Being a Chicago Concrete Contractor I always get phone calls in the springtime about other contractors’ work. The most common question is, “Why did my new concrete crack?” With that, I regretfully tell them that the sad truth is that all concrete will crack, and usually well within the first year of placement. Why?? When concrete is curing it will shrink on average 1/16th of an inch for every 10 linear feet. This may sounds like an insignificant number, but shrinkage cracking is a common concrete flaw. Concrete is a super product under compression, but when subjected to tension it is prone to failure much more rapidly. Add to that, in colder climates such as Chicago, we have a freeze/thaw cycle to contend with.
There are ways to help avoid new concrete from cracking (in visible locations). How?? As bad as it sounds, EVERY contractor hides them in what is called a “control joint”. This is basically a grove tooled or cut into the concrete to help relieve the stress of the concrete. There are basic rules to follow when placing these control joints regarding spacing and at corners. When a contractor has been finishing concrete long enough, they know where to place these joint and maintain a pleasing appearance.
The next problem that sidewalks, patios, driveways, and other slab on grade concrete faces in Northern climates is freeze/thaw cycles. Every winter the ground freezes and heaves the ground upwards. When the sun comes out, it thaws the ground, and it does not always do it evenly. This means that a portion of the slab in the sun may thaw and start to drop while the section it is attached to is in a shadow and stuck on higher frozen ground. This stress will also cause the concrete to crack, “hopefully” at the control joints which were placed there for just that reason.
As silly as it may sound, try looking a little closer to those joints and see if you can spot the cracks. Hopefully this article will help you understand some of the behaviors of concrete a bit better and will allow you to interview your Concrete Contractor more carefully.