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51318-11581-Exploratory evaluation of interface effects of cathodic prevention in concrete

Experiments on whether an intrinsic (predominantly interfacial effects of polarization) or an extrinsic (predominantly concentration changes due to polarization) mechanism may be dominant in the cathodic polarization of steel in concrete.

Product Number: 51318-11581-SG
Author: Krittin Rattakham / Alberto A. Sagüés
Publication Date: 2018
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Exploratory experiments were conducted seeking to provide empirical information on whether an intrinsic (predominantly interfacial effects of polarization) or an extrinsic (predominantly concentration changes due to polarization) mechanism may be dominant in the beneficial effect of cathodic polarization during cathodic prevention of steel in concrete. Tests used concrete specimens, each with a cast-in steel plate, constantly exposed to a high-chloride environment. The specimens were polarized at 4 different levels ranging from open circuit to -400 mV vs Saturated Calomel Electrode. Shortly after corrosion started specimens were demolished and measurements of pH using a novel procedure, and of chloride ion concentration, were done on the steel concrete interface. The experimental data confirmed the general expectation that concrete reinforcement benefits from cathodic polarization, as the specimens polarized at high cathodic polarization voltage tended to take longer to reach an active corrosion condition. The interfacial pH and chloride ion concentrations measured favored to some extent a dominant intrinsic mechanism interpretation, while the evidence in support of a dominant extrinsic mechanism interpretation at these moderate polarization levels remained elusive.

Key words: corrosion, passive film, in-situ leaching, pH, chloride threshold

Exploratory experiments were conducted seeking to provide empirical information on whether an intrinsic (predominantly interfacial effects of polarization) or an extrinsic (predominantly concentration changes due to polarization) mechanism may be dominant in the beneficial effect of cathodic polarization during cathodic prevention of steel in concrete. Tests used concrete specimens, each with a cast-in steel plate, constantly exposed to a high-chloride environment. The specimens were polarized at 4 different levels ranging from open circuit to -400 mV vs Saturated Calomel Electrode. Shortly after corrosion started specimens were demolished and measurements of pH using a novel procedure, and of chloride ion concentration, were done on the steel concrete interface. The experimental data confirmed the general expectation that concrete reinforcement benefits from cathodic polarization, as the specimens polarized at high cathodic polarization voltage tended to take longer to reach an active corrosion condition. The interfacial pH and chloride ion concentrations measured favored to some extent a dominant intrinsic mechanism interpretation, while the evidence in support of a dominant extrinsic mechanism interpretation at these moderate polarization levels remained elusive.

Key words: corrosion, passive film, in-situ leaching, pH, chloride threshold

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