comparison of alternative asphalt concrete rut characterization

COMPARISON OF ALTERNATIVE TEST METHODS FORPREDICTING ASPHALT CONCRETE RUT PERFORMANCEPrepared By:Curtis Berthelot, Assistant ProfessorBill Crockford, PresidentRobert Lytton, ProfessorPresented in:Canadian Technical Asphalt Association Proceedings44 th Annual ConferenceVol XLVL, pp 405-4341999ACKNOWLEDGMENTSThe authors would like to acknowledge the assistance provided by Ms. Stella White P.Eng. ofSaskatchewan Highways and Transportation. In addition, the participation and support provided byPounder Emulsions Division of Husky Asphalt Marketing, Imperial Oil, Koch Materials, Moose JawAsphalt, and the National Science and Engineering Research Council is greatly appreciated.

BERTHELOT, CROCKFORD & LYTTON 3NRadisson SPS-9A Test Site LayoutDirection of TrafficBasic SPS-9A RequirementsTransition7+1357+0896+8176+3546+0826+0195+1505+7474+9534+8294+6174+5294+2574+1883+9163+870900961SHT MarshallTransition900962SuperpaveRecycleTransition900960SuperpaveTransition900901SHT MarshallTransition900903SuperpaveTransition900902SuperpaveTransition900959SuperpaveTransitionRadisson SPS-9A Pavement Structure Cross-SectionC L120 mm Asphalt Concrete200 mm Granular Base230 mm Silty Sand SubbaseClay Till Subgrade (CBR 6)Figure 1 Radisson Specific Pavement Studies -9A Test Site Layout and Pavement StructureCross-SectionTable 1 Asphalt Binder Grade and Mix Design Method used in Radisson Specific PavementStudies - 9A Test Sections GoodSPS-9A Test SHRP PG and SDHT Penetration Mix Design MethodSectionAsphalt Binder Grade900901900959PG 58-28 (AC 150/200)PG 58-28 (AC 150/200)SHT Marshall Mix DesignSuperpave Mix Design900903900961PG 52-34 (AC 200/300)PG 52-34 (AC 200/300)Superpave Mix DesignSHT Marshall Mix Design900960 PG 46-34 (AC 300/400) Superpave Mix Design900902900962PG 52-40PG 52-40Superpave Mix DesignSuperpave Recycle Mix DesignSDHT = Saskatchewan Department of Highways and Transportation

BERTHELOT, CROCKFORD & LYTTON 44.0 RADISSON SPS-9A ASPHALT CONCRETE CHARACTERIZATION RESULTS4.1 Marshall Stability and Flow CharacterizationMarshall stability and flow testing of asphalt concrete has been widely used by the road industry and isstandardized in ASTM D 1560 and AASHTO T245. Marshall stability and flow measurements weretaken on triplicate gyratory compacted samples at seven percent air voids from each Radisson SPS-9Aasphalt concrete mix. Table 2 summarizes the Marshall stability measurements and Table 3 summarizesthe Marshall flow measurements of the Radisson SPS-9A asphalt concrete mixes.Table 2 Marshall Stability Measurements and Duncan's Pairwise Comparison of RadissonSpecific Pavement Studies-9A Asphalt Concrete MixesSPS-9A TestDuncan's Grouping*SectionMean MarshallStability(N)MarshallStabilityCoefficient ofVariation(Percent)900901 3958 10.84 C900902 7562 6.55 A900903 5115 15.72 B C900959 7176 13.02 A900960 5975 8.63 B900961 4685 14.22 C900962 7828 9.30 AMean 6042 11.18* Asphalt concrete mixes with same letter are not significantly different.Table 3 Marshall Flow Measurements and Duncan's Pairwise Comparison of Radisson SpecificPavement Studies9A Asphalt Concrete MixesSPS-9A TestDuncan's Grouping*SectionMean MarshallFlow(0.25 mmIncrements)Marshall FlowCoefficient ofVariation(Percent)900901 12.0 8.33 C900902 14.3 4.03 B C900903 14.3 4.03 B C900959 16.3 18.70 A B900960 14.3 4.03 B C900961 12.0 8.33 C900962 18.7 17.22 AMean 14.6 9.23* Asphalt concrete mixes with same letter are not significantly different.A statistical analysis was performed at a 95 percent confidence level to evaluate the significance of theMarshall stability and flow measurements of the Radisson SPS-9A asphalt concrete mixes. A one-wayanalysis of variance concluded that Radisson SPS-9A asphalt concrete mix type had a significant effecton the mean Marshall stability measurements. Duncan's pairwise comparison (25) determined that themean Marshall stability measurements of mixes 900902, 900959, and 900962 were not significantly

BERTHELOT, CROCKFORD & LYTTON 5different; mixes 900903 and 900960 were not significantly different; and mixes 900901, 900903, and900961 were not significantly different.A one-way analysis of variance concluded that Radisson SPS-9A asphalt concrete mix type had asignificant effect on the mean Marshall flow measurements. Duncan's pairwise comparison determinedthat the mean Marshall flow of mixes 900959 and 900962 were not significantly different; mixes 900902,900903, 900959, and 900960 were not significantly different; and mixes 900901, 900902, 900903,900960, and 900961 were not significantly different.The Marshall stabilometer is widely used throughout the road industry due to its simplicity, costeffectiveness, repeatability, and concomitant empirical experience. The Marshall stabilometer was foundto distinguish some significant differences between the Radisson SPS-9A asphalt concrete mixes.Limitations of the Marshall stabilometer include: it is unable to provide feedback controlled on-samplemulti-axial mechanistic measurements; it specifies a small sample size (62.5 mm by 101 mm); it appliesboundary tractions under curvilinear platens resulting in nonlinear stress-strain fields; it does not have theability to apply confinement tractions to the sample; and it is designed for testing asphalt concrete at 60°Cat a specified displacement rate of 1.3 mm/min. As a result, the Marshall stabilometer cannot be used tocharacterize the fundamental thermomechanical constitutive behavior of asphalt concrete across stressand strain states, stress and strain rates, and temperatures representative of those experienced in the fieldas required for mechanistic road-modeling. The Marshall stabilometer was found not to provide properranking of the Radisson SPS-9A asphalt concrete mixes concomitant to field rutting performance afterthree years of service.4.2 Hveem Stability CharacterizationHveem stability characterization of asphalt concrete has been widely used by the road industry and isspecified in ASTM D1561 and AASHTO T246. Hveem stability testing was performed on triplicategyratory compacted samples at seven percent air voids from each Radisson SPS-9A asphalt concrete mix.Table 4 summarizes the Hveem stability measurements across the Radisson SPS-9A asphalt concretemixes.A statistical analysis was performed at a 95 percent confidence level to evaluate the significance of theHveem stability measurements across the Radisson SPS-9A asphalt concrete mixes. A one-way analysisof variance concluded that Radisson SPS-9A asphalt concrete mix type had a significant effect on themean Hveem stability measurements. Duncan's pairwise comparison determined that the mean Hveemstability of mix 900902 was significantly different from all other mixes; however, mixes 900960 and900962 were not significantly different; mixes 900903, 900959, and 900961 were not significantlydifferent; and mixes 900901 and 900961 were not significantly different.The Hveem stabilometer was found to distinguish some significant differences between the RadissonSPS-9A asphalt concrete mixes and produced a low mean coefficient of variation. A drawback to theHveem stabilometer is it requires a high capacity load frame, which increases the owning and operatingcosts and renders it impractical for field testing. In addition, like the Marshall stabilometer, the Hveemstabilometer does not provide feedback controlled on sample multi-axial mechanistic measurements and itspecifies a small sample size (62.5 mm diameter by 101 mm tall). As a result, the Hveem stabilometercannot be used to characterize the fundamental thermomechanical constitutive behavior of asphaltconcrete across stress and strain states, stress and strain rates, and temperatures representative of thoseexperienced in the field as required for mechanistic road-modeling. The Hveem stabilometer was found

