Pore Distribution Characteristics Research Articles

The Application of Computed Tomography to Study the Soil Porosity of Mountain Red Earth

Mountain red soil, as a special type of soil in the South, has received widespread attention for its soil erosion problems. Its pore structure restricts water infiltration, thereby affecting the occurrence and development of soil erosion. In order to systematically obtain the distribution characteristics of the pore structure within the surface mountain red soil, this paper uses non-destructive CT detection technology to scan the soil column samples taken from the typical mountain red soil distribution area in Chenggong District, Kunming City, Yunnan Province. Image processing technology is applied to CT slices, and ImageJ (1.46r) software is used to obtain the distribution characteristics of pores within the soil column, including pore sizes and the number of pores at each depth, the proportion of pore area, roundness, and box-counting dimension. The results show that with the increase in depth, the proportion of pore area decreases linearly from the maximum value of 52.25% at the top to the minimum value of 2.02% at the bottom; the roundness of pores fluctuates between 0.8 and 0.9, overall increasing; the total number of pores generally first increases then decreases, and small pores are predominant, with the least number of large pores in the topsoil layer; the box-counting dimension shows a gradual linear decrease, with a maximum value of 1.7980 and a minimum value of 0.9878. The number of pores affects both roundness and the box-counting dimension, and the proportion of pore area also affects the box-counting dimension. There is a negative correlation between roundness and the box-counting dimension. The 3D visualization reconstruction of pores shows that most are interconnected, with the pore size significantly reducing with increasing depth. The quantitative analysis of parameters and 3D visualization reveal, to some extent, the impact of pore structure on the occurrence and development of soil erosion in mountain red soil. These research findings form the foundation for studying soil erosion in this region and provide a basis for systematically understanding its processes and mechanisms.

Mechanism of uneven densification in PBX compression molding

The uneven density distribution during compression molding of polymer bonded explosive (PBX ) seriously affects the mechanical properties of high-energy material components and the precise output ability of shock waves. Investigating the multi-scale densification evolution laws and density non-uniformity mechanism of PBX composite powders is crucial for understanding the density non-uniformity phenomenon of energetic material components and evaluating the differences in macroscopic mechanical response. To this end, we developed a new dual-scale 3D discrete element method (DEM) model for PBX compression molding, which can increase the computational quantity of macroscopic powders by about an order of magnitude while considering the true morphology of mesoscopic explosive crystals. First, the densification behavior at different scales were analyzed using the developed 3D DEM models, including the rearrangement of macroscopic powder during the low strain stage, the deformation of macroscopic powders and mesoscopic bonding failure inside the powders during the high strain stage. Furtherly, the types and percentages of microcracks at the crystal-binder interface and inside the binder at the mesoscale during the macro powder deformation in the compression densification process were quantified. The characteristics of pore distribution and evolution laws of porosity and density uniformity during compression densification were revealed by simulations and X-ray μCT scanning. Finally, the mechanism of density non-uniformity was elucidated from multiple perspectives including displacement, force chain, contact fabric, and stress distribution. Subsequently, different degrees of energy dissipation behavior and the same gradient attenuation pattern were captured at different scales. This indicates that axial stress attenuation and density inhomogeneity are co-dominant results of the gradient attenuation of different scales of energy during layer-by-layer transfer along the loading direction. The potential induced mechanism of uneven density and stress attenuation were explained for the first time from the perspective of energy dissipation by this finding.

Effects of pore characteristics on CO2 adsorption performance of coal slime with different metamorphic degrees

