Correct Answer - Option 5 : Flow time by Marsh cone
Concept:
Workability of concrete:
Workability is the relative ease with which concrete can be mixed, transported, molded, and compacted. we can also say, it is the energy to overcome friction while compacting.
The workability of concrete can be measured using the following methods,
1) Slump test:
The slump test is a measure of consistency or the wetness of the concrete mix. It is suitable for field applications, suitable for concrete of high and medium workability. Slumps for various types of concrete is measured in mm.
2) Compacting factor test:
It is more accurate than a slump test. It is suitable for concrete mixes of medium and low workability. It is suitable for determining workability in the laboratory.
3) Vee-bee consistometer:
The time required for complete remoulding of concrete in seconds after placed in the mould with a slump cone. It is expressed in seconds. It is the method used to determine the workability of very dry mixes with low workability.
4) Flow table test:
Based on the percentage flow the workability of the concrete is determined. The values could range from 0 to 150 %
5) Kelly ball test:
It is a simple field testing machine that determines the depth to which a 15 cm diameter metal hemisphere weighing 13.6 kg, will sink under its own weight into the fresh concrete. Based on the depth of the penetration workability of concrete is determined
Hence Flow time by Marsh cone is not used for measuring workability.
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Consistency
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Slump in mm
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Compaction Factor
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Vee-Bee time in seconds
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Very Dry
|
0-25
|
0.7-0.8
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20-10
|
|
Dry
|
25-50
|
0.8-0.85
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10-5
|
|
Plastic
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50-100
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0.85-.95
|
5-2
|
|
Semi-fluid
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100-175
|
0.95-1
|
2-0
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