The aluminum Bayer production process is the most diffused process in the world, but it creates a high amount of basic waste material known as red mud (RM). The use of RM as a precursor of alkali-activated materials is one of the best opportunities for both the ecosystem and the economy. In the present work, mortar samples were obtained by alkali activation of RM with various percentages of blast-furnace slag (BFS) and inert construction and demolition sands. This process creates samples that have a low environmental impact and that can be used as an alternative in the construction industry to cement materials or ceramic ones. The development of these new materials could also represent a way to reduce the CO₂ emissions linked to cement and ceramic brick production. In the present study, cubic 40 mm samples reported very interesting values in compressive strength, with a maximum of about 70 MPa for low environmental impact mortars. With such a material, it is possible to create solid bricks for structural use and concrete tiles for road paving or use it for other purposes. Mortar specimens were prepared and characterized, and an LCA analysis with a “cradle-to-gate” approach was carried out for a comparison of the environmental impact of the studied mortars with other materials currently marketed.

Xonotlite forms under hydrothermal conditions and it dehydrates to β-wollastonite between 770 to 800 °C. The solubility of xonotlite is purely restrained, as the experimental solubility datasets reported in literature differ by as much as 10 log units. This study investigates the impact of temperature (7, 20, 50 and 80 °C) on the solubility of xonotlite by dissolution experiments from undersaturation. The derived solubility data are comparable to that reported in literature at 25 °C for synthesized xonotlite, while the much higher solubility reported in literature for natural xonotlite seems to describe the solubility of amorphous C-S-H. The solubility of xonotlite increases moderately at lower temperature. Below 7 °C, xonotlite was found to co-exist with tobermorite.

Understanding the factors that control the early age hydration kinetics of belite calcium sulfoaluminate (BCSA) cements is important for their use. Here, two industrial BCSA cements with different setting behaviour, BCSA-F and BCSA-S, were investigated to clarify the roles of soluble sulfates and citric acid during early-age hydration. Isothermal calorimetry, in-situ synchrotron X-ray powder diffraction, pore solution analysis and thermodynamic modelling with GEMS were used.,The two reference cements showed different hydration kinetics, mainly associated with the availability of soluble sulfates. In particular, the bassanite content affected the formation and subsequent dissolution of secondary gypsum. Citric acid strongly delayed ye’elimite dissolution, although the overall sequence of hydration products remained unchanged. Dissolved organic carbon measurements showed that citrate was rapidly removed from the pore solution. This behaviour is consistent with citrate adsorption on reactive surface sites rather than extensive complexation in the pore solution. Thermodynamic modelling reproduced the general phase evolution and indicated that the retardation was mainly kinetic, delaying the approach to equilibrium without changing the predicted hydration pathway.,The results indicate that the early hydration of these BCSA cements depends on both soluble sulfate availability and the interaction of citrate with reactive ye’elimite surfaces.