Abstract: Described in a displacement body for forming cavities in concrete structures. The displacement body lends itself to simple and cost-effective production, is extremely light-weight and still capable of meeting stability requirements. In a preferred embodiment the displacement body consists of a grid structure (1) formed of intersecting longitudinal and transverse rods, and plastic sheets (2a, 2b) applied to both sides of the grid structure and connected to one another and to the grid structure by welding and/or heat-shrinking. Further described are structures formed under employ of such displacement bodies, as well as advantageous methods for making same.

Abstract: Described is a universally usable and durable cover structure formed of a framing and a flexible plastic sheet. The framing consists of a metal grid structure onto which the flexible plastic sheet is shrunk or welded. In a preferred embodiment shown in FIG. 3, a thinner and closer-meshed mesh structure overlays the grid structure 1. This embodiment employs an upper and a lower plastic sheet 2a and 2b, respectively, connected to one another in such a manner that the grid structure and mesh structure are sealingly enclosed therebetween. Further described are preferred uses of the cover structure as for the construction of water retention structures.