Maximum Pore Research Articles

Stearic acid-capped mesoporous silica microparticles as novel needle-like-structured drug delivery carriers.

Mesoporous silica are widely utilised as drug carriers due to their large pore volume and surface area, which facilitate effective loading. Additionally, they can be used to enhance drugs stability and protect against enzymatic degradation due to their silica framework. However, without the addition of a capping material, the loaded cargo may be prematurely released before reaching the target site. This work reports the functionalisation of a commercially available silica microparticle (SYLOID XDP 3050) with stearic acid at various stearic acid loading concentrations (20-120% w/w). Scanning electron microscopy (SEM) analysis revealed that the pores were capped with stearic acid, with the filling ratio increasing proportionally to the loading concentration. Notably, needle-like structures appeared when the stearic acid amount exceeded 80% w/w, surpassing the calculated theoretical maximum pore filling ratio (64.32%). The molecular interactions were highlighted using Fourier-transform infrared spectroscopy (FTIR), as the intensity of the CH3 increased with increased stearic acid loading concentrations. The needle-structures phenomenon was corroborated by 3D confocal imaging. It utilised the autofluorescence properties of stearic acid to demonstrate its presence within the carrier, with fluorescence intensity increasing alongside the stearic acid concentration. Differential scanning calorimetry (DSC) indicated the crystalline nature of these needle structures, which was further confirmed by X-ray diffraction (XRD) analysis, validating the crystallisation of the stearic acid needles. Moreover, nitrogen porosimetry was employed to assess the pore volume and surface area, where the formulation containing 120% stearic acid exhibited the lowest pore volume (0.59cc). This value was smaller than unloaded SYLOID (2.1cc), indicating near-complete filling of the carrier. This newly developed SYLOID-stearic acid carrier will now be used to enhance formulation development as a platform to enhance protein oral drug delivery.

Facial Skin Quality Improvement After Treatment With CPM-HA20G: Clinical Experience in Korea.

Intradermal injection of CPM-HA20G, a low-viscoelasticity hyaluronic acid (HA) dermal filler with glycerol, has been shown to be effective for facial rejuvenation in Caucasians, but research in Asians is limited. This study aimed to evaluate the effectiveness and safety of CPM-HA20G in enhancing facial skin quality in Korean women using a protocol developed by local aesthetic experts. In this 24-week prospective, single-arm, open-label study, 20 women received CPM-HA20G injections in the immediate subdermal layer on the anterior cheek (1 mL per side; total 2 mL) in three sessions every 4 weeks. Evaluations included biophysical assessments covering the four emergent perceptual categories (EPCs) for skin quality and subjective assessment using the Global Aesthetic Improvement Scale. Significant improvements in skin glow (skin gloss, epidermal hydration), skin firmness (dermal elasticity, dermal hydration), skin surface evenness (average pore volume, pore area, pore density, pore count, maximum pore depth, total pore volume, skin roughness, sebum secretion, and skin depression volume), skin tone evenness (skin color brightness, skin redness), and transepidermal water loss were observed at Week 12 and Week 24 following the first injection with CPM-HA20G. Most subjects and investigators reported improvements in overall aesthetic appearance with the treatment, with a 100% improvement rating from both groups at Week 12. No serious adverse reactions were observed. Our study provides real-world insights into the effectiveness and safety of CPM-HA20G in improving facial skin quality in an Asian population, evaluated through both objective and subjective assessments.

A Relative Permeability Model of Coal Based on Fractal Capillary Bundle Assumption

Summary As the pore and fracture structure of coal significantly influence gas-water relative permeability (GWRP), it is crucial to study the GWRP in coal reservoirs for optimizing gas production. This paper provided parameters such as pore size range and capillary bundle porosity by referring to existing mercury intrusion porosimetry (MIP) experiments. The effective porosity coefficient and gas-water phase critical pore size were introduced to improve the GWRP model for coal based on the assumption of fractal capillary bundle. The GWRP model depends on changes in phase saturation, maximum and minimum capillary tube pore diameters, porosity, capillary size distribution dimension Df, and fractal dimension of tortuosity Dt. It demonstrated that models for various coal samples from the southern Qinshui Basin exhibit good agreement with the GWRP experimental data. In addition, the improved GWRP model was used to simulate coalbed methane (CBM) production and water production. The findings suggested that as water and gas are continuously extracted, effective stress rises as reservoir pressure and water saturation decline, leading to a more even distribution of capillary diameter and an increase in capillary degree. Furthermore, the effect of structural parameters on CBM production was also discussed.

