Equivalent Pore Size Research Articles

Geotextile filtration characteristics in piping rescue under extreme soil-retained state

Geotextiles have significant potential in rescuing backward erosion piping (BEP) occurring in levees. To investigate the filtration characteristics of woven geotextile for BEP prevention under the extreme soil-retention state, laboratory experiments were conducted using woven geotextiles with different pore sizes. The extreme soil-retention characteristics of the geotextile were analyzed, and the optimal relationship between filter pore size and particle size of the protected soil was explored. Additionally, the impact of fine particle content of the protected soil on the filter’s filtration performance was studied. The results indicated that, for the medium sand and silty sand tested, the filter still met soil retention requirements when the ratio of the geotextile’s equivalent pore size (O95) to the protected soil’s characteristic particle size (d85) was 5.2 and 4.3, respectively. With the increase of filter pore size, the clogging degree of the filter showed a trend of rapid decrease followed by an increase, indicating that there was an optimal matching relationship between the filter aperture and the particle size of protected soil. When woven geotextiles are used for preventing BEP, to ensure optimal filtration performance of the filter, the recommended values for O95/d85 in medium sand and silty sand are 5.2 and 3.3, respectively.

Replacing nitrogen in mineral fertilizers with nitrogen in maize straw increases soil water-holding capacity

Soil water-holding capacity decreases due to long-term mineral fertilizer application. The objective of this study was to determine how replacing mineral fertilizer with maize straw affected the soil water retention curve, soil water content, soil water availability, and soil equivalent pore size. Replacement treatments in which 25% (S25), 50% (S50), 75% (S75), and 100% (S100) of 225 kg ha−1 nitrogen from mineral fertilizer (CK) was replaced with equivalent nitrogen from maize straw were conducted for five years in the Loess Plateau of China. The Gardner model was used to fit the soil water retention curve and calculate the soil water constant and equivalent pore size distribution. The results indicated that the Gardner model fitted well. Replacing nitrogen from mineral fertilizer with nitrogen from straw increased soil specific water capacity, soil readily available water, soil delayed available water, soil available water, soil capillary porosity, and soil available water porosity over time. S25 increased field capacity and wilting point from the fourth fertilization year. S50 enhanced soil readily available water, soil delayed available water, soil available water, and soil available water porosity from the fifth fertilization year, whereas S25 and S75 increased these from the third fertilization year or earlier. Soil specific water capacity, soil readily available water, soil delayed available water, soil available water, soil capillary porosity, and soil available water porosity could better reflect soil water-holding capacity and soil water supply capacity compared with field capacity and wilting point.

Study on the pore structure and capillary water migration characteristics of microbially improved strongly weathered phyllite

Phyllite is in a loose accumulation state after weathering, and there is a lack of suitable slag dump sites. The engineering properties of strongly weathered phyllite with poor strength and water stability can be improved by microbiological modification so that it is suitable for roadbed filling. This paper uses microorganisms to improve the strongly weathered phyllite filler, which does not conform to the hydrophysical properties of highway roadbed filler and studies the effects of different gelling fluids on the improvement. The spontaneous imbibition experiment is carried out on the modified sample to analyze the change rule of pore structure with time. The capillary water migration of the three sample groups is studied by using the nuclear magnetic resonance technique and finite element software. The results show that the carbonates produced by different gelling liquids have different particle encapsulation properties. After the calcium acetate improvement, the crystal content of calcium carbonate reached 20.5%. The pore ratio and equivalent average pore size of the three groups of samples increased with increasing spontaneous imbibition time. The fractal dimension of capillary pores is inversely proportional to the proportion of capillary pores. The capillary water absorption coefficient of the modified sample is 0.01. Both laboratory tests and numerical simulation results show that the improvement effect of calcium acetate is superior to that of the other two gelling liquids. The research results provide a reference for predicting the distribution of groundwater movement in strongly weathered phyllite modified by microorganisms as roadbed fillers.

