The concrete Slump test is a quick procedure to ascertain how thick and consistent fresh concrete is. This test is very important for making sure that the concrete used in a construction project is of good quality and can be right away used in construction. This test is employed on almost every construction site. The Slump test is extremely easy to use and has considerable accuracy. It also requires a lesser quantity of tools and can be conducted in a short span of time.

In this article, we will get to know about the Concrete Slump Test, its Importance, and the Slump Test Procedure in detail. This topic is important in Concrete Technology, and questions from this topic are often asked in various exams like SSC JE CE, and RRB JE Civil.

What is a Concrete Slump Test?

Concrete Slump Test determines the workability of concrete. The Slump test of concrete is a measure of its consistency and is a field test. This test indicates the uniformity of different concrete batches. This test has been used since 1922 because the equipment and process are easy to use. On the basis of the Slump obtained, the workability of concrete can be ascertained, i.e. the ease with which concrete can be mixed, transported, placed, and compacted. The apparatus consists of a cone in which concrete is placed in 4 layers, and each layer is thoroughly compacted. The cone is removed after some time, and the Slump is measured. Notably, the Slump test IS code is IS 1199. 

The slump test is an essential on-site method to monitor the workability of concrete before placing. It helps site engineers quickly assess the consistency of the mix, ensuring that it meets structural and workability requirements.

Three types of Slump can be observed:

• Shear Slump 
• Collapse Slump
• True Slump.

Fig 1: Types of Concrete Slump

• True Slump refers to a general drop of the concrete mass evenly all around without disintegration.
• Shear Slump indicates that the concrete lacks cohesion. It may undergo segregation and bleeding and thus is undesirable for the durability of concrete.
• Collapse Slump indicates that the concrete mix is too wet, and the mix is regarded as harsh and lean.

Concrete Slump Test Working Principle

The Slump test result is a measure of the behavior of a compacted inverted cone of concrete under the action of gravity. It measures the consistency or the wetness of concrete which then gives an idea about the workability condition of the concrete mix. The slump test is based on the principle that the consistency of fresh concrete can be assessed by the behavior of a concrete sample when it is subjected to controlled conditions. The test involves the use of a conical mold, called a slump cone, which is filled with concrete in three layers. Each layer is tamped with a rod to ensure proper compaction. Steps Involved:

• Preparation: The mold, typically a truncated cone with a base diameter of 200 mm, a top diameter of 100 mm, and a height of 300 mm, is cleaned and placed on a flat, non-absorbent surface.
• Filling the Mold: The cone is filled with fresh concrete in three equal layers. Each layer is tamped 25 times with a steel rod to ensure uniform compaction and eliminate air pockets.
• Lifting the Mold: Once the cone is filled and compacted, it is lifted vertically without any lateral or torsional movement. This allows the concrete to settle or slump under its own weight.
• Measuring the Slump: The difference in height between the top of the mold and the highest point of the slumped concrete is measured. This difference is called the slump.

Procedure of Concrete Slump Test

• The mould for the concrete Slump test is a frustum of a cone, 300 mm (12 in) in height. The base is 200 mm (8in) in diameter and has a smaller opening at the top of 100 mm (4 in).
• The base is placed on a smooth surface, and the container is filled with concrete in three layers, whose workability is to be tested.
• Each layer is temped 25 times with a standard 16 mm (5/8 in) diameter steel rod, rounded at the end.
• When the mould is completely filled with concrete, the top surface is struck off (leveled with mould top opening) by means of screening and rolling motion of the temping rod.
• The mould must be firmly held against its base during the entire operation so that it cannot move due to the pouring of concrete, and this can be done by means of handles, or footrests brazed to the mould.
• Immediately after the filling is completed and the concrete is leveled, the cone is slowly and carefully lifted vertically; an unsupported concrete will now Slump.
• The decrease in the height of the center of the Slumped concrete is called a Slump.
• The Slump is measured by placing the cone just beside the Slumped concrete and the temping rod is placed over the cone so that it should also come over the area of Slumped concrete.
• The decrease in the height of concrete to that of mould is noted with scale. (usually measured to the nearest 5 mm (1/4 in).

