2002 Volume 51 Issue 10 Pages 463-466
The critical chloride concentration above which corrosion of carbon and stainless steel (type 304) reinforcements in concrete occurs has been examined as a function of pH that reflects neutralization of concrete. A saturated Ca(OH)2 solution, pH 12.4-12.5, was used to simulate the fully alkaline concrete and mixed solutions of Ca(OH)2 and CaCO3 saturated solutions in varying ratios to simulate neutralized concrete of lower pH values. The test solution for stainless steel contained active carbon powder and was thoroughly aerated by bubbling through air. The chloride concentration was changed by adding NaCl to the solutions. To simulate crevice between reinforcement and concrete, semi-spherical deposits of an epoxy resin adhesive were provided to the carbon steel specimen, and a multiple crevice washer to the stainless steel specimen. The critical NaCl concentrations below which corrosion of carbon steel was slight in solutions of pH 12 and 11.5 were 0.20, 0.10 and 0.05g/L, respectively. Below pH 11.0 corrosion occurred generally regardless of the chloride concentration. Type 304 showed no corrosion with 150g/L NaCl at pH 12.5 but the critical concentration was in the range of 100-150g/L NaCl at pH 11.5. The critical chloride concentration decreases for both carbon and stainless steels as the pH falls, but that for stainless steel is much higher than the reported maximum chloride concentration near the surface of concrete structures exposed to a high deposition of chlorides from the ocean, indicating a high corrosion resistance of the steel in the hostile environment.
