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Chloride Distribution and Steel Corrosion in a Concrete Bridge after Long-Term Exposure to Natural Marine Environment.

ABSTRACT: Chloride-induced steel corrosion is the most concerning issue for the durability of concrete structures. Concrete and steel samples were obtained from a 30-year-old reinforced concrete bridge. The chloride content was measured by a potentiometric titration method and the microstructure of concrete was obtained by scanning electron microscopy and mercury intrusion porosimetry. The rust phases of the steel were detected by X-ray diffraction and Raman analysis. It was found that the convection depth for chloride transport in cracked concrete was significantly larger than that in uncracked concrete. The concrete in a pier column facing upstream had greater porosity due to the water impact and calcium leaching. The coefficients of variability of chloride diffusivity of concrete for the bridge deck and the pier column were significantly different. Rust phases including lepidocrocite, goethite, akaganeite, magnetite, and maghemite were detected using Raman spectroscopy and X-ray diffraction. The major phases of steel rust in the atmospheric zone were lepidocrocite and goethite, while they were lepidocrocite and maghemite in the tidal zone. The results of this study would provide information concerning the chloride-induced steel corrosion under a marine environment in order to predict long-term behaviors of a reinforced concrete structure.

SUBMITTER: Liu J

PROVIDER: S-EPMC7503823 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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Chloride Distribution and Steel Corrosion in a Concrete Bridge after Long-Term Exposure to Natural Marine Environment.

Liu Jun J Jiang Zhilu Z Zhao Yulong Y Zhou Hao H Wang Xiaodong X Zhou Haijun H Xing Feng F Li Shanglin S Zhu Jihua J Liu Wei W

Materials (Basel, Switzerland) 20200903 17

Chloride-induced steel corrosion is the most concerning issue for the durability of concrete structures. Concrete and steel samples were obtained from a 30-year-old reinforced concrete bridge. The chloride content was measured by a potentiometric titration method and the microstructure of concrete was obtained by scanning electron microscopy and mercury intrusion porosimetry. The rust phases of the steel were detected by X-ray diffraction and Raman analysis. It was found that the convection dept ...[more]

PMID: 32899317

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Project description:Corrosion-induced damage to concrete reinforced with bars is a serious problem regarding technical and economic aspects and strongly depends on used materials, corrosion environment, and service life. Tests described in this paper refer to a two-year evaluation of the effectiveness of protection provided by zinc-coated low-carbon reinforcing steel of grade B500SP in concrete against chloride corrosion. Performed tests were comparative and included measurements conducted on four groups of concrete test elements with dimensions of 40 mm × 40 mm × 140 mm reinforced with a bar having a diameter of ?8 mm. Particular groups were a combination of different types of concrete with or without chloride additives, with galvanized or black steel. Chlorides as CaCl2 were added to the concrete mix in the amount of 3% of cement weight in concrete. Reinforced concrete specimens were periodically monitored within two years using the following techniques: linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). Polarization measurements were conducted in a three-electrode arrangement, in which a rebar in concrete served as a working electrode, stainless steel sheet was used as an auxiliary electrode, and Cl-/AgCl,Ag was a reference electrode. Comparative tests of changes in the density of corrosion current in concrete specimens without chloride additives basically demonstrated no development of corrosion, and possible passivation was expected in case of black steel. Higher densities of corrosion current were observed for galvanized steel during first days of testing. The reason was the dissolution of zinc after the contact with initially high pH of concrete pore solution. Six-month measurements demonstrated a higher density of corrosion current in concrete specimens with high concentration of chlorides, which unambiguously indicated corrosion in concrete reinforced with galvanized or black steel. Densities of corrosion current determined for selected specimens dramatically decreased after an 18-month interval in measurements. Corrosion was even inhibited on black steel as an insulating barrier of corrosion products was formed. The above observations were confirmed with structural studies using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. Results obtained from corrosion (LPR, EIS) and structural (SEM, EDS) tests on specimens of concrete reinforced with steel B500SP demonstrated a very favorable impact of zinc coating on steel by providing two-year protection against corrosion in the environment with very high chloride content.

Dataset Information

Chloride Distribution and Steel Corrosion in a Concrete Bridge after Long-Term Exposure to Natural Marine Environment.

Publications

Chloride Distribution and Steel Corrosion in a Concrete Bridge after Long-Term Exposure to Natural Marine Environment.

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