The degradation of passive film on carbon steel in concrete pore solution under compressive and tensile stresses

The degradation of passive film on carbon steel in concrete pore solution under tensile and compressive stresses is studied using electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) techniques. As the applied stress increases, the corrosion potential and impedance of the samples decrease. When the same stress magnitude is applied, under compressive stress the samples show more negative corrosion potentials and lower impedance values than those subjected to tensile stress. Two different modes for the failure of the passive film are proposed: tensile stress creates micro-cracks perpendicular to the surface, while compressive stress induces de-bonding of the interface between the passive film and the substrate. Thus, compressive stress produces more severe degradation of the passive film than does the tensile stress. (C) 2011 Elsevier Ltd. All rights reserved.