Assessment of Degradation in Dynamic Mechanical Properties and Aging Degree of Cement Emulsified Asphalt Mortar under Ultraviolet Aging

The ultraviolet-induced aging of cement-emulsified asphalt (CA) mortar in slab ballastless tracks progressively degrades its dynamic mechanical properties, compromising both ride comfort and operational safety. In order to investigate the ultraviolet (UV) aging of CA mortar, the changes in asphalt components and the degradation patterns of its dynamic mechanical properties were analyzed. Moreover, the linear rheological solid model with a fractional derivative, which accurately reflects the viscoelastic properties of CA mortar, was established to evaluate its UV aging degree. Results showed that CA mortar with an asphalt/cement (A/C) ratio of 0.9 exhibited greater aging sensitivity than that with a ratio of 0.3, with 33% higher increases in asphaltenes, 47% higher increases in dynamic modulus, and the peak loss factor also exhibited a greater decrease after 48 days of UV exposure. Cement enhances the UV-aging resistance of CA mortar by physically shielding asphalt through hydration products and by strengthening cement-asphalt interfacial adhesion at lower A/C ratios, which helps limit light fractions migration and volatilization. The linear rheological solid model demonstrated great fitting accuracy for the dynamic mechanical properties of CA mortar under UV aging, with the fractional order (α) serving as a reliable metric for quantifying the degree of aging.