Workshop on Service Life of Concrete Structure -Concept ... · Service Life Prediction of Cracked...

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

Service Life Prediction of Cracked Reinforced Concrete Structures subjected to Chloride Attack and Carbonation

Service Life Prediction of Cracked Reinforced Service Life Prediction of Cracked Reinforced Concrete Structures subjected to Concrete Structures subjected to Chloride Attack and CarbonationChloride Attack and Carbonation

H.-W. Song

Professor School of Civil and Environmental Engineering

Yonsei Univ., Seoul 120-749, KOREA

Workshop on Service Life of Concrete Structure-Concept and Design-

4 Feb. 2005 Sapporo, Japan


Introduction

Durability concept Durability concept and strategyPerformance-based durability designScheme of service life prediction

Models for service life predictionEarly-age cracks in concreteChloride diffusion-penetration modelCO2 carbonation modelSteel corrosion model

• Electric corrosion cell model• Oxygen diffusion model

Corrosion cracking model

Examples for Service life prediction

Conclusion

OutlineOutline


Korean daily nKorean daily newspapers warning ewspapers warning durability durability problems of concrete structuresproblems of concrete structures

Recently, severe deteriorations in concrete structures, such as bridges, buildings etc., has been criticized in major mass media in Korea : “ Korea is Republic of Concrete ” .


Recently, spalling of concrete from concrete structures, such as bridges, tunnels, etc., has become a big problem criticized in mass media in Japan.

Japanese daily nJapanese daily newspapers warning ewspapers warning durability relateddurability relatedsafetysafety problems of concrete structuresproblems of concrete structures


Deterioration in Concrete StructuresDeterioration in Concrete Structures


Corrosion of PC strands due to poor consolidationCorrosion of PC strands due to poor consolidation


Old Codes: AASHTO, EC2,BSSimple deemed-to-satisfyrules (deterministic)Experience based rules ofthumbPoor environmental classification

ResultNo relation between performance and service life (implicit 50 years)

Old Codes: AASHTO, EC2,BSSimple deemed-to-satisfyrules (deterministic)Experience based rules ofthumbPoor environmental classification

ResultNo relation between performance and service life (implicit 50 years)

New Codes: Performance-based designDegradation models Material parameters Detailing of environmental actionsStatistical quantification (mean, standard deviation, distribution) Choice of service life

New Codes: Performance-based designDegradation models Material parameters Detailing of environmental actionsStatistical quantification (mean, standard deviation, distribution) Choice of service life

ResultDocumented service life design, failure probability

ResultDocumented service life design, failure probability

Old and New Durability ConceptsOld and New Durability Concepts


Service Life of RC structures (ISO/WD 13823)Service Life of RC structures (ISO/WD 13823)

Time

Transfer mechanism

Resistancemechanism (R)

Degradation Agents(moisture, Cl-, CO2,

micro cracks etc)

Damage ordisfigurement

mechanism (Slim)

Degradation mechanism

ULS : R ≥ S? SLS : S ≤ Slim?

collapse malfunction

Durable Structure

Durability limit state

Service lifets ≥ td

Yes

texp

tstart

ts

Mass transport analysis

Environmental Actions(combination of

rain, de-icing salts etc)Boundary conditions

Corrosion of reinforcementConcrete crackDeterioration of concrete

Structural analysis

tS = tstart + texp


Service life = durability limit + safety limit Service life = durability limit + safety limit tS = tstart + texposure

START Size, shape, mix proportions, initial and boundary conditions

Governingequations 0=−+

∂∂

iii QdivJtθα

Temperature,Hydration level ofEach component

Hydrationcomputation

Bi-model porosityDistribution,Interlayer porosity

Microstructurecomputation

Pore pressures,RH and moisturedistribution

Pore pressureComputation

Dissolved andBound chlorideconcentration

ChlorideTransport and

equilibrium

Corrosion rate,Amount of O2

consumption

Corrosion model

Dissolved OxygenTransport andequilibrium

Ion equilibriummodel

Gas and dissolvedCO2 concentration

Carbon dioxideTransport and

equilibriumConservationLaws satisfied?

no

yes

Incr

emen

t ti

me,

co

nti

nue

Nextiteration

Du

rabi

lity

An

alys

isD

ura

bilit

y A

nal

ysis

Corrosion rate, crack,tension stiffening factorOutput

Ser

vice

abili

ty/S

afet

y A

nal

ysis

Ser

vice

abili

ty/S

afet

y A

nal

ysis

Deformation Compatibility,MomentumConservation

ContinuumMechanics

tε

tt f/σ

Tension stiffening model

Performancedegradation

Max.Load

time

Service-lifedecrease

Structural analysis (FEM etc.)

