The Response of Protective Current to Environmental Conditions During Hybrid Anode Concrete Repair Treatments

A favourable feature of galvanic anodes used in concrete repair is the variation of their current output in response to changing environmental conditions, such as concrete moisture content, chloride content and temperature. This means that the anodes provide more protective current to the steel reinforcement when the environment is aggressive and less current when it is more benign, thus conserving sacrificial anode life.

Over the last two years, the current outputs of several hybrid anode systems installed in laboratory made concrete samples have been monitored with respect to changes in temperature, moisture and chloride content (variable concrete resistivity). The study analysed both the impressed current and galvanic phases of the hybrid anode treatment. The aim was to investigate the relative effects of environmental parameters on the protective current output.

The results confirmed that the applied anode systems were responsive to variations in concrete resistivity brought about by changes in environmental conditions during both the impressed current ‘re-alkalisation’ and galvanic ‘pH maintenance’ treatment phases. The data also showed that the impressed current treatment significantly increased the protective current passed to the steel during the galvanic phase, especially in aggressive environments.

The data collected fits better with the Pit Re-alkalisation model for corrosion monitoring of steel in atmospheric concrete, rather than the Pitting Potential model used frequently in the industry.