Effect of particle gradation on pore structure and seepage law of solution in weathered crust elution-deposited rare earth ores

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.

Basic Farmland Plan Based on Farmland Gradation

Taking B District in A City as an example, quality classification of basic farmland was evaluated based on farmland gradation. It can be concluded from the analysis that utilization grade of basic farmland in current round was 16.82 without consideration of farmland gradation updating, and the grade enhanced by 0.08, still lower by 0.11 than that in last round, when the updating was taken into account. Finally, the reasons for problems occurred in the round were analyzed as follows： less consideration of protection on basic farmland in orientation of urban development; neglecting of basic farmland quality in Overall Plan of Land Utilization; non-classification of excellent lands after land consolidation; untimely updating of farmland gradation. In addition, the countermeasures were proposed correpondingly, including strengthening of basic farmland quality in the Plan, classification of excellent lands after consolidation, timely updating and inclusion of farmland gradation into ＂one map＂ project.

Effect of particle gradation of aluminum on the explosion field pressure and temperature of RDX-based explosives in vacuum and air atmosphere

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.

Effect of TiO2 pigment gradation on the properties of thermal insulation coatings

This study was designed to evaluate the thermal performance and mechanical properties of coatings with different gradations of TiO2 pigments. The solar reflectance, cooling performance, wash resistance, and film adhesion strength of the coatings were investigated. The influence of TiO2 powder gradation on the final properties of the coatings was studed. The solar reflectance and the thermal insulation were observed to increase with increasing content of nanosized TiO2. The mechanical properties of the coatings, such as their wash resistance and film adhesion strength, were observed to increase with increased incorporation of nanosized TiO2. Such improvements in the properties of the coatings were attributed to the greater specific surface area and lower thermal conductivity of nanosized TiO2 particles compared to normal TiO2 particles.

Mass-front velocity of dry granular flows influenced by the angle of the slope to the runout plane and particle size gradation

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.

Classification and Gradation of Cultivated Land Quality in Bishan County of Chongqing, China

The conflicts among food security, economic development and ecological protection are the “sticking point” of undeveloped southwestern mountainous areas of China. The objectives of this study are to identify appropriate inte- grated indicators influencing the classification and gradation of cultivated land quality in the southwestern mountainous area of China based on semi-structure interview, and to promote the monitoring of cultivated land quality in this region. Taking Bishan County of Chongqing as a study case, the integrated indicators involve the productivity, protection, ac- ceptability, and stability of cultivated land. The integrated indicators accord with the characteristics of land resources and human preference in southwestern mountainous area of China. In different agricultural zones, we emphasize different indicators, such as emphasizing productivity, stabilization and acceptability in low hilly and plain agricultural integrative zone (LHP-AIZ), protection, productivity and stability in low mountain and hill agro-forestry ecological zone (LMH-AEZ), and acceptability in plain outskirts integrative agricultural zone (PO-IAZ), respectively. The pronounced difference of classification and gradation of cultivated land, regardless of inter-region or intra-region, is observed, with the reducible rank from PO-IAZ, LHP-AIZ to LMH-AEZ. Research results accord with the characteristics of assets management and intensive utilization of cultivated land resources in the southwestern mountainous area of China. Semi-structure interview adequately presents the principal agent of farmers in agricultural land use and rural land market. This method is very effective and feasible to obtain data of the quality of cultivated land in the southwestern mountainous area of China.

Integrated Indicators-based Gradation of Cultivated Land Quality in Mountainous Region of Southwestern China

The gradation of cultivated land is to assess the suitability of cultivated land for agricultural production in terms of natural and economic properties of land. It can be used to evaluate sustainability of land use and soil management practices. Formal and informal surveys, Delphi and comprehensive index method are adopted to identify appropriate integrated indicators, and measure the gradation of cultivated land quality. The determination of integrated indicators presents three basic features of cultivated land quality： stable plant productivity, social acceptability and maintenance of environmental quality. Pronounced concentration-dissipation law of total function score value occurs in paddy field units, with three ranges, i.e., 79-68.5, 68.5-59 and 59-51. Total function score value in dryland units mainly ranges from 40 to 70, but slight concentration-dissipation law of each unit is still observed, with four ranges, i.e., 79-68, 68-51, 51-37 and 37-15. Paddy field quality is divided into three gradations, and the scales are 18 220.9 ha, 5410.6 ha and 2890.9 ha. Dryland quality is classified into four gradations, and the scales are 1548.6 ha, 8153.8 ha, 3316.3 ha and 685.2 ha. The total function score value of every gradation unit is conformed to the results of farmers＇ assessment. Research results meet with the needs of accurate degree of the gradation of cultivated land quality. Integrated indicators-based gradation of cultivated land assessment accords with the characteristics of land resources and human preference in the mountains of southwestern China. This study will be useful to promote the monitoring of cultivated land quality, and to supply fine ground and knowledge for establishing appropriate cultivated land management practices in Southwestern China.

