The issue of top contact in paste backfill materials is a common technical challenge in coal mine filling processes,and overcoming this problem has become a significant research direction in current studies and engine...The issue of top contact in paste backfill materials is a common technical challenge in coal mine filling processes,and overcoming this problem has become a significant research direction in current studies and engineering practices.This paper utilizes coal gangue as aggregate and hydrogen peroxide as a foaming agent to prepare foamed paste backfill materials.Three close-packing theories were employed to investigate the effects of different coal gangue particle gradations on the mechanical properties,expansion ratio,water absorption,and dry density of foamed paste backfill materials under the same foaming agent content.The hydration mechanism and pore structure evolution were analyzed using XRD,SEM,and OSM techniques.The results indicate that when the hydrogen peroxide addition is 5%,the foamed paste backfill material regulated by MAA gradation theory exhibits the best comprehensive performance,achieving a 28-day compressive strength of 0.89 MPa,an expansion ratio of 155.5%,and a dry density of 1.24 g/cm^(3).The regulation of coal gangue aggregate particle gradation not only improves the foaming efficiency but also allows the formation of CH to fill the material pores,enhancing the overall structural support capacity and forming a closer microstructure.This research provides new insights into controlling the properties of foamed paste backfill materials.展开更多
To optimize the energy output and improve the energy utilization efficiency of an aluminized explosive,an explosion device was developed and used to investigate the detonation pressure and temperature of R1(A16)alumin...To optimize the energy output and improve the energy utilization efficiency of an aluminized explosive,an explosion device was developed and used to investigate the detonation pressure and temperature of R1(A16)aluminum powder and the aluminum powder particle gradation of R2(Al6+Al13),R3(Al6+Al24)and R4(Al6+AI flake)in a confined space.By using gas chromatography,quantitative analysis and calculations were carried out to analyze the gaseous detonation products.Finally,the reaction ratios of the aluminum powder and the explosion reaction equations were calculated.The results show that in a confined space,the quasi-static pressures and equilibrium temperature of the aluminum powder in air are higher than in vacuum.In vacuum,the quasi-static pressures and equilibrium temperatures of the samples in descending order are R1>R3>R4>R2 and R3>R4>R1>R2,respectively.In air,the quasi-static pressures and equilibrium telperatures of the samples in descending order are R1>R2>R4>R3 and R1>R4>R2>R3,respectively.R4(Al6+AI flake)and R3(Al6+A124)have relatively higher temperatures after detonation,which shows that the particle gradation method can enhance the reaction energy output of aluminum during the initial reaction stage of the explosion and increase the reaction ratio by10.6%and 8.0%,respectively.In air,the reaction ratio of AI6 aluminum powder can reach as high as 78.16%,and the reaction ratio is slightly reduced after particle gradation.Finally,the reaction equations of the explosives in vacuum and in air were calculated by quantitative analysis of the explosion products,which provides a powerful basis for the study of RDX-based explosive reactions.展开更多
Both CT and Avizo software were used to explore the effect of particle gradation on the evolution characteristics of pore structure and seepage paths in weathered crust elution-deposited rare earth ores during leachin...Both CT and Avizo software were used to explore the effect of particle gradation on the evolution characteristics of pore structure and seepage paths in weathered crust elution-deposited rare earth ores during leaching.The results showed that the pore areas in four kinds of ore samples before leaching were mainly concentrated in 10^(4)–10^(7)μm^(2),whose pore quantities accounted for 96.89%,94.94%,90.48%,and 89.45%,respectively,while the corresponding pore volume only accounted for 30.74%,14.55%,7.58%,and 2.84%of the total pore volume.With the decrease of fractal dimension,the average pore throat length increased,but pore throat quantities,the average pore throat radius and coordination number decreased.Compared with that before leaching,the change degree of pore structure during leaching increased with the fractal dimension decreasing.For example,the reduction rate of the average coordination number of ore samples was 14.36%,21.30%,28.00%,and 32.90%,respectively.Seepage simulation results indicated that seepage paths were uniformly distributed before leaching while the streamline density and seepage velocity increased with the fractal dimension decreasing.Besides,the phenomenon of the streamline interruption gradually reduced during leaching while preferential seepage got more obvious with the decrease of the fractal dimension.展开更多
