Title:
Effects of Si/Al Molar Ratio on the Structure and Properties of Metakaolin-Based Alkali Activated Binders
Author(s):
Jessica Lohmann and Frank Schmidt-Döhl
Publication:
Symposium Paper
Volume:
362
Issue:
Appears on pages(s):
268-282
Keywords:
geopolymer, metakaolin, alkali activated binder, Si/Al molar ratio
DOI:
10.14359/51740888
Date:
6/6/2024
Abstract:
The reaction of metakaolin with alkaline activators produces an X-ray amorphous, aluminosilicate gel matrix, as well as sodium or calcium aluminate-silicate hydrate phases in varying proportions. The degree of crosslinking depends on the Si/Al ratio of the starting products. This study investigates fundamental relationships between the Si/Al ratio of alkali-activated metakaolins and their mechanical properties. In particular, porosity, compressive strength, and thermoanalytical properties were considered. The crystallinity was determined by X-ray diffraction. The precondition for the formation of an amorphous microstructure is the solution of the reactive starting materials. The sodium cations contained in the solution serve to balance the charge in the network. It was found that a Si/Al ratio of 2 resulted in the highest strength. A higher ratio was associated with a higher pore volume and lower bulk density. Thermogravimetric investigations showed that at lower molar ratios, more water was incorporated into the structure. In addition, as the ratio increases, the dehydration temperature decreases, indicating weaker bonds in the network.
Related References:
1. Davidovits J. Geopolymer: Chemistry and applications. 5th ed. Saint-Quentin: Institut Géopolymère; 2020.
2. Elimbi A, Tchakoute HK and Njopwouo D. Effects of calcination temperature of kaolinite clays on the properties of geopolymer cements. Construction and Building Materials. 2011;25:2805–12. doi: 10.1016/j.conbuildmat.2010.12.055
3. McConville, C. J. and Lee, W. E. Microstructural Development on Firing Illite and Smectite Clays Compared with that in Kaolinite. Journal of the American Ceramic Society. 2005;88:2267–76.
4. Gualtieri AF and Ferrari S. Kinetics of illite dehydroxylation. Phys Chem Minerals. 2006;33:490–501. doi: 10.1007/s00269-006-0092-z
5. Csáki Š et al. Thermal Properties of Illite-Zeolite Mixtures up to 1100 °C. Materials (Basel). 2022;15:3029. doi: 10.3390/ma15093029
6. Rodriguez-Navarro C, Cultrone G and Sanchez-Navas A et al. TEM study of mullite growth after muscovite breakdown. American Mineralogist. 2003;88:713–24. doi: 10.2138/am-2003-5-601
7. Lohmann J and Schmidt‐Döhl F. Einfluss der Kristallinität auf die Festigkeit und die Mikrostruktur alkalisch aktivierter Metakaoline: [Influence of crystallinity on the strength and microstructure of alkali-activated metakaolins]. ce papers. 2023;6:460–70. doi: 10.1002/cepa.2796
8. DIN EN 196-1:2016-11. Prüfverfahren für Zement – Teil 1: Bestimmung der Festigkeit [Test methods for cement - Part 1: Determination of strength]. 2016. Berlin: Beuth.
9. Bernal SA et al. Activation of Metakaolin/Slag Blends Using Alkaline Solutions Based on Chemically Modified Silica Fume and Rice Husk Ash. Waste Biomass Valor. 2012;3:99–108. doi: 10.1007/s12649-011-9093-3
10. He P et al. Effects of Si/Al ratio on the structure and properties of metakaolin based geopolymer. Ceramics International. 2016;42:14416–22. doi: 10.1016/j.ceramint.2016.06.033
11. Duxson P et al. Understanding the relationship between geopolymer composition, microstructure and mechanical properties. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2005;269:47–58. doi: 10.1016/j.colsurfa.2005.06.060
12. Duxson P et al. Geopolymer technology: the current state of the art. J Mater Sci. 2007;42:2917–33. doi: 10.1007/s10853-006-0637-z
13. Zhang M-H, Malhotra VM and Wolsiefer J. Determination of Free Silicon Content in Silica Fume and Its Effect on Volume of Gas Released from Mortars Incorporating Silica Fume. ACI Materials Journal. 2000;97:576–86. doi: 10.14359/9290
14. Hanein T et al. Clay calcination technology: state-of-the-art review by the RILEM TC 282-CCL. Mater Struct. 2022;55:3. doi: 10.1617/s11527-021-01807-6
15. Winnefeld F et al. Assessment of phase formation in alkali activated low and high calcium fly ashes in building materials. Construction and Building Materials. 2010;24:1086–93. doi: 10.1016/j.conbuildmat.2009.11.007
16. Parra-Huertas RA et al. Synthesis and characterization of Faujasite-Na from fly ash by the fusion-hydrothermal method. Boletín de la Sociedad Española de Cerámica y Vidrio. 2023;62:527–42. doi: 10.1016/j.bsecv.2023.01.004
17. Abdulkareem OA et al. Effects of elevated temperatures on the thermal behavior and mechanical performance of fly ash geopolymer paste, mortar and lightweight concrete. Construction and Building Materials. 2014;50:377–87. doi: 10.1016/j.conbuildmat.2013.09.047.
18. Soares JC, Azevedo JS de and Dias DP. Effect of temperature on metakaolin-quartz powder geopolymer binder with different combinations of silicates and hydroxides. Case Studies in Construction Materials. 2022;16:e00813. doi: 10.1016/j.cscm.2021.e00813
19. Kaufhold S et al. Comparison of methods for distinguishing sodium carbonate activated from natural sodium bentonites. Applied Clay Science. 2013;86:23–37. doi: 10.1016/j.clay.2013.09.014
20. Juenger M and Ostertag C. Alkali–silica reactivity of large silica fume-derived particles. Cement and Concrete Research. 2004;34:1389–402.
doi: 10.1016/j.cemconres.2004.01.001
21. Nmiri A et al. Replacement of alkali silicate solution with silica fume in metakaolinbased geopolymers. Int J Miner Metall Mater. 2019;26:555–64. doi: 10.1007/s12613-019-1764-2