4.3.1 Wall-effects
A cylindrical container was applied to determine the packing density. Its size affects the
packing density, which is due to the varying percentage of the volume perturbed by the
walls compared with the unperturbed volume. The porosity of the granular skeleton of
the bulk is lower compared with that of the disturbed area. Ben-Aïm [1970] limited the
effect of a wall on the packing density of aggregates to a distance of half the diameter of
a grain. The packing density of the disturbed area close to the walls decreases with a
factor kW. He proposed 0.88 for round and 0.73 for crushed aggregates respectively.
Equation 4.7 describes the effect of a wall on the mean (actual) packing density: