A predictive failure indicator to detect impending macroscopic fracture during compression in ultra high performance concrete

In recent years, there has been growing interest in applying statistical physics principles to understand the fracture behaviour in cementitious materials. This approach provides valuable insights into the underlying mechanisms governing the material response under stress. In this study, an experimental investigation was conducted to study the compressive fracture process in ultra-high-performance concrete (UHPC) under the framework of non-extensive statistical mechanics (NESM). The acoustic emission (AE) waveform parameters were recorded during compressive loading. The occurrence of AE inter-event time of successive hits was analysed using a q-exponential function. We examined a descriptor known as the Tsallis entropic index or q-index and correlated its variation with damage progression in UHPC at various loading stages. A q-index greater than unity indicated long-range microcrack interactions, while a q approaching unity suggested enhanced short-range interactions. The toughening mechanism provided by steel fibres and coarse aggregate enhances long-range microcrack interaction forces by redistributing stresses over a larger area, resulting in an increased q-index. Conversely, a decrease in q-index towards unity was associated with the transition from long-range to short-range interaction forces, leading to macroscopic failure, aligned with Boltzmann–Gibbs statistics. Therefore, the q-index could be used as a predictive failure indicator to detect imminent failure of cementitious materials.