Pore Content Research Articles

The formation mechanism of geological disasters on loess fill slopes revealed by the deformation characteristics of remolded loess under different stress paths

In recent years, geological disasters on loess fill slopes have occurred from time to time, which has attracted widespread attention. In order to deeply understand its deformation and failure laws and promote the disaster prevention and mitigation work, this paper takes remolded loess as the research object, systematically explores the effects of three different stress paths (conventional triaxial compression test (CTC), triaxial compression test with constant average principal stress (TC), and triaxial compression test with reduced confining pressure (RTC)) on its mechanical properties, and observes and analyzes its microstructural characteristics by scanning electron microscopy (SEM). The results show that the soil is strain hardening under the CTC path, while it is strain weak hardening under the TC and RTC paths. In the order of CTC, TC, and RTC paths, the shear strength and volume shrinkage of the soil are reduced in turn, and its deformation has both shear reduction and shear expansion plastic deformation. In the order of CTC, TC, and RTC paths, the degree of particle crushing decreases in turn and the pore content increases in turn. It is inferred that in the initial deformation of loess under loading, the soil is compressed and compacted, and its strength is improved to a certain extent. As the loading continues to increase, the deformation rate increases steadily, and the soil deformation develops gradually, which is mainly axial compression deformation, while the lateral bulging deformation is small until it is destroyed. For the deformation behavior in the form of lateral unloading, the soil is maintained in a relatively stable state at the beginning, and the deformation is very small. When the lateral constraint is reduced to a critical state, the structure is completely unstable, and the deformation develops rapidly in a short time until it is destroyed. This study is of great significance for reducing the occurrence of geological disasters on fill slopes in loess areas.

Effect of Solvents on Porous Properties of Microporous Polyphenylenes

Microporous organic polymers are of considerable interest for the development of gas separation technologies, catalysis, gas storage systems and other areas. This study shows the effect of porogenic solvents (toluene, o-xylene, DMF) on the pore size distribution, volume and content of micropores in microporous polyphenylenes. Using scanning electron microscopy, a strong effect of solvents on the morphology of the resulting polymers was shown. The nitrogen adsorption–desorption isotherms allowed for determining the optimal conditions for the synthesis of soluble microporous polyphenylenes, leading to samples with the highest degree of microporosity.

Relationship Between the Carbonation Depth and Microstructure of Concrete Under Freeze-Thaw Conditions.

Concrete structures in cold regions are affected by freeze-thaw cycles (FTCs) and carbonation, which lead to the premature failure of concrete structures. The carbonation depth, relative dynamic elastic modulus (RDEM), compressive strength, porosity, and pore size distribution of concrete under FTC conditions were tested through an accelerated carbonation experiment to study the carbonation performance evolution. The freeze-thaw effect mechanism on concrete carbonation was further analyzed via the obtained relationship between carbonation depth and pore structure. The results showed that the FTC, as a powerful source of concrete damage, accelerates the carbonation reaction. Carbonization products fill some microcracks caused by the freeze-thaw process, improve the compressive strength and dynamic elastic modulus, and alleviate the damage to concrete caused by the FTC. After carbonization under freeze-thaw damage conditions, the content of macropores with d > 1000 nm decreases, while the content of transition pores with d ≤ 10 nm increases, which is the direct reason for the decrease in porosity and the improvement in strength. Therefore, the carbonation durability of concrete under freeze-thaw conditions can be improved by controlling the content of macropores with d > 1000 nm and increasing the content of transition pores with a pore size of 10 nm ≤ d < 100 nm. In addition, the relationship between carbonation depth and pore structure under freeze-thaw conditions was established, and the research results can provide a reference for the study of the carbonation performance of concrete under freeze-thaw conditions.

