Different Test Methods for Workability Measurement
Depending upon the water cement ratio in the concrete mix, the workability may be determined by the following three methods.
Compaction Factor Test
Vee-bee Consistometer Test
1. Slump Test
This method is suitable only for the concrete of high workability.
This test is carried out with a mould called slump cone whose top diameter is 10 cm, bottom diameter is 20 cm and height is 30 cm.
The test is performed in the following steps:
Place the slump mould on a smooth flat and non-absorbent surface.
Mix the dry ingredients of the concrete thoroughly till a uniform colour is obtained and then add the required quantity of water in it.
Place the mixed concrete in the mould to about one-fourth of its height.
Compact the concrete 25 times with the help of a tamping rod uniformly all over the area.
Place the mixed concrete in the mould to about half of its height and compact it again.
Similarly, place the concrete upto its three-fourth height and then up to its top. Compact each layer 25 times with the help of tamping rod uniformly. For the second and subsequent layers, the tamping rod should penetrate into underlying layer.
Strike off the top surface of mould with a trowel or tamping rod so that the mould is filled to its top.
Remove the mould immediately, ensuring its movement in vertical direction.
When the settlement of concrete stops, measure the subsidence of the concrete in millimeters which is the required slump of the concrete.
Recommended Slump Values for Various Concrete Works
Type of Construction
Recommend slump in mm
Mass concrete structure
Caissons and bridge decks
Reinforced foundation, footings and walls
Reinforced slabs and beams
Limitations of Slump Test
Following are the limitations
Not suitable for concrete containing aggregates larger than 40 mm.
Not suitable for concrete of dry mix.
Not suitable for very wet concrete.
Not reliable because slump may be of any shape.
2. Compaction Factor Test
According to this test, the workability may be defined as the amount of applied work required to compact the concrete to its maximum density.
This method is adopted for determining the workability of concrete mix in laboratories. It gives fairly good results for concrete of low workability.
The apparatus required for performing the compaction factor test is shown below.
The test is performed in the following steps:
Clean and dry the internal surface of the mould.
With the help of hand scoop, place the concrete in upper hopper A.
Open the trap door of hopper in order to facilitate the falling of the concrete into lower hopper B. the concrete sticking to the sides of the hopper A, should be pushed downward with the help of a steel rod.
Open the trap door of the hopper B and allow the concrete to fall into cylinder C.
Remove the surplus concrete from the top of the cylinder with the help of a trowel. Wipe and clean the outside surface of the cylinder.
Weigh the cylinder with partially compacted concrete nearest to 10 g.
Fill in the cylinder with fresh concrete in layers not exceeding 5 cm in thickness and compact each layer till 100 percent compaction is achievd.
Wipe off and clean the outside surface of the cylinder and weigh the cylinder with fully compacted concrete nearest to 10 g.
Calculate the value of compaction factor using the following formula.
Compaction factor = weight of partially compacted concrete/weight of fully compacted concrete
Recommended Values of Workability for Various Placing Conditions
Values of Workability
Concreting of shallow sections with vibrations
20 – 10 seconds Vee-Bee time
or 0.75 to 0.80 compacting factor
Concreting of lightly reinforced sections with vibrations
10 – 5 seconds Vee-Bee time or
0.80 to 0.85 compacting factor
Concreting of lightly reinforced sections without vibrations or heavily reinforced sections with vibrations
5-2 seconds Vee-Bee time or
0.85 to 0.92 compacting factor or
25 – 75 mm slumps for 20 mm aggregates
Concreting of heavily reinforced sections without vibrations
Above 0.92 compacting factor or 75 – 125 mm slump for 20 mm aggregates.
Advantages of Compaction Factor Test
Following are the advantages:
Suitable for testing workability in laboratories
Suitable for concrete of low workability
Suitable to detect the variation in workability over a wide range
Its results are more precise and sensitive.
3. Vee-bee Consistometer Test
The apparatus used in this method of test is shown below.
This method is suitable for dry concrete having very low workability
The test is performed as given described below
Mix the dry ingredients of the concrete thoroughly till a uniform colour is obtained and then add the required quantity of water.
Pour the concrete into the slump cone with the help of the funnel fitted to the stand.
Remove the slump mould and rotate the stand so that transparent disc touches the top of the concrete.
Start the vibrator on which cylindrical container is placed.
Due to vibrating action, the concrete starts remoulding and occupying the cylindrical container. Continue vibrating the cylinder till concrete surface becomes horizontal.
The time required for complete remoulding in seconds is the required measure of the workability and it is expressed as number of Vee-bee seconds.
COMPARISON OF WORKABILITY MEASUREMENTS BY VARIOUS METHODS