Performance Testing for Superpave and Structural Validation

CHAPTER 2. EXPERIMENTAL DESIGN AND CONSTRUCTION

This chapter describes the asphalt binders selected for the experiment as well as the construction and layout of the test lanes. Also described is the framework that was used to quantify the strength of the relationships between binder properties, mixture properties, and full-scale pavement performance.

ASPHALT BINDER SELECTION

The asphalt binders and test results from NCHRP 9-10 and NCHRP 90-07 guided the selection of binders used in TPF-5(019).^(20,22) NCHRP 90-07 was conducted by FHWA and evaluated the moisture susceptibility of the modified asphalts in NCHRP 9-10. These experiments considered asphalt modification with catalytic air blowing, crumb rubber, elastomeric polymers, and elastomeric-plastomeric polymers. The overarching strategy of the asphalt binder selection and design was to obtain a suite of asphalts with similar or identical high-temperature rutting PG (|G*|/sinδ) but differing intermediate-temperature fatigue cracking PG (|G*| × sinδ). A series of premodified preconstruction binders was provided to FHWA from asphalt modifiers and suppliers. These were characterized to confirm the larger quantities of the binders that would be delivered to the paving contractor for the test lane construction.

Table 3 and figure 15 describe the constructed lane asphalt binders, modification type, placement in the test lanes, and HMA thickness in the study. A control asphalt binder without modification (PG70-22) was necessary for experiments of this nature. The air-blown binder was a second asphalt binder without polymer modification, a softer asphalt binder that underwent a catalytic air blowing process to increase its stiffness. Two styrene-butadiene-styrene (SBS) elastomeric polymer modified binders were used: (1) a typical SBS modified asphalt with approximately 3 percent linearly grafted (LG) SBS polymer by weight (referred to as SBS-LG) and (2) SBS 64-40, which used a larger quantity of SBS polymer at approximately 3.5 percent with a softer base asphalt binder. Terpolymer elastomeric-plastomeric polymer modified asphalt binder utilized 2.2 percent reactive terpolymer or three copolymers (DuPont™ Elvaloy^®) that react with the base asphalt instead of simply mixing and 0.4 percent polyphosphoric acid as a catalyst to enable the reaction of the polymer with components of the base asphalt. Two crumb rubber modified asphalt binders were included. The crumb rubber terminal blend (CR-TB) modified asphalt binder was produced in a process that blends recycled tire crumb rubber (5.5 percent) with new SBS rubber (1.8 percent) at asphalt terminals and creates a more homogeneous crumb rubber modified asphalt that can be handled without the challenges associated with less homogeneous crumb rubber modified asphalt binder. The Arizona wet process crumb rubber modified (CR-AZ) asphalt binder was produced from an unmodified asphalt binder and blended with recycled tire crumb rubber particles following the Arizona wet process.

1 mm = 0.039 inches
1 kg = 2.202 lb
1 kPa = 0.145 psi
°F = 1.8(°C) + 32

MVR = Material volumetric-flow rate.
ORIG = Original.
RTFO = Rolling thin film oven.
PAV = Pressure-aging vessel.

BBR = Bending beam rheometer.
*Estimated properties, details provided in section entitled, "Arizona Wet Process Crumb Rubber."
Note: Blank cells indicate tests were not conducted and data are not available.

1 mm = 0.039 inches

°F = 1.8(°C) + 32
1 g = 0.035 oz
1 cm = 0.39 inches

— Indicates test data were not measured at every point in time.

The size of the crumb rubber particles in the modified asphalt limited the ability to age and test the binder in standard instruments for the PG grading system. The unaged crumb rubber asphalt binder was successfully tested in the DSR, and the temperature at which it met the specification criteria |G*|/sinδ value of 0.145 psi (1 kPa) at 10 radians/s was 202 °F (94.4 °C). The binder could not be successfully aged in the rolling thin film oven (RTFO) and pressure-aging vessel (PAV) or tested in the DSR for the high-temperature rutting specification criteria |G*|/sinδ value of 0.32 psi (2.2 kPa) and intermediate-temperature fatigue cracking specification criteria of |G*| × sinδ value of 725 psi (5,000 kPa).