Effects of Soil Compaction Stress Combined with Drought on Soil Pore Structure, Root System Development, and Maize Growth in Early Stage.

Soil compaction is a major environmental stress to root development and plant growth. Meanwhile, drought always results in increasing soil mechanical impedance, which in turn aggravates soil compaction stress. In this study, a column experiment with three levels of compaction stress (low, moderate, and severe) and two levels of soil water content (well-watered and drought,) was established to investigate the effects of soil compaction combined with drought on soil pore structure, root development, and maize growth properties. The results showed that soil compaction combined with soil water stress significantly affected the characteristics of soil pore structure. With the increase in soil compaction, the porosity, larger pores (>500 μm), and maximum pore diameter significantly decreased (p < 0.05) regardless of soil water status. Additionally, both pore morphology and network parameters also deteriorated under soil compaction with drought conditions. Soil compaction substantially affected the root length, root volume, root surface area, and root average diameter in the whole profile (p < 0.05). Compared to well-watered conditions, the effects of soil compaction on root characteristics under drought conditions were more obvious, which indicated that appropriate soil water content could alleviate compaction stress. The aboveground biomass and plant height showed a consistent trend with root traits under soil compaction stress regardless of water status. A Pearson's correlation analysis showed that there were significant correlations between most soil pore parameters and maize growth traits. In addition, soil compaction showed a significant effect on both stomatal conductance and transpiration rate while soil water showed a significant effect on SPAD (Soil Plant Analysis Development).

Enhancing biochar production: A technical analysis of the combined influence of chemical activation (KOH and NaOH) and pyrolysis atmospheres (N2/CO2) on yields and properties of rice husk-derived biochar

The production of biochar from biomass has received considerable interest due to its potential in environmental applications; however, optimizing biochar properties remains a major challenge. The objective of the present study was to investigate the synergistic effects of pyrolysis atmospheres (N2 and CO2) and chemical activation (pre- and post-pyrolysis) with NaOH and KOH on the properties of biochar useful for its environmental applications. In this study rice husk and biochar were impregnated with KOH and NaOH before and after pyrolysis, which was carried out at 600 °C under N₂ and CO₂ atmosphere. The pyrolytic yields (biochar, liquid and gas) and detailed characterization of biochar were performed. The results showed that pre-activation with both alkalis under a CO2 atmosphere slightly decreased the biochar yield and carbon contents while increasing oxygen in biochars compared to N2 atmosphere. Alkali pre-activation in the CO2 atmosphere considerably increased the specific surface area and pore volume of biochars compared to the N2 atmosphere, with KOH being more effective than NaOH. The maximum specific surface area (SSA) and pore volume (PV) of biochar obtained were 178.4 m2/g and 0.60 cm3/g for KOH activated biochar under CO2, which were 3.2 times and 30 times higher than the untreated biochar. The post-activation of biochars with both alkalis resulted in moderate improvements in textural properties. Overall, chemical activation under CO2 pyrolysis facilitated a higher level of chemical activation reactions leading to increased formation of oxygen functional groups and contributed to enhanced SSA and PV of the biochar useful for adsorption.

Simple fabrication of breathable poly (vinylidene fluoride) fibrous membranes decorated by silica nanoparticles with enhanced waterproof property

In recent years, scientists have undertaken various preparation approaches to improve the waterproof and moisture permeability of fiber membranes, among which electrospinning has emerged as the simplest and most effective one. In this paper, poly (vinylidene fluoride)/silica (PVDF/SiO2) fibrous membranes were prepared by one-step electrospinning combined with heat treatment. The morphology, surface wettability, water resistance and moisture permeability of the fibrous membranes were also characterized. When the concentration of PVDF was 12 wt%, the nanofiber membranes exhibited the most uniform and optimal morphology. In addition, the fiber membranes not only exhibited a high water contact angle (WCA) (135.56°) and a small maximum pore size (dmax) (1.77 μm), but also demonstrated a large hydrostatic pressure (116.86 kPa) and a moderate water vapor transmission rate (WVTR) (3.53 kg m−2 d−1). The PVDF/SiO2 fibrous membranes with good waterproof and moisture permeability obtained in this work are expected to improve the comfort of protective textiles and expand the application range.

