169 CHAPTER 4 OPERATIONS This chapter describes the various elements of the operation of the WesTrack facility, including the trafficking operations and the performance monitoring program. The performance monitoring program consisted of the collection of visual con- dition survey information (including raveling, flushing, rut- ting, fatigue cracking, and other forms of cracking), rut depth measurements, longitudinal profile, subsurface transverse pro- file, deflection, friction, weather data, pavement temperature, and moisture and post mortem evaluations. 4.1 TRAFFICKING Pavement traffic loading was performed by using four (driverless) tractor/triple-trailer combinations (Figure 13). The weights per single axle were 89 kN (20,000 lb). Each pass of the truck-trailer combination applied 10.49 80-kN (18,000-lb) ESALs. The trucks were equipped with 700 kPa (100 psi), 295/75R22.5 radial tires. The truck speed was 64 km/h (40 mi/h). 4.1.1 Trafficking History The four driverless vehicles were operated up to 22 hours per day with an average loading rate of 16 hours per day throughout the duration of trafficking. The average operating hours per day include delays caused by periodic rehabilita- tion and maintenance of the track, vehicle maintenance, and unfavorable weather conditions. The original plan for traf- ficking was targeted for 10 million ESALs or until the pave- ment test sections failed. The actual traffic applied was 4.9 million ESALs over a 2 1 / 2-year period. The accumulation of traffic in terms of ESALs is shown in Figure 86. Monthly traffic totals in terms of ESALs are shown in Figure 87. The driverless trucks accumulated 1.31 million km (821,000 mi). The primary objective of integrating driverless vehicles into the accelerated pavement testing program was to minimize incidents resulting from driver fatigue and drowsiness as a result of monotonous operation of the vehicles for extended periods of time. The vehicle automation also ensured close monitoring of operating speed and vehicle passes and close control of lateral wander. Two supervisors (lead electronic technician and lead mechanic) supervised the track loading operation and main- tained the vehicles. Three operators (8 hours per shift, 24 hours per day, 7 days per week) were assigned to the vehi- cle control room. These operators kept records pertinent to the traffic operation. The vehicles were stopped once every 24 hours for refuel- ing and routine inspections. The staging and launching of the trucks was closely monitored to ensure that the actual load- ing duration was recorded. 4.1.2 Traffic Wander WesTrack and other driverless vehicle systems have proved to be extremely repeatable in terms of lateral truck position control. For example, without the wander control built into driverless vehicle systems, the repeatability of the truck paths (less than ± 2 mm (0.08 in.) of variation from the center per pass) would reproduce the tire tread in flushed HMA pave- ment. Thus, the use of a vehicle guidance system can greatly accelerate the effects of traffic on pavements because actual highway traffic has wander. Figure 88 shows typical highway wander distribution and the distribution of wander of the Accelerated Load Facility (ALF) testing device currently used by the FHWA. WesTrack trucks were initially designed to operate “on the wire,” (cen- tered over the guide wire embedded in the pavement). To reproduce actual driver variation relative to the wire, the wan- der at WesTrack was achieved by moving the antennas on the trucks relative to the center line of the truck. A capability that allows the trucks to generate a distributed traffic pattern that approaches the wander of actual traffic was partially developed during the conduct of WesTrack. A Gaussian wheelpath distribution was programmed with a stan- dard deviation of 100 mm (4 in.) into the lateral position sys- tem of the truck. This system was partially tested during the trafficking at WesTrack, but was abandoned when some con- trol problems appeared. With additional work, this system can be perfected and would have applications to driverless vehicle control systems in the future. Traffic wander was introduced into WesTrack by offset- ting the front antenna on the truck to either left or right of the centerline of the truck for various periods of time. The truck antennas were moved 125 mm (5 in.) to the left or to the right in 25-mm (1-in.) increments. Tables 131 and 132
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CHAPTER 4
OPERATIONS
This chapter describes the various elements of the operationof the WesTrack facility, including the trafficking operationsand the performance monitoring program. The performancemonitoring program consisted of the collection of visual con-dition survey information (including raveling, flushing, rut-ting, fatigue cracking, and other forms of cracking), rut depthmeasurements, longitudinal profile, subsurface transverse pro-file, deflection, friction, weather data, pavement temperature,and moisture and post mortem evaluations.
