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13 Table 9. Dynamic modulus test data. angle, respectively. In this analysis, a factor was considered significant if it was found to be statistically significant in 25 per- Parameter Type Dynamic Modulus Material Property cent or more of the tests. For the factors controlled by the SPT: Phase Angle Material Property temperature, strain level, and confinement, these figures show Load Standard Error Data Quality Indicator the change in modulus and phase angle over the tolerance Deformation Standard Error Data Quality Indicator Deformation Uniformity Data Quality Indicator range of the SPT. For the user-selected factors: air or water as Phase Uniformity Data Quality Indicator the conditioning fluid and with or without a membrane for unconfined tests, these figures show the higher modulus or phase angle condition. For example for 40C confined tests, 2.2.1 Factors Affecting Dynamic Modulus the dynamic modulus when water is used as the conditioning and Phase Angle fluid is 6 percent higher than when air is used. Table 14 was constructed to combine the results from both Data on the repeatability of the dynamic modulus test were mixtures tested in both laboratories. It presents the percentage collected in Phase II of this project (11). The Phase II experi- of times a specific factor was found to be significant. The notes ment included eight replicates of two mixtures tested by single indicate when a factor was significant for only one laboratory operators in two laboratories. Laboratory and mixture effects or only one material. were found to not be significant, therefore, the 32 observa- Table 14 shows that the factors included in the ruggedness tions were pooled to obtain estimates of the repeatability of experiment were not found to be significant very often indicat- the dynamic modulus and phase angle. The coefficient of vari- ing that the degree of control provided for the dynamic mod- ation for the dynamic modulus obtained from this experi- ulus test by the SPT is reasonable. From this analysis, it is clear ment was 13 percent and the standard deviation of the that the transfer time, end condition, and friction reducer phase angle was 1.7 degrees. It is likely that the repeatability have little effect on the dynamic modulus and phase angle. of the dynamic modulus test will improve in the future as The effects of the statistically significant factors are shown specimen fabrication techniques are improved and operators in Figure 6 and Figure 7 for the dynamic modulus and phase become more familiar with the equipment. However due to Table 10. Significance of dynamic modulus ruggedness test factors on dynamic modulus and phase angle for the dense mixture tested in AAT's Laboratory with the ITC SPT. Dynamic Modulus Phase Angle 4C 20 C 40 C 40 C 4C 20 C 40 C 40C Factors Confined Confined Equilibrium Temperature (-1 vs +1 C) 0.12 0.10 0.87 0.71 0.66 0.95 0.37 0.46 Transfer time (3 vs 5 min) 0.44 0.40 0.50 0.73 0.94 0.66 0.43 0.62 Conditioning Fluid (Water vs Air) 0.45 0.74 0.04 0.66 0.97 0.74 0.60 0.39 Strain Level 0.18 0.43 0.03 0.02 0.95 0.15 0.14 0.37 Membrane (No vs Yes) 0.09 0.21 0.52 NA 0.83 0.72 0.49 NA Confinement (135 vs 145 kPa) NA NA NA 0.63 NA NA NA 0.57 End Condition (Mill vs Saw) 0.39 0.49 0.70 0.32 0.84 0.73 0.70 0.39 Friction Reducer (Teflon vs Latex) 0.27 0.09 0.00 0.15 0.98 0.92 0.52 0.73 Table 11. Significance of dynamic modulus ruggedness test factors on dynamic modulus and phase angle for the SMA mixture tested in AAT's Laboratory with the ITC SPT. Dynamic Modulus Phase Angle 4C 20 C 40 C 40 C 4C 20 C 40 C 40C Factors Confined Confined Equilibrium Temperature (-1 vs +1 C) 0.59 0.17 0.99 0.66 0.00 0.53 0.28 0.06 Transfer time (3 vs 5 min) 0.50 0.43 0.68 0.79 0.33 0.89 0.91 0.69 Conditioning Fluid (Water vs Air) 0.64 0.65 0.49 0.88 0.83 0.53 0.85 0.97 Strain Level 0.90 0.99 0.35 0.01 0.63 0.94 0.15 0.04 Membrane (No vs Yes) 0.91 0.42 0.33 NA 0.06 0.22 0.06 NA Confinement (135 vs 145 kPa) NA NA NA 0.22 NA NA NA 0.06 End Condition (Mill vs Saw) 0.24 0.92 0.76 0.26 0.66 0.91 0.15 0.17 Friction Reducer (Teflon vs Latex) 0.15 0.64 0.62 0.85 0.16 0.25 0.49 0.96

