## 4 Results and Discussion
### Raw Materials
It is very easily hydrated to Mg(OH)\({}_{2}\) or carbonized to MgCO\({}_{3}\) even with the humidity or CO\({}_{2}\) of the atmosphere. XRD results indicate the new major phase of periclase to coexist with low amounts of brucite and portlandite (or lime), and the primary remaining magnesite and quartz (Figure 5). The same diffractogram, by its low peak intensities, reveals the fine-grained character of this material. Scarcely, in the microstructure of this calcined product, enriched microregions with the CaO/Ca(OH)\({}_{2}\) phases were observed (Figure 6a,b). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multicolumn{8}{c}{**Chemical Compositions**} \\ \cline{2-10}  & **CaO** & **MgO** & **Al\({}_{2}\)O\({}_{3}\)** & **SiO\({}_{2}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **SO\({}_{3}\)** & **Na\({}_{2}\)O** & **K\({}_{2}\)O** & **Loss** & **Total** \\ \hline Cement & 63.16 & 1.43 & 4.75 & 19.47 & 3.43 & 2.68 & 0.28 & 0.62 & 3.26 & 99.08 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Chemical compositions of cement (%). In this study, fly ash was also used, as numerous researchers have used fly ash as an additive for the production of cements of normal and of increased mechanical strength. For this reason, fly ash derived from a Kardia lignite-fired power plant in Ptolemais Basin was collected and studied in order to investigate the behavior and physicochemical properties of the produced cement in combination with MEA. The characterization of the tested fly ash, which includes mineralogical composition, morphological determination, and chemical composition, revealed that fly ash is enriched in CaO (Table 4). The increased specific surface of its particles makes fly ash capable of restraining elements and participating in chemical reactions due to the microporous minerals included, such as clays and micas [26; 27]. Furthermore, the SiO\({}_{2}\) presence constitutes the main carrier of pozzolanic properties, making it useful in cement as an additive. The mineralogical analysis results are shown in Table 3, while powder X-ray diffraction patterns are shown in Figure 7. The basic components of Kardia fly ash are lime, anhydrite, calcite, gehlenite, and less quartz, and the water is  
plagioclase, and hematite. Micas appear in minor amounts. According to the XRPD results, in the fly ash, amorphous phase ranges to percentages of 25 wt%. Lime anhydrite and quartz appear as the major crystalline phases. Anorthite, portlandite, and gehlenite were also detected in lower amounts. Table 5 presents the chemical composition of the investigated fly ash, and the XRD pattern of Figure 7 shows the mineralogical composition of fly ash. The presence of silica dioxide in calcium-rich fly ashes is important even in small amounts [28]. It has been demonstrated that when incorporating high-calcium fly ashes in cementitious systems, the soluble silica present in the ash significantly affects their hydration. Although fly ash rich in active silica is generally more preferable, this does not exclude the possibility of achieving higher reaction rates and superior performance when utilizing different ashes [25]. The  
Figure 6: **(a,b)** Backscattered image indicating microregion in the matrix of the final product enriched in lime/portlandite (white), and periclase (grey). investigated fly ash presents SiO\({}_{2}\) + Al\({}_{2}\)O\({}_{3}\) + Fe\({}_{2}\)O\({}_{3}\) less than 70% as it is required for Class C classification according to ASTM standards (ASTM 618C) (Table 5). SiO\({}_{2}\) + Al\({}_{2}\)O\({}_{3}\) + Fe\({}_{2}\)O\({}_{3}\) content also has to be >50%, which is not the case in Greek fly ash due to its high CaO content. However, several authors [25; 26] classify Greek fly ash in Class C, taking into consideration the significantly high CaO concentration.