Pore Structure Parameters Research Articles

Effects of calcium sulfate whiskers and basalt fiber on gas permeability and microstructure of concrete

This paper aims to investigate the influence of introducing calcium sulfate whiskers (CSW) and basalt fiber (BF) on the gas permeability coefficients of concrete. Employing the Cembureau method, the research quantifies gas permeability while utilizing Nuclear Magnetic Resonance (NMR) to precisely measure pore structure parameters. The results highlight that the incorporation of CSW leads to a substantial reduction in gas permeability, exhibiting a remarkable 57.6% decrease when utilized at a dosage of 3.0 kg/m³ compared to the standard concrete. In contrast, the introduction of BF at the same dosage does not yield a commensurate reduction in permeability. Notably, the combined application of CSW and BF at 3.0 kg/m³ each yields the most effective mitigation of gas permeability. Furthermore, the judicious addition of either CSW or BF demonstrates the capacity to diminish the overall porosity of concrete, alongside a reduction in the proportion of harmful pores (R100, featuring diameters larger than 100 nm). Optimal outcomes manifest when both CSW and BF are introduced at the 3.0 kg/m³ dosage, effectively minimizing R100 and the gas permeability coefficient. It is interesting to find that in comparison to the correlation observed between the total porosity and gas permeability of concrete, the relationship between the proportion of R100 and gas permeability emerges as more statistically significant (R2 approximately 0.800), especially for CSW concrete. This can reveal the interconnection between the concrete's pore structure and its gas permeability characteristics more appropriately.

Study on damage-stress loss coupling model of rock and prestressed anchor cable in dry-wet environment

The loss of anchoring force is one of the problems to be solved urgently. The anchorage loss is a key factor causing the failure of anchoring engineering, so it is crucial to study the time-dependent variation of anchoring force. Alternating dry and wet (D-W) conditions have a significant effect on deformation of rock. The anchoring system is composed of anchoring components and rock mass, and thus rock deformation has a significant impact on the loss of anchoring force. Quantifying rock deformation under the effects of D-W cycles is a prerequisite to understanding the factors that influence loss of anchoring force in anchor bolts. In this study, we designed an anchoring device that enabled real-time monitoring of the variation in strain during D-W periods and rock testing. Nuclear magnetic resonance (NMR) measurements showed that under D-W conditions, the increment in porosity was smaller for prestressed rock than unstressed rock. The trends of prestress loss and strain variation are consistent, which can be divided into three characteristic intervals: rapid attenuation stage, slow attenuation stage and relatively stable stage. At the same stress level, the rate of stress loss and strain for the soaking specimen was the highest, while that of the dried specimen was the lowest. In the same D-W cycling conditions, the greater the prestress, the smaller the strain loss rate of the rock, especially under soaking conditions. The characteristics of pore structure and physical mechanical parameters indicated that prestress could effectively suppress damage caused by erosion related to D-W cycles. The study reveals the fluctuation behavior of rock strain and prestress loss under D-W conditions, providing a reference for effectively controlling anchoring loss and ideas for inventing new anchoring components.

Experimental investigation of gas diffusion kinetics and pore-structure characteristics during coalbed methane desorption within a coal seam

The desorption-diffusion properties of coalbed methane (CBM) are not only the theoretical basis for investigating gas outburst hazards in a coal mine, but also impose a non-negligible impact on CBM recovery performance. In this paper, the pore structure of coal with five different metamorphism degrees was qualitatively and quantitatively characterized with the scanning electron microscopy (SEM) and low-temperature nitrogen gas adsorption (LTNGA) measurements. The isothermal methane ad/desorption experiments were performed with four initial gas desorption pressure scales. Subsequently, the matching degree between eight empirical correlations (ECs) and the measured methane desorption data was determined, and the methane diffusion coefficient (Dfg) was numerically calculated combining with an FGDG (free gas density gradient) diffusion model. Importantly, we evaluated and discussed the sensitivity of pore structure parameters, initial gas desorption pressure, and volatile fraction to Dfg. The results show that pore density distribution differs among coal samples and the pore structure, especially the micropores, is developed better in high-rank coals than in low- and medium-rank ones. Initial gas release velocity increases with an increase in coal rank and decreases negatively with the increasing particle size in an exponential manner. Among the eight ECs, EC-VIII can be applied to more accurately describe gas desorption process during the whole time scale, and its correlation coefficient with the measured data is larger than 0.9900. Dfg increases with an increase in pore volume and specific surface area (SSA), and it is negatively correlated with the average pore diameter. Additionally, Dfg exhibits an asymmetric U-shaped pattern with an increase in the volatile fraction, which is mainly related to the switch between the dominant roles of mesopores and micropores during coal metamorphism. At a lower volatile fraction, the diffusion coefficient is more sensitive to micropores, while, at a higher volatile fraction, mesopores contribute more to the diffusion coefficient.

