Corrosion Resistance of a Cr-Bearing Low-Alloy Reinforcing Steel: Effect of Surface Condition, Alkaline Solution, and Chloride Content

Abstract

A Cr-bearing low-alloy (LA) reinforcing steel with two different surface conditions (polished surface and as-received ribbed surface) was investigated using various electrochemical measurements and microstructural characterization techniques for their corrosion resistance when exposed to alkaline solutions containing low chloride concentration (0.1 M NaCl) and high chloride concentration (3.0 M NaCl). Low-alkaline saturated Ca(OH)2 solution (CH solution) and high-alkaline solution (CP solution) were used to simulate the electrolytic environments of concrete. It was confirmed that, due to the presence of defective mill scale and ribs on the steel surface, which are susceptible to chloride-induced corrosion, the ribbed LA steel exhibited much lower corrosion resistance than the polished LA steel exposed to the two alkaline solutions with chlorides. In the low-chloride condition (0.1 M), both steels in CP solution had higher corrosion resistance than in CH solution. However, in the presence of 3.0 M NaCl, CH solution provided unexpectedly higher protection to both ribbed and polished LA steels than did CP solution, which was attributed mainly to the formation of Ca-containing precipitates on the surface of the corroded steel exposed to CH solution, thereby suppressing the cathodic reaction by delaying the oxygen diffusion.