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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]

An efficient, environmentally friendly, and economical polyphosphate/nitrogen-containing composite inhibitor (APNI) has been developed to prevent coal spontaneous combustion (CSC) disasters. Using temperature rise experiments during coal spontaneous combustion, mercury pressure experiments, and Fourier transform infrared spectroscopy (FTIR), the samples treated with the APNI were compared with those treated with MgCl2 and NH4H2PO4 inhibitors, and the inhibitory effects of the three inhibitors on CSC were studied. The results showed that the APNI effectively limited the reactions between the coal and oxygen, reduced the amount of CO gas generated, sealed most of the cracks, large pores and mesopores in the coal, and reduced the number of active functional groups in the coal. The APNI was more effective in preventing CSC than MgCl2 and NH4H2PO4. [ABSTRACT FROM AUTHOR]

Sulfate resistance is evaluated in mortars containing sulfate-resistant cementitious materials (SRCMs) developed by mixing ground granulated blast furnace slag, fly ash, silica fume and desulfurisation gypsum. Compressive strength testing, X-ray diffraction analysis, differential thermal analysis and mercury intrusion porosimetry are carried out. Results show that the sulfate resistance of mortars mixed with SRCMs at a replacement percentage of 74 wt% is superior to that of mortars with 30 wt% fly ash when exposed to drying–wetting cycles in sodium sulfate solution, because adding SRCMs decreases the calcium hydroxide content, causing a reduction in gypsum formation. Moreover, reducing the water-to-binder ratio (W/B) from 0.50 to 0.35 increases the loss of compressive strength ratio (Lf) of mortars with SRCMs immersed in ammonium–magnesium sulfate complex solution. Specifically, the Lf values of mortars with W/B of 0.50 and 0.35 are 42.7% and 36.0% after 100 days of immersion, respectively. Furthermore, the main component of samples subjected to complex solution is identified as gypsum. In addition, both Lf and porosity exhibit a strong linear positive correlation with W/B. Finally, the findings confirm that optimising the composition of cementitious materials and lowering W/B could improve the sulfate resistance of concretes used for a sulfate-rich sewage environment. [ABSTRACT FROM AUTHOR]

With improvements to the performance of ramjets, the ablation environment in afterburning chambers has become more severe, leading to an urgent demand for high-performance thermal protection materials (TPMs). In this study, the reinforcing effects of silicon carbide (SiC) nanowhiskers and nanopowders on silicone rubber composites and their synergistic effects were investigated. Both SiC nanowhiskers and nanopowders improved the thermal stability of the TPMs. SiC nanowhiskers enhanced the thermal conductivity of the TPMs by forming thermal conductivity pathways. Furthermore, SiC nanofillers can reinforce the ablation resistance of the TPM. The best performance was demonstrated by the TPM formulated with five parts SiC nanowhiskers and five parts SiC nanopowders. The ablation rate was reduced by 72.7% relative to the TPM with a basic formulation, and the back temperature increased by only 27.1%. In this study, the SiC nanofiller improved the ablation resistance of composites by densifying the pore structure and strengthening the skeleton of the char layer. Furthermore, the more compact char layer improved the thermal conductivity of the composites. The increase in the thermal conductivities of the composites and the char layer led to a decrease in the thermal insulation properties of the composites. [ABSTRACT FROM AUTHOR]

This study investigates, for the first time ever, the suffusion on gap‐graded granular soils under torsional shear conditions from a microscopic perspective. A numerical model of the hollow cylinder torsional shear test (HCTST) using the discrete element method (DEM) is first developed, where an algorithm for simulating the real inner and outer rubber membranes of the hollow cylinder apparatus (HCA) is introduced. After the validation, the computational fluid dynamics (CFD) approach is introduced for the coupling between the particle and fluid phases. Then, a series of the coupled CFD‐DEM suffusion simulations considering the rotation of the major principal stress axis (α) and intermediate principal stress ratio (b) are conducted. It is found that more fine particles are eroded in cases having smaller α and b, and the clogging phenomenon in the middle zones becomes more significant as both α and b increase. From the microscopic perspective, the specimens whose contact anisotropy principal direction is close to the fluid direction will lose more fines, and the anisotropy magnitude also plays an important role. In addition, the differences in structure and vertical connectivity of the pores in HCTST samples under various complex loading conditions cause fine particles to have different migration paths, further resulting in different fines mass loss. [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]

Graphene oxide (GO) significantly enhances cement hydration. This study investigates the effects of GO on the early hydration and pore structure evolution of cement paste by examining its impact on the setting time and mechanical properties of cement-based materials. In situ monitoring of the hydration process and microstructural changes was conducted using low-field nuclear magnetic resonance technology. The findings reveal that GO's nucleation effect accelerates cement hydration, reducing the setting time and increasing both the hydration rate and degree. Moreover, hydration products utilize GO as a template, leading to adjusted morphologies and enhanced interlinking of C–S–H gels. This results in a marked reduction in porosity and a denser microstructure within the cement paste. Consequently, the early mechanical properties of the cement paste are improved, with a significant increase in flexural strength observed at 72 hours. These results suggest that GO, which is cost-effective, size-controllable and suitable for mass production, holds great potential for applications in cement-based materials. [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]

When mining deep coal seams, the overlying mined-out area must be pumped and drained, and the remnant coal in the mining void area is vulnerable to spontaneous combustion via water immersion and air drying. To investigate the effect of soaking time on the spontaneous combustion characteristics of lignite, low-temperature N2 adsorption experiments and Fourier transform infrared spectroscopy (FTIR) experiments were used in this study to investigate the changes in pore structure and functional group content of coal samples by increasing the soaking time. Based on programmed warming experiments, macroscopic characteristic indicators of coal spontaneous combustion (CSC) oxidizability, such as the oxygen consumption rate and index gas, were derived. Results showed that the effect of soaking caused the total pore volume and specific surface area of lignite to increase to different degrees, which enhanced the adsorption capacity of coal to oxygen and improved the effective contact of oxygen with the active sites on the coal surface. However, there was no consistency in the effect of different soaking times on the content of reactive functional groups of the coal, with higher methyl and methine contents after 60 days of soaking (S60) and 120 days of soaking (S120) than in the raw coal (RC), and less in 90 days of soaking (S90). The propensity of coal to spontaneously combust is determined by both the pore structure and reactive functional groups, which shows the propensity of spontaneous combustion S60>S120>RC>S90. Results from this study are important in understanding the mechanism of CSC of water-soaked lignite in mined-out areas and can provide theoretical guidance to prevent CSC in mining areas. [ABSTRACT FROM AUTHOR]

This is an article in the field of ceramics and composites. In this article, the effects of IOT and polyvinyl alcohol (PVA) fiber (PF) on the compressive strength, four-point flexural strength, flexural toughness, pore structure of cement-based composites were studied and discussed in detail. The conversion relationship between compressive strength and four-point flexural strength was established. The results showed that the incorporation of IOT had an enhanced effect on the mechanical properties, and this enhanced effect showed a trend of first increasing and then decreasing with the increase in the substitution rate of IOT. However, when PF was added, the mechanical properties under the combined effect of PF and IOT were further improved and showed good toughness. In addition, the internal pores of the matrix with IOT substitution rate of 40% and PF were obviously reduced. Thus, it was concluded that the cement-based composite material had good mechanical properties when the 40% IOT was combined with PF.

