Though concrete has a tendency to crack and does crack in most cases, cracks can be controlled by joints, or planned separations in concrete. Cast-in place concrete walls use three types of joints:
- Contraction joints are weakened planes built into walls to control the location of cracking caused by volume changes, especially those related to shrinkage and temperature changes.
- Expansion joints are separations between adjoining parts of a structure to allow movement. Expansion joints also work as contraction joints and may have smooth dowels to maintain the plane of the wall. Expansion joints that allow completely independent movement between adjoining components are sometimes called isolation joints.
- Construction joints separate adjacent placements of concrete to make large pours manageable. Construction joints are commonly located to coincide with contraction or expansion joints.
