Sawing and Sealing of expansion joints in asphalt or concrete is done quickly and precisely. It is performed when new asphalt or concrete is placed. The asphalt or concrete is saw cut and cleaned as per specs and sealed with a hot rubberized material.
As it cures, standard concrete pavement cracks. The pavement always will crack as it cures. The purpose of the “control” joint sawed into curing or “green” slabs is to control where the concrete cracks as it cures, that is, along the path of least resistance, the sawed joint.
Because the sawed crack control joints offer a point of ingress for water and incompressibles into the pavement structure and base, it’s perceived by most road agencies that they should be sealed to keep water and debris out of the structure.