Research by Shenoy on a variety of binders has shown that RTFO- and PAV-aged PGs can be estimated with some degree of accuracy by relying on the unaged asphalt binder properties.^(28,29) The RTFO-aged specification was estimated by adding 11 °F (6 °C) to the temperature at which the original unaged binder met a |G*|/sinδ value of 0.32 psi (2.2 kPa). The PAV-aged specification was estimated by adding 11 °F (6 °C) to the temperature at which the original unaged binder met a |G*| × sinδ value of 725 psi (5,000 kPa). The results of the PG grade estimation were a continuous high-temperature grade of 194 °F (90.1 °C) (PG82) and an intermediate-temperature grade of 74 °F (23.4 °C).

The CR-AZ binder was characterized a second time in a more comprehensive manner. The original unaged binder was tested in the DSR using 0.975-inch (25-mm)-diameter plates but with a 0.078-inch (2-mm) gap rather than the standard 0.039-inch (1-mm) gap. The binder did not run out from between the plates and could be trimmed satisfactorily. The original high-temperature PG was 195.98 °F (91.1 °C), which was similar to the 194.18 °F (90.1 °C) PG determined in the earlier characterization. The binder was then aged in an RTFO oven that was tilted backwards to the limit of the specification to prevent the binder from coming out of the bottles. The binder did not completely coat the bottles. The RTFO-aged binder was then characterized in the DSR using 0.975-inch (25-mm)-diameter plates with a 0.078-inch (2-mm) gap. The RTFO high-temperature PG was 187.52 °F (86.4 °C), which was lower than the estimated value discussed above. The binder was then aged in a PAV, degassed, and characterized in a DSR with a 0.312-inch (8-mm)-diameter plate and a 0.078-inch (2-mm) gap as well as a BBR. The intermediate PG was 53.42 °F (11.9 °C), which was lower than the estimated value discussed above. The low temperature PGs from the BBR S-value and m-value were -35.14 and -30.64 °F (-37.3 and -34.8 °C), respectively.

MIX DESIGN AND AGGREGATE

The experiment was designed such that the primary variable among the test lanes was binder type, with identical aggregate type and volumetric mix design. The primary mix design of the experiment was based on a standard mixture specified by the Virginia Department of Transportation—a coarse, dense-graded, Superpave^®, 0.487-inch (12.5-mm) nominal maximum aggregate gradation. Reclaimed asphalt pavement was excluded from the mix design and experiment to eliminate any influence on the experimental binders. A job-mix formula was submitted to FHWA by the paving contractor for the Superpave^® mixture with the unmodified PG70-22 asphalt binder. The optimum asphalt binder content was 5.3 percent by total mass of the mixture based on a 4.0 percent design air-void content at 75 gyrations.

Both coarse and fine aggregate stockpiles were 100 percent crushed stone and did not contain any natural sand. The petrography of the aggregate was a diabase (traprock). To reduce the potential for moisture damage, 1.0 percent hydrated lime was prescribed in all mixtures. Two coarse aggregate stockpiles were used, a No. 78 and No. 68 local designation. Two fine aggregate stockpiles were used, a No. 10 screenings and a grade F and G sand designation. The grade F and G sand was manufactured sand, not natural quartzite sand. The aggregate blending percentages provided by the paving contractor were 16.5 percent No. 68 stockpile, 36.5 percent No. 78 stockpile, 27.0 percent grade F and G sand stockpile, and 20.0 percent No. 10 screenings stockpile.

