Selecting the Proper Concrete Expansion Joints

Concrete is susceptible to the laws of physics just like anything else. When a material becomes cooler and loses some of its energy, it contracts. When it again gains energy, it expands. This is the premise behind concrete expansion joints.

Concrete expansion joints are responsible for allowing concreted to expand and contract without damaging the material. These joints are actual, visible spaces between the piece of concrete and the adjacent material, usually steel or some other strong, supportive material.

There are two main types of concrete expansion joints: doweled and non-doweled. A doweled joint is just what it suggests. It is comprised of a flexible “board” or strong rod that loosely ties the piece of concrete to another piece or to a solid fixture. The board or rod is covered with a waterproof sealant to prevent deterioration. One end of the dowel is threaded and is placed in the slab when it is wet and still forming. The other slab is tapped and the dowel is inserted into it and provided with enough room to easily slide back and forth, providing support, but not limiting expansion.

Non-doweled concrete expansion joints are usually not used too often, as they do not provide the support of a doweled joint, but are used where the secondary slab cannot be tapped. A non-doweled concrete expansion joint consists of a compressible board that is inserted between the two surfaces when the formed concrete is still soft. Usually, a temporary cap board is placed above the filler board to prevent concrete from seeping into the joint. After the concrete dries, the cap board is removed and a waterproof sealant is covered over the filler board to prevent deterioration. This joint provides a area that can alleviate the pressures exerted on the slabs.