This synthesis will be of interest to pavement designers, maintenance engineers, and others interested in reducing reflection cracking of asphalt overlays on portland cement concrete (PCC) pavement. Information is presented on the technique of breaking or cracking of the concrete pavement into small segments before overlaying with asphalt concrete. Asphalt concrete overlays on existing PCC pavements are subject to reflection cracking induced by thermal movements of PCC pavement. This report of the Transportation Research Board discusses the technique of breaking/cracking and seating of the existing PCC before an overlay as a means to reduce or eliminate reflection cracking.

This report presents details of a study conducted to evaluate the long term performance of asphalt overlays on broken and seated (B/S) concrete pavements, using field expe riments. The primary purpose of this study is to evaluate the effectiveness of breaking and seating as a reh abilitation strateg y for retarding reflection crac king in asphalt concrete (AC) overlays on jointed reinforced concrete pavements. Test sections were constructed by milling the original AC layer, breaking and seating the concrete slabs and constructing new AC overlays. Control sec tions were co nstructed ad jacent to the B /S sections in the same way, but without breaking the underlying concrete slabs. The test sections carried a large volume of traffic. The original pavements selected in this study were fairly uniform with respect to their structural and surface conditions. Two types of pavement breakers were used in this study, namely guillotine and pile hammer. The extent of breaking was closely monitored. The performance of the test sections was monitored for a total period of nine years. The monitoring data included deflection measurements, crack mapping, a pavement condition surveys and roughness surveys on the original pavement and on the overlay. The results, in general, strongly indicate an improved performance of AC overlays on broken and seated concrete pavements. The B/S treatment has a significant effect on the structural response and behavior of the resulting pavement. Breaking the concrete slabs into smaller pieces resulted in a reduction in the flexural strength, an increase in the surface deflection (50% to 100%), and a decrease in AREA and Spreadability (20 to 30%). Breaking and seating has been extremely effective in delaying and minimizing reflection cracking. Hence, the breaking and seating procedure does indeed result in improved pavement performance. Ultimately, economics and serviceability will govern its use, based on the length of time future maintenance and rehabilitation is deferred.

Asphalt concrete overlays of a jointed or cracked portland cement concrete (PCC) pavement can develop reflective cracking because of either horizontal or vertical movement of the PCC. One method that can be used to reduce reflective cracking is to crack and seat the PCC prior to placement of the asphalt concrete overlay. The description, applicability, benefits, limitations, costs, recommended uses, and location of demonstration sites for cracking and seating technology are discussed.