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.
Apparatus Used:
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
Procedure:
- 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.
Slump Patterns:
True slump:
If concrete subsides evenly it is called true slump.
Shear 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.
Collapse slump:
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 |
