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