Search2023 Vol. 30, No. 8
Display Method:
2023, vol. 30, no. 8, pp.
1430-1443.
https://doi.org/10.1007/s12613-023-2609-6
Abstract:
The development of industry is inseparable from the support of mining. However, mining processes consume a large amount of energy, and increased tailing emissions can have a significant impact on the environment. In the past few decades, the mining industry developed many technologies that are related to mineral energy management, of which cemented paste backfill (CPB) is one of the representative technologies. CPB has been successfully applied to mine ground control and tailings management. In CPB technology, the mixing process is the key to achieving materials with good final quality and controlled properties. However, in the preparation process, the mixed homogeneity of the CPB is difficult to achieve because of fine tailings, high solid volume fraction, and high viscosity. Most research focused on the effect of mixing ingredients on CPB properties rather than on the preparation process of the CPB. Therefore, improving the performance and reducing the production cost of CPB by optimizing the mixing process are important. This review summarizes the current studies on the mixing technology of CPB and its application status in China. Then, it compares the advantages and disadvantages of multiple mixing equipment and discusses the latest results and research hotspots in paste preparation. Finally, it concludes the challenges and development trends of mixing technology on the basis of the relevant application cases in China to promoting cement-based material mixing technology development.
The development of industry is inseparable from the support of mining. However, mining processes consume a large amount of energy, and increased tailing emissions can have a significant impact on the environment. In the past few decades, the mining industry developed many technologies that are related to mineral energy management, of which cemented paste backfill (CPB) is one of the representative technologies. CPB has been successfully applied to mine ground control and tailings management. In CPB technology, the mixing process is the key to achieving materials with good final quality and controlled properties. However, in the preparation process, the mixed homogeneity of the CPB is difficult to achieve because of fine tailings, high solid volume fraction, and high viscosity. Most research focused on the effect of mixing ingredients on CPB properties rather than on the preparation process of the CPB. Therefore, improving the performance and reducing the production cost of CPB by optimizing the mixing process are important. This review summarizes the current studies on the mixing technology of CPB and its application status in China. Then, it compares the advantages and disadvantages of multiple mixing equipment and discusses the latest results and research hotspots in paste preparation. Finally, it concludes the challenges and development trends of mixing technology on the basis of the relevant application cases in China to promoting cement-based material mixing technology development.
2023, vol. 30, no. 8, pp.
1444-1454.
https://doi.org/10.1007/s12613-023-2601-1
Abstract:
The technology of cemented paste backfill (CPB) is an effective method for green mining. In CPB, mixing is a vital process aiming to prepare a paste that meets the non-stratification, non-segregation, and non-bleeding requirements. As a multiscale granular system, homogenization is one of the challenges in the paste-mixing process. Due to the high shearing, high concentration, and multiscale characteristics, paste exhibits complex rheological properties in the mixing process. An overview of the mesomechanics and structural evolution is presented in this review. The effects of various influencing factors on the paste’s rheological properties were investigated, and the rheological models of the paste were outlined from the macroscopic and mesoscopic levels. The results show that the mechanical effects and structural evolution are the fundamental factors affecting the rheological properties of the paste. Existing problems and future development trends are presented to change the practice where the CPB process comes first and the theory lags.
The technology of cemented paste backfill (CPB) is an effective method for green mining. In CPB, mixing is a vital process aiming to prepare a paste that meets the non-stratification, non-segregation, and non-bleeding requirements. As a multiscale granular system, homogenization is one of the challenges in the paste-mixing process. Due to the high shearing, high concentration, and multiscale characteristics, paste exhibits complex rheological properties in the mixing process. An overview of the mesomechanics and structural evolution is presented in this review. The effects of various influencing factors on the paste’s rheological properties were investigated, and the rheological models of the paste were outlined from the macroscopic and mesoscopic levels. The results show that the mechanical effects and structural evolution are the fundamental factors affecting the rheological properties of the paste. Existing problems and future development trends are presented to change the practice where the CPB process comes first and the theory lags.
2023, vol. 30, no. 8, pp.
1455-1473.
https://doi.org/10.1007/s12613-023-2663-0
Abstract:
Mining is the foundation of modern industrial development. In the context of the “carbon peaking and carbon neutrality” era, countries have put forward the development strategy of “adhering to the harmonious coexistence of humans and nature.” The ongoing progress and improvement of filling mining technology have provided significant advantages, such as “green mining, safe, efficient, and low-carbon emission,” which is crucial to the comprehensive utilization of mining solid waste, environmental protection, and safety of re-mining. This review paper describes the development history of metal mine filling mining in China and the characteristics of each stage. The excitation mechanism and current research status of producing cementitious materials from blast furnace slag and other industrial wastes are then presented, and the concept of developing cementitious materials for backfill based on the whole solid waste is proposed. The advances in the mechanical characteristics of cemented backfill are elaborated on four typical levels: static mechanics, dynamic mechanics, mechanical influencing factors, and multi-scale mechanics. The working/rheological characteristics of the filling slurry are presented, given the importance of the filling materials conveying process. Finally, the future perspectives of mining with backfill are discussed based on the features of modern filling concepts to provide the necessary theoretical research value for filling mining.
