Hello Mike - The E80 UHPC material is very attractive but they could not tell me the tensile modulus. The E80 is the compressive modulus. The E80 they are reluctant to sell for machine use and they do not sell in small quantities and do not sell any product outside of the EU. E45 is relatively easy to achieve and my local concrete chemists can help with that. My other aim with developing a cold casting material was that it be machinable so surfaces can be finished accurately. Concrete can be machined with hard tooling and a wet machine. There is a local stonemason here with such a machine that expressed interest in machining my stuff but when it came to actually doing it he baulked due to the accuracy required. Headstones don't have to be very accurate.... Importing granite from china and having them machine it or locals machine it was an attractive route. But I decided against that method. Prefer to make my own moulds and use GF or CF to optimise shapes.
Carbon fibre ticks all the boxes and I use diamond tooling on my router for machining composites dry or wet. I don't think its expensive relative to the project. Make the parts with thick skins 10-15mm thick then back fill with CSA grout (or UHPC) I think is a cost effective approach. The CF I regularly make and test at E80 for yacht masts and industrial springs. So confident in that number (tension comp and flexure). Would make it at E70 to improve its shear stiffness and it would be a good all round material. You will need to get familiar with infusion to go down the CF path. Wet lay up and hand layup will not achieve the consolidation required to get to E50 or better. Peter