United States Department of Transportation
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An evaluation of factors affecting permeability of superpave designed pavements
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2003-06-01
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[PDF-413.85 KB]
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Abstract:It can be expected that the life of a permeable pavement would be shorter than that of an impermeable pavement, due to deterioration of mix through water and air infiltration, and subsequent stripping and oxidation and hardening of binder. Recent work has indicated that coarse graded Superpave mixes can be excessively permeable to water at air void levels around 6 percent. The objectives of this study were to evaluate the permeability of Superpave designed mixes used by Maine Department of Transportation and determine the effect of gradation, lift-thickness, and in-place density on the permeability of these mixes. Five Superpave projects were selected for this study. These projects included coarse-graded 9.5 mm, 12.5 mm, 19.0 mm, and 25.0 mm nominal maximum aggregate size (NMAS) mixes and one fine-graded 9.5 mm NMAS mix. Based on the National Center for Asphalt Technology permeameter, a field permeameter was developed at the Worcester Polytechnic Institute (WPI) laboratory. This permeameter was used for testing at ten locations per project. One core was obtained at each of these test locations. The cores were used to determine in-place density at each of the test locations. Field testing was done at random locations, immediately behind the finish roller. Loose mixes were also obtained from each project. The loose mixes were compacted to 5 percent air voids, and to different thickness to evaluate the effect of thickness on permeability. On the basis of results obtained in this study, the following conclusions can be made: 1. Air void content (as measured by voids in total mix) of dense graded HMA has a significant effect on in-place permeability of pavements, 2. There is a significant effect of NMAS on the permeability of coarse-graded Superpave designed mixes. It was shown that at a given in-place air void content the permeability increased by one order of magnitude as the NMAS increased, 3. Samples with different thicknesses showed that there is a decrease in permeability with an increase in thickness. It is recommended that State DOTs consider designing mixes to be placed 100 mm below the pavement surface on the fine side of the maximum density line. By designing base mixes on the fine side of the maximum density line, these mixes could be made less permeable than coarse graded mixes at similar void levels and thus less susceptible to allowing moisture or moisture vapor to propagate upward through the pavement structure. This in turn should reduce the potential for moisture damage within pavement structures. References, appendix, 12 figures, 2 tables, 33 pages.
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