Slump test is the most commonly used test of measuring workability of concrete. It can be employed either in laboratory or at site of work. It is used conveniently as a control test and gives an indication of the uniformity of concrete from batch to batch.
The apparatus for slump test consists of a metallic mould in the form of a frustum of a cone with internal dimension as follow
Bottom diameter = 20cm
Top diameter = 10cm
Height = 30cm
- The internal surface of the mould is thoroughly cleaned and freed from superfluous moisture and adherence of any old set concrete before commencing the test.
- The mould is placed on a smooth, horizontal and non- absorbent surface.
- The mould is filled with concrete in 4 equal layers. Each layer is tamped with 25 strokes of tamping rod.
- After the top layer has been tamped, the concrete is struck off level with a trowel and tamping rod.
- Then, the mould is removed by lifting it slowly and carefully in a vertical direction. This allows the concrete to subside. This subsidence is referred as slump of concrete.
If concrete subsides evenly it is called true slump.
If one half of the concrete cone slides down, it is called shear slump. The shear slump is measured as a difference in height between the height of the mould and the average value of subsidence.
The collapse indicates a leaner mix.
Recommended slumps of concrete:
|S.No||Type of concrete||Slump|
|1||Concrete for road construction||20 to 40mm|
|2||Concrete for tops of curbs, parapets, piers, slabs and walls that are horizontal||40 to 50mm|
|3||Concrete for canal linings||70 to 80mm|
|4||Concrete for arch and side walls of tunnels||90 to 100mm|
|5||Normal R.C.C work||80 to 150mm|
|6||Mass concrete||25 to 50mm|
|7||Concrete to be vibrated||10 to 25mm|