3D Printable One-Part Alkali-Activated Mortar Derived from Brick Masonry Wastes

The exponential growth in demand for housing has resulted in a greater focus on rapid construction methods that adhere to circular economy principles. 3D concrete printing is becoming a powerful tool to find solutions to the common challenges of affordable housing for more people, rapid construction, and the digitalization of the construction industry. However, a coherent synthesis of green and digital initiatives has not yet been achieved. For 3D printable materials, recycling of materials that have reached the end of their service life should also be enabled and supported, in line with circular economy goals that prioritize waste reduction and maximization of resource efficiency. With these objectives in mind, the current study focuses on the development of a one-part 3D printable alkali-activated mortar (3DPM) derived from brick masonry waste (BMW). BMWs were used as the main precursor and filler phase, whereas materials such as ground granulated blast furnace slag, kaolin clay, and limestone have been utilized to enhance/control the mechanical and rheological properties. To investigate the evolution of alkali-activation and the effect of anisotropy, the macromechanical properties of the developed 3DPM were investigated by compressive strength, flexural strength, split tensile, and direct tensile tests. The micromechanical properties were analyzed using X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetry (TG), differential scanning calorimetry (DSC), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDX), and computed tomography (MicroCT) tests. Overall, the results revealed the presence of anisotropy, which can be reduced by optimizing the layer height. Through this optimization, reductions in pore content and distribution, validated by MicroCT, indicated that the disadvantage of the weak interlayer bond zone in stress transfer could be diminished. Micromechanical analysis showed that the gel formation responsible for the strength was the calcium-based gel structures. Considering these findings, it is believed that the BMW-based 3DPM can be an important alternative for the digitalization of the construction industry and its transition to a circular economy.

Tunable Absorption and Photochromism in Polyheptazine Imides Via a Solvent Mediated Synthetic Pathway

Layered, two dimensional metal containing polyheptazine imides (M-PHI) offer a complex playground for structure variation resulting in fascinating optoelectronic properties for several energy conversation and storage applications and beyond.1,2,3 Ionothermal or high temperature synthesis using both bottom-up molecular precursor routes and top-down approaches from melon have been used to synthesize M-PHI.4,5 A pressing problem for M-PHIs and infact for most polymeric carbon nitrides (PCN) is their insufficient visible light absorption arising from their symmetry forbidden n-π* electronic transition and fast charge recombination.4 Varying precursor ratios during thermal condensation of urea and oxamide, low pressure-high temperature melamine polymerization, urea pyrolysis, salt-melt synthesis using amino tetrazoles and many other methods have been successfully applied to synthesize red carbon nitrides with extended vis-absorption. These methods are majorly cumbersome and since each synthetic pathway is unique to one final material, structural relations between red carbon nitrides vs. their poor light-absorbing counterparts does not exist.7 In this work, we show the first solvent mediated route for red carbon nitride synthesis by a post-synthetic modification of yellow K-PHI via polymeric self-assembly. A competition between the solvent mediator bulkiness and its basicity, reaction temperature and time is shown to tailor KPHI absorption spectra, according to need. A combination of solid-state NMR, p-XRD, thermogravimetric analysis, with ground and excited state photophysical characterizations offer structural insights into red PHI. Variation in the long-ranged stacking order and pore content seem to have an impact on light absorption but does not limit their charge storage behavior as seen from electron paramagnetic resonance data upon illumination and time-delayed H2 production from water-splitting, experiments. In fact, this spectrally modified red PHI acts as a photochromic switch by a complete disappearance of the n-π* electronic transition during the formation of a stable photo-reduced state.

