Sugarcane bagasse ash as an alkali activator: production and characterization of geopolymer mortars with partial sodium silicate replacement

Abstract Portland cement production accounts for about 9% of global CO 2 emissions, underscoring the need for alternative materials with a lower environmental impact. In this context, geopolymers emerge as a promising option, offering good mechanical performance, chemical stability, and a reduced carbon footprint. Among the residues with potential for geopolymer applications is sugarcane bagasse ash (SCBA), which is abundant in Brazil and rich in silica. In this study, the partial replacement of sodium silicate with SCBA (5%, 10%, and 15%) in the activating solution of metakaolin-based geopolymer mortars was evaluated. Flow table and compressive strength tests (14, 21, 28, and 90 days) were performed. The 10% replacement level achieved the best performance, reaching 16.58 MPa at 90 days, higher than the reference mix (12.03 MPa). The reference samples and those with 10% SCBA were further characterized by XRD, TGA, calorimetry, SEM, and density, porosity, and water absorption tests. In a subsequent stage, the effect of activator molarity (6 M, 8 M, and 9 M) was investigated, maintaining the 10% replacement. The 6 M solution was the most efficient, reaching 17.82 MPa at 28 days. Replacing 10% of commercial SiO₂ with SCBA-derived silica in a 6 M solution may reduce approximately 7.3 kg of CO 2 per ton of mortar produced.