With the rapid development of Carbon Capture, Utilization and Storage (CCUS) technology, it is necessary to explore the feasibility of coal slime as a porous carbon material for CO2 capture. In this paper, scanning electron microscopy (SEM) was used to observe the morphological characteristics of coal slime samples with different metamorphic degrees, and the pore structure of coal slime was explored by low temperature N2 adsorption and low-pressure CO2 adsorption experiments. The pore distribution characteristics were analyzed, and the adsorption law of different metamorphic degrees were summarized through CO2 isothermal adsorption experiments. The results showed that: The specific surface area (SSA) and pore volume (PV) of the mesopores of the coal slime exhibited a U-shaped distribution with coal rank, and are much smaller than that of its micropores. Micropores less than 2 nm are the main adsorption space of coal slime, its PV accounted for 59%, 60%, 71%, and SSA accounted for 92%, 93%, 95%, obviously, which are dominant at all stages. The linear correlation fitting coefficients R2 between the limiting adsorbed amount a of CO2 and the micropores PV and the SSA were up to 0.830 and 0.887, respectively. The coal slime has good adsorption performance for CO2. Based on the Langmuir model to fit the limit adsorption amount, a-value can reach 41.774 cm3 g−1, 32.072 cm3 g−1, 38.457 cm3 g−1 at 303 K with the increase of Rmax. Studying the impact of coal slime on CO2 adsorption performance provides a theoretical basis for the subsequent preparation of energy storage materials and is of great significance for the safe, efficient and economic capture and sequestration of CO2, to alleviate the serious situation of the environment and realizing the dual-carbon goal.

A new strategy to prepare ammonium aluminum carbonate hydroxide using plasma electrolytic oxidation in electrolyte containing carbon nanotubes

In this work, a plasma electrolytic oxidation (PEO) technique was used to prepare ammonium aluminum carbonate hydroxide (AACH) in an electrolyte containing carbon nanotubes (CNTs). CNTs were also involved in the composite coating on the surface of 6063 aluminum alloy. The formation mechanism of AACH and effects of CNTs on the microstructure and corrosion behavior of the PEO coatings were investigated. The surface morphology, pore distribution, phase composition, functional groups and electrochemical characteristics of the PEO composite coatings were examined using scanning electron microscopy (SEM), Image Pro software, X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR) and electrochemical workstations, respectively. Results showed that the rod-like AACH was generated around the discharge channel by reacting between ammonia, carbon dioxide and AlOOH under transient high temperature and high pressure environment with the presence of CNTs. The surface micropores of the composite coatings were enlarged due to the excellent electrical conductivity of CNTs. With the by addition of CNTs of 1.5 g/L, the self-corrosion current of the coating was the smallest, and the polarization resistance Rp was larger than that of 1.0 g/L and 2.0 g/L CNTs.

Optimal development of the new type of ultra-fine fly ash semi flexible pavement grouting material: Rheological, mechanical, pore distribution, and hydration characteristics

In order to solve the problems that the fluidity of semi-flexible pavement grouting materials (SFPGM) is not up to standard, the early strength is not enough, or the fluidity meets the requirements but the early strength is not up to standard, the power plant by-Product -ultra-fine fly ash (UFA) was used to optimized the performance of grouting materials (GM) in this study. The microstructure of hardened slurry was analyzed by XRD, FTIR, MIP and SEM. The findings indicate that when the UFA content increases, the fluidity of the GM initially increases and then declines, whereas the compressive strength initially reduces and then increases. The sample exhibits optimal fluidity performance when the content of UFA is 9 %. The flow cone fluidity of the initial and 20 min is 12.33 % and 17.63 % lower than that of the reference sample. When the amount of UFA is 12 %, the compressive strength of sample is the highest at each age. Additionally, that the fluidity of sample S12 is sub-optimal in all samples, only worse than that of sample S9. In the early stage of GM hydration, UFA with slow hydration rate produces a significant ‘ball-bearings effect’ between irregular cement particles. This is beneficial to the relative sliding between the slurry particles, reduces the yield stress and plastic viscosity of the fresh slurry, and improves the flow performance of the GM. The pozzolanic effects of UFA in GM primarily manifests during the later stages of hydration. The primary hydration products of UFA modified GM include ettringite, C-S-H gel, C-A-S-H gel, calcium carbonate, and aluminium glue (AH3). During the progression of the hydration reaction, the quantity of ettringite (AFt) in the slurry steadily augments, causing the initial fine needle-like structure to evolve into a more fully formed needle-like structure. A complex three-dimensional network of interlocking spatial structures is formed by many hydration products that continually interlace and develop, improving strength. The higher the perfusion rate of the GM, the higher the compactness of the SFPGM, and the better the high temperature stability and low temperature crack resistance.

