Packing Density Improvement through Addition of Limestone Fines, Superfine Cement and Condensed Silica Fume

Adoption of a low water/powder (W/P) ratio is the key to improve the strength and durability of concrete, which relies on a high packing density because fresh concrete requires excess water to offer flowability. To obtain a high packing density, powders with different particle sizes, including limestone fines (LSF), superfine cement (SFC), condensed silica fume (CSF), were added to the cement paste and the resulting packing densities were measured directly by a newly-developed wet packing test. Results demonstrated that addition of powders with a finer size would more significantly improve the packing density but the powders should be at least as fine as 1/4 of the OPC to effectively improve the packing density. Packing density and voids ratio relationship showed that a small increase in packing density can significantly decrease the voids ratio, which could allow the W/P ratio to be reduced to improve the strength and durability of the concrete without compromising the flowability.

Understanding the influence of crystal packing density on electrochemical energy storage materials

Crystal structure determines electrochemical energy storage characteristics;this is the underlying logic of material design.To date,hundreds of electrode materials have been developed to pursue superior performance.However,it remains a great challenge to understand the fundamental structure–performance relationship and achieve quantitative crystal structure design for efficient energy storage.In this review,we introduce the concept of crystal packing factor(PF),which can quantify crystal packing density.We then present and classify the typical crystal structures of attractive cathode/anode materials.Comparative PF analyses of different materials,including polymorphs,isomorphs,and others,are performed to clarify the influence of crystal packing density on energy storage performance through electronic and ionic conductivities.Notably,the practical electronic/ionic conductivities of energy storage materials are based on their intrinsic characteristics related to the PF yet are also affected by extrinsic factors.The PF provides a novel avenue for understanding the electrochemical performance of pristine materials and may offer guidance on designing better materials.Additional approaches involve size regulation,doping,carbon additives,and other methods.We also propose extended PF concepts to understand charge storage and transport behavior at different scales.Finally,we provide our insights on the major challenges and prospective solutions in this highly exciting field.

Effect of packing density and packing geometry on light extraction of Ⅲ-nitride light-emitting diodes with microsphere arrays

The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip In Ga N/Ga N quantum well light-emitting diodes（LEDs） with TiO2 microsphere arrays. The extraction efficiency for LEDs with microsphere arrays was investigated by focusing on the effect of the packing density,packing configuration, and diameter-to-period ratio. The comparison studies revealed the importance of having a hexagonal and close-packed monolayer microsphere array configuration for achieving optimum extraction efficiency, which translated into a 3.6-fold enhancement in light extraction compared to that for a planar LED. This improvement is attributed to the reduced Fresnel reflection and enlarged light escape cone. The engineering of the far-field radiation patterns was also demonstrated by tuning the packing density and packing configuration of the microsphere arrays.

Disordered packing density of binary and polydisperse mixtures of curved spherocylinders

Particle elongation is an important factor affecting the packing properties of rod-like particles. However, rod-like particles can be easily bent into non-convex shapes, in which the effect of bending should also be of concerned, To explore the shape effects of elongation and bending, together with the size and volume fraction effects on the disordered packing density of mixtures of non-convex particles, binary and polydisperse mixtures of curved spherocylinders are simulated employing sphere assembly models and the relaxation algorithm in the present work. For binary packings with the same volume, curves of the packing density versus volume fraction have good linearity, while densities are plotted as a series of equidistant curves under the condition of the same shape. The independence of size and shape effects on the packing density is verified for mixtures of curved spherocylinders. The explicit formula used to predict the density of binary mixtures, by superposing the two independent functions of the size and shape parameters, is extended to include a non-convex shape factor. A polydisperse packing with the shape factor following a uniform distribution under the condition of the same volume is equivalent to a binary mixture with certain components. The packing density is thus predicted as the mean of maximum and minimum densities employing a weighing method.