Mining is the foundation of modern industrial development. In the context of the “carbon peaking and carbon neutrality” era, countries have put forward the development strategy of “adhering to the harmonious coexistence of humans and nature.” The ongoing progress and improvement of filling mining technology have provided significant advantages, such as “green mining, safe, efficient, and low-carbon emission,” which is crucial to the comprehensive utilization of mining solid waste, environmental protection, and safety of re-mining. This review paper describes the development history of metal mine filling mining in China and the characteristics of each stage. The excitation mechanism and current research status of producing cementitious materials from blast furnace slag and other industrial wastes are then presented, and the concept of developing cementitious materials for backfill based on the whole solid waste is proposed. The advances in the mechanical characteristics of cemented backfill are elaborated on four typical levels: static mechanics, dynamic mechanics, mechanical influencing factors, and multi-scale mechanics. The working/rheological characteristics of the filling slurry are presented, given the importance of the filling materials conveying process. Finally, the future perspectives of mining with backfill are discussed based on the features of modern filling concepts to provide the necessary theoretical research value for filling mining.
2023, vol. 30, no. 8, pp.
1474-1489.
https://doi.org/10.1007/s12613-023-2640-7
Abstract:
The mesoscale fiber–matrix interfacial transition zone (FM-ITZ) under induced curing pressure plays a key role in the effectiveness of fiber reinforcement and the engineering application of fiber-reinforced cementitious composites (FRCCs). This critical review establishes the link among induced curing pressure (i.e., external loading condition), multiphysics processes (i.e., internal governing mechanism), and interface behavior (i.e., material behavior) for FRCC materials through analysis of the state-of-the-art research findings on the FM-ITZ of FRCC materials. The following results are obtained. For the mechanical process, the induced curing pressure changes the stress state and enhances multicracking behavior, which can strengthen the FM-ITZ. For the hydraulic process, the strengthened seepage of the FM-ITZ under induced curing pressure weakens the effective stress and exaggerates the deficiency in water retention capacity between the bulk matrix and the FM-ITZ. For the thermal process, the induced curing pressure causes a steep temperature gradient in the FM-ITZ and thus influences the temperature evolution and thermally-induced microcracks in the FM-ITZ. For the chemical process, the induced curing pressure enhances hydration kinetics and results in the formation of additional hydration products in the FM-ITZ. Moreover, recommendations are proposed on the basis of findings from this review to facilitate the implementation of fiber reinforcement in cemented paste backfill technology.
The mesoscale fiber–matrix interfacial transition zone (FM-ITZ) under induced curing pressure plays a key role in the effectiveness of fiber reinforcement and the engineering application of fiber-reinforced cementitious composites (FRCCs). This critical review establishes the link among induced curing pressure (i.e., external loading condition), multiphysics processes (i.e., internal governing mechanism), and interface behavior (i.e., material behavior) for FRCC materials through analysis of the state-of-the-art research findings on the FM-ITZ of FRCC materials. The following results are obtained. For the mechanical process, the induced curing pressure changes the stress state and enhances multicracking behavior, which can strengthen the FM-ITZ. For the hydraulic process, the strengthened seepage of the FM-ITZ under induced curing pressure weakens the effective stress and exaggerates the deficiency in water retention capacity between the bulk matrix and the FM-ITZ. For the thermal process, the induced curing pressure causes a steep temperature gradient in the FM-ITZ and thus influences the temperature evolution and thermally-induced microcracks in the FM-ITZ. For the chemical process, the induced curing pressure enhances hydration kinetics and results in the formation of additional hydration products in the FM-ITZ. Moreover, recommendations are proposed on the basis of findings from this review to facilitate the implementation of fiber reinforcement in cemented paste backfill technology.
2023, vol. 30, no. 8, pp.
1490-1501.
https://doi.org/10.1007/s12613-023-2642-5
Abstract:
Estimation of stressses within the tailings slurry during self-weight consolidation is a critical issue for cost-effective barricade design and efficient backfill planning in underground mine stopes. This process requires a good understanding of self-weight consolidation behaviors of the tailings slurry within practical stopes, where many factors can have significant effects on the consolidation, including drainage condition and cement addition. In this paper, the prepared tailings slurry with different cement contents (0, 4.76wt%, and 6.25wt%) was poured into 1.2 m-high columns, which allowed three drainage scenarios (undrained, partial lateral drainage near the bottom part, and full lateral drainage boundaries) to investigate the effects of drainage condition and cement addition on the consolidation behavior of the tailings slurry. The consolidation behavior was analyzed in terms of pore water pressure (PWP), settlement, volume of drainage water, and residual water content. The results indicate that increasing the length of the drainage boundary or cement content aids in PWP dissipation. In addition, constructing an efficient drainage boundary was more favorable to PWP dissipation than increasing cement addition. The final stable PWP on the column floor was not sensitive to cement addition. The final settlement of uncemented tailings slurry was independent of drainage conditions, and that of cemented tailings slurry decreased with the increase in cement addition. Notably, more pore water can drain out from the cemented tailings slurry than the uncemented tailings slurry during consolidation.
