Electrochemical impedance spectroscopy in the study of carbon steel passivation for reinforced concrete

Abstract

The behaviour of carbon steel in Ca(OH)(2) saturated solution with pH=13.2 was studied. In this paper, the passive film formed on the carbon steel and its natural growth were studied by means of Electrochemical Impedance Spectroscopy (EIS). The impedance spectra were recorded after 1 hour, 24 hours and 7 days of immersion, in order td see if the passive layer continues for a carbon steel previously sprinkled with sea water. Result interpretation is based on a double-layer model of the oxide film, consisting of an inner thim film, barrier-like, and of an outer porous film. The corresponding equivalent circuits are being compared; the conclusion is that as the outer oxide layer is thim and its pores are filled with electrolyte its contribution to the electrochemical properties of the steel is very little and the impedance response is dominated by the inner layer.