BERTHELOT, CROCKFORD & LYTTON 6not to provide proper ranking of the Radisson SPS-9A asphalt concrete mixes concomitant to field ruttingperformance after three years of service.Table 4 Hveem Stability Measurements and Duncan's Pairwise Comparison of Radisson SpecificPavement Studies-9A Asphalt Concrete MixesSPS-9A Test Mean Hveem HveemDuncan's Grouping*Section Stability StabilityCoefficient ofVariation(Percent)900901 28.61 1.94 D900902 40.02 1.44 A900903 32.53 3.32 C900959 30.95 7.38 C900960 34.78 3.71 B900961 30.80 2.70 C D900962 35.32 3.68 BMean 33.29 3.45* Asphalt concrete mixes with same letter are not significantly different.4.3 Unconfined Compressive Strength CharacterizationUnconfined compressive strength testing of asphalt concrete is standardized in ASTM D1074 andAASHTO T167. Unconfined compressive strength testing was performed on triplicate gyratorycompacted samples at seven percent air voids from each Radisson SPS-9A asphalt concrete mix at 5°C,20°C, 40°C, 70°C, and 100°C. Tables 5 and 6 summarize the mean unconfined compressive strengthmeasurements across the Radisson SPS-9A asphalt concrete mixes and test temperatures respectively.A statistical analysis was performed at a 95 percent confidence level to evaluate the significance of theunconfined compressive strength measurements across the Radisson SPS-9A asphalt concrete mixes andtest temperatures employed in the analysis. A two-way analysis of variance concluded that RadissonSPS-9A asphalt concrete mix type, test temperature and the interaction effects of mix type and testtemperature had a significant effect on the mean unconfined compressive strength measurements..Duncan's pairwise comparison determined that the mean unconfined compressive strength of mixes900959 and 900962 were significantly different from all other mixes; however, mixes 900901, 900902,900903, and 900960 were not significantly different; and mixes 900901, 900902, 900903 and 900961were not significantly different. Duncan's pairwise comparison across the test temperatures grouped byRadisson SPS-9A asphalt concrete mix determined that the mean unconfined compressive strengths at5°C, 20°C, and 40°C were significantly different from those at all other temperatures; however, there wasno significant difference between 70°C and 100°C.

BERTHELOT, CROCKFORD & LYTTON 7Table 5 Unconfined Compressive Strength Measurements and Duncan's Pairwise Comparison ofRadisson Specific Pavement Studies-9A Asphalt Concrete Mixes Grouped by Test TemperatureSPS-9A TestDuncan's Grouping*SectionMeanUnconfinedCompressiveStrength(kPa)MeanUnconfinedCompressiveStrengthCoefficient ofVariation(Percent)900901 1725 17.66 B C900902 1679 11.57 B C900903 1726 16.16 B C900959 2576 5.40 A900960 1874 7.89 B900961 1589 13.10 C900962 1222 9.60 DMean 1770 11.31* Asphalt concrete mixes with same letter are not significantly different.Table 6 Unconfined Compressive Strength Measurements and Duncan's Pairwise Comparisonacross Test Temperatures Grouped by Radisson Specific Pavement Studies -9A Asphalt ConcreteMixTestTemperatureMeanUnconfinedCompressiveStrength(kPa)MeanUnconfinedCompressiveStrengthCoefficient ofVariation(Percent)Duncan's Grouping*5°C 6134 10.90 A20°C 1601 6.37 B40°C 713 11.46 C70°C 298 14.51 D100°C 106 13.31 DMean 1770 11.31* Test temperatures with same letter are not significantly different.Unconfined compressive strength testing was found to distinguish some significant differences betweenthe Radisson SPS-9A asphalt concrete mixes. However, because confinement tractions are not applied tothe sample and the compressive tractions required to fail the sample are significantly greater than thosetypically experienced under field loading conditions, the stress state generated during the unconfinedcompressive strength test does not accurately represent the true stress state experienced under fieldloading conditions. Unconfined compressive strength testing also requires a heavy capacity load frame,which increases owning and operating costs and renders it impractical for field testing. Like the Marshalland Hveem stabilometers, unconfined compressive strength testing does not provide feedback control onsample multi-axial measurements and therefore cannot characterize the thermomechanical constitutivebehavior of asphalt concrete across stress and strain states, stress and strain rates, and temperaturesrepresentative of those experienced in the field as required for mechanistic road-modeling. The

BERTHELOT, CROCKFORD & LYTTON 8unconfined compressive strength test was found not to provide proper ranking of the Radisson SPS-9Aasphalt concrete mixes concomitant to field rutting performance after three years of service.4.4 SHRP Shear Tester CharacterizationThe Strategic Highway Research Program developed a prototype suite of tests to characterize thethermomechanical behavior of asphalt concrete mixes and they are specified in AASHTO TP7-94 (25).The SHRP suite of shear tests include: volumetric-hydrostatic test, uniaxial strain at constant radius test,simple shear at constant height test, frequency sweep shear at constant height test, and repeated shear atconstant stress ratio test.The repeated shear at constant height is specified in AASHTO TP7-94 (25) as optional procedure F.However, it was not performed in this study. Asphalt concrete samples used for the SHRP Level III sheartester characterization were prepared using SHRP specified gyratory compaction protocols as outlined inAASHTO TP4 (25). Figure 2 shows an asphalt concrete sample mounted in the SHRP shear tester for thevolumetric-hydrostatic and uniaxial strain at constant radius tests. Figure 3 shows an asphalt concretesample mounted in the SHRP shear tester for the simple shear at constant height, frequency sweep shearat constant height and repeated shear at constant stress ratio tests.Figure 2 SHRP Shear Tester Uniaxial Strain and Volumetric-Hydrostatic Sample Configuration