Unveiling the role of pore characteristics in sludge dewatering: Visualization by Nano-CT and micromodel study

The solid-liquid separation is an indispensable and primary link in the process of sludge treatment and disposal. The past research was focused primarily on the technique explorations of sludge dewatering and always disregarded the internal pore structure and water migration behavior in sludge. In this work, the real three-dimensional pore structure of sludge was obtained by Nano-CT. Based on this, a pore-scale heterogeneous sludge micromodel was firstly presented, and the water flooding experiment was carried out to visualize the water migration behavior. The results showed that the sludge structure transformed from sheet-like floc to microsphere particles, and then agglomerated into large globular granules during anaerobic ammonia oxidation. And the equivalent pore size increases from 342 μm to 617 μm, improving the sludge dewaterability characterized by capillary suction time (CST). The most significant implication of this work was revealing the critical role of invalid connected pore in sludge dewatering. Such pore was not contributed to fluid flow but the circulating vortex in it even induced energy dissipation, thus deteriorated the sludge dewaterability. This work may be helpful to understand the critical role of pore characteristic in water migration and shed light on the new dewatering techniques from the perspective of regulating sludge structure.

Experimental study on filtration performance of geotextile filter used in emergency rescue of dike piping

Geotextiles, as a type of common filtration material, have broad prospects in emergency rescue of dike backward erosion piping (BEP). To investigate the filtration performance of geotextile in BEP emergency rescue, several experiments were conducted using nonwoven and woven geotextiles to simulate the process of rescuing BEP with geotextiles. The influence of geotextile specifications and types on hydraulic compatibility of the filter system was analyzed, and the clogging mechanism of geotextile during dealing with BEP was revealed at a microscopic level. The results showed that the nonwoven geotextile filter with an equivalent pore size of 0.103 mm had a gradient ratio value of less than 3, and it had a highest flow rate of 260 mL/min. Increasing the thickness and pore size of nonwoven geotextiles within a certain range helped enhance their anti-clogging ability. The main mechanism of clogging in nonwoven geotextiles was the deposition of fine sand particles on their surface, forming a layer of low permeability soil. Plain woven geotextiles experienced severe clogging with a 42% reduction in flow rate, and it was not suitable for rescuing BEP. The clogging mechanism of woven geotextile involved the blocking of horizontal water passages by fine sand particles.

Assessing the effects of agricultural waste returning on soil moisture characteristics

AbstractAgricultural waste is an emerging and promising resource due to its abundant organic compounds and high water‐holding capacity. It plays a crucial role in improving soil water use efficiency and contributing to sustainable agricultural development. This study aimed to investigate the impact of returning agricultural waste on soil moisture characteristics. Different volume ratios (4:5:1:0, 3:5:1:1, 2:5:1:2, 1:5:1:3, and 0:5:1:4) of agricultural waste blend (AWB) consisting of cattle manure, yellow loam soil, wheat straw, and distiller's grains were examined, and the water‐holding performance of the five AWB ratios under various suction forces was compared. The analysis confirmed the suitability of the Van Genuchten‐Mualem model for fitting soil moisture characteristic curves at different ratios. The study also examined the influences of AWB ratios on soil‐specific water capacity, hydraulic parameters, and equivalent pore size. The results showed that agricultural waste effectively increased soil‐specific water capacity, available water content, soil WHC(Water‐holding capacity), and soil pore count. Furthermore, reducing cattle manure and increasing distiller's grains enhanced these effects. For instance, when the AWB ratio was 0:5:1:4, soil‐specific water capacity increased by 47.7%, while field WHC and available water content increased by 9.9% and 3.8%, respectively. Additionally, the number of extremely small and small pores increased by 1.4% and 0.77%, respectively. These findings provide valuable theoretical guidance for agricultural waste treatment and improving soil WHC. Based on the results, it is recommended to increase the proportion of distiller's grains and reduce organic fertilizer when using agricultural waste for improving soil WHC.

