What is a contraction joint?
Contraction joints are joints placed in concrete at regular intervals so that concrete cracks where contraction joints are located instead of at random locations throughout the concrete.
More in depth definition of a Contraction Joint
Contraction joints are used because slabs naturally have dimensional changes over time. When people refer to a “joint” in concrete they are generally referring to a contraction joint, which is the most common joint in concrete. Contraction joints can be created either during the forming process or after the concrete has been set using a concrete saw. Contraction joints are normally 25%-33% of the depth of a slab and as a general rule contraction joints are placed no farther apart than 2 to 3 times (in feet) the total width of the concrete slab (in inches).
Example of a Contraction Joint Being Used
The lines you see in sidewalks are examples of contraction joints. They are generally spaced four to eight feet apart and have a minimum depth of ¼ inch. Sidewalk contraction joints are most commonly created during the forming process by creating a grooved line with a concrete trowel, but in some cases, the contraction joint may be created using a concrete saw.
