Mercury Intrusion Porosimetry Research Articles

Pore characteristics and microscopic damage mechanism of disintegrated carbonaceous mudstone exposed to dry-wet cycles

Disintegrated carbonaceous mudstone (DCM), derived from pre-disintegration treatments of waste carbonaceous mudstone, is utilized as filler for highway embankments with the aim of conserving resources. However, the mechanical behavior of DCM is greatly influenced by its microstructure, particularly pore characteristics. The aim of this study is to investigate the pore characteristics and microscopic damage mechanisms of DCM subjected to dry-wet cycles. Triaxial tests, along with microscopic observations using scanning electron microscopy and mercury intrusion porosimetry, were performed. Three-dimensional pore models were reconstructed from the microscopic test results via the Markov chain-Monte Carlo method. Subsequently, a finite element method that accounts for the anisotropy of porosity was proposed based on these pore models. Finally, numerical triaxial tests were performed to analyze stress changes in DCM under triaxial loading using the proposed method. The results show that the shear strength and cohesion of the DCM decrease with an increase in dry-wet cycles, stabilizing notably after four cycles. Meanwhile, the porosity and the number of slender pores in the specimen increase, leading to intricate alterations in pore shape and distribution. A comparison between numerical and laboratory triaxial tests demonstrates closely aligned results, with distinct stress concentration behavior related to porosity anisotropy. It is revealed that dry-wet cycles cause an increase in porosity and the occurrence of more irregular-shaped pores, subsequently leading to a decrease in the cohesion. This microscopic mechanism is responsible for the shear strength damage of DCM.

Study on Sensitivity Mechanism of Low-Permeability Sandstone Reservoir in Huilu Area of Pearl River Mouth Basin

Reservoir sensitivity is a parameter that is used to evaluate the degree of change in reservoir permeability under the influence of external fluids. Accurate evaluation of reservoir sensitivity is conducive to the optimization of fluid parameters during exploration and development. Taking the Wenchang Formation and Enping Formation of the Paleogene in the Huilu area of the Pearl River Mouth Basin as the research object, reservoir sensitivity experiments were carried out. Combined with the corresponding experimental results obtained using methods such as thin section identification, scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and screening analysis, based on mineral sensitization and pore structure sensitization, qualitative and quantitative evaluations of reservoir sensitivity were carried out, and factors affecting sensitivity and sensitization mechanisms were analyzed. This work shows the following: (1) The sandstone reservoirs in the two areas have the same clay type, but the total clay content of the Wenchang Formation is greater than that of the Enping Formation. The porosity of the Wenchang Formation is less developed than the Enping Formation. (2) The Wenchang Formation has weak or moderately weak water sensitivity and moderately weak or moderately strong flow velocity sensitivity. The water sensitivity of the Enping Group samples is moderately weak or moderately strong, the flow rate sensitivity is moderately weak, the alkali sensitivity is weak, the acid sensitivity is moderately weak, and the salinity sensitivity is moderately weak or moderately strong. (3) The sensitivity of the Wenchang Formation is mainly affected by the content of clay minerals. The sensitivity of the Enping Formation is also affected by the clay content and type. Although the clay content is not high, the permeability is more susceptible to sensitivity due to the pore structure and debris particle distribution characteristics. These conclusions are beneficial for the selection of fluid parameters and efficient reservoir development.

Porosity Characteristics of Coal Seams and the Control Mechanisms of Coal Petrology in the Xishanyao Formation in the Western Part of the Southern Junggar Basin

The porosity characteristics of coal seams serve as a pivotal factor in assessing the development potential of coalbed methane (CBM) resources, significantly influencing the adsorption and permeability capabilities of coal reservoirs, as well as the accumulation, entrapment, and preservation of CBM. In this study, we focused on the coal seams of the Xishanyao Formation in the western part of the southern Junggar Basin (NW China). By leveraging the complementarity of nuclear magnetic resonance (NMR), low-temperature liquid nitrogen experiments, and high-pressure mercury intrusion porosimetry (MIP) in spatial exploration range and precision, we conducted a comprehensive analysis to achieve a fine description of porosity characteristics. Furthermore, we explored the coal petrology factors controlling the pore characteristics of the Xishanyao Formation, aiming to provide geological evidence for the selection of favorable areas and the development potential evaluation of CBM in the study area. The results indicate the following: (1) The total pore volume of the coal samples is 6.318 × 10−3 cm3/g on average, and the micropore volume accounts for a relatively high proportion (averaging 44.17%), followed by the fine pores (averaging 39.41%). The average porosity is approximately 3.87%, indicating good gas storage and connectivity of the coal seams, albeit with some heterogeneity. The coal reservoir is dominated by micropores and fine pores with diameters less than 100 nm, and the pore structure is characterized by low pore volume and high pore area. (2) The pore structure is influenced by both the coalification degree and the coal maceral. Within the range of low coalification, porosity increases with the increase in coalification degree. Building upon this, an increase in the vitrinite content promotes the development of micropores and fine pores, while an increase in the inertinite content promotes the development of meso–macropores. The clay mineral content exhibits a negative correlation with the adsorption pore volume ratio and a positive correlation with the seepage pore volume ratio.

