Search Results (43)

Developing green mining technology for medium-to low-grade mines requires achieving minimal or no damage to the mining area’s ecological environment. A medium-to low-grade phosphate mine in Hubei Province was taken as the research object in this study. The tailings were selected as the main filling aggregate. Indoor tests and theoretical analysis were conducted to analyze the influence of curing age, the water–cement ratio, the cement–sand ratio, and slurry concentration on the strength of the cemented backfill. Furthermore, a multi-factor non-linear mathematical model of the strength of the cementitious filler was established. The study results indicated that the strength of backfill increased linearly with the increase in the curing age, decreased negatively with the increase in the water–cement ratio, and increased exponentially with the increase in the cement–sand ratio and the slurry concentration. The multivariate non-linear prediction model of the strength of the filling body at different ages was also established based on the test results. This predictive model could effectively predict the strength of the cemented backfill, and the error value was not larger than 4%. Our research results can lay a theoretical foundation for developing medium-to low-grade phosphate mine filling with tailings as the main filling aggregate. Full article

In response to the high cost and environmental impact of backfill materials in Xinjiang mines, an eco-friendly, large-volume composite was developed by bonding desert-sand mortar to waste concrete. A rock-filled concrete process produced a highly flowable mortar from desert sand, cement, and fly ash. Waste concrete blocks served as coarse aggregate. Specimens were cured for 28 days, then subjected to uniaxial compression tests on a mining rock-mechanics system using water-to-binder ratios of 0.30, 0.35, and 0.40 and aggregate sizes of 30–40 mm, 40–50 mm, and 50–60 mm. Mechanical performance—failure modes, stress–strain response, and related properties—was systematically evaluated. Crack propagation was tracked via digital image correlation (DIC) and acoustic emission (AE) techniques. Failure patterns indicated that the pure-mortar specimens exhibited classic brittle fractures with through-going cracks. Aggregate-containing specimens showed mixed-mode failure, with cracks flowing around aggregates and secondary branches forming non-through-going damage networks. Optimization identified a 0.30 water-to-binder ratio (Groups 3 and 6) as optimal, yielding an average strength of 25 MPa. Among the aggregate sizes, 40–50 mm (Group 7) performed best, with 22.58 MPa. The AE data revealed a three-stage evolution—linear-elastic, nonlinear crack growth, and critical failure—with signal density positively correlating to fracture energy. DIC maps showed unidirectional energy release in pure-mortar specimens, whereas aggregate-containing specimens displayed chaotic energy patterns. This confirms that aggregates alter stress fields at crack tips and redirect energy-dissipation paths, shifting failure from single-crack propagation to a multi-scale damage network. These results provide a theoretical basis and technical support for the resource-efficient use of mining waste and advance green backfill technology, thereby contributing to the sustainable development of mining operations. Full article

There is currently no research examining the rheological properties of cementitious paste backfill (CPB) materials containing aluminium oxide nanoparticles (nAlO). Knowing the yield stress and viscosity of CPB containing nAlO is crucial, especially when applying nano-CPB technology in underground mines. The purpose of this work is to thoroughly examine how nAlO affects the rheological characteristics of CPB and how those characteristics change over time. Yield stress and viscosity measurements are performed on CPB samples with different compositions (e.g., nAlO content, binder type, and superplasticizer content) at intervals of 0 min, 20 min, 1 h, 2 h, and 4 h. The study also includes measurements of the pH and zeta potential of the materials, microstructural studies (TG/DTG and XRD), and electrical conductivity (EC). The findings show that adding nAlO to CPB significantly changes its rheological properties, which in turn affects flowability. The yield stress and viscosity of CPB samples are greatly increased by the incorporation of nAlO, with the degree of influence varying based on variables including water content, curing duration, and type of binder. Because of the nAlO-induced microstructural changes in the CPB material, the interaction of nAlO and a larger fraction of nAlO, along with an increase in curing time, raises rheological characteristics and decreases paste flowability. The results of EC, DTG, and XRD, which show that binder hydration improves with nAlO dosage, corroborate this. Moreover, as nAlO content increases, the zeta potential decreases in magnitude, resulting in stronger repulsion forces and reduced flowability. However, EC, XRD, and DTG analyses suggest that the addition of 0.125% superplasticizer counteracts the flowability reduction caused by nAlO, as the superplasticizer slows down the cement hydration rate at very early curing stages. Moreover, the increase in the slag percentage from 0% to 50% and 75% of the binder content slightly decreases viscosity but greatly increases yield stress. The study’s fresh perspectives contribute to the advancement of nano-CPB technology and have important ramifications for the practical use of this technology in underground mine backfill operations. Full article

