Effects of Zinc alloy layer on corrosion and service life of galvanized reinforcing steels in chloride-contaminated concrete

Abstract

Corrosion of reinforcing steel affects the service life of structures. A chloride environment exposed to reinforced concrete structures accelerates the corrosion process. Hot-dipped galvanized steel was used as reinforcing steel instead of bare carbon steel to provide better protection against corrosion. The coating layers of galvanized steel have different compositions which can affect corrosion behavior. When galvanized steel has been corroded, it will expose the zinc-alloy layer that has a different composition than the top pure zinc layer. A comparative study on electrochemical properties such as concrete resistivity, polarization resistance, corrosion current density, anodic Tafel slope, cathodic Tafel slope, and corrosion rate of bare carbon steel (BS), galvanized steel (GS), and corroded galvanized steel (CGS) was conducted. The BS, GS, and CGS were embedded in concrete with different mix proportions by varying water-to-binder ratios, chloride contents, and types of binder. The electrochemical properties data were measured by the Wenner four-probe, linear polarization resistance (LPR), and potentiodynamic polarization resistance (PPR) tests. The measurement results show that the resistivity of 0.4 w/b concrete is higher than 0.6 w/b concrete. Corroded galvanized steel's polarization resistance is lower than bare carbon steel's and galvanized steel's. The corrosion rate calculated from the Stern-Geary equation of corroded galvanized steel is higher than bare carbon steel and galvanized steel. Based on the calculation results, the specimens with galvanized steel have a longer crack-initiating life than the bare carbon steel. The crack-initiating life of the reinforced concrete structures using galvanized steel can be more precisely predicted by considering the corroded galvanized layer.