# Enhancing Clay Soil's Geotechnical Properties Utilizing Sintered Gypsum and Glass Powder
## 4 Conclusions  
The investigation focused on assessing the physical, mechanical, and microstructural alterations induced by varying proportions of GP (0%, 4%, 8%, and 12%) and sintered gypsum (0%, 5%, 10%, and 15%) at different curing durations (7, 28, and 56 days) and dry densities (1500 and 1700 kg/m\({}^{3}\)). The experimental program encompassed various tests, including UCS, wetting-drying cycle durability, UPV tests, and microstructural analyses via SEM and XRD. * The results showed strong relationships between the test variables and the samples' strength and stiffness. The strength and stiffness of the clay specimens were continuously enhanced by increased density and gypsum content, which is notable. Conversely, the influence of glass-powder content exhibited a non-uniform behavior, where the addition of 12% GP emerged as a critical threshold, revealing an unexpected shift in the trend toward improved strength and stiffness features compared to lower GP percentages;
* The study also found a strong link between the P/B index and UCS and \(G_{0}\). Normalization of the data enhanced the predictability of these properties, yielding valuable equations for predicting \(q_{u}\) and \(G_{0}\) for specific clay blends and facilitating efficient material design and assessment. Additionally, the durability assessment revealed that low GP content aggravated the durability factor of the specimens. The worst GP content for durability was 4%, while an increase to 12% GP led to a slight decrease in porosity and improved durability. The generated equation for the ALM proved to be an accurate tool for predicting the ALM for varying additive contents;
* Microstructural analyses via SEM and XRD clarified critical insights into the pozzolanic reactions induced by GP and sintered gypsum. SEM microphotographs unveiled the formation of ettringite, C-A-H, and C-S-H compounds, contributing significantly to enhanced strength, stiffness, and erosion resistance in the treated samples. Moreover, microstructural analyses highlighted the pronounced impact of the curing duration on the soil's structure, explaining its significant influence on mechanical behavior. Figure 12: SEM photos for tested samples with 8% GP and 5% gypsum content at (a) 56 curing days and (b) 28 curing days. In conclusion, this comprehensive study demonstrated the significant potential of glass powder and sintered gypsum as effective additives for improving the geotechnical characteristics of clay soil. The research findings offer valuable insights into the intricate relationships between test variables, strength and stiffness features, and microstructural transformations, providing a foundation for informed material design and application in geotechnical engineering practices. The established correlations and predictive equations are practical tools for optimizing additive compositions and assessing the mechanical performance of clay-based materials in diverse construction applications. Ultimately, this study contributes to advancing sustainable practices by repurposing waste materials, especially from EoL PV panels, and developing innovation in geotechnical engineering. All authors contributed to the study's conception and design. Material preparation, data collection, and analysis were performed by [PERSON] and A.E. The first draft of the manuscript was written by [PERSON] and A.I. and all authors commented on previous versions of the manuscript. All authors have read and agreed to the published version of the manuscript. The authors express their appreciation to the Office of Research Coordination and Support, Middle East Technical University, Northern Cyprus Campus, for funding this research group. The Scientific Research Project Code is FEN-20-YG-4. Not applicable. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to safety concerns. The authors greatly appreciate the discussions and help from [PERSON] from the Universida de Federal do Rio Grande do Sul.