Observation of crack propagation in asphalt mixtures with acoustic emission

Fracture in quasi-brittle materials is associated with the formation of microcracks, which release energy in the form of elastic waves called acoustic emissions. The use of acoustic emission (AE) in the characterization of the fracture behavior of asphalt mixtures at low temperatures is investigated, and a method that uses AE to locate the crack path is presented. An application of the method is detailed for fracture tests performed with the semicircular bend specimen on asphalt mixtures at low temperatures. A network of seven piezoelectric sensors was used to capture AE signals, and a nonlinear regression algorithm was employed to locate the AE events. The locations of microcracks were in good agreement with the crack path observed at the end of the test. When the load increased beyond 70% of the peak load, the rate of AE activity was significant, indicating the formation of microcracks, and the location of AE was concentrated in a distinct area called the process zone. Moreover, the location of AE in the postpeak load showed the movement of the process zone and identified the crack propagation in the macroscale.