With the advancement of backfill mining technology, cemented high-concentration backfill (CHB), composed of solid particles, such as high-concentration tailings or waste rock mixed with a small amount of binder, has gained widespread applications due to its superior filling performance. Given the complexity of the backfill pipeline network, studying the characteristics of pipe transportation is crucial. The local resistance in bending pipes represents an important parameter for CHB pipeline transportation. However, existing research on the local resistance characteristics of bending pipes lacks comprehensiveness and depth. This study proposes a novel definition of the local resistance coefficient as the ratio of pressure loss per unit length of a bend pipe compared to that of a straight pipe. Utilizing the computational fluid dynamics (CFD) method the impact of six different factors on the local resistance coefficient of the bending pipe is investigated: flow velocity, pipe diameter, slurry concentration, binder content, turning radius, and bending angle. The results indicate that the local resistance coefficient positively correlates with the flow velocity and pipe diameter but negatively correlates with the slurry concentration, turning radius, and bending angle. Among these factors, the slurry concentration exerts the most significant influence on the local resistance coefficient. The recommended approach to control the local resistance coefficient in the mine is to use CHB with a 76% solid fraction at a 1.5 m/s flow velocity, along with pipe parameters of a 0.15 m diameter, a 2.5 m turning radius, and bending angles between 90° and 150°. The findings provide a valuable reference for determining the optimal parameters for bend pipes and CHB and facilitate the theoretical calculation of resistance in complex filling pipeline networks. Full article

Cemented tailings backfill (CTB), composed of tailings, binder, and water, is widely used for filling underground goaves in mining operations. Unmanaged tailings can occupy extensive land and pose significant environmental risks. Microwave technology offers a promising approach to enhance the utilization of tailings, reducing dependency on natural resources. However, limited research on microwave heating parameters has impeded its broader adoption. This study uses the orthogonal experimental method to study the influence of various factors on the strength of the CTB and to determine the impact capacity of each factor. Additionally, this study conducted a visual analysis of the microwave heating time (MHT), microwave delay time (MDT), cement-tailings ratio, slurry concentration and microwave power (MP) to verify the experimental results. The results show that microwave heating can enhance or diminish the mechanical properties of CTB samples at different curing ages, depending on the specific microwave parameter settings. Research indicates that microwave technology can be effectively applied to mine backfill materials to improve their early strength and the modulus of elasticity. Full article

Advancements in mine tailings treatment technology have increased the use of superfine tailings, but their extremely fine particle size and high specific surface area limit the performance of superfine tailings cemented paste backfill (STCPB). This study investigates the effects of using superfine cement as a binder to enhance the fluidity, strength, and pore structure of STCPB. The influence of water film thickness (WFT) on STCPB performance is also examined. The results show that the cement-to-tailings ratio (CTR) and solid content (SC) significantly affect the spread diameter (SD) and unconfined compressive strength (UCS), following distinct linear/logarithmic and exponential trends, respectively. WFT has an exponential impact on SD and a non-linear effect on UCS, enhancing strength at low levels (0 μm < WFT < 0.0071 μm) and balancing hydration and flowability at moderate levels (0.0071 μm < WFT < 0.0193 μm) but reducing strength at high levels (WFT > 0.0193 μm). Additionally, superfine cement significantly improves the pore structure of STCPB by reducing porosity and macropore content. These findings provide valuable insights into optimizing STCPB for enhanced performance and sustainability in mine backfilling applications. Full article

With the escalating demand for advanced and eco-friendly processing technologies in mining engineering, the potential applications of microwave heating technology in the treatment of cement tailings backfill (CTB) are expanding significantly. This research comprehensively investigates the mechanisms through which microwave irradiation duration and power influence the mechanical properties of CTB with varying concentrations and cement-to-sand ratios. The aim is to reveal the influencing patterns through experimental methods, providing scientific evidence for optimizing CTB treatment processes. This paper conducted microwave heating tests, uniaxial compression tests, and SEM-EDS tests on CTB. The research results indicate that heating time and power significantly enhance the early strength of CTB, with a more pronounced effect on CTB with higher concentrations and higher cement–sand ratios. When the heating time is 7 min and the heating power is 340 W, the cement hydration reaction is maximally promoted, thereby increasing the density and strength growth rate of CTB. However, excessively long heating time or overly high heating power may cause microcracks or thermal stress concentration within the CTB, adversely affecting the strength growth rate of CTB. Optimal thermal exposure duration and microwave power settings facilitate the activation of cementitious materials and the nucleation of calcium-silicate-hydrate (C-S-H) phases, thereby accelerating the compressive strength evolution of cemented tailings backfill (CTB). The outcomes of this research offer valuable insights into the deployment of microwave heating methodologies in underground mine backfilling, which are pivotal for augmenting the economic viability and environmental sustainability of mining operations. Full article

