Thin Concrete Overlay Types and Definitions

Thin concrete overlays are classified according to the type of the existing pavement and the design composite action (i.e., bonding condition). When the overlay is bonded to the existing pavement in order to behave as a monolithic structure, the overlay is referred to as “bonded.” If the overlay is separated from the underlying pavement (by placing a separator layer) or designed assuming some degree of slippage at the interface with the existing pavement, the overlay is considered “unbonded.” Concrete overlays placed on existing asphalt or composite (i.e., asphalt overlay of a concrete pavement) pavements are sometimes called “whitetopping.” These concrete overlay types are summarized in figure 1.