Abstract
Corrosion behavior of epoxy-coated rebar with different size of microdefects in uncarbonated/carbonated simulated pore solution (U/CSPS) of seawater concrete was investigated. Specimens in both solutions underwent two stages of corrosion, according to the electrochemical impedance spectroscopy (EIS) response. The initial stage was the extension of corrosion. The second stage was dominated by the diffusion process, due to the corrosion products blocking the defects and hindering the transportation of the reaction matter. Local electrochemical impedance spectroscopy (LEIS), scanning vibrating electrode technique (SVET) measurements and the observation of corrosion products indicated that 50 μm might be the threshold, because the corrosion of specimens with defects bigger than 50 μm in diameter was significantly more severe. Crevice corrosion was identified to occur in the experiments. The corrosion products of specimens in USPS and CSPS were mainly Fe3O4 and FeOOH, respectively. α-FeOOH and β-FeOOH exhibited an anion ion-selective property in the corrosion process, which induced crevice corrosion in CSPS. In particular, it is contended herein that Fe3O4 has the cation ion-selective property to protect the substrate in USPS.
Highlights
Due to the costs of transportation and fresh water, in far-sea marine construction, seawater and sea sand concrete have been regarded as effective alternatives for ordinary Portland cement-based concrete [1,2]
The specimens were immersed in uncarbonated simulated pore solution (USPS) and carbonated simulated pore solution (CSPS), respectively, for 2 h, and open-circuit potential was stabilized before test
electrochemical impedance spectroscopy (EIS) experiment was adopted to investigate the corrosion behavior of defective samples immersed in USPS and CSPS
Summary
Due to the costs of transportation and fresh water, in far-sea marine construction, seawater and sea sand concrete have been regarded as effective alternatives for ordinary Portland cement-based concrete [1,2]. Corrosion behavior and mechanisms of defective coated steel have been studied extensively. Oxygen is consumed in cathodic reduction, and corrosion products form in the defect, hindering the transportation of dissolved oxygen These regions are polarized anodically and, in turn, give rise to the formation of cathodic areas [9,10]. O2 is reduced to OH− at the cathodic areas, the dissolution of oxide film on the substrate or degradation of coatings in a high alkalinity environment (pH 10~14) [11] causes the disbonding of coatings [12] These cathodic areas around the defect will do damage to the coating–substrate adhesion, resulting in the delamination or blistering of coatings [9,13]. Sylvia et al [21] proposed that ECR can prolong the service life of a concrete structure, even in the presence of defects in the epoxy coating. The results and the fundamental knowledge in this study are beneficial for the appropriate application of epoxy-coated rebar in seawater-mixed concrete systems
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