# Research and Application of Slag-Nanosilica Stabilizer for Silt Subgrade
## 4 Results and Discussion
### Micromechanism of Stabilization  
#### 4.3.1 SEM  
Figure 5a is the SEM image of the original silt at magnification of 2000 times. It can be clearly seen from the figure that the microstructure of the silt was mainly agglomerated or lamellar, and the existence of flocculating structure and network structure was not observed. The soil surface had irregular shape and uneven distribution, and the structural elements were mainly the point-surface and edge-surface contacts [37]. Many black shadows could be observed, which represented the gaps between the soil particles or between the soil particles and the minerals. These gaps were haphazard and large in area. This was also good indication that there was obviously a lack of effective connection between the soil  
Figure 4: The damage shape of SNS-S after freeze–thaw cycle test. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type of Stabilizer** & **Cycles/Times** & \(R_{w}\)/MPa & \(R_{f}\)/MPa & \(BDR\)/\% \\ \hline \multirow{2}{*}{SNS} & 1 & \multirow{2}{*}{4.58} & 3.83 & 83.62 \\  & 5 & & 3.50 & 76.42 \\ \multirow{2}{*}{CS} & 1 & \multirow{2}{*}{3.05} & 2.31 & 75.74 \\  & 5 & & 2.21 & 72.46 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Freeze–thaw cycle test results. particles [38]. When the soil encounters water flow, the gaps will be filled with water and the soil particles will be softened, resulting in poor strength characteristics and poor pavement performance of the soil. It can be seen from Figure 5b that the soil was still dominated by lumpy agglomeration. Compared with Figure 5a, it can be seen that the soil surface became relatively flat, and hydration products were produced. However, there were fewer products, which could not play a good filling role. Therefore, although adding a small amount of SNS improved the compressive strength to a certain extent, the effect of improvement was not obvious. As can be seen from Figure 5c, with the increase in SNS content, more needle-like ettrigite crystals (AFt), C-S-H gel, and C-A-S-H gel were produced [39; 40]. This indicates that the hydration reaction in the early period became more sufficient with the increase in the content of SNS, and the hydration products increased significantly. The formation of needle-like crystals and flocculating substances could effectively fill the gaps between soil particles and played a stabilizing role, which made the soil structure more compact. This explains the variation of soil strength with the content of stabilizer. At the same time, as can be observed from Figure 5c, the microstructure of soil in the early period was mainly lamellar. There were a lot of AFt and hexagonal crystal Ca(OH)\({}_{2}\) (C-H) on the surface of the soil. Compared with the original soil in Figure 5a, the gaps between soil particles were obviously reduced, and the direct connection mode of soil particles was also changed to the filling type, which improved the stability of the soil. As can be seen from Figure 5d, with the increase in curing age, the soil microstructure changed from lamellar structure to flocculated structure, and the gaps between soil particles decreased significantly. This indicates that with the increase in curing age, the hydration  
Figure 5: SEM photomicrographs of soil and SNS-S.  
product C-H fully participated in the formation of C-S-H gel and C-A-S-H gel in the pozzolanic reaction and played the role of cementation and filling. The strength of stabilized soil increased with the increase in curing age, which indicates that flocculated structure can improve the strength of soil better than lamellar structure. To sum up, the SNS contributes to an obvious improvement in the structure of silt. With the increase in stabilizer content and curing age, the generation of gaps on the surface of the soil decreases significantly and the products of pozzolanic reaction also increases, which can fill and cement the gaps of soil particles and make the soil structure more compact.