Cracking and crackling in concrete-like materials: A dynamic energy balance

An analysis of the Acoustic Emission (AE) activity and of the energy fields is carried out with reference to three-point bending (TPB) tests on concrete beams with different sizes. First, a cracking mode classification is performed on the basis of AE parameters like the average frequency and the rise angle of the waveforms. A compression test is also performed to verify if the identification of the fracture mode by means of the AE parameters is appropriate. Then, regarding the TPB tests, the fracture energy (dissipated) and the energy detected by the AE sensors (emitted) per unit of fracture surface are compared. The former energy increases with the specimen size whereas the latter one decreases. Therefore, a direct relation cannot be established between the two forms of energy, although an indirect relationship is given by the fact that their sum corresponds to the total energy released during the tes