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

• Published in: Acta metallurgica sinica : English letters Vol. 31; no. 11; pp. 1171 - 1182
• Main Authors: Mao, Yao-Zong, Wei, Ying-Hua, Zhao, Hong-Tao, Lv, Chen-Xi, Cao, Hai-Jiao, Li, Jing
• Format: Journal Article
• Language: English
• Published: Beijing The Chinese Society for Metals 01.11.2018; Springer Nature B.V
• Subjects: Alkalinity; Carbonation; Characterization and Evaluation of Materials; Chemistry and Materials Science; Chloride; Concrete; Corrosion; Corrosion and Coatings; Corrosion products; Crevice corrosion; Diameters; Diffusion coating; Electrochemical impedance spectroscopy; Electrodes; Epoxy resins; Heating; Holidays & special occasions; Hydroxyl ions; Ion diffusion; Iron chlorides; Localized corrosion; Materials Science; Metallic Materials; Nanotechnology; Organometallic Chemistry; Oxide coatings; Photoelectrons; Pinhole defects; Rebar; Reinforced concrete; Seawater; Spectroscopy/Spectrometry; Spectrum analysis; Tribology; X ray photoelectron spectroscopy; Epoxy-coated rebar (ECR); Corrosion; Pinhole defects; Seawater concrete
• ISSN: 1006-7191; 2194-1289
• DOI: 10.1007/s40195-018-0755-z

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 ·4H 2 O and Fe 2 (OH) 3 Cl to Fe 2 O 3 ·H 2 O, and the corrosion area was expanded outward in the carbonated SPS.