## 3 Results and Discussion
### Hydration Products  
Figure 3 shows the XRD results for the analysis of the hydration products. The main hydration products of the slag-SF-CSAe cement were ettrinigite. As the substitution rate of CSAe increased, the ettrinigite and ye'elimite peak increased. As CSAe decreases from 30% to 10%, the ettrinigite peak gradually decreases, and it can be seen that the order of Figure 3c > Figure 3b > Figure 3a decreases. It also shows that ye'elimite peak also decreases with ettrinigite. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**CSAe (\%)**} & \multirow{2}{*}{**SF (\%)**} & \multicolumn{4}{c}{**The Rate of Change in Strength (\%)**} \\ \cline{3-6}  & & **1 d** & **3 d** & **7 d** & **28 d** \\ \hline \multirow{2}{*}{10} & 5 & 128.6 & 126.6 & 120.6 & 112.5 \\ \cline{2-6}  & 10 & 147.3 & 140.6 & 140.5 & 136.1 \\ \hline \multirow{2}{*}{20} & 5 & 120.8 & 106.7 & 108.7 & 110.3 \\ \cline{2-6}  & 10 & 129.8 & 111.5 & 116.2 & 120.0 \\ \hline \multirow{2}{*}{30} & 5 & 118.8 & 112.8 & 105.7 & 107.7 \\ \cline{2-6}  & 10 & 133.2 & 131.5 & 113.9 & 115.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The rate of change in strength of with SF to without SF samples by measurement age Figure 3: XRD results (a) 10% CSAe at 1 d and 28 d (b) 20% CSAe at 1 d and 28 d, (c) 30% CSAe at 1 d and 28 d, E: ettrinigite, A: anhydrite, Y: ye’elimite, C: C-S-H/calcite (overlap). The increase in CSAe promoted the production of ettrinigite, and the increase in ye'elimite confirmed the presence of dehydrated CSAe. However, changes in hydration products were not observed due to the presence or absence of SF and the substitution rate. In addition, the change in the peak of the C-S-H gel, the major hydration product of slag, was almost unchanged regardless of the substitution ratio of CSAe and SF. In Figure 3a-c, changes in the peaks of ettrinigite and C-S-H, which are major hydration products, were insignificant despite the increase in the SF substitution rate to 0%, 5%, and 10%. According to previous studies, SF is formed by dense reaction products at the early age hydration stage of hydration reactions by a pozzolanic reaction with portlandite [39; 40]. In Figure 3, no portlandite peak was observed regardless of the substitution ratio of CSAe. Unlike previous studies, this study did not use OPC, so there was no major source of portlandite. Thus, no pozzolanic reaction of SF occurred. Portlandite is also consumed in the hydration of slag. In conclusion, the lack of portlandite affected the production of C-S-H gel by reducing the pozzolanic reaction of SF and hydration of slag. Therefore, the change in the C-S-H gel peak was very small compared with other hydration reactants. Previous studies on CSA and the present study have certain differences. The XRD analysis in the current work did not identify stratlingite (C\({}_{2}\)ASH\({}_{8}\)) in the hydration products. Stratlingite is observed at \(w/c\) exceeding 0.6 or under sufficient moisture-supply-maintaining conditions, such as water curing [26; 41]. Moreover, portlandite [26; 42] and monosulfate (C\({}_{4}\)ASH\({}_{12}\)) [26] were not detected in the present study. Previous studies are mostly about CSA cement mixed with CSA and OPC. By contrast, the present work did not use OPC. Therefore, the calcium, silicate, and aluminum supplied from OPC are not enough. In the case of slag, the formation of a relatively rich reactant was difficult due to the lower hydration reactivity of slag compared with OPC. In this study, some of the hydration reactants observed in previous studies on binders without OPC were not seen. Previous studies have shown that fly ash is mostly a filler because it exhibits little reactivity in binary binders wherein it is mixed with CSA [43; 44; 45]. The slag in the current study showed low hydration reactivity in the binder of slag-CSAe-SF. However, the low hydration reactivity of slag was complemented by the substitution of SF.