The primary objective of the Vee-Bee test is to determine in situ or in lab workability of the freshly mixed
Concrete. The Vee-Bee test provides necessary information related to the mobility and compaction ability aspects of freshly mixed concrete having definite water to cement ratio.
During Vee Bee Test the relative effort is measured out in order to convert the mass of concrete from one shape to another. According to the test of the conical shape is converted into a cylindrical shape with the help of a simple vibration process.
The effort is measured in the form of time mostly in seconds. The measured work done in seconds is called the “forming effort”. The time it took for the complete shape conversion from conical to cylindrical is a measure of the workability which is exclusively expressed in the Vee-Bee Seconds.
This test method is named after the famous Swedish developer V. Bahrmer. The method can also be used for concrete having very little workability (dry concrete). For concrete having a slump value of more than 50 mm, the forming activity will be so fast that timing will not be possible so time-sensitive devices must be used to accurately measure time.
This test method is designated with ASTM C1176 / C1176M – 20 code and the standard can be downloaded from ASTM C1176.
Apparatus required for conducting Vee-Bee test
The complete set of instruments required for the Vee Bee test are:
- Vee-Bee Consistometer: The main part of the test which consists of a an electrically operated vibrating table which is supported and stored on elastic supports. It also consists of a metallic cone, a balance and cylindrical container
- Iron rod which is used for compaction of the concrete and trowels.
VEE BEE test Procedure
First, the sheet metallic cone is placed in the cylinder container of the consistometer upside down. In four layers the cone is filled with concrete. Each layer of concrete is about one-fourth, the height of the cone. Each layer is compacted by giving twenty-five tamping blows with a standard tamping rod after pouring.
The compaction through tamping is done with the rounded end of the rod. The Strokes are evenly distributed tamping from the edges towards the center. The compaction process should be done in such a manner, that the strokes which are carried out for the second and subsequent concrete layers must penetrate the ground Layers. After the last layer has been applied and compacted, the excess concrete is removed and the top surface is made one level with the help of a trowel. This will fill up the cone exactly.
After the preparation of the concrete, cone, the movable pane of glass attached to the arm is moved and
is placed on top of the setting cone, which is located in the cylindrical container. The pane of glass has
be placed in such a way that it touches the top edge of the concrete scales and the value is measured by the graduated rod.
Now the cylindrical cone is immediately removed by slowly lifting the cone in a vertically upward direction. The transparent disk on top of the concrete is placed in the new position and the measured value is noted.
The difference between the measured values from step 3 and step 4 results in the value of slump. so slump value is indirectly measured during this test.
Finally, the electric vibrator is switched on and at the same time, start the stopwatch to note down the time. The concrete is allowed to spread in the cylindrical container. After some time the concrete surface becomes completely horizontal and the concrete surface adheres completely and evenly to the transparent pane.
The time in seconds also known as vee bee time required for complete reshaping is recorded. This time in seconds gives us the measure of the workability of the fresh concrete. This time is noted and expressed as Vee-Bee seconds.
Observation and calculations in the Vee-Bee test
- Initial reading on the graduated rod before demoulding in mm = a
- The last reading on the graduated rod after removing the shape in mm = b
- Settling dimension (Slump value) = a – b in mm
- The time in seconds required for complete deformation
Therefore, the consistency of the concrete is measured in ———- Vee-Bee seconds.
- Check VEE BE test vs slump, VEE BE test relation with slump values, VEE BE test relation with compacting factor:
Advantages and Disadvantages of Vee-Bee test
The test procedure of the Vee-Bee test performs a similar procedure with that of slump value but there is an added benefit of the Vee Bee Test when compared to other tests namely the slump test, and the compaction factor test. which is the fact that it can measure very little workability.
One disadvantage of this test is that the reshaping of the completion is determined visually, which can complicate the measurement of the endpoint and therefore have the chance of having a human error. This probability of error is even more pronounced in the Concrete mixes with higher workability.
This mixture, therefore, has a lower value for the Vee-Bee time. For concrete mixes with
a workability of more than 125 mm, the deformation phenomenon is very rapid
and time cannot be measured practically. That means the Vee Bee test is not suitable for
Measurement of the workability of concrete with higher workability.
This higher workability comes in the area of the slump greater than 75 mm. In some situations this problem is overcome by using an automatic mechanism like a control gear that records the time of movement.
In general, the Vee-Bee test is more suitable for concrete mixes that have a low or very low value
the ability to work.
Among the standards like the slump test, the Compaction Factor Test, and the Vee-Bee Test, the slump test method is the most popular test for
measure the workability of concrete. The following table shows the Vee-Bee time in seconds for various
Processability according to American Concrete Institute 211 (ACI Committee 211).
Vee-Bee Test Precautions
- The vee bee mould should be cleaned and moisture free on the inside before adding
- While the strokes are being applied over the layers, ensure that they are applied evenly
and in the layers. This will help get the full depth effect of the strokes.
- The removal of the setting cone should be lifted up in such a way so that the
Concrete cone is not disturbed.
- The Vee-Bee tests must be carried out at some distance from other sources
of Vibration as the vibration method is sensitive in the test.
- The test must be stopped when a state is reached in which the transparent disc tab completely covers the concrete and all voids and voids in the concrete surface disappear.