Contraction Joint (Control Joint)

A contraction (control) joint is a deliberately created plane of weakness — usually a sawn or tooled groove cutting one-quarter to one-third of the slab depth — that forces the inevitable drying-shrinkage and thermal-contraction cracking to occur along a straight, sealed, maintainable line instead of randomly across the surface. The reinforcement may be continuous or discontinued depending on whether movement or only crack control is intended.

In rigid (concrete) pavements, IRC 15 specifies transverse contraction joints typically at 4.5 m spacing with dowel bars for load transfer, and longitudinal joints with tie bars. In buildings, ground-bearing floor slabs use contraction joints at roughly 24-36 times the slab thickness or 4.5-6 m grids. The groove is later cleaned and filled with an elastomeric sealant to keep water and grit out. Liquid-retaining structures follow IS 3370's more stringent joint + water-stop rules.