Acquiring the size gradation for particle aggregates is a common practice in the granule related industry,and mechanical sieving or screening has been the normal method. Among many drawbacks of this conventional means...Acquiring the size gradation for particle aggregates is a common practice in the granule related industry,and mechanical sieving or screening has been the normal method. Among many drawbacks of this conventional means,the major ones are time-consuming,labor-intensive,and being unable to provide real-time feedback for process control. In this letter,an optical sieving approach is introduced. The two-dimensional images are used to develop methods for inferring particle volume and sieving behavior for gradation purposes. And a combination of deterministic and probabilistic methods is described to predict the sieving behaviors of the particles and to construct the gradation curves for the aggregate sample. Comparison of the optical sieving with standard mechanical sieving shows good correlation.展开更多
The mass-front velocities of granular flows results from the joint action of particle size gradations and the underlying surfaces.However,because of the complexity of friction during flow movement,details such as the ...The mass-front velocities of granular flows results from the joint action of particle size gradations and the underlying surfaces.However,because of the complexity of friction during flow movement,details such as the slope-toe impedance effects and momentum-transfer mechanisms have not been completely explained by theoretical analyses,numerical simulations,or field investigations.To study the mass-front velocity of dry granular flows influenced by the angle of the slope to the runout plane and particle size gradations we conducted model experiments that recorded the motion of rapid and long-runout rockslides or avalanches.Flume tests were conducted using slope angles of 25°,35°,45°,and 55° and three particle size gradations.The resulting mass-front motions consisted of three stages:acceleration,velocity maintenance,and deceleration.The existing methods of velocity prediction could not explain the slowing effect of the slope toe or the momentum-transfer steady velocity stage.When the slope angle increased from 25° to 55°,the mass-front velocities dropped significantly to between 44.4% and59.6% of the peak velocities and energy lossesincreased from 69.1% to 83.7% of the initial,respectively.The velocity maintenance stages occurred after the slope-toe and mass-front velocity fluctuations.During this stage,travel distances increased as the angles increased,but the average velocity was greatest at 45°.At a slope angle of 45°,as the median particle size increased,energy loss around the slope toe decreased,the efficiency of momentum transfer increased,and the distance of the velocity maintenance stage increased.We presented an improved average velocity formula for granular flow and a geometrical model of the energy along the flow line.展开更多
In order to improve the efficient and high-value recycling utilization rate of waste red bricks from construction waste,this study crushed and ground the waste red bricks to produce recycled brick powder(RBP)with diff...In order to improve the efficient and high-value recycling utilization rate of waste red bricks from construction waste,this study crushed and ground the waste red bricks to produce recycled brick powder(RBP)with different fineness,used the Andreasen model to explore the influence of RBP on the compact filling effect of cementitious material system based on the basic characteristics of RBP.The influence of grinding time(10,20,30 min)and content(0%,5%,10%,15%,20%)of RBP on the macroscopic mechanical properties of cementitious materials was investigated.We analyzed the significant impact of RBP particle characteristics on the compressive strength of the specimen with the aid of grey entropy theory,and revealed the influence mechanism of RBP on the microstructure of cementitious materials by scanning electron microscope(SEM)and nuclear magnetic resonance(NMR).The results show that the fineness of RBP after grinding is smaller than that of cement.The fineness of recycled brick powder increases gradually with the extension of grinding time,which is manifested as the increase of<3μm particles and the decrease of>18μm particles.Compared with the unitary cement cementitious material system,the particle gradation of the RBP-cement