slump-cone-test

Slump Cone Test: Why it is done?

There are many tests that are performed on concrete, one such test is slump cone test. Now, you may wonder What is concrete slump cone test is and Why it is done?

So, slump test is performed to check the workability of concrete. Let me explain What is workability of concrete?

What is workability of concrete?

Workability of concrete is a technical term which describes how easily the fresh concrete can be mixed, placed and compacted without loosing its homogeneity. This property directly impact the strength, quality and time in construction work.

Workability of concrete mainly depends on the quality of water, grade of aggregate and percentage of fine materials in the mixture. Following tests are used to check workability of concrete.

  1. Slump cone test
  2. Compaction factor test
  3. Flow test
  4. Kelly ball test
  5. Vee Bee Consistometer test
  6. K-Slump test

From the above test Slump cone test is widely performed because it is easy to do and gives accurate results. Also, it can be carried on site.

1. Slump cone test-

The test execution is easy and is not suitable for very wet and very dry type of concrete. This test helps to control the water cement ratio (i.e. w/c ratio), over usage of cement, aggregate and water as well. Apparatus requirement to perform the test are frustum cone, tamping rod, metal sheet, measuring tape, pouring mould and trowel.

slump-cone-test-apparatus-image

a. Frustum cone-

The frustum cone is made of metal which has two different diameters, one at top and other at bottom. The dimensions of the frustum cone is mentioned below.

SR.No-DescriptionDimensions
1.Bottom Diameter of Metallic Mould20 cm
2.Top Diameter of Metallic Mould10 cm
3.Height of Frustum cone30 cm
4.Thickness of sheet1.60 mm

b. Tamping Rod-

This rod have a diameter of 16mm and bullet end at other end. The height of tamping rod is 0.6m long

Slump Test Procedure-

Let us now go through the slump cone test procedure.

  • Before performing the test make sure the inner surface of the cone is clean. It must be free from moisture and any old dried concrete.
  • Place the frustum cone on smooth and flat metallic steel plate surface.
  • Now, using the pouring mould start filling the concrete into the cone. The concrete must be in four layer, each of height 1/4th of the cone.
  • After each layer tamp the concrete using tamping rod. Tamp the layer evenly for 25 times each.
  • After completely filling the cone level the cross-section using the trowel.
  • Remove the cone filled with concrete immediately in vertical direction slowly and carefully.
  • The concrete will subside(i.e. sink down). This subsidence or sinked concrete is slump.
concrete-pouring-image
frustum-cone-removal

Result-

  • Now, using the measuring tape measure the height of the cone and highest point of the slump in mm.
  • The difference between the top of the cone and highest point of the subside gives the slump value.

Slump test values for Different Concrete Mixes-

Concrete Mixes Slump range in mm
Columns, Retaining walls 75-150 mm
Beams & Slabs 50-100 mm
CC Pavements 20-30 mm
Decks of bridge 30-75 mm
Vibrated Concrete 12-25 mm
Huge Mass constructions 25-50 mm

Different Types Of Slump in Concrete-

The different types of slump in concrete are-

True Slump-

After removal of concrete filled frustum cone, if the concrete slump is even and has a shape of the cone then it is true slump.

true-slump-image

Shear Slump-

After removing, if the slump slides down more than the half the height of the concrete filled frustum cone then it is shear slump. This indicates that the concrete is non-cohesive(i.e it is loose in nature) and have characteristics of segregation.

shear-slump=image

Collapse slump-

If the slump slides down completely in all directions and does not have shape of the cone then it is collapse slump. Collapse slump formation takes place if the water percentage is more in the concrete.

collapse-slump=image

Advantages-

  • Slump cone test is performed easily on site and in laboratory.
  • It requires less number of apparatus with respect to other tests.
  • It requires less time to take out the results.

Disadvantages-

  • The slump cone test can be carried if the aggregate used in concrete mix is above 40 mm.
  • In very wet and very dry type of concrete the test results fails.

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