Hovis builds a garden office*

GFRC = glass fibre reinforced concrete?
The ridges in rebar prevent the drying/curing concrete shrinking as much as it would like,
putting the concrete in compression, where it is much stronger than in tension.

I seem to remember reading about concrete being reinforced with materials other than steel in structures where light(er) weight was required, bridge sections.

For a concrete slab rebar and mesh is so cheap it is hard to argue against,
as long as you have adequate cover, the frameworks is sturdy enough,
and the wet/liquid concrete is vibrated enough to avoid voids.