Compaction factor test- Objective, Procedure, advantages, disadvantages

What is Compaction factor test?

The compaction factor test for concrete was developed in the UK by Glanville in 1947 and the degree of compaction is measured by it. This test gives the seasonably a reliable assessment of the workability of concrete.

This test requires measurement of the wt. of partially and fully compacted concrete sample. The ratio of partially compacted weight to the fully compacted weight is known as the compaction factor, which is always less than one.

For normal concrete, compaction factor ranges from 0.8 to 0.92.

Why compaction factor test is done?

Simply it is done to calculate the work-ability of concrete. It means that It checks weather the quantity of water that should be maintain for the required strength of structure.

The compaction factor test is designed for use in the laboratory but it is also used in the field. This test is more sensitive and precise than the slump test. It is particularly useful for concrete mixes of very low workability and generally used when concrete is compacted by vibration.

This method is applied to air-entrained and plain concrete, made with normal weight, lightweight or heavy aggregates having a nominal maximum size of 38 mm or less but not to aerated concrete or no-fines concrete.

Apparatus Required

1. Compaction factor machine
2. Weighing machine and compacting rod
3. Steel trowel or mechanical vibrator

Procedure

• Place the concrete in the upper hopper.

• Then, the hopper door is opened. The sample of concrete drops to lower hopper filling it to overflowing.
• Now, open the lower hopper of the trap door and fill the sample of concrete up to overflowing.

• The extra concrete sample is removed from the top of the cylinder with the help of a trowel.
• The outer surface of the cylinder is wiped and cleaned.
• The cylinder is weighed and recorded as the weight of partially compacted concrete.
• The cylinder is again filled with concrete in layers of thickness, not more than 50 mm. Each layer of concrete is fully compacted with the help of a tamping rod.
• The cylinder is again weighted after cleaning the outer surface of the cylinder and this weight is recorded as the wt. of fully compacted concrete.

The compacting factor is calculated from the formula which is given below;

Compaction factor test values- Observation

The compaction factor is the ratio of wt. of partially compacted concrete to the wt. of fully compacted concrete.

S. No.	Description	Sample 1	Sample 2	Sample 3
1	Weight of empty cylinder (W1)
2	Weight of empty cylinder + free fall concrete (W2)
3	Weight of empty cylinder + Hand compacte4d concrete (W3)
4	Wt. of partially compacted concrete (Wp = W2 – W1)
5	Weight of fully compacted ( WF = W3 – W1)
6	Compaction factor = Wp / WF

Precautions:-

• Use hand gloves and shoes during the test.
• Equipment should be cleaned before and after testing.
• Petroleum jelly is applied to the mold.
• At the time of the test, wear the apron.

Advantages of compaction factor test

The advantage of compaction factor test is as follows;

1. Suitable for testing workability in the laboratory.
2. This test is suitable for concrete of low workability.
3. The compaction factor test gives more information about compatibility as compared to the slump test.
4. This test is more precise than static tests for highly thixotropic concrete mixtures and is a dynamic test.
5. It gives sensitive results.

Disadvantages

The disadvantage of compaction factor test is as follows;

1. Due to the large and bulky nature of the device, its use reduces in the field.
2. This method requires a balance to measure the mass of the concrete in the cylinder.
3. In this method, there is no use of vibration and it is used rarely.
4. Although the test is commercially available and but used rarely.

I hope this article remains helpful for you.

Happy Learning – Civil Concept

Contributed by,

Civil Engineer – Pradip Thakur

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