Search

The Al 2 O 3 –SiO 2 porous ceramics (ASPC) prepared from phosphorus tailings usually showed a large fluctuation in material properties due to the complex composition of the raw material, which required extensive experimental exploration to optimize their properties. To solve the above problem, a novel deep learning strategy for automatically adjust hyperparameters had been proposed to predict the property of ASPC based on the small experimental datasets in this work. Initially, phosphate tailings and bauxite were used as raw materials. Active carbon, ranging from 0 to 15 wt%, was added as a pore-forming agent. After mixing the raw materials, they were shaped under a pressure of 5 MPa and sintered in the temperature range of 1000–1200 °C to produce ASPC, the density and compressive strength of the ASPC were measured to train the artificial neural network (ANN). An exhaustive search was conducted to identify the optimal combination of hyperparameters suitable for small datasets, then the influence of each hyperparameter on the training performance of ANN was analyzed. Subsequently, the trained model was used to predict the feature space of ASPC, and the key processes for regulating ASPC performance were explored, thereby the experimental schemes that meet target performance (density and compressive strength) were identified. Three groups of experimental schemes were predicted, whose properties were compared with the experimental ones. The results showed that the mean squared errors (MSE) of 0.03 and 0.85 for density and compressive strength, respectively. Furthermore, the ASPC exhibited excellent comprehensive properties when 70 wt% phosphorus tailings and 30 wt% bauxite were added, whose apparent porosity was 59.11 %, density was 1.16 g/cm3 and cold compressive strength was 6.49 MPa. And the predicted data trend influence of the pore-forming agent content and sintering temperature on the performance of ASPC is the same as the experimental data. This research provides valuable guidance for addressing the limited controllability of traditional experimental design processes and accelerate the preparation of ASPC from solid waste. [ABSTRACT FROM AUTHOR]

Solid waste-based lightweight glass ceramics aroused a great deal of attention with the introduction of green building materials. This material demonstrated high performance while alleviating the pressure of waste accumulation. Lightweight glass ceramic was fabricated from phosphorus tailings and coal gangue as raw materials in this work. The effects of phosphorus tailing ratios (50 wt.% - 100 wt.%) and heat-treatment temperatures (1130 °C – 1170 °C) on the pore morphology, properties and toxicity evaluation of lightweight glass ceramics were investigated. Differential Scanning Calorimetry (DSC), and Thermogravimetric mass spectrometry (TG-MS) tests were performed to characterize the sintering behavior of lightweight glass ceramics. The research found that Fe 2 O 3 in the phosphorus tailings and C and FeS 2 within the coal gangue achieve in-situ foaming by creating the gas at elevated temperatures. Results revealed that increasing the proportion of phosphorus tailings facilitated the generation of the molten glassy phase, which favored the formation of bubbles and the expansion of pores. The average pore size of lightweight glass ceramics enlarged from 15.33 μm to 75.02 μm upon increasing the amount of phosphorus tailings from 50 wt.% to 100 wt.%. Increasing the amount of the glassy phase could be achieved by adjusting the heat-treatment temperature. This not only formed a protective film preventing water penetration into the interior of the lightweight glass ceramics but also effectively protected them from corrosion by acidic and alkaline solutions. The water absorption dropped dramatically from 16.44 % to 3.63 % and the corrosion resistance was greater than 98 % when the temperature rose from 1130 °C to 1170 °C. From the toxicity evaluation, the leaching toxicity of Cr, Cu, Pb and Zn in lightweight glass ceramics was 4 orders of magnitude below the limiting value and an extremely low potential ecological risk index (RI = 3.32) was obtained. The optimal preparation parameters were phosphorus tailings addition of 80 wt.% and a heat-treatment temperature of 1160 °C. The corresponding porosity, bulk density, compressive strength, water absorption, acid resistance and alkali resistance were 51.29 %, 1.38 g/cm3, 10.62 MPa, 4.81 %, 98.63 % and 99.96 %. The findings of the research offered a feasible solution for the development of novel green building materials, simultaneously reducing the environmental hazards of solid wastes. [ABSTRACT FROM AUTHOR]

