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From page 1... ... NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Responsible Senior Program Officer: Edward T Harrigan October 2014 Research Results Digest 390 CHAPTER 1 -- INTRODUCTION AND RESEARCH APPROACH 1.1 Background The Hamburg wheel tracking test (HWTT) Read the entire page →
From page 2... ... 2a. Analyze data received from laboratories to determine variability of the HWTT measurements. Read the entire page →
From page 3... ... 3of gyratory specimens, Location 6 should be at the joint where the two adjoining samples abut. The wheel makes 52 ± 2 passes across the specimen per minute. Read the entire page →
From page 4... ... 4the data. Given that preparation of gyratory and slab specimens is different, different sets of instructions were prepared for the two types of specimens. Read the entire page →
From page 5... ... 5• Twenty-two laboratories sent complete sets of data on the properties of the gyratorycompacted WY mixture. • Eleven laboratories sent complete sets of data on the properties of the slab-compacted WY mixture. Read the entire page →
From page 6... ... 6Evaluation of the difference between the SSD and Corelok values in Table 3-2 might indicate the method that is more reliable for measuring the air voids of HWTT samples. For the WY samples, at 7% SSD air voids, Corelok air voids were 0.8% higher (7.8%) Read the entire page →
From page 7... ... 7Table 3-2 Air voids of Field and WY samples measured by AMRL and participating laboratories. Mixture Lab Test Average STD Min Max N WY AMRL SSD 6.86 0.24 6.51 7.49 51 Corelok 7.73 0.17 7.42 8.15 51 Participating Labs SSD 6.44 0.32 5.72 7.00 62 Corelok 7.54 0.36 6.95 8.32 22 Field AMRL SSD 6.94 0.19 6.48 7.52 95 Corelok - - - - Participating Labs SSD 6.86 0.27 6.25 7.45 63 Corelok 8.05 0.37 7.60 8.70 19 0 2 4 6 8 10 12 6.4 6.5 6.6 6.7 6.8 6.9 7 7.1 7.2 7.3 7.4 to to to to to to to to to to to 6.49 6.59 6.69 6.79 6.89 6.99 7.09 7.19 7.29 7.39 7.49 N o. Read the entire page →
From page 8... ... 8website) Read the entire page →
From page 9... ... 9the measurements from the right and left wheels in a two-wheel machine or replicate measurements in a one-wheel machine. Several observations can be made from the profiles: 1. Read the entire page →
From page 10... ... 10 the mixtures from individual laboratories in Appendix B (which is available on the TRB website) Read the entire page →
From page 11... ... a b c d Figure 3-6 Deformation profiles of (a) Field gyratory, (b) Read the entire page →
From page 12... ... 12 ratories with different results from each other and from those in the first group. The large spread in the deformation measurements of the laboratories in the second group suggests problems with either the calibration or alignment of the HWTT device or the specimen-mold assembly in those laboratories. Read the entire page →
From page 13... ... 13 easily determined without major manipulation of the signal data. However, if the noise in the data is high, significant smoothing and averaging are required to determine the value of the parameters. Read the entire page →
From page 14... ... 14 The comparison of the properties of the gyratory and slab specimens is explained as follows. 3.10.1.1 Creep Slopes of Gyratory and Slab. Read the entire page →
From page 15... ... 15 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 Gyratory Slab Cr ee p S lo pe , m m /p as s Specimen Type Average of Slope1 StdDev of Slope1_2 Figure 3-11 Comparison of average and standard deviation of creep slopes of gyratory and slab specimens of well-performing mixture. 0 0.5 1 1.5 2 2.5 3 3.5 4 Gyratory Slab D ef or m ati on , m m Specimen Type Average of Def_End StdDev of Def_End2 Figure 3-12 Average deformation of gyratory and slab specimens of the well-performing mixture at the end of the test. Read the entire page →
From page 16... ... 16 0 0.5 1 1.5 2 2.5 3 3.5 4 Gyratory Slab Field 19 mm D ef or m ati on , m m Specimen Shape/Material Average of Def_1000 Average of Def_2000 Average of Def_5000 Average of Def_10000 Average of Def_End Figure 3-13 Average deformation of the Field mixture after various number of passes. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Gyratory Slab Field 19 mm D ef or m ati on , m m Specimen Shape/Material StdDev of Def_1000 StdDev of Def_2000 StdDev of Def_5000 StdDev of Def_10000 StdDev of Def_End Figure 3-14 Standard deviation of deformation of Field mixture after various number of passes. Read the entire page →
From page 17... ... 17 3.10.2 Comparison of Properties of Gyratory and Slab Specimens of Wyoming Mixture Test properties for the poorly performing WY mixture include number of passes to threshold rut depth, creep and stripping slopes, and inflection point. Different state DOTs specify different rut depth thresholds to define test failure. Read the entire page →
From page 18... ... 18 3.10.2.4 Number of Passes to Inflection Point. Figure 3-18 shows the average and standard deviation of the number of passes to the inflection point for the gyratory and slab specimens of the WY mixture. Read the entire page →
