Up here the ties are mainly wood as concrete ties crack with the hot/cold cycle.
When water gets in the cracks and freezes it blows the ties apart.
They are still used in many places I've travelled but wood is predominant.
Switches and bridges are wood ties, I'm told this is because you get more adjustment with wood ties.
The concrete ties have been used overseas for some time, can't say just when they showed up here.
I have some track with concrete ties and am planning to model the rebar showing on the ends:
My wife always says I don't pay attention, or something like that.