# Research on Solidification Methods and Stabilization Mechanisms of Sulfate Saline Soils
## 4 Results and Analysis
### Microstructure Analysis of Stabilized Soils
#### 4.3.3 FTIR Analysis  
The FTIR of stabilized soil L3, F3, and P3 after curing for 1, 3, 7, and 28 d is shown in Figure 11.  
Figure 11a shows the main reactive functional groups in L3-stabilized saline soils. The unique absorption peak near 3490 cm\({}^{-1}\) relates to the stretching vibration of hydroxyl (\(-\)OH) groups [46], attributed to Ca(OH)\({}_{2}-\)OH, which weakens as it increases in time, suggesting the transformation and reduction of Ca(OH)\({}_{2}\) into other compounds. The vibration at 1603 cm\({}^{-1}\) is caused by the bending vibration of adsorbed water (\(-\)OH). The absorption peaks near 463-473 cm\({}^{-1}\) and 779-797 cm\({}^{-1}\) correspond to the asymmetric bending vibrations of Si\(-\)O\(-\)Si and Al\(-\)O, respectively [47]. In addition, a band at 1360 cm\({}^{-1}\) indicates O\(-\)C\(-\)O production in carbonate compounds [47]. The deformation of C\(-\)O causes the creation of CO3\({}^{2-}\) when lime reacts with CO\({}_{2}\) in the air. XRD and SEM showed that lime combined with Na\({}_{2}\)SO4 to form a binding compound, which is chemically solidified.  
Figure 11b shows the FTIR spectrum of the F3-stabilized soil. All specimens exhibit steadily strengthening vibration peaks between 3490 cm\({}^{-1}\) and 1601 cm\({}^{-1}\), which belong mainly to the \(-\)OH stretching vibrations of adsorbed water and C\(-\)S\(-\)H, showing an increase in C\(-\)S\(-\)H production, agreeing with the SEM results. The peak at 1360 cm\({}^{-1}\) was attributable to the stretching vibration of C\(-\)O, showing that CO3\({}^{2-}\) originates via the reaction of alkaline chemicals in FA with CO\({}_{2}\) in the air. The absorption bands at  
Figure 11: FTIR spectra of stabilized saline soils for 1, 2, 7, and 28 d: (**a**) L3; (**b**) F3; (**c**) P3.  
970 cm\({}^{-1}\) and 450 cm\({}^{-1}\) were characteristic of C\(-\)S\(-\)H gels [46]. The asymmetric bending vibration range of Si\(-\)O\(-\)Si is 463 cm\({}^{-1}\) to 473 cm\({}^{-1}\) originates mainly from C\(-\)S\(-\)H and unhydrated SiO\({}_{2}\)[48]. The absorption peaks near 779-797 cm\({}^{-1}\) were attributed to the asymmetric bending vibrations of Al\(-\)O [17], which may have formed as a consequence of the substitution of Si\({}^{4+}\) by Al\({}^{3+}\) in C\(-\)S\(-\)H gels. The combination of XRD and SEM results revealed that FA stabilized to form C\(-\)S\(-\)H and (hydrated calcium aluminate) C\(-\)A\(-\)H, which are classified as being chemically solidified.  
Figure 11c shows the FTIR spectrum of the P3-stabilized soil. The absorption peaks at 3490 cm\({}^{-1}\) and 1603 cm\({}^{-1}\) are the characteristic \(-\)OH stretching vibrations of adsorbed water. The peak at 1360 cm\({}^{-1}\) was attributable to the stretching vibration of C\(-\)O, showing CO\({}_{3}\)\({}^{2-}\) absorption in the carbonate of saline soils. The absorption peaks near 463 cm\({}^{-1}\) to 473 cm\({}^{-1}\) and 779 cm\({}^{-1}\) to 797 cm\({}^{-1}\) correspond to the asymmetric bending vibrations of Si\(-\)O\(-\)Si and Al\(-\)O in soil, respectively. During the stabilization of saline soils by PAM, no new functional groups were formed, indicating that PAM did not react with the soil components, resulting in physical solidification.