Corrosion resistance of galvanized steel in concrete: effect of wet-dry cycles in chloride solution after carbonation process

The effect of chloride ions on corrosion resistance of galvanized steel in carbonated concrete was investigated. Galvanized steel sheets were embedded in cubic concrete specimens manufactured with a 52.5 R Portland cement; after curing in atmosphere for 39 days, the concrete specimens were submitted to carbonation and then to wet-dry cycles both in a 3.5 % NaCl solution and in tap water. Results show that concrete carbonation destroys the passivating layer of calcium hydroxyzincate, with formation of less protective products. Wet-dry cycles in tap water after carbonation do not increase appreciably corrosion rate of galvanized steel with respect to that measured in not carbonated concrete. On the contrary, corrosion rate measurements performed during wet-dry cycles in 3.5 % NaCl solution, after concrete carbonation, indicate that in these conditions galvanized steel is not passive.