Deteriorationincrease

α

εεσ )(

t

tutt f=

4.0=α0.1=α

Tension stiffening factor : α

at each time step


Schematic description of service life designSchematic description of service life design

Time

S(t)

Pf

Distribution of R(t)R,S

Distribution of S(t)

R(t)

Service life density

Mean service life

Target Probabilityof Failure Pf

P failure at tD = P tS≤ tD ≤ Ptarget

tS = tstart + t exp

P failure at tD = P R(tD) ≤ S(tD) <0 < Ptarget

tD : design service life


Durability Failure of Concrete StructureDurability Failure of Concrete Structure

22SR

mm SRσσ

β+

−=

Durability Failure of Structure Reliability Index

PPff = P(R = P(R -- SS≤≤0)0)

FailureFailure SafeSafe

RR--S<0S<0 RR--S>0S>0

(R(R--S)S)mm (R(R--S)S)

FrequencyFrequency

P(RP(R--S)S)

)( SR −βσ

PPff

RR : Durability resistance: Durability resistanceSS : Degradation agents: Degradation agents


Measures:High quality and impermeableconcrete

- low chloride diffusivity(material)

- sufficient concrete cover(design)

- no early-aged cracks(construction)

Performance evaluation tool

verification of 100 yearsservice life

min covermax. Dcl

Durability Design StrategyDurability Design Strategy


Early-age cracks in concrete limit life span of concrete structures

• Temperature variation properties• Shrinkage properties• Strength and stiffness development properties

• Temperature variation properties• Shrinkage properties• Strength and stiffness development properties

Degradation of long-term

durability performance

Degradation of long-term

durability performanceMicrocracks

Hardening Hardening ConcreteConcrete

Drying

EnvironmentLoadThermal cracksShrinkage cracks


It is necessary to develop an analytical algorithm of steel corrosion, which considers pre-existing early-age crack and cover concrete quality, for accurate prediction of service life of cracked RC structures subjected to chloride attack or/and carbonation.

Service Life Prediction on Cracked ConcreteService Life Prediction on Cracked Concrete


Scheme of Service Life PredictionScheme of Service Life Prediction

Micro Structure Development

Heat Generation Analysis

Early Age Behavior

Initiation period

time

Propagation period

Acceleration period

Deterioration period

Loss of performance

related to corrosion of

steel Time to corrosionTime to corrosion cracking

Corrosion initiation Corrosion cracking

Corrosion cracking and service life of RC structure

Wcrit < Wrust

Mixing PropertiesExposure Condition

•Weather•Temperature•Relative Humidity•Crack in Cover

Location of Structures

Geometric Boundary

•Cement•Aggregate•Water•Blend

Cement

C2SC3SC3AC4AF •Length

•Shape•Boundary

Finite Element Method

Hygro Migration Analysis

Cl -Cl -

Cl -

Free chloride content

Total chloride content

criticalclC

Chloride diffusion-penetration model

CO2

CO2CO2

CO2 Carbonation model

• pH distribution• Ca(OH)2 & CaCO3 distribution• Carbonation depth CO2

pH = 9 pH = 12

Steel corrosion model

Corrosion current density(corrosion rate)

Corrosion product amount(rust)

Chloride content, pH

time

crack Deq

Crack model

• equivalent diffusion coefficient

• crack width


Governing equations for mass and energy conservation for service life prediction

0)(-),(

)(=∇+

∂∂⋅ iiii

ii XQXXdivJ

tXα

Tcρ TK H∇− HQ

PPS

∂∂φρ PKK vl ∇+− )( t

SQhyd ∂∂

−−)( φρ

clC

Sφ clclcleqcl CDorCD ∇−∇−

clQ

2coC

SKS co φφ +−2

)1( 2222 cococoeqco CDorCD ∇−∇−

2coQ

2oC

SKS O φφ +−2

)1( 2222 oooeqo CDorCD ∇−∇−

2OQ [mol/ m3·s]

- O2 consumption due to corrosion process

[mol/ m2·s]

- Mass and Knudsen diffusion in sound and/or cracked surface- Temperature and porosity change dependent

[mol.l/mol·m3]

- Path dependent transport of mass- Porosity change dependent

O2 concentration

[mol/ m3·s]

- CO2 consumption due to carbonation process

[mol/ m2·s]


[mol.l/mol·m3]

- Path dependent transport of mass- Porosity change dependent

CO2 concentration

[mol/ m3·s]

- Reactive chloride ion content due to binding capacity

[mol/ m2·s]


[mol.l/mol·m3]

- Porosity change dependentChloride concentration

[kg/ m3·s]

- Water combined due to hydration; bulk porosity change effect

[kg/ m2·s]

- Random geometry of pores and Knudsen vapor diffusion

[kg/Pa·m3]

- Path dependent moisture isotherms

Pore pressure

[Kcal/m3·s]- Multi component heat of hydration model of cement

[Kcal/ m2·s]

- Constant

[Kcal/K·m3]

- Constant

Temperature

Sink termFlux termPotential termVariables

iX iα iJ iQ


Equivalent diffusion coefficient for earlyEquivalent diffusion coefficient for early--age age cracks in concretecracks in concrete

Total area : AoArea of crack : Acr

Area of solid : As Area of capillary pore : Acp

Gas (H2O, CO2, O2)

Liquid (H2O, cl -, CO2, O2)

0

1

2

3

4

0 0.1 0.2 0.3 0.4 0.5

Crack width (mm)

Nor

mal

ized

ch

loir

dedi

ffu

sivi

ty

0

40

80

120

160

200

0 0.1 0.2 0.3 0.4 0.5

Crack width (mm)

No

rmal

ized

CO

2

dif

fusi

vity

W/C=45% W/C=45%

Cracks in REV(Representative Elementary Volume) (Song, 2002)

LVDT

RCPT(Rapidly Chloride Penetration Test)

WPT (Water Permeability Test)

General durability test machine

Average method

Flux of chloride ionFlux of CO2

Capillary flux Jcp Crack flux Jcr

Equivalent diffusivityEquivalent diffusivity


Chloride diffusionChloride diffusion--penetration modelpenetration model

pore structures, moisture transportdiffusion & permeability coefficient with crack

