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Quaternary mudstone biogas reservoirs in the Qaidam Basin have shown great potential. However, complex pore structures with high clay contents and high heterogeneity limit the understanding of the storage and migration principles of these reservoirs. In this paper, HPMI and nitrogen adsorption experiments, in combination with NMR experiments under water saturation, centrifugation, various drying temperatures and other conditions, were adopted to determine the pore structure characteristics. Specifically, the reservoir space types and pore radius distribution characteristics were clarified. The cutoff values for different types of pores were identified based on the water-saturated mudstone NMR T2 spectra for full aperture distribution scales jointly characterized by mercury injection and nitrogen adsorption experiments. Furthermore, the three pore components and the saturation of different fluids were obtained. The research results indicate that the mudstone biogas reservoir has developed various reservoir spaces, and the pore size is primarily in the micronanometer range. The average total porosity reaches 27.28%, but the proportion of movable water pores is only 9.23% with poor fluid mobility, and the fluids in the pores are mostly capillary-bound water and clay-bound water. Among the different lithologies, argillaceous sand is more likely to become a good production layer. [ABSTRACT FROM AUTHOR]

Nowadays, when regenerable alternative green sources are attracting more caution under sustainability targets, kapok and coconut fibers, known as natural fibers, have come to the fore as a very significant raw material source. In this experimental study, compressive strength, thermal insulation, and pore structure characteristics of kapok fiber (KP)– and coconut fiber (CC)–incorporated concrete samples under different curing conditions were analyzed. For that purpose, randomly distributed fiber-incorporated concrete mixtures containing 0%, 0.5%, 1%, and 1.5% KP and CC fiber by the weight of cement were prepared and under H2O2 and NaClO curing conditions, the effects of KP and CC fiber inclusion on properties mentioned above of fiber-incorporated concrete samples were researched in detail. Experimental results depict that a maximum thermal conductivity coefficient decrease of 24.31% was detected at a content ratio of 1.5% by the reason of the pore modification effect of used natural fibers in the H2O2 curing group. Because of the remarkable pore modification effect of KP fiber incorporation into the cement matrix compared to the CC fiber inclusion cases, strong linear correlations revealing the insulation-strength mechanism could be detected for both H2O2 and NaClO curing cases. This work intends to promote sustainable development in the building industry by integrating natural fibers into concrete mixtures as an innovative design approach. [ABSTRACT FROM AUTHOR]

In order to tackle the issue of excessive coal dust and hydrogen sulfide (H2S) concurrently in underground coal mines, an alkaline dust suppressant was formulated by combining surfactant sodium sec-alkyl sulfonate (SAS60) and sodium carbonate (Na2CO3) at a certain mass ratio, meant for injection into coal seams. This study principally targeted long-flame coal extracted from Hequ County, located in Shanxi Province, China. The objective was to investigate and analyze the underlying process of how alkaline dust suppressants affect the wettability of coal. A comprehensive strategy including contact angle determination, Fourier transform infrared absorption spectrometer(FTIR) analysis, low-temperature nitrogen adsorption tests, scanning electron microscope(SEM) experimental studies, and molecular dynamics simulations was employed for this examination. The results revealed that merging Na2CO3 with SAS60 could reduce the coal's contact angle. Despite the core structure of the coal surface staying unchanged after alkaline dust suppressant treatment, a rise in the number of hydrophilic functional groups was observed. This count notably surpassed the amount of hydrophobic functional groups, consequently boosting the coal's hydrophilicity. The permeability of the examined coal specimens was chiefly affected by the existence of macropores and mesopores. Processing with 0.05 wt% SAS60 and 1.0 wt% Na2CO3, the coal acquired additional pores and cracks, causing an upswing of average pore size by 25.79% and a 30.64% increase in the maximum gas adsorption. This facilitated more straightforward infiltration of water into the coal dust. Molecular dynamics simulation outcomes indicated a closer affiliation between coal and water following the incorporation of Na2CO3. It led to a heightened activity in water molecule movement, fortifying intermolecular electrostatic interactions, and fostering the creation of hydrogen bonds. Consequently, this improved the coal's wettability. The increase in the mass fraction of Na2CO3 directly corresponds to a more considerable enhancement in the solution's ability to wet the coal. The outcomes of the molecular dynamics simulation validated the experimental results' precision. [ABSTRACT FROM AUTHOR]

Rock pore structure coupled with fluid pressure plays an important role in controlling fault slip behavior. Observation of fluid-induced seismicity in geoenergy extraction has raised fundamental questions about the physics of fault rock structure and fault frictional stability in the presence of fluid. Here, we change the pore structure of faults by thermal treatment and report on the frictional stability of granite faults with pore evolution and pore fluid pressure in velocity stepping experiments under the rate-and-state framework, where the variation of pore fluid is monitored. The experiments under constant fluid pressure show that pore structure propagation leads to an increase in friction coefficient from 0.71 to 0.78. As the degree of pore propagation increases, the drained fault exhibits a transition from velocity strengthening to weakening behavior. The decrease in frictional stability could be caused by the coupling between the pore fluid and the well-connected pores, namely “fluid oscillation”. Pore pressure overpressurization could develop and cause non-uniform stress distribution along the fault surface due to pore fluid oscillation at velocity steps. The time required to equilibrate fluid pressure could be prolonged by fluid oscillation, leading to intrinsic velocity strengthening behavior appearing as velocity weakening. The decrease in rate-and-state parameter with elevating pore fluid pressure on high-porosity fault corroborates the fluid-induced fault destabilization. The fluid oscillation at the greater pore pressure could be responsible for fault reactivation. Therefore, the coupling effect of rock pore structure with pore fluid could be a potential mechanism governing fault frictional stability. [ABSTRACT FROM AUTHOR]

The modification of petroleum resin (PR) by catalytic hydrogenation is an upgrading technology for producing high-value-added hydrogenated petroleum resin (HPR) from of pyrolysis petroleum by-product. This research employed alumina supports with different pore size distributions to prepare supported Mo-Ni type catalysts and investigated their catalytic hydrogenation performance on C9 petroleum resin. Catalysts prepared with bimodal pore alumina (BPA) supports effectively overcome the limitations of internal diffusion and increase the quantity of active sites, thus increasing the catalytic activity for hydrogenation. The experimental results demonstrated that MoNi/BPA achieved a hydrogenation degree of 99.94% for HC9PR, with the hydrogenated product having a Pt–Co colour of 2.37 Hazen. After 140 h of reaction, the hydrogenation degree of HC9PR remained at 96.51%, and the Pt–Co colour value was lower than 40 Hazen. This investigation confirms that solving the mass transfer issues of petroleum resin molecules in the pores of supported catalysts is key to designing efficient hydrogenation catalysts for petroleum resin. [ABSTRACT FROM AUTHOR]

Radon release rate is one of the most important indicators to assess the environmental radon hazard. In the loess-covered area of northern China, the decay of uranium ore associated with the coal seams has caused elevated radon concentrations in overlying soil layers, significantly increasing the risk of various respiratory diseases to residents. In this paper, the effects of burial depth and soil type on radon release rate were investigated by X-ray diffraction (XRD) analysis, low-temperature nitrogen adsorption (LTNA) experiments, and measurement of radon concentrations in the soil based on the pore structure characteristics of soil layers. The results showed that all N2 adsorption isotherms in the soil were inverse-S shaped with well-developed mesopores. The number of mesoporous materials was positively correlated with the radon release rate of the soil. The overall tendency of the radon release rate was to firstly increase and then decrease with increasing depth. The relative degree of variation in radon exhalation rate between adjacent soil layers was in the order as follows: red clay > paleosoil > loess > pedocal. The results of this study can help to understand the release pattern of radon in different soils and provide valuable references in reflecting the characteristics of radon release in regional soils. [ABSTRACT FROM AUTHOR]

