Proportioning of Cement-Based Grout for Sealing Fractured Rock-Use of Packing Models

Fractured, very permeable rock hosting repositories for radioactive waste will require grouting. New grout types of possible use where long-term performance is needed should have a small amount of cement for minimizing the increase in porosity that will follow from the ultimate dissolution and erosion of this component. They have to be low-viscous and gain strength early after injection and packing theory can assist designers in selecting suitable proportions of various grout components. Optimum particle packing means that the porosity is at minimum and that the amount of cement paste needed to fill the voids between aggregate particles is very small. Low porosity and microstructural stability must be guaranteed for long periods of time. Organic additives for reaching high fluidity cannot be used since they can give off colloids that carry released radionuclides and talc can be an alternative superplasticizer. Low-pH cement reacts with talc to give high strength with time while Portland cement gives early but limited strengthening. The clay mineral palygorskite can be used for early gelation because of its thixotropic properties. Once forced into the rock fractures or channels in soil it stiffens and serves as a filter that prevents fine particles to migrate through it be lost. However, its hydrophilic potential is too high to give the grout a high density and high strength. According to the experiments carried out, most of the investigated grouts are injectable in fractures with apertures down to 100 μm.

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.

Modeling for critical state line of granular soil with evolution of grain size distribution due to particle breakage

Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of particle breakage on the CSL is mainly attributed to the change in GSD due to particle breakage.However,GSD has not been properly considered in modeling the CSL with influence of particle breakage.This study aims to propose a quantitative model to determine the CSL considering the effect of GSD.We hypothesize that the change of critical state void ratio with respect to GSD is caused by the same mechanism that influences of the change of minimum void ratio with respect to GSD.Consequently,the particle packing model for minimum void ratio proposed by Chang et al.(2017)is extended to predict critical state void ratio.The developed model is validated by experimental results of CSLs for several types of granular materials.Then the evolution of GSD due to particle breakage is incorporated into the model.The model is further evaluated using the experimental results on rockfill material,which illustrates the applicability of the model in predicting CSL for granular material with particle breakage.

Food packing: A case study of dining out in Beijing

the financial project supported by the State Key Program of the National Natural Science Foundation of China （71233007）

THE SERIAL MODEL IN LIQUID FLUIDIZATION AND ITS LIMITATIONS

The serial model of Epstein et al. （1981） is demonstrated to predict successfully the overall voidage of the mixed layer of incompletely segregated binary and ternary mixtures of liquid-fluidized solids that differ only in shape. Some speculations are then offered on the conditions for the success and failure of this model. Finally, methods proposed in the literature for estimating the deviations from the serial model for a binary-solids bed, which manifest themselves as a bed contraction, are discussed, with emphasis on packing models.

Particle packing theory guided multiscale alumina filled epoxy resin with excellent thermal and dielectric performances

Polymers and composites with high thermal conductivity are promising yet challenging for the growing demand of thermal management in electrical and electronic equipment.Guided by the closest packing model,a multiscale filling Al_(2)O_(3) strategy was designed and incorporated with epoxy resin(EP)to form high thermal conductive composites in this work.Epoxy composites with single filler loading were also prepared.The microstructures,thermal,rheological,and dielectric characteristics of the multiscale filling Al_(2)O_(3)/EP composites have been investigated.Compared with single-scale Al_(2)O_(3) filled epoxy based composites,it is found that the multiscale filling Al_(2)O_(3)/EP composites exhibit higher thermal conductivity under the same filler loading of 50 vol%,which is attributed to the efficient heat conduction paths formed by appropriate multiscale fillers.Particularly,a remarkably improved thermal conductivity of 2.707 W m^(-1) K^(-1) was acquired in Al_(2)O_(3)/EP composites at filler loading of 50 vol%(5 mm Al_(2)O_(3)(26.67 vol%),30 mm Al_(2)O_(3)(27.41 vol%)and 70 mm Al_(2)O_(3)(45.92 vol%)),which is about 1300%higher than that of the pure epoxy resin.In addition,the dielectric constant of the Al_(2)O_(3)/EP composites were significantly improved while keeping the dielectric loss almost unchanged.The finite element simulation further verified the effectiveness of improving the thermal conductivity of materials in the heat dissipation of electrical equipment.Therefore,this research provides a simple strategy for manufacturing high thermal conductive composite materials with a wide range of potential applications as packaging materials.

Mathematical simulation of radial heat transfer in packed beds by pseudohomogeneous modeling

Uniform flow regime and constant effective thermal conductivity inside packed beds are commonly accepted in the evaluation of the fluid dynamics and heat transfer in such systems. However, several authors have confirmed the presence of an oscillatory velocity profile caused by the effective contribu~ tion of porosity profile in the fluid dynamic behavior of packed beds, which directly influences the heat transfer inside the beds. This paper describes the application of a pseudo-homogeneous mathematical model for describing heat transfer in packed beds with oscillatory profiles of velocity and porosity, using a radius-dependent model for effective thermal conductivity kr. Several temperature profiles were obtained in a packed bed system with thermal source located on the wall. The simulated temperature and effective thermal conductivity obtained from simulations were compared with experimental data and calculation from a model based on uniform kr fitting. The results indicate that the proposed mathematical modeling was capable of better reDresenting the heat transfer in the packed bed.

EFFECT OF CHEMICAL STRUCTURE OF POLYCARBONATES ON ENTANGLEMENT SPACING

The master curves of a series of aliphatic polycarbonates （APCs） with different lengths of methylene segments in the repeat unit were obtained by dynamic rheological measurements. The plateau modulus and entanglement molecular weight were determined and cross-checked by different methods. Though having distinct difference in chemical structure of repeat units, both APCs and bisphenol-A polycarbonates have the similar entanglement weight and entanglement spacing. On the other side, the plateau modulus decreases with increasing the length of the side group of aliphatic polycarbonates with different side-chain lengths in the literature. The packing length model can explain the relationship between chain structure and entanglements.

Use of multiscale particle simulations in the design of nuclear plant decommissioning

The application of a digital modelling method that can faithfully take account of three-dimensional shape and inherent physical and chemical properties of each particulate component provides an essential tool in decommissioning design. This is useful in handling of high, medium and low level radioactive waste. The processes involve making decisions on where to cut existing plant components and then how to pack these components into boxes, which are then cemented and kept for long term storage as the level of radioactive declines with time. We illustrate the utility of the method and its ability to take data at plant scale （m-scale） and then deduce behaviours at sub millimetre scale in the packed containers. A variety of modelling approaches are used as a part of this approach including cutting algorithms, geometric and dynamic （distinct element） force models, and lattice Boltzmann methods. These methods are applicable to other complex particulate systems including simulation of waste, building recycling, heap leaching and related minerals processes. The paper introduces the basic concepts of this multi-scale and multi-model approach.