I can’t see the Rebar as a solid in a 3D View, why is that?
As default Rebar elements in a 3D model are obscured by the wall, beam, column, etc it’s hosted in. You can override this selecting all the rebar elements.
To do this you may need to select the host element by using a crossing window if you can’t see the rebar, then filter out all the other elements other than the rebar.
On the Properties Palette > Graphics > View Visibility States – Click Edit.
In the Rebar Element View Visibility States dialog box you can select which views you wish for the rebar to Unobscured and view as a Solid. Then press OK and you should now be able to see the Rebar.