Packing Of Granular Materials Research Articles

Efecto de empaquetamiento de las partículas en la durabilidad de los hormigones de alto desempeño

Due to the high aggressiveness in which the concrete structures are exposed, many researches have been developed in this area and search for materials with superior mechanical performance and durability has been the target of the researchers of concrete technology. Therefore, concrete obtained from the microstructure engineering are needed. Being composites made of fine grain particles and a low water/binder ratio, these materials have dense matrix by optimizing the packing of granular materials. Thus, this paper uses the concept of particles packing in the design of special concretes, analyzing the durability of these materials by determining the water absorption by immersion and by capillary, and chloride ion penetration. The properties of concrete designed based on this concept are compared to high performance concrete designed from conventional methodology, indicating superior properties in terms of durability.

The Effects of Swelling and Porosity Change on Capillarity: DEM Coupled with a Pore-Unit Assembly Method.

In this study, a grain-scale modelling technique has been developed to generate the capillary pressure–saturation curves for swelling granular materials. This model employs only basic granular properties such as particles size distribution, porosity, and the amount of absorbed water for swelling materials. Using this model, both drainage and imbibition curves are directly obtained by pore-scale simulations of fluid invasion. This allows us to produce capillary pressure–saturation curves for a large number of different packings of granular materials with varying porosity and/or amount of absorbed water. The algorithm is based on combining the Discrete Element Method for generating different particle packings with a pore-unit assembly approach. The pore space is extracted using a regular triangulation, with the centres of four neighbouring particles forming a tetrahedron. The pore space within each tetrahedron is referred to as a pore unit. Thus, the pore space of a particle packing is represented by an assembly of pore units for which we construct drainage and imbibition capillary pressure–saturation curves. A case study on Hostun sand is conducted to test the model against experimental data from literature and to investigate the required minimum number of particles to have a Representative Elementary Volume. Then, the capillary pressure–saturation curves are constructed for Absorbent Gelling Material particles, for different combinations of porosity values and amounts of absorbed water. Each combination yields a different configuration of pore units, and thus distinctly different capillary pressure–saturation curves. All these curves are shown to collapse into one curve for drainage and one curve for imbibition when we normalize capillary pressure and saturation values. We have developed a formula for the Van Genuchten parameter alpha (which is related to the inverse of the entry pressure) as a function of porosity and the amount of absorbed water.

High-Precision MRI Reconstruction Algorithm for 3D Sphere Packings

Packings of granular materials are complex systems consisting of large sets of particles interacting via contact forces. Their internal structure is interesting for several theoretical and practical reasons, especially when the model system consists in a large amount (up to 105) of identical spheres. We herein present a method to process three-dimensional water density maps recorded in wet granular packings of mm-size spheres by magnetic resonance imaging (MRI). Packings of spheres with highly mono-dispersed diameter are considered and the implementation of an ad hoc reconstruction algorithm tailored for this feature allows for the determination of the position of each single sphere with an unprecedented precision (with respect to the scale of the system) while ensuring that all spheres are identified and no non-existing sphere is introduced in the reconstructed packing. The reconstruction of a 0.5 L sample containing about 2 × 104 spheres is presented to demonstrate the robustness of the method.

Numerical Simulation on Dense Packing of Granular Materials by Container Oscillation

The packing of granular materials is a basic and important problem in geomechanics. An approach, which generates dense packing of spheres confined in cylindrical and cuboidal containers in three steps, is introduced in this work. A loose packing structure is first generated by means of a reference lattice method. Then a dense packing structure is obtained in a container by simulating dropping of particles under gravitational forces. Furthermore, a scheme that makes the bottom boundary fluctuate up and down was applied to obtain more denser packing. The discrete element method (DEM) was employed to simulate the interactions between particle-particle and particle-boundary during the particles' motions. Finally, two cases were presented to indicate the validity of the method proposed in this work.

FREQUENCY DISTRIBUTION OF CONTACT ANGLES IN RANDOM PACKINGS OF GRANULAR MATERIALS

ABSTRACT For a certain spectrum of stable grain configurations in randomly packed granular aggregates it is possible to determine the frequency distribution of relative contact angles among neighboring grains. This possibility is explored in the present paper for both two-dimensional and three-dimensional random packings of granular materials. Two relationships are first derived for the local void ratios of any stable “Voronoi Cell“ within the spectrum of stable configurations for the two and the three dimensional random packings, respectively. These relationships depend on the local distribution of relative contact angles, i.e., directions of contact normals. These local void ratios are then related to the gross void ratios of the random 2-D and 3-D assemblies through two integral equations of the Fredholm type of the first kind, their arguments being the frequency distribution functions. The first integral equation corresponding to a two-dimensional random disk packing is solved, exactly by a set of exp...