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10 variability in specimen air voids is a significant contributor to the order of the determinations from Table 7 was randomized. the overall test variability and that a high degree of control over The data for each mixture/confinement combination will be air void content is needed. However, the current tolerance of analyzed separately to draw conclusions on appropriate levels 0.5 percent is probably the tightest control obtainable using of control for the individual factors. The entire ruggedness current specimen fabrication techniques. Therefore, air void testing program was performed in two laboratories: AAT's content was not a factor considered in the ruggedness testing. laboratory using the ITC SPT and FHWA's Mobile Asphalt The current tolerance of 0.5 percent should be used until Laboratory using the IPC SPT. specimen fabrication equipment is improved. As discussed for the dynamic modulus test, end parallelism was included as a factor in the ruggedness testing for the flow 1.4 Equipment Effects Experiment number test. Different conclusions concerning the effects of Since equipment from multiple vendors will be used in end parallelism may be drawn from the small strain dynamic future interlaboratory studies for the SPT, a study was per- modulus test and the large strain flow number test. Addi- formed after the ruggedness testing to quantify differences in tionally, the platen configurations are different in the two data obtained with equipment from various manufacturers. tests. For the dynamic modulus test, a ball joint that allows The objective of this experiment was to verify that the same the top platen to conform to the plane of the specimen is material properties are obtained in the dynamic modulus and used. For the flow number test, the platens are fixed in a par- flow number tests using devices from different manufacturers. allel arrangement. Specimens with sawed ends and milled Table 8 presents the design of this experiment. For each ends were included in the dynamic modulus ruggedness test- test condition, four replicate tests were performed with each ing program. device on the 9.5-mm dense-graded mixture. Analysis of variance techniques was used to analyze the data from each column of the experiment in Table 8. This approach assumes 1.3.3.3 Flow Number Test Summary homogeneity of variances for data obtained from the various Table 7 summarizes the factors and factor levels that were devices. Based on the data collected in Phase II of NCHRP included in the ruggedness testing for the flow number test. Project 9-29, this is a reasonable assumption. Using 4 repli- As shown, dwell time and contact stress were included only cates per cell provides 9 degrees of freedom for the error term, in the unconfined tests. The effect of dwell time was evaluated and 2 degrees of freedom for the equipment effect. As shown only with the IPC equipment. The effect of contact stress was in Figure 5 this results in an efficient design as a larger number evaluated only with the ITC equipment. Flow number tests of replicates have only a minor effect on the critical F-statistic were performed at 50C for three combinations of material used in the analysis of variance to detect the significance of and confinement: dense-graded, unconfined; dense-graded, differences caused by equipment effects. confined; and SMA, confined. Since the flow number test is a Since the dynamic modulus test is nondestructive, only destructive test, the testing program required the fabrication 12 specimens, four for each device were needed to complete and testing of 48 specimens, 16 for each mixture/confinement the dynamic modulus portion of the study. The flow number, combination. For each mixture/confinement combination, which is a destructive test, required 24 specimens. Table 7. Summary of factors and levels for the flow number ruggedness test. Unconfined Tests Confined Tests Factor Low High Low High Equilibrium Temperature 49 C 51 C 49 C 51 C Specimen Transfer Time 3 min 5 min 3 min 5 min Conditioning Fluid Air Water Air Water Dwell Time (IPC only) 0.85 sec 0.95 sec Not included Not included Contact Stress (ITC only) 5 kPa 10 kPa Not included Not included Deviatoric Stress 135 kPa 145 kPa 945 kPa 985 kPa Confining Stress Not included Not included 135 kPa 140 kPa Specimen End Condition Milled Sawed Milled Sawed Friction Reducer Greased latex TeflonTM Greased latex TeflonTM

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11 Table 8. Equipment effects experiment. Dynamic Modulus Flow Number Condition Test Test Temperature, C 10 20 35 35 50 50 Confining Stress, kPa 0 0 0 135 0 140 Deviatoric Stress, kPa To obtain 100 strain 140 965 Manufacturer Replicates Interlaken 4 4 4 4 4 4 IPC Global 4 4 4 4 4 4 MDTS 4 4 4 4 4 4 7 6 5 Critical F Value, =0.05 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 Replicates Per Cell Figure 5. Effect of replicates per cell on critical F-statistic for design in Table 8.