Particle Size Distribution Of Aggregates Research Articles

Dry Aggregate Particle Size Distribution Optimization for Soderberg Anode Paste Production Applied to Aluminum Industry

For a Soderberg Technology, paste production process consists of four basic steps: raw material handling; dry aggregate preparation; mixing; and briquettes loading at electrolytic cells for aluminum production. Dry aggregate is prepared from calcined petroleum coke, where the grains are crushed and separated between 3 different fractions of pre-determined sizing and a dust component. Petroleum pitch blended with the finest particles from dry aggregate forms the binder used for wetting, lubricating and filling open pores of larger coke grains, resulting into a higher anode paste quality with adequate mechanical properties, higher density, oxidation resistance and lower electrical resistivity. Raw materials recent trends showed significant quality degradation and cost raise, pushing up industry to look forward for untraditional suppliers, in addition to process optimization. This paper describes enablers chosen to improve paste properties, through dry aggregate particle size distribution using two of the most traditional particle packing models: Andreasen and Alfred. The formulations developed in this work were compared to the formulation originally used by an industry through measures flowability and apparent baked density. The results have shown that both the equations of Alfred and Andreasen, for distribution coefficient 0.30 and 0.52 respectively, can be applied to the Aluminum Industry, resulting into products significantly different from the point of view of quality.

Composição granulométrica, densidade e porosidade de agregados de Latossolo Vermelho sob duas coberturas do solo

Em geral, os Latossolos sob cerrado apresentam distribuição equilibrada do tamanho de agregados podendo sofrer, quando cultivados, alterações com reflexos negativos para a produção agrícola. Com o objetivo de estudar a composição granulométrica, a densidade e a porosidade de agregados de diferentes tamanhos foram retiradas amostras de um Latossolo Vermelho textura argilosa, a duas profundidades (0-5 e 5-10 cm). Os fatores em estudo, analisados separadamente para cada profundidade, foram duas coberturas vegetais (vegetação de cerrado e milho cultivado durante trinta anos) e cinco classes de agregados (2,0-1,0, 1,0-0,5, 0,5-0,25, 0,25-0,105 e < 0,105 mm). Nos materiais separados por via seca se determinaram a proporção, a composição granulométrica e a densidade dos agregados, pelo método do cimento em pó calculando-se a porosidade intra-agregados. As amostras retiradas do solo sob cerrado apresentaram diâmetro médio maior que as retiradas do solo cultivado com milho. Considerando a classe conclui-se que quanto menor o tamanho do agregado maior a proporção de argilas, menor a densidade do agregado e maior a porosidade intra-agregado, devido à exclusão de areias de maior tamanho que o dos agregados da classe em análise.

Effects of biochar amendment on rapeseed and sweet potato yields and water stable aggregate in upland red soil

A field experiment was conducted to study the effect of biochar amendment (0, 2.5, 5, 10, 20, 30 and 40t·ha−1) on rapeseed and sweet potato yields, aggregate particle size distribution, aggregate stability, soil organic carbon, total N content and C:N ratio in soil water stable aggregate under a rapeseed–sweet potato rotation system in upland red soil in Jiangxi Province of southern, China. The results were as follows: compared with control treatment (CK), when the amount of biochar was 40t·ha−1, rapeseed and sweet potato yields were increased by 36.02% and 53.77% respectively; the soil water stable aggregate (>0.25mm) in the 0–15cm soil layer had a remarkable increase than other treatments, especially the macroaggregate with particle size larger than >2mm. In the rapeseed harvest season, the mean weight diameter of soil water stable aggregate was enhanced by 28.02% compared to CK with the application rate of biochar being 40t·ha−1. A significant increment in soil organic carbon, total N and C:N ratio was observed in the >2mm, 2–0.5mm, 0.5–0.25mm and <0.25mm aggregate fractions with respect to the maximum treatment. These results suggest that biochar's incorporation into upland red soil will increase crop productivity and improve soil structure.

Characterization of lime plasters used in 16th century Mughal monument

This paper addresses the results of mineralogical and physico-chemical investigation of 16th century Mughal plaster of Bibi Ka Maqbara, the Taj of Deccan. The study investigated micro-morphological structure of various components of the plaster for the great to provide a basis for future restoration. The investigation on particle size distribution of aggregates in the plaster was carried and the result correlated to the strength of the plaster. Sieve/petrological analysis indicate the addition of creamy white zeolites (also detected by Raman spectrum) along with crushed amygdaloidal basalt of different grain sizes as aggregate in the plaster. The component material of the plaster and its purity has been studied through thermal analysis. The outer plaster layer was characterized for addition of hygroscopic organic additive with active carbonyl group by FTIR spectroscopy. The SEM images show salt crystallization in the pores as one of the reason for failure of plaster at some location, probably due to recent conservation with cement mortars/plaster of paris.

Assessment of optimum threshold and particle shape parameter for the image analysis of aggregate size distribution of concrete sections

Aggregate gradation is one of the key design parameters affecting the workability and strength properties of concrete mixtures. Estimating aggregate gradation from hardened concrete samples can offer valuable insights into the quality of mixtures in terms of the degree of segregation and the amount of deviation from the specified gradation limits. In this study, a methodology is introduced to determine the particle size distribution of aggregates from 2D cross sectional images of concrete samples. The samples used in the study were fabricated from six mix designs by varying the aggregate gradation, aggregate source and maximum aggregate size with five replicates of each design combination. Each sample was cut into three pieces using a diamond saw and then scanned to obtain the cross sectional images using a desktop flatbed scanner. An algorithm is proposed to determine the optimum threshold for the image analysis of the cross sections. A procedure was also suggested to determine a suitable particle shape parameter to be used in the analysis of aggregate size distribution within each cross section. Results of analyses indicated that the optimum threshold hence the pixel distribution functions may be different even for the cross sections of an identical concrete sample. Besides, the maximum ferret diameter is the most suitable shape parameter to estimate the size distribution of aggregates when computed based on the diagonal sieve opening. The outcome of this study can be of practical value for the practitioners to evaluate concrete in terms of the degree of segregation and the bounds of mixture's gradation achieved during manufacturing.

Andreasen Particle Packing Method on the Development of Geopolymer Concrete for Civil Engineering

AbstractAlkali-activated binders (AAB) or geopolymers are new ceramic materials with the potential to replace portland cement in a wide range of applications, from immobilization of heavy metals to concretes for civil engineering. They rely on the alkaline activation of aluminosilicates, such as blast furnace slag (BFS), pulverized fly ash (PFA), and metakaolin (MK). Despite their high mechanical strength and chemical durability, geopolymer concretes are in many cases marked with high porosity and permeability, which could negatively affect the performance or long-term durability of concretes. This paper employs the Andreasen particle packing method, commonly used for ceramic materials, to improve the geopolymer formulations studied on the development of micro-concretes. Three parameters were investigated: (1) the Andreasen packing factor q, 0.21, 0.235, and 0.26, which alter particle size distribution of aggregates; (2) the solution to solids rate, 1.3, 1.4, and 1.5; and (3) the type of aggregates, eithe...

Effects of particle size distribution, shape and volume fraction of aggregates on the wall effect of concrete via random sequential packing of polydispersed ellipsoidal particles

Concrete can be viewed as granular materials at the mesoscopic level. A specific distribution of aggregate particles in boundary layers, known as the wall effect, plays an important role in the mechanical properties and durability of concrete. However, the detailed and systematic experimental and simulated data about the wall effect of concrete is hardly adequate yet. Specially, the modeling study of spherical and two-dimensional (2D) elliptical aggregates distribution for the wall effect has been focused on in previous work, little is known about three-dimensional (3D) ellipsoidal aggregates. In the present work, based on a mesostructure model of concrete, the wall effect of concrete is quantified by configuration parameters such as the volume fraction, the specific surface area and the meaning free spacing of the solid phase. In addition, the influences of ellipsoidal particle size distribution (EPSD), shape and volume fraction (Vf) of ellipsoidal aggregates on the configuration parameters are evaluated by stereological methods and serial section analysis technique. Furthermore, the effect mechanisms of EPSD, shape and Vf are analyzed and discussed in this paper. The reliability of the statistical results is verified by experimental data and theoretical analytical results.

Effect of particle size distribution and calcium aluminate cement on the rheological behaviour of all-alumina refractory castables

Previous works based on statistical design of experiments (DoE) defined a model all-alumina self-flow refractory castable (SFRC) with optimized particle size distribution for simultaneous high flowability index (FI) and superior post-sintering performance.This work compares the SFRC rheological behaviour and setting time with those of alternative all-alumina castables with different Andreasen aggregate particle size distribution modulus, and of the equivalent castables containing calcium aluminate cement. The model castable showed Bingham behaviour with low yield stress, viscosity and thixotropy, guaranteeing easier casting and less wear in the casting and/or projection equipment. However, as the coarse particle fraction increases, the castable flow tends to be non-linear and changes from Bingham to Herschel–Bulkley. The cement containing castables quickly loose flowability despite the applied shear.This work confirmed previous conclusions based on FI measurements and demonstrates the adequacy of the use of FI values in the calculation of FI response surface by DoE.

Design of nanomaterial synthesis by aerosol processes.

Aerosol synthesis of materials is a vibrant field of particle technology and chemical reaction engineering. Examples include the manufacture of carbon blacks, fumed SiO(2), pigmentary TiO(2), ZnO vulcanizing catalysts, filamentary Ni, and optical fibers, materials that impact transportation, construction, pharmaceuticals, energy, and communications. Parallel to this, development of novel, scalable aerosol processes has enabled synthesis of new functional nanomaterials (e.g., catalysts, biomaterials, electroceramics) and devices (e.g., gas sensors). This review provides an access point for engineers to the multiscale design of aerosol reactors for the synthesis of nanomaterials using continuum, mesoscale, molecular dynamics, and quantum mechanics models spanning 10 and 15 orders of magnitude in length and time, respectively. Key design features are the rapid chemistry; the high particle concentrations but low volume fractions; the attainment of a self-preserving particle size distribution by coagulation; the ratio of the characteristic times of coagulation and sintering, which controls the extent of particle aggregation; and the narrowing of the aggregate primary particle size distribution by sintering.

The optical volume scattering function in a surf zone inverted to derive sediment and bubble particle subpopulations

The effects of particle fields including bubbles on the optical volume scattering function (VSF) were investigated in the surf zone off Scripps Pier as part of an ongoing effort to better understand the underlying dynamics in the VSF in the subsurface ocean. VSFs were measured at 20 Hz at angles spanning 10°–170° in 10° increments with a device called the Multiangle Scattering Optical Tool (MASCOT). Modification of the phase function was observed in passing suspended sediment plumes, wave‐injected bubble plumes, and combinations of these particle populations relative to the background. Phase function enhancement in the 60°–80° range was observed in association with bubble plumes, consistent with theoretical predictions. VSFs were inverted to infer size distributions and composition using a least squares minimization fitting procedure applied to a library of phase functions, each representing a lognormally distributed subpopulation with refractive index and coating, where applicable. Phase functions representative of nonspherical mineral particle subpopulations were computed using discrete dipole approximation (DDA) and improved geometric optics method (IGOM) techniques for randomly oriented, asymmetric hexahedra. Phase functions for coated bubbles were computed with the Lorenz‐Mie theory. Inversion results exhibited stable solutions that qualitatively agreed with concurrent acoustical measurements of bubbles, aggregate particle size distribution expectations, and anecdotal videography evidence from the field. Although a comparable inversion with a library that assumed spherical shaped particles alone provided less stable results with some incorrectly assigned subpopulations, several dominant subpopulation trends were consistent with the results obtained using nonspherical representations of mineral particles.

