- To determine the workability of concrete
- Mould for the test shall be in the form of the frustum of a cone having the following internal dimensions bottom diameter-20 cms, top diameter-l0 cms, height-30 cms.
- The mould shall be made of metal (Brass or Aluminum shall not be used) of at least 1.6 mm thickness and the top and bottom shall be open and at right angles to the axis of the cone.
- The mould shall have a smooth surface.
- It shall be provided with suitable foot pieces and also handles to facilitate lifting it during the test in a vertical direction as required.
- Tamping rod shall be of steel or other suitable material, I 6mm diameter, 0.6 m long rounded at one end with graduations of least count 1mm.
Sampling in the Field
- If the test is to be conducted in the field collect the true representative sample of the batch not less than 0.02 in3 in volume.
- Mix the sample on a non-absorbent base either with a trowel or by other suitable implements to ensure uniformity.
- Use the sample immediately for the purpose of carrying out the test. In the case of concrete containing an aggregate of maximum size more than 38 mm wet sieve the concrete through 1 .5 inch screen to exclude aggregate particles bigger than 38 mm.
Sampling from Laboratory Mix
- If the slump is to be checked in the laboratory mix the sample homogeneously and take the representative sample.
Preparation of the Mould –
- Thoroughly clean the internal surface of the mould free from superfluous moisture and any concrete.
- Place the mould on a smooth, horizontal rigid and non-absorbent surface such as a carefully leveled metal plate and held the mould firmly in the place while it is being filled.
- Fill the mould in four layers each approximately one-quarter of the height of the mould.
- Prod each layer with twenty-five strokes of the rounded end of the tamping rod.
- Distribute the strokes uniformly over the cross-section of the mould such that the second and subsequent layers shall penetrate into the underlying layer.
- Prod the bottom layer throughout its depth.
- After the top layer has been prodded, struck off the concrete in level with the slump cone with a trowel or with the tamping rod so that the mould is exactly filled.
- Clean the mortar if any, which has been leaked out between the mould and base plate.
- Remove the mould from concrete immediately by raising it slowly and carefully in a vertical direction.
- Measure the slump immediately by determining the difference between the height of the mould and that of the highest point of the specimen
- Complete the whole process within a period of 2 minutes after sampling.
- Record the slump measured in terms of millimeters of subsidence of the specimen during the test.
- Any slump specimen, which collapses or shears off laterally gives the incorrect result and if this occurs repeat the test with another sample
- If in the repeated test also the specimen collapses or shears off laterally measure the slump and record the fact.
- Carry out the slump test at a place free from vibration or shock and within a period of 2 minutes after sampling.