4.1 TRAFFICKING
Pavement traffic loading was performed by using four(driverless) tractor/triple-trailer combinations (Figure 13).The weights per single axle were 89 kN (20,000 lb). Eachpass of the truck-trailer combination applied 10.49 80-kN(18,000-lb) ESALs. The trucks were equipped with 700 kPa(100 psi), 295/75R22.5 radial tires. The truck speed was 64km/h (40 mi/h).
4.1.1 Trafficking History
The four driverless vehicles were operated up to 22 hoursper day with an average loading rate of 16 hours per daythroughout the duration of trafficking. The average operatinghours per day include delays caused by periodic rehabilita-tion and maintenance of the track, vehicle maintenance, andunfavorable weather conditions. The original plan for traf-ficking was targeted for 10 million ESALs or until the pave-ment test sections failed. The actual traffic applied was 4.9million ESALs over a 21/2-year period. The accumulation oftraffic in terms of ESALs is shown in Figure 86. Monthlytraffic totals in terms of ESALs are shown in Figure 87. Thedriverless trucks accumulated 1.31 million km (821,000 mi).
The primary objective of integrating driverless vehicles intothe accelerated pavement testing program was to minimizeincidents resulting from driver fatigue and drowsiness as aresult of monotonous operation of the vehicles for extendedperiods of time. The vehicle automation also ensured closemonitoring of operating speed and vehicle passes and closecontrol of lateral wander.
Two supervisors (lead electronic technician and leadmechanic) supervised the track loading operation and main-
tained the vehicles. Three operators (8 hours per shift, 24 hours per day, 7 days per week) were assigned to the vehi-cle control room. These operators kept records pertinent tothe traffic operation.
The vehicles were stopped once every 24 hours for refuel-ing and routine inspections. The staging and launching of thetrucks was closely monitored to ensure that the actual load-ing duration was recorded.
4.1.2 Traffic Wander
WesTrack and other driverless vehicle systems have provedto be extremely repeatable in terms of lateral truck positioncontrol. For example, without the wander control built intodriverless vehicle systems, the repeatability of the truck paths(less than ±2 mm (0.08 in.) of variation from the center perpass) would reproduce the tire tread in flushed HMA pave-ment. Thus, the use of a vehicle guidance system can greatlyaccelerate the effects of traffic on pavements because actualhighway traffic has wander.
Figure 88 shows typical highway wander distribution andthe distribution of wander of the Accelerated Load Facility(ALF) testing device currently used by the FHWA. WesTracktrucks were initially designed to operate “on the wire,” (cen-tered over the guide wire embedded in the pavement). Toreproduce actual driver variation relative to the wire, the wan-der at WesTrack was achieved by moving the antennas on thetrucks relative to the center line of the truck.
A capability that allows the trucks to generate a distributedtraffic pattern that approaches the wander of actual trafficwas partially developed during the conduct of WesTrack. AGaussian wheelpath distribution was programmed with a stan-dard deviation of 100 mm (4 in.) into the lateral position sys-tem of the truck. This system was partially tested during thetrafficking at WesTrack, but was abandoned when some con-trol problems appeared. With additional work, this systemcan be perfected and would have applications to driverlessvehicle control systems in the future.
Traffic wander was introduced into WesTrack by offset-ting the front antenna on the truck to either left or right ofthe centerline of the truck for various periods of time. Thetruck antennas were moved 125 mm (5 in.) to the left or tothe right in 25-mm (1-in.) increments. Tables 131 and 132
show a summary of the number of truck passes and ESALsimparted to the pavement at each antenna position. Figure 89shows a histogram of the theoretical traffic wander calcu-lated based on the distribution shown in Table 131. Thewheelpath distribution represents a normal distribution trun-cated at 413 mm (16.25 in.). This covers approximately 83percent of a typical highway traffic distribution. WesTrackTechnical Report NCE-6 (57) provides the background infor-mation upon which this theoretical distribution is based.
The investigation of the theoretical traffic wander repre-sents only the start of a more extensive analysis of the actualwander at WesTrack. A number of factors influenced the traf-fic wander experienced at WesTrack. These factors includethe following:
• Antenna offset.• Oscillations introduced by the guidance system.• Trailer wander relative to the steering axle wander. • Cross-slope induced wander.• Trailer tracking into rutted wheelpaths.
