The Effects Of Shielding On Current Distribution In Impressed Current Cathodic Protection In Reinforced Concrete

Cathodic protection (CP) has been widely used to protect steel reinforcement in concrete structures against corrosion. Distribution of the protective current is known to directly affect the performance of a CP system, but the specific impacts of multiple layers of steel on performance has not been definitively established. When surface mounted (or near-surface) anodes are used, the distribution of current to deeper reinforcement is influenced by the presence of steel layers between the concrete surface and the deeper reinforcement. In addition to attenuation caused by concrete resistance, a reduction in current to the inner layers is observed as a result of the obstructive influence of outer layers, an effect referred to as ‘shielding’. The study presented here evaluates the shielding effect through a simple experiment where a fixed current was applied to three concrete specimens with steel bars arranged in layers from the surface anode. The total amount of current flowing to each layer was logged, along with the polarisation of each layer (as measured using embedded reference electrodes). The shielding effect was clearly demonstrated from the results obtained. The findings suggest that reinforcement layers in closest proximity to surface-mounted anodes may be susceptible to over-protection, whereas the inner layers in scenarios where protection may be necessary, face a risk of under-protection.