Hydrothermally synthesized nitrogen-doped hydrochar from sawdust biomass for supercapacitor electrodes

Porous carbon generated from biomass is among the most promising electrode materials for supercapacitor applications. In this research work, sawdust was used as a carbon source to synthesize N-doped hydrochars via the hydrothermal method in the presence of nitrogen-containing compounds including ammonium chloride, urea agar, ammonium molybdate tetrahydrate, and mammalian urine, followed by chemical activation by potassium hydroxide. Using the hydrothermal technique, it was possible to dope 7.06 wt% of nitrogen into the hydrochar. The as synthesized materials were characterized by TGA/DTA, FTIR, BET, XRD, SEM/EDS, XPS, and proximate analysis. Furthermore, EIS, CV, and GCD were used to assess electrochemical performance. All the N-doped hydrochars synthesized samples possess crystalline and mesoporous structures with hydroxyl and amide functional groups. The KOH activation improved the specific surface area and pore volume by 8.5 % and 21 %, respectively. The maximum specific surface area and pore volume were found to be 560.72 m2/g and 0.2246 cc/g, respectively. The CV findings demonstrate the battery-like characteristics of the electrocatalysts made with molybdenum (VI) oxide (MoO3) embedded in these N-doped hydrochars, yielding 35.16 F/g specific capacitance at 10 mV/s. In contrast, the GCD's specific capacitance displays 80 F/g at 0.5 Ag−1.

Liquefaction and reliquefaction mitigation of sand specimen treated with prefabricated vertical drains: An experimental investigation

This study examines the performance of prefabricated vertical drains (PVD) against liquefaction and reliquefaction. A series of 102 shakings were performed using 1g shaking table apparatus on untreated and treated sand specimens prepared with 25% relative density. Sinusoidal waveform experimented with three different repeated shaking patterns and independent events for two different frequencies (2 Hz and 3.5 Hz) with 1-min duration. Two different installation methods; drainage alone method (PVD-D) and drainage along with densification (PVD-DD) were experimented. Durability of PVD were examined from geotextile tensile testing apparatus and digital image correlation. These experiments demonstrated excellent durability characteristics of PVD filter even after exposed to repeated shakings. Treated specimens improved the resistance to reliquefaction due to radial drainage offered by PVD which has retarded the excess pore pressure (EPP) generation. In addition, densification induced during the installation of PVD also contributed for restricting EPP, however, the induced sand densification achieved during repeated shaking events were not responsible for increased resistance against liquefaction/reliquefaction. Results indicate that the maximum pore pressure ratio in treated specimens were restricted within threshold design limit (≤0.60) for most of the events, even when the untreated specimens completely liquefied or generated a maximum value near unity.

Influence of laminated porous cathode structure on the performance and mass transfer of Li[sbnd]O2 batteries

The porous cathode is a crucial component of LiO2 batteries, and its porous structure significantly impacts the battery's performance. In this study, a stacked porous cathode was fabricated via roller pressing. The influence of the cathode structure on the battery performance and mass transfer characteristics were examined using experimental and simulation methods. The structural characteristics, electrochemical properties, and overall battery performance of the stacked porous cathode were analyzed. Furthermore, the effects of the cathode structure on mass transfer within the cathode and battery performance were explored through numerical simulation. The results indicate that when the mass ratio of CNTs to ACET on the diaphragm side is 5:1, the cathode exhibits optimal structural parameters, with an average pore size of 24 nm and a maximum pore volume of 0.85564 cm3/g. Concurrently, the battery demonstrates an exceptionally high area specific capacity of 30.35 mAh/cm2. Integrating the simulation findings, it was observed that adjusting the structural parameters of the cathode enhances material transfer efficiency, thereby improving battery performance.

