Compacting factor Apparatus Test

Compacting factor test is a more precise and more accurate test for determining the workability of concrete. This is test is widely used in the construction fields and laboratories. The ratio of the weight of partially compacted concrete to the fully compacted concrete is called compacting factor also called a compaction factor. The maximum value is 1 which represents the highest degree of workability.

What is compacting factor apparatus?

The compacting factor apparatus is a device that is used to determine the compaction factor of concrete having low, medium, and high workability. Workability usually represents “the ease with which concrete can be used”.

The compaction factor apparatus consists of three main parts including two conical funnels with a hinged trap door. The trap door is attached to the bottom of each funnel to allow the concrete sample to flow freely into the cylindrical shape. The funnels and the mold are installed on a sturdy steel frame and can be easily removed for cleaning.


Compaction factor apparatus is used to determine the workability of concrete more precisely and accurately than the simple slump test. The usual dimensions of compacting factor apparatus are:

Dimensions(Length, width and height): 500x400x1510 mm
Mass: 55 kg approx.

Compacting factor test lab report:


This test is widely performed to determine the workability and consistency of the fresh concrete mix by the method of compacting factor test. The main standards like Astm, IS and British follow almost the same method which is discussed in this lab report.


This test is used to provide a simple and convenient method of measuring the workability of freshly mixed concrete and to control the batch-to-batch control Uniformity of ready-mixed concrete. This test provides an added advantage to the slump test as it is more precise and versatile. The slump test cannot be used when the concrete mix is too hard.

There are three types of slump namely the true, shear, and collapse slump. The slump test fails when there is a shear or collapse case. So compacting factor test has another advantage over the slump test, which is it can measure the workability in any case.

Compacting factor test Apparatus

The most commonly used apparatus for this test includes:

  • Weighing balance
  • compacting steel alloy rod
  • compaction factor apparatus with two conical hoppers mounted above cylinder
  • Trowels for levling the surface
  • Tamping rod.


The compacting factor test is performed in the lab or field following these steps:

  • Make sure that all of the trap doors are closed.
  • Carefully place the freshly made concrete sample in a certain mix ratio with the hand shovel or any sutibale tool up to the edge in the upper hopper and level it with the help of a trowel.
  • Open the trap door by releasing its lock at the bottom of the upper hopper to let the concrete fall due to the gravity into the lower hopper Funnel. Use the steel rod to gently press down on the concrete sticking to the sides.
  • Release the next trap door of the lower hopper and let the concrete fall due to gravity into the cylinder below.
  • Use trowels to remove the excess concrete above the top level of the cylinder, then level it. Clean
    the outside surface of the cylinder with help of a cloth.
  • Using a balance Weigh down the cylinder with concrete to the nearest 10 g. This weight is known as the weight of partially compacted concrete labled as (W1).
  • After noting the weight of partially compacted concrete, empty the cylinder, then refill it with fresh concrete and fully compact it with the help of a tamping rod or vibrator. Level the surface using a suitable tool.
  • Weigh the cylinder with fully compacted concrete. This weight is known as the weight of full
    compacted concrete and denoted with (W2).


The compaction factor is an index which is basically the ratio of the weight of partially compacted concrete to
the weight of fully compacted concrete and represent the workability of the freshly mixed concrete. It should normally be specified to the second Decimal place. The compression factor values range from 0.7 to 0.95

compacting factor apparatus,
compacting factor

Compacting factor vs Slump Values

Degree of workabilitySlump value in mmCompacting factorUses and suitability of concrete
Very Low0-250.78Represent very dry mixes, used in road-making, roads vibrated by powerful machinery
Low25-500.85Low workability mixes, used for light reinforced concrete and foundations, Road vibrated by hand-operated machines
Medium50-1000.92Medium workability mixes, Manually compacted flat slabs using crushed aggregates, manually compacted medium reinforced concrete, and highly reinforced concrete compacted through vibrator
High100-1750.95High workability, for the congested reinforced section where vibrator cannot be used
Compacting factor vs Slump

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Multiple tests are used to calculate the workability of freshly mixed concrete. Three of them are most popular: The slump test, compaction factor test, and the vebe consistometer test. In this lab report, I discussed the compaction factor test in detail. The slump test is the most simple one and is widely used for calculating workability in the field. Vebe consistometer test is used for concrete having very little mobility. While compacting factor test is used for determining the workability more precisely.

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