Large-scale construction 3D printing is a promising platform technology that can be leveraged to fabricate structural elements such as columns, piers, pipes, and culverts. In this study, the axial compression and split tensile performance of 3D-printed steel-fiber-reinforced circular elements fabricated with different configurations (hollow, hybrid, mold-cast, and fully 3D-printed) is evaluated. This study further investigates the performance of multi-material circular hybrid elements (3D-printed shells with different backfilled core materials) in an attempt to assess their suitability as a new construction paradigm. The experimental results revealed that the fully 3D-printed steel-fiber-reinforced circular elements exhibited a higher load capacity (up to 36%) and a distinct crack pattern compared to the other configurations. The void ratio of circular elements has varying effects on its axial load capacity depending on the printing material and significantly influences its splitting tensile load capacity. Furthermore, the compatibility between the 3D-printed shell and the cast-in-place core is identified as an influential factor in the structural performance of the hybrid elements. The results suggest a promising construction approach where low-cement material can be utilized as infill material for a cost-effective 3D-printed permanent formwork, offering a viable solution for specific infrastructure development applications. Full article

The high consumption and high cost of cement are the bottleneck problems that limit the development of cemented tailings backfilling technology. The low-consumption cement backfill is immersed in a weak acid/alkaline groundwater environment for a long time. Reducing the consumption of cement can easily lead to problems such as a sudden decrease in strength and the leakage of heavy metals. Through the monolithic leaching test in static and uniaxial compressive tests, the heavy metals’ leaching concentration and the compressive strength of low-consumption cement backfills in different pH soaking solutions were measured at different soaking times. Results show that a lower cement concentration will result in a lower CTB compressive strength and a higher rate of heavy metal leaching. Long-term exposure to an acidic/alkaline environment will lead to the instability and destruction of the CTB structure. A microscopic examination reveals that the creation of hydration products can improve the structure’s compactness while also lowering the internal porosity of CTB but can also solidify heavy metal ions in various ways. A first-order reaction/diffusion model (FRDM) can better evaluate the leaching behavior of CTB. This study helps to improve backfilling technology, thereby contributing to the creation of sustainable mining geotechnologies. Full article

This paper proposes a technique for producing underground backfilling materials using enzyme-induced calcium carbonate precipitation (EICP) technology to address the growing ecological security concerns caused by coal mining. To augment the mineralization impact of EICP, diverse levels of organic substances, including yeast extract, peptone, and skimmed milk powder, were incorporated into the cementing solution to offer a greater number of nucleation sites for the precipitation of calcium carbonate. The results indicate that (1) based on visual observations, all the sand columns remained intact after cementation, demonstrating a good cementation effect; (2) unconfined compressive strength (UCS) test findings demonstrated that the introduction of organic components effectively augmented the strength of EICP. Among these materials, skimmed milk powder exhibited the most significant effect, resulting in a 66.01% increase in the UCS of EICP at a concentration of 6 g/L. Peptone also showed a positive impact, albeit to a lesser extent, while yeast powder had a relatively lower effect; (3) The utilization of scanning electron microscopy (SEM) revealed a significant diversification in the crystal morphology of calcium carbonate when combined with organic materials through the EICP process. An X-ray diffraction (XRD) test confirmed the presence of calcite and vaterite. This finding implies that the molecular structure of calcium carbonate is enhanced by the inclusion of organic materials. Full article

Air-entraining agents have the function of optimizing pores and improving the performance of backfill. In this study, we used tailings and cement as the main raw materials and added different amounts of air-entraining agents to make backfill samples. By testing the uniaxial compressive strength (UCS) and microstructure, macro- and micro characteristics were studied. Nuclear magnetic resonance technology was used to explore pore characteristics, and fractal theory was used to quantitatively discuss the complexity of pore structure. Finally, a cross-scale relationship model between UCS and pores was established. The main conclusions are as follows: (1) Adding the appropriate amount of air-entraining agents can optimize pore structure and increase the UCS of backfill materials, which is beneficial to backfill materials. (2) The pores of backfill materials have fractal characteristics, the fractal effects of pores with different pore size ranges are different, and the air-entraining agent has a certain influence on the fractal characteristics of the pores. (3) There are inverse relationships between UCS and different pore size ranges. Full article