Effect of Replacing Mineral Fertilizer with Manure on Soil Water Retention Capacity in a Semi-Arid Region

The long-term and excessive use of mineral fertilizers in a semi-arid region with severe water shortage will lead to soil compaction and poor water-holding capacity. The fertilization method of manure instead of mineral fertilizer has attracted wide attention. It has adverse consequences for the growth and development of crops. Hence, the objective of this study was to determine how replacing mineral fertilizer with manure affects the soil water retention curve, soil water constant, soil water availability, and soil equivalent pore size distribution, and to seek the best scheme of applying manure in semi-arid area and provide theoretical a basis for improving soil water retention capacity. Here, 0% (CK), 25% (M25), 50% (M50), 75% (M75), and 100% (M100) of 225 kg ha−1 nitrogen from mineral fertilizer were replaced with equivalent nitrogen from manure in the Loess Plateau of China under semi-arid conditions. The centrifuge method was used to determine the soil volumetric water content under different water suction levels, and the Gardner model was used to fit and draw its soil water retention curve, and then calculate the soil water constant and equivalent pore size distribution. The results showed that the Gardner model fitted well. The soil saturated water content with the M100 treatment was the highest, whereas the specific water capacity, water availability, and soil porosity with the M75 treatment were the highest. The soil saturated water content showed a downward trend with the increase in nitrogen from manure instead of nitrogen from mineral fertilizer in the partial replacement treatments. This downward trend slowed down over time. The M75 treatment increased field capacity. The M100 treatment increased soil capillary porosity, soil available water porosity, and soil water availability compared with CK from the fifth fertilization. Replacement treatments increased the specific water capacity, soil saturated water content, soil water availability, soil porosity, and reduced the wilting point over time. In the replacement treatments, specific soil water capacity, soil water availability, and soil porosity first rose and then declined with the increase in nitrogen provided by manure replacing that provided by mineral fertilizer. Therefore, the soil water holding capacity and water supply capacity with the M75 treatment were the best.

Estimation of the soil hydraulic properties and parameter characteristics of Benggang erosion in granite in southern China

AbstractBenggang is an erosional landform that forms in granite hills due to coupled hydraulic and gravity erosion, and its unique development makes it difficult to obtain moisture characteristics through direct means. In this study, the soil moisture characteristics were investigated on the collapsing walls with different weathering degrees of two different Benggang types defined as scoop‐shaped Benggang and strip‐shaped Benggang in the typical Benggang erosion areas of southeastern Guangxi. The soil water characteristic curves (SWCCs) of the collapsing wall were measured by the centrifuge method to explore the moisture transport mechanism of Benggang development. The response of moisture characteristics to the Benggang morphology was not significant, but the soil layer changes in the collapsing wall had a significant impact. The Atterberg limits of the surface layer and laterite layer were significantly higher than those of the transition layer and sandy layer, with a liquid limit (LL) value exceeding 55%, indicating high LL clay. The Van Genuchten (VG), Gardner and Fredlund–Xing (FX) models were used to fit the SWCCs, and the results indicated that the VG model had a high fitting accuracy (R2 > 0.984), followed by the FX model (R2 > 0.943); however, the Gardner model had a low fitting accuracy (R2 > 0.891). With the change in matrix suction, the sandy layer had the maximum water release capacity, followed by the transition layer, and finally the surface layer and laterite layer. The variation in equivalent pore size distributions with soil layers showed that the micropores in the laterite layer of the two Benggangs accounted for 44.91% and 44.38% of the total porosity. The macropores of the sandy layer accounted for 35.40% and 36.84% of the total porosity. Both the unsaturated hydraulic conductivity K(θ) and water diffusivity D(θ) exhibited two abrupt changes with increasing soil volumetric water content, and K(θ) and D(θ) of the lower layers were larger than those of the upper layers. The heterogeneity of soil texture and pore conditions among different collapsing wall soil layers can significantly affect the Benggang water conditions. This study provides a database for further investigation of the Benggang development mechanism.

Influence of the Graphene Oxide on the Pore-Throat Connection of Cement Waste Rock Backfill.

