00801 EFFECT OF METAL SURFACE CONDITION ON THE CHLORIDE CORROSION THRESHOLD OF REINFORCING STEEL IN ALKALINE SOLUTIONS

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Product Number: 51300-00801-SG

ISBN: 00801 2000 CP

Author: Lianfang Li and A. Sagiies

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Reinforcing steel bars with three types of surface conditions (as-received mill scale, prerusted in 3 5% NaCl solution, or sandblasted) were exposed in open-circuit immersion tests in pH 12.6 saturated Ca(OH)2 solution 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 and then the chloride concentration 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 took place in both the pH 12.6 saturated Ca(OH)2 solution and pH 13.3 SPS1, when the [CI'] reached threshold levels. However, sustained active corrosion of steel was not found in pH 13.6 SPS in a testing period of about two years, although the final [CI] in that solution reached 3.0M. Removing the mill scale or rust from the surface by sandblasting was beneficial in elevating the chloride corrosion threshold in alkaline solutions, although the corrosion rate of sandblasted steel aRer pitting initiation was higher than those of the other two groups. The threshold [CI]/[OH] ratio increased significantly with pH, suggesting the strong inhibiting effect of OH ions at high levels. Estimated ranges of the total chloride corrosion threshold in concrete based on the liquid solution measurements and on available chloride binding data were in general agreement with values observed in practice. Keywords: threshold, surface, pitting, rebar, Ca(OH)2, SPS, chloride, hydroxide, potential, corrosion