PorositySaturation

DclDeq

cl

Free Chloride Contents

Pore structureformation

0)()( =+Ω

+∂∂

clclscl

clcl QCqCDSCSt

-∇-φφ

Governing equation of chloride transfer

Potential term Flux term Sink term

Early-agebehavior

Reactive chloride ion contents in materials

Sink term modeling (Tang, 1996)

Sink term

Flux term

Equivalent diffusion coefficient of Equivalent diffusion coefficient of clcl -- permeability coefficient

cbclpow

nn

nbound

nbound

cl QWtt

CCQ −×⋅−−

−= −

+

+2

1

1

10

2

1

1

10 −

+

+

×⋅−−

−= usednn

nbound

nboundcb W

ttCCQ

cl

Sink termSink term in coupled deterioration analysisin coupled deterioration analysis

usedW : consumption of cement components at carbonated area

Where, Decreasing of binding capacityDecreasing of binding capacity


Analysis results for chloride attackAnalysis results for chloride attack

Beam Analysis (H:6cm, L: 28cm)

W/C 55% sound surface

W/C 55% cracked surface (0.1mm)

W/C 55% sound surface


COCO22 carbonation modelcarbonation model

Flux term

)(2/1)1( 4

2

2mmm

gco

gco trlSD

D−+

−Ω

⋅=φ

dcodco DSD

22

4

Ω⋅

=φ

• Diffusion coefficient of gaseous CO2 in pores :

• Diffusion coefficient of dissolved CO2 in pores :

22222)( dcodcocogcoco DKDJ ρ∇+⋅−=

CO2 flux

Molecular diffusion theoremKnudsen diffusion theorem

Potential term

2222

2

2 dcocodcococo

gco KHRTM

ρρρ ⋅=⋅⋅=

2222 coOHcoco MnHH ⋅⋅=′OH

coco

co nRTH

RTM

K2

2

2

2

1⋅

==

Henry constant

Ideal gas equation

Density of CO2 :

Ion equilibrium

Sink term

( ) [ ][ ]−+=∂

∂= 2

323

2COCak

tC

Q CaCOco

−+ +↔ OHHOH 2−+ +↔ OHCaOHCa 2)( 2

2

−+ +↔ 23

23 COCaCaCO

−+−+ +↔+↔ 23332 2 COHHCOHCOH

θaco

cracksoundeqco R

KDDD 2

2Ω⋅+=

PorositySaturation

co2

Carbonation depth, Ca(OH)2 & CaOH3, pH distribution

Governing equation of CO2 transfer


( )[ ] 0122=−+⋅+⋅−

∂∂

cocodg QJdivSSt

ρρφ

Cracked concrete Sound concrete

Dco2

Deq

• Equivalent diffusion coefficient of COEquivalent diffusion coefficient of CO22 in cracked concrete : in cracked concrete :

Carbonation areaHealthy area


Analysis results for carbonationAnalysis results for carbonation

0

2

4

6

8

10

12

14

16

18

0 20 40 60 80 100

Exposed period (days)

Car

bon

atio

n d

peth

(m

m)

EXP (55%) Analysis(55%)

EXP(65%) Analysis(65%)

EXP(45%) Analysis(45%)

9

10

11

12

13

0 2 4 6 8 10 12

cover depth(cm)

0.00

0.04

0.08

0.12

0.16

0.20

PHCO2 (mol/l)

0

20

40

60

80

100

120

140

0 2 4 6 8 10 12

cover depth(cm)

0

2

4

6

8

10

12

14

Ca(OH)2 (kg/m3)

CaCO3(mol/l)

A

A

Coating for 1-D diffusionCracked area

Sound area

Crack width

10% CO2

10mm

Dsound

Deq

2mm Time step : 0.1days to 28 days

0.5days to 120 days

W/C 55% , COW/C 55% , CO22 10%, 1800days after10%, 1800days after

(a) pH and CO2 concentration distribution (b) Ca(OH)2 and CaCO3 distribution


Alkali aggregate reaction,Chemical decomposition of hydrated cement

Freeze-thaw damageTemperature gradientsHumidity gradients

Abrasion and Chemical Attack

Reinforcing steel corrosion

Con

cret

eR

ein

forc

ing

stee

l

Submergedconcrete

Concrete at atmospheric zone

Concrete atsplash and tidal zone

Low tide

High tide

Oxygen supplying condition

Insufficient oxygen

Decreasing of icorr

Oxygen concentrationpolarization

Limit Current Density

Sufficient oxygen

Increasing of icorr

Electric corrosion cell

Corrosion cracking

Oxygen

diffusion

model

Oxygen

diffusion

model

Oxygen

diffusion

model

Electric corrosioncell m

odelElectric corrosionElectric corrosion

cell model

cell model

Steel corrosion modelSteel corrosion modelSteel corrosion model


Computational flow of steel corrosion modelComputational flow of steel corrosion model

Early-age behavior analysis

Salt attack analysis

Carbonation analysis

Moisture transport

Hydration heat analysis

• Micro structure• Pore pressure• Pore saturation

• Free chloride content• pH in concrete• Porosity and saturation

Corrosion Analysis Models

(Splash zone) (Submerged zone)

Tafel method analysis

Electric corrosion cell Model Oxygen diffusion Model

Formulation of O2 diffusion

Prediction of life timein RC structures


Cor

rosi

on A

naly

sis

Alg

orit

hm

[V]