Development of ultra-light foamed insulation materials and interfacial bond behavior with fiber-reinforced alkali-activated composites

Due to the complex construction process, short service life and serious environmental pollution, the traditional insulation engineering and formwork engineering have caused great challenges and obstacles to the realization of the " dual carbon " goal. This study developed a new green external insulation system that integrates insulation and formwork based on alkali activation technology. The preparation technology of ultra-light foam insulation material (ULFIM) and the interface design method between ULFIM and fiber reinforced alkali-activated composite material (FRAC) were proposed. The effects of rice husk ash (RHA) and polyethylene (PE) fiber content on the dry density, thermal conductivity, compressive strength, volumetric water absorption, and pore structure parameters of ULFIM were studied. The effects of groove width, groove depth, groove spacing, and groove density on the interfacial bond behavior of FRAC-ULFIM were discussed. The microstructure of ULFIM and the interface transition zone morphology of FRAC-ULFIM and FRAC-extruded polystyrene (XPS) were observed using scanning electron microscopy (SEM), and the mechanism of influencing factors on the corresponding indicators were revealed. The results showed that adding an appropriate amount of RHA and PE fiber had a significant positive effect on improving the performance of ULFIM. In the past, the optimal dry density and thermal conductivity of ULFIM were only 191.5 kg/m3 and 0.0494 W/(m·K), respectively, and the compressive strength at 7 d could be as high as 0.49 MPa. In addition, interface shear performance test results have shown that the "bridging effect" of PE fiber can effectively improve the shear strength and ductility of FRAC-ULFIM, which was 23.7% higher than the interface shear strength of FRAC-XPS under the same conditions. The groove treatment increased the interfacial shear strength of FRAC-ULFIM from 74.59 kPa to 266.37 kPa, with a maximum increase rate of 257.11%. The proposed new green external insulation system has significant potential application value.

Characterization of Tight Gas Sandstone Properties Based on Rock Physical Modeling and Seismic Inversion Methods

Tight sandstones produce an increasing amount of natural gas worldwide. Apart from identifying the gas enrichment, the predictions of lithology and permeable zones are crucial for the prediction of tight gas sandstones. In the present study, a seismic inversion method is developed based on rock physical modeling, by which it is possible to directly predict the lithology and pore structure in tight formations. The double-porosity model is used as a modeling tool in considering complex pore structures. Based on the model, the microfracture porosity is then predicted using logging data, which are used as a factor to estimate microfractures. Parameters representing the lithology and pore structure are proposed and estimated using logging data analyses and rock physical modeling based on the framework of the Poisson impedance. Thereafter, a new AVO equation is established and extended to the form of an elastic impedance for a direct prediction of the lithology and pore structure parameters. Real data applications show that the indicators of lithology and permeable zones are consistent with the production status. They agree with the petrophysical properties measured in wellbores, thereby proving the applicability of the proposed method for the effective characterization of tight gas sandstones.

