Investigation of the anticorrosive effect of organic coatings on concrete reinforcement

in the presence or absence of corrosion inhibitor by the Strain Gauge technique

P.Pantazopoulou1, S.Kalogeropoulou1, A.Routoulas1, D.Tseles2

Technological Educational Institute of Piraeus,1 Physics, Chemistry & Materials Technology Department

2 Automation Department

eRA – 8,  Piraeus, Greece, 23-25 September 2013

Aim of the study

This paper refers to the investigation of the action of organic coatings and corrosion inhibitor in the protection of steel reinforcement in highly corrosive conditions. Reinforced mortar specimens were coated with five different organic protective coatings: a two-pack epoxy paint, a two-pack polyurethane paint, a nanotechnology paint and two acrylic dispersions. The results of the applied methodology were encouraging for the fast monitoring and the classification of the protective action of the organic coatings against corrosion.

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Reinforcement corrosion – Protection measures

Reinforcement corrosion: basic cause of reduction of a structure’s life

epoxy-coated reinforcement

stainless steel reinforcement

coating reinforcement

cathodic protection

paints on the surface of the

concrete

corrosion inhibitors

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available

protection

measures

Organic coatings

The use of organic coatings on the surface of reinforced

concrete is the most widespread protective method,

especially when long-term durability and superior

performance are extremely significant. Coatings prevent

the access of harmful substances for both the concrete and

the embedded steel from the environment into the

concrete, such as chloride ions, carbon dioxide or sulphur

dioxide.

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Properties of organic coatings

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Good adhesion to concrete even when wet.

Resistance to high alkalinity of concrete.

Ability to penetrate into the pores and cracks of concrete.

Good resistance to ultraviolet (UV) radiation and weathering.

Good mechanical strength.

Prevent entry of water but allow water vapor permeation.

High resistance to the permeation of sulfur dioxide and carbon

dioxide and to the penetration of chloride ions in the pores and

cracks (less than 0,3 mm)of the concrete.

Corrosion inhibitors

Corrosion inhibitors have been successfully used as admixtures

to concrete to reduce the risk of reinforcement corrosion.

Alkanolamine-based corrosion inhibitors can make use of the

porosity of concrete, by moving through the pore structure of

concrete to reach the surface of reinforcing steel, where they form

a protective film.

They reduce chloride ion ingress into concrete.

They are classified as mixed inhibitors, because they influence

both the cathodic and the anodic process of corrosion.

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Investigation methodology

Corrosion measurement with the Strain Gauge (SG) technique. This technique, used for the fast evaluation of corrosive behavior of reinforcement caused under impressed anodic potential, is based on the appearance of swelling strain near the steel reinforcement in the concrete. The cause of the swelling tension is the formation of corrosion products (iron oxides, Fe3O4, Fe2O3, FeO(OH)) having greater specific volume than iron.

Determination of the gravimetric mass loss of reinforcing steel bars after a certain period of exposure in the corrosive environment. Mass loss (according to ISO/DIS 8407) is estimated as the difference between the initial and the final mass of the bars, as determined by removing the corrosion products from the bars.

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Materials

Quarry sand Quarry sand Coatings

Cement CEM ΙΙ 32.5

Water

Reinforcement B500C

1 : 3 : 0.51 : 3 : 0.5

standard proportionscement : sand : water

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Inhibitor

Chemical composition of Portland cement (%wt)

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SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O SO3 CaO(f) LOI

CEM II 32.5 20.67 4.99 3.18 63.60 2.73 0.37 0.29 2.41 2.41 2.52

Chemical composition of steel (%wt)

C Mn S P Si Ni Cr Cu V Mo

0.22 1.24 0.044 0.032 0.28 0.09 0.10 0.52 0.075 0.028

Coatings categories

Two-pack epoxy coating

Two-pack polyurethane coating

Nanotechnology coating

Acrylic dispersion 1

Acrylic dispersion 2

Uncoated specimens were used as reference

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Coating procedure

The coating procedure for all coatings involves three layers:The appropriate for each coating primer is applied on the

dried surface of the specimen, to achieve the best adhesion between coating and mortar.

