Sacrificial Anodes for Cathodic Prevention of Reinforcing Steel Around Patch Repairs Applied to Chloride-Contaminated Concrete

摘要

When steel reinforcement suffers localised corrosion in chloride-contaminated concrete, the most anodic regions of the metal effectively provide cathodic protection to the bars in adjacent cathodic areas. If conventional patch repair is applied to the structure, this form of adventitious cathodic protection is removed and bars which were previously behaving as cathodes in moderately contaminated areas may be transformed to anodes of cells, coupled to cathodic steel in the repaired areas. This paper demonstrates the effectiveness of combining patch repair with embedded sacrificial anodes as a means of providing continuing protection to the surrounding reinforcing bars. The sacrificial anodes designed for this purpose consist of metallic zinc in a specially formulated mortar saturated with lithium hydroxide. The high pH pore electrolyte serves to maintain the activity of the zinc, whilst the presence of lithium ions avoids the risks of alkali-silica reaction that would be incurred if other forms of alkali metal hydroxide were used.