NCHRP 90-07 research was completed by FHWA and included an evaluation of optimum asphalt content at 75 gyrations at a compaction temperature of 284 °F (140 °C) for a variety of modified asphalts.⁽²⁰⁾ Modifications included terpolymer, ethylene vinyl acetate, SBS-LG, unmodified PG70-22, SBS radial grafted, and an ethylene styrene interpolymer. The optimum asphalt binder contents at 4.0 percent air void content were 4.4, 4.4, 4.5, 4.6, 4.6, and 4.6 percent, respectively. An air-blown asphalt provided a binder content of 4.8 percent, a chemically modified crumb rubber product provided a binder content of 4.9 percent, and a mixture containing the unmodified PG70‑22 asphalt binder with 0.3 percent polyester fiber by aggregate mass provided a significantly higher binder content of 5.4 percent.

In this study, the asphalt binder content was fixed if it provided air voids within a range of 3.5–4.5 percent. The study was designed to evaluate effects of asphalt binder properties on performance. It was expected that there would be a greater tendency to question whether small differences in asphalt binder content confounded the conclusions of the experiment compared to small differences in the design air void level.

Large quantities of coarse and fine aggregate from the paving contractor were delivered to FHWA. The unmodified PG70-22 binder was used to conduct trial compactions. Binder contents of 4.8, 5.3, and 5.8 percent were evaluated. These contents provided air-void levels of 5.9, 5.0, and 3.9 percent, respectively. The hydrated lime to be used in the mixture was added to the fine aggregate stockpile by the paving contractor. The lime and fine aggregate were mixed together in the hot mix drum plant without asphalt. The lime-treated aggregate was then stockpiled. This method of addition resulted in the formation of some lime nuggets. It was hypothesized that the variability in air voids could be the result of inconsistent samples of the lime-treated fine aggregate when batching the aggregates. Compaction tests were performed using samples of the lime-treated No. 10 aggregate taken directly from the stockpile at the hot mix plant to make sure that the Turner-Fairbank Highway Research Center (TFHRC) stockpile was representative of the stockpile at the plant. This mixture also provided air voids of 5.9, 5.0, and 3.9 percent at asphalt binder contents of 4.8, 5.3, and 5.8 percent, respectively. These tests provided no insight concerning the inconsistencies in the air voids and did not rule out the possibility that the dispersion of the hydrated lime was part of the problem.

Construction proceeded with the contractor’s mix design. Volumetric data of the production mixes are shown in table 6. The air-blown, SBS-LG, and SBS 64-40 mixtures fell within the desired air void content range of 3.5–4.5 percent. The CR-TB mixture fell 0.1 percentage points higher than the desired range at 4.6 percent. The 5.0 percent design air void content of the PG70‑22 mixture fell outside the desired range by 0.5 percentage points. The fiber mix was evaluated with 0.3 percent fiber by weight of aggregate, and air void contents were outside the desired range at 5.1 percent. Increasing the binder content in laboratory tests created very erratic volumetrics, indicating fibers could be trapping air voids. The weight of the fiber was reduced to 0.2 percent by weight of aggregate, and the air void content was 4.8 percent. The paving contractor needed a tolerance for the amount of polyester fiber to be used, so the allowable range was set at 0.2–0.3 percent by mass of aggregate.

Voids in the mineral aggregate (VMA) of all mixtures met the minimum requirement of 14.0 percent and were greater than 16.0 percent even if the volumetrics of the mixtures were adjusted to a 4.0 percent design air void level. The voids filled with asphalt (VFA) for most of the mixtures met the 65 to 75 percent requirement. The only mixture where the VFA deviated significantly from the requirement was SBS 64-40, which had a VFA of 78 percent. The VMAs and VFAs in table 6 indicate that the aggregate structure provided a high amount of void space, which is rich in asphalt binder.