Coral reef limestone at different depositional depths and facies differ remarkably on the textural and mineralogical characteristics, owing to the complex sedimentary diagenesis. To explore the effects of pore structure and mineral composition associated with diagenetic variation on the mechanical behavior of reef limestone, a series of quasi-static and dynamic compression tests along with microscopic examinations were performed on the reef limestone at shallow and deep burial depths. It is revealed that the shallow reef limestone (SRL) is classified as a porous aragonite-type carbonate rock with high porosity (55.3±3.2)% and pore connectivity. In comparison, the deep reef limestone (DRL) is mainly composed of dense calcite-type calcium carbonate with low porosity (4.9±1.6)% and pore connectivity. The DRL strengthened and stiffened by the tight grain framework consistently displays much higher values of the dynamic compressive strength, elastic modulus, brittleness index, and specific energy absorption than those of the SRL. The gap between two types of limestone further increases with an increase in strain rate. It appears that the failure pattern of SRL is dominated by the inherent defects like weak bonding interfaces and growth lines, revealed by the intricate fracturing network and mixed failure. Likewise, although the preexisting megapores in DRL may affect the crack propagation on pore tips to a certain distance, it hardly alters the axial splitting failure of DRL under impacts. The stress wave propagation and attenuation in SRL is primarily controlled by the reflection and diffusion caused by plenty mesopores, as well as an energy dissipation in layer-wise pore collapse and adjacent grain crushing, while the stress wave in DRL is highly hinged on the insulation and diffraction induced by the isolated megapores. This process is accompanied by the energy dissipation behavior of inelastic deformation resulted from the pore-emanated microcracking.

The pore structure has a significant impact on the capability of coal seams to adsorb methane. But there is currently limited research on the features of adsorption pore structure in high-rank coal and its influence on methane adsorption capability. Taking the high-rank coal samples from Nuodong Coal Mine of Guizhou Xing'an Coal Industry Co., Ltd. as the research object, low-temperature N2 adsorption and low-temperature CO2 adsorption experiments are conducted. Combined with fractal theory, this paper studies the pore structure features of high-rank coal adsorption pores. Through high-pressure isothermal methane adsorption experiments, the influence of coal reservoir properties, pore structure features, and fractal dimension on methane adsorption capability is analyzed. The results show the following points. ① The pore morphology of high-rank coal reservoirs is relatively simple, mostly consisting of parallel plate pores and narrow slit pores with open ends. Micro pores dominate the pore structure of coal, with pore volume and pore specific surface area accounting for more than 98%, providing space for gas enrichment. ② The method calculates the comprehensive fractal dimension of high-rank coal pores based on the proportion of pore volume in different aperture segments, with micropore fractal dimension dominating the comprehensive fractal dimension. The pore structure of coal samples has obvious fractal features and strong heterogeneity of pores. ③ The Langmuir model can describe the adsorption behavior of high-rank coal. The physical properties, pore structure, and fractal dimension of coal reservoirs have a significant impact on methane adsorption capability. Langmuir volume is linearly positively correlated with maximum vitrinite reflectance, vitrinite content, ash content, and moisture content. It is linearly negatively correlated with inertinite content. The Langmuir volume is linearly positively correlated with the pore specific surface area and pore volume of the adsorption pores. The Langmuir volume is weakly linearly correlated with the fractal dimension. The research results can provide theoretical guidance for the exploration and development of high-rank coalbed methane and the prevention and control of coal mine methane disasters in southwestern Guizhou.

Among the raw material production industries that use a large amount of limestone, the effectiveness of limestone usage in the steel production industry has been evaluated and the optimization of limestone addition ratio has been investigated. Based on the past research and development results concerning the CaO added basic sinter production technology, the phenomena of permeability deterioration caused by the excessive CaO addition and the actual operation tests, the multi-component calcium ferrites (SFCA) in sinter that have been currently intensively researched and developed have been evaluated. The reducibility of sinter in blast furnace has so far focused on the lumpy zone up to 1000 °C, but in the future research, it will be necessary focused on the reducibility and permeability in the cohesive zone up to 1000~1500 °C. The current chemical compositions of SFCA has the good reducibility and permeability in the cohesive zone, but the research and development are needed to maintain the appropriate range of CaO (CaO/SiO2 = 1.5~2.0) and further to improve the reducibility and permeability. The future progress of the research and development has been presented.

Abstract 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 Fluid movability in tight sands may not be accurately characterized by pore size-based classification methods solely because of the complex pore structure and heterogeneity in pore size. In this study, on the basis of casting thin slices and scanning electron microscope observation, pore structure was analyzed using mercury injection, NMR, and micron CT to classify and evaluate the tight oil reservoir. The experiment suggest that the quality of tight reservoir is determined by its pore structure, particularly the throat radius, with the microthroat being an essential factor in permeability. Uniquely, we divide the reservoir by Q-cluster with throat radius, displacement pressure, permeability and other parameters. Based on reservoir classification, this study proposed a method for studying the pore size classification of samples on the T2 spectrum by combining CT scanning with mercury intrusion and a NMR experiment. Pore fluids are generally classified into movable fluid and irreducible fluid by one or two NMR T2 cut-offs. The pore size distributions and capillarity boundaries are converted from T2 and mercury injection capillary pressure (MICP). We categorized pores into micropores (T2 10, with T2 > 300 as fractures), and medium pores (the rest). The saturation of movable fluid and the percentage of micro-fractures can characterize the seepage characteristics of tight reservoirs, which is of great significance for the later periods of oilfield development.

Abstract To quantitatively characterize the complexity of shale pore structures and their controlling factors in the Longmaxi Formation of Western Hubei, our study focused on the organic‐rich shale outcrops of the Longmaxi Formation in the Yidu‐Hefeng compound anticline. We conducted tests for shale organic content, maturity, and whole‐rock mineral composition, along with employing high‐pressure mercury injection and low‐temperature gas adsorption experiments. Utilizing the V‐S, FHH, and sponge models, we calculated the fractal dimensions of micro‐, meso‐, and macropores. In the Yidu‐Hefeng region, the Longmaxi Formation is characterized by calcium‐rich shales that are abundant in organic matter. Our analysis of samples revealed a total organic carbon (TOC) ranging between 1.04% and 4.24%, with an average of 2.5%. The Ro values fluctuate between 2.98% and 3.57%, with a mean value of 2.845%, indicating an over‐mature stage from early to late thermogenesis. Constituents such as quartz span from 39.8% to 51.3%, with a median of 44.3%, while feldspar oscillates between 3.8% and 12.4%, averaging at 8.48%. Clay minerals constitute 24.3% to 41.7% of the samples, with a mean of 34.16%. Shale porosity exhibits a segmented fractal nature. For instance, D1 varies from 2.1278 to 2.4056, with a mean of 2.2767; D2 fluctuates between 2.4995 and 2.7492, averaging at 2.6309; and D3 ranges from 2.6835 to 2.9427, centering around 2.8111. These variations indicate the intricacies of the macropore structure. Positive correlations between TOC and maturity with D1 and D2 are evident, whereas a negative association is observed with D3. The collaborative interplay between siliceous minerals and organics mirrors the relationship between the siliceous mineral content and its fractal dimensions, akin to TOC. Clay mineral transformations, due to accumulation and dehydration, predominantly contribute to macro‐porosity, weakly aligning negatively with D1 and D2 but positively with D3. Variations in carbonate and siliceous minerals and their role in primarily yielding dissolution macropores manifest a subtle negative link with D1 and D2 while enhancing D3. Pore volume correlates positively with D1 and D2, exhibits no conspicuous association with D3, and trends negatively. The compaction and transformation processes of clay minerals seem to favor the generation of macropores, mildly aligning positively with D3.