To select suitable high-temperature foaming agents, SiO 2 –Al 2 O 3 –CaO-based foam ceramics (SACFC) were successfully prepared with different foaming agents based on phosphorus tailings and coal gangue. The effects of high-temperature foaming agents (CaCO 3 , carbon black, MnO 2 and Fe 2 O 3) on the microstructure and compressive strength of the SACFC were investigated, and the corresponding foaming mechanism was revealed. The results indicated that CaCO 3 could increase the porosity of SACFC due to high-temperature decomposition. However, the precipitation of needle-like anorthite reduced the mechanical properties. Because the high-temperature oxidation temperature of carbon black was lower than the molten phase formation temperature, bubbles floated up and gathered on the surface of SACFC, leading to a decrease in strength. The continuous release of O 2 from MnO 2 during the sintering process promoted the growth and aggregation of large pores, which was detrimental to the strength. The CO 2 generated by the redox of Fe 2 O 3 by CO/C was the main factor for the foaming of SACFC. During the high-temperature foaming, the synergy effect of Fe2+ and Fe3+ promoted the formation of a uniformly distributed pore structure. When 2 wt.% Fe 2 O 3 was added, SACFC obtained the optimal comprehensive performance with bulk density and compressive strength of 0.78 g/cm3 and 3.50 MPa. [ABSTRACT FROM AUTHOR]

A kind of foamed glass-ceramics (FGC) that can be used in the construction field was synthesized by self-foaming technology using untreated phosphorus tailings (PT) and coal gangue (CG) as raw materials in this study. The effects of PT addition and sintering temperature on the phase transformation, microstructure, and properties of FGC were explored, also its self-foaming mechanism during the sintering process was revealed. The results showed that FGC with 80 wt.% PT addition had the best comprehensive performances when treated at 1150 °C, whose porosity was 61.6%, bulk density was 1.04 g/cm3, and compressive strength was 10.11 MPa. Based on the theoretical calculation, CaO and K 2 O included in the tailings acted as sintering aids , promoting the formation of a glassy phase, which increased the pore size and solidified Ba2+ and Ni2+ within FGC. The pore formation mechanism included in-situ pore formation caused by the combustion of C and the gas released by the reduction of Fe 2 O 3 was wrapped by the glassy phase. This self-foaming synthesized FGC from total tailings provided a novel approach to the high-value utilization of tailings and the development of novel environmentally friendly construction materials. [ABSTRACT FROM AUTHOR]

A machine learning model was proposed to accelerate the preparation of Al 2 O 3 –SiO 2 porous ceramics (ASPC) based on few-shot datasets. Phosphate tailings and bauxite were used as raw materials to prepare ASPC and obtain the initial dataset. The accuracy and generalization ability of the model are heavily influenced by the dataset partitioning method. 10-fold cross-validation and random sampling were compared to identify the optimal approach for training and testing the model on the limited data. Four commonly used regression algorithms of RF, KNN, SVR and BPNN were selected to predict the mechanical properties of ASPC. Based on the evaluation of model performance, the random forest algorithm was found to be the most suitable for small sample datasets. Using the trained random forest model, the feature importance of ASPC performance was analyzed, and a new ASPC database was established. Experimental schemes with the desired performance were obtained through screening from ASPC database. Finally, the ASPC with the target performance was prepared experimentally. The result demonstrated that employing machine learning techniques on few-shot datasets could effectively tackle the issues of low efficiency and insufficient data samples. [ABSTRACT FROM AUTHOR]

In order to address the issues of emergency decision-making and optimization (EDMO) of fire accidents in colleges, this paper proposes the EDMO way to take into account the synergies among divergent divisions replacements and the psychology of decision makers (DMs) on the basis of the best-worst method (BWM) and VIKOR within an interval 2-tuple linguistic (ITL) surroundings and cumulative prospect theory (CPT). First, DMs use the ITL to evaluate the degree of synergy among replacements from divergent divisions, the language information can be processed accurately and the information loss can be avoided. Then, the multi-alternative amalgamations consisted of divergent divisions replacements are built. On the grounds of the DMs' value assignment, the collaborative decision matrix of multi-alternative amalgamations can be gained. And the optimal weight of the evaluation standards can be computed based on the ITL-BWM method. The CPT is extended into VIKOR to think about the effect of the DMs' psychological behavior on the decision result. Furthermore, the positive and negative utility matrices can be computed through the value function of CPT. On the grounds of the positive and negative utility matrices, the distance from the utility value of multi-alternative amalgamations to the desired right solution of positive and negative utility can be obtained, and the cumulative foreground value function is used to replace the distance among each replacement to the positive and negative right desired solutions, it can avoid ignoring the effect of the correlations among different attributes on the outcome. Furthermore, the model is applied to the example and an analysis of the sensitivity of the factors of the decision-making mechanism coefficient and the weights of synergistic indicators is carried out to prove the validity and stability of the model. [ABSTRACT FROM AUTHOR]