Packing,compressibility,and crushability of rockfill materials with polydisperse particle size distributions and implications for dam engineering

In rockfill dam engineering,particle breakage of rockfill materials is one of the major factors resulting in dam settlement.In this study,one-dimensional compression tests on a series of coarse granular materials with artificially-graded particle size distributions(PSDs)were carried out.The tests focused on understanding the role of initial PSDs in the dense packing density,compressibility and crushability of coarse granular materials.The effects of fractal dimension(D)and size polydispersity(θ)of PSDs were quantitatively analyzed.Two different loading stages were identified from the logarithms of the stress-strain relationships,with the turning point marked as the yield stress.A similar effect of initial PSDs was observed on the packing density and low-pressure modulus of coarse granular materials.The packing density and low-pressure modulus increased monotonically withθ,and their peak values were attained at a D value of approximately 2.2.However,there was no unique correspondence between the dense packing density and low-pressure modulus.The particle breakage was influenced differently by the initial PSDs,and it decreased with the values of D andθ.The emergence of the unique ultimate state was also identified from both the compression curves and PSDs of the samples after the tests.The potential implications of the test results in the design of both low and high rockfill dams were also demonstrated.

Computer Simulation of Random Packing of Spherical Particles in Two Dimensions

Random packings of spherical particles have attracted attention for many years.An algorithm based on compression is developed to generate random packings of spherical particles in this paper.This method is different from previous compression-based algorithm.In order to increase the packing density,a process of shaking is applied during packing process.The algorithm is mainly composed of three procedures:generating initial packing configuration by using random sequential adsorption(RSA),compressing packing domain,and shaking.The packing structure is characterized by packing density and coordinate number.The packing density increases with iteration number and a stable packing configuration is obtained after the iteration number is more than 34 000.The packing density is 0.85 and the average coordinate number is 3.7 in a stable packing configuration.

Protein Conformational Change Based on a Two-dimensional Generalized Langevin Equation

A two-dimensional generalized Langevin equation is proposed to describe the protein conformational change, compatible to the electron transfer process governed by atomic packing density model. We assume a fractional Gaussian noise and a white noise through bond and through space coordinates respectively, and introduce the coupling effect coming from both fluctuations and equilibrium variances. The general expressions for autocorrelation functions of distance fluctuation and fluorescence lifetime variation are derived, based on which the exact conformational change dynamics can be evaluated with the aid of numerical Laplace inversion technique. We explicitly elaborate the short time and long time approximations. The relationship between the two-diraensional description and the one-dimensional theory is also discussed.

New expressions for the surface roughness length and displacement height in the atmospheric boundary layer

An alternative model for the prediction of surface roughness length is developed. In the model a new factor is introduced to compensate for the effects of wake diffusion and interactions between the wake and roughness obstacles. The experiments are carried out by the use of the hot wire anemometry in the simulated atmospheric boundary layer in a wind tunnel. Based on the experimental data, a new expression for the zero-plane displacement height is proposed for the square arrays of roughness elements, which highlights the influence of free-stream speed on the roughness length. It appears that the displacement height increases with the wind speed while the surface roughness length decreases with Reynolds number increasing. It is shown that the calculation results based on the new expressions are in reasonable agreement with the experimental data.

Assessment of Vulnerability of Oxisols to Compaction in the Cerrado Region of Brazil

The Cerrado region of Brazil,one of the fastest-growing agricultural areas in the world,is undergoing very rapid mechanization;this development is good for the country's economy but may also snowball into substantial loss of agricultural land and other environmental degradation if the soil susceptibility and vulnerability to compaction is not well understood.In this study we explored different techniques for estimating soil intrinsic abilities to withstand applied pressure using the prevalent Oxisols of the Cerrado region under native vegetation.Undisturbed samples were collected from three sites within the region and subjected to 1) compressibility test;2) manual penetration resistance test;3) automated penetration resistance test;and 4) packing density analysis.The four methods produced analogous results.Our results showed the significant influence of soil structure on the inherent strength and compaction susceptibility of the soils.We also established the association of soil structure with the mineralogy of the soil.It is noteworthy that the packing density which was developed from very simple and easily obtained parameters could give a picture of the tendency of the soil to compact.Thus,this approach would be useful in developing compaction susceptibility maps for the region.It could be concluded that most of the Oxisols in the Cerrado region would support mechanized agricultural production very successfully.However,there is need for careful management of the mechanization process to avert degradation.The management techniques should include conservationist practices such as no till in order to maintain as much as possible the favorable structure and drainage of these very old soils.

