## 3 Results and Discussion
### Characterization of Steel Reinforcement Passivation Based on Electrochemical Impedance Spectrum
The observation that the electrode resistance reaches a relatively stable state after the fifth day highlights the significance of the protective oxide film in safeguarding the steel electrode from corrosion. The film's ability to establish a high-impedance barrier effectively curtails further corrosion reactions. It is noted that the 7-day R\({}_{\text{s}}\) value is about 2-3 times the 3-day R\({}_{\text{s}}\) value, which may be attributed to the difference in electrode spacing. Figure 6 presents the variation pattern of the electrode resistance with time during the passivation process. Notably, this pattern is consistent with the variation pattern of the open-circuit potential. After an initial increase in impedance, a relatively stable state is reached after the fifth day. This observation further validates the assertion that the protective oxide film on the steel electrode surface achieves a stable state that provides effective corrosion protection. Overall, these results suggest that as the soaking test progresses, the steel electrode's passivation process--marked by the formation and growth of an oxide film--contributes significantly to an increase in the electrode impedance and resistance. By extension, this passivation process provides a reliable protective layer that guards against corrosion, promoting the long-term stability and durability of steel components in concrete structures. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Passivation** & **R\({}_{\text{s}}\)** & \multicolumn{2}{c}{**CPE\({}_{\text{f}}\)**} & \multicolumn{2}{c}{**R\({}_{\text{f}}\)**} & \multicolumn{2}{c}{**CPE\({}_{\text{dl}}\)**} & \multicolumn{2}{c}{**R\({}_{\text{ct}}\)**} & \multicolumn{2}{c}{**R\({}_{\text{p}}\)**} \\
**Time (d)** & **(\(\Omega\cdot\)cm\({}^{2}\))** & **Q\({}_{\text{f}}\) (uF\(\cdot\)s\({}^{\text{n}}\))** & **n\({}_{\text{f}}\)** & **(k\(\Omega\cdot\)cm\({}^{2}\))** & **Q\({}_{\text{dl}}\) (uF\(\cdot\)s\({}^{\text{n}}\))** & **n\({}_{\text{dl}}\)** & **(k\(\Omega\cdot\)cm\({}^{2}\))** & **(k\(\Omega\cdot\)cm\({}^{2}\))** \\ \hline
0 & 43.32 & \(4.81\times 10^{-11}\) & 0.909 & 39.967 & \(5.76\times 10^{-11}\) & 0.935 & 0.095 & 40.105 \\
1 & 51.08 & \(4.06\times 10^{-11}\) & 0.932 & 217.96 & \(3.57\times 10^{-11}\) & 0.873 & 38.317 & 256.328 \\
2 & 56.10 & \(3.90\times 10^{-11}\) & 0.915 & 378.00 & \(3.40\times 10^{-11}\) & 0.830 & 230.290 & 608.346 \\
3 & 62.47 & \(3.71\times 10^{-11}\) & 0.919 & 468.82 & \(3.10\times 10^{-11}\) & 0.816 & 407.000 & 875.882 \\
4 & 143.90 & \(3.34\times 10^{-11}\) & 0.923 & 546.02 & \(2.86\times 10^{-11}\) & 0.829 & 431.150 & 977.314 \\
5 & 76.37 & \(3.55\times 10^{-11}\) & 0.921 & 600.37 & \(3.15\times 10^{-11}\) & 0.846 & 475.360 & 1075.806 \\
6 & 76.24 & \(3.57\times 10^{-11}\) & 0.917 & 604.85 & \(2.97\times 10^{-11}\) & 0.882 & 449.170 & 1054.096 \\
7 & 175.4 & \(3.29\times 10^{-11}\) & 0.924 & 599.12 & \(2.83\times 10^{-11}\) & 0.837 & 465.310 & 1064.605 \\
10 & 82.81 & \(3.52\times 10^{-11}\) & 0.921 & 619.07 & \(3.13\times 10^{-11}\) & 0.847 & 505.560 & 1124.713 \\ \hline \end{tabular}
\end{table} 
Table 1: The electrochemical parameters of steel reinforcement passivation tested by EIS.