Estimation of stressses within the tailings slurry during self-weight consolidation is a critical issue for cost-effective barricade design and efficient backfill planning in underground mine stopes. This process requires a good understanding of self-weight consolidation behaviors of the tailings slurry within practical stopes, where many factors can have significant effects on the consolidation, including drainage condition and cement addition. In this paper, the prepared tailings slurry with different cement contents (0, 4.76wt%, and 6.25wt%) was poured into 1.2 m-high columns, which allowed three drainage scenarios (undrained, partial lateral drainage near the bottom part, and full lateral drainage boundaries) to investigate the effects of drainage condition and cement addition on the consolidation behavior of the tailings slurry. The consolidation behavior was analyzed in terms of pore water pressure (PWP), settlement, volume of drainage water, and residual water content. The results indicate that increasing the length of the drainage boundary or cement content aids in PWP dissipation. In addition, constructing an efficient drainage boundary was more favorable to PWP dissipation than increasing cement addition. The final stable PWP on the column floor was not sensitive to cement addition. The final settlement of uncemented tailings slurry was independent of drainage conditions, and that of cemented tailings slurry decreased with the increase in cement addition. Notably, more pore water can drain out from the cemented tailings slurry than the uncemented tailings slurry during consolidation.
2023, vol. 30, no. 8, pp.
1502-1514.
https://doi.org/10.1007/s12613-023-2617-6
Abstract:
The mechanical properties of cemented paste backfill (CPB) determine its control effect on the goaf roof. In this study, the mechanical strength of polymer-modified cemented paste backfill (PCPB) samples was tested by uniaxial compression tests, and the failure characteristics of PCPB under the compression were analyzed. Besides, acoustic emission (AE) technology was used to monitor and record the cracking process of the PCPB sample with a curing age of 28 d, and two AE indexes (rise angle and average frequency) were used to classify the failure modes of samples under different loading processes. The results show that waterborne epoxy resin can significantly enhance the mechanical strength of PCPB samples (when the mass ratio of polymer to powder material is 0.30, the strength of PCPB samples with a curing age of 28 d is increased by 102.6%); with the increase of polymer content, the mechanical strength of PCPB samples is improved significantly in the early and middle period of curing. Under uniaxial load, the macro cracks of PCPB samples are mostly generated along the axial direction, the main crack runs through the sample, and a large number of small cracks are distributed around the main crack. The AE response of PCPB samples during the whole loading process can be divided into four periods: quiet period, slow growth period, rapid growth period, and remission period, corresponding to the micro-pore compaction stage, elastic deformation stage, plastic deformation stage, and failure instability stage of the stress–strain curve. The AE events are mainly concentrated in the plastic deformation stage; both shear failure and tensile failure occur in the above four stages, while tensile failure is dominant for PCPB samples. This study provides a reference for the safety of coal pillar recovery in pillar goaf.
The mechanical properties of cemented paste backfill (CPB) determine its control effect on the goaf roof. In this study, the mechanical strength of polymer-modified cemented paste backfill (PCPB) samples was tested by uniaxial compression tests, and the failure characteristics of PCPB under the compression were analyzed. Besides, acoustic emission (AE) technology was used to monitor and record the cracking process of the PCPB sample with a curing age of 28 d, and two AE indexes (rise angle and average frequency) were used to classify the failure modes of samples under different loading processes. The results show that waterborne epoxy resin can significantly enhance the mechanical strength of PCPB samples (when the mass ratio of polymer to powder material is 0.30, the strength of PCPB samples with a curing age of 28 d is increased by 102.6%); with the increase of polymer content, the mechanical strength of PCPB samples is improved significantly in the early and middle period of curing. Under uniaxial load, the macro cracks of PCPB samples are mostly generated along the axial direction, the main crack runs through the sample, and a large number of small cracks are distributed around the main crack. The AE response of PCPB samples during the whole loading process can be divided into four periods: quiet period, slow growth period, rapid growth period, and remission period, corresponding to the micro-pore compaction stage, elastic deformation stage, plastic deformation stage, and failure instability stage of the stress–strain curve. The AE events are mainly concentrated in the plastic deformation stage; both shear failure and tensile failure occur in the above four stages, while tensile failure is dominant for PCPB samples. This study provides a reference for the safety of coal pillar recovery in pillar goaf.
2023, vol. 30, no. 8, pp.
