Smaller Pore Volume Research Articles

Impact of early-age vibration on the permeability and microstructure of mature-age concrete

Dynamic excitation in early-age significantly impacts the performances of mature concrete in underground structures, such as tunnels beneath railways supported by cast-in-place concrete. This study explores the impact of early dynamic excitation on properties of mature concrete. Vibration tests at a fundamental frequency of 114Hz, with peak acceleration levels ranging from 0.1g to 0.4g, were conducted using shaking table. Specimens underwent 33seconds of dynamic excitation every 15minutes over the initial 48hours, excluding a night break from 0-6am, totaling 114 vibration cycles. Various lab tests were employed to assess the properties and microstructure of mature concrete post-vibration, including water penetration resistance, capillary water absorption, Coulomb electric flux, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and Nitrogen adsorption-desorption measurement (NAM). The results proves that vibration causes water secretion and air bubbles discharge before the initial setting of concrete, thereby enhancing the hydration reaction. The relationship between vibration loads with varying peak accelerations and the cohesion resulting from hydration reaction influences the microstructural evolution of concrete, leading to the weakening and strengthening of permeability of mature concrete. Under the vibration spectrum and test conditions described in this paper, vibration loads with peak values less than 0.234g decrease the total volume of large and middle pores (>20nm) by up to 50% and increase the total volume of small pores (<20nm) by up to 200%. Due to these changes in pore structure, the permeability coefficient (Sk), cumulative capillary water height (i) and Coulomb electric flux decrease by up to 47.84%, 39.5% and 31.6%, respectively. However, when the amplitudes of vibration loads exceed 0.234g, the total volume of large and medium pores (>20nm) increases, and that of small pores (<20nm) decreases, leading to a reduction of the impermeability of mature concrete. Additionally, the SEM analysis corroborates these microstructural variations.

Effects of solvent extraction on pore structure properties and oil distribution in shales of alkaline lacustrine basins

Shale contains numerous nano-scale pores, whose pore structure property changes affect petroleum flow, complicating shale oil accumulation and exploration. Twelve shale samples from the Permian Fengcheng Formation in the Mahu Sag and the Permian Lucaogou Formation in the Jimusar Sag in northwestern China were analyzed to investigate the coupled oil distribution and pore structure in shales from alkaline lacustrine basins. Shale samples were comprehensively analyzed before and after solvent extraction using X-ray diffraction, total organic carbon measurement, Rock-Eval analyses, field emission-scanning electron microscopy, nitrogen physisorption (NP), and (ultra) small-angle X-ray scattering [(U)SAXS] to assess nanoscale pore structure (2-300 nm in diameter) and oil distribution. Solvent extraction increased total pore volume and specific surface area (SSA). However, the accessibility of nanoscale pores remains limited. Additionally, even after retained oil removal, (U)SAXS-derived total pore volumes are 1 to 10.4 times larger than NP-derived connected pore volumes. Complex variations in pore volume and SSA mainly result from the removal of extractable organic matter (EOM) and the refilling of small pores by organic matter. Despite the relatively small pore volume of mesopores (2-50 nm), the amount of EOM distribution in mesopores is comparable to that in macropores (50-300 nm); therefore, it is crucial not to overlook the retention capacity of mesopores for EOM. Macropores, particularly interparticle pores associated with quartz and feldspar, play a crucial role in oil mobility. The quantity and composition of EOM, along with other factors, can alter pore structure before and after solvent extraction and should be considered in evaluating the distribution and content of free oil.

