This question was originally posed on the Aggregate Research Industries (ARI) Industry Forum, www.aggregateresearch.com/forum. As the forum respondents indicated, specific surface area can be described as a function of particle geometry, quantity, gradation/sizes, and specific gravity.
One respondent presented a simple approach to the calculation. His method is to assume that the shape characteristics of the aggregate particles are identical to those of spheres. Then it follows that each sieve size that the aggregate passed through represents the diameter of the spheres.
First divide the amount retained on each sieve by the number of particles per pound. Then multiply by the surface area of each sieve respectively.
Do not forget to convert to proper units. Once you quantify spherical surface area, you may classify aggregates of different shape and texture by multiplying a coefficient by the spherical surface area.
The coefficient will represent the degree of inefficiency (relative to spherical-specific surface) that the shape of the particle holds. This still may not be precise, but it will allow us to differentiate between particles of obviously different specific surfaces (e.g., a smooth, rounded particle will have a lower coefficient than that of a rough-textured angular particle).
It seems that there was a great deal of research conducted on this topic in the 1960s. There have been many articles on this subject published in ASTM journals.