## 4 Microscopic Tests of Alkali-Activated Grout Materials
### Microstructural Properties  
The properties of alkali-activated grout materials at a macroscopic level are determined by its microstructural characteristics. These characteristics comprise variations in particle size, shape, micropore features, distribution patterns, as well as the modes of particle contact, compositional makeup, and interconnectivity methods. However, the microstructural evolution and features of alkali-activated grout materials are not discernible to the naked eye. Therefore, SEM is necessary to investigate them. The aim of this approach is to uncover the mechanisms of strength formation and S/S principles based on microstructural attributes. Figure 15 shows the SEM and EDS test results for in situ soil in Shenzhen, alkali-activated composites, and alkali-activated grout materials.Alkali-activated composites consist of oxygen, silicon, and aluminum as the three elements with the highest content, with mass fractions of 41.5%, 33.9%, and 14.3%, respectively. The addition of slaked lime as an alkaline additive in alkali-activated grout materials increases the calcium content. As a result, the four elements with the highest content are oxygen, calcium, silicon, and alu  
Figure 14: FTIR test results. minum, with mass fractions of 40.2%, 27.9%, 15.3%, and 14.3%, respectively. Observations made using SEM and EDS of both in situ soil and alkali-activated grout materials reveal that the in situ soil mainly consists of disordered and loosely arranged particle units. These particles are interconnected through agglomeration, contact cementation, and micropores between particles, resulting in a loose soil structure with limited strength. In contrast, soil treated with alkali-activated composite S/S undergoes a significant transformation. The previously loose particle units are encapsulated and firmly cemented by alkali-activated composites, establishing a robust network structure among fine soil particles, granules, and flocculants, forming larger-scale agglomerates. The relationship between these agglomerates and the cementitious structure becomes tighter and more uniform, significantly enhancing the microstructure and markedly reducing the voids between soil particles. The observation of alkali-activated grout materials under a 250\(\times\) microscope reveals a smooth cross-section interspersed with larger particles (shown in Figure 16). These particles,  
Figure 15: SEM test results at 1000-times magnification and EDS test results for different materials. originating from the in situ soil's sand and gravel, do not participate in the chemical reaction. However, the alkali-activated composites immobilizes them, incorporating them into the structure as a coarse aggregate framework, which in turn contributes to the strength of the grouting materials. However, cracks are visible on the cross-sections of both the solidified soil and the alkali-activated composites (shown in Figure 15b,c). This is due to the introduction of excess water to maintain the fluidity of the grouting materials as a grouting material. After the alkali activation reaction has completed in the alkali-activated composites system, any remaining water that did not participate in the reaction or evaporate will remain within the specimen. As the system loses moisture, the previously water-filled pores become visible, resulting in cracks. It is important to note that the EDS test provides qualitative evidence of the formation and production of substances in polymer-solidified soils, rather than quantitative indicators. In untreated soils, the atomic percentage of silicon (Si) elements is relatively high due to the abundance of SiO\({}_{2}\) in the soil. The presence of calcium (Ca) in alkali-activated grout materials is attributed to the addition of slaked lime, which retains calcium in the soil. The introduction of alkali-activated composites material further increases the concentration of silicon and aluminum elements in the soil.