## 3 Results and Discussion
### Microstructure
This is supported by previous studies that also did not observe any significant or sufficient strength gain in cement and EAF slag blends, despite CaCO\({}_{3}\) formation due to carbonation [44]. However, it is suggested that EAF slag still helps maintain sufficient CO\({}_{2}\) sequestration during the carbonation process so that it can serve as a supplementary cementitious material, both for environmental reasons and to promote pozzolanic reactions in subsequent hydration [44]. This, once again, supports the idea that EAF slag is optimally used as a supplementary material in cement manufacturing and that excess slag can lead to a decrease in strength. Figure 4: SEM images revealing the microstructure of mortar samples. Figure 5: Results of the XRD and MIP investigations. It was noticed from the TGA results that weight losses due to the decomposition of the main binder products in the samples based on wollastonite and EAF slag were found to fall within the temperature range of 30-800 \({}^{\circ}\)C. This weight loss region indicates the formation of calcite and aragonite in all mixtures. WS40 and WS60 demonstrate a significant weight loss in these regions, indicating that a higher level of CO2 capture can be achieved using EAF slag due to the observed increase in CaCO3 production. This could be attributed to the high amount of CaO present in the EAF slag, which can then form calcite and aragonite when exposed to CO2 under pressure. Calcite and aragonite are both polymorphs of CaCO3, where calcite has a trigonal crystal structure and aragonite has an orthorhombic crystal structure. Table 2 lists the weight losses due to the decomposition of CSH, calcite, and aragonite formed in carbonated samples. The total weight loss due to the decomposition of the binder products in WS60 was calculated to be 73% greater than in WS0. Weight loss due to the decomposition of aragonite and calcite was greater in WS60 compared with the remaining samples. The formation of calcite and aragonite in WS60 was 4.3 and 1.3 times higher than that of WS0. The dehydroxylation of CSH was found to be lower in WS0 and WS20, but the use of EAF slag greater than 20% increased this phase alteration in mortar samples. Weight losses in WS40 and WS60 samples indicated the decomposition of aragonite regions as early as 470 \({}^{\circ}\)C. Similar research with EAF slag and carbonated cement-based materials has shown that aragonite is observed to form when the system is allowed to dry [39]. The main binder product of the EAF slag is still calcite, but traces of aragonite were also observed [17]. The molecular bonds of aragonite tend to be weaker than those of calcite, and aragonite is observed to dissolve more easily than calcite. It is suggested that various reaction conditions, such as the water-to-solids ratio, relative humidity, and partial pressure of CO2, affect the hydration reaction and that there are optimal conditions for the formation of each silicate [34]. The reaction conditions here  
Figure 6: Results of the thermogravimetric analyses. were kept as constant as possible, so the variation in CaCO\({}_{3}\) formation is likely due to the different contents of EAF slag and, therefore, the variation in mineral contents. There is also a slight loss of structural water that can be observed within the range of 70-100 \({}^{\circ}\)C for the WS40 mix. The tobermorite mineral is formed during prolonged hydrothermal reactions of silica and calcium compounds at specific starting ratios. A study identified that reactions with a starting calcium-to-silica ratio of 1.5 resulted in tobermorite [45]. This same study confirmed that tobermorite dehydroxylation occurs when water is lost at 90 \({}^{\circ}\)C [45]. Figure 5 also shows the results of the MIP test, representing the pore entry size distributions rather than the pore size distributions. The Hg intrusion pressure achievable by the equipment is limited to a maximum pressure of up to 400 MPa, which corresponds to a minimal pore radius of 2 nm following a cylindrical pore model [46].