Two-dimensional transition metal-sulfide-modified V2O5-WS2/TiO2 catalysts for SCR: Comprehensive mechanistic insights into the in situ inhibition of SO3 generation

The by-product SO3, generated by the conventional catalyst V2O5-WO3/TiO2 employed in selective catalytic reduction (SCR) systems, has garnered attention in pollution control efforts. Studies on existing control have predominantly concentrated on the tail gas section, with insufficient understanding of in-situ suppression theories and methods at the source of SO3 generation. We propose for the first time the introduction of low-valence reduced sulfur to synthesize a novel SCR catalyst, V2O5-WS2/TiO2, which elucidates the remarkable effect and in-situ mechanism of action in inhibiting SO3 formation at its source. Compared to conventional catalysts, the new catalysts showed enhanced SO3 inhibition, particularly at 350 °C, where SO3 production was 64.1 % and 33.9 % lower than that with VTi and VW/Ti catalysts, respectively. This was due to their reduced surface area, smaller pore volume, and fewer alkaline sites, which hindered SO2 adsorption and oxidation. The results revealed that S2− on the catalyst surface reacts with V5+, reducing it to V4+ and V3+. This reaction hinders the interaction between V5+-OH and adsorbed SO2, thereby reducing the formation of VOSO4 intermediates. Furthermore, the WS bond in WS2 impedes the formation of intermediate HSO4−, and the reduction of these intermediates ultimately leads to a decrease in SO3 generation. Additionally, the incompletely depleted S2− reacts with the final SO3 produced, forming SO2 and SO42−, which further decreases the SO3 generation rate and supports the maintenance of a reduced state on the catalyst surface. It is evident that low-valence reduced sulfur plays a crucial role in inhibiting SO3 generation.

Dynamic Adaptive Porous Cu Current Collector for Low N/P Ratio Li Metal Batteries

AbstractPorous copper (Cu) current collectors effectively suppress the growth of lithium (Li) dendrites and enhance the stability of Li metal anodes. However, the current development of porous Cu hosts generally involves a high proportion of Cu, mostly rigid structures, small pore volumes, and low Li utilization. Here, we propose a dynamic adaptive porous Cu (DAP−Cu) host, which is lightweight with a high pore volume, fabricated using a large aspect ratio of Cu nanowires as the building blocks. This DAP−Cu allows for the precise loading of metallic Li, and the symmetric battery assembled with Li/DAP−Cu electrode operates at the high current density of 5 mA cm−2 for 4000 hours while exhibiting a low polarization voltage of ~60 mV. The Li/DAP−Cu anode achieves high‐performance compatibility with LiFePO4 and sulfur cathodes, with optimal N/P ratios of 1.20 : 1 and 4.0 : 1, respectively. Full and pouch cells with low N/P ratios exhibit exceptionally high specific capacities and long‐term cycling life. The establishment of standards for the matching of anodes and cathodes provides a reference for the quantitative preparation of electrode materials and is of significant guidance for enhancing the efficient utilization of metallic Li.

Preparation of ultra-high-strength alumina microspheres based on fiber reconstruction via multistage low-carbon alcohol elution

Catalytic reactions play a central role in chemical production, wherein the strength of the catalyst support is key to long-term stable operation. Simple and efficient strength enhancement methods for heterogeneous catalysis have received significant attention. Herein, we developed a variable-temperature gradient elution technology for low-carbon alcohols to improve the crushing strength of microspheres prepared using the sol–gel method in a microfluidic system. Based on gel fiber growth and rearrangement utilizing the hydrogen-bonding effect between low-carbon alcohols and pseudo-boehmite, the pore structure and fiber network can be reconstructed. Low-carbon alcohols with strong hydrogen bonds and low steric hindrance are more conducive to the formation of short fibers when constructing a dense gel network coordinated with higher alcohols. By combining long and short fiber cross-linked networks, the crushing strength of microspheres is significantly improved, and a dense pore structure with a small pore volume forms. After gradient elution, a crushing strength of up to 71.78 N/mm2 can be achieved with a high specific surface area of 254.27 m2/g, which significantly exceeds that of commercial alumina supports with the same pore volume. This efficient method provides an important solution for the long-term, stable operation of catalysts.