Due to excavation disturbances and the coupled hydro-mechanical effects, deep rock masses experience nonlinear large deformations in the surrounding rock, necessitating an urgent exploration of the rock damage and failure mechanisms from the perspectives of hydro-mechanical coupling and mechanical properties. Therefore, this study conducted uniaxial cyclic loading-unloading tests on sandstone samples with different water contents (0%, 0.26%, 0.52%, 0.78%, and 1.04%) to investigate the microstructural evolution, energy evolution laws, and failure characteristics under varying water contents and cyclic loading conditions. The main conclusions are as follows:(1) Concerning micro-pore structures, as the water content increases, the porosity and maximum pore size of the sandstone first decrease and then increase. At 0% water content, the porosity is 4.82% and the maximum pore size is 31.94 µm. At 0.26% water content, both porosity and maximum pore size decrease to 3.03% and 16.15 µm, respectively. When the water content reaches 1.04%, the porosity and maximum pore size increase to 14.34% and 45.99 µm, respectively. (2) Regarding energy evolution laws, the energy evolution of the specimens during cyclic loading-unloading mainly converts to elastic energy, showing a step-wise increase in energy. Further analysis reveals that the water content has a significant impact on the dissipation energy coefficient of the sandstone. At lower stress levels (<0.4σmax), the water content has a negligible effect, while at higher stress levels (>0.85σmax), an increase in water content leads to increased fluctuations in the dissipation energy coefficient. (3) In terms of failure characteristics, with increasing water content, the failure mode of the specimens shifts from primary crack failure to microcrack failure, corresponding to the energy evolution during cyclic loading-unloading processes. [ABSTRACT FROM AUTHOR]

To explore the influence of surfactant concentration on the pore structure and permeability of coal samples during the chemical enhancement of coalbed methane production, different kinds and different concentrations of surfactants were added to the chemical solution, and the coal samples were soaked. Methods such as low-field nuclear magnetic resonance testing (NMR), fractal theory, permeability testing, surface tension testing, and contact angle testing were employed to analyze the variation patterns of coal sample pore structure, fractal characteristics, and permeability, and to explore the correlation between surface tension, contact angle, and the degree of pore structure development. The results show that the increase in total porosity of coal samples, the increase in the seepage pore porosity, the decrease in Dt, and the growth rate of permeability increase with the increase in surfactant concentration, and are negatively correlated with the surface tension of the solution and the contact angle of the coal-solution interface, while the decrease in Ds is not significantly correlated with surfactant concentration, surface tension, or contact angle. In terms of the erosion effect of a chemical solution on coal samples, the influence of contact angle is greater than that of surface tension, while surface tension has the greatest impact on the development of adsorption pores. By adding different surfactants, the surface tension of the chemical solution and the contact angle of the coal-solution interface can be controlled, further promoting the erosion of coal samples, which is of positive significance for the chemical enhancement of coalbed methane production. [ABSTRACT FROM AUTHOR]

Rock pores crack and expand subjected to freeze-thaw cycles, resulting in the reduction of their physical and mechanical properties, it is necessary to study its evolution and deterioration mechanism. However, the majority of existing studies employ a singular pore testing methodology, and neglecting the impact of the thawing process on frost heave damage in rocks. To address this, this study employs a combination of non-destructive testing techniques, including nuclear magnetic resonance (NMR) and computed tomography (CT) scanning, to comprehensively analyze the evolution of pores during freeze-thaw cycles. Investigating the migration and redistribution of pore water and its effect on frost heave damage in sandstone during the freeze-thaw process. Finally, the study examines the mechanisms of pores frost heave initiation and propagation in sandstone during freeze-thaw cycles. The results demonstrate that freeze-thaw cycles result in an expansion of pore volume at all scales within the samples. However, the degree of expansion varies, with macropores, mesopores, and micropores exhibiting a less pronounced increase in sequence. During the freeze-thaw process, water in sandstone pores redistributes, moving from larger to smaller pores. The saturation of water increases in micropores, but decreases in mesopores and macropores, thereby rendering micropores more susceptible to frost heave initiation in subsequent freeze-thaw cycles. With repeated freeze-thaw, the expansion of rock pores will continue in the direction of the lowest tensile strength, eventually forming macroscopic cracks. This study provides valuable insights into the mechanisms of freeze-thaw disaster genesis in rock masses. [ABSTRACT FROM AUTHOR]

Under the influence of geostress, the thick hard sandstone roof layer at the upper end of the mining area is prone to faults, rockbursts, and sudden collapses during deep coal mining. Blasting top-cutting and depressurization technology centered on over-the-top deep hole blasting is an important method for this type of dynamic disaster control. To characterize the pore structure of sandstone damaged by blast loads and the change in energy dissipation in different pressure environments, specimens with different degrees of blasting damage were measured via nuclear magnetic resonance (NMR) spectroscopy. A triaxial test loading device was used to carry out compression tests on undamaged, vibration-damaged, and blast-damaged specimens under different pressures. The effects of blast load and confining pressure on the porosity, pore structure, energy dissipation, and fracture morphology characteristics of sandstone specimens were analyzed. (1) The T2 spectral curves of the sandstone specimens were all bimodal, and the signal intensity of the main peak was much greater than that of the secondary peak. The peak T2 spectrum curves of the blast-damaged specimens and vibration-damaged specimens were 1.21 and 1.14 times greater than those of the undamaged specimens, respectively, and the mean values of the peak relative area were 1.11 and 1.20 times greater than those of the undamaged specimens, respectively. The number of internal pores in the specimens increased significantly after blast loading. (2) The pore structure distributions in the sandstone specimens were dominated by the proportions of micropores and small holes. The blast load changed the internal pore ratio structure of the specimen, transformed the small holes into medium holes and large holes, and increased the porosity of the specimen. (3) Blast load damage could reduce the energy absorption and energy storage effects of sandstone specimens and weaken roof sandstone and reduce the stress concentration. Furthermore, the impact of the blasting damage area was greater than that of the vibration damage area. (4) With increasing confining pressure, the fracture degree of the specimen first decreased and then increased. Due to the high-energy storage abilities of the undamaged specimens, the macroscopic rupture degrees of the undamaged specimens were greater than those of the specimens damaged by vibration and blasting. The blasting load will cause damage to the roof sandstone to achieve the effect of pressure relief, so as to reduce the occurrence of geological disasters such as roof fault and rock burst. [ABSTRACT FROM AUTHOR]

Fly ash (FA) contents and water-binder ratio (w/b) are the important factors influencing the mechanical characteristics of cement-based materials, meanwhile the porous structure of material plays a vital role. The compressive strength and water permeability of cement-based samples with high-volume FA contents (0%, 30%, 40%) and different w/b (0.3, 0.4, 0.5) were measured. The results demonstrated that higher FA contents or greater w/b led to lower compressive strength and higher water permeability at an early stage. The pore structure features of samples were obtained using mercury intrusion porosimetry and low-temperature nitrogen gas adsorption (LT-NGA). The pore size distributions (PSDs) and the matrix compressibility in cementitious materials were also analyzed, with the compression coefficient KC ranging from 11.919 to 1.249 × 10−4 MPa−1. Increasing the FA content and reducing the w/b resulted in an optimized pore structure of the samples, characterized by changing the main pore type from mesopores (10–50 nm) to micropores (< 10 nm). The pores and fractures in the samples also had distinct multifractal characteristics. The strongest negative correlation between the compressive strength and the width of the multifractal generalized spectrum was proved by Pearson correlation analysis, and the correlation coefficient (ρ) was − 0.93. Furthermore, the water permeability had the strongest positive correlation with porosity, with ρ of 0.91. The content of macropores (50–10 μm) had greater influence on its macroscopic properties. The dense structure accompanied by homogeneous PSDs is advantageous for enhancing the strength and anti-permeability properties of cement-based materials. [ABSTRACT FROM AUTHOR]

Activated carbon paper is a type of porous carbon material with a highly developed pore structure and a large specific surface area. It finds extensive applications in adsorption, complexation, and catalyst support. To prepare high-performance activated carbon paper, this study investigates the changes in performance and structure of Poly(p-phenylene terephthalamide) (PPTA) paper under CO2 activation, ZnCl2 activation, H3PO4 activation, and NaOH activation conditions. The research reveals that carbon paper after CO2 activation has a certain tensile strength (0.36 MPa), while chemically activated carbon paper lacks tensile strength. Incorporating 15% carbon fiber (CF) into PPTA paper increases the tensile stress (1.26 MPa) and tensile strain (4.18%) of the activated carbon paper. NaOH-activated carbon paper has the highest specific surface area (1321.6 m2/g), the most disordered carbon structure (ID/IG = 1.22), the lowest carbon yield (23.9%), and a pore rate 4.16% higher than that of CO2-activated samples. The activated carbon paper prepared by ZnCl2 activation has the highest content of C = N bonds, with the nitrogen content of pyridine increasing by 31.8% compared to CO2 activation. This indicates that ZnCl2 protects the N elements in PPTA paper during the activation process, preventing their decomposition during carbonization. The activated carbon paper prepared by H3PO4 activation has the lowest electrical conductivity (1.62 S/cm). [ABSTRACT FROM AUTHOR]

