13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- The critical stress intensity factors (KIc and KIIc) were calculated from Eq. 1 for each test conducted under mode-I or mode-II loading conditions. Table 2 shows the average values of Pcr, KIc and KIIc obtained for asphalt samples. According to this Table, the critical stress intensity factor under pure mode-II loading is about 26% higher than that under pure mode-I loading. In other words, when a cracked asphalt concrete is under pure mode-II loading, its resistance against brittle fracture at low temperatures is more than that of mode-I loading. Moreover, the mode-II fracture load in the asphalt SCB specimens is more than twice the mode-I fracture load (see Table 2). While the crack extension in mode-I fracture tests took place along the pre-crack direction, all the mode-II cracks kinked out of the initial plane (see Fig. 6). This is mainly because the maximum tensile stress around the crack tip is no longer along the crack line when a cracked specimen like SCB is subjected to pure mode-II loading conditions [10]. 4. Conclusion In this paper, a suitable procedure was suggested for conducting fracture experiments on cracked asphalt concretes under pure mode-II loading and at low temperatures. The modified SCB specimens used for the experiments can be produced conveniently by a gyratory compactor or by coring from an existing asphalt pavement. The specimen can be used both for pure mode-I tests and for pure mode-II tests. The mode-I and mode-II tests were performed successfully on an asphalt mixture sample at -20oC. The results showed that both the fracture load and the critical stress intensity factor obtained from the mode-II experiments were considerably higher than those obtained from the mode-I experiments. References [1] D.A. Anderson, D.W. Christensen, R. Dongre, M.G. Sharma, J. Runt, P. Jordhal, Asphalt Behavior at Low Temperatures, Publication No. FHWA-RD-88-078, RHWA, US Dept. of Transportation, 1990. [2] B. Buttlar, Reflective crack relief interlayers. OMP Brown Bag Seminar Series, 2007. [3] X. Li, M.O. Marasteanu, Using semi-circular bending test to evaluate low temperature fracture resistance for asphalt concrete. Exp. Mech., 50 (2007) 867-876. [4] J.M.M. Molenaar, A.A.A. Molenaar, Fracture toughness of asphalt in the semicircular bend test. In. 2nd Eurasphalt and Eurobitume Congress, Barcelona, Spain, (2000). [5] X. Li, M.O. Marasteanu, Evaluation of the low temperature fracture resistance of asphalt mixtures using the semi circular bend test. Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions, 73 (2004) 401-426. [6] R. Dongre, M.Cl. Sharma, D.A. Anderson, Development of fracture criterion for asphalt mixes at low temperatures. Transp. Res. Rec., 1228 (1989) 94-105. [7] S.A Tekalur, A. Shukla, M. Sadd, K.W. Lee, Mechanical characterization of a bituminous mix under quasi-static and high-strain rate loading. Constr. Build. Mater., 23 (2008) 1795-1802. [8] M. Ameri, A. Mansourian, M. Heidary-Khavas, M.R.M. Aliha, M.R. Ayatollahi, Cracked asphalt pavement under traffic loading – A 3D finite element analysis. Eng. Fract. Mech., 78 (2011) 1817-1826.
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