Workability of Concrete

It must be easily mixed and transported. It must be uniform throughout a given batch, and

between batches. It must keep its fluidity during the transportation

period. It should have flow properties such that it is

capable of completely filling the forms. It must have the ability to be fully compacted

without segregation. It must set in a reasonable period of time. It must be capable of being finished properly,

either against the forms or by means of troweling or other surface treatment.

Requirement of Fresh Concrete

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That property of freshly mixed concrete or mortar which determine the ease and homogeneity with which it can be mixed , placed, consolidated and finished.

( ACI )

Definition

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Workability is the property of concrete which determine the amount of useful internal work necessary to produce full compaction.

Road Research lab, UK

Definition

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Water content Mix Proportions Size of Aggregate Shape of Aggregate Surface texture of Aggregate Grading of Aggregate Use of Admixtures

Factors affecting Workability

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Slump Test Compacting Factor Test

Flow Test Kelly Ball Test

Vee Bee Test

Measurement of Workability

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Slump Test

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Compacting Factor TestConcrete is filled in top hopper 1 meter highAllowed to drop in second hopperConcrete is dropped from second hopper into cylinder and leveledWeighed and emptiedFilled with fully compacted concrete and weighed againRatio of fallen weight to fully compacted concrete is compacting factor

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Vee Bee Test Slump cone test

is performed in a closed cylinder of 300 mm dia.

Perspex plate is placed on top.

Vibration are applied at standard rate till plate is fully in contact.

Time in second to achieve state of concrete shown below is called Vee Bee

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Flow

Test

Conical mould is filled with concrete and placed in centre of boardBoard is raised and dropped 15 timesSpread of concrete is measured and is called Flow

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Kelly Ball Test

Simple field test which measures indentation of 15 cm dia metal hemisphere weighing 13.6 kg.Not suitable for thin or small concrete works.

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Comparison of Slump and Flow Table Tests

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Comparison Vee Bee and Compacting Factor Tests with Slump Test

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Comparison of Slump and Kelly Ball test

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Workability tests

Comparison

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Variability in Results

Slump

Vebe

Comp Factor04/13/2023 16Plain and Reinforced Concrete - 1

Affects of temperature on Workability of

Concrete

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Affect of time on Workability

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Setting time of Concrete

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Setting of concrete is caused by water cement reaction.

Setting time of cement and concrete do not coincide.

Initial and final setting times are arbitrarily defined by method of penetration of needle

Final set of concrete do not mean complete loss of workability.

Initial set represent time after which concrete can not be mixed placed and compacted properly.

Final set indicates time after which strength development is at significant rate.

Setting time of concrete

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Affect of temperature and cement type on workability

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