We had a long discussion of this at the Trains forum last year.
They seem to be starting to use concrete ties under turnouts, but most are still wood. I think there is a problem making concrete ties in all the different variations needed for a turnout; with wood you just drill a hole in a different place.
I've noted that the Toronto subway uses variations of concrete ties and full concrete base (in tunnels) but goes to wood ties in ballast for turnouts -- even in the tunnel.