鉄筋コンクリートの防食電流・電位の変動要因と防食効果

抄録

Protecting steel bars in concrete against corrosion through the use of cathodic protection system has been successfully used for marine structures as the most effective method in controlling corrosion current taking place in reinforced concrete. DC current flowing into steel bars in concrete is required to be uniformly distributed, which is essential in controlling the corrosion via lowered potentials along the steel bars. The design criteria commonly used for the cathodic protection is a polarization measured on the steel bars which is greater than 0.1V immediately after power supply stops (instant-off). It has been pointed out that the current distribution varies owing to the heterogeneity of composite materials in concrete including moisture distribution and chloride ion concentration, defects typically present in concrete including cold-joint and cracks and the deterioration stages such as incubation and propagation periods. This led to variations observed in the potentials which may result in unsatisfactory protection potentials. In this study, the influence of localized defects and corrosion on the current density and potentials were examined using segmented steel bars embedded in concrete, which was investigated via electro-chemical measurements. Based on findings, a design criteria required for reinforced concrete with defects in the case of chloride-induced corrosion was shown in controlling the potential on the steel bar below -0.85V vs. CSE reference electrode especially during propagation period.