Figure 90 shows the path that WesTrack Truck 1 (WT-1)with its front axle centered, followed down the south tangenton August 9, 1997. These data indicate that the truck had atendency to weave rather than follow the guidewire and thatthe rear antenna (located on the third trailer’s rear axle) wasalways offset down the cross-slope of the pavement. This off-set between the front antenna (front or steering axle of trac-tor) and the rear antenna (rear axle of third trailer) is of theorder of 200 mm (8 in.) to 250 mm (10 in.). Similar sets ofdata collected on the other trucks at WesTrack is reported inWesTrack Technical Report NCE-6 (57) and indicates a vary-ing amount of cross-slope induced antenna offset. Becausethe trucks and their guidance systems were essentially iden-tical, it was assumed that the difference in cross-slope inducedwander (offset) was due to differences in the front antennalocations relative to the wheelpath rutting.
The information presented above and that contained inWesTrack Technical Report NCE-6 indicated that the theo-retical distribution of traffic calculated was not what wasexperienced at WesTrack. A detailed analysis contained inWesTrack Technical Report NCE-6 provides a good esti-mate of traffic wander. The data in Table 133 suggest thatWesTrack traffic wander was about 95 percent of the wanderthat typically occurs on highways.
4.2 PERFORMANCE MONITORING
The methods and frequency of performance monitoring areshown in Table 134. Visual condition surveys and 35 mm pho-tographs were taken to record the type, severity, and extent ofdistress on the test sections. Transverse profiles at the surfaceof the pavement were measured by the “Dipstick” (commer-cially available profile device), the Arizona DOT transverse
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profile device, and a newly developed laser device. Trans-verse profile at the interface of the subgrade and engineeredfill and base course and at the interface of the base course andHMA were measured using the U.S. Forest Service liquidlevel gage.
Deflection measurements were made with a falling weightdeflectometer (FWD). Longitudinal profile was measuredwith the K. J. Law Profilometer. Friction was measured witha modified ASTM locked wheel skid trailer. An accelerome-ter and load cells were mounted on one of the trucks to moni-tor vehicle dynamics. Strain gages were installed at the bottomof the HMA in each section. An LTPP weather station waslocated at the track, along with two LTPP seasonal monitor-ing devices for measuring temperature variations with depthand for measuring moisture conditions in the subgrade andengineered fill and base course. An additional thermocouple“tree” was installed at a single location to record HMA tem-perature with depth.
4.2.1 Visual Condition Surveys
Visual condition surveys were performed at 2-week inter-vals during the trafficking of the track. During periods of rapidrutting (summer months) or fatigue cracking (winter months),the frequency of performing condition surveys was increased.The data were collected by a single person for the entire proj-ect to ensure the highest quality of data possible. In additionto the visual condition surveys, 35-mm photographs werealso obtained during the life of the research program.
The LTPP Distress Identification Manual provided thebasic definitions and method for conducting the survey. Thetypes of distress recorded included rutting, raveling, bleed-ing, alligator cracking, longitudinal cracking, transverse crack-ing, and fatigue cracking.
WesTrack Technical Report NCE-1 (58) provides detailson the survey procedure and the data reduction techniquesused. The collected visual condition survey data are availablein the WesTrack database described in Part III of this report.
4.2.2 Rut Depth Measurements
Rut depths were measured with the Dipstick (Figure 91),the Arizona DOT transverse profile device (Figure 92), andthe laser transverse profile device (Figure 93) developed byNATC. The frequency of testing was once every 2 weekswhen the track was subjected to traffic. During periods of rapidrutting or fatigue cracking, testing frequency was increased.
WesTrack Technical Report NCE-7 (59) provides detailson the measurement techniques used, the precision of themeasuring systems, methods of calculation of the rut depth,and data for each of the monitoring sessions by section. Rutdepths for the first six monitoring sessions were calculatedfrom the transverse profile measured with the Dipstick. TheArizona DOT device was used for making measurements for
monitoring sessions 7 through 32. The NATC-developed laserdevice was used for the remainder of the project. Fluctuationsin accumulation of permanent deformation with ESALs areprimarily due to precision and bias of the measuring devicesand changes in traffic wander.
