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27 250 Average Permeability x E-05 cm/sec 200 Recommended maximum 150 permeability, 125 x 10-5 100 50 0 2:1 3:1 4:1 2:1 3:1 4:1 2:1 3:1 4:1 2:1 3:1 4:1 2:1 3:1 4:1 2:1 3:1 4:1 2:1 3:1 4:1 9.5 ARZ 9.5 BRZ 9.5 SMA 12.5 SMA 19.0 ARZ 19.0 BRZ 19.0 SMA t/NMAS @ each mix Figure 34. Relationships between permeability and t/NMAS. less than a 3:1 t/NMAS, the air voids have to be lower to 4.9 PART 2--EVALUATION OF RELATIONSHIP ensure that the mixes are impervious. OF LABORATORY PERMEABILITY, DENSITY AND LIFT THICKNESS OF FIELD COMPACTED CORES 4.8 EVALUATION OF EFFECT OF t/NMAS ON PERMEABILITY FROM FIELD STUDY The average thickness, the average air void content by the vacuum seal device method, and the average laboratory Permeability tests were conducted on the seven HMA sec- permeability values were determined for each of the cores tions that were evaluated in the field. These tests were con- obtained from the work under NCHRP Project 9-9 (1). Figures ducted in-place with the field permeameter and in the labora- 35 through 37 present the plots of in-place air voids versus tory with the lab permeability test. Cores were taken from the permeability for each NMAS mix. The relationship between in-place pavement for measurement of density and for mea- in-place air voids and permeability for 9.5-mm NMAS is illus- surement of lab permeability. The field permeability values trated in Figure 35. The R2 values for both coarse-graded were determined adjacent to the location where the cores were and fine-graded mixes were relatively high (0.70 and 0.86, taken for density and for lab permeability. The results of these respectively) and both relationships are significant (p-value tests for the 7 sections are provided in Table 14. = 0.000). At 8 percent air voids, the pavement is expected to In summary, the coarse-graded mixes had permeability have a permeability of 60 × 10-5 cm/sec for coarse-graded values that exceeded the recommended value when the air mix and 10 × 10-5 cm/sec for fine-graded mix. Because there voids exceeded about 8 percent. The fine graded mixes never are only a couple of data points for fine-graded mix above exceeded the recommended value even up 9 to 10 percent approximately 10 percent air voids, this model should not air voids. be used to predict permeability at these higher void levels. At TABLE 14 Comparison of laboratory and field permeabilities Section Mix Type In-Place Air Field Lab Number Voids Permeability Permeability (percent) (cm/s x 10-5) (cm/s x 10-5) 1 9.5mm FG 6.6 to 8.8 1 to 28 1 to 35 2 9.5mm CG 9.0 to 12.6 14 to 632 107 to 1070 3 9.5mm SMA 7.7 to 12.6 110 to 651 29 to 168 4 12.5mm SMA 4.1 to 17.9 3 to 1778 0.1 to 5850 5 19.0mm FG 5.7 to 9.5 38 to 161 1 to 77 6 19.0mm CG 5.3 to 9.8 10 to 1760 1 to 141 7 19.0mm CG 4.8 to 15.2 72 to 3030 0 to 1203