Abstract 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.

Ion-adsorption rare earth (RE) ore is a typical kind of rare earth ore derived from the weathering crust of igneous rocks. Variation in permeability of ion-adsorption rare earth ore is one of the indicative factors of mining efficiency. Permeability of the RE ore is controlled by its pore structure. Previous studies mainly kept on the RE ores in completely weathered zones, little on those in the zones with other weathering degrees. With the exhaustion of rare earth resources in the completely weathered zone, the extraction of the RE ore from the zones with other weathering degrees has gained more attention from the industrial sectors. This study shows a study on variations in pore structures and permeabilities of the RE ores in the zones with different weathering degrees, including the residual soil and completely weathered and highly weathered zones. The undisturbed samples were taken from an un-mining section of the Zudong mining area in Jiangxi province. Simulated in situ leaching experiments were conducted on the samples to measure their permeability coefficients before and after leaching. X-ray computer tomography scanning techniques were applied to the capture structure of the samples before and after leaching, and image processing techniques were used to construct their three-dimensional pore structure and extract their pore structure parameters. Variations in pore structure parameters and permeability coefficients of the RE ores from the zones with different weathering degrees were then carried out by a quantitatively comparative analysis. The results indicate that (1) the variation rate in permeability coefficient, and the pore structure parameters, including porosity, connectivity, and average coordination number, decrease with the decrease in weathering degree. Notably, these variation rates for the RE ores in the highly weathered zone are the smallest, indicating the RE ores in this zone are more leachable than those in residual soil if their abundance is not much different. (2) The mechanism leading to their differences was further investigated by the analyses of particle size distribution and mineralogical composition before and after leaching. The analysis results indicate that the differences in their variation of pore structure and permeability among the RE ore in the zones with different weathering degrees are caused by the differences in followings during leaching, including the chemical decomposition of plagioclase and mica, ion exchange, and disaggregation.The results can provide reference for the full development and utilization of similar ion-adsorption rare earth ore.

A growing rock engineering activity in cold regions is facing the threat of freeze-thaw (FT) weathering, especially in high mountains where the sunny-shady slope effects strongly control the difference in weathering behavior of rocks. In this paper, an investigation of the degradation of petrophysical characteristics of sandstone specimens subjected to FT cycle tests to simulate the sunny-shady slope effects is presented. To this aim, non-destructive and repeatable testing techniques including weight, ultrasonic waves, and nuclear magnetic resonance methods on standard specimens were performed. For the sunny slope specimens, accompanied by the enlargement of small pores, 100 FT cycles caused a significant decrease in P-wave velocity with an average of 23%, but a consistent rise of 0.18% in mass loss, 34% in porosity, 67% in pore geometrical mean radius, and a remarkable 14.5-fold increase in permeability. However, slight changes with some abnormal trends in physical parameters of the shady slope specimens were observed during FT cycling, which can be attributed to superficial granular disaggregation and pore throat obstruction. Thermal shocks enhance rock weathering on sunny slopes during FT cycles, while FT weathering on shady slopes is restricted to the small pores and the superficial cover. These two factors are primarily responsible for the differences in FT weathering intensity between sunny and shady slopes. The conclusions derived from the interpretation of the experimental results may provide theoretical guidance for the design of slope-failure prevention measures and the selection of transportation routes in cold mountainous regions.

Abstract 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%.

The long-term durability of basalt fiber-reinforced geopolymer concrete (BFRGC) in marine environments is importance for the development of sustainable construction practices. This study examines the long-term durability of basalt fiber-reinforced geopolymer concrete exposed to dry-wet cycles and immersion treatment in marine conditions. A geopolymer concrete with 1% fiber content was prepared and subjected to dry-wet cycles and immersion treatments in a 5% sulfate solution (Tehmina et al., 2014; Nasir et al., 2016; John et al., 2016) [1-3]. Density measurements, ultrasonic pulse velocity tests, and uniaxial compression tests were conducted on the BFRGC after various treatment durations. The mechanical properties of BFRGC were compared with geopolymer concrete without fibers in marine environments. Additionally, the changes in compressive strength of geopolymer concrete with and without fibers in different immersion environments were further discussed. Using low-field nuclear magnetic resonance (LF-NMR) technology, the variations in pore structure were also analyzed. The results show that the mechanical property loss from dry-wet cycles was greater than from immersion treatment. In BFRGC, strength decreased by 10.1% after 192 days of dry-wet cycles, compared to a smaller decrease of 5.6% in immersion environments. The inclusion of basalt fibers effectively enhances stability. When in dry-wet cycle tests, BFRGC strength decreased from 49.6 MPa to 44.6 MPa, a reduction of 10.1%. Conversely, geopolymer concrete without fibers dropped from 49.7 MPa to 42.1 MPa, a reduction of 15.5%. LF-NMR test results show that the porosity of geopolymer concrete without fibers increased by 21.6% and 17.5% in dry-wet cycles and immersion environments, respectively. In contrast, the porosity of BFRGC increased by 16.1% and 12.7%.

The radial gas seepage flow regime of the coal body around borehole is one of important factors reflecting the seepage movement of extracted gas. In order to investigate the effects of different pore structures and gas pressure on the radial seepage motion of gas in the perimeter of borehole, five kinds of pore-bearing coal samples with different gradations were made, and the radial seepage test was carried out on the pore-bearing coal samples by using the self-designed gas radial seepage test system and the steady-state seepage method to analyze the changes of the Forchheimer number and non-Darcy error with the seepage velocity and gradation, and the flow velocity intervals and the Reynolds number ranges of different flow regimes were obtained by using the Hazen-Dupuit-Darcy equation and the Reynolds number theory. The results show that: ① Through the analysis of the Forchheimer number and non-Darcy error with the change curve of seepage velocity, the Forchheimer number increases with seepage velocity in a quadratic polynomial curve, while non-Darcy error increases linearly, the Forchheimer number and non-Darcy error are closely related to pore structure, and both become larger with the increase of gradation, indicating that seepage velocity and pore structure of the coal body around the pore are important factors for gas seepage deviating from linear seepage; ② The Hazen-Dupuit-Darcy equation was used to characterize and delineate the gas radial permeability flow regime. With the increase of seepage velocity, the gas radial seepage motion appears in order of pre-Darcy, Darcy and Forchheimer flow regimes. The small-graded porous specimens with n=0.2 and n=0.4 are more prone to the Darcy laminar flow, while the porous samples with n=0.6, n=0.8 and n=1.0 are more prone to the Forchheimer flow regime; ③ Through the analysis of the relative error curve of pressure gradient when Darcy’s law was applied, the relative error with the increase of seepage velocity shows the change law of decreasing, keeping stable, and then increasing, which is consistent with the change law of gas seepage flow pattern with seepage velocity; ④ In double logarithmic coordinates, the relationship between different flow regimes of gas seepage and Reynolds number was analyzed, and the Reynolds number intervals of different flow regimes were derived, and it was found that the radial seepage motion of gas conforms to the Reynolds number range of 0.0012～0.0025 for Darcy laminar flow. The results of the study can provide an important theoretical basis for the design of drilling parameters by determining the influence range of drilling extraction based on the flow regime of coal seepage movement around the borehole in coal seam gas pre-drainage work.

