Viscoelastic Rheology and Constitutive Modeling of Crumb Rubber Modified Asphalt Under Radiation–Low-Temperature Coupled Aging

The asphalt pavements on the Qinghai–Tibet Plateau suffer from severe performance degradation under the coupling effect of intense ultraviolet radiation and cyclic low temperature. Crumb rubber modified asphalt (CRMA) is regarded as a durable pavement material suitable for alpine high-altitude regions, yet the viscoelastic damage mechanism of CRMA under radiation–low-temperature coupled aging remains unclear. In this study, six groups of CRMA specimens with two rubber particle sizes (40 mesh and 80 mesh) and three dosages (10%, 15%, and 20%) were prepared. A laboratory accelerated aging device was adopted to simulate plateau coupled aging with ultraviolet irradiation durations of 0, 4, 6, and 12 months, while rolling thin-film oven aging (RTFO), a pressure aging vessel (PAV), and ozone aging were set as control groups. Dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests were conducted to characterize the high-temperature rutting resistance and low-temperature crack resistance of aged CRMA, and the Burgers viscoelastic constitutive model was employed to quantitatively fit the low-temperature creep curves and analyze the evolution law of constitutive parameters. The results show that prolonged ultraviolet radiation aggravates the hardening and embrittlement of CRMA synergistically: the complex modulus and rutting factor increase continuously, while the phase angle decreases, which improves high-temperature deformation resistance but deteriorates low-temperature performance; the creep stiffness modulus rises, and the creep rate declines, indicating a weakened stress relaxation capacity and elevated cracking risk at low temperatures. Thermal oxidation pre-aging and ozone aging further amplify the coupled aging damage. Increasing the crumb rubber dosage from 10% to 20% simultaneously optimizes the high- and low-temperature durability of aged CRMA. Under the same dosage, 40-mesh coarse rubber powder better enhances the anti-rutting performance at high temperatures, whereas 80-mesh fine rubber powder presents superior low-temperature crack resistance, which is hypothesized to originate from greater interfacial interaction with the asphalt matrix. The Burgers model achieves outstanding fitting accuracy for all creep curves with the coefficient of determination R2 > 0.994, and the four model parameters E1, E2, η1, and η2 can quantitatively reveal the evolution of instantaneous elasticity, delayed elasticity, and viscous flow behavior during aging. For pavement material design in plateau regions, 40-mesh CRMA with a 20% dosage is recommended for high-temperature rutting control, and 80-mesh CRMA with a 20% dosage is preferred to mitigate low-temperature thermal cracking. This work provides theoretical support for the performance evaluation and material optimization of long-life rubber asphalt pavements serving in extreme plateau environments.