#1.2 Concrete Technology – Tests

Part 2

In previous article, we learnt a few basic things about concrete. composition, ingredients, properties etc. Now in this article we will learn about tests performed on concrete.

Tests performed on Concrete

Workability tests – Slump cone test, compaction factor test, Vee-bee consistometer test, flow table test, etc

Strength tests- compressive strength, flexural strength, etc

Slump Cone Test

It is an empirical test to measure workability of concrete.

The test measures consistency of concrete of a specific freshly mixed batch. Consistency is the ease with which concrete flows. It is used to indicate degree of wetness. Consistency affects workability of concrete. That is, wetter mixes are more workable than drier mixes, but concrete of the same consistency may vary in workability. The test is also used to determine consistency between individual batches.

The test is popular due to the simplicity of apparatus used and simple procedure. Unfortunately, the simplicity of the test often allows a wide variability in the manner in which the test is performed. The slump test is used to ensure uniformity for different batches of concrete under field conditions.

There is a standard procedure for this test specified by BIS (Bureau of Indian Standards).

Apparatus – 

slump

Slump/Abram’s cone apparatus

  • Cone – A cone also called as abram’s cone is having Top of 10 cm dia, bottom of 20 cm dia and total vertical height of 30 cm.
  • A Tamping Rod.
  • Metal ruler, brush, oil etc

Procedure –

  • Clean the apparatus with oil. put the cone on the plane platform on which we can measure the horizontal and vertical dimension of slump.
  • Take out ample amount of concrete from the batch and pour it in cone in three layers. Each layer to be tamped 25 times with standard tamping rod.
  • Fill the cone completely with concrete, avoid air voids.
  • Now, after the third layer, cone is lifted and removed in twisting motion so that the cone of concrete should not get disturbed.
  • Concrete subsides on its own. This subsidence is due to workability of concrete.
  • Now, measure the height of slump. Height will give us the workability of concrete. Sometimes we can predict the workability of concrete by the shape of concrete heap.

Types_of_concrete_slump

Following table shows the observations and conclusions on workability of concrete :

slump result

For better understanding you can watch the test here

With this test we can perform compaction factor test, Vee-bee consistometer test, flow table test, etc to obtain workability of concrete.

Compression Test

This test is to know the compressive strength of concrete structure. In this method we prepare sample cubes of concrete and apply compression on cube. We keep it increasing until the cube fails.

As we can not test the entire structure, we take out some sample from the batch and pour in moulds and after 24 hrs cure them for 28 days in water.

Apparatus – 

compresion machine

We need moulds for concrete cubes. sizes may vary but according to BIS there are specific sizes of moulds. Cubes of 15 cm are most common in all, compression testing machine, curing arrangement i.e. a water tank.

Procedure –

  • As discussed above we take sample from batch and cast cubes of size 150 mm in respective mould.
  • While pouring concrete in mould the care should be taken that oiling of mould should be done neatly, nuts should be tightened properly.
  • Cube is filled in three stages and each layer is tamped 25 times all over the surface with standard tamping rod so that all voids and entrapped air is removed.
  • Surface of cube is matched with the edges of mould and left undisturbed for setting and covering plastic to its surface to avoid water loss.
  • After 24 hrs the cubes are removed from mould and put in water tank for curing for 28 days.
  • After 28 days curing cube gains all the strength and hardened completely. Thus the cube is taken out for testing.
  • Cube is placed in jaw of compression testing machine, jaw is tightened and made sure that cube does not move away.
  • Load is applied and kept increasing until the cube fails.

The moment when we see cracks to the cube we consider it as failure.

  • The load at which cube has failed is noted and termed as its strength. and the concrete batch gets it’s Grade.

For better understanding you can watch the test here

These are the two important tests on concrete which are used commonly.

If you want to know about more tests on concrete, leave us comments.

In next Article we will be covering BIS recommendations for concrete.

Thank You!

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