Water vapor diffusion in cracked HDPE sheaths of bridge cables under ultraviolet radiation, coupled environmental temperature-humidity and alternating strain

The diffusion mechanism of water vapor in cracked high-density polyethylene (HDPE) sheaths of cable-stayed bridges under alternating strain remains unclear, limiting durability assessments. Here we investigate vapor diffusion in cracked HDPE sheaths under coupled temperature–humidity and alternating strain using a custom gravimetric penetration device; cracks were introduced via alternating UV–fatigue pretreatment. Experiments show that UV degradation reduces mechanical integrity and increases microchannel density, enhancing vapor ingress; the diffusion flux J scales linearly with the inside–outside RH difference Δ RH , while the diffusion coefficient D exhibits an Arrhenius temperature dependence. Alternating strain widens crack micro-pores and raises D by 6–10% via an influence factor f ( ε ). Integrating Fick’s law with measurements, we formulate a diffusion-coefficient model D (T, ΔRH, ε , A ) that incorporates temperature–humidity coupling, strain effects, and equivalent crack area; multivariate analysis ranks governing factors as temperature > strain magnitude > crack area > strain period > RH difference. The model predicts time-to-critical humidity from environmental conditions and A , directly informing sheath sealing/coating and maintenance decisions and bridging key gaps in environmental–load coupled degradation of cable sheaths. • The HDPE diffusion flux linearly correlates with the relative humidity gradient and increases exponentially with temperature, following the Arrhenius equation • An influence factor f ( ε ) quantifying strain-induced moisture diffusion enhancement was established. • A computational model for cracked HDPE diffusion coefficients was developed, incorporating temperature-humidity coupling and alternating strain effects. • Multivariate regression analysis identified key factors affecting diffusion coefficients