Gas breakthrough in compacted Gaomiaozi bentonite under rigid boundary conditions

Predicting the gas breakthrough pressure of saturated compacted bentonite is crucial for ensuring the long-term safe operation of deep geological repositories for the disposal of high-level radioactive nuclear wastes. In this work, the swelling pressure, water injection, gas injection and mercury intrusion porosimetry (MIP) tests on saturated compacted Gaomiaozi (GMZ) bentonite specimens with a dry density of 1.3 Mg/m³, 1.4 Mg/m³, 1.5 Mg/m³, 1.6 Mg/m³ and 1.7 Mg/m³ were conducted. Subsequently, the relationships between the swelling pressure and average inter-particle distance, as well as between the gas entry pressure and the maximum effective pore size were analyzed and established. Considering that gas migration and breakthrough are all closely related to the pore structures of the tested geomaterials, a novel gas breakthrough pressure prediction model based on the pore size distribution (PSD) curve was constructed using an existing prediction model based on gas entry pressure and swelling pressure. Finally, based on the test results of the specimens 1.5 Mg/m³, 1.6 Mg/m³ and 1.7 Mg/m³, gas breakthrough pressures of the specimens with dry densities of 1.3 Mg/m³ and 1.4 Mg/m³ were predicted. The results show that the calculated gas breakthrough pressures of 0.76 MPa and 1.28 MPa are very close to the measured values of 0.80 MPa and 1.30 MPa, validating the accuracy of the proposed model.

Investigation of hydrodynamic characteristics of an oyster reef under regular waves

Oyster reef living shorelines are popular solutions to mitigate coastal hazards while providing ecosystem services, and their hydrodynamic characteristics deserve further examination. This paper reports an experimental and numerical study of the hydrodynamic behavior of a bagged oyster shell (BOS) reef under regular waves. The dependence of the pore pressure within the reef and the hydrodynamic coefficients on the reef height, length, porosity, and wave parameters are investigated. The results show that the normalized maximum pore pressure ps_m∗ decreases from the seaside of the BOS reef to its leeside and decreases with increasing dimensionless reef length. With increasing wave steepness, ps_m∗ fluctuates with an overall increasing trend. With increasing BOS reef porosity, ps_m∗ decreases at seaside locations and increases at leeside locations; simultaneously, the wave reflection coefficient Kr and the wave dissipation coefficient Kd decrease, and the wave transmission coefficient Kt increases. With increasing wave steepness for a given wave period, Kr and Kt tend to increase, but Kd exhibits the opposite trend. As the dimensionless reef height and length increase, Kt decreases and Kd increases. Multivariate nonlinear regression and genetic programming-based symbolic regression methods are individually used to derive two formulas for predicting the wave transmission coefficient, with the formula from the latter method being found to give a higher prediction accuracy.

Selective laser melting of 316L stainless steel: Porosity dependence on geometric feature size

This technical brief reports an experimental study on the effect of geometric feature size on the porosity in parts made via selective laser melting. Cylindrical features of different diameters were designed on a single part and printed using the same scan strategy. The resultant pores at different cylindrical feature diameters were captured by optical microscopy. The image processing results showed that as the cylindrical feature diameter decreased from 10 mm to 0.8 mm, the porosity increased from 0.11 % to 4.1 %, and the maximum pore size increased from 41.7 µm to 102.2 µm. To identify the reason for this interesting finding, the average areal energy density was calculated at each cylindrical feature diameter. The calculations showed that the different cylindrical feature diameters resulted in local energy density discrepancies. Because the scan strategy had a disparity for the border in comparison to the volume infill, and the areal ratio of the border to the volume infill naturally varied at different cylindrical feature diameters, the average areal energy density was found to vary significantly for cylindrical features of different diameters. The average areal energy density increased from 2.8 J/mm2 to 5.9 J/mm2 as the cylindrical feature diameter decreased from 10 mm to 0.8 mm. That change in the average areal energy density was identified as the cause for the porosity variation in this study.