To accurately evaluate the distribution and potential of deep coalbed methane resources, it is critical to identify the coal sedimentary and pore distribution characteristics of deep coal reservoirs. Therefore, based on the analysis of coal macerals, nuclear magnetic resonance porosity, and electron microscopy, the characteristics of coal macerals and pore distribution in the Yulin area were identified, as well as the relationship between the coal sedimentary and pore structure characteristics of No.8 coal was evaluated. The results indicated that: ① The organic macerals of No.8 coal seam in the study area were predominantly composed of vitrinite, indicating a predominance of woody plants during the early stages of coal formation. As the degree of water cover increases, it gradually transitions into a mixture of woody and herbaceous plants. ② During the Benxi period, No. 8 coal evolved from an early wetland forest swamp to a later open water swamp with stagnant swamp water, creating a stable environment conducive to organic matter enrichment and coal seam stability. ③ The proportion of macropores in No.8 coal seam was negatively correlated with the structure preservation index (TPI), while it was positively correlated with the gel index (GI). ④ Matrix vitrinite developed dense or sparse banded pores, mass vitrinite developed few pores, and the structure vitrinite developed original tissue pores, mostly filled with minerals, while the homogeneous vitrinite did not develop pores. In conclusion, pore distribution in Yulin's coal seams was controlled by sedimentation and macerals. The pore structure of coal seams in the open water swamp sedimentary presented three peaks, with micropores and macropores developing best, which can simultaneously enrich free gas and adsorbed gas. The pore structure of coal seams in the wetland forest swamp sedimentary presented two peaks, with micropores developing well and macropores developing poorly, mainly enriching adsorbed gas.

Mineral carbonation is emerging as a reliable CO2 capture technology that can mitigate climate change. In lime-treated clayey soils, mineral carbonation occurs through the carbonation of free lime and cementitious products derived from pozzolanic reactions. The kinetics of the reactions in lime-treated clayey soils are variable and depend primarily on soil mineralogy. The present study demonstrates the role of soil mineralogy in CO2 capture and the subsequent changes caused by carbon mineralization in terms of the unconfined compressive strength (UCS) of lime-treated soils during their service life. Three clayey soils (kaolin, bentonite, and silty clay) with different mineralogical characteristics were treated with 4% lime content, and the samples were cured in a controlled environment for 7 d, 90 d, 180 d, and 365 d. After the specified curing periods, the samples were exposed to CO2 in a carbonation cell for 7 d. The non-carbonated samples purged with N2 gas were used as a benchmark to compare the mechanical, chemical-mineralogical, and microstructure changes caused by carbonation reactions. Experimental investigations indicated that exposure to CO2 resulted in an average increase of 10% in the UCS of lime-treated bentonite, whereas the strength of lime-treated kaolin and silty clay was reduced by an average of 35%. The chemical and microstructural analyses revealed that the precipitated carbonates effectively filled the macropores of the treated bentonite, compared to the inadequate cementation caused by pozzolanic reactions, resulting in strength enhancement. In contrast, strength loss in lime-treated kaolin and silty clay was attributed to the carbonation of cementitious phases and partly to the tensile stress induced by carbonate precipitation. In terms of carbon mineralization prospects, lime-treated kaolin exhibited maximum carbonation due to the higher availability of unreacted lime. The results suggest that, in addition to the increase in compressive strength, adequate calcium-bearing phases and macropores determine the efficiency of carbon mineralization in lime-treated clayey soils.

Shale oil and gas resources mainly exist in the pore and fracture system. Quantitative characterization of pore development characteristics and gas-bearing properties is crucial for shale reservoir evaluation. The pore development of shale reservoir exhibits strong complexity and heterogeneity, and research on pore development characteristics of coal measure shale lags behind that of marine shale reservoir. Hence, it is urgent to investigate the pore heterogeneity characteristics of coal-bearing shale and its influence on gas bearing properties. Therefore, the coal-bearing Cretaceous Nenjiang shales from the Songyuan area of the Songliao Basin were selected as the research object in this study. Through total organic carbon (TOC) analysis, X-ray diffraction experiments, porosity analysis, nitrogen adsorption–desorption experiments, and methane isothermal adsorption experiments, the characteristics of pore structure, heterogeneity, and gas bearing properties of coal-bearing shale were analyzed. The influence of rock and mineral components on pore structure and heterogeneity characteristics, the relationship between pore structure characteristics and fractal characteristics, and the effects of pore structure and heterogeneity on gas bearing properties were also discussed. The results show that: (1) The organic matter abundance of the shale in the Nenjiang Formation does not change significantly (the average TOC content is 2.38%). Ink bottle-shaped pores are mostly developed, and the Nenjiang shale is rich in clay minerals (average content 55.6%), with slit-shaped pores mostly developed. The pore surface of shale exhibits obvious fractal characteristics, with average fractal dimensions D1 and D2 of 2.54 and 2.74, respectively, indicating that the internal structure is more complex than the surface structure. (2) The enrichment of organic carbon increases the specific surface area by affecting the development of micropores and pores, consequently increasing the fractal dimension of pores. Similarly, the development of clay minerals increases the number of mesopores and macropores, thereby increasing the fractal dimension of pores. (3) Small pores develop larger specific surface areas, which increases the complexity and heterogeneity of the pore structure. This promotes remarkable fractal characteristics, expands the adsorption sites, and improves the adsorption capacity. This work will provide a scientific theoretical basis for the comprehensive evaluation of coal-bearing shale reservoirs and research on shale gas reservoir formation theory.

Abstract 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 (H f) 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 H f 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.

Coal is a porous material containing pore structures and mineral components, exhibiting pronounced anisotropy and size effects.In order to investigate the influence of coal anisotropy and size effects on its failure characteristics, this paper proposes a simulation method for characterizing and reconstructing three-dimensionally the internal pores and mineral components of coal samples based on CT scanning, nuclear magnetic resonance, and X-ray diffraction.Specifically, we obtained simulation parameters of three-dimensional reconstruction models of coal matrix and mineral components through inverse laboratory uniaxial compression experiments, while simulated and analyzed the strength damage characteristics of coal bodies with different aspect ratios.The simulation results show that: ① During the loading process, the plastic zone first gradually expands and connects outward around the pores and mineral components.In terms of spatial distribution, the plastic zone expands vertically from the loading end to the interior in the early stage, and in the later stage, it expands horizontally from the surroundings to the interior.After the model is damaged, a "double truncated cone structure" is formed in the non-plastic zone.② The increase of aspect ratio leads to an increase in the compressive strength(p) of coal samples, the strain(ζ) at yielding strength, and the elastic modulus(K), among which ζ and K increase linearly, while the margin of increase in p gradually decreases.③ The total energy and elastic energy of coal sample loading increase exponentially, while the dissipated energy increases linearly.The increase of aspect ratio leads to an increase both in the accumulated elastic energy in the coal body and in the released energy during failure, which easily induce dynamic impact-related disasters.This study provide references for the reasonable selection of coal pillar size in impact mine pressure area.

