A formwork assembly is adapted to receive concrete to produce structures such as wall structures. The formwork includes PVC tubular form elements having recessed female engagement portions. The female engagement portions are adapted to receive respective male engagement portions. An octagonal form element has a female engagement portion positioned at each vertex between adjacent sides. A recessed female engagement portion is closed to the interior of the form element but open to the exterior of the form element. Thus, the form element includes a plurality of vertices open to the exterior. The form elements also include male engagement portions at an open side. Wall panels, corner panels, and joint connectors can also include male engagement portions. The male engagement portions and female engagement portions are adapted to mate to form a formwork arrangement having a substantially flat exterior wall. A formwork assembly can additionally include concrete flow apertures and insulation.