binary cementitious material system is closer to the closest packing state.With the increase of RBP content and grinding time,the compactness of the binary cementitious system gradually decreases,indicating that the incorporation of RBP reduces the mechanical strength of the specimen.The results of grey entropy show that the specific surface area D(0.1)and<45μm particles are the significant factors affecting the mechanical properties of cementitious materials mixed with RBP.RBP mainly affects the macroscopic properties of cementitious materials by affecting the internal compactness,the number of hydration products and the pore structure.The results of SEM show that when the RBP content is less than 15%,the content of C-S-H in cement paste increase,and the content of Ca(OH)2 decreases,and the content of C-S-H decreases and the content of Ca(OH)2 increases when the RBP content is more than 15%.The NMR results show that with the extension of grinding time,the pore size of micropore increases gradually,that of middle-small pores decreases gradually,and that of large pores remains unchanged.With the increase of RBP content,the micropores first decrease and then increase,and the middle-small pores and large pores gradually decrease.In summary,the compactness of cementitious material system can be improved by adjusting the fineness of RBP.Considering the performance of cementitious materials and the utilization rate of RBP,it is recommended that the grinding time of RBP is 20 min and the content is 10%-15%.展开更多
The multipath application of green resources needs to be realised under the carbon neutrality goal.Worldwide,biomass is a resource in urgent need of treatment.In this paper,corn stover biomass(YM)or biochar with diffe...The multipath application of green resources needs to be realised under the carbon neutrality goal.Worldwide,biomass is a resource in urgent need of treatment.In this paper,corn stover biomass(YM)or biochar with different particle sizes(YMF or YMX)was added during the preparation of coal-water slurry to investigate its effect on the performance of coal-water slurry and the micro-mechanism.The results showed that the fixed viscosity concentration of coal-water slurry(CYWS)with YM was only 47.42%,and the flowability was 49.9 mm,which made the slurry performance poor.The fixed viscosity concentration of coal-water slurry(CFWS)blended with YMF and coal-water slurry(CXWS)blended with YMX increased by 10.41%and 14.24%,respectively,compared with CYWS.Meanwhile,CXWS had the lowest thixotropy and yield stress,with a yield stress of only 16.13 Pa,which was 77.31 Pa lower than that of CYWS.This indicates that YMX treated by charring and milling is more favorable to be blended with coal to prepare coal-water slurry.This is due to the enhanced hydrophilicity and electronegativity of YMX.The enhanced hydrophilicity reduces the tendency to form three-dimensional networks in coal-water slurry,while the enhanced electronegativity improves the electrostatic repulsion between particles,which is beneficial to the dispersion of particles.In the subsequent EDLVO analyses,the same idea was proved.展开更多
The particle gradation of sand has a significant influence on its shear strength,yet the similarities and differences between the effects of continuous and gap grading have yet to be fully explored.In this study,the d...The particle gradation of sand has a significant influence on its shear strength,yet the similarities and differences between the effects of continuous and gap grading have yet to be fully explored.In this study,the discrete element method(DEM)was used to simulate biaxial tests on granular samples that were both continuously graded and gap-graded.The macroscopic analysis revealed that the shear strength of continuously graded sands increases initially and then decreases as the uniformity of particle size distribution decreases.On the other hand,the lack of medium particles in gap-graded sands amplifies the difference in particle size between coarse and fine particles,leading to a decrease in shear strength.Microscopically,both continuous and gap gradings affect the internal packing structure of the particle assembly,which consequently affects particle stress distributions,contact forces,coordination numbers,stress-induced anisotropies,and contact force networks,thus having an impact on the macroscopic shear strength.The global uniformity of particle size distribution was unidirectionally affected by continuous grading,while gap grading had a locally bidirectional influence.These findings provide a better understanding of the effects of particle grading on the macroscopic shear strength of sands.展开更多
基金National Natural Science Foundation of China(Project No.:U1905216).