Prediction of Sand Production from Poorly Consolidated Formations Using Artificial Neural Network: A Case Study, Nahr Umr Formation in Subba Oil Field

Sand production in poorly consolidated formations is a significant challenge to the oil and gas industry, resulting in reduced production and compromised equipment integrity. The oil and gas industry has recently become interested in data analytics because it has significantly simplified, accelerated, and reduced the cost of data visualization. The intriguing new approaches in artificial intelligence development promise to offer long-term solutions to the increasing problems affecting the petroleum industry's operations. Any completion operation in sandstone formations is based on determining whether or not a well will produce sand. It is economically unfavorable to the Nahr Umr Formation to install sand control equipment for wells that don't produce sand. This study aims to create an efficient and precise artificial neural network that can predict sanding in sandstone formations. To achieve this, we developed a two-layered ANN with a back-propagation algorithm using JMP software. The model formulation included various geological and mechanical factors that could impact sand detachment, such as Young’s modulus (YME), Poisson’s ratio, minimum and maximum horizontal stresses (SHMIN and SHMAX), pore pressure, shale volume, and formation strength. The study acquired data from both local fields, specifically the Amarah oilfield, and non-local fields from the literature. Two sets were created from the data: a training set comprising 75% of the data, and a test set comprising 25% of the data, both of which were classified. The speed and accuracy of a learning process in an Artificial Neural Network depends on the size of the data set, the number of hidden layers, and the input parameters. The statistical measures such as accuracy, confusion matrix, root mean square error, and generalized RSquare demonstrate the strong efficacy of the created Artificial Neural Network model. The results indicate a significant likelihood of sand production occurring over the perforation intervals across Su-4 and Su-5 wells. The method's unique feature is its ability to isolate shale areas and identify weak areas capable of producing sand in sandstone formations. In conclusion, it is determined that an Artificial Neural Network employing the back-propagation algorithm is a simple, reliable, and easy-to-use method for accurately predicting sand production.

Core‐flooding experiments of various concentrations of CO2/N2 mixture in different rocks: II. Effect of rock properties on residual water

AbstractDuring CO2 storage in deep saline aquifers, the presence of residual water has an important influence on the storage efficiency and safety. In this study, natural rock cores taken from deep reservoirs in the Ordos Basin and Fukang, Xinjiang are used as research objects. Nine groups of core‐flooding experiments are performed under different CO2/N2 gas mixture ratios to study the influence of rock properties (mineral composition, permeability, porosity and pore structure) on the residual water. Furthermore, the geophysical and chemical properties of rock cores are analyzed by X‐ray diffraction, electron microscopy, field emission scanning electron microscopy and piezoelectric mercury method. The results show that residual water saturation is a quantitative power function of drainage time. The residual water saturation is positively correlated with the total amount of quartz and feldspar and increases with increasing permeability. Moreover, both the average and median pore throat radius show a strong inverse correlation with irreducible residual water saturation; as these radius increase, the residual water saturation decreases. In contrast, the porosity and maximum pore throat radius display a weaker correlation with irreducible residual water saturation. This study is of great value for engineering practices such as the site selection of CO2 storage projects in saline aquifer and improvement of CO2 storage efficiency. © 2024 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

A modified pore evolution particle model applied to CaCO3 decomposition and CaO sintering during calcium looping CO2 cycles

The calcium looping of calcium-based carbonation/calcination cyclic reaction is an efficient decarbonization technology that can be applied to post-combustion carbon capture, solar thermal storage, and enhanced methane reforming hydrogen. The pore structure generated during the calcination stage greatly affects adsorption performance. Hence, the change of pore structure is crucial during the calcination. Existing models related to pore structure still need to be further improved regarding pore formation mechanisms. In this paper, a modified pore evolution model is proposed. The modified pore evolution model contains the kinetic equation, the CO2 diffusion equation, and the vacancy aggregates equation. The modified model considers the possibility of spontaneous pore formation in the mechanism, which can better fit the experimental results and provide higher simulation accuracy. The model reveals the diffusion of CO2 within the particles during decomposition, and spatiotemporal evolutionary properties of pore parameters. The pore change trend is the most obvious when the initial pores are mainly 3 nm mesopores. The pore evolution is relatively stable when the initial pores are mainly 25 nm mesopores. Besides, the particles experience significant pore migration during the sintering stage when the temperature reaches 1273 K. At 1073 K, the maximum pore size occurring during pore evolution did not exceed 40 nm. The model estimates a maximum pore size of more than 60 nm at 1273 K. The modified model can aid in a deeper comprehension of how the pore structure changes throughout the calcination process.

