Compacting Factor Test

IS 456 of 2000 advises that in the “extremely low” category of workability where rigorous control is required, such as pavement quality concrete, measuring workability by determining compacting factor will be more appropriate than slump, with a compacting factor of 0.75 to 0.80 recommended.

Compaction factor apparatus

The compacting factor test is primarily intended for laboratory usage, although it can also be applied in the field.

It is more precise and sensitive than the slump test, and it is especially beneficial for very low workability concrete mixtures, which are commonly employed when concrete is compacted by vibration.


This test is based on the principle of determining the degree of compaction accomplished by allowing concrete to fall through a standard height with a standard amount of work. The density ratio, or the ratio of the density actually attained in the test to the density of the same concrete fully compacted, is used to determine the degree of compaction, also known as the compacting factor.

Compacting Factor Test Procedure

  1. The concrete sample to be analysed is filled to the brim in the upper hopper.
  2. The concrete falls into the bottom hopper after the trap-door is opened.
  3. The bottom hopper’s trap door is then opened, allowing the concrete to fall into the cylinder.
  4. If the concrete is dry-mix, it is unlikely that it will fall when the trapdoor is opened.
  5. In this scenario, a little poke with a rod may be necessary to get the concrete moving.
  6. The extra concrete that remains over the cylinder’s top level is subsequently chopped away with plane blades included with the apparatus.
  7. The cylinder’s exterior has been scrubbed clean. The concrete is precisely filled to the cylinder’s top level. It’s weighted to the tenth of a gramme. “Weight of partially compacted concrete” is the name given to this weight.
  8. The cylinder is then emptied and refilled with concrete from the same sample in 5 cm thick layers.
  9. To achieve thorough compaction, the strata are severely rammed or, preferably, vibrated.
  10. The fully compacted concrete’s top surface is then carefully struck off level with the cylinder’s top and weighed to the closest 10 grams. “Weight of thoroughly compacted concrete” is the name given to this weight.
Shubhajna Rai
Shubhajna Rai

A Civil Engineering Graduate interested to share valuable information with the aspirants.

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