Experimental investigation on fractal mechanism and shear failure characteristics of cement mortar at different curing ages

In this paper, the NMR and direct shear tests were conducted successively on cement mortar specimens with different curing ages (7 days, 14 days and 28 days). The porosity, shear strength, shear stiffness and shear energy of cement mortar are measured and analyzed through interpreting the pore distribution patterns and their corresponding fractal dimensions. The cross-sections of shear surface were characterized into point cloud data via 3D laser scanning and quantified by three dimensionless parameters (the root mean square value of the first derivative, root mean square value and joint roughness coefficient). The grey relation analysis (GRA) method and principal component analysis (PCA) is employed to analyze the relationship between the pore structures (i.e., gel pores, transition pores, capillary pores and pores or cracks) and distribution and the fractal dimensions. The results indicate that the shear peak strength is linearly correlated with the joint roughness coefficient. Compared to the fractal characteristics of pore size (T2 spectra) and pore distribution (MRI), we demonstrated that there is a strong correlation between the peak shear strength and the fractal dimension of shear fracture surface, which suggests that the quantitative characterization of internal pores and shear strength variations in cement mortar specimens can be achieved through the numerical values of fractal dimensions.

Seasonal Grazing Does Not Significantly Alter the Particle Structure and Pore Characteristics of Grassland Soil

Seasonal grazing is a recognized and sustainable approach to livestock management, but there is still a lack of comprehensive research on its impact on soil structure. This study utilizes advanced scanning electron microscopy technology to quantitatively evaluate the long-term effects of seasonal grazing on grassland soil structure, focusing on soil pore distribution characteristics and particle size. The investigation offers a detailed visual representation of the arrangement of soil particles at a micro-level. In both grazed and ungrazed plots (NG), soil particles ranging from 0.005 to 0.05 mm and 0.075 to 0.25 mm in size were predominant, constituting 20% and 60%, respectively. In plots subjected to seasonal grazing (grazing in June and August, G68, and grazing in July and September, G79), micro-particles (0.002–0.005 mm) and particles sized 0.05–0.075 mm were significantly lower compared to NG. Scanning electron microscope (SEM) images demonstrate structural differences, with NG displaying a higher proportion of small to medium-sized particles, more small pores, and fewer large pores. Analysis of pore size and morphology reveals the prevalence of large pores in both grazed and ungrazed plots. Continuous grazing plots exhibit significantly higher proportions of large pores compared to NG, while seasonal grazing plots show no significant differences. Correlation analyses indicate associations between soil physicochemical properties, particle size, and pore structure. Total soil nitrogen (TN), total soil carbon (TC), and soil moisture positively correlate with 0.005–0.05 mm particle proportions, while EC is negatively correlated with 0.05–0.075 mm particles. This study enhances our understanding of the effects of grazing practices on soil structure and provides scientific evidence for sustainable land management.

Predicting permeability coefficient in soil-rock mixtures using parameters from the negative exponential continuous grading equation

Soil-rock mixtures (SRMs) are widely utilized for embankment filling of highways in mountainous areas. The permeability characteristics of SRMs must be investigated as mountain highways are often exposed to strands of rainwater subjected to extreme rainfall. For the same species of SRM, its permeability is determined by its pore distribution and grading characteristics, which can be considered as an expression of particle grading and pore parameters. The predictive model of the SRMs permeability coefficient encompassing gradation coefficients and porosity was proposed based on the negative exponential continuous gradation equation and the Kozeny–Carman model. The applicability of the prediction model was verified based on the existing literature and performing SRMs seepage tests. The findings indicated that the permeability coefficient formula for SRMs established on the particle grading parameters and porosity was reasonable. Nevertheless, its current applicability is limited to the prediction of permeability coefficients for continuously graded SRMs. Consequently, further investigation is required to assess the suitability of the model for intermittently graded SRMs.

