Title: The pore structure of compacted and partly saturated MX-80 bentonite at different dry densities
Authors : Keller, Lukas
Seiphoori, Ali
Gasser, Philippe
Lucas, Falk
Holzer, Lorenz
Ferrari, Alessio
Published in : Clays and Clay Minerals
Volume(Issue) : 62
Issue : 3
Pages : 174
Pages to: 187
Publisher / Ed. Institution : The Clay Minerals Society
Issue Date: 2014
License (according to publishing contract) : Licence according to publishing contract
Type of review: Peer review (Publication)
Language : English
Subjects : Map
Subject (DDC) : 620.11: Engineering materials
Abstract: Compacted MX-80 bentonite is a potential backfill material in radioactive-waste repositories. Pore space in MX-80 has been the subject of considerable debate. 3D reconstructions of the pore space based on tomographic methods could provide new insights into the nature of the pore space of compacted bentonites. To date, few such reconstructions have been done because of problems with the preparation of bentonite samples for electron microscopy. The nanoscale intergranular pore space was investigated here by cryo-Focused Ion Beam nanotomography (FIB-nt) applied to previously high-pressure frozen MX-80 bentonite samples. This approach allowed a tomographic investigation of the in situ microstructure related to different dry densities (1.24, 1.46, and 1.67 g/cm3). The FIB-nt technique is able to resolve intergranular pores with radii >10 nm. With increasing dry density (1.24 – 1.67 g/cm3) the intergranular porosity (>10 nm) decreased from ∼5 vol.% to 0.1 vol.%. At dry densities of 1.24 and 1.46 g/cm3, intergranular pores were filled with clay aggregates, which formed a mesh-like structure, similar to the honeycomb structure observed in diagenetic smectite. Unlike 'typical' clay gels, the cores of the honeycomb structure were not filled with pure water, but instead were filled with a less dense material which presumably consists of very fine clay similar to a colloid. In the low-density sample this honeycomb-structured material partly filled the intergranular pore space but some open pores were also present. In the 1.46 g/cm3 sample, the material filled the intergranular pores almost completely. At the highest densities investigated (1.67 g/cm3), the honeycomb-structured material was not present, probably because of the lack of intergranular pores which suppressed the formation of the honeycomb framework or skeleton consisting of clay aggregates.
Departement: School of Engineering
Organisational Unit: Institute of Computational Physics (ICP)
Publication type: Article in scientific Journal
DOI : 10.1346/CCMN.2014.0620302
ISSN: 0009-8604
URI: https://digitalcollection.zhaw.ch/handle/11475/2127
Appears in Collections:Publikationen School of Engineering

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