Seminar in Hokkaido University
MEASUREMENT OF STEEL CORROSION IN CONCRETE
2 March 2010
K.Y. Ann
Concrete Materials, Mechanics and EngineeringSchool of Civil and Environmental Engineering
Yonsei Univ., Seoul 120-749, KOREA
Contents
1. Importance of corrosion-induced problematic issue
2. Mechanism of corrosion- Corrosion model- Onset of corrosion: corrosive/inhibitive- Corrosion propagation
3. Measurements- Visual examination- Half-cell potential- Half-cell potential- Polarisation resistance- Galvanic current- AC impedance- Mass loss
4. Electrochemical repair- Cathodic protection- Electrochemical chloride extraction- Realkalisation
5. Conclusion
Importance of corrosion in concrete bridges
Heringsdorf Bridge, Germany (taken by K.Y. Ann, 2004)
Concrete spalling out
Severe rusting
Volume change of rusting
Volume
Fe
FeO
Corroded
Fe3O4
Fe2O3
Fe(OH)2
Fe(OH)3
Fe(OH)33H2O
Mehta and Monteiro, Properties of concrete, 1993
Blackfriar bridge UK, 2004
Life of concrete structures exposed to marine
Damage limit
Physical damage
Loss of steel/concrete
propertiesChloride threshold
Abating
Corrosion initiation
Cover protection
Seawater contamination
properties
Cl-free
Abating
Time
Concrete quality
OH- OH-OH-
Ca+
Na+
K+
Ca+
Na+
K+Paste
Steel
Cl-Cl-
Cl-
Cl-
Cl-
Steel
Pores at the interface
Hydrations Hydrations Ann and Song Corros Sci 2007
Chloride binding vs buffering
Cl-Cl-
Cl-
Cl-
Cl-
C3A Hydrations C4AF
pH fall
Cl- Cl-
Solid precipitated hydrations: Ca(OH)2
Solid precipitated hydrations
Buffering a pH fall
Buffering a pH fall
Pores at the interface
Steel
Ann et al, Consec 07, 2007
Steel-concrete interface
Hydration layer
Pores at the interface
Cl-Cl-
Cl-
Cl-
Cl-
External chlorides
Steel
Hydration layer
Reou and Ann, Mag Concr Res 2008
Corrosion initiation
Fe2+Fe2+Fe2+Fe2+Fe2+
Pit Nucleation Events
Fe2++OH-→ Oxide Film
SALT
ANODE
HCl
Cl- H2O
Cl- Cl-
Concrete
CO2
H2CO2
FeFeFeFeFe
Fe +OH → Oxide FilmHCl
Fe2+
2 Stages of Cl- induced corrosion initiation– Pit Nucleation– Stable Pit Growth
• local pH reduction• local chloride build up
Steel
Passive Film
Half-cell potential
Critical potential for corrosion
(ASTM C 876)
• -350 mV vs CSE
• -275 mV vs SCE
Pourbaix, Corrosion, 1966
Qualitative information, but not quantitative for the corrosion rate (rust amount)
Half-cell potential
Principle
Voltmeter
Electrode
Passive
Corrosive
Corrosive
Half-cell potential mapping
Passive
Passive
Corrosive
Corrosive
Polarisation technique
E Anodic
Cathodic
InterceptCorrosion potential
Anodic polarisationPrinciple
I
E Anodic
Corrosion current
Ann et al Cem Concr Res 2006
Concrete resistance
Polarisation technique
-600
-500
-400
-300
-200
E (mV)
Tafel extrapolationAnodic polarisation
-600
-500
-400
-300
-200
E (mV)
Anodic activity (Ba)
I
ERp
∆
∆=
-800
-700
-600
0.1 1 10 100 1000
I (mA)
Reou and Ann, Mater Chem Phy, 2008
-800
-700
-600
0.1 1 10 100 1000
I (mA)
)(3.2 BcBaRp
BaBcI
+=
Cathodic activity (Bc)
Rp
BI = B: 26 mV (corrosive)
52 mV (passive)
Quantitative, conclusive
AC Impedance
Electric circuit for AC impedance
-jZ’’
Quantitative, but too sensitive to noise and wave
Z’
Polarisation resistance of steel
Resistance of passivation
Resistance of concrete
Galvanic current
Principle
e- e- e-
Corroded
Galvanic current
2
3
Galvanic current (mA/m2) Corrosion initiation
Uncorroded
Galvanic current
0
1
0 10 20 30 40 50
Time (days)Galvanic current (mA/m
Ann and Buenfeld, Mag Concr Res, 2007
Informative for detecting corrosion initiation, but less conclusive for its propagation
Galvanic current
Ladder system
Concrete
Steel
Cl-
Cl-
Reference steel bars
Cl-
Cl-
Noble metal (uncorrosive)
Mass loss
Principle
y = 0.455x - 0.2118
R2 = 0.939
0.5
1.0
1.5
2.0
Mass loss (%)
tAIM wcorr
=
0.0
0.5
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Chlorides in cast (%, cement)
Reou and Ann, Chem Phy, 2008, unpublished
0.8%
the most tangible information, but destructive
nF
tAIM wcorr
=
M : Mass (g)
Icorr : Corrosion rate
t : Time
Aw : Atomic weight
n : Valency
F : Faraday constant
Corrosion values at a given condition
0.1
1
10
100
1000
Corrosion rate (mA/m
2)
Galvanic current
Linear polarisation