Improved macro-microscopic characteristic of gypsum-slag based cementitious materials by incorporating red mud/carbide slag binary alkaline waste-derived activator

The expensive cost and high carbon footprint of commercial alkaline activators hindered the promotion and industrialization of geopolymers. The rising demand for geopolymer as low carbon and excellent building materials will lead to enormous research works towards to low carbon alkaline activator. This study aimed to explore the impact of red mud (RM)/carbide slag (CS) binary alkaline wasted-derived activator (RCA) on the macroscopic and microscopic properties of RCA activated cementitious materials (RCM) prepared with titanium gypsum (TiG) and granulated blast furnace slag (GBFS). It is proposed to adjust the pH value of solid waste powder for calibrating the waste-derived activator, prepare RCM and explore the relationship between its mechanical properties and hydration products. The research showed that the highest flexural and compressive strengths at 28 days occurred with a dosage of 0.8 wt% CS, meeting the strength requirements of 52.5 R Portland cement. It is worth noting that RCM with binary alkaline waste-derived activators with appropriate pH values can exhibit excellent early mechanical properties. Raising the pH of RCA significantly improves the compressive and flexural strength, increasing them to 30.7 MPa and 6.3 MPa at 3 d, and to 60.7 MPa and 10.8 MPa at 28 d. The primary hydration products of RCM include C(N)-A-S-H gels, ettringite, and gypsum crystal phase, which contribute to the development of mechanical strength. Due to the difference in the alkaline environment required for the growth of C(N)-A-S-H gel and ettringite crystal, the increase in RCA pH value has been found to both inhibit the growth of ettringite to a certain extent and promote the precipitation of C(N)-A-S-H gels, improving the chemical structure of the hydration products and the pore distribution characteristics of the RCM. Furthermore, the research has been successfully applied in a pilot test in Jiaozuo, China. RCM introduces a novel concept for the efficient and industrial-scale utilization of solid waste. This study can provide a fundamental academic and industrialized support and a novel concept for the whole solid waste cementitious materials especially from alkaline industrial solid wastes such as RM and CS.

Implications of Temperature for the Modification of High-Overmature Shale Reservoirs: Experimental and Numerical Analysis

Summary High-temperature pore reconstruction technology is a reservoir reconstruction measure that has emerged in recent years. It is of great significance to study the variation in pore structure characteristics of shale under high temperature for reservoir reconstruction. To study the effect of high temperature on shale pores, scanning electron microscopy (SEM) experiments and fluid injection experiments were used to analyze the variation of pore structure characteristics under high temperature. Studies have shown that temperature has a great influence on the morphology and distribution characteristics of shale pores. In particular, there is a temperature between 300°C and 400°C that is suitable for modifying pores. The distribution characteristics, surface area, and volume of pores vary dramatically under this temperature threshold. The pore morphology and distribution characteristics changed from small and sparse to large and dense. The Brunauer-Emmett-Teller (BET) surface area increased by 95%. The cumulative surface area of Barrett-Joyner-Halenda (BJH) adsorption and desorption increased by 71.7% and 72%, respectively. The pore volume of the 2-nm to 20-nm pore size increased by 63.2%. The pore volume of pore sizes greater than 20 nm increased by 191.6%. The pore variation characteristics were in line with the typing law, and the fitting result R2 ranged from 0.92201 to 0.99882.

Study on freeze-thaw deterioration model of new-to-old concrete based on pore surface fractal characteristics

New-to-old concrete (NTOC) structures are widely used in engineering practice, the adhesive interface as a weak part is easily damaged under freeze-thaw environment. At present, most of NTOC deterioration models are grounded in the empirical summary of experiment data. In this paper, the bonding and durability of NTOC adhesive interface under different freeze-thaw cycles were investigated by splitting tensile test and ultrasonic nondestructive test, and the pore distribution characteristics of adhesive interface were obtained by mercury intrusion porosimetry. Based on the S-N equation and the constitutive relationship of damaged concrete, the phenomenological freeze-thaw damage model of NTOC was established. According to the fractal analysis of the effective bearing area of the pores, the freeze-thaw deterioration model of NTOC adhesive interface was further established, which was named PDM model. The splitting tensile strength (macroscopic mechanical properties) and ultrasonic wave velocity (microscopic defects) of the concrete repaired by four kinds of alkali activated slag-fly ash were used to verify PDM model. The results showed that PDM model could reflect the change of bonding properties and the defects of NTOC adhesive interface under freeze-thaw conditions. The microscopic pore evolution characteristics reflected the macroscopic mechanical properties. With a restricted number of monitoring sites, the PDM model could n forecast the changing trend of the whole freeze-thaw degradation process of NTOC.