Long term properties of Nano-engineered temperature self-controlled concrete served for mass concrete structure

Due to the advantages of low-cost and superior electrical conductivity, Nano-carbon black (NCB) can endow hydraulic concrete with long-term and stable self-heating capacities at affordable costs, thus allowing active and intelligent temperature control for high-altitude and high-latitude dams. This study, for the first time, investigated the long-term mechanical behaviors, freeze-thaw resistance and impermeability of temperature self-controlled concrete (TSC). Moreover, the modification mechanisms of TSC were revealed with the help of mercury intrusion porosimetry (MIP), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). Finally, the long-term performance and cost assessment of TSC are comprehensively evaluated by the entropy weight method. The results indicate that the incorporation of 4.5 wt% NCB improves the compressive and splitting tensile strengths of TSC at 180 days by 17.4 % and 7.9 %, respectively, and shows an excellent response against impermeability and a slightly lower response against frost resistance. Besides, NCB accelerates the hydration degree and repairs the interfacial transition zone of TSC. The presence of NCB densifies the microstructures of the matrix and reduces the content of harmful pores by nearly 50 %. Finally, TSC with 4.5 wt% NCB is the optimal mixture that shows excellent comprehensive performances.

Organic and Inorganic Modifications to Increase the Efficiency in Immobilization of Heavy Metal (Zn) in Cementitious Composites-The Impact of Cement Matrix Pore Network Characteristics.

This research investigated the properties of modified cementitious composites including water purification from heavy metal-zinc. A new method for characterizing the immobilization properties of tested modifiers was established. Several additions had their properties investigated: biochar (BC), active carbon (AC), nanoparticulate silica (NS), copper slag (CS), iron slag (EAFIS), crushed hazelnut shells (CHS), and lightweight sintered fly ash aggregate (LSFAA). The impact of modifiers on the mechanical and rheological properties of cementitious composites was also studied. It was found that considered additions had a significantly different influence over the investigated properties. The addition of crushed hazelnut shells, although determined as an effective immobilization modifier, significantly deteriorated the mechanical performance of the composite as well as its rheological properties. Modification by iron slag allowed for a significant increase in immobilization properties (five-fold compared to the reference series) without a substantial impact on other properties. The negative effect on immobilization efficiency was observed for nanoparticulate silica modification due to its sealing effect on the pore network of the cement matrix. The capillary pore content in the cement matrix was identified as a parameter significantly influencing the immobilization potential of most considered modifications, except biochar and active carbon.

CO2 Utilization and Sequestration in Organic and Inorganic Nanopores During Depressurization and Huff-n-Puff Process.

CO2 injection in shale reservoirs is more suitable than the conventional recovering methods due to its easier injectivity and higher sweep efficiency. In this work, Grand Canonical Monte Carlo (GCMC) simulation is employed to investigate the adsorption/desorption behavior of CH4-C4H10 and CH4-C4H10-CO2 mixtures in organic and inorganic nanopores during pressure drawdown and CO2 huff and puff processes. The huff and puff process involves injecting CO2 into the micro- and mesopores, where the system pressure is increased during the huffing process and decreased during the puffing process. The fundamental mechanism of shale gas recovery using the CO2 injection method is thereby revealed from the nanopore-scale perspective. During primary gas production, CH4 is more likely to be produced as the reservoir pressure drops. On the contrary, C4H10 tends to be trapped in these organic nanopores and is hard to extract, especially from micropores and inorganic pores. During the CO2 huffing period, the adsorbed CH4 and C4H10 are recovered efficiently from the inorganic mesopores. On the contrary, the adsorbed C4H10 is slightly extracted from the inorganic micropores during the CO2 puffing period. During the CO2 puff process, the adsorbed CH4 desorbs from the pore surface and is thus heavily recovered, while the adsorbed C4H10 cannot be readily produced. During CO2 huff and puff, the recovery efficiency of CH4 is higher in the organic pores than that in the inorganic pores. More importantly, the recovery efficiency of C4H10 reaches the highest levels in both the inorganic and organic pores during the CO2 huff and puff process, suggesting that the CO2 huff and puff method is more advanced for heavier hydrocarbon recovery compared to the pressure drawdown method. In addition to CO2 storage, CO2 sequestration in the adsorbed state is safer than that in the free state. In our work, it was found that the high content of organic matter, high pressure, and small pores are beneficial factors for CO2 sequestration transforming into adsorbed state storage.

