A platform for research: civil engineering, architecture and urbanism
A platform for research: civil engineering, architecture and urbanism
Water/clay ratio, clay porosity models and impacts upon clay transformations
Abstract The performance of bentonite used in geological repositories for radioactive waste may be impaired by long-term clay transformations to non-swelling minerals. Intrinsic to alteration processes is the role of water/clay ratio, defined in a bentonite-pore fluid system by (the inverse of) porosity. Water/(water+clay) mass ratios are low for both ‘total’ (≤0.25) and ‘free’ (≤0.05) porosities in compacted bentonite at the dry density envisaged for waste package buffers (≥1500kgm−3). A survey of laboratory experimental studies of clay alteration has shown that they have tended to focus on systems with dispersed clays at high water/(water+clay) mass ratios (≥0.75) because of experimental practicalities and a desire to accelerate reactions. New thermodynamic calculations have illustrated that the fluid/clay ratio can have an important impact not only upon the magnitude of alteration, but also upon the nature of the reaction path. Reaction of a pure Na-montmorillonite with cement pore fluids, a Fe-rich fluid and a KCl solution to attempt to simulate reaction of clay with cement/concrete, iron/steel, and potassium-rich fluids (to investigate the smectite to illite reaction path), respectively has shown that under fluid-dominated conditions (high water/clay ratio), clay alteration consisted of C–S–H solids, low-Si zeolites, and chlorite. Under clay-dominated conditions (low water/clay ratios), alteration typically consisted of high-Si zeolites, feldspar and Mg-corrensite. Consequently, it is of key importance that the most relevant water/clay ratio (‘porosity’) is used not only in geochemical calculations, but also in experimental systems.
Highlights Alteration in lab experiments with dispersed clays may not be typical of that in compacted clays. Modelling shows that water/clay ratio impacts upon the magnitude and nature of alteration. The most relevant water/clay ratio should be used in modelling and experimental systems.
Water/clay ratio, clay porosity models and impacts upon clay transformations
Abstract The performance of bentonite used in geological repositories for radioactive waste may be impaired by long-term clay transformations to non-swelling minerals. Intrinsic to alteration processes is the role of water/clay ratio, defined in a bentonite-pore fluid system by (the inverse of) porosity. Water/(water+clay) mass ratios are low for both ‘total’ (≤0.25) and ‘free’ (≤0.05) porosities in compacted bentonite at the dry density envisaged for waste package buffers (≥1500kgm−3). A survey of laboratory experimental studies of clay alteration has shown that they have tended to focus on systems with dispersed clays at high water/(water+clay) mass ratios (≥0.75) because of experimental practicalities and a desire to accelerate reactions. New thermodynamic calculations have illustrated that the fluid/clay ratio can have an important impact not only upon the magnitude of alteration, but also upon the nature of the reaction path. Reaction of a pure Na-montmorillonite with cement pore fluids, a Fe-rich fluid and a KCl solution to attempt to simulate reaction of clay with cement/concrete, iron/steel, and potassium-rich fluids (to investigate the smectite to illite reaction path), respectively has shown that under fluid-dominated conditions (high water/clay ratio), clay alteration consisted of C–S–H solids, low-Si zeolites, and chlorite. Under clay-dominated conditions (low water/clay ratios), alteration typically consisted of high-Si zeolites, feldspar and Mg-corrensite. Consequently, it is of key importance that the most relevant water/clay ratio (‘porosity’) is used not only in geochemical calculations, but also in experimental systems.
Highlights Alteration in lab experiments with dispersed clays may not be typical of that in compacted clays. Modelling shows that water/clay ratio impacts upon the magnitude and nature of alteration. The most relevant water/clay ratio should be used in modelling and experimental systems.
Water/clay ratio, clay porosity models and impacts upon clay transformations
Savage, David (author) / Liu, Jinsong (author)
Applied Clay Science ; 116-117 ; 16-22
2015-08-09
7 pages
Article (Journal)
Electronic Resource
English
Water/clay ratio, clay porosity models and impacts upon clay transformations
| Online Contents | 2015
Compression of unsaturated double-porosity clay
| British Library Conference Proceedings | 1995
| Engineering Index Backfile | 1929
Processing Bavarian clay to activated clay (bleaching clay)
| TIBKAT | 1948