What Is Slump Cone Test | Procedure | Slump patterns | Slump Value | Observations | FAQ

 

SLUMP TEST

The slump test is the most popular because of the simplicity of the equipment required and the test procedure. The slump test indicates the behaviour of a compacted concrete cone under the action of gravity. The slump test is a practical means of measuring workability. Changes in slump values obtained during operation can indicate changes in material, moisture content, or mixing ratio, which is useful for controlling the quality of the concrete produced.

The test performed with a mould called the slump cone. The slump cone is placed on a horizontal, non-absorbent surface and filled with three equal layers of fresh concrete, each layer being stuffed 25 times with a standard tamping rod. The top layer is flattened and the mold is lifted vertically without disturbing the concrete cone. The sag of concrete in millimetres is called sag. After the test, a uniform slump all around is called a true slumps.

In the case of very thin concrete, half of the cone may slide down the other side, which is called a shear slump, or in the case of very wet concrete, it can collapse. A slump test is basically a measure of the consistency or wettability of a mix.

 

What is a slump test in construction?

Concrete slump testing is used to determine the correct moisture content in a concrete batch. "Slump" is the distance (in inches) that concrete settles after the slump cone is removed.

 

What Does Slump Test Determine?

To determine the effect of slump on different water/cement ratio and concrete mix.

 

Procedure for Concrete Slump Cone Test

1. Filled mould in three equal layers.

2. Each layer is rodded 25 times to settle the concrete before the next layer is added.

3. Full mould is ready to be pulled off to measure slump.

4. Remove the cone from the concrete by raising it vertically, slowly and carefully, in 5 to 10 seconds.

5. Partial mix being revealed by the removal of mould.

6. Immediately after the cone is removed, measure the slump to the nearest 5mm by using the rule to determine the height of the cone and of the highest point of the specimen being tested

Must read: Compressive Strength of Concrete | Cube Test, Procedure, calculation & facts

 

When a standard slump cone is filled with concrete and when the cone is lifted up slowly, leaving the moulded concrete unsupported laterally, the concrete subsides under the force of gravity to a smaller height. The decrease in height is measured as its slump.

The following figure gives the general slump patterns

 

True Slump (Slump 1-2 Inches)

In a real slump, the concrete simply disappears and retains its shape somewhat. This is the only slump used by multiple tests.

 

Mixtures with a hard consistency exhibit zero slumps, so in the very dry range, no deviations are detected between mixtures of different workability.

 

However, in lean mixtures with a tendency to roughness, the actual slump can easily change or even collapse into a shear slump type, yielding very different slump values in different samples of the same mixture. Therefore, the slump test is not reliable for lean mixtures.

 

 

Collapse Slump (Slump Greater Than 4 Inches)

In this type, the new concrete will completely collapse. Mixes that are too wet or workability high mix, slump tests are not suitable for these mixes.

Shear Slump (Slump 2-4 Inches)

When half of the cone slides down on an inclined plane, this is called a shear slump. This indicates a lack of cohesiveness in the mix. Perform the experiment again to avoid a shear slump.

 

Zero Slump: If concrete maintains the actual shape of the mould, it is called zero slumps which represents stiff, consistent and almost no workability.

 

Observations And Calculations:

Mix ratio = --------

W/C ratio	Initial level  (mm)	Final slump  (mm)	Slump in mm

RESULT:

The slump of concrete at water-cement ratio         =    mm.

 

Slump Value for Different Grades of Concrete

The following table gives the slump required for different situations. Discuss your test result.

 

Types Of Construction	Recommended slumps in mm
	Minimum	Maximum
Pavements	25	50
Mass Concrete Structures	25	50
Unreinforced Footing	25	75
Cassions And Bridge Deck	25	75
Reinforced Foundation, Footing And  Walls	50	100
Reinforced Slabs And Beams	30	125
Columns	75	125

 

Slump Test Values

 

WORKABILITY	COMPACTION FACTOR	SLUMP (MM)
Very Low	0.78	0 – 25
Low	0.85	25 – 50
Medium	0.92	50 – 100
High	0.95	100 – 175

 

FAQ

Why is the slump test suitable for site use?

 

Slump test is the most commonly used method of measuring the workability of concrete which can be employed either in the laboratory or at site because there is only simple apparatus, equipment and simple procedure involved hence slump test is suitable for site use. The slump test is the simplest workability test for concrete, involves low cost and provides immediate results. The slump cone apparatus is cheap, convenient to handle and moreover, it is portable.

 

What are the limitations of the slump test?

There are chances of many shapes of slump to occur and it is difficult to decide which is the correct value. It is not suitable for concrete in which the maximum size of aggregates excess 40mm. There is no direct relationship between the workability and the value of slump. It does not occur in case of dry mixes. The slump test is suitable for slumps of medium to high workability, slump in the range of 5 – 260 mm, the test fails to determine the difference in workability in stiff mixes which have zero slumps, or for wet mixes that give a collapse slump. It is limited to concrete formed of aggregates of less than 38 mm (1.5 inches).

 

Will the addition of measured water to a ready concrete mix gave the desired water/cement ratio?

Yes. If the concrete mix almost loss the water content, we can add in water so that it is more effective, if no addition of water it may affect the workability.

Slump Cone Size

Height of 12” (300 mm),

Bottom Diameter of 8” (200 mm)

Upper Diameter of 4” (100 mm).

Must read: Compaction factor test | Workability test for concrete | Fresh concrete test

 

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