# Research and Application of Slag-Nanosilica Stabilizer for Silt Subgrade
## 4 Results and Discussion
### Laboratory Test Results  
#### 4.2.1 Unconfined Compressive Strength Test  
For this test, 6%, 8%, 10%, 12%, and 14% SNS were added, compared with silt addition of 10% CS, to explore the influence of different curing ages and content of SNS on the stabilizing effect of silt.  
As can be seen from Figure 2, with increasing curing age of stabilized soil, the UCS of silt increased rapidly at first and then was slowly influenced by SNS. For specimens with standard curing ages of 7 and 28 d, the maximum UCS of SNS-S was 4.21 and 5.59 MPa, respectively, while the UCS of CS-S was only 2.84 and 3.11 MPa, respectively. Therefore, the UCS of SNS-S was about 1.6 times that of CS-S. The UCS of SNS-S increased first and then decreased slowly with the increase in stabilizer content. When the content was 10%,  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test No.** & **Quicklime Content** & **Nanosilica Content** & **Vacant Column** & **Slag Content** \\  & **A/\%** & **B/\%** & **C/\%** & **C/\%** \\ \hline A1 & 2 (1) & 0.2 (1) & 0 (1) & 4 (1) \\ A2 & 2 (1) & 0.3 (2) & 0 (2) & 6 (3) \\ A3 & 2 (1) & 0.4 (3) & 0 (3) & 5 (2) \\ A4 & 3 (2) & 0.2 (1) & 0 (2) & 5 (2) \\ A5 & 3 (2) & 0.3 (2) & 0 (3) & 4 (1) \\ A6 & 3 (2) & 0.4 (3) & 0 (1) & 6 (3) \\ A7 & 4 (3) & 0.2 (1) & 0 (3) & 6 (3) \\ A8 & 4 (3) & 0.3 (2) & 0 (1) & 5 (2) \\ A9 & 4 (3) & 0.4 (3) & 0 (2) & 4 (1) \\ \(k_{1}\) & 0.190 & 0.367 & 0.500 & 0.417 \\ \(k_{2}\) & 0.647 & 0.483 & 0.457 & 0.623 \\ \(k_{3}\) & 0.637 & 0.623 & 0.517 & 0.433 \\ \(R\) & 0.457 & 0.256 & 0.060 & 0.206 \\ \hline \hline \end{tabular}
\end{table}
Table 10: Range analysis of orthogonal test results.  
the UCS of SNS-S reached the peak value (5.59 MPa) at 28 d. The strength increases of 3, 7, 14, and 28 d were 68.5%, 21.7%, and 8.5%, respectively. The UCS values of SNS-S were almost all higher than those of CS-S.  
According to the analysis, the slag in SNS underwent hydration reaction to generate Ca(OH)\({}_{2}\) in the early period of stabilizing. Nanosilica and quicklime in the stabilizer with Ca(OH)\({}_{2}\) underwent pozzolanic reaction to generate calcium silicate hydrate (C-S-H) gel, calcium aluminate silicate hydrate (C-A-S-H) gel, and other hydration reaction products, which played a cementing role between soil particles. This was also the main reason for the improvement of the strength characteristics of stabilized soil [28; 29; 30]. The nanosilica used in this test had smaller particle size and larger specific surface area, so it could more effectively promote the hydration reaction of the slag in the stabilizer and significantly improve the early compressive strength of silt [31]. Appropriate SNS can significantly improve the UCS of silt, but excessive SNS destroys the overall uniformity, leading to excess of hydration reaction products of slag, an increase in gaps between soil particles, a few cracks on the soil surface, and imperfect overall structural development, thereby resulting in the strength of stabilized soil decreasing slowly from the peak value. It can be seen that when the content of SNS was 10%, the improvement on the compressive properties of silt was the most significant.