The use of microfocus X-ray computed tomography in characterising the hydration of a clay pellet/powder mixture

Geet, Maarten Van; Volckaert, G.; Roels, Staf

doi:10.1016/j.clay.2004.12.007

Cited by 79 publications

(37 citation statements)

References 20 publications

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“…However, much more powerful X-rays provided by synchrotron radiation and microfocus X-ray systems have recently allowed moving a step forward in the analysed domain and going to micrometric scale, narrowing the gap between meso and microstructural techniques , Takahashi et al 2006. Recent applications of these mesostructural techniques in unsaturated soils have been devoted to the monitoring of hydro-chemo-mechanical processes (Comina et al 2008), to the detection of desiccation cracks (Gebrenegus et al 2006;Mukunoki et al 2006), to the visualisation of diffusion/hydration phenomena and to the study of fluid movements (Rolland et al 2003;Rolland et al 2005;Van Geet et al 2005;Rodríguez-Rey et al 2006;Carminati et al 2006;Koliji et al 2006a).…”

Section: Introductionmentioning

confidence: 97%

Microstructure Investigation in Unsaturated Soils: A Review with Special Attention to Contribution of Mercury Intrusion Porosimetry and Environmental Scanning Electron Microscopy

2008

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With the advent of modern microstructural testing techniques and microstructure based constitutive models the microstructural characterisation of soils is gaining prominence. This paper reviews the history of microstructure investigation in unsaturated soils and discusses the engineering significance of this research to date. After a brief overview of the main microstructural techniques, the paper focuses on the evaluation of the current state of use and the development of two widely used techniques to study the microstructure of partially saturated soils, namely mercury intrusion porosimetry and the environmental scanning electron microscopy. The details of these techniques, their advantages and limitations, are first covered, followed by the presentation of selected test results. These results highlight the use of these techniques for understanding different hydro-mechanical behavioural features observed at macroscopic scale. Specifically, the paper shows the use of these techniques to explore the fundamental properties of water retention characteristics, water permeability, and micro and macrostructural interactions along different hydro-mechanical paths.

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Section: Introductionmentioning

confidence: 97%

Microstructure Investigation in Unsaturated Soils: A Review with Special Attention to Contribution of Mercury Intrusion Porosimetry and Environmental Scanning Electron Microscopy

2008

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“…Direct observations of the hydration process were obtained by Van Geet et al (2005) using microfocus X-ray computed tomography. A 50/50 powder-pellet mixture of FoCa clay at a dry density of 1 .…”

Section: Basic Features Of the Behaviour Of Powder-pellets Mixtures Dmentioning

confidence: 99%

Hydromechanical behaviour of a heterogeneous compacted soil: experimental observations and modelling

Gens¹,

Valleján²,

Sánchez³

et al. 2011

Géotechnique

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127

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The paper describes a theoretical and experimental study of the coupled hydromechanical behaviour of a compacted mixture of bentonite powder and bentonite pellets intended as sealing material in underground repositories for nuclear waste. One of the main advantages of the use of powder/pellets mixtures is the reduction of the compaction effort required to achieve the value of average dry density necessary to attain the required swelling potential. However, the heterogeneous fabric of the material requires special approaches in order to describe adequately its behaviour during hydration. A double porosity formulation is presented to account for the presence of two distinct structural levels in the material. Hydraulic equilibrium between the two porosities is not assumed; instead a water exchange term between them is postulated. The formulation is applied to the modelling of a number of one-dimensional swelling pressure tests performed in the CEA (Commisariat à l'Énergie Atomique, France) and CIEMAT (Spain) laboratories. A very satisfactory quantitative description of the experimental observations is obtained that includes a number of complex behaviour features such as size effects and non-monotonic development of swelling pressures. Some microfabric observations using X-ray tomography and mercury intrusion porosimetry lend support to the conceptual approach adopted. The formulation is then applied to the analysis of a long-term large-scale sealing test performed at the Hades underground facility in Belgium, using the same set of hydraulic and mechanical parameters employed in the modelling of the laboratory tests. Although the field observations exhibit a much higher degree of scatter, the basic behaviour of the field sealing test is satisfactorily simulated. A formulation that incorporates basic features of the microfabric of the mixture is thus able to span successfully over a large range of space and time scales.

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“…Owing to operational convenience, pellet-based materials have been considered as an alternative to compacted blocks [2][3][4][5]. Pellets are emplaced in the galleries as a granular material.…”

Section: Introductionmentioning

confidence: 99%

Effects of the initial granular structure of clay sealing materials on their swelling properties: experiments and DEM simulations

Darde

Tang

Roux

et al. 2020

EPJ Nuclear Sci. Technol.

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Pellet-based expansive clay materials are considered as a sealing material for closing the galleries in radioactive waste disposal concepts. In repository conditions, the granular mixture progressively homogenises upon hydration by the host rock pore water. The present study focuses on the material behaviour before homogenisation. A grain-scale experimental characterisation is first performed in the laboratory. A model describing the hydromechanical behaviour of a pellet is proposed based on the experimental results. Then, suction-controlled swelling pressure tests are performed in the laboratory. Using Discrete Element Method (DEM) and the model proposed for a single pellet, the tests are successfully simulated. It is highlighted that (i) the swelling pressure evolves in two phases in the investigated suction range, controlled by the granular structure of the mixture; (ii) wall effects at the laboratory scale affects the material response; (iii) measurement variability associated to the sensor diameter is non-negligible; (iv) DEM is a valuable tool able to provide insight into the material behaviour.

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The use of microfocus X-ray computed tomography in characterising the hydration of a clay pellet/powder mixture

Cited by 79 publications

References 20 publications

Microstructure Investigation in Unsaturated Soils: A Review with Special Attention to Contribution of Mercury Intrusion Porosimetry and Environmental Scanning Electron Microscopy

Microstructure Investigation in Unsaturated Soils: A Review with Special Attention to Contribution of Mercury Intrusion Porosimetry and Environmental Scanning Electron Microscopy

Hydromechanical behaviour of a heterogeneous compacted soil: experimental observations and modelling

Effects of the initial granular structure of clay sealing materials on their swelling properties: experiments and DEM simulations

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