I've been working on a sculpture made out of .080 aluminum and I need to weigh down the base somehow so it is stable.

It is crescent shaped cylinder so space is a little difficult. If there was something I could pour in that would be great. I thought about buying some workout weights and suspending them within the shape with string and then filling the void with an expandable two part form to act as an insulator to prevent the cast iron from touching the aluminum.

I'd love to just pour in some concrete but I've been reading bad things about AL and concrete. Sand has been suggested but would it hold moisture? The sculpture is going to be indoors.

What would I be able to use without having to worry about corrosion or problems down the road?

Thanks!