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In the present work the acoustic emission (AE) technique is applied to examine some aspects influencing concrete failure in compression. By monitoring a structure by means of the AE technique, it proves possible to detect the occurrence of stress-induced cracks. Cracking, in fact, is accompanied by the emission of elastic waves that propagate within the bulk of the material. These waves can be received and recorded by transducers applied to the surface of the structural elements. This technique can be used for diagnosing structural damage phenomena. The current paper presents a mixed experimental and theoretical approach to evaluate the energy density dissipated during compression at each value of strain. Through this method, the two semi-empirical Gutenberg-Richter (GR) laws, well-known in seismology, are verified, the fractal interpretation results of which are very close to the essence of the AE phenomenon. Furthermore, the mentioned approach allows the parameter of ‘magnitude’ to be identified, appearing in the laws, with the number of oscillations larger than a given threshold measured in volts. Finally, the developed concepts are applied to the study of the compression phenomenon. In particular, by this approach, it is possible to distinguish between the energy progressively dissipated or stored in a compressed structural element. [ABSTRACT FROM AUTHOR]

In the current paper, the effect of tensile softening parameters, the tensile strength σt and the initial slope k1 of the stress-crack width curve, on the structural size-effect law in bending of concrete are studied by a bending model. The model results show that the size-effect law in bending strength normally presented by flexural strength and beam height diagram (σf-logH) is strongly dependent on σt and k1. With increase of beam height, the general size-effect law in bending can be characterised as a fast reduction stage followed by a stable decreasing stage and finally converged to the tensile strength of concrete. With increasing tensile strength, the σf-logH curve goes up and the value of dσf/dlogH gradually increases. In the meantime, for a given beam height, bending strength increases with increase of k1. The model predictions are compared with experimental results. Good agreement between model predictions and experiments has been obtained. [ABSTRACT FROM AUTHOR]