Corroaion-oaused cH11tr11&11 to reinforcenconcrete structures is a serious and continuing problem. A practical mitigation measure is cathodic protection of the embedded reinforcing steel. In this paper the results of an ongoing laboratory and field study that tests proprietary conductive paints and flame-spray metallizing as conductive coatings/anodes on concrete are described, and their physical characteristics, behavior, and economics as part of cathodic protection systems are also discussed, Results to date indicate that several of the paints and most of the metals tested provide adequate conductivity and bond to the concrete, but differ significantly in ease of application, toxicity, aesthetics, and economics. Of the materials tested, zinc metallizing appears to provide the most viable combination of physical characteristics and economics for cathodic protection of concrete reinforcement.

Concrete normally provides excellent protection from corrosion to embedded reinforcinq steel by forminq a thin, stable oxide layer on the surface of the metal. This layer acts as a barrier to further corrosion, a phenomenon known as passivation. Chloride ions can destroy this passivating oxide film and allow corrosion to proceed at a rapid rate, given an adequate supply of oxygen and moisture. One successful method of stopping or significantly reducing the corrosion process is the introduction of direct current (de) to the corrosion cell, but flowing in the opposite direction to the natural process. This current, delivered by an external source, blocks the normal flow of charges and thus converts the corrodinq area (the anode) into a noncorroding area (a cathode). This method is called cathodic protection (CP). The firot reported application of CP to aboveground reinforced concrete was by the state of California in 1959 (1), and the first application of CP to a concrete bridge deck was reported by the state of California in 1974< 1>· Since then a number of agencies have revised and improved the pioneering system (3-5) and, currently, CP is considered a reliable-m; ans of controlling corrosion in the top mat of bridge deck reinforcing steel (6-10). The pioneering system distributed~ CP current evenly throughout the surface of the concrete by means of a layer of coke breeze (small particles of coke, a byproduct of the petroleum industry, consisting of approximately 97 percent carbon: it is a good conductor)•