An Investigation on Mild Steel Pitting Corrosion in Concrete Pore Solution and Inhibitive Effect of Nitrite by Measuring Couple Current Density and Potential of Identical Electrodes

Pitting corrosion of embedded mild steel in concrete is one of the main concerns of civil engineers. Introducing a reliable measuring method for prediction its corrosion has been intensely considered by corrosion researchers. The aim of the present study is to demonstrate the pitting potential measurement correlation between potentiodynamic polarization and zero resistance ammeter on two identical electrode techniques. Potentiodynamic polarization of mild steel in concrete pore solution (saturated Ca(OH)2) shows passivition prior to transpassivity due to water oxidation. Addition of 0.5 M NaCl to the above solution caused pitting corrosion at 327 mV. Meanwhile the presence of nitrite ions as an inhibitor by addition of 0.5M NaNO2 to the concrete pore solution containing 0.5M NaCl caused an increase of 562 mV in pitting potential. Zero resistance ammeter (ZRA) technique was employed to measure the galvanic current density and potential of two coupled identical electrodes of investigated mild steel in the mentioned environments. The results of ZRA investigation revealed passivity behavior in concrete pore solution and concrete pore solution containing chloride and nitrite ions but pitting corrosion in concrete pore solution containing chloride ions after 300 second of immersion. Pitting corrosion occurrence was attributed to the establishment of pitting criteria by exceeding pitting corrosion from pitting potential. The value of pitting potential obtained by ZRA technique was very close to the one measured by potentiodynamic polarization technique.