Low-carbon alkali-activated geopolymer of industrial byproducts: Parameter optimization and life-cycle advantages for...

The accumulation of coal gangue (CG), blast furnace slag (BFS), and silica fume (SF) poses significant environmental challenges, while research on ternary alkali-activated composites derived from these three materials remains scarce, especially for ternary mixed systems using CG as the main raw material. Therefore, to solve the problem of insufficient alkalinity optimization in the CG-BFS-SF system, this study innovatively combines CG, BFS, and SF at optimized ratios, utilizing Na₂SiO₃ and NaOH as alkaline activators and river sand as fine aggregate to develop low-carbon system alkali-activated materials (designated as CBS), providing a sustainable alternative to reduce cement consumption. The effects of Na₂SiO₃ modulus (1.0, 1.2, 1.5 and 1.8) and Na₂O/B content (4 %, 5 %, 6 %, 7 % and 8 %) on the properties of the CBS were systematically investigated, the hydration mechanism and microstructure were analyzed using macro testing, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Via life cycle assessment (LCA), a quantitative environmental analysis was conducted based on a cradle-to-gate system boundary to examine the environmental impact of CBS in terms of global warming potential (GWP), acidification potential (AP), and other factors. The results revealed that the optimal mechanical performance was achieved at an alkalinity optimization with modulus of 1.2 and 8 % Na₂O/B content (shortened as N8M1.2), exhibiting 28-day compressive and flexural strengths of 51.09 MPa and 7.26 MPa, respectively. Both excessively high and low modulus or Na₂O/B content were found to reduce the ability of solidification. By comparing with cement-based composite materials (CCMs), CBSs have 19.9 % lower costs, 43 % lower energy consumption, and 61.8 % lower carbon emissions, respectively. It is also found that the N8M1.2 CBS demonstrates a much better overall performance compared with CCMs. The proposed CBS effectively promotes the utilization of solid waste and enhances potential applications, such as restoration materials and road infrastructure.