Effect of NaOH molarity and ratio of Na2SiO3 to NaOH on fresh and hardened properties of geopolymer mortars containing wastes from iron and aluminum factories

In this article, the ground granulated blast-furnace slag and red mud, which are waste products of iron and aluminum factories, were used as aluminosilicate base materials in the design of geopolymer mortar mixture. The activation of base materials was done with a combination of sodium hydroxide solution (caustic soda) and sodium silicate (water glass). In order to investigate the influence of soda molarity and water glass to soda ratio on flow ability, setting time, drying shrinkage, as well as compressive and flexural strengths, 9 mixes of geopolymer mortar were prepared and cured at ambient temperature. Moreover, molar ratios of H2O/Na2O and SiO2/Na2O were defined and investigated as key parameters affecting the fresh and hardened properties of geopolymeric mortar. The results of the experiments showed that with the increase in the molar ratio of H2O/Na2O in the mixture design, the flow ability of the mortar increases. Also, there is an optimal value for the molar ratio of SiO2/Na2O, so that by passing it, the compressive and flexural strength decrease. Considering the use of waste materials in the design of geopolymer mortar and as well as the optimization in the use of alkaline activators, it can be concluded that the conducted research is an effective and forward step in the production of geopolymeric products with an environmental and economic approach.