Study on the mechanism of methane “solid–liquid–gas” conversion controlled by the evolution of coal micro- and nanopore structure

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

Preparation of geopolymer for in-situ pavement construction on the moon utilizing minimal additives and human urine in lunar regolith simulant

Constructing lunar pavements is of great significance for improving the transportation efficiency of materials and personnel transfer at lunar bases. Utilizing lunar regolith for the in-situ preparation of geopolymer is an effective means of supplying raw materials for lunar pavement construction. This present study prepared geopolymers for pavement material with lunar regolith simulant. The influence of NaOH on the compressive strength of geopolymers was understood by using different percentages of NaOH as alkaline activator. The effect of urine on the compressive strength of geopolymers by using artificial urine of different pH values as liquid phases. The results indicated that the addition of artificial urine slightly reduces the compressive strength of geopolymers, and the effects of pH and NaOH percentage are different. Microstructural analysis performed by Mercury Intrusion Porosimetry and Scanning Electron Microscope, indicated that choosing fine-particle lunar regolith simulant as precursor is more conducive to the preparation of high-strength geopolymers using human urine.

Recycled Excavation Soils as Sustainable Supplementary Cementitious Materials: Kaolinite Content and Performance Implications.

In response to the environmental implications of the massive quantities of excavation soil generated by global urbanization and infrastructure development, recent research efforts have explored the repurposing of calcined excavation soils as sustainable supplementary cementitious materials (SCMs). As it is still at an early stage, current research lacks systematic analysis across diverse soil deposits regarding their reactivity and mechanical properties within cementitious binders, despite recognized geographical variability in kaolinite content. Through comprehensive experimentation with soils sourced from four major southern Chinese cities, this study presents a pioneering assessment of the compressive strength, pozzolanic reactivity (X-ray diffraction, Fourier-transform infrared spectroscopy, solid-state nuclear magnetic resonance), and microstructural development (mercury intrusion porosimetry, scanning electron microscopy) of mortars modified by various calcined excavation soils (up to 28 days curing). The experimental data suggest that soils with a kaolinite content above 53.39% produce mortars of equal or superior quality to plain cement mixes, primarily due to their refined pore structures, microstructural densification, and enhanced hydration reactions. The findings highlight kaolinite-specifically, aluminum content-as the principal indicator of excavation soil viability for SCM application, suggesting a promising avenue for sustainable construction practices.

Gas permeability characteristics of granite-manufactured sand concrete and its numerical simulation using NMR-MIP modified method

Natural sand resources are becoming increasingly scarce with the rapid development of infrastructure. Therefore, manufactured sand usage is inevitable. However, the significant differences in granite powder content between manufactured- and natural sand have a remarkable impact on the pore structure and permeability of cement-based materials, which are crucial for material durability. In this work, several granite powder dosages (0–32 %) of granite-manufactured sand were considered for preparing manufactured sand concrete, and a suitable physical filling model was chosen to quantify the material particle filling for characterizing the overall pore-filling effect. Mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) were used to examine the pore structure of the specimens. The quasi-stationary flow method was used to test the gas permeability of concrete. Finally, a random hierarchical bundle model using the NMR-MIP method is proposed to predict the gas permeability of cementitious materials based on their pore size distribution. The results show that granite-manufactured sand and an appropriate amount (i.e., 8 %) of granite powder can improve the filling effect and anti-permeability performance of concrete. There is a good correlation between the pore structure parameters and gas permeability, where the physico-mathematical relationships can be modeled. The maximum relative difference between the predicted and experimental values of the random tube bundle model was reduced to 30.93 % using the NMR-MIP method compared to 70.87 % with the traditional MIP method.