Effects of preform structure on microstructure and mechanical properties of long/short fiber‐coupled C/C–SiC composites

AbstractC/C–SiC composites with four different preform structures were prepared via chemical vapor infiltration and reactive melt infiltration (RMI). The effects of preform structure on the microstructure and mechanical properties of the C/C–SiC composites were thoroughly investigated. The results indicate that the porous C/C composites with multidirectional long/short fiber‐coupling exhibited consistent pore size distribution (diameter: 5–300 µm) and periodicity pore distribution characteristics. As the effective fiber volume fraction in the loading direction of the C/C–SiC composites increased from 11.71% to 21.04%, the tensile and flexural strength significantly increased by 64.44% and 44.03%, respectively, with minimal effect on compressive and interlaminar shear properties. The introduction of Z‐direction fiber, such as stitched structure, increased the compressive and interlaminar shear strength of the composites by 10.87% and 15.67%, respectively. A theoretical predictive model of ultimate tensile strength after modification was validated for application to the C/C–SiC composites prepared by RMI, through characterization of the volume fraction of each layered unit and the content of each component. However, the presence of defects caused by the stitched structure, such as fiber bending, occupancy, and pores, reduced tensile and flexural strength by 30.45% and 28.56%, thereby impacting the effectiveness of the predictive model negatively.

Triaxial compression test of MICP sand column and simulation of failure process

Microbially induced calcium carbonate precipitation (MICP) technology can induce calcium carbonate crystals with cementation and stable performance in the process of microbial metabolism or enzymization through the regulation of environmental factors MICP can be used as a cementing agent to cement cohesionless sand particles to form the materials with the characteristics of higher strength, better durability and environmental friendliness, as well as a good engineering application prospect. In this paper, the shear strength of sand column was tested by triaxial compression tests, and the strength index was obtained. In order to further study the micro-strength mechanism and the failure process, based on the discrete element method, a numerical model of MICP cemented sand column was established considering the factors of matrix soil particle gradation, particle morphology, content ratio of induced calcium carbonate, pore distribution characteristics, inter-particle cementation and so on. The failure process of MICP cemented sand column under load was analysed by numerical simulation, and the reliability of the numerical model was tested by combining with the stress intensity curve of samples under test conditions. The results indicate that compared with the actual triaxial tests of MICP cemented sand column, although there are deviations in stress and strain, cohesion and internal friction angle, the numerical simulation shows similar development law and intensity amplitude, and the same failure trend. The work in this paper verifies the reliability of the numerical model and provides a theoretical basis for the subsequent analysis of the factors influencing the geotechnical mechanical properties of biomineralized materials.

Initial pore distribution characteristics and crack failure development of cemented tailings backfill under low impact amplitude

The stability of the cemented paste backfill is threatened by the dynamic disturbance during the excavation of the surrounding ore body. In this paper, the computerized tomography (CT) and Split Hopkinson Pressure Bar (SHPB) tests were conducted to explore the initial pore distribution characteristics of the cemented tailings backfill (CTB) and the development of the crack under low impact amplitude. SHPB tests were conducted with impact amplitudes of 34, 37, and 39 mV, respectively. Results show that the initial pores of CTB were steadily distributed with the height of CTB. The CTB contained many initial pores with similar pore size distribution characteristics, and the largest number of pores is between 0.1 and 0.3 mm. Most of the cracks in CTB after low impact amplitude develop and expand along the initial pores, and the damage of CTB mainly exists in shear cracks. A dependence has been established that the dynamic uniaxial compressive strength of the CTB increases, the total crack volume first increases and then decreases, and the number of cracks increases as the impact amplitude increases. The research results can provide a valuable reference for the dynamic performance of CTB under low impact amplitude and the design of mining backfill.

