SLUMP TEST METHOD
Slump Cone slump test or concrete The slump test is to determine the workability or consistency of the concrete mixture prepared in the laboratory or on the construction site during the work.To check the uniform quality of the concrete during construction, a concrete slump test is performed from batch to batch.
The slump test is the simplest workability test of concrete, involves low costs and provides immediate results. Thanks to this fact, it has been widely used for workability tests since 1922.In general, the concrete shrinkage value, which indicates the water-cement ratio, is used to determine workability, but several factors also affect the amount of concrete shrinkage, including material properties, mixing method, dosage, additives, etc.
The result of the slump test is a measure of the behavior of the compacted inverted concrete cone under the action of gravity. It measures the consistency or moisture content of the concrete, which gives an idea of the workability of the concrete mix.
Concrete slump test procedure:
The mold for the concrete slump test is a 300 mm high cone-shaped log. The base is 200 mm (8 in) in diameter and has a smaller opening at the top of 100 mm (4 in).The substrate is placed on a smooth surface and the container is filled with concrete in three layers, the workability of which must be tested.Each layer is tempered 25 times using a standard 16 mm (5/8 inch) diameter steel bar that is rounded at the end.
When the mold is completely filled with concrete, the top surface (flush with the top opening of the mold) is achieved by screening and rolling the tempering rod.The form must be held firmly to the base throughout the operation so that it cannot move due to the flow of concrete, by means of handles or feet welded to the form.
As soon as the filling and leveling of the concrete is complete, the cone is slowly and carefully raised vertically. The unsupported concrete will now sag.The drop in the height of the center of the slumped concrete is called slump.
The slump is measured by placing the cone just next to the slumped concrete and placing the fire rod above the cone so that it also extends over the slumped concrete area.The drop in concrete height relative to form height is observed in (usually measured to the nearest 5 mm (1/4 inch).
Measures in the drop test Concrete slump test To reduce the influence of slump fluctuations in surface friction, the inside of the form and its base must be wetted at the start of each test and the area immediately around the base must be de-coned before lifting the form. concrete that could accidentally slide off.
Types of concrete slumps
Landslide concrete comes in various forms and according to the profile of the concrete land slide is called as; A real downer Shear drop Collapse slump
1. The real slump In a true slump, the concrete simply disappears and more or less retains its shape. This is the only sink used in several tests. Solid consistency mixes show zero slip, so in a very dry area no differences can be detected between mixes with different workability. However, in a lean mixture with a tendency to roughness, a true slump can easily change to a slump type of slump or even collapse, and very different slump values can be obtained from different samples of the same mixture; therefore, the Slump test is not reliable for lean mixtures.
2. Slump Collapse In collapse collapse, the concrete collapses completely. Collapse Collapse generally means that the mix is too wet or it is a highly workable mix for which the slump test is not suitable.This means that the water-cement ratio is very high, it means that the concrete mix is very wet or it is a highly workable mix for which the slump test is not suitable.
3. Shear drop In a complete slump, the upper part of the concrete is cut and slides to the side. Or If half of the cone slides down the inclined plane, the slump is considered a complete slump. A complete slump means that the result is incomplete and the concrete must be retested to obtain valid results. If shear failure or collapse is achieved, a new sample must be taken and the test repeated.
If the shear drop persists, as can happen with aggressive mixes, this is a sign of insufficient mix cohesion. The casting test is used to ensure uniformity for different batches of similar concrete under field conditions and to verify the effects of plasticizers on their setting. This test is very useful on site as it checks for day-to-day or hourly changes in materials fed to the mixer. For example, an increase in slump may mean that the moisture content of the aggregate has unexpectedly increased.
Another cause would be a change in aggregate classification, e.g. lack of sand. A very high or very low drop gives an immediate warning and allows the mixer operator to resolve the situation. This application of Slump tests, as well as its simplicity, is responsible for its wide use.
SR.NO CONCRETE MIXTURE RANGE OF RANGE IN MM
1 beams and slabs 50-100 mm
2 columns, retaining walls 75-150mm
3 CC Pavers 20-30mm
4 bridge slabs 30-75mm
5 Vibrated concrete 12-25mm
6 Huge mass structures 25-50mm
Drop test values
DROP IN WORKABILITY FACTOR COMPACTION (MM)
Very low 0.78 0-25
Low 0.85 25-50
Medium 0.92 50 – 100
High 0.95 100 – 175
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