1μm = 0.039 mil

Gap-Graded Crumb Rubber Mix Design

The CR-AZ mixture was designed according to the Arizona Department of Transportation’s asphalt-rubber asphaltic concrete design specifications.⁽³⁰⁾ Five materials were used: No. 68 diabase, No. 78 diabase, No. 8P diabase, No. 10 diabase, and hydrated lime. The aggregate blending percentages were 32.7 percent No. 68 stockpile, 46.5 percent No. 78 stockpile, 8.9 percent No. 8P stockpile, and 10.9 percent No. 10 screenings. In addition, 1 percent hydrated lime was used. The 75 blow-per-side Marshall Method was used for the mixture design. The compaction temperature was 325 °F (163 °C). The volumetric requirements were that the air voids had to be between 4.5 and 6.5 percent and the VMA had to be a minimum 19.0 percent. Four asphalt binder contents were tried: 6.0, 7.0, 8.0, and 9.0 percent. The optimum asphalt binder content was found to be 7.1 percent and may appear lower than typical contents near 8 percent for this type of mixture. However, the effective volumetric binder content was 16 percent, and the high specific gravity of the diabase aggregate (2.98) can make gravimetric binder contents appear lower. If the aggregate specific gravity was lower (i.e., around 2.7), then the gravimetric binder content would have been around 7.8 percent.

PAVEMENT TEST FACILITY LAYOUT AND CONSTRUCTION

The FWHA Pavement Test Facility (PTF) and two ALFs are used to rapidly collect data on pavement performance under conditions in which axle loading and pavement temperature are controlled. This facility is also used to study the complex interactions among pavement structures, construction materials, and axle loads. The primary objective of the PTF is to develop and verify new specifications, designs, and test procedures. Previous studies have addressed the relationship of tire pressure to pavement performance, the impact of super-single tires on asphalt pavement performance, the validation of SHRP binder and mixture specifications, and design procedures for ultra-thin white topping concrete overlays. (See references 16–18, 31, and 32.) The two ALF machines can run tests on alternative pavement designs (structures or materials) with fixed loading configurations or, conversely, on identical pavement designs with alternative loading configurations (e.g., by varying tire pressure or axle loading). Each machine is capable of applying an average of 35,000 passes per week with a half-axle load ranging from 7,500 to 19,000 lbf (33 to 84 kN). Each of the PTF’s test lanes is long enough to include two 46- by 14-ft (14- by 4-m) test sections, and each test section can be divided transversely into two test sites. As a result, full paving of the 12 test lanes provides sufficient space for a 48-cell experiment.

The configuration of mixture types in the lanes and layer thickness is shown in figure 16. Each pavement lane is 13 ft (4 m) wide and 160 ft (50 m) long and is divided into four test sites. All pavement lanes consist of an HMA layer and a dense-graded, crushed aggregate base (CAB) course over a uniformly prepared silty clay subgrade categorized as soil classification AASHTO A-4. The total thickness of the HMA and CAB layers is 26 inches (660 mm). Lanes 1 through 7 were constructed with a 4-inch (100-mm)-thick layer of HMA, and lanes 8 through 12 were constructed with a 5.8-inch (150-mm)-thick layer.

1 mm = 0.039 inches

Figure 16. Illustration. Oblique diagram of the test section’s three-dimensional layout.

Trenches were cut in past ALF studies and indicate that total rutting was distributed within the asphalt layers and crushed stone layers but did not appear to deform or disturb the subgrade layer, as shown in the example in figure 17. The subgrade was not exposed or disturbed in the construction of the test lanes, but historical data on gradation are available and are summarized in table 7.^(33,34) Neither source provides any liquid limits, plastic limits, or plasticity indices or categorizes the subgrade as non-plastic. References 33 and 34 provide additional data, as follows:

• California bearing ratio is reported to be 6.7.
• AASHTO T 99 optimum moisture content and maximum dry densities are reported as 14.9 percent and 111.9 lb/ft³ (1,792 kg/m³), respectively.⁽³⁵⁾
• AASHTO T 180 optimum moisture content and maximum dry densities are reported as 11.4 percent and 121.6 lb/ft³ (1,984 kg/m³), respectively.⁽³⁶⁾
• The specific gravity of the subgrade was found to be 2.840.

