Use of acoustic emission for exploring characteristics and behaviors of mixed-mode fracture process of asphalt mixtures.

The mixed-mode fracture is one of the main failure forms of asphalt mixtures subjected to external loads. Acoustic emission (AE) technique could dynamically evaluate the fracture properties of materials. The objective of this paper is to investigate the fracture characteristics and behaviors during the failure process of asphalt mixtures aiming at the mixed-mode fracture problem. Firstly, the dynamic damage process of asphalt mixtures was characterized through simultaneously conducting the semi-circular bending (SCB) tests and AE tests under three fracture modes. Secondly, the fracture toughness of asphalt mixtures was calculated by the AE-based critical load corresponding to the macro-crack formation point. Thirdly, the failure mechanism of asphalt mixtures was revealed through the temporal characteristics of rise angle (RA) and average frequency (AF) values. Finally, the crack development process of asphalt mixtures was exhibited by the spatial characteristics of AE location results. The results show that the failure process of asphalt mixtures could be divided into four stages through the simultaneous mutations of cumulative AE energy, amplitude and count rate. The duration at each damage stages could clearly present the differences of damage behaviors between various fracture modes. The fracture toughness of asphalt mixtures obtained by AE method is 10–20% lower than that of the traditional mechanical method. The conversion form of the dominant mechanical behaviors could distinctly reveal the differences of the failure mechanism under various fracture modes. The concentration degree of the spatial distribution of AE location results could explicitly exhibit the distinction of the cracking behaviors under different fracture modes. [ABSTRACT FROM AUTHOR]