Electrochemical Impedance Spectroscopy as a Tool for Studying Steel Corrosion Inhibition in Simulated Concrete Environments—Red Mud Used as Rebar Corrosion Inhibitor

Abstract

Abstract Red mud is the main by-product of the Bayer process for alumina extraction from bauxite. Rich in iron, aluminum and silicon oxides, it is believed to have corrosion protection properties. Some are studied in the present paper. The corrosion behavior of steel rebars in chlorine containing solutions and mortars is studied and compared with the same systems containing red mud in suspension (case of solutions) or added as powder to the mix (case of mortars). The results in solution show that red mud is able to maintain steel passivity for more than 90 days in highly chlorinated alkaline solutions while in NaOH and Ca(OH)2 solutions having the same pH pit formation is observable at 25 and 55 days, respectively. Additions of red mud to mortar as powder representing 2 % by weight of cement are able to block chloride depassivation. EIS data allow understanding the protecting mechanism and comparing the behavior in mortar and in solution.