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

Visual examination

Blackfriar bridge UK 2004 Deck of Po-Hang harbour Korea 2007

Inconclusive

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