On determination of critical strain energy release rate for mode II failure of asphaltic composite mixtures using assymetric SCB configuration

Understanding the crack resistance of hot mix asphalt (HMA) composites under dominantly in-plane shear (mode II) at intermediate temperatures is an important issue for design and life assessment of asphaltic pavements. While at low temperatures the critical value of stress intensity factor (e.g. KIIc) is often used as the fracture resistance index for asphalt mixtures, the J-index is probably a more reliable fracture parameter for medium temperatures to capture the inelastic behavior of HMA mixture. Accordingly, the concept of J-integral has been adopted for determining JIc value of bituminous mixtures under mode I using semi-circular bend (SCB) test. In this paper, this concept is extended to propose an index (called JIIc) for investigating mode II failure resistance of HMA mixtures. To do that the strain energy values are determined at pure mode II using the multiple asymmetric SCB (ASCB) samples with different crack lengths. Using this method the JIIc value was determined at 25 degrees C for four HMA mixtures made of limestone aggrgate-60/70 bitumen (L60), limestone aggregate-85/100 bitumen (L85), siliceous aggregate-60/70 bitumen (S60) and siliceous aggregate-85/100 bitumen (S85). The corresponding values of JIIc for the investigated asphaltic mixtures varied from 3.5 to 7 kJ/m2 that were significantly higher than the JIc value of asphaltic mixtures. The JIIc value obtained from the L60 mixture was greater than the other mixtures and the S85 mixture showed the lowest JIIc. In addition, corresponding values of critical mode II stress intensity factor and mode II fracture energy were determined for each mixture and their relationships with the JIIc were investigated. In general, there were no proportional and linear relations between KIIf, GIIf and JIIc in the HMA mixtures.