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Slump: The Key To Proper Concrete Installation

Concrete tends to strike people as a tough and highly durable substance; and it is, so long as has been correctly installed. Amateurs often take for granted what a subtle art this can be. Yet there is a myriad of factors that will keep a concrete surface from behaving the way it should both during the installation process, and later during its life as fully cured pavement.  
Nobody expects you to be able to install a concrete slab perfectly yourself. By educating yourself about how the process works, you will be better able to hire a concrete installation company who really knows what they are doing. To that end, this article will arm you with vital information about one of the key aspects of installing concrete: slump.


Before delving into the specifics of that mysterious term, "slump," it will help to understand a bit more about how concrete behaves. The term workability denotes three aspects of fresh concrete's behavior. For one thing, workability refers to the degree of fluidity displayed by the concrete when it comes to things like pouring, handling, and screening.
Workability also communicates key information about the concrete's ability to resist the phenomenon known as segregation. Segregation is the process by which the key ingredients of concrete--water, gravel, and cement--separate from one another during the curing process. Lastly, workability conveys information about how the concrete will behave when it comes time for compaction.
To be deemed workable, a particular mix of concrete must be able to fall within acceptable limits for each of these categories. While this is an easy enough idea to grasp, it is notoriously difficult to quantify in a way that satisfies all three criteria. That's where the concrete's slump value comes into play.

Slump Value

Slump is an ingeniously simple concept, yet one of the most useful when discussing concrete. As you can likely guess from the term itself, slump refers to how readily the concrete will deform or "slump" under its own weight. Each particular concrete mix will possess its own slump value, which designates the ideal slump behavior.
When mixing up a batch of concrete, all an installer has to do is test the slump and see whether it falls within an acceptable range, given the slump value of the mix. To measure slump, a concrete worker needs a special type of mold that resembles a cone. Four layers of concrete are placed in the mold, with the worker tamping down each layer before adding the subsequent one.
With all four layers packed into place, the mold is flipped over and lifted cleanly away. A worker then measures the height of the cone. This value is then compared to the height of the mold itself; the difference between these two values designates the slump.

Slump Loss

Here's where slump starts to get a little more complicated. You see, slump is not a static value. On the contrary, the slump of concrete will steadily change as more and more time passes. This is due to the natural process of evaporation, which will yield progressively stiffer concrete. In other words, the slump value will go down.
Another way to state this is that the concrete will become less workable the longer it sits. This has the result of making the concrete more difficult to apply. It may also result in a less strong product once the concrete has finished curing. You can controll slump loss through proper storage in a manner that will prevent excessive evaporation and by selectively adding small amounts of additional water to the mixture.

Concrete Installation

Now that you understand the basic concepts of concrete slump, you can start to see what a subtle art concrete installation really is. The best results can only be achieved a professional with years of relevant experience. For more information about what it will take to make your next concrete project a success, feel free to contact the experts at B M H Concrete Inc.