Mineralogical control on the dissolution induced microscopic pore alternations of high-rank coal during CO2 sequestration

The microstructure of deep coal seam plays a crucial role in determining the CO2 geological sequestrations. To investigate the effects of pore and mineral distribution on the changes and mechanisms of coal microstructure under supercritical CO2 (SC–CO2) interactions, we employed low-temperature N2 (LTN2) adsorption, low-temperature CO2 (LTCO2) adsorption, and X-ray diffraction (XRD) techniques to explore the development of microstructures and mineral compositions of coal samples with distinct pore distribution characteristics under SC-CO2 exposure. The results revealed that mineral dissolution under SC-CO2 saturation led to an increase in both specific surface area (SSA) and pore volume (PV) of mesopores, with SSA increasing by 13.6%–332.31% and PV increasing by 4.59%–148.61%. Subsequently, SC-CO2 exposure induced the formation of numerous new pores with diameters smaller than 3 nm within the coal matrix, particularly an abundance of new ultra-micropores (r > 0.5 nm) and large micropores (r > 0.85 nm). This significantly altered the irregularity of pore structure and adsorption capacity, thereby playing a crucial role in CO2 storage. Micropores exhibited much larger SSA and PV than mesopores, underscoring their significant contribution to CO2 geological sequestration. The spatial mineral distribution in coal influences the alteration characteristics of pores, which explains the different microscopic pore structures formed after SC-CO2 exposure. The impact of spatial mineral distribution on SC-CO2-induced pore alteration is analysed, emphasising the intrinsic heterogeneity of minerals within coal as the fundamental factor behind the diversity observed in pore development during CO2 sequestration. Finally, we found that the changes in micropores and mesopores under SC-CO2 exposure are closely related to the initial structure of microscopic pores. The development of micropores under SC-CO2 exposure is associated with the average pore size and fractal dimension of micropores, with the increment in mesopore irregularity increasing with the increase in micropore volume fractal dimension. By studying the influence of mineral and pore distribution on the evolution of coal microstructures, this study provides new insights into pore development under SC-CO2 geological sequestration, which can be valuable for predicting reservoir development in CO2-ECBM.

Pore-scale modeling and investigation on the effect of calendering on lithium-ion battery cathodes

The cathode of lithium-ion batteries (LIBs) is a porous electrode that has a crucial influence on cell performance and durability. In making the electrode, a metal foil is first coated with a cathode slurry and dried. The electrode then undergoes a hard-pressing by rollers, i.e., calendering process. In the present study, the effects of calendering on the cathode's effective transport properties and its impact on the battery's charging performance are investigated using a multiscale approach. Microscopic images of LiNi0.8Co0.1Mn0.1O2 samples are obtained using X-ray computed tomography and SEM. This material's three-dimensional microstructure is generated using a numerical reconstruction algorithm based on the distribution characteristics of active material, additives, and pores observed from the microscopic images. Pore-scale simulations are performed on models of various calendering ratios (CRs) to evaluate the pore distribution, effective lithium-ion diffusivity, and electrical conductivity of the cathode material at different CRs. The computed effective transport properties of the cathode are applied to a macroscopic model to study the charging performance of LIBs at various CRs. It is found that the battery performance increases with CR and reaches optimal electrochemical performance at CR = 20 %. When the cathode is calendered to CR = 35 %, the battery's charging performance deteriorates, and this effect is more pronounced at high charging rates. The present study demonstrates a multiscale approach combining experiment characterization and pore-scale simulation for investigating the effects of calendering on LIB cathode. This approach can be employed for the future optimization of LIB fabrication processes.

Experimental and Numerical Simulations of Pore Structures and Seepage Characteristics of Deep Sandstones

Previously conducted studies have established that deep underground rock masses have complex pore structures and face complex geological conditions. Therefore, the seepage problem of such rock masses seriously affects engineering safety. To better explore the seepage law of deep rock masses and ensure engineering safety, indoor experimental methods such as casting thin sections, scanning electron microscopy, and mercury intrusion testing were utilized in this study. The microscopic pore shape, size, distribution, and other structural characteristics of sandstone in coal bearing strata were analyzed. The tortuosity calculation formula was obtained by the theoretical derivation method. And a numerical model was established for seepage numerical simulation research through microscopic digital image methods. The seepage law of surrounding rocks in the Tangkou Coal Mine roadway under different conditions is discussed. The research results indicate that the complexity of the pore structure in porous media leads to an uneven distribution of flow velocity and pressure within the medium. Meanwhile, with the change of physical properties, the fluid flow characteristics also undergo significant changes. The research results can effectively guide micropore water blocking, reduce the impact of groundwater on the environment, ensure the environment and safety of the project, and provide guidance for other geological projects.

