# Chloride Resistance of Assembled Bridge Piers Reinforced with Epoxy-Coated Steel Bars
## 4 Service Life Prediction
### Simulation Results  
Figure 20 presents the numerical simulation results of Joint 1, including a contour map of chloride ion concentrations after 200 years of natural diffusion and time-varying curves of chloride ion concentrations on the surface of steel bars over a 200-year simulation period. From Figure 20a, it is evident that the chloride ion concentrations are ranked from highest to lowest as follows: post-cast strip interface > pier body > post-cast strip. This ranking corresponds to the order of the chloride ion diffusion coefficients (\(D_{\rm NSSD}\)) for each material and interface. Although the \(D_{\rm NSSD}\) at the post-cast strip interface is 4 to 5 times higher than that of the adjacent concrete, the concentration and penetration depth of chloride ions at the interface do not show a proportional relationship due to the two-dimensional diffusion of chloride ions. In Figure 20b, the chloride ion concentration on the surface of the steel bars within the post-cast strip interface is higher than that within the pier body segment associated with defects at the interface, which facilitates a faster transportation \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Joint Type** & \multicolumn{3}{c}{**Joint 1**} & \multicolumn{3}{c}{**Joint 2**} \\ \hline
**Treatment Method** & **Bent** & **Knocked** & **Untreated** & **Bent** & **Knocked** & **Untreated** \\ \hline \(C_{\rm cr}/(\rm mol/m^{3})\) & 79 & 150 & 163 & 29 & 48 & 65 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Critical chloride ion concentration. rate of chloride ions. Additionally, the distance between the two curves gradually increases during the early stages of diffusion and then slows down in the later stages, indicating that as chloride ion diffusion progresses, the concentrations at different locations on the steel bar surfaces reach a certain level and gradually stabilize. As the critical chloride ion concentration values for the steel bars in Table 5 correspond to the concentration on the surface of bars within the pier body, the data from the time-varying curve of chloride ion concentration on the surface of steel bars within the pier body in Figure 20(b) were exported and re-plotted usingOrigin 2022. Then, the service life of Joint 1 using different types of steel bars can be predicted, as illustrated in Figure 21. The results indicate that even using bent steel bars with a coating damaged area ratio of about 4%, the service life of Joint 1 can still reach 122 years, while using steel bars that have been knocked or untreated could extend the service life to over 200 years (assuming no epoxy coating aging effects). This demonstrates that Joint 1 has a strong resistance to chloride ion erosion and that the integrity of the epoxy coating has a significant impact on the joint's service life. Figure 21: The service life prediction for Joint 1. Figure 20: Numerical simulation results of Joint 1. Figure 22 presents the numerical simulation results of Joint 2, including a contour map of chloride ion concentrations after 200 years of natural diffusion and time-varying curves of chloride ion concentrations on the surface of steel bars over a 200-year simulation period. Due to the effects of concrete and mortar shrinkage, coupled with the lack of prestressing, the vertical grouting interface in Joint 2 is prone to cracking (as evidenced in Figure 13b, where the chloride ion content at the grouting interface in Joint 2 is considerably high). Considering the most unfavorable scenario, the diffusion coefficient of chloride ions at the vertical grouting interface in Joint 2 is assumed to be the same as that in water. In Figure 22a, the chloride ion concentration at the grouting interface is significantly higher than at other locations, consistent with the phenomena observed in Section 3.4 of the experiments.