Slump Test

Slump Test

Standard test method for the slump of hydraulic cement concrete. (ASTM C-143/C-143 M-03)

Scope & significance:This test method is used in lab and in field for finding out the slump (decrease in the height of concrete when we lift up the mould). This test is used extensively in site works all over the world. The slump test does not measure the workability of concrete directly but it co-relates the workability with some physical measurement.The main significance of this test is as follows;This test method is used to determine the slump of plastic hydraulic cement concrete.

Slump <15mm (Non-Plastic)
Slump>15 (Plastic)

This test method is applicable to plastic concrete having coarse aggregate upto 37.5mm in size. If the coarse aggregate is larger than the 37.5mm then this test method is not applicable.This test method is not applicable to non-plastic and non-cohesive concrete (due to larger amount of water presence).

Apparatus:
                    

                     1-     Metal mould, thickness is 1.15mm, it is in cone form with the base 200mm diameter and 300mm height with the top diameter 100mm. the top and base of cylindrical mould is open and parallel to each other. The mould is provided with foot pieces and handles.

                     2-      Temping rod, 16mm diameter and 600mm in length having temping ends.Related theory:SlumpThe decrease in the height of concrete when the mould of standard dimensions is lifted.Types Of SlumpThere are three types of slump.

1-      True Slump
2-      Shear Slump
3-      Collapse slump

We discard the collapse slump due to the very high value of slumpShear slump occurs due to the lack of cohesion in mix.
We often use the term 100% compaction but actually in 100% compaction we have percentage of air voids less than 3% by volume of concrete.

Workability Compacting Factor
Slump (mm)

Very Low     0.780 – 25

Low              0.8525 – 50

Medium      0.9250 – 100 

High             0.95100 – 175

Note: More is the slump value more will be the workability.

Procedure:

The mould is placed on a flat moist non-absorb surface with the smaller opening at the top. It is then held firmly in place during filling of concrete by the operator standing on two foot pieces. The mould is filled to a depth of 70mm and 2/3 of volume fills to a depth of 160mm. Each layer is given 25 strokes with the help of temping rod uniformly distributed over the cross-section of each layer. Rod the 2nd and 3rd layer through out its depth so that strokes just penetrates into the under lying layer. After the top layer is rodded strike off the surface of the concrete by means of rolling motion of temping rod. Complete the entire test with an elapsed time of 2.5minutes. After filling, the cone is slowly lifted and the unsupported concrete slumps. The decrease in the height of concrete is called slump.  It is measured with the nearest 5mm. at the beginning of every test, before lifting the mould the area immediately around the base of the cone should be cleaned off of concrete which may be dropped accidentally.

The minimum value of slump = 1”= 25mm
The maximum value of slump = 4” =100mm
Results: Slump Value =  …75…  mm

Comments:
        A change in slump height would demonstrate an undesired change in the ratio of the concrete ingredients; the proportions of the ingredients are then adjusted to keep a concrete batch consistent. This homogeneity improves the quality and structural integrity of the cured concrete. From the performed experiment we came to know that our mean slump value was 75mm which describes that it is True Slump and its workability is medium