Evaluation of hexavalent chromium-free passivation treatment of galvanized bars for reinforced concrete

The zinc coating of galvanized rebars is often subjected to a passivation surface treatment by immersion in a hexavalent chromium aqueous solution in order to improve the corrosion resistance of the reinforcements when stored in air as well as when embedded in concrete. The chromate ion causes serious health problems to the operators working with the solution. Therefore, a hexavalent chromium-free passivation treatment of galvanized rebars is desirable. Two free-hexavalent chromium surface passivation treatments of galvanized rebars were obtained by immersion either in a trivalent chromium based solution or in a cobalt and titanium salts solution both harmless to the workers. Conventional (hexavalent chromium based) passivated galvanized steel bars and galvanized rebars passivated with the two above alternative treatments were embedded in very porous concrete specimens manufactured with three different cements. These reinforced concrete specimens were exposed to wetting and drying cycles in a 3% sodium chloride aqueous solution. Free corrosion potential, corrosion rate, and visual observations of galvanized rebars indicated that the two hexavalent chromium free passivation treatments can give comparable or better protection than the conventional chromating treatment, independent of the type of cement used.