Monitoring of steel corrosion in concrete in the presence of IFKhAN-78 corrosion inhibitor by electrochemical methods. Electrochemical impedance spectroscopy

• V.E. Kasatkin, I.V. Kasatkina, I.G. Korosteleva, L.P. Kornienko and V.N. Dorofeeva

Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia

Abstract: Six-month monitoring of the electrochemical and corrosive behavior of steel reinforcement in concrete without additives and with the migrating corrosion inhibitor (MCI) IFKhAN-78, was performed using electrochemical impedance spectroscopy (EIS). The samples were mainly in a solution of 3% NaCl, but for 7 weeks they were subjected to cycles of air drying and immersion in the solution to activate corrosion. Earlier, we published the results of a study of this system using polarization methods and found that samples with the addition of this inhibitor to the concrete mass remained passive only for the first month after immersion in the solution. Then their corrosion condition deteriorated sharply compared to untreated concrete. At the same time, additional periodic impregnation of the sample surface with this corrosion inhibitor reduced the rate of steel corrosion for up to 50 days. It has been suggested that the loss of the protective effect may be associated with an increased concentration of surfactants in the IFKhAN-78 inhibitor. This can accelerate its leaching from the pores of concrete and enhance the counter diffusion of Cl^– ions from the solution into the metal, which will accelerate its corrosion. After processing the EIS results obtained regularly during the entire observation period, it was found that concrete samples with MCI added to the concrete mass have an order of magnitude lower resistance of the concrete layer and an increased diffusion coefficient compared to untreated concrete. The loss of protective properties after a month of concrete being under a layer of chloride electrolyte is accompanied by a change in the nature of the impedance spectrum (and the equivalent circuit) and does not contradict the previously proposed model of reducing the concentration of the inhibitor at the steel surface (including due to chemical interaction) and increasing the chloride content in the pore fluid. This type of inhibitor is not suitable for protecting concrete that has been under a layer of chloride-containing solution for a long time. The presence of a surfactant in this MCI has an adverse effect and leads to a deterioration in corrosion resistance compared to concrete samples without additives.

Keywords: carbon steel, concrete, IFKhAN-78 inhibitor, MCI, corrosion monitoring, electrochemical impedance spectroscopy, EIS

Int. J. Corros. Scale Inhib., 2025, 14, no. 3, 1057-1079
doi: 10.17675/2305-6894-2025-14-3-3

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