So,
I was thinking about this again and while rounded aggregate is best in terms of total volume, there is a large downside. With rounded media, you're now more at the whims of fracture propagation. With sharp/jagged media, a fracture shouldn't propagate as far since the fracture should run into a perpendicular surface, unlike with round media.
The promise behind EG is that you take the innate strength of a compressed aggregate and ensure that you're locking it into place using epoxy. At this point, the youngs modulus for a structure is now mainly based on the strength of the compacted aggregate. So, at this point... you have the mix of aggregate sizes and shapes to take into account. I believe that regardless of the media used at larger sizes, the extraneous volume can be filled with smaller rounded media to take up gaps. But the larger media is what should be assumed as the strength point.
I also think that a gel coat with reenforcing fibers would make quite a difference in terms of fracture propagation from the surface (perhaps to the point where embedded features could be inlaid closer to edges.
Mark,
Did you have a look at the cost/pricing on the media available from the seller at all? I'm only able to get pricing on shipping to myself, but would be interested in hearing what it's like further afield.
Thanks,
--
Scott