Non-Traditional and Natural Pozzolans as Precursors for Sustainable Alkali-Activated Binders: Reactivity, Phase Assemblage, and Composition Analysis

• Assessed coal byproducts and natural pozzolans for use in alkali-activated binders. • Analyzed reaction behavior and microstructure using FTIR, SEM, EDS, and NMR. • Reaction rate is similar to fly ash, with 38-82% lower total heat release than OPC. • NMR confirmed C-A-S-H, N-A-S-H, and C(N)-A-S-H phases with Al/Si ranged 0.07-0.36. • Low-purity calcined clays and ground bottom ash showed superior performance. • Al-NMR-based reactivity index for evaluating precursor performance. This study evaluates four groups of non-traditional aluminosilicate industrial coal byproducts and natural pozzolans—ground bottom ashes (GBAs), low-purity calcined clays (CCs), volcanic ashes (VAs), and fluidized bed combustion ashes (FBCAs)—as potential precursors for alkali-activated binders. Each group was activated using a mixture of sodium silicate and sodium hydroxide solution under optimized solution parameters. Their reaction behavior, pore solution changes, phase assemblage, and composition were analyzed using various material characterization tools. Results indicate that the reaction rate and total heat are similar to those of conventional fly ash precursors, with total heat release 38%–82% lower than that of Portland cement. Pore solution analyses reveal the formation of typical alkali-activated gel phases, and nuclear magnetic resonance (NMR) revealed calcium sodium aluminosilicate hydrates with aluminum/silicon (Al/Si) ranging 0.07–0.36. A novel reactivity index was proposed using Al-NMR. CCs and GBAs exhibited superior performance compared to other two materials used.