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109 Three 150 mm cores were obtained from each of the six sections. Table 62 presents the average laboratory permeability values from each section as well as average in-place air void contents. Statistically, no significant differences exist between the permeability values; however, the DC and DCP sections did have the highest average permeability at 74 and 70 m/day, respectively. In-place air void contents ranged from 15 to 19 percent. Bulk specific gravity measurements were determined by volumetric measurements. It is interesting that this range of air void contents correspond well with the roadway core air void contents (at the time of construction) presented in Table 60. Again, this appears to provide validity to the selection of 18 percent air voids minimum in the new mix design system. This criterion appears to be related to air void contents at both construction and during the life of an OGFC pavement. Additionally, it appears that the mix design procedure used by GDOT in this experiment resulted in OGFC mixes with stone-on-stone contact even though it was not specifically tested. Table 62: Average Permeability and In-Place Air Void Contents for the Six Test Sections Section Avg. Permeability m/day Avg. In-Place Air Voids, % D 25 16.7 D16R 38 15.8 DM 28 19.9 DC 74 16.2 DP 16 13.9 DCP 70 19.2 1.23.8 Structural Design No specifics on inclusion within structural design were given. 1.23.9 Limitations No limitations on use were given. 1.24 Molenaar, J.M.M. and A.A.A. Molenaar. âAn Investigation into the Contribution of the Bituminous Binder to the Resistance to Raveling of Porous Asphalt.â 2nd Eurasphalt & Eurobitume Congress. Barcelona, Spain. pp 500-508. 2000. 1.24.1 General This paper provides the results of a research project designed to evaluate the effect of polymer modification on the properties of porous asphalt as related to short-term raveling and to develop a method for selection of an appropriate asphalt binder to improve the resistance to short-term raveling. For the purposes of this paper, short-term raveling was defined as raveling caused by intense shearing forces at the tire/pavement interface that occurs within newly placed porous asphalt. Long-term raveling was assumed by the authors to be caused by gravity segregation of the mastic during the service life of the
110 porous asphalt. Upon the mastic segregating from the coarse aggregate, the action of traffic will break loose the aggregate particles. 1.24.2 Benefits of Permeable Asphalt Mixtures No specific benefits were given. 1.24.3 Materials and Mix Design The researchers utilized two laboratory tests to evaluate the short-term potential for raveling: the Wheel Fretting Test and the Californian Abrasion Test. For the Wheel Fretting Test (WFT), a treaded tire inflated to 600 kPa (87 psi) and loaded with 3 kN (675 lb) was run in a circular path on top of porous asphalt test specimens under an inclination angle of 2 to 5 degrees. A total of 3 million revolutions (applications) of the treaded tire were applied to the porous asphalt test specimens at a test temperature of approximately 20ºC. The fretting performance was characterized as a mass loss after the wheel passes. The Californian Abrasion test (CAT) utilizes a mechanical shaker that is operated at 20 cycles per second with a given vibration amplitude. A sample of porous asphalt is placed within a container along with water and steel spheres and subjected to the vibration action for 15 minutes at a test temperature of 4ºC. Test results are expressed as mass loss after the 15 minutes of abrasive action. During the research, porous asphalt was prepared with a total of eight asphalt binders. Two of the binders were neat (non-modified) binders while six were polymer-modified. Of the six modifiers used, four were elastomeric and two were plastomers. Based upon the results of testing, the authors concluded that polymer modification is beneficial to resist the effect of short-term raveling, whether this raveling occurs at low or at high pavement temperatures. The WFT and CAT were effective at providing an indication of short-term raveling at their respective test temperature. 1.24.4 Construction Practices No specifics on construction practices were given. 1.24.5 Maintenance Practices No specific maintenance practices were given. 1.24.6 Rehabilitation Practices No specific rehabilitation practices were given. 1.24.7 Performance No performance measures were given. 1.24.8 Structural Design No specifics on inclusion within structural design were given.
