Construction joints are indented, or flat, joints that split a concrete section through its full thickness without a defined joint gap.  They are created by interruptions in concrete placement or from positioning of precast units and must allow displacements between both sides of the slab while allowing for the transfer of flexural stresses which are produced in the slab by external loads.  They must allow for horizontal displacement, right-angled to the joint surface that is usually caused by thermal and shrinkage movements but at the same time they must not allow vertical or rotational displacement.  Construction joint locations are usually predetermined as much as is possible.