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Self Consolidating Concrete

Ketan Sompura, Ph.DProduct EngineerSika Corporation

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AgendaSCC – DefinitionSCC ApplicationsMaterialsMix DesignSCC PropertiesBenefits of SCC

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Self Consolidating ConcreteBasic Definition:

Self-consolidating concrete (SCC) can be defined as a highly fluid concrete that is able to flow in the interior of the formwork, passing through the reinforcement and filling the volume, under its own weight without internal or external methods of consolidation.

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Vertical ApplicationsCan be poured from the top or pumped from bottom to topCan be poured from a single point

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Horizontal ApplicationsFaster placing timeNo Vibration requiredLess labor

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Need for SCC today...Slender sections Congested reinforcementHigh productivityBetter surface finish

Producers:Ready Mix IndustryPrecast IndustryContractors

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Case Study – Precast Double T’s

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Cost Analysis – Double T’sUsing SCC:

Higher material cost Low labor costLesser pouring timeLess equipment cost (vibration)Less/No patch repair costHigher Productivity

Lower Overall Cost per cubic yard

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High flow concrete v/s SCCHigh Flow Concrete

Slump 8” to 10”Vibration neededNot self Leveling

SCC

Slump flow 24” to 30”No Vibration neededSelf Leveling

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SCC - Key PropertiesFresh SCC must possess:

Filling ability : Ability to flow into all spaces within the form-work under self weight

Passing ability :Ability to flow through tight openings such as spaces between steel reinforcing bars, under self weight

Resistance to segregation :Its composition at any stage must be uniform through the process of transportation and placement

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Concrete Technology for SCC

SCC is so designed that:It is Self LevellingDefoam itself by its self weightNo air entrapmentFair faced exposed surfaceSelf compaction and no external vibrationFlowable without bleeding / segregationNon-sedimentation of bigger aggregates

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SCC MaterialsAggregates:

Normal concreting aggregates for structural concrete can be used.

Maximum size of aggregate to be used depends on reinforcement layout in the same way as in traditional concrete.

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SCC Materials

Cement and fines:

Cement and fillers are required for cohesion and stability in larger proportions.

Fillers like lime stone powder derived from crushed rock,or active materials like slag, Fly ash, silica fume may be used.

Fillers must be assessed for their effect on water demand.

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SCC MaterialsChemical admixtures:

High Range Water Reducers- Polycarboxylate based- Conventional admixtures can also be used

Viscosity Modifying Admixtures (VMA’s)- Enhances Viscocity, provides stability- Resists bleeding and segregation

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Trace18%

46%

24%

12%

0.01 %20%

28%

34%

18%

Traditionalconcrete

SCC

Admixture

Water

Coarse Aggregate

Fine Aggregate

Fines (Cement+ SCM+ Filler)

Typical Mix Design Volume Percentage

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SCC – Focus area in the Mix Design

Reduction in coarse aggregate contentIncrease in paste content to increase fluidityManage the Rheology

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SCC – Fluid PropertiesTests to evaluate typical fluid properties:

Characteristic Test Method

Flowability Slump Flow test

Viscosity (Rate of flow) T500 of Slump Flow testV-funnel testRheometer

Passing ability L-Box testJ-Ring testU-box

Segregation Column segregation testSegregation resistance(Sieve test)Visual Stability Index

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Flowability and Viscosity (Slump flow test)- ASTM C 1611

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Visual Stability Index (VSI)-ASTM C 1611

Ref: ASTM

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Passing ability (L-box test)

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J-Ring Test –ASTM C 1621

Ref: ASTM

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Stability – Column segregation test

www.cement.org

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SCC -Hardened propertiesCompressive strengths greater than 10000 psi can be easily achieved

Tensile strength comparable to traditional concrete

Drying shrinkage similar to traditional concrete

Stronger bond to the reinforcement

Improves durability

Very low surface absorptions

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Quality ControlHigher degree of quality control needed as compared to Conventional ConcreteAggregate gradation should be optimizedConsistent quality of aggregatesMoisture content and W/Cm ratioFormwork - Increased form pressure

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BenefitsEase in placementCost saving, through reduced equipment and labour requirementsHigh productivityReduced casting time in the production cycleReduction of on-site repairsReduced noise pollutionUse of SCM’s which are “by-products” which helps environmental considerations

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Summarizing...

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SCC will flow through this…..

This….

And that……

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….and it will flow “quietly”

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A finish which is truly fair-faced

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SCC – A boon for Environment, Health & Safety

Improved environment for both concrete workers and the people in the neighborhoods due to less noise pollution

The work (ie execution) will be less physically strenuous.

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Thank you !!