Tables 135 and 136 and Figures 94 through 97 providetypical data for rut depth “peak to valley” obtained during theproject. Figures 94, 95, and 96 show rut depth data for sec-tions placed during original construction of the track. Figure94 shows rut depth versus ESALs for a fine-graded mixture,Figure 95 for a fine-plus-graded mixture, and Figure 96 forthe coarse-graded mixture. Figure 97 shows the rut depthversus ESAL relationship for a coarse-graded replacementsection mixture. A complete set of rut depth data in tabularform and in figures is available in the WesTrack databasedescribed in Part III of this report.
Figure 98 shows accumulated traffic and pavement tem-perature at 12.7-mm (0.5-in.) depth tied to time of year andmonitoring session. By combining the information providedin Figure 98 with the data in Tables 135 and 136 and Figures94 through 97, it is evident that the rut depth is very depen-dent on pavement temperature.
A review of rut depth data contained in the WesTrackdatabase indicates that the rut depths are larger in the left(down cross-slope) wheelpath than in the right wheelpath.This difference is likely due to the fact that the left sides ofthe trucks were slightly heavier than the right side of thetrucks (due to truck fixed weight distribution and shift in thesteel plates used to load the trucks).
4.2.3 Fatigue Cracking
The presence of fatigue cracking was recorded during thevisual condition survey. Fatigue cracking was assessed onceevery 2 weeks when the track was subjected to traffic or morefrequently during periods of rapid development of fatiguecracking.
WesTrack Technical Report NCE-1 (58) provides detailson the measurement technique used, the precision of themeasuring systems, and methods of calculating the amountof fatigue cracking. Differences in accumulation of fatiguecracking with ESALs are primarily due to precision of thevisual condition survey method. During certain periods ofthe year (summer primarily), fatigue cracking is often diffi-cult to see and healing of the cracks may also occur. Tables137 and 138 and Figures 99 through 102 provide typical datafor fatigue cracking obtained during the project. Table 137and Figures 99 through 102 show fatigue cracking data forsections placed during original construction of the track.Figure 99 shows fatigue cracking development versusESALs for the fine-graded mixture, Figure 100 shows fatiguecracking development versus ESALs for the fine-plus-gradedmixture, and Figure 101 shows fatigue cracking at variousESAL levels for the coarse-graded mixture. Figure 102
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shows the fatigue development for the coarse-graded re-placement section mixture. A complete set of fatigue crackingdata in tabular form and in figures is available in the WesTrackdatabase described in Part III of this report. As with rutting,fatigue cracking almost always developed faster in the leftwheelpath than the right wheelpath because of higher loadsdue to the pavement cross-slope and load shifting.
The information provided in Tables 137 and 138 andFigures 99 through 102 indicate that the formation of fa-tigue cracking largely occurred during the winter months. Figure 98 shows the accumulated traffic and pavement tem-perature at 12.7-mm (0.5-in.) depth tied to time of year andmonitoring session.
4.2.4 Longitudinal Profile
Surface longitudinal profile data for the WesTrack projectwere collected approximately once per month using the K. J.Law Profilometer. During periods of rapid development ofdistress, the data were collected more frequently.
WesTrack Technical Report NCE-5 (61) provides detailson the measurement technique used, data reduction tech-niques, precision estimates, and QC/QA analysis. Tables 139and 140 and Figures 103 through 106 provide typical longi-tudinal data obtained during the project. Table 139 andFigures 103 through 105 show surface longitudinal profiledata collected for sections placed during original construc-tion of the track. Figure 103 shows longitudinal profile ver-sus ESALs for a fine-graded mixture, Figure 104 shows afine-plus-graded mixture, and Figure 105 shows a coarse-graded mixture. Figure 106 shows changes in surface longitu-dinal profile for a coarse-graded replacement section mixture.A complete set of surface longitudinal data in tabular form andin figures is available in the WesTrack database described inPart III of this report.
Longitudinal profile data collected show that differencesin roughness can exist between the two wheelpaths. Some ofthis difference was associated with fatigue cracking devel-oping in the left wheelpath at a faster rate than in the rightwheelpath. An equation relating roughness at any age to ini-tial roughness, fatigue cracking, and rut depth was developedand is reported in WesTrack Technical Report NCE-5 (61).
4.2.5 Subsurface Transverse Profile
Subsurface transverse profile measurements were madewith the U.S. Forest Service liquid level device. The fre-quency of measurement was approximately once per monthwhen the track was subjected to trafficking. During periodsof rapid development of fatigue cracking or rutting, the mea-surement frequency was increased.
