Concrete slump test procedure | Slump values and their uses

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What is slump test of concrete?

In this article, we discuss the concrete slump test. Before this, we have to know a term called workability. So, what is the workability of concrete?

Workability is the ease with which the concrete ingredient can be mixed, transported from one place to another, compacted, placed in the mold, and finished with less amount of homogeneity loss.

Homogeneity is simply to mix all gradient-like cement, sand, aggregate, and water like a single compound. They should not be separated from each other. It is the property of fresh concrete because workability tests can be measure only in fresh concrete.

The workability of concrete can be measured in different ways. They are given below.

  1. Slump test
  2. Compaction factor test
  3. Flow test
  4. Kelly ball test
  5. Vee Bee Test

From the above explanation, you might have got the idea that the slump test is a workability test of concrete, Right?

Here, among all types of tests above, we will only talk about the concrete slump test. The slump test is mostly used on-site for the workability test of concrete.

It measures the consistency of concrete before it set. Slump tests allow us to know the proper amount of cement, sand, and aggregate has used to prepare the required grade of concrete or not.

But, It is not suitable for very wet and dry concrete. For this test, the maximum size of aggregate should not exceed more than 38 mm.

Apparatus required for slump test

Concrete slump test procedure | Slump values and their uses

1) Plate:- Plate is a flat metal sheet on which we conduct a slump test. It is nonporous and nonelastic.

2) Frustum: – Frustum is a hollow cone-shaped metal whose both sides are open. It is also known as a slump cone.

Its upper diameter of the opening is 10 cm and bottom diameter of the opening is 20 cm and the height of the frustum is 30 cm. Two-handle are mounted on the side of the frustum to hold and move the frustum. The frustum is used to hold the concrete prepared to test for workability.

3) Tamping Rod:- The tamping rod is a metal or steel rod in a rounded shape whose end is pointed like a bullet. Its diameter is 16 mm and its height is 60 cm. It is used to compact the concrete held in the frustum.

4) Trowel:- Trowel is used to place concrete in the frustum. Actually does not have a big role in the parts of the concrete slump test apparatus.

5) Measuring tape:- It is used to measure the slump value.

We have discussed the apparatus required for the slump test. Now we will move toward the procedure for the slump test. Before conducting the slump test all the apparatus (Slump cone and tamping rod) should be cleaned with water and dried.

Concrete slump test procedure

  1. At first, the frustum is placed on the plate. And then fresh concrete whose workability has to best should be poured in a frustum with the help of a trowel.
  2. Concrete should be poured in frustum in four layers. So, the first layer of concrete is filled with concrete and then concrete should be compacted by tamping 25 times with the help of a tamping rod. We should compact in whole spread area of concrete. Don’t compact only in specific areas.
  3. After that, the second layer of concrete is poured into the frustum, and step second is repeated and so on till four-layer up to the upper end of the frustum.
  4. Now remove the excess concrete going up from the upper end of the frustum and level it horizontally with the help of a trowel.
  5. Then, the frustum should be rotated slightly by holding the handle of the frustum and decreasing height of concrete in the frustum should be observed.

As soon as you remove the frustum the height of concrete in it began to decrease. The decreased height of concrete should be taken.

Concrete slump test procedure | Slump values and their uses

The shape and decreased height of concrete decide the types of a slump. There are three types of slumps. They are true slump, shear slump, and collapse slump.

Types of Slump

Concrete slump test procedure | Slump values and their uses
  1. True slump:- It has low workability. True slump occurs when the decreased height of concrete is very low.
  2. Shear slump:- It has medium workability. The surface of the concrete takes place in slope form. It may occur due to the uneven tamping of concrete.
  3. Collapse slump:- It has high workability. As soon as we lift the frustum the height of the concrete suddenly decreases. A collapse slump occurs when the decreased height of concrete is very high. Concrete may undergo segregation and bleeding.

How to take measurement of slump value?

Slump value is measured in millimeter (mm).

  • The value for the true slump is taken by subtracting the final height of concrete from the initial upper height of concrete i.e. height of frustum.
  • The value for the shear slump is taken by subtracting the average height of plane of concrete from the initial upper height of concrete i.e. height of frustum.
  • The value for the true slump is taken by subtracting the final height of concrete from the initial upper height of concrete i.e. height of frustum.

Important slump values and their uses

Slump Value (mm)Degree of workabilityConsistencyUses
0Extremely LowMoist EarthPrecast Paving slab
0-25Very lowVery DryRoads (Power vibrator)
25-50LowDryMass concreting, light reinforcement section (Hand vibrator)
50-100MediumPlasticHeavily reinforced section (Manual vibrator)
100-175HighSemi FluidR.C.C with congested reinforcement (Can’t be vibrated)

Factors affecting the workability of concrete

  1. Water-cement ratio:-  As the water-cement ratio increases the workability of concrete increases. The water-cement ratio decreases the friction between the ingredient in the concrete mix and increases the workability.
  2. Mix Proportion:- If the ingredient in concrete increases then workability decreases.
  3. Surface Texture:- If the surface texture of concrete is smooth then workability Increases but if it is rough then workability decreases.
  4. The shape of coarse aggregate:- If the coarse aggregate used in concrete is flaky and angular then workability decreases and if the coarse aggregate used in the concrete mix is rounded then workability Increases.
  5. Admixture:- The use of admixture may increase or decrease the workability of concrete. It depends on the types of admixtures used in the mix.

I hope this article on “Concrete slump test procedure” remains helpful for you.

Happy Learning – Civil Concept

Contributed by,

Civil Engineer – Ranjeet Sahani

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