Deposition of CdSe Nanocrystals in Highly Porous SiO2 Matrices-In Situ Growth vs. Infiltration Methods.

Embedding quantum dots into porous matrices is a very beneficial approach for generating hybrid nanostructures with unique properties. In this contribution we explore strategies to dope nanoporous SiO2 thin films made by atomic layer deposition and selective wet chemical etching with precise control over pore size with CdSe quantum dots. Two distinct strategies were employed for quantum dot deposition: in situ growth of CdSe nanocrystals within the porous matrix via successive ionic layer adsorption reaction, and infiltration of pre-synthesized quantum dots. To address the impact of pore size, layers with 10 nm and 30 nm maximum pore diameter were used as the matrix. Our results show that though small pores are potentially accessible for the in situ approach, this strategy lacks controllability over the nanocrystal quality and size distribution. To dope layers with high-quality quantum dots with well-defined size distribution and optical properties, infiltration of preformed quantum dots is much more promising. It was observed that due to higher pore volume, 30 nm porous silica shows higher loading after treatment than the 10 nm porous silica matrix. This can be related to a better accessibility of the pores with higher pore size. The amount of infiltrated quantum dots can be influenced via drop-casting of additional solvents on a pre-drop-casted porous matrix as well as via varying the soaking time of a porous matrix in a quantum dot solution. Luminescent quantum dots deposited via this strategy keep their luminescent properties, and the resulting thin films with immobilized quantum dots are suited for integration into optoelectronic devices.

Mechanical integrity analysis of caprock during the CO2 injection phase

Abstract CO2 geological storage is one of the important means to mitigate the greenhouse effect. The safe underground storage of CO2 largely depends on the mechanical integrity of the caprock. This paper establishes a fluid-solid coupling model for CO2 geological storage to study the changes in pore pressure, vertical displacement, and effective stress in the caprock during the CO2 injection process. Combined with the Mohr-Coulomb criterion, the study determines whether mechanical failure occurs in the caprock. The results indicate that, at the beginning of CO2 injection, significant changes occur in the pore pressure, vertical displacement, and effective stress at the bottom of the caprock near the injection well, which then tend to stabilize; the maximum pore pressure at the bottom of the caprock reaches 36.08 MPa; the caprock near the injection well is considered the most critical area, where the risk of mechanical failure is highest; at the end of CO2 injection, the stress state does not reach the limit, and the caprock remains stable.

Influence of physical properties and shear rate on static liquefaction of saturated loess

Flow sliding instability of saturated loess slopes is a common geological hazard in loess areas of China. Previous studies have found that the occurrence of flow-slip loess landslides is closely related to static liquefaction and is controlled by physical characteristics and load conditions. In this work, we comprehensively study these influences of physical properties (i.e. initial pore structure, gradation, dry density) and shear rate on the static liquefaction of saturated loess through a series of consolidated undrained triaxial tests, and the effect mechanism of these related factors on the static liquefaction of saturated loess are also discussed. The results present that: (1) The peak deviator stress and the maximum pore pressure of the undisturbed loess are much greater than these of the remodeled one under each level of confining pressure (except 450 kPa). Further, the calculated liquefaction potential index (LPI) of undisturbed loess is much greater, indicating that undisturbed loess is more prone to static liquefaction due to the initial pore structure. (2) The lower the relative clay/silt content ratio of the saturated remodeled loess, the stronger the potential liquefaction ability. With the increase of the relative content of clay from 0.125 to 0.698, the stress-strain curve gradually transitions from strain softening to hardening. (3) The remodeled loess show the steady-state strength tends to continuously increase with the increase of dry density from 1.38 g/cm3 to 1.56 g/cm3, while the LPI increases first and then decreases, and the largest value appears when the dry density reaches to 1.44 g/cm3. The reason is that the value of 1.44 g/cm3 is the normal consolidated condition, which essentially reflects the potential liquefaction change during the transformation from under consolidated to over consolidated state.(4) The effect of shear rate on the stress-strain curve of remolded loess is not significant, but the peak strength and ultimate pore pressure show a trend of increasing and then decreasing with the increase of shear rate. There exists a “critical shear rate “of 0.1 mm/min reflecting the liquefaction of loess is more likely to occur when reaches to this critical value. (5) Based on the comparison of static liquefaction tests, the influencing factors of static liquefaction of saturated loess are: initial pore structure> gradation > dry density > shear rate. This study can provide a systematic evaluation for understanding the influencing factors of static liquefaction capacity of saturated loess (especially remolded one), and also has a reference for explaining the loess flow-sliding failure mechanism under disturbance conditions.