The grain grading model and prediction of deleterious porosity of cement-based materials

The calculating model for the packing degree of spherical particles system was modified. The grain grading model of cement-based materials was established and could be applied in the global grading system as well as in the nano-fiber reinforced system. According to the grain grading model, two kinds of mortar were designed by using the global grain materials and nano-fiber materials such as fly ash, silica fume and NR powder. In this paper, the densities of two above systems cured for 90d were tested and the relationship of deleterious porosity and the total porosity of hardened mortar was discussed. Research results show that nano-fiber material such as NR powder can increase the density of cement-based materials. The relationship of deleterious porosity and the total porosity of hardened mortar accords with logarithmic curve. The deleterious porosity and the rationality of the grading can be roughly predicted through calculating the packing degree by the grain grading model of cement-based materials.

Sand Textural Control on Shear-Enhanced Compaction Band Development in Poorly-Lithified Sandstone

Sand textural control on SECB （shear-enhanced compaction band） formation is analyzed combining field observations, detailed material characterization and mechanical testing for poorly lithified sandstone units in Provence （France）. Field observations show that SECBs are densely distributed in a coarse-grained unit with moderate porosity （27%）, whereas few SECBs are developed within the overlying fine-grained, high-porosity （39%） unit. Results from textural characterization show that the main difference between the two sand units is grain size and sorting, whereas they are similar with respect to composition and grain angularity. Packing density is introduced as an important parameter for comparing the compaction properties independent of the textural variations between the two units. Compaction experiments show a slightly faster compaction of the coarse-grained sand as compared to the fine-grained sand, and more pronounced grain crushing is observed in the coarse-grained unit. The results indicate that the preferential localization of SECBs to the coarse-grained unit is controlled by a slightly denser packing of the coarse-grained material at the time of band formation together with higher stress concentrations on grain contacts. Hence, this study emphasizes that porosity alone is an insufficient parameter for predicting deformation band evolution in sand （stone）.

Dense packing properties of mineral admixtures in cementitious material

The effect of ultra-fine fly ash （UFFA）, steel slag （SS） and silica fume （SF） on packing density of binary, ternary and quaternary cementitious materials was studied in this paper in terms of minimum water requirement of cement. The influence of mineral admixtures on the relative density of pastes with low water/hinder ratios was analyzed and the relationship between paste density and compressive strength of the corresponding hardened mortars was discussed. The results indicate that the incorporation of mineral admixtures can effectively improve the packing density ofcementitious materials; the increase in packing density of a composite with incorporation of two or three kinds of mineral admixtures is even more obvious than that with only one mineral admixture. Moreover, an optimal amount of mineral admixture imparts to the mixture maximum packing density. The dense packing effect of a mineral admixture can increase the packing density of the resulting cementitious material and also the density of paste with low water/binder ratio, which evidently enhances the compressive strength of the hardened mortar.

Random packing of tetrahedral particles using the polyhedral discrete element method

The random packing of tetrahedral particles is studied by applying the discrete element method （DEM）, which simulates the effects of friction, height ratio, and eccentricity. The model predictions are ana- lyzed in terms of packing density and coordination number （CN）. It is demonstrated that friction has the maximal effect on packing density and mean CN among the three parameters. The packing den- sity of the regular tetrahedron is 0.71 when extrapolated to a zero friction effect. The shape effects of height ratio and eccentricity show that the regular tetrahedron has the highest packing density in the family of tetrahedra, which is consistent with what has been reported in the literature. Compared with geometry-based packing algorithms, the DEM packing density is much lower. This demonstrates that the inter-particle mechanical forces have a considerable effect on packing. The DEM results agree with the published experimental results, indicating that the polyhedral DEM model is suitable for simulating the random packing of tetrahedral particles.