In order to solve the problem of underground goafs, particularly in light of the importance ranking of evaluation indices being more subjective and catastrophe progression values being large and too concentrated in the catastrophe progression method, the importance of multiple indices is ranked by the maximizing deviation method. An S-shaped curve is used to establish a regression function to improve the value of catastrophe progression method. First, three first-level evaluation indices and eight second-level evaluation indices are selected to establish an index system for risk evaluation of the underground goaf. Next, based on the principle of catastrophe progression method, an improved catastrophe model for its risk evaluation is established. Finally, sample training and verification are performed based on the improved evaluation model. The evaluation results show that the improved catastrophe progression method objectively ranks the importance of the evaluation indices of each layer, which improves the credibility of the evaluation results. The evaluation results are consistent with the actual geological data and detection results, which verifies the validity and accuracy of the evaluation model. However, only 87.5% of the risk levels obtained by the fuzzy comprehensive evaluation method are completely consistent with the improved catastrophe progression method, and the ranking error of risk value within one rank also accounted for 87.5%. Therefore, the results calculated by the improved catastrophe progression method are more accurate. The numerical gap of the improved catastrophe progression values becomes larger, from [0.796, 0.969] to [0.275, 0.691], which is 2.405 times of the interval difference of the catastrophe progression values before the improvement, which makes the numerical distribution of the catastrophe progression values more scientific and reasonable, with a higher resolution level. Therefore, it is reasonable and feasible to use the improved catastrophe progression method for the risk evaluation of the underground goaf, which can provide a certain theoretical basis and engineering guidance for underground goaf disaster control and management. [ABSTRACT FROM AUTHOR]

In order to research the forming mechanism of zonal disintegration, the stress distribution of surrounding rock in deep roadway was studied through three dimensional photoelastic test with stress freezing. In this work, the loads of 5, 30, 50, 70 and 90 kN were respectively applied to the axes of the roadway based on radial constraint in photoelastic test models, also the stress fields of surrounding rock were transparently presented via observing photoelastic slice. The results show that when the axial stress reaches a certain level, the stress distribution of surrounding rock of roadway is presented as concentric circles of roadway, and the stress shows its maximum near roadway. In addition, the number of stress circles increases and the level of stress improves with increasing axial stress of roadway, and the increased distance between the area of maximum stress and roadway surface can be obtained. Studies show that the range of layered fractures is determined by the magnitude of the axial stress, which is a critical influence on zonal disintegration. Furthermore, high stress 'bypass' roadway as the axial loads increases. The method of three dimensional photoelastic test brings methodological progress for the study of zonal disintegration. The research results can provide new ideas for the stability control of surrounding rock, and give a theoretical guidance for the roadway excavation and supporting design. [ABSTRACT FROM AUTHOR]

Melilite-spinel porous ceramics with high apparent porosity, sufficient strength and ultralow thermal conductivity were successfully prepared via a direct-thermal decomposition route using the solid waste of phosphorus tailings and coal gangue as raw materials. The micropores are derived from the in situ decomposition of dolomite and kaolinite, whose morphology, distribution form and quantity determine the thermal insulation performance and physical properties of porous ceramics. Melilite-spinel porous ceramics with an ultralow thermal conductivity of 0.036 W/(m·K) (tested at 200 °C), an apparent porosity of 61.3% and a compressive strength of 2.95 MPa, exhibited promising application prospects in thermal insulation materials used for high-temperature fields. [ABSTRACT FROM AUTHOR]

A simple strategy for preparing MgO–Al 2 O 3 –CaO-based porous ceramics (MACPC) with high strength and ultralow thermal conductivity has been proposed in this work based on the raw material of phosphorus tailings. The effects of phosphorus tailings content, carbon black addition and heat treatment temperature on the properties of MACPC were studied, and their pore-forming mechanism during sintering was revealed. The results showed that the main phase composition of MACPC was magnesia alumina spinel and calcium aluminate after sintering at 1225 °C. Furthermore, the MACPC exhibited excellent comprehensive properties when 60 wt% phosphorus tailings and 40 wt% alumina were added, whose apparent porosity was 62.8%, cold compressive strength was 14.8 MPa, and the thermal conductivity was 0.106 W/(m·K) at 800 °C. The synchronously enhanced strength and thermal insulation properties of MACPC were related to the formation of uniformly distributed micropores (<2 μm) and passages in the matrix, which originated from the decomposition of phosphorus tailings and the burnt out of carbon black during the sintering process. The preparation of MACPC with high temperature resistance and excellent mechanical and thermal insulation properties with the raw material of phosphorus tailings provided an effective method for the high-value utilization of phosphorus tailings. [ABSTRACT FROM AUTHOR]

