They can have the steel from the atomic tests in the pacific. It glows in the dark!
If it's concrete it doesn't glow...:^)
One of the Bikini Atoll atomic test ship is now a breakwater in Powell River, BC. - SS Quartz has a concrete hull.
https://powellriver.info/Tourism-Powell-River/images/brochures/The_Hulks_Brochure.pdf