## 5 Results and Discussions
### Depolarization Potential Measurement  
Next, the depolarization potential was measured over 4 years. As mentioned previously, seven columns of the reinforced concrete bridge structure were equipped with an SACP system with conductive mortar over four years, and the measurements were conducted seven times. The 4 h depolarization potential was measured using the instant-off test, excluding the IR drop that appeared at the beginning of the measurement stage. Specifically, there was a sharp change at the beginning of the measurement (within one second) called the IR drop. It was not considered in depolarization calculations. As previously mentioned, a conductive mortar with 5% activated carbon was considered. Table 3 and Figure 10 summarize the depolarization potentials of several piers over four years. Because the SACP system with general mortar was already in operation before replacing the SACP system with conductive mortar, the results with general mortar on the respective piers are included for comparison. Of course, the general mortar was replaced by conductive mortar due to its low protection efficiency. The data provided in Figure 10 for general mortar were based on the most recent data measured when the SACP system with general mortar was applied before SACP with conductive mortar was considered. The results indicate that depolarization potentials of 100 mV or more were measured in the four bridges after four years, satisfying the criteria set by the NACE standard. However, the remaining three bridges did not satisfy these criteria. Moreover, the CP effects tend to decrease over time. For up to 18 months, most of the columns with conductive mortar exhibited depolarization potentials of over 100 mV. However, after two years, there was a gradual increase in the possibility of partial protection in some piers with a depolarization potential of less than 100 mV, although they were still maintained at a certain level. Furthermore, compared to the original SACP system with general mortar (black bar), the columns with conductive mortar exhibited superior CP effects, with more sustainable protection overall. Considering the variations in sacrificial anode behavior due to surrounding environmental factors (e.g., tidal variation and humidity), slight differences in the measurement values can occur. Given the exposure of the concrete structure to high and low tides twice a day, the overall performance of the CP system was considered smooth. \begin{table}
\begin{tabular}{c c c c} \hline
**Item** & **Unit** & **Test Results** & **Quality Standards** \\ \hline Flexural strength & N/mm\({}^{2}\) & 6.50 & 6.0 or more \\ \hline Compression strength & N/mm\({}^{2}\) & 42.10 & 20.0 or more \\ \hline Bonding strength (standard condition) & N/mm\({}^{2}\) & 2.30 & 1.0 or more \\ \hline Bonding strength (after repeating warming and cooling) & N/mm\({}^{2}\) & 1.60 & 1.0 or more \\ \hline Permeability quantities & g & 6.30 & 20.0 or less \\ \hline Water absorption coefficient & kg/m\({}^{2}\)h\({}^{0.5}\) & 0.09 & 0.5 or less \\ \hline Moisture permeation resistance & m & 1.00 & 2.0 or less \\ \hline Length variation ratio & \% & \(-\)0.08 & within \(\pm\)0.15 \\ \hline \end{tabular}
\end{table} 
Table 2: Property of conductive mortar including 5% activated carbon. To support the hypothesis that CP workability is acceptable even if a few columns have depolarization potentials of less than 100 mV after four years, a visual inspection was conducted. Since the only way to visually check the corrosion and anticorrosion condition of the rebar embedded inside the concrete is through the coring, a separate segment was installed in the lower part of the pile, in order not to destroy the concrete, for checking the corrosion and protection status of the rebar. One segment was electrically connected to the sacrificial anode, and the other segment was exposed to the corrosive environment without being connected to the sacrificial anode.