Microstructural rejuvenation of oxidized asphalt: Synergizing Lewis acid deagglomeration and amine-mediated stabilization

Rejuvenation of oxidized asphalt requires not only restoration of bulk rheological properties but also effective control of aging induced molecular association. This study investigated a mechanism-driven strategy coupling the Lewis acid ferric chloride (FeCl 3 ) with two chemically distinct model co-rejuvenators: a non-polar aromatic oil, phenylcyclohexane (PCH), and a polar antioxidant aromatic amine, 4,4′-dioctyldiphenylamine (ODA). Rheological performance, molecular size distribution, surface morphology, chemical characteristics, thermal mass stability, and durability under extended secondary aging were systematically evaluated. All four rejuvenation schemes substantially restored the macroscopic rheological response of the aged binder, while their physicochemical and long-term behaviors differed substantially. GPC showed pronounced reductions in apparent molecular size after FeCl 3 incorporation, consistent with disruption of asphaltene associations. However, this change was not accompanied by comparable atomic force microscopy (AFM) refinement in the PCH-based compound system, whereas the ODA-FeCl 3 system exhibited a finely dispersed morphology statistically comparable to that of the virgin binder. Infrared analysis further indicated altered oxygenated-group environments, although the specific coordination pathway could not be directly identified. At 165°C, the PCH-based binders exhibited considerably greater mass losses (6.29% and 4.45%) than the ODA-based systems (1.72% and 2.01%). More importantly, after 40 h of secondary PAV aging, the low-temperature cracking resistance indicator, Δ T C , deteriorated to −7.15°C and −13.79°C for P and PF, respectively, but remained positive at 1.99°C and 2.43°C for O and OF. These findings indicate that Lewis acid-induced deagglomeration alone does not ensure durable rejuvenation; stabilization of the dispersed species by a chemically compatible co-rejuvenator is also critical. Chemical deagglomeration with physical stabilization therefore represents a promising framework for designing durable asphalt rejuvenation systems.