## 3 Results and Discussion  
### Compressive Strength  
Figure 2 shows the results of the compressive strength measurements at each age. The compressive strength tended to increase with age. This means that the hydration of slag and CSAe continued to progress with age. Moreover, regardless of the substitution rate of CSAe, the compressive strength improved as the substitution rate of SF increased to 0%, 5%, and 10%. However, the 1 d strength of all CSAe mixed samples showed a low \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Level**} & \multicolumn{3}{c}{**Mix Ratio (wt.\%)**} \\ \cline{2-4}  & **Slag** & **SF** & **CSAe** \\ \hline G90F0C10 & 90 & 0 & 10 \\ G85F5C10 & 85 & 5 & 10 \\ G80F10C10 & 80 & 10 & 10 \\ \hline G80F0C20 & 80 & 0 & 20 \\ G75F5C20 & 75 & 5 & 20 \\ G70F10C20 & 70 & 10 & 20 \\ \hline G70F0C30 & 70 & 0 & 30 \\ G65F5C30 & 65 & 5 & 30 \\ G60F10C30 & 60 & 10 & 30 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mix properties. value of less than 7 MPa. Therefore, subsequent studies should be conducted to improve the early age (1 d) compressive strength of the proposed material so that it can be used as structural concrete. Figure 2: Cont. In the 10% CSAe samples, the 28 d compressive strengths at 0%, 5%, and 10% SF were 23.2, 26.8, and 31.6 MPa, respectively. Those for the 20% CSAe samples were 34.7, 38.3, and 41.7 MPa, and those for the 30% CSAe samples were 32.8, 35.3, and 37.87 MPa, respectively. The highest compressive strength was measured on a 20% CSAe sample. In the 30% CSAe samples, the excessive expansion effect at the early age of CSAe may have caused cracks on the specimen surface and interior, thereby inhibiting the increase in strength. The compressive strength results in Figure 2 show that the strength-improving effect of increasing the CSAe replacement rate was consistent with the experimental results of OPC mixed with CSA reported by previous studies [31; 32]. However, compared with CSA mixed with OPC, the CSAe used in this study had a specific substitution ratio that affected the increase in compressive strength due to its higher expandability. The decrease in compressive strength at 30% CSAe, which was increased to 20% CSAe, can be attributed to excessive expansion. The CSAe showed high expansibility in the early hydration stage before hardening. As the substitution ratio of CSAe increased, C4A3\(\overline{5}\) increased, and the expansion action of C4A3\(\overline{5}\) also increased. C4A3\(\overline{5}\) promotes setting with its rapid early hydration reaction [33]. This quick setting reduces workability and leads to a surfeit of reaction material, which forms pores and weakens the matrix. Another reason may be the formation of voids around the CSAe particles due to the rapid formation of ettrinigite during the early hydration step [18; 34; 35; 33]. As shown in the XRD analysis, the highest ettrinigite peak was observed at 30% CSAe. It can be presumed that ettrinigite, which was initially formed in a large amount, covered the slag particles and played a role in preventing the hydration reaction [36; 37]. A large amount of mixing water is required for C4A3\(\overline{5}\) to be completely hydrated. When the \(w/b\) is less than 0.6, C4A3\(\overline{5}\) does not fully hydrate and causes excessive expansion [5]. Therefore, this study's \(w/b\) of 0.5 was not sufficient for the complete hydration of C4A3\(\overline{5}\). This excessive expansion affected the distribution and size of pores in the material, weakening the hardened samples. In addition to the insufficient water, the sulfates contained in the CSAe may have been a factor. In [PERSON] et al. [38], an increase in sulfate ions indicated the effect of delayed hydration. In this study, increasing the replacement rate of CSAe increased the sulfate ions present. Increasing the replacement rate of CSAe  
Figure 2: Compressive strengths of slag-SF-CSAe cement pastes, (**a**) 10% CSAe samples, (**b**) 20% CSAe samples, and (**c**) 30% CSAe samples.The.