文摘The issue of top contact in paste backfill materials is a common technical challenge in coal mine filling processes,and overcoming this problem has become a significant research direction in current studies and engineering practices.This paper utilizes coal gangue as aggregate and hydrogen peroxide as a foaming agent to prepare foamed paste backfill materials.Three close-packing theories were employed to investigate the effects of different coal gangue particle gradations on the mechanical properties,expansion ratio,water absorption,and dry density of foamed paste backfill materials under the same foaming agent content.The hydration mechanism and pore structure evolution were analyzed using XRD,SEM,and OSM techniques.The results indicate that when the hydrogen peroxide addition is 5%,the foamed paste backfill material regulated by MAA gradation theory exhibits the best comprehensive performance,achieving a 28-day compressive strength of 0.89 MPa,an expansion ratio of 155.5%,and a dry density of 1.24 g/cm^(3).The regulation of coal gangue aggregate particle gradation not only improves the foaming efficiency but also allows the formation of CH to fill the material pores,enhancing the overall structural support capacity and forming a closer microstructure.This research provides new insights into controlling the properties of foamed paste backfill materials.
基金supported by National Natural Science Foundation of China (Grant no.11502194)
文摘To optimize the energy output and improve the energy utilization efficiency of an aluminized explosive,an explosion device was developed and used to investigate the detonation pressure and temperature of R1(A16)aluminum powder and the aluminum powder particle gradation of R2(Al6+Al13),R3(Al6+Al24)and R4(Al6+AI flake)in a confined space.By using gas chromatography,quantitative analysis and calculations were carried out to analyze the gaseous detonation products.Finally,the reaction ratios of the aluminum powder and the explosion reaction equations were calculated.The results show that in a confined space,the quasi-static pressures and equilibrium temperature of the aluminum powder in air are higher than in vacuum.In vacuum,the quasi-static pressures and equilibrium temperatures of the samples in descending order are R1>R3>R4>R2 and R3>R4>R1>R2,respectively.In air,the quasi-static pressures and equilibrium telperatures of the samples in descending order are R1>R2>R4>R3 and R1>R4>R2>R3,respectively.R4(Al6+AI flake)and R3(Al6+A124)have relatively higher temperatures after detonation,which shows that the particle gradation method can enhance the reaction energy output of aluminum during the initial reaction stage of the explosion and increase the reaction ratio by10.6%and 8.0%,respectively.In air,the reaction ratio of AI6 aluminum powder can reach as high as 78.16%,and the reaction ratio is slightly reduced after particle gradation.Finally,the reaction equations of the explosives in vacuum and in air were calculated by quantitative analysis of the explosion products,which provides a powerful basis for the study of RDX-based explosive reactions.
基金the National Natural Science Foundation of China(Nos.52174258,92162109,52222405 and 52004184).
文摘Both CT and Avizo software were used to explore the effect of particle gradation on the evolution characteristics of pore structure and seepage paths in weathered crust elution-deposited rare earth ores during leaching.The results showed that the pore areas in four kinds of ore samples before leaching were mainly concentrated in 10^(4)–10^(7)μm^(2),whose pore quantities accounted for 96.89%,94.94%,90.48%,and 89.45%,respectively,while the corresponding pore volume only accounted for 30.74%,14.55%,7.58%,and 2.84%of the total pore volume.With the decrease of fractal dimension,the average pore throat length increased,but pore throat quantities,the average pore throat radius and coordination number decreased.Compared with that before leaching,the change degree of pore structure during leaching increased with the fractal dimension decreasing.For example,the reduction rate of the average coordination number of ore samples was 14.36%,21.30%,28.00%,and 32.90%,respectively.Seepage simulation results indicated that seepage paths were uniformly distributed before leaching while the streamline density and seepage velocity increased with the fractal dimension decreasing.Besides,the phenomenon of the streamline interruption gradually reduced during leaching while preferential seepage got more obvious with the decrease of the fractal dimension.
