Electrochemical Experimental Study on Passivation Behavior of Steel Bars Embedded in Fly Ash Cement Paste

doi:10.12068/j.issn.1005-3026.2025.20249028

Abstract

Abstract:

In order to investigate the passivation process of steel bars embedded in fly ash（FA）cement paste， five FA dosages（0， 10%， 20%， 30% and 40%） were taken into consideration. The cement paste-cylindrical steel bar specimens were prepared. Open-circuit potential and electrochemical impedance spectroscopy methods were applied to monitor the formation of the passivation film on the steel bar during the cement hydration process. The impedance spectra of cement paste-steel bar specimens with different FA dosages were obtained during the cement hydration process. Based on the equivalent circuit model R（Q（R（QR）））， the electrochemical parameters such as the resistance of the passivation film， the charge transfer resistance， and the apparent interface capacitance of the specimens were recorded. The results indicate that the passivation film is formed on the steel bars embedded in the FA cement pastes within seven days. The R（Q（R（QR）））equivalent circuit model can effectively fit the electrochemical impedance spectral curves of the FA cement paste-steel bar specimens. The chi-square test results are less than 10^-4. FA delays the passivation of the steel bars embedded in the cement paste. When 20% FA is added， the passivation film of steel bars embedded in the cement paste is more stable， and it has a better protective effect on the steel bars.

Key words: fly ash, cement paste, passivation of steel bar, electrochemical impedance spectroscopy, equivalent circuit model

CLC Number:

TU 578

Ying-fang FAN, Yu-xuan SU, Qiu-chao LI, Hao CHEN. Electrochemical Experimental Study on Passivation Behavior of Steel Bars Embedded in Fly Ash Cement Paste[J]. Journal of Northeastern University(Natural Science), 2025, 46(11): 143-153.

Figures/Tables 20

Table 1 Chemical composition of cement and FA(mass fraction)

材料	CaO	SiO₂	Al₂O₃	MgO	Fe₂O₃	SO₃	K₂O	Na₂O	其他
水泥	59.30	21.91	6.27	1.64	3.78	2.41	—	—	4.69
FA	4.78	49.89	34.81	1.28	2.17	1.10	2.97	1.25	1.75

Fig.1 Dimensional and morphological characteristics of cement and FA

Fig.2 Specimen preparation process

Fig.3 Electrochemical test device

Table 2 pH of FA cement paste

试件

编号

FAC

Fig.4 Open-circuit potentialof specimens during cement hydration process

Fig.5 Phase angle plots of specimens during cement hydration process

Fig.6 Phase angle peak of specimens during cement hydration process

Fig.7 Impedance modulus of specimens during cement hydration process

Fig.8 Nyquist curves of specimens during cement hydration process

Fig.9 SEM micromorphology of FA cement paste

Fig.10 Equivalent circuit model

Fig.11 Nyquist plots of simulated data by equivalent circuit and measured data

Table 3 Chi-square results by equivalent circuit simulation

龄期/d	OPC	FAC10	FAC20	FAC30	FAC40
1	3.59×10^-4	9.80×10^-5	6.80×10^-4	1.00×10^-4	1.74×10^-4
7	2.34×10^-4	7.41×10^-4	6.72×10^-4	2.18×10^-4	5.78×10^-4

Fig.12 Rbulk of specimens during cement hydration process

Fig.13 Dielectric constant of specimens during cement hydration process

Fig.14 Rf of specimens during cement hydration process

Fig.15 Rct of specimens during cement hydration process

Table 4 Parameter values of equivalent circuit

试件编号	龄期/d	Y₀·10^-2/(kΩ^-1·cm^-2·s^-1)	n
OPC	1	4.02	0.91
OPC	7	3.22	0.94
FAC10	1	4.09	0.91
FAC10	7	3.59	0.93
FAC20	1	4.10	0.90
FAC20	7	3.29	0.93
FAC30	1	4.66	0.93
FAC30	7	3.49	0.94
FAC40	1	4.43	0.90
FAC40	7	3.94	0.95

Fig.16 Capp of specimens during cement hydration process

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