BERTHELOT, CROCKFORD & LYTTON 9Figure 3 SHRP Shear Tester Simple Shear, Frequency Sweep Shear, and Repeated Shear SampleConfiguration4.4.1 SHRP Volumetric-Hydrostatic CharacterizationThe SHRP volumetric-hydrostatic test evaluates the bulk elastic properties of asphalt concrete underdifferent states of hydrostatic stress and temperature. SHRP volumetric-hydrostatic testing wasperformed on triplicate gyratory compacted samples at seven percent air voids from each Radisson SPS-9A asphalt concrete mix at test temperatures of 4°C, 20°C, and 40°C, and corresponding peak hydrostatictractions of 830 kPa, 690 kPa, and 550 kPa, respectively. Tables 7 and 8 summarize the SHRP bulkmodulus measurements across the Radisson SPS-9A asphalt concrete mixes and stress states-testtemperatures considered in this analysis respectively.A statistical analysis was performed at a 95 percent confidence level to evaluate the significance of theSHRP bulk modulus measurements across the Radisson SPS-9A asphalt concrete mixes and stress statestesttemperatures employed in the analysis. A two-way analysis of variance concluded that RadissonSPS-9A asphalt concrete mix type had a significant effect on the mean SHRP bulk moduli measurements.However, test temperature-stress state, and the interaction effects between Radisson SPS-9A asphaltconcrete mix type and test temperature-stress state did not have a significant effect on the mean SHRPbulk measurements. Duncan's pair wise comparison of the mean SHRP bulk modulus of the RadissonSPS-9A asphalt concrete mixes grouped by test temperature-stress state determined that: mixes 900901,900902, 900903, 900960, and 900962 were not significantly different; mixes 900901, 900902, 900903,900959, and 900962 were not significantly different; and mixes 900901, 900903, 900959, 900961, and900962 were not significantly different. Duncan's pairwise comparison of the mean SHRP bulk modulusacross test temperatures-stress states grouped by Radisson SPS-9A asphalt concrete mix determined that

BERTHELOT, CROCKFORD & LYTTON 10no significant difference existed between the mean SHRP bulk modulus measurements at 4°C (830 kPa),20°C (690 kPa), and 40°C (550 kPa).Table 7 SHRP Bulk Modulus Measurements and Duncan's Pairwise Comparison of RadissonSpecific Pavement Studies-9A Asphalt Concrete Mixes Grouped by Test Temperature-Stress StateSPS-9A TestDuncan's Grouping*SectionMean SHRPBulk Modulus(MPa)Mean SHRPBulk ModulusCoefficient ofVariation(Percent)900901 256.091 70.93 A B C900902 409.220 67.79 A B900903 374.032 53.25 A B C900959 205.111 25.80 B C900960 450.165 48.23 A900961 185.729 43.39 C900962 363.446 27.46 A B CMean 320.542 48.12* Asphalt concrete mixes with same letter are not significantly different.Table 8 SHRP Bulk Modulus Measurements and Duncan's Pairwise Comparison of TestTemperatures-Stress States Grouped by Radisson Special Pavement Studies -9A Asphalt ConcreteMixTestTemperature(HydrostaticTraction)Mean SHRPBulk Modulus(MPa)Mean SHRPBulk ModulusCoefficient ofVariation(Percent)Duncan's Grouping*4°C (830 kPa) 347.698 55.07 A20°C (690 kPa) 273.068 43.66 A40°C (550 kPa) 339.899 45.63 AMean 320.542 48.12* Test temperatures-stress states with same letter are not significantly different.4.4.2 SHRP Uniaxial Strain at Constant Radius CharacterizationThe SHRP uniaxial strain at constant radius test employs the SHRP shear tester to characterize the elasticand plastic behavior of asphalt concrete under constrained uniaxial loading. SHRP uniaxial strain atconstant radius testing was performed on triplicate gyratory compacted samples at seven percent air voidsfrom each Radisson SPS-9A asphalt concrete mix at test temperatures of 4°C, 20°C, and 40°C, andcorresponding uniaxial tractions of 655 kPa, 550 kPa, and 345 kPa, respectively. Tables 9 and 10summarize the SHRP uniaxial constrained modulus measurements across the Radisson SPS-9A asphaltconcrete mixes and stress states-test temperatures considered in this analysis respectively.A statistical analysis was performed at a 95 percent confidence level to evaluate the significance of theSHRP uniaxial constrained compression modulus measurements across the Radisson SPS-9A asphaltconcrete mixes and test temperatures-stress states employed in the analysis. A two-way analysis of

BERTHELOT, CROCKFORD & LYTTON 11variance concluded that Radisson SPS-9A asphalt concrete mix type had a significant effect on the themean SHRP uniaxial constrained compression modulus measurements. However, test temperature-stressstate and the interaction effects of Radisson SPS-9A asphalt concrete mix type and test temperature-stressstate had no significant effect on the mean SHRP uniaxial compression moduli measurements.. Duncan'spairwise comparison of the mean SHRP uniaxial constrained compression modulus of the Radisson SPS-9A asphalt concrete mixes grouped by test temperature-stress state determined that: mixes 900903,900959, and 900961 were not significantly different; mixes 900902, 900903, 900960, and 900962 werenot significantly different; and mixes 900901, 900902, 900960, and 900962 were not significantlydifferent. Duncan's pairwise comparison of the mean SHRP uniaxial constrained compression modulusacross the test temperatures-stress states grouped by Radisson SPS-9A asphalt concrete mix determinedthat no significant difference existed between the mean SHRP uniaxial constrained compression modulusmeasurements at 4°C (655 kPa), 20°C (550 kPa), and 40°C (345 kPa).Table 9 SHRP Uniaxial Constrained Compression Modulus Measurements and Duncan’s PairwiseComparison of Radisson Specific Pavement Studies -9A Asphalt Concrete Mixes Grouped by TestTemperature-Stress StateSPS-9A TestSectionMean SHRPUniaxialConstrainedCompressionModulus(MPa)Mean SHRPUniaxialConstrainedCompressionModulusCoefficient ofVariation(Percent)Duncan's Grouping*900901 73.570 31.05 C900902 108.728 58.20 B C900903 156.457 37.73 A B900959 209.890 37.22 A900960 112.784 18.42 B C900961 220.411 22.69 A900962 131.344 57.83 B CMean 144.741 37.59* Asphalt concrete mixes with same letter are not significantly different.Table 10 SHRP Uniaxial Constrained Compression Modulus Measurements and Duncan’sPairwise Comparison of Test Temperatures-Stress States Grouped by Radisson Specific PavementStudies -9A Asphalt Concrete MixTestTemperature(UniaxialTraction)Mean SHRPUniaxialConstrainedModulus(MPa)Mean SHRPUniaxialConstrainedModulusCoefficient ofVariation(Percent)Duncan's Grouping*4°C (655 kPa) 159.235 43.49 A20°C (550 kPa) 139.528 33.44 A40°C (345 kPa) 135.460 35.84 AMean 144.741 37.59* Test temperatures-stress states with same letter are not significantly different.

