Are you new to pouring concrete and you’ve heard about the slump test and don’t know quite what it is? Or do you have a concrete project that demands high quality?
For both of those questions, this article will try to answer to the best of my ability so you can have an easier time getting the results that you want. I’ve written before about concrete density and the concrete slump has everything to do with that.
That being said, what is the concrete slump meaning? The slump test measures the concrete density and how flowing it is. So to test that, we have to come up with some way to measure those qualities.
This should be basic qualities needed from the concrete slump explained. Let us move on to see how exactly it’s done and what the results will tell us.
Concrete slump guide
A concrete slump is measured with a cone that resembles a small traffic cone but is made with metal and usually attached to a movable platform tightly so it won’t move while it’s being filled.
It also has the top off so it can be filled from there. And there are handles on the sides so it can be lifted after it has been filled with concrete and some of them have some sort of measuring stick on the side to make it easier to measure the slump.
What is slump cone test
So you fill the cone attached to a platform with concrete and then what? Sounds pretty uninteresting I can imagine.
After the cone is removed by lifting it upwards, the gravity will pull the concrete downwards, right? The slump test is how much the concrete will give in at this point, how many inches will it go down.
Now, what does a concrete slump test tell you at this point? It tells you how much flow the concrete has like stated at the beginning and from that you can also make an educated guess about the density.
It’s one of the go-to tests done at construction sides where measuring on the spot is needed. Why is that? Slump cone test equipment, as you can see, is dead simple to use and it will give you fast directions about the quality of concrete you’re working with.
How to test concrete slump
So you have the basic idea now about what is slump cone test for concrete. Now you’re asked to do it at the site so how to do the slump cone test? Do you just pour the concrete in and lift the cone or what?
Step 1: Start by putting the cone where it’s not on the way, but not far from the place where you’re supposed to be doing pouring.
Step 2: Put some moisture inside the cone by spraying it with water or some other method. It’s for making it easy to remove the cone. If you shake it when you lift it, it will naturally cause the concrete to slump because of the vibration so you want to be able to lift it up smoothly to get proper results.
Step 3: To have the concrete in the cone without much air, you fill it in multiple parts. You can do something like ¼ or 1/3 and in between filling, tamp the concrete with something so it’s there as settled as possible.
Step 4: Now it’s filled to the top and you’ve made the top concrete level with the cone. It’s time to lift it up. Carefully lift the cone upwards and put it aside.
Step 5: Measure how much the concrete gave in by using the possible helping tool in the cone platform. If there is none, place the cone next to the slump, use a straight piece of wood or something else on top of it, and the slump.
You can measure down from the wood towards the slump to see how much it sunk.
Slump flow test
You can also run into a slump flow test during your career or hobbies. It’s a different test for concrete that is flowing enough that it can be done with the cone and steel plate.
The concrete is poured into a cone without compaction. After that, the top of the cone is leveled again the cone is lifted. This time, we know it’s going to spread on the plate.
We wait until the concrete slump has spread on the plate and then we measure how wide it is in diameter in 2 perpendicular directions.
How to judge concrete slump
What is the normal slump of concrete? There must be some standards now that we know there is a way to measure.
Concrete slump chart
A concrete slump chart is something that tells you what the qualities of the concrete are by the slump measured. I’ve seen many during the years by manufacturers and some by guidebooks.
Usually, the lower the concrete slump numbers are, the less it’s workable. You can imagine it by the concrete having less water in it or it has started to cure so it will be rougher and more effort has to be used to get it in the forms without leaving voids in it.
So the higher the concrete slump numbers are, the easier it is to pour. The concrete slump range is usually between 1 inch and 7 inches. 1 inch could be something that is used to build roads with, 2 inches could be for foundations, 3-4 inches for reinforced walls, etc.
Don’t take these values to heart as stated before, different manufacturers can provide slightly different info. It’s good to always check local standards when you build with concrete so you won’t have trouble with authorities. Or with the building itself.
Now you should know what is slump of concrete about. If you’re running your own project or work where concrete is poured, you should be able to do DIY slabs with these instructions.
These are something that are also reported and written down. Sometimes, it might even cause trouble if the slump is higher than lower than needed.
If you’re curious about concrete slump vs strength, the higher the slump value is the more water there is on the mix. This means weaker strength for the concrete and that’s why lower slumps are used for things like foundations.
So what is the ideal value of slump will depend on the use. If you want foundations, it is lower and for walls, it can be a little higher. This is why we need to refer to a proper table that should be provided by manufacturers.