Compacting Factor Test to Determine it’s Workability

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Introduction

The compacting factor test is conducted to determine the workability of fresh concrete. Although the most common method of determining workability is the slump test, it does not give an accurate result for the concrete with less workability, especially then the workability is less than 50 mm. But for much less workable concrete, the compacting factor test provides a more reliable result.

Objective

To determine the workability of a concrete mix of given proportion by compaction factor test.

Theory

Compacting factor test is adopted to determine the workability of concrete where the nominal size of the aggregate does not exceed 40 mm. It is based on the definition, that workability is that property of concrete, which determines the amount of work required to produce full compaction. The test consists essentially of applying a standard amount of work to a standard quantity of concrete and measuring the resulting compaction.

The compacting factor is defined as the ratio of the weight of partially compacted concrete to the weight of fully compacted concrete. It shall be stated to the nearest second decimal place.

Reference

IS 1199: 1959 Methods of Sampling and Analysis of Concrete (Eleventh revision). Reaffirmed- Dec 2013.

Apparatus

We need the following apparatus to conduct the compacting factor test

Compaction Factor test Apparatus
Schematic of Compaction Factor test apparatus
  • Compaction Factor Apparatus: conical hoppers mounted vertically above the cylindrical mould. The upper mould has internal dimensions as top dia 25 cm bottom dia 12.5 cm and height 22.5 cm. The lower hopper has internal dimensions, top 22.5cm bottom dia 12.5 cm and height 22.5 cm. The cylinder has internal dimensions as 15 cm dia and 30cm height. The dimensions between the bottom of the upper hopper and top of the lower hopper, bottom of the lower hopper and top of the cylinder are 20 cm, each case. The lower ends of the hoppers are filled with quick-release trap doors.
  • Tray
  • trowel
  • weighing machine

Procedure

Conduct test for W/C ratio 0.5, 0.6, 0.7, and 0.8, for each mix take 10 kg of coarse aggregate, 5 kg of fine aggregate and 2.5 Kg of cement are taken.

  1. First of all, Grease the inner surface of the hoppers and the cylinder.
  2. Fasten the hopper doors.
  3. Then, Weight the empty cylinder accurately (W1 Kg).
  4. Fix the cylinder on the base with fly nuts and bolts
  5. Then, Mix coarse and fine aggregates and cement dry until the mixture is uniform in colour and then with water until concrete appears to be homogeneous.
  6. Fill the freshly mixed concrete in upper hopper gently with trowel without compacting.
  7. Now, Release the trap door of the upper hopper and allow the concrete of fall into the lower hopper bringing the concrete into standard compaction.
  8. Immediately after the concrete comes to rest, open the trap door of the lower hopper and allow the concrete to fall into the cylinder, bringing the concrete into standard compaction.
  9. Remove the excess concrete above the top of the cylinder by a trowel.
  10. Then, Find the weight of cylinder i.e cylinder filled with partially compacted concrete (W2 kg)
  11. Now, Refill the cylinder with the same sample of concrete in approx. 4 layers, tamping each layer with tamping for 25 times in order to obtain full compaction of concrete.
  12. Finally, Level the mix and weigh the cylinder filled with fully compacted concrete (W3 Kg)
  13. Repeat the procedure for different a trowel.

Observations and Calculations

Sl No.DescriptionSample 1Sample 2Sample 3
1Weight of Empty Cylinder (W1)
2Weight of Empty Cylinder + Free Fall Concrete(W2)
3Weight of Empty Cylinder + Hand Compacted Concrete (W3)
4Weight of Partially Compacted Concrete (WP = W2 – W1)
5Weight of Fully Compacted Concrete (WF = W3 – W1)

Compaction Factor Value = WP/WF = (W2-W1) / (W3-W1)

Result

  1. Compaction Factor of Concrete is found out to be = ………….
  2. The vertical difference between the top of the mould and the displaced original centre of the top surface of the specimen ………… mm

Precautions

  1. The top hopper must be filled gently.
  2. The mix should not be pressed or compacted in the hopper.
  3. If the concrete in the hopper does not fall through when the trap door is released, it should be freed bypassing a metal rod. A single steady penetration will usually affect the release.

Comments

Compacting Factor Test is more sensitive and precise than slump test, and is particularly useful to concrete mixes of low workability

Suggested Values of Compacting Factor

Suggested ranges of values of compaction factors for different placing conditions. These are shown in the table below-

SL NoPlacing ConditionDegree of WorkabilityCompacting Factor
1Concreting shallow section with vibration Very low0.75 to 0.80
2Concreting of lightly reinforced section with vibration Low0.8 to 0.85
3Concreting of lightly reinforced section without vibration or heavily reinforced with vibration Medium0.85 to 0.92
4Concreting of heavily reinforced section without vibration High> 0.92

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