Der Senat der Deutschen Forschungsgemeinschaft (DFG) hat im Frühjahr 2010 die Einrichtung des Schwerpunktprogramms (SPP) 1542 „Leicht Bauen mit Beton – Grundlagen für das Bauen der Zukunft mit bionischen und mathematischen Entwurfsprinzipien“ beschlossen. Das Schwerpunktprogramm wurde initiiert, um dem konstruktiven Betonbau neue Impulse zu geben. Es sollten theoretische und konstruktive Grundlagen entwickelt werden um bei allen Bauwerken „Leicht Bauen mit Beton“ betreiben zu können. Die Koordination des an elf technischen Universitäten durchgeführten SPP wurde Prof. Dr.-Ing. Manfred Curbach vom Institut für Massivbau der TU Dresden übertragen. Im Sommer 2011 startete das Schwerpunktprogram – insgesamt wurden 16 Einzel- und Gemeinschaftsanträge von verschiedenen Antragstellern (Bauingenieure, Architekten, Maschinenbauer, Mathematiker) bewilligt. Beim Schlusskolloquium des Schwerpunktprogramms im September 2018 trafen sich die Antragsteller und Projektbearbeiter an der TU Dresden, um ihre gewonnenen Forschungserkenntnisse vorzustellen. Unter ihnen war der Autor dieses Beitrags, der nachfolgend über die Entwicklung einer neuartigen Hohlraumdeckenkonstruktion unter Berücksichtigung ökologischer und ökonomischer Aspekte berichtet.
Production of filigree cavity ceiling panels with displacement bodies made of recycled paper
The author of the article has developed a novel cavity ceiling construction, taking ecological and economic aspects into account. The goal of this new design is to minimize weight while maintaining the required load capacity. The crosswise arrangement of cavities in areas of low component stress results in a very light-weight supporting structure. The cavity construction is characterized by linear channels in both axial directions orthogonal to each other. The ceiling plate thus consists only of an upper and a lower shell, which are selectively connected to each other via the remaining punch (45 mm x45 mm). From an ecological point of view, the proportion of cement clinker should be minimized and substituted by alternative materials. The mixture should contain only natural aggregates and a minimum amount of chemicals to improve the fresh concrete properties. As it is a mass component it is necessary to offer a fair market price, so only a so-called "normal concrete" comes into question. The maximum grain diameter of aggregates was set at 16 mm. Steel fibres were added at 25 kg/m³ and PP fibres at 0.5 kg/m³ to achieve the desired ductility and for fire protection. The displacement bodies made of recycled paper each consist of two half-shells; these are joined in the precast plant or on the construction site by a simple plug connection. The transport volume of the stacked half-shells was minimized in favour of the carbon footprint. The concrete mixture has sufficient green strength after about 1 hour and by then the cardboard has already lost its function of supporting the cavities. In order to ensure good processability of the concrete mixture, a slump of approx. 60 cm must be aimed at because of the filigree geometry. The circular design of the cavity structure also ensures an optimal power flow without occurring notch stresses. The combination of a pre-compressor installed in the inlet hose and a bottle vibrator immersed exclusively on the surface to a depth of 5 cm resulted in the desired compaction or concrete quality. The very large fibre surface area of the plastic fibres of 225 m²/kg had a strong impact on the fresh concrete viscosity. The use of PP fibres should be avoided in future to improve the workability of the concrete.