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197 voids. They also contend that these rankings are in contrast to observed excellent high temperature performance of the asphalt rubber mixes. To refine the comparison, Kaloush et al then used the results of the confined tests. Using results from tests conducted at 20 psi confinement (for both conventional and asphalt rubber mixes), and using the ARAC mix as the reference mix, the authors show that the asphalt rubber mixes show lower modulus values at low temperature and higher modulus values at high temperature (compared to dense graded mixes) and therefore, rank, above conventional mixes, in terms of both low and high temperature performance. Citing the above results, Kaloush et al argues that since these results are in line with field performance results, the use of confined test results (for E*) is more appropriate for evaluating mixes which are gap- and open-graded courses. 1.47.8 Structural Design No information is provided on structural design of friction course. 1.47.9 Limitations No information is provided on limitations of use of friction course. 1.48 Poulikakos, L.D., Takahashi, S. and Partl, M.N. âA Comparison of Swiss and Japanese Porous Asphalt through Various Mechanical Tests.â 3rd Swiss Transport Research Conference. Monte Verita/Ascona. March 19-21, 2003 1.48.1 General This paper outlines a co-operative research project between Japanese and Swiss agencies to determine if new mix designs (SPPA & JPPA) for porous asphalt performed better than conventionally used porous asphalt mixes (SPA & JPA). The new mix designs were based on the Dry Packing Method (DPM) and Wet Packing Method (WPM). Aggregate gradations of these new mixes (SPPA & JPPA) are shown graphically in this report. The gradations of the SPPA and JPPA had a target porosity of 22%. The SPPA was constructed 4.1% (by mass) Styrelf 13/80 penetration grade SBS polymer modified Bitumen. The Conventional Swiss mix (SPA) used 4.8% by mass 50/70 penetration graded straight run bitumen with Trinidad NAF 501. Both the new and conventional Japanese mixes used a polymer modified bitumen with 9% SBS. A comparison of the binder is as follows: Property JPA and JPPA SPA SPPA Penetration 1/10 mm 45 15 50 Ring and Ball °C 90.1 80.7 56.5 Several tests were carried out by Poulikakos et al to compare the new and conventional porous asphalt mixes. Specifically the following tests were conducted, although not all were discussed in this paper:
198 ⢠Laboratory aging of mixes (short and long term) ⢠Cantabro (particle loss test) ⢠Water permeability ⢠Binder penetration ⢠Binder softening point ⢠Rheology of the binder using the DSR ⢠Interlayer shear strength ⢠Indirect tensile strength ⢠Shear modulus of mixes using the Coaxial Shear Test (CAST) ⢠Wheel Tracking The following observations were made based on these tests: 1. After long term aging binder draindown was observed. Thus long term aging is not an optimal procedure for porous asphalt. 2. The JPA and JPPA mixes maintained a higher porosity after over compaction as compared with the SPA and SPPA. The authors concluded that the difference may be the binder content differences between the mixes, thus emphasizing the importance of correct binder selection. 3. Using a constant head permeameter, the mixes were evaluated for permeability at compaction and over compaction. The SPPA and JPPA mixes did not show an improvement in water permeability. 4. The JPA and JPPA performed well in the wheel tracking tests, which the authors believe is due to the binder in the mix. No significant additional contribution was discovered in the SPPA mix during the wheel tracking test. 5. From the indirect tensile tests it was shown that the JPA and JPPA had higher tensile strength (both wet and dry) than the SPA and SPPA mixes. There was no significant difference in the water susceptibility of the four mixes. Water conditioning had a significant effect on the SPA mix, suggesting that that their resistances to water effects were poor. 6. No significant findings were discovered during the interlayer shear tests. Overall, the SPA and SPPA performed better during this test. 7. The Cantabro tests (particle loss) test results showed that the new mixes reduced the Cantabro loss values by 14%. Moreover, the Japanese mixes showed smaller particle loss then the Swiss mixes. Overall the research presented by Poulikakos et al suggests that the positive effects of the new mix design packing theory were clearly shown. The highest overall advantage was the reduction in Cantabro loss.