Mercury intrusion porosimetry (MIP) is widely used for coal pore structure characterization, however, the matrix compressibility (MC) can lead to overestimated measurement results. Determination of MC is crucial for revealing the influence of pore structure on coalbed methane (CBM) flow behavior. In this study, MIP and low temperature N2 adsorption (LT-N2A) were conducted on 15 coal samples from major coal-producing regions in Northern China. The MIP data were corrected using MC theory, and the effects of coal rank and pore structure on coal MC were analyzed. The influence of MC on fractal dimension was elucidated, and the sensitivity of three fractal models to MC was effectively evaluated. Finally, the impact of MC on the coalbed methane (CBM) exploitation was discussed. The results show that low-rank coals have higher MC than medium/high-rank coals, and the MC coefficient follows a cubic polynomial relationship with coal rank, with two inflection points located at 1.4–2.5%, respectively. Micropores and transition pores are the main contributors to MC, for corrected data, the pore volume of both types of pores decreases significantly. The corrected pore size distribution exhibits better agreement with the LT-N2A measurement results, particularly in peak position and size for pores between 5 and 50 nm. This suggests the potential of corrected MIP data to supersede the combined use of MIP and LT-N2A data. MC can lead to overestimation of the fractal dimension, with the thermodynamic model showing the lowest sensitivity to MC. After the microfractures in medium/high-rank coal are greatly compressed, the compressional deformation of micropores and transition pores begins to have a significant impact on the CBM transport. The research results are of great significance for deeply understanding the mechanism of CBM transport. [ABSTRACT FROM AUTHOR]

We focused on the efflorescence induced microstructural evolution of ettringite-rich systems prepared with calcium aluminate cement (CAC) and anhydrite. The effects of anhydrite on the visible efflorescence, and the corresponding capillary absorption of CAC-anhydrite mortars were revealed. The composition and microstructure of efflorescence-causing substances were investigated by optical microscope, in-situ Raman spectroscopy, scanning electron microscope, energy dispersive spectrometer, thermogravimetric analysis, and differential scanning calorimetry, at multi-scales. Results indicate that, besides the calcium carbonate, ettringite is another main component of efflorescence-causing substances. Compared with the neat CAC mortars, the addition of anhydrite has a significant effect on the degree of efflorescence by acting on the composition of hydration products and pore structure. In addition, methods are proposed for the prevention of efflorescence of CAC-anhydrite binary system. [ABSTRACT FROM AUTHOR]

To improve the efficiency of coalbed methane and recoverability of reservoirs, enhanced fracturing technology is usually required to improve the low porosity and permeability status of coal reservoirs. As a feasible method for strengthening permeability, microwave–LN2 freeze–thaw (MLFT) cycles modify the microscopic pore structure of coal through the coupled effect of temperature stress changes, phase change expansion, and fatigue damage. 1H nuclear magnetic resonance combined with fractal dimension theory was used to characterize quantitatively the pore system and geometric features of coal. The geometric fractal model constructed using the T2 spectrum indicates that the fractal dimensions Dp and De have high fitting accuracy, demonstrating that percolation and effective pores exhibit good fractal characteristics. Dp and De are correlated negatively and positively, respectively, with the cyclic parameters. The relevance analysis shows that the NMR fractal method can reflect the pore–fracture heterogeneity of coal, which has a significant effect on the percentage of fluid migration space. This study reveals that MLFT cycles have significant enhancement effects on promoting the extension of multi-type pores structures within the coal matrix, as well as the connectivity and permeability of cracks. [ABSTRACT FROM AUTHOR]

In China, significant progress has been made in the exploration and development of coalbed methane (CBM) in medium- to high-rank coals. However, the exploration and development potential of CBM in low-rank coals in the Zhalainuoer coalfield is unknown. In this study, various testing methods were utilized, including low temperature N2/CO2 adsorption, field emission scanning electron microscopy, and nuclear magnetic resonance, to investigate the pore structure characteristics of low-rank coals in the Zhalainuoer coalfield, so as to further evaluate the occurrence space of CBM therein. The results revealed that the prevalent pore types in the low-rank coals were "ink bottle" shaped pores and semi-closed pores, and micropores provide the main specific surface area (SSA) and total pore volume (TPV). Moreover, there is no significant correlation between vitrinite content and fractal dimension, while pore SSA and TPV are correlated positively with D1 but negatively with D2. The coalification degree significantly impacts the pore characteristics of the coal reservoirs. With coalification degree increasing, the SSA and TPV of micropores and transition pores generally exhibited a pattern of initially decreasing and then increasing. These research findings establish a theoretical foundation for the exploration and development of CBM in the Zhalainuoer coalfield. [ABSTRACT FROM AUTHOR]

As a crucial factor that influences the hydraulic fracturing effectiveness of coal seams, fracturing fluids have garnered increasing attention. Among them, acid fracturing fluids have demonstrated positive impact on the pore transformation of coal, but high-strength acid fracturing fluids can cause corrosion damage to mechanical equipment. In this study, we employed acetic acid to formulate four types of weak acid fracturing fluids with varying concentrations and conducted soaking experiments. We analyzed the changes in the physical and chemical structure of coal samples before and after treatment using Fourier-transform infrared spectroscopy and X-ray diffraction analysis. The changes in the pore structure of coal samples before and after treatment were characterized by nitrogen adsorption and scanning electron microscopy. Our findings indicate the following: (1) The effects of different concentrations of acetic acid fracturing fluid on functional groups and microcrystalline structure vary. The 5% concentration fracturing fluid had the most significant impact on the organic structure of coal samples, with decreases in the area of hydroxyl structure, aliphatic structure, and oxygen-containing structure of 2.97%, 1.37%, and 0.68%, respectively. The 6% concentration fracturing fluid had the most significant impact on crystal structure, leading to a high degree of recrystallization and a fragile crystal network structure. (2) Fracturing fluids with concentrations below 7% can increase the number of mesopores and simplify the pore structure, while concentrations above 7% can lead to an increase in micropores and a more complex pore structure. (3) After the action of fracturing fluid, carbonate minerals are dissolved, and the pores of coal samples increase. However, excessively high concentrations of acetic acid fracturing fluid can facilitate shedding of mineral particles and block some pore channels, worsening the connectivity between pores. (4) The octadecylamine acetate formed by the combination of octadecylamine and acetic acid develops as a partial film on the surface of a coal body, reducing the roughness of the fracture surface and facilitating the flow of the fracturing fluid. Our findings provide theoretical support for the preparation and selection of weak acid fracturing fluids. [ABSTRACT FROM AUTHOR]

To realize the resource utilization of solid waste (coal slime) and further the dual carbon goals, utilizing coal slime and coal ash as adsorbates for CO2 capture is crucial. This study employed low-temperature N2 adsorption, low-pressure CO2 adsorption, X-ray diffraction, X-ray fluorescence, and isothermal adsorption tests to assess coal slime and coal ash's pore/mineral composition characteristics. Subsequently, the influence on CO2 adsorption was analyzed to reveal the CO2 adsorption mechanisms of pores and clay minerals, and CO2 molecule adsorption behavior. The results showed that: (1) ashing led to reductions in total pore volume, specific surface area, micropore volume, and micropore specific surface area, accompanied by substantial decreases in micropores and mesopores; (2) ashing generated high-temperature stable mineral species, including quartz, andalusite, hematite, and gypsum, while all calcite decomposed into CaO; (3) coal slime exhibited greater CO2 adsorption capacity than coal ash, influenced by pore structure and clay minerals; (4) the adsorption behavior of coal slime and coal ash likely aligns with micropore filling theory, suggesting CO2 is adsorbed within the 0.30–1.47 nm pore structure. This research contributes to optimizing coal by-product utilization in mining areas and exploring adsorbate materials for CO2 sequestration in abandoned goaf. [ABSTRACT FROM AUTHOR]

The pore structure of coal plays a key role in the effectiveness of gas extraction. Conventional hydraulic fracturing techniques have limited success in modifying the pore structure using clean fracturing fluid (CFF), and the stimulating effects of ultrasonic can enhance the effectiveness of CFF in modifying coal pore structures. To research the effects of ultrasonic stimulation on the pore structure of medium to high-rank coal when using CFF, this study employed mercury intrusion porosimetry (MIP) and low-temperature nitrogen adsorption (LT-N2A) methods to analyze the changes in pore structures after cooperative modification. The results indicate that the pore volume and surface area of medium to high rank coal exhibit an increase and followed by a decrease with increasing Ro,max values, while the average pore diameter and permeability demonstrate a decrease and followed by an increase with Ro,max. Although there are some variations in the results of MIP and LT-N2A analysis for different pore size ranges, the overall findings suggest that ultrasonic stimulation in conjunction with CFF effectively alters the coal pore structure. The most significant improvement was observed in coking coal, where pore volume increased by 22%, pore area decreased by 11% and tortuosity decreased by 47%. The improvement of lean coal is the smallest, the pore volume increases by about 7%, and the surface area decreases by about 14%. It is found that the modification of coal pore volume is mainly concentrated in transition pores and macropores. These research outcomes provide valuable insights into the application of ultrasonic technology in coalbed gas extraction. [ABSTRACT FROM AUTHOR]

