Abstract
Bitumen, as the primary binding component in asphalt mixtures, plays a defining role in determining the structural integrity, durability, and overall performance of road pavements. However, unmodified bitumen frequently proves inadequate under the combined pressures of increasing traffic loads, extreme temperature cycles, moisture infiltration, and accelerated oxidative aging — challenges that are intensifying in the context of modern infrastructure demands. Modifiers introduced into bitumen composition serve a fundamental purpose: they alter the internal microstructure of the binder, improving its rheological properties, extending its service temperature range, and enhancing resistance to deformation, fatigue cracking, and premature aging. This review critically examines the specific roles that two major classes of sustainable modifiers — bio-based resins (including gossypol resin and technical lignin) and post-consumer recycled thermoplastics (polypropylene, polyethylene grades, and polyethylene terephthalate) — fulfill within bitumen composition. Bio-based resins integrate into the bitumen matrix through physico-chemical interactions that reinforce the colloidal structure, reduce oxidative susceptibility, and improve lowtemperature flexibility, while recycled thermoplastics form polymer networks within the binder that dramatically increase stiffness and rutting resistance at elevated service temperatures. Beyond performance improvements, these modifier classes address pressing contemporary problems: the depletion of high-quality petroleum resources, the accumulation of plastic waste in landfills and ecosystems, growing regulatory pressure to reduce the carbon footprint of construction materials, and the economic burden of frequent road maintenance and rehabilitation.