Despite the abundance of shale-oil and tight-oil reserves in the Fengcheng Formation within the Mahu Sag, exploration and development efforts for both types of reservoir are still in their early stages. A comprehensive examination and comparison of the pore structures of these reservoirs can establish rational classification and evaluation criteria. However, there is a dearth of comparative analyses focusing on the pore structures of shale-oil and tight-oil reservoirs within the Fengcheng Formation. This study addresses this gap by systematically analyzing and comparing the pore structures of these reservoirs using various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), low-temperature nitrogen adsorption, and mercury intrusion capillary pressure experiments (MICP). The results show that the shale oil within the Fengcheng Formation exhibits a higher content of carbonic acid compared to the tight-oil samples. Furthermore, it demonstrates smaller displacement pressure and median pressure, a larger sorting coefficient, and superior permeability in contrast to tight oil. Notably, the shale oil within the Fengcheng Formation is characterized by abundant striated layer structures and micro-fractures, which significantly contribute to the microstructural disparities between shale-oil and tight-oil reservoirs. These differences in microstructures between shale oil and tight oil within the Fengcheng Formation in the Mahu Sag region delineate distinct criteria for evaluating sweet spots in shale-oil and tight-oil reservoirs. [ABSTRACT FROM AUTHOR]

CO2–slickwater hybrid fracturing technology is an essential part of shale gas recovery and CO2 geo-storage. However, the exposure to supercritical CO2 (ScCO2) and slickwater can result in potential changes of the pore structures and surface wetting behavior, which affect the gas transportation and CO2 sequestration security in shale reservoirs. Therefore, in this paper, X-ray diffraction (XRD), low-pressure nitrogen gas adsorption (N2GA), mercury intrusion porosimetry (MIP), and fractal analysis were used to describe the pore characteristics of shale before and after ScCO2–slickwater coupling treatments. Shale's surface wettability was confirmed by contact angle measurements. After the ScCO2–slickwater treatments, the number of micropores (<3.5 nm) and mesopores (3.5–50 nm) increased, while that of macropores (>50 nm) declined based on the N2GA and MIP experiments. Combined with fractal analysis, we argue that the pore connectivity diminished and the pore structure became more complicated. By analyzing the results of XRD, shale pore changes occurring after the ScCO2–slickwater treatment can be explained by the adsorption of polyacrylamide (PAM). Contact angle measurement results showed that the shale's surface treated by ScCO2 and slickwater was more hydrophilic than that treated by ScCO2 and water, and indirectly prove our argument above. Hence, the coupling using effect of ScCO2 and slickwater can impair the negative effect of CO2 on the shale capillary force to improve shale gas productivity, but it can negatively affect the security of CO2 sequestration in shale reservoirs. [ABSTRACT FROM AUTHOR]

Shotcrete is widely used in mine and civil engineering as supporting structure. A new type of ultra-high-strength shotcrete (UHSSC) with viscosity-enhancing agent was taken as the research object in this paper. A microstructure model of UHSSC under different curing conditions (standard curing, natural curing and film curing) was reconstructed using X-ray computed tomography (X-CT). The grey theory was used to analyze the correlation between pore characteristics and strength of UHSSC. The results showed that the porosity and the pore size of UHSSC were significantly reduced, the compressive strength was obviously improved by the new spraying process. The effects of curing conditions on the pore characteristics and compressive strength of UHSSC were obvious. Under natural curing, the hydration degree was the highest, the maximum pore size was the smallest, and the compressive strength was the highest, reaching 95.8 MPa, but the porosity was the highest. The curing condition had a certain influence on the sphericity distribution of UHSSC pores. Under film curing, the proportion of special-shaped pores (S < 0.4) was the largest and compressive strength was the smallest. There was a good correlation between pore characteristic parameters and the compressive strength of UHSSC under different curing conditions. In particular, the large pore size (D ≥ 5000 µm) and special-shaped pores (S < 0.4) had obvious effects on the strength of UHSSC, and the grey correlation coefficients were 0.8539 and 0.8080, respectively. Additionally, the pore direction of UHSSC had obvious directionality, and the anisotropy of UHSSC may be more prominent than poured specimen. The results will lay a foundation for the study of its mechanical properties and durability. [ABSTRACT FROM AUTHOR]

This study aimed to decipher the influence of red mud on the mechanical properties, pore structure, and microstructure of basic magnesium sulfate cements (BMSCs). The results showed that BMSC prepared with an appropriate addition of red mud exhibited improved mechanical properties and yielded the highest compressive strength of 94.54 MPa after curing for 28 days. Adding red mud reduced the total porosity and optimized the pore structure of BMSC. The microstructure and hydration products of the specimens were examined using X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The results illustrate that the addition of 50% red mud did not affect the amount of the main strength phase 5-1-7 produced in BMSC. It could also reduce the residual amount of MgO and the generation of Mg(OH)2. The red mud and the M-S-H gel generated by the reaction between active SiO2 and α-MgO in the red mud together filled the pore structure of BMSC, making its microstructure denser and higher-strength. This study aims to improve the comprehensive use of red mud, and the results show that red mud can improve the mechanical properties of BMSCs, protecting the environment and simultaneously reducing BMSC production costs to create good economic benefits. [ABSTRACT FROM AUTHOR]

Geopolymer foam concrete (GFC), an emerging thermal insulation material known for its environmentally friendly and low-carbon attributes, has gained prominence for its use in bolstering building energy efficiency. A critical challenge in GFC production is foam destabilization by the alkaline environment in which foam is supersaturated with salt. In this study, GFC was prepared by using triterpene saponin (TS), sodium dodecyl sulphate (SDS), and cetyltrimethylammonium bromide (CTAB) as blowing agents, with fly ash as the precursor and calcium carbide slag (CA) combined with Glauber's salt (GS, Na2SO4 ≥ 99%) as the activator. The effect of GFC on mechanical properties was analyzed by examining its fluidity, pore structure, dry density, and compressive strength. The results show that TS has a stable liquid film capable of adapting to the adverse effects of salt supersaturation and alkaline environments. TS is highly stable in the GFC matrix, and so the corresponding pore size is small, and the connectivity is low in the hardened GFC. In addition, the hydration products of GFC exhibit different morphologies depending on the surfactant used. TS has better water retention due to hydrogen bonding, which facilitates the hydration process. [ABSTRACT FROM AUTHOR]

