Synthesis of nano-silica as a promising route of recycling phosphate waste rocks and its incorporation in mortars

This article is devoted to the synthesis of nano-silica from phosphate waste rocks as a promising route of recycling these silica-rich phosphate by-products. Furthermore, their reactivity potential will be investigated while incorporating them as nano-additive and as a partial replacement to cement in the conventionally used recipes of mortars. It has been shown that the synthesized nano-silica has a higher level of purity and a large specific surface area, which is about 8 times higher than the initial raw material. Various formulations of mortars were tested after adding different percentages of nano-silica to the ordinarily used recipe, at a constant water-to-cement ratio, and their microstructure, mineralogical composition, and mechanical properties were investigated. It was shown that compressive strength and flexural strength increased, and the fluidity of the mortars decreased when the ratio of nano-silica increased from 1% to 5%.