# Experimental Investigation and Mechanism of Fly Ash/Slag-Based Geopolymer-Stabilized Soft Soil+
## 4 Conclusions  
Soft soils were stabilized using a geopolymer, and the effects of the various factors on the stabilization of the soft soils were investigated through indoor tests. In addition, in-depth analysis of the water stability and resistance to wet-dry cycles of the stabilized soils was conducted. Microscopic analysis of the stabilized soils was carried out to reveal the principles and mechanisms corresponding to the macroscopic mechanical properties. Based on the results of this study, the following conclusions can be drawn.  
1. The application of FA/slag-based geopolymer as a curing agent to stabilize soft soil can significantly improve the strength of the soil. When the geopolymer content was fixed, the slag, alkali activator content, and the modulus of the alkali activator had significant effects on the stabilization of the soil. The strength initially increased and then decreased as the content and modulus of the alkali activator increased. The optimum mix proportion of geopolymer-stabilized soil required a modulus of the alkali activator of 0.6, a content of the alkali activator of 6%, and a slag-to-fly ash ratio of 1:1.
2. An FA/slag-based geopolymer can effectively improve the water stability of silty soft soils. The geopolymer-stabilized soil test specimens were intact after water immersion, without any peeling or cracking phenomena, and the strengths of the soaked specimens were significantly lower than those of the test specimens without water immersion.
3. The incorporation of an FA/slag-based geopolymer significantly improved the resistance of the soft soils to wet-dry cycles. The loss of strength of the specimen decreased as the geopolymer content increased. The specimens with geopolymer contents of 20% and 25% exhibited almost no peeling of the outer skin after six cycles.
4. Based on microscopic analysis, the cementing substances in the geopolymer-stabilized soil mixture system were identified as C-S-H and N-A-S-H. The main mechanism by which the geopolymer reinforced the soft soil was as follows. Some of the FA and slag particles did not react with the compound activator, but their smaller particles effectively filled the large voids between the soil particle and reduced the porosity of the soil. The geopolymerization reaction produced a large number of gelling products, which encapsulated and bonded the soil particles, forming a denser structure and increasing the compressive strength of the stabilized soil.  
Conceptualization, D.W.; methodology, Z.Z.; software, K.C.; validation, Z.Z. and L.X.; formal analysis, Z.Z.; investigation, Z.Z.; resources, Z.Z.; data curation, L.X.; writing--original draft preparation, Z.Z.; writing--review and editing, Z.Z.; visualization, D.W. and Z.Z.;  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Phase (yuan rmb/ton)** & **OPC** & **Geopolymer** \\ \hline Solid & P.O. 42.5: 500 & FA: 32.27; GGBFS: 161.37; NaOH: 146.91 \\ Liquid & Water: 0 & Na\({}_{2}\)SiO\({}_{3}\): 106.72; Water: 0 \\ Total cost & 300 & 447.27 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Assessment of the cost of two types of soft soil stabilizers.  
supervision, D.W.; project administration, K.C.; funding acquisition, D.W. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant number 51678533.  
Not applicable.  
Data Availability StatementDetails on all data supporting the reported results can be obtained in Tables 1-7 and Figures 1-13, this original manuscript.  
The authors declare no conflict of interest.