Electrochemical Changes of Pre-Corroded Steel Reinforced Concrete Due to Electrochemical Chloride Extraction

This paper presents the electrochemical changes of concrete specimen containing pre-corroded steel rebar with different periods of electrochemical chloride extraction (ECE) treatments. Concrete specimens were prepared with three w/b ratios (0.45, 0.38 and 0.32) and three levels of cement replacement by fly ash at 0%, 10%, 20%. And 3% chloride (NaCl) by mass of binder was added to the mixing water as a source of chloride ions for every mix. The measured electrochemical properties include half-cell potential E-corr, corrosion rate I-corr and concrete resistivity. The results show that a higher water to cement ratio or more addition of fly ash results in a severer corrosion happening on the reinforcing steel rebar prior to the ECE treatment. Although the resistivity of cover concrete is remarkably improved, the corrosion state is aggravated after ECE treatment according to the Ecorr and Icorr evolution. This worse corrosion state of steel is partly attributed to the temporary alkaline corrosion, confirmed by the highly localized accumulation of alkali (K+ and Na+) in the steel-concrete interface and some black-brown corrosion products formed on the steel surface. Therefore, electrochemical chloride extraction (ECE) is capable of removing the chloride ions but is not sufficient to guarantee the repassivation if the corrosion process of steel has already occurred.