13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- the mentioned specimens, the SCB specimen can be considered as a suitable and favorite configuration for asphalt mixtures because it can be manufactured easily from standard field coring equipments or gyratory compactor machines and then it can also be tested easily by using ordinary testing apparatuses and fixtures. Moreover, in comparison with the rectangular beam specimens, the SCB samples need less asphalt mixtures for specimen preparation and consequently decrease the weight of test samples and cost of experiments. Hence, the SCB specimen has been used in the past for investigating the fracture behavior of asphalt mixtures [6-12]. Fig. 1 shows the SCB specimen schematically which is a semi-circular specimen of radius R and thickness t. When the SCB specimen is subjected to symmetric three-point bending with a loading span of 2S, the vertical edge crack of length a experiences pure mode I deformation (crack opening). The specimen can also be used for mixed mode I/II (tension – shear) experiments simply by inclining its direction relative to the applied load P direction or changing its location relative to the loading points. 2S 2R P a Figure 1. The edge cracked SCB specimen subjected to symmetric bend loading. Since asphalt mixtures are complicated materials, their properties, performance, durability and mechanical strength depend strongly on the composition of the ingredients, manufacturing process, mix design, type of aggregates and binders, service and temperature conditions and etc. Therefore, in this research, fracture resistance of different compositions of asphalt mixture is investigated experimentally using SCB specimen and the effects of asphalt characteristic specifications including the aggregate size, air void percentage and bitumen type on fracture load and fracture toughness are studied. 2. Asphalt mixtures manufacturing For preparation of asphalt mixtures, two aggregate types made of limestone and siliceous with three gradations (i.e. aggregate sizes of No. 4, 5 and 6 according to Iranian paving standard- code 234) were considered. The corresponding nominal maximum aggregate size (NMAS) for these three aggregate size numbers are 12.5 mm, 9 mm and 4.75 mm, respectively. The aggregate gradations and their percentages used for asphalt mixtures of this study have been presented in Table 1. Also, two binder penetration grade of 60/70 (the most commonly used type for paving the roads in Iran) and 85/100 (a suitable type for cold climates) were utilized for preparation of asphalt mixtures. Specifications of
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