IMPROVING THE EFFICIENCY OF ZINC SACRIFICIAL ANODES IN REPAIRED CONCRETE

摘要

Zinc sacrificial anodes are considered an effective and economical method to prevent the electrochemical corrosion of steel bars by providing cathodic current to bars, which can provide corrosion protection at low galvanic current densities in the range of 0.2 to 2 mA/m~2. Sacrificial anodes are commonly used in RC structures particularly in bridge decks to mitigate a critical phenomenon that occurs in the original concrete beside the repaired patches, which is known as the 'halo effect'. One of the key factors affecting the efficacy of zinc anodes is the resistivity of concrete or cementitious repair material in which these anodes are embedded. There is a general notion that the higher the electrical resistivity of concrete or repair material, the less likely that zinc anodes produce the target galvanic current for optimum protection of steel bars. However, no systematic data are available on the maximum allowable electrical resistivity of repair materials/concretes beyond which zinc anodes cannot properly function to prevent corrosion. The specific objective of this study is to explore the effect of concrete resistivity on the efficiency of zinc anodes at mitigating patch accelerated corrosion (halo effect). Concrete slabs were cast to simulate the patch repair technique in the field, and the main parameter in this research was changing the resistivity of the repair section in the slabs (5,000, 15,000, and 25,000 ii-cm). Analysis of results shows a high level of effectiveness of the anode to prevent corrosion up to 20 weeks under a wetting-drying exposure.