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150 APPENDIX C: MATERIALS AND METHODS USED IN MIXTURE FATIGUE TESTS MATERIALS A 9.5-mm nominal maximum aggregate size (NMAS) virgin mix design was used for the mixture testing experiment in this study. The aggregate blend for this mix design consisted of four individual aggregates, including granite 89, natural sand, limestone 8910 and granite M10. The liquid asphalt binder used in the mix design was a PG 67-22 binder. A liquid anti-stripping agent (LOF 6500) was pre-blended with the binder at a rate of 0.5% by weight of virgin binder before mixing. The mix was designed at a design compaction effort of 80 gyrations. The design gradation, asphalt content, and volumetric properties are shown in Table C-1. The same mix design proportions were used to evaluate all the binders in this study. All mixtures were aged in loose mix condition at 95Â°C for 5 days prior to mixture performance testing, which was estimated to produce a degree of aging similar to the 40-hour PAV used for binder conditioning (Elwardany et al., 2017). Table C-1. Mix Design Sieve Size, mm (in.) % Passing Control Points 9.5 (3/8") 100 90-100 4.75 (#4) 77 Max 90 2.36 (#8) 55 32 â 67 1.18 (#16) 44 -- 0.6 (#30) 32 -- 0.3 (#50) 18 -- 0.15 (#100) 10 -- 0.075 (#200) 6.3 2 â 10 AC, % 6.0 -- Air Voids, % 4.0 -- VMA, % 16.8 > 15.0 VFA, % 76.0 -- Pbe, % 5.56 -- D/A Ratio 1.1 0.6 â 1.2 After the loose mix samples had been prepared in the laboratory, they were conditioned in accordance with the following procedure prior to preparation of compacted specimens. 1. Short-term oven aged (STOA) each loose mix sample in accordance with AASHTO R30 at 135Â°C for 4 hours. 2. Separated each short-term aged loose-mix sample into several pans, and ensured each pan had a relatively thin layer of loose mix (approximately equal to the NMAS of the mix). 3. Placed the pans with loose mix in an oven and long-term aged the loose mix samples at 95Â°C for 5 days (Figure C-1). The loose mix was agitated once per day during this process, and the pans in the oven were rotated once per day to minimize any effects of potential oven temperature gradient and/or draft on the degree of loose mix aging.
151 4. After long-term aging, the samples were taken out of the oven and mixed together to obtain a uniform sample. 5. The loose mix was reheated at the compaction temperatures for approximately 3 hours, and the compaction was performed when the compaction temperature was reached. Figure C-1. Loose Mix Long-Term Aging in Oven. TEST PROCEDURES Bending Beam Fatigue Test The bending beam fatigue test (BBFT) was conducted in accordance with AASHTO T321- 14. Six to eight beam specimens were tested for each mix as additional specimens were tested when results were variable. Within each set of six beam specimens, different strain levels were used to produce a range of fatigue life (from 10,000 to 1,000,000 cycles). The specimens were compacted in a kneading beam compactor (Figure C-2), and then trimmed to the testing dimensions of 380 Â± 6 mm long, 63 Â± 2 mm wide, and 50 Â± 2 mm high. Furthermore, the orientation in which the beams were compacted (top and bottom) was marked and maintained for the fatigue testing. An air void content of 7 Â± 1% was targeted for test specimens after trimming.