The Permian Fengcheng Formation (P1f.) in the Hashan area, situated on the southwestern margin of the Junggar Basin, has witnessed a remarkable breakthrough in shale oil exploration in recent years with nearly 789 million tons of shale oil resources. As a unique set of mixed sedimentary shales, the Fengcheng Formation in the Hashan area is characterized by mixed sedimentation of terrigenous siliciclastic sediments, authigenic minerals, and tuffaceous materials. However, the understanding of pore characteristics in the mixed sedimentary reservoir still remains limited, prohibiting accurate estimation of the oil content and insights into oil mobility. Scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury injection capillary pressure (MICP), nuclear magnetic resonance (NMR), X-Ray Computer Tomography (X-CT), and geochemical analysis were performed to investigate the pore size distribution and main controlling factors of the mixed sedimentary reservoir. Results showed that the main pore types in the mixed sedimentary reservoir are intergranular pores and dissolution pores. The pores of the P1f. mixed shales in the Hashan area were classified into II-micropores (< 25 nm), I-micropores (25–100 nm), mesopores (100–1000 nm) and macropores (> 1000 nm). In general, the mixed sedimentary rocks of P1f. formation feature few macropores but a large number of micropores and mesopores. The CS exhibits the most favourable physical properties among all lithofacies. It is concluded that the abundance and maturity of organic matter, mineral composition, sedimentary structure, and diagenesis of reservoir together impact the pore structure in the mixed sedimentary reservoirs. The maturity of organic matter and the content of tuffaceous minerals are the most significant in influencing the pore structure of P1f. shales. Overall, the pore structure of complex lithologic reservoir formed by mixed deposition and its influence on physical properties are studied, and the characteristics of the microscopic pore-throat system of the dominant lithofacies in the Hashan area are clarified, which is of great significance as a guide for the exploration and development of mixed sedimentary reservoirs in continental shale oil in China. [ABSTRACT FROM AUTHOR]

Nowadays, some fracking fluids can enable resourceful extraction of coalbed methane and reduce greenhouse gas emissions. However, their toxicity or corrosiveness will cause harm to downhole workers and pollute groundwater resources. Thus, five kinds of clean composite fracturing fluids were developed in this paper by using starch solution as the matrix and adding various preparations. The change rule of methane adsorption capacity by microstructure changes of coal samples was investigated systematically, and the optimal composite fracturing fluid was determined. The results showed that the new fracturing fluid increased the degree of aromatic ring condensation by 43.3% and the average pore size by 52.1%. Also, the adsorption constants of a value decreased by 11.6% and b value decreased by 23.9%, which can remarkably reduce the methane adsorption. The experimental results provide theoretical support for the clean production of coalbed methane. [ABSTRACT FROM AUTHOR]

The porosity and pore structure of mud shales are crucial for shale oil and gas storage and transportation. Although the change of organic matter state in thermal evolution has a significant effect on pore formation, the mechanism and main controlling factors still need to be deeply explored. In this paper, we selected the shale of the Yanchang Formation in the southeastern Ordos Basin as an object, and used low-pressure N2/CO2 adsorption, He density method, high-pressure mercury compression, and field FE-SEM to deeply investigate the relationship between thermal evolution and pore development in organic matter-rich shale. The experimental results show that FE-SEM observation reveals that the organic matter pores of the shale in the Long 7 section of the Extension Formation show four developmental states, in which the organic matter in the undeveloped pores is mainly of higher plant origin, solid asphalt and laminated organic matter. The organic matter with highly developed pores is nanofibrous, similar to extracellular polymers. Comparison of thermal simulation experiments shows that the high-pressure semi-closed system has stronger hydrocarbon drainage strength than the closed glass tube system. In the oil generation stage, the pore volume of both systems decreased, mainly due to oil filling; while the oil cracking stage was the main pore development period, especially in the high-pressure semi-closed system; Simulation experiments with different organic matter types and contents showed that the mud shale with better organic matter type and TOC content was more prone to hydrocarbon drainage and pore growth. Compared with type II/II mud shale, type I and II are more likely to form macropores, and compaction has an inhibitory effect on the formation of macropores. This study reveals the close relationship between the pore development of mud shale and its thermal evolution of organic matter, which provides an important reference for shale oil and gas exploration. [ABSTRACT FROM AUTHOR]

The current study examines the strength and transport properties of reclaimed asphalt pavement (RAP) inclusive pervious concrete (PC) pavement mixes containing various industrial and agricultural wastes such as silica fume (SF), fly ash (FA), and bagasse ash (BGA). Apart from a conventional PC mix (containing natural aggregates) and a 100% RAP inclusive PC mix, seven different mixes were developed by mixing 100% RAP aggregates with SF (5 and 10%), FA (10 and 15%), and BGA (5, 10, and 15%) as partial replacements for ordinary Portland cement. The above-mentioned PC pavement mixes were investigated for density, porosity, permeability, compressive strength, modulus of rupture, and abrasion resistance. The interconnected pore structure of conventional PC and RAP-PC pavement mixes was investigated using 2D image analysis and X-Ray microcomputed tomography. Based on the laboratory results, it can be stated that the inclusion of RAP significantly improves the transport properties of PC pavement mixes with increased porosity and permeability values. This was primarily due to a more interconnected pore matrix and lesser isolated voids in the RAP-PC pavement mix. The addition of SF could only improve the strength parameters (compressive strength and modulus of rupture) of the RAP-PC pavement mix. In contrast, BGA inclusion was observed to improve its transport properties (porosity and permeability). Furthermore, the inclusion of SF, FA, and BGA in a 100% RAP-PC mix improved abrasion resistance. When compared to the conventional PC pavement mix, incorporating RAP aggregates blended with SF, FA, and BGA can reduce the production cost of 1 m3 PC by 30–61% and lower CO2 emissions by 13–21%. However, considering the strength and transport property requirements of PC mixes, as well as the economic and environmental viability, the present investigation recommends using 5% SF, 10% FA, and 10% BGA in a 100% RAP-PC pavement mix. [ABSTRACT FROM AUTHOR]

Despite thorough exploration of the acidity properties and pore structure effects of zeolite catalysts on catalytic conversion, a comprehensive understanding of how these factors influence reaction pathways is still lacking. Herein, three common zeolites (ZSM-5, ZSM-22 and ZSM-48) of different shapes and size dimensions were introduced into catalytic conversion of isobutane, with combination of X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption and desorption, solid-state 29Si and 27Al MAS NMR, ammonia temperature programmed desorption (NH3-TPD) and pyridine adsorption infrared spectroscopy (Py-FTIR) to characterize their structure and acidity. And channels and topologies were associated with stability and catalytic activity. ZSM-5 performed best, showing the most active sites. Furthermore, ZSM-48 led to an increase in the propene yield by suppressing inhibitory secondary reactions in the monomolecular reaction pathway. Moreover, the amount of Brønsted acid sites (BASs) of ZSM-22 were a key factor in promoting light alkene formation. However, 1D channels contributed to the deactivation of ZSM-22 and ZSM-48. The detailed reaction pathways of zeolite catalysts with diverse pore structures and acidities are crucial for optimizing their catalytic performance. [ABSTRACT FROM AUTHOR]

The Chang 8 formation of the Yanchang Group, located in Yuancheng area of the Ordos Basin, is a typical tight oil reservoir in China. This reservoir is characterized by low porosity, low permeability, strong non-homogeneity, and significant difficulty in evaluating the reservoir parameters. To examine and investigate the microscopic pore structure characteristics of the Chang 8 formation, cast thin section and scanning electron microscopy techniques were utilized in this study, Moreover, tests on the core physical properties were conducted and the data from these tests were integrated into the analysis of basic characteristics of the reservoir rock mineralogy, pore permeability, and other fundamental characteristics. The shapes of piezomercury curves were systematically examined to study the characteristics and features of pore structures for the 17 samples. In accordance with the fractal dimension of the NMR T2 spectrum, the reservoir was classified into four categories, and a conversion model delineating the correlation between the NMR T2 spectrum and the capillary pressure curve was formulated through the application of the segmented power function method. This model was then implemented in the interpretation of NMR logging, facilitating the acquisition of a seamless pseudo-capillary pressure curve spanning the entire well section. Three essential parameters reflecting the microscopic pore structure, namely the expulsion pressure, median pressure, and sorting coefficient of the core samples, were extracted. The association between reservoir parameters and reservoir categorization was then determined through the application of a generalized regression neural network. The pseudo-capillary pressure curve reservoir parameters of the whole well section were processed to derive the classification profile of the reservoir, and the classification results demonstrated a strong alignment with those of the mercury injection experiments. This study highlights that the proposed method can provide crucial foundation for the investigations on pore structures in tight oil reservoirs and the evaluation of reservoir classification. [ABSTRACT FROM AUTHOR]