Effects of stone powder on microstructure of manufactured-sand concrete and its gas permeability

With the development of infrastructure construction, natural sand resources have become increasingly scarce, and the use of manufactured sand has become inevitable. The unique stone powder in manufactured sand could significantly influent the concrete performance. To characterize the stone powder, a physical filling model was used to quantify the particle grading buildup. Isothermal calorimetry and thermogravimetric analysis determined the corresponding chemical activities. Subsequently, non-destructive testing flow methods were designed, referred to as nuclear magnetic resonance (NMR) and hydrostatic balance (HB), to test the pore structure, and a quasi-stationary flow method was used to test the gas permeability of the manufactured sand concrete. Finally, a random hierarchical bundle model using the NMR-HB method was proposed to predict the gas permeability of concrete based on the pore size distribution. The results showed that a moderate amount of stone powder could reduce the heat of hydration, increase the hydration products, improve the filling effect, and decrease gas permeability. A certain fineness of the stone powder could increase the heat of hydration, increase the hydration products, compact the pores from 4.5 to 50 nm, reduce the filling effect, and increase gas permeability. The maximum relative difference between the predicted and experimental gas permeability values of the random tube bundle model was reduced to 34.38 % using the NMR-HB method, whereas this value was 70.87 % using the mercury intrusion porosimetry (MIP) method.

Recycling lithium slag into eco-friendly ultra-high performance concrete: Hydration process, microstructure development, and environmental benefits

To ascertain the viability of utilizing lithium slag (LS) in the development of eco-friendly ultra-high performance concrete (UHPC), this paper provides a detailed analysis of the effects of LS on UHPC. Specifically, the hydration and microstructural changes in UHPC containing LS (LS-UHPC) were comprehensively examined. Based on the results of isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP), LS primarily acts as a filler, promotes nucleation, provides internal curing, and participates in the pozzolanic reaction. Significantly, the internal curing effect and the pozzolanic reaction enhanced the strength development of LS-UHPC. UHPC with 20 % LS exhibited the highest 28 d compressive strength at 134.48 MPa and presented the densest microstructure. However, approximately 4 % of the calcium hydroxide in LS-UHPC would not be involved in the pozzolanic reaction. The presence of gypsum in LS led to increased ettringite formation in LS-UHPC. Although LS extended the induction period of UHPC, it intensified the hydration degree of cement. In LS-UHPC, the molar ratio of Ca/Si of C-(A)-S-H decreased, whereas the molar ratio of Al/Si increased, implying that the dissolved aluminum from LS was incorporated into the C–S–H chains. The integration of LS not only considerably reduced the carbon emissions and energy consumption of UHPC but also optimized LS recycling. Overall, the development of a sustainable UHPC by incorporating LS is both practicable and advantageous for environmentally conscious construction practices.

Enhancing Mechanical Properties and Microstructures of Mass-Manufactured Sand Concrete by Incorporating Granite Powder.

The production of manufactured sand and stone processing can cause dust pollution due to the generation of a significant amount of stone powder. This dust (mainly granite powder) was collected and incorporated as a cement replacement into mass-manufactured sand concrete in order to enhance the mechanical properties and microstructures. The heat of the hydration was measured by adding the granite powder into the cementitious material system. The mechanical properties, autogenous shrinkage, and pore structures of the concrete were tested. The results showed that the mechanical strength of the concrete increased first and then decreased with the increase in granite powder content. By replacing the 5% cement with the granite powder, the 28 d compressive and flexural strength increased by 17.6% and 20.9%, respectively. The autogenous shrinkage was mitigated by the incorporation of the 10% granite powder and decreased by 19.7%. The mechanism of the granite powder in the concrete was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). The porosity decreased significantly within the 10% granite powder. A microstructure analysis did not reveal a change in the type of hydration products but rather that the granite powder played a role in the microcrystalline nucleation during the hydration process.

Enhanced Resistance to Desiccation Cracking of Polymer-Bentonite Mixtures: An Experimental Investigation of Underlying Mechanisms

Polymers have been shown to enhance the resistance of swelling clay soils to desiccation cracking, a critical property in engineering applications, particularly in waste containment facilities. However, the microscopic and macroscopic mechanisms driving this improvement remain poorly understood. Additionally, the influence of different mixing methods on these mechanisms is not well-established. While dry mixing is more convenient for onsite implementation, wet mixing offers intercalation between clay and polymer, resulting in potentially more durable stabilization outcomes. In this paper, key properties related to desiccation cracking of a polymer-clay mixture were measured. The mixture was synthesised by amending Na-bentonite with sodium carboxymethyl cellulose (Na-CMC) using dry and wet mixing. Soil water retention characteristics curves (SWCC), swelling and shrinkage potential, tensile strength, and pore size distribution by mercury intrusion porosimetry (MIP) were measured for both mixtures and untreated bentonite. Compared to pure bentonite, mixtures were found to have slightly reduced air-entry values, significantly lower swelling and shrinkage potentials and higher tensile strengths. In all experiments, dry mixing exhibited superior performance compared to wet mixing. MIP analysis of the amended mixtures revealed a more porous structure when compared to untreated bentonite.