The pore-throat characteristics significantly affect the consolidated properties, such as the mechanical and permeability-related performance of the cementitious composites. By virtue of the nucleation and pore-infilling effects, graphene oxide (GO) has been proven as a great additive in reinforcing cement-based materials. However, the quantitative characterization reports of GO on the pore-throat connection are limited. This study applied advanced metal intrusion and backscattered electron (BSE) microscopy scanning technology to investigate the pore-throat connection characteristics of the cement waste rock backfill (CWRB) specimens before and after GO modification. The results show that the microscopic pore structure of CWRB is significantly improved by the GO nanosheets, manifested by a decrease in the total porosity up to 31.2%. With the assistance of the GO, the transfer among internal pores is from large equivalent pore size distribution to small equivalent pore size distribution. The fitting relationship between strength enhancement and pore reinforcement efficiency under different pore-throat characteristics reveals that the 1.70 μm pore-throat owns the highest correlation in the CWRB specimens, implying apply GO nanosheets to optimizing the pore-throat under this interval is most efficient. Overall, this research broadens our understanding of the pore-throat connection characteristics of CWRB and stimulates the potential application of GO in enhancing the mechanical properties and microstructure of CWRB.

Permeability prediction of pervious concrete based on mix proportions and pore characteristics

Permeability is the principal function of pervious concrete, and establishing a permeability prediction model is a prerequisite for designing and optimizing permeability. However, most of the current permeability prediction models depend on porosity or pore characteristics, which are difficult to guide the design of pervious concrete. Therefore, this study investigated the permeability of pervious concrete with different cement-aggregate ratios and gradations of aggregates, and developed prediction models for permeability coefficients based on the mix proportion parameters and pore characteristics. The results show that the two-dimensional porosity obtained from image analysis is slightly larger than the connected porosity obtained from the volumetric method. The three pore characteristics obtained from image analysis include the two-dimensional porosity, the pore number, and the equivalent pore size, all of which correlate significantly with the cement-aggregate ratio. The permeability coefficients measured by the constant and falling head methods show significant correlations with the cement-aggregate ratio and the pore characteristics and insignificant correlations with the equivalent aggregate size. Binary and ternary permeability coefficients prediction models based on the cement-aggregate ratio and the equivalent aggregate size, as well as on the two-dimensional porosity, the pore number, and the equivalent pore size, are developed, respectively. The predicted permeability coefficients are in good agreement with the experimental results, indicating that the permeability of pervious concrete can be designed and predicted according to the prediction models.

The compressive strength and damage mechanisms of pervious concrete based on 2D mesoscale pore characteristics

The compressive performance of pervious concrete depends largely on its pore characteristics. To study the effect of pore characteristics on the compressive strength of pervious concrete, different porosity specimens of pervious concrete were prepared. The Compression test and porosity test was performed on the pervious concrete specimens with a side length of 100 mm. A 2D numerical model of pervious concrete was developed by mesoscale pore characteristics of pervious concrete. The stress distributions and damage modes of pervious concrete during compression were analyzed by conducting uniaxial compressive simulation tests on the established model. The results indicate that the number of pores and maximum pore size of pervious concrete increase as the design porosity increases. The equivalent pore size follows a Gaussian distribution and the characteristic pore size is typically between 1 and 4 mm. The simulation results also indicate that porosity affects the stress distribution of pervious concrete mainly based on the solid phase percentage and contact area. The increase of the number of small pores (when the porosity is certain) is conducive to improving the uniformity of stress transmission, thereby enhancing the compressive strength of pervious concrete.