1515-1523.
https://doi.org/10.1007/s12613-023-2610-0
Abstract:
Wall slip is a microscopic phenomenon of cemented paste backfill (CPB) slurry near the pipe wall, which has an important influence on the form of slurry pipe transport flow and velocity distribution. Directly probing the wall slip characteristics using conventional experimental methods is difficult. Therefore, this paper established a noncontact experimental platform for monitoring the microscopic slip layer of CPB pipeline transport independently based on particle image velocimetry (PIV) and analyzed the effects of slurry temperature, pipe diameter, solid concentration, and slurry flow on the wall slip velocity of the CPB slurry, which refined the theory of the effect of wall slip characteristics on pipeline transport. The results showed that the CPB slurry had an extensive slip layer at the pipe wall with significant wall slip. High slurry temperature improved the degree of particle Brownian motion within the slurry and enhanced the wall slip effect. Increasing the pipe diameter was not conducive to the formation of the slurry slip layer and led to a transition in the CPB slurry flow pattern. The increase in the solid concentration raised the interlayer shear effect of CPB slurry flow and the slip velocity. The slip velocity value increased from 0.025 to 0.056 m·s−1 when the solid content improved from 55wt% to 65wt%. When slurry flow increased, the CPB slurry flocculation structure changed, which affected the slip velocity, and the best effect of slip layer resistance reduction was achieved when the transported flow rate was 1.01 m3·h−1. The results had important theoretical significance for improving the stability and economy of the CPB slurry in the pipeline.
Wall slip is a microscopic phenomenon of cemented paste backfill (CPB) slurry near the pipe wall, which has an important influence on the form of slurry pipe transport flow and velocity distribution. Directly probing the wall slip characteristics using conventional experimental methods is difficult. Therefore, this paper established a noncontact experimental platform for monitoring the microscopic slip layer of CPB pipeline transport independently based on particle image velocimetry (PIV) and analyzed the effects of slurry temperature, pipe diameter, solid concentration, and slurry flow on the wall slip velocity of the CPB slurry, which refined the theory of the effect of wall slip characteristics on pipeline transport. The results showed that the CPB slurry had an extensive slip layer at the pipe wall with significant wall slip. High slurry temperature improved the degree of particle Brownian motion within the slurry and enhanced the wall slip effect. Increasing the pipe diameter was not conducive to the formation of the slurry slip layer and led to a transition in the CPB slurry flow pattern. The increase in the solid concentration raised the interlayer shear effect of CPB slurry flow and the slip velocity. The slip velocity value increased from 0.025 to 0.056 m·s−1 when the solid content improved from 55wt% to 65wt%. When slurry flow increased, the CPB slurry flocculation structure changed, which affected the slip velocity, and the best effect of slip layer resistance reduction was achieved when the transported flow rate was 1.01 m3·h−1. The results had important theoretical significance for improving the stability and economy of the CPB slurry in the pipeline.
2023, vol. 30, no. 8, pp.
1524-1537.
https://doi.org/10.1007/s12613-022-2545-x
Abstract:
A backfilling body-coal pillar-backfilling body (BPB) structure formed by pillar-side cemented paste backfilling can bear overburden stress and ensure safe mining. However, the failure response of BPB composite samples must be investigated. This paper examines the deformation characteristics and damage evolution of six types of BPB composite samples using a digital speckle correlation method under uniaxial compression conditions. A new damage evolution equation was established on the basis of the input strain energy and dissipated strain energy at the peak stress. The prevention and control mechanisms of the backfilling body on the coal pillar instability were discussed. The results show that the deformation localization and macroscopic cracks of the BPB composite samples first appeared at the coal–backfilling interface, and then expanded to the backfilling elements, ultimately appearing in the coal elements. The elastic strain energy in the BPB composite samples reached a maximum at the peak stress, whereas the dissipated energy continued to accumulate and increase. The damage evolution curve and equation agree well with the test results, providing further understanding of instability prevention and the control mechanisms of the BPB composite samples. The restraining effect on the coal pillar was gradually reduced with decreasing backfilling body element’s volume ratio, and the BPB composite structure became more vulnerable to failure. This research is expected to guide the design, stability monitoring, instability prevention, and control of BPB structures in pillar-side cemented paste backfilling mining.
A backfilling body-coal pillar-backfilling body (BPB) structure formed by pillar-side cemented paste backfilling can bear overburden stress and ensure safe mining. However, the failure response of BPB composite samples must be investigated. This paper examines the deformation characteristics and damage evolution of six types of BPB composite samples using a digital speckle correlation method under uniaxial compression conditions. A new damage evolution equation was established on the basis of the input strain energy and dissipated strain energy at the peak stress. The prevention and control mechanisms of the backfilling body on the coal pillar instability were discussed. The results show that the deformation localization and macroscopic cracks of the BPB composite samples first appeared at the coal–backfilling interface, and then expanded to the backfilling elements, ultimately appearing in the coal elements. The elastic strain energy in the BPB composite samples reached a maximum at the peak stress, whereas the dissipated energy continued to accumulate and increase. The damage evolution curve and equation agree well with the test results, providing further understanding of instability prevention and the control mechanisms of the BPB composite samples. The restraining effect on the coal pillar was gradually reduced with decreasing backfilling body element’s volume ratio, and the BPB composite structure became more vulnerable to failure. This research is expected to guide the design, stability monitoring, instability prevention, and control of BPB structures in pillar-side cemented paste backfilling mining.