In order to realize accurate risk assessment and collaborative control of multi-hazard risk in non-coal underground mines, a space-oriented risk characterization and collaborative control model of multi-hazard risk in non-coal underground mines is proposed. Statistical analysis of non-coal underground mine accidents from 2000 to 2022, revealing the characteristics of non-coal underground mine accidents and 5 risk types were identified, including cage fall accident, powered haulage accident, fire accident, mine water inrush accident, and roof fall and rib spalling accident. A multi-hazard risk analysis and assessment framework for non-coal underground mines based on the inherent risk of the system, the vulnerability of the disaster-bearing body and the adaptability of the disaster-bearing area is proposed. The multi-hazard inherent risks in non-coal underground mines are comprehensively identified and evaluated in five aspects, including hazardous equipment and facilities, hazardous materials, hazardous processes, hazardous operations and hazardous places, and the characterization and unified measurement of multi-hazard risk is realized by combining the vulnerability index of disaster-bearing body and the adaptability index of disaster-bearing area. Regional multi-hazard risk aggregation is achieved through the Nemerow pollution index and space-oriented multi-hazard risk is obtained. Constructed a multi-hazard safety risk collaborative control system of source identification, classification and control, process control, continuous improvement, and full participation. Finally, the validity and rationality of the risk characterization model and the risk collaborative control system are verified. The research can both support the formulation of macro policies for non-coal underground mines and provide guidance for the specific spatial layout. [ABSTRACT FROM AUTHOR]

Rockburst forecasting plays a crucial role in prevention and control of rockburst disaster. To improve the accuracy of rockburst prediction at the data structure and algorithm levels, the Yeo–Johnson transform, K-means SMOTE oversampling, and optimal rockburst feature dimension determination are used to optimize the data structure. At the algorithm optimization level, ensemble stacking rockburst prediction is performed based on the data structure optimization. First, to solve the problem of many outliers and data imbalance in the distribution of rockburst data, the Yeo–Johnson transform and k-means SMOTE algorithm are respectively used to solve the problems. Then, based on six original rockburst features, 21 new features are generated using the PolynomialFeatures function in Sklearn. Principal component analysis (PCA) dimensionality reduction is applied to eliminate the correlations between the 27 features. Thirteen types of machine learning algorithms are used to predict datasets that retain different numbers of features after dimensionality reduction to determine the optimal rockburst feature dimension. Finally, the 14-feature rockburst dataset is used as the input for integrated stacking. The results show that the ensemble stacking model based on Yeo–Johnson, K-means SMOTE, and optimal rockburst feature dimension determination can improve the accuracy of rockburst prediction by 0.1602–0.3636. Compared with the 13 single machine learning models without data preprocessing, this data structure optimization and algorithm optimization method effectively improves the accuracy of rockburst prediction. [ABSTRACT FROM AUTHOR]

• The function mechanisms of solid waste in froth concrete are summarized. • The types and hydration mechanism of binders in froth concrete are summarized. • The frothing method and mechanism in froth concrete are summarized. • The mechanism of froth instability and froth stabilization of froth concrete are reviewed. • The raw material composition of froth concrete is reviewed. Frothed concrete (FC) could be a resent sort of energy-saving and naturally neighborly building material with light weight, great thermal insulation, great sound insulation, waterproof property, and good environmental protection property. At present, global metal ore chemical industry is the pillar industry of national economic development, with a large scale, and the stock of solid waste is increasing year by year. With the deepening of the concept of national energy conservation and emission reduction and green environmental protection, ordinary Portland cement as the primary raw material of traditional froth concrete has become a key factor limiting the production and application of froth concrete. To realize the productive utilization of solid waste such as slag and tailings and prepare green and environmentally friendly froth concrete materials with excellent function, this manuscript discusses the composition of FC raw materials according to the current research status and development trend based on the introduction of FC and its classification. The frothing mechanism of the FC frothing agent was summarized, and the prospect of using solid waste to prepare FC was prospected. [ABSTRACT FROM AUTHOR]

