|Waterstops are used to fluid-proof concrete joints. (Pictured is Earth Shield® PVC Waterstop part no. PVC638.)
Contraction joints are used to divide large pours of concrete into smaller structural units. Contraction joints create a man-made plane of weakness to regulate and control (another name for a contraction joint is a control joint) the location of a crack formed by moisture loss of concrete. Without this formed contraction joint, the concrete would freely crack in unexpected and unattractive places.
An interruption of the concrete pour 30 minutes or greater creates a construction joint.
Expansion joints are designed to negate the compressive forces from abutting concrete structures that may occur as a result of expansion, loads, or differential movements from the settlement. Expansion joints require an actual gap between the concrete pours, and a compressible joint filler material such as foam, rubber, cork, or cane fiberboard.