scholarly journals Study on the Mechanical Criterion of Ice Lens Formation Based on Pore Size Distribution

2020 ◽  
Vol 10 (24) ◽  
pp. 8981
Author(s):  
Yuhang Liu ◽  
Dongqing Li ◽  
Lei Chen ◽  
Feng Ming
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Water Content ◽  
Size Distribution ◽  
Initial Water Content ◽  
Mean Stress ◽  
Initial Water ◽  
Unfrozen Water Content ◽  
The Mean ◽  
Lens Formation

Ice lens is the key factor which determines the frost heave in engineering construction in cold regions. At present, several theories have been proposed to describe the formation of ice lens. However, most of these theories analyzed the ice lens formation from a macroscopic view and ignored the influence of microscopic pore sizes and structures. Meanwhile, these theories lacked the support of measured data. To solve this problem, the microscopic crystallization stress was converted into the macro mean stress through the principle of statistics with the consideration of pore size distribution. The mean stress was treated as the driving force of the formation of ice lens and induced into the criterion of ice lens formation. The influence of pore structure and unfrozen water content on the mean stress was analyzed. The results indicate that the microcosmic crystallization pressure can be converted into the macro mean stress through the principle of statistics. Larger mean stress means the ice lens will be formed easier in the soil. The mean stress is positively correlated with initial water content. At the same temperature, an increase to both the initial water content and the number of pores can result in a larger mean stress. Under the same initial water content, mean stress increases with decreasing temperature. The result provides a theoretical basis for studying ice lens formation from the crystallization theory.

Compaction behaviour of lime-treated metakaolin

2020 ◽  
Author(s):  
Mozhen Hu ◽  
Yu-Jun Cui ◽  
Yunzhi Tan
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Water Content ◽  
Size Distribution ◽  
Uniform Structure ◽  
Dry Density ◽  
Soil Stiffness ◽  
Effect Of Water ◽  
Compaction Curve ◽  
Lime Addition

Metakaolin has been widely used as pozzolanic additive to improve the pozzolanic activity of lime-based products. In this study, normal standard Proctor compaction test was performed on metakaolin with (5% lime) and without (0% lime) lime addition. The changes in stiffness, suction and microstructure with remoulding water content were investigated on statically compacted samples. Results show that lime-treated metakaolin exhibits one and half-peak compaction curve, while untreated metakaolin exhibits common one-peak compaction curve. The uncommon shape of the compaction curve of the treated metakaolin can be explained by the non-fully developed soil suction when water is not continuous. Treated and untreated samples compacted at both dry and wet of optimum show uni-modal pore size distribution characteristics, indicating the absence of aggregates. This is related to the specific thermal treatment, forming separate metakaolin platelets and leading to a modified uniform structure with diffuse platelets. The soil stiffness is rather dominated by the number of particle contacts or soil dry density, the effect of suction being insignificant. For the suction changes, on the dry side, the effect of pore size distribution prevails facing the effect of water content, while on wet side it is the effect of water content that becomes prevailing.

scholarly journals The impacts of freeze–thaw cycles on saturated hydraulic conductivity and microstructure of saline–alkali soils

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Wenshuo Xu ◽  
Kesheng Li ◽  
Longxiao Chen ◽  
Weihang Kong ◽  
Chuanxiao Liu
Keyword(s):  
Hydraulic Conductivity ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Water Content ◽  
Size Distribution ◽  
Saturated Hydraulic Conductivity ◽  
High Water Content ◽  
Soil Permeability ◽  
Freeze Thaw ◽  
Alkali Soil

AbstractStudy on the microscopic structure of saline–alkali soil can reveal the change of its permeability more deeply. In this paper, the relationship between permeability and microstructure of saline–alkali soil with different dry densities and water content in the floodplain of southwestern Shandong Province was studied through freeze–thaw cycles. A comprehensive analysis of soil samples was conducted using particle-size distribution, X-ray diffraction, freeze–thaw cycles test, saturated hydraulic conductivity test and mercury intrusion porosimetry. The poor microstructure of soil is the main factor that leads to the category of micro-permeable soil. The porosity of the local soil was only 6.19–11.51%, and ultra-micropores (< 0.05 μm) and micropores (0.05–2 μm) dominated the pore size distribution. Soil saturated water conductivity was closely related to its microscopic pore size distribution. As the F–T cycles progressed, soil permeability became stronger, with the reason the pore size distribution curve began to shift to the small pores (2–10 μm) and mesopores (10–20 μm), and this effect was the most severe when the freeze–thaw cycle was 15 times. High water content could promote the effects of freeze–thaw cycles on soil permeability and pore size distribution, while the increase of dry density could inhibit these effects. The results of this study provide a theoretical basis for the remediation of saline–alkali soil in the flooded area of Southwest Shandong.

scholarly journals Influence of Sodium Hypochlorite Treatment on Pore Size Distribution of Polysulfone/Polyvinylpyrrolidone Membranes

Membranes ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 356
Author(s):  
George Dibrov ◽  
George Kagramanov ◽  
Vladislav Sudin ◽  
Evgenia Grushevenko ◽  
Alexey Yushkin ◽  
...  
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Membrane Structure ◽  
Fold Increase ◽  
Active Chlorine ◽  
The Mean ◽  
Temperature Liquid ◽  
Liquid Displacement ◽  
Surface Pores

This work was focused on the study of hypochlorite treatment on the pore size distribution of membranes. To this end, ultrafiltration membranes from a polysulfone/polyvinylpyrrolidone blend with a sponge-like structure were fabricated and exposed to hypochlorite solutions with different active chlorine concentrations for 4 h at ambient temperature. Liquid–liquid displacement and scanning electron microscopy were employed to study the limiting and surface pores, respectively. After treatment with 50 ppm hypochlorite solution at pH = 7.2, a five-fold increase in water permeance up to 1400 L/(m2·h·bar) was observed, accompanied by a 40% increase in the limiting pore sizes and almost a three-fold increase in the porosity. After 5000 ppm treatment at pH = 11.5, a 40% rise in the maximum limiting pore size and almost a two-fold increase in the porosity and permeance was observed, whereas the mean pore size was constant. Apparently, changes in the membrane structure at pH = 11.5 were connected with polyvinylpyrrolidone (PVP) degradation and wash-out, whereas at lower pH and despite lower active chlorine concentration, this process was coupled with polysulfone (PSf) destruction and removal.