BERTHELOT, CROCKFORD & LYTTON 124.4.3 SHRP Simple Shear at Constant Height CharacterizationThe SHRP simple shear at constant height test employs the SHRP shear tester to characterize the elastic,viscoelastic, and plastic behavior of asphalt concrete mixes under states of mixed mode shear and uniaxialcreep loading. SHRP simple shear at constant height testing was performed on triplicate gyratorycompacted samples at seven percent air voids from each Radisson SPS-9A asphalt concrete mix at testtemperatures of 4°C, 20°C, and 40°C, and corresponding SHRP simple shear tractions of 345 kPa, 105kPa, and 35 kPa, respectively. Tables 11 and 12 summarize the total SHRP simple shear strainmeasurements across the Radisson SPS-9A asphalt concrete mixes and stress states-test temperaturesconsidered in this analysis respectively.A statistical analysis was performed at a 95 percent confidence level to evaluate the significance of thetotal SHRP simple shear strain measurements across the Radisson SPS-9A asphalt concrete mixes andtest temperatures-stress states employed in the analysis. A two-way analysis of variance concluded thatRadisson SPS-9A asphalt concrete mix type, test temperature-stress state, and the interaction effectsbetween Radisson SPS-9A asphalt concrete mix type and test temperature-stress state had a significanteffect on the mean total SHRP simple shear strain measurements. Duncan's pairwise comparison of themean total SHRP simple shear strain across the Radisson SPS-9A asphalt concrete mixes grouped by testtemperature-stress state determined that: mixes 900961 and 900962 were significantly different from allother mixes; however, mixes 900901, 900903, and 900960 were not significantly different; and mixes900901, 900959, 900960, and 900962 were not significantly different. Duncan's pairwise comparisonacross the test temperatures-stress states grouped by Radisson SPS-9A asphalt concrete mix determinedthat significant difference existed between the mean total SHRP simple shear strain measurements at 5°C(345 kPa), 20°C (105 kPa) and 40°C (35 kPa).Table 11 Total SHRP Simple Shear Strain Measurements and Duncan’s Pairwise Comparison(reference) of Radisson Specific Pavement Studies -9A Asphalt Concrete Mixes Grouped by TestTemperature-Stress StateSPS-9A TestSectionMean TotalSHRP SimpleShear Strain(mm/mm)Mean TotalSHRP SimpleShear StrainCoefficient ofVariation(Percent)Duncan's Grouping*900901 0.007145 6.21 B C900902 0.002038 55.49 D900903 0.008073 20.44 B900959 0.005119 31.53 C900960 0.006430 15.87 B C900961 0.011165 22.63 A900962 0.006000 31.96 CMean 0.006567 26.30* Asphalt concrete mixes with same letter are not significantly different.

BERTHELOT, CROCKFORD & LYTTON 13Table 12 Total SHRP Simple Shear Strain Measurements and Duncan’s Pairwise Comparison ofTest Temperatures-Stress States Grouped by Radisson Specific Pavement Studies -9A AsphaltConcrete MixTestTemperature(Simple ShearTraction)Mean TotalSHRP SimpleShear Strain(mm/mm)Mean TotalSimple SHRPShear StrainCoefficient ofVariation(Percent)Duncan's Grouping*4°C (345 kPa) 0.004491 18.50 A20°C (105 Pa) 0.006959 29.68 B40°C (35 kPa) 0.008251 30.73 CMean 0.006567 26.30* Test temperatures-stress states with same letter are not significantly different.4.4.4 SHRP Frequency Sweep Shear at Constant Height CharacterizationThe SHRP frequency sweep shear at constant height test employs the SHRP shear tester to evaluate thecomplex shear behavior of asphalt concrete. SHRP frequency sweep shear testing was performed ontriplicate gyratory compacted samples at seven percent air voids from each Radisson SPS-9A asphaltconcrete mix at 4°C, 20°C, and 40°C, respectively. Since the Radisson SPS-9A test site is located onHighway 16 where the design traffic loading is a truck tire traveling at a posted speed limit of 100kilometers per hour, detailed analysis of the SHRP frequency sweep shear data was restricted to 10 Hzcyclic frequency. Tables 13 and 14 summarize the complex SHRP shear modulus measurements at 10Hz cyclic frequency across the Radisson SPS-9A asphalt concrete mixes and test temperaturesrespectively.A statistical analysis was performed at a 95 percent confidence level to evaluate the significance of thecomplex SHRP shear modulus measurements at 10 Hz cyclic frequency across the Radisson SPS-9Aasphalt concrete mixes and test temperatures employed in the analysis. A two-way analysis of varianceconcluded that Radisson SPS-9A asphalt concrete mix type and test temperature had a significant effecton the mean complex SHRP shear modulus at 10 Hz cyclic frequency. However, the interaction effectsbetween Radisson SPS-9A asphalt concrete mix type and test temperature was found not to have asignificant effect on the SHRP complex shear modulus measurements at 10 Hz cyclic frequency.Duncan's pairwise comparison of the mean complex SHRP shear modulus measurements at 10 Hz cyclicfrequency of the Radisson SPS-9A asphalt concrete mixes grouped by test temperature determined that:mix 900902 was significantly different from all other mixes; however, mixes 900901, 900903, 900959,900960, 900961, and 900962 were not significantly different. Duncan's pairwise comparison of the meancomplex SHRP shear modulus at 10 Hz cyclic frequency across the test temperatures grouped byRadisson SPS-9A asphalt concrete mix determined that significant difference existed between the meancomplex SHRP shear modulus measurements at 4°C, 20°C, and 40°C.

BERTHELOT, CROCKFORD & LYTTON 14Table 13 Complex SHRP Shear Modulus Measurements and Duncan’s Pairwise Comparison at 10Hz Cyclic Frequency of Radisson Specific Pavement Studies-9A Asphalt Concrete Mixes Groupedby Test TemperatureSPS-9A TestSectionMean ComplexSHRP ShearModulus(MPa)Mean ComplexSHRP ShearModulusCoefficient ofVariation(Percent)Duncan's Grouping *900901 827.791 8.39 B900902 1491.639 55.21 A900903 855.529 11.15 B900959 1029.969 24.37 B900960 798.400 11.26 B900961 655.615 31.59 B900962 681.342 8.38 BMean 905.755 21.48* Asphalt concrete mixes with same letter are not significantly different.Table 14 Complex SHRP Shear Modulus Measurements and Duncan’s Pairwise Comparison at 10Hz Cyclic Frequency across Test Temperatures Grouped by Radisson Specific Pavement Studies-9A Asphalt Concrete MixTestTemperatureMean ComplexSHRP ShearModulus(MPa)Mean ComplexSHRP ShearModulusCoefficient ofVariation(Percent)Duncan's Grouping*4°C 1981.779 15.56 A20°C 526.286 14.97 B40°C 209.170 33.90 CMean 905.745 21.48* Test temperatures with same letter are not significantly different.Tables 15 and 16 summarize the mean complex SHRP shear phase angle measurements at 10 Hz cyclicfrequency across the Radisson SPS-9A asphalt concrete mixes and test temperatures, respectively. Astatistical analysis was performed at a 95 percent confidence level to evaluate the statistical significanceof the mean SHRP shear phase angle measurements at 10 Hz cyclic frequency across the Radisson SPS-9A asphalt concrete mixes and test temperatures employed in the analysis. A two-way analysis ofvariance concluded that Radisson SPS-9A asphalt concrete mix type and test temperature had asignificant effect on the mean SHRP shear phase angle measurements. However, the interaction effectsbetween Radisson SPS-9A asphalt concrete mix type and test temperature was found not to have asignificant effect on the mean SHRP shear phase angle measurements. Duncan's pairwise comparison ofthe mean SHRP shear phase angle measurements at 10 Hz cyclic frequency for each Radisson SPS-9Aasphalt concrete mix grouped by test temperature determined that: mixes 900901, 900903, 900959,900960, and 900961 were not significantly different; and mixes 900902 and 900962 were notsignificantly different. Duncan's pairwise comparison of the mean SHRP shear phase anglemeasurements at 10 Hz cyclic frequency across test temperatures grouped by Radisson SPS-9A asphalt

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.

