Temperature-Dependent Tensile Degradation of HDPE Sheaths for Bridge Cables Considering UV–Chloride Exposure

As the principal load-bearing components of cable-supported bridges, cables are critical to structural safety, and their durability is strongly governed by the integrity of high-density polyethylene (HDPE) sheaths. Prolonged exposure to ultraviolet (UV) radiation and chloride-rich environments can significantly degrade the mechanical performance of HDPE sheaths. To clarify the degradation behavior, HDPE sheaths were pre-exposed to UV alone, chloride alone, or a sequential two-stage UV–chloride protocol (with a single switch). Subsequently, uniaxial tensile tests were performed at different loading temperatures. The yield strength and O–A secant modulus decreased monotonically with increasing pre-exposure duration. A pronounced sequence effect was observed, with UV pre-exposure followed by chloride exposure causing greater deterioration than the reverse order. Under UV alone, the maximum reductions in yield strength and O–A secant modulus were 19.81% and 46.21%, respectively; under chloride alone, they were 10.97% and 22.00%; and under the sequential UV–chloride exposure, they were 31.97% and 26.24%. Moreover, the tensile response showed strong temperature sensitivity: under otherwise identical pre-exposure conditions, the yield strength measured at 60 °C was 64.89% lower than that measured at −10 °C, representing the maximum reduction within the investigated temperature range.