AASHTO T 394-21

This test method covers the determination of the fracture energy (Gf) of asphalt mixtures by means of the semicircular bend geometry (SCB). The method also includes procedures for calculating fracture toughness (KIC) and stiffness (S). The SCB specimen is a half disc with a notch (its length expressed in meters) that makes an angle a with the vertical axis of the disc. The SCB test can be used to determine mode I and mixed mode I and II stress intensity factors (Lim et al., 1993). In this standard, only mode I fracture toughness is addressed (a is equal to zero).

The procedures in this standard provide parameters that describe the fracture resistance of asphalt mixtures at low temperatures. These parameters are used in the new low-temperature module of the Mechanistic Empirical Pavement Design guide.

These procedures apply to test specimens having a maximum aggregate size of 19 mm or less. Specimens shall be 150 ± 9 mm in diameter and 24.7 mm ± 2 mm thick. These procedures are valid at temperatures below the performance grade (PG) lower limit of the asphalt binder used to prepare the asphalt mixture plus 22°C.