Working with concrete can be tricky if you aren’t sure what you’re doing. One of the most important things is to make sure that the consistency of the concrete is spot on. If it’s too wet then there’s a risk of cracking but if it’s not wet enough then it’ll be a nightmare to pour. And that’s where concrete slump tests come in.
Concrete slump refers to the consistency of the material and this affects how workable it is. Performing a concrete slump test is important as it’ll tell you a lot about how the concrete will be once it hardens.
In this guide, I’ll be explaining a bit more about concrete slump, why it’s important and how to test your concrete before it hardens.
Table of Contents
What Is Concrete Slump
When you hear the term concrete slump, this is referring to how workable the material is. In other words, its consistency or fluidity.
When concrete has a low slump, this means that it’s not very fluid and won’t be as easy to work with. On the other hand, concrete mix with a high slump is much more fluid in its consistency. But there is a sweet spot.
Finding this sweet spot means altering the mixture but in order to get an understanding of where things currently are, you’ll need to perform a concrete slump test.
What Is A Concrete Slump Test?
Before you can use fresh concrete, you need to make sure that it meets the expected standard otherwise it won’t perform as you would have hoped. This means doing a concrete slump test which will tell you everything you need to know about the consistency of the material.
This test measures the consistency of any given batch of concrete which tells you how well (or not) it will pour and flow. What’s great about doing this test is that you will be able to ensure consistency between batches as well as ironing out any issues before using the mix.
The test will tell you whether the concrete mix has too much water or cement which gives you a very clear idea of how workable the material will be.
How To Do A Concrete Slump Test
You might think that doing a concrete slump test isn’t really all that necessary. However, I cannot stress how important it is and if you were worried that it was going to eat into your project time, then think again. This is a quick and easy test that requires minimal equipment.
You’ll need:
- A slump cone
- A measuring stick
- A steel rod
- Some concrete mix
Once you’ve got everything together, you can follow these easy steps.
- Take your slump cone and put it onto a smooth, even surface. Place footholds on both sides to make sure that the cone doesn’t move.
- Start filling the cone, layer by layer. You’ll want to add three in total and make sure that you use your steel rod between layers to tamp them before adding the next one.
- When you have filled the cone, get rid of any excess concrete mix that’s on the top and ensure that the top is completely level.
- Now, lift the slump cone up making sure to go slowly and steadily. Put the cone down, upturned, next to the concrete.
- You’ll notice that the concrete will begin to slump; how much this happens will depend on the consistency but that’s where your measurements come in.
- Take your steel rod and place it over the top of the upside down cone so that the ends are over the concrete. You can now measure the distance between the top of the concrete and the rod to the closest 5 mm.
Why Do I Need To Do A Concrete Slump Test?
If you are going to be mixing multiple batches of concrete then you’ll want to make sure that they’re all the same consistency.
When you add water to the concrete, this will weaken it so adding more cement ensures that the strength of the mix isn’t affected. Using a concrete slump test will ensure that your mix is always strong but has the level of workability required.
The Concrete Slump Test Results
So, you’ve performed your concrete slump test and taken your measurement; now what? Well, this measurement will tell you everything you need to know about the consistency of the mix and you’ll end up with one of the results below.
Zero Slump
This is when the cone is removed and the concrete retains that cone-like shape without moving. This tells you that the mixture is too dry and will not be workable.
True Slump
When performing a slump test, you’ll be aiming for true slump which is when the concrete mix will keep its shape but subside slightly near the top of the cone.
Shear Slump
If you see that the concrete mixture has slumped significantly down one side of the cone then this tells you that there is too much water.
Collapse
Should your concrete mixture collapse entirely then you’ll need to remix it as the water content is far too high.
Final Thoughts
Getting your consistency right when working with concrete is super important as this determines how workable the material will be. You may hear the term concrete slump which refers to how fluid the mix is and therefore, how easy it will be to pour.
While you could trust your judgement in what you see from the mix, it’s always better to perform a concrete slump test which is a quick, simple and reliable way to tell the consistency and whether you need to make adjustments to the mix.
