Abstract
Discrete galvanic anodes are used to minimize the ring/incipient/halo anode effect in concrete repairs relying on sacrificial corrosion of a more active metal than conventional reinforcing steel to provide continued protection. The demand for this protection changes with time based on the corrosion activity of the steel requiring protection. When the concrete is repaired, the repair material creates a strongly cathodic area within the repair that accelerates corrosion in the reinforcing steel immediately adjacent to the repair area known as the ring or incipient anode or halo effect. This requires an initially high current flow from the discrete galvanic anode that decreases with time. New “hybrid technology” anodes uses a short interval of impressed current cathodic protection to create a passive condition in the halo area to move halides away from the reinforcing steel and restore alkalinity to the concrete in contact with the reinforcing steel. Following this impressed current treatment, protection is maintained through galvanic activity of zinc after the impressed current is removed. A novel “bimetallic” technology has been developed using two active galvanic metals, magnesium and zinc. A small amount of magnesium can provide the "jump start" to create an initial high polarization similar to these other hybrid anodes without the need of external power, rewiring of the cathodic protection system or reliance on complex electrical circuitry to control the impressed current phase of treatment. The new bi-metallic anode is simply installed exactly like conventional single stage anodes. Following consumption of the magnesium, maintenance current is provided by conventional zinc galvanic protection. Furthermore, because the galvanic reaction is controlled by the environmental conditions of the installation and corrosion activity of the reinforcing steel, there is no potential for overvoltage, complex wiring, or any additional activity required after the hybrid anode is installed.