EO2

EFe

log icorr

Passive Layer is Destroyed

Passive Condition

log ia for Fe Oxidationlog |ic| for O2 Restoration

Ecorr


Changing Anode Tafel Slope

Increasing Corrosion Current Density

Electric corrosion cell model

EO2

EFe

log i0 of O2

log i0 of Fe

log ia for Fe Oxidationlog |ic| for O2 Restoration

Concentration OverchargeEcorr

logicorrlogiLConsumption Dissolved O2

O2 Supply is Insufficient

Generation of Concentration Slope

icorr is Limit Current Density

Oxygen diffusion model

Chloride Thresholds

Exposure Conditions

Splash Zone Submersed Structure


Flux of Dissolved O2

O2 : Sufficient O2 : Sufficient O2 : Insufficient

)+(= clRDΩeq

cl DD θa

crack

wwD

D

cl

crack 962099 2 +=

Equivalent Diffusion Coefficient

Chloride Ion Penetration AnalysisChloride Ion Penetration Analysis

Oxygen Diffusion Analysis

Equivalent Diffusion Coefficient

dOcrack DD =

dOdOOgOLeq DLDKDLLD 441

1 5.0))(5.0[(2224

++= -Cra

ck E

ffec

t

L1 L4

L3

L2

Chloride Ion Penetration Analysis

Consideration of early age cracks for steel corrosion model


Electric corrosion cell modelElectric corrosion cell model

Chloride Thresholds

Condition of Steel Passive Passive Layer is Destroying No Passive LayerNo Passive Layer

Total Chloride Thresholds

Free Chloride Thresholds

1.2 kg/m3

(KCI, JCI specification)

Corrosion Start

No Passive Layers

EO2

EFe

Increasing of current density

Exchange current density of O

Exchange current density of Fe

1

2

23

[V]

Increasing of current density(passive layer is destroying)

Exchange current density of O2

Log icorr [A]

Decreasing of current density(passive layer exist)

Corrosion Potential

SHE+ Activation Overcharge

Anode :

Cathode :

Corrosion Current Density :

(Standard Hydrogen Electrode)a

Fecorr EE η+=

cOcorr EE η+=

2

cacorr iii ==

2.4 kg/m3

(Hausmann, 1969)

)1(2.1][ fixedi weightcementcl α−=−

)1(4.2][ fixede weightcementcl α−=−

Tafel slope of anode →∞


Corrosion stage Corrosion stage vsvs corrosion current densitycorrosion current density

[V]

EO2

EFe

[A]

Increasing of current density(passive layer is destroying)

Exchange current density of O2

Exchange current density of Fe

log icorr

1

2

23

Tafel slope of anode →∞

Decreasing of current density(passive layer exist)

Stage 1Passive Condition

Cl -< 1.2 kg/m3

Anode Tafel Slope = ∞

Cathode Tafel Slope = 2β

Stage 2

Passive Layer is Destroying1.2 kg/m3 (KCI) < Cl - < 2.4 kg/m3

Anode Tafel Slope( )

i

ie

clclclcl][][

][][059.0−−

−−

−−

=β

Stage 3

No Passive Layer Cl - = 2.4 kg/m3 (Hausmann, 1969)Not increase icorr

No exist

[ cl - ] : free chloride content(% wt of cement) at the stage[ cl - ]i : free chloride content(% wt of cement) for the stage of corrosion initiation[ cl - ]e : free chloride content(% wt of cement) for the stage of no passive layers

Being destroyed

Exist

Corrosion current density (A/m2)Condition of the passive layers

FeOcorr ii loglog =

059.0loglog059.006.0998.0

log 2

+

+−−=

ββ

FeOOcorr

iipHi

FeOOcorr iipHi log5.0log5.0508.0458.8log2++−=

( )i

ie

clclclcl][][

][][059.0−−

−−

−−

=β


Consideration of early age cracks for Consideration of early age cracks for oxygen diffusion modeloxygen diffusion model

Submerged structures

2O−Cl [ ] 0)()1(2222=−+⋅+⋅−

∂∂

OOdOgO QJdivSSt

ρρφ

Capacity Flux Sink

[V]

EO2

EFe

[A]

Oxygen diffusion controllog icorr

Oxygenconcentrationpolarization

log icorr

Reinforcement

Crack Width

L1L4

L3

L2

Equivalent Oxygen Diffusion Coefficient

)-(2/1)-1( 4

2

2 mmm

gO

trlSD

gOD +Ω=φ

dO

SdO DD

22 Ω= φ

dOcrack DD

2=

dOdOOgOL

eqO DLDKDLLD

222242 4411 5.0))(5.0-[( ++=

Modified 1-D Anisotropic Crack Model

elem

bar

O

corrOO V

AFziM

SQ ⋅−=2

2

2φ

2222

2

2 dOOdOOO

gO KHRTM

ρρρ ⋅=⋅⋅=

22222)( dOdOOgOO DKDJ ρ∇+⋅−=

•

•

•

eqD


Oxygen Diffusion ModelOxygen Diffusion Model

Flux term

)(2/1)1( 4

2

2mmm

go

go trlSD

D−+

−Ω

⋅=φ

dodo DSD

22

4

Ω⋅

=φ

Diffusion coefficient of gaseous O2 in pores :

Diffusion coefficient of dissolved O2 in pores :

