Joints In Slabs
Joints are necessary in large ground bearing concrete floor slabs in order to control cracking caused by shrinkage. Joints are often installed to force cracks to form along straight, pre-formed grooves rather than randomly across the slab and hence achieve a satisfactory appearance.
The spacing and type of joint selected depends on many factors, principally the slab thickness, the concrete mix design, the length/plan area of the slab, the method of construction and details such as edge thickenings which generate additional restraint forces and hence additional tension within the concrete.
Seek advice where and when to install joints from your engineer.