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This paper presents results from experimental studies on the thermal resistance and dilatometry analysis of various geopolymer formulations, which were prepared by mixing alkaline solutions, metakaolin and reinforcements. Nine compositions were tested by dilatometric analysis and thermal resistance at high temperature (800 °C). Structural and microstructural analysis was conducted to verify the geopolymerization, and differential thermogravimetric analysis was performed to evaluate the nature of water, depending on the formulation. Some key parameters were identified as critical parameters that influenced the geopolymer properties, such as the nature (Na or K) and the molar concentration of the alkaline cation ([M] < 16 mol/L), the molar concentration of silicon ([Si] < 39 mol/L) and the alkaline metal to aluminum ratio (M/Al < 0.65). Finally, it was possible to arrange the various formulations in a ternary scheme as functions of the metal, aluminum and silicon concentrations. This scheme may represent a roadmap for controlling the thermal resistance of geopolymer materials. [ABSTRACT FROM AUTHOR]

This study is focused on understanding the role of molybdic species during polycondensation reactions. For this purpose, several geopolymers were synthesized using two metakaolins of different reactivities and various amounts of ammonium molybdate (0.40, 0.80 and 1.57% molar molybdenum). The reactions involved were investigated by FTIR, Raman, DTA and MAS-NMR. The results showed that the addition of Mo induces the modification of (i) the silica species negative charge balance and (ii) their nature and size, and favors perturbations toward the polycondensation reactions, which differ in terms of metakaolin reactivity. The addition of Mo species to the silicate solution counterbalances the metakaolin reactivity (the presence of an Al-rich or Si-rich network). This highlights the modification and formation roles played by molybdenum atoms, depending on the amount of ammonium molybdate added. [ABSTRACT FROM AUTHOR]

Alkaline silicate solutions are of great interest for several industrial applications. Previous studies demonstrated the influence of different parameters such as the Si/M (Na, K) molar ratio, the dilution level, the cation size and the manufacturing process on the silicate species. The aim of this study was to complete the data from previous works. This study focuses on the effects of these various parameters on the polymerization and the reactivity of silicate solutions. To evaluate the effects, several solutions obtained from various processes with different cations and Si/M ratios were studied. All the solutions were characterized using spectroscopic investigations (FTIR, Raman and NMR). FTIR spectroscopy was used to define the polymerization state of the various solutions. The experiments revealed that increases in the Si/M molar ratio, the dilution level and the cation size lead to the polymerization of the species. However, the effect of the cation is less pronounced. Moreover, Raman spectroscopy revealed an increase in oligomers for Si/M molar ratios less than 1. It was also shown that the manufacturing process causes a slight variation in the amount of the different silicate species responsible of the reactivity of the solution. Knowledge of these key parameters is important for different applications, including geopolymer fabrication. Moreover, it was shown a correlation between the results obtained by NMR and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Geopolymers are new binders resulting from the activation of an aluminosilicate source by an alkaline solution. These binders are economically and environmentally profitable since they have the advantage of reusing recycled waste and industrial by-products as aluminosilicate sources. In this context, this paper focuses on the geopolymer wastes incorporation in different formulations and their effect on geopolymer formation and the properties of the final materials. For this purpose, the geopolymer wastes were at first characterized. Three compositions differing in the used alkaline solution and the amount of metakaolin added were investigated. A feasibility study allowed retaining 20% as the waste percentage added or substituted to the metakaolin to still obtain geopolymer materials. Moreover, it was shown that the incorporation of the geopolymer waste may disturb the polycondensation rate which was proven to strongly depend on the solid to liquid ratio and the Si/K ratio of the alkaline solution. Finally, relationships were demonstrated between the compressive strengths and the chemical compositions of the different samples. The low reactivity of geopolymer waste can be compensated with the use of highly reactive alkaline solution or the increase of the amount of metakaolin in the mixture. [ABSTRACT FROM AUTHOR]