Compaction and sealing properties of bentonite/claystone mixture: Impacts of bentonite fraction, water content and dry density

Abstract

Compacted block composed of 70% crushed Callovo-Oxfordian claystone and 30% MX80 bentonite has been proposed as a possible material for sealing a potential repository of radioactive waste. In this study, the compaction property of the bentonite/claystone mixtures with various bentonite fractions and water contents were first investigated to define an appropriate protocol for the fabrication of blocks. Results show that the increase of bentonite fraction decreased the overall compressibility and the achievable dry density at a given stress. As the water content increased, the compressibility at a relatively low vertical stress increased due to the increasing deformability of aggregates and the decreasing inter-aggregate friction; contrarily, at a high vertical stress, a lower compressibility was observed for the samples with a higher water content because a larger stress was required to squeeze water within aggregates. During demoulding, the required demoulding pressure increased with the increase of bentonite fraction and decreased with the increasing water content. Then, to assess the suitability of the material, the swelling pressures and hydraulic conductivities of the compacted blocks were determined. It was found that the swelling pressure increased and the hydraulic conductivity decreased with the increases of bentonite fraction and dry density. By contrast, as the water content increased, more water was intercalated in the interlayer spaces and the inter-aggregate pore volume decreased, resulting in reductions of the swelling pressure and hydraulic conductivity. • Compressibility, rebound property, demoulding pressure, swelling pressure, and hydraulic conductivity were investigated; • Effects of bentonite fraction, dry density and water content were identified; • The effect of water content on the compressibility depended on vertical stress; • The increase of water content reduced the swelling pressure and the hydraulic conductivity.