Fracture behavior of alkali-activated basalt powder/slag systems reinforced with basalt and hybrid fibers

Alkali-activated materials are gaining attention as a sustainable alternative to cement-based materials over the past years and studies on their fracture response are scarce. This paper presents the fracture behavior of alkali-activated fiber-reinforced basalt powder/slag blend mortars. Fracture characteristics such as the fracture toughness-K-IC(ini) and K-IC(un)-of the alkali-activated basalt powder/slag mortar mixes were determined using the double-K fracture model. Basalt fibers and a combination of basalt + polypropylene fibers (hybrid) were used to enhance the fracture properties of the mixes, and it was found that the basalt powder/slag binary mortars achieved performance comparable with that of cement-based systems in terms of compressive strength, fracture toughness, and fracture energy. The alkali-activated basalt powder/slag mixes exhibited good mechanical performance, which as established previously was due to the beneficial silicium and calcium-based resources and the synergy between the basalt powder and the slag. Incorporating basalt fibers was effective in improving flexural strength and fracture toughness significantly, and they contributed much more than the hybrid fibers did. On the other hand, incorporating hybrid fibers improved the fracture energy significantly. The fiber-matrix interface and the fiber behavior under flexure were visualized using scanning electron microscopy. The fiber-matrix bonding mechanism showed that the polypropylene fibers tended to cluster, resulting in less-improved fracture toughness compared to that with basalt fibers. The outcomes of this study show that basalt powder/slag blends can be used as structural materials: they have fracture characteristics similar to those of cement-based systems and incorporating basalt and hybrid fibers improve their fracture characteristics.