Study of Rust Effect on the Corrosion Behavior of Reinforcement Steel Using Impedance Spectroscopy
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UCTION
DEGRADATION of reinforced concrete structures is a matter of great practical importance. Problems are often related to the corrosion of steel reinforcement bars.[1] Under conditions of a good quality concrete, reinforcing steel is normally protected from corrosion by a passive film formed on the steel surface due to the high alkalinity provided by the concrete pore solution (pH > 12.5). However, this passivating environment is not always maintained. It can be modified by two mechanisms: one is chloride ion penetration from the marine environment and the other one is the atmospheric carbon dioxide diffusion.[2–5] The chloride content at the steel-concrete interface is one of the decisive factors for the initiation and propagation of localized corrosion in concrete structures.[6] Due to the complexity of reinforced concrete systems, simulated concrete pore solutions are usually used in studies of the corrosion behavior of reinforcing steel; most of these are based on KOH, NaOH, and Ca(OH)2, which are all products of cement hydration.[7–12] The studies on steel corrosion in concrete have most frequently been concentrated on polished steel surface (free of all oxides) in order to reproduce the same experimental conditions. Corrosion products on the surface of steel bars generally exist before the bars are embedded in the concrete. Rust is the most common of these products.
In atmospheric corrosion, steels in ordinary structures, not necessarily in strongly oxidizing environments, corrode to form rust. The rust is generally a coarse, porous, and flaky substance. It has been reported that the main products of rust formed on low alloy steel are a-FeOOH (goethite), b-FeOOH (akaganeite), c-FeOOH (lipodocrocite), c-Fe2O3 (maghemite), Fe3O4 (magnetite), and amorphous hydroxides.[13] The corrosion process of steel bars in atmosphere is affected by both steel chemistry and environmental conditions, namely, duration of exposure, temperature, wet-dry cycles, and the composition of the electrolyte that wets the metal surface.[14,15] According to the literature, some authors[16,17] reported that the presence of the oxide layers has no significant effect on the corrosion resistance of reinforcement in concrete. Others[18] consider that the presence of oxides on the surface rebar is beneficial, because they act as a physical barrier against aggressive ions. However, most authors[19–24] affirm that the preoxidized steel reinforcements exhibit a high corrosion rate. To our knowledge, the effect of rust on the reinforcement steel corrosion was well studied using different techniques.[16–23] However, studying this effect by using electrochemical impedance spectroscopy (EIS) has never been reported. Thus, the main objective of this work is to bring up the effect of oxides on reinforcement corrosion resistance in simulated concrete pore solution using EIS. II.
HAKIM BENSABRA, Ph.D. Candidate, and NOUREDDINE AZZOUZ, Professor, are with the De´partement de Ge´nie des Proce´de´s, Faculte´ des Sciences et de la Technologie, Universite´ de Jijel, 180
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