## 3 Results and Discussion
Figure 8 shows the SEM micrographs of the surface and bulk (fracture surface) of the Phases 3 and 5 samples scanned after 250 days of materials ageing. The EDS data measured from the surface, center, and bottom of the samples are also provided. Both MOC phases analyzed in this study exhibited fast formation of chlorartinite as a result of their reaction with carbon dioxide. The carbon footprint of MOC cement-based materials will be thus significantly and quickly reduced. Based on the great sorption activity of Phase 3 towards CO2,  
Figure 8: SEM micrographs of the surface and bulk (fracture surface) of samples of Phases 3 and 5 scanned after 250 days of ageing. The EDS measurements were performed from the surface, center, and bottom of the samples. it is estimated that 1 kg of Phase 3 could theoretically incorporate 211 g of CO2, as formulated in Equation (3):  
\[3 Mg(OH)_{2}\cdot MgCl_{2}\cdot 8H_{2}O+2\ CO_{2}\to 2\left[Mg_{2}(CO_{3})(OH)Cl \cdot 2H_{2}O\right]+6\ H_{2}O \tag{3}\]  
Similarly, assuming carbonation of Phase 5 in accordance with Equation (4),  
\[5 Mg(OH)_{2}\cdot MgCl_{2}\cdot 8H_{2}O+4\ CO_{2}\to 2\left[Mg_{2}(CO_{3})(OH)Cl \cdot 3H_{2}O\right]+2\ MgCO_{3}+6\ H_{2}O \tag{4}\]  
where maximum calculated theoretical CO2 uptake capacity of Phase 5 was 331 g/kg. However, these are theoretical assumptions only, requiring a high concentration of CO2 in the surrounding air, and full-volume carbonation of MOC phases. On the other hand, increased global CO2 emissions pose a threat to the Earth's atmospheric environments. It was reported that the annual CO2 concentration at the Earth's surface in 2017 reached 405 ppm [44], which is approximately quadruple that of the early 1960s [45]. Therefore, any attempt at a reduction of the carbon footprint of construction materials is of particular importance from a sustainability point of view. The production of Portland cement, as a material that is competitive to MOC cement, represents 5-8% of global CO2 emissions [46, 47]. In this sense, alternative approaches to reducing CO2 emissions associated with the manufacture of the binder phase in concrete and other construction materials are in demand [48]. [PERSON] et al. [44] reported on the potential of CO2 reduction materialized by carbonation curing. He calculated the CO2 uptake capacity of Portland cement during an accelerated carbonation test as 12.3%. The computing was done based on the thermogravimetry (TG) and calculation of the difference between the weight loss at 500-720 \({}^{\circ}\)C of carbonated and noncarbonated cement paste samples. This was a similar level of CO2 uptake as observed in a study published by [PERSON] and [PERSON] [41]. Nevertheless, this CO2 uptake capacity corresponds with the 5% CO2 concentration within the accelerated carbonation test. The normal level of CO2 concentration in the air is 250-400 ppm [49]. In occupied spaces with good air exchange, the concentration of CO2 varies in the 400-1000 ppm range. This means that the applied CO2 concentration in accelerated carbonation tests was typically even 200 times higher than the normal CO2 concentration in air. The significant reduction of CO2 uptake by Portland cement paste can be therefore be anticipated under standard atmospheric conditions. Moreover, the sequestration of CO2 as a result of the carbonation of Portland cement paste in normal environments is extremely slow [50], contrary to the fast formation of chlorarnitine from MOC phases. Based on the data provided and analysis conducted in this study, it can be concluded that MOC cement represents an alternative construction binder for the production of low carbon materials that can partially mitigate the atmospheric concentration of CO2, which is the main constituent of greenhouse gases related to global warming issues [51].