The Effect of Aggregate Gradation on the Fracture Resistance of Asphalt Mixtures Subjected to Freeze–Thaw Cycles

ABSTRACT This study investigates the effects of aggregate gradation and freeze–thaw cycles on the fracture toughness of hot‐mix asphalt (HMA) and stone mastic asphalt (SMA). Edge‐notched disc bend specimens were prepared using three aggregate gradations with nominal maximum aggregate sizes (NMAS) of 19, 12.5, and 9.5 mm, and PG 64‐22 binder. Fracture toughness was evaluated at −15 °C under three loading modes (I, II, and III), and the influence of 0–9 freeze–thaw cycles was examined. Results showed that increasing NMAS enhanced fracture toughness under mode I but had no significant effect under modes II and III. Freeze–thaw cycles reduced fracture toughness in both mixtures, stabilizing after the seventh cycle. SMA mixtures generally exhibited lower toughness than HMA with the same NMAS. Overall, fracture resistance was highest in mode I and lowest in mode III. The findings suggest that SMA mixtures with larger NMAS (e.g., 19 mm) can be effective alternatives to HMA in cold regions.