Fracture toughness determination of modified HMA mixtures with two novel disc shape configurations

In this paper two circular shape test specimens are designed and examined for experimental determination of mode I fracture toughness (KIc) in different modified hot mix asphalt (HMA) materials. The suggested configurations are (i) edge notched disc bend (ENDB) specimen subjected to three-point bend loading and (ii) edge notched diametrically compressed (ENDC) disc specimen. It was shown that both specimens are suitable for conducting fracture toughness experiments on HMA mixtures at low temperature conditions. In general, all the investigated modifiers enhanced the low temperature cracking performance of tested HMA mixtures such that, the nano-clay additive had the most effect on increasing the fracture toughness value relative to the control mixture. However, the KIc data obtained from the ENDB specimen were slightly greater than the corresponding values of ENDC specimen. It was demonstrated that this difference is attributed to the loading configuration (i.e. bending and compressive loads applied to the ENDB and ENDC specimens, respectively). By considering the combined influence of singular (KI) and first non-singular (T) components in the crack tip stress/strain field, the KIc data obtained from these two specimens were predicted by means of the maximum normal strain theory.