Determination of the Chloride Threshold of Cr-Based Steel Rebars in a Synthetic Concrete Pore Solution Based on Electrochemical Methods

Steel rebars are widely applied in reinforced concrete structures due to their contribution to significant improvements in mechanical properties. However, exposure to corrosive environments, such as solution-containing chloride, may induce an accelerated corrosion and jeopardize the sustainability and durability of reinforced concrete. The current work evaluated the chloride thresholds (in both wt% and [Cl-]/[OH-]) of steel rebar with different chromium contents (0 wt%, 4 wt%, and 23 wt%) in synthetic concrete pore solution based on AC and DC electrochemical measurements, and chemical and structural characterizations. The study found that the chloride threshold (CT) values varied slightly based on the different measurement methods and the values were compared with values obtained from the literature. The values are 0.01 wt% to 0.1 wt% (3.76), 0.1 wt% to 1 wt% (>23.8), and 2.9 wt% to 3.5 wt% (>23.8) for 615, 4% Cr, and SS23, respectively, where the values in parentheses are [Cl-]/[OH-]. Therefore, it is demonstrated that multiple measurements are necessary to determine a reliable CT value. Corrosion mechanisms giving rise to CT are included to illustrate the processes involved in establishing CT.