Brazilian test of concrete evaluated by AE

For a detailed evaluation of fracture processes due to tensile stresses using acoustic emission (AE) technique, a splitting test (Brazilian test) is particularly well-suited Thus, a Brazilian test was performed to generate a well-defined crack surface in a concrete cube. Using AE technique, the formation of micro cracks was observed and correlated with the stress distribution during the test. During the experiment, some 1800 acoustic emissions were recorded. Half of these events accompanied the evolution of the main crack. From these 900 events, 378 AE events were localized with an accuracy better than 5 mm. The well-defined crack in the center of the specimen allowed a mapping of the crack surface. For this purpose, the specimen was ground in a stepwise manner normal to the crack subsequent to testing. The run of the crack in the ground surfaces was digitized from photographs and interpolated. Inversion of AE amplitudes of the spatial displacement distribution yields a system of equivalent moments for selected AE events, the so-called moment tensors. Analysis of the moment tensor allows an interpretation of failure based on fracture mechanics and gives information about the stress field within the specimen.