THE DETERMINATION OF PORE SIZE DISTRIBUTION AND SURFACE AREA FROM ADSORPTION ISOTHERMS

1955 ◽  
Vol 33 (2) ◽  
pp. 215-231 ◽  
Author(s):  
E. M. Voigt ◽  
R. H. Tomlinson
Keyword(s):  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Surface Area ◽  
Pore Radius ◽  
Weighted Average ◽  
Vycor Glass ◽  
Porous Vycor Glass ◽  
The Mean

Theoretical isotherms have been developed which when compared to experimental isotherms showing hysteresis, allow the calculation of pore size, pore size distribution, and surface area of the sorbent. Interpretation of some experimental isotherms obtained with porous vycor glass shows that this system can best be represented by the "ink bottle" pore model with a Gaussian distribution of pore sizes. The mean pore radius of the porous glass is about two thirds of the Kelvin radius, and the surface area greater than that obtained from the B.E.T. theory. The Kelvin radius is interpreted as a weighted average, but the B.E.T. surface area appears more fundamentally different.

Influence of pore size distribution and soil water content on nitrous oxide emissions

Soil Research ◽  
2012 ◽  
Vol 50 (2) ◽  
pp. 125 ◽  
Author(s):  
Tony J. van der Weerden ◽  
Francis M. Kelliher ◽  
Cecile A. M. de Klein
Keyword(s):  
Nitrous Oxide ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Water Content ◽  
Size Distribution ◽  
Soil Water ◽  
Gas Diffusion ◽  
Field Conditions ◽  
Nitrous Oxide Emissions ◽  
N2o Emissions

Nitrous oxide (N2O) emissions from agricultural soils have been estimated to comprise about two-thirds of the biosphere’s contribution of this potent greenhouse gas. In pasture systems grazed by farmed animals, where substrate is generally available, spatial variation in emissions, in addition to that cause by the patchiness of urine deposition, has been attributed to soil aeration, as governed by gas diffusion. However, this parameter is not readily measured, and the soil’s water-filled pore space (WFPS) has often been used as a proxy, despite gas diffusion in soils depending on the volumetric fractions of water and air. With changing water content, these fractions will reflect the soil’s pore size distribution. The aims of this study were: (i) to determine if the pore size distribution of two pastoral soils explains previously observed differences in N2O emissions under field conditions, and (ii) to assess the most appropriate soil water/gas diffusion metric for estimating N2O emissions. The N2O emissions were measured from intact cores of two soils (one classified as well drained and one as poorly drained) that had been sampled to a depth of 50 mm beneath grazed pasture. Nitrogen (N, 500 kg N/ha) was applied to soil cores as aqueous nitrate solution, and the cores were drained under controlled conditions at a constant temperature. The poorly drained soil had a larger proportion of macropores (23.5 v. 18.7% in the well-drained soil), resulting in more rapid drainage and increased pore continuity, thereby reducing the duration of anaerobicity, and leading to lower N2O emissions. Emissions were related to three soil water proxies including WFPS, volumetric water content (VWC), and matric potential (MP), and to relative diffusion (RD). All parameters showed highly significant relationships with N2O emissions (P < 0.001), with RD, WFPS, VWC, and MP accounting for 59, 72, 88, and 93% of the variability, respectively. As VWC is more readily determined than MP, the former is potentially more suitable for estimating N2O emission from different soils across a range of time and space scales under field conditions.

Characterization of Porous Solids

MRS Bulletin ◽  
1994 ◽  
Vol 19 (4) ◽  
pp. 44-48 ◽  
Author(s):  
Douglas M. Smith ◽  
Duen-Wu Hua ◽  
William L. Earl
Keyword(s):  
Pore Structure ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Gas Absorption ◽  
Structure Characterization ◽  
Porous Solids ◽  
Hydraulic Radius ◽  
Wide Range ◽  
The Mean

Progress in the synthesis and engineering of advanced porous materials demands better pore structure characterization. The analysis of pore structure is complicated by (1) the wide range in pore sizes observed, from molecular (<1 nm) to macroscopic (>1 mm) dimensions, (2) complex pore shapes and connectivities, (3) chemical and physical heterogeneities, and (4) pore structure changes that can occur during characterization.The required pore structure information varies with application. Bulk density and the pore-size distribution are needed for thermal insulation. In this case, the dimension of interest is the so-called hydraulic radius since, for small pores, the gas-phase conductivity is proportional to the mean hydraulic radius to the mean free path. A few large but isolated pores will significantly affect conductivity but will go undetected in typical gas-absorption methods. In contrast, for separations, bottlenecks control performance. For transport, such as migration through geologic formations, both the pore-size distribution and pore connectivity are important. For adsorption, surface area and pore size are the relevant factors. Finally, the conventional concepts of pore structure lose meaning as the pore size approaches molecular dimensions, typical of adsorbents and gas-separation membranes.

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