## 3 Results and Discussion
### Characteristics of Activated Fly Ash
The distribution of lime and silica in the morphological composition of fly ash was studied through an EDS analysis of the material (Table 7). EDS analysis is semi-quantitative, and the figures shown in Table 7 are approximate but enable distinguishing the concentration points of crucial elements. The smallest fluffy-shaped particles mostly consist of CaO (spots 1, 5, 6, and 8 in Figure 4), whereas bigger and more profound particles are rich in SiO\({}_{2}\) (spot 2 in Figure 4). EDS analysis also confirmed the presence of unburned carbon in a form of micro-size particles. \begin{table}
\begin{tabular}{c c c c} \hline
**Property** & **FA(B)63** & **FA(B)125** & **FA(B)N** \\ \hline Fineness & 1.5\% & 16.3\% & 43.1\% \\ Specific surface (Blaine method) & 6281 cm\({}^{2}\)/g & 3416 cm\({}^{2}\)/g & 2559 cm\({}^{2}\)/g \\ Volume-specific surface (dynamic light scattering) & 12,445 cm\({}^{2}\)/cm\({}^{3}\) & 7573 cm\({}^{2}\)/cm\({}^{3}\) & 5738 cm\({}^{2}\)/cm\({}^{3}\) \\ Loss on ignition & 18.3\% & 11.8\% & 7.8\% \\ Strength Activity Index after 28 days & 89.2\% & 81.1\% & 64.3\% \\ Strength Activity Index after 90 days & 80.4\% & 79.6\% & 66.1\% \\ \hline \end{tabular}
\end{table} 
Table 5: Physical properties of sieved fly ash (FA(B)63 and FA(B)125) compared with untreated fly ash (FA(B)N). Figure 2: Grain size distribution of fly ash sieved with 63 \(\upmu\)m (FA(B)63) or 125 \(\upmu\)m (FA(B)125) sieve compared with untreated fly ash (FA(B)N). \begin{table}
\begin{tabular}{c c c c} \hline
**Oxide** & **FA(B)63** & **FA(B)125** & **FA(B)N** \\ \hline SiO\({}_{2}\) & 3.3\% & 5.9\% & 9.6\% \\ Al\({}_{2}\)O\({}_{3}\) & 0.0\% & 0.0\% & 2.4\% \\ P\({}_{2}\)O\({}_{5}\) & 0.0\% & 0.0\% & 0.0\% \\ K\({}_{2}\)O & 14.6\% & 14.7\% & 14.7\% \\ CaO & 65.4\% & 61.7\% & 56.1\% \\ MnO & 3.6\% & 3.4\% & 3.1\% \\ Fe\({}_{2}\)O\({}_{3}\) & 7.4\% & 8.5\% & 7.9\% \\ CuO & 0.1\% & 0.1\% & 0.0\% \\ ZnO & 0.6\% & 0.6\% & 0.5\% \\ As\({}_{2}\)O\({}_{3}\) & 0.0\% & 0.0\% & 0.0\% \\ SO\({}_{3}\) & 4.3\% & 4.2\% & 4.3\% \\ TiO\({}_{2}\) & 0.4\% & 0.6\% & 0.6\% \\ Cl & 0.0\% & 0.0\% & 0.7\% \\ BaO & 0.3\% & 0.3\% & 0.1\% \\ \hline \end{tabular}
\end{table} 
Table 6: Chemical oxide composition of sieved biomass fly ash. Figure 3: SEM photographs of fly ash (**a**) untreated (FA(B)N) (500\(\times\) magnification), (**b**) sieved with 63 \(\upmu\)m (FA(B)63) (500\(\times\) magnification), (**c**) untreated (FA(B)N) (2000\(\times\) magnification), and (**d**) sieved with 63 \(\upmu\)m (FA(B)63) (2000\(\times\) magnification). As shown in Tables 5 and 6, sieving influenced both the chemical composition and physical properties of the investigated wood biomass fly ash. FA(B)63 and FA(B)125 fly ash had higher amounts of CaO and smaller amounts of SiO\({}_{2}\) than untreated FA(B)N fly ash. CaO was observed in the form of lime and portlandite (Figure 1). These minerals, together with arcanite, were mostly responsible for the hydraulic reactivity of biomass fly ash [29]. Sieving separated SiO\({}_{2}\), which was mostly in the form of non-reactive quartz and increased the amount of reactive calcium-based minerals (Table 6). Lime and alkalis from biomass fly ash can function in the mix as a reservoir of alkalinity that can accelerate the dissolution of minerals from cement and other additives into the solution of fresh mortar mix, thus, quickening the initial stages of hydration reactions [30; 31]. Fineness and loss on ignition are the two most often required properties in international standards for fly ash [32]. They are the best predictor for the quality of siliceous fly ash [33; 34; 35]. In the case of FA(B)63 fly ash, fineness decreased from 43.1% to 1.5%. Sieving improved the grain size distribution of biomass fly ash. [PERSON] et al. [36] observed that biomass fly ash is capable of broadening the particle size distribution of cement by increasing the number of particles smaller than 45 \(\upmu\)m and by that can increase the self-cementitious strength of fly ash [36].