## Experimental Results and Discussion
### Drying Shrinkage  
Figures 5 and 6 show the drying shrinkages of the specimens according to the curing conditions. Table 3 summarizes the results of the 28-day drying shrinkage. Figure 5a shows drying shrinkage of the specimens cured in a normal curing environment (0% CO\({}_{2}\)) at a curing temperature of 23 \({}^{\circ}\)C. The drying shrinkage decreased as the replacement level of the AOD slag increased. At 28 days, the value of the drying shrinkage was approximately \(-1300\times 10^{-6}\) m/m for STP0 and reduced to \(-1100\) and \(-900\times 10^{-6}\) m/m for STP30 and STP60, respectively. As the AOD slag containing \(\gamma\)-C\({}_{2}\)S has non-hydraulic properties in environments without CO\({}_{2}\), drying shrinkage reduced as the replacement level of the AOD slag increased. Figure 4: Compressive strength of specimens according to temperature. Figure 5: Drying shrinkages according to CO\({}_{2}\) concentration: (**a**) 0% CO\({}_{2}\), (**b**) 5% CO\({}_{2}\), (**c**) 10% CO\({}_{2}\), and (**d**) 15% CO\({}_{2}\). Figure 6: Drying shrinkages according to curing temperature: (**a**) 40 \({}^{\circ}\)C and (**b**) 50 \({}^{\circ}\)C.  
Figure 5b shows the drying shrinkage of the specimen cured under 5% CO\({}_{2}\). For STP0, an 8.9% reduction in 28-day drying shrinkage was obtained when the CO\({}_{2}\) concentration was increased from 0 to 5%. In the cases of STP30 and STP60, the 28-day drying shrinkage reduction was 17.7% and 18.1%, respectively, and was relatively high compared to STP0. This result was similar to that of the compressive strength according to the CO\({}_{2}\) curing concentration. Unlike STP0, STP60 did not show shrinkage at early ages. This was due to the rapid reaction of CO\({}_{2}\) and the AOD slag containing \(\gamma\)-C\({}_{2}\)S inside the matrix at an early age. This reaction compensates for shrinkage as silica gel and calcite are generated as reaction products [20; 21]. Figure 5c,d show the results of the drying shrinkage for specimens cured under 10% and 15% CO\({}_{2}\) concentrations, respectively. The shrinkage reduction tended to be proportional to the CO\({}_{2}\) concentration. Drying shrinkage decreased further under the CO\({}_{2}\) concentration of 10% than it did under 5%, as shown in Figure 5c. For STP0, drying shrinkage at 28 days was approximately \(-1000\times 10^{-6}\) m/m, confirming that drying shrinkage was reduced by approximately 22% compared to non-CO\({}_{2}\) curing. Drying shrinkage of STP60 at 28 days was approximately \(-640\times 10^{-6}\) m/m, a reduction of approximately 29% compared to non-CO\({}_{2}\) curing. Drying shrinkage was lowest when curing was performed under the CO\({}_{2}\) concentration of 15% (see Figure 5d). The 28-day drying shrinkages of STP0, STP30, and STP60 were \(-975\times 10^{-6}\) m/m, \(-787\times 10^{-6}\) m/m, and \(-545\times 10^{-6}\), respectively. For STP0 and STP30, drying shrinkage was reduced by 24% and 28%, respectively, compared to non-CO\({}_{2}\) curing. For STP60, drying shrinkage was reduced by approximately 40%. In particular, STP60 showed a tendency to expand until 10 days. This is because the effect of calcite generated by the reaction between \(\gamma\)-C\({}_{2}\)S and CO\({}_{2}\) at an early age on shrinkage was greater than that caused by the drying shrinkage of cement. The drying shrinkages of the specimens cured at high temperature reduced (Figure 6) compared to those cured at 23 \({}^{\circ}\)C (Figure 5b). The reduction of drying shrinkage with curing temperature was observed in STP0, STP30, and STP60. Typically, drying shrinkage of cementitious materials using OPC tends to increase with temperature [32]. In this study, however, the drying shrinkage of STP0 reduced when the curing temperature increased from 20 \({}^{\circ}\)C to 40 \({}^{\circ}\)C. This is because the effect of carbonization was greater in drying shrinkage reduction than curing temperature.