Utilisation of Bayer red mud for high-performance geopolymer: Competitive roles of different activators
This study investigates the synergistic effects of anions in a ternary alkaline activator composed of NaOH (X1), Na2O•nSiO2 (X2), and Na2CO3 (X3) on the workability, setting time, and mechanical properties of Bayer red mud (RM)-based geopolymer. A simplex-centroid design was used to determine the op...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Elsevier
2025-12-01
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| Series: | Case Studies in Construction Materials |
| Subjects: | |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S2214509525008459 |
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| Summary: | This study investigates the synergistic effects of anions in a ternary alkaline activator composed of NaOH (X1), Na2O•nSiO2 (X2), and Na2CO3 (X3) on the workability, setting time, and mechanical properties of Bayer red mud (RM)-based geopolymer. A simplex-centroid design was used to determine the optimal proportion of the available raw materials in the fabrication of the RM-based geopolymers with optimal comprehensive performance and to reduce number of tests. The hydration products and the microstructure of the RM-based geopolymers were characterized using XRD, FTIR, and SEM-EDS analysis to reveal the reaction mechanism. This study demonstrates that the high reactivity of OH⁻ in X1 accelerates the dissolution of the precursor, while X2 improves the fresh properties of the paste by providing [SiO4]4-, which forms oligomers. Additionally, CO32- in X3 delays setting time by buffering the alkalinity. Microscopic analysis reveals that OH⁻ preferentially dissolves RM and GGBS, leading to the release of [SiO4]4- and [AlO4]5-, which then act as monomers to facilitate the formation of a silica-aluminate network through [SiO4]4-. Notably, the interaction between OH⁻ and [SiO4]4- enhances the densification of hydration products, whereas the combination of OH⁻ and CO32- induces a competition between sodium salt crystallization. CO32- competes with [SiO4]4- for binding sites and preferentially forms CaCO3, thereby inhibiting strength development in the later stages of hydration. These results provide experimental and theoretical basis for the properties of RM-based geopolymers under diverse alkaline activation conditions. |
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| ISSN: | 2214-5095 |