The various joints provided in the building are mainly classified into four main types.
- Expansion Joints.
- Contraction Joints.
- Construction joints
- Sliding Joints.
Isolation Joints :
The joints provided to accommodate the expansion of adjacent parts in a building are known as expansion joints.
Isolation joints ( Expansion Joints) allow movement to occur between a concrete slab and adjoining columns and walls of a building. Isolation joints are provided to separate new concrete from existing or adjacent construction, which might expand and contract differently or experience different soil settlement or other movement.
If the fresh concrete were not separated from these elements by an isolation joint, a crack could form where the two meet.
Isolation joints should be 1/4 in. to 1/2 in. wide, and filled with a molded fiber, cork, or rubber strip that is set 1/4 in. below the surface.
Contraction joints :
Contraction joints (also referred to as control joints) are the joints introduced in concrete structures to minimize shrinkage to a particular place are known as contraction joints.
Contraction joints are in the form of separations or planes of weakness so that cracking that may result from tensile stresses, occurs along predetermined locations.
Without them, drying shrinkage would result in random cracking
Normally control joints are provided:
At 2 times the slab thickness( in feet) for a maximum aggregate size of less than ¾”.
For example for a 5” slab with a ¾” coarse aggregate the maximum joint spacing would be 10′.
When the maximum coarse aggregate size is greater than ¾”, the spacing could be increased to 2 ½” times the thickness.
For the prior example this would increase to 13’.
Whenever required to convert an irregular slab shape into rectangular or square.
Reference : Building construction by N.L.Arora and B.R.Gupta