Unbonded Concrete Overlay. The purpose of breaking the bond between the old pavement and the proposed overlay is to separate the distresses in the old pavement from the new concrete overlay. Thus, the concrete overlay can be treated as a separate pavement, and the existing distressed pavement as a uniform base. There is little bene- fit derived from repairing the existing pavement prior to placing the overlay, as the bondbreaker will provide uniform support and interface for the concrete overlay. The bond- breaker is placed as a thin (1- to 3-in) asphalt overlay on the existing pavement, and the concrete overlay is placed on the bondbreaker. The thickness required for the concrete overlay can be determined using the following modified version of an equation developed by the Army Corps of Engineers: