After all of the work on this thread, here is the first formula:
<B>Aggregate: Round Grained Silica Sand</B>
<table border=1>
<TR><td>100%</td><td>Passes 1/4 inch sieve</td></tr><tr><td>12%</td><td>Retained #7 Sieve</td></tr><td>35%</td><td>Retained #14 Sieve</td></tr><tr><td>20%</td><td>Retained #18 Sieve</td></tr><tr><td>15%</td><td>Retained #30 Sieve</td></tr><tr><td>12%</td><td>Retained #230 Sieve</td></tr><tr><td>12%</td><td>Passes #230 Sieve</td></tr>
</table>
This aggregate recipe is a translation to sieve numbers of the Reichhold formula for polyester polymer concrete. Based on the sample formulas in Gamski, it ought to work quite well.
<B>Epoxy U.S. Composites #635 (Reichhold Epotuf 37-127 with 37-606 amine hardener) </B>
Mix epoxy thoroughly before addition of regulating charge or aggregate. Use of an epoxy dispenser with static mixer is preferred as it will provide the most uniform results. If an epoxy dispensing system is unavailable, mix thoroughly with electric paint or drywall mud mixer trying to avoid entraining air in the mixture. Be sure to add de-airing agent and if used, directly adding coupling agent while mixing the epoxy before the addition of the aggregate.
After mixing the epoxy, add the regulating charge and then the aggregate and de-air the mixture at 5mm Hg of vacuum (.19 inches Hg). A paint pot with a vacuum pump has been suggested as a possible method but a venturi system is likely to provide insufficient vacuum.
The exact amount of epoxy required is currently unknown but Gamski puts it between 10 and 14% of aggregate without carbon black. Gupta places it at 16% but Gupta's formula had much less fine aggregate. Gamski's formula used with Gupta's 33 micron binder thickness equates to 35% of aggregate weight. Huntsman puts the value at 9% by weight but their formula uses much less fine aggregate and no carbon black. The epoxy required goes up with the amount of fine aggregate and carbon black and an overabundance of epoxy seems to be less detrimental than too little.
In absence of better data it seems like 20% of aggregate weight is a reasonable starting amount.
<B>De-airing Agent BYK-A525 from BYK Chemie</B>
Add de-airing agent equivalent to 0.2% of epoxy weight when epoxy is mixed.
<B>Coupling Agent Dow Corning Z6040 </B>
Adjust the pH of a large container of water with vinegar to approximately 4 using ph test paper available from
http://scientificsonline.com/product.asp?pn=3021313.
Add 0.5% Z6040 to the volume of water which is about 0.5-.6 oz by volume per gallon and stir for 15 minutes. Treat the aggregate to be used by soaking it in the treated water and stirring for 5 minutes. Dry the treated aggregate under heat lamps until it appears bone dry and does not smell like methyl alcohol.
Alternately, add Z6040 equal to 1% of the weight to the epoxy directly to the mixed epoxy.
<B>Regulating Charge/ Dispersion Hardener Cabot Monarch 120 Carbon Black</B>
Add carbon black in an amount equal to 1.5 times the weight of the epoxy. This recommendation is from a russian paper cited by Gamski however it is not clear if it is by weight or volume but it seems like way too much.
<B>Molding</B>
Pour the vacuum de-aired resin into the mold taking care to entrap as few air bubbles as possible. After the epoxy has been added, cure the mold under heat lamps to avoid creep at higher temperatures.
<B>Notes</B>
I have not tried this formulation. It is my best attempt at a good simple formulation based on my research on the matter. The precise carbon black and epoxy fractions will need to be adjusted by experimentation. Use this formula at your own risk.