An empirical approach for the optimisation of aggregate combinations for self-compacting concrete

The fresh and hardened properties of self-compacting concrete (SCC) depend on number of factors such as paste composition, paste content, aggregate content, aggregate gradation etc. In the present investigation, the influence of the packing density of aggregates on the properties of SCC was evaluated. Experiments were conducted to measure the packing density for different combinations of aggregates precisely. A ternary packing diagram (TPD) was developed based on the packing density of measured and interpolated data. Considering the limitations in generalising the TPD and the difficulty involved in adopting mathematical models for aggregates, an attempt was made to establish a simple method for the selection of the combination of aggregates resulting in maximum packing density from the particle size distribution of aggregates (represented by the Coefficient of uniformity—C u). Further, studies were extended to investigate the effect of aggregate packing density on fresh and hardened SCC properties. The results indicate that for a constant paste volume and paste composition, with increase in packing density of aggregates, the fresh properties and the compressive strength of SCC were improved positively. An attempt was also made to identify the influence of 10 different proportions of aggregates having the same packing density on the properties of SCC. The results indicate that at the same aggregate packing density, the fresh concrete properties were influenced significantly by the choice of the aggregate combination, while there was little or no influence on the hardened properties. Furthermore, the experimental data obtained was used for supplementary validation of the existing model (compressible packing model) for predicting the packing density and the fresh behaviour of SCC.

Gradation Effects Influencing Mechanical Properties of Aggregate Base–Granular Subbase Materials in Minnesota

Aggregate gradation effects on strength and modulus characteristics of aggregate base–granular subbase materials used in Minnesota are described. The importance of specifying proper aggregate grading or particle size distribution has long been recognized for achieving satisfactory performance in pavement applications. In the construction of dense-graded unbound aggregate base–subbase layers, well-graded gradation bands were often established years ago on the basis of the experience of the state transportation agency and may not have a direct link to mechanical performance. To improve specifications for superior performance targeted in the mechanistic–empirical pavement analysis and design framework, there is a need to understand how differences in aggregate gradations may affect unbound aggregate base–subbase behavior for site-specific design conditions. Aggregates with different gradations and material properties were compiled in a statewide database established from a variety of sources in Minnesota. Analyses showed nonunique modulus and strength relationships for most aggregate base and especially subbase materials. Laboratory resilient modulus and shear strength results were analyzed for critical gradation parameters by common gradation characterization methods. The most significant correlations were between a gravel-to-sand ratio (proposed based on ASTM D2487-11) and aggregate shear strength properties. Aggregate compaction (AASHTO T99) and resilient modulus characteristics could also be linked to the gravel-to-sand ratio and verified with other databases in the literature. The gravel-to-sand ratio can be used to optimize aggregate gradations for improved base–subbase performances primarily influenced by shear strength.

Evaluation of aggregate gradation in lightweight concrete via image processing

The present work presents a means of evaluating the particle size distribution of aggregates on hardened concretes via an image processing based technique. Such a technique may be employed to the reconstitution of hardened concrete composition, which is a matter of interest concerning, specially, lightweight aggregate concretes. This work presents the results obtained by applying the proposed methodology to synthetic experiments and to pictures taken from lightweight aggregate concrete samples.

Effect of Cement Kiln Dust and Rock Dust as Mineral Fillers on Bulk Specific Gravity of Fine Aggregates

