Caltrans has been rebuilding Interstate 80 over the Sierras for more that a decade now. The technique they are using is a rebar cage at either end of a slab section with dowel pins between. Seem to be pretty durable. That said I haven’t seen any sign of steel in the main spillway at Oroville Dam. Good news is that no steel will make the demolition of the spillway faster when they start.
Slabs that are exposed to weather including freezing temperatures are going to suffer the freeze/thaw cycle damage that concrete has always had to suffer with for its longevity.
There are things that make it more durable to these forces but not immune.
Maintenance and occasional replacement are what is required. Many spillways aren’t constructed with a run-out feature at all but instead project the water onto rock below.