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Acidified CO2 fracturing is a viable method for increasing production in deep, tight sandstone reservoirs. However, the potential mechanism of changes in pore structure and mechanical properties of sandstone under acidified CO2 supercritical composite is not clear. Understanding this mechanism is important for the study of crack initiation and extension in tight sandstone reservoirs. This study utilizes sandstone samples from the Xujiahe Formation reservoir in Rongchang District as experimental specimens. The primary focus is to analyze the changes in pore structure and mechanical properties of these samples after acidification–supercritical CO2 composite action. Nuclear magnetic resonance (NMR) and uniaxial compression tests are employed as the main investigative techniques. The results show that there was a physicochemical synergy between the acidification–supercritical CO2 composite effect; the crack initial stress, damage stress, and peak stress of the sandstone after 16 MPa supercritical CO2 acidification treatment were reduced by 20%, 49.5%, and 49.8%, respectively; the crack volumetric strain accelerated and the sandstone evolved from brittle to ductile damage; and the larger pore space and microcracks of the sandstone increased significantly after the treatment, which can be attributed to the gradual dissolution of intergranular cement leading to the formation of new pores connected to the existing pore network. The change mechanism of sandstone after acidification–supercritical CO2 compound treatment is also proposed. [ABSTRACT FROM AUTHOR]

The utilization of aeolian sand resources for road construction is a specific measure to develop green and low-carbon transportation, and also conforms to the concept of green and sustainable development of roads in China. Based on this, the feasibility of using aeolian sand as a substitute for fine aggregate for cement stabilized graded crushed stone was explored, and the effects of different aeolian sand dosages on the unconfined compressive strength, bending and flexural strength, and splitting strength of cement stabilized crushed stone mixtures were studied. The results indicate that the addition of aeolian sand has a significant deterioration effect on the mechanical properties of cement stabilized graded crushed stone mixtures. The larger the amount of aeolian sand added, the more severe its impact on the mixture. Therefore, controlling the amount of aeolian sand within 6 % can meet the mechanical performance requirements. To ensure the large-scale utilization of aeolian sand resources, future research can comprehensively consider the shrinkage characteristics, durability, and water stability of cement stabilized crushed stone mixtures, and further recommend the maximum dosage of aeolian sand. [ABSTRACT FROM AUTHOR]

Paulownia wood, a fast-growing wood native to China, has limited application due to its loose texture. However, the mechanical properties of materials can be improved by densification after delignification. In this study, paulownia wood was treated with sodium hydroxide and hydrogen peroxide to remove most of the lignin, then densified by hot pressing with water or epoxy. The influence of the densification process of paulownia wood/epoxy composite on the mechanical properties, especially stab resistance, was discussed. The results show that densification after delignification significantly improves the mechanical properties of the materials. The densification improves the fracture strength (in the direction where fibers are arranged) and elasticity modulus of the materials, reaching 171.98 ± 11.22 MPa and 14.55 ± 0.68 GPa, respectively. Hybrid composites made of densified wood/carbon fiber/epoxy resin have good stab resistance. The punch strength per unit area density and puncture worker unit area density of these hybrid composites are superior to carbon fiber reinforced composites. [ABSTRACT FROM AUTHOR]

Copyright of Pearl River is the property of Pearl River Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Dental diseases such as dental caries and periodontitis often lead to tooth loss, which is common in China. Clinically, oral restoration is mainly used for treatment. Zirconia, with excellent mechanical properties, good biocompatibility and better aesthetic performance, has become an ideal restorative material in the field of dental restoration. Traditional computer aided design/ computer aided manufacturing (CAD/CAM) subtractive manufacturing has the high processing accuracy and good marginal adaptation, but it has shortcomings such as material waste, tool wear and insufficient accuracy in the production of occlusal grooves. As a typical representative of rapid prototyping technology, additive manufacturing (3D printing) meets basic requirements for building precision, personalization and structural complexity allceramic crowns, and is expected to be a potential technology for the preparation of all-ceramic crowns. The progress of domestic and foreign research teams in the development and application of zirconia all-ceramic crowns using stereolithography 3D printing were reviewed. The ceramic slurry composition, design of printing process support structure, optimization of printing parameters, post treatment process route and evaluation of the performance of the printed products were reviewed and analyzed accompanying by a large number of examples for explanation. Finally, the challenges that will be faced in the future in the field of zirconia all-ceramic crowns via stereolithography 3D printing have been pointed out, and some suggestions have been provided. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Technology (Natural Science) is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The rack railway has broad application prospects in the field of steep mountain rail transportation mainly for sightseeing in China due to its technical advantages such as strong grade ability, short railway mileage and less space occupation. The rack railway sleeper is an important force-transmitting component of the wheel-rail system, and its mechanical characteristics and application environment are very different from those of the normal railway sleeper. Based on the engineering characteristics of rack railway in mountain areas, the technical requirements of rack railway sleepers, the performance characteristics and the mix proportion of the reactive powder concrete applied to rack railway sleepers are analyzed, and the structural scheme of the reactive powder concrete sleeper for rack railway is proposed. Through theoretical analysis and trial production test, the mechanical properties of the sleeper structure are researched. The results show that the rack railway sleepers in mountain areas should meet the technical requirements of maintaining the stability of the track structure, higher structure strength, easy maintenance and anti-seismic performance. The reactive powder concrete has the features of ultra-high strength, high toughness, long durability and good volume stability. The reactive powder concrete sleeper for rack railway is constructed with RPC140 concrete, double-layer reinforcements of 8φ7 mm spiral rib steel wires with the sectional height of 160 mm, which meet the bearing capacity requirement of the rack railway with the designed axle load of 12 t and maximum train speed of 40 km/h. [ABSTRACT FROM AUTHOR]

Copyright of China Forest Products Industry is the property of China Forest Products Industry Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The characteristics of the materials used in early buildings in China have led to a large proportion of discarded red bricks among the construction waste generated by demolishing abandoned buildings. The application of red brick aggregate with a particle size ≤5 mm and red brick powder with particle size 0.125~0.75 mm (referred to as recycled brick powder) was studied in this study after the crushing of waste red brick in road structures. The research results will provide a theoretical basis for the whole-grain recycling of waste red brick aggregate. The aggregate of red brick with a particle size smaller than 2 mm was mixed with different amounts of cement soil and fiber to prepare a cement-stable binder for the sub-base material. The recycled brick powder of 0.125~0.75 mm was used to replace the quartz sand with different substitution rates. As pavement materials, different amounts of fiber were used to prepare fiber-reinforced recycled-brick-powder cementitious composites. The optimal mixing ratio of the two materials was evaluated from the mechanical properties. The results showed that the optimal mixing ratio of the cement-stable binder was as follows: waste-red-brick-aggregate content was 50%, cement content was 4%, and fiber content was 0.2%. The optimum ratio of fiber-reinforced recycled-brick-powder cementitious composites was determined to be as follows: the replacement rate of recycled brick powder is 25%, and the content of PVA fiber is 1%. The regression analysis was used to fit the equations between the fiber content and the 7d unconfined compressive strength and the tensile strength of the cement-stabilized binder for different red-brick-aggregate admixtures at 4% cement content. A scanning electron microscope was used to observe the failure modes of the fiber. The influence of failure modes, such as pulling out, fracture, and plastic deformation, on the mechanical properties was expounded. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The ecology of arid mining areas in western China is facing serious problems because underground coal mining destroys overlying aquifers, causing groundwater to shift along fracture zones and groundwater levels to drop. Therefore, it is important to construct strategically coal mine goafs as underground water reservoirs to store and utilize mining-affected water resources. During the long-term operation of underground water reservoirs, the stability of coal pillar dams is affected by the repeated rise and fall of mine water levels. To understand the repeated effects of water, nondestructive water immersion, ultrasonic velocity, uniaxial compression, and acoustic emission (AE) tests were performed to study the mechanical properties and damage mechanisms of coal samples under repeated drying–saturation conditions. The ultrasonic velocity test mainly achieved two functions: selecting consistent coal samples and providing evidence of changes after each drying and saturation process. Coal samples were grouped according to the number of drying–saturation processes (DSPs) to investigate and compare the mechanical and AE parameters. The post-peak phases of full stress–strain curves present perpendicular, L-shaped, and stepped forms, among which the latter two show obvious residual strength. The AE count, cumulative AE count, and stress can jointly determine the various stages and stress thresholds of the sample failure process (or crack development process), except the boundary between elastic stage and stable crack growth stage. Multiple immersions in water reduces the fractal dimension of broken blocks; that is, the degree of fragmentation decreases and the quantity and mass of large-size blocks increase. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Large deformation has always been a focus and difficult issue in the construction of deep-buried tunnels in squeezing rock. Previous studies mainly focused on the large deformation of medium and small span railway/highway tunnels in soft ground. However, there are limited researches on the large deformation control methods for large-span (three-lane) highway tunnels constructed in unfavorable geological environment. Based on the Lianchengshan Tunnel of the Baoji-Hanzhong expressway in Shaanxi Province, China, this paper studied the deformation behaviors and mechanical mechanisms of a large-span tunnel excavated in chlorite schist formation with single primary lining method and double primary lining method by in-situ test and numerical simulation. The achieved results indicate that the double primary lining method is much more effective than that of the single primary lining method in restraining the deformation of surrounding rock, and the maximum vertical displacement and horizontal convergence are reduced by 67% and 66%, respectively. The support method of double HK200b-type steel sets combined with large-diameter foot reinforcement bolt (FRB) and deep invert could effectively control the large deformation of the case tunnel, which effectively avoided the supporting structure failure, repeated clearance invasion and multiple reshaping work caused by the single primary lining method and conformed to the energy-saving construction concept of "no clearance interfering, no support reshaping" of tunnels in squeezing ground. Simulation analysis of surrounding rock deformation, supporting structure stress and plastic zone distribution was performed to evaluate the support effect of the two deformation-controlled methods. Finally, the deformation and stress characteristic curves of rock-support of the two deformation-controlled methods were established, which revealed the supporting mechanism of double primary linings for large-span tunnels in chlorite schist. The research results can provide a theoretical basis and practical reference for the large-deformation control of similar large-span tunnels in squeezing rock. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

MgO‐based expansive additive (MEA) is uniquely used in China to compensate for the thermal shrinkage. For mass concrete, its inner temperature can soar up to 60°C due to the accumulation of hydration heat, which will strongly impact the mechanical properties and microstructures. In this paper, the impacts of elevated curing temperatures on the compressive strength developments, the tensile strengths as well as the pore structures of MEA cement mortars are investigated by means of X‐ray diffraction, scanning electron microscope, and mercury intrusion porosimetry. The results show that the external addition of MEA weakens, not eliminates, the crossover effect found in the temperature‐affected strength developments, which is mainly attributed to the accelerated expansion of MEA. For the tensile strength, the weakness of the crossover effect is found more obvious. The ratio of tensile to compressive strength is also positively correlated to the MEA content and the curing temperature. A scattered prestress effect is proposed to explain this phenomenon. The microcosmic evidence proves that the elevated temperature promotes the hydration of MEA and cement, and thereby improves the early‐age microstructures but impairs the late‐age one, which is generally consistent with the mechanical results. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• The unique mineral composition and distribution of carbonate-rich shale were revealed. • Full-scale pore structure and fractal features were characterized. • The comprehensive mechanical properties of carbonate-rich shale were analyzed. • The inner link between micro-structural and macro-mechanical properties was established. • Development strategies for carbonate-rich reservoirs were discussed. As a new growth point of shale gas production, carbonate-rich shale has recently attracted great interest. However, gas production from this reservoir was poor since the properties of the carbonate-rich shale have not been systematically studied. This is an urgent need to be addressed. Downhole cores collected from an exploration well were analyzed by micro-structure experiments (X-ray diffraction, mineral quantitative evaluation, low-pressure nitrogen adsorption, and mercury intrusion piezometry test) and macro-mechanical tests (triaxial compression, Brazilian splitting, and fracture toughness test) to obtain multiscale characterization of carbonate-rich shale. The intrinsic relationship between the microstructural and mechanical characteristics of this reservoir has been revealed. The results showed that (1) The content of carbonate minerals exceeds 30%, just slightly lower than that of quartz. Calcite has large particle sizes and is closely cemented with quartz to form a dense rock skeleton. (2) The maximum adsorption volume, specific surface area, total pore volume and average pore diameter values are poor, which is unfavorable for shale gas accumulation. Limited porosity and permeability and great tortuosity can be obstacles to the release of accumulated gas. (3) High peak deviatoric stress, Young's modulus, and Poisson's ratio were contributed by dense rock skeleton. (4) Narrow maximum main fracture width is not favorable to place proppants and further to create effective gas transport channels. (5) High tensile strength and fracture toughness enhance high breakdown and extension pressure. These comprehensive insights are of great significance for both the exploration and development of carbonate-rich shale reservoirs. [ABSTRACT FROM AUTHOR]

The mechanical properties of the viscoelastic damper made of high damping rubber produced in China are investigated in order to provide the basis for its application. At first, the test on material properties of high damping rubber is conducted. The Mooney–Rivlin model, the Yeoh model and the Prony series are applied for simulating the nonlinear behavior of the high damping rubber with the aid of software ABAQUS. Then, three viscoelastic dampers with different sizes are tested under cyclic loading. The effects of strain amplitude and loading frequency on hysteretic behavior of dampers are analyzed. Viscoelastic dampers possess large deformation capability, stable energy-dissipation capacity and good fatigue-resisting property. The effect of strain amplitude is much more significant than loading frequency. The hysteretic behavior of the dampers is simulated by the Bouc–Wen model and the model of the equivalent stiffness and damping, respectively. The prediction results by using the Bouc–Wen model are in good agreement with the experimental results, which indicates that the Bouc–Wen model is applicable to simulate the mechanical properties of high damping viscoelastic dampers with a wide range of shear strain. As to the model of equivalent stiffness and damping, it has the advantages of clear concept and simple calculation. However, the good accuracy of prediction can be obtained only when the shear strain is not greater than 60%. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive review on the mechanism of pore formation, mechanical properties, and applications of metallic porous materials. The different manufacturing techniques of metallic porous materials using various pore-forming agents (e.g., sodium chloride, polymethyl methacrylate, magnesium, and cenosphere) are highlighted in the first part of this review. Subsequently, the pore formation mechanismand pore morphology in final products as well as corresponding pore-forming agent removal techniques (e.g., sintering-dissolution process, thermally stimulated decomposition, thermally melted elimination, and embedding cenosphere technique) are specifically discussed. Then, some major influential factors on the mechanism of pore formation, including pore size, shape, distribution, and porosity, are analyzed in detail. Meanwhile, the primary mechanical properties such as compressive strength, elastic modulus, fatigue properties, and flexural strength of metallic porous materials depending on pore morphology and porosity are explored in detail. Furthermore, their applications in structural and functional aspects according to their pore morphology and mechanical properties are emphatically summarized. Finally, this review article highlights some important factors for advanced wear-resistant tool and biomedical implant applications of porous metallic materials. [ABSTRACT FROM AUTHOR]

The properties of oriented bamboo scrimber boards (OBSB) have been investigated at three density levels (0.8, 0.9, and 1.0 g cm³), while the boards were made from moso bamboo (Phyllostachys pubescens ) grown in Taiwan (T-OBSB) and China (C-OBSB). A nondestructive technique (NDT), ultrasonic-wave velocity (Vu) measurements were applied and the dynamic modulus of elasticity (MOEdyn) was calculated. Moreover, static modulus of elasticity (MOE), modulus of rupture (MOR), profile density distribution, internal bond strength (IB), springback (SB), and dimensional stability were determined based on traditional methods. Positive linear relationships between density and Vu, MOEdyn, MOE and MOR were observed, no matter if the measurements were done parallel (//) or perpendicular ( ⊥ ) to the fiber direction of the OBSBs. Moreover, Vu (//), MOEdyn,u(//), MOE (//), and MOR(//) were higher than Vu(⊥), MOEdyn,u(⊥), MOE(⊥) and MOR( ⊥). C-OBSB had slightly lower Vu (//), Vu(⊥), MOEdyn,u(//) and DMOEu(⊥) values than T-OBSB. T-OBSB had higher MOE(//), MOE(⊥) and MOR(//) than C-OBSB, but less MOR(⊥). The profile density distribution of high-density T-OBSB showed significant data scattering. The profile density distribution of C-OBSB was homogeneous at all density levels. IB and SB data are directly proportional to density, but water absorption, thickness swelling and volumetric swelling are inversely proportional to density. T-OBSB has better bonding and strength properties, and dimensional stability than C-OBSB. [ABSTRACT FROM AUTHOR]

Continental shale is abundant with unconventional oil and gas and has considerable potential for exploitation. However, due to differences in the deposition environment, continental shale presents unique characteristics in terms of mineralogy and mechanical properties compared to marine shale. Furthermore, the mechanical influence of fracturing fluid immersion must be considered because of the dual effects on the productive shale system caused by fracturing fluids remaining in the formation. In this study, tri-axial compression tests were performed on Jurassic continental shale specimens collected from an exploratory well (2778–2816 m deep) in the Sichuan Basin of China before and after exposure to fracturing fluids. Meanwhile, two quantitative indicators, the roughness R , which characterizes the widely distributed yield deformation, and the complexity F , which evaluates the complex multi-fractures, were used to distinguish the different brittle-plastic characteristics of specimens before and after fracturing fluid immersion. The results showed that the immersion of fracturing fluids weakened the mechanical properties of continental shale. Two types of fracturing fluid immersion effects were distinguished by the statistics of the failure characteristics of the different layers: lubrication-dominated and softening-dominated. Unlike conventional smooth tri-axial stress-strain curves, many of the post-peak curves were in a 'step-like' shape, corresponding to two sources: one part came from the formation of multi-fractures (brittle characteristics), and the other part came from the softening deformation of main failure surface (plastic characteristics). A new brittleness index, BI new , was proposed considering failure characteristics with different brittleness effects, which could effectively distinguish the brittleness difference before and after exposure to fracturing fluids. • Mechanical variations of continental shale along longitudinal profile were studied. • Different effects of fracturing fluids were distinguished by failure characteristic. • Different sources of additional energy dissipation were recognized. • New brittleness index was proposed incorporating different failure characteristics. [ABSTRACT FROM AUTHOR]

Agricultural plastic films have caused serious plastic pollution. There are many studies that consider mechanical recycling an appropriate system for the recovery of post-consumption agricultural mulch film. The recovery effect of plastic film depends on the mechanical properties, the level of dirtiness of the post-consumption film, and the recycling process itself. In this study, the mechanical properties of four types of polyethylene plastic films with a thickness of 8, 10, 12, and 10 μm, weather-resistant, commonly used in Xinjiang cotton fields, were tested. As well as the friction coefficient between the film and soil, the cotton stalk, boll shell, and leaf with different moisture contents were measured. Then, the self-propelled straw chopping and residual film recycling combined machine collected the four types of mulch films. The results showed that the longitudinal mechanical properties of the plastic film were greater than the transversal ones, with the exception of the nominal tensile strain at break, and the tensile characteristics of the mulching film covered with soil were greater than those without soil. The dynamic or static friction coefficient between the film and the contact material had a linear relationship with the moisture content of the material. During the recycling operation, the better the mechanical properties of the plastic film, the higher the pick-up rate of the mulch film. The maximum longitudinal tensile force of 12-μm plastic film was 3.42 N, and the nominal tensile strain at break was 303.09%. The pick-up rate reached more than 93% when the 12-μm plastic film was recovered in autumn, which effectively reduced the residue of plastic film coverage in the current year. Moreover, the more soil that was present on the much film, the greater the soil content of the recycled film roll, and the stalk content also increased, but the change was small. The research provides a reference for the mechanical and the friction features of agricultural plastic film in Xinjiang, and provides a theoretical basis for the formulation of standards for film thickness and mechanical properties, as well as the design and optimization of a residual film collecting machine in the cotton field., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

An understanding of the mechanical properties of reservoir shale is of great significance for the efficient development of shale gas. Both marine and continental shale gas reservoirs in China have considerable development potential, but their different depositional environments may lead to substantial differences in their mechanical properties, which can result in production efficiency differences. In this study, nanoindentation, X-ray diffraction, backscattered electron imaging, and energy-dispersive X-ray spectroscopy were used to determine and analyze the mechanical properties and microtexture of marine and continental shale samples. The geogenesis of the microtexture of marine and continental shales and its influence on the mechanical properties were discussed. The results show that the elastic modulus of marine and continental shale samples are similar, but the hardness of latter is greater. The similar elastic modulus of the two shale samples may result from similar mineralogy. Due to differences in deposition and diagenesis, the marine shale sample forms a clay support matrix and the continental shale sample forms a rigid clastic support matrix, which results in lower hardness in the former and higher hardness in the latter. The low hardness of the shale with a clay support matrix indicates that it may be subject to more severe proppant embedment issue. The experimental results provide a useful reference for the development of these two types of shale gas reservoirs. • The micromechanical properties of Longmaxi shale and Yanchang shale were compared and analyzed. • The effect of microtexture on mechanical properties was investigated. • The geogenesis of the microtexture was discussed. • Rigid particle supported matrix is mechanically stronger and stiffer than clay supported matrix. • Watershed algorithm was used to segment mineral grain. [ABSTRACT FROM AUTHOR]

The resource utilization of the Yellow River silt is one of the key issues for the protection and management of the Yellow River in China. One of the effective methods for this goal is to prepare artificial stones using the Yellow River silt as the main raw materials. The purpose of this study is to explore the effect of calcination pretreatment on the mechanical properties of artificial stone incorporating Yellow River silt. The artificial stone was fabricated via the alkali-activation and pressure-forming method. The compressive strength and splitting tensile strength of fabricated artificial stone specimens with different alkali dosages, fly ash contents and curing ages were measured. The microstructures of alkali-activated artificial stone specimens were observed by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrum (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The results show that the mechanical properties of the artificial stone incorporating Yellow River silt can be improved obviously by calcination pretreatment. Moreover, it can be found that alkali dosages, fly ash contents and curing ages play important roles in the level of improvement on the mechanical properties. The highest compressive strength of the artificial stones at 90 days is 16.6 MPa, and the corresponding splitting tensile strength is 1.4 MPa. The main reason for the increase of strength is that calcination pretreatment facilitates the production of alkali-activated products, that is, hydration calcium silicate (C–S–H) gels. These results suggest the possibility of using calcinated Yellow River silt as reliable and economical building materials in a wide range of construction engineering applications, especially in river slope protection, flood control and other projects. [Display omitted] • Calcinated Yellow River silt was used as raw materials of artificial stone. • The most appropriate dosage of alkali was determined. • The addition of fly ash increases the maximum compressive strength to 16.6Mpa. • The main alkali-activation product is hydrated calcium silicate gel. [ABSTRACT FROM AUTHOR]

Abstract: Over the past century, fossil fuels have provided the majority of China's energy. However, their extensive utilization leads to a shortage and environmental pollution. Recently, submarine and permafrost gas hydrate deposits have been investigated as a possible clean and sustainable energy source by governmental institutions, research organizations, and energy industries in China. The primary objective of this paper is to review the potential studies pertaining to gas hydrate exploration and resource assessment, the safe and efficient exploitation of gas hydrates and the basic properties of gas hydrates. To date, there are over 20 institutions and organizations in China committed to gas hydrate investigation, among which the Guangzhou Marine Geological Survey (GMGS) and the Chinese Academy of Geological Sciences (CAGS) etc. primarily focus on gas hydrate exploration research, while the China National Offshore Oil Corporation (CNOOC) Research Center, Guangzhou Institute of Energy Conversion (GIEC) and China University of Petroleum-Beijing (CUPB) etc. concentrate on gas hydrate mining technologies. In this paper, the occurrence and exploration of gas hydrates in both permafrost regions and the continental slope of China have been determined from numerous research contributions and are presented. Moreover, the latest progress in gas hydrate fundamental studies, including hydrate phase equilibria, hydrate formation mechanisms, hydrate thermal physical properties and the acoustics and resistivity characteristics of gas hydrates are briefly reviewed, and relevant data are gathered and compared. Emphasis is also placed on gas hydrate mining technologies and gas production using depressurization methods, thermal stimulation methods or other methods. Furthermore, the security of natural gas hydrate-bearing sediments during gas production and the environmental impacts of gas hydrate are identified. With additional financial and political support and advanced research facilities, research on gas hydrates in China is progressing rapidly but is still in its early developing stage, thus, future work should be undertaken with greater diligence. [Copyright &y& Elsevier]

Abstract: A type of clayey diatomaceous earth of Pliocene Mangbang Formation (N2 m) was encountered in highway projects in the Tengchong region of Yunnan Province, Southwest China. The Tengchong clayey diatomaceous earth is characterized using multiple test methods, such as granulometric analysis, chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, shrinkage and swelling tests, unconfined or uniaxial compression test, triaxial test and direct shear tests. The chemical and mineralogical compositions, physical and hydraulic properties and engineering properties of the clayey diatomaceous earth are presented in this paper. It is revealed that the Tengchong clayey diatomaceous earth is an unusual soil or rock which has characteristics of both typical diatomaceous earth and swelling clayey soil or soft clay rock. The diatoms in the earth enhance the connection between micro-structures, and improve the mechanical properties of diatomaceous earth. However, due to the existence of a significant amount of swelling clay minerals, the Tengchong clayey diatomaceous earth becomes swelling soft rock, and is prone to engineering problems or geohazards. Based on the test results, a number of issues regarding classification, discrimination and geohazard control related with the clayey diatomaceous earth are discussed to provide both some basic understanding and new insight into the characteristics of the clayey diatomaceous earth deposits. [Copyright &y& Elsevier]

With structural steel becoming the main construction material in China, more high performance steel (HPS) is going to be applied in landmark building projects. Innovative structural systems and structural members need to be envisaged to take the advantages of HPS. The excellent properties of HPS with higher strength, moderate ductility, higher fracture toughness, better weldability, efficient machinability, can improve the structural performance significantly. The Q460 grade of structural steel has been successfully applied in the National Stadium and CCTV tower in China. It is demonstrated that the fabrication and construction efficiency of steel buildings can be improved remarkably, and economical solutions are provided by using HPS. This paper reviewed the availability of HPS in China and summarized the recent development to promote HPS in tall and large span buildings. The requirements on research to support the application of HPS in buildings are discussed. [ABSTRACT FROM AUTHOR]

Abstract: A series of investigations on the mechanical property, durability, and the structural performance of recycled aggregate concrete (RAC) have been carried out in the past 15years (1996–2011) in China. The achievements of researches on recycled concrete are relatively sufficient to review and share with investigators from other countries. Some research progress of micro- and meso-structure of RAC is introduced in the first part of this paper. The second part of this paper is devoted to the mechanical properties of RAC material: strength, elastic modulus, Poisson’s ratio, stress–strain curve. The third part of the paper gives research on durability of RAC: carbonization, chloride penetration, shrinkage and creep. The last part presents a review on the structural performance of RAC elements and structures: beams, columns, slabs, beam–column joints, shear walls as well as frames made with RAC. Results of all researches reveal that with proper design and construction, it is safe and feasible to apply RAC as a structural material in civil engineering. Moreover, in this paper, the relevant research results of RAC obtained in China and from other countries are compared and discussed. This review provides helpful directions to those who are already engaged in this research, and points out areas which are needed to promote safe and economic use of RAC. [Copyright &y& Elsevier]

Aiming at the problem that ordinary cement concrete is subjected to damage in heavy saline soil areas in China, a new type of magnesium oxychloride cement concrete is prepared by using the gelling properties of magnesium oxychloride cement in this study, and the erosion resistance of the synthesized magnesium oxychloride cement concrete in concentrated brine of salt lakes is studied through the full immersion test. The effects of concentrated brine of salt lakes on the macroscopic, microscopic morphology, phase composition and mechanical properties of magnesium oxychloride cement concrete are investigated by means of macro-morphology, erosion depth, SEM, XRD and strength changes. The salt erosion resistance mechanism of magnesium oxychloride cement concrete is revealed. The results demonstrate that under the environment of full immersion in concentrated brine of salt lakes, there is no macroscopic phenomenon of concrete damage due to salt crystallization, and the main phase composition is basically unchanged. The microscopic morphology mostly changes from needle-rod-like to gel-like. Due to the formation of a new 5·1·8 phase on the surface layer and the increase in compactness, its compressive strength has a gradual increase trend. Based on the engineering application of magnesium oxychloride cement concrete, it is further confirmed that magnesium oxychloride cement concrete has excellent salt erosion resistance and good weather resistance, which provides theoretical support for future popularization and application. [ABSTRACT FROM AUTHOR]

Antimony (Sb) is a trace element applied widely in modern industry. A large number of tailing solid wastes are left and accumulated in the mining area after purifying the precious antimony from the antimony ores, causing serious pollution to the environment. The major aim of this study is to investigate the feasibility of utilizing antimony tailing coarse aggregate (ATCA) as a complete substitute for natural coarse aggregate (NCA) in high-strength concrete. Concrete specimens with 25%, 50%, 75%, and 100% ATCA replacing the NCA in conventional concrete were prepared for evaluating the performance of ATCA concrete. The investigators find that ATCA concrete has good workability, and the mechanical properties and long-term behavior (shrinkage and creep) of ATCA concrete with all replacement levels are superior to those of NCA concrete. The durability indices of ATCA concrete, such as the frost-resistant, chloride permeability, and resistance to carbonation, are better than those of NCA concrete. While the alkali activity and cracking sensitivity behavior of ATCA concrete seem to be decreased, nevertheless, the difference is not significant and can be neglected. The researchers demonstrate that all of the control indices of ATCA concrete meet the requirements of the current industry standards of China. Overall, ATCA can be used in concrete to minimize environmental problems and natural resources depletion. [ABSTRACT FROM AUTHOR]

• The CLT bending panels fabricated with Karamatsu larch were tested. • The system effect of the CLT bending strength was analyzed. • The system strength factor of the CLT consisting of different longitudinal laminas in its outermost layer was calculated. • The bending strength or the flexural modulus of the Karamatsu larch CLT was evaluated. Cross-laminated timber (CLT) is recognized as a code-compliant construction material, which is commonly used as bending members (e.g., floor diaphragm and roofs) of mid- and high-rise timber structures. For one CLT bending panel that performs as an orthotropic plate, its transverse laminas can be regarded as a continuous load-distribution system, which connects the equally spaced longitudinal laminas. Therefore, for one CLT panel with more longitudinal laminas in its outermost layers, a higher bending strength might be resulted in due to the system effect, which is denoted by the system strength factor. In this study, for investigating the system effect of CLT panels, bending tests were conducted on 3-layer non-edge-glued CLT panels, which consisted of 3 longitudinal laminas, 5 longitudinal laminas, and 7 longitudinal laminas in their outermost layers, respectively. All the CLT were fabricated with the Karamatsu larch grown in China, which can be served as a potential wood species for CLT manufacturing. Then, their bending resisting properties and failure modes were analyzed. The bending strength or the flexural modulus of the Karamatsu larch CLT was evaluated. Finally, the system effect of the CLT bending strength was analyzed; the system strength factor for the CLT with 3 laminas, 5 laminas, and 7 laminas in its outermost layers was calculated, respectively. Results show that the CLT will provide more stable bending properties, whilst be more prone to the rolling shear failure in its transverse laminas, when the number of the outermost longitudinal laminas enhances. The system effect exists for the CLT bending strength; for the Karamatsu larch CLT consisting of 3 longitudinal laminas, 5 longitudinal laminas, and 7 longitudinal laminas in its bottom layer, the corresponding system strength factor can be approximated as 0.570, 0.720, and 0.920, respectively. [ABSTRACT FROM AUTHOR]

• A feasible technical route for utilizing deposited BOFSS in concrete is proposed. • The replacement ratio of BOFSS coarse (SSCA) and fine (SSFA) aggregates is optimized. • Improvement in compressive strength of concrete is achieved with an optimum replacement ratio of SSCA and SSFA. • BOFSS can significantly improve the interfacial transition zone (ITZ) of concrete. As an industrial by-product of steel manufacturing, steel slag would cause severe farmland occupation, water pollution and other environmental issues. It can be further categorized into basic oxygen furnace (BOF), electric arc furnace and ladle furnace slags, in which BOF steel slag (BOFSS) accounts for nearly 70% of the total steel slag production in mainland China. Therefore, massive consumption of BOFSS in reasonable fields is of unprecedented significance for resource recycling and environmental conservation. In this paper, BOFSS was adopted to replace coarse and fine aggregates of ordinary concrete to produce "Greener" concrete. A total of 15 concrete mixes with different replacement ratios of coarse and fine aggregates using BOFSS were designed, the mechanical property and microstructure (mercury intrusion porosimetry and scanning electron microscope tests) of which were studied. Results revealed that the optimum replacement ratios of coarse and fine aggregates were 50% and 30%, respectively. With these ratios, the later-age compressive strength and microstructure of concrete could be significantly improved. Therefore, it is concluded that the use of BOFSS in concrete not only benefits the environmental protection and material greenness, but also improves the behavior of concrete, which provides a win-win solution. [ABSTRACT FROM AUTHOR]

To rationally use low-grade phosphorous limestone as the raw materials for cement production, the influence of phosphorous introduced by fluorapatite during the clinker calcination process on the mechanical properties of cementitious materials is investigated. Hydration kinetics, phase evolutions, and microstructure of cement pastes have been studied by using calorimetry, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicate that the mechanical properties of cementitious materials can be slightly improved due to the mineralization effect of the small amount of phosphorous in the clinker and significantly decreased with an increase of phosphorous. High content of phosphorous will reduce the content of C3S and make the formation of α′-C2S-xC3P(x: 0–0.05), whose hydration reactivity is rather lower, such that on the one hand less-hydrated products, such as calcium silicate hydrate (C-S-H) gel, can be obtained, and on the other hand, the hydration reaction will be slowed by severely prolonging the induction period. Interestingly, small particles can be observed on the surface of hydration products, but no new phase can be detected by XRD. When the content of P2O5 is 2.0%, the cement can meet the requirements of P·II 42.5 cement in China. Hopefully, this can provide significant guidance for the use of cement prepared by fluorapatite as raw material. [ABSTRACT FROM AUTHOR]

Understanding fundamental aspects of the effects of water on both the mesostructure and mechanical characteristics of coal and coal-water interactions is important for increasing the utilization of coal and has not been thoroughly addressed by researchers. To fill this gap, a series of laboratory tests were carried out systematically using coal from the Tashan Coal Mine in China; both untreated samples and samples soaked for 3 h, 6 h, 12 h, 24 h, 36 h, 2 d, 4 d, 10 d, and 20 d. The water absorption characteristics, pore structure, mineral composition, surface morphology and wave velocities of the coal samples that varied with water-soaking time were studied comprehensively by using nuclear magnetic resonance, X-ray diffraction, scanning electron microscopy and ultrasonic testing. In addition, the mechanical properties, i.e., uniaxial compressive strength σ u and elastic modulus E , and the deformation and failure characteristics of the coal under different water-soaking periods were obtained by conducting uniaxial compression tests. The parameters of the water infusion techniques were also analyzed to address the hard coal roof of the Tashan coal mine. The results showed that as the water soaking time increased, the average pore sizes expanded and new pores developed; the pore types changed from micropores to mesopores to macropores. Longer water immersion led to not only greater pore connectivity and coal permeability but also changes in the mineral composition and structural characteristics. In addition, the velocity of the ultrasonic longitudinal wave first increased with seepage, enabling moisture to fill the macropores, and then decreased after 4 d due to the water wedge effect. Moreover, both σ u and E decreased and could be expressed by exponential functions in terms of soaking time; after 20 d, σ u and E decreased by 21.9% and 28.53%, respectively. The appropriate water infusion time and distance for advance were suggested to be 10–15 d and 60–90 m, respectively. [ABSTRACT FROM AUTHOR]

In order to study the evolution of the mechanical properties and macromolecular structures in different macerals of tectonically deformed coal (TDC), vitrinite and inertinite samples were handpicked from six block TDCs in the same coal seam with an increasing deformation degree (unaltered, cataclastic, porphyroclast, scaly and powdery coal). The micro mechanical properties were tested by the nanoindentation experiment and the macromolecular structures were measured using 13C nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The results show that the range of hardness and elastic modulus of inertinite is 0.373–1.517 GPa and 4.339–12.158 GPa, respectively, which is significantly higher than that of vitrinite with values of 0.278–0.456 GPa and 4.857–7.810 GPa, respectively. From unaltered coal to powdery coal, the hardness of vitrinite and inertinite gradually decreases, with the difference between these macerals becomes smaller and the elastic modulus of vitrinite shows an increasing trend, while that of inertinite was more variable. Both the NMR and FITR results reveal that the macromolecular structure of inertinite has similar structural transitions as vitrinite. As the degree of deformation increases, the aliphatic side chains become shorter and the aromaticity is increasing. Macromolecular alterations caused by tectonic stress is expected to produce defects in the TDCs, therefore there should be more interspacing among the macromolecular groups for the extrusion of macromolecules caused by the indenter of the nanoindentation experiment, thereby reducing the hardness. The elastic modulus of coal is believed to be related to intermolecular forces, which are positively correlated to the dipole moment. By calculating the dipole moments of the typical aromatic molecular structures with aliphatic side chains, the detachment of the aliphatic side chains and the growth of benzene rings can both increase the dipole moment, which can promote elastic modulus. In addition, the increasing number of benzene rings can create more π-π bonds between the molecules, which can lead to an increase in the intermolecular forces, further increasing the elastic modulus. [ABSTRACT FROM AUTHOR]

Slip zone soil is usually composed of clay or silty clay; in some special geological environments, it contains gravels, which make the properties of the slip zone soil more complex. Unfortunately, in many indoor shear tests, gravels are removed to meet the demands of apparatus size, and the in situ mechanical property of the gravelly slip zone soil is rarely studied. In this study, the shear mechanical property of the gravelly slip zone soil of Huangtupo landslide in the Three Gorges Reservoir area of China was investigated by the in situ shear test. The test results show that the shear deformation process of the gravelly slip zone soil includes an elastic deformation stage, elastic–plastic deformation stage, and plastic deformation stage. Four functions were introduced to express the shear constitutive model of the gravelly slip zone soil, and the asymmetric sigmoid function was demonstrated to be the optimum one to describe the relationship of the shear stress and shear displacement with a correlation coefficient of 0.986. The comparison between the in situ test and indoor direct shear test indicates that gravels increase the strength of the slip zone soil. Therefore, the shear strength parameters of the gravelly slip zone soil obtained by the in situ test are more preferable for evaluating the stability of the landslide and designing the anti-slide structures. [ABSTRACT FROM AUTHOR]