BERTHELOT, CROCKFORD & LYTTON 16Table 17 summarizes the cumulative repeated shear strain at 20,000 load cycles of the Radisson SPS-9Aasphalt concrete mixes. A statistical analysis was performed at a 95 percent confidence level to evaluatethe significance of the cumulative shear strain measurements at 20,000 load cycles across the RadissonSPS-9A asphalt concrete mixes. A one-way analysis of variance concluded that Radisson SPS-9A asphaltconcrete mix type had a significant effect on the mean cumulative shear strain measurements at 20,000load cycles. Duncan's pairwise comparison determined that the mean cumulative shear strainmeasurements at 20,000 load cycles of mix 900961 was significantly different from all other mixes;however, mixes 900901, 900903, 900959, and 900960 were not significantly different; mixes 900903,900959, 900960, and 900962 were not significantly different; and mixes 900902, 900959, 900960, and900962 were not significantly different.Cumulative Shear Strain (mm/mm)0.0500.0450.0400.0350.0300.0250.0200.0150.0100.0050.0000 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000Load Cycles900901 900902 900903 900959 900960 900961 900962Figure 4 Cumulative SHRP Repeated Shear Strain versus Number of Load Cycles of RadissonSpecific Pavement Studies -9A Asphalt Concrete Mixes

BERTHELOT, CROCKFORD & LYTTON 17Table 17 SHRP Repeated Shear Measurements and Duncan's Pairwise Comparison of CumulativeShear Strain at 20,000 Load Cycles across Radisson Specific Pavement Studies -9A AsphaltConcrete MixesSPS-9A TestSectionMean SHRPRepeated Shearat CSRCumulativeStrain(mm/mm)SHRPRepeated Shearat CSRCumulativeStrainCoefficient ofVariation(Percent)Duncan's Grouping*900901 0.028803 22.01 B900902 0.002730 67.35 D900903 0.021173 34.84 B C900959 0.015782 27.81 B C D900960 0.014654 33.01 B C D900961 0.046602 42.95 A900962 0.009083 14.59 C DMean 0.019832 34.65* Asphalt concrete mixes with same letter are not significantly different. CSR = Constant Stress RatioAlthough the SHRP shear tester is a highly capable characterization apparatus designed to independentlycontrol axial, confinement, and shear tractions, several limitations were found to exist in the SHRP sheartester and the Superpave TM shear testing protocols as specified in AASHTO TP7. The coefficient ofvariation of the SHRP shear tester measurements was significantly higher than the phenomenological andrapid triaxial test methods. The SHRP shear tester is expensive to own and operate, and the shear testingprotocols are quite sophisticated, rendering it impractical for use by most public road authorities, roadcontractors, road consultants, and materials suppliers. In addition, sample preparation requires samplesaw cutting and gluing end platens which is time consuming and not conducive to production testing.This research also found problems in regards to several samples failing during SHRP frequency sweepshear testing as illustrated in Figure 5.Another limitation to the SHRP Level III shear testing protocols outlined in AASHTO TP7 is thespecified three unique applied tractions and concomitant test temperatures. As a result, the non-linearstress sensitivity and temperature sensitivity of asphalt concrete mixes cannot be directly andindependently characterized using the current Superpave TM shear tester protocols.

BERTHELOT, CROCKFORD & LYTTON 18Figure 5 Failed SHRP Shear Test Sample4.5 Rapid Triaxial CharacterizationTriaxial testing has been used by the road industry to characterize all types of road materials [26, 27].However, drawbacks to traditional triaxial test apparatus include: limited stress state and test temperaturetesting capabilities; sample preparation and instrumentation is time consuming and therefore, notconducive to production testing; limited feedback control capabilities; limited dynamic testingcapabilities; and direct measurement of Poisson’s ratio is difficult. To overcome these drawbacks, thisstudy employed a new prototype full feedback controlled rapid triaxial test apparatus shown in Figure 6 tocharacterize the Radisson SPS-9A asphalt concrete mixes.Dynamic frequency sweep testing for characterizing road materials and is standardized in ASTM D3497.The real and imaginary components of the complex modulus may be expressed as:E *= E' + iE"where: E* = complex stiffness modulus (Pa)E’ = real component of stiffness modulus (Pa)E” = imaginary component of stiffness modulus (Pa)

BERTHELOT, CROCKFORD & LYTTON 19Figure 6 Rapid Triaxial TesterThe applied traction waveform and strain response of a dynamic frequency sweep test may be expressedas:iωt() t = eT11 T 11pεi( t )11 ( t)ω −φ= ε11pewhere: T 11 (t) = time dependent boundary traction in X 1 coordinate direction (Pa)T 11p = peak applied boundary traction in X 1 coordinate direction (Pa)ε11 (t) = time dependent axial strain response in X1 coordinate directionε11p= peak axial strain response in X1 coordinate directionω = angular load frequency (radians per second)t = load period (seconds)φ = phase angle (radians)By substitution, the complex modulus of a time dependent material may be expressed as:E * =T11P(t)ε11P(t)=εiωtT11pei(ωt−φ)11p e

BERTHELOT, CROCKFORD & LYTTON 20For an elastic material, strain response is instantaneous with the applied traction, therefore, the dynamicelastic modulus may be expressed as the absolute value of the complex modulus:*E D = E=T11pε11pIn addition to axial deformations, four radial LVDT’s were used to monitor radial deformations andPoisson’s ratio was measured directly as the ratio of the lateral and uniaxial strain.ν11()t =ε−ε2211() t() t=ε−ε3311() t() twhere:ν 11 = Poisson’s ratio in Xε 11ε 22ε 331 coordinate direction= strain in X1 coordinate direction= strain in X2 coordinate direction= strain in X3 coordinate directionTriaxial frequency sweep testing was performed at three fully reversed compression-extension boundarytractions illustrated in Figure 7; test temperatures of 4°C, 20°C, 40°C, 70°C, and 100°C; and loadfrequencies of 0.1 Hz, 1.0 Hz, 5.0 Hz, 10.0 Hz. However, since the Radisson SPS-9A test site is locatedon Highway 16, detailed analysis of the triaxial frequency sweep data analysis presented herein wasrestricted to compressive data at stress state three and 10 Hz cyclic frequency as illustrated in Figure 7.However, it should be noted that statistical differences were found to exist across all triaxialmeasurements at all stress states and cyclic frequencies-.Tables 18 and 19 summarize the triaxial complex compression modulus measurements at 10 Hz cyclicfrequency and stress state three across the Radisson SPS-9A asphalt concrete mixes and test temperaturesrespectively. A two-way analysis of variance concluded that Radisson SPS-9A asphalt concrete mix type,test temperature and the interaction effects of Radisson SPS-9A asphalt concrete mix type and testtemperature had a significant effect on the mean triaxial complex compression modulus measurements atstress state three and 10 Hz cyclic frequency. Duncan's pairwise comparison of the mean triaxial complexcompression modulus measurements at stress state three and 10 Hz cyclic frequency of the Radisson SPS-9A asphalt concrete mixes grouped by test temperature determined that: mixes 900959, 900901, and900962 were significantly different from all other mixes; however, mixes 900902 and 900903 and mixes900902, 900960, and 900961 were not significantly different. Duncan's pairwise comparison of the meantriaxial complex compression modulus at stress state three and 10 Hz cyclic frequency across the testtemperatures grouped by Radisson SPS-9A asphalt concrete mix type determined that the mean triaxialcompression modulus measurements at 5°C, 20°C, 40°C, 70°C, and 100°C were significantly different.