Electro-enhanced rapid separation of nanosized oil droplets from emulsions via the superhydrophilic micro-sized pore membrane

Waste oil-in-water emulsion is a special and unmanageable oily wastewater produced by several industries. Based on the sieving effect, the use of a membrane is a promising method to separate emulsion, whereas low flux remains a fundamental challenge. In this study, the coupling of an electric field with superhydrophilic fibrous membranes helped separate micro-/nano- paraffin in water emulsions (247–1887 nm) stabilized by SDS (100–500 mg/L) with a general applicability. The micro-sized pore membrane (0.634 μm) achieved outstanding rejection of nano-sized oil droplets (247 nm) using an electric field. It promoted flux from 1,202 to 18,388 LMH/bar by 1,429 % which was more than that in other literature by 1–2 orders of magnitude and improved oil removal from 97.61 % to 99.88 %. The reduction of equivalent pore size of membrane by the double layer force and the promotion of coalescence of oil droplets driven by the Laplace force rooted in the fibrous spindle of the membrane achieved enhanced selectivity. Electrophoretic force and double layer force mitigated the formation of the filter cake and irreversible fouling, respectively, to promote permeability and antifouling. This research provides a method for the simultaneous promotion of flux and improvement in effluent quality using an electric field, which breaks the limit of the trade-off effect.

Effect of morphological characteristics of aggregate on the performance of pervious concrete

The aggregate morphology plays a vital role in the performance of pervious concrete. This study investigates the effect of aggregate morphology on the mechanical properties and permeability characteristics of pervious concrete. Sphericity was selected as the index for describing the aggregate morphological characteristics using computed tomography (CT) and digital image processing (DIP) technology. Mechanical and single-phase seepage tests and simulations were conducted by Avizo software. The results show that the aggregates with more edges and corners are more favorable for forming an interlocking skeleton. With the addition of angular rich aggregates, the internal void distribution becomes more uniform, the equivalent pore size decreases, and the load-bearing capacity increases. The compatibility of particle morphology has an important influence on the properties of mixtures. As aggregate sphericity rises, the number of seepage paths reduces, the curvature of seepage channels improves, and the seepage velocity decreases. Based on the test results, the mechanical properties and permeability characteristics of pervious concrete can be optimized depending on engineering requirements by regulating the aggregate morphology.

Experimental study on the law of transitional gas flow in porous media

There are many nanoscale pores in deep low permeability coal seams. The flow of coalbed methane (gas) in nanoscale pores belongs to the gas flow in porous media with medium and high Knudsen numbers. Its flow mechanism is one of the key unsolved scientific problems. In order to explore the gas transport law in nanopores of coal, a gas transport model based on microscopic boundary restriction was adopted to describe the gas flow law, and its rationality was verified by experimental data. The Field Emission Scanning Electron Microscope was used to scan the nanopores of customized anodized aluminum membrane. Then, the Maximally Stable Extremal Regions (MSER) algorithm of MATLAB and binarization algorithm were employed to quantify the pore structure parameters (equivalent pore size and porosity) of the membrane nanoscale pores. Finally, PMI micro-flow permeability tester was used to carry out different rarefied degree gas penetration experiments through anodized aluminum membranes, and the adopted gas transport model was verified. The results show that the binarization method is more accurate to characterize sample whose theoretical pore sizes are 20–35 nm, while MSER characterizes samples whose theoretical pore sizes are 110–150 nm and 200–300 nm more accurately. In other words, binarization method is more accurate for characterizing mesopores, while MSER algorithm is more accurate for macropores. The results have important reference value for more accurate extraction of nanopore parameters of porous media. Compared with traditional gas transport model, the adopted model considering the microscopic boundary restriction in this paper is closer to the experimental results. Moreover, it is suitable for describing the gas flow law in multiscale nanopores. The study provided important guiding significance for ascertaining the gas migration law in low permeability coal seam, improving the prediction accuracy of gas extraction and taking effective measures to increase production. The research results can further enrich the theoretical system of gas transport in coal, which is conducive to the efficient gas extraction, and is of great significance to promote the realization of carbon peak and carbon neutrality.

