Proper Depth of Concrete
“Proper Depth of Concrete” – By Chris O’Brien – president of Rock Tred
Concrete Cracks! We all know that but do we understand why and do we know how to make the best out of a less than perfect material?
Concrete goes through a very stressful “giving of birth” material metamorphosis as it changes from a liquid/solid to a solid/liquid finished product. Once concrete is placed and begins to cure it gains volume and then it loses volume. This characteristic is one that is displayed at every change in season, moisture and temperature. It is as though concrete is a living organism.
But is concrete ever really finished changing? Like other materials the components of concrete continue to react within the atmosphere where is resides.
Concrete should be cut at engineered intervals to direct the cracking that is certain to occur. Failure to cut these joints early enough in the concrete’s life may render these joints useless. The depth of these control or contraction joints (two terms that speak to the same process) is to be 25% of slab thickness or should be figured by dividing slab depth by 4. This depth helps to weaken the concrete plane to a level sufficient enough to allow it to break free relieving the stress that the concrete’s reduction in volume requires.