Laboratory specimens prepared for the mechanical tests of asphalt mixtures are often extracted from cylindrical or slab specimens (using the gyratory compact machine, Marshall compactor machine or roller compactor machine). Thus, the majority of specimens that are used for conducting the mode I fracture toughness tests on asphalt mixtures are in the form of discs and beams. Circular and semi-circular specimens, such as the ENDB and SCB; and rectangular beam shape specimens, such as the SENB sample, are among the conventional fracture test configurations that can be easily prepared without requiring extra machining. Furthermore, all of the mentioned specimens are loaded with the conventional three-point bend fixture and can provide good  
Figure 1: Pure mode I tensile cracking of the pavement induced by traffic and thermal loads. simulations for top-down cracking phenomenon in real asphalt pavements subjected to actual traffic loads. Based on the previous studies the fracture behavior of brittle and quasi-brittle materials and the measured mode I fracture toughness value can be noticeably affected by the type of test specimen and applied loading [45]. For example, in an investigation conducted by [PERSON] et al. [46] the K\({}_{\text{lc}}\) values of a typical rock material obtained using some standard test specimens and procedures differ up to 40%. [PERSON] et al. [47] investigated the effect of specimen geometry on mode I fracture toughness and crack growth behavior of a brittle polymer called PMMA. Similarly, by testing different specimens subjected to three-point bend loading, [PERSON] et al. [48] demonstrated that the fracture toughness of plexiglass material depends on the type of specimen utilized for the testing. Furthermore, according to the previous fracture studies performed on rocks, it has been proven that the type of test specimen can noticeably affect the measured value of mode I fracture toughness [45; 46; 47; 48]. Although the effect of mix design and asphalt ingredients on the mechanical properties and fracture behavior of asphalt mixtures has been investigated extensively [16; 49; 50; 51; 52; 53; 54], the influence of specimen shape and testing method has received less attention by the asphalt fracture researchers. Some testing methods such as Semi-Circular Bending (SCB) and circular Disc Compact Tension (DCT) specimens have been proposed by ASTM for determining the fracture toughness or fracture resistance of asphalt mixtures as two standard testing methods [55; 56]. However, it is still not clear whether these two methods or other testing techniques provide the same results for the fracture toughness (as material property) of asphalt mixtures. Since such testing methods use different test geometries with different loading setups, the possible influence of geometry and loading type on the cracking resistance behavior of asphalt mixture materials is an interesting issue and it is necessary to study this topic for the asphalt concrete mixtures. The main aim of this paper is to investigate the effect of specimen geometry and loading type on the value of mode I fracture toughness of asphalt concrete mixtures. In order to achieve this purpose, a series of mode I fracture toughness experiments was performed on the same asphalt mixture with different test specimens (i.e., SCB and ENDB; and SENB and ENDC configurations). The fracture tests are conducted at two sub-zero temperatures and it is shown that although there is a general agreement and consistency between the experimental results, some differences exist in the value of determined K\({}_{\text{lc}}\). This difference can be attributed to both the geometry (i.e., shape) of the specimen and the method of applying the loads to the samples during the fracture toughness test. However, the effect of the type of loading is more obvious than the geometry (or shape) of the test sample.