Pore wetting process characterization of Equal-Sized granular coals by using LF-NMR technology

Understanding the pore wetting process is of great significance for determining fluid wetting behavior in porous media such as coal, and for the development and utilization of natural gas reservoirs, however, most studies on the process simplify porous media as glass capillaries, which may lack practical application. To better understand and quantitatively characterize the actual pore wetting process of coals, a new, low-field nuclear magnetic resonance (LF-NMR) experimental characterization method was developed. The experiment used equal grain sizes of glass beads and coals to yield porous media with variable pores of specific size ranges. LF-NMR was then used to characterize the pore wetting process of a given amount of water in the porous media at different times. Six groups of high-rank coals were also characterized by contact angle experiments to analyze the role of the surface contact angle on pore wetting. The results show that the pore wetting process can be divided into three ideal physical phases: a first touch state, a semi-free water state and an inter-granular diffusion or quasi-static state. The wetting pore size distribution (W-PSD) spectrum obtained by measurement of the transverse relaxation time and the transformation coefficient reflected change in pore size during wetting, with the location of the W-PSD quantified by the equivalent wetting pore size. The equivalent wetting pore size obtained at a final time of 24 h was used to characterize the pore wettability, it was significantly correlated with the surface contact angle with a linearity of up to 0.99. However, the W-PSD or the equivalent wetting pore size is dependent on the surface relaxivity. Overall, the experimental characterization method used in this study is an effective way to study the “black box problem” of the wetting process in porous media, as it is simple and has low sample requirements.

Porosity roles of micro-mesostructured ZSM-5 in catalytic fast pyrolysis of cellulolytic enzyme lignin for aromatics

Cellulolytic enzyme lignin could be utilized to produce aromatic-rich bio-oil in the catalytic fast pyrolysis (CFP) process, in which strong-acidic ZSM-5 is often used as the catalyst. The introduction of mesopores into conventional ZSM-5 catalysts can improve the diffusion of heavy components and thus enable the modulation of pyrolysis products. To investigate the effect of mesoporous structure parameters on the diffusion of heavy phenols and the regulation of pyrolysis products by different types of pore structures, three different mesoporous ZSM-5 were prepared (core-shell, hierarchical, composites), with textural properties being compared in detail. The structural parameters were adopted to analyze the relationship between mesopores distribution and catalytic performance, revealing the significant effect of equivalent mesopore size. Among the prepared catalysts, a micro-mesostructured composite zeolite (ZMA) with internal hierarchical pores and ununiform mesolayer shell had a suitable mesostructure, of which the interconnected meso-channels improved the accessibility of inner acidic sites. Also, it was optimum to balance aromatic yield (above 7.5 wt%) and the product distribution (MAHs/PAHs approaching 6), revealing that its moderate equivalent pore size maintained a certain shape-selectivity to suppress PAHs formation. It was further shown that the applicable catalyst to lignin ratio (C/L) ranges differed with various mesostructures, as ZMA and hierarchical samples were suitable for higher and lower ratios, respectively.

Influence of Lateral Limited Uniaxial Tensile Strain on Opening Sizes

Nonwoven geotextiles are widely used for seepage prevention, foundation improvement and reinforcement materials. They are usually under lateral limited uniaxial tension in engineering, which results in changing behaviour of the opening size of geotextiles. According to theoretical analysis of pore parameters people studied before, the equivalent pore size of nonwoven geotextiles under the lateral limited uniaxial tensile strain are derived in this paper. Two different nonwoven geotextiles were stretched under lateral limited uniaxial tensile strain of 3%, 5% and10% respectively. Dry sieving tests were exerted in order to eliminated electrostatic effects and measure the change of pore size of nonwoven geotextiles. The results show that theoretical solutions are good for predicting the change law of pore sizes for non-woven geotextiles. Pore size of nonwoven geotextiles increases with increasing of the lateral limited uniaxial tensile strain.