BERTHELOT, CROCKFORD & LYTTON 21Applied Boundary Tractions (kPa)2501505045025050650350T 11:pT 11:250/50 T22 =T 33:150Stress State 1T 22 =T 33:q• • •Stress State 2time (sec)T 11:450/50T 22 =T 33:250Stress State 3T 11:650/50T22=T 33:350• • •time (sec)• • •50time (sec)Figure 7 Triaxial Compression-Extension Frequency Sweep Boundary TractionsTable 18 Mean Triaxial Complex Compression Modulus and Duncan's Pairwise Comparison atStress State Three and 10 Hz Cyclic Frequency of Radisson Specific Pavement Studies -9A AsphaltConcrete Mixes Grouped by Test TemperatureSPS-9A TestSectionMean TriaxialComplexCompressionModulus(MPa)Mean TriaxialComplexCompressionModulusCoefficient ofVariation(Percent)Duncan's Grouping *900901 1245.862 6.46 B900902 1150.703 7.92 C D900903 1178.431 4.96 C900959 1325.216 5.97 A900960 1121.963 5.26 D900961 1117.473 5.17 D900962 941.386 5.96 EMean 1154.429 5.96* Asphalt concrete mixes with same letter are not significantly different.

BERTHELOT, CROCKFORD & LYTTON 22Table 19 Mean Triaxial Complex Compression Modulus and Duncan's Pairwise Comparison atStress State Three and 10 Hz Cyclic Frequency across Test Temperatures Grouped by RadissonSpecific Pavement Studies -9A Asphalt Concrete MixTestTemperatureMean TriaxialComplexCompressionModulus(MPa)Mean TriaxialComplexCompressionModulusCoefficient ofVariation(Percent)Duncan's Grouping *5°C 2460.274 3.51 A20°C 1938.216 4.31 B40°C 721.486 7.70 C70°C 376.704 5.19 D100°C 275.466 9.07 EMean 1154.429 5.96* Test temperatures with same letter are not significantly different.Tables 20 and 21 summarize the triaxial compression Poisson’s ratio measurements at 10 Hz cyclicfrequency and stress state three across the Radisson SPS-9A asphalt concrete mixes and test temperaturesrespectively. A two-way analysis of variance concluded that Radisson SPS-9A asphalt concrete mixtype, test temperature and the interaction effects of Radisson SPS-9A mix type and test temperature had asignificant effect on the mean triaxial compression Poisson's ratio measurements at stress state three and10 Hz cyclic frequency. Duncan's pairwise comparison of the mean triaxial compression Poisson's ratiomeasurements at stress state three and 10 Hz cyclic frequency across the Radisson SPS-9A asphaltconcrete mixes grouped by test temperature determined that: mixes 900901 and 900961 were notsignificantly different; mixes 900902, 900903, and 900960 were not significantly different; and mixes900959 and 900962 were not significantly different. Duncan's pairwise comparison of the mean triaxialcompression Poisson's ratio measurements at stress state three and 10 Hz cyclic frequency across the testtemperatures grouped by Radisson SPS-9A asphalt concrete mix determined that the mean triaxialcompression Poisson’s ratio measurements at 5°C, 20°C, 40°C, 70°C, and 100°C were significantlydifferentTables 22 and 23 summarize the triaxial phase angle measurements at 10 Hz cyclic frequency and stressstate three across the Radisson SPS-9A asphalt concrete mixes and test temperatures respectively. Atwo-way analysis of variance concluded that Radisson SPS-9A asphalt concrete mix type, testtemperature and the interaction effects of Radisson SPS-9A asphalt concrete mix type and testtemperature had a significant effect on the mean triaxial phase angle measurements at stress state threeand 10 Hz cyclic frequency. Duncan's pairwise comparison of the mean triaxial phase anglemeasurements at stress state three and 10 Hz cyclic frequency of the Radisson SPS-9A asphalt concretemixes grouped by test temperature determined that: mixes 900961, 900901, 900960 and 900959 weresignificantly different from all other mixes; however, mixes 900903 and 900962 were not significantlydifferent; and mixes 900902 and 900903 were not significantly different. Duncan's pairwise comparisonof the mean triaxial phase angle measurements at stress state three and 10 Hz cyclic frequency across thetest temperatures grouped by Radisson SPS-9A asphalt concrete mix determined that the mean triaxialphase angle measurements at 5°C, 20°C, 40°C, 70°C, and 100°C were significantly different.

BERTHELOT, CROCKFORD & LYTTON 23Table 20 Mean Triaxial Compression Poisson's Ratio and Duncan's Pairwise Comparison at StressState Three and at 10 Hz Cyclic Frequency of Radisson Specific Pavement Studies -9A AsphaltConcrete Mixes Grouped by Test TemperatureSPS-9A TestSectionMean TriaxialCompressionPoisson's RatioMean TriaxialCompressionPoisson's RatioCoefficient ofVariation(Percent)Duncan's Grouping*900901 0.265 4.42 A900902 0.224 15.01 B900903 0.232 22.20 B900959 0.177 23.34 C900960 0.221 9.49 B900961 0.267 15.37 A900962 0.193 14.75 CMean 0.226 14.94* Asphalt concrete mixes with same letter are not significantly different.Table 21 Mean Triaxial Compression Poisson's Ratio and Duncan's Pairwise Comparison at StressState Three and 10 Hz Cyclic Frequency across Test Temperatures Grouped by Radisson SpecificPavement Studies -9A Asphalt Concrete MixTestTemperatureMean TriaxialCompressionPoisson's RatioMean TriaxialComplexCompressionPoisson’s RatioCoefficient ofVariation(Percent)Duncan's Grouping *5°C 0.045 42.74 E20°C 0.166 9.32 D40°C 0.303 7.51 B70°C 0.269 6.59 C100°C 0.344 8.55 AMean 0.226 14.94* Test temperatures with same letter are not significantly different.

