Particle Packing Model Research Articles

Porosity and size gradation of saturated gravel with percolated fines

AbstractFine particles may infiltrate through coarse alluvial beds and eventually saturate the subsurface pore space. It is essential to understand the conditions that lead to bed saturation, and to forecast the packing characteristics of saturated beds to assess the effect of excess fine sediment supply on a number of processes that occur in the stream–sediment boundary. To address this problem, in this study, a new method is introduced to predict the grain‐size distribution for the saturated condition, and the resulting porosity decrease, given the characteristics of the bed and the supplied sediments. The new method consists of the numerical aggregation of infilling fines in a finite bed volume, during which the bed properties change to affect further infilling. An existing semi‐empirical, particle packing model is implemented to identify these properties. It is shown that these types of models are adequate to describe regimes of natural sediment fabric quantitatively, and are thus useful tools in the analysis of sediment infiltration processes. Unlike previous developments to quantify saturated bed conditions, which assume that the supplied material is uniform and finer than the bed pore openings, the method developed herein considers poorly sorted fines, and can identify size fractions that are able to ingress into the bed due to being smaller than the particles that form the bed structure. Application of the new method to published experimental data showed that the final content of infiltrated fines is strongly sensitive to the initial bed packing density, highlighting the need to measure and understand open‐work gravel deposits. In addition, the new method was shown to be suitable for assessing the degree of bed saturation, when it was applied to a published data set of field samples.

Energy absorption capacity of a sustainable Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) in quasi-static mode and under high velocity projectile impact

This paper investigates the energy absorption capacity of a sustainable Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) in quasi-static mode and under high velocity projectile impact. The design of the sustainable concrete mixtures aims on achieving a densely compacted cementitious matrix with a relatively low binder amount, employing the modified Andreasen & Andersen particle packing model. The experiments on UHPFRC are performed using a 4-point bending test and high velocity projectile impact tests. The obtained results show that although the utilization of hybrid steel fibre enhances the mechanical properties of the developed UHPFRC, the application of fibres with hooked ends is crucial in improving the energy absorption capacity of the sustainable UHPFRC in quasi-static mode. However, under high velocity projectile impact, the UHPFRC mixture with hybrid fibres shows a much better energy absorption capacity than the one with hooked steel fibres only, particularly in resisting the scabbing at the rear surface. The intrinsic mechanisms for the energy absorption capacity of the sustainable UHPFRC in quasi-static mode and under high velocity projectile impact are studied and analysed.

Experimental investigation of the utilization of quarry dust for the production of microcement-based building elements by self-flowing molding casting

The management and disposal of fine by-products produced by the aggregate industry, ready-mix concrete and asphalt concrete installations (also known as filler or quarry dust), emerges as a major environmental problem of quarrying and construction sector. Even though considerable research has been undertaken for the utilization of this fine by-product in several applications, it still remains under-utilized, while its disposal and stabilization is also problematic due to resulting emissions of airborne particle pollutants. In this study the production of self-flowing castable cement-based building elements incorporating high amounts of quarry dust was investigated in laboratory scale. Quarry dust, microcement, water and concrete admixtures were mixed and casted in steel molds for the production of the specimens. The initial study of mixtures composition was based on the Andreassen particle packing model, while the final mix design was determined via Box–Behnken fractional factorial design of experiments, in combination with the response surface method. The compressive strength and water absorption values of hardened specimens exceed the relevant technical requirements currently in force, regarding load-bearing as well as decorative building elements, thus opening a new promising field for the utilization of this by-product.

An improved particles model for stress sensitivity in low-permeability sandstones

Stress-dependent permeability and porosity of porous media is very important for the development of oil reservoirs, especially in low-permeability reservoirs. Porous structure can change in response to an increase in the effective stress to induce the decline of permeability and porosity, which ultimately affects the fluid flow property. In this study, a capillary module, considering the arrangement and the deformation of particles, has been established to express the stress sensitivity of porous media based on the particle packing model. The predictions of variation of permeability by the proposed model have been validated by comparing with the experimental data. The predictions by the current model show the same variation trend with the experimental data and are consistent with the compression experiments. The proposed variation of permeability with the increase in effective stress depends on the factors such as the arrangement of particles (contact angle), the deformation of particles (elastic module and Poisson’s ratio) and effective stress. The effects of these parameters on variation of permeability are discussed in detail.

