Slump Test: Workability of Concrete by Slump Cone Test

Slump Test

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Slump Test is the most common to test the consistency (or workability) of concrete.

The “slump cone” is a sheet metal “frustrated” cone, 300 mm tall, bottom diameter is 200 mm, and the top is 100 mm, it is placed on a stable surface, usually made of steel.

The cone is fitted with small steel tabs at the bottom; the operator stands on those tabs to hold the cone firmly on the surface.

Concrete is placed into the cone with the 3 layers, each being compacted in turn with 25 “rods” of a 16 mm diameter, a bullet ended rod.

After compaction is done, the concrete is struck off at the top, and excess cement is wiped away from the outside of the cone, especially lying on the surface.

The operator firmly holds the cone down manually and carefully steps away from the cone & then carefully lifts the cone and places it inverted adjacent to the concrete.

The tamping rod is placed on the top of the slump cone so that it runs across above the mound of concrete.

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A steel ruler is used to measure down from the underside of the rod to the average height of the top of the concrete, value is recorded as the “slump.”

Values can range from 0 to 250 mm is seen very rarely i.e. in the case for concrete with superplasticizer or self-compacting concrete, or concrete with 7 mm maximum particle size.

Slump Test Diagram:

slump test diagram

The slump test is a way to measure the workability of concrete, a small slump means the concrete is stiff; a massive slump implies the concrete will flow easily.

There are times when thick concrete is desired and times for flowing concrete.

The slump test is performed by packing a metal cone with the concrete according to a specified procedure, then lifting the metal cone off the pavement and measuring the fall of the top of the concrete.

In the US, the cone is 12 inches high, and the slump is measured in inches.

Different slumps have different applications and can imply something about the nature of the concrete while it is still fresh.

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Long ago, a 3–4-inch slump was considered ideal for workability because less was too challenging to work and much more slump meant too much water.

But within the last 40–50 years, admixtures (additives to the concrete) have been developed that will allow massive slumps without loss of cohesion or segregation.

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It can be defined as the difference between the height of the concrete before removing the slump cone (mould) and the height of the concrete after removing of slump cone as measured during the concrete slump test.

Slump Test Values:

  • Very low workability: slump value 0-25mm or 0-1 inch.
  • Low workability: slump value 25-50mm or 1-2 inch.
  • Medium workability: slump value 50-100mm or 2-4 inch.
  • High workability: slump value 100-175mm or 4-7 inch.

Also read 1. RQD 2. Chemical Oxygen Demand 3. Biochemical oxygen demand

Frequently Asked Questions:

What is the ideal value of slump?

In the case of a dry sample, the slope will be in the range of 25–50 mm which is 1–2 inches & in the case of a wet concrete, it may vary from 150–175 mm or say 6–7 inches.

What does a positive slump test mean?

A positive slump test result with the reproduction of radial symptoms is demonstrated.

What are the types of the slump?

1. true slump,
2. shear slump and
3. collapse slump.

How is Slump test calculated?

Place the cone next to the wet concrete mound and a steel strip extending over the mound.
Immediately measure the distance between the bottom of the steel bar and the top of the concrete mound.
Distance is the concrete slope measured to the nearest 1/4 inch.

Conclusion of the slump test:

The slump test is a way to measure the workability of concrete. A small slump means the concrete is stiff; a massive slump implies the concrete will flow easily.

The slump test is performed by packing a metal cone with the concrete according to a specified procedure, then lifting the metal cone off the pavement and measuring the fall of the top of the concrete.

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