What Is Slump Cone Test?
A concrete Slump test is performed from batch to batch to check the uniform quality of the concrete during construction.
The Slump test is the simplest test of workability 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 performed according to the procedures mentioned in the ASTM C143 standard in the United States, IS 1199 – 1959 in India, and EN 12350-2 in Europe.
Generally, the value of the concrete loss is used to find workability, which indicates the water-cement ratio, but there are several factors, including material properties, mixing methods, dosing, additives, etc. also affect the amount of concrete loss.
Principle of Slump Test
The result of the Slump test is a measure of the behavior of a compacted inverted concrete cone under the action of gravity.
It measures the consistency or moisture of the concrete, which gives an idea of the workability of the concrete mixture.
Slump Test Apparatus
- Slump Cone
- Scale for Measurement
- Temping Rod (steel)
Temping Rod (steel)
The Concrete Slump Test Procedure:
- The mold for the concrete Slump test is a 300 mm high cone-shaped trunk. The base is 200 mm (8 in) in diameter and has a smaller opening at the top of 100 mm (4 in).
- The base is placed on a smooth surface, and the container is filled with concrete in three layers, whose workability must be tested.
- Each layer is tempered 25 times with a standard 16 mm (5/8 in) diameter steel rod, rounded at the end.
- When the mold is completely filled with concrete, the upper surface is reached (flush with the upper opening of the mold) through the sieving and rolling motion of the quenching rod.
- The mold must be held firmly against its base during the entire operation so that it cannot move due to concrete leakage, and this can be done through handles or footrests welded to the mold.
- Immediately after completing the filling and leveling the concrete, the cone is slowly and carefully lifted vertically. An unsupported concrete will now Slump.
- The decrease in the height of the center of the Slumped concrete is called a Slump.
- The Slump is measured by placing the cone just beside the Slumped concrete, and the quenching rod is placed over the cone so that it also exceeds the area of the Slumped
- The decrease in the height of the concrete in relation to that of the mold is observed in (usually measured up to the nearest 5 mm (1/4 inch).
Precautions in the Slump Test
Concrete Slump Test To reduce the influence of Slumping variation in surface friction, the interior of the mold and its base must be moistened at the beginning of each test and, before lifting the mold, the area immediately around the base The cone must be cleaned of concrete that may have Slumped accidentally.
Types of Concrete Slump
Slumped concrete takes various forms and, according to the profile of Slump concrete, the Slump is termed as;
- True Slump
- Shear Slump
- Collapse Slump
In a real Slump, the concrete simply disappears, maintaining more or less the shape. This is the only Slump that is used in several tests.
Mixtures of rigid consistency show a Zero Slump, so that, in the very dry range, no variation can be detected between mixtures of different workability.
However, in a lean mixture with a tendency to roughness, a real Slump can easily change to the type of shear Slump or even collapse, and widely different Slump values can be obtained from different samples of the same mixture; therefore, the Slump test is not reliable for lean mixtures.
In a collapse Slump, the concrete Slumps completely. A collapse Slump generally means that the mixture is too moist or is a highly workable mixture, for which the Slump test is not appropriate.
This means that the water-cement ratio is very high, that is, the concrete mixture is very wet or is a highly workable mixture, for which a Slump test is not appropriate.
In a sheer Slump, the top of the concrete cuts and slides to the side. OR
If half of the cone slides downward on an inclined plane, the Slump is considered a sheer Slump.
The sheer Slump indicates that the result is incomplete, and the concrete needs to be tested again to obtain valid results.
If a shear Slump or collapse is achieved, a new sample must be collected, and the test is repeated.
If the shear Slump persists, as can happen with aggressive mixtures, this is an indication of a lack of cohesion of the mix.
Applications of Slump Test:
The Slump test is used to ensure uniformity for different batches of similar concrete under field conditions and to verify the effects of plasticizers on their introduction.
This test is very useful on the spot, as checking the variation from day to day or hourly in the materials being fed into the mixer.
An increase in a Slump may mean, for example, that the moisture content of the aggregate has increased unexpectedly.
Another cause would be a change in the classification of the aggregate, such as a sand deficiency.
A very high or very low Slump 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 widespread use.