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This study investigated the influence of different cooling regimes on the microstructure and consequent reactivity of belite-sulfoaluminate clinkers. The cement clinkers were synthesized by incorporating secondary raw materials, such as titanogypsum and bottom ash, to the natural raw materials. Clinker phases were determined by Rietveld quantitative phase analysis, while the distribution morphology and the incorporation of substitute ions in the phases were characterized by scanning electron microscopy using energy-dispersive X-ray spectroscopy (SEM/EDS). Clinker reactivity was studied using isothermal calorimetry and was additionally investigated through compressive strength, which was determined for the cement prepared from the synthesized clinkers. X-ray diffraction analysis showed that, as well as the three main phases (belite, calcium sulfoaluminate, and ferrite), the clinkers contained additional minor phases (mayenite, gehlenite, arkanite, periclase, and perovskite), the ratios of which varied according to the cooling regime utilized. Microscopic observations indicated that the cooling regime also influenced the crystal size and morphology of the main phases, which consequently affected clinker reactivity. Furthermore, a smaller amount of substitute elements was incorporated in the main phases when cooling was slowed. Results showed that, in comparison to clinkers cooled at slower rates, air quenched clinkers reacted faster and exhibited a higher compressive strength at 7 days.

The potential use of steel slag from treated steel slag in belite-sulfoaluminate cements was investigated in this study. Cement clinkers with two phase compositions were synthesized, allowing the incorporation of different amounts of steel slag. The phase composition and microstructure of cement clinkers at three different sintering temperatures were studied by X-ray powder diffraction and the Rietveld method, as well as scanning electron microscopy with energy dispersive spectrometry. The results showed that the targeted phase composition of clinkers was achieved at a sintering temperature of 1250 °C. However, a higher amount of perovskite instead of ferrite was detected in the clinker with a higher content of Ti-bearing bauxite. Apart from the main phases, such as belite, calcium sulfoaluminate, and ferrite, several minor phases were identified, including mayenite, perovskite, periclase, and alkali sulfates. In both clinker mixtures, a higher content of MgO in the steel slags resulted in the formation of periclase. Furthermore, the hydration kinetics and compressive strength at 7 and 28 days were studied in two cements prepared from clinkers sintered at 1250 °C. As evidenced by the results of isothermal calorimetry, the hydration kinetics were also influenced by the minor clinker phases. Cement with a higher content of calcium sulfoaluminate phase developed a higher compressive strength.

The influence of temperature on the early hydration of belite-calcium sulfoaluminate cements with two different calcium sulfate to calcium sulfoaluminate molar ratios was investigated. The phase composition and phase assemblage development of cements prepared using molar ratios of 1 and 2.5 were studied at 25, 40 and 60 °C by in situ X-ray powder diffraction. The Rietveld refinement method was used for quantification. The degree of hydration after 24 h was highest at ambient temperatures, but early hydration was significantly accelerated at elevated temperatures. These differences were more noticeable when we increased the temperature from 25 °C to 40 °C, than it was increased from 40 °C to 60 °C. The amount of calcium sulfate added controls the amount of the precipitated ettringite, namely, the amount of ettringite increased in the cement with a higher molar ratio. The results showed that temperature also affects full width at half maximum of ettringite peaks, which indicates a decrease in crystallite size of ettringite at elevated temperatures due to faster precipitation of ettringite. When using a calcium sulfate to calcium sulfoaluminate molar ratio of 1, higher d-values of ettringite peaks were observed at elevated temperatures, suggesting that more ions were released from the cement clinker at elevated temperatures, allowing a higher ion uptake in the ettringite structure. At a molar ratio of 2.5, less clinker is available in the cement, therefore these differences were not observed.

<p>Various industrial residues that are either landfilled or currently have a low recycling rate could represent important secondary mineral resource potential for the construction sector. An ever-increasing construction sector causes increased demand for cement-based materials and consequently implies in increase of CO<sub>2</sub> emission. Belite-sulfoaluminate cements are potentially an alternative cementitious binder to ordinary Portland cements, due to the lower embodied energy and reduced CO<sub>2</sub> emissions compared to OPC clinkers. Its production also allows the substitution of natural raw materials with secondary ones. In the frame of RIS-ALiCE project, funded by the EIT RawMaterials, various industrial and mine residues in Eastern-Southeastern Europe are being mapped. In addition, as a matchmaking tool between the waste holders/producers and potential end-users the registry of secondary mineral raw materials has been developed. In this study, mine and quarry residues have been valorised in order to evaluate their suitability for production of innovative and sustainable low CO<sub>2</sub>-mineral binders. Residues from three mine sites (mine spoils from two Pb-Zn mines from Slovenia and Serbia and brown coal open pit mine from Slovenia) and two quarry sites (limestone quarries from Slovenia) were considered. Samples were characterized with respect to their chemical, mineralogical, physical and radiological properties. Furhermore, to assess the usability of particular residue in cement production, cement clinkers with belite, calcium sulfoaluminate and ferrite as main phases were synthesised, incorporating certain amounts of mine and quarry waste replacing primary raw materials. Main and trace elements as well as REE of residues were determined by X-ray fluorescence spectroscopy and ICP optical emission spectrophotometry. Mineralogical composition of residues as well as sythesised clinkers was determined by X-ray powder difraction and Rietveled method. Content of radionuclides (<sup>40</sup>K, <sup>226</sup>Ra, and <sup>232</sup>Th) was determined by gamma spectroscopy. Depending on the chemical composition of the residues, lower or higher amounts were allowed to be incorporated in the raw mixture for clinker production with targeted phase composition. Potential barriers in the cement production and environmental impact are also discussed. Developed registry with the data valuable for both, waste providers as waste users in Eastern-Southeastern Europe region, can be later-on upscaled also to other regions of Europe. It will provide the data on the available and appropriate secondary resources for cement production which will contrbute to the implementation of sustainable management of raw materials and circular economy.</p><p><strong>Keywords:</strong> mine waste, quarry waste, cement, valorisation.</p>

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