Corrosion Behavior of Damaged Epoxy Coated Steel Bars Under the Coupling Effect of Chloride Ion and Carbonization

doi:10.11900/0412.1961.2019.00302

Acta Metall Sin

2020, Vol. 56

Issue (6): 885-897 DOI: 10.11900/0412.1961.2019.00302

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Corrosion Behavior of Damaged Epoxy Coated Steel Bars Under the Coupling Effect of Chloride Ion and Carbonization

WEI Jie¹, WEI Yinghua², LI Jing², ZHAO Hongtao², LV Chenxi², DONG Junhua¹(

), KE Wei³, HE Xiaoyan³

^1.Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
^2.Shenyang Research and Development Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
^3.Environmental Corrosion Center, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

Cite this article:

WEI Jie, WEI Yinghua, LI Jing, ZHAO Hongtao, LV Chenxi, DONG Junhua, KE Wei, HE Xiaoyan. Corrosion Behavior of Damaged Epoxy Coated Steel Bars Under the Coupling Effect of Chloride Ion and Carbonization. Acta Metall Sin, 2020, 56(6): 885-897.

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Abstract

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

Received: 11 September 2019

ZTFLH:

TG172.2

Fund: 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)

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	Articles by authors
	Jie WEI
	Yinghua WEI
	Jing LI
	Hongtao ZHAO
	Chenxi LV
	Junhua DONG
	Wei KE
	Xiaoyan HE

URL:

https://www.ams.org.cn/EN/10.11900/0412.1961.2019.00302 OR https://www.ams.org.cn/EN/Y2020/V56/I6/885

Table 1 Solution compositions for corrosion test

Fig.1 Low (a) and high (b) magnified SEM surface images of steel bar specimen with intact coating

Fig.2 Low (a) and high (b) magnified SEM cross-section images of steel bar specimen with intact coating

Fig.3 SEM-BSE image (a) and EDS analysis along the line in Fig.3a (b) of coating

Fig.4 SEM-SE (a) and SEM-BSE (b) images of the steel bar specimen with prefabricated damage coating

Fig.5 Corrosion morphologies of bare steel (a1~f1), intact coated steel (a2~f2) and damaged coated steel (a3~f3) immersed in solutions S1 (a1~a3), S2 (b1~b3), S3 (c1~c3), S4 (d1~d3), S5 (e1~e3) and S6 (f1~f3) for 60 d
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Table 2 Corrosion conditions of three different steel bars immersed in solutions S1~S6 for 60 d

Fig.6 CLSM three-dimensional morphologies of steel bar specimen with prefabricated damaged coatings immersed in solutions S1~S6 (a~f) for 60 d
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Fig.7 Longitudinal section contour maps of pits in steel bar specimen with prefabricated damaged coating immersed in solutions S1~S6 (a~f) for 60 d

Fig.8 Raman spectra of corrosion products in pits of steel bar specimen with prefabricated damaged coating in activated corrosion systems S2, S4~S6

Fig.9 Open circuit potential(E_OCP) evolution of steel bar specimen with prefabricated damaged coating in solutions S1~S4 (a) and S5, S6 (b)

Fig.10 Nyquist (a1~f1), Bode impedance modulus (a2~f2) and Bode phase angle (a3~f3) plots evolution of steel bar specimen with prefabricated damage coatings in solutions S1 (a1~a3), S2 (b1~b3), S3 (c1~c3), S4 (d1~d3), S5 (e1~e3) and S6 (f1~f3) (Z_Im—imaginary part of impedance, Z_Re—real part of impedance, |Z|— impedance modulus)
Color online

Fig.11 Schematics of equivalent circuit models for EIS fitting of solutions S1~S6
(a) passivation system of S1 and S3 (R_s—solution resistance, R_c—polarization resistance of cathodic oxygen reduction, Q_c—cathode oxygen reduction capacitance, R_a—charge transfer resistance, Q_a—double layer capacitance)
(b) activation system of S2, S4~S6 (Z_w—Warburg resistance)

Table 3 Fitting results of EIS data in S1 solution

Table 4 Fitting results of EIS data in S2 solution

Table 5 Fitting results of EIS data in S3 solution

Table 6 Fitting results of EIS data in S4 solution

Table 7 Fitting results of EIS data in S5 solution

Table 8 Fitting results of EIS data in S6 solution

Fig.12 Evolutions of R_c (a) and R_a (b)_{with time in solutions S1~S6}

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