2007d_2 Corrosion (Advanced Topic)

CORROSION OF CORROSION OF RREINFORCED CONCRETEEINFORCED CONCRETE(advanced topics)(advanced topics)--macromacro--corrosion vs. microcorrosion vs. micro--corrosioncorrosion--an example of corrosion rate analytical modelan example of corrosion rate analytical model--crack effectcrack effect

Ha-Won Song

Professor School of Civil and Environmental Engineering

Yonsei Univ., Seoul 120-749, KOREA

Concrete Materials, Mechanics & Engineering Lab., Yonsei Univ.

BasicBasicssThere is some reinforced concrete structures exposed under the severe environmental conditions.

Concrete

SteelAnode Cathode

Cl－The steels in concrete are corroded.

Steel Corrosion in ConcreteAnode Fe Fe2++2e-

Cathode O2+2H2O+4e- 4OH-

Pier, 60 years

e-

e-


BasicBasicss (cont.)(cont.)

The corrosion start timecould be estimated by analyzing the permeation of chloride ions in concrete.

It is necessary to check the durability of the reinforced concrete throughout long term.

00.20.40.60.81.0

0 10 20 30Distance from surface (cm)

Cl-

cont

ent (

wt%

)

SimulationMeasurement

Time

Deg

rada

tion

Cl- penetration

Corrosion start

Crack by corrosion

Depassivation

(CTL)


Corrosion initiationCorrosion initiation

pH of Portland cement = 12.5 ~ 13Cl-Cl- Cl-

Concrete

Steel

► Acidification

Passivation film

bound Cl- free Cl-

► A pH fall

depassivation

Chloride Threshold Level (CTL)

Fe2+ + 2Cl- → FeCl2FeCl2 + 2H2O → Fe(OH) 2 + 2H + + 2Cl-


Location of Defect and Steel ElementLocation of Defect and Steel Element

Concrete

Element-1 Element-2

Crack

Steel

Cl- O2


Effect of cracksEffect of cracks

Cl-

Cl-

Cl-O2 O2 O2

-→ eFeFe 2++2

-OH→eO+H+O - 442 22

Anode :

Cathode :

Corrosion Reaction

Change of Diffusivity

Crack

Chloride Oxygen

Corrosion Current Density


Corrosion rate due to cracksCorrosion rate due to cracks

It is necessary to predict the corrosion rateconsidering the macrocell corrosion at the bending crack.

Concrete

Anode C

Cl－

CC

Concrete

Cl－

C A C A C A

Macro-cellMicro-cell

Micro-cell

Micro-cell

cf) C. Andrade, I. R. Maribona, S. Feliu, J. A. Gonzalez, and S. Feliu, Jr (1992),N. Sato (1995)


Corrosion rate modelCorrosion rate modelThe basic model which estimates the corrosion rate in the reinforced concrete with the crack can beproposed.

Construction of model

Verification using specimenmortar concrete

Confirmation of engineering value of model

FlowFlow


Corrosion RateOutput dataInfluence on Corrosion Rate

Microcell Corrosion Rate Macrocell Corrosion Rate

Electric Resistancebetween Anode and Cathode

Input dataAnodic

Polarization Curve

Polarization Resistance

Cathodic Polarization

CurveConcrete

Resistance


anodic polarization curves of steel insaturated hydraulic calcium oxide

-0.7

-0.5

-0.3

-0.1

0.1

0.00001 0.0001 0.001 0.01 0.1 1Current (micro A/cm2)

Pote

ntia

l (V)

Cl-

: 0%

Cl-

: 3% Cl-

: 15%

Cl-

: 6%

Example of Polarization Curve


Corrosion RateOutput dataInfluence on Corrosion Rate

Microcell Corrosion Rate Macrocell Corrosion Rate

Electric Resistancebetween Anode and Cathode

Input dataAnodic

Polarization Curve

Polarization Resistance

Cathodic Polarization

CurveConcrete

Resistance

Crack HumidityParameter for specimen test W/C


CA

Microcell

CA CA

ACC C C

Macrocell

C

A : Anode: Cathode

Divided Rebar & Corrosion Cell

CA CA


Cathodic polarization curve

Current (A)

Potential loss

Anodic polarization curvePote

ntia

l (V)

Analysis Procedure of Analysis Procedure of Microcell CorrosionMicrocell Corrosion

Element-1 Element-2

Crack

Steel

Concrete

C A

Rp Rp

Imicro( ) microAC IRpRpEE ×+=− 2222

EA2

EC2

unknown


Analysis Procedure of Analysis Procedure of Macrocell CorrosionMacrocell Corrosion