Equipment of Concrete Slump Test 

Fig 2: Slump Test Equipment

The Slump test apparatus includes:

• Mould: The shape of the mould is a frustum of a cone. The cone is known as the Slump cone or Abrams cone. The slump cone is made of steel, plastic, etc. Its height is 12 inches (30 cm). The diameter of the base opening is 8 inches (20 cm), and the top opening is 4 inches (10 cm).
• Base plate: Base plate may be made of Aluminium, polymer, steel, etc. It may be equipped with a holding attachment.
• Tamping rod: Temping rod used in the Slump test is made of steel. Tamping Rod is usually 24" long and has a diameter of 5/8" diameter. Temping rod used in the Slump test is made of steel. Tamping Rod is usually 24" long and has a diameter of 5/8" diameter.
• Tape measure: Standard tap should be used for measurement.

IS Code Reference 

The slump test is conducted according to the guidelines mentioned in IS 1199:1959 – Methods of Sampling and Analysis of Concrete.
This Indian Standard provides detailed instructions on:

• How to prepare the concrete sample
• What apparatus to use (like slump cone, tamping rod, base plate, etc.)
• Step-by-step testing procedure
• How to measure and record slump values

Following IS 1199 ensures that the slump test is carried out correctly and the results are reliable.
This is especially important during inspections, audits, or when uniform concrete quality is required across multiple batches.

Concrete Slump Test International Standard

Various international codes have specific testing standards for the concrete Slump test. These standards specify methods and equipment for determining the consistency of fresh concrete by the Slump test. For acceptance and reliability, It is essential to maintain strict compliance with these standards during the Slump test for concrete. The standards for the concrete Slump test are the following.

1. American Society for Testing and Materials (ASTM): ASTM Slump test standards are ASTM C 143, and ASTM C143M.
2. The American Association of State Highway and Transportation Officials (AASHTO): AASHTO Slump test standards are AASHTO T119 and AASHTO BS1881.
3. British & European standard: The British & European Slump test standard is BS EN 12350-2.
4. Indian Standard: IS 1199 – 1959

Measurement of Workability from Concrete Slump Test

If a Shear Slump or Collapse Slump occurs, the test should be repeated. The result can be obtained from the True Slump only. The results of the Slump Test can be classified within some ranges according to the Slump value.

• Very low workability: Slump value 0-25mm
• Low workability: Slump value 25-50mm 
• Medium workability: Slump value 50-100mm 
• High workability: Slump value 100-175mm 

Precautions For Concrete Slump Test

Some important precautions that have to be taken are:

• The internal surface of the mould should be cleaned and free from moisture.
• The base plate or surface should be free from vibrations or shocks.
• This test is done just after sampling for nearly 2 minutes.

Comparison Table: Types of Concrete Slump

Before showing the table, let’s understand what the test results can look like. When the cone is lifted, the shape that the concrete takes tells us a lot about its workability and quality.

Note :

Sometimes, you may also come across the term "Zero Slump" (when concrete retains its cone shape and does not settle at all).
This isn’t a deformation like the other three, but it’s important in dry mixes like those used in precast elements or road pavements.

Field Example of Collapse Slump

Let’s understand with a simple site example.

You’re performing a slump test for concrete meant for a beam. After lifting the slump cone, the concrete completely collapses and spreads across the base plate.

What does this indicate?

• The concrete has too much water.
• The mix is too flowy and lacks strength.

Why is it risky?

• Such a mix might seem easy to place but can cause cracks, segregation, or even failure in load-bearing elements.

What should be done?

• Imediately stop the use of that batch.
• Inform the site engineer.
• Either adjust the mix (by reducing water or adding cement/sand) or make a fresh batch with correct proportions.

These quick checks using a slump test can save a structure from major damage or failure later on.

Conclusion

The present discussion included all about the Concrete Slump test and its principles, procedure, precautions, and other aspects. To reinforce your preparation level and to provide a fillip to your preparation, get enrolled in AE/JE Civil Coaching, available on the Testbook App. Test yourself through various SSC JE Civil Mock Tests and SSC JE Civil Previous Year Papers