Evaluation of particle packing models by comparing with published test results

The existing particle packing density models each with two or more parameters accounting for certain particle interactions （the loosening effect parameter, wall effect parameter, wedging effect parameter, and compaction index, denoted by a, b, c, and K, respectively） may be classified into the 2-parameter model （with a and b incorporated）, the compressible model （with a, b, and 1（incorporated）, and the 3- parameter model （with a, b, and c incorporated）. This paper evaluates these models by comparing their respective packing density predictions with the test results published in the literature. It was found that their accuracy varies with both the size ratio and volumetric fractions of the binary mix. In general, when the size ratio is larger than 0.65, all the packing models are sufficiently accurate. However, when the size ratio is smaller than 0.65, some of them become inaccurate and the errors tend to be larger at around the volumetric fractions giving maximum packing density. Relatively, the 3-parameter model is the most accurate and widely applicable.

Two-dimensional densely ordered packings of non-convex bending and assembled rods

The investigation of the problem of particle packing has provided basic insights into the structure,symmetry,and physical properties of condensed matter.Dense packings of non-spherical particles have many applications,both in research and industry.We report the two-dimensional dense packing patterns of bending and assembled rods,which are non-convexly deformed from simple objects and modeled as entangled particles.Monte Carlo simulations and further analytical constructions are carried out to explore possible densely packed structures.Two typical densely packed structures of C-bending rods are found,and their packing densities are identified as being functions of the aspect ratio and central angle.Six shapes of assembled rods,representing the combined deformations of rods,are employed in simulations with the packing structures classified into three types.The dense packing density of each packing pattern is derived as a function of different shape parameters.In contrast with the case of disordered packings,both the shape and order are verified to affect the packing density.

Carbon nanotube fibers with excellent mechanical and electrical properties by structural realigning and densification

Floating catalysis chemical vapor deposition(FCCVD)direct spinning process is an attractive method for fabrication of carbon nanotube fibers(CNTFs).However,the intrinsic structural defects,such as entanglement of the constituent carbon nanotubes(CNTs)and inter-tube gaps within the FCCVD CNTFs,hinder the enhancement of mechanical/electrical properties and the realization of practical applications of CNTFs.Therefore,achieving a comprehensive reassembly of CNTFs with both high alignment and dense packing is particularly crucial.Herein,an efficient reinforcing strategy for FCCVD CNTFs was developed,involving chlorosulfonic acid-assisted wet stretching for CNT realigning and mechanical rolling for densification.To reveal the intrinsic relationship between the microstructure and the mechanical/electrical properties of CNTFs,the microstructure evolution of the CNTFs was characterized by cross-sectional scanning electron microscopy(SEM),wide angle X-ray scattering(WAXS),polarized Raman spectroscopy and Brunauer–Emmett–Teller(BET)analysis.The results demonstrate that this strategy can improve the CNT alignment and eliminate the inter-tube voids in the CNTFs,which will lead to the decrease of mean distance between CNTs and increase of inter-tube contact area,resulting in the enhanced inter-tube van der Waals interactions.These microstructural evolutions are beneficial to the load transfer and electron transport between CNTs,and are the main cause of the significant enhancement of mechanical and electrical properties of the CNTFs.Specifically,the tensile strength,elastic modulus and electrical conductivity of the high-performance CNTFs are 7.67 GPa,230 GPa and 4.36×10^(6)S/m,respectively.It paves the way for further applications of CNTFs in high-end functional composites.

Nanocellulose/nitrogen and fluorine co-doped graphene composite hydrogels for high-performance supercapacitors

Three-dimensional graphene materials have been studied as typical supercapacitors electrode materials by virtue of their ultrahigh specific surface area and good ion transport capacity.However,improvement of the poor volumetric electrochemical performance of these graphene materials has been required although they have high gravimetric energy density.In this work,nanocellulose/nitrogen and fluorine co-doped graphene composite hydrogels(NC-NFGHs)were prepared through a convenient hydrothermal approach utilizing ammonium fluoride as the heteroatom source.Nanocellulose(NC)and high concentration of graphene oxide(GO)were utilized to adjust the structure of NC-NFGHs and increase their packing density.Subsequently,the aqueous symmetric supercapacitor based on NC-NFGH-80 exhibits remarkable gravimetric(286.6 F·g^(-1))and volumetric(421.3 F·cm^(-3))specific capacitance at 0.3 A·g^(-1),good rate performance,and remarkable cycle stability up to 10,000 cycles.Besides,the all-solid-state flexible symmetric supercapacitors(ASSC)fabricated by NC-NFGH-80 also delivered a large specific capacitance of 117.1 F·g^(-1)at 0.3 A·g^(-1)and long service life over 10,000 cycles at 10 A·g^(-1).This compact porous structure and heteroatom co-doped graphene material supply a favorable strategy for high-performance supercapacitors.