Tafel's extrapolation
Corrosion rate
-400
-300
-200
-100
0
Corrosion potential (mV, SCE)
Corrosion potential
Half-cell potential
0.001
0.01
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Chlorides in cast (%, cement)
-600
-500
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Chlorides in cast (%, cement)
Corrosion potential (mV, SCE)
Corrosion values at corrosion
Half cell potential
Galvanic current
Anodic polarisation
Tafel extrapolation
-343 mV
0.63 mA/m2
8.29 mA/m2
9.94 mA/m2
Principle of electrochemical treatment
DC PowerSupply +-
e-e-
ReductionReactions
OxidationReactionsSolution electrolyte
(Current conduction via ions)
O2 + H
2O H
2O
OxygenReduction
OxygenEvolution
Mechanism Application of in-situ
Control pipe
OH-
H2 + OH-
H2O
Fe3+
Fe2+ Fe2+
H+ + O2
Cl-
Cl2
Fe
Reduction
HydrogenEvolution
Iron oxideReduction
ChlorideEvolution
IronOxidation
OH- Cl- CO32-
Ca2+ Fe2+ Na+ H+
Ionic ConductionIon Migration
Glass 1986, Corros
Sacrificial anode
St. Kinston bridge, Canada, 2003
Cathodic protection
Potential
Current
Ann PhD thesis, Imperial College, 2005
1. Sacrificial anode: corrosive metal provides electrons to the steel (Eg. zinc). Attachment of anode on concrete is a key factor
2. Impressed current: electrons are provided by a DC power supply directly to the steel. Conductive paint serves as an anode
Chloride extraction
H2 gas
Titanium mesh
Chloride extraction
Shutter
Electrolyte
Bracket
Frame
Sealing
Steel rebar
Power supply
Titanium mesh Plastic sheet
Blocker
Cork
Setting-up of titanium mesh ( Tampa, US 2002)
Supplementary benefits
- Increasing OH- at the steel
-Densifying calcium hydroxide
- Supply of electrons to the steel then to repassivate
Realkalisation
Steel rebar
Sealing
H2 gas
Titanium mesh
Alkali ion injection
Jubilee line extension UK, 2001
Frame
Bracket
injection
Shutter
Electrolyte
Banfill 1997 Const Build Mater
Long term monitoring results concerning the effect of realkalisation have not been confirmed due to its short history
Cathodic prevention
Power supplye-
OH- generated at the steel
e-
Calcium hydroxide layer
Glass and Buenfeld, Corros Sci, 2001
Rusting Deposition of hydration products
Concrete block
OH- generated at the steel
Ca+ forced to move to steel
ConductiveSteel rebar
At present, only investigation has undergone with no application to in-situ
Application to in-situ
Cathodic protection Chloride extraction Realkalisation Cathodic prevention
Remove chlorides from the concrete
Increase the alkalinity of concrete at the steel depth to counter carbonation
Inhibit corrosion by enhancing passivity
Lower the potential to enhance passivity
Steel-bond reduction Hydrogen embrittlement
1-20 mA/m2
Permanent after application
1-2 A/m2
6-10 weeks
Steel-bond reduction
5 A/m2
(1 A/m2 to concrete)
1-3 weeks
Steel-bond reduction
Potential ASR
0.4-20 mA/m2
Permanent after application
None reported
Ann, PhD thesis, Imperial College, 2005
Recommendations
1. Corrosion of steel in concrete is subjected to both corrosiveness of acidification and inhibition effect of cement matrix.
2. Half-cell potential is easily applied to in-situ, but its results are only restricted to qualitative determination whether or not corrosion starts.
3. Polarisation technique may be the best option to detect the state of steel in terms of corrosion, as being the quantitative in determining corrosion.terms of corrosion, as being the quantitative in determining corrosion.
4. Galvanic current provide information on the onset of corrosion, but no more conclusive data for the rate of corrosion propagation.
5. AC impedance technique provides very convincible information on corrosion, but less applicable to field due to its sensitivity.
6. Electrochemical treatment is a noble option to cure corroded steel in concrete.
Acknowledgement
The author would like to thank for helpful comments and advice to:
Broomfield JP, Corrosion Doctors, UK
Buenfeld NR, Imperial College, UK
Glass GK, Boston Consulting, US
Head MK, Leeds University, UK
Syprounse S, ATCK Constructions, Greece
Kim JH, Yonsei University, Korea
Price WF, Lafarge Cement, UK
Zhang J-Z, Lafarge Cement, France