Antibacterial action of novel zeolite-based compositions depends upon doping with Ag(+) and Сu(2+) cations

Recently, there is a growing interest to exploration of sorption and catalytic properties of solid nanomaterials, in particular natural zeolites, as well as to study of their antimicrobial effects with the aim of potential using them as a principal component of disinfection and degassing remedies. The purpose of this work was to study the antimicrobial action of compositions based on the Transcarpathian clinoptilolite (CL) doped with Ag+ and Сu2+ cations or Ag microparticles (MPs). These compositions were subjected to mechanochemical modification in ethanol medium and with the addition of plant (Actinidia arguta) extract used as an antioxidant. Mechanochemical treatment (MChT) of all forms of CL MPs led to their grinding which caused better contact of CL with bacterial cells, while an increased content of larger pores improved their access to the active sites on the surface of the CL MPs. Treatment of CL samples with metallic silver used as a dopant with the help of the extract of Actinidia arguta plant did not increase the antibacterial activity regardless of treatment time. Treatment of AgNO3 with ethanol slightly increased the antibacterial action of the CL MPs towards Gram-positive bacteria and decreased it towards Gram-negative bacteria. The CL samples doped with copper and treated with ethanol and plant (Actinidia arguta) extract demonstrated comparable toxic action towards Bacillus subtilis regardless of grinding conditions. While such a treatment caused a significant decrease in the antibacterial activity towards Staphylococcus aureus and Pseudomonas aeruginosa strains, compared to the action of samples that were not treated with that plant extract. To address the potential biochemical mechanisms of the antibacterial action of the created zeolite-based compositions, their influence on generation of the reactive oxygen species (ROS) was studied using diphenylpicrylhydrazyl (DPH) fluorescent dye. Most versions of the CL composites demonstrated time-dependent antioxidant effect comparable with the effect of the ascorbic acid used as a positive control. Thus, the ROS generation is not the mechanism that is responsible for the antibacterial action of the created CL-based compositions. Probably, that action is explained by the peculiarities of interaction of doped CL microparticles with the surface of the bacterial cells. Keywords: antimicrobial action, clinoptilolite-based compositions, doping with Ag+ and Сu2+ cations, physicochemical treatment

Assessing the compression properties of Gravel-bearing forest soil in northeast China’s seasonally frozen regions under Freeze-thaw cycles and varying gravel content

Due to climate change, human activities and natural disturbances in high-latitude permafrost and seasonally frozen areas are gradually increasing, attracting more attention from scholars. However, research primarily focuses on soil biology and chemistry in these regions, with limited exploration of their mechanical properties, especially compression properties. This study aims to evaluate the effects of gravel content and freeze–thaw (F-T) cycles on the compression properties of coarse-grained layered forest soil from northeast China’s seasonally frozen regions, with the goal of predicting the soil’s compressive changes under heavy mechanical loads. Specifically, using uniaxial confined compression tests (UCCT) on 252 disturbed soil samples (including two soil layers: AB and Bhs; six gravel contents; and seven F-T cycles), three characteristic compression coefficients—precompression stress (σpc), compression index (Cc), and swelling index (Cs)—were measured. Additionally, scanning electron microscopy (SEM) was used to analyze the mesostructure evolution of coarse-grained gravel-bearing soil. Volume changes of samples were measured after 15F-T cycles with varying gravel contents. Results indicate non-linear effects of gravel content and F-T cycles on σpc. Gravel content below 50% positively influences σpc, while content above 50% increases soil pore content, decreasing σpc. Cc and Cs exhibit an approximately negative correlation with gravel content and initially increase followed by a decrease with more F-T cycles. Moreover, the σpc and Cc of the AB layer are higher than those in the Bhs layer, likely due to differences in clay and organic carbon contents. Notably, the observed trends differ from previous studies on other soil types such as farmland and paddy fields. This study fills a gap in understanding the compression characteristics of layered gravel-bearing forest soil in seasonally frozen regions, providing valuable insights for evaluating soil compression in both seasonally frozen and permafrost regions, and understanding mechanical vehicle-soil interactions. It also lays the theoretical groundwork and provides data support for constructing compression models of layered gravel-bearing forest soil.

Effect of Fluoride in Alkali-Free Liquid Accelerator on Corrosion of Reinforced Shotcrete by Chloride Ion.

Shotcrete is a crucial component of tunnel engineering. To investigate the impact of fluoride-containing alkali-free liquid accelerators on the structural safety of shotcrete, this study prepared shotcrete using three different fluoride-based alkali-free liquid accelerators: magnesium fluosilicate, fluosilicic acid, and hydrofluoric acid. The corrosion of steel rebar within the shotcrete was examined and compared with that of shotcrete prepared using a fluoride-free alkali-free liquid accelerator. Analysis of the hydration products and pore structure of the shotcrete revealed that fluoride-containing accelerators inhibited the hydration of C3S, increased the content of harmful pores, reduced the pH value, and decreased the chloride ion binding capacity of the shotcrete. As a result, steel reinforcement within the fluoride-containing shotcrete was not effectively protected during the early stages. Detection of corrosion products indicated that shotcrete containing fluosilicic acid and hydrofluoric acid accelerators led to the rapid formation of loose corrosion products, primarily Fe2O3, thereby accelerating the corrosion rate of the steel reinforcement. Among the accelerators studied, hydrofluoric acid posed the most severe threat to the reinforcement, with the open circuit potential reaching -520.2 mV after 24 days of accelerated corrosion testing. Additionally, the mechanisms by which fluorides influence the corrosion of steel reinforcement in shotcrete were explored through the analysis of concrete hydration products and corrosion products on the steel rebar.

Evaluation of MSA mortar pore structure characteristics in water-saturated curing environment based on Talbot gradation theory

To investigate the impact of aggregate gradation on the pore structure of manufactured sand aggregate (MSA) mortar and its fractal characteristics under water-saturated curing conditions. The static pore structure characteristics of the pore structure of MSA mortar with 10 aggregate gradations were explored. The analysis is based on the Talbot gradation theory, the NMR technique, and fractal theory. The surface area and roughness of aggregate particles contribute to a reduction in the porosity of MSA mortar. The aggregate gradation is quantified using the Talbot index. The correlation characteristics and intrinsic relationships between Talbot index and different pore structure parameters, such as total porosity, pore gradation, pore fractal dimension and permeability of MSA mortar, are analyzed. Two pore division methods are employed to explore the interrelationships among pore types, fractal dimensions and Talbot index. Additionally, A correlation model between Talbot index and permeability is developed to investigate the intrinsic correlation of parameter variations from a microscopic perspective. It is found that aggregate gradation is optimal with a Talbot index of 0.4, leading to the highest number of micropores and the lowest number of larger pores, thereby enhancing resistance to seepage and dissolution. Furthermore, The contribution of pore size, content and type to permeability varies with different aggregate gradations. Overall, this study serves as a valuable guide for the design and durability evaluation of mortar concrete projects in water-saturated curing environments.

Effect and mechanism of activators on the properties of Yellow River sediment/fly ash/cement-based alkali-activated cementitious materials used for coal mine filling