Study on Effect of Particle Size Distribution on Water-Retention Capacity of Coral Sand from Macro and Micro Perspective

The reclamation coral sand (CS) layer is the survival environment for island reef vegetation in the South China Sea. The root system within the CS bed draws water necessary for vegetation growth, implying that the water-retention capacity of CS plays a pivotal role in determining vegetation viability. Particle size distribution (PSD) significantly influences the water-retention capacity of geomaterials. This study examines the impact of PSD on the water-retention capacity of CS from both macro (soil–water characteristic curve, SWCC) and micro (pore water distribution) perspectives using the pressure plate test and nuclear magnetic resonance technique, and an F&amp;X model was used to analyze the SWCC of CS. The findings indicated that the F&amp;X model aptly describes the SWCC of CS with different PSDs. Both the air entry value and residual water content rise with an increased content of fine grains (d &lt; 0.25 mm), suggesting that the presence of fine grains augments the water-retention capacity of CS. It is considered that a size range of d = 0.075–0.25 mm predominantly impacts the water-retention capacity of CS. The PSD primarily influences the water-retention capacity by affecting the pore size distribution of CS. The volume of small pores swells with the surge of fine-grain content, while the maximum pore size contracts with increasing fine-grain content. Limited pore connectivity in CS means macropores can retain water even under high suction, bolstering the water-retention capacity of CS. These findings offer theoretical guidance for selecting gradation parameters for the planting layer on island reefs.

CO2–Water–Rock Interaction and Its Influence on the Physical Properties of Continental Shale Oil Reservoirs

Shale oil resources are abundant, but reservoirs exhibit strong heterogeneity with extremely low porosity and permeability, and their development is challenging. Carbon dioxide (CO2) injection technology is crucial for efficient shale oil development. When CO2 is dissolved in reservoir formation water, it undergoes a series of physical and chemical reactions with various rock minerals present in the reservoir. These reactions not only modify the reservoir environment but also lead to precipitation that impacts the development of the oil reservoir. In this paper, the effects of water–rock interaction on core porosity and permeability during CO2 displacement are investigated by combining static and dynamic tests. The results reveal that the injection of CO2 into the core leads to reactions between CO2 and rock minerals upon dissolution in formation water. These reactions result in the formation of new minerals and the obstruction of clastic particles, thereby reducing core permeability. However, the generation of fine fractures through carbonic acid corrosion yields an increase in core permeability. The CO2–water–rock reaction is significantly influenced by the PV number, pressure, and temperature. As the injected PV number increases, the degree of pore throat plugging gradually increases. As the pressure increases, the volume of larger pore spaces gradually decreases, resulting in an increase in the degree of pore blockage. However, when the pressure exceeds 20 MPa, the degree of carbonic acid dissolution will be enhanced, resulting in the formation of small cracks and an increase in the volume of small pores. As the temperature reaches the critical point, the degree of blockage of macropores gradually increases, and the blockage of small pores also occurs, which eventually leads to a decrease in core porosity.

Effects of cage topology on ethylene adsorption mechanism in silver exchanged CHA and RHO zeolites: An Inelastic Neutron Scattering and Density Functional study

Zeolite-based adsorbents have been successfully used for many challenging separations due to their tunable properties. A particularly notable application involves the separation of light olefins from paraffins, wherein the molecular sieving properties of zeolites play a pivotal role. Additionally, the selective interaction of alkenes with transition metal cations, positioned within the channels and cavities of microporous zeolites, further enhances separation capabilities.This study aims to comprehensively characterize the interactions between ethylene and Ag+ exchanged zeolites, employing a multidisciplinary approach, combining Inelastic Neutron Scattering (INS), Infrared (IR) spectroscopy, Nuclear Magnetic Resonance (NMR), UV–Vis and Density Functional Theory (DFT) calculations. CHA and RHO, zeolites largely applied in gas separation processes, were chosen due to their similar small pore sizes and pore volume, but different cavity shapes and flexibilities.The interpretation of derived DFT Electron Density Difference, experimentally supported by 13C Solid State NMR results, provide an understanding of each framework’s role during the charge transfer mechanisms between ethylene and transition metal species. Specific deformations in the flexible framework of zeolite RHO explain a blueshift of the band at 400 cm−1 in the librational region of INS spectra compared to CHA. This structural change in RHO, represented by the conic shape of the cage 8-ring side pockets, increases steric effects over the adsorbate while rendering the metallic adsorption center less exposed within the zeolite’s cavity, finally leading to a weaker adsorption energy. The redshift of C=C stretching frequencies observed by IR spectroscopy and DFT calculations, as well as C=C and C-H bond lengthening of ethylene confirm the formation of π-complexes on silver in both zeolites and allowed a further evaluation of the effects of the different frameworks cages on the aforementioned interaction.

