Nature of the clay - cation bond affects soil structure as verified by X-ray computed tomography

Soil Research ◽  
2012 ◽  
Vol 50 (8) ◽  
pp. 638 ◽  
Author(s):  
Alla Marchuk ◽  
Pichu Rengasamy ◽  
Ann McNeill ◽  
Anupama Kumar
Keyword(s):  
Computed Tomography ◽  
Hydraulic Conductivity ◽  
Zeta Potential ◽  
Structural Stability ◽  
Structural Parameters ◽  
Pore Connectivity ◽  
X Ray ◽  
Clay Dispersion ◽  
X Ray Computed ◽  
Cation Ratio

Non-destructive X-ray computed tomography (µCT) scanning was used to characterise changes in pore architecture as influenced by the proportion of cations (Na, K, Mg, or Ca) bonded to soil particles. These observed changes were correlated with measured saturated hydraulic conductivity, clay dispersion, and zeta potential, as well as cation ratio of structural stability (CROSS) and exchangeable cation ratio. Pore architectural parameters such as total porosity, closed porosity, and pore connectivity, as characterised from µCT scans, were influenced by the valence of the cation and the extent it dominated in the soil. Soils with a dominance of Ca or Mg exhibited a well-developed pore structure and pore interconnectedness, whereas in soil dominated by Na or K there were a large number of isolated pore clusters surrounded by solid matrix where the pores were filled with dispersed clay particles. Saturated hydraulic conductivities of cationic soils dominated by a single cation were dependent on the observed pore structural parameters, and were significantly correlated with active porosity (R2 = 0.76) and pore connectivity (R2 = 0.97). Hydraulic conductivity of cation-treated soils decreased in the order Ca > Mg > K > Na, while clay dispersion, as measured by turbidity and the negative charge of the dispersed clays from these soils, measured as zeta potential, decreased in the order Na > K > Mg > Ca. The results of the study confirm that structural changes during soil–water interaction depend on the ionicity of clay–cation bonding. All of the structural parameters studied were highly correlated with the ionicity indices of dominant cations. The degree of ionicity of an individual cation also explains the different effects caused by cations within a monovalent or divalent category. While sodium adsorption ratio as a measure of soil structural stability is only applicable to sodium-dominant soils, CROSS derived from the ionicity of clay–cation bonds is better suited to soils containing multiple cations in various proportions.

scholarly journals Characterisation of 3D printed sand moulds using micro-focus X-ray computed tomography

2019 ◽  
Vol 25 (2) ◽  
pp. 404-416 ◽  
Author(s):  
Tharmalingam Sivarupan ◽  
Mohamed El Mansori ◽  
Keith Daly ◽  
Mark Noel Mavrogordato ◽  
Fabrice Pierron
Keyword(s):  
Computed Tomography ◽  
Gas Permeability ◽  
Experimental Result ◽  
Pore Connectivity ◽  
Content Type ◽  
X Ray ◽  
3D Printed ◽  
X Ray Computed ◽  
Sand Mould ◽  
Non Destructive

Purpose Micro-focus X-ray computed tomography (CT) can be used to quantitatively evaluate the packing density, pore connectivity and provide the basis for specimen derived simulations of gas permeability of sand mould. This non-destructive experiment or following simulations can be done on any section of any size sand mould just before casting to validate the required properties. This paper aims to describe the challenges of this method and use it to simulate the gas permeability of 3D printed sand moulds for a range of controlling parameters. The permeability simulations are compared against experimental results using traditional measurement techniques. It suggests that a minimum volume of only 700 × 700 × 700 µm3 is required to obtain, a reliable and most representative than the value obtained by the traditional measurement technique, the simulated permeability of a specimen. Design/methodology/approach X-ray tomography images were used to reconstruct 3D models to simulate them for gas permeability of the 3D printed sand mould specimens, and the results were compared with the experimental result of the same. Findings The influence of printing parameters, especially the re-coater speed, on the pore connectivity of the 3D printed sand mould and related permeability has been identified. Characterisation of these sand moulds using X-ray CT and its suitability, compared to the traditional means, are also studied. While density and 3PB strength are a measure of the quality of the moulds, the pore connectivity from the tomographic images precisely relates to the permeability. The main conclusions of the present study are provided below. A minimum required sample size of 700 × 700 × 700 µm3 is required to provide representative permeability results. This was obtained from sand specimens with an average sand grain size of 140 µm, using the tomographic volume images to define a 3D mesh to run permeability calculations. Z-direction permeability is always lower than that in the X-/Y-directions due to the lower values of X-(120/140 µm) and Y-(101.6 µm) resolutions of the furan droplets. The anisotropic permeability of the 3D printed sand mould is mainly due to, the only adjustable, X-directional resolution of the furan droplets; the Y-directional resolution is a fixed distance, 102.6 µm, between the printhead nozzles and the Z-directional one is usually, 280 µm, twice the size of an average sand grain.A non-destructive and most representative permeability value can be obtained, using the computer simulation, on the reconstructed 3D X-ray tomography images obtained on a specific location of a 3D printed sand mould. This saves time and effort on printing a separate specimen for the traditional test which may not be the most representative to the printed mould. Originality/value The experimental result is compared with the computer simulated results.

