Effect of Incorporating Nano-silica on the Strength of Natural Pozzolan-Based Alkali-Activated Concrete
A new class of concrete with precursors such as fly ash and pozzolan, totally replacing ordinary Portland cement (OPC), together with alkaline activators is being extensively researched in producing alkali-activated concrete (AAC). The strength development of AAC depends on curing temperature, composition, and fineness of the source materials. Reactivity of the binders with the alkaline activators increases with the fineness, leading to the improved mechanical and microstructural properties. This study focuses on the development of AAC utilizing natural pozzolan (NP) as source material. In order to enhance the properties, NP is partially replaced with nano-silica up to 7.5% in the AAC mixes. Compressive strength was measured on the specimens cured for 0.5, 1, 3, 7, 14, and 28 days in the oven maintained at 60 °C. Scanning electron microscopy (SEM) was used to determine the morphology of the developed alkali-activated paste (AAP). The results indicated that AAC with NP as a binder gained reasonable strength after 3 days of curing at elevated temperature. Further, NP replaced with nano-silica (NS) exhibited improved strength and microstructural characteristics. AAC with 5% nano-silica showed better compressive strength results and denser microstructure compared to the ones prepared with other replacement levels.