Simple Performance Tester for Superpave Mix Design: First-Article Development and Evaluation (2003)

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B-1 APPENDIX B MATERIALS AND LABORATORY METHODS

B-2 1. INTRODUCTION This Appendix documents the laboratory methods used in the preparation and testing of specimens for the mixture testing component of the first-article evaluation. Although the first- article simple performance devices are capable of performing three tests: dynamic modulus, flow number, and flow time, only two of these tests were included in the mixture testing component of the evaluation due to budget constraints. The dynamic modulus and flow number were the tests selected for evaluation because these were the two tests for which criteria differentiating between good and poor performance were being developed in Project 9-19. Research in Project 9-19 found a good correlation between flow number and flow time, allowing flow time to be used as a surrogate test for flow number, but the criteria differentiating between good and poor performance will be based in the flow number test and the performance of in- service sections. Tables 1 and 2 present the experimental design for the dynamic modulus and flow number tests. Data for the two simple performance test devices in were collected in two laboratories (AAT and FHWA) on two mixtures (9.5 mm and 19.0 mm). Eight independent tests were included in each cell to provide sufficient replication to evaluate differences in means and differences in variances between devices, laboratories, and testing conditions. The dynamic modulus tests were conduced for three conditions selected to exercise the range of the equipment capabilities: • Unconfined dynamic modulus at 25 °C, a representative condition for evaluating mixtures for fatigue cracking potential. • Unconfined dynamic modulus at 45 °C, a representative condition for evaluating mixtures for rutting potential. • Confined dynamic modulus at 45 °C, a representative condition for possibly evaluating open or gap graded mixtures for rutting potential. B-3 The flow number was evaluated only at 45 °C for unconfined and confined conditions. The levels of confinement and deviatoric stress were selected to provide a relatively short test, less than 1000 cycles, and a relatively long test, greater than 5000 cycles. Table 1. Experimental Design for Dynamic Modulus Testing. Dynamic Modulus and Phase Angle Device Lab Mix Unconfined, 25 C Unconfined, 45 C Confined, 45 C 9.5 mm 8 8 8 AAT 19.0 mm 8 8 8 9.5 mm 8 8 8 Interlaken FHWA 19.0 mm 8 8 8 9.5 mm 8 8 8 AAT 19.0 mm 8 8 8 9.5 mm 8 8 8 Shedworks FHWA 19.0 mm 8 8 8 Table 2. Experimental Design for Flow Number Testing. Flow Number Device Lab Mix Unconfined, 45 C Confined, 45 C 9.5 mm 8 8 AAT 19.0 mm 8 8 9.5 mm 8 8 Interlaken FHWA 19.0 mm 8 8 9.5 mm 8 8 AAT 19.0 mm 8 8 9.5 mm 8 8 Shedworks FHWA 19.0 mm 8 8 2. MIXTURES Two mixtures that exhibited different levels of variability in mechanical properties when tested in NCHRP Project 9-18 “Field Shear Test for Hot-Mix Asphalt,” were used in the evaluation testing. The first was a 9.5 mm mixture with low variability, having a shear modulus coefficient of variation of approximately 5 percent when tested in NCHRP Project 9-18. The second was a 19.0 mm mixture that had a shear modulus coefficient of variation of

B-4 approximately 17 percent. Volumetric properties for the mixtures are provided in Table 3. As shown in Figures 1 and 2, both are coarse graded mixtures Superpave mixtures. The 9.5 mm mixture was made with limestone coarse and fine aggregates. Granite aggregates were used in the 19.0 mm mixtures. Both mixtures were made with the same PG 64-22 binder. AASHTO M320 properties for the binder are summarized in Table 4. Table 3. Volumetric Properties of Evaluation Mixtures. Property 9.5 mm 19.0 mm Ndesign 65 96 Coarse Aggregate Angularity. One Face/ Two Face 100/100 100/100 Fine Aggregate Angularity 45.0 52.1 Flat & Elongated, % (Ratio 5 : 1) 1.6 1.9 Sand Equivalent, % 83 80 Binder Content, % 6.2% 4.4% Gyratory Compaction, % Gmm Nini Ndes Nmax 85.2% 96.0% 97.8% 85.9% 95.8% 97.2% Voids in Mineral Aggregate (VMA), % 17.2 14.5 Voids in Total Mixture (VTM), % 4.0 4.2 Voids Filled with Asphalt (VFA), % 76.7 71.0 Fines to Effective Binder Ratio (F/A) 1.2 1.1 Gradation, % passing Sieve Size, mm 37.5 100 100 25 100 100 19 100 94 12.5 100 73 9.5 97 52 4.75 62 33 2.36 42 24 1.18 27 17 0.6 18 14 0.3 11 10 0.15 8 6 0.075 6.8 3.6 B-5 Figure 1. Gradation of 9.5 mm Mixture. Figure 2. Gradation of 19.0 mm Mixture. 0 10 20 30 40 50 60 70 80 90 100 SIEVE SIZE, mm P E R C E N T P A S S I N G P E R C E N T P A S S I N G 0.075 0.15 0.3 0.6 1.18 2.36 4.75 9.5 12.5 0 10 20 30 40 50 60 70 80 90 100 SIEVE SIZE, mm 0.075 0.15 0.3 0.6 1.18 2.36 4.75 9.5 12.5 19 25

