ABSTRACT
Thermal spayed zinc was first used as an impressed current anode by the California Department of Transportation (Apostolos et al. 1987). The anode is applied using either flame spraying or electric arc spraying. The latter is now more common as deposition rates are far higher. There is a standard for thermal spraying anodes, see American Welding Society (2002). After initial surface preparation by a light grit blast, the zinc is sprayed onto the surface of the concrete using flame or electric arc equipment. Although the material is non-proprietary, it requires specialist applicators and bulky spray equipment.As the coating is highly conductive it is important to avoid short circuits to the steel caused by tramp steel or tie wires. A simple electrical circuit with an audible alarm can be set up to warn of shorts between the reinforcement cage and the anode as it is applied; however, it can still be difficult to precisely locate short circuits. These must be eliminated for impressed current cathodic protection to work.The anode is ideal for bridge substructures where it has been widely used in the USA. The coating is more tolerant of water after application than conductive paint anode systems. However, bulky specialist equipment is required for installation and it cannot be applied in any other way. The anode system has a typical life-expectancy of up to 25 years and has a medium to high cost of installation compared with other impressed current cathodic protection anodes.Like a conductive paint there is little visual or other impact. The grey colour means it has limited acceptability on buildings. It can be overcoated, usually with silicate-based materials.
