Activation of Bentonite for the Development of a Low-Carbon Cement
Abstract: The development of alternative supplementary cementitious materials (SCMs) is essential for reducing the environmental impact of cement, and activated clays represent a promising option. This thesis investigates the influence of initial mineralogical composition and activation conditions on the physicochemical transformations of natural bentonites. Six bentonites were studied using various approaches, including calcination at different temperatures and by different methods, as well as mechanochemical activation (MCA). The results show that the clay mineral content alone is insufficient to predict the reactivity of bentonites, highlighting the role of accessory minerals, particularly silica polymorphs.
The pozzolanic performance was more closely related to the non-diffracting fraction than to the degree of dehydroxylation. However, the different activation processes produced non-diffracting materials with distinct local Al, Si, and hydroxyl environments, highlighting the importance of their structural nature for reactivity.
In addition, a compressive strength test method using 20-mm mortar cubes has been validated to facilitate testing with small amounts of material.
Finally, this dissertation deepens our understanding of the activation of non-kaolinitic clays, demonstrating that different processes can produce reactive bentonites through distinct structural mechanisms.
Keywords: Accessory minerals; Calcination; Dehydroxylation; Mechanochemical activation; Supplementary cementitious materials
Activation of bentonites for the development of low-carbon cement
Abstract: The development of alternative supplementary cementitious materials (SCMs) is essential to reduce the environmental impact of cement production, with activated clays emerging as promising options. This thesis studies the activation of natural bentonites, focusing on how the initial mineralogical composition and activation conditions influence the physicochemical transformations of the activated materials. Six natural bentonites were investigated using various experimental approaches, including thermal activation at different temperatures and using different calcination methods, as well as mechanochemical activation (MCA) as an alternative method. It was demonstrated that clay mineral content alone cannot predict bentonite reactivity, highlighting the influence of accessory minerals, particularly silica polymorphs.
The degree of dehydroxylation was not the primary indicator of pozzolanic performance, which was more closely associated with the non-diffracting fraction. Furthermore, it was observed that different activation processes produced non-diffracting materials with distinct local Al, Si, and hydroxylated environments, demonstrating that their structural nature strongly affects the reactivity of activated clays.
In addition, a reduced-scale compressive strength testing method using 20-mm mortar cubes was validated to facilitate testing with limited amounts of material.
Overall, this thesis advances our understanding of the activation of non-kaolinitic clays, demonstrating that different activation methods can produce reactive bentonites through various structural modification mechanisms.
Keywords: Accessory Minerals; Calcination; Dehydroxylation; Mechanochemical Activation; Supplementary Cementitious Materials
