Experiment-Based Simulation of Rust Propagation and Coalescence for Determining Repainting Timing of Heavy-Duty Coated Steel Bridges

This study proposes a simulation model to evaluate the long-term rust propagation behavior of heavy-duty coating systems for steel structures and support estimating repainting timing. An Indoor Cyclic Corrosion Test (Indoor CCT) was conducted for 24,000 h to validate the proposed model using experimental results obtained from coating systems for steel structures. The rust propagation behavior from initial defects was analyzed using sigmoid regression, and the area increase induced by the coalescence of adjacent rust regions was quantitatively incorporated into the model. The validation results showed that the differences between the simulated and Indoor CCT results ranged from −7.80 to 3.00%p. Furthermore, the model was cross-validated against seven-year outdoor exposure data obtained under an ISO 9223 C3 corrosivity environment. Finally, maintenance repainting timing was quantitatively estimated with reference to ISO-based criteria using the proposed model.