Abstract The bulk specific gravity (Gsb) of aggregates is a critical parameter in the design of asphalt mixes. In the Superpave volumetric mix design, Gsb is used to determine the amount of asphalt binder absorbed by aggregates and the percentage of voids in the mineral aggregate. Problems with the current test methods of measuring the Gsb of fine aggregates, i.e., AASHTO T84 or ASTM C128, have been reported in some previous studies as well as in the current study. These standard test methods remain questionable under certain conditions: (1) When rough and angular as well as small and varying particle size distributions of fine aggregates are present and (2) when water reactive mineral fillers (passing No. 200 sieve) are added to fine aggregates. This study examined the addition of two selected mineral fillers, namely, Cement Kiln Dust (CKD) and rock dust, on the overall Gsb of fine aggregates by employing the AASHTO T84 and the CoreLok-Aggplus test procedures. When using the AASHTO T84 test method, the overall Gsb values reduce for both the additives. When using a newly developed CoreLok method, the Gsb values increased for rock dust up to 10 %, beyond which a reduction is observed. With CKD, the Gsb values show an increase for up to 6 % addition of it and then a decrease is observed. The data suggest that the AASHTO T84 test method may not be applicable in the presence of CKD due to the chemical reactions in the presence of water and the formation of cementitious products. A possibility of chemical reaction due to the presence of limestone in the rock dust and its fine gradation influence the results of the AASHTO T84 test method. Thus, use of the CoreLok method appears more appropriate in the presence of such reactive materials. To further analyze the problem, the specific surface area of fine aggregates and mineral fillers was measured using water vapor and nitrogen adsorption methods. This study also reveals that angular fine aggregates with a high angularity and rough surface texture pose significant difficulty in measuring Gsb by the AASHTO T84 test method.

Enhanced performance of a passive direct methanol fuel cell with decreased Nafion aggregate size within the anode catalytic layer

The decrease in Nafion ionomer size within the anode catalytic layer for a passive direct methanol fuel cell (DMFC) results in a significant enhancement in fuel cell’s performance. Dynamic light scattering measurement demonstrates that the agglomerate size of Nafion ionomer in the solution decreases and the aggregate particle size distribution becomes narrow until a monodispersed Nafion ionomer was obtained with an increase in heat treatment temperature. The improved performance of the passive DMFC with smaller Nafion ionomer agglomerates within the anode catalytic layer can be ascribed to a decrease in charge-transfer resistance of anodic reaction obtained by electrochemical impedance analysis and to an improvement in catalyst utilization verified by cyclic voltammetric measurement. Furthermore, the small congeries formed between catalyst nanoparticles and Nafion ionomers could lead to a decrease in Nafion loading within the catalytic layer. This study confirms that the decrease in Nafion aggregation within the catalytic ink is beneficial to an improvement in both catalyst and Nafion ionomer utilization, thus enhancing fuel cell’s performance.

Modeling the Aggregation of Asphaltene Nanoaggregates in Crude Oil−Precipitant Systems

This study discusses the development of a generalized geometric population balance model for simulating the growth of asphaltene aggregates from the nanometer scale to micrometer-sized particles. The Smoluchowski kernel has been incorporated to describe the aggregation of asphaltene nanoaggregates, which is induced by the addition of a precipitant, e.g., heptane. Rather than using the discretization of particle sizes based on the particle volumes, a discretization scheme based on the number of asphaltene molecules is incorporated, which ensures that the mass is conserved in this model. The model is in good agreement with the experimental data for the evolution of asphaltene aggregates at different times collected by centrifugation. The particle size distribution (PSD) of the asphaltene aggregates as a function of time is also determined. It was observed that the shift of the PSD to larger diameters is faster in the case of higher heptane concentrations because of the greater mass of asphaltenes precipitat...

Effect of Phosphate Cement and Aggregate on the Fluidity and Strength of Phosphate Concrete

To prepare the concrete of high strength and high fluidity, some important factors were investigated, namely species of phosphate, the ratio of phosphate and magnesia, the surface area of phosphate cement, fineness of sand, particle size distribution of coarse aggregate and the ratio of phosphate cement and aggregate. Results showed that the fluidity and strength of phosphate concrete prepared by KH2PO4were lower than that prepared by NH4H2PO4and decreased as the ratio of P/M reduced. The surface area of phosphate cement increased from 210m2/kg to 400m2/kg, the fluidity and strength firstly increased, and then decreased. The fluidity and strength of phosphate prepared by medium sands were lower than that prepared by fine sands or super-fine sands. Fast harden and early strength phosphate concrete of high fluidity can be prepared by three kinds of coarse aggregate, namely 5～10mm, 5～20mm and 5～25mm. Besides the ratio of cement and aggregate had a significant effect on the fluidity and strength, and the best ratio fell between 1:1 and 1:2.

