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Extent of Cathodic Reaction on Epoxy Coated Rebar with Partially Disbonded Coating

Distress (controlled surface breaks) was created on production samples of epoxy coated rebar and some were further subject to cathodic disbondment. Samples were cast in concrete and subjected to  cyclic polarization and electrochemical impedance spectroscopy  measurements.

Product Number: 51317--9469-SG
ISBN: 9469 2017 CP
Author: Sylvia Kessler
Publication Date: 2017
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Corrosion of epoxy coated rebar (ECR) in chloride exposed concrete can be enabled by theoxygen reduction cathodic reaction taking place on steel exposed by coating breaks. The totalcathodic current would be expected to increase if the reaction locus were to extend into crevicesformed at disbonded coating regions around coating breaks. To examine the possible amount ofthis effect distress in the form of controlled surface breaks was created on production samplesof ECR some of which were further subject to cathodic disbondment to create surroundingdisbonded regions around the breaks. The samples were cast in concrete specimens kept at~80% RH in air and fitted with electrodes to perform cyclic polarization (CYP) in the cathodicdirection and electrochemical impedance spectroscopy (EIS) measurements under open circuitconditions. Measurements performed initially and after 6 years of aging showed for thedisbonded specimens a moderately greater extent of cathodic current and greater effectiveelectrode area compared to that of the simply distressed specimens. Results will be presentedas well for experiments in progress where concrete moisture is elevated to increase theelectrolyte content in the disbondment crevice. The implications of the findings on the estimatedservice life of ECR structures will be quantitatively assessed.

Key words: Epoxy-coated reinforcement, cathodic disbondment, electrode area

Corrosion of epoxy coated rebar (ECR) in chloride exposed concrete can be enabled by theoxygen reduction cathodic reaction taking place on steel exposed by coating breaks. The totalcathodic current would be expected to increase if the reaction locus were to extend into crevicesformed at disbonded coating regions around coating breaks. To examine the possible amount ofthis effect distress in the form of controlled surface breaks was created on production samplesof ECR some of which were further subject to cathodic disbondment to create surroundingdisbonded regions around the breaks. The samples were cast in concrete specimens kept at~80% RH in air and fitted with electrodes to perform cyclic polarization (CYP) in the cathodicdirection and electrochemical impedance spectroscopy (EIS) measurements under open circuitconditions. Measurements performed initially and after 6 years of aging showed for thedisbonded specimens a moderately greater extent of cathodic current and greater effectiveelectrode area compared to that of the simply distressed specimens. Results will be presentedas well for experiments in progress where concrete moisture is elevated to increase theelectrolyte content in the disbondment crevice. The implications of the findings on the estimatedservice life of ECR structures will be quantitatively assessed.

Key words: Epoxy-coated reinforcement, cathodic disbondment, electrode area

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