Effect of Citric Acid-Modified Chitosan on Hydration Regulation and Mechanism of Composite Cementitious Material System

The temperature stress caused by the large temperature difference is the main factor causing harmful cracks in large-volume concrete. The introduction of admixtures is beneficial to reduce the temperature difference inside and outside the large-volume concrete. This study investigated the mechanism of how citric acid-modified chitosan (CAMC) affects the hydration heat release process and hydration products of composite cementitious materials. Through methods such as hydration heat, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR), the mechanism of how CAMC controls the hydration heat release process and hydration products of composite cementitious materials was revealed. The results show that the addition of CAMC delayed the hydration process of cementitious materials without affecting the type of hydration products but affected the content of each phase of hydration products. As the hydration process proceeded, the total porosity of all samples decreased, the volume of large pores decreased, and the volume of small pores increased. As the content of CAMC increased, the pore diameter of the hardened paste gradually became smaller, the proportion of large pores decreased, and the later hydration microstructure became more dense. The increase in CAMC dosage resulted in a decrease in the peak intensity of Q2 in the paste, indicating that Al atoms in Q2 (1Al) existed in the form of Alcoordination, which proves that CAMC reduced its hydration degree and delayed cement hydration.

Coring tools have an effect on lithification and physical properties of marine carbonate sediments

Abstract. The International Ocean Discovery Program (IODP) JOIDES Resolution Science Operator typically uses an advanced piston corer (APC) in soft ooze and sediments and an extended core barrel (XCB) in firm sediments. The coring tool exchange typically occurs around the same depth in adjacent holes of the same site. However, during IODP Expedition 356, the coring tool switch occurred at different depths: IODP Sites U1463 and U1464 are marked by a stratigraphic interval (&gt; 25 m thick) that was XCB cored in one hole and APC cored in other holes. Shipboard scientists remarked that APC-cored sediments were unlithified or partially lithified, while XCB-cored sediments were fully lithified. This difference in sedimentological description of the same formation seems to be an effect of coring technique. To provide further insight, we assessed the physical properties (bulk density, porosity, and P-wave velocity), downhole wireline logging data, scanning electron microscope (SEM) images, and micro-computed tomography (µCT) scans of those intervals. We find systematic differences between the different coring techniques. XCB cores are characterized by systematically lower bulk density, higher porosity, and higher P-wave velocity than APC cores. Downhole logging data suggest that the original P-wave velocity of the formation is better preserved in XCB cores, despite the typical “biscuit-and-gravy” core disturbance (i.e. well-preserved core fragments surrounded by squelched core material). In conjunction with SEM and µCT images, we conclude that the APC tool destroyed early lithification by breaking cements between individual grains. Moreover, µCT images reveal denser packing and smaller pore volumes in the APC cores. These sedimentary changes likely occur when the APC pressure wave passes through the sediment. The destruction of grain-to-grain cements provides an explanation for the significantly lower P-wave velocities in APC cores. Interestingly, the gravy sections in XCB drilled cores mimic the destruction of early lithification and reduction of pore volume. We conclude that APC remains the tool of choice for recovering soft sediments, especially for paleoclimate purposes. However, for the study of lithification, XCB biscuits provide a more representative image of the formation. For the study of early diagenesis, further studies are required to ascertain the preservation of key sedimentary features using existing and new drilling tools.

