Theory and Testing Methods of Self-Consolidating Concrete
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Transcript of Theory and Testing Methods of Self-Consolidating Concrete
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8/9/2019 Theory and Testing Methods of Self-Consolidating Concrete
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Theory and Testing Methods of
Self-Consolidating Concrete
(SCC)
CEE 8813
03/14/07
Felix Kim
What is Self-Consolidating Concrete?
A highly flowable, yet stable concrete that
can spread readily into place and fill the
formwork without any consolidation and
without undergoing significant separation
(Khayat, Hu and Monty, 1999)
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Benefits
No vibration needed
Less labor needed
Low noise-level in the plants and construction
sites.
Easier to pump
Faster construction
Improved quality and durability
Higher strength
Comparison
Normal Concrete
Slump flow: 8 ~ 11 in
Vibration required
Somewhat self-leveling
No segregation
SCC
Slump flow: 24 ~ 30 in
No vibration needed
Self-leveling
No segregation
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Tight Spacing
(Kalkan, 2007)Concrete pour on 02/26/07
Video
(Kalkan, 2007)Concrete pour on 02/26/07
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3 Characteristics
Filling ability
Ability to flow under its own weight both horizontallyand vertically upwards without honeycombingaround any shape
Passing ability
Ability to flow freely through dense reinforcementwithout blocking
Segregation Resistance
Ability to maintain homogenous mix during and afterplacement, without separation of aggregate from thepast, or water from solids
(Petersson et al., 2002)
Flow ability vs. Segregation Resistance
Difficult to achieve both flow ability
and segregation resistance
Flow ability
Segregation Resistance
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Mix Design
Coarse Aggregate content: 28 32 %
Mortar fraction: 61%-68%
Sand / Aggregate Ratio: 48%-57%
Cementitious: 700-840 lb/cu yd
Water: 290-310 lb/cu yd
Admixtures: Viscosity Modifying Admixture
(VMA), Superplasticizer (PolyCarboxylate)
(Knight and Grace, 2002)
Aggregate Fraction
Coarse Aggregate
content: 28 32 %
Mortar fraction: 61%-
68%
Sand / Aggregate
Ratio: 48%-57% Gravel
Gravel
Sand
SandPaste
PW
W
Air
SCC
Conventional
Concrete
(Okamura and Ouchi, 2003)
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High Paste Volume
Increases flow ability by reducing inter
particle friction
Increases heat generation
Larger drying shrinkage
Substitution of SCM can partially solve this
problem Fly Ash for heat reduction, Silica
Fume for strength
(Ng et al., 2006)
Aggregate Gradation
CA/Tot. Vol. governs the flow ability
Gradation needs to be considered when
spacing is close to Max. Size Aggr. (MSA)
CA < 3/8 CA < FA (Ng et al., 2006)
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Aggregate Gradation
25%-32% CA (reduce
blocking)
Aggr. gradation is very
crucial
1 3/8 Sand Pan
(Knight and Grace, 2002)
TopS
ecrete
%
Viscosity and Flowability
Viscosity - Measure of
resistance of fluid to
deform under shear
Yield shear stress
required shear stress to
initiate the flow
o
+= 0
o
Rate of shear,
Shear
stress,
0 1
(Grace Construction Products, 2002)
0
- Yield value (Pa)
- Plastic viscosity (Pa-s)
0
Superplasticizer
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Superplasticizer
Steric Repulsion
PolyCarboxylic
Flow ability
Viscosity Superplasticizer
Water
(Okamura, 1997)
Shear Friction
Shear stresses
increases when the mix
goes through a close
spacing because of
higher probability of
inter praticle collision
(Sonebi and Bartos,
2002)
(Okamura, 2003)
CA
Mortar
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Effect of Fine Aggregate on Deformability
(Okamura, 2003)
Crushed sand
River sand
Land sand
Small
Large
Sand content
CA
Mortar
Blocking
(Knight and Grace, 2002)
Normal Concrete
SCC
Low CA content
High paste volumePassing ability
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Segregation Resistance
Powder Method (Fly Ash)
Viscosity Modifier Method
- Hydrolyzed starches, Bipolymers (welumgum)
- New generation Superplasticizer - Highlyflowable mix with cohesion
- Molecular structure of VMA facilitates theremoval of large amount of water by physicaladsorption (Mehta and Monteiro, 1993)
Stokes Law and Segregation Resistance
Yield stress low
enough to flow
Viscosity low enough
to flow but high enough
to prevent segregation
18
)( 212
= gD
V
(Grace Construction Products, 2002)
density=
ityvis cos=
diameterD=
velocityV=
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Bleeding
Reduce strength
Stiffness
Bond to reinforcing bars
Durability
SCC Hardened Properties
As good as or better than normal concrete
Compressive and Tensile Strength
- 28 day strength higher than normal concrete
Durability
- similar to conventional superplasticized
concrete Shrinkage
- similar to other high cementitious material
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Slump Flow Test (ASTM C-1611)
The most commonly
used test
Filling ability,
Segregation resistance
Slump flow = (d1+d2)/2
20 ~ 26 in
recommended
VSI
Slump flow test performed on 02/26/2007
at GaTech Lab (picture taken by Felix Kim)
Slump flow
The test judges the capability of concrete to
deform under its own weight against the
friction for the surface with no other external
restraint present (Sonebi and Bartos, 2002)
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Visual Stability Index (VSI)
Very Subjective!
(Horta, 2005)
J-Ring (ASTM C-1621)
(Horta, 2005)
2
)( 21 ddflowRingJ +
=
Blocking = slump flow J-ring flow
Passing Ability
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Proposed Method
Direct relationship
between SI and Pd (Bui
et al., 2002)
Dynamic and Static
Segregation
El-Chabib and Nehdi
Dr. Struble has
proposed a similar test
method that ASTM isconsidering
Segregation Index (SI)
Penetration
depth(Pd)
Pd
segregation
No segregation
Proposed Method
(El-Chabib and Nehdi, 2006)
SI-Static
SI-dynamic
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Future Research
Development of Prediction Model (ANN)
Optimum mix design
Question ???