Effect of mechanical ball milling on the electrical and powder bed properties of gas-atomized Ti-48Al-2Cr-2Nb and elucidation of the smoke mechanism in the powder bed fusion electron b eam melting process

Smoke is unexpected powder-splashing caused by electrostatic force and is one of the main problems hindering the process stability and applicability of the powder bed fusion electron beam(PBF-EB)tech-nology.In this study,mechanical stimulation was suggested to suppress smoke of gas-atomized(GA)Ti-48Al-2Cr-2Nb powder using Al_(2)O_(3) and WC ball milling.The deformation mechanism of the GA powder depending on the ball milling media was discussed based on the developed particle morphology distribu-tion map and contact mechanics simulation.It was revealed that the rapid decrement of flowability and packing density after WC ball milling owing to the formation of angular fragments by the brittle fracture.The variation of surface and electrical properties by mechanical stimulation was investigated via XPS,TEM,and Impedance analysis.The electrical resistivity of the ball-milled powders gradually decreased with increasing milling duration,despite the increased oxide film thickness,and the capacitive response disappeared in Al-60 and WC-30 via metal-insulator transition.This could be due to the accumulation of strain and defects on the oxide film via mechanical stimulation.The smoke mechanism of ball-milled powders was discussed based on the percolation theory.In the smoke experiment,smoke was more suppressed for WC-10 and WC-20 than that for Al-40 and Al-50,respectively,despite the longer charge dissipation time.This could be due to the high probability of contact with conductive particles.For the Al-60 and WC-30 powders,smoke was further restricted by the formation of a percolation cluster with metal-like electrical conductivity.We believe that this study will contribute to a better understanding of the smoke mechanism and process optimization of the PBF-EB.

Effect of recycled powder on the yield stress of cement paste with varied superplasticizers

The influence of superplasticizer on the yield stress of cement pastes with recycled powder(RP)was examined in the study.Four superplasticizers were used to obtain the similar fluidity by adjusting the dosage.The results show that the 10%RP decreases the yield stress of paste compared to the reference paste at the same fluidity,but 20%and 30%RP increases the yield stress,ranging from 11 to 599%.The superplasticizer with adsorptive group of phosphate-type minimizes the yield stress of paste than that of polycarboxylate-type,but it made a significant increment in yield stress as the incorporating of RP increased.Besides,the polycarboxylate superplasticizer with the higher molecular weight of side chain and charge density led to lower yield stress.Based on the Yodel model,the yield stress of paste with RP was analyzed by the polymer adsorption and particle packing density of particles to reveal the influence of RP with different superplasticizers on the colloidal interaction and contact network among the particles.The packing density of particles with recycled powder was a little higher than the reference paste,but the higher fraction of fine particles made a stronger PSD effect,which improved the particle contact interaction.On the other hand,due to the higher polymer adsorption of recycled powder than cement,especially for superplasticizer with phosphate group,the average surface coverage was increased,which extended the separation distance,so that colloidal interaction among particles was weaken.

Functionals on the Spaces of Convex Bodies

In geometry, there are several challenging problems studying numbers associated to convex bodies. For example, the packing density problem, the kissing number problem, the covering density problem, the packing-covering constant problem, Hadwiger＇s covering conjecture and Borsuk＇s partition conjecture. They are flmdamental and fascinating problems about the same objects. However, up to now, both the methodology and the technique applied to them are essentially different. Therefore, a common foundation for them has been much expected. By treating problems of these types as functionals defined on the spaces of n-dimensional convex bodies, this paper tries to create such a foundation. In particular, supderivatives for these functionals will be studied.