comparison of alternative asphalt concrete rut characterization

BERTHELOT, CROCKFORD & LYTTON 15concrete mix determined that significant difference existed between the mean SHRP shear phase anglemeasurements at 4°C, 20°C, and 40°C.Table 15 Mean SHRP Shear Phase Angle Measurements and Duncan’s Pairwise Comparison at 10Hz Cyclic Frequency of Radisson Specific Pavement Studies -9A Asphalt Concrete Mixes Groupedby Test TemperatureSPS-9A TestSectionMean SHRPShear PhaseAngle(Degrees)Mean SHRPShear PhaseAngleCoefficient ofVariation(Percent)Duncan's Grouping *900901 50.99 3.02 A900902 44.58 9.22 B900903 52.27 4.43 A900959 49.76 9.74 A900960 51.27 5.24 A900961 51.58 3.21 A900962 45.57 2.21 BMean 49.43 5.30* Asphalt concrete mixes with same letter are not significantly different.Table 16 Mean SHRP Shear Phase Angle Measurements and Duncan’s Pairwise Comparison at 10Hz Cyclic Frequency across Test Temperatures Grouped by Radisson Specific Pavement Studies -9A Asphalt Concrete MixTestTemperatureMean SHRPShear PhaseAngle(Degrees)Mean SHRPShear PhaseAngleCoefficient ofVariation(Percent)Duncan's Grouping*4°C 33.97 4.19 A20°C 53.99 3.88 B40°C 60.33 7.82 CMean 49.43 5.30* Test temperatures with same letter are not significantly different.4.4.5 SHRP Repeated Shear at Constant Stress Ratio CharacterizationThe SHRP repeated shear at constant stress ratio test employs the SHRP shear tester to characterize therelative potential for asphalt concrete mixes to exhibit tertiary creep under repeated loads. SHRP repeatedshear at constant stress ratio characterization was performed at the permanent deformation effectivetemperature (T effectivePD ) of 40°C at 98 percent reliability. SHRP repeated shear at constant stress ratiotesting was performed on triplicate gyratory compacted samples at seven percent air voids and wascontinued for 20,000 load cycles or until the accumulated strain reached five percent. Figure 4 illustratesthe cumulative SHRP shear strain measurements across the Radisson SPS-9A asphalt concrete mixes. Asseen in Figure 4, none of the Radisson SPS-9A asphalt concrete mixes exhibited tertiary creep at the endof 20,000 load cycles.