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Granulation, Mixing, and Packing of Particles
Published in Mohamed N. Rahaman, Ceramic Processing, 2017
Two continuous particle size distributions can be mixed to improve the packing density. Generally, the mean particle size of the two distributions should be very different and the particle size distribution of the smaller powder should be wider than that of the larger powder. On the other hand, for a wide particle size distribution where the packing density is already high, little benefit is achieved by mixing with another distribution.
Properties and characterization of aggregates
Published in Mark Alexander, Sidney Mindess, Aggregates in Concrete, 2005
Mark Alexander, Sidney Mindess
Notwithstanding these comments, modern high performance and ultra high performance concretes such as Self-Compacting Concrete, Very High Strength Concrete (>100 MPa), and Reactive Powder Concrete require very careful control of overall grading including aggregate and binder components to achieve optimum particle packing. Packing theories and models are used in designing these mixtures, and indeed proportioning such mixtures to achieve their high performance characteristics cannot be done without regard to overall grading. Most idealized packing models consider only geometrical parameters of the particle systems, such as particle size and possibly particle shape, and may only consider spherical, mono-sized particles. In reality, many factors influence packing density, including size, shape, surface texture, particle size distribution (PSD), the method of compaction, and the wall effect. The wall effect is of major importance when considering the packing of small particles on the surface of larger particles: the porosity at the surface of the larger particles is higher than in the bulk section, extending out from the surface to a range of up to five diameters of the smaller particles. (This is one of the important causes of the ITZ in concrete.)
Development of Precision Additive Manufacturing Processes
Published in Richard Leach, Simone Carmignato, Precision Metal Additive Manufacturing, 2020
Ahmed Elkaseer, Amal Charles, Steffen G. Scholz
Powder-related process parameters affect the morphology and the quality of the powder. They are described below. Particle size and distribution – the standard powder size distribution, as used in the L-PBF process, is between 15 µm and 45 µm (Sinico et al. 2018). The particle size and the size distribution significantly affect the packing density. Smaller particles provide larger surface area for absorption of energy from the laser; however, they can also cause larger gap formation in the powder bed, creating porosity in the final part. Smaller particles also increase agglomeration and reduce flowability (Sun et al. 2017).Powder bed density – high packing densities are generally preferred as they lower internal stresses and porosity and improve the surface texture. Spherical particle morphology greatly improves the flowability of powder, thereby improving the packing density (Sun et al. 2017). The powder bed packing density also affects the thermal conductivity of parts, as a higher density increases the number of contact points between powder particles and thereby improves the thermal conductivity of the powder bed.Layer thickness t – the distance between each successive layer in the PBF process; see Figure 3.4. In practice, a 30 µm layer thickness is commonly used for fine prints with higher strength, while a 60 µm–90 µm layer thickness is used for faster but coarser prints (Sufiiarov et al. 2017).
Optimization of ultra-high performance concrete, quantification of characteristic features
Published in Cogent Engineering, 2019
Yang Chen, Faris Matalkah, Parviz Soroushian, Rankothge Weerasiri, Anagi Balachandra
Given a unit volume filled with particles, packing density is defined as the volume of solids in a unit volume; it is equal to one minus the volume occupied by voids. Packing density provides an indication of how efficiently particles fill a certain volume. If a high volume of aggregates is packed in a given volume, the need for binder, which is particularly costly in the case of UHPC, to fill the voids and bind the particles will be decreased (de Larrard & Sedran, 1994, Elrahman & Hillemeier, 2014, Lange, Mörtel, & Rudert, 1997). UHPC achieves high-performance characteristics partly because it has a relatively low porosity. Increasing the packing density of the granular raw materials (aggregates, cementitious materials, etc.) is one step towards lowering the porosity of the hardened material.
Comparison of the experimental packing density values and values predicted by packing density models for electric arc furnace slag aggregates
Published in Particulate Science and Technology, 2021
Davatee Maharaj, Abrahams Mwasha
Particle packing describes the extent to which a unit volume is filled up with aggregate particles (Fennis, Walhaven, and Uijl 2013, 5). This degree of particle packing is measured in terms of packing density. Packing density describes the ratio of the solid volume of the particles to the bulk volume occupied by the particles (Raj, Patil, and Bhattacharjee 2014, 35). The packing of the aggregates is an essential factor to consider because it affects the mean particle size and the surface area of the aggregate particles. The particle size and surface area affect the quantity of cement paste needed such that a large surface area requires less cement paste and increases the density of the concrete.
A new framework for understanding aggregate structure in asphalt mixtures
Published in International Journal of Pavement Engineering, 2021
M. Reza Pouranian, John E. Haddock
Particle packing is a process whereby a system of interconnected particles is put into contact. One of the most important indices to describe the state of particle packing is packing density, defined as the fraction of the total volume the packed aggregates fill. The mass fraction of fine particles at three main thresholds was calculated using the proposed analytical model; the results of the simulation are given in Table 2.