Microcrack monitoring and fracture evolution of polyolefin and steel fibre concrete beams using integrated acoustic emission and digital image correlation techniques

The use of polymer and steel fibres in plain concrete appears to be an excellent solution for limiting crack propagation and improving the post-ductility performance of concrete structures. Based on this premise, this study investigated the fracture evolution of polyolefin fibre-reinforced concrete (PFRC) and steel fibre-reinforced concrete (SFRC) specimens through the integrated application of two diagnostic techniques, acoustic emission (AE) and digital image correlation (DIC), under three-point bending tests. Based on the processing of AE signals, different AE statistical parameters such as the cumulative number of hits, amplitude distribution, and some representative analysis methods including the b-value method, Ib-value method, and AE intensity analysis methods were selected to analyse the early detection of cracking and post-cracking behaviour in PFRC vs SFRC specimens during mechanical degradation. Simultaneously, the DIC technique was used to validate the fracture evolution of the AE results. Furthermore, to verify the reliability of the AE and DIC results, the damage localisation and fracture evolution of the PFRC versus SFRC specimens were confirmed by integrating the AE fracture energies and DIC outcomes. The tests and analysed results showed that the addition of steel fibres to plain concrete significantly improved the ability to restrict crack propagation and provided higher post-cracking resistance compared to PFRC specimens owing to their stronger fibre-matrix bonding, effective fibre bridging, and crack-arresting mechanism. The present study indicates that the combined AE and DIC techniques are highly effective for the early detection of damage and ductility performance in fibre-reinforced concrete structures.