Post on 11-Jul-2015
Electrochemical techniques for painting evaluation for protection
reinforced concrete against corrosion
Adriana de Araujo
Support: FAPESP
Zehbour Panossian
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-
Electrochemical techniques:
Corrosion potential and corrosion current density
Electric contact between electrodes:
Moisture of the concrete
Test specimen
Working electrode
Reference electrode
Counter-electrode
Varnishes
Low permeability
Low conductivity
film established in the surface
Test specimen
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
• corrosion potential;
• polarization resistance and corrosion current density
Reinforced concrete specimen
• mass variation;
• carbonatation depth;
• depth and % the chloride;
• film adherence;
• film visual inspection.
Test specimen – no bar
• 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
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
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
Working electrode
Reference eletrode
Corrosion potential
Active or passive state
Electric potential difference between carbon steel and satureted calomel
Automatic:
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)
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
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
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
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
...has the best properties and the best performance protection barrier for concrete structures against CO2 and Cl -
exposition
Conclusion - varnish
The polyurethane varnish...
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:
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
end
Thanks for your attention
Thanks Zehbour Panossian
Thanks FAPESP