Segregation Of Mixtures Research Articles

Concave distribution characterization of asphalt pavement surface segregation using smartphone and image processing based techniques

Surface segregation of bituminous mixtures is a criterion of pavement quality and largely affects the characteristics of the pavement. Simple yet effective evaluation of the surface segregation will enable pavement engineers to tailor timely strategies to mitigate the problem. In this paper, a more efficient image processing method with the aid of smartphone imaging was adopted to rate the segregation level of asphalt pavement surface. Twenty-seven asphalt mixture specimens with vast differences were prepared to acquire different surface images using three types of smartphones. A field test section was chosen to validate the practicability. Furthermore, the Fractal Dimensions (FD, DBC-FD) and Percentage of Concave Distribution Area (PCDA) were used to characterize Concave Distribution Characteristics (CDC) of asphalt pavement surface. Texture Depth (TD) and Mean Texture Depth (MTD) were gained through the sand patch method. It was found that it is an encouraging approach to evaluate the surface segregation based on CDC. The image processing technique relying on the selected smartphone type was proposed by the error rate of reliability analysis, which was not more than 3% compared to the other used smartphones. A newly developed indicator called e was presented to stand for PCDA. The coefficient of determination between e, FD, DBC-FD and TD/MTD are respectively 0.7958, 0.7882, and 0.7585. In the field validation, the coefficient of determination between e and TD/MTD reaches to 0.8546. Therefore, it was demonstrated that the proposed image processing method can be a promising approach to rate the segregation of asphalt pavement surface.

Mechanical properties improvement of Self Compacting Concrete (SCC) using polypropylene fiber

SCC (self-compacting concrete) is a type of concrete that can compact itself without the help of external compaction. Thus, it can fill all parts of the formwork that are narrow and have tight reinforcement. A problem that often arises in the use of SCC is the segregation of concrete mixture, which reduces the strength of the concrete. This paper presents the effect of polypropylene fiber on the fresh concrete workability, compressive strength, splitting-tensile strength, and flexural-tensile strength of SCC concrete. The variations of the polypropylene fiber added to the SCC mixture are 0%, 0.05%, 0.067%, 0.1%, and 0.15% of the concrete’s volume, with a water-cement ratio of 0.5 and 0.38 and dense-graded and gap-graded coarse aggregate. Each concrete variation is made into cubes (150x150x150 mm3) for the compressive strength test, cylinders (dia.150mm; height 300mm) for splitting-tensile test, and prisms (100x100x400 mm3) for the flexural-tensile test. The experiments were carried out with concretes with the age of 28 days. The result showed that, polypropylene fiber could reduce the segregation in the SCC concrete mixture. The optimal polypropylene fiber percentage is 0.05%, which could improve the compressive strength by 12.2%, the splitting strength by 17.7%, and flexural strength by 322.3% compared to SCC concrete without polypropylene fiber.

Streamlining of the Powder Mixing Process based on a Segregation Test.

In direct compression of tablets, it is crucial to maintain content uniformity within acceptable margins, especially in formulations with low drug loading. To assure it, complex and multistep mixing processes are utilized in the industry. In this study, we suggest the use of a simple segregation test to evaluate mixing process performance and mixture segregation to produce tablets having satisfying content uniformity while keeping the process as simple and low cost as possible. Eventually, the formulation propensity to segregation can be evaluated using process analytical technology (PAT) to adjust the mixing process parameters to changing source drug properties. In this study, that approach was examined on a model drug with a broad batch-to-batch variability in particle size and shape. Excipients were chosen so that the resulting blend composition mimicked some marketed formulations. For each drug batch, two formulation blends were prepared through different preparation processes (one simple and one complex) and subsequently subjected to segregation tests. From those, segregation coefficients were obtained to compare segregation tendencies and homogeneity robustness between the drug batches and the blend preparation methods. The inter-particulate interactions were substantially influenced by the drug particle morphology and size and resulted in different segregation behavior. Based on these findings, a simple segregation test proved to be a useful tool for determining the suitability of different batches of the model drug to be used in a certain formulation. Moreover, for a particular batch A, the test revealed a potential for mixing process simplification and therefore process intensification and cost reduction.

Density and size-induced mixing and segregation in the FT4 powder rheometer: An experimental and numerical investigation

Segregation of granular materials is often induced by differences in size, density, shape and surface properties. Density and size-induced mixing and segregation of binary mixtures of glass beads and/or resin particles in the FT4 powder rheometer are investigated experimentally using a new FT4 methodology. The proposed methodology allows for quantification of mixing and segregation of components based on a mixing index. It is observed that the mixing index increases with increasing density and size ratio. Variation of flow energy and torque is related to the mixing and segregation of the mixture components, thus demonstrating that the FT4 powder rheometer may be used as a predictive tool for the tendency of mixture components to segregate under various stress conditions. Numerical analysis by DEM shows that for non-cohesive systems mixing and segregation occur by sifting of fines through interstitial gaps formed between coarse particles in the dilated region. For the non-cohesive system, higher blade tip speeds reduce the rate of mixing and minimise the segregation of different-sized components. Increasing the interfacial energy reduces the rate of mixing and alleviates the segregation of particles. For the cohesive systems, mixing occurs by rupture of cohesive fine clusters with the mixing index increasing with increasing blade tip speed owing to the higher shear stresses that break the agglomerates.

