Agricultural By-Products, Biowastes, and Other Biogenic Materials as Bio-Rejuvenators for Aged Bituminous Binders: Mechanisms, Performance, and Challenges

Asphalt binders become stiffer and more brittle during aging, increasing their susceptibility to fatigue and thermal cracking. Rejuvenation is therefore a key strategy for restoring aged bitumen and enabling the effective use of reclaimed asphalt materials. This review examines agricultural by-products, biowastes, and other biogenic materials as bio-rejuvenators for aged bituminous binders. The reviewed materials are classified according to their source, processing route, functional role, chemical characteristics, rejuvenation mechanism, performance effects, and practical limitations. The main groups include waste cooking oils, virgin vegetable oils, reactive bio-oils, biomass-derived bio-oils, agricultural and forestry residues, tree-resin-derived products, animal-based rejuvenators, and other organic waste-derived materials. The literature indicates that these materials can restore aged bitumen through light fraction replenishment, colloidal rebalancing, diffusion, asphaltene deagglomeration, chemical interaction, and anti-aging effects. Waste cooking oils and agricultural/forestry residue-derived rejuvenators provide particularly strong recovery of conventional binder properties, whereas reactive bio-oils and tree-resin-derived systems offer a more balanced rheological response and cracking–rutting balance. However, their effectiveness strongly depends on dosage, feedstock variability, binder compatibility, processing route, and aging condition. Overall, bio-rejuvenators offer a promising pathway for sustainable asphalt recycling, but their practical implementation requires standardized dosage selection methods, long-term aging assessment, mixture- and field-scale validation, and life-cycle evaluation.