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Compaction Factor Test for Concrete Workability. 58

Compaction Factor Test for Concrete Workability.


The compacting factor test  process has an element of external force in it, compared to the slump test. This test measures the compactability of concrete, depending upon the external force application.

The compacting factor is defined as the ratio of the weight of partially compacted concrete to the weight of fully compacted concrete.

The test shows better results for concrete of low and medium workability (compacting factor of 0.9 to 0.8). The test is suitable foe laboratory environment.

Slump, Vee Bee, and Compaction Factor test results are compared below:

Workability  Test Results Compared

Workability Degree

Slump test


Vee Bee Test


Compaction Factor Test  (number)

Very Low

0 – 25

20 – 10



25 – 50 – 5

10 – 5



50 -100

5 – 3



100 – 150

3 – 1



For concrete of very low workability of 0.70 or below, the test is not suitable, because more external efforts are required for such concrete.

 Apparatus  for Compaction Factor test and Degree of Workability 

The Compaction Factor Test apparatus as shown above includes:

Container — (for degree of compatibility test) having followed dimensions:

  1. a) Base : 200 ± 2 mm × 200 ± 2 mm

  2. b) Height : 400 ± 2 mm

  3. c) Thickness of the base and walls shall be at least 1.5 mm


Ordinary trowels,

One scoop of adequate size,

Tamping rod made of steel, having a circular cross-section with a diameter of 16 ± 1 mm, 600 ± 5 mm in length and with rounded ends,

Measuring scales (or a balance) to weigh up to 50 kg, with an accuracy to the nearest 10 g.

Compaction Factor Test apparatus as shown above.


Procedure for Compaction Factor Test for Concrete

     Clean the hoppers and cylinder and dampen the inside of the hopper and cylinder with a moist cloth before its use. Find th  weight of empty cylinder (W1).

    The sample of concrete collected to   the specification shall  be placed  gently in the upper hopper, to fill it completely up  to   the top of hopper, with its trap door closed.

    Close the trap door of bottom hopper. Open the trap door of the upper hopper so that the material falls into bottom                hopper

     Next open the trap door of the bottom hopper and allow th  concrete to fall into the cylinder.

      Measure the weight of the cylinder plus concrete. Let it be  known as the weight of partially compacted concrete. (W2)

      Refill the cylinder with the same sampl  in  laye 

approximately 5 cm deep, with ramming for full compaction.

    The weight of the concrete in the cylinder shall then be determined to the nearest 50 g. This weight shall be known as the weight of fully compacted concrete. (WCompaction Factor is calculated as below:

   The degree of workability and their compacting factor are as follows:

  • (CF) is 0.78 –  it is considered as very low workability of concrete,

  • (CF) is 0.85 –  it is considered as low workability of concrete,

  • (CF) is 0.92  – it is considered as medium workability of concrete,

  • (CF) is 0.95  –  it is considered as high workability of concrete.

Degree of Compactability  of Fresh Concrete

Principle -The fresh concrete is uniformly placed with trowel in a container  with specifications given above, avoiding any compaction while filling. When the container is full, the top surface is scraped in level with the top of the container. At this stage, the height of concrete as shown figure is = h1

The concrete is,  refilled in the container in layer of 5 cm and fully compacted. The distance from the surface of the compacted concrete to the upper edge of the container (h2)  is used to define the degree of compactability.

  The degree of compatibility = h1/(h1 – h2)


The values lying between 1.04 and 1.46. If the degree of compactability is less than 1.04 or more than 1.46, this test is not suitable.

 Procedure  to find the Degree of compactability  of Concrete.

  1. a) Clean the container and dampen the inner surfaces using a moist cloth.

  2. b) Fill the container without tamping it, with the trowel up to all four upper edges of the container. When the container is full, remove all concrete above upper edges, using straight edged scrapper .

  3. c) Refill the concrete in layers and compact it by means of tamping rod / vibrator, until no further reduction in volume is determinable.

  4. d) After compaction, measure to the nearest millimetre, the distance between the surface of the compacted concrete and the upper edge of the container at the middle of each side of the container.

  5. e) Determine the mean value of the four measurements.


The degree of compactability is given by equation:

c = h1 / (h1 – h2) where c = degree of compactability


Workability Tests Compared for  Concrete


Suggested Workability Tests

Workability Degree

Vee Bee

Very Low

Vee Bee (VB); Compaction Factor (CF)


VB; CF; Slump Test


CF; Slump Test;


CF; Slump Test; Flow Test

Very High

Flow Test


Degree of Compactability Test Format

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