Fracture performance and damage behavior of fly ash-based geopolymers toughened by molybdenum tailings based on acoustic emission and digital image correlation

This research proposes the utilization of molybdenum tailings (MT) to toughen fly ash-based geopolymers. To fully understand the effect of MT on the fracture performance and damage behavior of fly ash-based geopolymers, the effect of mode I fracture toughness and fracture energy of fly ash-based geopolymers with different MT contents were researched by using semi-circular bending (SCB) tests. The damage and strain behavior of the semi-circular bending with notches (NSCB) specimens during the fracture process were evaluated by acoustic emission (AE) technology and digital image correlation (DIC) technology, and finally the micromorphology of the fracture surface of NSCB specimens after the loading finished were observed by scanning electron microscopy (SEM). The results show that the tensile strength, fracture toughness and fracture energy of fly ash-based geopolymers were significantly increased with the addition of MT, and the peak value was reached at 30 wt% MT contents, with the increase amplitude reaching 77%, 31% and 45% respectively. This was attributed to the filling effect of MT, which made the structure of fly ash-based geopolymers more dense, reduced the formation and expansion of internal microcracks, shifted the growth direction of microcracks from the pore structure to the gel phase and the interface between the gel phase and glassy microspheres during the fracture process, improved the stability of the structure and the fracture resistance.