Frictionless plain bearing for post-tensioned slab on ground A new method for building large concrete slabs on ground on a frictionless support was developed at Vienna University of Technology. An Austrian patent for this method was granted and an international patent application has been filed. The feasibility of this new method has been demonstrated in large field tests on concrete slab strips with a length of 60 m, a width of 1.0 m and a thickness of 30 cm. The frictionless support is obtained by first placing an air-tight membrane, then a geotextile and at last a second air-tight membrane on the ground where the concrete slab is to be built. In the next step the membranes are sealed at the boundary. After casting the slab on top of the second membrane, low air pressure is applied in the clearance between the two membranes. This clearance is created by the geotextile. Shortening of the slab due to the loss of hydration heat, early shrinkage and post-tensioning is possible without causing friction forces between slab and subsoil because the self-weight of the slab is balanced by the applied air pressure.