Pore fluid chemistry effects on homogenization of compacted bentonite specimen with technological voids

During the construction and operation of a geological repository, with the infiltration of groundwater, highly compacted bentonite blocks hydrate and swell freely to fill up technological voids and gradually turn to hydrate under a constant-volume condition. Additionally, these processes are inevitably influenced by the pore chemistry of the groundwater. Therefore, it is necessary to investigate the hydration process of compacted bentonite under the combined influences of chemistry and technological voids. In this study, hydration tests were conducted on compacted GMZ bentonite with artificial annular gaps with infiltration of deionized water, 1 M NaCl, and 1 M CaCl2 solutions, respectively. Variation of swelling pressure and hydraulic conductivity with time was measured during hydration. The distribution of dry density, water content, and microstructure feature in the specimens was determined. Results show that sealing of the technological voids resulted in a heterogeneous distribution of dry density and water content of the barrier formed. Compared to that of deionized water, infiltration of salt solutions weakened swelling capacity and increased the permeability, leading to more significant heterogeneity in dry density distribution. During hydration, the specimen could be divided into swelling and compression zones according to variations of dry density with time. The boundary between the swelling and compression zones moved with hydration time. Evolutions of microstructure features were also affected by solutions. For specimens infiltrated with NaCl, more macro-pores and meso-pores were observed, while for CaCl2 infiltration, more undetectable pores and less meso-pore pores could be detected. After the tests, all the specimens were still in non-homogeneous states.