O2 flux

Molecular diffusion theoremKnudsen diffusion theorem

Potential term

2222

2

2 doodooo

go KHRTM

ρρρ ⋅=⋅⋅=

2222 oOHoo MnHH ⋅⋅=′OH

oo

o nRTH

RTM

K2

2

2

2

1⋅

==

Henry constant

Ideal gas equation

Density of O2 :

Sink term

[V]

EO2

EFe

[A]

Oxygen diffusion control

Oxygenconcentrationpolarization

log icorr

O2 O2 O2

Governing equation of oxygen diffusion


[ ] 0)()1(2222=−+⋅+⋅−

∂∂

OOdOgO QJdivSSt

ρρφ

Ishida(1999)

elem

bar

O

corrOO V

AFziM

SQ ⋅−=2

2

2φ

FziMSR

Fe

corrFecorr

⋅= φ

Corrosion rate in concreteFaraday’s law

The rate of O2 consumption

22222]5.0))(5.0[(1

4411

dOdOdOOgO

totalO DLDKDLL

LJ ρ∇-- ++=

Equivalent coefficient of OEquivalent coefficient of O22 in cracked concretein cracked concrete


Loss of performance due to steel corrosionLoss of performance due to steel corrosion

Initiation period Propagation periodAcceleration periodDeterioration period

Loss

of

perf

orm

ance

rel

ated

to

corr

osio

n of

ste

el

Time to corrosion

Time to corrosion cracking

Corrosion initiation

Corrosion cracking


Analysis results for steel corrosion tendencyAnalysis results for steel corrosion tendency

0.E+00

2.E-03

4.E-03

6.E-03

8.E-03

1.E-02

0 2 4 6 8 10

Year

i corr

(A/m

2)

45%

55%

65%

0.E+00

2.E-03

4.E-03

6.E-03

0 2 4 6 8 10

Year

icorr

(A

/m2 )

65%

55%

45%

Splash zone structure Submerged zone structure

Visualization of steel analysis


Corrosion cracking modelCorrosion cracking model

3.11.81.1Yokozeki (1997)

3.22.01.4This study

3.73.12.3Morikawa (1987)

532cover ( cm )

Critical corrosion amount (mg/cm2)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0 2 4 6 8 10

cover (mm)

crit

ical

cor

roso

in a

mou

nt(m

g/cm

2)

Yokozekithis study

Morikawa

[ ] sstst

ruststcrit ddDW +

−= 0κρρ

ρρπ

Critical corrosion amounts

Deformation of steel

errps qKBd 1)21()1(2 2 −−−−= ννα

Thickness of corrosion product induced corrosion cracking

fck = 320 kgf/cm2, steel diameter : 16mm


Example for service life prediction of RC which does not Example for service life prediction of RC which does not considered the concept of service lifeconsidered the concept of service life

Sea water

Chloride in sea water

Ground water

Sea water

CO2 CO2 CO2

Underground RC tunnel• Cover depth = 5 cm

• CO2 = 670 ppm• Chloride concentration = 0.35~0.50 mol/ℓ• Relative humidity = 70~100 %• Temperature = 20

Splash zone

Submerged zone

Tunnel inside=atmospheric zone

Marine atmosphere

Mono Sulfate

C2S

C4AF

C3S

C3A

735

1102

3.9

27

9.4

47.2

10.4

365

45

812

1078

3.9

27

9.4

47.2

10.4

291

55

Coarse Aggregate (kg/m3)

Sand Aggregate (kg/m3)

Cement Composition

Ordinary Portland Cement (kg/m3)

Water/Cement Ratio (%)Temperature

Relative humidity

(%)

External chloride concentration

(mol/L)pHW/C

201000.510~1145, 55

20700.359~1145, 55

Mix proportions Environmental conditions


Analysis at Splash Zone (cover = 5cm)

Critical Cl - = 1.2 kg/m3

Corrosion initiation Critical Wcorr at 5cm cover

W/C=45% W/C=45% W/C=45%

W/C=55% W/C=55% W/C=55%

fck = 240 kgf/cm2 , steel diameter : 32mm


Analysis at Submerged Zone (cover = 5cm)

Decreasing of icorrfor insufficient oxygen

Corrosion does not propagate

W/C=45% W/C=45% W/C=45%

W/C=55% W/C=55% W/C=55%

Reduction of crack effectby poor quality of concrete



Quality of cover concrete (W/C =45% vs. W/C =55%)

Splash zone

Submerged zone

Splash zone Splash zone

Submerged zone Submerged zone



Corrosion rate with different pH

0.0E+00

2.0E-02

4.0E-02

6.0E-02

8.0E-02

1.0E-01

0 20 40 60 80 100

Year

i corr (

A/m

2 )

pH=12

pH=11

pH=10

pH=9

Icorr > 0.01 A/m2High Corrosion

0.005 < Icorr < 0.01 A/m2Moderate to High Corrosion

0.001 < Icorr < 0.005 A/m2Low to Moderate Corrosion

Icorr < 0.001 A/m2Passive Condition

Corrosion Current DensityCondition

Criteria for Corrosion (Broomfield, 1997)

High corrosion

High pH(=12)Does not increase to high corrosion rate


0

0.2

0.4

0.6

0.8

1

0 10 20 30 40 50

Cover depth(mm)

Chlo

ride

cont

ent

(% o

f co

ncre

te w

eigh

t)

