Here are my tests for making various epoxy granite mixes. All of my measurements are
BY WEIGHT. I tested the following formulations:
1 - Silica Sand 80um size (US mesh 170 - 200) + Epoxy in various amounts
2 - Aluminium Oxide aka Alumina aka Al203, 75um size (US mesh 170 - 200) + Epoxy in various amounts
3 - Silican Sand 50% by weight mixed with quartz (silica) pebbles from 1mm - 3mm size 50% by weight. This is the type of quartz / silica gravel you get for your aquarium
4 - Aggregate (epoxy granite aggregate) + Epoxy in various amounts
For the aggregate, I used from 40% - 50% by weight a gravel aggregate I bought from a local granite / marble counter top distributor. They call it granite gravel, but it also has bits of marble and other stone in it. It ranges in sizes from maybe 6mm up to 20mm. They are all jagged pieces, not round.
For 25% - 30%, I used the quarts gravel from the aquarium (1mm - 3mm) and for 25% - 30% I used the silica sand of 80um size. Once thoroughly mixed, I added Epoxy.
For my epoxy, I used an off the shelf epoxy for garage or industrial flooring. It is a 2 part epoxy (ISOMAT Durofloor PSF) in a ratio almost 2:1. It is actually 100:55 or 1.82:1 resin to hardener. This was mixed for 3 minutes and then mixed in to the sands or aggregates. I then kind of vibrated the mass, but not much, in order to try and eliminate some bubbles. They were cut out of the plastic cups after 24 hrs.
The pieces that were cut in half were cut using a diamond grinder blade used for masonry.
I find that the ideal mix of epoxy to aggregate is somewhere from 12.5% - 15% epoxy and 85% - 87.5% aggregate. Most of the literature on the subject seems to favour a maximum of 15% epoxy. After that, it is too much resin wasted.