# Influence of Some Additives on the Properties of OPC Solidified Sandy Silt
## 3 Results
### FESEM Micrographs Analysis  
Figure 10 shows the FESEM images of unconsolidated unreinforced sandy silt particles. The surface is smooth with no cementitious substances and only a small number of fine particles. Therefore, the sand silt particles cannot be well connected. When reflected in the macroscopic view, it has low friction, poor stability, low strength, and stiffness.  
Figure 11 illustrates the FESEM micrographs of specimens with and without additives after being cured for 28 days. A large number of needle-like (AFt) and Ca(OH)\({}_{2}\)/CaCO\({}_{3}\) particles can be observed on the surface of OPC-stabilized sandy silt as well as the strong bonds between the gelatinous C-S-H gel and matrix, as shown in Figure 11a. An alkaline solution in the pore space leached the soluble aluminosilicate composition available from fly ash (pozzolanic reaction), resulting in it coexistence with N-A-S-H and C-S-H gels [29; 30; 31]. When gypsum was added (see Figure 11c), the acicular AFt was bigger and denser than the unadulterated AFt, which could better fill the void in the later period. However, it can be seen that the clay particle-stabilized soil had a smaller particle size, which improved the gradation composition and contributed to the connection and fusion between the particles.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Additives**} & \multirow{2}{*}{**Content/\%**} & \multirow{2}{*}{**Mixture**} & \multicolumn{6}{c}{**Curing Days**} \\ \cline{4-8}  & & & **7** & **14** & **28** & **60** & **90** \\ \hline None & 0 & S11 & 389.36 \(\pm\) 28.66 & 545.71 \(\pm\) 45.19 & 694.18 \(\pm\) 53.12 & 963.32 \(\pm\) 66.23 & 1012.6 \(\pm\) 58.72 \\ Gypsum & 2 & SS2 & 314.05 \(\pm\) 13.54 & 674.96 \(\pm\) 34.23 & 811.96 \(\pm\) 42.15 & 1105.19 \(\pm\) 63.14 & 1133.77 \(\pm\) 68.05 \\ Clay particles & 4 & SN4 & 391.16 \(\pm\) 18.61 & 694.62 \(\pm\) 54.20 & 1059.44 \(\pm\) 33.14 & 1234.31 \(\pm\) 70.05 & 1248.5 \(\pm\) 57.62 \\ Fly ash & 4 & SF4 & 470.94 \(\pm\) 23.55 & 689.63 \(\pm\) 47.08 & 1170.19 \(\pm\) 72.12 & 1286.85 \(\pm\) 68.26 & 1321.01 \(\pm\) 86.10 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Test results for compression rebound modulus (MPa).  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Additives**} & \multirow{2}{*}{**Content/\%**} & \multirow{2}{*}{**Mixture**} & \multicolumn{6}{c}{**Curing Days**} \\ \cline{4-8}  & & & **7** & **14** & **28** & **60** & **90** \\ \hline None & 0 & S11 & 389.36 \(\pm\) 28.66 & 545.71 \(\pm\) 45.19 & 694.18 \(\pm\) 53.12 & 963.32 \(\pm\) 66.23 & 1012.6 \(\pm\) 58.72 \\ Gypsum & 2 & SS2 & 314.05 \(\pm\) 13.54 & 674.96 \(\pm\) 34.23 & 811.96 \(\pm\) 42.15 & 1105.19 \(\pm\) 63.14 & 1133.77 \(\pm\) 68.05 \\ Clay particles & 4 & SN4 & 391.16 \(\pm\) 18.61 & 694.62 \(\pm\) 54.20 & 1059.44 \(\pm\) 33.14 & 1234.31 \(\pm\) 70.05 & 1248.5 \(\pm\) 57.62 \\ Fly ash & 4 & SF4 & 470.94 \(\pm\) 23.55 & 689.63 \(\pm\) 47.08 & 1170.19 \(\pm\) 72.12 & 1286.85 \(\pm\) 68.26 & 1321.01 \(\pm\) 86.10 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Test results for flexural strength (MPa).  
Figure 9: Compression rebound modulus with different replacement ratios of the additives.  
Additionally, the figure shows that the amount of crystalline compound in SF4 is less than in the control group.