Permeability swelling bentonite

Bentonite is the name for a hydrous aluminum silicate comprised principally of the clay mineral montmorillonite, notable for its ability to swell in water and to form a very low-permeability seal." It is available as powder, granule (chip), or pellets. Powder and granule sizes are produced by processing after mining. Bentonite powder... 

Bentonite rocks have many uses in the chemical and oil industries and also in agriculture and environmental protection. The usefulness of bentonite for each of these applications is based on its interfacial properties. These properties are determined by geological origin, chemical and mineral composition (especially montmorillonite content), and particle size distribution, and they include the specific surface area (internal and external), cation-exchange capacity (CEC), acid-base properties of the edge sites, viscosity, swelling, water permeability, adsorption of different substances, and migration rate of soluble substances in bentonite clay. 

Parameter improvements (reduced rock mass permeability and rock mass thermal expansion by the KTH/SKI team, and increased thermal expansion coefficient and reduced swelling pressure constant of the buffer by JNC team) -Inclusion of the sealing of rock fractures by penetrating bentonite by the KTH/SKI team, which can explain the uniform (axisymmetric) wetting of the bentonite. 

The engineered buffer used in deep geological disposal sites is often pure bentonite or a bentonite - sand mixture. Bentonite is a material with very low permeability and swelling properties. The swelling properties are used as a seal against water intrusion. 

Figure 8 shows the evolution of the swelling during saturation under a vertical load of 1 MPa at two different temperatures for samples of initial dry density 1.70 g/cm . The increase of water permeability and the decrease of swelling capacity of the bentonite with temperature can be observed. 

This example is to test the swelling effects under capillary pressures up to 10 Pa occurring in extremely low-permeable bentonite materials. For this purpose, a simple 1-D case is set up. A one meter long bentonite column is heated on the left hand side. Element discretization length is 0.01m. The initial conditions of the system are atmospheric gas pressure, full liquid saturation and a temperature of 12°C. The heater has a constant temperature of 1(X) C. Flow boundary conditions on the left side are gas pressure of 10 Pa and 15% liquid saturation. On the right side we have atmospheric pressure, full liquid saturation and no diffusive heat flux. As a consequence, a typical desaturation process of bentonite is triggered. The complete set of initial and boundary conditions and the material properties for this example was described in detail by Kolditz De Jonge (2003). 

In case of constrained swelling, the potential of interlayer porosity change turns out to be swelling pressure owing to the further swelling compaction effect. The effective void ratio (interparticle porosity) decreases with the increase of the moisture content, hence results in the decrease of the bentonite permeability. 

Nishimura, T. 2001. Swelling pressure of a compacted bentonite subjected to high suction, pages 109-114. Clay Science for Engineering, Proceedings of the international symposium on suction, swelling, permeability and structure of clays - Is-Shizuoka. Balkema, Rotterdam. 

Up to now two-phase two-component flow under non-isothermal conditions and coupled THM (one-phase flow) have been implemented in this code and validated against different experimental results. For the modelling of water penetration into unsaturated bentonite or clay, a swelling model is available in the code. If the test sample is confined within a constant volume, then a swelling pressure will build up which causes changes to the pore structure and reduces the porosity. A small change in porosity can, however, create a considerable reduction in permeability. 

The buffer in this experiment is made of bentonite blocks. Because there are gaps of up to 30 mm at the upper contact to the host rock the swelling of the blocks is not hindered at these blocks. The differences in back pressure at each block leads to different changes of the pore structure and permeability at each block. 

Mixtures of naturally deposited sand, medium plasticity clay, and bentonite with recycled rubber produced composite materials suitable for use in ground improvement (Becker and Vrettos, 2011). Mechanical properties of soils relevant to the application of such composites in geotechnical engineering problems were investigated. The compaction, permeability, compressibility, and flexural and shear strength were determined for typical mixtures along swelling of the bentonite-mbber mixtures. 

Bentonite is the key material of the EBS, which retards the transport of radionuclides. This is because (1) it is an extremely low permeable material, which prevents movement of water and eventually radionuclides, (2) it seals cracks in the rock mass because of its swelling properties, and (3) it shows a high ability for cation adsorption, therefore it can retard the migration of radionuclides. 

OsCARsoN, D. W., Dixon, D. A. Gray, M. N. 1990. Swelling capacity and permeability of an unprocessed and a processed bentonitic clay. Engineering Geology, 28, 281-295. 

Here poly(ethyl aerylate) (PEA)/clay nanocompsite as the first example of rubbery polymer/elay nanocomposite synthesized by in situ emulsion polymerization is reported. The clay used is bentonite having extremely strong swelling characteristies in water. The resulting nanocomposite emulsion is directly cast to form film without coagulation process. This study focuses on microstructure, thermal and meehanical properties, and gas barrier permeability of the final PEA/clay nanoeomposites. 

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