Workability of concrete

 

OBJECT-

 

To determine the slump value and to know more about the workability of fresh concrete by slump cone.

APPARATUS-

 Iron Pan to mix the concrete, weighing machine, trowel, slump cone, tamping rod, cement, sand, aggregate, water etc.

THEORY-

         Workability of concrete generally implies the ease with which mix can be handled from the mixer to its finally compacted shape. the measurements of the workability Of fresh concrete is of importance in assisting the practicability of compacting the mix and also n maintaining consistency throughout the job. In addition, workability testes are often used as an indirect check on the water content and therefore on the water/cement ratio of concrete. Workability should be distinguished from consistency which term as used in concrete practice, relates to the degree of wetness of concrete. On the other hand, consistency has to do with the force flow relationship alone. A job starts with the mix just right cement and aggregate are measured, the right amount of water is add, and mixing is then carried out for the given time. A batch of concrete wetter than the rest will mean the batch of concrete that is weaker and less durable in the finished job. A job batch that is too dry will lead to difficulties in placing, compacting and finishing.

The slump test is used vary often in concrete work. It is easily performed at a job site and is useful in detecting variations in mixes of given properties.

PROCEDURE-

 

1.         Four mixes are to be prepared with water-cement ratio of 0.50, 0.60, 0.70, and 0.80 respectively and for each ratio mix the dry constituent thoroughly to get a uniform color and then add water

2.          Dampen inside of cone and place it on a smooth, moist, non-absorbent, level surface large enough to accommodate both the slumped concrete and the slump cone. Stand or, foot pieces throughout the test procedure to hold the cone firmly in place

3.              Fill cone 1/3 full by volume and tamp 25 times with the help of tamping rod. Distribute Roding evenly over the entire cross section of the sample.

4.          Fill cone 2/3 full by volume. Rod this layer 25 times with rod penetrating into, but not through first layer. Distribute Roding evenly over the entire cross section of the layer.

6.            Fill cone to overflowing. Rod this layer 25 times with rod penetrating into but not through second layer. Distribute Roding evenly over the entire cross section of this layer

7.           Remove the excess concrete from the top of the cone using tamping rod and clean overflow from the base of the cone.

8.          Immediately lift cone vertically with slow, even motion. Do not jar the concrete or tilt

the cone during this  process. Invert  the withdrawn cone,  and place next  to,  but  not touching the slumped concrete (Perform in 5-10 seconds with no lateral or torsional motion)

9.         
Lay a straight edge across the top of the slump cone. Measure the amount of slump in inches from the bottom of the straight edge to the top of the slumped concrete at a point over the original center of the base. The slump operation shall be completed in a maximum elapsed time of 2 and the 1/2 minutes. Discard concrete. DO NOT use in any other tests.

OBSERVATION TABLE-

Water-Cement Ratio	Slump
0.50	-
0.60	-
0.70	-
0.80	-

PRECAUTIONS-

 

1.           The Strokes are to be applied uniformly throughout the entire area of the concrete section.

2.          The cone should be removed very slowly by lifting it upwards without disturbing the concrete. The unsupported concrete should be allowed to spread and settle and after settlement the height should be measured.

3.         The experiment should be completed within 3 min.

 

4.           It should be ensured that the interior of the mould be quite clean and damp but not wet.

5.          The base plate should be smooth and clean so that the contact is made with bottom

of the mould around its whole circumference.

 

6.         During filling the mould must be firmly pressed against its base.

     7.          On completion of tamping any surplus concrete is carefully removed with a trowel so that the mould is exactly filled.

8.          Vibrations from nearby machinery might also increase subsidence hence test should be made beyond the range of ground vibrations.

 

CONCLUSIONS-

 This test is very easy to use in project to calculate the slump, but it is not a true determination of workability.

This test learnt us about mixing the concrete, and the amount used especially in big project.

 

VIVA QUESTION –

 1.                What is concrete and type of concrete?

2.                What are different test on concrete?

3.                Define the number of grading and purpose of that grading?

4.                What is workability, segregation, bleeding and heat of hydration?

5.                Define the test procedure?

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