B-6 Table 4. Binder Properties for Evaluation Mixtures. Condition Test Method Result Specific Gravity at 25 °C AASHTO T228 1.032 Viscosity at 135 °C ASTM D4402 0.38 Pa·s Unaged Asphalt G*/sinδ at 10 rad/sec, 64 °C AASHTO T515 1.58 kPa Mass Change, % AASHTO T240 -0.32 RTFO Aged Residue G*/sinδ , at 10 rad/sec, 64 °C AASHTO T315 5.27 kPa G*sinδ, at 10 rad/sec, 25 °C AASHTO T315 2800 kPa Creep Stiffness, at 60 sec, -12 °C AASHTO T313 138 MPa PAV Aged Residue m-value at 60 sec, -12 °C AASHTO T313 0.331 3. SPECIMEN PREPARATION The simple performance test specimens were prepared to a target air void content of 4.0 percent. First 150 mm diameter by 165 mm high gyratory specimens were prepared to an air void contents 5.5 percent. From these, 100 mm diameter by 150 mm high specimens were cored and sawed using a portable core drilling machine and double bladed saw. The sections that follow discuss procedures used in the specimen fabrication process for: • Binder and aggregate handling • Laboratory mixing, aging and compaction • Simple performance test specimens fabrication, and • Test specimen handling 3.1 Binder Handling The binder used in the first-article evaluation was an unmodified PG 64-22 obtained from the Paulsboro, New Jersey refinery of the Citgo Asphalt Refining Company (Citgo). This binder was being used by AAT on several NCHRP projects including: Project 9-29, Phase III of Project 9-29, Project 9-25, Project 9-31, and Project 9-34. For these projects, 37, five-gallon samples of PG 64-22 binder were obtained by Citgo representatives on November 9, 2001. The sample containers were sealed, marked, and forwarded to AAT. Each five-gallon sample was treated as a representative sample of the binder with no mixing of the binder from individual containers. Upon receipt at AAT, one five-gallon sample was divided into quart containers by heating the five-gallon container in an oven set at 135 °C, stirring with a mechanical stirrer, and pouring the B-7 binder into the individual quart containers. A representative sample was obtained from one of the quart containers and viscosities were determined at 135, 150, and 165 °C in accordance with ASTM D4402 to determine appropriate mixing and compaction temperatures. The quart containers were then used in the preparation of laboratory mixture batches. Quart containers were only heated once. Excess binder in the quart containers was discarded. As additional binder was required by the testing program, additional five-gallon samples were divided into quart containers using the procedure outlined above. 3.2 Aggregate Handling Representative samples of the aggregates used in the evaluation mixtures were obtained by AAT technicians in sample bags of varying sizes. The procedures described in the Appendix of Asphalt Institute Publication MS-2 were used to prepare the aggregate samples for laboratory batching. Coarse aggregate samples were separated into individual sizes, while individual samples of fine aggregate were mixed together to produce a homogeneous supply for subsequent batching. For the two mixtures, Table 5 summarizes the sizes that the aggregates were separated into for preparation of laboratory specimens. For the 19.0 mm mixture, stockpile samples of the #57 and #78 stone were combined prior to separating into the fractions shown. Table 5. Summary of Aggregate Sizes Used in Phase 1 Specimen Preparation. 9.5 mm Mixture 19.0 mm Mixture Material % Sizes, mm Material % Sizes, mm Retained 9.5 Retained 19.0 8P 31 Retained 4.75 Retained 12.5 1/4 in 63 As-received Retained 9.5 Manufactured Sand 5 As-received Retained 4.75 Lime 1 As-received Combined #57 and #78 72 Retained 2.36 #10 14 As-received #34 14 As-received 3.3 Mixing, Aging, and Compaction Gyratory specimens for the simple performance tests before sawing and coring were 150 mm diameter by 165 mm high. These specimens were prepared to a target air void content in

