Composition–structure–property relationships of crumb rubber modified asphalt under strong radiation–low temperature coupled aging

High-altitude and high-latitude pavements suffer simultaneous intense UV radiation and low temperatures, accelerating asphalt photo-oxidative aging and low-temperature cracking. This work explores aging mechanisms and cryogenic performance of 10%/15%/20% crumb rubber modified asphalt (CRMA) with 40/80-mesh rubber under radiation-low temperature coupled aging, plus RTFO, PAV and ozone aging. BBR tests from −6 to −24 °C characterize low-temperature rheology; SARA, GPC and FTIR capture microchemical changes. Coupled aging raises creep stiffness S, reduces m-value, consumes light fractions, accumulates heavy components, enlarges macromolecules and generates carbonyl/sulfoxide groups. The number-average molecular weight, Mn, dominates low-temperature rheology. Higher rubber dosage (20%) and finer 80-mesh rubber slow component transformation and molecular aggregation, preserving relaxation capacity. Grey correlation and ridge regression prove S depends on heavy fractions while m responds more to light fractions, with optimal m prediction at −24 °C. Crumb rubber alleviates UV-cold coupled hardening by buffering light fractions and inhibiting molecular aggregation, offering micro-macro guidance for cold high-radiation asphalt design.