Theory:
This test is adopted to determine workability of concrete where nominal size of 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 standard quantity of concrete and measuring the resulting compaction. The compaction 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. The relationship between degree of workability and compaction factor are:
size of coarse aggregate the workability will decrease. However, compaction factor test has certain limitations. When maximum size of aggregate is large as compare with mean particle size; the drop into bottom container will produce segregation and give unreliable comparison with other mixes of smaller maximum aggregate sizes. Moreover, the method of introducing concrete into mould bears no relationship to any of the more common methods of placing and compacting high concrete.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 as: 150 mm diameter and 300 mm height. The distances between bottom of upper hopper and top of lower hopper, and bottom of lower hopper and top of cylinder are 200 mm in each case. The lower ends of the hoppers are fitted with quick release flap doors. The hoppers and cylinders are rigid in construction and rigidly mounted on a frame. These hoppers and cylinder are rigid easily detachable from the frame. Figure below
shows the diagram of a compaction factor test apparatus.
Objective:
To measure the workability of concrete by compaction factor test.
Reference:
IS: 1199-1959, SP: 23-1982.
Apparatus:
Compaction Factor Apparatus, tamping rod, metallic sheet, weighing machine and scale.
Material:
Cement, sand, coarse aggregate and water
Procedure:
1. Prepare a concrete mix for testing workability. Consider a W/C ratio of 0.5 to
0.6 and design mix of proportion about 1:2:4 (it is presumed that a mix is
designed already for the test). Weigh the quantity of cement, sand, aggregate
and water correctly. Mix thoroughly. Use this freshly prepared concrete for the
test.
2. Place the concrete into the upper hopper up to its brim.
3. Open the trapdoor of the upper hopper. The concrete will fall into the lower
hopper.
4. Open the trapdoor of the lower hopper, so that concrete falls into the cylinder
below.
5. Remove the excess concrete above the level of the top of the cylinder; clean the
outside of the cylinder.
6. Weigh the concrete in the cylinder. This weight of concrete is the "weight of
partially compacted concrete", (W1).
7. Empty the cylinder and refill with concrete in layers, compacting each layer
well (or the same may be vibrated for full compaction). Top surface may be
struck off level.
8. Find cut weight of the concrete in the fully compacted state. This weight is the
“Weight of fully compacted concrete" (W2).
Observations:
• Weight of partially compacted concrete (W1) : _________ Kg
• Weight of fully compacted concrete (W2) : _________ Kg
• Compaction factor (F) = 𝑊𝑊1/𝑊𝑊2: _________.
Result:
The compaction factor of concrete is: ________.
Conclusions:
The compaction factor value indicates that the concrete has Low/ Medium/ High Degree of workability.
Precautions:
(Discuss about the precautions to be taken while conducting this experiment)
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Questions:
1. What is the difference between fully compacted and partially compacted concrete?
2. What is the significance of compacted concrete?
3. Define density of concrete & how it affects the strength of concrete?
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