Low temperature cracking behavior of modified asphalt mixture under modes I and III

•PCB and PHC were used to study fracture behavior of HMA under FTD.•FTD was a suitable criterion for evaluating long-term fracture performance.•Mixes containing additives had better KIC (KIIIC) and GIF (GIIIF) than base mix.•The additives recovered the reduction in KC and GF caused by the 3 FTD cycles.•The mixture containing 18% PCB+2.75% PHC had the best fracture behavior. The study of the short- and long-term cracking behavior of asphalt pavement under tensile and tear deformations, and the production of sustainable mixtures using recycled additives, were the two main goals of this study. For this purpose, two types of additives, namely pyrolysis carbon black (PCB) and pyrolysis hydrocarbon (PHC), which were made from hospital waste recycling as a result of the COVID-19 pandemic, were used to study the fracture behaviour of asphalt mixture under modes I and III (at -15 °C). For simulating the actual pavement conditions with the Edge Notched Disc Bend (ENDB) samples, 0 and 3 freeze-thaw damage (FTD) cycles were applied to mixtures. Laboratory findings indicated that the addition of 6, 12, and 18% PCB, 1.25, 2, and 2.75% PHC, and 18% PCB + 2.75% PHC into the asphalt mixtures resulted in an increase in the total fracture energy of mixtures at -15 °C by increasing the GIfpre-peak and GIIIfpre-peak as well as increasing the fracture toughness, for both FTD cycles. Also, the results of brittleness indices revealed that using 18% PCB + 2.75% PHC in the asphalt mixture had more flexible behaviour than the mixture containing PCB (due to a higher average brittleness index) and more brittle behaviour than the mixture containing PHC (due to a lower average brittleness index) under mode I. While the mixtures containing PCB, PHC, and 18%PCB+2.75%PHC were more flexible under mode III. Finally, the mixture containing 18% PCB+2.75% PHC had the best fracture performance under mode I. It increased the asphalt mixture's fracture energy and toughness respectively under 3 FTD cycles by 62 and 54%, in comparison with the unmodified mixture and without applying FTD cycles. Also, it was indicated that the modified mixture with 18%PCB+2.75%PHC can compensate for 97% of the fracture energy decrease due to the influence of FTD cycle (under mode III), while in terms of the fracture toughness index, a 12% increase was obtained.