We often need to carry out concrete slump test in construction sites. After mixing the concrete and before pouring, we need to run the slump test. Normally, we run one test for every twenty cubic meters of concrete.
Due to its simplicity, it is the most popular test in the concrete construction world.
In this post, I’ll share everything which you need to know about
Why Do We Carry Out Concrete Slump Test?
The question is, why do we need to run
We carry out concrete slump test for the following reasons –
- To check the workability of freshly made concrete: The workability is a thing which
tellus how the concrete is convenient to handle during pouring, vibrating, and finishing without segregation.
It is often said that adding more water increases the workability of concrete. But it isn’t always true.
Adding more water to concrete can cause
Segregation is a thing which separates concrete ingredients. And thus it can
So, to know the proper workability of concrete without segregation, the concrete slump test is carried out.
- To know the consistency of fresh concrete before it sets: Consistency means the degree of wetness of concrete. It indicates the flowability of concrete. By carrying out the slump test you can measure the consistency of concrete.
- To know the mixing condition of a batch: Slump test can also indicate the improperly mixed batch.
- To know the uniformity of different loads: By slump test, you can know the uniformity of different loads of concrete under field conditions.
- To make sure
correctamount of water is added: You can make sure (indirectly) the correct amount of water is added to the concrete mix.
Required Tools for Concrete Slump Test
You’ll need the following tools for carrying out concrete slump test –
- Base plate
- Temping rod
- Measuring scale
- Concrete pan
Slump Cone: Slump cone is a simple apparatus which has an internal diameter of 10 centimeters (4 in) at top and 20 centimeters (8 in) at bottom with a height of 30 centimeters (12 in).
Base plate: It is a steel plate which the slump cone is set on.
Temping Rod: To consolidate the concrete within slump cone, this tool is used. It’s a 16mm dia and 24 inches long steel bar.
Measuring scale: To take the measurement of slump this scale is used. You can also take the measurement with a steel measuring tape.
Trowel: To pour the concrete into the slump cone this tool is used.
Concrete Pan: To carry the concrete for testing this pan is used.
Okay. We now know about the tools we require to carry out concrete slump test. Now let’s see what steps involved in the concrete slump test.
Procedure Of Concrete Slump Test
The procedure of concrete slump test is really simple and anyone can do it. Just follow the following simple process.
#1. Clean the inside of slump cone thoroughly and apply a light coat of oil on the inside surface. So that concrete doesn’t stick with the cone.
#2. Place the base plate on a farm and truly horizontal place and set the slump cone on it.
#3. Bring some sample concrete with a concreting pan and fill one-third portion of the slump cone with concrete with the help of a trowel and tamp the concrete 25 times by the tamping rod.
#4. Again, fill the second-third portion of the slump cone with the concrete and tamp 25 times with the tamping rod.
#5. Do the same for third portion too.
#6. Once slump cone is fully filled with concrete, remove the excess concrete from the top of slump cone and level the top surface.
#7. Now remove the cone vertically. Be careful while removing slump cone. So that it doesn’t hamper the fresh concrete.
#8. After removing the cone, place that beside subsided concrete. And take a measurement of the distance between the top of slump cone and the top of subsided concrete.
#9. The distance is the slump of concrete.
The problem is, you only take slump measurement if the concrete forms a true shape after removing the slump cone. But it doesn’t always happen. You can get
That means, you can get different results of concrete slump test. So, let’s discuss how many types of results you can get after removing the slump cone.
Types Of Concrete Slump Test Result
Based on the resulted shape of concrete after removing the slump cone, we get four types of slumps –
- Zero slump
- Shear slump
- Collapse slump
- True slump
- Zero Slump: If the slump value is less than one-fourth niche, that is called Zero Slump. When the concrete is prepared with less water, this type of slump result you’ll get.
The zero slump concrete isn’t used in the building construction. It may be used in some road constructions. To tell the truth, I’ve never used zero slump concrete in my professional career.
- Shear slump: If the top portion of concrete shears off and slips sideways after removing the slump cone, that is called Shear slump. Shear slump indicates that the concrete slump test isn’t carried out properly. You should retest the concrete.
- Collapse slump: When the concrete collapses completely after removing the slump cone, that is called Collapse slump. If the collapse slump happens, you can know that the mix is too wet and slump cone test isn’t appropriate for this type of concrete mix.
- True slump: If the concrete is simply subsided and form a more or less to shape after removing the slump cone, that is called True slump. Only the True slump is of any use in the slump test.
You’ll get different values of True slump from the test. The slump value is normally measured in millimeter and it’s shown as the result of the slump test. Let’s discuss the different values of slump result.
Results Of Concrete Slump Test
0 to 25 millimeter: When the mix is very dry, you’ll get the result within this range. This mix is normally used in road construction.
25 to 50 millimeter: This result range indicates that the mix is low workability. This mix of concrete is used for foundations with light reinforcement.
50 to 100 millimeter: This mix indicates medium workable concrete mix and used in structure with normal reinforcement.
100+ millimeter: If you get slump value above 100
Factors Affecting Concrete Slump Test
There are some factors which affect the concrete slump test. Such as –
- Properties of concrete ingredients
- Concrete batching, mixing and transporting
- The amount of water in concrete mix
- Weather condition
- Admixture using in concrete
- Time span between mixing and testing
- Testing process
Limitations Of Concrete Slump Test
Despite the most popular test in the construction world, the concrete slump test has some limitations. Such as –
- This test is only suitable for the slump value of 25 to 125 millimeter.
- The test fails to determine the difference in workability of stiff mixes which have Zero Slump.
- It isn’t also suitable for very wet mixes which can give collapse slump.
- This test is limited to concrete which coarse aggregate size is 38-millimeter downgrades.
The concrete slump test is really suitable for the building construction sector. Because, the limitations, I’ve stated above, can be easily overcome. And, as it is a simple test, you can easily carry out the test in your building project.
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