2023, vol. 30, no. 8, pp.
1538-1547.
https://doi.org/10.1007/s12613-022-2587-0
Abstract:
Water-locking flocs formed by ultrafine tailings particles will damage the thickener underflow concentration in the thickening process during paste preparation. The relationship between the mesostructure and seepage characteristics of tail mortar is typically ignored when investigating the deep dehydration stage. A shearing seepage test of an unclassified tailing–sedimentation bed was performed with copper tailings, and the morphology and geometric distribution of micropores were analyzed via X-ray computed tomography. Moreover, the shearing evolution of the micropore structure and seepage channel was investigated to evaluate the dewatering performance of underflow slurry using a three-dimensional reconstruction approach. The results show that porosity decreases considerably under shearing. The connected-pore ratio and the average radius of the throat channel reach peak values of 0.79 and 31.38 μm, respectively, when shearing is applied for 10 min. However, the reverse seepage velocity and absolute permeability in the bed decrease to various extents after shearing. Meanwhile, the maximum flow rate reaches 1.537 μm/s and the absolute permeability increases by 14.16%. Shearing alters the formation process and the pore structure of the seepage channel. Isolated pores connect to the surrounding flocs to form branch channels, which then become the main seepage channel and create the dominant water-seepage flow channel.
Water-locking flocs formed by ultrafine tailings particles will damage the thickener underflow concentration in the thickening process during paste preparation. The relationship between the mesostructure and seepage characteristics of tail mortar is typically ignored when investigating the deep dehydration stage. A shearing seepage test of an unclassified tailing–sedimentation bed was performed with copper tailings, and the morphology and geometric distribution of micropores were analyzed via X-ray computed tomography. Moreover, the shearing evolution of the micropore structure and seepage channel was investigated to evaluate the dewatering performance of underflow slurry using a three-dimensional reconstruction approach. The results show that porosity decreases considerably under shearing. The connected-pore ratio and the average radius of the throat channel reach peak values of 0.79 and 31.38 μm, respectively, when shearing is applied for 10 min. However, the reverse seepage velocity and absolute permeability in the bed decrease to various extents after shearing. Meanwhile, the maximum flow rate reaches 1.537 μm/s and the absolute permeability increases by 14.16%. Shearing alters the formation process and the pore structure of the seepage channel. Isolated pores connect to the surrounding flocs to form branch channels, which then become the main seepage channel and create the dominant water-seepage flow channel.
2023, vol. 30, no. 8, pp.
1548-1559.
https://doi.org/10.1007/s12613-022-2540-2
Abstract:
Cemented paste backfill (CPB) is one of the effective methods for resource utilization of tailings, but the high cost of ordinary Portland cement (OPC) limits its utilization. Considering the poor performance of Na2CO3-activated binders, in this work, supplementary materials, including CaO, MgO, and calcined layered double hydroxide (CLDH), were used to modify their properties with the aim of finding an alternative binder to OPC. Isothermal calorimetry, X-ray diffraction, and thermogravimetric analyses were conducted to explore the reaction kinetics and phase assembles of the binder. The properties of the CPB samples, such as flowability, strength development, and heavy metal immobilization effects, were then investigated. The results show that the coupling utilization of MgO and CLDH showed good performance. The strength of the Mg2-CLDH3 sample was approximately 2.94 MPa after curing for 56 d, which was higher than that of the OPC-based sample. Moreover, the cost of the modified Na2CO3-activated binder was lower than that of the OPC-based binder. Modified sample showed satisfactory heavy metal immobilization effects. These findings demonstrate that carbonate-activated binder modified by supplementary materials can be suitable in CPB.
Cemented paste backfill (CPB) is one of the effective methods for resource utilization of tailings, but the high cost of ordinary Portland cement (OPC) limits its utilization. Considering the poor performance of Na2CO3-activated binders, in this work, supplementary materials, including CaO, MgO, and calcined layered double hydroxide (CLDH), were used to modify their properties with the aim of finding an alternative binder to OPC. Isothermal calorimetry, X-ray diffraction, and thermogravimetric analyses were conducted to explore the reaction kinetics and phase assembles of the binder. The properties of the CPB samples, such as flowability, strength development, and heavy metal immobilization effects, were then investigated. The results show that the coupling utilization of MgO and CLDH showed good performance. The strength of the Mg2-CLDH3 sample was approximately 2.94 MPa after curing for 56 d, which was higher than that of the OPC-based sample. Moreover, the cost of the modified Na2CO3-activated binder was lower than that of the OPC-based binder. Modified sample showed satisfactory heavy metal immobilization effects. These findings demonstrate that carbonate-activated binder modified by supplementary materials can be suitable in CPB.
2023, vol. 30, no. 8, pp.