Current (A)

Anodic polarization curvePote

ntia

l (V)

Element-1 Element-2C A

Imacro

Rp RpRc Potential

loss

( ) macroAC IRpRcRpEE ×++=− 21'

2'

1

EA2

EC1

’

’

unknown


Polarization resistance:Polarization resistance:The slope at the origin of the The slope at the origin of the polarization curve is defined as the polarization curve is defined as the polarization resistance, polarization resistance, RpRp::

( )cacorr

ca

0c,appp i3.2id

dRβ+β

ββ=⎟

⎟⎠

⎞⎜⎜⎝

⎛ η=

→η


)(3.2 caP

cacorr R

Iββ

ββ+

=

polarization resistancepolarization resistance==RRPP

cathodiccathodic curve slopcurve slop==ββcc

anodic curve slopanodic curve slop==ββaa

corrosion ratecorrosion rate==IIcorrcorr

TafelTafel’’ss extrapolation extrapolation technique technique corrosion rate corrosion rate

-600

-500

-400

-300

-200

-100

0

0.01 0.1 1 10 100 1000Current(㎂)

Pote

ntia

l(mV

)

Cathodic curve

Anodic curve

Corrosion potential

Corrosion rate

βa

βc


[ cm ]

Verification with Mortar Specimen Configuration

Mortar

(0.4mm, 0.2mm width)

20

52

Epoxy resinDefect

Specialsteel bar

dividedLead wire

6.00.5 6.00.5 6.00.5

Element No.1 2 3 4 5


30905

604

0.43

0.22

5090

No crack1

W/C (%)

Humidity (RH%)

Crack width (mm)No

Experimental and Analytical Cases

Control


Reference electrode(Ag/AgCl)

Stainless board

MortarSteel element

Potentiostat

Gulvanostat

Measurement Method of Polarization Curves


((11)) Influence of Crack Width Influence of Crack Width Comparison of Polarization Curve

CathodicAnodic

-1-0.8-0.6-0.4-0.2

00.20.40.6

0.00001 0.0001 0.001 0.01 0.1 1

Current density (mA/cm2 )

Pote

ntia

l (V

)

No

0.4mm

0.2mm-1

-0.8-0.6-0.4-0.2

00.20.40.6

0.00001 0.0001 0.001 0.01 0.1 1

Current density (mA/cm2)

Pote

ntia

l (V

) No 0.4mm

0.2mm


((22)) Influence of Humidity Influence of Humidity Comparison of Polarization Curve

CathodicAnodic

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.00001 0.0001 0.001 0.01 0.1 1

Current density (mA/cm 2)

Pote

ntia

l (V

)

60%

90%

-1-0.8-0.6-0.4-0.2

00.20.40.6

0.00001 0.0001 0.001 0.01 0.1 1


Pote

ntia

l (V

) 60%

90%


((33)) Influence of Influence of W/CW/C

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.00001 0.0001 0.001 0.01 0.1 1


Pote

ntia

l (V

)

30%

50%

Comparison of Polarization Curve

Cathodic

-1-0.8-0.6-0.4-0.2

00.20.40.6

0.00001 0.0001 0.001 0.01 0.1 1


Pote

ntia

l (V

) 30%

50%

Anodic


Reference electrode(Ag/AgCl)

Stainless board

Mortar

i

Potentiostat

Frequency ResponseAnalyzer

Measurement Method of Polarization Resistance


1

10

100

1000

10000Po

lariz

atio

n re

sist

ance

(kO

hmcm

2 )

Comparison of Polarization Resistance

No

crac

k

Wcr

=0.2

mm

Wcr

=0.4

mm

Crack


Mortar

Potentiostat

Frequency Response Analyzer

Measurement Method of Mortar Resistance


8

No

crac

k

Wcr

=0.2

mm

Con

trol

*

RH

60%

W/C

30%

0

2

4

6

Mor

tar r

esis

tanc

e (k

ohm

)

Comparison of Mortar Resistance

*Wcr=0.4mm, RH90%, W/C50%

RH90%, W/C50%


Anodic polarization curvePolarization Resistances

as potential loss


-1

-0.8

-0.6

-0.4

-0.2

0

0.0001 0.001 0.01 0.1 1Current density (mA/cm2)

Pote

ntia

l (V)

Imicro

Analysis of Microcell Corrosion Current

C A


-1

-0.8

-0.6

-0.4

-0.2

0

0.0001 0.001 0.01 0.1 1Current density (mA/cm 2)

Pote

ntia

l(V)

Imacro

Cathodic polarization curves

Anodic polarization curves

Analysis of Macrocell Corrosion Current

CA

polarization resistances and mortar resistance


(microA/cm2)

