Study on desiccation -shrinkage characteristic and shrinkage cracking mechanism of bentonite and sand mixtures

As a buffer material for nuclear waste storage, bentonite-sand mixture tends to shrink under high temperature and suction conditions, which affects the safety operation of engineering projects. Therefore, it is of great practical significance to study the shrinkage characteristics of bentonite-sand mixture. This paper investigates the influence of sand content and compactness on desiccation shrinkage characteristic of saturated compacted sample of bentonite-sand mixtures placed at custom designed thermostatic chamber. It is shown that water evaporation in the process of desiccation can be divided into deceleration and residual stages. In the former stage, the water migration is dominated by the dry density, while the final residual water content is mainly affected by bentonite content. An increase in the initial dry density and decrease in the bentonite content can coordinate the deformation of the mixture and hence reduce the anisotropy of shrinkage deformation. The bentonite content M and the initial dry density rho are the key physical parameters affecting the drying-shrinkage process and have a close correlation to the Cornelis model parameters and the final pore ratio eo. At a given dry density, the microstructures of compacted samples tend to densify as M decreases, thereby effectively inhibiting the development and evolution of cracks during the drying-shrinkage process.