Ultra-thin whitetopping (UTW) is a concrete overlay 2 to 4 inches thick, with closely spaced joints, bonded to an existing asphalt pavement. The concrete industry's newest remedy for rutted asphalt pavements, UTW combines current concrete bridge deck overlay bonding technology with early sawing of closely spaced contraction joints. This produces a bonded composite pavement, with minimized tensile stresses in the concrete layer.
The first controlled experiment with whitetopping less than 4 inches thick began in Louisville, Ky., in 1991. Test sections with 2 and 3 « inches of concrete overlay were installed on the access road to a landfill, where 400 to 600 heavily loaded trucks travel each day. Performance of the Kentucky UTW installation has been much better than predicted by conventional design procedures. This seems to be attributable to two factors: The concrete bond to asphalt creating a monolithic section, and the use of short joint spacings. Following the early success in Kentucky, UTW installations have spread as technology continues to advance. Though a rational design procedure has not been finalized, the American Concrete Pavement Association believes that UTW can provide a durable wearing surface and withstand normal loads on residential and low-volume roads.