Object: to determine workability of concrete by compaction factor test
Apparatus:
- Compaction factor apparatus consists of trowels,
- hand scoop (15.2 cm long),
- a rod of steel or other suitable material (1.6 cm diameter, 61 cm long rounded at one end ) an a balance.
Introduction:
Compaction factor test is the workability test for concrete conducted in laboratory. It was developed by Road Research Laboratory in United Kingdom and is used to determine the workability of concrete. The compaction factor is the ratio of weights of partially compacted to fully compacted concreteThe compaction factor test is used for concrete which have low workability for which slump test is not suitable.The compacting factor test is designed primarily for use in the laboratory but it can also be used in the field. It is more precise and sensitive than the slump test and is particularly useful for concrete mixes of very low workability and normally used when concrete is to be compacted by vibration. The method applies to plain and air-entrained concrete, made with lightweight, normal weight or heavy aggregates having a nominal maximum size of 38 mm or less but not to aerated concrete or no-fines concrete.
Dimension of apparatus Balance
Procedure :
- The sample of concrete to be tested shall be placed gently in the upper hopper, using the hand scoop. The hopper shall be filled level with its brim and the trap-door shall be opened so that the concrete falls into the lower hopper.
- Certain mixes have a tendency to stick in one or both of the hoppers. If this occurs, the concrete may be helped through by pushing the rod gently into the concrete from the top. During this process, the cylinder shall be covered by the trowels.
- Immediately after the concrete has come to rest, the cylinder shall be uncovered, the trap-door of the lower hopper opened, and the concrete allowed to fall into the cylinder. The excess of concrete remaining above the level of the top of the cylinder shall then be cut off 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, at the same time keeping them pressed on the top edge of the cylinder.
- The outside of the cylinder shall then be wiped clean. The above operation shall be carried out at a place free from vibration or shock. The weight of the concrete in the cylinder shall then be determined to the nearest 10 g.This weight is known as the weight of partially compacted concrete (W1).
- Empty the cylinder and then refill it with the same concrete mix in layers approximately 5 cm deep, each layer being heavily rammed to obtain full compaction.
- Level the top surface.
- Weigh the cylinder with fully compacted. This weight is known as the weight of fully compacted concrete (W2).
- Find the weight of empty cylinder (W).
Note:
The test is sufficiently sensitive to enable difference in workability arising from the initial process in the hydration of cement to be measured.
Each test, therefore should be carried out at a constant time interval after the mixing is completed, if strictly comparable results are to be obtained. Convenient time for releasing the concrete from the upper hopper has been found to be two minutes after the completion of mixing.
Calculation of Compaction Factor Value:
The compaction factor is defined as the ratio of the weight of partially compacted concrete to the weight of fully compacted concrete. It shall normally to be stated to the nearest second decimal place.
Compaction Factor Value= (W1-W) / (W2-W)
Result of Compaction Factor :
Compaction factor of the concrete Sample 1 = _________
Compaction factor of the concrete Sample 2 = _________
Compaction factor of the concrete Sample 3 = _________
Avg = _________
The Compaction factor values ranges from 0.7 to 0.95
