Fracture properties of tailings-based geopolymer incorporated with class F fly ash under mode I loading conditions

As a potential alternative of Portland cement concrete for construction and building applications, solid-like geopolymer made by alkali-activation of the mine tailings (MTs) shares the similar brittle properties with rocks and concrete. However, the pure MTs did not have sufficient amorphous aluminosilicates for better alkali activation. It is essential to add some materials as the source of amorphous aluminosilicates for better reactivity to adjust the geoploymeric cell structures and improve the cementitious properties. In this study, class F fly ash (FA), was utilized as the amorphous supplements source to improve the alkali reactivity to enhance the mechanical and fracture properties. FA and MTs were first characterized by conducting a series of laboratory tests, such as traditional geotechnical tests, X-ray diffraction (XRD) analysis, and scanning electron microscopy with Energy dispersive X-ray analysis (SEM-EDS) analysis. The geopolymer with different FA additions were created by activating the FA-MTs mixtures with 10 M NaOH solutions at the moisture ratio of 16% and then cured for 7 days with the slightly elevated temperature. The semi-circular bending tests (SCB) were then conducted to evaluate the influences of different FA additions on the fracture behavior of the geopolymer. In additions, digital image correlation (DIC) was applied to obtain the strain behaviors and crack propagation properties of the geopolymer. The influence of FA additions on the crack tip opening displacement (CTOD) and fracture process zone (FPZ) were also investigated. Results show that at currently curing condition, the supplements of class F FA will not improve the K_IC at lower additions but increased with higher FA additions. The links between microscopic insights and fracture behaviors of the geopolymer with inclusion of FA were also discussed.