## 3 Results and Discussion
### Microstructure and Mineralogical Analyses
#### 3.3.2 XRD and FT-IR  
Figure 15 illustrates the X-ray diffraction (XRD) patterns of the unsolidified loess, uncarbonated solidified loess, and carbonated solidified loess. The diffraction spectra of the unsolidified loess and uncarbonated solidified loess are nearly identical, except for the emergence of new peaks corresponding to brucite magnesium hydroxide (Mg(OH)\({}_{2}\)) in the stabilized loess. This observation suggests that the MgO reacted with water in the absence of carbonation, leading to the formation of magnesium hydroxide (Mg(OH)\({}_{2}\)) [49]. In contrast,  
Figure 14: Microscopic characteristics of carbonated solidified loess under different freeze–thaw cycle conditions: (**a**) SEM: CL = 1% + MgO = 10%, FT = 0; PCAS: CL = 1% + MgO = 10%, FT = 0; (**b**) SEM: CL = 1% + MgO = 10%, FT = 15; PCAS: CL = 1% + MgO = 10%, FT = 15.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **1\%CL + 10\%MgO; FT = 0** & **1\%CL + 10\%MgO; FT = 15** \\ \hline Number of Pores & 144 & 305 \\ Porosity & 3.08\% & 6.66\% \\ Probabilistic Entropy & 0.9559 & 0.9689 \\ Fractal Dimension & 1.1817 & 1.2099 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Pore-related parameters of carbonated solidified soil.  
the XRD pattern for the carbonated solidified loess reveals prominent peaks corresponding to hydromagnesite (Mg\({}_{5}\)(CO\({}_{3}\))\({}_{4}\)(OH)\({}_{2}\):5H\({}_{2}\)O) and usequehonite (MgCO\({}_{3}\):3H\({}_{2}\)O), indicating that carbonation induced new mineral phases. Furthermore, the absence of MgO peaks in the uncarbonated solidified loess implies that MgO hydration was nearly completed through carbonation reactions. This conclusion aligns well with the findings of [PERSON] et al. [50]. To gain a deeper understanding of the chemical reactions, Fourier-transform infrared (FT-IR) spectroscopy was conducted, as this technique applies to both crystalline and amorphous materials. The results are presented in Figure 16. For unsolidified loess (Figure 16a), a peak appeared at 3426.92 cm\({}^{-1}\), corresponding to O-H stretching vibrations, indicating the presence of free and structural water in the loess. Peaks at 2519.01 cm\({}^{-1}\), 1437.04 cm\({}^{-1}\), and 875.52 cm\({}^{-1}\) are attributed to C-O and CO\({}^{3-}\) vibrations in carbonate minerals (e.g., calcite). The peak at 1028.49 cm\({}^{-1}\) corresponds to Si-O vibrations, reflecting the abundance of silicate minerals. Figure 16b presents the FT-IR results after stabilization and carbonation. The peak at 3428.94 cm\({}^{-1}\) weakened, indicating a reduction in magnesium hydroxide (Mg(OH)\({}_{2}\)). Conversely, the peaks at 1432.21 cm\({}^{-1}\) and 878.66 cm\({}^{-1}\) intensified, suggesting the formation of a significant amount of magnesium carbonate (MgCO\({}_{3}\)), which markedly enhanced the stability of the solidified system. FT-IR analysis further confirmed the process of CO\({}_{2}\) mineralization and the formation of magnesium carbonate, consistent with the SEM analysis results.  
Figure 16: FT-IR test results: (**a**) unsolidated loess; (**b**) carbonated solidified loess.  
Figure 15: XRD of uncarbonated and carbonated solidified loess.