High-Temperature Rheological Evolution of Recovered Asphalt Composite Binders Under Laboratory Long-Term Aging Protocols

Asphalt mixtures are heterogeneous composite materials primarily composed of mineral aggregates and asphalt binder; depending on the mixture design, they may also incorporate reclaimed asphalt pavement (RAP) and polymer-modified binders. Their long-term performance is governed by the rheological evolution of the asphalt binder and its interactions with surrounding composite constituents during aging. Existing laboratory long-term aging (LTA) protocols have been developed primarily to evaluate mixture cracking resistance; however, their ability to reproduce the high-temperature rheological evolution of recovered asphalt binders remains insufficiently understood. This study evaluated the fidelity of accelerated LTA protocols by comparing the high-temperature rheological response of binders recovered from plant-produced asphalt mixtures with the conventional benchmark of 85 °C for 5 days. Five mixtures, including one containing an unmodified PG 67-22 binder with RAP and four containing SBS-modified PG 76-22 binders with varying RAP contents, were characterized using continuous high-temperature performance grade (PG-HT), dynamic shear rheometer rutting parameter (|G*|/sinδ), zero-shear viscosity, multiple stress creep recovery, and interrupted shear flow. Among the investigated protocols, loose-mixture aging at 135 °C for 6 h showed the closest agreement with the benchmark rheological response, whereas 135 °C for 8 h and 120 °C for 20 h produced greater rheological stiffening relative to the benchmark. The unmodified PG 67-22 binder exhibited the greatest aging sensitivity, while SBS-modified binders showed closer agreement overall.