[Display omitted] • The waste phosphorus tailings are used to obtain the 100% content of C/M-S-H cementitious material. • The thermal activation of C/M-S-H cementitious material can increase the early strength of cement concrete by 48%. • It reveals that the effect mechanisms of thermal activation temperature on the phase evolution and rehydration behavior of C/M-S-H. Aiming to reduce the CO 2 emission of the cement materials preparation, a novel strategy to fabricate C/M-S-H cementitious materials from phosphate tailings has been proposed. To reveal the dehydration and hydration behavior of C/M-S-H, an experimental program combining TG, XRD, SEM, and corresponding strength evaluation was performed. The agglomerate-shaped C-S-H and flake-shaped M-S-H were synthesized from phosphate tailings. The experimental results showed that the rehydration capacity of C-S-H increased and then decreased with the rise in temperature (200–600 °C). The basic structural framework of M-S-H was maintained below 400 °C and disrupted at 600 °C, where the rehydration capacity decreased sharply. The dehydrated M-S-H showed a structural recovery after rehydration. However, dehydrated C-S-H formed dense C-S-H particles on the surface after rehydration, increasing the accumulation volume in this region and improving early strength. Ultimately, appropriate dehydration temperatures and additions could increase early hydration reactivity, thereby enhancing the concrete. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lightweight foam ceramics were obtained by recycling phosphorus tailings and coal gangue. • The effect mechanisms of sintering time and heating rate on the evolution of phase, pore morphology and physical properties were revealed. • Lightweight foam ceramics manufactured by sintering at 5 ℃/ min rising to 1150 ℃ for 60 min satisfying the requirements of non-bearing building partitions and non-bearing bricks. • Heavy metals were well-consolidated in the glassy phase, and lightweight foam ceramics exhibit extremely low toxic leaching and potential ecological risks and are a green material. The heat treatment system was a key factor in the performance of lightweight foam ceramics. Phosphorus tailings and coal gangue were recovered for preparing lightweight foam ceramics by adjusting the sintering time and heating rate. The goal was to set a reasonable heat treatment regime for maximum optimized performance. The influences of sintering time and heating rate on the phase evolution, pore structure, physical properties and heavy metal solidification of lightweight foam ceramics were investigated by the results of XRD , SEM and ICP-MS examinations and theoretical calculations. As a result, extended sintering time promoted to formation glassy phase, which facilitated the average pore size growth from 34.88 µ m to 124.23 µ m. The larger heating rate (10 °C/ min) prevented the vitrification of lightweight foam ceramics with an increase in water absorption (2.31 % − 23.14 %) and a decrease in compressive strength (9.80 MPa − 3.56 MPa). The lightweight foam ceramics exhibited relatively uniform pore structure, high porosity (61.79 %), low density (0.99 g/cm3), satisfactory compressive strength (10.08 MPa), and low water absorption (2.87 %) when they were treated at 1150 °C for 60 min with the heating rate of 5 °C/ min. In particular, the extremely low leaching values of heavy metals and potential ecological risk index were detected for the lightweight foam ceramics. The fabricated lightweight foam ceramics satisfy the strength requirements of Chinese national standards for non-bearing building partitions and non-bearing bricks. This technology not only provided practical guidance for adjusting the sintering process to manufacture high-performance lightweight foam ceramics, but also the simultaneous high value-added utilization of phosphorus tailings and coal gangue could be achieved. [ABSTRACT FROM AUTHOR]

Porous ceramsite used for the adsorption of heavy metal ions in sewage was prepared with total phosphorus tailings as raw material, which can not only reduce the environmental problems caused by the accumulation of phosphorus tailings, but also achieve the goal of "treating waste with waste". The effects of high-silicon-phosphorus tailings addition, sintering temperature and soaking time on the properties of porous ceramsite were studied, also the mechanism of heavy metal solidification and Ag+ adsorption from sewage were revealed. The results indicated that the porous ceramsite exhibited excellent comprehensive properties after sintered at 1085 °C for 1.5 h, whose apparent porosity was 47.3%, bulk density was 1.53 g/cm3, compressive strength was 2.85 MPa, water adsorption was 27.05% and hydrochloric acid solubility was 8.5%. Furthermore, the preparation of porous ceramsite contributed to the solidification of heavy metals in phosphorous tailing due to the formation of liquid phase during the sintering. The leaching concentration of heavy metals within porous ceramsite was much lower than that in phosphorus tailings, which were far below the standard (GB 8978-1996). In addition, the numerous micropores formed by the decomposition of phosphorus tailings endowed the porous ceramsite with excellent adsorption ability. The removal efficiency of Ag+ by NaCl solution modified porous ceramsite could reach to 99.9% in the process of sewage treatment. • It is the first time to prepare porous ceramsite entirely with phosphorus tailings. • The porous ceramsite possessed high Ag+ removal efficiency of 99.9%. • The leaching concentration of heavy metals of porous ceramsite is far below standard. [ABSTRACT FROM AUTHOR]

Based on the systematic collection and collation of relevant data at home and abroad, and using the CiteSpace bibliometric tool, the research hotspots and evolutionary paths in the field of mine water inrush disaster research were analyzed using a combination of qualitative and quantitative methods to provide the basis for a new perspective on applied research in this field. The disaster-causing conditions and mechanisms of mine water inrushes were systematically analyzed, allowing us to propose a fourth condition, water disaster-inducing power, that plays a decisive role in the process of mine water hazards. We elaborate the methods of water source identification and risk prediction and assessment of mine water disasters, summarize and review their practical application value and theoretical research shortcomings, and point out that combining mine water disaster research methods and computer technology in the direction of intelligence and visualization is a hotspot and focus of future research. Finally, we discuss the prevention and control of water inrush disasters in mines, construct a model of water inrush disasters, and discuss specific prevention and control measures of water inrush disasters. [ABSTRACT FROM AUTHOR]

In order to solve the problems of limitations caused by the single subjective or objective weighing method in the gray target model and the problems of correction of evaluation indicators being out of consideration, the analytic hierarchy process, order relationship analysis method, entropy weight method and dispersion maximization method are used to build moment estimation theory to improve the subjective and objective weight integration assignment method. Then, the correction coefficient matrix is used to replace the covariance matrix in the Mahalanobis distance, which is introduced into the traditional gray target model to accurately characterize the correlation between evaluation indicators. What's more, applying the improved gray target model to the goof risk assessment, the results show that the optimal combination weight obtained by improving the subjective and objective weight integration assignment method is to optimize integration based on the minimum devein of the four weighting methods. This means that considering the human and empirical factors obtained in practice and the inherent attributes of the evaluation indicators. Finally, the evaluation results are more comprehensive. The correlation coefficient matrix is used to replace the covariance matrix in the Mahalanobis distance and the affluence of the correlation between the evaluation indicators is considered. Then, the accuracy of the evaluation results is improved. Hence, the rationality and effectiveness of the improved gray target model in the goof risk assessment are verified. [ABSTRACT FROM AUTHOR]

In order to study the effect of particle size gradation of filling aggregate on the strength and failure mode of the cemented backfill, specimens of waste rock cemented backfill with gradation index n of 0.2, 0.4, 0.6, and 0.8 were designed and prepared based on Talbol gradation theory. The strength and deformation failure characteristics of the backfill were obtained by uniaxial compression test and acoustic emission (AE) test, and the mechanism of the influence of gradation index n on the mechanical properties of the backfill was revealed. The results show that with the gradation index n increased, the compressive strength of the backfill first increased and then decreased, the failure mode gradually changed from shear failure to tensile failure, the crack expansion was more complex, and the failure degree was more serious. Before and after the stress peak, the AE ringing counts reaches the maximum value, and the b-value fluctuates in a wide range and jumps suddenly, which could be used as a precursor to judge the instability failure of the backfill. The microstructure of the backfill was analyzed by scanning electron microscope (SEM) test, and X-ray diffraction (XRD) test, which showed that the hydration products of the backfill were mainly calcium silicate hydrated (C-S–H) gels, ettringite (AFt), and calcium hydroxide (Ca(OH)2). The research results can provide reference for improving the particle size gradation of mine filling materials, thus ensuring the safe production of mines. [ABSTRACT FROM AUTHOR]

The strength of rock under combined compression and shear loading has been paid more and more attention, but still lacks a theoretical model that incorporates both compression–shear characteristics and influence of dip angle to estimate the strength of the rock. This work is aiming to solve the issue by combining experimental and theoretical methods. First, in the laboratory, 112 rock samples with different sizes were applied to obtain the dip effect characteristics of strength via combined compression–shear tests. The ratio of compression–shear strength to uniaxial compression strength is called the compression–shear coefficient, which is used to characterize the degree of dip effect. Second, according to the compression–shear load characteristics of inclined rock samples, a strength model was established considering both compression–shear characteristics and dip angle by the Mohr–Coulomb failure theory. This strength model is an extension of the Mohr–Coulomb criterion and was verified by experimental data. The verification results are consistent with experimental results. Finally, the mechanism of dip effect on strength was explained from the resistance to the sliding and stress path of the rock sample. The results show that the dip effect is an inevitable strength weakening characteristic of rock materials under combined compression–shear loading. Compared with the vertical rock sample loaded under pure pressure, the resistance to the sliding of inclined rock samples decreases and the stress path is changed, which reduces the ability of the rock sample to resist external loads, resulting in the decrease of strength. [ABSTRACT FROM AUTHOR]

In view of complexity and uncertainty of problems in the prediction of rockburst, a classified prediction model of rockburst using rough sets-normal cloud is established. Seven main influencing factors including uniaxial compressive strength of rock σc, uniaxial tensile strength of rock σt, maximum tangential stress of surrounding rock σθ, rock integrality coefficient kv, ratio between uniaxial compressive strength of rock and uniaxial tensile strength of rock σc/σt, ratio between maximum tangential stress of surrounding rock and uniaxial compressive strength of rock σθ/σc and rock elastic deformation energy index wet are selected as the evaluation index of rockburst. Sixteen groups of rockburst examples at home and abroad are used as model construction samples. Then, the weight value of evaluation index of rockburst is obtained by rough sets and fuzzy sets. According to normal cloud theory and classification standard of rockburst, the cloud maps of evaluation index of rockburst are generated. Based on the normal cloud generator and sample data, the evaluation index of the classified sample is determined, and the comprehensive determination of evaluation index of the classified sample is obtained by combining the weight of the evaluation index of rockburst. Finally, the rockburst level is identified according to the principle of maximum membership degree. The classified prediction model of rockburst is used to predict five groups of rockburst samples at home and abroad, and the rockburst classification is coincident with the actual situation. The results show that the classified prediction model of rockburst using rough sets-normal cloud has great practicability. [ABSTRACT FROM AUTHOR]

To study the occurrence process, as well as the temporal and spatial evolution laws, of rockburst disasters, the roof deformation of continuous heading roadways during rockburst was studied through a physical similarity simulation test with a high similarity ratio and low strength. The deformation and failure evolution law of the roadway roof in the process of rockburst were analyzed by using detection systems, including a strain acquisition system and a high-power digital micro-imaging system. The results show that the rockburst of the roadway roof can be divided into four stages: equilibrium, debris ejection, stable failure, and complete failure stage. According to the stress state of a I–II composite crack, the theoretical buckling failure strength of the surrounding rock is determined as 1.43 times the tensile strength. The flexural failure strength of a vanadium-bearing shale is 1.29–1.76 times its compressive strength. With continuous advancement in the mining time, the internal expansion energy of the roadway roof-surrounding rock in the equilibrium stage continuously accumulates. The fracture network continuously increases, developing to the stable failure stage, with bending deformation, accompanied by continuous particle ejection until the cumulative stress in the failure stage increases, and the tensile state of the rock surrounding the roof expands radially into deep rock. A microscopic damage study in similar material demonstrated that the deformation of the roadway roof is non-uniform and uncoordinated. In the four stages, the storage deformation of the rock surrounding the roadway roof changes from small accumulation to continuous deformation, to the left (or deep rock). Finally, the roadway roof-surrounding rock becomes completely tensioned. The research results presented in this study provide a reference for the prediction and control of rockburst in practical engineering. [ABSTRACT FROM AUTHOR]

Compared to general anisotropic rocks, the contact zone composite rock composed of strong and weak rocks has distinct characteristics in terms of structure and physical and mechanical properties. The uniaxial compression test of composite specimens with different degrees of material difference λ and interface inclination angle θ = 0° ~ 90° were carried out to study the effect of material difference and inclination angle on the anisotropy of strength, deformation and damage evolution with acoustic emission (AE) and digital image correlation (DIC) techniques. The results show that the UCS, elastic modulus, σci and σcd of the composite specimen roughly show U-shaped anisotropy. The damage evolution characteristics of two materials and inclined interface vary regularly with the inclination angle. There is differential deformation between the two materials, which forms the relative sliding tendency between the materials that changes with the inclination angle. The degree of relative sliding at different angles is 60° > 45° > 75° > 90° > 30° > 0°. The composite specimen has three types of failure modes: weak material failure mode (0° ~ 30°), interface shear mode (60°) and composite mode (45°, 75° ~ 90°). The anisotropy of the composite specimen is comprehensively affected by material difference and inclination angle. Increasing the material difference will increase the differential deformation and damage and relative sliding tendency between materials. Increasing the inclination angle will increase the shear stress on the interface and weaken the differential deformation and damage. Material difference affects the interface strength, which in turn affects the ability of the interface to resist shear failure and relative sliding. [ABSTRACT FROM AUTHOR]

• Two types of MgO-C refractories, namely, tight particle grading and non-tight particle grading, were prepared according to Andreasen Continuous Packing Theory. • Digital image correlation method and acoustic emission techniques were synchronously introduced to the investigation of fracture behavior of MgO-C refractories with different particle grading. • The mechanism of particle grading on the optimization of thermal shock resistance was revealed by analyzing localized stresses in the simplified spherical particle model based on the photoelastic method. Two types of MgO-C refractories with tight particle grading and non-tight particle grading were prepared according to Andreasen's continuous packing theory. Fracture behaviors were investigated using wedge splitting tests combined with digital image correlation method and acoustic emission techniques. The results indicated that MgO-C refractory with non-tight particle grading treated at 1400 ℃ had more in situ phases (e.g. , AlN and MgAl 2 O 4) and exhibited less brittleness than specimens with tight particle grading even though they had similar nominal tensile strengths. In contrast, specimens with non-tight particle grading had greater horizontal strain under various loading stages, reflecting their better ability to resist rupture deformation. In addition, more microcracks were initiated earlier in the pre-peak region, and more energy was consumed. The decrease in coarse particles and corresponding increase in fine powder content increased the interface between particles, benefiting for reducing the local stress concentration and improving the thermal shock resistance of refractories. [ABSTRACT FROM AUTHOR]

• The expansion evolution law and mechanism of expansive grout have been introduced. • The relationship of expansion parameters and material contents have been analyzed. • The engineering application prospect of expansive grout has been evaluated. Aiming to address the problem of traditional grouting reinforcement of jointed rock mass only providing bonding force to the joint surface, the grouting reinforcement technology of expansive grout was proposed. This technology generates compression force through the volume expansion of the grout itself, leading to a reinforcement idea of "first squeezing and then bonding" to increase the overall strength of the jointed rock mass. To solve the problem of the preparation of expansive grout materials, an expansive grout proportion test using high efficiency soundless crush agent (HSCA) as the expansion source and cement as the cementing material was performed. Considering the single free surface expansion rate (SFSER) and lateral expansion pressure (LEP) of expansive grout specimens as the investigated indices, the expansion evolution law of expansive grout and the effect of cement content and expansion agent content on its expansion characteristics were explored from both macro and micro level. The experimental results show that: (1) The expansion evolution processes of expansive grout after final setting can be divided into four phases viz. rapid expansion period, slow expansion period, residual expansion period and stable period. After 120 h of final setting, the grout expansion basically ended. (2) the expansive grout with different cement contents could produce SFSER between 0.83% and 18.54% and LEP between 0.08 MPa and 1.83 MPa when the content of the expansion agent was 3–12%. (3) The effects of the expansion agent content on the SFSER and LEP of the expansion agent were similar, and they all showed an S-shaped curve with increase in the expansion agent content. The experimental results provide a significant understanding of the expansion mechanism and characteristics of expansive grout. [ABSTRACT FROM AUTHOR]

• Distribution characteristics of waste rock particles in the mixed aggregate cemented backfill and its settlement delamination stratification mechanism. • Mechanism of the effect of waste rock contents on the strength of cemented backfill. • Effect of waste rock contents on deformation and failure characteristics of cemented backfill. • Acoustic emission characteristics of mixed aggregate cemented backfill during uniaxial compression. • Hydration products and microstructural characteristics of cemented backfill with different waste rock contents. To study the effects of waste rock (WR) contents on the delamination and mechanical characteristics of the cemented backfill, the backfill specimens with 40%-80% WR content were prepared based on the stacking density of mixed aggregate. The characteristics of the WR distribution inside the cemented backfill with various WR contents were examined by scanning the sections images of the specimens. The strength and damage properties of the cemented backfill were investigated by uniaxial compression acoustic emission (AE) tests, and the strength and damage evolution mechanisms were explained by microstructure testing experiments. The results show that the viscosity and yield stress of the filling slurry gradually decreased with the contents of WR increased, and the WR settlement and delamination more obvious. The uniaxial compressive strength (UCS) has the same trend as the stacking density of the mixed aggregate, showing the trend of "increased first and then decreased" with the content of WR increased. When the content of WR was 60%, it had the highest UCS. As the content of WR increased, the fracture area at the interface of WR and cementitious matrix gradually increased, and the extrusion between coarse aggregates became more obvious, leading to more complex crack extension and higher AE cumulative energy. The main products of hydration in the cemented backfill were calcium silicate hydrated (C-S-H gels), ettringite (AFt), and calcium hydroxide (Ca(OH) 2). The specimens with higher content of hydration products have better cementation among aggregate particles, denser microstructure, and higher compressive strength of cemented backfill. [ABSTRACT FROM AUTHOR]

Acid mine drainage (AMD) causes serious environmental pollution owing to its high acidity, toxic metal content, and sulfate content. This review describes the mechanism of formation and the effects of AMD, presents the prevention and treatment technologies, identifies critical research gaps, and explores the challenges and opportunities encountered by AMD prevention and treatment technologies. Although passivation and microencapsulation technology have good prospects, they are in the early experimental stage and focus on pure pyrite systems. Remediation technologies such as chemical neutralization, adsorption, microbial activity, and membrane technologies have been developed to reduce the negative impacts of AMD on environment and human health; however, a continuous supply of chemicals and energy, expensive maintenance costs, and long-term monitoring of the affected ecosystem are some of its limitations. The recovery and reuse of valuable resources (sulfuric acid, metals, and rare earth elements) during AMD treatment can reduce its cost and is crucial in achieving a sustainable treatment. Membrane technology can produce high-quality water, but cannot achieve resource recovery, especially selective recovery of valuable metals. The integrated of membrane and other technologies can realize the reuse of water and the recovery of valuable resources. In addition, the recycling of mine tailings as construction materials and geopolymers can greatly reduce the formation of AMD. Overall, this review provides resource recovery and reuse as a holistic approach to sustainable AMD treatment. Finally, integrated treatment technologies that is worthy of future exploration need to be emphasized. [Display omitted] • Acid mine drainage presents dire environmental impact. • Carrier microencapsulation process is the most promising prevention technology. • Remediation options are effective, but unsustainable. • Water reuse and valuable resource recovery potentially offset AMD treatment costs. • Integrated processes are prospective approaches for AMD treatment. [ABSTRACT FROM AUTHOR]