Compaction factor test | Workability test for concrete | Fresh concrete test

Compaction Factor Test

In this article, we will guide you to determine the workability of a fresh concrete mix by compaction factor test.

Theory and Scope of the test

Compression factor testing is used to determine the workability of concrete where the total nominal size does not exceed 40 mm. In terms of this definition, workability is the property of concrete that determines the amount of work required to create the full contraction. The test involves applying a standard amount of work to a standard amount of concrete and measuring the resulting shrinkage. According to IS:1199-1959, abrasive factor testing is carried out to determine the workability of freshly prepared concrete.

Apparatus

·       Compaction factor apparatus

·       Trowels

·       Graduated cylinder of 1000 ml capacity

·       Balance to weigh up to 30 kg (nearest to about 10g)

·       Tamping rod and Iron buckets.

 

Description of Apparatus

The compaction factor test apparatus consists of two conical hoppers, A and B, mounted vertically above a cylindrical mould C. The upper hopper A has internal dimensions as top diameter 250 mm, bottom diameter 125 mm and height 225 mm. The lower hopper B has internal dimensions as top diameter 225 mm, bottom diameter 125 mm and height 225 mm.

The cylinder has internal dimensions of 150 mm diameter and 300 mm height. The distances between the bottom of the upper hopper and top of the lower hopper, and the bottom of the lower hopper and top of the cylinder are 200 mm in each case. The lower ends of the hoppers are fitted with quick-release flap doors. The hoppers and cylinder are rigid in construction and rigidly mounted on a frame. These hoppers and cylinders are easily detachable from the frame.

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Procedure

Step 1: Place the compaction factor tool on level ground and moisten the inner surface of the hoppers and cylinder.

 

Step 2: Fasten the flap doors.

 

Step 3: Weigh the empty cylinder accurately and specify the weight as W1 kg.

 

Step 4: Adjust the cylinder at the base with the fly nuts and bolts so that the centre points of the hoppers and cylinder are in a vertical line. Cover the cylinder with a plate.

 

Step 5: Fill the freshly mixed concrete sample into the top hopper gently and carefully with a hand scoop without compacting.

 

Step 6: After two minutes, leave the trap door open so that the concrete falls into the bottom hopper and brings the concrete to constant compaction.

 

Step 7: As soon as the concrete has been set, open the lower hopper's trap door and allow it to fall into the concrete cylinder, bringing the concrete to constant compaction.

 

Step 8:nRemove excess concrete on the top of the cylinder with a pair of trowels in each hand, moving the blades horizontally from the opposite edges of the axis to the centre with a sawing motion.

 

Step 9: Clean the cylinder from all sides properly. Find the mass of partially compacted concrete thus filled in the cylinder, say W₂ kg.

 

Step 10: Refill the cylinder with the same sample of concrete in approximately 50 mm layers, vibrating each layer so as to expel all the air and to obtain full compaction of concrete.

 

Step 11: Strike off excess to level the concrete and weigh the cylinder filled with fully compacted concrete. Let the mass be W₃ kg.

 

Compaction factor test

Observations and Calculations

 

The compaction factor for the fresh concrete sample is ________

 

Mass of empty cylinder, W1 kg
Mass with partially compacted concrete, W2 kg
Mass with fully compacted concrete, W3 kg
Compaction factor,	CF	W2-W1
		W3-W1

 

Precautions to be done in Compaction Factor Test

1. The test should be carried out on a level and firm ground.

2. The top hopper should be filled slowly and evenly each time and the time between the end of the mix and the release of concrete from the top hopper should be constant, about two minutes comfortable.

3. The outside of mould must be wiped clean before weighing and mass should be recorded to the nearest 10g.

4. The mix should not be pressed or compacted in the upper hopper.

5. If the concrete in the hopper does not fall down when the flap is released, it should be released vertically through its centre, excluding a metal rod similar to the one used in the collapse test. A constant penetration will usually affect the output.

