Exp 8 Compacting Factor

Experiment No. 8:

To perform the compacting factor test.

Scope & significance:

This test also gives the workability of concrete indirectly. This test is appropriate for concrete with the maximum aggregate size of 40mm.


Apparatus consists of two hoppers each in the shape of frustum of a cone and one cylinder. The hoppers have hinge door at the bottom and all the surfaces are polished to reduce friction.

Related theory:

Compacting Factor

 The degree of compaction is also called the compacting factor and is measured with the help of density ratio that is the ratio of density actually achieved in the test to the density of same concrete when it is fully compacted.Its maximum answer is 1 but practically it is lesser than 1.

Relation Between Workability And Compacting Factor

Compacting Factor


Compacting Factor

Slump (mm)

Very Low


0 – 25



25 – 50



50 – 100



100 – 175

Note: More is the compacting factor more will be the workability.


First the concrete is placed gently at the upper hopper so that no work is done on concrete to produce compaction. The bottom door of the upper hopper is then released and the concrete falls into the lower hopper. The bottom door of the lower hopper is then released and the concrete falls into the cylinder. Excess concrete is then removed from the cylinder. The density of concrete in now calculated and this density divided by the density of fully compacted concrete is known as compacting factor. More is the compacting factor more will be the workability

Observations & Calculations:

Weight of empty cylinder                                = …………5.4………… kg
Weight of partially compacted concrete = m1 = …………11.4……… kg
Weight of fully compacted concrete       = m= …………13.4……… kg
Compacting Factor = =11.3/13.4 =   0.843


                              For the normal range of concrete the compaction factor lies between (0.8 – 0.92 ). The value of  compactness factor tells us that the workability of concrete is Low but the slump value tells us that the workability is Medium. This variation was due to the reason that when the first test was performed the then apparatus was not made wet which made the reading slightly more. The sensitivity of the compaction factor is reduced outside the normal range of workability and is generally unsatisfactory for compacting factor greater than 0.92 .

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