Figure 17. Graph. Pavement layer profile measured from a trench cut in an ALF test section from past study.⁽¹⁶⁾

1 mm = 0.039 inches

— Indicates test data were not measured for every sieve size.

The pavement test lanes were constructed in the summer and fall of 2002. The damaged CAB was removed. The first shaded area beneath the lanes in figure 16 shows where new CAB was placed. The new CAB was tested for gradation, density, moisture content, and surface elevation and met all requirements, as shown in table 8. The CAB was compacted with a vibrating steel wheel roller to a minimum of 156 lb/ft³ (2,529 kg/m³), which was 95 percent of the maximum density. Initially, some of the tests showed that the density was 94 percent of the maximum density, but these sections were reworked so that they met the requirement. The average moisture content was 5.3 percent. Gradation targets of the CAB are given in table 8.

1 mm = 0.039 inches

Tanker trucks of the experimental asphalt binders were sent to the paving contractor after coordination and confirmation of the asphalt binder properties with the producers supplying the binder. A blender was delivered to the hot-mix plant for the CR-AZ production, whereas the CR-TB was trucked to the hot mix plant from the terminal. The asphalt mixtures were produced in a counterflow drum plant located in Sterling, VA, 17 mi (27 km) from the PTF site. After transport, trucks unloaded the HMA into a material transfer device (MTD), which fed a rubber tire paver. An infrared camera used during construction verified the MTD was effective in eliminating temperature segregation. An example is shown in figure 18 and figure 19. The numerical image analysis of this particular thermal image taken during October 2002 construction indicates that the temperature of the mix coming out from the back of the paver was about 298–302 °F (148–150 °C) and the coolest parts of the loose mat within view were about 244–248 °F (118–120 °C). All of the test lanes were constructed in two lifts, each 2 or 3 inches (50 or 75 mm) thick, as appropriate. A 13.5-T (12.3-Mg) vibratory roller was used for the breakdown, followed by a 10-T (9.1-Mg) static steel roller for the finish rolling. The upper lift was placed as soon as the lower lift was cool enough to handle the paver, and no tack coat was used between the lifts.

Figure 18. Photo. Conventional photo of hot mix placement from the back of the paver.

Figure 19. Photo. Thermal image of hot mix placement from the back of the paver.

A control strip was constructed in the parking lot before each test pavement was placed. This strip was used to determine the appropriate rolling pattern needed to achieve the desired density, to check the calibration of the paving contractor’s nuclear density gauge, and to approve each HMA by determining its asphalt binder content, aggregate gradation, maximum specific gravity, and volumetrics. Density and thickness were checked by sawing rectangular blocks from the pavement. The materials had to meet the specifications before the test pavement could be constructed. These control strips indicated that the target density could be achieved by four to six vibratory passes followed by three to five static passes, depending on the type of mixture. The pavements were compacted within a temperature range of 220–302 °F (105–150 °C).

Specification criteria for the HMA are given in table 9. The paving contractor and FHWA randomly obtained two samples of each plant-produced mixture from the loaded trucks and split them according to AASHTO T 168 and AASHTO T 248.^(37,38) The samples were tested for binder content, aggregate gradation, and theoretical maximum specific gravity. The target gradation and limits for the gap-graded CR-AZ mix design and the dense-graded mix design are provided in table 10. Some material was placed and accepted out of specification. The following sections describe the construction data of note for each lane. Air void content taken on cores was measured on the entire core having both lifts. Three cores were taken from the left wheel path, and three cores were taken from the right wheel path. Cores were not split at the lift boundary except for lane 1, where the top lift was the gap-graded CR-AZ mix and the bottom lift was the dense-graded PG70-22 mix. Thickness was measured with two techniques: (1) cores were measured for thickness and (2) the depth of holes drilled to metal survey plates was measured.

