To determine the slump of a given fresh concrete mix sample.
Theory:Work-ability is the ease with which the given concrete mix can be mixed together, transported to the application place and can be placed/applied/compacted their within the initial setting time of cement. This property depends largely on the amount of water added i.e. water cement ratio of the concrete mix and kind of aggregates used. Generally work-ability increases with the addition of the water, however it results in the less strength of concrete. So we have to settle for an intermediate value of water cement ratio at which it may have the sufficient work-ability as well as sufficient strength.
Slump cone apparatus, cow tray
This is the standard apparatus used to determine the slump of the given fresh concrete. This is a metallic, conical shaped, of height 30 cm, 20 cm, and 10 cm as the larger and smaller diameters respectively at the far two ends. This is provided with two handles to lift it above the base.
Cow tray: This is used to mix the given materials in the given proportions (Water, Cement, Sand and coarse aggregates).
- Oil the inner side of the slump cone apparatus(so that concrete do not stick to its sides) and put it on the table/floor with the larger diameter base at bottom.
- After mixing the concrete,fill the slump cone with the freshly prepared concrete mix, compacting this in 3 layers, each layers tamped with the tamping rod giving 25 no. of blow.
- Remove the extra concrete overflowing from the top edge of the cone with the help of a strike.
- Hold the two handles of the cone in hand and then lift the cone up leaving the concrete on the base.
- After the cone support is removed, concrete will fall under its own weight. The initial height of the concrete cone was 30 cm and after the fall, you have to measure the amount of fall from its top with the help of a scale.
Calculations:Initial height of the concrete = 30 cm
Height after lifting the cone = h2.
slump = 30 - h2 (cm)
Interpretations of Results:
|Types of slumps|
- Slump of concrete is interpreted as collapse slump, shear slump and true slump.
- If it is collapse slump then the concrete is too wet, and shear slump also indicates a poor mix, concrete of true slump is of value.
- A concrete of slump value 0 to 25 mm is used in the road mixes, 10-40 mm mixes are used in the foundations with light reinforcement, and 50-90 mm used for normal concrete works compacted with vibrations, slumps .10 cm are considered of higher work-ability.