Corrosion behaviour in concrete of three differently galvanized steel bars

The increasing use of galvanized steel reinforcements in concrete structures submitted to aggressive environments induces research into innovative zinc coatings with higher corrosion resistance. In this work, several cylindrical concrete specimens were manufactured with two cements of different alkalinity and reinforced with different hot-dip galvanized bars obtained from the “traditional” Zn-Pb bath and from two “modified baths”: Zn-Ni-Bi and Zn-Ni-Sn-Bi. The corrosion rate and corrosion potential of the bars were monitored during the air curing period and during wet-dry exposure both in tap water and in a 5% sodium chloride solution. The results showed that the coatings obtained from Zn-Ni-Sn-Bi bath have the highest corrosion rates, when the aggressiveness of the concrete matrix is determined mainly by its alkalinity. On the contrary, when the corrosion process is determined mainly by the penetration of chlorides (concrete manufactured with cement having a low alkali content) Zn-Ni-Sn-Bi was attacked only when the chloride concentration at the concrete cover depth reached the threshold of 4.02 % (by weight of cement), which is higher than those necessary for the attack of the other coatings studied (1.36 % for Zn-Ni-Bi, 1.73 % for Zn-Pb).