Shrinkage behavior of compacted bentonite considering physicochemical effects

Abstract

Understanding the shrinkage behavior of bentonite considering physicochemical effects is important to assess the efficiency of buffer barriers in environmental geotechnical engineering. In this paper, shrinkage experiments were conducted on Na-bentonite specimens prepared with salt solutions at various concentrations. NMR and SEM tests were conducted to study the moisture distribution and structural evolution of specimens during the evaporation of water. After sample saturation, the porosity decreases as the pore water salinity increases due to the decreasing swelling deformation with pore water concentration during the saturation process. During drying, the shrinkage deformation of compacted bentonite is anisotropic, with larger axial strains than radial strains. At the fully dried state, the bentonite specimen prepared with distilled water is the densest due to the least crystalline salts in the specimen. At the microscale, as pore water salinity increases, pore water is distributed to smaller pores, and the microstructure is more aggregated. The saline effect on water retention and distribution is weakened as pore water evaporates, originating from physicochemical effects. The structure is also more aggregated after evaporation of pore water. Theoretically, the shrinkage behavior of Na-bentonite considering the influence of water salinity is well described from the perspective of an effective stress-based constitutive relationship.