Use of the mineralized phase in cements: mechanisms of interaction between the components and the long-term cement and alternative uses to SCM

Concrete is the second most used material, only after water. The main carbon dioxide emissions related to concrete production are related to the calcination process of limestone, including silica-alumina rich minerals. These materials must be burned around 1450°C to obtain clinker, including also calcium sulphate minerals for having cement. Portland cement production accounts for 7-8% of the global emissions. To mitigate the carbon footprint of cement, several strategies were proposed. These strategies essentially include the use of alternative fuels, optimization of energy efficiency in clinker production, and extensive clinker substitution with supplementary cementitious materials (SCMs). Incorporating supplementary cementitious materials presents a promising way to reduce carbon emissions and the utilization of new resources within cement manufacturing. But even these materials are not enough to be replaced in cement, knowing the yearly production and the needs of new infrastructure. For this reason, in this study a new possible SCM was evaluated, the so-called carbonate olivine. This is the final product of the ex-situ carbon mineralization process that use magnesium silicate rocks as raw material to react with CO2 to obtain magnesium carbonate and amorphous silica. The aim of this thesis was to evaluate the pozzolanic reaction and the magensite stability using thermodynamic modelling and actual experimental data. The material was first blended with cement and then with three different types of calcined clay to produce ternary blended cement. The pozzolanic properties were confirmed using both R3 test and x ray powder diffraction analysis, noticing that a minimum of 30% of substitution with cement was necessary to activate the reaction. The instability of magnesite using thermodynamic modeling was contradicted by the experimental part. The alkaline-magnesite reaction that could produce brucite was not confirmed using x ray powder diffraction analysis on samples aged between 7 days to 2 years. In addition, even using scanning electron microscopy on sample aged 28 days and 90 days. The stability of magnesite was then confirmed also in ternary blended cement. No synergetic effect between carbonated olivine and calcined clay were detected, in contrast to the reaction between limestone and calcined that yields more hemi-monocarboaluminate improving the mechanical properties of these blended cements. Finally, using a Full factorial design, a Response Surface Method and a mixture design, the mix design of a ternary blended cement were optimized, focusing on having lower yield stress, high mechanical properties coupled with lower water absorption values.