What type are you supposed to use to represent total cost when spending infinite money for 0 days?

In Javascript? probably a different type than if you took 0 days to spend infinite money.

It seems the Romans took their concrete type secrets to the grave.

https://www.archdaily.com/875212/scientists-uncover-the-chem... :)

Modern concrete with superplasticizers is far superior to Roman concrete.

The greatest limiting factor is not the concrete itself, but rebar. It will eventually rust, causing the concrete to spall and crack. So in most cases it makes no sense to really optimize the concrete lifetime, because why bother?

If you're willing to build structures that rely only on compression and gravity, then we can totally do stuff that the Romans never dreamt of. Just look at any modern concrete gravity dam as an example.

You need refinement types. Psuedocode:

    timespandays : int, timespandays > 0

your program can then be proven by the compiler not to NaN.