Electrochemical behavior of mild and corrosion resistant concrete reinforcing steels

Abstract

An experimental study is carried out in this paper to evaluate the corrosion performance of mild steel reinforcing bars (MS), high strength steel reinforcing bars (HS), epoxy-coated steel reinforcing bars (EC), and high-chromium steel reinforcing bars (HC) under harsh environmental conditions. Reinforcing bars (rebar) of 16 mm diameter and 310 mm length were embedded in cylindrical concrete samples of 60 mm diameter and 350 mm length, and subjected to a Southern Exposure test for sixteen months. The open circuit potential (OCP) was monitored during the exposure period until corrosion initiation. The linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and Tafel plot techniques were employed to assess the corrosion rates on the rebar surfaces. The macrocell corrosion current was monitored by connecting the corroding rebar with an external stainless steel bar of the same size. The polarization resistance of the HC was found to be 1.5 times higher than that of the MS. The EIS technique showed that EC, even with damaged epoxy coating, has the highest resistance to chloride attack. The macrocell current of HC rebar was 48% less than that of MS during the active corrosion state. The LPR, EIS and Tafel plots analysis provided the current densities, which were close to each other; indicating the validity of these techniques to study the problem at hand. The corrosion rates from electrochemical methods were compared against the ones calculated by gravimetric methods. The quantitative results from this research may be used in service life prediction of concrete structures with different types of rebar. Extensive analysis of the results indicates that the corrosion resistance of the evaluated steels was in the following decreasing order: EC, HC, MS, and HS.