In order to optimize the application of desert sand autoclaved bricks in rural construction in Xinjiang, this study focuses on the research and development of MU15-grade desert sand autoclaved bricks. Experimental investigations were conducted to examine the relationship between the water absorption rate of desert sand autoclaved bricks and the duration of water absorption while analyzing the impact of the water absorption rate on the compressive strength of these bricks. Additionally, experimental research was carried out to evaluate the appearance, compressive strength, and pore structure of autoclaved bricks after sulfate erosion. The results indicate the following. (1) With an increasing immersion time, the water absorption rate of desert sand-based autoclaved bricks initially rises and then declines, reaching approximately 14.74% when immersed for 4 h, which is close to the saturation water absorption rate. (2) The compressive strength of desert sand-based autoclaved bricks gradually decreases with an increasing water absorption rate, reaching its lowest point when saturation is attained, with a strength loss rate of approximately 33.18%. (3) Finally, after sulfate erosion, cracks and detachment appear on the surface of desert sand-based autoclaved bricks, and these cracks extend and propagate with the continuous accumulation of eroded products. Simultaneously, this process leads to an increase in the proportion of harmful pores by 0.96%, thereby causing a deterioration in strength. Through data analysis, a decay curve of the compressive strength erosion coefficient of desert sand-based autoclaved bricks with the number of sulfate erosion cycles was established, with good accuracy. This study provides theoretical references and technical support for the performance characteristics of desert sand-based autoclaved bricks and their application in rural construction in Xinjiang. [ABSTRACT FROM AUTHOR]

The Chang 6 reservoir group in the southeastern Wangjiawan area of the Ordos Basin is a tight sandstone reservoir. Reservoir sensitivity evaluation is an important means to study fluid damage to reservoirs and has important guiding significance for later water injection development. Reservoir sensitivity and its influencing factors were studied based on a scanning electron microscope, mercury injection test, and sensitivity test. The results show that the study area is mainly feldspar sandstone with high content of feldspar, quartz and rock debris, and clay minerals are mainly illite, chlorite and illite-montmorillonite mixed layer. The rock is dense, the pore structure is poor, and the pore throat distribution is uneven, which is a low porosity and low permeability reservoir. The sensitivity is characterized by medium-weak velocity sensitivity, medium-weak water sensitivity, medium-strong acid sensitivity, weak-medium-weak alkali sensitivity and medium-weak-weak salt sensitivity. The type and content of clay minerals affect the main factors of reservoir sensitivity. The mixed layer of illite and montmorillonite, illite and chlorite in clay minerals have great influence on salt sensitivity, water sensitivity and acid sensitivity respectively. Therefore, in the process of water injection development, targeted reservoir protection measures should be taken for salt sensitivity, water sensitivity and acid sensitivity. [ABSTRACT FROM AUTHOR]

Eutrophication of lakes has become one of the environmental health issues of widespread concern, among which endogenous ammonia nitrogen pollution is the key to control eutrophication. Granular natural volcanic rocks are often used for the adsorption treatment of endogenous nitrogen and ammonia wastewater, but the adsorption removal effect is not ideal. Therefore, volcanic rock that is conducive to dehydration and separation treatment is selected as the basic material, and two solutions, HCl and NaOH, are used to chemically modify volcanic rock to improve its adsorption performance and effectively remove ammonia nitrogen from water. Test the ammonia nitrogen adsorption effect of modified volcanic rocks from two aspects： characterization and experimental testing. The characterization observation results show that the modified volcanic rock surface forms more adsorption sites and more complex pore structures, which increases the specific surface area and the number of active sites of volcanic rock, thereby improving its adsorption capacity for ammonia nitrogen in solution. Experimental tests were conducted on the effects of modified volcanic stone adsorption capacity, adsorption isotherms, initial solution pH, and dosage on adsorption performance. The experimental test results show that the process of modified volcanic rock adsorbent adsorbing ammonia nitrogen pollutants in water after fitting belongs to quasi second order adsorption； And the maximum adsorption capacity of modified volcanic rock is 2. 29 times that of natural volcanic rock, indicating that modified volcanic rock has a good adsorption capacity for ammonia nitrogen pollutants and can effectively remove ammonia nitrogen pollution from water [ABSTRACT FROM AUTHOR]

Accurate pore structure characterization, as a basic tool for efficient exploration and development in reservoirs and digital rock, has become increasingly popular nowadays. However, using single-scale digital core data, it is difficult to evaluate the multi-scale pore structures in shales. This study proposes an integrated workflow for identifying and extracting pore parameters from multi-scale three-dimensional and two-dimensional digital rock images, which includes full-diameter core computed tomography (CT), micro-CT, focused ion beam-scanning electron microscopy and scanning electron microscopy images. This workflow realizes the identification and parameter extraction of pores and fractures from mesoscopic to microscopic scales. First, meso-fractures are extracted using the connected domain analysis method from full-diameter CT images, and the apparent attitudes are calculated using the least squares and connected domain analysis method. Then, micropores and fractures are identified from Micro-CT and focused ion beamscanning electron microscopy data, and the pore network models are established. Features, including pore radius, surface area, volume, throat radius, length, and coordination number, are calculated based on the maximum ball method. Different types of pores in scanning electron microscopy images are automatically identified using deep learning methods, and the pore parameters are computed using connected domain analysis methods. Subsequently, the workflow is applied to a practical case and the results show accurate extractions of pore structure information. This study provides important guidance and support for the quantitative evaluation of pores and fractures in unconventional reservoirs. [ABSTRACT FROM AUTHOR]

In order to explore the micro‐pore structure improvement mechanism of multi‐walled carbon nanotubes (MWCNT) on the frost resistance of concrete, five kinds of MWCNT concrete with different contents were prepared and the frost resistance test and mercury intrusion test were carried out. The results show that when the content of MWCNT is 0.1 wt%, the mass loss rate and compressive strength loss rate of concrete after freezing and thawing are 15.97% and 23.85% lower than that of ordinary concrete, respectively, indicating that this content is best amount to improve the frost resistance of concrete in this study. Moreover, 0.1 wt% MWCNT can significantly optimize the internal pore structure of concrete, and the average pore diameter growth rate and harmful pore ratio are 30.1% and 64.45%, respectively, after 200 freeze–thaw cycles. The proportion of more harmful pores has the greatest influence on compressive strength and relative elastic modulus, and the gray correlation degree is more than 0.8. Finally, the mathematical models of compressive strength‐pore parameters and relative dynamic elastic modulus‐pore parameters of MWCNT concrete after freeze–thaw cycle are established considering pore structure parameters and pore size distribution. [ABSTRACT FROM AUTHOR]