Grey correlation analysis of macro- and micro-scale properties of aeolian sand concrete under the salt freezing effect

To study the effect of the pore structure of aeolian sand concrete (ASC) with different compositions on its compressive strength in a freeze-thaw environment, ASC with 0% (S0), 25% (S25), 50% (S50), 75% (S75), and 100% (S100) of aeolian sand (AS) content was prepared in our experiment. The damage and degradation laws of the compressive strength of ASC cube in the presence of chloride freeze-thaw were studied, and the compressive strengths of S0, S50 and S100 were predicted from the pore structure parameters. Compressive strength, nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) tests of the ASC samples were carried out. Grey correlation analysis was used to analyze the correlation between the pore structure parameters and the compressive strength, and a model was developed to predict the compressive strength of S0, S50 and S100 ASC subjected to freeze-thaw cycles (FTCs). It was shown that ASC with 25% AS content showed a large improvement in compressive strength, which was 6.86% higher than that of the S0 group. With the progression of FTCs, the porosity of ASC increases, and the bound fluid saturation and the proportion of 0–0.1 µm pores decrease. According to the grey correlation analysis, the saturation of bound fluid and the proportion of 0–0.1 µm pores have the strongest correlation with the compressive strength of ASC. The joint prediction model for the compression strength has a correlation coefficient of 0.937, and is able to better predict the compressive strength of ASC at different AS replacement rates during the FTCs.

Evolution of organic pores in Permian low maturity shales from the Dalong Formation in the Sichuan Basin: Insights from a thermal simulation experiment

Shale oil and gas exploration is greatly impacted by the development and evolution of organic pore structures. In order to study the evolution of shale pore structures over maturities, we conducted thermal simulation experiments on low-mature organic-rich shale (Ro = 0.73%, TOC = 9.57%) obtained from the Dalong Formation. Various maturity stages were covered in these experiments, from low to over-maturity. By analyzing mineral composition, organic geochemistry, and characteristics of pore structures at various temperatures used for thermal simulation, we examined how organic matter pores generate and evolve during the formation of shale hydrocarbons. As a result, an integrated model of the evolution of pore structures in organic-rich shale was developed. Our study revealed the following insights: With increasing thermal simulation temperature, shale pore development exhibited three distinct stages: initial development, rapid development, and slow development. These stages correspond respectively to the three stages of organic matter thermal evolution. The distribution of pores in the shale transitioned from a unimodal structure dominated by larger pores to a bimodal structure with both micropores and macropores. Decomposition of organic matter and pressure compaction play a controlling role on organic porosity. Pore structure parameters and fractal dimensions of the pores were primarily influenced by organic matter decomposition, residual liquid hydrocarbons, and diagenetic processes. Additionally, kerogen type, morphology of organic matter debris, symbiosis of minerals-organic matter also impacted pore development.

An Evaluation Method of Gas-Bearing Properties Based on Gaussian Bimodal Function Pore Structure Characterization: A Case Study of Tight Sandstone in the East China Sea Basin

The Xihu Sag in the East China Sea Basin is located at the edge of the eastern Chinese continent and has great exploration potential. In recent years, the development of low-permeability and tight sandstone gas has become an important area of exploration and development in the Huagang Formation (E3h) of the Xihu Sag. The tight sandstone reservoir in the Xihu Sag is characterized by serious heterogeneity, high water saturation, low resistivity, and a complex gas–water relationship. Because of these characteristics of tight sandstone reservoirs, it is difficult to perform an evaluation of them. In this work, a bimodal Gaussian density function was constructed using the data of high-pressure mercury intrusion (HPMI) and nuclear magnetic resonance (NMR); this approach was used to analyze the pore structure parameters. The reservoirs were divided into four types using the fitting parameter η, and the rock electric parameters that correspond to different pore structures were quite different. When combined with the log response equation of η with acoustic interval transit time (AC), density (DEN), and natural gamma (GR) logging curves, an evaluation method of gas-bearing properties that was based on the characteristics of the pore structure was established. Compared with the water saturation test of the sealing core, it was found that the water saturation calculated by the classification of the pore structure was more accurate than that obtained by the conventional method, and the error was less than 8.35%, which proves that this method is feasible and effective. The findings of this study can help provide a better understanding of the distribution characteristics of gas and water in tight sandstone and provide help for tight gas exploration and development.