Effects of carbonation curing on chemical attack in cement paste incorporating liquid-crystal display glass powder as a partial binder replacement

This study investigates the chemical resistance of cement paste by incorporating liquid-crystal display (LCD) glass powder as a partial replacement for cement. The samples, cured under water and carbonation, were subjected to adverse chemical attacks over a period of up to 90 days, using MgSO4 and H2SO4 for the sulphate attack and acid attack, respectively. The results demonstrate a decrease in compressive strength by upto 14.63% and 32.32% for water- and carbonation-cured samples, respectively, and an increase in carbonation degree by upto 100% with the incorporation of glass powder at 28 days. Under sulphate attack, water curing and carbonation curing displayed strength increase of 21.24–36.13% and 7.56–8.06%, respectively, at 90 days. However, carbonation-cured samples experienced greater leaching of silica and calcium. The compressive strength decreased with acid attack duration, with glass powder incorporation mitigating strength loss in carbonation-cured samples. At 30 days, with an incorporation rate of 30% glass powder, the strength loss was reduced by 37.66% for the carbonation-cured samples. The enhanced resistance with incorporation of glass powder was also evident from mercury intrusion porosimetry results that indicated decreased intrusion levels. Visual inspection revealed a different consistency of white substance deposition, suggesting resistance mechanisms differed between curing methods.

Characterization of self-healing in cement-based materials with a low water-to-cement ratio during subsequent hydration

This study explores the role of subsequent hydration in healing cracks in cement-based materials, focusing on a water-cement ratio of 0.20 and aging up to 1260 days. A novel bond strength testing method and backscattered electron imaging (BSE) analyzed the relationship between bond strength and unhydrated cement. Techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) helped investigate crystal phase content and microstructural changes. Key findings reveal that subsequent hydration primarily produces calcium hydroxide (CH), calcium carbonate (CaCO3), and C–S–H gel. Bond strength notably increased to 36.08 % at 394 days, with a significant reduction in C3S and C2S phases and increases in CH and CaCO3. The calcium-silicon ratio varied across hydration products, with external products containing the highest ratio. The study demonstrates the transformation of C–S–H gel from low to high density and highlights the cohesive structure formation of CH and C–S–H gel, crucial for crack healing. Porosity showed an initial decrease followed by an increase, peaking at 54.14 % above the initial value. These findings underscore the importance of controlling unhydrated cement content for optimizing self-healing in cement-based materials.

Investigation of strength and water permeability of sustainable high-performance concrete containing high-volume ground bottom ash blended with fly ash and nano-silica

This investigation focussed on minimizing the Portland cement usage in developing sustainable high-performance concrete (HPC) as low-carbon concrete. High-volume ground bottom ash (GBA) was utilized as cement substitution in combination with fly ash (FA) and nano-silica (NS) for producing HPC with compressive strength of 100 MPa, and various concrete mixes were examined to assess its workability, mechanical performance, water permeability, and carbon emissions. The microstructure of the materials and pastes were also analyzed with X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA), and Mercury Intrusion Porosimetry (MIP). GBA was used to replace Ordinary Portland Cement (OPC) at very high levels of cement replacement, ranging from 60 to 80 % by weight of binder. As ternary binders, 10 % fly ash and 2 % nano-silica (NS) by weight of binder were also used to replace GBA. The early-age compressive strength of HPC containing high-volume GBA increased by using 2 % of NS. Incorporating 10 % of FA into HPC reduced the superplasticizer requirement, enhanced workability, and exhibited slightly lower early strength. The compressive strength of HPC containing 58 % GBA, 10 % FA, and 2 % NS could be developed at 90 days was more than 110 MPa. Moreover, the investigation indicated that employing GBA in the mix represents environmental sustainability for the development of high-performance concrete.