Life365

Experiment

Fick Law

This study

Humidity effect

Temperature effect

Time effectFixed Dcl1X10-12

m2/s

D28

Dcl

Diffusion-penetrationDiffusionDiffusionPenetration mechanism

This studyLife 365Fick’s law

)/40.206.12(28 101 CWD +−×=

mref

ref tt

DtD ⎟⎟⎠

⎞⎜⎜⎝

⎛=)(

)/40.206.12(28 101 CWD +−×=

mref

ref tt

DtD ⎟⎟⎠

⎞⎜⎜⎝

⎛=)(

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−=

TTRUDTD

refref

11exp)(

1

4

4

)1()1(1)(

−

⎟⎟⎠

⎞⎜⎜⎝

⎛−−

+=c

ref hhDhD

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−=

TTRUDTD

refref

11exp)(

Comparison of different prediction methods


Durability strategy using different mix proportion

--1102735-36516445OPC 45%

--1078812-29116055OPC 55%

0.0130.7597278512028016040W/B 40%Slag 30%

AESPSlagC

AdmixtureGS

BinderW

B X (%)Unit weight (kg/m3)W/C(%)

Items

Mixing

Change of mix proportion for design chloride diffusion coefficient using Slag with lower W/CSlag with lower W/C

--5.56.03T w/ crack

3.56.85.510.9Tw/o crack

55455545W/C

Submerged zoneSplash zoneEnvir.

Decreasing of DclDecreasing of W/CDecreasing of external cl - concentration

Increasing of cover depthIncreasing of pH in pore solutionIncreasing of cover concrete quality

Increased service life of RC structures


Service life analysis for RC at splash zone (1)

Critical chloride content

Corrosion does not occur !!

W/C =40%, Slag 30%No crack

W/C =40%, Slag 30%Crack width = 0.1mm

Service life


Service life

Critical Cl - content = 1.2 kg/m3 (KCI, JCI)


Service life analysis for RC at splash zone (2)

Corrosion initiation with 0.3mm crack= service life for chloride attack

Corrosion initiation with 0.1mm crack= service life for chloride attack

1.34Critical corrosion amounts

Corrosion cracking

Corrosion cracking

Corrosion initiation

Cracking time


Service life analysis for RC at submerged zone (1)

Critical chloride content

Corrosion does not occur !!

W/C =40%, Slag 30%No crack


Service life


Service life

Critical Cl – content= 1.2 kg/m3 (KCI, JCI)


Service life analysis for RC at submerged zone (2)

Decreasing of icorrfor insufficient oxygen

Corrosion initiation with 0.1mm crack=service life for chloride attack

Corrosion initiation with 0.3mm crack=service life for chloride attack

1.34Critical corrosion amounts

Corrosion does not propagate

Corrosion cracking dose not occur!!Corrosion cracking dose not occur!!


Summary for service life

--5.56.03T w/ crack

3.56.85.510.9T w/o crack

55455545W/C

Submerged zoneSplash zone-

--T w/ crack

Over 100 yrsOver 100 yrsT w/o crack

W/B=40%, Slag=30%W/B=40%, Slag=30%W/B

Submerged zoneSplash zone-

59.8 yrs

0.1mm

65 yrs

0.1mm

1.5 yrs2.5 yrsTservice

0.3mm0.3mmCrack width

Need to control cracking in early age !!


Carbonation analysis of liner concrete at tunnelCarbonation analysis of liner concrete at tunnel

Car

bona

tion

dept

h

CaCO3

Ca(OH)2

W/C=45%No crack

8

9

10

11

12

13

14

0 2 4 6 8 10

Cover depth (cm)

pH

No crackcrack width = 0.1 mmcrack width = 0.2 mm

0

2

4

6

8

0 20 40 60 80 100

Year

Car

bona

tion

dep

th (

cm)

No crack

crack width = 0.1 mm

crack width = 0.2 mm

cover depth

(a) Carbonation depth simulation (b) Distribution of pH at 100 years

(d) Contour of carbonation depth at 100 years(c) Distribution of Ca(OH)2 and CaCO3


Chloride attack in carbonated concrete (1)Chloride attack in carbonated concrete (1)

z

Carbonation front

Carbonation depth

0.0

0.5

1.0

1.5

2.0

2.5

0 10 20 30 40 50 60 70 80

Cover depth (mm)

Chlo

ride

cont

ent

(CaC

l 2 /c

emen

t, %

)

Front ofcarbonation

Chloride distribution at carbonated area (Tuutti, 1982)

cl-co

ncen

trat

ion

dist

ribut

ion

cl-co

ncen

trat

ion

dist

ribut

ion

cl-co

ncen

trat

ion

dist

ribut

ion

cl-co

ncen

trat

ion

dist

ribut

ion

cl-co

ncen

trat

ion

dist

ribut

ion

Fixed chloride ion (Friedel)

surface

surface

surface

surface

surface

surface

surface

surface

surface

surface

inside

inside

inside

inside

inside

inside

inside

inside

inside

inside

Chloride ion in pore

Carbonation initiationCarbonation initiation Carbonation propagationCarbonation propagation

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.001 0.01 0.1 1 10

Pore radius(10-6m)

Poro

sity

W/C 37% - 28days

W/C 37% - 180days, RH 65%

W/C 37% - fully carbonated

Decreasing of porosity

CO2

Cl -

CO2

CO2

CO2

CO2

Cl -

Cl -

Cl -

Cl -


Chloride attack in carbonated concrete (2)Chloride attack in carbonated concrete (2)

