## 5 Conclusions  
An experimental study was conducted to develop a carbon-capturing concrete composed of blast-furnace slag that can perform passive as well as active carbon reductions by replacing cement with industrial byproducts. To examine the applicability of this carbon-capturing concrete, we conducted experiments about the mechanical and durability characteristics with respect to the cement replacement ratio. The conclusions of this study are as follows. 1. The compressive strength experiment results with respect to the exposure conditions and cement replacement ratio showed that the compressive strength of the specimen exposed to high concentration CO\({}_{2}\) decreased very little over the exposure period in general. In the high-purity air exposure condition, the compressive strength increased greater than that of the high concentration CO\({}_{2}\) exposure condition. However, the increase of compressive strength with respect to the cement replacement ratio was insignificant. 2. The flexural strength experiment results showed that the increase of the flexural strength with respect to the cement replacement ratio was insignificant as in the compressive strength experiment results. The high-purity air exposure condition showed a higher flexural strength than that of the high concentration CO\({}_{2}\) exposure condition. This is considered to be due to the difference in the strength expression speed caused by the relative lack of the carbon absorption effect. 3. The carbon capture depth experiment result of the high concentration CO\({}_{2}\) exposure condition showed that the carbon capture depth changed very little with the rising cement replacement ratio, and almost no carbon capture occurred in the high-purity air exposure condition. 4. The freeze-thaw resistance experiment results showed that the air volume of the concrete before curing was approximately 3%, but the relative dynamic modulus of elasticity increased to much  
Figure 10: Image analysis experiment results. higher than 80% until 300 freeze-thaw cycles. No change was caused by the cement replacement ratio. The image analysis for the air-void structure showed that every variable satisfied the condition of 200 \(\upmu\)m (0.2 mm) or lower spacing factor and 25 mm\({}^{2}\)/mm\({}^{3}\) or higher specific surface area, which are the criteria for securing freeze-thaw resistance. Despite somewhat low air volume experiment result, the freeze-thaw resistance was excellent owing to the spacing factor of air bubbles and the entrained air. 5. The experiment results of chloride ion penetration resistance showed that the passed charge increased with rising cement replacement ratio, but the difference was not large. Furthermore, every variable showed a 'low' value in the total passed charge range of 1000-2000 coulomb, indicating excellent chloride ion penetration resistance. This is considered to be due to the increased water-tightness of concrete by the mixing of a large quantity of blast-furnace slag despite the cement replacement. 6. To summarize the experiment results on the mechanical and durability characteristics of the carbon-capturing concrete composed of blast-furnace slag, the carbon-capturing concrete had mechanical and durability characteristics above the appropriate levels for concrete. Furthermore, this study found that the active as well as passive carbon reduction functions can be achieved through the use of blast-furnace slag, an industrial byproduct, and the development of the carbon-capturing concrete can effectively reduce CO\({}_{2}\) emissions. Conceptualization, S.K. and C.P. ; methodology, S.K. and C.P. ; writing--original draft preparation, S.K. and C.P. ; writing--review and editing, S.K. and C.P. All authors have read and agreed to the published version of the manuscript.