Effect of red mud proportion on the strength and microstructure of ferrosialate based geopolymer mortar

This paper studies the effect of various red mud proportions on the strength and microstructural changes in the ferrosialate geopolymer mortar. The optimum percentage of red mud (RM) has to be found with respect to the molarity of Sodium hydroxide (NaOH) to maintain the suitable alkalinity of the mixture for maximum strength gain. This percentage has been found to be between 20 and 30% RM proportions. From XRD micrographs, it has been found that the crystallinity percentage increased with the increase in red mud content. For oven-cured samples, SEM images showed that, till the red mud replacement reaches 20%, any increase in the red mud leads to denser microstructure and a decrease in intensity of unreactive particles. Beyond that, samples displayed a higher number of undissolved phases. Whereas, for ambientcuring specimens, this limit is found to be 30%. Synergy has to be found among the red mud content, curing type and curing temperature for optimum results. Ferrosialate geopolymer samples has shown 53.34% higher maximum compressive strength than sialate geopolymer samples. The oxide ratios of SiO2/Al2O3 = 4.0 to 4.3, Na2O/SiO2 = 0.15 to 0.17 and Fe2O3/Al2O3 = 0.27 to 0.37 have found to be limits for favouring maximum strength gain.