The relationship between pore structure and strength of aeolian sand concrete under low temperature

To examine the relationship between microscopic parameters and compressive strength of aeolian sand concrete (ASC) at low temperatures, the compressive strength of ASC at different temperatures is predicted by factors such as the pore structure parameters and the ambient temperature. The experiments used 100 % replacement of river sand (RS) with aeolian sand (AS) to prepare fully ASC, and regular concrete with the same water-cement ratio as the control group. The experiment used nuclear magnetic resonance (NMR) technology and grey correlation analysis method to analyze the microscopic parameters and compressive strength of concrete specimens with three curing ages of 7d, 28d, and 60d at temperatures of 20 °C, 0 °C, −5 °C, −10 °C, −15 °C, and −20 °C. It was shown that the agglomeration between the fine particles during the mixing process results in a large number of pores in the interior of the ASC, resulting in a larger porosity compared to ordinary concrete. As a result, its compressive strength was lower than that of ordinary concrete, and the loose and porous internal structure provides room for the filling of more ice crystals. Therefore, the increase in compressive strength of ASC at different curing ages in an environment of −20 °C was greater than that of ordinary concrete. Among them, at-20 °C, the compressive strength of ASC with curing ages of 7d, 28d and 60d increased by 6.31 %, 3.59 % and 3.97 % respectively compared with ordinary concrete. Finally, a predictive model between parameters such as temperature, porosity, mean pore size distribution and gel content and compressive strength was developed, which was highly accurate.

Heterogeneity of Pore and Fracture Structure in Coal Reservoirs by Using High-Pressure Mercury Intrusion and Removal Curve

The pore structure determines the desorption, diffusion and migration of coalbed methane, and the heterogeneity of the pore structure seriously restricts the diffusion and seepage process and productivity of coalbed methane. Therefore, this paper takes eight coal samples in the Linxing area as the research target and uses the high-pressure mercury injection test to describe the pore structure distribution. On this basis, three kinds of single and multifractal models are used to calculate the progressive mercury removal curve, and the correlation analysis is carried out to determine the physical significance of the mercury removal fractal dimension. Finally, the relationship between the fractal dimension of the mercury curve and the pore structure parameters is defined, and the applicability of fractal models in characterizing pore structure heterogeneity is discussed. The conclusions of this paper are as follows. (1) Samples can be divided into two categories according to porosity and mercury removal efficiency. Among them, the mercury removal efficiency of sample 1–3 is higher than 35%, and porosity is less than 9.5%, while those of sample 4–8 are the opposite. The seepage pore volume percentage of sample 1–3 is 35–60%, which is higher than that in sample 4–8. (2) The difference of the samples’ fractal dimension calculated with the Menger and Sierpinski models is small, indicating that the pore structure distribution heterogeneity of the two types is similar. The multifractal model shows that the adsorption pore and macro-pore heterogeneity of sample 4–8 are stronger than those of sample 1–3, and the pore distribution heterogeneity is controlled by the low value of pore volume. (3) The results of the two single fractal calculations show that the pore structure distribution heterogeneity of sample 4–8 is stronger than that of sample 1–3. The multifractal model calculation shows that the adsorption pore distribution heterogeneity of sample 4–8 is stronger, and the low value of pore volume controls the pore distribution heterogeneity. (4) The mercury fractals based on the Menger model can reflect the adsorption pore distribution and macro-pore distribution heterogeneity, while the Sierpinski model can only reflect the adsorption pore distribution heterogeneity at the mercury inlet stage.

One-step solvent-free approach to constructing microporous BCNO to enhance adsorptive desulfurization

Construction of structurally stable and highly porous materials, like hexagonal boron nitride (h-BN), is a prerequisite for achieving efficient adsorptive desulfurization (ADS). Nevertheless, the present constraints in precisely adjusting the pore structure parameters of BN impede its further utilization in the field of adsorption. In this study, highly porous boron carbon oxynitride (BCNO) adsorbents were synthesized via a straightforward, one-step solvent-free reaction. By modifying the composition of nitrogen (N) precursors, it was possible to finer tuning the micropore ratio thereby leading to a substantial increase in micropore surface area. Moreover, the fitting coefficients (R2) between Smicropore, Vmicropore, and adsorption capacity are 0.81959 and 0.80547, indicating a strong correlation between the microporous structure and the ADS performance. The prepared BCNO-UM6:4 adsorbent showed excellent adsorption performance with a capacity of 47.2 mg S/g adsorbent, surpassing the adsorbents synthesized using solvent-based methods (39.4 mg S/g adsorbent) and single-source N synthesis (BCNO-U18 32.1 mg S/g adsorbent, BCNO-M6 12.1 mg S/g adsorbent). Experimental results revealed that the main adsorption mechanism is multi-layer adsorption by the micropore filling. Density functional theory (DFT) revealed that the newly formed S-N covalent bonds and C-H···N hydrogen bonds are the main driving forces. In summary, this synthetic method expands the production pathway of porous BCNO and has potential application in various research fields.

