Understanding the Impact of Polishing and Environmental Factors on Corrosion Potential—An Optimization by Robust Design

Abstract

ASTM G180-13, Standard Test Method for Corrosion Inhibiting Admixtures for Steel in Concrete by Polarization Resistance in Cementitious Slurries (Superseded), testing was used to determine the effectiveness of corrosion inhibiting admixtures. However, inconsistent results have been reported due to the polishing process. Although not standardized, polished metal specimens have been used to remove contaminants or native oxides prior to electrochemical measurements to acquire stabilized electrochemical measurements. Furthermore, the open circuit potential (OCP) delay before electrochemical testing was found to be critical to the consistency of the subsequent experiment. The goal of this study was to investigate the influence of polishing and environmental factors on the OCP value and its variation. The OCP of carbon steel in high pH simulated pore solutions was measured as functions of polishing, time, chloride content, and nitrite concentration. By using a full-factorial experimental design and regression analysis, the effects of the factors were studied on both the mean value and on the standard deviation of corrosion potential. The standard deviation of repeated tests was quantified and ranked to provide guidance on specimen preparation. The regression result showed that polishing does not influence the mean value of the OCP but that the OCP standard deviation heavily depends on the polishing consistency. Based on the experimental data and analysis, a suggestion was provided for specimen preparation to address the observed inconsistency in specimen preparation for ASTM G180-13 testing.