Damage assessment in concrete using quantitative acoustic emission

An acoustic emission (AE) is a localized rapid release of strain energy in a stressed material. Quantitative acoustic emission measurement techniques have recently been developed to estimate the location, size, orientation, and fracture mode of individual microcracks. Quantitative AE techniques were applied to a laboratory study of plain concrete beams under four point loading. Center-notched and off-center-notched beams were loaded in order to produce, respectively, mode I and mixed mode failure. Using AE seismic moment tensor representation, microcracking was characterized as mode I, mode II, or mixed mode. The mode of microcracking was compared to the mode of the visible crack. Most microcrack planes were in a direction normal to the tensile stress for a mode I macrocrack (center-notched), whereas microcrack planes were relatively uniformly distributed for a mixed-mode macrocrack (off-center notched). A large number of mixed-mode microcracks were observed even for the center-notched beam indicating that fracture mechanisms of microcracks may differ from the main macromechanical crack. It is shown that AE measurements can provide a potentially powerful tool in assessing damage.