Sustainable flexible pavements: a comprehensive review of waste plastic, crumb rubber, and basalt fiber integration

Rapidly increasing traffic loads and climatic variations have accelerated the deterioration of flexible pavements. At the same time, the exponential accumulation of solid waste, such as plastic packaging and end-of-life tires, presents a severe global environmental crisis. To address these dual challenges, this literature review evaluates the integration of waste plastic, crumb rubber, and basalt fiber as modifiers and reinforcing agents to simultaneously enhance road durability and mitigate waste disposal issues. By synthesizing recent experimental studies, life-cycle assessments, and field applications, the review examines various incorporation techniques, including the "dry process" for coating aggregates with plastic, the "wet process" for blending rubber and polymers into bitumen, and the three-dimensional dispersed reinforcement mechanism provided by basalt fibers. Investigations reveal that waste plastics (such as high-density polyethylene, low-density polyethylene, and polyethylene terephthalate) significantly increase Marshall stability, minimize aggregate water absorption, and substantially enhance resistance to high-temperature rutting. Similarly, crumb rubber-modified bitumen substantially improves the binder's viscosity, elastic recovery, and resistance to fatigue and thermal cracking. Furthermore, the introduction of basalt fiber provides structural reinforcement that amplifies flexural tensile strength, frost resistance, and overall durability against climatic fluctuations. At the same time, hybrid combinations of these materials demonstrate an optimized balance between mixture stiffness and elasticity. Ultimately, transitioning to emissions- and e-modified, and fiber-reinforced asphalt mixtures extends the service life and structural integrity of road networks, lowers life-cycle construction costs, significantly reduces carbon footprint emissions, and firmly anchors civil infrastructure development within the principles of a circular economy.