COMPACTION FACTOR TEST- ALL YOU NEED TO KNOW
Compaction factor test is the workability test for concrete conducted in laboratory. The compaction factor is the ratio of weights of partially compacted to fully compacted concrete. It was developed by Road Research Laboratory in United Kingdom and is used to determine the workability of concrete. The compaction factor test is used for concrete which have low workability for which slump test is not suitable.
The compaction factor test is carried out to measure the degree of workability of fresh concrete with regard to the internal energy required for compacting concrete thoroughly.
The compacting factor test is used to find out the low workability of concrete. it is a fact that the slump cone test of concrete is not given accurate results for the low workability of concrete when the slump is <50mm.
Compaction factor test Apparatus:-
Compaction factor test apparatus consists of two conical hoppers and a bottom cylinder which is arranged properly
Steel rod of 1.6cm, diameter with a length of 61cm is is used to level the concrete.
A weight balance is used to weight the concrete.
Hand scoop (15.2 cm long) and a balance.
PROCEDURE:
1.Prepare M15 grade concrete.the mixture with 1: 2: 4 by mixing the required amount of water according to the water cement ratio and mix the fresh concrete.
2.See that the inner surface of the conical hopper should be free of moisture and apply grease to it. Close the trap door of the upper/top hopper.
3.Then measure the weight of the empty bottom cylinder as W1.
4.Fill fresh concrete into the upper/top conical hopper without disturbing the sample.
5.After this, the trap door of an upper hopper is opened. Thus the concrete falls on the lower/bottom hopper.
6.Wait for 2-3 seconds and check if the entire concrete has fallen from the top hopper to the bottom hopper. If not, a slight tamping is done until the entire concrete falls into the bottom hopper.
7.Now open the bottom hopper trap door, and the entire concrete has fallen on the cylinder. Using the trowel, remove excess concrete on the top surface of the cylinder.
8.Weigh the cylinder with partially filled concrete as W2.
9.Then the cylinder is emptied, and the concrete sample is filled again in 3 layers, each layer being given 25 blows using a steel rod. Now, the concrete inside the cylinder is completely compacted.
10.Measure the weight of the cylinder completely with concrete as W3 .
ADVANTAGES:
- Compression factor test gives more information than slump test
- The test is a dynamic test and is thus more suitable for concrete mixture static tests.
DISADVANTAGES:
- The large and heavy nature of the device reduces its usefulness in the field. In addition, the test method requires an equilibrium to measure the mass of concrete in the cylinder.
- The amount of work applied to the concrete being tested is a function of friction between the concrete and the hopper, which probably does not reflect additional conditions.
- The test method does not use vibration, the main compaction method used in the field.
- This test is commercially available and is often used.
Relation Between Slump Test Result and Compaction Factor Test Result
| Workability | Slump in mm | Compaction Factor |
| Very Stiff | – | 0.70 |
| Stiff | 0 to 25 | 0.75 |
| Stiff Plastic | 25 to 50 | 0.85 |
| Plastic | 75 to 100 | 0.90 |
| Flowing | 150 to 175 | 0.95 |
Compaction factor formula
Compaction factor = (W1-W) /(W2-W)
Limitations of the compaction factor test
- The test shows sensitivities to the workability which means, the compaction factor value decrease as workability increases.
- The dry mixes can adhere to the hoppers and thus poking with a rod is necessary to remove them.
- The compaction factor doesn’t show any relationship between the richness of the mix. But in a practical approach, a leaner mix needs more external work than a richer one.
- Mixes with the same value of compaction factor might need different amounts of external work. So, the work needed to be done doesn’t only depend on the compaction factor.