Freeze-thaw cycling of nano-SiO2-modified recycled aggregate in concretes: Hydro-thermal-mechanical modeling

The freeze-thaw cycling in the cold region causes severe damage to the concrete, which seriously affects the durability of concrete. In this paper, nano-SiO₂ (NS) modified RAC (NS-RAC) specimens were prepared by impregnating RCA with a 3 % NS dispersion for 48 h with following frost resistance assessed experimentally. To further fully understand the performance of NS-RAC under freeze-thaw (F-T) cycles, a comprehensive hydro-thermal-mechanical coupling model was established to simulate the damage behavior of NS-RAC under F-T conditions. A random polygon microstructure model of RAC was developed, and the characteristics of RCA and three types of ITZs were discussed. The damage control equation for RAC during the F-T process was defined based on the coupling effects of percolation, temperature, and stress in a porous medium. The F-T cycle tests show that the compressive strength of NS-RAC samples after 100 F-T cycles is 9.04 MPa higher than that of RAC. Numerical simulation results indicate that, compared to RAC without NS, the maximum pore pressure, crystallization pressure, and maximum principal stress of samples with 3 % NS after the first F-T cycle are reduced by 3.84 %, 4.36 %, and 2.26 %, respectively. During the F-T cycle, with increases in ITZ width, aggregate gradation range, RCA replacement rate, and temperature difference, the internal stress of NS-RAC specimens increased to varying degrees. This study provides insights into the F-T damage of RAC in severe cold regions and promotes the practical engineering application of RAC in such environments.

Comparison of non-reactive solute transport models for the evaluation of fluid flow in packed beds with implications for heap leaching practice

This study investigated the effects of mean particle size fraction, bottom particle size, particle porosity and wettability on solution scale preferential flow behaviour via step input tracer tests in drip irrigated, narrowly and mixed-sized beds under steady state fluid flux. Nine solute transport models were used to quantify this behaviour reflected in the residence time distribution (RTD) profiles. Four were empirical models: three compartmental model configurations (CM-1, CM-2, CM-3) and tanks-in-series (TIS) model. The remainder five models were semi-empirical: advection dispersion (AD), piston exchange (PE), piston exchange - diffusion variant (PE-D), piston dispersion and exchange (PDE) and piston dispersion and exchange - diffusion variant (PDED). The model fit results showed that the mono-porosity TIS, AD and CM-2 models were the worst performers, while the dual porosity PDE and novel PDE-D models achieved the lowest average error values across the various systems. Higher levels of particle wettability coupled with capillary effects produced peculiar RTD curves that were relatively more difficult for the mono-porosity models to simulate. The model parameters investigated included the longitudinal dispersion coefficient (Dds), dead to total volume fraction (VD/VT), dynamic to total saturation fraction (βd/βT), overall mass transfer coefficient (Kma) and maximum diffusional pore length (X). The results showed that an increase in the average particle size within the beds led to higher VD/VT, Dds and X values, but lower βd/βT and Kma values. These indicate an overall increase in solution scale preferential flow behaviour. Decreased capillary suction and connectivity between particle pores and inter-particle voids were deemed responsible for the results. Higher levels of particle porosity acted as a buffer against these effects. Overall, the results highlight the benefit of the addition of fines (0.1–1 mm particles) during the agglomeration process in heaps to help reduce solution scale preferential flow behaviour and increase liquid hold-up. This is more necessary when the ore has low to moderate levels of porosity (surface area: <2 m2/g) and will also increase the modelling options available as most models performed better fitting data from such beds.