Hi Vitali - Epoxy is expensive everywhere and using less is a usual requirement to reduce cost. Weight ratios are useful for making product but not useful for understanding the engineering of the product. So understanding volume ratios is important. Lets call it solids and void or aggregate and matrix. You are making a composite material of solids and using epoxy to bind it all together. Two aspects to consider 1) achieving high solids volume ratio a) to minimise epoxy usage/cost and b) to maximise material stiffness. Epoxy is not stiff its E=3.5GPa whereas your sand and gravel (aggregate) is about 70GPa stiffness.
Air equals porosity and mixing this sort of aggregate in epoxy its really difficult to not introduce air in the process. Especially if you use a cement mixer!! Plus if you use a laminating epoxy it is designed to be thick and not flow so it holds air really well. It won't "degas" by itself. Its something you have to live with. If you use an infusion epoxy or an epoxy for making river tables these degas well. I use a vacuum process to make this sort of thing so air is not in the mould when infused so very little porosity.
Epoxy is used as it has minimal shrinkage and a long gel time. Other resins can be used if you understand them and can get them. Urethanes and PMMA are possible. Not sure if they are cheaper though. Polyester and vinylester resins shrink too much to use as machine parts. Portland cement shrinks and cracks over time and is therefore unsuitable for machine parts as well.
Engineering - Sand and gravel have a low stiffness to start with and couple that with low volume ratios and low strain transfer ratios you potentially end up with a low modulus material. eg your sand is 70gpa your volume ratio is 65% and your round particles transfer strain at about 50% efficiency so your E=70*0.65*0.5= 23GPa. Aluminium is 70Gpa and steel is 200GPa. I suggest you look for CSA concrete grout. Not Portland cement but CSA grout. Its cheaper and stiffer then epoxy. Here's my cost breakdown on a project at the moment. Its the cheapest material, out of the bag you get 34GPa.... just add water. Look up ultra high performance concrete UHPC many machines are being made with it for 50 years... Below costs are in australian dollars..
https://durcrete.de/
I'll do a search for a commercial mix I found in another thread ... are you in eurpoe? cheers and Keep Making Peter
