13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Experimental Determination of Mode II Fracture Resistance in Asphalt Concretes M.R. Ayatollahi1,*, Sadjad Pirmohammad1 1 School of Mechanical Engineering, Iran University of Science and Technology, 16846, Iran * Corresponding author: m.ayat@iust.ac.ir Abstract This paper presents a test set-up using semi-circular bend (SCB) specimen for measuring pure mode-II fracture toughness of asphalt concretes. Three-point bend fracture tests were performed on the SCB specimens at low temperature. The results showed that this set-up could be used for conducting mode-II fracture tests on hot mix asphalt (HMA) specimens. Linear elastic fracture mechanics (LEFM) concept was used to study the fracture behavior of cracked asphalt concrete. Mode-II critical stress intensity factor, KIIc, was calculated using the fracture load measured from the three-point bend tests. In addition to pure mode-II tests, similar tests were carried out for pure mode-I loading. Results showed that mode-II critical stress intensity factor was higher than that of pure mode-I loading. Keywords Asphalt concrete, Critical stress intensity factor, Low temperature, Pure mode-II fracture. 1. Introduction Cracking at low temperatures is one of the major sources of deterioration in asphalt concretes imposing significant costs on the pavement rehabilitation agencies annually. There are many causes for crack nucleation on asphalt pavement surface such as the temperature fluctuation and the traffic load induced from vehicle wheels. Good understanding of cracking mechanism could be helpful for reducing those costs. Asphalt concrete is a temperature dependant material that may fall within a category of materials that are defined as brittle or quasi-brittle at low temperatures. Many researchers have studied fracture behavior of hot mix asphalt (HMA) mixtures at low temperatures (e.g. see [1-3]). Linear elastic fracture mechanics (LEFM) is a reliable approach to investigate fracture behavior of brittle materials. In LEFM, the stress intensity factor, K, is a fundamental parameter characterizing the fracture phenomenon from the crack tip. This parameter has been used by many researchers (e.g. see [4-6]) for cracks in asphalt concrete mixtures. In the recent decades, many researchers have studied the fracture behavior of asphalt concretes under pure mode-I (opening mode) loading (see e.g. [4-7]). The temperature cycling is one of the main causes of mode-I cracking in asphalt pavements. In some cases such as reflective cracks, the crack extension is known to take place under a combination of mode-I and mode-II loading. Similarly, according to the research performed by Ameri et. al. [8], the traffic load induced by vehicle wheels at top down cracks (TDC) also results in mixed mode I-II loading. Therefore, it is important to investigate the behavior of cracked asphalt concretes under pure mode-I, pure mode-II, and mixed mode I-II loading conditions. In particular, pure mode-II fracture in asphalt concretes has been rarely studied in the past. In this research, the semi-circular bend (SCB) specimens, prepared from the cylindrical samples were utilized for conducting three-point fracture tests under pure mode-II loading. In addition to the mode-II tests, fracture tests were performed for mode-I loading as well and the critical stress
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