Larger steel or synthetic fibers can replace rebar or steel completely in certain situations. Fiber reinforced concrete has all but completely replaced bar in underground construction industry such as tunnel segments where almost all tunnel linings are fiber reinforced in lieu of using rebar. Indeed, some fibers actually reduce the compressive strength of concrete.
The passage discusses how larger steel or synthetic fibers can be used as substitutes for rebar or steel in certain situations. It also highlights that fiber-reinforced concrete has largely replaced traditional rebar in underground construction, particularly for tunnel linings.  Some fibers even decrease the compressive strength of concrete.