Impacts of Pore Structure on the Occurrence of Free Oil in Lacustrine Shale Pore Networks

The ultimate recovery of shale oil is mostly dependent upon the occurrence and content of free oil within the nano-scaled pore network of shale reservoirs. Due to the nanoporous nature of shale, quantitatively characterizing the occurrence and content of free oil in shale is a formidable undertaking. To tackle this challenge, 12 lacustrine shale samples with diverse organic matter content from the Chang7 Member in the southern Ordos Basin were selected, and the characteristics of free oil occurrence were indirectly characterized by comparing changes in pore structure before and after organic solvent extraction. The free oil enrichment in shale was assessed using the oil saturation index (OSI), corrected oil saturation index (OSIcorr), and percentage of saturated hydrocarbons. The results revealed that slit-like interparticle pores with diameters less than 30 nm are dominant in the Chang7 shale. Conceptual models for the pore structures containing free oil were established for shale with total organic carbon (TOC) content less than 9% and greater than 9%, respectively. Shale samples with TOC content less than 9% exhibit a well-developed pore network characterized by relatively larger pore volume, surface area, and heterogeneity. Conversely, shale samples with TOC content exceeding 9% display a less developed pore network characterized by relatively smaller pore volume, surface area, and heterogeneity. Larger pore volume and lower organic matter abundance favor the enrichment of free oil within the lacustrine shale pore network. This study may have significant implications for understanding oil transport in shales.

Facile synthesis and life cycle assessment of Iron oxide-Douglas fir biochar hybrid for anionic dye removal from water

Development of low-cost and safe IONPs-based biochar hybrids with efficient multiple pollutant removal abilities is critical. In the present study, we studied the potential of an Fe3O4-modified wood-based biochar (FDBC) composite to remove an aqueous anionic dye, bromophenol blue (BPB) via simple magnets. Smaller surface area (1.5 times) and a smaller pore volume (∼2 times) of FDBC over the original biochar (DBC) does not impede the BPB uptake by FDBC. The Langmuir monolayer BPB adsorption capacities of FDBC and DBC are 448.0 and 451.0 mg/g (removal percentages, 89.8 % vs. 90.3 %) (adsorbent dose 50 mg, 25 mL of 1000 mg/L BPB concentration, 2 h, pH 5.0). The larger surface area (248 m2/g) and abundant nano Fe3O4 (11.0 nm) sites account for FDBC's excellent BPB removal compared to recent IONPs-based adsorbents. At pH 5.0–8.0, the BPB is bound to the FDBC (points of zero charge = 8.2) via H-bonding and π-π stacking, as confirmed by pH, desorption, and thermodynamic studies. Compared to NaOH and H2O2, methanol desorbs more BPB from the spent adsorbent at pH 7.0. Moreover, this composite removes even the BPB residuals from real wastewater, becoming an ideal adsorbent for BPB removal. A limited life cycle assessment of FDBC's synthesis revealed a higher impact for global warming (2.38 kg CO2eq) per kg of the adsorbent, whereas the lower impacts for ozone depletion, particulate matter emissions, and air quality. The FDBC is more economical because of its green and facile synthesis, excellent dye removal capacity, easy and fast recovery. Efficient multiple dye uptake of FDBC produces large concentration of recovered dyes, which can be possibly reused in various economic applications.

