Fire resistant materials based on argilite or metakaolin as a refractory geopolymer

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Antennas and absorbing materials based on geopolymers

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Synthesis of geopolymer binders using clays and sands from Fez Morocco and mechanical

International audienc

Alkali-activated materials from different aluminosilicate sources: Effect of aluminum and calcium availability

International audienc

Impact of different metakaolin mixtures on oligomer formation and geopolymer properties: Impurity effect

The impact of metakaolin mixtures on geopolymer formation and corresponding properties was evaluated by synthesizing geopolymers from mixtures of different metakaolins and 5 M potassium silicate. Mixture reactivity was investigated by viscosity, thermogravimetric (DTA-TGA), and in situ infrared spectroscopy (FTIR) measurements. Furthermore, mechanical strength and porosity measurements were undertaken on consolidated materials. The results have shown that the aluminum molar concentration governs the setting time and oligomer formation energy. Indeed, the high aluminum content associated with the high purity of the metakaolins lead to a low formation energy of oligomer, whereas for the metakaolins containing more impurities, the energy required for oligomer formation was higher. Regardless of the formulation, the mechanical strength and porosity trends were similar. Network characteristics were assessed by amorphous material content and in situ infrared spectroscopy (FTIR) analysis. It was demonstrated that (i) for Si/Al  1.5, different networks are formed. The zeta potential values of the different metakaolin mixtures corroborated these findings. Zeta potential values of metakaolins are governed by the impurities present in the metakaolins, which limit the release of aluminous species from the metakaolins in solution, emphasizing that knowledge of raw materials is essential to understand the local networks formation

Recycling of geopolymer waste: Influence on geopolymer formation and mechanical properties

International audienc

Addition of low reactive clay into metakaolin-based geopolymer formulation: Synthesis, existence domains and properties

International audienc

Shaping and thermal resistance of geopolymers based on different aluminosilicate sources

International audienc

Predictive tools to control the structure and the properties of metakaolin based geopolymer materials

Geopolymers are innovative mineral binders. These materials are still under research development in order to better understand the formation mechanism, the local structure and the final working properties. The aim of this study is to provide predictive tools permitting to control the geopolymerisation reaction. At first, it is important to determine the parameters responsible of raw materials reactivity. For alkaline solutions, the siliceous species distribution and connectivity control the reactivity. Concerning metakaolins, the Si/Al molar ratio, the wettability value, the amorphous phase content and the amount of reactive tetrahedral aluminum are responsible of metakaolin reactivity. Moreover, the reactivity of raw materials was proven to determine the geopolymer existence domains in the Si–Al–M/O ternary diagram. Thermal analysis during and after curing give informations about the amount of water consumed during the reaction and trapped in the final structure as well as the energy required for oligomer formation which seem to be directly related to raw materials reactivity. The pores distribution and size are also influenced by raw materials reactivity. Reactive precursors, especially reactive alkaline solutions, induce higher densification rate and, therefore, lower porosity and larger pore size. Furthermore, reactive precursors favor the formation of geopolymer network. This fact was evident by Si NMR. As a consequence, the increase of geopolymer phase in the structure improves the mechanical strength while the competition of different networks is source of weakness

FT-IR study of early stages of alkali activated materials based on pyroclastic deposits (Mt. Etna, Sicily, Italy) using two different alkaline solutions

The huge availability of volcanic deposits in Mt. Etna volcano and the wide use of volcanic materials as aggregates in local architecture encouraged us to apply them in alkaline environment to produce geopolymeric binders to restore historical buildings of Mt. Etna area. Two clusters of samples for each volcanic precursor (volcanic ash and ghiara paleo-soil) were produced, using 10 and 20% wt. of metakaolin and two different alkaline solutions based on sodium and potassium respectively. A comparative study was made in relation to activators used, focusing on evaluation of polycondensation step (in ATR); chemical and structural characterization (FT-IR); TGA analysis, qualitative XRD analysis and mechanical compressive test after 7 and 21 curing days. ATR results confirmed the occurrence of geopolymerization for all samples; FT-IR analysis showed a higher content of carbonates in potassium-samples, decreasing at increasing of metakaolin content. A low weight lost was recorded in consolidated samples, as well as a partial dissolution of volcanic phases. Higher mechanical compressive strengths for K-samples, reaching 89 MPa as highest value after 21 days, differently to sodium-samples (51 MPa) were recorded, reflecting the porosity of the different specimens