Those of us in the home building business (and many others, I’m sure) hear a phrase about concrete very commonly. It’s an old concrete adage that construction professionals worldwide are all too happy to share with you… It goes something like this: “There are two types of concrete: Concrete that’s cracked, and concrete that’s gonna crack.” But they are not wrong. It’s a guarantee, a promise, and a fact. We will get to the science, but first, why do we even use a material that is guaranteed to crack? When we build a new community in Knoxville, we have to choose which building materials to use in our homes, driveways, foundations, finishes, etc. Which one is always on the list? CONCRETE. It is one of the best construction materials the world has ever known. We use it in our foundations, our slabs, street curbs, sidewalks, and driveways. Sometimes, it even finds itself in our kitchen countertops. Some people love it, and some hate it. So what is it about concrete and new home construction that gives people these polarized opinions? It cracks. And it’s usually not anyone’s fault but the material itself. So why use it?! We use concrete for our homes here in Knoxville for the same reasons it is used worldwide:
So why does it crack? The primary reason for concrete cracking is shrinkage. As concrete dries and cures, it will literally shrink. This is a great example of how water evaporation can affect construction processes. The more water that is used in the concrete, the more shrinkage will occur as it evaporates. So there is actually a small human element to pouring concrete as well: use the correct amount of water in your concrete mixture. Luckily, this is well defined and taken care of by proper workmanship. That won’t solve all your cracking problems, although it may explain why brand new concrete can show cracks in just a short time. Shrinkage occurs when you add any amount of water to concrete, and it’s absolutely necessary to make the pour. This shrinkage creates a lot of internal tension in the concrete, and therefore – perfectly mixed and poured concrete will crack under this immense pressure. That’s where control joints come into play. Rather than just let the concrete crack on its own (because we know it will, but not how or where), we can place these control joints to actually determine where the concrete will crack. This eliminates any unsightly random cracks and actually prevents other cracks by relieving some of the tension cause by evaporation. This controlled method produces a nice, straight line through a concrete slab and lets us “control” the effects of the curing process. Other methods of preventing cracks (you can never do this completely), are reinforcement with steel, wire mesh, and some types of man-made fibers. We use a fiber reinforced concrete to reduce the likelihood of cracking. So next time you are walking to your mailbox, running on the sidewalk, or sitting on your patio, take a look at your feet. Do you see cracks? If not, you probably see control joints. And if you don’t see any cracks or control joints in your settled concrete slab… maybe there is reinforcement. And if that’s not the case, don’t worry: It’ll crack, we guarantee it.