Fracture resistance of asphalt concrete under different loading modes and temperature conditions

• Fracture tests were conducted under mixed I/II loading using an improved SCB specimen.
• Both loading mode and temperature affect the fracture behavior of asphalt concretes significantly.
• Depending on loading mode, SBS copolymer improves fracture resistance of asphalt concrete at lower temperatures.
• Asphalt concretes are more vulnerable to fracture under mixed mode I/II loading than pure mode I or II.

This paper deals with the effects of loading mode and temperature on the fracture resistance of asphalt concretes under static loading. Three-point fracture tests were successfully performed on the cracked asphalt concrete samples under different modes of loading including pure mode I, pure mode II and mixed-mode I/II at several subzero temperatures. Improved semi-circular bend (SCB) specimen containing an asymmetric vertical edge crack was employed to provide the desired loading modes. Critical stress intensity factors (KIf and KIIf) were then computed using the fracture load obtained from the experiments and the geometry factors determined from the finite element analyses. Furthermore, two different asphalt concrete mixtures (called normal and modified asphalt concretes) were used for specimen preparation. Results showed that both temperature and loading modes influence the fracture resistance of asphalt concrete significantly. For all the fracture tests performed under different modes of loading and decreasing temperature, the fracture resistance of asphalt concretes first increased and then below a certain temperature (−20 °C) decreased. Moreover, the minimum fracture resistance of asphalt concrete occurred under a specific mixed-mode I/II loading that can be considered as an index to assess the onset of crack growth in asphaltic materials. According to the test results, the modified asphalt concretes showed higher resistance against crack growth than the normal asphalt concretes particularly at lower temperatures.