## 4 Results and Discussion  
### Fracture Resistance Values of Tested Samples  
Figure 3 shows some of the load-displacement curves obtained for the tested ENDB, SCB, BD and SENB samples at low and medium temperature conditions. For the low temperature tests, it can be seen that the loading curves are linear and asphalt mixture exhibits as a brittle material. Therefore, the framework of linear elastic fracture mechanics (LEFM) is valid for this testing condition. However, some evidences of non-linearity in the load-displacement curves are seen for the medium temperature condition due to viscosity of bitumen material. However, the onset of fracture takes place for both temperature conditions at a critical level of loading applied to each sample. This situation is known by the peak load value in the load-displacement curve. Therefore, the critical value of stress intensity factor for each specimen can be determined by replacing the peak loads into Equations (1)-(4) and using the geometry factors given in Table 1. The results of critical stress intensity factors (K\({}_{\text{Hf}}\), K\({}_{\text{Hf}}\) and K\({}_{\text{IIIf}}\)) that are representative values for the resistance of tested asphalt mixtures at the onset of fracture initiation under different fracture modes and temperatures are presented in Table 5. The results illustrated in this Table, demonstrate the sensitivity of critical stress intensity factor value a same asphalt mixture to the geometry of test specimen (disc, semi disc and rectangular beam), loading mode (i.e., modes I, II, III or tensile, shear or tear type), loading type (compression, bending) and temperature (low and medium temperature). For example, for pure mode I loading and low temperature conditions in which the LEFM is valid, as shown in this research and explained in many previous works e.g., [1; 2; 3; 4; 5; 6; 7; 8; 9; 10], where it can be seen that the K\({}_{\text{Hf}}\) value of a same asphalt mixture depends on the test specimen utilized for testing. The value of mode I fracture toughness increases from 0.66 MPam\({}^{0.5}\) (obtained from the BD specimen) to 0.82 MPam\({}^{0.5}\) (obtained from the SCB specimen). According to recent works published by [PERSON] and co-workers [25; 26; 48], the mode I fracture toughness of asphalt mixtures depends on the geometry and loading conditions of the employed test specimen. Based on their finding (that is confirmed in this research as well), the mode I fracture toughness value obtained from the diametral compression test is lower than the value obtained by bending type specimen. They also proposed a theoretical model for considering the influence of geometry and loading condition on the mode I fracture toughness value of asphalt mixtures. Comparison of presented results in Table 5 also demonstrates that the fracture and cracking resistance of an asphalt mixture reduces generally under application of shear type loads (i.e., mode II and mode III) relative to opening mode failure. Furthermore, according to Table 5, the cracking resistance of the asphalt mixture decreases significantly by moving from the low temperature condition to the medium temperature condition. This could be due to reducing the stiffness of mastic or bitumen part at higher temperatures.