The effect of thermal stabilization process on mineralogy, morphology and engineering properties of red soil in southern Iran

Red soil from southern Iran is widely utilized in structural foundations, road construction, brick making, and high-level landfills. When subjected to heat, soils undergo significant changes in their physical, mechanical, and microstructural characteristics. This study aims to investigate the impact of temperature on the engineering properties of red soil, with a focus on the microstructural perspective. To achieve this, we conducted a series of macrostructural tests (unconfined compressive strength, gradation, weight loss, and permeability) and microstructural analyses (pH, electrical conductivity, X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM)) on Iran red soil samples. The samples were subjected to temperatures ranging from 100 ℃ to 900 ℃ for 2 h. The key findings of this research highlight significant changes in the engineering properties of red soil, particularly at temperatures between 500 ℃ and 900 ℃. Microstructural observations revealed various alterations, including dehydration, dehydroxylation, changes in soil texture, formation of cavities, and increased porosity within the soil structure. Notably, at high temperatures (approximately 900 ℃), new crystalline minerals such as Gehlenite, Diopside, Anorthite, Sanidine, and Mullite were formed. The unconfined compressive strength values exhibited a remarkable increase, reaching nearly 20 times, from 0.12 MPa to 2.3 MPa, concurrently with the formation of new compounds, including the α -β quartz transition. Overall, this study sheds light on the profound effects of temperature on the engineering properties of red soil in southern Iran, offering crucial insights for its practical applications in construction and related fields.