I've been to LZ-1 and I can assure you center circle is poured concrete. Moreover it has dilatation gaps sealed with some kind of elastomer.
Note from the picture above that we are not the only people who have debated or been confused by the "Landing Complex" / "Landing Zone" naming debate. Notice the label on the surveyor's benchmark: LC-1. Dated 2015, so things changed afterward, probably to avoid confusion with "Launch Complex".