Damage monitoring of three-point bending concrete specimens by acoustic emission and resonant frequency analysis

The crack propagation process in pre-notched concrete beam specimens, tested in the lab under three-point bending, was monitored by the Acoustic Emission (AE) technique and the extraction of resonant frequencies. The loading process was carried out in displacement-controlled conditions up to the final failure of the specimen. Average frequency vs. RA value analysis was used to characterize the crack propagation mode, whereas the cumulative AE energy and the variation in the resonant bending frequencies were selected as the main parameters to monitor the damage progress due to crack advancement. Moreover, finite element models were implemented to reproduce the load–deflection curve and to evaluate the resonant frequencies for different notch depths. An inverse procedure was therefore applied to estimate the crack advancement based on the measured and calculated frequencies.