Experimental and microstructural investigation on ternary blended geopolymer concrete at varying NaOH molarities

Cement production is a major contributor to global CO₂ emissions, necessitating the development of sustainable alternative binders. Although geopolymer concrete produced from industrial by-products offers a promising low-carbon alternative, the influence of NaOH molarity on the performance of ambient-cured ternary blended geopolymer concrete has not been comprehensively investigated. Therefore, this study investigates the influence of NaOH molarities ranging from 2 M to 12 M on ambient-cured ternary blended geopolymer concrete (TBGPC) mixes consisting of fly ash, GGBFS, and silica fume. Fresh properties were evaluated using the slump test, and mechanical performance was evaluated through compressive, split-tensile, and flexural strength tests, while concrete quality was evaluated using the ultrasonic pulse velocity (UPV) tests. Results showed that workability decreased with increasing NaOH molarity and GGBFS content. Superior mechanical performance was achieved in the M3 and M4 mixes at 6 M and 8 M, with the 8M-M4 mix performing best. Durability evaluation (water absorption and sorptivity), microstructural analyses (SEM-EDS, XRD, and FTIR), environmental assessment (embodied energy and global warming potential), and cost analysis were conducted on optimized and reference mixes. At 28 days, the optimized 8M-M4 mix (50% fly ash, 40% GGBFS, and 10% silica fume) reached a compressive strength of 47.47 MPa alongside a UPV of 4.60 km/s, showing its superior quality of concrete. These results clarify how NaOH molarity affects ambient-cured ternary blended geopolymer concrete and provide guidance for developing sustainable, high-performance concrete for practical applications.