Evaluation on use of half-cell potential for measuring corrosion potential of steel bars in reinforced concrete subjected to carbonation

Abstract

This paper describes corrosion activity of reinforcing steels in reinforced concrete which was attacked by carbonation. The half-cell potential (HCP), corrosion current density (i_corr) and depth of carbonation were measured to investigate the corrosion status of the reinforcing steels. Six fly ash concrete (FA) mixtures with water to binder ratios of 0.4, 0.5 and 0.6 were compared to three mixtures of ordinary Portland cement concrete (OPC). The specimens were exposed in a carbonation chamber in which the conditions were controlled at 4 % carbon dioxide concentration, 40ºC, and 55±5% RH. Results demonstrated that HCP measurement was not appropriate for being used to investigate probability of steel corrosion due to carbonation. When carbonation front extended to surface of steel bars, i_corr suddenly jumped to more positive values. However, the HCP showed different tendency when compared with i_corr. HCP showed almost constant values even though steel bars had corroded by carbonation. This study clearly indicates that HCP measurement may not be appropriate for being applied to investigate probability of steel corrosion due to carbonation. On the other hand, i_corr and depth of carbonation showed good correlation in detecting corrosion initiation in laboratory measurement.