## Experimental Results and Discussion
### Chloride Diffusivity  
The chloride diffusivity was measured by the NT Build 492 to evaluate the durability of the mortar specimens with AOD slag. The results are summarized in Table 4. The thicknesses of the specimens ranged from 49.85-50.25 mm, and the experiment was performed at 23 \({}^{\circ}\)C.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{3}{*}{**Variables**} & \multicolumn{4}{c}{**28-Day Drying Shrinkage**} & \multicolumn{4}{c}{**Drying Shrinkage Reduction**} \\  & \multicolumn{4}{c}{**(\(\times\) 10\({}^{-6}\) m/m)**} & \multicolumn{4}{c}{**((SH(0) 1\({}^{-}\)SH(x) 2)/SH(0,\%))**} \\ \cline{3-8}  & **STP0** & **STP30** & **STP60** & **STP0** & **STP30** & **STP60** \\ \hline \multirow{3}{*}{T = 23 \({}^{\circ}\)C} & CO\({}_{2}\) = 0\% & \(-\)1283 & \(-\)1097 & \(-\)900 & - & - & - \\  & CO\({}_{2}\) = 5\% & \(-\)1169 & \(-\)903 & \(-\)737 & 8.9 & 17.7 & 18.1 \\  & CO\({}_{2}\) = 10\% & \(-\)1003 & \(-\)85  
Figure 7 shows the chloride diffusivity of the specimens according to the CO\({}_{2}\) concentration at 23 \({}^{\circ}\)C. As shown in the graph, the chloride diffusivity of STP0 decreased as the concentration increased, but the effect was not significant. An approximately 20% decrease was observed with the 5% CO\({}_{2}\) curing process compared to normal curing. For STP30, the decrease in the chloride diffusivity was clearly observed with 5% CO\({}_{2}\) curing compared to that of plain. For STP60, the chloride diffusivity significantly decreased as the CO\({}_{2}\) concentration increased. The chloride diffusivity of STP60 at 5% CO\({}_{2}\) curing was \(49\times 10^{-12}\) m\({}^{2}\)/s, which was a decrease of more than 50% compared to the case of non-CO\({}_{2}\) curing (\(93\times 10^{-12}\) m\({}^{2}\)/s). At 15% CO\({}_{2}\) curing, the chloride diffusivity was approximately \(22\times 10^{-12}\) m\({}^{2}\)/s, which was approximately 130% of STP0.  
In the cases of STP30 and STP60 incorporating the AOD slag, the chloride diffusivity tended to converge to STP0 as the CO\({}_{2}\) curing concentration increased, as shown in Figure 7. This confirms  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Variables** & **Voltage (V)** & **Test Duration** & **Temperature** & **Thickness** & **Penetration** & **Chloride** \\  & & **(h)** & **(K)** & **(mm)** & **Depth (mm)** & **Diffusivity** \\ \hline T = 23 \({}^{\circ}\)C & STP0 & 10 & 8 & 293 & 50.12 & 7.72 & 26.80 \(\times\) 10\({}^{-12}\) \\ CO\({}_{2}  
that the reaction products of \(\gamma\)-C\({}_{2}\)S with CO\({}_{2}\) filled the pores and decreased the chloride diffusivity. The porosity of the specimen containing AOD slag without carbonation curing increased as the replacement level of the AOD slag increased. However,, the porosity is reduced by calcite and silica gel formed by carbonation curing [20; 21]. Therefore, the specimens incorporating the AOD slag should increase their durability by pore structure densification through carbonation curing.  
Figure 8 shows chloride diffusivity according to curing temperature at 5% CO\({}_{2}\) curing condition. For STP0, the chloride diffusivity decreased as the curing temperature increased. Similar tendencies occurred for STP30 and STP60 with the AOD slag. For STP30, chloride diffusivity was similar at curing temperatures of 23 and 40 \({}^{\circ}\)C, but it decreased at 50 \({}^{\circ}\)C. STP60 exhibited the largest change in chloride diffusivity as the curing temperature increased. Its diffusivity decreased by approximately 35% when temperature was increased from 23 \({}^{\circ}\)C to 40 \({}^{\circ}\)C. It was found that STP60 was significantly affected by the temperature. [PERSON] et al. [24] reported that the strength of paste incorporating AOD slag increased with increasing temperature. Moreover, the acceleration of the reaction of \(\gamma\)-C\({}_{2}\)S and the reaction products made the microstructure dense. The same tendency was observed in the compressive strength measurements.