Experimental study on the effect of granular backfill with various gradations on the mechanical behavior of rock

Backfilling is a common practice in the mining industry and the backfilling performance plays a significant role in supporting the surrounding rock mass.To evaluate the backfilling performance,an experimental apparatus has been developed to understand how backfill affects the compressive strength of sandstone specimens in the laboratory.Pebbles were selected to model the backfill and divided into six groups with different particle sizes using a set of standard sieves.The backfilling pebbles with three types of particle size compositions were then produced,i.e.single gradation,two adjacent gradations,and increasingly widening gradations.A series of compressive tests were carried out to study the mechanical behavior of the sandstone specimens confined by these pebbles.The effects of the gradations of the filled pebbles on the peak and residual compressive strengths were analyzed.It is found that the increasing amount of the compressive strength is over 10%in most cases,even up to 20%.Based on the experiment data,the increasing amount was also estimated theoretically under some assumptions and it further confirmed the experimental results.The effects are closely related to the gradations of the filled pebbles except for their dense degree.

Laboratory performance of stone matrix asphalt mixtures with two aggregate gradations

Stone matrix asphalt （SMA） is a gap-graded bituminous mixture which can be used in surface layer of high volume pavements. The mixture has higher concen- trations of coarse aggregates, providing strength and rut resistance to the mixture, and higher asphalt content giving durability. There must be a proper stone-to-stone contact between the coarse aggregates of SMA, and hence aggre- gate gradation is an important factor in this mixture. In the current study, two aggregate gradations, with nominal maximum aggregate sizes （NMAS） 16 and 13 mm were adopted to prepare SMA mixtures and their laboratory performances were compared. Polymer-modified bitumen （PMB） was used as the binder material and no stabilising additive was used, since drain down was within permissible limits for both mixtures with PMB. Conventional cylin- drical specimens were prepared in superpave gyratory compactor with bitumen contents 5.0 %, 5.5 %, 6.0 %, 6.5 % and 7.0 % by weight of aggregates, and volumetric and Marshall properties were determined. Tensile strength, behaviour to repeated loading etc. were checked for cylindrical specimens prepared at optimum bitumen con- tent, whereas specially prepared slab specimens were used to check the rutting resistance of SMA mixtures. From the laboratory study, it was observed that, out of the two SMA mixtures, the one with NMAS 16 mm performed better compared to the other. These improved properties may be attributed towards the larger coarse aggregate sizes in the mixture.

Effect of aggregate gradation on low temperature performance of asphalt paving mixtures

Low temperature cracking has become one of the important factors that diminish asphalt pavement's ride quality and service life.Especially in cold region,cracking caused by low temperature is the main distress form.This paper discussed the effect of aggregate gradation on the low temperature performance in asphalt paving mixtures.A total of 11 asphalt mixtures with 11 different aggregate gradations and one asphalt binder content were studied.Volumetric properties of the coarse aggregate and asphalt mixtures showed aggregate grading has a significant impact on the degree of aggregate interlock in asphalt mixtures.A trend is existed in the low temperature performance with the change of gradation.With the aid of mathematic statistics,it indicates gradation affects the low temperature performance significantly.The findings also indicate the relationship between the degree of aggregate interlock in asphalt mixtures and the low temperature performance:With the stone-to-stone contact developed,the mixture has a high energy to resist contract and deformation at low temperature.The properties of fine aggregate and asphalt play an important part in resisting low temperature cracking in floating structure.But it provides lower energy to resist low temperature cracking compared to the skeleton structure.

2D IMAGE BASED SIEVING FOR PARTICLE AGGREGATE GRADATION

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.

