Steel corrosion-inhibiting effect of sodium nitrate in simulated concrete pore solutions

Abstract

When chloride-induced corrosion takes place, a local acidification occurs at the corrosion pit. Therefore, it is necessary to study the performance of corrosion inhibitors in low-pH environments. Reinforcing steel bars have been exposed to solutions that simulate the electrolytic environment of concrete micropores during the corrosion propagation period in a chloride-induced corrosion process. Sodium nitrate (NaNO3) has been added to these solutions to study its performance as a corrosion inhibitor. Solutions consisted of saturated calcium hydroxide (CaOH]2) with progressive additions of iron(II) chloride (FeCl2) to obtain different pH in the basic zone; sodium chloride (NaCl) was used for neutral solutions; and different concentrations of FeCL2 for acid solutions. Corrosion rates of steels were measured using the polarization resistance technique. Electrochemical impedance spectroscopy results are also presented to support the observations. According to the results. NaNO3 reduces corrosion levels in basic environments and does not show significant improvements in acid solutions. Corrosion of steel seems to be related to the Cl-]/OH-] ratio in three different pH regions, from acid to basic pH values. © 2011, NACE International.