ELECTROCHEMICAL TECHNIQUES FOR EVALUATION OF PROTECTIVE COATINGS AGAINST CORROSION IN CONCRETE...
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Transcript of ELECTROCHEMICAL TECHNIQUES FOR EVALUATION OF PROTECTIVE COATINGS AGAINST CORROSION IN CONCRETE...
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Electrochemical techniques for painting evaluation for protection
reinforced concrete against corrosion
Adriana de Araujo
Support: FAPESP
Zehbour Panossian
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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-
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Electrochemical techniques:
Corrosion potential and corrosion current density
Electric contact between electrodes:
Moisture of the concrete
Test specimen
Working electrode
Reference electrode
Counter-electrode
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Varnishes
Low permeability
Low conductivity
film established in the surface
Test specimen
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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
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• corrosion potential;
• polarization resistance and corrosion current density
Reinforced concrete specimen
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• mass variation;
• carbonatation depth;
• depth and % the chloride;
• film adherence;
• film visual inspection.
Test specimen – no bar
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• 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
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Sponge (for avoiding the penetration of the cement past
and aggregates)
Protection painting (bars extremities)
Cup
per b
ar
Car
bon
stee
l bar
Plas
tic tu
beTest specimen - bar
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Potentostat PAR 273 A
Reference eletrodeSodium sulfate (10%)Electrolyte solution
Working electrode Steel carbon bar
Saturated Calomel
Parcial painting removed
Electrochemical techniques
Introducting electrolyte solution
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Working electrode
Reference eletrode
Corrosion potential
Active or passive state
Electric potential difference between carbon steel and satureted calomel
Automatic:
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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)
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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 stabil ize the mass of the concrete
Must improve the consolodation
Must increase the adherence (change the paint type)
Resultados – test specimen
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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
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CO2 exposition
Conclusion – Electrochemical techniques
The corrosion potential is the best test for the varnish evaluation, although it is recommended that i t 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
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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 pitt ing corrosion
number: 10 specimens
Conclusion – Electrochemical techniques
Cl- exposition
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...has the best properties and the best performance protection barrier for concrete structures against CO2 and Cl -
exposition
Conclusion - varnish
The polyurethane varnish...
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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:
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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 f i lm didn´t reduce its eff iciency such as in CO2 exposit ion
polyurethane:
Acrylic:
Cl- exposition
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end
Thanks for your attention
Thanks Zehbour Panossian
Thanks FAPESP