corrosion of concrete design, prevention and repair
TRANSCRIPT
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Corrosion of ConcreteDesign, Prevention and Repair
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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.
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� 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.
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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)
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2. Design of concrete for crack control ◆ ‘Expansive concrete’
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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
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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
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Expansive additive for concreteControl
Expansive Concrete
Control the crack
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Production of Expansive Concrete
9
Expansiveconcrete
Expansiveconcrete
⇒+
Mixer
� Mixed at the ready mixed concrete plant.
Expansive additive
NormalconcreteNormal
concrete
Precast Concrete
Construction site
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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.
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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.
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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.
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YURIKAMOME, The New Transit, 1995 ( Tokyo )
CSAAppliedCSAApplied
CSA was used for concreterail reducing crack.
13
Application of Denka CSA Viaduct
Past 20years
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3. Prevention and repair ◆ ‘Desalination’ and ‘Re-alkalization’
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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.
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Desalination, Re-alikalization method
Installation of temporary anode
High way pillars in the sea Osaka castle
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3. Prevention and repair ◆ ‘Chloride ion fix agent’
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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
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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,
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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.
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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
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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
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Resistant to external salt
1. Permeability of chloride ions2. Corrosion of steel bar
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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
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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
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Production line up
Chlore fix grout
Chlore fix shot Chlore fix patch
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Concrete wall was repaired by patching mortar.
construction example in Japan
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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.
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Thank you for your attention !