BERTHELOT, CROCKFORD & LYTTON 24Table 22 Mean Triaxial Phase Angle and Duncan's Pairwise Comparison at Stress State Three andat 10 Hz Cyclic Frequency of Radisson Specific Pavement Studies -9A Asphalt Concrete MixesGrouped by Test TemperatureSPS-9A TestSectionMean TriaxialPhase Angle(Degrees)Mean TriaxialPhase AngleCoefficient ofVariation(Percent)Duncan's Grouping*900901 16.81 6.20 B900902 14.71 3.89 E900903 15.02 3.45 D E900959 14.06 3.17 F900960 16.05 4.32 C900961 17.76 1.87 A900962 15.39 5.60 DMean 15.69 4.07* Asphalt concrete mixes with same letter are not significantly different.Table 23 Mean Triaxial Phase Angle and Duncan's Pairwise Comparison at Stress State Three andat 10 Hz Cyclic Frequency across Test Temperatures Grouped by Radisson Specific PavementStudies -9A Asphalt Concrete MixTestTemperatureMean TriaxialPhase Angle(Degrees)Mean TriaxialPhase AngleCoefficient ofVariation(Percent)Duncan's Grouping *5°C 7.63 7.16 E20°C 14.73 3.46 D40°C 19.67 4.19 A70°C 18.48 2.35 B100°C 17.93 3.20 CMean 15.69 4.07* Test temperatures with same letter are not significantly different.In the past, triaxial testing of road materials has specified a 2:1 sample height to diameter dimensionalratio. One of the benefits to the rapid triaxial tester employed in this study is that it characterizes 150 mmtall by 150 mm diameter SHRP specified gyratory compacted samples without the need for sampletrimming, gluing end platens to the sample, or attaching membranes to the sample. This greatly decreasessample preparation and testing time. In addition, since end platens do not have to be glued to the samples,spatial stress/strain gradients and end shear effects are reduced. The ability to mechanisticallycharacterize 150 mm diameter by 150 mm tall gyratory compacted samples is beneficial given the roadindustry’s adoption of the SHRP gyratory compactor for laboratory compaction of asphalt concrete. Therapid triaxial tester could therefore, be employed as a complementary mechanistic characterization tool tothe SHRP gyratory compactor for asphalt concrete mix design and analysis such as the Superpave TM LevelI system. The rapid triaxial tester has also been demonstrated in the field for production testingapplications such as construction quality control/quality assurance [28].

BERTHELOT, CROCKFORD & LYTTON 25This research found the rapid triaxial tester to be capable of characterizing the fundamentalthermomechanical constitutive behavior of asphalt concrete mixes required for mechanistic roadmodelingapplications. The rapid triaxial tester distinguished significant differences in the compressionmodulus, compression Poisson’s ratio, and phase angle among the Radisson SPS-9A asphalt concretemixes across load frequencies, stress states and test temperatures. The rapid triaxial compressive complexmodulus, Poisson’s ratio and phase angle can be mathematically transformed to provide linearviscoelastic materials constitutive relations that can be input into viscoelastic road models to directlypredict permanent deformation of road structures. As a result, the ability to accurately measureviscoelastic constitutive properties under stress states, temperatures and load frequencies representative ofthose in the field may pose significant promise for reliably predicting rutting behavior of asphalt concretepavements.5.0 COMPARITIVE ANALYSISGood repeatability and accuracy of characterization results is essential for materials specification androad-modeling purposes. Figure 8 illustrates the mean coefficient of variation obtained from each asphaltconcrete characterization method from triplicate test samples grouped by SPS-9A asphalt concrete mix,stress state, and test temperature.As seen in Figure 8, the coefficient of variation of the traditional phenomenological and rapid triaxialcharacterization methods was relatively low. However, the SHRP Level III shear characterization and therapid triaxial compression Poisson’s ratio produced a relatively high coefficient of variation with theexception of the SHRP shear phase angle measurements. Given that the operator of the SHRP shear testerin this research had considerable materials testing experience with complex feedback control systems andthat system control problems with the SHRP shear tester could not be detected through detailed and timeconsuming system diagnostics, the high coefficient of variation could only be attributed to experimentalerror. It is believed that the relatively short 50 mm sample height may have had a significant influence inthe high variability of the SHRP shear tester measurements as witnessed in the high number of samplesthat failed during SHRP shear testing.This study found the coefficient of variation of the rapid triaxial compression Poisson’s ratiomeasurements to be slightly higher than the other rapid triaxial measurements Since the rapid triaxialtester radial transducer instrumentation was not designed for testing at 5°C and 20°C, the Poisson’s ratiomeasurement coefficient of variation at 5°C and 20°C were found to be higher than at other temperatures.As a result, the high coefficient of variation in the rapid triaxial Poisson’s ratio measurements can beremedied by employing more sensitive linear variable differential transducers at lower temperatures.Figure 9 shows the coefficient of variation across the characterization methods at the high testtemperatures only. As can be seen, the coefficient of variation of the rapid triaxial compressive Poisson’sratio decreased significantly when the cold test temperature was excluded from the analysis. However,the coefficient of variation of the SHRP shear modulus obtained form the frequency sweep shear testincreased significantly, further illustrating the uncertainty in the shear modulus measurements at hightemperature across the Radisson SPS-9A asphalt concrete mixes.Table 24 summarizes the mean observed rut measurements taken with a 1.5 m rut bar of the RadissonSPS-9A test sections after three years of service. As can be seen in Table 24, the coefficient of variationof the 1.5 m straight edge rut depth measurements across the SPS-9A asphalt concrete mixes relativelyhigh.

BERTHELOT, CROCKFORD & LYTTON 2650Coefficient of Variation (%)454035302520151050Marshall FlowMarshall StabilityHv eem StabilityUnconfined Compressive StrengthSHRP Bulk ModulusSHRP Constrained Compression ModulusTriaxial Compression ModulusSHRP Total Simple Shear StrainSHRP Complex Shear ModulusSHRP Shear Phase AngleSHRP RSCSR Cumulative StrainSHRP RSCSR Cumulative Strain RateTriaxial Extension ModulusTriaxial Compression Poisson's RatioTriaxial Extension Poisson's RatioTriaxial Phase AngleFigure 8 Asphalt Concrete Characterization Coefficient of Variation of Characterization MethodsGrouped by Radisson Specific Pavement Studies-9A Asphalt Concrete Mix, Stress State and TestTemperatureTable 24 Mean Rut Measurements in Radisson Specific Pavement Studies -9A Test Sections afterThree Years of ServiceSPS-9A TestSectionMean RutMeasurementsUsing 1.5 m RutBar (mm)RutMeasurementsCoefficient ofVariation Using1.5 m Rut Bar(Percent)900901 4.3 29.65900902 5.9 23.45900903 4.9 22.78900959 3.5 30.65900960 5.4 16.85900961 7.3 23.31900962 3.4 30.31Mean 5.0 25.29

BERTHELOT, CROCKFORD & LYTTON 2750Coefficient of Variation (%)454035302520151050Marshall StabilityMarshall FlowHveem StabilityUnconfined Compressive StrengthSHRP Bulk ModulusSHRP Total Simple Shear StrainSHRP Complex Shear ModulusSHRP Shear Phase AngleSHRP Constrained Compression ModulusSHRP RSCSR Cumulative StrainSHRP RSCSR Cumulative Strain RateTriaxial Compression ModulusTriaxial Extension ModulusTriaxial Compression Poisson's RatioTriaxial Extension Poisson's RatioTriaxial Phase AngleFigure 9 Asphalt Concrete Characterization Coefficient of Variation of Characterization MethodsGrouped by Radisson Specific Pavement Studies-9A Asphalt Concrete Mix, Stress State and HighTest TemperatureTable 25 summarizes the Duncan’s pairwise comparison results of the alternative asphalt concretecharacterization methods. As can be seen in Table and 25, the rapid triaxial tester best ranked the relativerutting behavior of the Radisson SPS-9A asphalt concrete mixes with the exception of mixes 900902 and900962 which appear to be reversed in order.