Preparing Yellow River sediment/fly ash/cement-based alkali-activated cementitious materials for coal mine filling can realize the large-scale consumption of Yellow River sediment and reduce the cost of coal mine filling materials. This paper studied the effects of Ca(OH)2, NaOH, and water glass on the properties of coal mine filling materials. Adding activators Ca(OH)2, NaOH, and water glass can improve the compressive strength and shorten the setting time of the filling materials. NaOH and water glass can also significantly reduce the bleeding rate. The mechanism of activators' influence on the mechanical properties of filling materials was explored based on XRD, TGA, FTIR, MIP, and SEM. The alkaline environment provided by NaOH and Ca(OH)2 accelerated the hydration reaction of cement, and the SiO32- from the hydrolysis of water glass can bind to Ca2+ to form C-S-H gel. The co-mixing of water glass and NaOH can make fly ash and Yellow River sediment's active components react more fully, generating more C-S-H and C-A-S-H gels. This can refine the pore size distribution of the filling materials, reduce the content of harmful pores, make the matrix dense, and improve the filling materials' working and mechanical properties. When the NaOH is 0.5 wt%, and the water glass is 13 wt%, the strength of the filling materials prepared by compound doping was the highest, and the working performance met the requirements. The results had broad application prospects and economic value, contributing to ecological and environmental protection and sustainable development.

Experimental Study on Influence of Lime on Cross-Scale Characteristics of Cemented Backfill with Multiple Solid Wastes.

The utilization of industrial solid waste in mines is an important approach to resource utilization. The backfill material in mines is mainly composed of solid waste, which plays a supporting role. The excitation effect of lime on phosphogypsum and fly ash in backfill was studied in this paper. The macroscopic and microscopic characteristics of the backfill material were tested using uniaxial compression, nuclear magnetic resonance, scanning electron microscopy, and electrochemical techniques, and a relationship model was established between them. Furthermore, the influence of industrial solid waste on the properties of the backfill material under the action of lime and the hydration mechanism between different industrial solid wastes were studied. The results show that (1) under the action of lime, fly ash reacts with lime to produce C-S-H and C-A-H, and then C-A-H reacts with phosphogypsum to produce AFt. (2) The excess phosphogypsum also fills the pores. Therefore, 1.8% lime reduces the porosity of the backfill by 17.88% and increases the strength by 21.57%. (3) The cross-scale relationship shows that strength is inversely proportional to each type of pore content and fractal dimension, and it logarithmically increases with impedance at different frequencies. The lower the frequency, the stronger the relationship is. (4) This study indicates that industrial solid waste is a suitable cement replacement.

Study on gas transport characteristics of manufactured sand concrete and modeling of random hierarchical bundle based on pore structure

Overexploitation of natural sand has caused severe damage to the environment, and manufactured sand to replace natural sand has become an inevitable trend in construction projects. Anti-gas permeability performance is an important index characterizing the durability of concrete, and its performance directly affects the service life and quality of concrete structures. This study evaluates the feasibility of applying manufactured sand to concrete based on its mechanical properties. In addition, we systematically investigated the influence of the properties of manufactured sand on the pore structure and gas permeability resistance of concrete with different strength grades. Furthermore, we established a random hierarchical bundle model based on the nuclear magnetic resonance(NMR) and predicted the gas permeability coefficient by simulating the pore structure distribution of concrete. The following test results were derived: First, at the same strength grade, the late compressive strength of limestone (LMS) and granite manufactured sand (GMS) concrete is higher than that of natural river sand (NRS) concrete. Therefore, choosing manufactured sand as a fine aggregate to formulate concrete in practical engineering applications is feasible. Secondly, by comparing the gas permeability resistance of concrete with different fine aggregate mechanism sands, it was found that small aggregate particles can significantly improve the gas permeability resistance of concrete. Finally, the pore structure significantly affects the anti-gas permeability property of manufactured sand concrete, in which the pore content in the range of 10–100 nm is the main factor affecting the gas permeability coefficient. Moreover, the NMR-based stochastic layered beam model predicts the gas permeability resistance of concrete with a maximum deviation of up to 30.89 %.

