## 3 Results and Discussion
### SEM and EDX Analysis  
The SEM images of the gypseous soil-lime mixture after 90 days of curing showed that a significant amount of crystalline mineral needles (ettrinigite) had formed, as shown in Figures 20a and 21a. This resulted in a decrease in strength, a high capacity for swelling, and the destruction of the soil specimen's structure. The improvement in the gypseous soil samples was determined by measuring the Si/Al ratio (%) utilizing EDX to explain the strength development. Generally, an increase in the Si/Al ratio refers to the forming of a high number of Si-O-Si bonds. Consequently, the mechanical strength of the soil sample structural matrix was enhanced [45]. The Si/Al ratio in the (10% and 20%) L-G specimens obtained from the EDX pattern ranged from 1.06 to 1.12, which was low due to the ettrinigite formation and high porosity in the microstructure of the samples. The EDX pattern of the gypseous soil-lime mixture and its elemental composition is represented in Figures 20b and 21b. Figure 19: Flexural load curves of test gypseous soils treated with 20% mixture content after 7 and 28 days of curing. Figure 20: SEM photo and EDX spectrograph of stabilized gypseous soils after 90 days of curing: (**a**) SEM photo of 10L:10G and (**b**) EDX spectrograph of 10L:10G. Figures 22a and 23a show SEM observation images of the sulfate soil-M-G mixture, revealing spherical and irregular particles of magnesium silicate hydrate (MCH). The EDX information showed a slight increase in the Si/Al ratio (1.1 and 1.14) for M-G-stabilizer specimens with 10% and 20% when compared to the L-G specimens (1.06 and 1.12), which was probably due to the absence of ettrinigite and the formation of MSH product. Figures 22b and 23b, respectively, present the EDS spectrum and elemental composition of the gypseous soil-M-G mixture. Figure 21: SEM photo and EDX spectrograph of stabilized gypseous soils after 90 days of curing: (**a**) SEM photo of 20L:10G and (**b**) EDX spectrograph of 20L:10G. Figure 22: SEM photo and EDX spectrograph of stabilized gypseous soils after 90 days of curing: (**a**) SEM photo of 10M:10G and (**b**) EDX spectrograph of 10M:10G. Figures 24a, 25a and 26a show the SEM observation images of M-GGBS, M-RHA, and M-GGBS-RHA, respectively. In terms of particle shape and surface features, M-GGBS was quite different from M-RHA and M-GGBS-RHA. M-RHA and M-GGBS-RHA particles were spherical, as shown in Figures 25a and 26a. The particles had shiny surfaces without any dust covering them. The M-GGBS particles were rather angular, irregular in shape, and the presence of plate-shaped particles was evident (Figure 24a), which had rough, gritty surface textures. Figures 24a, 25a and 26a show the surface morphologies of the soil-M-GGBS, -M-RHA, and -M-GGBS-RHA specimens after 90 days of curing. As indicated, no ettrinigite formation was observed. This proves that the addition of M with GGBS and RHA as a stabilizing agent contributed to the formation of CSH gel to a significant degree. The presence of some crystalline structures, such as MSH (magnesium silicate hydrate), was also observed. The pozzolanic activity occurring between M, GGBA, and RHA as a stabilizer and clay was attributed to the formation of CSH gel. Based on the results derived from the EDX spectrum, the highest Si/Al ratios (1.23, 1.59, and 1.41) were observed in the 7.5M-12.5 RHA, 5M-15 GGBS, and 5M-12.5 GGBS-2.5 RHA samples, respectively. This improvement was due to GGBS and RHA dissolving in an alkaline activator to generate extra soluble alumina and silica, which increased the Si/Al ratio of the specimen, leading to the complete activation of the particles and producing calcium-alumino-silicate hydrate (CASH) in the matrix. Figures 24b, 25b and 26b show the EDS spectrum and elemental composition of the gypesous soil-M-GGBS, -M-RHA, and -M-GGBS-RHA mixtures, respectively. Figure 23: SEM photo and EDX spectrograph of stabilized gypesous soils after 90 days of curing: (**a**) SEM photo of 20M:10G and (**b**) EDX spectrograph of 20M:10G.