Consistency of Concrete by Vee-Bee Consistometer Test

1. objective

The workability of fresh concrete is a composite property, which includes the diverse requirements of stability, mobility, compactability, placeability and finishability. There are different methods for measuring the workability. Each of them measures only a particular aspect of it and there is really no unique test, which measures workability of concrete in its totality. This test gives an indication of the mobility and to some extent of the compactibility of freshly mixed concrete. The test measures the relative effort required to change a mass of concrete from one definite shape to another (i.e., from conical to cylindrical) by means of vibration. The amount of effort (called remoulding effort) is taken as the time in seconds, required to complete the change. The results of this test are of value when studying the mobility of the masses of concrete made with varying amounts of water, cement and with various types of grading of aggregate. The time required for complete remoulding in seconds is considered as a measure of workability and is expressed as the number of Vee-Bee seconds. The method is suitable for dry concrete. For concrete of slump in excess of 50mm, the remoulding is so quick that the time cannot measured.

2. apparatus required

Vee-Bee Consistometer

Fig. 1: Vee-Bee Consistometer

a) A vibrator table resting upon elastic supports

b) A metal pot

c) A sheet metal cone, open at both ends

d) A standard iron rod, Tamper (20 mm in diameter and 500 mm length)

Balance

Fig. 2: Balance

Balance should be able to weigh upto 1 g accuracy.

2.1 Container - It is cylindrical in shape, having an internal diameter of 240 ± 5mm and a height of 200 ± 2 mm and made of a metal, not readily attacked by cement paste. The thickness of wall shall be 3 mm and that of the base 7 mm. The container shall be watertight and of sufficient rigidity to retain its shape under rough usage. It shall be fitted with handles and protected from corrosion 2.2 Mould - Mould, suitable of forming the test specimen, shall be made of metal, not readily attacked by cement paste and having at least 1.6 mm thickness. The mould shall be visually checked prior to each use to ensure that it is clean and not damaged or dented. 2.3 Disc - A transparent and horizontal disc attached to a rod that slides vertically through a guide sleeve mounted on swivel arm and which can be fixed in a position by a screw. The swivel arm also supports a funnel the bottom of which coincides with the top of the conical mould when the latter is positioned concentrically in the container. The swivel arm is located by a hold and can be fixed in a position by set screw. When in the proper position, the axes of the rod and of the funnel shall be coincident with the axis of the container. The transparent disc shall be 230 ± 2 mm in diameter and 10 ± 2 mm in thickness. A weight placed directly above the disc shall be provided such that the moving assembly consisting of the rod, the disc and the weight has a mass of 2 750 ± 50g. The rod shall be provided with a scale graduated to at least 5 mm intervals to record the slump of the concrete. 2.4 Vibrating table - It shall be 380 ± 3 mm in length and 260 ± 3 mm in width, supported on four rubber shock absorbers. A vibrator unit, carried on a base resting on three rubber feet, shall be securely fixed beneath it. The vibrator shall operate at a frequency of 55 ± 5.5 Hz and the vertical amplitude of vibration of the table with empty container on the top of it shall be approximately 0.5 ± 0.02 mm. The vibrating table shall be checked annually to ensure that the frequency and the vertical amplitude remain within tolerances. All the elements of the vibration table shall be checked annually to ensure that their dimensions remain within tolerance 2.5 Tamping rod: - It is a straight rod, made of steel or other suitable material, of circular cross-section, having a diameter of 16 ± 1 mm, 600 ± 5 mm in length, and with rounded ends. 2.6 Stop-Watch: capable of recording time to an accuracy of 1 s. 2.7 Remixing container: It is of rigid construction, made from non-absorbent material not readily attacked by cement paste. 2.8 Scoop: of adequate size.

3. reference

IS 1199:2018 (First Revision)Fresh Concrete— Methods of Sampling, Testing and Analysis, Part 2-Determination of Consistency of Fresh Concrete

4. procedure

  1. It shall be ensured that Vee Bee Meter (Consistometer) is placed on a rigid horizontal base free from extraneous vibration and shock. Make sure that the container is firmly fixed to the vibrating table by means of wing nuts.
  2. Dampen the inside of the mould with a moist cloth and place it in the container.
  3. From the sample of concrete obtained, immediately fill the mould in three layers, each approximately one-third of the height of the mould when compacted. When adding the concrete, ensure that it is distributed symmetrically around the mould.
  4. Tamp each layer with 25 strokes of the tamping rod. The strokes shall be distributed in a uniform manner over the cross-section area of the mould. For the bottom layer, this will necessitate inclining the rod slightly and positioning approximately half the strokes spirally towards centre. Tamp the second layer and top layer each throughout its depth, so that the strokes just penetrate into the underlying layer. In filling and tamping the top layer, heap the concrete above the mould before tamping is started.
  5. The operation of raising the mould shall be performed in 7 ± 2s by a steady upward lift with no lateral or torsional motion being imparted to the concrete. If the concrete shears, collapses or slumps to the extent that it touches the wall of the container, this information shall be recorded.
  6. Swing the transparent disc over the top of the concrete, loosen the screw and very carefully lower the disc until it just comes in contact with the concrete. When the disc just touches the highest point of the concrete without disturbing it, tighten the screw.
  7. The screw shall be loosened to allow the disc to follow the concrete as it settles under the subsequent vibration. Simultaneously, start the vibration of the table and the timer. Observe through the transparent disc how the concrete is being re-moulded.
  8. As soon as the lower surface of the disc is fully in contact with cement paste of the concrete, stop the timer and switch off the vibrating table. Record the time taken to the nearest second. Complete the procedure within a period of 5 min from the start of filling.
  9. 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.

5. observation and recording

  • 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
  • 6. Result

  • The Vee Bee Degree of concrete ......... second(s) indicate Low/ Medium/ High Degree of workability

  • Work Description Workability Measurement Vee-Bee time (seconds)
    Slump (mm) Compaction Factor
    Moist earth - - 40 to 25-20
    Very Dry - 0.70 20 to 15-10
    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

    Table 1 : Workability of Concrete based on Vee-Bee Test

    8. Download

    Download PDF