Damage due to microcracking in cementitious composites using AE frequency characteristics

This study presents the transformation of acoustic emission (AE) waveforms from time domain to frequency domain using fast fourier transform (FFT) to understand the mechanisms underlying the fracture of cementitious composites.The motivation of the study is to introduce a real-time monitoring method based on frequency content of AE.The mode I fracture experiments are performed on plain concrete (PC) and steel fiber reinforced concrete (SFRC) in the laboratory.The fracture mechanisms of PC and SFRC are analyzed using the centroid of the frequency spectrum obtained from spectral analysis.The results indicate that there is no change in the frequency centroid spectrum (FCS) until the onset of microcracking in mode I crack deformation.After the microcracking begins, the slope of the FCS continuously decreases, indicating the rate of material damage over time.An accelerated crack growth denoted by slope of mean FCS is 2.7 times higher for PC when compared with SFRC.The slope of the mean FCS is nearly the same for both the initial and final regions of fracture mechanisms in PC.In SFRC, this rate is 29.2% lower due to fiber bridging mechanisms.A damage parameter, based on the FCS, is proposed to assess the damage and validated with the existing damage parameters.These observations suggests that FCS of AE waveforms may be used for real time damage monitoring of concrete structure.