Performance Evolution of Hydraulic Concrete under the Coupled Action of Ultraviolet Radiation and Freeze–Thaw Cycles

• The damage conditions of concrete under two different action sequences are investigated. • The performance of concrete is influenced by different damage sequences. • Quantitative damage models under actual environmental conditions were established based on extensive experimental data. The coupled action of ultraviolet (UV) radiation and freeze-thaw (FT) process in harsh high-altitude environments is a critical factor causing the deterioration of hydraulic concrete. In this study, the durability evolution of face panel concrete was systematically investigated under two exposure sequences: UV radiation followed by FT cycles and FT cycles followed by UV radiation. Mass loss, dynamic elastic modulus, ultrasonic pulse velocity, permeability, and compressive strength were measured to analyze the damage mechanisms under different loading sequences. The results showed that exposure sequence significantly influenced the degradation path. UV radiation induced severe initial deterioration and notable mass loss, whereas in the reverse sequence, FT process dominated the damage with limited UV contribution. A damage model based on response surface methodology (RSM) exhibited high predictive accuracy (adjusted R²=0.97) and confirmed a positive synergistic interaction between FT and UV aging. This study provides a theoretical and quantitative basis for the durability design and service life prediction of hydraulic concrete in high-altitude regions.