The Effect of Sodium and Magnesium Sulfate on Physico-Mechanical and Microstructural Properties of Kaolin and Ceramic Powder-Based Geopolymer Mortar

Recent trends in reducing the ecological footprint of the construction industry have increased the attention surrounding the use of alternative binding systems. Among the most promising are geopolymer binders, which were found to have the capability to substantially reduce the environmental impact of Portland cement use. However, even the use of this alternative binding system is known to be heavily dependent on the use of industrial byproducts, such as precursors and an alkaline source, produced through an energy intensive process. To address this and provide a greener route for this binding system, this study adopts the use of natural kaolin and raw ceramic powder as the main precursors. The activation process is performed by using solid potassium hydroxide in conjunction with sodium and magnesium sulfate, which are naturally available, to produce geopolymers. To assess the resulting geopolymer samples, 28 mixes are produced and a series of physico-mechanical and microstructural analyses is conducted. The results show that the use of ceramic powder can improve the physico-mechanical properties by reducing porosity. This, however, requires a relatively higher alkalinity for activation and strength development. These findings are further confirmed with the XRD and FTIR results. Nonetheless, the use of ceramic powder with sodium and magnesium sulfate is found to result in a more coherent and homogenous microstructure, compared to the geopolymers produced with potassium hydroxide and kaolin. The findings of this study point to the suitability of using sodium and magnesium sulfate for the cleaner production of kaolin and ceramic powder-based geopolymers.