Organic-rich shale in Sichuan Basin of China preserves tremendous oil and gas resources, one important type of which is the continental shale gas. Owing to the special lacustrine depositional environment, continental shale showed strong heterogeneity in longitudinal profile and had not been fully characterized. Using the cores of an exploratory well within Lower Jurassic continental shale formation, rock mechanical experiments, including tri-axial compression, Brazilian splitting and fracture toughness, were performed systematically. Basic mechanical parameters of the entire reservoir section were acquired at the first time. Reservoir brittleness was also evaluated by a newly proposed method based on complete stress-strain curve. Results showed that mineral compositions exhibited a feature of wide fluctuation in longitudinal profile, with the good gas-bearing layers (D1-3, D1-4) containing high content of clay minerals, 63.93% and 59.67%, respectively. Mechanical parameters from tri-axial compression tests also showed noteworthy difference in longitudinal section. With increasing confining pressure, the dispersion reduced to a certain extent, but was still obvious. The newly proposed brittleness index could reasonably reflect the influence of buried depth and lithology difference. Formation brittleness tended to reduce with increasing confining pressure. Layers of D1-3 and D1-4 still maintained relatively high brittleness at high confining pressure. The biggest brittleness reduction occurred in the interlayer of shelly limestone. Tensile strength and type-Ⅰ fracture toughness at various depths exhibited high dispersion. The anisotropy was also obvious, with the values in vertical direction generally higher than those in horizontal orientation. The experimental findings would provide a basis for the optimum design of reservoir stimulation in this area. • Systematic rock mechanical tests were conducted for an exploratory continental shale gas well in Sichuan Basin. • Mechanical properties of continental shale exhibited noteworthy difference in longitudinal profile. • The newly proposed brittleness index could reasonably reflect influence of buried depth and lithology difference. • Tensile strength and fracture toughness also showed strong anisotropy in vertical and horizontal direction. [ABSTRACT FROM AUTHOR]

• Innovative preparation of CSA cement entirely with FGD gypsum providing the CaO. • Decomposition characteristics of FGD gypsum in CSA clinker preparation were elaborated. • Properties of CSA cement made from FGD gypsum were investigated. Flue gas desulfurization (FGD) gypsum is an industrial by-product of the desulfurization process. The gross product of FGD gypsum has reached 550 million tons in China by 2016 and quite a portion was discarded. The purpose of this study is to investigate the feasibility of an innovative concept of producing the CSA cement based on sulfur recovery and entirely made of the FGD gypsum to replace natural gypsum and limestone as CaO and SO 3 sources. A mixture of industrial solid waste was calcined under different calcination conditions to study the decomposition behavior of FGD gypsum and properties of CSA cement made from the FGD gypsum. Experimental results show that it is feasible to use the FGD gypsum to entirely supply the CaO and SO 3 of this cement, the optimized calcination temperature is between 1270 and 1310 °C, and the suitable retention time is 60–100 min. The highest compressive strengths of 63.3, 85.3, 102.8 MPa were attained at 1, 3, and 28 d, respectively when the temperature was kept at 1310 °C for 60 min. Results also indicate that the FGD gypsum decomposition, which is mainly influenced by calcination temperature, retention time and alumina–silica ratio, has a significant impact on the clinker mineral phase formation. The novel technical idea developed in this research can greatly improve the utilization of FGD gypsum and may reduce about 50% of CO 2 emission in routine production. [ABSTRACT FROM AUTHOR]

This study investigated the microstructural stability and mechanical properties exhibited by China low activation martensitic (CLAM) steels with different yttrium (Y) contents over 3000 h of aging at 550 °C. Scanning electron microscopy, electron backscatter diffraction analysis, and transmission electron microscopy were employed to investigate the microstructural evolution of the steels. Results indicated that grain boundary migration was slow and the Laves phase precipitation was delayed in Y-containing steels. Grain boundaries at different angles in 0Y and 6Y CLAM steels were significantly affected, and those in 36Y and 71Y alloys exhibited negligible changes during the long-term thermal aging. Moreover, Y contents had appreciable effects on the strength and toughness of the aged steels. The stable microstructure of Y-containing CLAM alloys is responsible for improved strength and impact toughness during aging. [ABSTRACT FROM AUTHOR]

Given that normal filling technology generally cannot be used for mining in the western part of China, as it has only a few sources for filling gangue, the feasibility of instead using cemented filling materials with aeolian sand as the aggregate is discussed in this study. We used laboratory tests to study how the fly ash (FA) content, cement content, lime–slag (LS) content, and concentration influence the transportation and mechanical properties of aeolian-sand-based cemented filling material. The internal microstructures and distributions of the elements in filled objects for curing times of 3 and 7 days are analyzed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The experimental results show that: (i) the bleeding rate and slump of the filling-material slurry decrease gradually as the fly ash content, cement content, lime–slag content, and concentration increase, (ii) while the mechanical properties of the filled object increase. The optimal proportions for the aeolian sand-based cemented filling material include a concentration of 76%, a fly ash content of 47.5%, a cement content of 12.5%, a lime–slag content of 5%, and an aeolian sand content of 35%. The SEM observations show that the needle/rod-like ettringite (AFt) and amorphous and flocculent tobermorite (C-S-H) gel are the main early hydration products of a filled object with the above specific proportions. After increasing the curing time from 3 to 7 days, the AFt content decreases gradually, while the C-S-H content and the compactness increase. [ABSTRACT FROM AUTHOR]