Direct carbonation of porous materials produced from self-hardened paper mill fly ash

A high-Ca fly ash generated from a paper mill using a fluidized bed boiler was used as the potential medium to sequester CO2 via the direct carbonation process. In this study, the fly ash samples were exposed to accelerated carbonation to produce hardened pastes. The influence of the porosity controlled by the amount of foam in the matrix for maximizing CO2 sequestration was determined. The effect of porosity on carbonation was evident. The samples prepared with 40 % foam and a water-to-fly ash ratio of 0.79 recorded porosities of 56.1 % (carbonated) and 66.8 % (naturally carbonated (NC)) with the lowest mechanical strength of 2.1 and 1.1 MPa, respectively. These naturally carbonated (NC) samples have been cured naturally without using high CO2 pressure. Meanwhile, the samples prepared with 10 % foam and a water-to-fly ash ratio of 0.5 recorded porosities of 41.1 % (carbonated) and 52.9 % (NC) with the highest strength at 10.2 and 4.6 MPa, respectively. The highest carbonation efficiency determined by thermogravimetric analysis was obtained from the carbonated samples with 40 % foam. Scanning electron microscopy–energy-dispersive spectroscopy depicted the areas with high Al/Si content but low Ca–O content (dark areas) and carbonated areas with high Ca–O content (bright areas). Mercury intrusion porosimetry was used to determine the pore size distribution, whereby the samples were dominated by large capillary pores, resulting in their high porosity in this study.

Influences of metakaolin and calcined clay blended cement on chloride resistance and electrical resistivity of concrete

There are many different grades of kaolinite clays around the world. Low-grade kaolinite clay is more abundant than high-grade kaolinite clay in various regions. To aim toward the utilization of low-grade kaolinite clay having an original kaolinite content of about 40% to produce calcined clay, this paper investigated the durability properties of concrete incorporating calcined clay produced from high-grade kaolinite clay or high kaolinite content (commercially available metakaolin or CC1) and calcined clay produced from a low-grade kaolinite clay (CC2). Concrete mixtures were designed to have a water-to-binder ratio of 0.60. A fly ash-to-binder ratio of 0.20 and calcined kaolinite clay-to-binder ratios of 0.10 and 0.20 were studied. The chloride penetration resistance and the electrical resistivity of concrete were assessed, while the mercury intrusion porosimetry (MIP) was utilized in evaluating the pore structure of concrete. The test results revealed that concrete with CC1 and CC2 exhibited superior chloride penetration resistance and chloride binding capacity than OPC and FA20 concretes. Moreover, using a higher calcined clay-to-binder ratio resulted in a more refined pore structure, which significantly enhanced the chloride resistance of concrete. Although CC2 revealed less performance in improving chloride resistance than CC1, it had superior performance compared to fly ash.

Analysis of Mechanical Properties of Fiber-Reinforced Soil Cement Based on Kaolin.

Adding fibers into cement to form fiber-reinforced soil cement material can effectively enhance its physical and mechanical properties. In order to investigate the effect of fiber type and dosage on the strength of fiber-reinforced soil cement, polypropylene fibers (PPFs), polyvinyl alcohol fibers (PVAFs), and glass fibers (GFs) were blended according to the mass fraction of the mixture of cement and dry soil (0.5%, 1%, 1.5%, and 2%). Unconfined compressive strength tests, split tensile strength tests, scanning electron microscopy (SEM) tests, and mercury intrusion porosimetry (MIP) pore structure analysis tests were conducted. The results indicated that the unconfined compressive strength of the three types of fiber-reinforced soil cement peaked at a fiber dosage of 0.5%, registering 26.72 MPa, 27.49 MPa, and 27.67 MPa, respectively. The split tensile strength of all three fiber-reinforced soil cement variants reached their maximum at a 1.5% fiber dosage, recording 2.29 MPa, 2.34 MPa, and 2.27 MPa, respectively. The predominant pore sizes in all three fiber-reinforced soil cement specimens ranged from 10 nm to 100 nm. Furthermore, analysis from the perspective of energy evolution revealed that a moderate fiber dosage can minimize energy loss. This paper demonstrates that the unconfined compressive strength test, split tensile strength test, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) pore structure analysis offer theoretical underpinnings for the utilization of fiber-reinforced soil cement in helical pile core stiffening and broader engineering applications.

