The Most Suitable Test for Very Dry Concrete

Answer: B. Vee-Bee test

The most suitable test for a very dry concrete mix having very low workability is Vee-Bee test.

Solution

Workability: Workability of concrete is a broad and subjective term describing how easily freshly mixed concrete can be mixed, placed, consolidated, and finished with minimal loss of homogeneity.

Slump test: The Slump Cone apparatus for conducting the slump test essentially consists of a metallic mould in the form of a frustum of a cone having the internal dimensions as : Bottom diameter : 20 cm, Top diameter : 10 cm, Height : 30 cm and the thickness of the metallic sheet for the mould should not be thinner than 1.6 mm

In case of a dry sample, slump will be in the range of 25-50 mm. But in case of wet concrete, the slump may vary from 150-175 mm.

Vee-Bee test: The apparatus consists of a vibrating table which is supported and mounted on elastic supports. It also consists of a sheet metal slump cone, a weighing balance, cylindrical container, a standard iron tamping rod and trowels.

It allows the evaluation of freshly mixed concrete, measuring its workability by determining the characteristics of mobility and compactibility. The principle of the test is to change the shape of the concrete and measure the remolding in seconds.

Compaction factor test: The compaction factor test is the workability test for concrete conducted in a laboratory. 

• The compaction factor is the ratio of weights of partially compacted to fully compacted concrete. 
• It was developed by the Road Research Laboratory in the United Kingdom and is used to determine the workability of concrete.
• The Compacting Factor Apparatus is used to determine the compaction factor of concrete with low, medium and high workability. 
• Comprising two conical hoppers having a hinged trap door attached to the lower end of each hopper, allowing the concrete sample to flow freely into the cylindrical mould.

Work Description	Workability Measurement		Vee-Bee time (seconds)
	Slump (mm)	Compaction Factor
Moist earth	–	–	40 to 20
Very Dry	–	0.70	20 to 10
Dry	0 – 25	0.75	10 to 7-5
Plastic	25 – 50	0.85	5 to 4-3
Semi Fluid	75 – 100	0.90	3 to 2-1
Fluid	150 – 175	0.95	More Fluid than 1

For very dry concrete, the most useful test for workability of concrete is the Vee-Bee test . The time will take around 10- 20 seconds to remoulding the concrete.

∴ Hence, the correct option is B. Hence, the most suitable test for a very dry concrete mix having very low workability is Vee-Bee test.

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