SLUMP TEST - TESTING PROCEDURE AND USES

Slump test is performed to check the workability of concrete. A good workable concrete has good strength.

Workability of Concrete

Workability is a complex property of concrete which is defined as the ease with which it can be mixed, transported and placed in position within a homogenous state. Workability depends upon the quantity of water, aggregate grade and percentage of fine materials in the mix. 

The following tests are commonly employed to check the workability of concrete. Slump test, Compaction factor test, Flow test, Vee-Bee consistometer test, K-Slump Test and Kelly ball test. Slump test is usually performed on site and lab due its ease and results. It gives quick result about the workability of concrete.

SLUMP TEST

This test can be used as a control test and gives an indication of the concrete uniformity from batch to batch. Repeated batches of the same mix, brought to the same slump, will have the same water content and water cement ratio, weights of aggregate, cement and admixtures are uniform and aggregate grading is within acceptable limits.

In this test, the quality of concrete Can be obtained by observing the Manner in which concrete
Slumps or deforms.

APPARATUS
The apparatus required for conducting Slump test are Metallic Mould which is in the shape of

frustum cone, a tamping rod with bullet end, Scale or tape for measuring the slump. Metallic sheet for placing Slump and trowel for pouring concrete in the slump.

1.         Frustum Cone

Frustum cone has two different diameters one at the top and other at the bottom. The dimensions of Frustum cone is mentioned below.

Bottom diameter of metallic mould - 20.0cm

Top diameter of metallic mould - 10.0cm

Height of cone frustum -  30.0cm

Thickness of sheet       - 1.60mm

2.         Tamping rod

This rod has a Dia of 16mm and bullet end at one side. The height of tamping rod should be 0.6m long.

Slump test Procedure

1.         Thoroughly clean the inner surface of Frustum cone and it should be free from moisture content and adherence of any old set concrete.

2.         Now place the Mould (Cone) on the metallic steel plate or on any smooth, horizontal, rigid, and non-absorbant   surface.

3.         Fill the cone with concrete in four layers each with an approximate height of 1/4th of the mould.

4.         Each layer is tamped 25 times by tamping rod taking care to distribute the strokes evenly over the cross section.

5.         Now after filling the 4th layer, the concrete is struck off with the trowel.

6.         The mould is removed from the concrete immediately in a vertical direction by raising it slowly and carefully.

7.         This allows the concrete to subside. This subsidence is called a SLUMP.

Result

Now measure the height of the mould and highest point of the slump in mm.

The difference between the Height of the mould and highest point of the Subside gives the Slump value.

Very low workability: slump value 0-25mm  - Used in Roads vibrated by power operated machines.

Low workability: slump value 25-50mm  - used for foundations with light reinforcement.

Medium workability: slump value 50-100mm - Normal reinforced concrete manually compacted and heavily reinforced sections with vibrations.

High workability: slump value 100-175mm - For sections with congested reinforcement. Not normally suitable for vibration

For Columns, retaining walls - 75-150mm slump 

For Beams and Slabs - 50-100mm

CC Pavements -20-30 mm

Mass concrete - 25-75mm

Different Types of Slump in Concrete

True Slump

If Concrete Slumps evenly and forms a shape same as a mould then it is treated as the true slump. This type of Slump is most desirable.

Shear Slump

If half of the slump is slides down then it is called as Shear Slump. Itindicates that the concrete is non-cohesive and have characteristics of segregation. Shear Slump may occur in the case of a Harsh mix

Collapse Slump

When the whole slump disintegrates in all directions and does not hints the shape of mould then it is called as collapse slump. Collapse slump is formed by adding excessive amount of water in concrete to increase the workability.

Zero Slump

This test doesn’t suitable for Dry and Stiff concrete. For very Dry and high stiff concrete does not show any difference after removing the mould.

Factors influencing Slump Cone value

1.         Water –cement ratio of concrete.

2.         The quality of coarse and fine aggregates, their shape, moisture content, texture, and grading.

3.         The use of plasticizer, superplasticizer admixture, and the sequence of their mixing.

4.         The void ratio of concrete and air content of concrete.

5.         The time of the test after mixing of concrete.

Limitations

1.         Slump test shouldn’t be carried if the aggregate used in concrete is above 40mm.

2.         This test is not suitable for very dry and high stiff concrete.

Advantages

1.         Slump test procedure can be performed in laboratory as well as construction site.

2.         It requires less apparatus when compared with the other tests.

3.         It doesn’t take much time to evaluate the results.