From page 19... ... 19 deformation and number of passes because creep slope explains how fast mixtures reach the same level of deformation. 3.10.2.6 Stripping Slopes of Gyratory and Slab of Wyoming Mixture. Read the entire page →
From page 20... ... 20 Another observation from Figure 3-21 is that the most frequent readings of maximum deformation occur at Locations 7 and 8 and not at Location 6, which is the midpoint. This indicates that there is a possibility that the positions of the measurement locations (and therefore the spacing between measurement locations) Read the entire page →
From page 21... ... 21 two-wheel HWTT machines for the WY gyratory specimens. Figure 3-22 shows that the two-wheel HWTT causes about a 10% greater average rut depth than one-wheel HWTT. Read the entire page →
From page 22... ... 22 that this material does not rut significantly, even after 10,000 cycles. The two-wheel system may produce more precise replicate measurements for well performing mixtures with low rut depths; however, the variability between replicates increases significantly with the increased rut depth of the specimens, probably due to the dynamic effect of one wheel on another. Read the entire page →
From page 23... ... 23 Those variability values that were not statistically significantly different were pooled to prepare the precision estimates. Statistical t- and F-tests were used to examine the significance of the following differences: 1. Read the entire page →
From page 24... ... 24 Table 4-1 Summary of statistics of rut depth (mm) and creep slope (mm/pass) Read the entire page →
From page 25... ... 25 Figure 4-1 Graphical comparison of average properties of Field mixture measured using data from all measurement locations, all except middle three measurement locations, and all except two measurement locations at each end. 0.00 0.50 1.00 1.50 2.00 2.50 3.00 Rut after 10,000 cycles Rut after 15,000 cycles Rut after 20,000 cycles A ve ra ge , m m Average Deformation, Gyratory Field gyratory (all sensors) Read the entire page →
From page 26... ... 26 20,000 passes. This could be because deformation at and around the midpoint of the slab, where the speed of the wheel is the highest, is the smallest. Read the entire page →
From page 27... ... 27 averages and the COVs of the measurements from slab and gyratory specimens. Table 4-5 through 4-7 provide the results of statistical comparison of the averages and repeatability/reproducibility COVs of deformation and creep slope from gyratory and slab specimens. Read the entire page →
From page 28... ... 28 depth and creep slope of gyratory and slab specimens become smaller. This is because by excluding the end measurement locations, the average deformation of gyratory specimens slightly increases and average deformation of slab specimens slightly decreases, resulting in smaller differences between properties of the two specimen types. Read the entire page →
From page 29... ... 29 ferences between variability of gyratory and slab specimens are statistically significant. From the above observations it can be concluded that the type of specimens used for the HWTT should be recorded along with the test results, given that the average of one or more properties could be significantly different depending on which measurement location data are used in the analysis. Read the entire page →
From page 30... ... 30 using different measurement locations: all measurement locations, all except three middle measurement locations, and all except two measurement locations at each end. In each table, the first two comparisons correspond to gyratory specimens and the third and fourth comparisons correspond to the slab specimens. Read the entire page →
From page 31... ... 31 Table 4-5 Statistical t-test on averages of rut depth (mm) after 10,000, 15,000, and 20,000 passes and of creep slope (mm/pass) Read the entire page →
From page 32... ... 32 not show any consistent trend of decrease or increase in the average properties. This might be because the deformation of slabs is more uniform among various measurement locations than those of gyratory specimens. Read the entire page →
From page 33... ... 33 Table 4-8 Summary of statistics of HWTT properties for gyratory and slab specimens of WY mixture computed from all measurement locations, all except the middle three measurement locations, and all except the end measurement locations. Specimens Type/ Measurement Locations Set Property # of Labs Average Repeatability Reproducibility STD COV, % STD COV, % Sx WY gyratory (all measurement locations) Read the entire page →
From page 34... ... 34 Figure 4-5 Comparison of the average properties measured using all measurement locations, all except middle three measurement locations, and all except the end measurement locations. 0 2000 4000 6000 8000 10000 12000 14000 Cycles to 6 mm Cycles to 12 mm Cycles to Inﬂection Point # of P as se s Average, # of Passes WY gyratory (all sensors) Read the entire page →