Influence of complex component and particle polydispersity on radiative properties of soot aggregate in atmosphere

The effects of morphological structure, water coating, dust mixing and primary particle size distribution on the radiative properties of soot fractal aggregates in atmosphere are investigated using T-matrix method. These fractal aggregates are numerically generated using a combination of the particle–cluster and cluster–cluster aggregation algorithms with fractal parameters representing soot aggregate in atmosphere. The radiative properties of compact aggregate notably deviate from that of the branched one, and the effect of morphology changes on the radiative properties in wet air cannot be neglected. However it is reasonable to use realization-averaged radiative properties to represent that of the aggregates with certain morphology. In wet air, the scattering, absorption and extinction cross-section and symmetry parameter of soot aggregates coated with water notably increase with water shell thickness. The mixing structures of dust have little effect on radiative properties of aggregates, but the volume fraction of dust has an obvious effect on extinction, scattering and absorption cross-section of aggregates when the size parameters are above the Rayleigh limit. Although the primary particle size distribution of soot aggregate has mild effect on the scattering albedo and asymmetry parameter, the deviations of the extinction, scattering, absorption cross-section among the three size distributions are significant in this study. The size distribution has a significant effect on forward scattering of phase function, while the effect can be neglected as the size parameter approaches to the Rayleigh limit.

Characterization of Renders, Joint Mortars, and Adobes from Traditional Constructions in Aveiro (Portugal)

The huge and special architectural heritage of Aveiro (Portugal) from the beginning of the past century is characterized by the use of stone or adobe (mud sun-dried blocks), as structural material, with lime renders and mortars. Some of those buildings are situated in the city core and show different degradation degrees, promoted either by weathering in urban context, lack of maintenance, or the seaside proximity. To preserve this type of construction, a study was carried out in order to characterize renders, joint mortars and adobes, to know the composition and behaviour of each in the construction. For this purpose, samples were extracted from various locations of several buildings. The study of mineralogy was performed by x-ray diffraction (XRD), their thermal behaviour was obtained by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and these data were complemented by chemical analysis by x-ray fluorescence spectroscopy (XRF). The aggregate particle size distributions were obtained by dry sieving. Mechanical compressive strength (Rc) and capillarity performance were also evaluated. The results have shown that the mineralogical composition of joint mortars, renders and adobes are similar and the presence of efflorescences was detected in some samples. In general the capillary coefficients of the adobe samples are higher than those of the renders and mortars related with them. The Rc values were similar for the renders, mortars, and adobes. These studies have also been undertaken to support sustainable interventions, allowing the extraction of salts, the consolidation of renders and production of new compatible renders and mortars to substitute and refill the gaps capable of guaranteeing the integrity and prolonging the existence of this kind of architecture and building technique.

Effect of content and particle size distribution of coarse aggregate on the compressive strength of concrete

Coarse aggregate fraction is known to strongly influence both fresh and hardened concrete’s properties. Consequently, selection of both content and particle size distribution (PSD) for concrete mixture is an important issue regarding the predicted performance of concrete. In the present study, and based on previous results obtained, four granular fractions were combined in different proportions in order to investigate the effect of the PSD of aggregate on the properties of concrete. Two types of chemical admixtures, water reducer agent (WRA) and superplasticizer (HRWRA) were used to decrease the water-cement ratio (w/c) which ranges from 0.58 to 0.40. Compressive strength function the PSD of coarse aggregate was determined at 7, 14 and 28 days. Results have revealed that the mixtures without chemical admixture made with a ternary combination of granular fraction and having a maximum size of 25 mm, that assures a continuous granular size distribution, have shown the highest compressive strength. However, decreasing the w/c by the inclusion of WRA or HRWRA requires a decrease of the maximum size of coarse aggregate and some adjustment in the granular size distribution system. The binary granular system has led to the highest compressive strength when dealing with low w/c.