1 mm = 0.039 inches

NMAS = Nominal maximum aggregate size.
Note: Blank cells indicate test data were not measured at sieve size.

Quantitative descriptions of each lane’s construction are as follows:

Lane 1, top, CR-AZ: One sample was taken for gradation. Aggregate gradation was within tolerances for the No. 4 (4.75 mm) and No. 30 (0.6 mm) sieves. The No. 200 (0.075 mm) sieve was 0.1 percentage points higher than the tolerance. Only one ignition oven binder content measurement was taken instead of three. The value was 6.7 percent, 0.4 percentage points lower than the target of 7.1 percent. One of three maximum specific gravity measurements was outside the tolerance, resulting in an average outside the tolerance. Two of six cores were outside the air void tolerance, but the average air void content was within the tolerance.

Lane 1, bottom, PG70-22: One sample was taken for gradation. Aggregate gradation was within all three tolerances for the No. 4, No. 30, and No. 200 (4.75, 0.6, and 0.075 mm) sieves. Only one ignition oven binder content measurement was taken instead of three, and it was within the target binder content range. All three maximum specific gravity tests were within tolerance. Two of six cores were outside the air void tolerance, but the average air void content was within tolerance. A total of 4 of 17 drilled holes were outside the thickness tolerance, but the average was within tolerance. Two of six cores were outside the thickness tolerance, but the average was within tolerance.

Lane 2, PG70-22: One sample was taken for gradation data. The aggregate gradation data on the No. 4 (4.75 mm) sieve was 0.8 percentage points lower than tolerance, while the No. 200 (0.075 mm) sieve was 0.2 percentage points lower than tolerance. Only one ignition oven binder content measurement was taken instead of three, and it was within the target binder content range. All three maximum specific gravity tests were within tolerance. Two of six cores were outside the air void tolerance, but the average air void content was within tolerance. A total of 6 of 12 drilled holes indicated thickness outside of tolerance, and average thickness was 0.029 inches (0.75 mm) above tolerance. All six cores and average were within the thickness tolerance.

Lane 3, air blown: Two of three samples were above tolerance on the No. 4 (4.75 mm) sieve, but the average was 1.2 percentage points above tolerance. One of three samples on the No. 30 (0.6 mm) sieve and on the No. 200 (0.075 mm) sieve was above tolerance, but the averages were within tolerance. One of three ignition oven binder content measurements was outside the range, resulting in an average air void content outside the tolerance. One of three maximum specific gravity tests was below tolerance, but the average maximum specific gravity was within tolerance. Four of six cores were outside the air void tolerance, with one high and three low. This resulted in an average air void content below tolerance. Only 1 of 12 drilled holes indicated thickness outside tolerance, and the average was within tolerance. One of the six cores was outside the thickness tolerance, and the average was within tolerance.

Lane 4, SBS-LG: Two gradation samples on the No. 4 (4.75 mm) sieve were outside tolerance. One was above and the other below, but the average was within tolerance. All samples on the No. 30 and No. 200 (0.6 and 0.075 mm) sieves were within tolerance. One of three ignition oven binder content measurements was below tolerance, but the average binder content was within tolerance. All three maximum specific gravity measurements were within tolerance. Three cores were within tolerance and three cores were below tolerance, resulting in an average air void content below tolerance. All 12 drilled holes indicated thickness within tolerance. One of six cores was outside the thickness tolerance, and the average was within tolerance.

Lane 5, CR-TB: All three gradation samples on the No. 4 (4.75 mm) sieve were above tolerance, and the average was 2.1 percentage points above tolerance. All gradation samples on the No. 30 and No. 200 (0.6 and 0.075 mm) sieves were within tolerance. One of three ignition oven asphalt content measurements was above tolerance, and the average was within tolerance. All three maximum specific gravity measurements were within tolerance. Four of six air void cores were outside the air void tolerance, with one high and three low. This resulted in an average air void content within tolerance. Only 3 of 17 drilled holes indicated thickness outside tolerance, but the average was within tolerance. Two of six cores were below the thickness tolerance and resulted in an average thickness 0.052 inches (1.33 mm) below tolerance.

