Some Notes on Granular Mixtures with Finite, Discrete Fractal Distribution

Why fractal distribution is so frequent? It is true that fractal dimension is always less than 3? Why fractal dimension of 2.5 to 2.9 seems to be steady-state or stable? Why the fractal distributions are the limit distributions of the degradation path? Is there an ultimate distribution? It is shown that the finite fractal grain size distributions occurring in the nature are identical to the optimal grading curves of the grading entropy theory and, the fractal dimension n varies between –¥ and ¥. It is shown that the fractal dimensions 2.2–2.9 may be situated in the transitional stability zone, verifying the internal stability criterion of the grading entropy theory. Micro computed tomography (μCT) images and DEM (distinct element method) studies are presented to show the link between stable microstructure and internal stability. On the other hand, it is shown that the optimal grading curves are mean position grading curves that can be used to represent all possible grading curves.

СRUSHED STONE MATERIALS AND GRAVEL MATERIALS BOUND BY MINERAL BINDERS. STANDARDIZATION

Introduction. This paper presents the results of the standardization of requirements for granular mixtures bound by mineral binders for bases, sub-bases and top layers of road pavements used as framework for national standard «Crushed stone materials and gravel materials for the road building industry — Specifications. Part 3: The materials bound by mineral binders». Standardization. The standard covers the requirements for crushed stone-sand and sand-gravel mixtures treated with mineral binders and derived from them hardened materials as well as the requirements for source constituents. Mineral binder for the standardized type of road materials shall be selected from following main constituents: cement, slag or fly ash each separately or combinations thereof using an activator if required. Standard mixtures shall be produced in a factory or mixed in situ on the road surface. Clauses of the standard also comprise the requirements for mixtures and related hardened materials from active slag or ash-slag materials which can act as the main constituent of the mixture (aggregate) and part of the binder. Standardized mandatory characteristics include mixtures physical properties comprising grading envelopes, and mechanical properties; the obligatory sections of the standard include requirements on quality control, transporting and marking of mixtures. Conclusions. Conclusions outline main results of standardization in view of the ongoing works on processing the related European Norms as national normative documents. It is emphasized that the developed standard supplements the fundamental requirements of adapted European normative documents regarding the composition and properties of said mixtures, particularly the requirements on frost resistance. The subsequent work shall be aimed at the adaptation of national regulations on road pavement design and construction to implement the newly standardized requirements for hydraulically bound mixtures.

Axial Segregation of Polydisperse Granular Mixtures in Rotating Drum Flows

Axial segregation of polydisperse granular mixtures in rotating drums have been observed in several experimental and discrete particle simulation studies reported in the literature. A common thread to both experimental and numerical studies is the formation of (alternating) bands which eventually coarsen in the long-time limit due to logarithmic merging. Models to explain the experimental observations are generally limited to bidisperse mixtures, and often unable to reproduce band coarsening. One such mechanism for bidisperse mixtures argues that the grains eventually diffuse into axial bands as a consequence of concentration fluctuations in the free surface layer caused by friction-limited mobility. We generalise this model to multi-species mixtures and show that the solution produces banding that evolves more complexly than binary mixtures, with sinusoidal-like variations of the band structure that evolves non-linearly in time. In addition, we successfully recover band coarsening with time—an observation that is generally difficult to reproduce, even experimentally. Contrary to literature findings, the configurations herein did not produce bands within bands for ternary and quaternary mixtures.