基金Ningbo Natural Science Foundation (No. 2006A610016)Foundation of National Education Ministry for Returned Overseas Students & Scholars (SRF for ROCS, SEM. No.2006699).
文摘Acquiring the size gradation for particle aggregates is a common practice in the granule related industry,and mechanical sieving or screening has been the normal method. Among many drawbacks of this conventional means,the major ones are time-consuming,labor-intensive,and being unable to provide real-time feedback for process control. In this letter,an optical sieving approach is introduced. The two-dimensional images are used to develop methods for inferring particle volume and sieving behavior for gradation purposes. And a combination of deterministic and probabilistic methods is described to predict the sieving behaviors of the particles and to construct the gradation curves for the aggregate sample. Comparison of the optical sieving with standard mechanical sieving shows good correlation.
基金supported by the National Natural Science Foundation of China (Grant Nos.41272297,41401195)the Applied Basic Research Fund of the Science and Technology Department of Sichuan Province (2014JY0121)the Key Research Fund of the Education Department of Sichuan Province (14ZA0095)
文摘The mass-front velocities of granular flows results from the joint action of particle size gradations and the underlying surfaces.However,because of the complexity of friction during flow movement,details such as the slope-toe impedance effects and momentum-transfer mechanisms have not been completely explained by theoretical analyses,numerical simulations,or field investigations.To study the mass-front velocity of dry granular flows influenced by the angle of the slope to the runout plane and particle size gradations we conducted model experiments that recorded the motion of rapid and long-runout rockslides or avalanches.Flume tests were conducted using slope angles of 25°,35°,45°,and 55° and three particle size gradations.The resulting mass-front motions consisted of three stages:acceleration,velocity maintenance,and deceleration.The existing methods of velocity prediction could not explain the slowing effect of the slope toe or the momentum-transfer steady velocity stage.When the slope angle increased from 25° to 55°,the mass-front velocities dropped significantly to between 44.4% and59.6% of the peak velocities and energy lossesincreased from 69.1% to 83.7% of the initial,respectively.The velocity maintenance stages occurred after the slope-toe and mass-front velocity fluctuations.During this stage,travel distances increased as the angles increased,but the average velocity was greatest at 45°.At a slope angle of 45°,as the median particle size increased,energy loss around the slope toe decreased,the efficiency of momentum transfer increased,and the distance of the velocity maintenance stage increased.We presented an improved average velocity formula for granular flow and a geometrical model of the energy along the flow line.
基金Funded by National Natural Science Foundation of China(No.52108219)Lanzhou University of Technology Hongliu Outstanding Young Talent Program,China(No.062407)The High Quality of Green Machine-made Aggregate and the Evolution Mechanism of Concrete Life Cycle Performance in the Harsh Environment of Northwest China(No.U21A20150)。
文摘In order to improve the efficient and high-value recycling utilization rate of waste red bricks from construction waste,this study crushed and ground the waste red bricks to produce recycled brick powder(RBP)with different fineness,used the Andreasen model to explore the influence of RBP on the compact filling effect of cementitious material system based on the basic characteristics of RBP.The influence of grinding time(10,20,30 min)and content(0%,5%,10%,15%,20%)of RBP on the macroscopic mechanical properties of cementitious materials was investigated.We analyzed the significant impact of RBP particle characteristics on the compressive strength of the specimen with the aid of grey entropy theory,and revealed the influence mechanism of RBP on the microstructure of cementitious materials by scanning electron microscope(SEM)and nuclear magnetic resonance(NMR).The results show that the fineness of RBP after grinding is smaller than that of cement.The fineness of recycled brick powder increases gradually with the extension of grinding time,which is manifested as the increase of<3μm particles and the decrease of>18μm particles.Compared with the unitary cement cementitious material system,the particle gradation of the RBP-cement binary cementitious material system is closer to the closest packing state.With the increase of RBP content and grinding time,the compactness of the binary cementitious system gradually decreases,indicating that the incorporation of RBP reduces the mechanical strength of the specimen.The results of grey entropy show that the specific surface area D(0.1)and<45μm particles are the significant factors affecting the mechanical properties of cementitious materials mixed with RBP.RBP mainly affects the macroscopic properties of cementitious materials by affecting the internal compactness,the number of hydration products and the pore structure.The results of SEM show that when the RBP content is less than 15%,the content of C-S-H in cement paste increase,and the content of Ca(OH)2 decreases,and the content of C-S-H decreases and the content of Ca(OH)2 increases when the RBP content is more than 15%.The NMR results show that with the extension of grinding time,the pore size of micropore increases gradually,that of middle-small pores decreases gradually,and that of large pores remains unchanged.With the increase of RBP content,the micropores first decrease and then increase,and the middle-small pores and large pores gradually decrease.In summary,the compactness of cementitious material system can be improved by adjusting the fineness of RBP.Considering the performance of cementitious materials and the utilization rate of RBP,it is recommended that the grinding time of RBP is 20 min and the content is 10%-15%.
