Chloride Corrosion Threshold of Reinforcing Steel in Alkaline Solutions—Open-Circuit Immersion Tests

Abstract

Abstract Reinforcing steel bars with three types of surface conditions (as-received mill scale, prerusted in 3.5% sodium chloride [NaCl] solution, or sandblasted) were exposed in open-circuit immersion (OCI) tests in pH 12.6 saturated calcium hydroxide (Ca[OH]2) solution (SCS) and pH 13.3 (SPS1) and pH 13.6 (SPS2) simulated concrete pore solutions. These solutions were free of chlorides at the beginning of the test to allow the steel specimens to passivate. Then the chloride concentration ([Cl−]) was increased in several steps. The corrosion potential was monitored, and electrochemical impedance spectroscopy tests were performed periodically on selected specimens. It was found that active corrosion for all three surface conditions tookplace in the pH 12.6 SCS andpH 13.3 SPS1, when the [Cl−] reached threshold levels. However, sustained active corrosion of steel was not found inpH 13.6 SPS2 in a testing period of ∼ 2 years, although the final [Cl−] in that solution reached 3.0 M. Removing the mill scale or ...