Sawcut joints minimize random cracking due to drying shrinkage and temperature changes. The weakened sections created by the joint cause the cracks to form at these locations. Cracking occurs beneath the sawed slot when the shrinkage stress exceeds the tensile strength of the concrete.
Sawcut joints in the same location as hand-tooled joints. In general, joint spacing to control drying and thermal shrinkage should range from 12 to 25 feet in unreinforced and lightly reinforced floors. Joint spacing on commercial industrial floor slabs subject to forklift traffic is usually wide, about 36 times the slab thickness.
Current accepted practice is to cut the joint one-quarter to one-third the slab thickness. This forms a plane of weakness in which the crack forms. Vertical loads are transmitted across the joint by aggregate interlock between the opposite faces of the crack, providing the crack is not too wide.