Lane 6, terpolymer: One of three gradation samples on the No. 4 (4.75 mm) sieve was above tolerance, but the average was within tolerance. All gradation samples on the No. 30 and No. 200 (0.6 and 0.075 mm) were within tolerance. Only two measurements were taken for binder content. One of two ignition oven binder content measurements was above tolerance, but the average binder content was within tolerance. Two of three maximum specific gravity tests were taken, and both were within tolerance. Two of six cores were below the air void content tolerance, and the average was within tolerance. A total of 5 of 12 drilled holes were out of the thickness tolerance, but the average was within tolerance. Three of six cores were within the thickness tolerance, and the average was within tolerance.

Lane 7, fiber: All three gradation samples were within tolerance on all sieves. All three ignition oven binder content tests were within tolerance. Corrections were made because fibers were affected by the burn-off oven. All three maximum specific gravity measurements were within tolerance. All six cores taken were within the air void content tolerance. Ten of 32 drilled holes indicated thickness within tolerance. Four of six cores were outside tolerance, and the average was 0.097 inches (2.5 mm) above tolerance.

Lane 8, PG70-22: One of three gradation samples on the No. 4 (4.75 mm) sieve was above tolerance, but the average was within tolerance. All samples on the No. 30 (0.6 mm) sieve were within tolerance. The No. 200 (0.075 mm) sieve had one of three samples below tolerance, but the average was within tolerance. Two of the three binder content measurements were outside tolerance, with one high and one low. The average binder content was within tolerance. All three maximum specific gravity measurements were within the tolerance level. Five of six cores were below the air void tolerance, and the average level was below tolerance. All 12 drilled holes and all six cores were within the thickness tolerance.

Lane 9, SBS-LG: One of three No. 4 (4.75 mm) sieve gradation samples was well below tolerance, resulting in the average being 0.7 percentage points below tolerance. All three gradation samples on the No. 30 (0.6 mm) sieve were within tolerance. All three gradation samples on the No. 200 (0.075 mm) sieve were below tolerance, resulting in an average that was 0.4 percentage points below tolerance. Two of three binder content measurements were outside tolerance, with one high and one low. The average binder content was within tolerance. One of three maximum specific gravity tests was above tolerance, with the average within tolerance. All six cores had air voids lower than tolerance. Three of 12 drilled holes were outside the thickness tolerance, and the average was within tolerance. Five of six cores were below the thickness tolerance, and the average was 0.163 inches (4.17 mm) below tolerance.

Lane 10, air blown: One of three gradation samples on the No. 4 (4.75 mm) sieve was above tolerance, and the average was within tolerance. The No. 30 and No. 200 (0.6 and 0.075 mm) sieves had all samples within tolerance. All three binder content measurements were above tolerance. All three maximum specific gravity tests were within tolerance. One of six cores was within the air void tolerance and contained a mixture of above and below tolerance. The average was below tolerance. Only 1 of 12 drilled holes was outside the thickness tolerance, and the average was within tolerance. One of six cores was outside tolerance, and the average was within tolerance.

Lane 11, SBS-LG: All gradation samples on all sieves were within tolerance. All three binder contents were within tolerance. All three maximum specific gravity measurements were within tolerance. Five of six cores were below tolerance, and the average was below tolerance. A total of 4 of 12 drilled holes were outside the thickness tolerance, and the average was within tolerance. One of six cores was outside the thickness tolerance, and the average was within tolerance.

