The Effect Of Admixtures On Properties Of Co`ncrete
[CASE STUDIES OF SUGAR, COW BONE ASH, GROUDNUT SHELL ASH, AND LIME STONE POWDER]

  3.6.2         Slump Test
    Slump Test is used to determine the workability or consistency of concrete mix prepared at the laboratory or the construction site during he progress of the work.
    Concrete slump test is carried out from batch to batch to check the uniform quality of concrete during construction.
    The slump test is the most simple workability test for concrete, involves low cost and provides immediate results. Due to this fact it has been widely used for workability tests since 1922. The slump is carried out as per procedures mentioned in ASTM C143 in the United States IS:1199 – 1959 in India and EN12350 – 2 in European.
    Generally concrete slump value is used to find the workability which indicates water – cement ratio but there are various factors like properties of materials, mixing methods, dosage, admixtures e.t.c which affect the concrete slump value.
    James (1988) the concrete slump test is an empirical test that measures the workability of fresh concrete. More specifically, it measures the consistency of the concrete in that specific batch.
    The test is performed top check the consistency of fresh made concrete. Consistency is term very closely related to workability. It is a term which describes the state of fresh concrete. it refers to the ease with which the concrete flows. It is used to indicate the degree of wetness. Workability of concrete is mainly affected by consistency i.e. wetter mixes will be more workable than drier mixes, but concrete of the same consistency may vary in workability. It is also used to determine consistency between individual batches.
    The test is popular due to its simplicity of apparatus used and simple procedure. Unfortunately, the simplicity of the test often allows a wide variability in the matter that the test is performed. The slump test is used to ensure uniformity for different batches of similar concrete under field conditions and to ascertain the effects of plasticizer on their introduction. This test is done to:
i.    To check the consistency of the concrete,
ii.    To determine if the concrete flow smoothly into the shape of the formwork,
iii.    It is a quick check to see if the concrete is suitable for use.
Equipment Required:
    Mould for slump test, non – porous base plate, measuring scale, tamping rod. The mould for the test is the form of the frustum of a cone having height 30cm (300mm), bottom diameter 20cm (200mm) and top diameter 10cm (100mm). The tamping rod is of steel 16mm diameter and 60cm (600mm) long and rounded at one end.
Procedure for Slump Test
i.    Clean the internal surface of the mould and apply oil.
ii.    Place the mould on a smooth horizontal non – porous base plate
iii.    Fill the mould with the prepared concrete mix in 4 approximately equal layers
iv.    Tamp each layer with 25 stokes of the rounded end of the tamping rod in a uniform manner over the cross – section of the mould. For the subsequently layers, the tamping should penetrate into the underlying layer.
v.    Remove the excess concrete and level the surface with a trowel.
vi.    Clean away the mortar or water leaked out between the mould and the base plate.
vii.    Raise the mould from the concrete 2m are diatily and slowly in vertical direction.
viii.    Measure the slump as the difference between the height of the mould and that of heightest point of the specimen being tested.
Note: The above operation should be carried out at a place free from vibrations or shock and within a period of 2 minutes after sampling.
Slump Value observation
    The slump (vertical settlement) measured shall be recorded in terms of millimetres at subsidence of the specimen during the test.

When the slump test is carried out, following are the shape of the concrete slump that can be observed.
1.    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 as shown above
2.    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.    Collapsed Slump: 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.
4.    Shear Slump: It indicates that the result is incomplete, and concrete to be retested.
3.7    PRODUCTION OF CUBES  
          The concrete mix was placed into the mould which has been smeared with oil to ease opening. Concrete was poured and compacted in three layers using steel rods of 25mm in size and with 25 blows per layer and the surface was levelled or smoothed using a hand trowel. Each cube was marked by identification to know the date and percent(for those with admixtures) after adequate setting was allowed for 24 hours, the concrete cubes were removed from the mould and they were cured according to the requirements of BS:1881; part III.