Effect of silica on the properties of red mud based geopolymer mortar for synthesis of sustainable bricks

The use of sodium silicate solution for geopolymerisation has heavy impact on the environment and its cost of production is also high. The present research was undertaken to minimize the use of the alkaline activator and assess the effect of molarity of sodium hydroxide on the properties of red mud based geopolymer mortar and based on the results to synthesize sustainable first-class bricks that could cater to structural applications. Red mud-GGBS (ground granulated blast furnace slag) binder was synthesized with varying red mud percentage and molarity. The maximum strength was obtained at 4 M alkaline solution at 40% red mud. The strength of the paste was found to be significant even at a molarity of 2 M. To utilize the red mud to maximum strength, 50% red mud at 2 M molarity was used for further investigation on mortar. The results show that the decrease in the ratio of sodium silicate to sodium hydroxide from 2.5 to 1.5 improved the compressive strength of the geopolymer mortar. Microscopic and mineralogical studies through X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) were conducted on the mortar samples to analyze the result of compression testing. Bricks cast from the blend of red mud and GGBS with 50% red mud at low molarity exhibited excellent mechanical properties and found suitable to be used for all structural applications.