A sand–Na–bentonite mixture is widely used as engineering barrier material, which usually possesses hydraulic conductivity below the regulatory limit (10⁻⁷ cm/s). However, in some areas natural Na–bentonite is not readily available; instead, an abundantly prevailing local expansive soil can be an alternative. This study assesses the suitability of a local expansive soil mixed with zeolite, easily obtained from natural reserves in Turkey, proposed to be used as a landfill liner in a semi-arid climate. The choice of zeolite is due to its already well-understood high adsorption capacity for heavy metals as well as its pozzolanicity. The volume change, strength, and hydraulic conductivity characteristics were studied with respect to durability through ageing. When an expansive soil to zeolite ratio of 0.5 was used, the results indicated improved properties with curing. Swell potential was observed to decrease by 85% within a 90 day curing period, while a 30%–34% reduction was noted in shrinkage and compressibility characteristics. The hydraulic conductivity was observed to remain below the regulatory limit under all confining pressure ranges studied, provided the curing time was at least 90 days. Moreover, the mixture attained improved strength characteristics with time, and proved to be sustainable over the period studied. Therefore, it was concluded that expansive soil mixed with zeolite could be a good alternative to sand–Na-bentonite, mainly in developing areas of growing population and environmental degradation.