## 3 Results and Discussion
### Effects on Engineering Performance
#### 3.1.3 Chemical Composition Analysis  
Figure 9 shows the CaO/SO\({}_{3}\) and SO\({}_{3}\)/Al\({}_{2}\)O\({}_{3}\) molar ratios based on the GGBS replacement ratio. When the GGBS replacement ratio increased, the CaO/SO\({}_{3}\) and SO\({}_{3}\)/Al\({}_{2}\)O\({}_{3}\) molar ratios decreased. With respect to the representative chemical components, CaO, Fe\({}_{2}\)O\({}_{3}\), and SO\({}_{3}\) exhibited a tendency to decrease, although SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and MgO increased when the GGBS replacement ratio increased. This  
Figure 8: Results of (**a**) compressive strength and (**b**) CS (56 d)/CS (28 d) ratio with respect to the replacement ratio.  
Figure 7: Result of compressive strength with respect to age.  
is because GGBS exhibited higher SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and MgO content when compared to OPC. Regression analysis on the triangular graph of CaO/SO\({}_{3}\) and SO\({}_{3}\)/Al\({}_{2}\)O\({}_{3}\) indicated that construction must be managed by considering long-age strength when the GGBS replacement ratio is increased.  
Figure 10a shows the compressive strength based on the CaO content. When the CaO content increased, the compressive strength also increased. Under the mixing conditions of the study, the ratio of the maximum strength among the specimens to the minimum strength was observed as 239.7% at 3 d of age, 165.0% at 7 d, and 122.8% at 28 d. Conversely, all the specimens at 56 d exhibited similar compressive strengths irrespective of the CaO content. The result suggested that the long-term compressive strengths measured after 28 d were found to be similar because the total binder weight was fixed at 330 kg/m\({}^{3}\). To analyze the compressive strength increase rate after 28 d, the regression curves of the rate of increase in compressive strength with increasing age at the same CaO content level are shown in Figure 10b. The results indicated that the rate of increase in compressive strength after 28 d exhibited a tendency to decrease. Specifically, the compressive strength (C.S., 7 d)/C.S. (3 d) ratio regression curve exhibited the largest reduction rate. This indicated that when the CaO content increased, the rate of increase in compressive strength exhibited a relative decrease when compared with that for low CaO content after 28 d because the compressive strength was rapidly developed at an age lower than 7 d.  
Figure 11 shows the compressive strength based on the basicity. The basicity was calculated as the CaO content/SiO\({}_{2}\) content ratio. When the basicity increased, the compressive strength increased  
Figure 10: Results of (**a**) compressive strength and (**b**) compressive strength ratio with respect to CaO content.  
Figure 9: CaO/SO\({}_{3}\) and SO\({}_{3}\)/Al\({}_{2}\)O\({}_{3}\) molar ratios based on the replacement ratio.  
at all ages with the exception of 56 d. Specifically, when the basicity exceeded 2.3, the compressive strength at 28 d was similar to that at 56 d. The result was similar to the aforementioned CaO content analysis result. This was potentially because GGBS affected the development of long-term strength in specimens with low basicity in the case of long-term strength after 28 d. Figure 12 shows the CaO content and CaO/SiO\({}_{2}\) ratio based on the GGBS replacement ratio. The two variables decreased when the replacement ratio increased. The CaO content decreased to approximately 82.2% and the CaO/SiO\({}_{2}\) ratio to 56.8% when compared to that of the plain specimen. It is expected that these chemical composition analysis data will be used as basic data for the development of binders for high volume GGBS concrete.