Microstructural Characteristics of Asphalt Concrete with Different Gradations by X-ray CT

The main objective of this paper is to evaluate the effects of asphalt concrete types on the microstructural characteristics at high-temperature. Suspend-dense structure and Skeleton-dense structure were selected to investigate the deformation of pavement at meso-scale. The internal microstructures of typical asphalt concretes, AC, SUP and SMA, were scanned by X-ray CT device, and microstructural changes before and after high-temperature damage were researched by digital image processing. Adaptive threshold segmentation algorithm（ATSA） based on image radius was developed and utilized to obtain the binary images of aggregates, air-voids and asphalt mastic. Then the shape and distribution of air-voids and aggregates were analyzed. The results show that the ATSA can distinguish the target and background effectively. Gradation and coarse aggregate size of asphalt mixtures have an obvious influence on the distribution of air-voids. The movements of aggregate particles are complex and aggregates with elliptic sharp show great rotation. The effect of gradation on microstructure during high-temperature damage promotes the research about the failure mechanism of asphalt concrete pavement.

Aggregate gradation design of asphalt mixture with stone-to-stone contact based on fuller's model

Based on Fuller＇s model, a gradation design is presented for the load-carrying capacity of an asphalt mixture with stone-to-stone contact. The coarse aggregate gradation, fine aggregate and filler gradation are respectively designed for their different effects on an asphalt mixture with stone-to-stone contact. The equation of coarse aggregate gradation is deduced from the Fuller＇s model. Fine aggregate gradation is calculated by using Fuller＇s equation. The asphalt mixture with the 16 mm maximum size of aggregate is verified. When the coefficient of coarse aggregate gradation is 0.35 and fine aggregate gradation is 0.25, the volume parameters of asphalt mixture meet the technical specifications. Moreover, the high temperature stability and crack resistance at low temperature are all well.

The Aggregate Gradation for the Porous Concrete Pervious Road Base Material

The effects of the proportion of fine aggregate, the maximum size of the aggregate and the proportion of the 9.5 mm to 4.75 mm particle in the coarse aggregate on the properties of the porous concrete are investigated. Results indicate that the porous concrete with a cement dosage only 150 kg/m^3 has high strength and satisfying permeability when the aggregate has a passing percentage of 4.75 mm around 10% to 15%, with the increase of the maximum size of the aggregate, the strength of the porous concrete decreases and the permeability increases. When the proportion of the 9.5 mm to 4.75 mm particle in the coarse aggregate is about 20%, there are no interference among the particles by Weymouth theory, the strength of the pervious porous concrete reaches the peak value. The optimum continues gradation limit of the aggregate for porous concrete pervious road base material is recommended according to the theoretical calculation and experimental results.

THE RESEARCH OF GRADATION FUSION ALGORITHM BASED ON MULTISENSOR ASYNCHRONOUS SAMPLING SYSTEM

This letter explores the distributed multisensor dynamic system, which has uniform sampling velocity and asynchronous sampling data for different sensors, and puts forward a new gradation fusion algorithm of multisensor dynamic system. As the total forecasted increment value between the two adjacent moments is the forecasted estimate value of the corresponding state increment in the fusion center, the new algorithm models the state and the forecasted estimate value of every moment. Kalman filter and all measurements arriving sequentially in the fusion period are employed to update the evaluation of target state step by step, on the condition that the system has obtained the target state evaluation that is based on the overall information in the previous fusion period. Accordingly, in the present period, the fusion evaluation of the target state at each sampling point on the basis of the overall information can be obtained. This letter elaborates the form of this new algorithm. Computer simulation demonstrates that this new algorithm owns greater precision in estimating target state than the present asynchronous fusion algorithm calibrated in time does.

Gradation equation of coarse-grained soil and its applicability

Gradation equation is one way to describe the gradation of coarse-grained soil conveniently,exactly and quantitatively.With the gradation equation,the influence of gradation on the mechanical behaviors of coarse-grained soil can be expressed quantitatively.A new gradation equation with a parameter is proposed.The basic properties and applicability of the new equation are studied.The results show that the proposed equation has the applicability to express coarse-grained soil gradation(CSG),and the range of the parameter β is found to be 0<β<1.The value ofbdetermines the gradation curve shape.If β>0.5,the gradation curve is sigmoidal,otherwise the gradation curve is hyperbolic.For well graded gradations,the parameter has the value of 0.13<β<1.Several CSGs used in domestic and foreign earth-rockfill dams are probed,and the value of the parameterbfalls in the range of 0.18 to 0.97.The investigation of the range of β is of value to guide the design for CSG of earth-rockfill dam.

