factors to chloride threshold level for steel corrosion

Factors to chloride threshold level for steel corrosion

Seminar in Hokkaido University

Concrete Materials, Mechanics and EngineeringSchool of Civil and Environmental Engineering

Yonsei University, Seoul 120-749, KOREA

1 March 2010

Ki Yong Ann

Definition and detection

Definition

A. The chloride content at the depth of the steel which will result in the breakdown of the passive film, and hence initiate corrosion.

Detection

A. Chloride content at the steel depth

B. Onset of corrosion

Measuring a chloride profiles from the surface of concrete cover

3

Galvanic current (m

A/m

2)

Concrete Materials, Mechanics

& Engineering Lab., Yonsei Univ.

B. The chloride content at the depth of the steel which leads to corrosion-induced deterioration of the concrete structure.

- Half cell potential

- Galvanic current

- Polarisation resistance

- Mass loss of steel

0

1

2

0 10 20 30 40 50

Time (days)

Galvanic current (m

A/m

2)

Ann and Buenfeld, Mag Concr Res 2007

Corrosion initiation

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 2008

Water:Binder Binder typeSystem

1.0

1.5

2.0

Chloride threshold (%, cem

) .

Concrete quality VS Chloride threshold



0.40

0.45

0.55

0.60

OPC

GGBS

PFA SF

SRPC

0.0

0.5

concrete

mortar

paste

System

Chloride threshold (%, cem

) .

Ann et al, J Mater Sci 2010, submitted

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




Steel

Binding and buffering VS chloride threshold

0.7

0.8

0.9

1.0

Binding capacity

10

15

20

25

Bufferin

g cap

acity (m

ol/kg)



0.5

0.6

0.7

0 0.3 0.6 0.9 1.2 1.5

Binding capacity

OPC

30% PFA

60%GGBS

10%SF

Chloride threshold (%, binder)

Song et al, ACI Mater J 2010, accepted

0

5

10

0 0.3 0.6 0.9 1.2 1.5

Bufferin

g cap

acity (m

ol/kg)

Chloride threshold (%, binder)

Steel-concrete interface

Hydration layer


Cl-Cl-

Cl-

Cl-

Cl-

External chlorides



Steel

Hydration layer

Ann et al Mag Concr Res 2009

Interface VS chloride threshold

1.0

1.5

2.0

2.5

Chloride threshold (%, binder) .

OPC (rich) OPC (lean) 30% PFA 65% GGBS

Voids

Rust



0.0

0.5

1.0

0.0 0.5 1.0 1.5 2.0 2.5

Interfacial air voids (%)

Chloride threshold (%, binder) .

Ann and Song, Corros Sci 2008

Enhancement 1

Calcium aluminate cement (CAC)

CACCACCACCAC

OPCOPCOPCOPC



CaOCaOCaOCaO

AlAlAlAl2222OOOO3333

SFSFSFSF

PFAPFAPFAPFA

GGBSGGBSGGBSGGBS

CACACACA----based hydrationsbased hydrationsbased hydrationsbased hydrations

Enhancement 1

CACACAH

CAHC2AH8

C2AH8C3AH6

C3AH6

30303030℃℃℃℃

40404040℃℃℃℃



CACA

H2O

CAHCAH

C2AH8

C2AH8C3AH6

C3AH6

C : CaO, A : AlC : CaO, A : AlC : CaO, A : AlC : CaO, A : Al2222OOOO3333, H : H, H : H, H : H, H : H2222OOOOHydration processHydration processHydration processHydration process

20202020℃℃℃℃

Bradbury. C. et al,.Materials Science and Engineering, 1976

OPC

0.9

1.2

1.5

Bounded chloride (%

, binder) 1

OPC_28 days OPC_56 days OPC_91days

CAC

0.9

1.2

1.5

Bounded chloride (%

, binder) 1

CAC_28 days CAC_56 days CAC_91days

Enhancement 1



0.0

0.3

0.6

0.9

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Total chloride (%, binder)Bounded chloride (%

, binder)

0.0

0.3

0.6

0.9

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Total chloride (%, binder)

Bounded chloride (%

, binder)

Enhancement 1

10.00

100.00

Corrosion rate (m

A/m

2) 1

10.00

100.00

Corrosion rate (m

A/m

2) 1

CAC OPC

1.00

10.00

100.00

Corrosion rate (m

A/m

2) 1

CAC OPC

Corrosion initiation zone



0.01

0.10

1.00

0 5 10 15 20Number of cycle (weeks)

Corrosion rate (m

A/m

0.01

0.10

1.00

0 5 10 15 20Number of cycle (weeks)

Corrosion rate (m

A/m

Chloride freeChloride 0.5%Chloride 1.0%Chloride 2.0%Chloride 3.0%

Chloride freeChloride 0.5%Chloride 1.0%Chloride 2.0%Chloride 3.0%0.01

0.10

1.00

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Chloride concentration (%, binder)

Corrosion rate (m

A/m

Chloride thereshold level(CAC)

=0.58-1.18%

Chloride thereshold level(OPC)

=0.12-0.31%

Enhancement 2

Chemical inhibitor

Steel

Passivation



OHNOOFeNOOHFe 2322

2 222 ++−→++−−+

γ

Reinforced passivation

Increase the resistance to corrosion, but rapid rate of chloride transport in concrete

Enhancement 2

3.0

4.0

Chloride threshold (%,cem

.)

1.23% Nitrite

2.5% Nitrite

5.0% Nitrite

Chloride threshold level

600

900

Tim

e to corrosion (days)

Rich mix

Lean mix

Chloride transport



0.0

1.0

2.0

0.0 0.5 1.0 1.5 2.0 2.5

Air void content (%)

Chloride threshold (%,cem

.)

0

300

0 1 2 3 4 5

Calcium nitrite (%, cem.)

Tim

e to corrosion (days)

Conclusion

� Concrete quality including binder type, W/C and aggregate has a marginal effect on the chloride threshold level, despite different chemistry of the pore solution.

� Chloride binding capacity has less dominant effect on the chloride threshold level, whereas the buffering of hydrations against a pH fall of the pore solution has a strong proportional relation with the threshold values irrespective of binders.



� As corrosion starts in the voids at the steel-concrete interface, the chloride threshold is significantly influenced by the physical condition of the interface.

�Calcium aluminate cement may be an alternative inhibitor to raise the resistance to corrosion with no detrimental effect of rapid transport of chloride ions

�Chemical inhibitor is effective in enhancing the prevention of corrosion but is expected to increase the surface chloride, when concrete is exposed to a salt water environment

factors to chloride threshold level for steel corrosion

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