Why does concrete crack? Why are joints necessary?
There are two types of concrete: concrete that is cracked and concrete that has the potential to crack. When exposed to wetting and drying conditions concrete will expand and contract (similar to a sponge). If the stress associated with these volume changes exceeds the tensile capacity of the concrete, a crack will form. This specific type of crack is referred to as a shrinkage crack. Cracks are expected to form in concrete and act as a “pressure release valve”. By intentionally jointing concrete, you decrease the thickness of the slab in that location. This allows a crack to form along a straight line within the joint since the thin section provides a path with less resistance than a thicker section.