Manufacturing Ceramic Foams at Very High Temperature by the Unconventional Process of Direct Microwave Heating


 
 
 
 Abstract 
 SiC ceramic foams were manufactured by direct microwave heating up to 1520 ºC. Silicon carbide (42-68 wt.%), quartz sand as a silica supplier (20-38 wt.%), coal fly ash (12-20 wt.%) and a constant water addition of 15 wt.% were used as starting materials. The ceramic foam samples had semi-open microstructures in which neighboring cells are partially connected to each other and partially closed. Due to the very dense cellular walls and the very low cells size (below 21 μm), the compressive strength had very high values (41.3-56.5MPa), the porosity was within an average value range (52.4-57.6%) and the thermal conductivity and the apparent density had relatively high values. In energy terms, the technique of direct microwave heating was very advantageous, the specific energy consumption being very low (1.04-1.21 kWh/kg) compared to the consumptions achieved by conventional methods. The application field of SiC ceramic foams obtained by the bonding method and using silica as a bonding agent includes hot gas or molten metal filters, porous burners, catalytic supports and others. From the four tested experimental variants, it could be concluded that the optimal sample was that achieved at 1520 ºC with 68% silicon carbide, 20% quartz sand, 12% coal fly ash and 15% water addition, having the porosity of 57.6%, thermal conductivity of 0.174 W/m·K, compressive strength of 56.5 MPa and the equivalent pore size between 9-21 μm.
 
 
 

Effects of pore structure characterized by synchrotron-based micro-computed tomography on aggregate stability of black soil under freeze-thaw cycles

Soil structure affects soil quality, which in turn influences agricultural productivity. In north-eastern China, periodic melting of the frozen layer is very common in late autumn and early spring. Such freeze-thaw cycles affect soil structure, aggravating soil erosion and affecting soil quality. The objective of this study was to evaluate the effects of aggregate pore characteristics on the aggregate stability of black soil under freeze-thaw cycles. Undisturbed topsoil samples were submitted to 0, 1, 3, 5, 7, 10, 15, and 20 freeze-thaw cycles under controlled laboratory conditions. Then, 5–7 mm aggregates were collected from each treatment for synchrotron-based X-ray micro-computed tomography (SR-μCT) scanning with 3.25 μm voxel resolution at the Shanghai Synchrotron Radiation Facility (SSRF); 3D micro tomography images were then reconstructed using ImageJ software. Aggregate stabilities against slaking (MWDFW) and mechanical breakdown (MWDWS) were also measured after each treatment. The relationships between pore parameters and aggregate stability were then analyzed using the method of partial least squares regression (PLSR). 2D and 3D image visualization showed that the aggregate microstructures developed increasingly porous and connected pore networks following repeated freeze-thaw cycles. Quantitative analysis showed that total porosity, porosity of elongated pores (EP), and porosity of equivalent pore size >100 μm (P>100) significantly increased with an increasing number of freeze-thaw cycles. Such cycles decreased the aggregate stability, which was closely associated with pore characteristics. According to PLSR, the pore characteristics accounted for 86 % and 81 % of the variation in MWDFW and MWDWS, respectively. Total porosity, EP, and P>100 were identified as the primary factors controlling the air content, water entrance, and failure stress of interior aggregates, all of which could weaken aggregate stability. These results improve the understanding of pore characteristics and aggregate stability, which are key factors influencing soil erosion and soil quality during the seasonal freeze-thaw period.

Permeating behaviour of porous SiC ceramics fabricated with different SiC particle sizes

Permeating behaviour is one of the most important factors of porous ceramics used for gas/liquid filters or membrane/catalysis supporters. Insufficient research has reported on the effect of raw particle size on permeating behaviour and the relationship between particle size and pore size of fabricated porous ceramics. In this work, porous SiC ceramics were fabricated with raw SiC particles of different grit designations and the effect of particle size on the permeating behaviour and equivalent pore size of the resulting porous ceramics were investigated. Due to oxidation of the SiC particles during the firing process, resulting materials with finer raw particles exhibited higher mass gain and lower bulk and true density. When the grit designation changed from 2000# to 120#, the strength of the resulting materials declined, and the Darcy permeability k1 increased from 6.65 × 10−15 to 4.85 × 10−13 m2. The ratio of the hydraulic equivalent diameter of pores to raw particle size in the resulting materials decreased from 0.25 to 0.11, indicating that the hydraulic equivalent pore size did not increase proportionally with the particle size increase. Further measures should be employed to enlarge pore size in porous ceramics to enhance its permeability.