BERTHELOT, CROCKFORD & LYTTON 28Table 25 Characterization Method Duncan's Pairwise Comparison of Radisson Specific PavementStudies -9A Asphalt Concrete MixesRANKING [Duncan's Pairwise Comparison]MIX PROPERTIES 1 2 3 4 5 6 7Marshall Stability 900901[C]900961[C]900903[B,C]900960[B]900959[A]900902[A]900962[A]Marshall Flow 900901[C]900961[C]900902[B,C]900903[B,C]900960[B,C]900959[A,B]900962[A]Hveem Stability 900901[D]Unconfined Compressive Strength 900962[D]SHRP Bulk Modulus 900961[C]SHRP Constrained Modulus 900901[C]SHRP Total Simple Shear Strain 900902[D]SHRP Complex Shear Modulus at 10Hz900961[B]SHRP Shear Phase Angle at 10 Hz 900902[B]SHRP RSCSR Shear Strain at 20000CyclesTriaxial Complex CompressionModulus at 10 Hz and SS3Triaxial Compression Poisson’s Ratioat 10 Hz and SS3Triaxial Phase Angle at 10 Hz andSS3Mean Field Rutting After ThreeYears Service {mm}900902[D]900962[E]900959[C]900959[F]900961{7.3}SHRP = Strategic Highway Research ProgramRSCSR = Repeated Shear at Constant Stress RatioSS3 = Stress State Three900961[C,D]900961[C]900959[B,C]900902[B,C]900959[C]900962[B]900962[B]900962[C,D]900961[D]900962[C]900902[E]900902{5.9}900959[C]900902[B,C]900901[A,B,C]900960[B,C]900962[C]900960[B]900959[A]900960[B,C,D]900960[D]900960[B]900903[D,E]900960{5.4}900903[C]900901[B,C]900962[A,B,C]900962[B,C]900960[B,C]900901[B]900901[A]900959[B,C,D]900902[C,D]900902[B]900962[D]900903{4.9}900960[B]900903[B,C]900903[A,B,C]900903[A,B]900901[B,C]900903[B]900960[A]900903[B,C]900903[C]900903[B]900960[C]900901{4.3}900962[B]900960[B]900902[A,B]900959[A]900903[B]900959[B]900961[A]900901[B]900901[B]900901[A]900901[B]900959{3.5}900902[A]900959[A]900960[A]900961[A]900961[A]900902[A]900903[A]900961[A]900959[A]900961[A]900961[A]900962{3.4}6.0 SUMMARY AND CONCLUSIONSThis study sought to investigate alternative methods for characterizing the rutting behavior of asphaltconcrete mixes that can be used for material specifications and road modeling Seven Specific PavementStudies-9A asphalt concrete mixes (two Marshall and five Superpave TM ) built at the Radisson SPS-9A testsite were characterized with respect to Marshall stability and flow, Hveem stability, unconfinedcompressive strength, SHRP Level III shear tester, and triaxial frequency sweep properties. Thecoefficient of variation of the traditional phenomenological and rapid triaxial characterization methodswas relatively low. However, the SHRP Level III shear characterization produced a relatively high

BERTHELOT, CROCKFORD & LYTTON 29coefficient of variation with the exception of the SHRP shear phase angle measurements. The highcoefficient of variation could only be attributed to experimental error. It is believed that the relativelyshort 50 mm sample height may have had a significant influence in the high variability of the SHRP sheartester measurements as witnessed in the high number of samples that failed during SHRP shear testing.This study determined that traditional phenomenological asphalt concrete characterization methodsdistinguished some significant differences between the Radisson SPS-9A asphalt concrete mixes.However, they did not provide material constitutive relations necessary for mechanistic road responsemodeling. The SHRP shear tester also distinguished some significant differences between the asphaltconcrete mixes and can provide material constitutive relations necessary for mechanistic road responsemodeling. However, the SHRP shear tester is expensive to own and operate, produces relatively highvariability, and was found to be impractical for use by most public road authorities, road consultants, androad contractors. The rapid triaxial tester determined the most significant difference between the asphaltconcrete mixes and was found to be an efficient mechanistic testing apparatus to complement the SHRPgyratory compactor. The measured materials properties obtained from the rapid triaxial tester were alsofound to best correlate predict correlate with the relative rutting behavior of the SPS-9A test sections afterthree years of service. The complex properties measured by the rapid triaxial tester could bemathematically transformed into linear viscoelastic constitutive relations which could be used forviscoelastic mechanistic road modeling. This ability to accurately measure viscoelastic constitutiveproperties under stress states, temperatures and load frequencies representative of those in the field maypose significant promise for reliably predicting rutting behavior of asphalt concrete pavements.DISCLAIMERThe viewpoints expressed herein are those of the authors, and are not necessarily endorsed by theagencies involved with this research.7.0 REFERENCES1. University of Illinois at Urbana-Champaign Construction Technology Laboratories. "CalibratedMechanistic Structural Analysis Procedures for Pavements" NCHRP 1-26 Final Report, Champaign,Illinois, (1990).2. Von Quintas H. "Development of Asphalt-Aggregate Mixture Analysis System: AAMAS" FinalReport, NCHRP 9-6(1), Washington, DC, (1989).3. Fernando E,, Lytton R. "Demonstration of Potential Benefits of Performance-Oriented Specifications"Transportation Research Record 1353, TRB, National Research Council, Washington, DC, 73-81(1992).4. Anderson D. "Performance Related Specification for Hot Mix Asphalt Concrete" Final Report,NCHRP 10-26A. Pennsylvania Transportation Institute, Pennsylvania State University, UniversityPark (1990).5. Uzan J, Zollinger D, Lytton R. "Mechanistic/Empirical Model for the Structural Design of FlexiblePavements" Report No. 455-1. FHWA. Texas Transportation Institute, The Texas A&M UniversitySystem, College Station (1991).6. Little D, Youssef H. "Improved ACP Mixture Design: Development and Verification" Report 1170–1F. Texas Transportation Institute, The Texas A&M University System, College Station, (1992).

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