We conducted a series tests on surface layers of plateau concrete at the ages of 180 and 540 days, including the most superficial cement paste, the 5 mm thick surface mortar, and the 50 mm thick surface concrete. Thermogravimetry and nitrogen absorption porosimetry on cement past, mercury intrusion porosimetry on mortar, and microhardness test on interface transition zone between mortar and coarse aggregate were conducted to evaluate the hydration degree and characterize the micro-structure. Whilst, tests for the rebound strength, abrasion resistance, and chloride ion impenetrability of concrete were conducted to assess the macroperformance. The experimental results show that, affected by the harsh plateau climate, outward surfaces have lower hydration degrees and worse pore structure than inward surfaces. As the hydration of concrete surface is ongoing after the age of 180 days, both the micro-structure and the macro-performance are continuously improved. In the long-term, either the orientation or the depth towards surface does not significantly affect concrete performance. Surface carbonation brings positive effects on mechanical properties but negative effects on the durability. Additionally, standard test result of chloride ion impenetrability is found significantly affected by the atmospheric pressure. For a same batch of concrete, charge passed in plateau regions is obviously lower than that in common regions. [ABSTRACT FROM AUTHOR]

Water–rock interactions affect mineral inclusions and the pore structure of rock, subsequently affecting its mechanical and seepage properties. A method for quantitative analysis of the pore and mineral inclusion evolution characteristics of coal samples based on CT scanning is proposed. Accordingly, numerical model construction and block division of mineral inclusions and pores in coal samples were realized. The effects of mineral inclusions and the pore structure on coal failure were simulated and analyzed. The results showed that the porosity and pore distribution in coal influence its strength. The development of plastic zones in coal affected by pores can be divided into three stages: (1) tensile failure initiation stage, (2) shear failure penetration stage, and (3) failure rapid expansion stage. The higher the fractal dimension of the pores is, the greater the strength of coal. Pores and mineral inclusions degrade the strength of coal and accelerate the development of plastic zones. In the loading process, plastic zones preferentially emerge around pores and mineral inclusions. The plastic zones around mineral inclusions connect gradually with those around pores, thus accelerating coal failure. [ABSTRACT FROM AUTHOR]

Seismic emission is the spontaneous emission of waves in a porous or fractured medium. There is still no explanation for the dependence of these phenomena on the medium parameters and pore structure, as well as for the transition from slow to fast movements. The paper proposes a description of the transition process from statics to dynamics using a model of a structured continuum. The most important parameters of the model are the specific surface area and porosity of the medium. The reason for the emission is that the forces caused by internal stresses are only on average equal to zero over a representative volume, being different at each point of the medium. It is shown that the model of a structured continuum predicts the emission of waves under static load and gives an estimate of the vibration periods. In this case, the characteristic vibration periods depend neither on the characteristic time of destruction of particles, nor on the loading time. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are potential alternatives of lithium-ion batteries (LIBs) due to the abundant and cost-effective availability of sodium and potassium resources. Unfortunately, they are difficult to use for large-scale grid energy storage due to the lack of suitable anode materials for sodium/potassium energy storage. Biomass-derived carbon, which is widely available and environmentally friendly, is one of the most promising anode materials for SIBs/PIBs, but the design and regulation of its microstructure is exceptionally complex. By selecting suitable biomass precursors, it is expected that biomass-derived carbon with suitable microstructures can be simply prepared. In this study, Wedelia chinensis were selected as biomass precursors, and biomass-derived carbon materials with large interfacial spacing, suitable pores and high-specific surface area were prepared by a simple one-step pyrolysis method. The material exhibited fast energy storage kinetics when electrochemically tested as an anode and showed different performance advantages in storing sodium/potassium. When tested as an anode for SIBs, it exhibited excellent specific capacity and cycling stability (380.7 mA h g−1 after 500 cycles at 100 mA g−1); When tested as an anode for PIBs, it exhibited excellent rate performance (128.6 mA h g−1 at 10 A g−1). [ABSTRACT FROM AUTHOR]

Deep shale has the characteristics of large burial depth, rapid changes in reservoir properties, complex pore types and structures, and unstable production. The whole-rock X-ray diffraction (XRD) analysis, reservoir physical property parameter testing, scanning electron microscopy (SEM) analysis, high-pressure mercury intrusion testing, CO2 adsorption experimentation, and low-temperature nitrogen adsorption–desorption testing were performed to study the pore structure characteristics of marine shale reservoirs in the southern Sichuan Basin. The results show that the deep shale of the Wufeng Formation Longyi1 sub-member in the Luzhou area is superior to that of the Weiyuan area in terms of factors controlling shale gas enrichment, such as organic matter abundance, physical properties, gas-bearing properties, and shale reservoir thickness. SEM is utilized to identify six types of pores (mainly organic matter pores). The porosities of the pyrobitumen pores reach 21.04–31.65%, while the porosities of the solid kerogen pores, siliceous mineral dissolution pores, and carbonate dissolution pores are low at 0.48–1.80%. The pores of shale reservoirs are mainly micropores and mesopores, with a small amount of macropores. The total pore volume ranges from 22.0 to 36.40 μL/g, with an average of 27.46 μL/g, the total pore specific surface area ranges from 34.27 to 50.39 m2/g, with an average of 41.12 m2/g. The pore volume and specific surface area of deep shale gas are positively correlated with TOC content, siliceous minerals, and clay minerals. The key period for shale gas enrichment, which matches the evolution process of shale hydrocarbon generation, reservoir capacity, and direct and indirect cap rocks, is from the Middle to Late Triassic to the present. Areas with late structural uplift, small uplift amplitude, and high formation pressure coefficient characteristics favor preserving shale gas with high gas content and production levels. [ABSTRACT FROM AUTHOR]

Freeze–thaw cycles are frequently overlooked as a pivotal factor contributing to leakage and structural failures in clayey soil-impermeable barriers used in landfills or tailings repositories in regions subject to seasonal freezing. This investigation explores the recovery and residual strength properties of Jilin ball clay undergoing six freeze–thaw cycles, and assesses the pore structure characteristics through a series of nuclear magnetic resonance (NMR) tests. The results indicate that normal stress has a greater impact on peak recovery strength than dry density and rest periods. Cohesion increases earlier and more significantly during rest periods compared to internal friction angle. Although the pore diameter remains consistent within the micropores during the freeze–thaw cycles, the soil's structural integrity undergoes notable changes. The concluding analysis provides valuable insights for the construction and management of impermeable barriers in landfills or tailings repositories within seasonally frozen areas. [ABSTRACT FROM AUTHOR]

Porous ceramics were synthesized using porcelain tile polishing residue (PTPR) and slaked lime (Ca(OH)2) as a reinforcing agent through a hydrothermal autoclaving method. The process parameters, including the quantity of slaked lime added, the hydrothermal autoclaving temperature, and the reaction duration, were optimized meticulously. The composition, structure, thermal and physical properties of the samples were thoroughly analyzed via Brunauer–Emmett–Teller (BET) measurements, powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). The results indicated that the incorporation of slaked lime and hydrothermal autoclaving led to the formation of calcium silicate hydrate, which corresponded with an enhancement in the strength of the sample. Notably, when the quantity of slaked lime added was optimized at 30 wt%, the formation of tobermorite (5CaO·6SiO2·5H2O) was detected. At a hydrothermal autoclaving temperature of 150 °C, the formation of only sheet-like calcium silicate hydrate was observed. In contrast, at an elevated temperature of 180 °C and 210 °C, needle-like tobermorite was successfully synthesized. The porous ceramic with the most favorable structure was obtained through autoclaving at 180 °C for 10 h with 30 wt% slaked lime, exhibiting a total pore volume of 0.11 mL/g, a specific surface area of 26.35 m2/g, and a mesoporous volume fraction of 90.40%. [ABSTRACT FROM AUTHOR]

