Influence of Silica Fume on the Mechanical and Microstructural Properties and Life Cycle Assessment of Fly Ash-Based Geopolymer Mortar

Abstract This study aims to investigate the influence of substituting silica fume with fly ash in fly ash-based geopolymer mortars. The replacement ratios of silica fume were 2%, 4%, 6%, 8%, and 10% on a mass basis with fly ash. The NaOH was used as an alkali activator. The produced geopolymer mortars were heat cured at a temperature of 75 °C for various durations: 24 and 48 h. The workability, unit weight, flexural strength, and compressive strength were conducted on geopolymer mortars. Selected mortars underwent abrasion and elevated temperature tests (300 °C, 600 °C, and 900 °C) based on their mechanical and compressive strength performance. Additionally, thermogravimetric analysis (TGA) and field emission scanning electron microscope (FESEM) imaging for microstructure and life cycle assessment (LCA) analysis for environmental performance were conducted. According to test results, optimum replacement ratio of silica fume (%2–4) with fly ash showed better performance than that reference geopolymer mortar in terms of strength properties and environmental impact categories of global warming potential, terrestrial ecotoxicity and abiotic depletion. These results indicate that silica fume replacement within this range enhances geopolymerization while maintaining structural integrity.