Not sure what CLR is, but is it oxalic acid? That's what Rust Out is.

What is the best way to clean these marks off? Looking at Google for
concrete cleaning I see muriatic (hydrochloric) acid or phosphoric acid.
These tend to be nasty to work with. Is there something else that will
work?
The stains look like rust, but C-L-R doesn't seem to touch it. I tried
some
full strength. It might have worked a little.

I am not sure it is rust. I don't know what has been put in the concrete.
The driveway does not show rust marks where it is exposed to the weather.


Charlie