Abstract: Compacted bentonite is a crucial material used in high-level waste engineering barriers as a buffer/backfill material. However, the high plasticity of bentonite and uneven distribution of water can result in drying shrinkage of the compacted bentonite, which negatively impacts the quality of buffer/backfill blocks. To address this issue, a new method called the alcohol method has been proposed as an alternative to the traditional water spray method. In the alcohol method, the ethanol content ranges from 5% to 35%, unlike the water spray method. Several factors were considered to evaluate the feasibility of the alcohol method in adjusting the water content of compacted bentonite. These factors included mixing efficiency, mass loss rate, agglomerate content, strength, shrinkage cracks of compacted samples, drying efficiency, and expansibility. The results demonstrated that as the ethanol content increased, at the same liquid content the mixing efficiency significantly improved, while the mass loss rate and agglomerate content decreased noticeably. Relationships between agglomerates, dry-shrinkage cracks, and the quality of compacted samples were also observed. The compacted samples produced using the alcohol method exhibited more homogeneous soil density in the compacted direction and significantly reduced dry-shrinkage cracks compared to samples produced using the water spray method. Additionally, the shear strength and expansion characteristics of air-dried samples adjusted by the alcohol method were similar to those adjusted by the water spray method. The alcohol method, along with the findings from this study, provides valuable insights for the production of buffer/backfill materials in high-level waste disposal.

Key words: bentonite, buffer/backfill material, alcohol method, water content, agglomerates