From page 35... ... 35 Table 4-9 Statistical t-test for comparison of the average # of cycles to 6-mm and 12-mm rut depths, creep and stripping slopes, and # of cycles to inflection point of WY gyratory and slab specimens from various measurement location sets. Comparison Property Averages S T df Critical t P Decision WY gyratory (all measurement locations) Read the entire page →
From page 36... ... 36 Table 4-11 Statistical F-test on repeatability COV of creep slope and stripping slope of gyratory and slab specimens of Wyoming mixture measured using different measurement locations sets. Comparison Property COV, % F Critical F df1 df2 P Decision WY gyratory (all measurement locations) Read the entire page →
From page 37... ... 37 Table 4-12 Statistical F-test on reproducibility COV of number of cycles to 6-mm and 12-mm rut depth and number of cycles to inflection point of gyratory and slab specimens of Wyoming mixture measured using different measurement locations sets. Comparison Property COV, # of Cycles F Critical F df1 df2 P Decision WY gyratory (all measurement locations) Read the entire page →
From page 38... ... 38 the averages and repeatability/reproducibility statistics of the properties of the gyratory and slab specimens. Tables 4-14 through 4-18 provide the results of statistical comparison of the averages and variability of the properties of gyratory and slab specimens. Read the entire page →
From page 39... ... 39 Tables 4-15 through 4-18 indicate that the COVs of the majority of the properties of slab specimens are significantly smaller than those of gyratory specimens. However, this could be attributed to the significantly smaller degrees of freedom (the number of values in the final calculation of F statistics) Read the entire page →
From page 40... ... 40 4.3.3 Pooled Statistics Precision estimates were prepared for the properties of the two types of mixtures. For the well performing mixture, the precision estimates were prepared for deformation after specific numbers of passes and for creep slope. Read the entire page →
From page 41... ... Table 4-14 Statistical t-test for comparison of average properties of gyratory and slab specimens of WY mixture using various measurement location sets. Comparison Property Averages S T df Critical t P Decision WY gyratory (all measurement locations) Read the entire page →
From page 42... ... 42 Table 4-16 Statistical F-test for comparison of repeatability COV of creep and stripping slope of gyratory and slab specimens of WY mixture using various measurement location sets. Comparison Property COV (%) Read the entire page →
From page 43... ... 43 considering the magnitude of the difference between the variability of creep slope of gyratory and slab specimens, this difference is considered significant from a practical stand point. Given that the number of gyratory specimens is larger than the number of slabs, the COVs measured from gyratory specimens are considered more accurate and, therefore, the precision estimates of creep slope are determined using the COVs corresponding to gyratory specimens as presented in Table 4-19. Read the entire page →
From page 44... ... 44 A statistical comparison of the repeatability and reproducibility COV of the number of passes to 6-mm and 12-mm rut depth and to the inflection point was conducted to determine if the COVs are the same and can be pooled together. The results are provided in Table 4-26. Read the entire page →
From page 45... ... 45 Table 4-23 Results of statistical comparison of repeatability COVs of the properties of gyratory and slab specimens. Property COV F Critical F df1 df2 P Decision Cycles to 6 mm 16 vs. Read the entire page →
From page 46... ... 46 CHAPTER 5 -- FINDINGS AND PROPOSED CHANGES TO AASHTO T 324 AND THE HWTT EQUIPMENT 5.1 Findings This report presents the results of an interlaboratory study (ILS) to determine precision estimates for AASHTO T 324, "Hamburg Wheel-Track Testing of Compacted Hot Mix Asphalt (HMA) Read the entire page →
From page 47... ... 47 5. The possibility of increasing the specimen length should be explored. Read the entire page →
From page 48... ... 48 9. http://en.wikipedia.org/wiki/Signal-to-noise_ratio_ (imaging) Read the entire page →
From page 49... ... 49 tory study. Their willingness to volunteer their time and conduct the testing under tight time constraints at no cost to the study is most appreciated. Read the entire page →
From page 50... ... Transportation Research Board 500 Fifth Street, NW Washington, DC 20001 These digests are issued in order to increase awareness of research results emanating from projects in the Cooperative Research Programs (CRP) Read the entire page →

From page 1...

... NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Responsible Senior Program Officer: Edward T Harrigan October 2014 Research Results Digest 390 CHAPTER 1 -- INTRODUCTION AND RESEARCH APPROACH 1.1 Background The Hamburg wheel tracking test (HWTT)