Lane 12, terpolymer: All three No. 4 (4.75 mm) gradation samples were above tolerance, resulting in an average that was 2.6 percentage points above the tolerance. One of the three No. 30 (0.6 mm) sieve samples and No. 200 (0.075 mm) sieve samples was above tolerance, but the average was within tolerance. All three binder contents were above tolerance. One of three maximum specific gravity measurements was outside tolerance, and the average was within tolerance. Two cores were within tolerance, and four were below tolerance, with the average air void level outside tolerance. All 12 drilled holes and the average were within the thickness tolerance. Two of six cores were outside the thickness tolerance, but the average was within tolerance.

The overall conclusion regarding the construction of the test lanes was that a very tight tolerance was set for the contractor because of the research requirements. The contractor had trouble staying within those tight tolerances for all work. When tolerances were exceeded, the average values lay on or very near the set specification limits. Some construction was rejected. Lanes 4, 7, 8, and 11 were removed and replaced (data not included in this report). Ultimately, lane 7 was reconstructed twice before being accepted. One reconstruction was due entirely to the wrong gradation being delivered. The other lanes that were removed and replaced were due to thickness and density. Practicality had to be balanced with the objective of the experiment. FWD analyses are given chapter 4. Data for the control strips in the parking lot are not included in this report.

Hydrated Lime Distribution

The hydrated lime was added to the No. 10 screenings aggregate by the paving contractor to produce each asphalt mixture. The lime and No. 10 aggregate were mixed together in the hot mix drum plant without asphalt. The lime-treated aggregate was then stockpiled. This method of lime addition resulted in the formation of some lime nuggets, as observed during pavement construction. The lime nuggets are shown in figure 20 and figure 21. The actual lime content distributed in the pavement test lanes was evaluated. Three 6-inch cores were taken from the end and middle of lanes 2 and 3. The cores were drilled with a hammer drill to obtain a sample of dust containing the components of the asphalt mix. Two different drill bits were used to explore the sensitivity of lime content to the size of the dust sample taken. The dust samples were analyzed using the method developed in the TFHRC Chemistry Laboratory.⁽⁴⁸⁾ The lime content was calculated assuming that the mix contained 5.3 percent binder.

Figure 20. Photo. Characteristic lime nuggets indicating less than desired uniform mixing.

Figure 21. Photo. Relative size of lime nuggets.

The average lime content for the lane 2 cores was 0.42 percent with a standard deviation of 0.05 percent. The highest value was 0.53 percent, and the lowest was 0.33 percent. The average for dust using the ³/₈-inch (9.5-mm) drill was 0.45 percent with a standard deviation of 0.05 percent. The highest value was 0.53 percent, and the lowest was 0.38 percent. The ⁵/₈-inch (16-mm) drill samples gave an average of 0.40 percent lime with a standard deviation of 0.04 percent and values between 0.45 and 0.33 percent.

The results from lane 3 showed one outlier with a lime level of 1.10 percent compared to the average of 0.5 percent. This could be caused by variations in the method. However, since the other results were closer together, it is more likely that the drilling contained a higher lime level, perhaps an undispersed particle. The average for lane 3 was 0.5 percent, with a standard deviation of 0.20 percent. Ignoring the outlier yields an average of 0.45 percent with a standard deviation of 0.06 percent. Ignoring the outlier, the average for dust using the ³/₈-inch (9.5-mm) drill was 0.48 percent with a standard deviation of 0.01 percent. The highest value was 0.49 percent, and the lowest was 0.46 percent. The ⁵/₈-inch (16-mm) drill samples gave an average of 0.42 percent, a standard deviation of 0.07 percent, and values between 0.30 and 0.49 percent.

The detailed analysis of lime in lanes 2 and 3 were compared against samples taken from other lanes in table 11. Most tests used hydrochloric acid instead of acetic acid in the procedure, but that has little consequence on the test results. Single samples from the middle of the lanes were taken from lanes 7–10. The conclusion from the lime analysis of all lanes is that all lanes contained hydrated lime but at a content that is noticeably less than the target of 1 percent and that is different from lane to lane.

— Indicates that test data were not measured.