Development and performance evaluation of alkali-activated multiple solid waste-based building foam insulation materials

To reduce building environmental pollution and energy consumption has become the mainstream development trend of today’s society. The building foam insulation materials (SWFIM) was developed by using blast furnace slag (BSF), waste photovoltaic glass (WPG), rice husk ash (RHA), and plant ash (PA), and the corresponding preparation technologies were proposed. The dry density, thermal conductivity, compressive strength, volumetric water absorption and pore structure parameters of SWFIM were measured. The effects of the amount of hydrogen peroxide solution (HPS), foam stabilizer (FS) and polyethylene (PE) fiber on the basic properties of SWFIM were discussed. The microscopic morphology of SWFIM was characterized by SEM (Scanning electron microscope) technology, and the mechanism of three influencing factors were revealed. The relationship between the basic properties of SWFIM was discussed and the corresponding prediction models were established. The test results showed that the effects of HPS and FS on the basic properties of SWFIM were complementary. When the amount of HPS and FS was 10 % and 1 %, respectively, SWFIM have achieved encouraging performance. PE fiber had different degrees of negative effects on the thermal properties of SWFIM, and the negative effects gradually increased with the increase of PE fiber content. The improvement effect of PE fiber on the compressive strength of SWFIM changes from positive influence to negative influence with the fiber content. When the fiber content increased to 0.6 %, the improvement effect was most obvious, increased by about 12.20 %. Statistics showed that the thermal conductivity and compressive strength of SWFIM were 0.0497 ∼ 0.0581 W/(m·K) and 0.33 ∼ 0.52 MPa, respectively. This showed that SWFIM was expected to become a potentially competitive building insulation material.

Reservoir tortuosity prediction: Coupling stochastic generation of porous media and machine learning

Accurate reservoir tortuosity prediction is the foundation of the high-quality evaluation of reservoir petrophysical properties. However, conventional empirical equations as a form of experimental data fitting lacks universality because the data are usually from a single horizon or block. We developed a model combining the stochastic generation of porous media with machine learning (ML) to predict reservoir tortuosity based on pore structure parameters. Real core scanning images from public databases were employed in stochastic generation as reference, which is an economic and accurate method of meeting the dataset quality and scale requirements of ML. The particle swarm optimization algorithm, an efficient method of obtaining the best hyperparameter combination, was introduced for the hyperparameter tuning of six commonly used ML algorithms to determine the optional model for tortuosity prediction. Our trained ML models demonstrated superior tortuosity prediction accuracy over deterministic linear and exponential empirical equations with porosity as the only variable, which effectively demonstrates the potential of tortuosity prediction using pore structure parameters. The proposed ML model enables precise tortuosity predictions based on a few measurable pore structural features, which can be obtained from well logging data and CT scanning; thus, it can be widely used in petroleum and logging fields.

Development of green ternary-blended-geopolymers for multifunctional engineering applications

Many industrial-wastes/clays, such as ground granulated blast-furnace slag (GGBFS), fly ash (FA), cement kiln dust (CDK), and metakaolin (MK), are employed in developing geopolymeric materials used in the construction sector. Accordingly, this work aims to find a green approach to benefit from the synergistic impacts of the precursors in developing ternary-blended geopolymers (TBGs; GGBFS/FA/CKD and GGBFS/MK/CKD) having multifunctional engineering applications. Five mixes were prepared: the control specimen (100 % GGBFS, S0) and the others contained different portions from GGBFS, FA, MK, and CKD. All mixes were cured in high humidity for up to 28-days. The impact of the TBGs’ mix-design on the fresh properties (workability and setting time), compressive-strength, pore-structure parameters, firing resistivity (200–900 °C), high dose gamma-radiation withstanding (1000–3000 kGy), and anti-microbial activity (against Aspergillus-oryzae, Aspergillus-fumigatus, Bacillus-Cereus and Salmonella-typhi) were investigated. Moreover, the phase composition (X-ray diffraction (XRD) and thermogravimetric analysis (TGA/DTG)) and microstructure (scanning electron microscope (SEM/EDX)) were studied. The obtained results demonstrated that CKD greatly impacts the lowering of workability and shortening of setting time due to high fineness/alkali-content in contrast with FA and MK. The obtained strength values by TBGs after 28-days ranged from 46.3 to 52.2 MPa. TBGs have significant strength retention and resistance to higher temperatures and higher doses of gamma-radiation compared to control due to the formation of highly-stable zeolitic phases. The S0 specimens cannot inhibit the growth of Salmonella-typhi in variance with TBGs that inhibit the growth of all micro-organisms owing to the presence of Fe2O3 and TiO2 in the matrix.

