Microstructural and Strength Investigation of Geopolymer Concrete with Natural Pozzolan and Micro Silica

In pursuit of finding sustainable building material, geopolymer concrete is developed utilizing aluminosilicate materials such as fly ash. Silica and alumina are the main precursors of alkali activation. The amount of silica and alumina in the source materials plays a significant role in the strength and microstructural development of such a concrete. If the source materials are supplemented by the addition of these precursors, the properties can be enhanced. Therefore, the reported study investigates the effect of incorporating micro silica at 5%, 7%, and 10% by weight, as partial replacement to natural pozzolan on the strength and microstructural properties of geopolymer concrete. Compressive strength was determined on the specimens cured in the oven maintained at 60 °C as well as at room conditions. Scanning electron microscopy (SEM) was utilized to determine the morphology of the developed alkali-activated paste (AAP). The results indicated that the natural pozzolan could be utilized, without any silica fume addition, to develop geopolymer concrete with reasonable strength that could be used for construction purposes if cured at elevated temperature. Further, concrete developed by replacing natural pozzolan with silica fume exhibited improved strength and microstructural characteristics. Seven percent micro silica replacement showed better compressive strength results and denser microstructure compared to the ones prepared with other replacement levels. The results of this study provided important information to synthesize natural pozzolan-based sustainable building material with enhanced properties.