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0 20 40 60 80 100

Year

Ch

lori

de c

onte

nt

(kg/

m3)

free chloride

total chloride

0

0.4

0.8

1.2

1.6

2

2.4

0 2 4 6 8 10

Cover depth(cm)

Chl

orid

e co

nten

t (k

g/m

3) free chloride

bound chloridetotal chloride

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0 2 4 6 8 10Cover depth(cm)

Ch

lori

de

con

ten

t (k

g/m

3 )

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0 2 4 6 8 10

Cover depth(cm)

Chl

orid

e co

nten

t (k

g/m

3)

5 years5 years 45 years 45 years 100 years 100 years

Only chloride attack Coupled deterioration analysis

Coupled deterioration analysisCoupled deterioration analysis

Only chloride attack

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0 20 40 60 80 100

Year

Chl

orid

e co

nten

t (k

g/m

3)

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0 2 4 6 8 10

Cover depth(cm)

Chl

orid

e co

nten

t (k

g/m

3)


Service life prediction of RC structures Service life prediction of RC structures --an example of an example of BusanBusan--GeojeGeoje Fixed Link project in KoreaFixed Link project in Korea

Immersed tunnel

Cable stayed bridgeCable stayed bridge

L=8.2 km

Concrete pier and pylon

Concrete pier and pylon

65.320.0670-Tunnel inside

65.315.3-0.19Atmospheric

82.615.3-0.51Splash

10015.3-0.51Submerged

Relative humidity (%)Temperature ( )CO2 concentration (ppm)Chloride concentration (mol/ℓ)Type of zones

Environmental conditions

Design life:

100 years.

Nominal end of service life: corrosion initiation

Level of Reliability:

90% (β = 1.3)


Specific gravity· Coarse aggregate : 2.64 · Sand : 2.58· Cement : 3.16 · Slag : 2.89· Fly ash : 2.19 · Silica fume : 2.21

Air content : 4.0%

Submerged Tunnel

BridgeStructures

Area

102076576-1521521420.375T4

102077838-1701701420.375T3

102075180-1601601400.350T2

102076440-1801801400.350T1

102078272-1431431430.375B4

102076576-1521521420.375B3

1020797-11.41841841420.375B2

SP : 0.65~2.0%AE : 0.014~0.023%

102075180-1601601400.350B1

FASFSLAGOPCAdmixture

G(kg/m3)

S(kg/m3)

Binder (kg/m3)W(kg/m3)

W/B

Possible mix proportions


Analysis result at atmospheric zone(1)

0.0

1.0

2.0

3.0

4.0

5.0

0 20 40 60 80 100 120

Concrete cover (mm)

Chlo

ride

cont

ent (k

g/m

3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200 250

Exposed time (year)

Chl

orid

e co

nten

t (k

g/m

3 )

1.2 Critical Cl - content

Concrete cover = 50mm

Critical Cl - content

Service life

[[ Atmospheric Atmospheric –– B1 B1 ]]

0.0

1.0

2.0

3.0

4.0

5.0

0 20 40 60 80 100 120

Concrete cover (mm)Chl

orid

e co

nten

t (k

g/m

3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chl

orid

e co

nten

t (k

g/m

3 )


Service life

0.0

1.0

2.0

3.0

4.0

5.0

0 20 40 60 80 100 120

Concrete cover (mm)

Chlo

ride

cont

ent

(kg/

m3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

cont

ent

(kg/

m3 )


Service life


Analysis result at atmospheric (2)

0.0

1.0

2.0

3.0

4.0

5.0

0 20 40 60 80 100 120

Concrete cover (mm)

Chlo

ride

cont

ent (k

g/m

3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150

Exposed time (year)

Chlo

ride

cont

ent

(kg/

m3 )

0.0

1.0

2.0

3.0

4.0

5.0

0 20 40 60 80 100 120

Concrete cover (mm)Ch

lorid

e co

nten

t (k

g/m

3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

cont

ent

(kg/

m3 )

0.0

1.0

2.0

3.0

4.0

5.0

0 20 40 60 80 100 120

Concrete cover (mm)

Chlo

ride

cont

ent

(kg/

m3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

con

tent

(kg

/m3 )

[[ Atmospheric Atmospheric –– B4 B4 ]] [[ Atmospheric Atmospheric –– T1 T1 ]] [[ Atmospheric Atmospheric –– T3 T3 ]]








Service life Service life Service life


Analysis result at submerged zone (1)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 20 40 60 80 100 120

Concrete cover (mm)

Chlo

ride

con

tent

(kg

/m3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

con

tent

(kg

/m3 )

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 20 40 60 80 100 120

Cover depth(mm)Ch

lori

de c

onte

nt (

kg/m

3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

con

tent

(kg

/m3 )

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 20 40 60 80 100 120

Concrete cover (mm)

Chlo

ride

con

tent

(kg

/m3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

con

tent

(kg

/m3 )

[[ Submerged zone Submerged zone –– B1 B1 ]] [[ Submerged zone Submerged zone –– B2 B2 ]] [[ Submerged zone Submerged zone –– B3 B3 ]]






Analysis result at submerged zone (2)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 20 40 60 80 100 120

Concrete cover (mm)

Chlo

ride

con

tent

(kg

/m3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

con

tent

(kg

/m3 )

[[ Submerged zone Submerged zone –– B4 B4 ]] [[ Submerged zone Submerged zone –– T1 T1 ]] [[ Submerged zone Submerged zone –– T3 T3 ]]