152 Figure C-2. Kneading Beam Compactor. During each test, a beam was held by four equally-spaced clamps, and a sinusoidal load was applied at a frequency of 10 Hz at the two inner clamps to yield a pre-determined target strain level at the center of the specimen. Testing was performed at 10Â°C and 20Â°C. Table C-2 summarizes the testing conditions and specimen requirements. Data acquisition software was used to record load cycles, applied loads, and beam deflections. The software also computed and recorded the maximum tensile stress, maximum tensile strain, phase angle, beam stiffness, dissipated energy, and cumulative dissipated energy at user-specified cycle intervals. The stiffness at the 50th loading cycle is defined as the initial stiffness of the beam. The failure point is the number of cycles where the peak of the product of the flexural stiffness times the number of cycles occurs. Table C-2. Testing Conditions and Specimen Requirements for Bending Beam Fatigue Test Parameter Value/Type Target Test Temperature (Â°C) 10 and 20 Loading Frequency (Hz) 10 Loading Waveform Sinusoidal Specimen Size 380 Â± 6 mm in length 63 Â± 2 mm in width 50 Â± 2 mm in height Target Specimen Air Voids 7 Â± 1%
153 Uniaxial Fatigue Test To characterize the fatigue characteristics of each mixture using the S-VECD model, two tests were performed in the AMPT. First, the dynamic modulus of the mixture was determined to quantify the linear viscoelastic (LVE) characteristics of the mix. Second, the uniaxial fatigue test was performed using the fatigue testing software in the AMPT to develop the damage characteristic curve. Dynamic Modulus. The dynamic modulus test was performed in accordance with AASHTO T378-17 in an IPC Global Asphalt Mixture Performance Tester (AMPT), shown in Figure C-3. The specimens were prepared in accordance with AASHTO R83-17. The specimens were compacted to a height of 180 mm and a diameter of 150 mm, then cut and cored to meet the specifications. Three replicate specimens were prepared for each mix. The temperatures and frequencies used for testing were in accordance with AASHTO R84-17. The high test temperature was selected based on the high performance grade of the base binder being tested. Dynamic modulus testing was performed unconfined and test data were screened for data quality in accordance with the limits set in AASHTO T378-17. Figure C-3. IPC Global Asphalt Mixture Performance Tester Uniaxial Fatigue Test. The uniaxial fatigue test was performed in accordance with AASHTO TP 107-14. Three to four specimens were tested for each mix as more specimens were tested when test results were variable. The specimens with dimensions of 150 mm in diameter and 180 mm in height were compacted in a Superpave gyratory compactor, and then trimmed to the dimensions of 100-mm in diameter and 130-mm in height. An air void content of 7 Â± 0.5 % was targeted for test specimens after trimming. Two test temperatures were used based on the performance grade of the binder used: (high PG + low PG)/2 -3 and (high PG + low PG)/2 +3. Table C-3 summarizes the testing conditions and specimen requirements. To conduct this test, a uniaxial fatigue sample was glued with steel epoxy to two end platens using a gluing jig. The test specimen and end platens were then attached with screws to the actuator and reaction frame of the AMPT, prior to installing LVDTs on the specimen.
154 Table C-3. Testing Conditions and Specimen Requirements for Uniaxial Fatigue Test Parameter Value Temperature (Â°C) (high PG + low PG)/2 -3 and (high PG + low PG)/2 +3 Loading Frequency (Hz) 10 Specimen Size 100-mm in diameter 130-mm in thickness Specimen Air Voids 7 Â± 0.5% Each test consisted of two steps: fingerprint dynamic modulus test and cyclic fatigue test. The fingerprint test was performed in the tension-compression mode of loading. During the test, the load level was controlled to achieve 50 to 75 micro-strains, and this load was applied for 50 cycles. The fingerprint dynamic modulus was then computed using the data of the last five cycles. The dynamic modulus ratio (DMR), the ratio of the fingerprint dynamic modulus to the dynamic modulus determined from the previous dynamic modulus test, was calculated. This value should be between 0.9 and 1.1 an acceptable test. For the cyclic fatigue test, a repeated pull-pull load was applied at a frequency of 10 Hz on the test specimen. A maximum displacement of the AMPT actuator was controlled, testing was conducted at three strain levels to yield a wide range of fatigue life (from 1,000 to 100,000). During this test, load cycles, applied loads, and sample deflections were recorded. Additionally, the software computed and recorded the tensile stress, tensile strain, phase angle and stiffness.