Mexico is the volume leader in UTW use, placing 621,000 sq yd in 21 different projects. The largest is in Ensenada, Baja California. It covers 299,000 sq yd, is 2.5-in. thick and has joints spaced on a 3 ft grid. Second largest is a 2.5-in. thick overlay at the Ford plant in Hermosillo, Sonora, covering 120,000 sq yd.
Mexico has a UTW research project on an urban arterial in Tijuana. Test sections include thicknesses of 2.5 and 3.5 in. and square-joint spacings of 3, 4 and 6 ft. Initial results indicate the UTW is a rehabilitation technique that significantly extends the useful life of flexible pavements.
Sweden also has done research with UTW in an effort to determine if they could use concrete to stop studded-tire wear of asphalt. Projects in 1989 and 1993 found that concrete did stop the studded-tire wear and that the concrete bonded to the asphalt, improving the structural capacity of the roadway.
Two of the largest instrumented UTW experiments in the U.S. are those at the St. Louis Airport and on Route 21 in Iowa near Belle Plain. The airport is being used to develop a UTW design procedure. The Iowa project has 64 different test sections. Variables include thickness, maximum joint spacing, and the use of fibers. To date, both projects are performing exceptionally well.
Experience gained from these research and in-service projects will lead to new design criteria and optimum use of UTW.
