This paper attempts to enhance the mechanical properties of weak kaolin soil, partially replaced by calcined sepiolite (CS). The CS is highly reactive due to its high concentration of CaO and SiO2 oxides. This characteristic is chemically required to form polymeric bonds, which basically improve the mechanical properties of weak soil. Systematic analytical methods were employed to distinguish the textural and mineralogical properties of soil, sepiolite, CS, and new products. A series of geotechnical tests were conducted to examine the effects of varying percentages of CS admixture on Atterberg limits, standard Proctor test, and unconfined compressive strength (UCS). Samples were cured until the ages of 3, 7, and 28 days. The maximum UCS value was obtained after 28 days of curing when 3 wt% of CS was mixed with the primary soil. Also, replacing 3 wt% of CS lowered the soil plasticity index (PI) to about 60%. Further, incorporating 5 wt% CS into the soil increased the modulus of elasticity by 6.82 times compared to the control sample. Microstructural investigations indicated that the strength enhancement of kaolin soil was yielded by filler effects and chemical reactions/exchanges, including flocculation, carbonation, and solid solution reactions. Collectively, the results showed that CS could effectively enhance the strength properties of kaolin soil due to its high specific surface area (SSA), reactivity, and alkalinity.

The importance of physical, chemical, and mineralogical properties in selecting soils stabilized by activated natural pozzolan (ANP) was demonstrated. Five soil banks were identified, and two were selected: B1Z due to its SiO2 content and the presence of Montmorillonite and B3M for its granulometry and plasticity. Electrical con- ductivity (EC) was measured to monitor reactivity by testing two stabilizers, ANP and lime. Soils with 2.5% ANP exhibited higher EC than those with 10% lime. Compressive strength (CS) was analyzed. Soils with 10% ANP recorded higher CS than those with lime. Chemical and mineralogical properties were more relevant than physical ones in selecting soils stabilized through ANP.