Tables 141 and 142 and Figures 107 through 110 provideexamples of subsurface transverse profiles at the interfacebetween the base course and HMA collected on the project.
Data were obtained at 0.1-m intervals across the width of thepavement section. Table 141 and Figures 107 through 109show subsurface rut depth data collected for several sectionsplaced during original construction of the track. Figure 107shows subsurface rut depth versus ESALs for a fine-gradedmixture, Figure 108 shows subsurface rut depth versus ESALsfor a fine-plus-graded mixture, and Figure 109 shows sub-surface rut depth versus ESALs for a coarse-graded mixture.Figure 110 shows changes in subsurface rut depth for a coarse-graded section mixture. A complete set of subsurface rut depthdata in tabular form and in figures is available in the Wes-Track database described in Part III of this report.
An examination of the subsurface rut depth data suggeststhat the surface rutting recorded at WesTrack is largely asso-ciated with the HMA layer. The data collected from the postmortem trenching effort support this conclusion.
4.2.6 Deflection
FWD data were obtained at 4-week intervals at severallocations along each test section. This information was exten-sively analyzed and used in the development of the perfor-mance models. The techniques used to reduce the deflectiondata are discussed in Section 5.2.
4.2.7 Friction
Friction was measured on WesTrack pavements with alocked wheel skid trailer according to ASTM E 274. The fric-tion tests were conducted nine times during the trafficking ofthe track. The friction measurements were made in the leftwheel track approximately 2 hours after daybreak. A stan-dard rib tire for pavement friction measurement was used onthe trailer operating at 64 km/h (40 mi/h).
Tables 143 and 144 and Figures 111 through 114 show fric-tion numbers with traffic levels as measured by cumulativeESALs. Table 143 and Figures 111 through 113 show frictionvalues for sections placed during original construction of thetrack. Figure 111 shows friction values versus ESALs for afine-graded mixture, Figure 112 for a fine-plus-graded mix-ture, and Figure 113 for a coarse-graded mixture. Figure 114shows friction values for the coarse-graded replacement sec-tion mixture. A complete set of friction data in tabular formand in figures is available in the WesTrack database describedin Part III of this report.
4.2.8 Weather Data
Weather information including air temperature, humidity,wind speed and direction, and moisture were recorded at theWesTrack site during the operation of the track. The datawere collected continuously.
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WesTrack Technical Report NCE-3 (60) provides com-parison of weather data collected at the WesTrack site to datafrom the relatively close NOAA weather stations at Yering-ton and Lahontan Dam. Close agreement among data fromthe three sites is evident in the report.
Data were used from the Yerington and Lahontan Damsites to select the asphalt binder PG grade. The fact that thetemperatures recorded at the three stations (WesTrack, Yer-ington, and Lahontan Dam) were nearly identical suggeststhat the PG selection was appropriate.
Table 145 contains the temperature and moisture data col-lected at the WesTrack weather station site at 10-day inter-vals. Daily average, high, and low temperatures are reportedtogether with moisture (rain and snowfall). Plots of the tem-perature data are shown in Figures 115 through 117 for theWesTrack and Lahontan Dam sites. Figures 115 through 117show the daily average, maximum, and minimum tempera-tures, respectively, at the two sites.
4.2.9 Pavement Temperature and Moisture
Pavement temperature was measured in sections 12, 19,and 25, while pavement moisture profiles were established atsections 12 and 25 with the LTPP seasonal monitoring equip-ment as described in Section 2.7. The pavement temperatureswere measured at sections 12 and 25 with the LTPP seasonalmonitoring equipment; a thermocouple tree was used at sec-tion 19 to provide temperature data at five depths. Pavementtemperatures from sections 12 and 25 were collected everyhour, while the pavement temperature for section 19 was col-lected every 1/2 hour.
WesTrack Technical Report NCE-4 (35) describes theQC effort associated with the temperature, compares thepavement temperatures recorded at the various locations,and compares the temperature profiles with the Superpavetemperature model.
Table 146 shows high and low air and pavement tempera-tures collected for a typical section during the life of the proj-ect; Figure 118 plots these same data. Figures 119 and 120show profiles of the pavement temperature with depth fortypical summer and winter days, respectively. A complete setof pavement temperature and moisture data in both tabularform and in figures is available in the WesTrack databasedescribed in Part III of this report.
