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Los capítulos: resumen, capítulo 4 y conclusiones están sujetos a confidencialidad por la autora. 277 p.

Despite a wide range of applications, naturally occurring minerals suffer from some limitations for industrial use. Consequently, many research efforts have been conducted to develop a fast, optimized, and sustainable methodology to produce synthetic minerals. In the case of calcium silicate hydrates (CSH), the hydrothermal flow approach allows to mimic the environment at high temperature and pressure of the natural geological processes for the synthesis of xonotlite under sub- and supercritical conditions in only few seconds. The ultra-fast, flexible, and effective production of xonotlite particles reported in this work expands its use towards industrial requirements, especially for applications to cement-based materials. In this context, CSH nanominerals can be used to impart new functionality or to accelerate the hydration process of cement for developing green cement materials. This study sheds light on the acceleration effect of crystalline xonotlite seed, measured using isothermal calorimetry and synchrotron radiation based X-ray microtomography, as a means of lowering the cement content without compromising the performance of the paste.

Los capítulos: resumen, capítulo 4 y conclusiones están sujetos a confidencialidad por la autora. 277 p.

[EN]: The main objective of the thesis project was to develop a sustainable and scalable manufacturing route for the synthesis of calcium silicate hydrate minerals, namely xonotlite and tobermorite. The main advantage of this methodology is related to the ultra-fast reaction kinetics, which allow the synthesis of these mineral phases in supercritical water in only few seconds. Furthermore, in addition to the boosted synthesis times, the synthetic minerals are characterised by high crystallinity and purity, rather than their natural counterparts that are often found mixed with other phases or impurities. Thanks to that property, synthetic xonotlite and tobermorite can be used to disclose some aspects of the calcium silicate hydrate structures, which are still not fully elucidated. Afterwards, the high crystalline xonotlite and tobermorite were employed in two different fields. The first one is related to the use of the mineral phases as nanoseeds for accelerating the early-stage hydration of cement to develop a denser and resistant cement matrix. Instead, the second one regards the use of xonotlite as pristine material to produce upon dehydration a calcium silicate phase, wollastonite. With the aim of expanding the synthetic mineral production towards industrial requirements, the environmental profile of this methodology was analysed by life cycle assessment analysis. The impacts of the most relevant parameters, as energy, nature and concentration of precursors, were analysed to identify where possible optimization can be realised to enhance the attractiveness of the supercritical fluid technology as an environmentally sustainable synthesis methodology., [FR]: L’objectif principal du projet de thèse était de développer une méthode durable et extrapolable à l’échelle industrielle pour la synthèse de silicates de calcium hydratés, c’est à dire, la xonotlite et la tobermorite. Le principal avantage de cette méthodologie est lié à la cinétique de réaction ultrarapide, qui permet la synthèse de ces phases minérales dans l’eau supercritique en quelques secondes seulement. Aussi, en plus des temps de synthèse très courts, les minéraux synthétiques sont caractérisés par une cristallinité et une pureté élevées, au contraire de leurs homologues naturels qui se trouvent souvent mélangés à d’autres phases ou impuretés. Grâce à cette propriété, la xonotlite et la tobermorite synthétiques peuventêtre utilisées pour approfondir la structure des silicates de calcium hydratés, qui n’est pas encore complètement élucidée. Par la suite, la xonotlite et la tobermorite hautement cristallines ont été utilisées dans deux domaines d’application différents. Le premier est lié à l’utilisation des phases minérales sous forme de germes pour accélérer l’hydratation du ciment afin de développer une matrice cimentaire plus dense et plus résistante. La deuxième application considère l’utilisation de la xonotlite comme précurseur pour produire, suite à sa déshydratation, un autre silicate de calcium, la wollastonite. Enfin, dans le but d’élargir la production de minéraux synthétiques aux exigences industrielles, l’impact environnemental de cette méthodologie a été étudié par l’analyse du cycle de vie. Les impacts des paramètres les plus pertinents, tels que l’énergie, la nature et la concentration des précurseurs, ont été analysés pour permettre une optimisation éventuelle.

Calcium silicate hydrates are members of a large family of minerals with layered structures containing pendant CaOH and SiOH groups that interact with confined water molecules. To rationalize the impact of the local chemical environment on the dynamics of water, SiOH- and CaOH-rich model nanocrystals were synthesized by using the continuous supercritical hydrothermal method and then systematically studied by a combination of spectroscopic techniques. In our comprehensive analysis, the ultrafast relaxation dynamics of hanging hydroxy groups can be univocally assigned to CaOH or SiOH environments, and the local chemical environment largely affects the H-bond network of the solvation water. Interestingly, the ordered “ice-like” solvation water found in the SiOH-rich environments is converted to a disordered “liquid-like” distribution in the CaOH-rich environment. This refined picture of the dynamics of confined water and hydroxy groups in calcium silicate hydrates can also be applied to other water-containing materials, with a significant impact in many fields of materials science.