Modelling segregation of bidisperse granular mixtures varying simultaneously in size and density for free surface flows

Abstract

Introducing a New Quantitative Evaluation Method for Segregation of Normal Concrete

The aim of this research is to provide a quantitative method for evaluating concrete segregation. Because of various conditions of concrete materials, mix proportions, and delivery, concrete can be segregated. The acquisition inspection executed in construction field for supplied ready-mixed concrete is an important quality control process for concrete. Among the inspections conducted at the project site, segregation of concrete mixture should be evaluated before placing the concrete mixture, currently a qualitative inspection on concrete segregation was conducted. For a normal concrete mixture with slumping behavior, shear slump or collapse slump often occur as an indication of segregation. The suggested evaluation index of segregation for normal concrete (EISN) was induced from the shape of the concrete slumping: relation between the maximum distance of flow and the minimum distance of flow. To evaluate the feasibility of EISN, two different concrete mixture conditions were tested. The recommended EISN parameter of segregation is 1.09 using the three grades of concrete quality. This new quantitative method of evaluating segregation of the concrete mixture is expected to contribute to a more efficient quality control in concrete construction.

Electrostatic separation of polymer waste by tribocharging system based on friction with PVC

The improper disposal and accumulation of polymer waste in the environment cause several ecological damages, and it is a challenge for our society. The mechanical recycling of polymer waste is the most appropriate alternative to decrease these problems. However, polymer recycling is not a trivial process and some difficulties, such as the segregation of different kinds of polymers in post-consume polymeric waste, represent their complexity. The segregation of post-consume polymeric waste is the main barrier for mechanical recycling of polymers. Electrostatic separation of polymeric waste based on tribocharging of polymer particles when rubbed with different surfaces has emerged as a promising method for mechanized separation of polymer waste. In present study, an apparatus for electrostatic separation of polymer waste based on tribocharging in polyvinyl chloride pipe with air flow has been development. The system has showed considerable efficiency for polyvinyl chloride segregation in binary mixtures with high-density polyethylene waste and with polyethylene terephthalate as well as in ternary mixture polyvinyl chloride/high-density polyethylene/polyethylene terephthalate.

Mixing and segregation of binary mixtures of biomass and silica sand in a fluidized bed

In this work, mixing and segregation of binary mixtures involving biomass materials in a fluidized bed was experimentally investigated. A frozen bed method was employed to investigate both axial and radial distribution of biomass particles in silica sand. Three different biomass materials were studied: willow sawdust, pelletized soy and oat hull materials. Biomass loading investigated ranged from 5% to 30% by weight. The extent of mixing for each of the biomass composition was investigated using Lacey’s mixing index which is based on the standard deviations of the sample at different axial positions in the bed. The radial composition was also investigated by means of digital imaging analysis using a high-resolution digital camera. The experiments revealed the differences in the extent of particle distribution for pelletized biomass materials vs non-densified materials as a result of differences in particle size, density and importantly, the particle shape of the materials utilized. The results showed an increase in the extent of mixing as the fluidizing velocity increased for both pellet materials while the mixing index for sawdust decreased beyond a loading of 20%. With an increase in biomass loading, an increase in mixing index was found for the two pellet materials. A similar trend was observed for sawdust at the lower loading level. However, the mixing index started to decrease at higher loading level beyond 20%. The results greatly contributed to the understanding of the hydrodynamics of binary and multicomponent mixtures involving biomass materials, especially pelletized materials in fluidized beds.

Mixing and segregation of freely-falling granular materials through a vertical pipe

Mixing and segregation of binary mixtures of freely-falling grains are demonstrated in a cylindrical pipe with an obstacle. Previously, the same setup was used to spatially focus monodisperse granular materials. As each grain is dropped one at a time from a random position at the entrance of the cylindrical pipe, it may collide with a steady or oscillating obstacle and the wall. We performed a time-driven multi-scale simulation and use Routh’s impact model for collisions to show that the focusing of grains for monodisperse granular materials is dependent on the geometry of the pipe, the elastic properties of the grain, and the amplitude of oscillation of the obstacle. For binary granular mixtures, segregation may be achieved when the elastic properties of the grain species have a big difference. However, the efficiency of segregation is diminished when the amplitude of obstacle oscillation is increased, leading to granular mixing. Just as a high degree of segregation can be attained with a stationary obstacle, a high degree of mixing can be obtained with a moving obstacle.

