ELECTROCHEMICAL TECHNIQUES FOR EVALUATION OF PROTECTIVE COATINGS AGAINST CORROSION IN CONCRETE STRUCTURES

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Electrochemical techniques are one of the main tools for studying corrosion in civil engineering. They can be used to evaluate for example the performance of concrete components, ratios and also protective coatings. In this paper, some electrochemical measurements are discussed and an appropriate specimen configuration is proposed to the evaluation of concrete protection coatings by electrochemical techniques using a potenciostat. This configuration is conceived in order to permit the accomplishment of electrochemical measurement during accelerated corrosion tests without causing damages to the applied coating due to the humidification of the concrete specimen and/or the electrical connections of the electrodes. For such, accelerated corrosion tests were conducted with the support of FAPESP, in two different environments: one contaminated with chloride and the other with carbon dioxide. It was verified that the proposed specimen is adequate for concrete protection coating evaluation, and that the corrosion potential was the most appropriate electrochemical parameter for both aggressive environments, but the corrosion rate was appropriate only for the carbon dioxide contaminated environment.

As técnicas eletroquímicas constituem uma das principais ferramentas de estudo da corrosão na construção civil. Estas podem ser utilizadas, por exemplo, para avaliação do desempenho de componentes do concreto, traços e, também, revestimentos de proteção. Neste artigo, algumas medidas eletroquímicas são discutidas e é proposto um corpo-de-prova armado apropriado para a sua realização, usando um potenciostato, para a avaliação do desempenho de pinturas de proteção ao concreto. Esta adequação foi feita para permitir que as medições ocorressem durante ensaios de desempenho, sem causar prejuízos às pinturas na etapa de umedecimento do concreto e/ou de contado elétrico entre eletrodos. Para tanto, foram realizados, com o apoio da FAPESP, ensaios acelerados em que corpos-de-prova revestidos foram expostos a dois diferentes ambientes: um contaminado com cloretos e outro com dióxido de carbono. Ao final dos trabalhos, verificou-se que o corpo-de-prova proposto é adequado para avaliar revestimentos por meio de técnicas eletroquímicas. De todos os ensaios de acompanhamento realizados, o potencial de corrosão foi o mais importante em ambos os ambientes agressivos, enquanto a obtenção da velocidade de corrosão foi relevante somente no ambiente contaminado com dióxido de carbono.

ARAUJO, A.; PANOSSIAN, Z. Técnicas eletroquímicas para avaliação de pinturas de proteção contra corrosão nas estruturas de concreto. In: CONGRESSO LATINO AMERICANO DE CORROSÃO, 26, 2006, Fortaleza. Anais... Rio de Janeiro: LATINCORR 2006

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ELECTROCHEMICAL TECHNIQUES FOR EVALUATION OF PROTECTIVE COATINGS AGAINST CORROSION IN CONCRETE STRUCTURES

  1. 1. Electrochemical techniques forpainting evaluation for protectionreinforced concrete againstcorrosionAdriana de AraujoSupport: FAPESPZehbour Panossian
  2. 2. Test specimenElectrochemical techniques :Evaluation of the performanceEstablishment of selectionmethodologyProtection varnishes studies for reinforcedconcrete:AcrylicPolyurethaneExecution and integrity of varnishesthoughout the testsCO2Cl-
  3. 3. Electrochemical techniques:Corrosion potential and corrosioncurrent densityElectric contact between electrodes:Moisture of the concreteTest specimenWorking electrodeReference electrodeCounter-electrode
  4. 4. VarnishesLowpermeabilityLowconductivityfilm established in thesurfaceTest specimen
  5. 5. Electrochemicaltechniquesmoisture of the concrete at the regionof the electrodes through the plastictube (for reference electrode)Test specimenReference electrode and counter-electrode embedded in concrete withmeasurements in your stretchdisplayed
  6. 6. • corrosion potential;• polarization resistance andcorrosion current densityReinforced concrete specimen
  7. 7. • mass variation;• carbonatation depth;• depth and % the chloride;• film adherence;• film visual inspection.Test specimen – no bar
  8. 8. • number and dimensions of the testspecimen;• concrete proportion;• protetion: test specimen edges andelectrodes extremeties;• concrete consolidition;• surface finishing.Exposition to agressive environmentsAchievement of the companions testsTest specimen
  9. 9. Sponge (for avoiding thepenetration of the cement pastand aggregates)Protection painting(bars extremities)CupperbarCarbonsteelbarPlastictube Test specimen - bar
  10. 10. Potentostat PAR 273 AReference eletrodeSodium sulfate (10%)Electrolyte solutionWorking electrode Steel carbon barSaturated CalomelParcial painting removedElectrochemical techniquesIntroducting electrolytesolution
  11. 11. Working electrodeReferenceeletrodeCorrosion potentialActive or passivestateElectric potentialdifference betweencarbon steel andsatureted calomelAutomatic:
  12. 12. Counter-electrodeCorrosion current densityEcorrLinear polarization curve (Ecorr±10 mV, scanning speed ±10 mV/s);Tafel constantsConstants B (also for reference)Rp (also obtained in the besttangent slop of the curve, aroundthe Ecorr)Icorr (also by manual results)
  13. 13. Concrete proportion: interference in the resultsCure: insufficientFinishing: failure in the concrete executionElements embebed: infiltration (Cl-test)Should use a/c ratio0,65Should stabilize the mass of the concreteMust improve the consolodationMust increase theadherence (change thepaint type)Resultados – test specimen
  14. 14. Conclusion – test specimenThe test specimen is adequate......as long as it is well executed, cured,painted and the electrodes were protectedand adherent to the concrete...nevertheless in highly aggressiveatmosphere (Cl-) the adherence of theleaded elements has to be improved
  15. 15. CO2 expositionConclusion – Electrochemical techniquesThe corrosion potential is the best test for thevarnish evaluation, although it is recommended thatit is carried out with another test (carbonationdepth)number: 5 specimensThe color of the concrete changed (by pHtest) after the corrosion was detectedCorrosion current density is only useful forfurther studies more complex
  16. 16. The corrosion potential can be obtained togetherwith profile chlorates which is the best test forvarnish evaluationActive state occurs after high % chlorateshave been detectedCorrosion current density is notrepresentative of pitting corrosionnumber: 10 specimensConclusion – Electrochemical techniquesCl-exposition
  17. 17. ...has the best properties andthe best performance protectionbarrier for concrete structuresagainst CO2 and Cl-expositionConclusion - varnishThe polyurethane varnish...
  18. 18. Acrylic:CO2 expositionRecently applied film, 3 coats, leaded to protectionsuch as the aged polyurethaneRecently applied film in 2 coats and aged film, 2 e3 coats, didn´t protect the concrete (was similar tothe specimen without painting)Recently applied film, 2 and 3 coats, leaded tobetter protectionAged film, 2 and 3 coats, is less efficient than thenew one (the protection was similar to the recentapplied acrylic, 3 coats)Polyurethane:
  19. 19. Recently applied film and aged film, 2 e 3 coats,didn´t protect the concrete (was similar to thespecimen without painting)Recently and aged applied film , 2 and 3 coats,leaded to better protectionThe aging film didn´t reduce itsefficiency such as in CO2 expositionpolyurethane:Acrylic:Cl-exposition
  20. 20. endThanks for your attentionThanks Zehbour PanossianThanks FAPESP

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