Study of the passivation of carbon steel in simulated concrete pore solution using scanning electrochemical microscope (SECM)

Abstract

A protective passive layer is formed on the surface of embedded reinforcing carbon steel bar in the alkaline environment of concrete. Corrosion of steel in concrete environment is a function of formation, strengthen and stability of this layer. In this study, Scanning Electrochemical Microscopy (SECM) was exploited to study the kinetic and the formation of the passive layer in a simulated concrete pore solution. The specimen was cut, epoxy mounted and polished from a carbon steel reinforcing bar. Then, it was immersed in a concrete simulated pore solution containing 0.5 mM potassium ferrocyanide as a mediator for 48 h and amperometry SECM approach curves were recorded over the unbiased surface of the freshly polished surface. A platinum microelectrode tip with the diameter of 25 µm was used in the experiment. The effective heterogeneous electron rate coefficient (keff) variation for the mediator regenerating surface reaction was estimated during the time of exposure. Decreasing values of keff, throughout passivation period, indicates formation and increase in the strength of the passive layer formed on the surface of the steel in the alkaline environment in concrete pore solution.