Theory and Testing Methods of Self-Consolidating Concrete

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



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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


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


Normal Concrete

SCC

Low CA content

High paste volumePassing ability


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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 ???

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Theory and Testing Methods of Self-Consolidating Concrete