Corrosion Behavior of Epoxy-Coated Rebar with Pinhole Defect in Seawater Concrete

Abstract

Experiments were carried out to investigate the corrosion behavior of epoxy-coated rebar (ECR) with pinhole defect (diameter in hundreds of microns) immersed in the uncarbonated/carbonated simulated pore solution (SPS) of seawater concrete. Corrosion behavior was analyzed by electrochemical impedance spectroscopy. The composition and morphology of corrosion products were characterized by X-ray diffraction, energy-dispersive spectrometry and scanning electron microscopy. Meanwhile, oxide film produced by preheating before spray coating was investigated by X-ray photoelectron spectroscopy and Mott-Schottky technology. Results indicated that corrosion behavior of ECR with pinhole defect exhibited three stages when immersed in the uncarbonated/carbonated SPS. In the initial stage, steel in defect was passivated when exposed in the uncarbonated SPS and corroded when exposed in the carbonated SPS, due to competitive adsorption between chloride and hydroxyl ions. In the second stage, the oxide film under coating reconstituted (the thickness and defects density decreasing) in the uncarbonated SPS, which was caused by the synergy between high hydroxide and chloride activity, while in the carbonated SPS, crevice corrosion happened under the coating around pinhole, because of the different oxygen concentrations cell at the coating/steel interface. In the third stage, localized corrosion occurred under the coating around the pinhole in the uncarbonated SPS, which was probably induced by ion diffusion at the nano-scale coating/steel interface. The corrosion products adjacent to the defects were re-oxidized from FeCl 2 Á4H 2 O and Fe 2 (OH) 3 Cl to Fe 2 O 3 ÁH 2 O, and the corrosion area was expanded outward in the carbonated SPS.

Development of Nano-tetragonal Zirconia-Incorporated Ni–P Coatings for High Corrosion Resistance

“…In the present case, the higher value of charge transfer resistance (R ct = 16.75 kX/cm 2 ) and large radius of the semicircle obtained for Ni-P-nano-tetragonal zirconia coating confirmed high corrosion resistance of the coating. The double-layer capacitance also can be considered as a function of corrosion on the coating [87]. A low C dl value exhibited by Ni-P-nano-tetragonal zirconia coating revealed the enhanced corrosion resistance due to improvement in surface homogeneity and low porosity of the coating.…”

A comparative study on the microstructure, hardness and corrosion resistance of epoxy coated and plain rebars

“…It is also well known that the reaction between corrosive media and base metal causes substrate anode dissolution in the gap which is t away from the defected areas with a lower oxygen concentration of the coatings. It has been reported earlier that the main corrosion reactions of iron occur at the anodic site under the coating in the saline environment as shown below [76] The produced Fe 2+ cations as shown by equation (9) can be further hydrolysed and oxidized with acidification according to the following reactions as shown by equations 10-12. The above reactions led to the generation of corrosion products as FeCl 2 .4H 2 O, Fe 2 (OH) 3 Cl, and FeO(OH) which were also validated in the XRD analysis shown in figures 11(c) and (d).…”

“…XRD study of corrosion products Figure 11 shows the x-ray diffraction (XRD) analysis of the corrosion products formed on both the plain rebar and ECR sample surfaces in 3.5% NaCl and 1% HCl solution. For the plain rebar samples, the x- [53,76]. It is also well known that the reaction between corrosive media and base metal causes substrate anode dissolution in the gap which is t away from the defected areas with a lower oxygen concentration of the coatings.…”

Effect of Cu2+ on Corrosion Behavior of A106B Carbon Steel and 304L Stainless Steels in Seawater

“…Presently, the corrosion of steels in seawater had been widely investigated all over the world [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], and the influence of Cu 2+ on material corrosion is mainly focused on different materials in nonseawater environment, such as steel [21][22][23][24][25][26][27][28][29][30], aluminum alloy [31,32], 690 alloy [33], and copper alloy [34]. However, the works focused on the corrosion behavior of steels in seawater containing Cu 2+ and the influence of the Cu 2+ and copper oxides on the corrosion of the equipment in the secondary circuit system were little reported [35].…”