Shear-induced particle segregation in binary mixtures: Verification of a percolation theory

Granular materials composed of different-sized grains may experience undesired segregation. Segregation is detrimental for a lot of industries because it leads to an increase in production costs and wastes. For these reasons, the segregation phenomena have been intensively studied in the last decades, and a lot of models have been provided by many researchers. However, these models are mainly based on empirical relations rather than physical considerations. This paper aims to confirm the main assumptions made by Volpato, Tirapelle, and Santomaso (2020) in their percolation theory by means of DEM simulations. The simulated geometry is a tilting shear box filled with few tracer particles in a bed of coarser sized grains, and simulations are performed for a range of tilting frequencies and size ratios. The results provide meaningful insight on the mathematical model parameters and allow us to say that the percolation theory relies on physically consistent assumptions.

Particle shape-induced axial segregation of binary mixtures of spheres and ellipsoids in a rotating drum

Particles with different properties such as size and shape in rotating drums tend to segregate axially to different sections. In this work, we report an interesting phenomenon that for ellipsoid-sphere mixtures, spheres tend to segregate axially to the middle section of the drum. The axial segregation becomes severe and reaches a maximum at aspect ratios of 0.67 and 2.0. Further increasing the deviation leads to a lower segregation degree. It is observed that the acceleration effect on particles by the frictional end walls induces the axial flow of particles. Both ellipsoids and spheres in the outer region of the transverse slice tend to migrate to the middle section while particles in the inner region migrate to the end walls. Generally, the axial flow induced by the frictional end walls and the radial segregation are essential for the development of particle shape-induced axial segregation.

Experimental investigation of segregation of granular mixtures during heap formation

The present study is on segregation of granular mixtures during heap formation in a quasi two-dimensional rectangular bin where binary mixture of a specified composition is poured intermittently into the auxiliary hopper and then allowed to pass through the gap (k = 10 mm) between the divider and the plate and finally settle on to the heap. The profiles of number fraction of big particles are plotted along the flow directions to study the segregation phenomena for surface profile. It shows that larger particles travel more distance and smaller particles settle near the pouring point for all cases studied.

Granular size segregation in silos with and without inserts.

The storage of granular materials is a critical process in industry, which has driven research into flow in silos. Varying material properties, such as particle size, can cause segregation of mixtures. This work seeks to elucidate the effects of size differences and determine how using a flow-correcting insert mitigates segregation during silo discharge. A rotating table was used to collect mustard seeds discharged from a three-dimensional (3D)-printed silo. This was loaded with bidisperse mixtures of varying proportions. A 3D-printed biconical insert was suspended near the hopper exit to assess its effect on the flow. Samples were analysed to determine the mass fractions of small particle species. The experiments without the insert resulted in patterns consistent with segregation. Introducing the insert into the silo eliminated the observed segregation during discharge. Discrete element method simulations of silo discharge were performed with and without the insert. These results mirrored the physical experiment and, when complimented with coarse graining analysis, explained the effect of the insert. Most of the segregation occurs at the grain-air free surface and is driven by large velocity gradients. In the silo with an insert, the velocity gradient at the free surface is greatly reduced, hence, so is the degree of segregation.

Shear-driven density segregation: an experimental study

Granular materials can segregate spontaneously due to differences in particle properties when subjected to vibrations, shear strain or because of the equipment geometries. Although the difference in particle size is the most critical factor that drives segregation, the effects of large density difference may also be detrimental for a lot of industries. In this work, we experimentally investigate density-driven segregation in bi-disperse mixtures of particles having the same size but different density when subjected to non-uniform shear rates. We found that the features of the segregation process are related to the density ratio as well as to the dimensionless loaded mass. The experimental outcomes are then compared with the solution of a simple density-driven segregation model. The model can successfully capture the main features of segregation driven by density for a range of density ratios.

Quantitative analysis and visual presentation of segregation in asphalt mixture based on image processing and BIM

Segregation of asphalt mixture is one of the main concerns causing early-stage failure of asphalt pavement. However, currently, the generation and degree of segregation are mostly judged according to the visual observation which is highly subjective and only applicable to large particle size and coarse asphalt mixture. Otherwise, facing to tedious and huge detection results, inefficient traditional recording and Excel presentation methods reveals a poor productivity. Therefore, this study proposes a new framework for quantitative analysis and visual presentation of segregation in asphalt mixture by integrating both digital image processing (DIP) and Building Information Modeling (BIM) technologies. In this method, a new algorithmic language is established for DIP approach, which could extract more image information, such as segmentation number and edge length in each area. Furthermore, a quantitative index is proposed to evaluate extent of segregation in asphalt mixture, which classifies segregation of asphalt mixture into mild, moderate and severe segregation. Besides, the framework incorporates BIM as a supporting technology to visualize the detection results of pavement segregation on 3D images. Meanwhile, warning points are generated for future maintenance. Finally, a case study demonstrates the feasibility of the proposed framework. This paper contributes by offering a new approach for the detection of the segregation in asphalt mixture by an easy operation and low cost way. Additionally, this approach also represents the DIP result by an intuitive review based on BIM, which improve the efficiency and decrease time-consuming during the construction phase.

