SLUMP TEST

• Slump test is the most commonly used method of measuring workability of concrete.
• it can be done either in laboratory or at site of work.
• It is not suitable for suitable for very wet or very dry concrete.
• It does not measure all factors  contributing to workability.

The apparatus for conducting the slump  test essentially consist of metallic mould in the form of frustum of a cone having the internal dimensions under,

Bottom Diameter = 20 cm

Top Diameter = 10 cm 

Height = 30 cm

The thickness of metallic sheet for the mould should not the thinner than 1.6mm. Sometime the mould is provided with suitable guides for lifting velocity up. For tamping the concrete, a steel tamping rod 16mm dia, 0.6 meter long with bullet end is used.

The mould is placed on a smooth, horizontal, rigid and non absorbant surface. The mould is then filled in four layers, each approximately 1/4 of height of the mould. Each layer tamped 25 times by the tamping rod taking care to distribute the strokes evenly over the cross section. After the top layer has been roded, the concrete is struck off level with trowel and tamping rod. The mould is removed from the concrete immediately by raising it slowly and carefully in a vertical direction. This allows the concrete to subside. The subsidence is referred as SLUMP of concrete. The difference in level between the height of the mould and that of highest point of the subsided concrete is measured. The difference in height in mm is taken as a slump of concrete.

ASTM measures the center of the slumped concrete as the difference in height. ASTM also specifies 3 layers.