Experimental investigation on I-II mixed mode fracture of hot mix asphalt using double-edge notched Brazilian disk test

The I-II mixed mode fracture is a typical failure pattern observed in asphalt pavement. In this study, the fracture behavior under I-II mixed mode of three diverse asphalt mixtures was scrutinized. The investigation involved performing double-edge notched Brazilian disk (DNBD) tests at two different temperatures: -10 degrees C and 25 degrees C. DNBD specimens were prepared with two notch lengths (10 mm and 20 mm) and seven notch angles, including 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees. Stress intensity factor (K-IC and K-IIC), equivalent stress intensity factor (K*(IC) and K*(IIC)), and fracture energy were used to characterize the fracture behaviors. The findings suggest that the generation of mixed-mode fractures can be manipulated through variations in notch length and angle. An increase in notch angle shifted the fracture behavior towards a more mode I-dominant pattern, while elongating the notch length amplified the significance of mode II fracture contributions to the overall fracture process. The influence of reclaimed asphalt pavement (RAP) on the fracture performance of asphalt mixtures exhibited variation across the temperatures ranging from -10 degrees C to 25 degrees C. At -10 degrees C, mixture C, which contained an SBS-modified binder, demonstrated the most robust fracture performance, as evidenced by higher values of K-IC and K-IIC. This was succeeded by mixture B that used a #70 binder, with mixture A incorporating RAP trailing behind. Conversely, at 25 degrees C, the presence of RAP contributed to achieving the highest indices of K*(IC) and K*(IIC), surpassing even the performance of mixture C with its SBS-modified binder, followed by mixture B with its #70 binder. For specimens with identical notch lengths and angles, the stress intensity factors recorded at -10 degrees C were substantially higher compared to those at 25 degrees C. This observation suggests that fracture resistance diminishes as temperature rises. Furthermore, an increase in notch angle correlated with a reduction in fracture energy at -10 degrees C, whereas at 25 degrees C, the notch angle's influence on fracture energy appeared to be negligible. When examining the performance at -10 degrees C, mixture C exhibited the highest fracture energy, with mixtures B and A following in descending order. In contrast, at 25 degrees C, mixture A outperformed mixtures C and B in terms of fracture resistance, as gauged by fracture energy. Notably, the effect of mixture type on fracture energy was consistent with the effect of mixture type on stress intensity factor.