See, this is why I’m not a millionaire. Every time I think I have a good idea, I google it and someone else beat me to it.
LOL yeah I know what you mean.
If it helps you to feel worse [snarky comment] the Romans were adding pumice stone to their concrete mix to create a lighter concrete kind of like your hollow balls aggregate.
https://hesspumice.com/pumice-pages/pumice-uses/pumice-concrete.html