In this study, the pore structure and oil-water phase seepage characteristics of sandstone reservoirs of the Yanchang Formation in the Ordos Basin were deeply analyzed. Through scanning electron microscopy observation, oil-water phase percolation experiments and nuclear magnetic resonance (NMR) experiments on 30 core samples, the pore structure was categorized into uniform macroporous, striated, microfractured and dense types. The experimental results show that the uniform macroporous type pore structure shows the strongest seepage capacity, and its ratio of liquid-measured to gas-measured permeability is 0.724 on average, while the dense type pore structure has the weakest seepage capacity, and the ratio is 0.091 on average; NMR T2 spectral analysis reveals that the cores with different types of pore structure show significant characteristic differences in the water-driven oil drive process, especially in the substitution of oil in the macroporous and micrometer pore In particular, the oil substitution in large pores and micron pores is remarkable, that is, the oil-water seepage process and the response of seepage and suction of cores with different types of pore structure are obviously different, which is a better way to study the characteristics of oil-water seepage and distribution of oil and water; the uniform macroporous type and the striptype pore structure are more effective in oil-water two-phase seepage, and the microfracture type and the dense type are relatively poor. This paper provides a basis for the exploitation of tight reservoirs in the study area, which is of great theoretical and practical significance for optimizing the oilfield development strategy and improving the efficiency of oil and gas exploitation. [ABSTRACT FROM AUTHOR]

Experimental and modeling approaches on the soil water retention of low-plasticity undisturbed silty clay were presented in this study to incorporate the combined effects of the pore structure and volume change. Two experimental procedures under the K0 stress state were performed to understand the dependency of hysteretic water retention on both pore structure and volume change effects. The water retention test results show that the hydraulic hysteresis gradually decays when either the suction or vertical compressive stress increases due to a substantial reduction in the macrostructural porosity. Distinct pore structures, including macro- and transitional extra-pore structures with a median size identified through the Mercury Intrusion Porosimetry technique, can induce a noticeable bimodal feature of the SWRC in capillary suction range. The effect of vertical stress, leading to different initial void ratios but a consistent microfabric, can also considerably restrain the irreversible suction-induced volume change and thus influence the water retention as vertical stress increases. The results from K0 compression tests indicate that the variation in the degree of saturation presents an approximate linear negative correlation with the volume change, and the hydromechanical coupling can be, therefore, interpreted through considering the effect of stress-induced volume change on the variation in the degree of saturation. A novel unified formulation of the hydraulic model was developed by incorporating the modified Gallipoli's SWRC model and an unsaturated volume change equation, which can simultaneously describe the combined effects of a heterogeneous pore structure and an elasto-plastic volume change on the variation in the degree of saturation. The proposed model was found to have a good accuracy compared to the test data, testifying to its enhanced predictive capability in modeling the bimodal water retention and the hydromechanical coupling effect. [ABSTRACT FROM AUTHOR]

This study investigates the influences of moisture content and freeze–thaw (FT) cycles on the compression behaviors of a compacted clay. Compacted specimens were first conditioned to different moisture contents (w) and then subjected to FT cycles. The treated specimens were either (i) directly used for constant water content (CW) compression tests or (ii) saturated and used for conventional consolidation tests to determine the compression curves under unsaturated and saturated conditions, respectively. Mercury intrusion porosimetry (MIP) tests were performed to track the evolution of the soil's pore structure during moisture and FT conditionings. The compression indexes (including the recompression index Cr, preconsolidation pressure σvp or σ'vp, and compression index Cc of the specimens) derived from the experimental results demonstrate that (i) within the initial elastic compression range, the Cr is independent of moisture content changes but increases after FT conditioning. The variations of Cr are associated with the volume of soil's large pores (el), which remains constant during moisture conditioning but increases after FT cycles; (ii) within the elastoplastic compression range, the σvp or σ'vp increases, while the Cc decreases as the moisture content decreases. However, the σvp, σ'vp, and Cc decrease after FT cycles. The σvp, σ'vp, and Cc are related to the volume of the soil's medium pores (em), which decreases after moisture and FT conditionings. A few unique relationships are established to reveal the influences of pore structure changes on compression characteristics. The variations of the soil's shrinkage curves under different external stress are also analyzed considering the effects of the changes in the pore structure. A model was proposed for the void ratio–moisture content–external stress relationships. This model was demonstrated useful for describing soils' compression behaviors at different moisture contents and shrinkage characteristics under different external stress. [ABSTRACT FROM AUTHOR]

Enzyme-induced carbonate precipitation (EICP) is an attractive bio-geotechnical technique for soil improvement. As promising alternatives to commercial ureases, legume ureases crudely extracted from primary agricultural products can provide remarkable cost savings. This study investigated the bio-cementation effect of legume ureases with different protein contents on pore-scale, mechanical, and hydraulic properties of EICP-treated sand and revealed the causes, mechanisms, and effects of the bio-clogging induced by high protein level-legume urease. Urease centrifugal liquids of sword bean (JU), pigeon pea (PU), and soybean (SU) were prepared at equal activity of 10 mM/min for sand bio-cementation. Mechanical properties were analyzed based on CaCO3 content and soil strength. Pore-features were revealed by mercury intrusion porosimetry and scanning electron microscopy, and permeability was measured to evaluate the hydraulic properties. Results showed that JU and PU with lower protein content were more effective in multi-cycle EICP-treatments, since denser bio-cemented sands with higher strengths were obtained while being vertically uniform in CaCO3 distribution and pore structure. Conversely, the high protein level of SU induced uneven bio-cementation and surface bio-clogging, resulting in bad mechanical properties, such as low strength and a destruction pattern of bottom collapse. Bio-clogging virtually eliminated the effectiveness of subsequent EICP-treatments. SU exhibited an advantage over JU and PU in reducing soil permeability, as a dramatically lower permeability was achieved at a lower treatment cycle. Comprehensive analysis concluded that the high protein level, salting-out, different precipitation rate between protein and CaCO3, and limited soil filtration capacity were the key reasons for bio-clogging induced by SU. [ABSTRACT FROM AUTHOR]

To investigate the impact of relative humidity on the mechanical properties and microscopic pore structure of air lime-stabilized compressed earth, unconfined compression strength (UCS), mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) tests were conducted by varying the air lime content and relative humidity (RH) in compressed earth. The results revealed three typical failure modes in unconfined compression strength tests of lime-stabilized compressed earth. Both the unconfined compression strength and characteristic parameters of pore structure in lime-stabilized compressed earth exhibited a trend of initial increase, following by a decrease as the air lime content and relative humidity increased. At the microscopic level, the relative humidity and air lime content interacted with the changes in macro-level unconfined compression strength, and the increase of both could promote the lime hydration reactions, inhibiting the crack development. Considering the influence of relative humidity, mechanical performance, and economic benefit improvement, the recommended air lime content for high humidity and low humidity were 0–28% and 0–26%, respectively, offering valuable insights for the optimization and application of lime-stabilized compressed earth as a modern construction material for structural walls. [ABSTRACT FROM AUTHOR]

Foam concrete is characterized by lightweight, self-compacting and high flowability, thereby widely used as a subgrade bed filler. High-speed railway subgrades usually experience inhomogeneous deformation due to the occurrence of freezing-thawing cycles in seasonally frozen soil areas. It is essential to study the deformation behavior of foam concrete under the coupling effect of freezing-thawing cycles and dynamic loading. In this paper, dynamic triaxial tests were performed to study the accumulative deformation of the foam concrete under different numbers of freezing-thawing cycles, freezing temperatures, amplitudes and frequencies of dynamic loading. Based on the scanning electron microscopy (SEM) tests, the characteristics of the pore structure were analyzed quantitatively by introducing the directional distribution frequency and fractal dimension. The research results illustrate that the damage caused by freezing-thawing progress to the pore structure results in more significant deformation of the foam concrete subjected to dynamic loading. There exists an accumulative damage effect induced by the coupling action of long-term dynamic loading and freezing-thawing progress on the microstructure and mechanical properties of foam concrete. The development of the fractal dimension agrees with that of the accumulative strain, indicating a close connection between the microstructure and the dynamic behavior of foam concrete. The findings concluded in this study contribute to a sufficient understanding of the performance of foam concrete used as high-speed railway subgrade fillers subjected to seasonal freezing. [ABSTRACT FROM AUTHOR]

