Chemical and thermal stabilization of gypseous loess soils: Comparative study of natural environmental friendly materials (zeolite and gypsum) and cement

Gypseous loess soils exhibit complex and unpredictable behavior under environmental moisture variations, posing significant challenges in geotechnical engineering. Chemical stabilization and thermal stabilization are commonly used methods for stabilizing gypseous loess soils. Common materials such as cement and lime are expensive and unsustainable. This study investigates the stabilization of gypseous loess soils by zeolite as an environmentally friendly stabilizer to reduce carbon footprint and cement as a common stabilizer. Two distinct methods were employed to activate zeolite: sodium hydroxide and co-activation with cement. Gypseous soils were stabilized by 3 %, 5 %, 7 %, and 10 % stabilizing agents, and the performance of the stabilized soils was subsequently assessed under various environmental conditions such as wetting-drying by unconfined compressive strength, P-wave velocity, XRD, and SEM/EDAX tests. The results reveal that zeolite exhibits effective soil stabilization for low and high gypsum content, unlike cement, which demonstrates limitations in stabilizing soils. Cement stabilization leads to the formation of ettringite minerals, and increasing cement content increases ettringite formation. In contrast, stabilization with zeolite prevents the formation of ettringite minerals and enhances soil strength as the zeolite dosage increases. However, when zeolite partially replaces cement, soil strength improves up to a substitution level of 30 %; beyond this level, higher substitution ratios lead to a decrease in strength. The absence of ettringite in zeolite-stabilized soils, along with zeolite's unique ability to limit the leaching of dissolved gypsum, explains its superior performance during wetting-drying cycles compared to cement. In thermal stabilization, an increase in the percentage of gypsum present in the sample leads to an increase in uniaxial compressive strength. The study revealed that zeolite could effectively improve gypseous soil's properties and exhibit unique advantages over conventional cement stabilization, which is not an environmentally friendly and sustainable method. This study introduces a novel application of zeolite as a dual-activated, eco-friendly stabilizer for gypseous loess soils, offering a sustainable and technically effective alternative to traditional cement-based methods.