B-8 accordance with AASHTO T314. An Interlaken compactor meeting the requirements of AASHTO T314 and AASHTO PP35 was used to prepare the gyratory specimens. Mixing and compaction temperatures were determined from viscosities measured at 135, 150, and 165 °C in accordance with ASTM D4402. These were converted to kinematic viscosities using the binder specific gravity measured at 25 °C and the specific gravity temperature correction factors given in Annex A1 of AASHTO T201. This resulted in a mixing temperature of 158 °C and a compaction temperature of 145 °C. Prior to compaction, materials for all specimens were short-term oven aged in accordance with AASHTO PP2 for two hours at the compaction temperature. 3.4 Sawing and Coring of Simple Performance Test Specimens The simple performance test specimens were manufactured by coring and sawing 100 mm diameter by 150 mm high test specimens from the middle of 150 mm by 165 mm high gyratory compacted specimens. The procedure is described in the test protocols submitted to the NCHRP in Project 9-19, Superpave Support and Performance Models Management. There are three reasons for using smaller test specimens obtained from larger gyratory specimens in the simple performance tests. The first is to obtain an appropriate aspect ratio for the test specimens. Research performed during Project 9-19, found that a minimum specimen diameter of 100 mm was needed in the flow number and flow time tests, and that a minimum height to diameter ratio of 1.5 was needed in all three simple performance tests: dynamic modulus, flow number, and flow time. The second reason is to eliminate areas of high air voids in the gyratory specimens. Gyratory compacted specimens typically have high air voids near the ends and the circumference the specimen. The third reason is to obtain relatively smooth, parallel ends for testing. In Phase I of this project, measurements on a large number of specimens prepared in accordance with the Project 9-19 draft test protocols showed that some of the specimen dimensional tolerances could not be achieved with standard laboratory saws and drills. The tolerances in the Project 9-19 test protocols were based on those presented in AASHTO T231 for capping concrete cylinders. The revised tolerances listed in Table 6 were recommended and incorporated in the first-article specifications. B-9 Table 6. Project 9-29 Specimen Dimension Tolerances. Item Specification Remarks Average Diameter 100 mm to 104 mm Standard Deviation of Diameter 1.0 mm See note 1 Height 147.5 mm to 152.5 mm End Flatness 0.3 mm See note 2 End Parallelism 1 degree See note 3 Notes: 1. Measure the diameter at the center and third points of the test specimen along axes that are 90 degrees apart. Record each of the six measurements to the nearest 1 mm. Calculate the average and the standard deviation of the six measurements. The standard deviation shall be less than 1.0 mm. The average diameter, reported to the nearest 1 mm, shall be used in all material property calculations. 2. Check this requirement using a straight edge and feeler gauges. 3. Check this requirement using a machinists square and feeler gauges. Several laboratories have adapted equipment for preparing the simple performance test specimens that range from elaborate feed control drills combined with sophisticated holders and double bladed saws to standard drills and single bladed saws with simple clamping arrangements. For this project, specimens meeting the tolerances listed in Table 6 were prepared using a portable core drilling machine, and a double bladed saw. As shown in Figure 3, the portable core drilling machine was mounted to a heavy stand on the laboratory floor to facilitate vertical drilling of the specimen. The 150 mm diameter by 165 mm high gyratory compacted specimen was held in place under the drill by blocks of wood cut to provide a tight fit between the gyratory specimen and the stand. A sophisticated clamp for holding the gyratory specimen is not needed to obtain the tolerances on the specimen diameter listed in Table 6. Figure 4 shows the 100 mm diameter core and the waste portion of the gyratory specimen.

