The disclosure presents a composite conduit formwork structure which includes a cylindrical outer casing adapted to bond with a cylindrical inner casing which are maintained at a fixed distance apart by a plurality of radial stanchions. The inner casing and outer casing form an interior void which is filled with concrete during manufacture. The outer casing and inner casing remain in place to protect the structure once completed. A novel method of assembly is also provided whereby radial stanchions are rotated between the outer casing and inner casing. All of the components in a preferred embodiment are formed of a fiberglass material.