-1.30.1

5.71.4

17.05.0

-2.50.1

-0.40.4

MacrocellMicrocellSteel element

Analyzed Corrosion Current Density

*Macrocell: + anode, - cathode


-5

0

5

10

15

20

-4 -2 0 2 4Steel location (cm)

Cor

rosi

on c

urre

nt d

ensi

ty

(mic

roA

/cm

2 )

Defect

Macrocell

Microcell

Distribution of Analyzed Corrosion Current Density


(microA/cm2)

-1.30.1

5.71.4

17.05.0

-2.50.1

-0.40.4

MacrocellMicrocellSteel element No


0.1

7.1

22.0

0.1

0.4

Total

*Macrocell: + anode, - cathode


Measurement Method of Real Macrocell Corrosion Current

Ii+1.iIi-1.i

i-1 i i+1

Non resistance ammeterAA

Mortar

cf)P. Schiebl, &M. Raupach


dens

ity (m

icro

A/c

m2 )

0.01

0.1

1

10

100

0.01 0.1 1 10 100Analyzed total corrosion current density (micro A/cm2 )

Mea

sure

d to

tal c

orro

sion

cur

rent

No crackWcr=0.2mmControl*RH60%W/C30%

Comparison between Analyzed and Measured Values

*Wcr=0.4mm, RH90%, W/C50%


10

355

10

ConcreteBending crackReinforcing

bar

40

Verification with Concrete Specimen Configuration

Special divided steel(D10)

Element-No. Lead line

1 2 3 4 5 6 7 8 9 10

551.50.3 31.7

Epoxy resin

[cm]


821-8489542731915370

111-8868483701854950

-47708647045971794530

WRSP

Chem. Ad.GSCW

(g/m3)Unit weight (kg/m3)s/a(%)

W/C(%)

Mixture Proportions of Concrete


7010

509

30

0.4

8

0.1750

No crack6

W/C (%)Crack width (mm)No

Experimental and Analytical Cases

Control


-1.2-1

-0.8-0.6-0.4-0.2

00.2

0.0001 0.001 0.01 0.1Current (micro A/cm2)

Pote

ntia

l (V)

Anodic polarization curve

Imicro

polarization resistances


Analysis of Microcell Corrosion Current




polarization resistances and mortar resistance

Imacro-1.2

-1-0.8-0.6-0.4-0.2

00.2

0.0001 0.001 0.01 0.1

Current (micro A/cm2)

Pote

ntia

l (V)

Analysis of Macrocell Corrosion Current


(micro A/cm2)

0.1-0.70.1100.5-0.40.590.2-1.20.280.1-1.80.172.12.00.160.1-0.80.159.47.22.244.43.70.730.1-0.50.120.3-1.20.31

TotalMacrocellMicrocellSteel element No


Crack part


-2

0

2

4

6

8

0 10 20 30Steel location (cm)

Cor

rosi

on c

urre

ntde

nsity

(mic

roA

/cm

2 )Crack

Macrocell

Microcell

Distribution of Analyzed Corrosion Current Density


(micro A/cm )

Comparison between Analyzed and Measured Values

0.001

0.01

0.1

1

10

100

0.001 0.01 0.1 1 10 100Analyzed total corrosion current density

2

Mea

sure

d to

tal c

orro

sion

cur

rent

dens

ity (m

icro

A/c

m2 )

No crackWcr=0.2mmW/C30%ControlW/C70%

*Wcr=0.4mm, W/C50%


0

5

10

15

20

25


Tota

l cor

rosi

on c

urre

nt d

ensi

ty(m

icro

A/c

m2 )

Defect (except “No”)

No

0.2mm 0.4mm

Influence of Crack

cf)A. W. Beeby

(1983)


Defect

90%

60%

0

5

10

15

20

25


Tota

l cor

rosi

on c

urre

nt d

ensi

ty(m

icro

A/c

m2 )

Influence of Humidity


Steel location (cm)

0

5

10

15

20

25

-4 -2 0 2 4

Tota

l cor

rosi

on c

urre

nt d

ensi

ty(m

icro

A/c

m2 )

Defect

50%

30%

Influence of W/C


Application of the Modelto Existing Structure

ConcreteCrack

Analytically divided into element considering crack and soundness.

From database, input data ordered material condition andenvironmental condition.

2Rp

１

SoundDefect

Rp 2Rp1

SoundDefect

Rp1< Rp2

Polarization resistanceConcrete resistance



PartInput data

Rc

Steel bar

2007d_2 Corrosion (Advanced Topic)

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