Object: To determine workability of fresh concrete by Vee-Bee consistometer test method.
Code:
IS : 119-1959
Apparatus:
- Vee bee test machine
- tamping rod of dia 20mm length 500mm
- Cylindrical Container
- Trowels
- Stopwatch.
Theory:
Workability of concrete is a complex property of concrete. Finding the workability of concrete involves various parameters as workability depends upon stability, mobility, compactibility, place-ability and finish-ability of concrete. There are different methods for determining the workability of concrete:
- Slump test
- Compaction factor test
- Vee bee consistometer test
- Flow table test.
Each test has their importance, and there is no unique test to measure the workability of concrete in total. Vee bee consistometer test determines the mobility and some extent of compactibility of concrete.Vee bee consistometer test is named after the developerV Bahrmer ofSweden, and it is covered byIS: 119 – 1959. In this test, we measure the relative effort led by concrete to change from one definite shape to another definite shape by conducting vibration (Conical to cylindrical). This effort is known as Remoulding effort and it is measured in ‘t’ secs. (time) or called asVee beeSecs.The time taken by the concrete to undergo complete remoulding is determined as a measure of workability of concrete, and it is shown asVee beeSecs.This test is usually performed on dry concrete and it is not suitable for very wet concrete. Concrete having slumpvalue more than 50mm remoulds quicker where measuring the time is not possible.
Vee bee Test machine:
Vee bee test machine consists of a vibrating table which is mounted on an elastic supports. The vibrator is operated electrically. The length and width of a vibrating table are 380mm and 260mm.On the surface of the vibrating table, a Cylindrical container of height is attached using wing nuts. Slump cone and a cylindrical jar are placed. The cylindrical container is screwed to the vibrating table through wingnuts.The slump cone of height 300 is open on both sides and has a dia of 200mm at the bottom and 100mm at the top. The slump cone is inserted into the cylindrical container to perform the test.The whole arrangement is mounted on a sturdy base.The bottom base consists of a swivel arm holder where the swivel arm is fixed to the funnel and guide sleeve.A graduated rod which has a scale is used to measure the workability of the sample.A graduated rod is fixed to the swivel arm through the guide sleeve. The graduated rod has the provision for screwing the transparent disc.
Procedure:
- Insert the Slump cone in the attached cylindrical container. Fill the concrete sample in the cone in three layers; each layer should be one-third of the height of slump cone and tamped with tamping rod for 25 strokes each. After tamping the top layer, struck off the concrete with a trowel making the cone correctly filled.
- After filling the concrete in the slump cone, the transparent glass disc attached to a swivel arm is moved and placed on the top surface of the concrete and Note the reading from the graduated scale as an “initial reading”
- And then remove the cone slowly in the vertical direction and wait until the concrete settles in the new position. Again move the swivel arm and place it on the lowered concrete for the final reading. Note it as “final reading”
- Now find out value of slump value by using the formula,
- slump value = Final reading – initial reading .
- Now, switch on the vibrator and start the stopwatch. The vibrations are continued until the concrete is wholly remoulded i.e, the surfaces become horizontal and the whole concrete surface adheres uniformly to the transparent disc.It can also said as that concrete changes shape from slump cone shape to cylindrical shape. The time required for complete remoulding in seconds is recorded.
- Note the time taken by concrete to become horizontal (remoulding) as Vee bee Secs.
- The consistency of concrete is measured as Vee bee Secs. The level of workability is estimated by comparing vee bee seconds found with the following table.
Calculations and Observations:
Initial Reading :- _________________
Final Reading :- __________________
Slump Value :- __________________
Time required for remolding :- ________________
Results:
By comparing your recorded vee bee seconds with table given the workability of your concrete is ____________________ .