The process of soil moisture phase transitions (SMPT) under freeze–thaw cycling is considered a key factor driving changes in soil pore structure. However, there is still no consensus on which indicators related to SMPT affect the soil pore structure. The objectives of this study were to compare SMPT and soil pore characteristics under freeze–thaw cycling, and to analyze the inherent relationship between them as affected by different bulk densities. Hence, we employed thermal pulse time-domain reflection technology (T-TDR) and X-ray CT scanning technology (X-CT) to quantitatively study the process of SMPT and pore characteristics of soil core samples (60 mm diameter, 100 mm height) repacked with three different bulk density levels: 1.10 g·cm−3 (NC), 1.30 g·cm−3 (LC) and their combination (1.10 g·cm−3 for upper half, 1.30 g·cm−3 for lower half, SC) under freeze–thaw cycling. Our results showed that compared with NC, the porosity of LC's 0–5 cm soil column decreased by 0.070 cm3·cm−3, the imaged porosity (ϕ>60μm) decreased by 0.034 cm3·cm−3, and the maximum soil ice content (MIC) decreased by 0.030 cm3·cm−3. The pores within the range of 200−300 mm (ϕ2) and 300–400 mm (ϕ3) contribute the most significantly to ϕ>60μm (50–60%). Soil initial moisture content (IMC) and MIC explained 50.1% of the change in ϕ2, and the bulk density explained 49.3% of the change in ϕ3. During the melting process, higher moisture content promotes the thaw collapse of soil particles, resulting in a decrease in ϕ>60μm. The mean pore radius of the limiting layer (MRLL) and the hydraulic radius (HR) show that changes in bulk density from 1.10 g·cm−3 to 1.30 g·cm−3 do not have significant differences. Our results show the relationship between SMPT and pore structure change during freeze–thaw cycles as affected by initial soil bulk density and moisture condition. [ABSTRACT FROM AUTHOR]

Currently, microscopic research on the tensile fracture properties of recycled brick coarse aggregate concrete has mainly adopted microscopy techniques, which can clearly observe the actual damage situations of each phase material but are unable to individually analyze the effect of a specific material factor on the tensile properties of recycled concrete. This brings much uncertainty to the practical application of recycled concrete. Therefore, this study proposes a cohesive zone model (CZM) for simulating the tensile fracture of recycled brick coarse aggregate (RBCA) concrete. To this end, the study explores the effects of various critical factors on the fracture mode and bearing capacity of recycled brick aggregate concrete, including the replacement rate of recycled brick coarse aggregate, pore structure, interfacial transition zone (ITZ) strength, mortar strength, and volume fraction of brick aggregate. The results indicate that, when the minor to major axis ratio of elliptical pores is 0.5 ≤ K < 1, the following order of influence can be observed: random convex polygonal pores, circular pores, and elliptical pores. Moreover, excessively strengthening the ITZ and mortar does not significantly enhance the tensile performance of RBCA concrete. The distribution location of aggregate has a significant impact on the crack shape of recycled concrete, as does the pore structure, due to their randomness. Therefore, this article also discusses these. These findings contribute to a comprehensive understanding of the tensile properties of recycled brick coarse aggregate and provide insights into optimizing its behavior. [ABSTRACT FROM AUTHOR]

Fatigue damage can occur in surface rock engineering due to various factors, including earthquakes, blasting, and impacts. The underlying cause for the variations in physical and mechanical properties of the rock resulting from impact loading is the alteration in the internal pore structure. To investigate the evolution characteristics of the pore structure under impact fatigue damage, red sandstone subjected to cyclic impact compression by split Hopkinson pressure bar (SHPB) was analyzed using nuclear magnetic resonance (NMR) technology. The parameters describing the evolution of pore structure were obtained and quantified using fractal methods. The development of the pore structure in rocks subjected to cyclic impact was quantitatively analyzed, and two fractal evolution models based on pore size and pore connectivity were constructed. The results indicate that with an increasing number of impact loading cycles, the porosity of the red sandstone gradually increases, the T2 cutoff (T2c) value decreases, the most probable gray value of magnetic resonance imaging (MRI) increases, the pores' connectivity is enhanced, and the fractal dimension decreases gradually. Moreover, the pore distribution space tends to transition from three-dimensional to two-dimensional, suggesting the expansion of dominant pores into clusters, forming microfractures or even macroscopic fissures. The findings provide valuable insights into the impact fatigue characteristics of rocks from a microscopic perspective and contribute to the evaluation of time-varying stability and the assessment of progressive damage in rock engineering. [ABSTRACT FROM AUTHOR]

The Qinshui Basin is located in the southeast of Shanxi Province, China. It is one of the most abundant coal resources from Permo-Carboniferous North China. It is rich in coal and coalbed methane resources. However, the accumulation of coalbed methane is complex and the enrichment law has not been fully understood because of the high heterogeneity of coal reservoirs in the Qinshui Basin. The examination of dissimilarities between tectonically deformed coals (TDCs) and primary coals at multiple scales holds paramount importance in advancing our understanding of the occurrence and flow patterns of coalbed methane, and in providing guidance for exploration efforts. In the present study, the samples from the Jincheng Mine, Qinshui Basin, were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), CO2 gas adsorption and 3D X-ray micro-computed tomography. The results showed that the dominant minerals in coal were illite, kaolinite, and calcite, with minor amounts of quartz and ankerite. In comparison to primary coal, tectonism could increase the microfractures density of type A (the fracture of width ≥ 5 μm and length > 10 mm) in TDCs. In CO2 gas adsorption in mylonite coal, it was observed that the volume of micropores (<2 nm) was significantly reduced leading to a decrease in gas adsorption capacity. The result of Micro-CT scanning revealed that the minerals occurred as veins in primary coal, but as irregular aggregates in TDCs. Moreover, tectonism had a staged impact on fracture structure, which was initially closed in cataclastic coal and then formed into granulated coal during the tectonic evolution. The effects of tectonism on coal structure had an impact on the connectivity of micropores at the micrometer scale by the destruction of the pore throat structure, increasing the heterogeneity of the reservoir. These findings help to better understand the changes in TDC structure at different scales for developing effective strategies for coalbed methane exploration and production. [ABSTRACT FROM AUTHOR]

Tectonism is one of the dominant factors affecting the shale pore structure. However, the control of shale pore structure by tectonic movements is still controversial, which limits the research progress of shale gas accumulation mechanism in the complex tectonic region of southern China. In this study, 34 samples were collected from two exploratory wells located in different tectonic locations. Diverse experiments, e.g., organic geochemistry, XRD analysis, FE-SEM, low-pressure gas adsorption, and high-pressure mercury intrusion, were conducted to fully characterize the shale reservoir. The TOC, Ro, and mineral composition of the shale samples between the two wells are similar, which reflects that the shale samples of the two wells have proximate pores-generating capacity and pores-supporting capacity. However, the pore characteristics of shale samples from two wells are significantly different. Compared with the stabilized zone shale, the porosity, pore volume, and specific surface area of the deformed zone shale were reduced by 60.61%, 64.85%, and 27.81%, respectively. Moreover, the macroscopic and fine pores were reduced by 54.01% and 84.95%, respectively. Fault activity and uplift denudation are not conducive to pore preservation, and the rigid basement of Huangling uplift can promote pore preservation. These three factors are important reasons for controlling the difference in pore structure between two wells shales. We established a conceptual model of shale pores evolution under different tectonic preservation conditions. This study is significant to clarify the scale of shale gas formation and enrichment in complex tectonic regions, and helps in the selection of shale sweet spots. [ABSTRACT FROM AUTHOR]

