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Concrete Workability Tests Guide

This document discusses several tests used to evaluate the workability of concrete, including: - The flow test, which measures how far concrete spreads after being dropped and measures consistency and cohesiveness. - The Vee Bee consistometer test, which indirectly measures workability by timing how long it takes for concrete to change shape under vibration. - Segregation and bleeding, which refer to the separation of concrete ingredients and the rising of water to the surface. Proper mixing and use of additives can reduce these effects.

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312 views7 pages

Concrete Workability Tests Guide

This document discusses several tests used to evaluate the workability of concrete, including: - The flow test, which measures how far concrete spreads after being dropped and measures consistency and cohesiveness. - The Vee Bee consistometer test, which indirectly measures workability by timing how long it takes for concrete to change shape under vibration. - Segregation and bleeding, which refer to the separation of concrete ingredients and the rising of water to the surface. Proper mixing and use of additives can reduce these effects.

Uploaded by

RT
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Tuesday, March 24, 2020 1:42 PM

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Flow Test
This is a laboratory test, which gives an indication of the quality of
concrete with respect to consistency, cohesiveness and the proneness
to segregation.
The table top is cleaned of all gritty material and is wetted. The
mould is kept on the centre of the table, firmly held and is filled in
two layers.
Tests on Workability Page 4
two layers.
Each layer is rodded 25 times with a tamping rod 1.6 cm in diameter
and 61 cm long rounded at the lower tamping end.
The mould is lifted vertically upward and the concrete stands on its
own without support.

The table is then raised and dropped 12.5 mm 15 times in about 15


seconds. The diameter of the spread concrete is measured in about 6
directions to the nearest 5 mm and the average spread is noted.

Vee Bee Consistometer Test


This is a good laboratory test to measure indirectly the workability of
concrete.
This test consists of a vibrating table, a metal pot, a sheet metal cone, a
Tests on Workability Page 5
This test consists of a vibrating table, a metal pot, a sheet metal cone, a
standard iron rod.
The time required for the shape of concrete to change from slump cone shape
to cylindrical shape in seconds is known as Vee Bee Degree.
This method is very suitable for very dry concrete whose slump value cannot
be measured by Slump Test, but the vibration is too vigorous for concrete with
a slump greater than about 50 mm.

Segregation
Segregation can be defined as the separation of the constituent materials of concrete.
A good concrete is one in which all the ingredients are properly distributed to make a
homogeneous mixture.
There are considerable differences in the sizes and specific gravities of the constituent
ingredients of concrete.
Therefore, it is natural that the materials show a tendency to fall apart.

Bleeding
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Bleeding
Bleeding can be reduced by proper proportioning and uniform and complete mixing.
Use of finely divided pozzolanic materials reduces bleeding by creating a longer path for
the water to traverse.
Air-entraining agent is very effective in reducing the bleeding.
Bleeding can be reduced by the use of finer cement or cement with low alkali content.
Rich mixes are less susceptible to bleeding than lean mixes.

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