Degradation behavior of aggregate skeleton in stone matrix asphalt mixture

The degradation behavior of aggregate skeleton in stone matrix asphalt mixture was investigated based on theoretical analysis, laboratory test and field materials evaluation. A stress-transfer model was established to provide the fundamental understanding of the stress distribution and degradation mechanism of stone matrix asphalt (SMA) aggregate skeleton. Based on the theoretical analysis, crushing test and superpave gyratory compactor (SGC) test were used to evaluate the degradation behavior of aggregate skeleton of SMA. To verify the laboratory test results, gradation analysis was also conducted for the field materials extracted from SMA pavements after long-time service. The results indicate that the degradation of SMA aggregate skeleton is not random but has fixed internal trend and mechanism. Special rule is found for the graded fine aggregates generated from coarse aggregate breakdown and the variation of 4.75 mm aggregate is found to play a key role in the graded aggregates to form well-balanced skeleton to bear external loading. The variation of 4.75 mm aggregate together with the breakdown ratio of aggregate gradation can be used to characterize the degradation behavior of aggregate skeleton. The crushing test and SGC test are proved to be promising in estimating the degradation behavior of SMA skeleton.

Fractal Dimension Analysis of the Fine Aggregate Gradation of Interlocking Skeleton Asphalt Mixture

By analyzing the fine aggregate gradation scales from standards,fine aggregate in the asphalt mixture is regarded as a whole research object and fractal dimensions X of the samples were obtained by linear regression and（AC-13）is 2.43-2.56,Sup-13 is 2.28-2.54,SMA-13 is 2.66-2.88 and SAC-13 is 2.54-2.73.In the dense gradation mixture,there are little different between fractal dimensions of coarse and fine aggregates but it makes sense for skeleton asphalt mixture.For a given coarse aggregate gradation and the same percentage of coarse aggregates,the compressive strengths and splitting strengths of the asphalt mixture are studied when the fractal dimensions are selected as 2.60,2.65 and 2.70,respectively.When asphalt-stone ratio is less than optimal asphalt-stone ratio,the higher compressive strength is,the bigger X can be gotten.When asphalt-stone ratio is larger than optimal asphalt-stone ratio,little difference of compressive strength can be observed under these three conditions.The largest splitting strength can be got when X is 2.65,and larger splitting strength can be observed with the ascending of the asphalt-stone ratio.

Deformation characteristics of coarse-grained soil with various gradations

By using large scale triaxial shearing apparatus,consolidated-drained shear tests were conducted on coarse-grained soil with different gradations.In order to describe their deformation rules,three main characteristics of tangent Poisson ratio curves were summarized and the reason was revealed by dividing the movement of soil particles into two kinds: the movement of fine particles and the movement of coarse particles.Then,a volumetric strain expression and a tangent Poisson ratio expression were put forward,and two defects of widely used Duncan-Chang model were fixed.Results calculated from them agree well with test results.There are three parameters,namely L,G and F,in this new model.Parameter L reflects the dilatancy of a specimen and L=4 can be used as a criterion to estimate whether a certain kind of soil has dilatancy quality or not.Parameters G and F relate to the initial slope of tangent Poisson ratio curves,and G=F=0 indicates a special situation which happens in dense granular material of the same diameter.Influences of various gradations on volume deformation are mainly reflected in parameter L which is smaller when there are more gravels in specimens.

Experimental Characterization of Rutting Performance of HMA Designed with Aggregate Gradations According to Superpave and Marshall Methods

The permanent deformation (rutting) of pavement is a major distress in flexible pavement. It is related to vehicles properties and/or pavement materials and conditions. This article presents an extensive experimental investigation in order to compare between the aggregate gradation according to Superpave and Marshall methods of asphalt concrete mix design on pavement rutting and to examine the sensitivity of rutting resistance to aggregate gradation. A wheel truck machine has been used for measurement of pavement rutting (permanent deformation). The tests were carried out at two controlled different air temperature 55℃ and 25℃. The results obtained showed that the adopting of aggregate gradation procedure of Superpave method of pavement mix design for Marshall method of asphalt concrete mix design can reduce the pavement rutting by about 50%. This achievement may be related to missing of three sieves in aggregate gradation procedure of Marshall method which controls rounded and finer aggregate particles. These sieves provide more continuity for aggregate gradation to ensure filling unnecessary gaps and produce more contact points between the aggregates in Hot Mix Asphalt (HMA). The outputs of the research support modifying Marshall method of asphalt concrete mix design by adopting aggregate gradation proposed in Superpave method. The results of study also showed that the coarser aggregate provided more resistance to pavement rutting.