Slump Test :

The slump test identifies the consistency or the wetness of concrete and is employed in the laboratory or at the site very easily due the simplicity of the apparatus and the test procedure. For a wet mix the slump collapses, and gives a shear slump for a lean mix but the desired value is calculated, in the test, by the true slump i.e. the concrete which slumps evenly all around is shown by the rich concrete. The slump so obtained, gives the idea of water content to be used for concrete at different works.

Types of slump

 

Sr. No.	Name of Work	Slump in mm	Water Cement Ratio
1.   2.   3.   4.	Concrete for road and mass concrete Concrete for R.C.C beams and slabs Columns and retaining walls Mass concrete in foundation	25 to 50   50 to 100   75 to 125   25 to 50	0.70   0.55   0.45   0.70

 

Mould for slump test

Apparatus :

Steel mould in the form of a frustrum of cone with internal dimensions as given below : The typical mould for test is this.

(a) Bottom diameter = 200 mm

(b) Top diameter = 100 mm

(c) Height = 300 mm

(d) Thickness = atleast 1.6 mm

(e) Tamping rod of 16 mm dia. and 0.6 m long with bullet end.

 

Procedure

1.    Four mixes are prepared, with a ratio of cement-to-sand-to-course aggregates as 1:2:4 for each mix, with the water-cement ratio of 0.5, 0.6, 0.7 and 0.8 respectively.

2.    The internal surface of mould is cleaned and made free from any dust or moisture. Then, this mould is placed on a smooth, horizontal, rigid and  non-absorbant surface.

3.    Mould is filled with the concrete is four layers, each approximately 1/4 of the height of the mould with each layer tampered 25 times evenly by using the tamping rod.

4.    Trowel is used to struck off and level the concrete.

5.    The  mould is removed immediately by raising it carefully in a vertical direction.

6.    The subsidence of concrete in mm is noted which will give the value of  slump.

7.    If concrete does not gives the true slump then the test is repeated.

 

Limitations

         I.            It is not suitable for concrete in which aggregates of size less than 19 mm and more than 38 mm is used.

       II.            It is does not suitable  for very wet and dry concretes as the wet concrete produces a collapse slump while dry concrete produces no slump at all.

    III.            The slump can take any shape so difficult to decide the correct value of slump.

   IV.            There is no relationship between workability and the value of slump obtained as the concrete of different workabilities may give the  same value of slump.

      V.            It is only suitable for concrete of high or medium workability.

 

Merites :

       I.            The procedure and the apparatus is very suitable for site use.

     II.            Suitable value of water content can be determined for a given type of work using table