Ultraviolet-induced aging of bitumen in the context of climate change: a critical review of chemistry and mitigation strategies

Climate change is accelerating the long-term deterioration of asphalt pavements, with ultraviolet (UV) radiation increasingly recognised as a key driver of photo-oxidative ageing (POA). Despite its importance, the photochemical mechanisms, depth-dependent oxidation behaviour, and links between molecular-scale changes and pavement performance remain insufficiently resolved. This review synthesises recent advances in bitumen chemistry, molecular dynamics simulations, and depth-resolved spectroscopic techniques to clarify UV-induced oxidation pathways and their implications for rutting, cracking, adhesion, self-healing, and durability. Current mitigation strategies, including polymer modification, UV absorbers, antioxidants, and nanotechnology-based additives, are critically assessed, together with emerging multifunctional solutions such as hybrid systems and bio-derived modifiers aimed at suppressing radical formation and enhancing binder stability. Cost implications and life-cycle performance considerations are also discussed. Finally, future research directions are outlined, emphasising integrated laboratory ageing protocols and instrumented field studies to establish predictive relationships between molecular degradation kinetics and pavement performance under intensified UV exposure.