OCR for page 13
14 Table 12. Significance of dynamic modulus ruggedness test factors on dynamic modulus and phase angle for the dense mixture tested in FHWA's Laboratory with the IPC SPT. Dynamic Modulus Phase Angle 4C 20 C 40 C 40 C 4C 20 C 40 C 40C Factors confined Confined Equilibrium Temperature (-1 vs +1 C) 0.02 0.00 0.03 0.00 0.06 0.27 Transfer time (3 vs 5 min) 0.90 0.30 0.11 0.73 0.54 0.56 Conditioning Fluid (Water vs Air) 0.05 0.03 0.02 0.07 0.32 0.35 Strain Level 1.00 0.09 0.51 0.53 0.01 0.01 Membrane (No vs Yes) 0.36 0.22 NA 0.00 0.01 NA Confinement (135 vs 145 kPa) NA NA 0.38 NA NA 0.29 End Condition (Mill vs Saw) 0.96 0.43 0.13 0.42 0.28 0.20 Friction Reducer (Teflon vs Latex) 0.91 0.88 0.32 0.34 0.13 0.78 Table 13. Significance of dynamic modulus ruggedness test factors on dynamic modulus and phase angle for the SMA mixture tested in FHWA's Laboratory with the IPC SPT. Dynamic Modulus Phase Angle Factors 4C 20 C 40 C 40 C 4C 20 C 40 C 40C confined Confined Equilibrium Temperature (-1 vs +1 C) 0.03 0.00 0.00 0.82 0.15 0.03 0.36 0.42 Transfer time (3 vs 5 min) 0.50 0.81 0.72 0.28 0.59 0.15 0.46 0.37 Conditioning Fluid (Water vs Air) 0.87 0.80 0.45 0.00 0.89 0.43 0.83 0.04 Strain Level 0.49 0.49 0.29 0.30 0.78 0.87 0.12 0.88 Membrane (No vs Yes) 0.85 0.74 0.05 NA 0.02 0.06 0.02 NA Confinement (135 vs 145 kPa) NA NA NA 0.10 NA NA NA 0.04 End Condition (Mill vs Saw) 0.39 0.88 0.34 0.72 0.98 0.90 0.78 0.42 Friction Reducer (Teflon vs Latex) 0.62 0.97 0.89 0.62 0.64 0.49 0.29 0.19 the non-homogeneous nature of asphalt mixtures, it is unlikely to approximately 8 percent and the standard deviation of the that the repeatability will improve to that obtained with the dy- phase angle to improve to 1.5 degrees. Using these limits, the namic shear rheometer (DSR) on homogeneous asphalt binder following observations were made concerning the dynamic samples. The coefficient of variation for DSR measurements modulus test: on original binder samples is 3.4 percent (12). Considering these levels of repeatability, it may be reasonable to expect the 1. Temperature control of 0.5C is adequate. This range re- coefficient of variation for the dynamic modulus to improve sults in a change in modulus that is less than 6 percent and a change in phase angle that is less than 1 degree. Table 14. Percentage of times each 2. Confining pressure control of 2 percent is adequate. ruggedness factor was found This range results in a change in modulus that is less to be significant. than 1 percent and a change in phase angle that is less Dynamic Phase than 0.5 degrees. Factors Modulus Angle 3. Either air or water can be used as a conditioning fluid. Equilibrium Temperature (-1 vs +1 C) 47 33 4. Strain control of 25 strain is adequate for unconfined Transfer time (3 vs 5 min) 0 0 Conditioning Fluid (Water vs Air) 33 131 tests, but not for confined tests. For unconfined tests this Strain Level 27 20 range results in a change in modulus that is less than 4 per- Membrane (No vs Yes) 18 54 cent and a change in phase angle that is less than 1.7 degrees. Confinement (135 vs 145 kPa) 252 503 End Condition (Mill vs Saw) 0 0 However for confined tests, the strain control must be im- Friction Reducer (Teflon vs Latex) 134 0 proved to 15 strain to keep the effect on the modulus Notes: below 8 percent. 1 FHWA Laboratory with IPC 5. Unconfined tests can not be performed with the membrane 2 SMA in FHWA Laboratory with IPC in place. Either the membrane adds a level of confinement 3 SMA only that significantly affects the modulus and phase angle at 4 Dense in AAT Laboratory with ITC high temperatures or since the instrumentation is mounted