scholarly journals Cation ratio of soil structural stability (CROSS)

Soil Research ◽  
2011 ◽  
Vol 49 (3) ◽  
pp. 280 ◽  
Author(s):  
Pichu Rengasamy ◽  
Alla Marchuk
Keyword(s):  
Hydraulic Conductivity ◽  
Structural Stability ◽  
Control Treatment ◽  
Recycled Water ◽  
Clay Dispersion ◽  
Soil Structural Stability ◽  
Salt Affected Soils ◽  
Highly Correlated ◽  
Irrigation Waters ◽  
Cation Ratio

Sodium salts tend to dominate salt-affected soils and groundwater in Australia; therefore, sodium adsorption ratio (SAR) is used to parameterise soil sodicity and the effects of sodium on soil structure. However, some natural soils in Australia, and others irrigated with recycled water, have elevated concentrations of potassium and/or magnesium. Therefore, there is a need to derive and define a new ratio including these cations in place of SAR, which will indicate the dispersive effects of Na and K on clay dispersion, and Ca and Mg on flocculation. Based on the differential dispersive effects Na and K and the differential flocculation powers of Ca and Mg, we propose the concept of ‘cation ratio of soil structural stability’ (CROSS), analogous to SAR. This paper also gives the results of a preliminary experiment conducted on three soils varying in soil texture on hydraulic conductivity using percolating waters containing different proportions of the cations Ca, Mg, K, and Na. The relative changes in hydraulic conductivity of these soils, compared with the control treatment using CaCl2 solution, was highly correlated with CROSS. Clay dispersion in 29 soils treated with irrigation waters of varying cationic composition was highly correlated with CROSS rather than SAR. It was also found that CROSS measured in 1 : 5 soil/water extracts was strongly related to the ratio of exchangeable cations. These results encourage further study to investigate the use of CROSS as an index of soil structural stability in soils with different electrolytes, organic matter, mineralogy, and pH.

scholarly journals Quantitative Study of Loess Microstructure At Micrometer Scale Via X-Ray Computed Tomography

2021 ◽  
Author(s):  
Weina Yuan ◽  
Wen Fan
Keyword(s):  
Computed Tomography ◽  
Three Dimensional ◽  
Orientation Angle ◽  
Transversely Isotropic ◽  
Pore Throat ◽  
Pore Connectivity ◽  
Spherical Coordinate ◽  
X Ray ◽  
X Ray Computed ◽  
Micrometer Scale

Abstract The macroscopic properties of loess are significantly controlled by its microstructure. Quantitative analysis of loess microstructure is essential for modeling the microstructure and further incorporating the microstructural effects into geotechnical practice. However, loess has a multi-scale microstructure ranging from nanometer to millimeter scales, and researches at the particle resolution are still inadequate. This study systematically investigates the micrometer-scale microstructure of loess from Jingyang, China, via X-ray computed tomography and the image segmentation method that was explored for loess. The statistical analyses of three-dimensional (3D) microstructure reveal that the particle size follows the Weibull distribution, and the distributions of pore and pore throat sizes obey the gamma distribution. Most particles are blade-shaped, with a peak length ratio of (1.53–1.64):1.28:1. The particles are oriented in the polar directions but not azimuthally, in a spherical coordinate system, exhibiting a transversely isotropic structure. The quantitative microstructures of the loess and paleosol samples were slightly different irrespective of the large aggregates developed in paleosol sample. Moreover, the representative elementary volume obtained through porosity is also applicable for the analysis of microstructural parameters such as size distribution, shape factor, orientation angle, and pore connectivity. Besides, the two-dimensional (2D) distributions of the particle, pore, and pore throat sizes agree with the 3D distributions, except that the former were marginally smaller. However, the 2D sectional analysis of shape, arrangement, and pore connectivity cannot adequately represent the 3D characteristics.

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