Development of Ultra-Lightweight Fibre Reinforced Concrete applying expanded waste glass

This paper presents the development of Ultra-Lightweight Fibre Reinforced Concrete (ULFRC) applying expanded waste glass in form of lightweight aggregates. The modified Andreasen & Andersen particle packing model and an optimal amount of polypropylene fibres are utilized in the design and production of ULFRC. The density, mechanical properties and thermal conductivity of the developed ULFRC are measured and analyzed. The ULFRC with a dry density of 750 kg/m3 is produced. It is found that hybridization and an optimized amount of polypropylene fibres are beneficial for improving the mechanical properties of ULFRC. Moreover, compared to the other lightweight concretes with the same density, the ULFRC developed in this study has improved mechanical properties and lower thermal conductivity, therefore it can be utilized as a new material for the production of floating structures, insulating elements or even for load bearing applications. As sustainable development is currently a crucial global issue and various industries are striving to save the energy and lower the environmental impact, the developed ULFRC has a good prospect in the near future.

Development of Ultra-High Performance Fibre Reinforced Concrete (UHPFRC): Towards an efficient utilization of binders and fibres

This paper presents a method to develop Ultra-High Performance Fibre Reinforced Concrete (UHPFRC). Towards an efficient utilization of binders and fibres in UHPFRC, the modified Andreasen & Andersen particle packing model and the hybridization design of fibres are utilized. Particularly, the UHPFRC with ternary fibres is appropriately designed and tested. The flowability, mechanical properties and flexural toughness of the designed UHPFRC are measured and analyzed. The results show that, based on the optimized particle packing and hybrid macro and micro fibres, it is possible to produce UHPFRC with a relatively low binder amount (about 620kg/m3) and low fibre content (Vol. 2%). Moreover, due to the mutual effects between the utilized fibres, the hybrid fibre reinforced UHPFRC shows an improved flowability and better mechanical properties. Nevertheless, the flexural toughness of UHPFRC is dominated by the hooked steel fibres. Due to the specific characteristics of UHPFRC, the JSCE SF-4 standard is found more suitable than ASTM C1018-97 to be used to evaluate the flexural toughness of UHPFRC.

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.

Development of an eco-friendly Ultra-High Performance Concrete (UHPC) with efficient cement and mineral admixtures uses

This paper addresses the development of an eco-friendly Ultra-High Performance Concrete (UHPC) with efficient cement and mineral admixtures uses are investigated. The modified Andreasen & Andersen particle packing model is utilized to achieve a densely compacted cementitious matrix. Fly ash (FA), ground granulated blast-furnace slag (GGBS) and limestone powder (LP) are used to replace cement, and their effects on the properties of the designed UHPC are analyzed. The results show that the influence of FA, GGBS or LP on the early hydration kinetics of the UHPC is very similar during the initial five days, while the hydration rate of the blends with GGBS is mostly accelerated afterwards. Moreover, the mechanical properties of the mixture with GGBS are superior, compared to that with FA or LP at both 28 and 91days. Due to the very low water amount and relatively large superplasticizer dosage in UHPC, the pozzolanic reaction of FA is significantly retarded. Additionally, the calculations of the embedded CO2 emission demonstrate that the cement and mineral admixtures are efficiently used in the developed UHPC, which reduce its environmental impact compared to other UHPCs found in the literature.

IMPACT RESISTANCE CAPACITY OF A GREEN ULTRA-HIGH PERFORMANCE HYBRID FIBRE REINFORCED CONCRETE (UHPHFRC): EXPERIMENTAL AND MODELING STUDY

This article addresses the impact resistance capacity of a green Ultra-High Performance Hybrid Fibre Reinforced Concrete (UHPHFRC). The design of concrete mixtures is based on the aim to achieve a densely compacted cementitious matrix, employing the modified Andreasen & Andersen particle packing model. The modified Charpy test device is employed to test the energy absorption ability of the UHPHFRC under the external impact loading. The results show that the long steel fibres play a dominating role in improving the impact resistance capacity of the UHPHFRC. Additionally, the failure mechanism of the UHPHFRC under impact loading is analyzed and modeled. The proposed model can well predict the energy absorption ability of the UHPHFRC samples.

Static properties and impact resistance of a green Ultra-High Performance Hybrid Fibre Reinforced Concrete (UHPHFRC): Experiments and modeling

This paper addresses the static properties and impact resistance of a “green” Ultra-High Performance Hybrid Fibre Reinforced Concrete (UHPHFRC). The design of concrete mixtures aims to achieve a densely compacted cementitious matrix, employing the modified Andreasen & Andersen particle packing model. The flowability, static mechanical properties and impact resistance capacity of UHPHFRC are measured and analyzed. The results show that by utilizing the improved packing model, it is possible to design a type of UHPHFRC with a relatively low binder amount, which can make the concrete more “green”. Moreover, due to the mutual effect between the long and short steel fibres, the hybrid fibre reinforced concrete shows better workability and higher static mechanical properties. Nevertheless, the impact resistance capacity of UHPHFRC is dominated by the long steel fibres. Additionally, the energy absorption process of UHPHFRC under dynamic loading is analyzed and modeled.

