Patch repairs are a common repair technique for corrosion-damaged reinforced concrete structures.
When you undertake a concrete patch repair with a proprietary cement-based repair material you turn the repaired area from an anodic zone into a cathodic zone due to the highly alkaline nature of the new cement.
Removing the spalled concrete that is saturated with chlorides causes a redistribution of the anodic and cathodic sites and new anodic zones are formed around the perimeter of the patch repair.
Area prior to repair with the anodic zone shown in Red
Area post repair with the anodic zones now forming around the perimeter of the repaired area.
If untreated these newly formed anodic zones lead to further corrosion issues and spalling of the concrete surface.
This phenomenon known as the “incipient anode” effect and an example from a recent survey is shown in the video below:
The video shows an example of the incipient anode effect
Galvanic anodes are used to stop to the incipient anode effect from initiating. The galvanic anode is connected to the reinforcing steel and the potential difference between the anode and the steel causes a small positive protection current to flow from the anode to the steel making the steel more negatively charged, thus becoming the cathode.
Area post repair with galvanic anodes installed around the perimeter of the repair to prevent the incipient anode effect from initiating.
During this process, the galvanic anode corrodes in preference to the steel reinforcement. You can read more about how galvanic anodes are used to extend the life of patch repairs here.
Aleternativley, you can book the "Protecting and refurbishing reinforced concrete structures" CPD here which covers galvanic anodes and much more.
StructureCare are specialists in concrete repair and corrosion management. To discuss any potential renovation or repair enquiries with us, please contact info@StructureCare.com and a member of the team will be happy to assist you!