Repassivation of Prestressed Corroded Steel Strand in Sodium Molybdate Composite Solution

doi:10.16552/j.cnki.issn1001-1625.2026.0019

Abstract

Abstract:

To extend the service life of prestressed reinforced concrete structures， this study developed a composite sodium molybdate solution for repassivation treatment of corroded steel strands. Electrochemical measurements， mechanical tests， and microstructural characterization were conducted to compare uncorroded， corroded， and repassivated steel strands. Results indicate that repassivation significantly enhances the corrosion resistance of steel strands： the potential shifts toward a more positive value， corrosion current density decreases， and the Nyquist arc widens. After repassivation， the yield strength and tensile strength of steel strands remain largely unchanged. While corrosion reduces ductility by 15%， repassivation restores 10% of the lost ductility. Bond strength between repassivated strands and concrete improves compared to uncorroded strands. Microstructural analysis reveals that the performance enhancement of the repassivated steel strands stems from the formation of a dense， needle-like film composed of molybdate and phosphate phases. These findings confirm that repassivation technology effectively restores the properties of corroded steel strands without compromising tensile performance， offering a highly promising repair solution for prestressed concrete infrastructure.

Key words: repassivation of corroded steel strand, molybdate-phosphate composite film, electrochemistry, mechanical property, reinforced concrete structure

CLC Number:

TU511

SHAN Zhilong, ZHANG Yunsheng, ZHANG Shouqi, ZHANG Yu, LIU Qingyang, WANG Youping. Repassivation of Prestressed Corroded Steel Strand in Sodium Molybdate Composite Solution[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(7): 2549-2560.

Figures/Tables 16

Table 1 Mechanical properties of steel strand

Diameter/mm	Yield strength/MPa	Tensile strength/MPa	Elastic modulus/GPa	Linear density/（kg·m^-1）
15.2	1 770	1 930	197	1.101

Fig.1 Surface appearance diagram of steel strand before and after repassivation

Table 2 Performance index of grouting material

Setting time/h		Fluidity/s			28 d flexural strength/MPa	28 d compressive strength/MPa
Initial setting	Final setting	Initial	30 min	60 min	28 d flexural strength/MPa	28 d compressive strength/MPa
6	16	15	18	22	11	60

Fig.2 Schematic diagram of electrochemical test specimen structure

Fig.3 Schematic diagram of adhesion test specimen structure

Fig.4 Test specimen preparation process and test method

Fig.5 OCP and polarization curve results of specimens

Table 3 Corrosion potential and corrosion current density of specimens

Treatment status	OCP/V	J/（μA·cm^-2）
Uncorroded	-0.456 2	10^-1.99
Corroded	-0.672 9	10^-0.86
Passivated	-0.541 6	10^-1.49

Table 4 Variation of equivalent parameters in analogue circuits

Treatment status	L/μH	R_s/（kΩ·cm²）	R_ct/（kΩ·cm²）	CPE/（nS·s ^N ）	C/（μF·cm^-2）	χ²
Uncorroded	177	0.443	4.09	261， N=0.93	137	0.000 12
Corroded	119	0.593	2.06	203， N=0.81	261	0.000 29
Passivated	157	0.519	3.04	237， N=0.85	193	0.000 07

Fig.6 Equivalent circuit diagram and ac impedance test results of specimens

Fig.7 Drawing test results of steel strand

Table 5 Residual coefficient of specimens

Item	Uncorroded	Corroded	Repassivated
Yield strength f_y，D/MPa	1 770	1 710	1 715
Residual coefficient k_fy	1	0.966	0.969
Tensile strength f_u，D/MPa	1 930	1 860	1 885
Residual coefficient k_fu	1	0.964	0.967
Modulus of elasticity E_D/GPa	197	197	197
Residual coefficient k_E	1	1	1
Elongation δ_D/%	6.684	5.581	6.398
Residual coefficient k_δ	1	0.835	0.957

Fig.8 Bond test results between steel strand and concrete

Fig.9 Surface microstructure and elemental composition of steel strands

Fig.10 XPS test results of steel strand

Fig.11 Schematic diagram of surface repassivation mechanism for steel strand

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