Analogue Particle and Random Packing Models of Ecological Community Formation

The apparent constancy of the near linear relationship between logarithm of a specie’s abundance in a community and their rank order led to a brief review of existing species abundance distribution (SAD) models; a proposal of three further classes of analogue models; and an evaluation of a meta data set of empirical vegetation composition data. A new class of models is proposed considered particle packing of circles (2D) or spheres (3D) as representing individuals of species which under different scenarios of arrival, growth, displacement and mortality determine community maximum packing and SAD. Besides the existing random models treating each species as an entity, two further classes are added which considered dismantling rather than assembly models, or retaining identity of taxa species through successive stages of assembly or dismantling models. In each of the models, the resulting form of the SAD was dependent on which metric of an individual (density, area, volume etc) was used as a measure of abundance. A comparison was made between the resulting 576 different models and 432 sets of 10 species and 110 sets of 5 species empirical observations. There was a wide variation in species proportions and a lack of clustering around a particular model. In those comparisons, the particle packing models of individuals were as good as the random models treating species as an entity and did offer a functional explanation of the formation of the SAD. In most models and empirical data the species ranking is done retrospectively so there will always be a high negative correlation between abundance and rank implying a need for a revaluation of the ecological significance of the relationship.

Effect of nano-silica on the hydration and microstructure development of Ultra-High Performance Concrete (UHPC) with a low binder amount

This paper presents the effect of nano-silica on the hydration and microstructure development of Ultra-High Performance Concrete (UHPC) with a low binder amount. The design of UHPC is based on the modified Andreasen and Andersen particle packing model. The results reveal that by utilizing this packing model, a dense and homogeneous skeleton of UHPC can be obtained with a relatively low binder amount (about 440kg/m3). Moreover, due to the high amount of superplasticizer utilized to produce UHPC in this study, the dormant period of the cement hydration is extended. However, due to the nucleation effect of nano-silica, the retardation effect from superplasticizer can be significantly compensated. Additionally, with the addition of nano-silica, the viscosity of UHPC significantly increases, which causes that more air is entrapped in the fresh mixtures and the porosity of the hardened concrete correspondingly increases. In contrary, due to the nucleation effect of nano-silica, the hydration of cement can be promoted and more C–S–H gel can be generated. Hence, it can be concluded that there is an optimal nano-silica amount for the production of UHPC with the lowest porosity, at which the positive effect of the nucleation and the negative influence of the entrapped air can be well balanced.

A study of multiple effects of nano-silica and hybrid fibres on the properties of Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) incorporating waste bottom ash (WBA)

This article addresses the multiple effects of nano-silica and hybrid fibres on the properties of an Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) incorporating waste bottom ash (WBA). The design of the concrete mixtures was based on the aim to achieve a densely compacted matrix, employing the modified Andreasen and Andersen particle packing model. The workability, porosity, flexural and compressive strengths of the UHPFRC are measured and analyzed. The results show that due to the existence of the metallic aluminium particles in WBA, the generated hydrogen can cause some visible macro-cracks in the concrete, which could reduce the mechanical properties of the concrete. However, with a simultaneous utilization of nano-silica and hybrid fibres (steel and polypropylene fibres), the negative influence from the WBA can be effectively minimized and the flexural strength of the UHPFRC can be improved.

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 K 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.

Mix design and properties assessment of Ultra-High Performance Fibre Reinforced Concrete (UHPFRC)

This paper addresses the mix design and properties assessment of Ultra-High Performance Fibre Reinforced Concrete (UHPFRC). The design of the concrete mixtures is based on the aim to achieve a densely compacted cementitious matrix, employing the modified Andreasen & Andersen particle packing model. One simple and efficient method for producing the UHPFRC is utilised in this study. The workability, air content, porosity, flexural and compressive strengths of the designed UHPFRC are measured and analyzed. The results show that by utilizing the improved packing model, it is possible to design UHPFRC with a relatively low binder amount. Additionally, the cement hydration degree of UHPFRC is calculated. The results show that, after 28day of curing, there is still a large amount of unhydrated cement in the UHPFRC matrix, which could be further replaced by fillers to improve the workability and cost efficiency of UHPFRC.