Hot water flooding is an effective way to develop heavy oil reservoirs. However, local channeling channels may form, possibly leading to a low thermal utilization efficiency and high water cut in the reservoir. The pore structure heterogeneity is an important factor in forming these channels. This study proposes a method that mixes quartz sand with different particle sizes to prepare weakly heterogeneous and strongly heterogeneous models through which hot water flooding experiments are conducted. During the experiments, computer tomography (CT) scanning identifies the pore structure and micro remaining oil saturation distribution to analyze the influence of the pore structure heterogeneity on the channeling channels. The oil saturation reduction and average pore size are divided into three levels to quantitatively describe the relationship between the channeling channel distribution and pore structure heterogeneity. The zone where oil saturation reduction exceeds 20% is defined as a channeling channel. The scanning area is divided into 180 equally sized zones based on the CT scanning images, and threedimensional (3D) distributions of the channeling channels are developed. Four micro remaining oil distribution patterns are proposed, and the morphology characteristics of micro remaining oil inside and outside the channeling channels are analyzed. The results show that hot water flooding is more balanced in the weakly heterogeneous model, and the oil saturation decreases by more than 20% in most zones without narrow channeling channels forming. In the strongly heterogeneous model, hot water flooding is unbalanced, and three narrow channeling channels of different lengths form. In the weakly heterogeneous model, the oil saturation reduction is greater in zones with larger pores. The distribution range of the average pore size is larger in the strongly heterogeneous model. The network remaining oil inside the channeling channels is less than outside the channeling channels, and the hot water converts the network remaining oil into cluster, film, and droplet remaining oil. [ABSTRACT FROM AUTHOR]

The efficient pyrolysis and conversion of organic matter in organic-rich shale, as well as the effective recovery of pyrolysis shale oil and gas, play a vital role in alleviating energy pressure. The state of carbon dioxide (CO2) in the pyrolysis environment of shale reservoirs is the supercritical state. Its unique supercritical fluid properties not only effectively heat organic matter, displace pyrolysis products and change shale pore structure, but also achieve carbon storage to a certain extent. Shale samples were made into powder and three sizes of cores, and nitrogen (N2) and supercritical carbon dioxide (ScCO2) pyrolysis experiments were performed at different final pyrolysis temperatures. The properties and mineral characteristics of the pyrolysis products were studied based on gas chromatography analysis, Xray diffraction tests, and mass spectrometry analysis. Besides, the pore structure characteristics at different regions of cores before and after pyrolysis were analyzed using N2 adsorption tests to clarify the impact of fracturing degree on the pyrolysis effect. The results indicate that the optimal pyrolysis temperature of Longkou shale is about 430 °C. Compared with N2, the oil yield of ScCO2 pyrolysis is higher. The pyrolysis oil obtained by ScCO2 extraction has more intermediate fractions and higher relative molecular weight. The ScCO2 can effectively improve the pore diameter of shale and its effect is better than that of N2. The micropores are produced in shale after pyrolysis, and the macropores only are generated in ScCO2 pyrolysis environments with temperatures greater than 430 °C. The pore structure has different development characteristics at different pyrolysis temperatures, which are mainly affected by the pressure holding of volatile matter and products blocking. Compared to the surface of the core, the pore development effect inside the core is better. With the decrease in core size, the pore diameter, specific surface area, and pore volume of cores all increase after pyrolysis. [ABSTRACT FROM AUTHOR]

Ionic thermoelectric effect based on thermal migration of ion in the pore solution is emerging as a new branch of research on the thermoelectric effect of cement-based materials. However, the dense and tortuous pore structure of the cementitious materials may limit the ionic electrical conductivity and reduce the ionic thermal migration in pore solutions. Therefore, improving the pore structure may be a promising direction to enhance the thermoelectric effect of pore solution in cementitious materials. In this study, the pure cement paste with three water-cement ratios (w / c ratio = 0.3, 0.4, 0.5) and two curing methods (sealed curing and wet curing) are used. The effects of the ion concentration of the pore solution on the electrical conductivity and the Seebeck coefficient are investigated by the treatment of the vacuum saturation and the leaching process of the cement pastes. In addition, the pore structure of the cement paste is measured by mercury intrusion porosimetry (MIP). The effect of pore structure on the ionic thermoelectric effect of the cement pastes is studied. The results show not only the porosity and pore connectivity, but also the higher specific surface area of cement matrix is an important parameter for improving the ionic Seebeck coefficient of cementitious materials. The finer pore distribution in the cement matrix will cause a larger thermoelectric voltage. By improving the pore structure, the power factor (PF) of cement paste has been improved by two orders of magnitude, from 0.0027 μWm−1K−2 to 0.178 μWm−1K−2. The findings of this study can guide further understanding of the ionic thermoelectric effect of cementitious materials and provide a method for enhancing the thermoelectric effect of high-efficiency ionic thermoelectric materials (such as polyelectrolytes and ionic liquid) in cement matrix, which can develop ultra-high performance ionic thermoelectric cement-based materials for zero energy buildings. [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]

The evaluation of the pore structure in dolomite, particularly with regard to pore heterogeneity, geometry, and connectivity, is crucial for oil and gas field production and reservoir prediction. The subsalt dolomite reservoir in the Ordovician strata of the Ordos Basin has shown promising exploration results and is anticipated to have a high hydrocarbon potential. However, there has been limited research on the pore structure and primary controlling factors of the Ordovician Majiagou reservoir in the south-central Ordos Basin. Therefore, we conducted a comprehensive analysis of the pore structure and fractal characteristics using routine petrophysical measurements, thin-section analysis, and high-pressure mercury injection (HPMI) data. We also discussed the relationship between fractal dimension, reservoir physical properties, and pore structure, along with exploring the origin of potentially prolific reservoirs. Our observations from the thin section identified four main pore types: intercrystalline pores, intercrystalline dissolved pores, dissolved pores, and micro-fractures. The data from HPMI revealed that the average pore-throat radii range from 0.009 μιτι to 0.015 μιτι with porosity ranging from 0.4% to 5.26%, and permeability ranging from 0.011 mD to 0.059 mD. They were further categorized into three reservoir types: dissolved pore type, intra-crystalline (dissolved) pore type, and micro-porous type. The fractal dimension was calculated based on HPMI data, and the reservoir's fractal characteristics were divided into two segments. The dissolved pore type was identified as the potentially prolific reservoir due to its larger pore size and volume, moderate permeability, and homogeneity on pore structure. Additionally, the fractal dimension is negatively correlated with porosity and permeability and positively correlated with sorting coefficient and skewness, suggesting that fractal dimensions are valuable for evaluating reservoir quality and quantitatively characterizing pore networks. [ABSTRACT FROM AUTHOR]

Air tightness machine-made sand concrete suitable for gas tunnel was prepared by adding air-tight agent and its influence on cement hydration was studied. The heat release and hydration products of cement were analyzed by isothermal calorimeter, XRD. thermogravimetric analyzer, scanning electron microscope and mercury injection method. The results show that, compared with the concrete without air tightness, the apparent permeability of concrete decreases from 497.50×10-18m² to 29.16×10-18 m², the chloride permeability coefficient decreases by 54.96%, the drying shrinkage decreases by 8.63%, and the compressive strength increases by 11.2% at 56 d. According to the analysis, the addition of air-tight agent has no adverse effect on the generation of cement hydration products, compared with the sample without adding air-tight agent significantly reduces the large capillary pores (100~1000 nm) inside the cement hydration products, makes the hydration products more dense, and improves the structure of the transition zone of the concrete interface, so that the strength, air tightness and durability of the concrete can be improved. [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]