Corrosion Behavior of Damaged Epoxy Coated Steel Bars Under the Coupling Effect of Chloride Ion and Carbonization
Received date: 2019-09-11
Revised date: 2019-12-20
Online published: 2020-03-23
Supported by
National Natural Science Foundation of China(51501201);Strategic Priority Research Program of Chinese Academy of Sciences(XDA13040501);Shenyang Key Research and Development and Technology Transfer Program(Z17-7-021)
It is unavoidable for coated steel bars to be scratched during transportation and construction, which will lead to the damage of coating and exposure of steel matrix. Consequently, the corrosion resistance of coated steel bars after damage will directly affect the durability of structures. The corrosion evolution behavior of damaged epoxy coated steel bars under the coupling action of chloride ion and carbonization was studied by comparing with bare steel bars and perfectly coated steel bars. On the basis of characterizing the composition and structural characteristics of epoxy coating, the corrosion morphology and product composition at the damage site of the coating were analyzed by CLSM and Raman spectroscopy, and the corrosion process was monitored by corrosion potential and electrochemical impedance spectroscopy to reveal the dynamic of corrosion evolution. The results show that the epoxy coating without damage has a good protective effect on steel matrix, and no corrosion occurs during long-term immersion in all six solutions including the chloride ions and carbonization corrosive environments. The corrosion activation or passivation behavior of damaged coated steel bars is consistent with that of uncoated bare bars, which is obviously affected by chloride ion and carbonization. Passivation occurs in the system without Cl- and with pH of 12.6 or 9.8. Activation dissolution occurs in the chloride-free system with pH of 9.2, and in the system of different pH values with 0.6 mol/L NaCl. In the active systems, the corrosion rate increases with time. In the chloride-free system, the corrosion products after long-term corrosion are mainly α-FeOOH, while in the chloride-containing system with different pH, the corrosion products contain not only α-FeOOH, but also β-FeOOH and a small amount of Fe3O4. Under the coupling action of chloride ion and carbonization, the corrosion of damaged coated steel bars occurs only in the damaged site, and the corrosion extends towards to the depth of the matrix, which will not cause the peeling of coatings in other sites.
Key words： epoxy coated steel bar; corrosion evolution; chloride ion; carbonization
Jie WEI , Yinghua WEI , Jing LI , Hongtao ZHAO , Chenxi LV , Junhua DONG , Wei KE , Xiaoyan HE . Corrosion Behavior of Damaged Epoxy Coated Steel Bars Under the Coupling Effect of Chloride Ion and Carbonization[J]. Acta Metall Sin, 2020 , 56(6) : 885 -897 . DOI: 10.11900/0412.1961.2019.00302
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