Estimation of thermophysical properties of solid propellants based on particle packing model

A method for the estimation of thermophysical properties of two- and multi-phase solid propellants is proposed in this paper. The theoretical solutions for thermal conductivity and specific heat of a homogeneous solid propellant cell in the transient thermal conductivity process are deduced on the condition that one boundary of the cell is heated while others are adiabatic. A homogenization theory and the finite element method are employed to compute the mean temperature and heat flux of a representative volume element (RVE). According to the mean results and the theoretical solutions, the effective thermal conductivity and specific heat of solid propellant can be estimated. A packing algorithm, considering the solid particles (ammonium perchlorate (AP) or aluminum) as spheres or discs, is used to match the size distribution and volume fraction of solid propellants, and some mesoscopic models of two-phase and three-phase solid propellants are established. According to the estimation theory proposed in this paper, the effective thermal conductivity and specific heat of solid propellants are predicted. The effect of AP or Al volume fraction is also discussed in this paper.

DEM을 이용한 골재다짐모형 개발을 위한 기존 모형 분석

PURPOSES : Determination of particle packing model variables that can be used for formulation of new DEM based particle packing model by examining existing particle packing models METHODS : Existing particle packing models are thoroughly examined by analytical reformulation and sensitivity analysis in order to set up DEM based new particle packing model and to determine its variables. All model equations considered in this examination are represented with consistent expressions and are compared to each others to find mathematical and conceptual similarity in expressions. RESULTS : From the examination of existing models, it is observed that the models are very similar in their shapes although the derivation of the models may be different. As well, it is observed that variables used in some existing models are comprehensive enough to estimate particle packing but not applicable to DEM simulation. CONCLUSIONS : A set of variables that can be used in DEM based particle packing model is determined.

Development of cement-based lightweight composites – Part 2: Durability-related properties

Cement-based lightweight composites were developed in Part 1 of this study [1], employing the modified Andreasen and Andersen particle packing model. The design was targeted on a good balance between the mechanical and thermo-physical performance of the material. By the application of expanded glass lightweight aggregates in a form of closed spheres, the design was also targeted on a low permeability to fluids, which is a unique feature for this type of material. The durability-related properties of the developed lightweight composites were investigated in this paper. The durability was quantified based on the measurements of water-permeable porosity, capillary water absorption, chloride transport properties, electrical resistivity, freeze–thaw resistance and alkali-silica reaction. The results show that by using the proposed design methodology, it is possible to develop lightweight composites of low density and thermal conductivity, sufficient strength and low permeability to fluids.

Hydration and time-dependent rheology changes of cement paste containing ground fly ash

The use of ground fly ash in concrete can increase the risk of slump loss due to the drastic surface change of the particles after the grinding treatment and the accelerated reaction compared to the untreated ash. This study is aimed at the early age hydration and time-dependent rheology changes of cement paste containing ground fly ash. An original fly ash is ground into different fineness and the hydration of cement paste containing the ground fly ash is monitored with the ultrasound propagation method. The zeta potentials of the solid particles are measured and the changes of rheological parameters of the cement pastes with time are analyzed with a rheometer. A particle packing model is used to probe packing of the solid particles. The results show that the early age hydration of the paste is strongly promoted by replacing Portland cement with fly ash up to 30 percent (by mass), causing increase of the yield stress of the paste. The viscosity of a paste containing ground fly ash is lower than that containing the untreated ash, which is explained by the denser packing of the solid particles.

Vegetation Productivity/Stability and Other Possible Ecological Invariant Relationships Demonstrated in a Microplot Multispecies Pasture Sward

The relationship between vegetation functional characteristics of production, stability and descriptive characteristic of species diversity or dominance, and other possible compositional invariants were investigated in 2400 micro-plot sward of 20 species at randomly assigned positions and using different matrix sizes of adjacent plots and four harvest to derive a combination of “vegetations” of differing species configurations.Within the highest frequency section of the data there was little relationship between productivity and stability (deviance) and either species diversity or dominance (% contribution of 1st ranked species). However, considering all data, productivity increased with increasing dominance and was unrelated to species diversity, while stability increased with diversity. Of single parameters combining diversity and dominance, the gradient of the log abundance/rank relationship was superior to Shannon H, with both showing productivity increasing with dominance rather than diversity. The fate of individual micro-plots from a mixed species stand through successive harvests was consistent with the −3/2 thinning rule, though with species cumulative yields. The abundance/rank relationship was compared with many models. Where there was simultaneous fitting to both density and biomass relationships, self-thinning random particle packing models were best and offered an explanation of the process. The positive correlation between regional and local frequency was related to sample area in a random placement model. Observed species composition and mortality was simulated by consideration of plant size related growth and mortality, initial establishment, growth potential and variation in plant size.