INFLUENCE OF COARSE AGGREGATES AND MORTAR MATRIX ON PROPERTIES OF LIGHTWEIGHT AGGREGATE CONCRETES

Lightweight Aggregate Concrete (LWAC) with many advantages such as low density, good insulating capacity, and high fire resistance has been widely used around the world. LWAC may be considered as a two-component composite material consisting of a coarse aggregate and mortar matrix. The characteristics of these two components affect the properties of LWAC especially homogeneity. Therefore, this paper presents research results of the influence of lightweight coarse aggregates and mortar matrix on properties of this type of concrete. In the study, the raw materials were keramzit, polystyrene foam, type I cement, class F fly ash, and R4 plasticizer. A Suttard viscometer was mainly used to evaluate the workability named the flow of mortar. The experimental results showed that slump and segregation of concrete mixtures were remarkably increased when the flow of mortar was ≥ 21 cm; and the compressive strength of concrete was only about 40% and 20% the mortar strength when keramzit and polystyrene foam was used as coarse aggregates in the concretes respectively.

Laboratory Method to Characterize Coarse Aggregate Segregation for HMA

AbstractAggregate gradation segregation in asphalt mixtures can result in early damage and reduced durability in asphalt pavement. However, presently, most methods of segregation detection can be p...

DEM study of particle segregation in a rotating drum with internal diameter variations

Discrete Element Method (DEM) simulations are carried out to study size segregation of binary mixture in a rotating drum with inner diameter variations. The simulation results agree well with the experimental observations, both indicating that larger particle enrichment occurs in the smaller inner diameter regions. The effect of the inner diameter contracting ratio (CR) on the particle dynamics are further studied by 5 CRs. When CR is 0.9, the contracting wall affects the smaller particles through the strengthened percolation mechanism. Smaller particles move towards the dilated larger inner diameter regions. When CR is 0.5 or 0.3, the contracting wall provides additional shearing to the bed and acts as a barrier to the migration of particles of both sizes. The overall effects indicate that concentrating the larger particles in the smaller inner diameter region requiring a smooth inner diameter changing (i.e., CR > 0.7 in this work).

Collective Transport of Magnetic Microparticles at a Fluid Interface through Dynamic Self‐Assembled Lattices

AbstractThe transport of confined micron‐sized particles plays an important role in a range of phenomena in biology, colloidal science, and solid‐state physics. Here, an easily implementable strategy that allows for the collective and monitored transport of magnetic colloidal particles along fluid–fluid interfaces is introduced. Adsorbed microparticles are carried on time‐dependent magnetic potentials, generated by dynamic self‐assembled lattices of different‐sized particles confined onto a parallel plane. In such binary system, the synchronized inversion of the precessing applied field allows for the ballistic and directional transport of the motile components along prescribed directions. The transportation mode can be tuned through the stoichiometry or the strength and orientation of the applied field. The described methodology can be used in the capture and manipulation of drugs or pollutants adsorbed on liquid surfaces, the segregation of colloidal mixtures or the assisted mixture of surface active molecules.

Fourier-Spectral Method for the Phase-Field Equations

In this paper, we review the Fourier-spectral method for some phase-field models: Allen–Cahn (AC), Cahn–Hilliard (CH), Swift–Hohenberg (SH), phase-field crystal (PFC), and molecular beam epitaxy (MBE) growth. These equations are very important parabolic partial differential equations and are applicable to many interesting scientific problems. The AC equation is a reaction-diffusion equation modeling anti-phase domain coarsening dynamics. The CH equation models phase segregation of binary mixtures. The SH equation is a popular model for generating patterns in spatially extended dissipative systems. A classical PFC model is originally derived to investigate the dynamics of atomic-scale crystal growth. An isotropic symmetry MBE growth model is originally devised as a method for directly growing high purity epitaxial thin film of molecular beams evaporating on a heated substrate. The Fourier-spectral method is highly accurate and simple to implement. We present a detailed description of the method and explain its connection to MATLAB usage so that the interested readers can use the Fourier-spectral method for their research needs without difficulties. Several standard computational tests are done to demonstrate the performance of the method. Furthermore, we provide the MATLAB codes implementation in the Appendix A.