Investigation of Organic Coatings Durability on Concrete Reinforcement Corrosion

Protection with the Synergistic Influence of Corrosion Inhibitors

S.Kalogeropoulou1, P.Pantazopoulou1, Th.Zafeiropoulou2, K. Sideris3

1. Electrical Engineering Department, Technological Educational Institute of Piraeus, Athens, Greece2. Faculty of Chemical Engineering, National Technical University of Athens, Greece

3. Democritus University of Thrace, Dept. of Civil Engineering, Xanthi, Greece

eRA – 9, T.E.I. of Piraeus, 22-24 September 2014

In this work the results obtained until now in the framework of an ARCHIMEDES III research project entitled "Investigation of Organic Coatings Durability on Concrete Reinforcement Corrosion Protection with the Synergistic Influence of Corrosion Inhibitors” are presented.

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Aim of the study

The action of various organic coatings and corrosion inhibitors in the protection of steel reinforcement in highly corrosive conditions is investigated. Five different types of organic protective coatings have been chosen to be studied: a two-pack epoxy paint, a two-pack polyurethane paint, a nanotechnology paint and two acrylic dispersions. A classification of the protective action of the organic coatings against corrosion, based on the results of various experimental methods, is presented.

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Reinforcement corrosion – Protection methods

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

coatings on the surface of concrete

corrosion inhibitors

cathodic protection

stainless steel reinforcement

coating of reinforcement

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available

protection

methods

Organic coatings

Surface coatings on concrete:prevent the deterioration by creating a

physical barrier between the concrete structure and the harmful substances from the environment

improve or maintain the appearance offer an effective and reliable solution for the

protection both of the concrete and the embedded steel

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Desired properties of organic coatings

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

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Corrosion inhibitors

Corrosion inhibitors have been successfully used as admixtures to concrete to reduce the risk of reinforcement corrosion.

Alkanolamine-based corrosion inhibitors move through the pore structure of concrete to reach the

surface of reinforcing steel, where they form a protective filmreduce chloride ion ingress into concreteare classified as mixed inhibitors, because they influence

both the cathodic and the anodic process of corrosion

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Degradation of coatings

Μain factors influencing the durability of coatings:

sunlight (ultraviolet radiation)

moisture

heat

Τhe result of the combination of these factors is much

more serious than each factor individually.

Degradation can vary from mere surface discoloration

affecting the aesthetic appeal of a product to substantial

loss of mechanical properties.

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Properties studied and methods used

Reinforcement’s corrosion behavior

Effect of UV-radiation to coatings

Liquid water and water vapor transmission rates

Carbonation depth

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Reinforcement’s corrosion behaviorUse of the Strain Gauge (SG) technique, which is based on

the appearance of swelling strain near the steel reinforcement in the concrete and is measured by embedded SG sensors in mortar specimens. 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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Effect of UltraViolet-radiation to coatingsDry Film Thickness was measured according to ASTM

D4138 “Standard Practices for Measurement of Dry Film Thickness of Protective Coating Systems by Destructive, Cross-Sectioning Means”.

Cross cut test was performed according to ISO 2409:1992(E) “Paints and varnishes – Cross cut test” and ASTM D3330 / D3330M - 04(2010) “Standard Test Method for Peel Adhesion of Pressure-Sensitive Tape”.

In coated specimens coatings’ adhesion was measured according to BS EN 24624:1993/ BS EN ISO 4624:2003 “Paints and varnishes - Pull off test for adhesion” and ASTM D4541 - 09e1 “Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers”.

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Liquid water and water vapor transmission rates

Liquid water transmission rate of each coating is determined according to standard DIN EN 1062-3:2008-04 “Paints and varnishes - Coating materials and coating systems for exterior masonry and concrete - Part 3: Determination of liquid water permeability”.

Water vapor transmission rate is determined according to standard DIN EN ISO 7783-2 “Coating materials and coating systems for exterior masonry and concrete - Part 2: Determination and classification of water-vapor transmission rate (permeability)”.

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Carbonation depth

Measurements of carbonation depth are performed

according to BS EN 13295:2004 "Products and systems for

the protection and repair of concrete structures - Test

methods - Determination of resistance to carbonation" and

BS EN 14630:2006 "Products and systems for the protection

and repair of concrete structures - Test methods -

Determination of carbonation depth in hardened concrete

by the phenolphthalein method".

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Materials

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Quarry sand Quarry sand

Reinforcement B500C

1 : 3 : 0.51 : 3 : 0.5

standard proportionscement : sand : water

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

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Organic Coatings Categories

Two-pack epoxy coating (E)

Two-pack polyurethane coating (P)

Nanotechnology coating (N)

Acrylic emulsion (A)

Elastomeric acrylic dispersion (R)

Uncoated specimens were used as reference (O)

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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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Organic coatings - technical characteristics

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.eRA-9 1822/9/2014

Primers – 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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Conclusions A: Corrosion evaluation The protective action of all organic coatings against

corrosion of the embedded reinforcement is confirmed. Epoxy and polyurethane coatings present an exceptional

performance. The nanotechnology coating presents reduced protective

ability in accelerated corrosion conditions. For the system “corrosion inhibitor – organic coating” the

results have shown that their action is not added. However there is an improvement of the protection given by the coatings with the inhibitor presence, especially in the case of the less effective coatings.

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Conclusions B: UV radiation & Water/Water vapor permeabilities

Polyurethane coatings present excellent resistance to ultra violet radiation as compared to epoxy coatings that suffer from yellowing. Both coatings present very low water vapor transmission rate and liquid water permeability.

Radiation causes mild degradation to the acrylic and elastomeric emulsions. Both coatings present fairly good behavior towards moisture.

The nanotechnology coating resists very well to radiation and presents an improved behavior compared to all other coatings systems regarding water vapor transmission rate and liquid water permeability.

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Conclusions C: Carbonation

The two-component industrial coatings with organic solvent (epoxy and polyurethane coatings) provide the best protection.

Aqueous dispersions conventional coatings (elastomeric and acrylic dispersions) offer a satisfying level of protection.

The nanotechnology coating provides a low and negligible protection rate.

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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!