Microstructural evolution of buffers

A buffer consisting of blocks of compacted Na bentonite powder absorbs wate r by which the grains expand and exfoliate. yielding clay gels that occupy the voids between them. The expandability of the grains and thereby the bul k density and hydraulic conductivity depend on the density of the gel filli ngs and hence on the grain density. Since the porewater electrolytes affect the pore size distribution of the gels they have an impact on the hydrauli c conductivity as well. The density distribution in matured MX-80 clay dete rmines both the hydraulic conductivity and the ion diffusion transport as w ell as the swelling pressure. It can be evaluated from micrographs covering a sufficiently large fraction of a cross-section of the clay. (C) 1999 Els evier Science B.V. All rights reserved.