Effect of Crack Sealant Material and Reservoir Geometry on Surface Roughness of Bituminous Overlays

Many state, county, and municipal highway agencies have experienced the formation of bumps when placing single-lift overlays or the first lift of a multiple-lift overlay. These bumps are produced at the location of a previously existing crack, and even then almost exclusively when the crack has been sealed in advance of the overlay. When such bumps are not covered with a subsequent lift, what remains is often a rough ride on a newly overlaid roadway. The effects of crack sealant material type and geometry (shape) of the routed cracks in the existing surface on the formation of bumps in bituminous overlays are described. A matrix of four sealant type treatments and six geometries was designed and implemented in a test section in Jackson County, Minnesota. The overlay on the test section was constructed in September 2007. Results of this investigation indicate that cooler pavement surface temperatures, no over-band, hot-poured crumb rubber, and hot-poured elastic sealants provide the best resistance to the formation of bumps in overlays.