Abstract
The criterion of 100 mV depolarization is adopted in many cases of cathodic protection (CP) for reinforced concrete under atmospheric conditions. This criterion is very applicable and its validity is confirmed in many cases. However, it is not suitable for members under high moisture conditions such as upper members of piers, which are exposed to splash and tidal zones. Due to poor diffusion of oxygen into the concrete, the potential of steel in the concrete does not shift to a noble value after the CP current is interrupted. In this paper, another criterion, “less noble than -850 mV vs. Saturated Copper Sulphate Electrode (CSE)” (-850 mV) was examined for specimens in a laboratory. The results show that under the 100 mV depolarization criterion, it was difficult to control the current density in order to gain the 100 mV depolarization. On the other hand the -850 mV criterion is more applicable under high moisture conditions. It is also found that the pH of the corrosion spots of the rebars decrease to pH4 due to hydrolysis of Fe2+ ions. And corrosion products on the steel are seemed to be reduced by the CP current.
