Durability of coastal RC envelopes in salt-spray environments: A study through integrated normalized phase-field and dynamic THMC modeling

Abstract

The long-term performance of building envelopes in coastal regions is severely challenged by salt spray, humidity, and wind-driven rain, which accelerate chloride ingress, steel corrosion, and cracking in reinforced concrete (RC) structures. To accurately capture the coupled degradation processes, this study develops an integrated computational framework that combines a normalized phase-field fracture model with dynamic thermo-hydro-mechanical-chemical (THMC) simulations. The phase-field variable serves as a unified bridge linking corrosion-induced expansion, crack evolution, and multi-physical transport processes—including chloride penetration, oxygen diffusion, and coupled heat and moisture transfer. A staggered solution scheme with adaptive time-stepping ensures numerical stability under strong nonlinearities. The model is validated against experimental and field data, showing relative errors below 15%. Simulations of representative coastal RC walls reveal a four-stage corrosion-cracking process: ingress/induction, expansion accumulation, exponential crack acceleration, and stable propagation. Key findings include: (1) subsurface peak chloride concentrations due to leaching–re-enrichment under wind-driven rain; (2) asymmetric degradation, where moisture and chloride transport amplify by > 100% after cracking, versus < 8% change in thermal properties; and (3) crack-enhanced positive feedback loops that accelerate deterioration. SHAP-based sensitivity analysis identifies crack damage and maximum crack width as dominant factors in later stages (>50% contribution to transport property decline), surpassing environmental variables after initial chloride ingress. The results underscore the critical role of cover thickness in delaying crack interconnection and provide mechanistic insights for the durable design of coastal concrete building envelopes under aggressive marine climates.