# Enhancing Clay Soil's Geotechnical Properties Utilizing Sintered Gypsum and Glass Powder
## 3 Results and Analysis
### Microstructural Analysis  
XRD and SEM analyses were performed to provide a comprehensive microstructural assessment in this investigation. Figure 9 presents the XRD findings, encompassing 12 distinct samples characterized by two levels of GP content (0% and 8%) and two gypsum content variations (5% and 15%) across curing durations of 7, 28, and 56 days, maintaining a density of 1700 kg/m\({}^{3}\). The predominant phases identified in these samples are quartz (Q) and calcite (C), with silicon (Si) and alumina (Al) present as minor constituents. The reflections observed indicate the presence of smectite, illite, and a chlorite-kaolinite mix within the phyllosilicates, suggesting a complex mineralogical composition.  
Notably, the XRD patterns exhibit a visible peak (silicon) between the two prominent peaks (quartz and calcite). This intermediary peak demonstrates an increasing trend from samples 1 to 3, shown in a red oval (Figure 9), with the extension of curing duration for samples lacking GP, whereas the converse is observed for samples containing GP from samples 10 to 12. This distinct variation is attributed to the heightened silicon concentration inherent in the glass powder. Across the 7- to 56-day curing period, a pronounced rate of pozzolanic reactions involving silicon was observed within the samples incorporating GP, explaining the observed trends in the XRD patterns.  
Figure 8: The associations between the ALM and the modified P/B index for all curing durations and different amounts of sintered gypsum with (**a**) 0% GP, (**b**) 4% GP, (**c**) 8% GP, (**d**) 12% GP, (**e**) all GP-improved samples in one chart, and (**f**) all normalized ALM for GP-improved samples with additives in one chart for both samples’ dry densities.  
Figure 9: XRD results for tested samples’ GP content of 0 and 8 percent and gypsum content of 5 and 15 percent at different curing days, at a density of 1700 kg/m\({}^{3}\).  
The SEM microphotograph in Figure 10 illustrates a sample containing 15% gypsum content, subjected to a 28-day curing period, and without glass powder, showcasing crucial features influencing the strength properties of clay soil. Needle-like structures, representing ettrin  
Figure 10: SEM photo of treated sample, which includes major structures.  
Figure 12a shows a big difference between a sample with the same additives cured for only 28 days (Figure 12b) and one cured for 56 days (Figure 12a). The difference is that the sample in Figure 12a has more pores and clear particle separation. This observation supports the different behavior exhibited in Figures 3c and 4c. Specifically, the distinct soil structures shown in Figure 12b contribute to enhanced strength and are more significant than the sample in Figure 12a. Differences in soil structure and composition due to varying curing periods show their effects on strength and stiffness. This highlights a considerable association between curing time, soil microstructure, and the resulting mechanical behavior in specific blends.  
Figure 11: SEM microphotographs of samples with 8% GP and 15% gypsum content at (**a**) 7 curing days, (**b**) 28 curing days, (**c**) 56 curing days, and (**d**) samples with 0% GP and 15% gypsum content at 56 curing days.