Cement is a traditional binder commonly used with soil to enhance its mechanical properties or to create plastic barriers, such as cement-bentonite slurry walls. Due to its relatively high cost, consumption of natural resources, and significant carbon footprint, cement production is one of the most unsustainable binders. Recently, there has been considerable progress in developing more sustainable binders, with a growing focus on environmental sustainability. One promising alternative is alkali-activated materials derived from industrial by-products, which generally have a minimal environmental impact. Several studies are exploring the potential for alkali-activated materials to replace cement. An ongoing project funded by the Italian Ministry is investigating the use of geopolymer, created from the alkaline activation of silica-rich waste material from stone processing, as a substitute for traditional cement in bentonite-based mixtures used to construct plastic barriers. The project aims to identify an optimal bentonite-geopolymer mixture that leads to mechanical and hydraulic properties useful for geotechnical and geoenvironmental applications. To achieve this, mechanical and permeability tests have been conducted on different mixtures, and their performance data compared with existing literature on cement-bentonite mixtures.