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.
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.
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)
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 Color online
Steel sample
S1
S2
S3
S4
S5
S6
Bare
Passivation
Activation
Passivation
Activation
Activation
Activation
Intact coated
Unchanged
Unchanged
Unchanged
Unchanged
Unchanged
Unchanged
Damaged coated
Passivation
Activation
Passivation
Activation
Activation
Activation
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 Color online
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(EOCP) 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) (ZIm—imaginary part of impedance, ZRe—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 (Rs—solution resistance, Rc—polarization resistance of cathodic oxygen reduction, Qc—cathode oxygen reduction capacitance, Ra—charge transfer resistance, Qa—double layer capacitance) (b) activation system of S2, S4~S6 (Zw—Warburg resistance)
Time
d
Rs
Ω·cm2
Qc-Y0
10-3 Ω-1·cm-2·s-n
nc
Rc
Ω·cm2
Qa-Y0
10-3 Ω-1·cm-2·s-n
na
Ra
Ω·cm2
χ2
0
2.20
1.04
0.97
1268
1.47
0.74
3397
8.78×10-4
1
2.18
1.17
0.97
1.487×104
0.89
0.80
6258
7.24×10-4
5
2.10
1.07
0.96
4.171×104
0.89
0.80
7276
9.17×10-4
20
2.40
0.85
0.94
7.250×104
0.98
0.76
9192
9.76×10-4
60
2.77
0.75
0.91
6.431×104
1.09
0.76
9665
8.01×10-4
Table 3 Fitting results of EIS data in S1 solution
Time
d
Rs
Ω·cm2
Qc-Y0
10-3 Ω-1·cm-2·s-n
nc
Rc
Ω·cm2
Zw
10-3 Ω-1·cm-2·s-0.5
Qa-Y0
10-3 Ω-1·cm-2·s-n
na
Ra
Ω·cm2
χ2
0
0.48
12.04
0.75
618.90
6.82
1.14
0.82
1311.0
2.77×10-4
1
0.46
13.49
0.76
114.50
13.49
1.75
0.77
842.7
6.34×10-4
5
0.48
2.07
0.73
52.88
18.49
3.01
0.75
211.3
6.06×10-4
20
0.55
5.83
0.70
9.78
58.60
11.74
0.79
30.5
3.43×10-4
60
0.51
7.60
0.70
2.67
68.89
30.98
0.66
22.4
1.11×10-4
Table 4 Fitting results of EIS data in S2 solution
Time
d
Rs
Ω·cm2
Qc-Y0
10-3 Ω-1·cm-2·s-n
nc
Rc
Ω·cm2
Qa-Y0
10-3 Ω-1·cm-2·s-n
na
Ra
Ω·cm2
χ2
0
6.06
1.28
0.97
1667
1.10
0.76
5165
4.89×10-4
1
5.85
6.17
0.97
4038
0.86
0.78
5435
6.08×10-4
5
5.73
1.03
1.00
3.060×104
0.56
0.82
5085
8.55×10-4
20
5.30
0.93
1.00
3.036×104
0.49
0.83
6707
5.62×10-4
60
4.63
0.89
1.00
2.502×104
0.44
0.84
8162
1.81×10-4
Table 5 Fitting results of EIS data in S3 solution
Time
d
Rs
Ω·cm2
Qc-Y0
10-3 Ω-1·cm-2·s-n
nc
Rc
Ω·cm2
Zw
10-3 Ω-1·cm-2·s-0.5
Qa-Y0
10-3 Ω-1·cm-2·s-n
na
Ra
Ω·cm2
χ2
0
0.93
7.21
0.75
36.24
13.86
31.96
0.79
277.80
2.26×10-4
1
0.95
11.23
0.73
28.86
26.54
22.30
0.76
255.60
1.98×10-4
5
0.90
8.53
0.72
23.46
29.73
42.22
0.80
107.60
5.08×10-4
20
1.00
6.35
0.69
13.46
56.05
197.90
0.68
76.92
2.15×10-4
60
1.72
10.89
0.42
7.59
70.76
72.73
0.90
59.60
1.26×10-4
Table 6 Fitting results of EIS data in S4 solution
Time
d
Rs
Ω·cm2
Qc-Y0
10-3 Ω-1·cm-2·s-n
nc
Rc
Ω·cm2
Zw
10-3 Ω-1·cm-2·s-0.5
Qa-Y0
10-3 Ω-1·cm-2·s-n
na
Ra
Ω·cm2
χ2
0
5.33
9.10
0.83
477.50
6.38
3.06
0.73
1614.2
9.92×10-4
1
5.47
10.40
0.79
73.44
7.49
24.65
0.41
512.9
5.19×10-4
5
3.79
78.03
0.77
81.32
10.82
83.14
0.29
467.4
2.19×10-4
20
2.87
152.40
0.76
76.14
8.50
62.60
0.24
187.6
2.03×10-4
60
2.66
42.27
0.68
69.35
8.64
21.12
0.24
70.6
2.57×10-4
Table 7 Fitting results of EIS data in S5 solution
Time
d
Rs
Ω·cm2
Qc-Y0
10-3 Ω-1·cm-2·s-n
nc
Rc
Ω·cm2
Zw
10-3 Ω-1·cm-2·s-0.5
Qa-Y0
10-3 Ω-1·cm-2·s-n
na
Ra
Ω·cm2
χ2
0
0.45
2.88
0.88
31.19
47.33
3.83
0.80
206.8
5.76×10-4
1
0.65
6.76
0.81
8.54
73.58
10.19
0.74
261.8
3.53×10-4
5
0.72
6.45
0.85
12.63
62.40
10.74
0.73
258.3
4.92×10-4
20
0.89
3.14
0.82
15.28
100.10
17.15
0.60
229.2
7.98×10-4
60
2.42
0.83
0.80
11.95
45.20
35.68
0.29
87.9
3.75×10-4
Table 8 Fitting results of EIS data in S6 solution
Fig.12 Evolutions of Rc (a) and Ra (b)with time in solutions S1~S6
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