1560-1572.
https://doi.org/10.1007/s12613-023-2658-x
Abstract:
The great challenge of cemented tailings backfill (CTB) is difficult simultaneously maintaining its excellent mechanical properties and low cost. Fly ash (FA) can potentially address this problem and further replace cement in favor of low carbon development. However, its mechanism on CTB with low cement dosage and low Ca system remains unclear. Consequently, this study conducted uniaxial compression, X-ray diffraction (XRD), and scanning electron microscopy (SEM)–energy dispersive spectrometer (EDS) tests to investigate the effect of FA dosage on the mechanical property and microstructure of CTB. A molecular model of FA-CSH was constructed to reproduce the molecular structure evolution of CTB with FA based on the test results. The influences of FA dosage and calcium/silica molar ratio (Ca/Si ratio) on the matrix strength and failure model were analyzed to reveal the mechanism of FA on calcium silicate hydrated (C–S–H). The results show that the strength of CTB increases initially and then decreases with FA dosage, and the FA supplement leads to a decrease in Ca(OH)2 diffraction intensity and Ca/Si ratio around the FA particles. XRD and SEM–EDS findings show that the Ca/Si ratio of C–S–H decreases with the progression of hydration. The FA-CSH model indicates that FA can reinforce the silica chain of C–S–H to increase the matrix strength. However, this enhancement is weakened by supplementing excessive FA dosage. In addition, the hydrogen bonds among water molecules deteriorate, reducing the matrix strength. A low Ca/Si ratio results in an increase in water molecules and a decrease in the ionic bonds combined with Ca2+. The hydrogen bonds among water molecules cannot withstand high stresses, resulting in a reduction in strength. The water absorption of the FA-CSH model is negatively correlated with the FA dosage and Ca/Si ratio. The use of optimal FA dosage and Ca/Si ratio leads to suitable water absorption, which further affects the failure mode of FA-CSH.
The great challenge of cemented tailings backfill (CTB) is difficult simultaneously maintaining its excellent mechanical properties and low cost. Fly ash (FA) can potentially address this problem and further replace cement in favor of low carbon development. However, its mechanism on CTB with low cement dosage and low Ca system remains unclear. Consequently, this study conducted uniaxial compression, X-ray diffraction (XRD), and scanning electron microscopy (SEM)–energy dispersive spectrometer (EDS) tests to investigate the effect of FA dosage on the mechanical property and microstructure of CTB. A molecular model of FA-CSH was constructed to reproduce the molecular structure evolution of CTB with FA based on the test results. The influences of FA dosage and calcium/silica molar ratio (Ca/Si ratio) on the matrix strength and failure model were analyzed to reveal the mechanism of FA on calcium silicate hydrated (C–S–H). The results show that the strength of CTB increases initially and then decreases with FA dosage, and the FA supplement leads to a decrease in Ca(OH)2 diffraction intensity and Ca/Si ratio around the FA particles. XRD and SEM–EDS findings show that the Ca/Si ratio of C–S–H decreases with the progression of hydration. The FA-CSH model indicates that FA can reinforce the silica chain of C–S–H to increase the matrix strength. However, this enhancement is weakened by supplementing excessive FA dosage. In addition, the hydrogen bonds among water molecules deteriorate, reducing the matrix strength. A low Ca/Si ratio results in an increase in water molecules and a decrease in the ionic bonds combined with Ca2+. The hydrogen bonds among water molecules cannot withstand high stresses, resulting in a reduction in strength. The water absorption of the FA-CSH model is negatively correlated with the FA dosage and Ca/Si ratio. The use of optimal FA dosage and Ca/Si ratio leads to suitable water absorption, which further affects the failure mode of FA-CSH.
2023, vol. 30, no. 8, pp.
1573-1583.
https://doi.org/10.1007/s12613-022-2560-y
Abstract:
Detecting a pipeline’s abnormal status, which is typically a blockage and leakage accident, is important for the continuity and safety of mine backfill. The pipeline system for gravity-transport high-density backfill (GHB) is complex. Specifically designed, efficient, and accurate abnormal pipeline detection methods for GHB are rare. This work presents a long short-term memory-based deep learning (LSTM-DL) model for GHB pipeline blockage and leakage diagnosis. First, an industrial pipeline monitoring system was introduced using pressure and flow sensors. Second, blockage and leakage field experiments were designed to solve the problem of negative sample deficiency. The pipeline’s statistical characteristics with different working statuses were analyzed to show their complexity. Third, the architecture of the LSTM-DL model was elaborated on and evaluated. Finally, the LSTM-DL model was compared with state-of-the-art (SOTA) learning algorithms. The results show that the backfilling cycle comprises multiple working phases and is intermittent. Although pressure and flow signals fluctuate stably in a normal cycle, their values are diverse in different cycles. Plugging causes a sudden change in interval signal features; leakage results in long variation duration and a wide fluctuation range. Among the SOTA models, the LSTM-DL model has the highest detection accuracy of 98.31% for all states and the lowest misjudgment or false positive rate of 3.21% for blockage and leakage states. The proposed model can accurately recognize various pipeline statuses of complex GHB systems.
