At the time of mixing any type of concrete, it is essential to measure first the consistency of the mix using the concrete slump testing procedure.
Always check the fluidity of the concrete mix before laying it into a structure, as it ensures that the concrete is workable and will set properly.
How To Perform A Slump Test
The most popular method of performing concrete slump testing is by filling a metal cone, also known as an Abrams cone, with concrete mix.
Then, the cone is carefully removed to measure how much of the concrete stays in its place.
A concrete slump is the measure of the difference between the height of mold and the highest point of a specimen.
If the concrete mix contains excess water, it will eventually slump sideways. This type of concrete mix is not suitable, and it indicates that the concrete is weaker and has more chances of cracking when the mixture is too watery.
Similarly, if the mix is too dry, it will not slump and will require more water.
Typically there are four categories of concrete slumps. However, to create a workable mix, builders try to make a true slump.
A true slump is where the top of the concrete mass will slump evenly in all directions; however, the bulk of the mass continues to stay in one place.
If the test does not show relevant results, remix the concrete. The following are some other types of results:
- Shear slump – If the test shows a shear slump, only one side of the concrete mass continues to stay in place. The other side drops and is known as a shear slump.
- Collapse slump – A collapse slump is when the concrete mass collapses entirely during the test. This indicates that there is too much water in the concrete mix.
- Zero slump – Zero slumps result from extremely dry concrete and will show no slump at all.
Different Concrete Slump Measurements For Various Projects
Another type of project typically requires different amounts of concrete slump. For instance, the concrete used for making roads is primarily dry and has shallow levels of workability, hence why it mainly involves the use of power tools and machines. For such projects, the slump measures around 1 inch.
Other applications for concrete, like paving, the making of slabs, and driveways, require more workability, meaning the concrete slump should be slightly higher.
For example, when constructing driveways, the concrete slump should be at least 5 inches.
The following is a list of the maximum and minimum allowable slump range for different applications.
| Type Of Construction | Maximum Allowable Slump | Minimum Allowable Slump |
| Plain footing, substructure wall, caissons | 3 inches | 1 inch |
| Reinforced footing | 3 inches | 1 inch |
| Building columns | 4 inches | 1 inch |
| Slab, beam, reinforced wall | 4 inches | 1 inch |
Slump Measurement At The Project Site
Usually, contractors do not conduct any formal concrete slump testing at the job site.
Nevertheless, the use of the slump test is essential for all types of applications. Contractors must understand the need for slump tests and how it affects the overall finish and structural integrity of a concrete structure.
Beginners in the business should always perform slump tests before laying a concrete structure. Changing the slump value with the addition of excess water changes the complete intensity and color of the mix.
At times, it is observed that using excess amounts of water makes the concrete permeable. Such a mix is also not suitable for harsh weather conditions.
Some builders adjust the slump with chemicals instead of water. Using water does not affect the structural integrity of the mixture.
High-range water reducers, popularly known as superplasticizers, help increase the fluidity of concrete mix and improve its workability. They allow for a more even dispersing of the cement mix by lowering the amount of water in the mixture by a specified percentage.
It helps in making for a more durable product, but the effectiveness maintains only for a short period.
Use Of Admixtures
There are a wide variety of admixtures available in the market. Some of these products can be directly tossed into the cement mixing truck at the job site.
These agents help in restoring the consistency of the concrete mixture and make it suitable for various applications. Admixtures also help in improving the workability of the concrete mix.
Concrete slump testing has a significant effect on the workability of concrete, its transportation placement, and its application.
It is also considered as an indicator of reliability from batch to batch. Therefore, this is one of the most critical factors that builders and contractors need to consider while working with concrete.
For instance, the construction of concrete flooring requires a tight slump to obtain flat floors. A truckload of concrete with high slump can help with achieving the desired strength and finish.
Slump and the placement of structures
Slump also plays an important role in the placement of structural units like walls and columns.
It is entirely dependent on the contractor’s preferences to control the slump and other properties of a concrete mix. While working with concrete, attaining the right amount of slump is vital to fulfil the intended purpose.
Testing around air content and compressive strength are also necessary to keep an eye on the durability and strength of concrete.
