I think I understand aggregate. There is no optimal formula that doesn't take into account what is available to use, and some measurements on it I haven't even taken on what I do have. The rule of thumb is that for a density in the high 80% range, 4 orders of magnitude size difference are needed between the biggest and smallest particles. The other observation from the model is that aggregate designs that use equal intrinsic volumes of all the components should tend to work fairly well although they have a greater tendency to segregate under vibration. I'm what you might call an aggregator I can run the model if you have a component list you want to try.
I posted a trial aggregate formulation using several aggregates from Agsco in Chicago but I'd have to search the thread to find it. One question is whether an accurately made version of this formula has bad flow characteristics and can't be molded.
That's a good Question: what to do next.
I'd say that the trouble is in the epoxy right now. Roach suggested Isophorone Diamine as a hardener which seems to work great with the Hexion low viscosity resin I've been working with but is quite brittle at the initial cure. I don't know how long it would take to get a reasonable cure at room temperature but I know that overnight won't do it without an hour at 125C using Hexion 813 resin. I haven't tried the Vestamin IPDA with Reichhold 37-127. I also haven't made a D790 test of this Hexion 813/IPDA formulation due to the first batch deforming during the oven cure to the point I couldn't cut samples. I've solved this in the second batch by using 4 hours at room temp, 4 hours at 70C and 1 hour at 125C but I need to make another batch before I can test it.
bloefeld suggests heated DER331 medium viscosity resin and Huntsman curatives with vacuum infusion which I haven't been able to try yet. I'm worried about having to heat the resin before initial cure as it seems like it might be hard to hold machine tool like tolerances due to the extra shrinkage it might cause. I also need to fix my vacuum pump and small vacuum chamber.
So Chris, if you're used to working with epoxy, dealing with epoxy vendors, and you have a balance, you might try getting some samples and investigating the properties of bloefeld's Dow Epoxy Resin 331 / with Huntsman curatives like T403 and D400.
Another thing that needs to be done is more work with both epoxy and aggregates together. I haven't made any samples with aggregate yet as the work of others convinced me that we started with the wrong epoxy hardener. I have tested 5 samples of each of 4 different formulas with different aggregate sent by jhudler and greybeard. Three of these used the Reichhold 37-127 / 37-606 epoxy which isn't strong or stiff enough while graybeard used some kind of epoxy he got in England. All had flexural strengths around 2ksi and moduli around 200ksi.
Once the epoxy choice settles down, there are tests with epoxy and amine active silane and titanate bonding agents. There also need to be some tests of the performance of hard surfaces made with the Inhance Titanium Carbide particles. bloefeld also suggested Wollastanite spicules as an aggregate which would be very good. Unfortunately, long needle like particles will break the model I have been using to predict density until I add that theory to the model from de Larrard's book.
I provide free ASTM D790 flexural tests to this group for all samples sent to me provided I can saw them to 7 1/2 x 3/8 x 1/2 so if you want to make samples of known components, I'll be glad to test them and post the results.
We all usually work together here so if you would like to contribute: theory, samples, and collaboration are all things that help. I personally also would gladly hand over the job of indexing the thread to somebody else as I haven't managed to work on it lately. (I have written some software to link referenced posts in the index provided that the index entries are kept in my special text format).
Glad to have you aboard Chris and hope you get some sleep. I find that I lie awake wondering about epoxy molecules
For what it's worth....I'm in the Madison Wisconsin area.
I have access to some pretty good sized CNC's as well as a few walk in ovens. I also have 2 vac pumps for composite type stuff as well as an array of bagging materials.
I'm not saying this to come off as bragging, but I would like to help, and I feel that if I use E/G for something and don't contribute, I feel like a thief after everything that has already been done.
-Chris
Edit: While I am very eager and capable of helping, I suffer the same problem as many of you out there; a job to pay the bills, a 2 year old and a 6 month old. As you can see, I have been very efficient with some aspects of my life, but I am finding that sleep is a great thing.
Regards all,
Cameron