Sustainable One-Part Alkali-activated Concrete using Microwave-Synthesized Silica Fume Solid Activator (MiSFA): A Taguchi Optimization Study

Compared to Ordinary Portland Cement (OPC) concrete, alkali-activated concrete has a lower carbon footprint and can be produced using industrial by-products. Alkaline activators, such as sodium silicate or sodium hydroxide solution, are typically used to initiate the reaction of precursors in alkali-activated concrete. However, their production requires high energy consumption and releases CO₂. To address this and enhance sustainability, researchers have explored alternative activators derived from industrial and agricultural waste, including biomass, glass, and rice husks. This study focuses on the optimization of the microwave synthesis of silica fume-derived alkali activators using the Taguchi statistical approach for application in one-part Alkali-Activated Concrete (AAC). Compared with conventional thermal methods, microwave technology offers a faster and more sustainable synthesis route, lowering energy consumption. Four factors (microwave power, microwave duration, Na₂O/binder ratio and SiO₂/Na₂O ratio) were examined at three levels using an L9 orthogonal array. Activators were synthesized for each experimental condition and subsequently used to produce alkali-activated material (AAM) mixtures incorporating fly ash and GGBS precursors. Compressive strength, setting time, and workability were evaluated for each mix, alongside XRD and FTIR for microstructural characterization. The results indicate that microwave-synthesized silica-fume activator (SFA) is a sustainable alternative to commercial sodium metasilicate, with similar or even superior mechanical performance. Further research is needed to assess its durability in AAC.