Acoustic emission data analyses based on crumb rubber concrete beam bending tests

Acoustic emission (AE) is a vital analysis method used to explain the fracture properties of concrete specimens. Four representative analyses methods, including the b-value method, AE signal intensity, average frequency (AF) versus RA (RA means rise time divided by the amplitude) value, and cluster analyses, are utilised to characterise and analyse the damage mechanisms and failure modes of three-point and four-point crumb rubber concrete bending beams with different rubber contents, including, 0%, 5%, 10%, and 15%. Tests and analysed results show that the fracture magnitude in the crumb rubber concrete is larger than that in the normal concrete before the main collapse stage. The improved b-value (Ib-value) fluctuations in local regions are more closely clustered with increase of rubber content. Based on intensity analyses, the severity (Sr) and historical index (HI) boundaries of the safe regions of crumb rubber concrete are proposed. Three clusters that correspond to the three different stages of the fracture process are mainly observed. There is a very clear distinction between the different clusters based on RA and AF values for all specimens. Furthermore, the AE rise time, ring down counts, energy, duration, and amplitude, are indicators used in the cracking mode characterization of the tested specimens.