## 6 Conclusions  
Grouting and filling are important ways of treating cavities. The aim of this study is to explore a new type of green, environmentally friendly, and economical grouting material to minimize the environmental impact caused by existing engineering grouting materials. The following conclusions were obtained by studying the optimal ratio, macroscopic and microscopic properties, and field test of alkali-activated grout materials:  
1. The feasibility of slag, fly ash, and alkaline activators (water glass and sodium hydroxide) as alkali-activated composites was verified by indoor tests. Through the UCS tests, the influence of each factor on strength was obtained: within the scope of this test, the UCS of alkali-activated composites showed a tendency of increasing and then decreasing with the increase in the slag-fly ash ratio, modulus of alkaline activator, and alkalinity. The ratio of slag:fly ash = 7.3, alkaline activator alkalinity = 10%, and alkaline activator modulus = 1.3 were found to be optimal for the gelling effect of alkali-activated composites. 2. The alkali-activated grout materials were formed by mixing the alkali-activated composites with Shenzhen sandy clay. Indoor orthogonal tests show that the highest UCS of 30.18 MPa is achieved at 28 days, with the main strength growth occurring from 0 to 7 days. The UCS increases with a lower soil-to-binder ratio, higher slaked lime content, and lower water-to-solid ratio. The optimal mix is a soil-to-binder ratio of 5.5, slaked lime content of 4.5%, and water-to-solid ratio of 0.26. When the soil-to-binder ratio is less than 8:2, the fluidity of the alkali-activated composite grouting material meets the specific construction requirements. The primary factor affecting fluidity is the soil-to-binder ratio, which decreases as the ratio decreases. The water-to-solid ratio also influences fluidity, increasing as this ratio rises. The addition of slaked lime has a minimal impact on fluidity. 3. The setting time of alkali-activated grout materials is primarily influenced by the soil-to-binder ratio, slaked lime content, and water-to-solid ratio. The soil-to-binder ratio is the main factor affecting the setting time, followed by the slaked lime content and the water-to-solid ratio. The setting time of alkali-activated grout materials shortens with a decrease in the soil-to-binder ratio, decreases with an increase in the slaked lime content, and increases with an increase in the water-to-solid ratio. To meet the setting time requirements for karst treatment in Shenzhen Metro, the soil-to-binder \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Specimen** & **Drill Location** & \begin{tabular}{c} **Strength Design** \\ **Requirements (MPa)** \\ \end{tabular} & \begin{tabular}{c} **Specimen Size (mm)** \\ **Caliber** \\ \end{tabular} & \
\begin{tabular}{c} **Compressive** \\ **Rigents** \\ \end{tabular} &
\begin{tabular}{c} **Average** \\ **Compressive** \\ **Strength (MPa)** \\ \end{tabular} \\ \hline TDB16-JCK01-1 & & & 70.3 & 69.2 & 3.0 & \\ TDB16-JCK01-2 & & \(\geq\)0.8 & 70.5 & 69.5 & 3.4 & 3.2 \\ TDB16-JCK01-3 & & & 70.6 & 69.3 & 3.2 & \\ \hline \hline \end{tabular}
\end{table} 
Table 13: The 28-day unconfined compressive strength test report for cement-based grouting material core samples. ratio of the alkali-activated composite grouting material should be set to 5:5. With a soil-to-binder ratio of 5:5, adjusting the slaked lime content and water-to-solid ratio within the scope of this study can achieve an appropriate setting time. 4. The curing mechanism of alkali-activated composites were derived by FTIR, SEM, and EDS. The UCS of alkali-activated grout materials mainly occurs by applying an alkaline activator to slag and fly ash. The alkali-activated composites' polymerization reaction generates gelling substances, such as N-A-S-H and C-A-S-H, which encapsulate and cement the soil particles in situ.