Damage growth monitoring in cementitious materials by nonlinear ultrasonic and acoustic emission techniques

This article reports the observation made during the compressive fracture process of cementitious materials which has been studied using nonlinear ultrasonic testing (NUT) and acoustic emission (AE) testing techniques. The generated higher harmonics were recorded at a specific time interval and normalised with respect to the peak amplitude of the fundamental wave. The AE based damage index (D) was compared with the normalized second harmonic amplitude (X). The X parameter decreased to a minimum at failure load where the AE based b-value also reached its minimum value. Another nonlinear ultrasonic technique namely Sideband Peak Count Index (SPC-I) showed a similar variation when correlated with X parameter. It is concluded that both techniques - the normalized second harmonic amplitude and the sideband peak count index can be used as an indicator of internal damage growth. A parallel may exist between AE based damage index (D) and normalized second harmonic amplitude (X) and SPC-I for the damage growth monitoring in cementitious materials. Since SPC-I technique is much easier to implement in comparison to the higher harmonic generation technique, it is concluded that the SPC-I can replace HHG for monitoring the damage growth in heterogeneous cementitious materials.