K Ic and K IIc measurement for hot mix asphalt mixtures at low temperature: Experimental and theoretical study using the semicircular bend specimen with different thicknesses

Pure mode I and mode II fracture toughness of asphalt mixture was investigated both experimentally and theoretically using vertical edge crack semicircular bend (SCB) specimen with symmetric and asymmetric bottom loading spans. The thickness of SCB specimen was considered in the range from 30 to 70 mm, and the fracture toughness tests were performed at three subzero temperatures (−5°C, −15°C and −25°C). The results showed that K Ic and K IIc are increased by reducing the test temperature. The thickness had no sound effect on the fracture toughness, but the thickness of 50 mm was more suitable for fracture study on this material. The fracture load of mode II specimen was significantly greater than the mode I fracture load at the same testing condition. The fracture toughness ratio ( K IIc / K Ic ) that varies in the range between 1 and 1.4 was predicted theoretically using three well‐known stress/strain‐based fracture criteria.