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Slump Cone Test for Concrete Workability
In this article “Slump Cone Test for Concrete Workability”, the workability of concrete is defined and slump test is described.
What is Concrete Workability?
The quantity of beneficial internal labor required to achieve complete compaction without encountering the aforementioned concrete difficulties. Internal useful work is the effort or energy necessary to overcome internal friction between the concrete’s individual particles.
However, more energy is necessary in reality to overcome the friction between the concrete and the structure or reinforcement.
Thus, in reality, it is hard to estimate workability as stated above; instead, we quantify workability as it relates to the specific approach used.
One of the methods to measure the workability of concrete is the slump test, which is discussed in this post.
Objective of Slump test
The term “workability” or “workable concrete” has a considerably broader and deeper meaning than the phrase “consistency,” which is sometimes used interchangeably with “workability.” Consistency is a broad concept that refers to the degree of fluidity or movement.
The following elements contribute to concrete having a greater lubricating effect, hence reducing internal friction and facilitating compaction:
(a) Water Content (b) Mix Proportions (c) Aggregate Size (d) Aggregate Shape (e) Aggregate Surface Texture (f) Aggregate Grading (g) Utilization of Admixtures.
The slump test is the most often used technique for determining the consistency of concrete. It may be performed in the laboratory or on-site. It is not good for either wet or very dry concrete. It does not account for all elements affecting workability, nor is it always reflective of the concrete’s placeability.
Additionally to the slump value, it reflects the concrete’s feature. True slump occurs when the concrete slumps uniformly. Shear slump occurs when one side of the cone falls downward. In the event of a shear slump, the slump value is calculated as the height difference between the mould’s height and the subsidence’s average value.
Apparatus of Slump test
The Slump Cone apparatus for conducting the slump test consists essentially of a metallic mould in the shape of a frustum of a cone with the following internal dimensions: Bottom diameter: 20 cm, Top diameter: 10 cm, Height: 30 cm, and the thickness of the metallic sheet used to make the mould should not be less than 1.6 mm.
The equipment consists of a Slump Cone and a Tamper (16 mm in diameter and 600 mm in length). The rod’s tamping end should be shaped to a hemispherical point), Ruler, and so on.
Procedure of Slump test
- When conducting this test in the field, a sample of mixed concrete should be acquired. When concrete contains aggregate with a maximum particle size of more than 38 mm, it should be wet sieved using a one and a half inch screen to remove aggregate particles larger than 38 mm.
- Prior to beginning the test, the inside surface of the mould should be completely cleaned and clear of excess moisture and any set concrete. The mold must be put on a flat, smooth, stiff, and non-absorbent surface, such as a thoroughly leveled metal plate, with the mold securely kept in place while filling.
- Fill the mold in 4 layers, each roughly one-quarter of the mold’s height. Twenty-five strokes of the rounded end of the tamping rod must be used to tamp each layer. Strokes should be spread uniformly over the cross-section of the mould and shall penetrate into the underlying layer for the second and subsequent layers.
- Throughout its depth, the bottom layer should be tamped. After rodding the top layer, the concrete should be knocked off level using a trowel or tamping rod to ensure that the mould is completely filled.
- After rodding the top layer, scrape the concrete’s surface using a screeding and rolling action of the tamping rod.
- Remove any mortar that has spilled out between the mold and the base plate. The mould must be promptly withdrawn from the concrete by gently and gently elevating it vertically. This enables the concrete to settle and the slump may be determined instantly by subtracting the height of the mould from the height of the highest point on the specimen being evaluated.
- The preceding processes should be performed in a vibration- and shock-free environment and within two minutes after sampling.
The vertical distance between the top of the mold and the specimen’s top surface’s displaced original center………… mm
The slump pattern is shown. Slump Types: True Slump, Shear Slump, and Collapse Slump.
The slump value must be expressed in millimetres of specimen sinking during the test. Any slump specimen that collapses or shears off laterally produces a false result, and the test must be redone with another sample if this happens. If the specimen shears again during the repeat test, the slump must be determined and the fact that the specimen sheared shall be noted.