Direct ink writing of vascularized self-healing cementitious composites

Direct ink writing of cementitious materials can be an alternative way for creating vascular self-healing concrete by intentionally incorporating hollow channels in the cementitious matrix. In this study, a 3D-printable fibre reinforced mortar was first developed. Three groups of specimens were fabricated using direct ink writing, where the two top and bottom printing layers were printed with different printing directions. The macrostructure of the hardened specimens was studied using CT scanning. Four-point bending tests were carried out to investigate the initial flexural strength and the strength recovery after healing with injected epoxy resin. Furthermore, water permeability test was used to evaluate the healing potential of the samples. The results from CT scanning show that printing direction influences the actual volumes of hollow channels and the volume of small pores which are a consequence of the deposition process. The hollow channels of all samples were squeezed by the upper layers during the printing process, and the longitudinally printed samples were the most affected. When printing direction changes from longitudinal to transverse, the initial flexural strength decreases. Similarly, the average permeability of the cracked samples increases when the printing direction changes from longitudinal to transverse. Although the healing effectiveness regarding flexural strength is remarkable for all specimens, it was only possible to perform a single healing process as hollow channels were then blocked by the epoxy resin. The rough surface of the hollow channels is inferred to make it difficult to extract the epoxy resin out of the specimens.

Catalytic activity of two-dimensional cobalt-ZIF catalyst for NaBH4 hydrolysis

In this work, cobalt-ZIF catalysts were synthesized by water-based synthesis methods. Various hydrogen bond acceptor (tetramethylammonium bromide (TMAB), tetraethylammonium bromide (TEAB), tetrapropylammonium bromide (TPAB), tetrabutylammonium bromide (TBAB) and trimethylphenylammonium bromide (TMPAB)) were co-added during cobalt-ZIF catalyst synthesis procedures to promote the deprotonation of 2-methyl imidazole and the deprotonated 2-methyl imidazole was then further coordinated with cobalt ion to form a ZIF framework. Co-addition of TMPAB during synthesis resulted in 3D imperfect rhombic dodecahedrals with high surface area (432.3 m2/g), while, the rest of used hydrogen bond acceptors (TMAB, TEAB, TPAB and TBAB) provided 2D ZIF-L structure with relatively small surface area and pore volume. All synthesized cobalt-ZIF with different structures and morphologies were used as a catalyst for H2 generation by NaBH4 hydrolysis reaction. It was found that all 2D cobalt-ZIF structures exhibited higher hydrogen production rate than that of the 3D imperfect rhombic dodecahedral structure. This can be explained by the cushion-shaped cavity of a two-dimensional framework exhibiting higher flexibility which can promote more diffusion of reactants than the tetrahedral structure of a 3D-framework. X-ray absorption spectroscopy was used to investigate the electronic state of cobalt and to monitor the changing of cobalt probe atom during hydrolysis reaction. The electronic state of cobalt for all catalysts was Co2+ with the same tetrahedral symmetry. The lowering of pre-edge peaks of cobalt K edge XANES spectra during hydrolysis reaction indicated to distortion of the symmetry which is related to the reduction of the catalytic performance.

Effects of dry-wet cycles on compacted loess: from macroscopic to microscopic investigation

To investigate the response mechanism of mechanical properties for compacted loess to dry-wet cycles, multi-scale tests including direct shear, consolidation compression, crack quantification, SEM, NMR and XRD were designed and performed on samples from 0 to 9 cycles. The results indicate that both the shear strength and overall compressibility deteriorate substantially after the first dry-wet cycle and stabilize after five cycles. Meanwhile, mesoscopic cracks appear on the loess surface during the initiation, propagation and equilibrium phases, accompanied by a growth in the crack ratio, as well as a more chaotic crack distribution with cycles. The penetration of the pore space during repeated dry-wet leads to a decrease in the volume of micropores and small pores and an increase in that of mesopores and macropores. Additionally, particle rounding and orientation are slightly enhanced and the soil microstructure becomes more fragmented. Furthermore, the relative content of the primary minerals has grown insignificantly after performing the dry-wet cycles, while the clay minerals and soluble salts content has decreased inconsiderably. The deterioration of the macroscopic mechanical properties of compacted loess can be considered as the comprehensive manifestation of irreversible fatigue damage to its microscopic and mesoscopic structures induced by dry-wet cycles.