Optimization of porous layer structure of high-temperature proton exchange membrane fuel cell based on deep learning and Monte Carlo method

The optimization of the membrane electrode assembly (MEA) is a crucial aspect in improving the performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Through experimental validation, a three-dimensional HT-PEMFC computational fluid dynamics (CFD) model was established to simulate the transport of charge, mass, and momentum across various porous layers. A deep neural network (DNN) was designed to quantify the influence of porous layer structures on cells performance and determined the optimal solution of the MEA parameters for different Pt loadings. The training data of DNN were generated using 11 porous layer structural parameters selected via a Monte Carlo method, and their corresponding current densities predicted by the validated HT-PEMFC CFD model. The DNN model showed an average relative error of only 0.76% in predicting current density when compared to CFD simulations. Using a bi-objective genetic algorithm (GA) in conjunction with the DNN model, the optimized cell power densities at a voltage of 0.4 V and Pt loadings of 0.3 mg/cm2 and 0.5 mg/cm2 are 18% and 9% higher than the maximum values reported in the literature, respectively. The proposed approach combining DNN model and GA can serve as a useful guide for the design of HT-PEMFC in practical applications.

Modeling and petrophysical properties of digital rock models with various pore structure types: An improved workflow

Pore structure is a crucial factor affecting the physical properties of porous materials, and understanding the mechanisms and laws of these effects is of great significance in the fields of geosciences and petroleum engineering. However, it remains a challenge to accurately understand and quantify the relationship between pore structures and effective properties. This paper improves a workflow to focus on investigating the effect of pore structure on physical properties. First, a hybrid modeling approach combining process-based and morphology-based methods is proposed to reconstruct 3D models with diverse pore structure types. Then, the characteristics and differences in pore structure in these models are compared. Finally, the variation laws and pore-scale mechanisms of the influence of pore structure on physical properties (permeability and elasticity) are discussed based on the reconstructed models. The relationship models between pore structure parameters and permeability/elastic parameters in the grain packing model are established. The effect of pore structure evolution on permeability/elasticity and the microscopic mechanism in three types of morphology-based reconstruction models are explored. The influence degree of pore structure on elastic parameters (bulk modulus, shear modulus, P-wave velocity, and S-wave velocity) is quantified, reaching 29.54%, 51.40%, 18.94%, and 23.18%, respectively. This work forms a workflow for exploring the relationship between pore structures and petrophysical properties at the microscopic scale, providing more ideas and references for understanding the complex physical properties in porous media.

Moisture Diffusion Coefficient of Concrete under Different Conditions

Humidity change in concrete is the leading cause of concrete shrinkage. Moreover, the moisture diffusion coefficient of concrete is an essential parameter for assessing and predicting the internal moisture content of concrete. However, there is a lack of theoretical construction and experimental studies on the effect of different conditions, especially different constraints, on the moisture diffusion coefficient of concrete. Therefore, the internal humidity, pore structure parameters, and basic mechanical properties of concrete under different strength grades C30, C40, C50, and C60 (C stands for concrete and numbers indicate the strength class of the concrete), curing environments (dry and sealed curing conditions), and constraints were tested in this study. In addition, a calculation model of concrete’s internal humidity and humidity diffusion coefficient was established. The research findings show that the internal humidity of concrete decreased with age due to hydration and drying. External humidity had a significant effect on the moisture change of concrete, and the lower the external humidity, the larger the humidity diffusion coefficient and the faster the internal humidity of concrete decreases. Reinforcement (confinement) changes the pore structure parameters of the concrete, which in turn affects the transport of moisture within the concrete. The higher the reinforcement rate, the larger the pore structure parameters of the concrete, the larger the humidity diffusion coefficient, and the faster the concrete humidity decreases. The method proposed in the study can accurately predict the internal humidity of concrete using the humidity diffusion coefficient. The research results are a reference for preventing concrete shrinkage and cracking in construction.

