A methodology to characterise the resistance of asphalt concrete mixtures to fatigue crack propagation has been developed to construct fundamental structure-fracture toughness relationships. Experimental techniques to evaluate parameters controlling the crack propagation process are presented. These parameters include crack driving force and the change in work done on the crack tip damage (active zone). A linear relationship between the width of the active zone and the crack length is assumed in order to quantify the amount of damage at each crack length. A constitutive equation is used to extract the specific energy of damage, a material parameter characteristic of the asphalt concrete mixture's resistance to crack propagation, and a dissipative coefficient. The capability of this approach to discriminate the subtle effect introduced by different chemical structures of asphalt is demonstrated on Elvax-modified AC-5 and AC-20 concrete mixtures. The validity of the current approach to describe the fatigue behaviour of asphalt concrete mixtures over the entire range of energy release rate is verified. The practical utilisation of this methodology is evident. It forms a basis on which structure- or processing condition - fracture toughness relationships of asphalt concrete mixtures can be constructed. Such relationships can guide the development of asphalt concrete mixtures with superior crack resistance and aid in the design of primary and secondary pavements. (Author/publisher)
Abstract