Fluidity, mechanical properties, shrinkage of alkali-activated slag/stainless steel slag mortars with composite activators

In order to efficiently utilize steel slag and reduce carbon emissions, the performance of alkali-activated slag/stainless steel slag mortar (ASM) prepared with a composite activator is investigated. In this work, CaO, Na2CO3 and water glass (WG) are used as composite activators, where the alkali equivalents of CaO and Na2CO3 are maintained at 4% and the alkali equivalents of WG (i.e. WG content) as variables were 0, 0.5%, 1.0%, 1.5% and 2.0% respectively. The properties of ASM, including mechanical properties, autogenous and drying shrinkage, are investigated. Results show that the mechanical properties of ASM decrease and then increase as the WG content increases, with the worst mechanical properties of ASM occurring when the WG content is 0.5%. The autogenous shrinkage of ASM decreases as the WG content increases from 0 to 0.5% followed by an increase as the WG content increases further to 2.0%. Autogenous shrinkage depends on chemical shrinkage, small pore (<50 nm) volume, MCL and capillary pressure. When the WG content is increased from 0 to 0.5%, the hydration reaction is inhibited by the reaction of the WG and CaO which reduces the pH of activator solution and gel amount, leading to a reduction in chemical shrinkage, small pore volume, MCL and capillary pressure. However, the high WG content accelerates the hydration reaction when the WG content is greater than 0.5%, which increases the autogenous shrinkage. The drying shrinkage of ASM decreases and subsequently increases as the WG content increases. The higher drying shrinkage is associated with weight loss due to the excellent connectivity of the pores.The pore structure also affects the drying shrinkage, which can be justified on the basis of capillary pressure.

Diagenetic differentiation of tuffaceous interstitial materials in sandy conglomerate and their effect on reservoir properties

Tuffaceous material of the Lower Triassic Baikouquan Fm., NE Junggar Basin is closely associated with detrital particles and particularly with crenulated quartz grains and kaolinite. The amount tuff is reduced closed to the source area. The main component of the tuffaceous interstitial material is SiO2, followed by K2O, FeO, and MgO. The tuffaceous interstitial material can be further divided into three types: medium (basic) potassium-rich tuffaceous material, ultrabasic iron-magnesium tuffaceous material, and ultrabasic iron-magnesium rich tuffaceous material. Medium (basic) potassium-rich is dominated by fusiform shrinkage pores, often associated with kaolinite, while ultrabasic iron-magnesium rich tuff pores are not developed, and ultrabasic iron-magnesium tuffaceous material is dominated by dissolution pores. The solution pores have large diameters and large volume of pores and throats, but low pores and throats coordination number. The pore size and the pores and throats volume of shrinkage fractures are small, but the pores and throats coordination number are large. Dissolution pores are mainly distributed in Mbr 1, whereas shrinkage pores mainly occur in Mbr 2. However, the interlayer productivity data from a single well show that the Mbr 1 has a higher productivity than Mbr 2. However, the interlayer productivity data from a single well show that Mbr 1 has a higher productivity than Mbr 2. In addition, tuff is not responsible for wind action, but the cause of intermittent water flow transport in volcanic rocks. Distributary channels at the fan delta front comprise the dominant facies for development of tuffaceous interstitial materials. The composition of tuffaceous interstitial material clearly determines reservoir quality. Medium basic potassium-rich tuff has a high SiO2 content and is prone to devitrification, so it is dominated by shrinkage pores, whereas ultrabasic iron-magnesium tuff contains FeO and MgO and is vulnerable to acid corrosion and the formation of corrosion pores. However, acid minerals such as kaolinite reduce reservoir connectivity. Compared with solution pores, shrinkage pores have a small pore volume, but high pores and throats coordination number, indicating that they have a high seepage capacity. Shrinkage pores are an important factor in causing production differences between single layers and should be given more attentions.

