Corrosion of ConcreteDesign, Prevention and Repair

Contents

2. Design of concrete for crack control ◆ ‘Expansive concrete’

3. Prevention and repair ◆ ‘Desalination’ and ‘Re-alikalization’◆ ‘Chloride ion Fix agent’

１. IntroductionImportance of crack control for prevention of corrosion

4. Conclusion

※Some figures and pictures are taken from ‘Practical Guideline for investigation, Repair and Strengthening of cracked concrete Structures -2009- published by JCI.

� Carbonation often progress along the wide crack.

� Steel corrosion starts under a pH 11.0

Therefore it’s necessary to control the cracks of concrete for prevention of corrosion.

Importance of crack control for prevention of corrosion

� The surface of rebar is protected by high alikaline solution.

Back ground

� Drying shrinkage is one of the general factor of concrete cracks.

� Concrete can’t contract freely, cause the minute cracks.

Restraint by steel bar (Slab)

2. Design of concrete for crack control ◆ ‘Expansive concrete’

Length change of concrete

Surface tension

→shrinkage

Surface tension

→shrinkage

余剰水

硬化体

硬化体

Water

tension

Surface tensionSurface tension

tension

Hydrates

Expansion control

the cracks of concrete

ExpansiveConcrete

Reduction

of water by

drying

Normal

Expansion

ShrinkageCrack

0 5 10 15

Leng

th c

hang

e Time (week)

0

Mechanism of shrinkage compensation

StrainE

xpan

sion

＋

Shr

inka

ge－

Age

Dry

Stress

Age

Tens

.＋

Com

p.－

Expansive concrete

Slab

Wall

CSA concrete

CSA concrete

How does expansion contribute to concrete?

7

Normal concrete

Slab

Wall

Ft： Tensile strength×

Cracking

Normal Concrete

Normal Concrete

Expansive additive for concreteControl

Expansive Concrete

Control the crack

Production of Expansive Concrete

9

Expansiveconcrete

Expansiveconcrete

⇒＋

Mixer

� Mixed at the ready mixed concrete plant.

Expansive additive

NormalconcreteNormal

concrete

Precast Concrete

Construction site

Formulation (24MPa)

NoSlump(cm)

Air(%)

Unit weight (kg/m3)Admixture

(kg/m3)Cement Water

Fineaggreg

ate

Coarse aggregat

e

Power-CSA

A-1 16.0 5.0 302 175 812 989 0 2.8

A-2 16.5 5.0 282 175 812 989 20 2.8

【Power-CSA」】

10

Slab concrete in a plant

Example of expansive concrete

Cast-in-place Power CSA concrete

� CSA is replaced to Portland cement.

Slab concrete in a plant

Strain gage

Example of the Expansive Concrete短辺方向：短辺方向：短辺方向：短辺方向：D10D10D10D10----@200@200@200@200 長辺方向：長辺方向：長辺方向：長辺方向：D10D10D10D10----

@200@200@200@200

180m

m

11

� Strain gage was attached to the steel bar.� Compared to the concrete without CSA.

Strain of concrete

0 1 2 3 4 5 years

Age (years)

Str

ain

in s

lab

conc

rete

(×

10-6

)

0

100

200

-200

-100

-300

40

20

010

30

Temp.（

℃）

CSA concrete

Normal concrete

Temp.

Difference of strain between CSA and PlainExpansion

Shrinkage

Example of the Expansive Concrete

12The effect of CSA has continued over 5years.

YURIKAMOME, The New Transit, 1995 ( Tokyo )

CSAAppliedCSAApplied

CSA was used for concreterail reducing crack.

13

Application of Denka CSA Viaduct

Past 20years

3. Prevention and repair ◆ ‘Desalination’ and ‘Re-alkalization’

Electrolyte solutionCa(OH)2, Li3BO3

（8 weeks）

Direct current (1A/m2 as standard）

� The direct current move the chloride ions to the concrete surface.

Cl－

Cl－

Cl－

External electrode

Internal electrode

Desalination, Re-alikalization

� A temporary anode with Ca(OH)2 is attached on the concrete .

Internal electrodeRebar

Concrete

＋

－

＋

� This method contribute to the diffusion of alkaline solution.

Desalination, Re-alikalization method

Installation of temporary anode

High way pillars in the sea Osaka castle

3. Prevention and repair ◆ ‘Chloride ion fix agent’

Chloride ion Fix agent

Rebar corrosion by chloride attack

Standard mortar

With Chlorfix

Cement ＋CementMatrix

Mechanism Generate the hydro-calmiteChlorfix

5～10％

＜Operation＞

①Replace Chlorfix to Cement.

②Generate the hydro-calmite3CaO･Al2O3･Ca(OH)2･12H2O

③Fix the Cl- in between the layer

Prevent Corrosion

World first addivite technology to achieve the long service life of reinforced concrete.

Immobilize Cl-

Confidential

Rust fluid and crack Surface float, and peel off

What is salt damage of Concrete Structures？

In this case we have to repair and replace.

If the corrosion of rebar proceed,

Chloride ion attack

Pore structure of hardened paste

Cl- Free Chloride：

move in the pore solution freely ⇒ Reacts with rebar, cause the corrosion.

Cl- Bound Chloride：

present in the cement hydrates⇒ it is not related to the corrosion.

Ca(OH)2＋ 2Cl-→ CaCl2High Solubility（59.5g/100gH2O）

Ca(OH)2

Cl-Cl-

Cl-

Cl-

Cl-

Cl-

Cl-

Cl-

Cl-

Cl-

CaCl2

CaCl2

CaCl2

CaCl2

CaCl2

CaCl2

Leaching of Ca(OH)2 ⇒ Accelerate the Cl- intrusion.

NaClFriedel’s salt

ChroridBinding Additive

Ca(OH)2

H2O

CementParticle

H2O

◆Chloride binding mechanism of calcium aluminates

Chloride ion is bounded as Friedel’s salt.

OH-

Hydrocalumite(HC)【C4AH13】

Cl-Cl-

OH-

Chlore Fix

Hydration mechanism

XRD pattern of paste at 28 days

Paste with CF generated hydro-calmite(HC)

HC

CH

Normal cements OPC100%

5 55504540353025201510

Inte

nsity

(arb

.uni

t)

2q/q(Cu-ka)60

CH

CH

OPC 90% + CF: 10%

CH

CH

CH

CHC

H

Resistant to external salt

1. Permeability of chloride ions2. Corrosion of steel bar

5 mm

OPC CF 10%

Chloride penetration depth was controlled by the additive.

CF 5%

1. Permeability of chloride ionsBSE images of Mortar Cl penetrated test

after NaCl 10mass% solution 4 weeks immersion

OPC

CF 7%

Rebar state after accelerated corrosion 1 year by external salt

Corrosion ratio: 18.6% 6.5%

14cm

10%NaCl solution

40 C dry atmosphere

Nitrite type hydrocalumite 10%0%

1. Permeability of chloride ionsAccelerated corrosion test

Production line up

Chlore fix grout

Chlore fix shot Chlore fix patch

Concrete wall was repaired by patching mortar.

construction example in Japan

Required level of performance

Elapsed year

Ser

vice

abili

ty

Conclusion

Repair

◆ The repair method and material taking into account durability

◆ Design of concrete for crack control ‘Expansive concrete’

New

construction

⇒ Contribute the extension of service life.

⇒ Reduction of cost for maintenance.

Reducing the speed of deterioration will enhance the authenticity to extend the service life of concrete structure.

Thank you for your attention !