Multiscale modeling and thermal conductivity evaluation of nano-reinforced composite materials with pore defect

The performance of resin-based composite materials often exhibits diversity due to the designability of various components. Thermal conductivity, an important thermal parameter of the composite, plays a significant role in thermal-chemical reactions, thermal stress analysis, temperature conduction, etc. However, it is relatively difficult to experimentally explore the thermal conduction mechanism of hybrid composite materials, mainly due to the relatively difficult control of various components. Therefore, this paper proposes a sequentially coupled cross-scale numerical method to characterize the thermal conductivity of nano-reinforced composite materials with pores by a multiscale periodic Representative Volume Element model generated by an improved Random Sequential Absorption algorithm. Firstly, periodic temperature boundary conditions are described, and the thermal conductivity performances of nano-reinforced matrix and composite with pores are investigated based on the finite element homogenization theory. Then, the proposed modes are validated and grid sensitivity analysis is conducted, indicating that the optimal grid sizes for the RVE models are 1.9 nm for the nano-reinforced matrix and 0.14 μm for the composite with pores based on a comprehensive comparison of four pore characterization methods, respectively. Furthermore, the study explored the effect of multiple parameters including nanoparticle content, pore content, and pore shape on thermal conductivity. Numerical findings reveal that the thermal conductivity of the nanocomposite matrix exhibits a linear increase with higher particle content. Specifically, compared to 0 % particle content, the thermal conductivity rises by 141.92 % at 12 % particle content. While the composite material's transverse thermal conductivity is sensitive to porosity content, it is less influenced by pore shape. The method proposed in this paper provides an effective approach for studying the thermal conduction of nano-reinforced composite materials with pores, and the research findings also offer theoretical guidance for process engineers.

Influence of powder particle size distribution on the creep performance of Ti-48Al-2Cr-2Nb alloy fabricated via electron beam-powder bed fusion

The effects of particle size distributions (PSDs) on the microstructure and creep behavior of Ti-48Al-2Cr-2 Nb fabricated via electron beam-powder bed fusion (EB-PBF) were investigated. Three PSDs of 45–150 (PSD-A), 38–150 (PSD-B), and 38–180 µm (PSD-C) were used as powder feedstock. Widening the PSD range decreased the relative density of fabricated parts and promoted the formation of banding microstructure. Moreover, samples fabricated with wider PSDs had a higher volume of lack-of-fusion (LoF) defects; however, the content of gas pores decreased significantly in PSD-C, which was related to the presence of coarse powder particles. The volume of the LoF defects in PSD-C was approximately 2.8 times of the same defects in PSD-A, which influenced the creep performance (at 750℃) and failure mechanism of Ti-48Al-2Cr-2 Nb. A longer steady-state creep period at different stress levels was identified for the samples fabricated with the narrowest PSD (45–150 µm). Widening the PSD span also caused weakness in the creep properties and data scattering at higher stress levels of 300 and 350 MPa. The LoF defects and coarse grains accelerated the crack initiation and propagation in Ti-48Al-2Cr-2 Nb during creep. This study represents the first report on the impact of PSD on the creep properties of TiAl alloys fabricated via EB-PBF, which offers new insights and enhances understanding of the powder-process-microstructure-property relationship.

Effect of modifiers on the properties of bamboo scraps/magnesium oxychloride composites under dry-wet cycling environments

Bamboo scraps/magnesium oxychloride composites (BS/MOC) is a new low-carbon and eco-friendly building material, which is composed of magnesium oxychloride cement (MOC) as the matrix and bamboo scraps as the reinforcing materials. However, the poor strength and durability of BS/MOC under special environmental conditions seriously restrict its application range. To solve the above problems, citric acid (CA), D-gluconic acid sodium salt (GS), and styrene-acrylate emulsion (SAE) were used as modifiers to improve BS/MOC properties. The effect of modifier addition on the mechanical strength and durability of BS/MOC was investigated under dry-wet cycling environments. The phase composition, microstructure, pore structure, and Clˉ concentration of BS/MOC were characterized by XRD, TGA, SEM, MIP, and ICS-600. The results showed that CA and GS improved the interface adhesion between bamboo scraps and MOC matrix, and both inhibited the hydration reaction of the residual MgO and the hydrolysis of phase 5 crystals, resulting in good mechanical properties and microstructural stability of BS/MOC under dry-wet cycles. GS outperformed CA in refining pore structure, improving mechanical properties and durability of BS/MOC under identical dry-wet cycles. Conversely, the addition of SAE increased initial defects and interfacial transition zones in the BS/MOC matrix, and increased the total porosity and the harmful pores content, which negatively affected the mechanical properties and durability of BS/MOC.