Statistical distribution of micro and macro pores in acrylic bone cement- effect of amount of antibiotic content

Aseptic loosening due to mechanical failure of bone cement is considered to be a leading cause of revision of joint replacement systems. Detailed quantified information on the number, size and distribution pattern of pores can help to obtain a deeper understanding of the bone cement's fatigue behavior. The objective of this study was to provide statistical descriptions for the pore distribution characteristics of laboratory bone cement specimens with different amounts of antibiotic contents. For four groups of bone cement (Palacos) specimens, containing 0.3, 0.6, 1.2 and 2.4 wt/wt% of telavancin antibiotic, seven samples per group were micro computed tomography scanned (38.97 μm voxel size). The images were first preprocessed in Mimics and then analyzed in Dragonfly, with the level of threshold being set such that single-pixel pores become visible. The normalized pore volume data of the specimens were then used to extract the logarithmic histograms of the pore densities for antibiotic groups, as well as their three-parameter Weibull probability density functions. Statistical comparison of the pore distribution data of the antibiotic groups using the Mann–Whitney non-parametric test revealed a significantly larger porosity (p < 0.05) in groups with larger added antibiotic contents (2.4 and 0.6 wt/wt% vs 0.3 wt/wt%). Further analysis revealed that this effect was associated with the significantly larger frequency of micropores of 0.1–0.5 mm diameter (p < 0.05) in groups with larger antibiotic content (2.4 wt/wt% vs and 0.6 and 0.3 wt/wt%), implying that the elution of the added antibiotic produces micropores in this diameter range mainly. Based on this observation and the fatigue test results in the literature, it was suggested that micropore clusters have a detrimental effect on the mechanical properties of bone cement and play a major role in initiating fatigue cracks in highly antibiotic added specimens.

Influence mechanism of Nano-SiO2 on geopolymer recycled concrete: Change mechanism of the microstructure and the anti-carbonation mechanism

To improve the durability of geopolymer recycled aggregate concrete based on waste concrete powder (WCP), and realize its application and promotion, this study utilized WCP, fly ash (FA), and ground granulated blast-furnace slag (GGBS) as raw materials, and recycled concrete aggregate (RCA) as aggregate, with Nano-SiO2 as the modifying material to prepare WCP-based geopolymer recycled concrete (WCPGRC). The carbonation depth, uniaxial compressive strength (UCS), and dynamic elastic modulus (DEM) of WCPGRC without Nano-SiO2 (P-WCPGRC) and with Nano-SiO2 (NS-WCPGRC) were investigated. The phase composition, microstructure morphology, and pore distribution characteristics of the two WCPGRCs were investigated using XRD, SEM, and MIP tests. The mechanism of influence of Nano-SiO2 on the carbonation effect and microstructure of WCPGRC was revealed. The findings demonstrate that: (1) The carbonation depth of P-WCPGRC was higher than that of NS-WCPGRC, and both increased linearly with the carbonation times. (2) Both UCS and DEM of P-WCPGRC were lower than those of NS-WCPGRC, and both showed a two-phase change, with the inflection point from a rapid to a slow increase in UCS and DEM occurred on day 7 for P-WCPGRC, while the inflection points for NS-WCPGRC occurred on the day 14. (3) The addition of Nano-SiO2 generated more geopolymer gels, changed the microstructure, reduced the porosity, changed the pore size distribution, and enhanced the physical and mechanical properties and carbonation resistance of WCPGRC. It is feasible to improve the durability of WCPGRC by adding Nano-SiO2.

3D Percolation Modeling for Connectivity and Permeability of Sandstone with Different Pore Distribution Characteristics

3D Percolation Modeling for Connectivity and Permeability of Sandstone with Different Pore Distribution Characteristics