Job # 10:
To perform the compacting factor test:
Significance:
- This test also gives the workability of concrete indirectly.
- This test is appropriate for concrete with the maximum aggregate size of 40mm.
Apparatus:
- Two hoppers each in the shape of frustum of a cone and one cylinder.
- The hoppers have hinge door at bottom and all the surfaces are polished to reduce friction.
- Cylinder of 150*200 mm
- Concrete sample
Figure showing compacting factor testing apparatus
Related theory:
Compacting factor
The degree of compaction is also called the compacting factor and is measured with the help of density ratio that is the ratio of density actually achieved in the test to the density of same concrete when it is fully compacted.
Its maximum answer is 1 but practically it is lesser than 1.
Workability of concrete
ACI, 1990 “That property of freshly mixed concrete or mortar which determines the ease and homogeneity with which it can be mixed, placed, consolidated and finished”
ASTM, 1993 “That property determining the effort required to manipulate a freshly mixed quantity of concrete with minimum loss of homogeneity”
Methods of measurement of workability:
- Slump test
- Slump flow test
- Compacting factor test
- Degree of compactability test
- VB test
- Flow table test
Relation between workability and compacting factor
Note: More is the compacting factor more will be the workability.
Procedure:
- First the concrete is placed gently at the upper hopper so that no work is done on concrete to produce compaction.
- The bottom door of the upper hopper is then released and the concrete falls into the lower hopper.
- The bottom door of the lower hopper is then released and the concrete falls into the cylinder.
- Excess concrete is then removed from the cylinder.
- The density of this partially compacted concrete is now calculated.
- Parallel to this make fully compacted concrete cylinder
- Give 25 no. of blows to each layer and make 3 layers.
- Find the density of this fully compacted concrete.
- The compacting factor will be calculated from the formula given below
- More is the compacting factor more will be the workability.
Observations and Calculations
Comments:
- As our CF value is 0.94, hence the workability is high.