## 5 Results and Discussions
### Depolarization Potential Measurement
As shown in Figure 11, after four years, it can visually confirm the results that the steel segment under CP does not exhibit corrosion, while the segment without protection shows significant corrosion. This indicates that the CP of the target bridge effectively prevented corrosion. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Period** & **P2C2** & **P2C1** & **P3C1** & **P4C5** & **P7C1** & **P8C3** & **P8C1** \\ \hline \
\begin{tabular}{c} Before using \\ conductive mortar \\ \end{tabular} & 10 & 173 & 10 & 31 & 31 & 10 & 10 \\ \hline \multirow{4}{*}{
\begin{tabular}{c} After \\ using \\ conductive \\ \end{tabular} } & 1 month & 150 & 155 & 177 & 158 & 195 & 103 & 160 \\ \cline{2-8}  & 6 months & 146 & 102 & 187 & 144 & 79 & 130 & 91 \\ \cline{2-8}  & 12 months & 210 & 150 & 165 & 122 & 133 & 123 & 112 \\ \cline{2-8}  & 18 months & 108 & 70 & 126 & 115 & 112 & 118 & 155 \\ \cline{2-8}  & 24 months & 75 & 72 & 205 & 136 & 109 & 208 & 72 \\ \cline{2-8}  & 36 months & 60 & 52 & 145 & 82 & 117 & 220 & 102 \\ \cline{2-8}  & 49 months & 65 & 50 & 181 & 88 & 108 & 250 & 122 \\ \hline \end{tabular}
\end{table} 
Table 3: Depolarization measurement results for four years (unit is in mV). Figure 10: Depolarization measurement results for four years. The results of the depolarization potential and visual inspection are discussed below. If the steel is surrounded by seawater or underground, sustainable protection exists under low resistivity. This can result in a consistent depolarization potential of 100 mV or higher. However, in concrete, which has high resistivity, the measured depolarization potential may not consistently exceed 100 mV, depending on the measurement environment. The target bridge, located in an area where it is exposed to tidal fluctuations twice a day, faces challenges in achieving a depolarization potential exceeding 100 mV when the structure duties out after the seawater level recedes. In such cases, it is presumed that the corrosion of the reinforcement in the structure is halted or reduced. On the one hand, during high tide when the structure is submerged in seawater, depolarization potential exceeding 100 mV is expected, indicating no issues with protection. Moreover, several piers had depolarization potentials of less than 100 mV. In this case, the amount of activated carbon in the conductive mortar can be adjusted to allow more conductivity, resulting in an enhanced current flow. Therefore, the amount of activated carbon could be adjusted depending on the surrounding environment under the condition that the physical properties of conductive mortar satisfy the standards. The results of the pilot test demonstrated the feasibility of the conductive mortar application to the SACE system. Further investigations of actual marine structures can be  
Figure 11: Noncorroded steel segment before CP operation (**a**), location of steel segment (**b**), and results of visual inspection of corrosion with and without CP (**c**). performed with different amounts of conductive mortar to determine whether the amount of activated carbon plays a key role in the variation in CP performance.