additive. Binders were analyzed in unaged, RTFO-, and PAV-aged conditions by rotational viscosity (RV), flow activation energy (FAE), multiple stress creep recovery (MSCR), linear amplitude sweep (LAS), frequency sweep, and bending beam rheometer (BBR) tests. It was found that RAB increased viscosity and thermal stability but decreased fatigue life and low-temperature cracking resistance. WMA reduced viscosity by approximately 20% in the unaged state, improved aging resistance, decreased rutting susceptibility, and reduced J_nr from 9.50 in the control binder to 0.85 in 50% RAB binders without RA addition. RA reduced viscosity by 30-70% and restored PG grades by one to two levels, but it worsened rutting resistance, increasing J_nr by 30-190% and diminishing percent recovery ®). Their combination, however, exerted a synergistic effect: RA enhanced the fatigue life (N_f) of WMA-RAB binders by 70-270% (e.g., PAV-aged 50% RAB-WMA's N_f rose from 100,000 cycles to 378,000 cycles as a result of adding RA) and outperformed even neat WMA binders, while WMA reversed the detrimental effect of RA on rutting performance. BBR testing confirmed that although RAB accelerated embrittlement (reducing grades to PG XX-16 or below), RA consistently restored one to two low-temperature PG grades even under PAV aging, mitigating cracking susceptibility and aligning with LAS improvements in fatigue life. Overall, the RA and WMA integration resulted in binders with a good balance of rheological performance, enhanced aging durability, and superior fatigue and low-temperature resistance, thus presenting a workable approach toward the production of high-quality, sustainable, and high-RAP pavements.