Durability Life Assessment of Prestressed Concrete Box-Girder Bridges Considering Chloride Ingress and Carbonation Process Under Realistic Climate

Abstract Harsh environmental conditions (de-icing salts, CO 2 emissions, freeze–thaw, etc.) in northern China threaten the durability of reinforced concrete (RC) highway bridges, with carbonation and chloride ingress acting synergistically. This paper presents an integrated COMSOL framework that couples nonlinear PDEs for heat, moisture, chloride, and CO 2 transport, where carbonation’s effect on chloride diffusion is quantified by the reduction in bound chlorides. The framework is validated against eight-year field data from an in-service prestressed concrete box-girder bridge, showing good agreement (max error ~ 16%). Latin Hypercube Sampling is used for probabilistic reliability-based durability life prediction. The critical vulnerable zone is located at the web–bottom slab intersection of the mid-span section, where the chloride concentration and carbonation depth are at least 1.5 times the corresponding values at the center of the bottom slab. Including the synergistic effect reduces the predicted service life to 81.1 years, compared to carbonation‑ignored scenarios. This framework provides a robust tool for assessing durability under realistic multi‑field coupling.