CLR can safely be used to clean concrete as long as the concrete is not tinted, colored or has not been poured freshly a year or less ago.
As long as the concrete is older than 1 year old and the concrete is not a tinted or colored concrete then you can safely use the CLR on the concrete.
I use CLR to clean rust and other stuff off of my concrete patio and driveway and the CLR works great for cleaning the concrete patio and concrete driveway.
It has never damaged the concrete and I've been using CLR on my concrete patio and concrete driveway for 10 years now.
The CLR works great for cleaning concrete, toilets, shower heads etc.
It's some great stuff when used properly.