External boundaries, i.e. the walls of containers, and internal boundaries, for example, reinforcement bars, exert an influence on the packing and hence porosity of granular particles. Many attempts, both theoretically and practically based, have been made to establish correction factors for this influence so that the porosity of a material in one container could be predicted from its known porosity in a different container. The limitations of such approaches are discussed and the general conclusion reached that although these methods may be of use for containers and particles of certain shape and for circumstances where the particle size does not approach the size of the container, they are not universally applicable to containers and particles of all shapes or to cases where the aggregate size approaches the size of the container.
The consequent conclusion is made that where it is desired to know the porosity in a given container, for example where such knowledge is a pre-requisite for design of an aggregate grading, there may be no alternative to making the porosity determination in a container of the size and shape in which it is intended the aggregate should ultimately be placed.