Cemented paste backfill (CPB) as a solid waste treatment technology that prepares tailings as aggregate into a highly concentrated slurry to be transported to the underground mining area, is now widely used in mines. However, the pipeline resistance loss and erosion wear during CPB slurry transportation considering the coupling effect of inlet velocities, viscosities, and particle sizes have not yet been well evaluated and analyzed. Hence, the CFD-based three-dimensional network simulation of CPB slurry flow in an L-shaped pipe at different combinations of the three parameters was developed using COMSOL Multiphysics software. The results showed that the pipe resistance loss was most affected by the inlet velocity and viscosity, with the minimum pipe resistance loss occurring at an inlet velocity of 1.5 m/s, a viscosity of 2.0 Pa·s, and a particle size of 150 μm. In particular, pipe erosion wear was severest at the bend and was positively correlated with inlet velocity and particle size, and negatively correlated with slurry viscosity, with maximum pipe erosion wear occurring at an inlet velocity of 3.5 m/s, a viscosity of 3.0 Pa·s, and a particle size of 2000 μm. The findings would be important for the design of the CPB pipeline transportation, which will improve the safety and economic level of a mine. Full article

The pore-throat characteristics significantly affect the consolidated properties, such as the mechanical and permeability-related performance of the cementitious composites. By virtue of the nucleation and pore-infilling effects, graphene oxide (GO) has been proven as a great additive in reinforcing cement-based materials. However, the quantitative characterization reports of GO on the pore-throat connection are limited. This study applied advanced metal intrusion and backscattered electron (BSE) microscopy scanning technology to investigate the pore-throat connection characteristics of the cement waste rock backfill (CWRB) specimens before and after GO modification. The results show that the microscopic pore structure of CWRB is significantly improved by the GO nanosheets, manifested by a decrease in the total porosity up to 31.2%. With the assistance of the GO, the transfer among internal pores is from large equivalent pore size distribution to small equivalent pore size distribution. The fitting relationship between strength enhancement and pore reinforcement efficiency under different pore-throat characteristics reveals that the 1.70 μm pore-throat owns the highest correlation in the CWRB specimens, implying apply GO nanosheets to optimizing the pore-throat under this interval is most efficient. Overall, this research broadens our understanding of the pore-throat connection characteristics of CWRB and stimulates the potential application of GO in enhancing the mechanical properties and microstructure of CWRB. Full article

The utilization of solid waste for filling mining presents substantial economic and environmental advantages, making it the primary focus of current filling mining technology development. To enhance the mechanical properties of superfine tailings cemented paste backfill (SCPB), this study conducted response surface methodology experiments to investigate the impact of various factors on the strength of SCPB, including the composite cementitious material, consisting of cement and slag powder, and the tailings’ grain size. Additionally, various microanalysis techniques were used to investigate the microstructure of SCPB and the development mechanisms of its hydration products. Furthermore, machine learning was utilized to predict the strength of SCPB under multi-factor effects. The findings reveal that the combined effect of slag powder dosage and slurry mass fraction has the most significant influence on strength, while the coupling effect of slurry mass fraction and underflow productivity has the lowest impact on strength. Moreover, SCPB with 20% slag powder has the highest amount of hydration products and the most complete structure. When compared to other commonly used prediction models, the long-short term memory neural network (LSTM) constructed in this study had the highest prediction accuracy for SCPB strength under multi-factor conditions, with root mean square error (RMSE), correlation coefficient (R), and variance account for (VAF) reaching 0.1396, 0.9131, and 81.8747, respectively. By optimizing the LSTM using the sparrow search algorithm (SSA), the RMSE, R, and VAF improved by 88.6%, 9.4%, and 21.9%, respectively. The research results can provide guidance for the efficient filling of superfine tailings. Full article

Backfill is a very important technology that can be used to reduce the environmental footprints resulting from coal mining. The selection of proper filling materials is of great significance to the operation cost and the stability of the goaf. This paper investigated the feasibility of using the coal gangue as the main component of the filling paste so as to reuse the byproducts in coal mining to the maximum extent. The filling pastes were composed of coal gangue as the aggregates, cement or gypsum as cementitious materials, and some additives. In order to determine the optimal recipe, the performances of filling pastes were first comprehensively evaluated according to their fluidity, mechanical properties, shrinkage, and permeability. The results showed that cement content was the most influential factor, while the fly ash addition was the weakest factor for the performance of filling pastes. Moreover, the appropriate use of a water reducer and expansion agent improved the working performance of the paste. Based on the performances of filling pastes, the fuzzy mathematics evaluation method was then used to establish the weight vector and index vector. The principle of maximum membership degree and the principle of maximum closeness were used to identify the identified objects and find the best recipe for the filling paste. The results showed that this evaluation method could fully reflect the influence of various factors and provide accurate evaluation results. Full article