24 hours The first layer of the organic coating is applied by brush. 24 hours The second layer of the organic coating is applied by brush

perpendicularly to the first one.Coated mortar specimens are stored in the laboratory for at

least 7 days, so as coatings are dried and all quantity of solvents has evaporated.

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S/N Code Product Color Characteristics

1 Ε Epoxy Grey Two-pack epoxy paint with amine hardener, density 1,55 kg/Lt, spreading rate 6 m²/kg (100

μm), solids 95% w/v.

2 P Polyurethane Grey Two-pack polyurethane with aliphatic isocyanic hardener, density 1,20-1,40 kg/Lt, spreading

rate 9-11 m²/ Lt (50μm).

3 N Paint for exterior use

White Siloxane paint, density 1,60 kg/Lt, solids 50% w/v, spreading rate 8,6 m²/Lt.

4 A Acrylic emulsion paint for exterior

use

White Acrylic dispersion, density 1.46±0.05 g/ml, solids 61±2.5% w/w, pH 8.4±1, spreading rate 9±1

m²/Lt (2 coats).

5 R Elastomeric insulating acrylic

paint

White Acrylic dispersion, undiluted for final coat, density 1.35 g/ml, solids 60±2% w/w, spreading

rate 2±1 m²/Lt.

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Categories of organic coatings - technical characteristics

S/N Code Product Color Characteristics1 ΕΑ Epoxy primer

(coatings 1-2)Colorless Two-pack epoxy primer, Α:Β-2:1 w/v with

hardener, solids 58% w/v, density 0,99 kg/Lt, spreading rate 10 m²/Lt.

2 ΑΑ Acrylic water-based primer

(coating 3)

Colorless Density 1kg/Lt, solids 25,9% w/v, dilution up to 1:4 with water, spreading rate 8-32 m²/Lt.

3 SΑ Styrene-acrylic primer

(coatings 4-5)

Colorless Copolymers of styrene and acrylic resins, density 0.85 g/ml, solids 26±2% w/w,

spreading rate 7.5-8.5 m²/Lt.

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Categories of primers – technical characteristics

SG specimens

S/N Category Inhibitor Primer Coating

1 SGE - EP E

2 SGP - EP P

3 SGN - AA N

4 SGA - SΑ A

5 SGR - SΑ R

6 SGO - - -

7 SGN-A A AΑ N

8 SGA-A A SΑ A

9 SGR-A A SΑ R

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Shape and dimensions of Strain Gauge specimens (mm)

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REINFORCEMENT

MORTAR

ARALDITE

35

10

35

15

85

15

20 10 50

CABLE

SG SG

Schematic diagram of corrosion test set-up

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+ + - -

SG AMPLIFIER POTENTIOSTAT

STEEL BAR STRAIN GAUGE

GRAPHITE

ELECTRODE

SG SPECIMEN

3.5% NaCl sol

REFERENCE

ELECTRODE

V

V A

SG values vs. time for all specimens

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Anodic current values for all SG specimens

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Mass losses of steel reinforcement in SG specimens

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Protection offered (%)

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Protection offered : [(MLU.S. – ΜLC.S.) / MLU.S. ] . 100Classification SGP – SGE > SGA > SGR > SGN

SG values vs. time for specimens with corrosion inhibitor

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Mass losses of steel reinforcement in SG specimens with corrosion inhibitor

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Conclusions 1

The measurements performed in this study verify the protective action of all organic coatings against corrosion of the embedded reinforcement, whereas epoxy and polyurethane coatings present an exceptional performance.

The coating with the nanotechnology characteristics presents reduced protective ability, which can be attributed to the very slow action of its components compared to the rate of the implied corrosion.

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Conclusions 2

The results of the total corrosion protection of the

system corrosion inhibitor – organic coating insinuates

that their action is not added, but there is a selective

improvement of the protection given by the coatings,

especially in the cases when this protection is

comparatively lower.

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SG specimens

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Laboratory corrosion test set-up

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Laboratory SG corrosion control system

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Cracked specimen

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Steel reinforcement

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Acknowledgements

This research has been co-financed by the European Union

(European Social Fund – ESF) and Greek national funds through

the Operational Program "Education and Lifelong Learning" of the

National Strategic Reference Framework (NSRF) - Research

Funding Program: ARCHIMEDES III. Investing in knowledge society

through the European Social Fund.

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Thank you for your attention!

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