The Chemical Compatibility of Sand–Attapulgite Cut-Off Walls for Landfills

Soil–bentonite cut-off walls have been widely used to control landfill pollution but they do not have good chemical compatibility with landfill leachate. Attapulgite can be substituted for bentonite in landfill cut-off walls. However, little is known about the chemical compatibility of attapulgite cut-off walls and leachate. This study experimentally investigated the chemical compatibility of attapulgite cut-off wall specimens with organic and inorganic contaminants and found that a sand–attapulgite cut-off wall has good chemical compatibility with organic contaminants. A CaCl2 solution was used to represent inorganic contaminants, and chemical oxygen demand (COD) was used as an indicator of organic content. The hydraulic conductivity of the cut-off wall initially decreased and then increased to become approximately constant as Ca2+ concentration increased. Changes in COD concentration were divided into a decreasing stage (0–10,000 mg/L) and a constant stage (10,000–40,000 mg/L). The increase or decrease in hydraulic conductivity was by no more than one order of magnitude. The increase in the hydraulic conductivity of the sand–attapulgite cut-off wall is explained in terms of bound water content and pore structure. An increase in Ca2+ concentration decreased the bound water content of the cut-off wall while the CaCl2 solution increased macropore and mesopore volume and decreased small pore volume in the sand–attapulgite cut-off wall. The purpose of this study was to elucidate the chemical compatibility of a sand–attapulgite cut-off wall with organic and inorganic contaminants and to increase the understanding of the interactions between the cut-off wall and the contaminants. The results of this research are informative for improving the application, design, and construction of sand–attapulgite cut-off walls.

On the benefits of vegetable oil addition for the pore structure and acid resistance of alkali-activated systems

The impact of high additions of vegetable oil (12 vol%) on the mechanical and microstructural properties of metakaolin-slag-based alkali-activated materials (AAMs) was studied. The addition of oil resulted in a slight decrease in initial polymerization kinetics but did not affect the final degree of reaction. AAM-oil-composite-mortars exhibited approximately ∼30% lower compressive strength primarily due to the entrainment of air voids. Newly formed soap phases significantly reduced the volume of small capillary and gel pores (pore radii <15 nm), leading to a decrease in specific inner surface area by a factor of up to 15. The porosity modification induced by the oil addition greatly enhanced the resistance of AAMs against sulfuric acid attack, shifting the dominant processes from diffusion and cracks to framework-dissolution controlled by the inherent phase stabilities. Following the immersion in sulfuric acid (pHstat = 2) for 8 weeks, the depth of corroded layer decreased by 70% and no cracks due to expansive phases were observed. These promising findings suggest that the incorporation of vegetable oil in AAMs has the potential to address durability concerns associated with diffusion-based corrosion processes, thereby expanding the range of future applications.

Functional and microstructural alterations in hydrated and freeze–thawed cement-oil shale ash composites

The oil shale industry generates a large amount of solid waste, the finer fraction of which can be utilized in civil engineering projects. However, for environmental, economic or technological reasons, oil shale is blended with other fuels, resulting in significant changes in the chemical composition of the residual ash. In this laboratory work, the fly ash from the combustion of oil shale with and without biomass in an industrial power plant was used as a binder substitute in cement-based materials to assess the potential of reuse of this ash. The hydration and pore structure of blended cementitious material subjected to long-term hydration and freeze–thawing has been characterized with a range of techniques, such as XRD, TGA and N2 physisorption. The results revealed that the ash type influences the phase assemblage related to the content of ettringite and monocarboaluminate, significantly affecting the volume of gel (1–6 nm) pores and small (10–30 nm) capillary pores. These microstructural changes impact the mechanical strength and water sorptivity properties in an opposite way after both long-term hydration and freeze–thawing. The results showed that the incorporation of ash obtained after combustion with biomass possesses higher mesoporosity and delays the hydration of cement, increases the total volume of gel (<6 nm) and small capillary pores (20–30 nm) of the composition, and deteriorates the functional properties after freeze–thawing.