Laboratory investigation of the effect of using metakaolin and clay on the behaviour of recycled glass powder-based geopolymer mortars

Civil infrastructure relies on cement, a common building material. However, Portland cement production pollutes the world by consuming mineral resources and emitting carbon dioxide. Using modern, cost-effective, and eco-friendly cement materials seems necessary. One such material is geopolymer cement, also known as green cement, composed of aluminosilicate base materials and alkaline-silicate activators. In the present study, waste glass powder was utilised to provide a rich aluminosilicate base material by substituting 10%, 20%, and 30% of the metakaolin or clay with calcium carbide residue as an alkaline activator. The samples were processed under two distinct temperature conditions: natural environment and thermal processing at 80 °C in an autoclave. The mechanical and microstructural properties of the mortars were evaluated regarding compressive strength, bending strength, setting time, volume control, and Scanning Electron Microscope (SEM). The results indicate that the type and amount of glass powder alternatives significantly determine the final sample strength. Substituting 10% metakaolin and 20% clay for glass powder maximises compressive strength. The optimal bending strength of geopolymer samples was obtained by substituting 10% clay with 10% metakaolin. SEM images validate this discovery by exhibiting a more compact and cohesive arrangement. Additionally, the processing conditions of geopolymer samples significantly influence the mechanical properties of geopolymer mortars. The results of the V-cut test indicate that geopolymeric mortars are sluggish and require additional time to reach their primary and secondary strength. This study suggests that geopolymers could produce environmentally friendly concrete by reducing cement use and advancing economic and environmental goals.