Evaluation of bond strength degradation between FRP bars and normal concrete under seawater exposure: An explainable modeling approach

The harsh conditions in corrosive environments impose critical demands on the durability of concrete structures. The replacement of steel reinforcement with corrosion-resistant fibre-reinforced polymer (FRP) bars offers a viable solution for enhancing structural durability. The bond strength retention (BSR) is a significant factor in evaluating the bond durability between FRP bars and concrete. The traditional methods face significant challenges in accurately assessing bond durability due to the complexity of corrosion mechanisms. To address the challenges, this paper presented a novel approach for predicting the BSR between FRP bars and concrete under seawater immersion using explainable modelling. A dataset of 153 pull-out test data points incorporating 12 parameters was compiled, and a Random Forest (RF) model was developed, achieving an R2 of 0.954 and 0.937 on training and testing sets, respectively. SHAP (SHapley Additive exPlanations) analysis was employed to interpret the prediction results, revealing the significance and influence patterns of the input parameters. The effects of input parameters, including the properties of FRP bars, concrete, environmental effects and bond, were analysed and discussed in detail. Furthermore, an explicit equation for predicting BSR was derived based on SHAP analysis, exhibiting superior accuracy (R2 of 0.836) and applicability compared to existing methods based on Fib Bulletin 40 (R2 of 0.795) and Arrhenius relationship (R2 of 0.186 and -1.830). The proposed approach provides valuable insights for designing durable marine structures and other engineering applications in corrosive environments.