4.2.10 Post Mortem Sampling and Testing
Post mortem sampling and testing was performed on thetest sections when they were taken out of service. WesTrackTechnical Report NCE-7 (59) contains a summary of the postmortem sampling and testing program performed at Wes-Track. Slab and core samples were removed from the trackat the time of post mortem sampling. The slab sampling pro-gram was laid out such that a trench across the pavement was
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formed with the samples. Measurements were made on theexposed face of the trench to establish the relative elevationsof the HMA, base course, and engineered fill.
Deflection testing with the FWD and dynamic cone pen-etrometer, in-place density determinations on the base courseand moisture content determination on the base course test-ing were performed as part of the post mortem testing. Testresults for sections 5, 6, 8, 24, and 26, which were removedfrom service after 1.7 million ESALs, are contained in Wes-Track Technical Report NCE-7 (59). These test results indi-cate that the rutting recorded at the pavement surface was dueto permanent deformation in the HMA layer only. A com-plete set of post mortem test results is available in the Wes-Track database described in Part III of this report.
4.3 REHABILITATION AND MAINTENANCE ACTIVITIES
Pavement rehabilitation and maintenance activities werecarried out during the trafficking of WesTrack. These activi-ties were initiated when a section reached a “failed” conditionor the track become unsafe for the operation of the trucks.
Failure at WesTrack for the purposes of activating rehabil-itation and maintenance operations was defined as rut depthsof approximately 25 mm (1 in.) or fatigue cracking in excessof 50 percent of the wheelpath. When the pavement becamerutted to a depth of approximately 25 mm (1 in.) or when theroughness of the pavement (largely due to fatigue cracking orroughness in the transitions) became excessive, the track was
repaired. Safe operation of the driverless vehicles and exces-sive vehicle maintenance caused by roughness necessitatedthese approximate failure definitions for WesTrack.
Table 147 contains a listing of the maintenance and reha-bilitation activities performed at WesTrack. “Permanentpatches” were placed with HMA in two configurations. “T”patches, whose configuration is shown in Figure 121, gavemuch better performance than straight-sided patches.
Some temporary patches were made with cold patchingmaterials obtained from Granite Construction and with spe-cialty commercial mixtures. The conventional patching mate-rials typically had a very short life. The commercially avail-able patching material had a longer service life, but failed atthe onset of hot weather. The patching materials were usedto fill ruts and to repair some potholes that formed during wetweather.
In some cases, mill-and-fill operations were used acrossthe entire lane; in other cases, mill-and-fill operations wererestricted to the wheelpaths. Five of the original pavementsthat failed prematurely by rutting were milled and filled to adepth of 50 mm (2 in.) in November 1996. These sections per-formed until the replacement sections were placed in theirlocations in May through June 1997.
Wheelpath mill-and-fill operations were also used toremove fatigue cracking. Typically, a 25- to 50-mm (1- to2-in.) mill-and-fill operation was performed in the wheel-paths. This repair strategy was used to extend the life of thepavement until more permanent rehabilitation methods couldbe used.
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Figure 88. Wheelpath distribution for typical highway and ALF machine (1 in. = 25.4 mm).
Figure 94. Rut depth versus ESALs for section 1: fine-graded mixture at optimum asphalt binder content and 8 percentin-place air void content (1 in. = 25.4 mm).
Figure 95. Rut depth versus ESALs for section 11: fine-plus-graded mixture at optimum asphalt binder content and 8 percent in-place air void content (1 in. = 25.4 mm).
Figure 96. Rut depth versus ESALs for section 5: coarse-graded mixture at optimum asphalt binder content and 8 percentin-place air void content (1 in. = 25.4 mm).
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Figure 97. Rut depth versus ESALs for section 35: coarse-graded replacement mixture at optimum asphalt binder contentand 8 percent in-place air void content (1 in. = 25.4 mm).
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Figure 98. WesTrack time history (°F = 1.8°C + 32).
Figure 101. Fatigue cracking versus ESALs for section 5: coarse-graded mixture at optimum asphalt binder content and 8 percent in-place air void content.
Figure 111. Friction numbers versus ESALs for section 1: fine-graded mixture at optimum asphalt binder content and 8 percent in-place air void content.