Performance and microstructure of sintered sludge ash-modified cement paste

Sintered sludge ash (SSA) has garnered attention for its potential to mitigate carbon emissions by replacing cement. This study investigates the consequential changes in the macro and micro properties of cement paste following the addition of SSA. Fluidity tests unveiled that the high specific surface area of SSA was the primary factor contributing to the reduction in fluidity and the delayed setting time. In terms of strength, SSA affected the cement paste to a greater extent at 3 days (3 d) than at 28 days (28 d). X-ray diffraction (XRD) analyses indicated that hydration-inert components such as quartz and feldspar in SSA may be responsible for the observed early hydration retardation. For 28 d strength, thermogravimetric and differential scanning calorimetry (TG/DSC) were employed to quantify Ca(OH)2 content and the degree of cement hydration. It was found that the participation of SSA in the pozzolanic reaction could additionally produce calcite, which promoted hydration and improved the strength of cement paste at 28 d. Scanning electron microscopy (SEM) revealed that amorphous hydration products, including C–S–H and Ca(OH)2 crystals covering the SSA surface, formed a robust structure conducive to 28 d strength development. Results from mercury intrusion porosimetry (MIP) were found to be in good contrast with SEM.

Estimation of unfrozen water content of saturated sandstones using nuclear magnetic resonance, mercury intrusion porosimetry, and ultrasonic tests

The unfrozen water content (UWC) is a crucial parameter that affects the strength and thermal properties of rocks in relation to engineering construction and geological disasters in cold regions. In this study, three different methods were employed to test and estimate the UWC of saturated sandstones, including nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and ultrasonic methods. The NMR method enabled the direct measurement of the UWC of sandstones using the free induction decay (FID). The MIP method was used to analyze the pore structures of sandstones, with the UWC subsequently calculated based on pore ice crystallization. Therefore, the MIP test constituted an indirect measurement method. Furthermore, a correlation was established between the P-wave velocity and the UWC of these sandstones based on the mixture theory, which could be employed to estimate the UWC as an empirical method. All methods demonstrated that the UWC initially exhibited a rapid decrease from 0 °C to –5 °C and then generally became constant beyond –20 °C. However, these test methods had different characteristics. The NMR method was used to directly and accurately calculate the UWC in the laboratory. However, the cost and complexity of NMR equipment have precluded its use in the field. The UWC can be effectively estimated by the MIP test, but the estimation accuracy is influenced by the ice crystallization process and the pore size distribution. The P-wave velocity has been demonstrated to be a straightforward and practical empirical parameter and was utilized to estimate the UWC based on the mixture theory. This method may be more suitable in the field. All methods confirmed the existence of a hysteresis phenomenon in the freezing-thawing process. The average hysteresis coefficient was approximately 0.538, thus validating the Gibbs–Thomson equation. This study not only presents alternative methodologies for estimating the UWC of saturated sandstones but also contribute to our understanding of the freezing-thawing process of pore water.

Feasibility of compacted attapulgite/diatomite amended clayey soils as gas barrier materials

Compacted clay liners are extensively used as barriers to control the upward diffusion of vapors of volatile or semi-volatile organic contaminants released from unsaturated contaminated soils at industry-contaminated sites. This study aimed to investigate the gas diffusion barrier performance of compacted clayey soils amended with three agents including attapulgite and diatomite individually, and attapulgite/diatomite mixture. The properties including water retention, volumetric shrinkage, gas diffusion, and unconfined compressive strength were evaluated through a series of laboratory tests of amended compacted clayey soils. The results demonstrate that the decrease in volume proportions of inter-aggregate pores leads to an increase in unconfined compressive strength (qu). Both hydrophilic groups and microstructures of attapulgite and diatomite result in an increase in water retention percent (Wt) of compacted clayey soil specimens after amendment regardless of the type of agent or initial water content (w0). Furthermore, the ratio of the gas diffusion coefficient (De) to the gas diffusion coefficient in the air (Da) was significantly reduced owing to a decrease in volume proportions of inter-aggregate pores, hydrophilic group, and microstructures of attapulgite and diatomite. Scanning electron microscope analyses revealed that rod-shaped attapulgite filled the inter-aggregate pores formed by clay particles, whereas the disc-shaped diatomite particles, characterized by micropores, failed to obstruct the inter-aggregate pores due to their larger particle size. Mercury intrusion porosimetry (MIP) analyses showed a reduction in pore volume in the inter-aggregate pores, leading to a reduction in the total pore volume for both the attapulgite and attapulgite/diatomite mixture amended clays, which is in accordance with the scanning electron microscope (SEM) results. The findings are pertinent to the practical application of compacted clay liners as gas barriers against the upward migration of volatile or semi-volatile organic contaminants at contaminated sites.