Relationship between Alternated Current Impedance Spectrum and Microstructure of Graphene Enhanced Concrete

This study presented experimental research on the alternating current (AC) impedance spectrum of graphene-enhanced cement matrix composites with dosage amounts of 0.1%, 0.2%, 0.4%, 0.8%, 1.6%, and 3.2%, respectively. The electrical properties were compared and analyzed with the Nyquist diagram, Bode diagram, and phase angle diagram. The microscopic pore structure was studied using mercury intrusion porosimetry (MIP) to establish the relationship between the pore structure parameters, the equivalent circuit fitting parameters of the AC impedance spectrum, and the mechanical properties. This study found that the incorporated graphene decreases the arc diameter of the impedance spectrum and causes the slope of the straight lines of the low-frequency region to drop. For the Bode curves, within low frequencies (1 Hz and 10 Hz), the impedance gradually increases as the graphene dosage increases. However, when the frequency is between 100 KHz and 1000 KHz, the impedance drops with an increase in the amount of graphene. According to the MIP test results, the proper incorporations of graphene increase the proportion of pores below 0.1 μm, which leads to a denser micro-structure and higher strength.

Bayesian fluid prediction by decoupling both pore structure parameter and porosity

Carbonate reservoirs exhibit complex pore structure, which significantly affects the elastic properties and seismic response, as well as the prediction of physical parameters. As one of the main factors impacting fluid prediction, pore structure parameter directly involves in few inversion methods. In order to directly predict pore structure parameter in inversion, a novel quantitative reflection coefficient formula is proposed, that integrate Russell's poroelasticity theory with Sun's petrophysical model. This formula separates fluid bulk modulus from porosity and pore structure parameter, allowing for accurate determination of pore-fluid distribution through Bayesian framework. Both theoretical model analysis and multi-component digital core experiments of carbonates validate the importance of pore structure parameter on fluid identification. The practical application of carbonate reservoirs in Sichuan Basin demonstrates that the proposed fluid factor, eliminating the prediction illusion caused by heterogeneity in porosity and pore structure parameter within strata, provides more precise and reliable predictions compared to the Russell fluid factor. Furthermore, the similarity between the Russell fluid factor obtained directly from the Russell approximation and the Russell fluid factor calculated indirectly from the proposed method confirms the stability and accuracy of the new reflection coefficient formula.

Gray Model Study of Strength and Pore Structure of Recycled Concrete Powder (RCP) Concrete Based on Low-Field NMR Technology.

In order to improve the resource utilization of recycled concrete powder (RCP), this study aimed to investigate the effect of RCP admixture, curing age, and alkali excitation on the strength of RCP concrete. In addition, the pore structure characteristics of RCP concrete were analyzed in combination with low-field NMR. Furthermore, a gray predictive GM (1, 4) model was established to predict the mechanical properties of the concrete based on the pore structure parameters, especially the compressive and flexural tensile strengths. The results of the study indicate that the mechanical properties, namely compressive strength and flexural strength, of RCP concrete exhibit an initial increase followed by a subsequent decrease with increasing RCP content at 3 d, 7 d, and 28 d curing ages. In particular, the concrete exhibits the highest mechanical properties when the RCP content reaches 10%. As the curing age increases, the RCP gradually achieves full hydration, resulting in further refinement of the concrete pores and a denser structure, which subsequently improves the mechanical properties. In addition, the strength growth rate of alkali-excited recycled concrete (ARC) showed a continuous increase, indicating that alkali excitation increasingly improved the mechanical properties of the concrete. Furthermore, the study accurately predicted the mechanical properties of RCP concrete by using GM (1, 4) prediction models for its compressive strength and flexural tensile strength using pore characteristic parameters.