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• The pressurizing rate model considering the physical properties of CO 2 is proposed. • A novel breakdown pressure model considering fluid infiltration effect is proposed. • The low viscosity and pressurization rate of CO 2 decreases breakdown pressure. • Influence of the pore pressure distribution on breakdown pressure is analyzed. • The pressurization rate affects breakdown pressure at different injection rates. Precisely predicting the breakdown pressure of rock fractured by supercritical CO 2 (SC-CO 2) is one of the major challenges for optimize in-situ fracturing schemes. However, the influence of the infiltration effect caused by the unique properties of SC-CO 2 on the fracture mechanism remains unclear, which may lead to inaccurate prediction of breakdown pressure. In this work, a pressurization rate model considering the physical properties changes of SC-CO 2 is proposed to describe the relationship between the pressurization rate and the injection pressure of the fracturing fluid in a wellbore. Ultimately, combined with the pressurization rate model and the point stress criterion, a breakdown pressure model is established by considering the changes in the in-situ stress of wellbore surrounding rock, the fluid injection pressure inside the wellbore, and the pore pressure distribution. The results show that for permeable reservoirs, the breakdown pressure increases as the viscosity and injection rate of fracturing fluid increase, but it decreases with increasing rock permeability. The low viscosity and pressurization rate of SC-CO 2 effectively increase the stress generated by the infiltration effect, which is negatively correlated with the breakdown pressure. In addition, the unique pressurization rate of SC-CO 2 is the key factor for the abnormal breakdown pressure at different injection rates. [ABSTRACT FROM AUTHOR]

Abstract As a simple supporting structure, rockbolts are responsible for maintaining the integrity and stability as well as controlling the deformation, displacement, and crack development in the surrounding rock mass. Knowledge of rockbolt load-transfer behaviors constitutes valuable information, as the rockbolt functionality is affected by load-transfer processes. A series of pullout tests was conducted on a rockbolt with a long embedment length (1500 mm). The critical rockbolt embedment length at which yielding or necking occurs together with the friction coefficient at the residual axial stress was analyzed numerically. Additionally, the failure modes of rockbolt-grouted systems and the effects of several parameters, including the rockbolt diameter (18, 20, and 25 mm) and cement mortar strength, were assessed. The rockbolt strain and energy absorption during the pullout process were also investigated. The identified rockbolt failure modes, which are dependent on the cement mortar strength and rockbolt diameter, include pullout accompanied by partial concrete splitting failure parallel to the rockbolt. Under the same cement mortar strength, the maximum load increases and the rockbolt displacement at the maximum load decreases as the rockbolt diameter increases. When diameter is held constant, the maximum load and corresponding displacement increase as the cement mortar strength increases, but the residual load is irregular. The energy absorbed by the rockbolt in the pullout test is related to the cement mortar strength and failure mode. With an increasing embedment length, the failure process is converted from a completely damaged interface with little simultaneous damage to the cement mortar at the free end to the expansion of the cracks at the loaded and free ends toward each other. The interface is completely damaged when the cracks at both ends become connected. [ABSTRACT FROM AUTHOR]

Abstract The reliable prediction of excavation responses for squeezing rock remains a challenging issue in rock engineering. This paper presents a numerical procedure for a strain-softening rock mass around highly deformed circular opening based on the finite strain theory, so the overall elasto-plastic analysis is a Lagrangian method which focuses on the motion of each material point and is well suited for the problems involving large deformation. The influence of axial in-situ stress is considered by introducing the initial axial stress into the elastic constitutive equations, and the axial plastic flow is realized by redefining the plastic internal variable and considering different stress distributions in the plastic zone. Thus, the numerical procedure enables prediction of the rock deformation and squeezing potential in a more rational and rigorous manner. The capability of the method for estimating the small strain and squeezing deformation is verified by being compared with the existing analytical results and the field measuring data. Negligence of the axial in-situ stress or the axial plastic flow underestimates the rock deformation, and the induced deviation essentially depends on the post-peak constitutive relation and the rock heterogeneity after rock yields. The higher level of the material homogeneity in the plastic zone, the lower effects of the axial in-situ stress on the rock responses. The stress distribution and strain-softening behavior of surrounding rock can be significantly affected by the axial in-situ stress and the critical plastic internal variable η *. Tunnel instability is independent of large deformation for the high η * but is closely associated with the squeezing problem when η * is small. As η * decreases, both of the plastic radius and wall convergence increase initially and remain constant afterwards. Lastly, the paper investigates the rock responses and ground-support interaction when the small strain theory is applied on the squeezing rock. [ABSTRACT FROM AUTHOR]

Highlights • The FBGs were used to measure CTB temperature and internal strain evolution. • In the liquid stage, the binder content had no effect on settlement behavior. • CTB internal strain was influenced by combined chemical and thermal effects. • No significant change occurred in settlement and strain in the hardened stage. Abstract The philosophy of the use of backfill is to return much of tailings waste to underground voids and increase working place stability to safely extract more minerals. The key issue for the safe and efficient design of cemented tailings backfill (CTB) structure is its mechanical properties and interaction with the surrounding rock. As a cemented material, CTB's strength is a function of hydration degree. As hydration is an exothermic reaction and results in net volume reduction, thermal expansion and chemical shrinkage occur simultaneously in the mixture. Each CTB component plays a significant role during this process and the most important factor is the binder content, because it influences the amount of cement hydration products that provide binding phases between tailing particles. In this paper, a number of fiber Bragg gratings (FBGs) were directly embedded into the 7-day cured CTB specimens to measure their temperature and internal strain evolution, with settlement development measured by Linear Variable Differential Transformer (LVDT). The experimental results showed that binder content had a significant effect on CTB temperature and internal strain evolution. Furthermore, the evolution of internal strain and settlement was an indicator of the transformation in different stages (such as fluid, skeleton formation and hardening) during the hydration process. [ABSTRACT FROM AUTHOR]

During the injection of CO 2 into coalbed for geologic sequestration, CO 2 is likely both adsorbed and dissolved in coals, and swells them slightly. When coal is swollen due to the adsorption and dissolution, the induced strain is relieved as the coal structure rearranges to a lower free energy state, causing coal damage and resulting in permeability change. This adsorption- and dissolution- induced coal damage is usually ignored in the permeability model, even though this kind of damage has been observed and detected in the past CO 2 injection experiments. In a previous study we generated a sequence of coal permeability profiles from the “V” shape as observed in experiments through a newly dual-permeability model. Based on this work, in this paper, the dual-permeability model is extended to take the coal damage induced by gas adsorption and dissolution into account according to the principle of damage mechanics, and this model is used to examine the permeability evolution during the injections of different gases, including CO 2 , CH 4 and N 2 , into coal specimen. Numerical simulation indicates that the model predicts well the permeability increase during the high injected gas pressure. In addition, since the highest gas adsorption into coal occurs for CO 2 , the coal permeability during CO 2 injection decreases most pronounced, in contrast, the permeability reduction during N 2 injection is the smallest. Also, it is confirmed that the adsorption-induced coal damage is dominated by tensile damage of coal during the injection of CO 2 . [ABSTRACT FROM AUTHOR]

• Chloride salts' effects on strength, hydration and microstructure of CTB were studied. • The influence of chloride salts is highly dependent on their cation type. • NaCl slightly weakens CTB's strength due to the C-(A)-S-H decalcification. • CaCl 2 promotes slag hydration and thus improves the CTB's microstructure and strength. • MgCl 2 inhibits slag dissolution due to the reaction between Mg2+ and OH–, markedly lowering CTB's strength. For mines located in saline areas, the use of mine water containing chloride salts to prepare cemented tailings backfill (CTB) for mined-out area treatment can realize the resource utilization of mine water and save a large amount of precious freshwater. However, the hydration behavior of binder and strength properties of CTB in the presence of chloride salts is still not well understood. This research investigates the effects of NaCl, CaCl 2 and MgCl 2 with different Cl- concentrations (0.50, 0.77 and 1.0 mol/L) on strength of CTB prepared with one-part alkali-activated slag binder. It analyzes the hydration process of binder and the microstructure of CTB. The results indicated that the decalcification of C-A-S-H (replaced by sodium to create N(C)-A-S-H at high Na+ concentrations) leads to numerous 0.01–0.1 μm micropores within the hardened backfill, increasing porosity while decreasing strength by 3.2–25.0%. Calcium ion (Ca2+) contributes to the formation of dense internal structures and high-strength backfill. Magnesium ion (Mg2+) reduces alkalinity by consuming Ca(OH) 2 , seriously impacts slag decomposition, but accelerates the dissolution of desulfurized gypsum. The study's findings will help the application of chloride-containing mixing water in mines situated in saline regions. [ABSTRACT FROM AUTHOR]

The 3D reconstruction of rock joint surfaces is crucial for quantifying rock joints. Through the uniform discretization of 2D and 3D rock joints, it was determined that both the climbing angles along the shear direction and the projection lengths of the consecutive ascending/descending segments follow normal distributions. This statistical distribution of climbing angles and projection lengths provides an important reference for rock joint reconstruction, although hypothesis testing indicated that some joint profiles/surfaces do not follow normal distributions. A normal distribution-based method and a bubbling method were used to reconstruct the 2D joint profiles. The bubbling method demonstrated good applicability for the generation of 3D rock joint surfaces, especially because it included surfaces with different roughness in two orthogonal directions. Therefore, ten typical 3D rock joint surfaces were reconstructed using the bubbling method, where both the size of asperities (waviness or unevenness) and the joint roughness coefficient values were quantified. To reconstruct a joint surface with a certain roughness coefficient, scaling the elevation of a generated surface was demonstrated as an effective supplementary approach. • Rock joints were statistically analyzed via normal distributions owing to a uniform discretization operation. • The normal distribution-based method and the bubbling method were both suitable for reconstructing 2D joint profiles. • The bubbling method could generate 3D joint surfaces with different roughness in two orthogonal directions. • Rock joints with different joint roughness coefficients were reconstructed by scaling their elevation coordinates. [ABSTRACT FROM AUTHOR]

[Display omitted] • A plastic-damage method considering inelastic behavior is developed to predict GRC. • Damage-induced inelastic response is significant for strain-softening rock mass. • The preliminary critical support pressure for the residual failure zone is given. During opening construction, the accumulated wall displacement and the developing excavation damaged zone are the results of stress redistribution and inelastic behavior induced by both the microcracking damage and the irreversible plastic deformation. The current approach to predict ground response to excavation disturbance is usually based on the Convergence-Confinement Method, which fails to consider the rock damage and the plastic-damage coupled mechanism, resulting in inaccurate estimation of rock deformation, particularly in the case of the weak rock with high deformability. This study establishes a plastic-damage theoretical approach for a circular opening by a kinematic decomposition of strains into an elastic, plastic and damage parts within the framework of finite strain using a hypoelastic–plastic theory, in order to investigate the inelastic behavior-induced excavation response. In this regard, the damage model provides the effective stress to the plasticity model defining the yield criterion, in combination with the strength-stiffness degradation and damage evolution. The numerical implementation is given and two examples are considered for validation. Extensive works are then carried out to clarify some issues, including the capacity of the model to characterize the inelastic behavior, the role of rock damage and confining stress dependence on ground response, and the preliminary critical support pressure for the residual failure zone. [ABSTRACT FROM AUTHOR]

Abstract: The rational integration of conductive nanocarbon scaffolds and insulative sulfur is an efficient method to build composite cathodes for high-energy-density lithium–sulfur batteries. The full demonstration of the high-energy-density electrodes is a key issue towards full utilization of sulfur in a lithium–sulfur cell. Herein, carbon nanotubes (CNTs) that possess robust mechanical properties, excellent electrical conductivities, and hierarchical porous structures were employed to fabricate carbon/sulfur composite cathode. A family of electrodes with areal sulfur loading densities ranging from 0.32 to 4.77mgcm−2 were fabricated to reveal the relationship between sulfur loading density and their electrochemical behavior. At a low sulfur loading amount of 0.32mgcm−2, a high sulfur utilization of 77% can be achieved for the initial discharge capacity of 1288mAhgS −1, while the specific capacity based on the whole electrode was quite low as 84mAhgC/S+binder+Al −1 at 0.2C. Moderate increase in the areal sulfur loading to 2.02mgcm−2 greatly improved the initial discharge capacity based on the whole electrode (280mAhgC/S+binder+Al −1) without the sacrifice of sulfur utilization. When sulfur loading amount further increased to 3.77mgcm−2, a high initial areal discharge capacity of 3.21mAhcm−2 (864mAhgS −1) was achieved on the composite cathode. [Copyright &y& Elsevier]

Abstract: The Li–S battery is with a much greater theoretical energy density than those of conventional lithium ion batteries. The key to achieve a high performance electrode for Li–S battery lies in the arrangement of the building blocks into a well-designed structure, in which the nanocarbon framework not only acts as an electronic conduit to the encapsulated active materials but also serves as a mini-electrochemical reaction chamber. Therefore, a nanocomposite with sulfur entrapped into hierarchical porous graphene was proposed and fabricated for Li–S batteries. The nanocomposite electrode exhibits high discharging capacitance of 1068 and 543mAhg−1 at a current density of 0.5 and 10C, respectively. The discharging capacity of 386mAhg−1 can be presented at ultra-low temperature of −40°C, which far exceeds the operating range of conventional lithium-ion batteries. The large scale produced hierarchal graphene was mainly decorated with epoxy and hydroxyl groups, which can enhance the binding of S to the C–C bonds due to the induced ripples by the functional groups. These results provided a promising electrode material for energy storage device with high capacitance, which is important for the increasing demands of power sources in cold environments, such as battery systems for electric vehicles in cold zone or for aeronautic applications. [Copyright &y& Elsevier]

Abstract: Toward the efficient and cost effective synthesis of three-dimensional hierarchical architectures at mild condition and their potential applications in environmental protection, the materials chemistry for green synthesis of strontium carbonate (SrCO3) superstructures and their application as adsorbents for methylene blue solution and heavy metal ions were explored. Uniform hierarchical mesoporous SrCO3 microspheres with a narrow diameter distribution were synthesized via a mild hydrothermal treatment (110°C, 6.0h) of the slurry derived from the room temperature coprecipitation of SrCl2 and Na2CO3 solution, in the presence of ethylenediaminetetraacetic acid (EDTA). The as-synthesized mesoporous SrCO3 microspheres had a specific surface area of 56.3m2 g−1 and a narrow pore size distribution concentrating on 2–20nm, with an average pore diameter of 9.45nm. The introduction of EDTA in due case with tuned pH value was favorable for the formation of SrCO3 microspheres, whereas the mild hydrothermal treatment promoted the morphology uniformity of the mesoporous microspheres with narrow diameter distribution. The adsorption evaluation indicated that the present mesoporous SrCO3 microspheres exhibited excellent adsorption performance for deionized (DI) water containing methylene blue, or heavy metal ions such as Fe3+ and Pb2+, revealing the as-synthesized uniform hierarchical mesoporous SrCO3 microspheres as potential adsorbents with wide applications in environmental protection. [Copyright &y& Elsevier]

Abstract: Micro/nanostructured nickel borate (Ni3(BO3)2) has been widely explored as advanced materials for energy conversion and non linear optical applications, fabricating one-dimensional micro-/nanostructures of Ni3(BO3)2 has thus become increasingly necessary. In this contribution, pure phase of rod-like micron Ni3(BO3)2 particles were synthesized via a facile flux NaCl and surfactant poly(oxyethylene)9 nonylphenol ether (NP-9) assisted thermal conversion route at 750–800°C for 2.0h. The introduction of NaCl and NP-9 was favorable for the formation of the Ni3(BO3)2 particles with rod-like morphology and smaller size, respectively. When calcined at 750°C in the presence of 8.0mL of NP-9 and with the molar ratio of Ni:B:Na=3:8:3, high aspect ratio rod-like micron Ni3(BO3)2 particles were obtained. The FT-IR and UV–vis properties of the as-synthesized Ni3(BO3)2 particles were also presented. The as-synthesized Ni3(BO3)2 rod-like particles further enlarged the metal borate family, with corresponding potential applications in the areas of nanocomposites, catalysis, energy conversion and storage, etc. [Copyright &y& Elsevier]

Abstract: Uniform high crystallinity short belt-like Ca2B2O5·H2O nanostructures (nanobelts) were facilely synthesized through a room temperature coprecipitation of CaCl2, H3BO3, and NaOH solutions, followed by a mild hydrothermal treatment (180°C, 12.0h). By a preferential growth parallel to the (100) planes, Ca2B2O5·H2O nanobelts with a length of 1–5μm, a width of 100–400nm, and a thickness of 55–90nm were obtained. The calcination of the nanobelts at 500°C for 2.0h led to short Ca2B2O5 nanobelts with well preserved 1D morphology. Calcination at 800°C led to a mixture of Ca2B2O5 and Ca3B2O6. The products were with belt-like and quasi-polyhedron morphology, while they turned into pore-free micro-rod like and polyhedron morphology when the calcination was taken in the presence of NaCl. NaCl assisted high temperature calcination at 900°C promoted the formation of Ca3B2O6 in the products. When dispersed in deionized water or absolute ethanol, the Ca2B2O5·H2O nanobelts and Ca2B2O5 nanobelts showed good transparency from the ultraviolet to the visible region. The as-synthesized Ca2B2O5·H2O and Ca2B2O5 nanobelts can be employed as novel metal borate nanomaterials for further potential applications in the area of glass fibers, antiwear additive, ceramic coatings, and so on. [Copyright &y& Elsevier]

Abstract: Uniform orthorhombic Li3B5O8(OH)2 micro-rods were hydrothermally synthesized at 150–210°C for 6.0–24.0h, using LiOH·H2O and H3BO3 as the reactants. The resulting Li3B5O8(OH)2 micro-rods had a length of 20–60μm, an aspect ratio of 6–14, and a high crystallinity. The presence of hexadecyl trimethyl ammonium bromide was favorable for the oriented growth of the Li3B5O8(OH)2 micro-rods. The orthorhombic Li3B5O8(OH)2 was decomposed into Li2B4O7 and α-LiBO2. Pore-free high crystallinity Li2B4O7 with quasi polyhedron morphology can be obtained by NaCl assisted calcination. This enlarged the controllable synthesis of the alkali borates, especially enriched the study on the lithium borates which can be potentially used as a perspective superionic conductor and electrode of lithium ion batteries. [Copyright &y& Elsevier]

Abstract: Mass production of one-dimensional (1D) nanomaterials has emerged as one of the most significant challenges in powder technology. In this contribution, MgBO2(OH) nanowhiskers were hydrothermally produced at a kilogram scale in a 150L stainless steel autoclave at 200°C for 12.0h by using MgCl2·6H2O, H3BO3 and NaOH as the raw materials. The subsequent thermal conversion of the MgBO2(OH) nanowhiskers at 700°C for 6h led to 3.75kg of high crystallinity monoclinic Mg2B2O5 nanorods, with a length of 0.47–1.3µm, a diameter of 55–160nm, and an aspect ratio of 3–15. After the nanorods have been surface modified with the silane coupling agent KH-550, the reinforcing and toughening effects of the Mg2B2O5 nanorods on the biaxially oriented polypropylene resins (BOPP-D1) were evaluated. The filling of the Mg2B2O5 nanorods into the resins resulted in the increase in the tensile strength, the impact strength, and the melt flow index of the BOPP-D1 composites. The appropriate ratio of coupling agent to fillers (Mg2B2O5 nanorods) and the ratio of fillers to resins were determined within the range of 0.6–1.2wt.% and 8–15wt.%, respectively. The optimal ratio of fillers to resins was ca. 10wt.%. The present mass production of MgBO2(OH) nanowhiskers and Mg2B2O5 nanorods is believed to be helpful for enlarging and propelling the applications of the 1D magnesium borate nanostructures in the near future. [ABSTRACT FROM AUTHOR]