## 3 Results and Discussion
### Drying Shrinkage  
Figure 7 plots the drying shrinkage ratio against the substitution ratio of CSAe and SF. The drying shrinkage decreased as the CSAe substitution ratio increased from 10% to 30% (without SF). As shown in Figure 7c, the drying shrinkage of the 30% CSAe sample was the least. Then, the drying shrinkage decreased in the order of the 20% CSAe sample shown in Figure 7b, and finally the 10% CSAe sample shown in Figure 7a. As the substitution rate of CSAe increased, drying shrinkage tended to decrease. The 30% CSAe + 0% SF specimen showed fine cracks on the surface when measured after 28 d of aging. This cracking can be attributed to the excessive expansion caused by the high proportion of CSAe. However, cracks were not observed in the 5% and 10% SF specimens at the same 30% CSAe replacement ratio. Regardless of the rate of substitution of CSAe, there was a large variability in length variation from the early stage to 28 d of the measurement. However, after 28 d, the variability of the length changes became smaller. Figure 7: Cont. [PERSON] and [PERSON] [51] showed that, when CSA cement was substituted at 0%, 7%, 15%, and 30% in OPC, the specimen expanded as the CSA substitution rate increased. In particular, the 30% CSA sample showed cracking due to excessive expansion. In the current study, the 30% CSAe samples showed the highest expansion rate (Figure 7c). This high expansion produced fine cracks on the sample surface and also affected the sample interior, resulting in a decrease in the compressive strength and a change in the pore structure. The swelling effect of C\({}_{6}\)A\(\overline{\text{S}}_{3}\)H\({}_{32}\) produced by C\({}_{4}\)A\({}_{3}\)\(\overline{\text{S}}\) is most activated before 28 d of aging, which has a large effect on the reduction of drying shrinkage [42]. According to the results of Figure 7, the increase in the substitution ratio of CSAe increased the swelling  
Figure 7: Drying shrinkage ratios, (**a**) 10% CSAe, (**b**) 20% CSAe, and (**c**) 30% CSAe. and reduced the drying shrinkage. In previous studies, the shrinkage reduction effect was mentioned by the improvement of expandability due to the increase of CSA [31; 33; 43]. As shown in Figure 7a, substitution of SF in the dry shrinkage graph of the 10% CSAe sample showed a tendency to increase the dry shrinkage. This is clearly observed as the substitution rate of SF increases. In addition, in Figure 7b,c, where the substitution rates of CSAe are 20% and 30% CSAe, it can be seen that the effect of increasing drying shrinkage by substitution of SF is further promoted. That is, the drying shrinkage increased as the proportion of SF increased from 0% to 10% at the same CSAe replacement ratio. Drying shrinkage increases for three main reasons. First, the increase in drying shrinkage due to the substitution of SF is explained by the fineness of the SF particles and the resulting increase in surface area. A large amount of compounding is required because of the large surface area, and as a result, an insufficient amount of compounding is available for the hydration of C\({}_{4}\)A\({}_{3}\)\(\overline{\text{S}}\). The presence of unhydrated C\({}_{4}\)A\({}_{3}\)\(\overline{\text{S}}\), which is not fully hydrated, reduces expansion [5]. Second, the SF content reduces the pH of the pore solution, which slows down the hydration of C\({}_{4}\)A\({}_{3}\)\(\overline{\text{S}}\) and decreases the expansion force [54]. Third, the reduction in drying shrinkage due to SF replacement is due to the reduction in pore size due to the filler effect of SF. This is because the capillary tension increased due to the reduced pores. [49; 50]. The substitution of SF is effective in inhibiting the excessive swelling caused by the use of CSAe. SF substitution increases the drying shrinkage but increases the compressive strength and decreases the size and number of pores.