Compacting Factor
Although primarily intended for laboratory use, the compacting factor test is also applicable in field conditions. This test is known for its higher level of precision and sensitivity when compared to the slump test. It is particularly useful for concrete mixes that have very low workability and require compaction through vibration. The test can be used for plain and air-entrained concrete that uses lightweight, normal weight, or heavy aggregates with a nominal maximum size of 38mm or less. However, it is not suitable for aerated concrete or no-fines concrete.
General Procedure
Gently place the sample of concrete to be tested in the upper hopper using the hand scoop.
Fill the hopper level with its brim and open the trap-door so that the concrete falls into the lower hopper.
If certain mixes have a tendency to stick in one or both of the hoppers, push the rod gently into the concrete from the top while covering the cylinder with trowels.
Immediately after the concrete has come to rest, uncover the cylinder, open the trap-door of the lower hopper, and allow the concrete to fall into the cylinder.
Cut off the excess concrete remaining above the level of the top of the cylinder by holding a trowel in each hand, with the plane of the blades horizontal, and moving them simultaneously one from each side across the top of the cylinder, while keeping them pressed on the top edge of the cylinder.
Wipe the outside of the cylinder clean. Ensure that this operation is carried out in a place free from vibration or shock.
Determine the weight of the concrete in the cylinder to the nearest 10 g.
Cut off the excess concrete remaining above the level of the top of the cylinder again, using the same process as in step 5. Wipe the outside of the cylinder clean.
Record the weight of the partially compacted concrete.
Refill the cylinder with concrete from the same sample in layers approximately 5 cm deep. Heavily ram or preferably vibrate the layers to obtain full compaction.
Carefully strike off the top surface of the fully compacted concrete level with the top of the cylinder.
Wipe the outside of the cylinder clean.
Observation
To determine the compacting factor of the concrete sample, the weight of partially compacted concrete and the weight of fully compacted concrete shall be measured as per the procedure mentioned earlier. The compacting factor shall then be calculated as the ratio of the weight of partially compacted concrete to the weight of fully compacted concrete. The value obtained shall be rounded off to the nearest second decimal place.
Result
he vertical difference between the top of the mold and the displaced original center of the top surface of the specimen is a measure of the settlement or subsidence of the concrete during compaction. It indicates how much the concrete has settled after it has been placed in the mold and subjected to compaction. This measurement is important in assessing the workability and consistency of the concrete. It is usually measured in millimeters.
Workability
Very low: 0.78 (Slump 0-25mm)
Low: 0.85 (Slump 25-50mm)
Medium: 0.92 (Slump 50-100mm)
High: 0.95 (Slump 100-175mm)