Concrete Slump Test
A slump test is a method used to determine the consistency of concrete. The consistency, or stiffness, indicates how much water has been used in the mix. The stiffness of the concrete mix should be matched to the requirements for the finished product quality
Concrete Slump Test
The concrete slump test is used for the measurement of a property of fresh concrete. The test is an empirical test that measures the workability of fresh concrete. More specifically, it measures consistency between batches. The test is popular due to the simplicity of apparatus used and simple procedure.
The slump test result is a measure of the behavior of a compacted inverted cone of concrete under the action of gravity. It measures the consistency or the wetness of concrete.
Procedure of Concrete Slump test:
In order to reduce the influence on slump of the variation in the surface friction, the inside of the mould and its base should be moistened at the beginning of every test, and prior to lifting of the mould the area immediately around the base of the cone should be cleaned from concrete which may have dropped accidentally.
Types Of Slump
The slumped concrete takes various shapes, and according to the profile of slumped concrete, the slump is termed as;
In a collapse slump the concrete collapses completely. A collapse slump will generally mean that the mix is too wet or that it is a high workability mix, for which slump test is not appropriate.
In a shear slump the top portion of the concrete shears off and slips sideways. OR
If one-half of the cone slides down an inclined plane, the slump is said to be a shear slump.
In a true slump the concrete simply subsides, keeping more or less to shape
However , in a lean mix with a tendency to harshness, a true slump can easily change to the shear slump type or even to collapse, and widely different values of slump can be obtained in different samples from the same mix; thus, the slump test is unreliable for lean mixes.
Applications of Slump Test
Table : Workability, Slump and Compacting Factor of concrete with 19 or 38 mm (3/4 or 11/2 in) maximum size of aggregate.
Difference in Standards
The slump test is referred to in several testing and building code, with minor differences in the details of performing the test.
In the United States, engineers use the ASTM standards and AASHTO specifications when referring to the concrete slump test. The American standards explicitly state that the slump cone should have a height of 12-in, a bottom diameter of 8-in and an upper diameter of 4-in. The ASTM standards also state in the procedure that when the cone is removed, it should be lifted up vertically, without any rotational movement at allThe concrete slump test is known as "Standard Test Method for Slump of Hydraulic-Cement Concrete" and carries the code (ASTM C 143) or (AASHTO T 119).
In the United Kingdom, the Standards specify a slump cone height of 300-mm, a bottom diameter of 200-mm and a top diameter of 100-mm. The British Standards do not explicitly specify that the cone should only be lifted vertically. The slump test in the British standards was first (BS 1881-102) and is now replaced by the European Standard (BS EN 12350-2)
Ques : 1
What is the ideal value of slump?
In case of a dry sample, slump will be in the range of 25-50 mm that is 1-2 inches. But in case of a wet concrete, the slump may vary from 150-175 mm or say 6-7 inches. So the value of slump is specifically mentioned along the mix design and thus it should be checked as per your location.
Slump depends on many factors like properties of concrete ingredients - aggregates etc. Also temperature has its effect on slump value. So all these parameters should be kept in mind when deciding the ideal slump
How does a super plasticizer effect the slump of concrete?
Value of Slump can be increased by the addition of chemical admixtures like mid-range or high-range water reducing agents (super-plasticizers) without changing the water/cement ratio.
How much time one should take to raise the cone?
Once the cone is filled and topped off [ excessive concrete from top is cleared ] raise the cone within 5-10 seconds.
What are the dimensions of the cone used in Slump Test?
The dimensions are:
Top Diameter - 10cm