Study on pore structure and acoustic emission characteristics of Mg(OH)2 modified expired cement

This study investigated the preparation of cementitious mortar specimens (ECM) by blending different dosages of pure magnesium hydroxide (AR), active magnesium oxide, and nano magnesium hydroxide as external additives with expired composite Portland cement. The optimal solution was selected by comparing their “nuclear magnetic resonance” (NMR), mechanical properties, and acoustic emission characteristics. NMR experiments revealed that the addition of 4 wt% nano magnesium hydroxide to expired cement resulted in the largest decrease in harmful pore content in ECM, reaching 21.9%. Mechanical performance testing and acoustic emission monitoring results indicated that the strength of ECM reached a maximum of 21.356 MPa with the addition of 4 wt% nano magnesium hydroxide, representing a 20.2% increase compared to the control group. This suggests that adding 4 wt% nano magnesium hydroxide to expired cement is a preferable option.

Waste glass powder as a high temperature stabilizer in blended oil well cement pastes: Hydration, microstructure and mechanical properties

Recycling waste glass for diversified utilization has received increasing attention in recent years. This work aimed to reuse waste glass powder (GP) as a high temperature stabilizer to replace silica flour (SF) in blended G class oil well cement (GOWC) pastes. Blended pastes containing 40 % and 66.7 % GP were prepared and compared to pure GOWC paste and blended paste containing 40 % SF commonly used in the oil industry. Under simulated field conditions in a steam injection well, these pastes were cured at 50 °C for seven days, followed by three rounds of thermal cycling curing at high temperature and high pressure (HTHP, 300 °C/13 MPa) conditions. The effects of GP on the hydration kinetics, hydration products, microstructure, and mechanical properties of hardened pastes were evaluated. The results demonstrated that the addition of GP or SF reduced the compressive strength of the pastes at 50 °C due to dilution effect. Compared with SF, GP exhibited higher pozzolanic activity, prolonged the induction period, and promoted the formation of more C-(N)-S-H gels with lower Ca/Si ratios, which led to an increase in the gel pores content of the matrix and partially compensated for the loss of compressive strength due to the dilution effect. Additionally, due to the pozzolanic reaction of GP, the content of CH in the matrix decreased and its crystal size became smaller. After three rounds of thermal cycling curing, the incorporation of GP significantly increased the compressive strength of the hardened pastes. The compressive strengths of the hardened pastes with 40 % and 66.7 % GP were 20.33 MPa and 22.25 MPa, respectively, which were 7.62 % and 17.79 % higher than those of the hardened paste containing 40 % SF. In addition, the compressive strengths of hardened pastes containing 40 % and 66.7 % GP after three rounds of thermal cycling curing decreased by 22.49 % and 5.52 %, respectively, compared to the pastes at the low-temperature stage, while that of the pure GOWC pastes decreased by 83.8 %. Characterization analyses indicated that GP could further reduce the Ca/Si ratio of the system, modulate the crystallization of the gels at high temperatures, and generate foshagite or xonotlite phases with high polymerization structure and thermal stability, instead of reinhardbraunsite. These products effectively refined pore structure and enhanced microstructure densification. Furthermore, the precipitation of Na+ ions during hydration did not affect the microstructure of the matrix. This study offers some guidelines for recycling waste glass, conserving raw materials, and producing sustainable blended cement pastes.