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

1. Electrochemical techniques for
painting evaluation for protection
reinforced concrete against
corrosion
Adriana de Araujo
Support: FAPESP
Zehbour Panossian

2. Test specimen
Electrochemical techniques :
Evaluation of the performance
Establishment of selection
methodology
Protection varnishes studies for reinforced
concrete:
Acrylic
Polyurethane
Execution and integrity of varnishes
thoughout the tests
CO2
Cl-

3. Electrochemical techniques:
Corrosion potential and corrosion
current density
Electric contact between electrodes:
Moisture of the concrete
Test specimen
Working electrode
Reference electrode
Counter-electrode

4. Varnishes
Low
permeability
Low
conductivity
film established in the
surface
Test specimen

5. Electrochemical
techniques
moisture of the concrete at the region
of the electrodes through the plastic
tube (for reference electrode)
Test specimen
Reference electrode and counter-
electrode embedded in concrete with
measurements in your stretch
displayed

6. • corrosion potential;
• polarization resistance and
corrosion current density
Reinforced concrete specimen

7. • mass variation;
• carbonatation depth;
• depth and % the chloride;
• film adherence;
• film visual inspection.
Test specimen – no bar

8. • number and dimensions of the test
specimen;
• concrete proportion;
• protetion: test specimen edges and
electrodes extremeties;
• concrete consolidition;
• surface finishing.
Exposition to agressive environments
Achievement of the companions tests
Test specimen

9. Sponge (for avoiding the
penetration of the cement past
and aggregates)
Protection painting
(bars extremities)
Cupperbar
Carbonsteelbar
Plastictube Test specimen - bar

10. Potentostat PAR 273 A
Reference eletrode
Sodium sulfate (10%)Electrolyte solution
Working electrode Steel carbon bar
Saturated Calomel
Parcial painting removed
Electrochemical techniques
Introducting electrolyte
solution

11. Working electrode
Reference
eletrode
Corrosion potential
Active or passive
state
Electric potential
difference between
carbon steel and
satureted calomel
Automatic:

12. Counter-electrode
Corrosion current density
Ecorr
Linear polarization curve (Ecorr
±10 mV, scanning speed ±10 mV/s);
Tafel constants
Constants B (also for reference)
Rp (also obtained in the best
tangent slop of the curve, around
the Ecorr)
Icorr (also by manual results)

13. Concrete proportion: interference in the results
Cure: insufficient
Finishing: failure in the concrete execution
Elements embebed: infiltration (Cl-
test)
Should use a/c ratio
0,65
Should stabilize the mass of the concrete
Must improve the consolodation
Must increase the
adherence (change the
paint type)
Resultados – test specimen

14. Conclusion – test specimen
The test specimen is adequate...
...as long as it is well executed, cured,
painted and the electrodes were protected
and adherent to the concrete
...nevertheless in highly aggressive
atmosphere (Cl-
) the adherence of the
leaded elements has to be improved

15. CO2 exposition
Conclusion – Electrochemical techniques
The corrosion potential is the best test for the
varnish evaluation, although it is recommended that
it is carried out with another test (carbonation
depth)
number: 5 specimens
The color of the concrete changed (by pH
test) after the corrosion was detected
Corrosion current density is only useful for
further studies more complex

16. The corrosion potential can be obtained together
with profile chlorates which is the best test for
varnish evaluation
Active state occurs after high % chlorates
have been detected
Corrosion current density is not
representative of pitting corrosion
number: 10 specimens
Conclusion – Electrochemical techniques
Cl-
exposition

17. ...has the best properties and
the best performance protection
barrier for concrete structures
against CO2 and Cl-
exposition
Conclusion - varnish
The polyurethane varnish...

18. Acrylic:
CO2 exposition
Recently applied film, 3 coats, leaded to protection
such as the aged polyurethane
Recently applied film in 2 coats and aged film, 2 e
3 coats, didn´t protect the concrete (was similar to
the specimen without painting)
Recently applied film, 2 and 3 coats, leaded to
better protection
Aged film, 2 and 3 coats, is less efficient than the
new one (the protection was similar to the recent
applied acrylic, 3 coats)
Polyurethane:

19. Recently applied film and aged film, 2 e 3 coats,
didn´t protect the concrete (was similar to the
specimen without painting)
Recently and aged applied film , 2 and 3 coats,
leaded to better protection
The aging film didn´t reduce its
efficiency such as in CO2 exposition
polyurethane:
Acrylic:
Cl-
exposition

20. end
Thanks for your attention
Thanks Zehbour Panossian
Thanks FAPESP