United States Department of Transportation
i
Overlay design for unstable asphalt mixes : final report.
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1995-09-01
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[PDF-4.98 MB]
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Abstract:The first objective of this study was to evaluate the relative rutting characteristics of overlaid pavements, where the overlaid section (i.e., new "base") had previously exhibited rutting. A second study objective was to develop criteria for the design of overlays for unstable "bases". The mixtures were evaluated in an LCPC Wheel Tracker. Slabs of the dense graded "base" mixtures and a typical open graded overlay mixture were evaluated by themselves as well as in three alternative configurations of composite layered slabs to simulate an overlaid pavement. A Repeated Load Creep Test was also conducted on cylindrical specimens of the base and overlay mixtures.
The use of the wheel tracking device did not provide a satisfactory means of evaluating either the open-graded overlay mixture or the composite slabs. This was predominantly because of the need to confine the open-graded mixture in the test "mold". This could be achieved in the future by preparing the specimens in the molds, an option not available to the researchers for this study.
Tentative criteria for overlaying rutted pavements were developed. It is proposed that the Repeated Load Creep Test be conducted at 25 deg C for both base and overlay mixtures. After 2000 load repetitions, if the permanent strain for either mix exceeds 1 percent (10,000 microstrain), the overlay of this base should not be pursued. If the mixes pass the creep criterion, they should be tested at 60 deg C in a layered slab configuration in the Wheel Tracker and if the rutting is less than 10 mm after 50,000 passes, the field overlay project should proceed. If the rutting is more than 10 mm after 10,000 passes, the project should not proceed. If the rutting falls between these two limits, an overlay could proceed with an adjusted mix design or if the truck traffic for the project is light.
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