## 3 Experiment Overview
### Experiment Method
#### 3.3.2 Properties of Concrete after Curing  
Exposure Conditions  
A literature review revealed that in the high concentration exposure condition of 20% (200,000 ppm) CO\({}_{2}\), the carbon capture depth of alkali-activated concrete was approximately 5 mm or lower in 1 month and approximately 20 mm or lower in 12 months [16]. As shown in this literature review, the change of carbon capture depth was insignificant even though the concrete was exposed to a high concentration of CO\({}_{2}\) for a long time. In the present study, a CO\({}_{2}\) concentration of 10% (100,000 ppm) was set as the high concentration CO\({}_{2}\) exposure condition for the accelerated carbonation tester. The relative humidity and temperature inside the accelerated carbonation tester during exposure were 50% and 23 \(\pm\) 2 \({}^{\circ}\)C, respectively. Furthermore, in the case of the high-purity air exposure conditions for comparison with high concentration CO\({}_{2}\) exposure conditions, an exposure experiment was performed in a constant temperature and humidity room at the relative humidity and temperature of 50% and 23 \(\pm\) 2 \({}^{\circ}\)C using a plastic chamber that can be fully sealed by applying a urethane foam solution. The used high-purity air was composed of only nitrogen and oxygen and contained less than 0.01% of other \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & & & \multicolumn{6}{c}{**Unit Weight (kg/m\({}^{3}\))**} & & & \\ \cline{3-8}
**Variables** & **W/B (\%)** & **S/a (\%)** & **W** & **BFS** & **Cement** &
\begin{tabular}{c} **Activator** \\ **Ca(OH)\({}_{2}\)** \\ \end{tabular} & **Na\({}_{2}\)SiO\({}_{3}\)** & **F.A.** & **C.A.** & **(HRWR)** \\ \hline S90 Ca20 Na20 & & & & 495 & 55 & & 472.44 & 630.12 & \\ S80 Ca20 Na20 & 0.325 & 0.45 & 250.3 & 440 & 110 & 110 & 474.19 & 632.40 & \\ S70 Ca20 Na20 & & & 385 & 165 & & 475.85 & 634.68 & \\ S60 Ca20 Na20 & & & 330 & 220 & & 477.54 & 636.90 & \\ \hline \hline \end{tabular}  
* W/B: Water/Binder (BFS+C+Activator), W: Water, BFS: Blast-Furnace slag, C: OPC, Ca(OH)\({}_{2}\): Calcium Hydrooxide, Na\({}_{2}\)SiO\({}_{3}\): Sodium Silicate. F.A.: Fine Aggregate, C.A.: Coarse Aggregate. Admixture: Polycarboxylate High Range Water Reducer. S00: BFS/C, Ca: Ca(OH)\({}_{2}\)/BFS+C, Na: Na\({}_{2}\)SiO\({}_{3}\)/BFS+C.  
\end{table} 
Table 6: Mix variables of carbon-capturing concrete. components (N\({}_{2}\)+O\({}_{2}\)\(>\) 99.99%), which was considered as a control for comparison with the high concentration CO\({}_{2}\) exposure conditions. Cylindrical specimens of \(\phi\)100 mm \(\times\) 200 mm were fabricated for the compressive strength experiment. To measure the compressive strength for each variable and each exposure condition, the compressive strength characteristics of carbon-capturing concrete were analyzed using the specimens at 1, 7, 28, 56, and 90 days of exposure. Prismatic specimens of 100 mm \(\times\) 100 mm \(\times\) 400 mm were fabricated for the flexural strength experiment. The flexural strength characteristics of the specimens were analyzed at 7 and 28 days of exposure. To analyze the carbon capture depth of carbon-capturing concrete, the carbon capture depth was measured with respect to the progress of exposure period for each exposure conditions and variables at 1, 7, 28, 56, and 90 days. A freeze-thaw resistance experiment was conducted as an indoor experiment to measure the freeze-thaw resistance of concrete specimens in rapid iterative cycles. The same prismatic specimens of 100 mm \(\times\) 100 mm \(\times\) 400 mm as those used in the flexural strength experiment were fabricated and cured for 14 days. Then their freeze-thaw resistance was evaluated in accordance with ASTM C 666, Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing [17].