SLUMP TEST FOR WORKABILITY OF FRESH CONCRETE

The concrete slump test measures the consistency of fresh concrete before it sets.It is performed to check the workability of freshly made concrete, and therefore the ease with which concrete flows. It can also be used as an indicator of an improperly mixed batch. The test is popular due to the simplicity of apparatus used and simple procedure. The slump test is used to ensure uniformity for different loads of concrete under field conditions.

A separate test, known as the flow table test or slump flow test is used for concrete that is too fluid (workable) to be measured using the standard slump test, because the concrete will not retain its shape when the cone is removed.

FACTOR EFFECTING CONCRETE SLUMP TEST

• Temperature of the concrete,
• Chemical admixtures dosage, type, combination, interaction, sequence of addition and its effectiveness,
• Air content of concrete,
• Material properties like chemistry, fineness, particle size distribution, moisture content and temperature of cementitious materials. Size, texture, combined grading, cleanliness and moisture content of the aggregates,
• Concrete batching, mixing and transporting methods and equipment, Sampling of concrete, 
• slump-testing technique and the condition of test equipment,
• The amount of free water in the concrete, and
• Time since mixing of concrete at the time of testing.

OBJECTIVE

To determine the workability of fresh concrete.

SAMPLE/SPECIMEN

A sample of concrete mix M15 by weight with suitable water cement ratio is prepared in the laboratory.

EQUIPMENT  

Mould for slump test, non porous base plate, measuring scale, temping rod.

Matalic mould:-  top dia 10 cm and bottom dia 20 cm with hieght 30 cm,connected with bottom non porous base platetemping.

Rod(steel) :-  16 mm diameter and 60cm long rounded at one end.

CONCRETE SLUMP TEST PROCESURE

• Clean the internal surface of the mould and apply oil.
• Place the mould on a smooth horizontal non- porous base plate.
• Fill the mould with the prepared concrete mix in 4 approximately equal layers.
• Tamp each layer with 25 strokes of the rounded end of the tamping rod in a uniform manner over the cross section of the mould. For the subsequent layers, the tamping should penetrate into the underlying layer.
• Remove the excess concrete and level the surface with a trowel.
• Clean away the mortar or water leaked out between the mould and the base plate.
• Raise the mould from the concrete immediately and slowly in vertical direction.
• Measure the slump as the difference between the height of the mould and that of height point of the specimen being tested.

SLUMP VALUE OBSERVATION

The slump (Vertical settlement) measured shall be recorded in terms of millimeters of subsidence of the specimen during the test.

TEST RESULT

Shape of the concrete slump that can be observed after test performed.

1. True Slump – True slump is the only slump that can be measured in the test. The measurement is taken between the top of the cone and the top of the concrete after the cone has been removed.

2. Zero Slump – Zero slump is the indication of very low water-cement ratio, which results in dry mixes. These type of concrete is generally used for road construction.


3. Shear Slump : the shear slump indicates that the result is incomplete and concrete to be retested.

4. Collapsed Slump : This is an indication that the water-cement ratio is too high. i.e. concrete mix is too wet or it is a high workability mix for which a slump test is not appropriate.