investigation of the anticorrosive effect of organic coatings on concrete reinforcement in the...
TRANSCRIPT
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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