Marinaressa Coral Tree

Lightweight concrete construction at the Architecture Biennale in Venice 

The Marinaressa Coral Tree is a filigree concrete structure that shows how innovations in planning, material technology and production can contribute to the sustainable transformation of the construction industry. The structure was designed and built for the "Time Space Existence" exhibition organised by the European Cultural Centre as part of the 18th Architecture Biennale (2023) in Venice. The prototype was created as part of a research project investigating sustainable production of lightweight concrete structures using zero-waste sand formworks. The technology used here was jointly developed and tested by the Institute of Lightweight Structures and Conceptual Design (ILEK) and the Institute for Control Engineering of Machine Tools and Manufacturing Units (ISW) at the University of Stuttgart.

Lightweight concrete construction without waste

The premise of the project was to promote the sustainable development of concrete construction towards CO₂ neutrality. To this end, concrete design and production scenarios for the concrete structures of the future were investigated. The application of lightweight construction principles can significantly reduce material consumption and emissions, also in concrete construction. However, the complex geometries associated with lightweight structures, such as doubly-curved surfaces, can only be produced with a great deal of labour and massive amounts of waste. From a holistic perspective, a "lightweight" solution not only requires a drastic reduction in the amount of material used, but also the minimisation of emissions and waste in all phases of the structure's life cycle, from production to dismantling and recycling. The investigation of corresponding interactions between innovative design and new production methods for the design and realisation of even lighter constructions are therefore important focal points of this research.

At the centre of the project is the development of a production technology for the zero-waste manufacturing of complex-shaped concrete structures using recyclable sand formwork. This is made possible by a combination of additive manufacturing (3D printing in a powder bed) and a specially developed mixture of sand and an organic water-soluble binder. A 3D printing system with a powder bed volume of 70 cm x 100 cm x 40 cm was developed especially for the project, which enables the production of formwork bodies. The binder, supplied in powder form, is activated by the precise application of tiny drops of water from an adapted inkjet print head, which selectively "binds" the sand. Subsequent drying with infrared emitters solidifies the mixture so that the moulds can withstand the hydrostatic pressure during concrete casting. As the solidification process is based purely on physical processes, i.e. without chemical reactions, the moulds are reversibly stable and easily soluble in water, which enables the casting and demolding of spatially complex structures and ensures the complete reuse of the sand for subsequent production cycles.

Architectural demonstrator

To prove the potential of this technology in the production of lightweight concrete structures, especially precast concrete components, an architectural demonstrator was designed and realised, which was manufactured on the campus of the University of Stuttgart and erected in the Marinaressa Gardens in Venice in May 2023. The filigree construction is a reinterpretation of the traditional transition from ceiling to column, in which the loads are transferred from the horizontal plate to the columns via the capital. With a height of 3.2 metres and an area of 2.7 x 2.7 metres, the structure was designed as a modular system consisting of a total of 9 segments that are connected to each other by steel implants. The structural optimisation, taking into account production parameters, made it possible to reduce material consumption by 60% while maintaining the same load-bearing capacity. This was achieved by distributing the material according to the stresses that occur under the specified loads. This resulted in the spatial lattice structure, which is orientated to the three main stress trajectories in space.

All concrete modules were produced using water-soluble moulds, which were additionally subdivided to match the dimensions of the powder bed. First, the formwork segments for the upper slab modules were 3D-printed, assembled and sealed. Carbon fibre reinforcement was then inserted before the concrete was poured. The reinforcement followed the tensile stress trajectories in the upper area. To ensure the quality of the casting for such complex structures, the self-compacting, high-strength casting mortar SikaGrout®-551 with a grain size of 1 mm was used. After curing, the modules were transported to a washing station and demolded by hosing them down with water. The resulting sand mixture was then separated from the residual water and dried. It was then crushed so that it could be reused in subsequent production cycles, including for the formwork of the capital and column modules.

In view of the environmental impact of the construction industry, holistic lightweight construction approach that leads to a minimisation of resources, emissions and waste is of the utmost importance for sustainable concrete construction. However, in order to correctly assess the ecological footprint of a building, the grey emissions saved through lightweight construction should always be compared with those that occur in the other phases of the life cycle. Production plays a significant role in this. A further potential for footprint reduction is seen in the increased CO₂ sequestration potential of lightweight concrete structures due to their geometric properties. While the volume of the structure is reduced, the surface-to-volume ratio increases by a factor of 5 or more. In combination with the filigree cross-sections of the individual struts, this could lead to a complete carbonation of the structure over time. In order to fully prove this statement, several series of tests are currently being carried out by the institutions involved.

PROJECT PARTNERS
Institute for Lightweight Structures and Conceptual Design (ILEK), University of Stuttgart, Prof. Dr.-Ing. Lucio Blandini
Institute for Control Engineering of Machine Tools and Manufacturing Units (ISW), University of Stuttgart, Prof. Dr.-Ing. Alexander Verl

SCIENTIFIC DEVELOPMENT
Daria Kovaleva, Maximilian Nistler

SUPPORT WITH THE IMPLEMENTATION
Lennon Toeche-Mittler, Justus Schwörer, Ali Moradi and Materials Testing Institute at the University of Stuttgart

STRUCTURAL ANALYSES
Oliver Gericke and Ivan Tomovic, Werner Sobek AG, Stuttgart

SPONSORS
The project was supported by Sika Deutschland GmbH, Fachverband Beton- und Fertigteilwerke Baden-Württemberg e.V., InformationsZentrum Beton GmbH, Industrieverband Steine und Erden Baden-Württemberg e.V., Bauwirtschaft Baden-Württemberg e.V., Solid UNIT Baden-Württemberg.

FUNDING
Research into the development of zero-waste sand moulds for lightweight concrete components was funded by the German Research Foundation (DFG) as part of the SPP 2187: Adaptive modularised constructions made in flux (project number 423987937).