6. At the end of the test the hoppers and cylinder must be washed clean and wiped dry.

 

Discussion

The compression factor test, which is popular in laboratory conditions, is more sensitive and gives more consistent results than the collapse test, especially for medium and low-performance concrete compounds, i.e. the compression factor of 0.9 to 0.8 is commonly used when the concrete is present. Should be compressed by vibration. Such concrete mixtures with low workability may not continue to collapse. The test is not suitable for very low-performance concrete with a series shrinkage factor of 0.70 or less, as this concrete cannot be fully compressed as compared to the method described in the test.

The compaction factor test is a dynamic test, so it is more suitable than standard tests for high thixotropic concrete mixes. It provides more information (hence about conciseness) than the collapse test. The test will indicate small variations in the wide range of workloads.

However, the amount of work applied to the concrete being tested is a function of the friction between the concrete and the hopper, which does not reflect field conditions. When the maximum volume of the aggregate is large compared to the average particle size, the droplet in the container below will form a fraction and give an incredible comparison with other compounds of smaller maximum aggregate size.

The method of inserting concrete into the mould has nothing to do with the general methods of placing and compacting high-quality concrete. For example, the main compression method used in the field is vibration.

The large and bulky nature of the device and the need for balance to measure the concrete mass in the cylinder reduce its usefulness in the field.

The relationship between the shrinkage factor and the depreciation values ​​is given in the article, whereas the approximate relationship between the workload size and the shrinkage factor is given in the table below. The recommended values ​​of the compression factor for use in different types of concrete work are listed in the table

Relationship between degree of workability and C.F., and recommended values for use for various types of concrete works

 

Degree of workability	Slump mm	Compaction factor	Use for which concrete is suitable
Very low	0 to 25	0.78	Roads vibrated by power-operated machines
Low	25 to 50	0.85	Roads vibrated by hand-operated machines,
Medium	50 to 100	0.92	Less workable, flat slabs, manually compacted reinforced concrete
High	100 to 180	0.95	For sections with congested reinforcement. Not suitable for vibrations

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FAQs: Compaction Factor Test

What is the compaction factor test?

A compaction factor test is performed to measure the workability level of new concrete, depending on the internal strength required to fully compact the concrete. The compression factor is defined as the ratio of the compacted concrete mass to the compact factor machine and the fully compacted concrete mass.

 

Why compaction factor test is done?

Compaction factor testing is performed to measure the workability level of new concrete, depending on the internal strength required to fully compact the concrete. Compacting factor testing is used to detect the low workability of concrete.

Is Compaction Factor Test better than Slump Test for Workability of Concrete?

Typically, a slump test is used to detect work efficiency on the field, but it is not effective when the slope value is less than 50 mm. Used in mass concrete of low workability concrete foundations and light reinforced structures. Compression factor testing is most appropriate in such a situation. Furthermore, the compression test gives more accurate results compared to the slope test.

NATIONAL STANDARDS

1. IS 1199-1959 (reaffirmed 2008): Methods of Sampling and Analysis of Concrete

2. IS 6461 (Part 10) -1973 (reaffirmed 2011): Glossary of Terms Relating to Cement Concrete; Part 10: Tests and Testing Apparatus

REFERENCES

1. BS EN 12350-2:2000, Testing of Fresh Concrete: Slump Test

2. BS EN 12350-3:2000, Testing of Fresh Concrete: Vee-Bee Test

3. BS EN 12350-4:2000, Testing of Fresh Concrete: Degree of Compactability

4. BS EN 12350-5:2000, Testing of Fresh Concrete: Flow Table Test

5. Gambhir, M. L., Concrete Technology, 4th edition, McGraw-Hill Education (India), 2009

 6. Gambhir, M. L. and Neha Jamwal, Building Materials: Products, Properties and Systems, McGraw-Hill Education (India), 2011.