B-10 Figure 3. Portable Core Drilling Machine and Stand. B-11 Figure 4. 100 mm Diameter Core and Waste Ring. Reasonably smooth, parallel ends for the test specimen were then provided by trimming the 100 mm diameter core using the double bladed saw shown in Figure 5. This step is more critical than the coring step and requires the 100 mm diameter core to fit tightly in the saw clamp, and sufficient waste material on each end to keep the saw blades from bending. Figure 5. Double Bladed Saw With 100 mm Core.

B-12 All coring and sawing was done using water to cool the cutting tools. After all cutting was complete, the bulk specific gravity of the finished specimen was determined in accordance with AASHTO T166 by first measuring the immersed mass, then the saturated surface dry mass, and finally the dry mass. The cores were measured for compliance with the NCHRP Project 9-29 specimen tolerances, which are summarized the Table 6. Figure 6 shows a completed test specimen. Figure 6. Final Simple Performance Test Specimen. 4. SPECIMEN HANDLING The evaluation testing program required fabrication and testing of 192 specimens. Sample fabrication and testing was split into two phases as shown in Table 7. In the first phase the Interlaken equipment was operated in the FHWA laboratory and the Shedworks equipment was operated in AAT’s laboratory. In the second phase, the location of the equipment was switched. Each phase was divided into two blocks, and all of the testing for a given block in both laboratories was completed before the next block began. To allow reasonable productivity during specimen fabrication, the over-height gyratory specimens were fabricated on a regular schedule of four specimens per day. To minimize aging of the test specimens, the simple B-13 performance test specimens were sawed and cored from the over-height gyratory specimens when needed. All of the simple performance test specimens for a specific mixture for a block were cored, sawed, and measured at the same time. They were then distributed to the two laboratories based on their air void contents to obtain approximately the same average and range of air void contents. 5. TESTING The dynamic modulus and flow number tests were performed with the simple performance test devices in accordance with the Project 9-19 test protocols. Test specimens were conditioned in a separate environmental chamber prior to testing. Dummy specimens with thermocouples were used to ensure that the test specimens were with the specified 0.5 °C tolerance of the target test temperature. The test chamber of the simple performance test device was also equilibrated to the target testing temperature. Once the specimens and the test chamber reached the target temperature, the specimens were removed from the separate environmental chamber, placed in the test chamber, and instrumented if required. The test chamber was then closed and allowed to equilibrate to the test temperature before the testing began. The three dynamic modulus tests, 25 °C unconfined, 45 °C confined, and 45 °C unconfined, were performed on the same test specimen. For each condition dynamic moduli and phase angles were measured at frequencies of 25, 10, 5, 1, 0.5, and 0.1 Hz. Stress levels were varied automatically by the simple performance testers to achieve a target strain level of 100 µstrain. A confining pressure of 138 kPa was used in the confined testing. Separate test specimens were used for each of the flow time tests. Table 8 summarizes the confining and deviatoric stresses used in the flow number testing for the two mixtures. These stress levels were selected to obtain a short test, less than 1000 load repetitions and a long test, greater than 1000 load repetitions.

B-14 Table 7. Evaluation Testing P rogram . D y n am ic M odulus Flow N um ber Phase Block D evice Lab M ix 25 °C U nconfined 45 °C Confined 45 °C U nconfined 45 °C U nconfined 45 °C Confined 9.5 m m 4 4 4 Interlaken A A T 19.0 m m 4 4 4 9.5 m m 4 4 4 1 Shedw orks FH W A 19.0 m m 4 4 4 9.5 m m 4 4 4 Interlaken A A T 19.0 m m 4 4 4 9.5 m m 4 4 4 1 2 Shedw orks FH W A 19.0 m m 4 4 4 9.5 m m 4 4 4 Shedw orks A A T 19.0 m m 4 4 4 9.5 m m 4 4 4 1 Interlaken FH W A 19.0 m m 4 4 4 9.5 m m 4 4 4 Shedw orks A A T 19.0 m m 4 4 4 9.5 m m 4 4 4 2 2 Interlaken FH W A 19.0 m m 4 4 4 Total 64 128 B-15 Table 8. Flow Number Test Conditions. Mixture Condition Deviatoric Stress, kPa Confining Pressure, kPa 9.5 mm Unconfined 400 0 9.5 mm Confined 600 20 19.0 mm Unconfined 600 0 19.0 mm Confined 900 20