Detecting a pipeline’s abnormal status, which is typically a blockage and leakage accident, is important for the continuity and safety of mine backfill. The pipeline system for gravity-transport high-density backfill (GHB) is complex. Specifically designed, efficient, and accurate abnormal pipeline detection methods for GHB are rare. This work presents a long short-term memory-based deep learning (LSTM-DL) model for GHB pipeline blockage and leakage diagnosis. First, an industrial pipeline monitoring system was introduced using pressure and flow sensors. Second, blockage and leakage field experiments were designed to solve the problem of negative sample deficiency. The pipeline’s statistical characteristics with different working statuses were analyzed to show their complexity. Third, the architecture of the LSTM-DL model was elaborated on and evaluated. Finally, the LSTM-DL model was compared with state-of-the-art (SOTA) learning algorithms. The results show that the backfilling cycle comprises multiple working phases and is intermittent. Although pressure and flow signals fluctuate stably in a normal cycle, their values are diverse in different cycles. Plugging causes a sudden change in interval signal features; leakage results in long variation duration and a wide fluctuation range. Among the SOTA models, the LSTM-DL model has the highest detection accuracy of 98.31% for all states and the lowest misjudgment or false positive rate of 3.21% for blockage and leakage states. The proposed model can accurately recognize various pipeline statuses of complex GHB systems.
2023, vol. 30, no. 8, pp.
1584-1595.
https://doi.org/10.1007/s12613-022-2574-5
Abstract:
The use of aeolian sand (AS) as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits. Owing to the lack of research on the mechanism of cemented AS backfill (CASB), the response surface method (RSM) was adopted in this study to analyze the influence of ordinary Portland cement (PO) content (x1), fly ash (FA)–AS (FA–AS) ratio (x2), and concentration (x3) on the mechanical and microscopic properties of the CASB. The hydration characteristics and internal pore structure of the backfill were assessed through thermogravimetric/derivative thermogravimetric analysis, mercury intrusion porosimetry, and scanning electron microscopy. The RSM results show that the influence of each factor and interaction term on the response values is extremely significant (except x1x3, which had no obvious effect on the 28 d strength). The uniaxial compressive strength (UCS) increased with the PO content, FA–AS ratio, and concentration. The interaction effects of x1x2, x1x3, and x2x3 on the UCS at 3, 7, and 28 d were analyzed. In terms of the influence of interaction items, an improvement in one factor promoted the strengthening effect of another factor. The enhancement mechanism of the curing time, PO content, and FA–AS ratio on the backfill was reflected in the increase in hydration products and pore structure optimization. By contrast, the enhancement mechanism of the concentration was mainly the pore structure optimization. The UCS was positively correlated with weight loss and micropore content but negatively correlated with the total porosity. The R2 value of the fitting function of the strength and weight loss, micropore content, and total porosity exceeded 0.9, which improved the characterization of the enhancement mechanism of the UCS based on the thermogravimetric analysis and pore structure. This work obtained that the influence rules and mechanisms of the PO, FA–AS, concentration, and interaction terms on the mechanical properties of the CASB provided a certain theoretical and engineering guidance for CASB filling.
The use of aeolian sand (AS) as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits. Owing to the lack of research on the mechanism of cemented AS backfill (CASB), the response surface method (RSM) was adopted in this study to analyze the influence of ordinary Portland cement (PO) content (x1), fly ash (FA)–AS (FA–AS) ratio (x2), and concentration (x3) on the mechanical and microscopic properties of the CASB. The hydration characteristics and internal pore structure of the backfill were assessed through thermogravimetric/derivative thermogravimetric analysis, mercury intrusion porosimetry, and scanning electron microscopy. The RSM results show that the influence of each factor and interaction term on the response values is extremely significant (except x1x3, which had no obvious effect on the 28 d strength). The uniaxial compressive strength (UCS) increased with the PO content, FA–AS ratio, and concentration. The interaction effects of x1x2, x1x3, and x2x3 on the UCS at 3, 7, and 28 d were analyzed. In terms of the influence of interaction items, an improvement in one factor promoted the strengthening effect of another factor. The enhancement mechanism of the curing time, PO content, and FA–AS ratio on the backfill was reflected in the increase in hydration products and pore structure optimization. By contrast, the enhancement mechanism of the concentration was mainly the pore structure optimization. The UCS was positively correlated with weight loss and micropore content but negatively correlated with the total porosity. The R2 value of the fitting function of the strength and weight loss, micropore content, and total porosity exceeded 0.9, which improved the characterization of the enhancement mechanism of the UCS based on the thermogravimetric analysis and pore structure. This work obtained that the influence rules and mechanisms of the PO, FA–AS, concentration, and interaction terms on the mechanical properties of the CASB provided a certain theoretical and engineering guidance for CASB filling.
2023, vol. 30, no. 8, pp.
