Assessment of Localized Damage in Concrete under Compression Using Acoustic Emission

This paper describes an experimental investigation to assess the development of the localized damage zone in concrete tested in compression. Cylindrical specimens were loaded and unloaded at different maximum strain levels. The mechanical response was measured and compared with acoustic emission activity. As expected, the acoustic emission activity increased with an increase in load. To establish a correlation between mechanical damage and acoustic emission activity, the acoustic emission events were categorized on the basis of their amplitude and duration. Higher amplitude and longer duration events occurred in the specimens at higher damage levels. A linear correlation was observed between the mechanical fracture energy and the measured acoustic emission energy. Triangulation was used to locate the position of the acoustic emission events and to assess the development of the damage zone during testing. The compression damage zone (CDZ) was found to develop at the time of peak stress with a length of approximately 1.2 times the diameter of the specimen. The size of the CDZ was observed to increase to double the diameter of the specimen at 1.6 times the strain at peak. While preliminary, these results indicate how the damage develops to form a zone that influences the stiffness degradation and the postpeak response of the concrete.