On predicting mode II fracture toughness (KIIc) of hot mix asphalt mixtures using the strain energy density criterion

Mode II or in-plane sliding of crack faces is one of the possible fracture modes for asphalt pavements which can often take place due to traffic loads passing over the crack at low temperature conditions. Hence pavement engineers need to know the value of mode II fracture toughness (K-IIc) of asphalt mixtures as an important design parameter. However, despite a large number of mode I fracture toughness (K-Ic) values available in the literature for different asphalt concrete materials, only limited K-IIc values have been reported for such construction materials. In this paper to fill this research gap, a number of pure mode I and pure mode II fracture toughness experiments are conducted at low temperature using symmetric and asymmetric semi-circular bend specimens made of different asphalt mixtures. It was found that the mode II fracture toughness of each mixture is approximately 0.9-1.1 times the corresponding value of K-IC. It was demonstrated that the experimentally obtained fracture toughness ratio (K-IIc/K-Ic) for the investigated asphalt concretes are in good agreement with theoretical predictions of the minimum strain energy density criterion. Consequently, as an engineering application of this research, mode II fracture toughness of investigated asphalt mixtures was estimated in terms of their more common mechanical parameters such as K-Ic and Poisson's ratio values.