In cold areas, the steel fiber reinforced rubber concrete (SFRRC) pavement is exposed to natural environment and experiences varying degrees of damage from freezing and thawing. This can have a serious impact on the normal usage and safe operation of the pavement structure. This research examines the impact of varying rubber concentrations on multiple variables, such as the rate of mass reduction, relative dynamic modulus of elasticity, compressive strength, and thickness of the damage layer (Hf) during freeze–thaw (F-T) durability testing conducted on SFRRC. Furthermore, an analysis is conducted to determine the degradation pattern exhibited by SFRRC. The internal structure evolution and pore structure characteristics of SFRRC were examined using scanning electron microscopy and mercury intrusion porosimetry techniques, which revealed the underlying damage mechanism in SFRRC during F-T cycles. The results suggest that the addition of an appropriate amount of rubber can effectively enhance the frost resistance of SFRRC in water. A gradual improvement in the frost resistance of SFRRC is observed when increasing the rubber content from 0 to 10%. The optimal frost resistance is observed in SFRRC with 10% rubber content. However, when the rubber content reaches 15%, SFRRC exhibits significant degradation and lower level of resistance to freezing compared to SFRRC without rubber. Microcracks form within SFRRC due to the freezing–thawing forces experienced during the experiment, resulting in the development of a damage layer that extends from the surface to the interior. The compressive strength of the damaged layer significantly decreases as Hf increases. The addition of appropriate rubber in SFRRC improves its pore structure, leading to an increased proportion of harmless or less harmful pores and a reduction in average pore size, thereby significantly enhancing its frost resistance. [ABSTRACT FROM AUTHOR]

Phenanthrene (PHE) is a polycyclic aromatic hydrocarbon categorized as a high priority organic pollutant being toxic for the ecosystem and human health, and its sorption on natural organic or inorganic substances seems a well-promising method for its removal from water streams. The goals of the present work are (i) to assess the capacity of low-cost adsorbents fabricated by treating coffee wastes and diatomaceous earth to remove PHE from water; (ii) to elucidate the role of the pore structure on PHE sorption dynamics; and (iii) to assess the potential to regenerate adsorbents loaded with PHE, by using the novel technology of cold atmospheric plasma (CAP). Diatomaceous earth (DE) and DE pre-treated with sodium hydroxide (NaOH) or phosphoric acid (H3PO4) were chosen as inorganic adsorbents. Coffee waste (CW) and activated carbons (AC) produced from its pyrolysis at 800 °C (CWAC), either untreated (CWAC-800) or pre-treated with NaOH (CWAC-NaOH-800) and H3PO4 (CWAC-H3PO4-800), were chosen as organic adsorbents. The adsorbents were characterized with nitrogen adsorption–desorption isotherms, attenuated total reflectance-Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and mercury intrusion porosimetry. Based on the PHE sorption capacity and pore structure/surface characteristics, the CWAC-NaOH-800 was chosen as the most efficient adsorbent for further equilibrium and kinetic sorption studies. The multi-compartment model was used to describe the PHE sorption dynamics in CWAC-NaOH-800 by accounting for the pore/surface diffusion and instantaneous sorption. The CWAC-NaOH-800 exhibited remarkable values for (i) the specific surface area (SBET = 676.5 m2/g) and meso- and micro-pore volume determined by nitrogen sorption (VLN2 = 0.415 cm3/g); (ii) the macro- and meso-pore volume determined by mercury intrusion porosimetry (VMIP = 3.134 cm3/g); and (iii) the maximum PHE sorption capacity (qmax = 142 mg/g). The percentage of adsorbent recovery after its regeneration with CAP was found to be ~ 35%. From the simulation of sorption dynamics, it was found that at early times, the sorption kinetics is governed by the film diffusion towards the external surface of grains, but at late times, most of the adsorbed mass is transferred primarily to meso-/macro-pores via diffusion, and secondarily to micro-porosity via surface diffusion. Based on the adsorbent characteristics, effect of pH on sorption efficiency, and numerical analysis of sorption dynamics, it was concluded that probably the dominant adsorption mechanism is the π-π interactions between hydrophobic PHE aromatic rings and CWAC-NaOH-800 graphene layers. The high PHE removal efficiency of CWAC-NaOH-800, the successful interpretation of sorption dynamics with the multi-compartment model, and the potential to regenerate PHE-loaded adsorbents with the green and economic technology of CAP motivate a strategy for testing CWACs towards the adsorption of other PAHs, application of adsorbents to real wastewaters, and scaling-up to pilot units. [ABSTRACT FROM AUTHOR]

Capillary water absorption is an important parameter to evaluate the durability of cement mortars. For testing the capillary water absorption of cement mortars, drying is a necessary and crucial procedure. However, different standards have different requests on drying temperatures for doing the tests. Since the calcium aluminate cement-hemihydrate gypsum (CAC-C S ¯ H0.5) mortars are temperature-sensitive, three temperatures of 20 °C, 40 °C and 70 °C were selected to study the effect of hydroxypropyl methyl cellulose (HPMC) on the capillary water absorption of these mortars. The influence of temperature on the capillary water absorption of the mortars was analyzed from the perspectives of pore structure and hydration. The results show that when the viscosity of HPMC is the same, the higher the dosage of HPMC used, the higher the capillary water absorption of mortars. When the dosage of HPMC is the same, the higher the viscosity of HPMC, the greater the capillary water absorption of mortars. The addition of HPMC can significantly increase the total porosity of mortars, especially the volume of the large pores. However, pore structure is not the main factor influencing the capillary water absorption of HPMC-modified CAC-C S ¯ H0.5 mortar. When the drying temperature rises to 40 °C, a small amount of AFt is decomposed. When the drying temperature reaches 70 °C, most of AFt is carbonized to form hemicarboaluminate and AH3, and the latter is the key to refining the pore structure of mortars. The temperature change causes a phase transition of the hydration products, thereby altering the pore structure. 40 °C is suggested as an appropriate drying temperature for the capillary water absorption test of the investigated mortars. [ABSTRACT FROM AUTHOR]

Shale matrix permeability is vital to the evaluation of shale petrophysical property. In this study, an analytical model that considers pore size distribution, tortuosity, adsorption, and slippage effects is developed, to calculate the permeability of shale samples. Specifically, field emission scanning electron microscope (FE-SEM), the ImageJ software, and the MATLAB programming and numeric computing environment are employed to experimentally characterize the pore structure and to fit and optimize the pore size distribution. The discrete pore size distributions of organic matter and inorganic matter pores for Longmaxi and Qiongzhusi shale samples are determined based on FE-SEM images. According to the sum of squares error (SSE), coefficient of determination (R2), root-mean-square error (RMSE), and outcome of the fit, the Gaussian 2 correlation function is optimized to fit the continuous pore size distribution. Finally, the permeabilities of five shale rock samples are calculated and compared with the measured results from the Longmaxi and Qiongzhusi Formations. The results illustrate that the multi-term Gaussian fit is more suitable for calculating the permeability of samples with multimodal pore size distributions than the multi-segment Gaussian fit. The calculated results from the pore size distribution are more accuracy than those from the representative mean pore radius. The influence of pore size distribution on permeability and how seepage mechanisms in different pore sizes work together to represent permeability changes at the core scale will be investigated in the future. The study provides a more reliable calculation of the shale matrix permeability compared to previous methods. [ABSTRACT FROM AUTHOR]

Driven by capillary adsorption, moisture and aggressive media can easily intrude into unsaturated concrete and shorten the service life of concrete structures. In the present study, gangue-based concrete (GBC) was produced by replacing cement (substitution rate 0%, 10%, 20% and 30%) with mechanical-microwave activated coal gangue powder (ACGP) to explore the effect of freeze-thaw damage on the water absorption performance of GBC. ACGP improved the frost resistance of GBC, but the frost resistance declined at 30% mixing. The water absorption performance of GBC was promoted by freeze-thaw damage. Besides, the water absorption performance of GBC decreased first and then enhanced with the growth of ACGP content, especially the weakest at 20% content. The correlation analysis between the macroscopic characteristics of freeze-thaw damage and water absorption performance suggested that the coefficient of capillary absorption was highly linearly correlated with the damage layer thickness (R2 > 0.9). The pore structure of GBC was optimized by the increase of small pores as well as the decrease of large pores after ACGP mixing. Furthermore, the coefficient of capillary absorption showed an apparent positive correlation with the transitional pores. [ABSTRACT FROM AUTHOR]