基金support from the Scientific Research Foundation for the Introduction of Talent,Anhui University of Science and Technology(2023yjrc90)the Fundamental Research Funds of the AUST(2024JBQN0015)the Open Research Fund Program of Anhui Provincial Institute of Modern Coal Processing Technology,Anhui University of Science and Technology(MTY202302).
文摘The multipath application of green resources needs to be realised under the carbon neutrality goal.Worldwide,biomass is a resource in urgent need of treatment.In this paper,corn stover biomass(YM)or biochar with different particle sizes(YMF or YMX)was added during the preparation of coal-water slurry to investigate its effect on the performance of coal-water slurry and the micro-mechanism.The results showed that the fixed viscosity concentration of coal-water slurry(CYWS)with YM was only 47.42%,and the flowability was 49.9 mm,which made the slurry performance poor.The fixed viscosity concentration of coal-water slurry(CFWS)blended with YMF and coal-water slurry(CXWS)blended with YMX increased by 10.41%and 14.24%,respectively,compared with CYWS.Meanwhile,CXWS had the lowest thixotropy and yield stress,with a yield stress of only 16.13 Pa,which was 77.31 Pa lower than that of CYWS.This indicates that YMX treated by charring and milling is more favorable to be blended with coal to prepare coal-water slurry.This is due to the enhanced hydrophilicity and electronegativity of YMX.The enhanced hydrophilicity reduces the tendency to form three-dimensional networks in coal-water slurry,while the enhanced electronegativity improves the electrostatic repulsion between particles,which is beneficial to the dispersion of particles.In the subsequent EDLVO analyses,the same idea was proved.
基金the financial support provided by the National Natural Science Foundation of China(grant No.51608112)the Fundamental Research Funds for the Central Universities(grant No.2242023K40018).
文摘The particle gradation of sand has a significant influence on its shear strength,yet the similarities and differences between the effects of continuous and gap grading have yet to be fully explored.In this study,the discrete element method(DEM)was used to simulate biaxial tests on granular samples that were both continuously graded and gap-graded.The macroscopic analysis revealed that the shear strength of continuously graded sands increases initially and then decreases as the uniformity of particle size distribution decreases.On the other hand,the lack of medium particles in gap-graded sands amplifies the difference in particle size between coarse and fine particles,leading to a decrease in shear strength.Microscopically,both continuous and gap gradings affect the internal packing structure of the particle assembly,which consequently affects particle stress distributions,contact forces,coordination numbers,stress-induced anisotropies,and contact force networks,thus having an impact on the macroscopic shear strength.The global uniformity of particle size distribution was unidirectionally affected by continuous grading,while gap grading had a locally bidirectional influence.These findings provide a better understanding of the effects of particle grading on the macroscopic shear strength of sands.
