Joints in unreinforced pavements are located to control cracking, aid in construction and delineate driving or parking lanes while insuring the structural integrity and riding quality of a concrete pavement. Proper jointing aids in preventing random cracking of pavements that can occur when concrete changes volume with changes in moisture and temperature.
It is vital that jointing practices accommodate early shrinkage in the pavement. If joints are sawed, the work should be done after the concrete has attained sufficient strength to support the weight of the saw and to allow the blade to cut through the aggregate. But it should be done early enough to prevent shrinkage cracks from occurring; some slight raveling may consequently occur during sawing. For transverse contraction joints, sawing time is critical, with sawing being done between 4 and 24 hours after concrete placement, depending on job conditions.
For unreinforced (plain) jointed pavements, the maximum joint spacing should be between 15 and 20 feet based on slab thickness, aggregates and the environment. For pavements less than 6 inches thick, maximum spacing should be 15 feet. In order to establish a plane of weakness, joints should have a minimum depth of one-fourth the thickness of the slab. Joints should be continuous and extend through integral curbs. Joints in each lane should match those in adjoining lanes. As long as good joint practices are followed, the contractor should be allowed some latitude in changing joint locations and type to accommodate his method of placement and the equipment used. The ultimate aim is to provide a joint system for concrete pavements designed to insure the structural integrity and riding quality of the pavement.