Chemo-Mechanical Recovery of Aged Asphalt Binders: Evaluating Bio-Rejuvenators Across Multiple Life Cycles

Efforts to promote circular economic strategies in road infrastructure require evaluating asphalt binder recyclability under repeated aging and rejuvenation. This case study investigates three modified binders in the United Arab Emirates (UAE): terminally blended rubberized bitumen, crumb rubber modified binder, and styrene-butadiene-styrene polymer modified bitumen. A two-cycle laboratory protocol simulated service life in hot climate using Rolling Thin Film Oven (RTFO) aging followed by Pressure Aging Vessel (PAV) conditioning, including an extended aging duration to represent end-of-life binder states. Two bio-based rejuvenators sourced from renewable waste streams were applied at supplier-recommended dosages and evaluated through integrated mechanical, chemical, and thermal analyses. Mechanical recovery was assessed using Dynamic Shear Rheometer (DSR) master curves and relaxation indicators, with embrittlement tracked using the Glover-Rowe parameter. Chemical restoration was quantified using Fourier Transform Infrared Spectroscopy (FTIR) oxidation markers (carbonyl and sulfoxide indices) and ester signatures indicating rejuvenator uptake. Thermal resilience was evaluated using Differential Scanning Calorimetry (DSC) through shifts in glass-transition temperature. Terminally blended rubberized bitumen achieved the most balanced recovery in stiffness, relaxation, and thermal behavior, particularly with the second rejuvenator, and retained meaningful performance after re-aging. Crumb rubber modified binder showed greater oxidation sensitivity but maintained durable recovery across the second cycle. Polymer modified bitumen exhibited modest relaxation recovery yet clear chemical and thermal restoration, consistent with partial irreversibility of polymer-network aging. Overall, results indicate that multi-cycle bio-based rejuvenation can extend service life, reduce reliance on virgin materials, and support agency recycling frameworks aligned with circular economic objectives.