Particle size distribution The particle size distribution is the relative frequency
of particles of a given size. The distribution can be gaussian, bimodal
or something else. Theoretically, some special distributions are beneficial for
the packing density. An example is the 49:7:1 rule that states that the smaller
particles fill the voids between larger particles [99, 139]. Often, this particle
size distribution is characterised by separate factors [99], of which some are
described below.