1.2


1.2




0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 20 40 60 80 100 120

Concrete cover (mm)Ch

lori

de c

onte

nt (

kg/m

3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

con

tent

(kg

/m3 )

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 20 40 60 80 100 120

Concrete cover(mm)

Chlo

ride

con

tent

(kg

/m3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

con

tent

(kg

/m3 )

Critical Cl - content Critical Cl - content


Analysis result at splash zone

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 20 40 60 80 100 120

Concrete cover (mm)

Chl

orid

e co

nten

t (k

g/m

3 )

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 20 40 60 80 100 120

Concrete cover (mm)

Chlo

ride

cont

ent (

kg/m

3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

con

tent

(kg

/m3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

cont

ent

(kg/

m3 )

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 20 40 60 80 100 120

Concrete cover (mm)

Chlo

ride

con

tent

(kg

/m3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

cont

ent

(kg/

m3 )

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 20 40 60 80 100 120

Concrete cover (mm)

Chlo

ride

cont

ent

(kg/

m3 )

0

0.3

0.6

0.9

1.2

1.5

0 50 100 150 200

Exposed time (year)

Chlo

ride

cont

ent

(kg/

m3 )

[[ Splash zone Splash zone –– B1 B1 ]] [[ Splash zone Splash zone –– B2 B2 ]] [[ Splash zone Splash zone –– B3 B3 ]] [[ Splash zone Splash zone –– B4 B4 ]]




Service life Service life Service lifeService life


Summary of chloride attack analysis results

168A-T-4178A-T-3212A-T-2167A-T-1

Immersed tunnel (inside)

132A-B-4168A-B-3162A-B-2212A-B-1

Bridge (Piers & Pylons)

Atmospheric Zone

Service Life (year)Mix TypeStructuresArea

184S-T-4143S-T-3188S-T-2152S-T-1

Immersed tunnel (outside)

171S-B-4184S-B-3165S-B-2188S-B-1

Caissons (external)

Submerged Zone

176T-B-4193T-B-3175T-B-2180T-B-1

Pylons, Piers & CaissonsTidal and Splash Zone

Satisfy the required service lifefor chloride attack


0

20

40

60

80

100

0 20 40 60 80 100

Exposed time (year)

Carb

onat

ion

dept

h (m

m)

9

10

11

12

13

0 10 20 30 40 50 60

Concrete cover (mm)

pH

0

5

10

15

20

25

30

Ca(O

H) 2

(kg

/m3 )

pHCa(OH)2

0

20

40

60

80

100

0 20 40 60 80 100

Exposed time (year)

Carb

onat

ion

dept

h (m

m)

9

10

11

12

13

0 10 20 30 40 50 60

Concrete cover (mm)

pH

0

2

4

6

8

10

Ca(

OH

) 2 (

kg/m

3 )

pHCa(OH)2

Analysis result for carbonation (1)

[[ Carbonation at tunnel inside Carbonation at tunnel inside –– T1 T1 ] ] [[ Carbonation at tunnel inside Carbonation at tunnel inside –– T2 T2 ] ]

Cover depth = 75 mm


Analysis result for carbonation (2)

0

20

40

60

80

100

0 20 40 60 80 100

Exposed time (year)

Carb

onat

ion

dept

h (m

m)

9

10

11

12

13

0 20 40 60

Concrete cover (mm)

pH

0

5

10

15

20

25

30

Ca(O

H) 2

(kg

/m3 )

pHCa(OH)2

Cover depth = 75 mm

0

20

40

60

80

100

0 20 40 60 80 100

Exposed time (year)

Carb

onat

ion

dept

h (m

m)

9

10

11

12

13

0 20 40 60

Concrete cover (mm)

pH

0

2

4

6

8

10

Ca(

OH

) 2 (

kg/m

3 )

pH

Ca(OH)2

[[ Carbonation at tunnel inside Carbonation at tunnel inside –– T3 T3 ] ] [[ Carbonation at tunnel inside Carbonation at tunnel inside –– T4 T4 ] ]


Summary of carbonation analysis results

Over 25033T4

Over 30010T3

Over 25025T2

Over 3009.2T1

Service life for carbonation (yr)Carbonation depth after 100 yrs (mm)Mix

0

20

40

60

80

100

0 20 40 60 80 100 120

Exposed time (year)

Car

bona

tion

dept

h (m

m)

T1 배합

T2 배합

T3 배합

T4 배합

Cover depth = 75mm

Satisfy the required service lifefor carbonation


ConclusionConclusion

Concepts for durability design and strategy along with performance based service life prediction in current RC design codes are presented.

A scheme of coupled deterioration analysis using chloride penetration model and a carbonation model which consider the early-age behaviour and time-space dependent diffusivity of concrete as well as cracks inside concrete are proposed.

In order to predict the service life of cracked concrete structures by both chloride attacks and carbonation, a microscopic steel corrosion model is also proposed and implemented into a finite element analysis program.

- electric corrosion cell model : cl -, pH- oxygen diffusion model : supplied O2

The service life of RC structures become shortens significantly with increased crack width, increased W/C, and decreased pH of pore water (i.e. carbonation).

Optimum concrete mix proportions which make RC structures to possess the design service life can be obtained using this performance tool.


Thank you for Thank you for your kind attention!your kind attention!

[email protected]@yonsei.ac.kr

Workshop on Service Life of Concrete Structure -Concept ... · Service Life Prediction of Cracked...

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