Evaluation of the effectiveness of migrating corrosion inhibitors and hydrophobizers for protection against corrosion of steel reinforcement in concrete using bimetallic batch sensor

• D.S. Shevtsov and I.D. Zarcyn

Voronezh State University, Universitetskaya pl., 1, 394006 Voronezh, Russian Federation

Abstract: A method is proposed for quantitative evaluation of the effectiveness of the protective action of hydrophobizers and inhibitors in relation to the corrosion process of reinforcement in reinforced concrete. Surface treatment of reinforced concrete structures with hydrophobizers leads to a significant increase in the specific electrical resistance of the protective layer of concrete. This makes it difficult to use electrochemical methods to determine the rate of corrosion of reinforcement, in particular, the method of polarization resistance. In this work, as a sensor for determining the rate of corrosion under a layer of concrete, it is proposed to use a bimetallic batch sensor – a package of galvanic cells (copper/low-carbon steel) capable of generating an electric current upon contact with the electrolyte. In this case, the copper plates of the sensor correspond to passive, steel – active sections on the surface of the steel reinforcement, and the magnitude of the current between the artificial cathode and anode can be considered as a measure of the corrosion rate of the reinforcement. The distance between the sensor plates is comparable to the distance between individual pits. Therefore, using the above described method, the corrosion process is modeled on the “active” sections of steel reinforcement, areas of microcell–pit/passive steel surfaces. The effectiveness of this method is demonstrated by the example of a commercial hydrophobizer based on alkoxysilanes, which also possesses inhibitory properties. Surface treatment of concrete samples contaminated with chlorides (1.00 and 3.25 mass% relative to the dry cement mass), a hydrophobizer, leads to a sharp decrease (up to 90%) of the galvanic current at the sensor. The protective effect persists for twenty cycles of wetting / drying (10 months) and when the water in the humidification cycle is replaced with a 3% solution of sodium chloride (six cycles of wetting / drying). When processing a concrete sample with a hydrophobizer, a sharp increase in the specific electrical resistance of concrete (up to 20 times on samples contaminated with chlorides) is observed and the potential for free corrosion of steel plates shifts to positive values. At the same time, the values of the potential of free corrosion and concrete resistivity of concrete, for the passive and active states determined by the sensor, meet the criteria given in RILEMTC 154-EMC. It is shown in the model calculations that an increase in the specific electrical resistance of the protective layer of concrete up to 10–20 times using a hydrophobizer can not explain the significant reduction in the corrosion rate (galvanic current at the sensor). It is suggested that a consistent change in corrosion rate and resistivity of the protective layer of concrete is due to a similar dependence of these values on the degree of filling of pores in the concrete with water.

Keywords: corrosion of reinforcement in concrete monitoring, batch bimetal sensor, secondary protection of concrete, hydrophobizer, penetrating corrosion inhibitor

Int. J. Corros. Scale Inhib., 2018, 7, no. 3, 427-442 PDF (633 K)
doi: 10.17675/2305-6894-2018-7-3-12

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