Mechanical and durability performance of gypseous soils stabilized with zeolite and lime

Gypseous soils create engineering challenges because of their unpredictable behavior when exposed to moisture. In practice, traditional stabilizers such as cement and lime are widely used but are often costly and less sustainable. This study investigates natural clinoptilolite zeolite as an eco-friendly stabilizer for gypseous soils (10-40% gypsum content) compared to lime. Zeolite was activated by sodium hydroxide (mol/L) and in combination with lime. Stabilizers were applied at 3-10% dosages by dry weight. Mechanical performance (UCS, P-wave velocity) and durability under wetting-drying and freeze-thaw cycles were evaluated, supported by SEM/EDAX, XRD, and MIP analyses. Results show that zeolite stabilization outperforms lime across all gypsum contents in terms of strength and durability. For soils containing 40% gypsum, treated with 10% zeolite resulted in a 406% increase in UCS after 28 days of curing, compared to only a 129% increase for lime-treated samples. SEM/EDAX, XRD analyses show that zeolite addition suppresses ettringite formation, unlike lime-stabilized samples. When a small portion of lime was used with zeolite, the overall strength increased, although some ettringite still appeared. During wetting-drying cycles lime-stabilized soils failed before 9 cycles while zeolite-stabilized samples mostly maintain their integrity after 9 cycles. Post-cycle MIP revealed only 1-2% porosity increase for zeolite versus 4-5% for lime after wetting-drying cycles. The better performance of zeolite stabilization over lime is attributed to the absence of ettringite, as well as its ability to limit gypsum dissolution and leaching during wetting-drying cycles. Although zeolite shows slightly higher moisture sensitivity under freeze-thaw, it offers significant advantages over conventional calcium-based stabilization for sulfate-rich soils.