Seawater sea-sand concrete (SSC) structures reinforced with fiber reinforced polymer (FRP) bars were proposed to capture CO2 by means of carbonation curing in this study. FRP-SSC structures allowed sufficient carbonation to occur since the steel corrosion in traditional reinforced concrete structures would not exist. Herein, the pore structure of CO2-cured SSC with sufficient carbonation was examined, and the mechanical behaviors under uniaxial compression were also investigated. MIP testing was employed, and surface fractal dimension in various pore-size regions was calculated. The results indicate that CO2 curing leads to a more significant variation in smaller mesopores of SSC than CC. Regarding middle capillary pores, the surface fractal dimension in almost all CO2-cured specimens ranges from 2.6617 to 2.8124, which means that these pores show distinct fractal characteristics, but this phenomenon does not be observed in water-cured specimens. This indicates that CO2 curing can greatly reduce ink-bottle pores in concrete. Furthermore, the compressive strength gain of CO2-cured SSC with sufficient carbonation is above 30% at the 180-days age. The compressive strength gain can be attributed to the improvement in the surface fractal dimension. Moreover, CO2-cured specimens exhibit higher peak stress, smaller peak strain, and greater elastic module, resulting in lower plasticity. Consequently, CO2 curing renders SSC and CC more brittle. [ABSTRACT FROM AUTHOR]

The haulage roadway of the F15-22080 working face, No.8 mine is situated within a special non-uniform stress zone. In this area, the extraction-boreholes drilling process frequently triggers coal and gas outburst. Against this background, this study systematically conducted high-pressure gas adsorption experiments and high-pressure gas desorption experiments on coal samples collected from different stress zones and obtained their adsorption/desorption characteristics. Subsequently, coal pore structure characteristics at various scales were investigated by employing scanning electron microscopy, low-pressure N2 adsorption and low-pressure CO2 adsorption techniques and fractal analysis to assess the impact of varying stress levels. On this basis, a comprehensive analysis was carried out to explore the connections between stress, pore structure, adsorption/desorption traits, and the risk of outburst. The results indicate that, with increasing stress, the Protodyakonov coefficient f and the Langmuir pressure PL decrease, while the index of diffusion initial velocity of coal gas Δp and the Langmuir volume VL increase. The desorption amount and rate of gas also increase significantly. The total pore volume and specific surface area of micropores increase, while those of mesopores and macropores show an overall decreasing trend. The surface fractal dimension DF1 increases by 9%, the spatial fractal dimension DF2 decreases by 5.2%, and the volume fractal dimension DSIE increases by 1%. The induced stress leads to a decrease in the abundance of macropores and mesopores, with concurrent increase in micropores. The VL exhibits a linear increase with the DSIE, whereas the PL demonstrates a linear decrease with it. The initial desorption rate rises with the reduction of the DF2 and the increase of the DSIE. The influence of superimposed-stress on outburst stems from alterations in pore structure and adsorption–desorption capabilities. Simultaneously, it collectively heightened the outburst risk by increasing the gas pressure gradient and weakening the strength of the coal. [ABSTRACT FROM AUTHOR]

Coalbed methane (CBM) mining has always been plagued by low mining efficiency. CBM-rich areas have high mining efficiency, but their formation is affected by CBM seepage. Through on-site mining, it is found that gas seepage in low-permeability areas presents nonlinear characteristics. In this paper, the causes and rules of nonlinear seepage are analyzed. The pore structure characteristic parameters such as pore size distribution, pore proportion and fractal dimension were obtained by nuclear magnetic resonance technology, and the pore structure characteristics of low permeability coal are analyzed. The results showed that the proportion of porosity was 6.30–11.02% and the proportion of percolation pores was 7.52–19.59%. Both total porosity and percolation pores had fractal characteristics. Aiming at the nonlinear problem of gas seepage law in low permeability coal, the permeability and gas flow data of coal samples under different gas pressures were measured by the self-designed coal core permeability automatic tester, and the gas seepage characteristics of low permeability coal samples are studied. The experiment showed that there was a starting pressure gradient in gas seepage in coal samples, and the relationship between gas permeability and gas pressure turned over at 1.25 MPa, indicating that there is a slip effect in coal pores. Considering the influence of pore structure parameters on the nonlinear seepage characteristics of CBM, the relationships between porosity, tortuosity, pore proportion, and fractal dimension and Kirschner permeability, slippage factor, and starting pressure gradient were fitted. The analysis showed that the pore size distribution characteristics with large proportion of micro-pores in low permeability coal made the pressure gradient required for the internal gas seepage larger, the influence of the slippage effect was enhanced, and the seepage of gas was nonlinear. To conclude, the influence of micro-pores developed in low permeability coal on nonlinear gas seepage was significant. [ABSTRACT FROM AUTHOR]

Exposure to heavy metals in water bodies is of environmental concern; hence, their removal is necessary. As-received coals obtained from two sedimentary basins in Nigeria were characterized and tested for their potential application as adsorbent in the removal of lead(II) ions from contaminated water. Physical and chemical properties of the coals including their elemental composition, conductivity, density, pH, pore structure, surface morphology and thermal behaviour were studied using standard instruments and techniques. The removal efficiency of the coals, adsorption isotherms and kinetics were studied from batch experiments. Results showed that the coals possessed adsorbent properties in terms of carbon content, pH, density, surface morphology and pore structure. The removal efficiency of Pb(II) ions from aqueous media using Ogwashi-uku coal ranged from 89.01 to 99.45%, while it ranged from 80.77 to 98.51% with Onyeama coal. Adsorption equilibrium for the removal of lead ions was established at pH of 6, 1 g dosage, at 100 ppm concentration with the contact time of 90 and 75 min for Ogwashi-uku and Onyeama coals, respectively. The adsorption process followed Langmuir isotherm, while the kinetics best fitted the pseudo-second-order model. The adsorption data did not fit Elovich isotherm for chemisorption. Factors such as pore structure, density and morphology influence the ability of a coal to adsorb heavy metals from lead aqueous solution. The availability, adaptability, ease of use, cost effectiveness and environmental considerations recommend the tested raw coals for application in the removal of lead from contaminated water bodies. [ABSTRACT FROM AUTHOR]

Currently, the utilization of coalbed methane resources in the Guizhou region faces challenges such as complex reservoir structure, high gas content, and microporous development. Based on these, the pore structure and adsorption capacity of Guizhou tectonic deformed coals (TDCs) were evaluated using a suite of integrated diagnostic techniques including low-temperature nitrogen adsorption (LT-N2A), mercury intrusion porosimetry (MIP), methane isothermal adsorption. Through the above methods, the pore structure and adsorption characteristics of the samples were characterized; The samples were divided into the range of joint pores by combining the results of MIP and LT-N2A; Using the molecular simulation software, the 2 nm, 4 nm, 10 nm pores affecting the methane endowment state were investigated respectively, and from the perspective of the heat of adsorption and energy, the concept of the three-phase transition of methane was proposed, and explore the change of the pore spacing affecting the endowment state of methane from the solid state pore to the gas state pore. The results provide new ideas for the in-depth study of gas storage in tectonic coal reservoirs in Guizhou Province. [ABSTRACT FROM AUTHOR]

In this work, an efficient utilization method for red mud (RM) is provided through recycling RM as a mineral admixture for the preparation of foamed concrete (FC). Specifically, FC with different RM contents was prepared and investigated in terms of workability, mechanical properties, and hydration products. Results show that adding RM can significantly shorten the setting time, while it inevitably weakens the mechanical properties and fluidity of FC. However, the compressive strength of FC can still meet the strength predicted by the specification requirements when the RM replaces cement with 60% content (3d > 1.6 MPa). Most importantly, the heavy metals leaching from RM-based FC under the action of rain is still unclear, so a device for simulating stormwater runoff was designed to test the heavy metal leaching risk of RM-based FC. The findings indicate that the solidification of cement and the high basicity of the matrix can effectively reduce the leaching risk of heavy metals from RM in FC. Although the pore structure analysis demonstrates that the porosity and connected pores of FC will be deteriorated as RM concentration increases. The results are of great significance for the recycling of waste and the sustainable development of building materials. [ABSTRACT FROM AUTHOR]

In loess area, understanding the mechanical properties of loess impacted by micro pore structure is essential for assessing the stability of slopes, mitigating landslide risks and protecting people' lives and property. In order to investigate the relationship between changes in pore structure and shear behaviors, the discrete element method (DEM) and image processing techniques were employed to analyze the macroscopic features such as sample deformation, bond breakage, and porosity distribution within the numerical samples. Simultaneously, the changes in micro pore structure, including pore size, pore axis ratio, and pore orientation within and outside the shear band zone were investigated. The results present that the shear band formation is relevant to particle displacement, bond breakage, and force chain development, thereby impacting porosity distribution. In addition, the shear band significantly influences changes in macropores and pore orientation distribution, whereas there is a slight connection between the development of the shear band and alterations in micropores, small pores, mesopores and pore axis ratios. A comprehensive insight into the relationship between the occurrence of the shear band and the pore structure development contributes to landslide prevention and mitigation strategies. [ABSTRACT FROM AUTHOR]