1596-1607.
https://doi.org/10.1007/s12613-023-2644-3
Abstract:
Paste flow patterns and microscopic particle structures were studied in a pressurized environment generated by a pulse pump. Complex loop-pipe experiments and fluid–solid coupling-based simulations were conducted. The scanning electron microscopy technique was also applied. Results revealed that flow resistance is closely related to pipeline curvature and angle in a complex pipe network. The vertical downward–straight pipe–inclined downward combination was adopted to effectively reduce the loss in resistance along with reducing the number of bends or increasing the radius of bend curvature. The maximum velocity ratio and velocity offset values could quantitatively characterize the influences of different pipeline layouts on the resistance. The correlation reached 96%. Particle distribution and interparticle forces affected flow resistance. Uniform particle states and weak interparticle forces were conducive to steady transport. Pulse pump pressure led to high flow resistance. It could improve pipe flow stability by increasing flow uniformity and particle motion stability. These results can contribute to safe and efficient paste filling.
Paste flow patterns and microscopic particle structures were studied in a pressurized environment generated by a pulse pump. Complex loop-pipe experiments and fluid–solid coupling-based simulations were conducted. The scanning electron microscopy technique was also applied. Results revealed that flow resistance is closely related to pipeline curvature and angle in a complex pipe network. The vertical downward–straight pipe–inclined downward combination was adopted to effectively reduce the loss in resistance along with reducing the number of bends or increasing the radius of bend curvature. The maximum velocity ratio and velocity offset values could quantitatively characterize the influences of different pipeline layouts on the resistance. The correlation reached 96%. Particle distribution and interparticle forces affected flow resistance. Uniform particle states and weak interparticle forces were conducive to steady transport. Pulse pump pressure led to high flow resistance. It could improve pipe flow stability by increasing flow uniformity and particle motion stability. These results can contribute to safe and efficient paste filling.
2023, vol. 30, no. 8, pp.
1608-1620.
https://doi.org/10.1007/s12613-023-2672-z
Abstract:
Pipeline hydraulic transport is a highly efficient and low energy-consumption method for transporting solids and is commonly used for tailing slurry transport in the mining industry. Erosion wear (EW) remains the main cause of failure in tailings slurry pipeline systems, particularly at bends. EW is a complex phenomenon influenced by numerous factors, but research in this area has been limited. This study performs numerical simulations of slurry transport at the bend by combining computational fluid dynamics and fluid particle tracking using a wear model. Based on the validation of the feasibility of the model, this work focuses on the effects of coupled inlet velocity (IV) ranging from 1.5 to 3.0 m·s−1, particle size (PS) ranging from 50 to 650 μm, and bend angle (BA) ranging from 45° to 90° on EW at the bend in terms of particle kinetic energy and incidence angle. The results show that the maximum EW rate of the slurry at the bend increases exponentially with IV and PS and first increases and then decreases with the increase in BA with the inflection point at 60° within these parameter ranges. Further comprehensive analysis reveals that the sensitivity level of the three factors to the maximum EW rate is PS > IV > BA, and when IV is 3.0 m/s, PS is 650 μm, and BA is 60°, the bend EW is the most severe, and the maximum EW rate is 5.68 × 10−6 kg·m−2·s−1. In addition, When PS is below or equal to 450 μm, the maximum EW position is mainly at the outlet of the bend. When PS is greater than 450 μm, the maximum EW position shifts toward the center of the bend with the increase in BA. Therefore, EW at the bend can be reduced in practice by reducing IV as much as possible and using small particles.
Pipeline hydraulic transport is a highly efficient and low energy-consumption method for transporting solids and is commonly used for tailing slurry transport in the mining industry. Erosion wear (EW) remains the main cause of failure in tailings slurry pipeline systems, particularly at bends. EW is a complex phenomenon influenced by numerous factors, but research in this area has been limited. This study performs numerical simulations of slurry transport at the bend by combining computational fluid dynamics and fluid particle tracking using a wear model. Based on the validation of the feasibility of the model, this work focuses on the effects of coupled inlet velocity (IV) ranging from 1.5 to 3.0 m·s−1, particle size (PS) ranging from 50 to 650 μm, and bend angle (BA) ranging from 45° to 90° on EW at the bend in terms of particle kinetic energy and incidence angle. The results show that the maximum EW rate of the slurry at the bend increases exponentially with IV and PS and first increases and then decreases with the increase in BA with the inflection point at 60° within these parameter ranges. Further comprehensive analysis reveals that the sensitivity level of the three factors to the maximum EW rate is PS > IV > BA, and when IV is 3.0 m/s, PS is 650 μm, and BA is 60°, the bend EW is the most severe, and the maximum EW rate is 5.68 × 10−6 kg·m−2·s−1. In addition, When PS is below or equal to 450 μm, the maximum EW position is mainly at the outlet of the bend. When PS is greater than 450 μm, the maximum EW position shifts toward the center of the bend with the increase in BA. Therefore, EW at the bend can be reduced in practice by reducing IV as much as possible and using small particles.
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