13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- mm were manufactured using super pave gyratory compactor machine (SGC). The numbers of gyratory rotations (i.e.35, 70 and 90) were also varied that results in changing the void percentage in the prepared mixtures. The cylinder were then sliced using a rotary diamond saw machine to obtain circular discs of height approximately about 30 mm. Each disc was splited into two halves to produce two semi circles. A very narrow notch with length of 20 mm and width of 0.4 mm was then introduce at the middle of flat edge by a very thin rotary high speed diamond saw blade. Consequently, several edge cracked SCB specimens were manufactured and maintained in a freezer with temperature of -15oC for 6 hours to conduct the fracture tests. Fig. 2 shows some of the steps of specimen preparation for fracture toughness experiments. Figure 2. Some of the steps for preparing the SCB test specimens. After preparation of the test samples, they were tested using a compression test machine having capacity of 15kN. The tests were carried out at -15oC under displacement control conditions with a constant cross head speed of 3 mm/min. The SCB specimens were tested using a three-point bend fixture with the loading span of 2S = 100 mm (i.e. S/R = 0.67). For conducting the tests, the SCB specimens were placed carefully inside the fixtures and then were loaded until the final fracture. The complete load-displacement data were recorded during the tests using a computerized data logger. The load-displacement curves for all the samples were nearly linear, showing the brittle failure behavior of the tested asphalt mixtures at low temperature of -15oC. Others [13-15] have also mentioned that the asphalt mixtures behave as a linear elastic material at low subzero temperatures. Therefore, fracture toughness of the tested asphalt mixtures were determined from the maximum load recorded for each test. A total number of 45 specimens with different compositions were manufactured and for each mix design, three SCB specimens were tested successfully. Fig. 3 shows the test setup and a typical load-displacement curve obtained for one of the tested specimens. Figure 3. loading setup used for testing of SCB specimen made of asphalt mixture and a typical load-displacement curve obtained for -15oC.
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