Strengthening – may be required in order to extend the pavement’s life due
to increased traffic levels or because the slab in its present unimproved state
is unable to carry the traffic predicted. This is accomplished using overlays.
This is a more difficult process than for bituminous pavements due to the
existence of joints. Therefore, concrete overlays are carried out either by
forming joints in the overlay at the same location as those underneath or by
separating the two concrete layers using a regulating layer of bituminous
material. If a bitumen-based overlay is used, added thickness may be
252 Highway Engineering
required to deal not only with the structural requirements of the slab but
also to counteract reflection cracking resulting from movements in the joints
within the underlying concrete slab (HD 32/94) (DoT, 1994d).