TMW Graded Slabs

Functionally Graded Concrete at the Vienna Museum of Science and Technology

TMW Graded Slabs is part of the newly opened permanent exhibition “Material Worlds” at the Vienna Museum of Scoence and Technology. The exhibit was designed and realized in collaboration with Werner Sobek to demonstrate the potential of two technologies developed at ILEK for lightweight and sustainable construction with concrete: mesogradation and zero-waste sand formworks. The exhibit represents a 5.0 x 2.5 m² cut-out of a 7.2 x 7.2 m² spanning and 0.25 m thick point-supported slab. In the depicted area around the support, the principal stresses, which invert their trajectories in the zero-moment zone, can be clearly visualized. The structure was optimized according to the load-bearing behavior of a flat slab under a distributed vertical load of 5 kN/m². The exhibit consists of two parts: a Mesograded Slab on the left and a Coral Slab fabricated using sand formwork on the right.

Coral Slab

The right side of the exhibit illustrates the use of sand formwork to optimize the distribution of material within the slab. Coral Slab consists of a three-dimensional lattice aligned along the three principal stress directions and reinforced with basalt rods measuring 3 to 5 mm in diameter.

The panel was manufactured using recyclable sand formwork technology developed at ILEK. Thanks to the combination of 3D printing and a special mixture of sand and water-soluble binder, the formwork offers design freedom for geometrically complex structures while eliminating production waste. The internal formwork structure was segmented into 16 individual element, 3D-printed with a resolution of 1.5 mm and assembled prior to casting. 

Before the concrete was poured, the lower reinforcement was first installed, then the formwork segments were placed in positions using a crane; finally, the upper reinforcement and the fasteners for the suspension points were fitted. The slab, with a total weight of 1,700 kg, was cast in a single operation using self-compacting pumped concrete. After 48 hours, the slab was demoulded with water hose and all the formwork material was recycled.

Mesograded Slab

The left-hand section of the exhibit demonstrates the potential of mesograding using hollow mineral spheres with a diameter of 15 cm. The technology involves placing hollow mineral bodies formed from a mortar suspension into areas of low stress in order to reduce the weight of the structure without compromising its load-bearing capacity.

The position and geometry of these mineral hollow bodies were defined using a specially developed calculation method. Based on the structural analysis of a comparable solid reinforced concrete slab, the acting shear force is determined and, in an iterative process, hollow bodies with the largest possible diameter are positioned. Subsequently, the size of the mineral hollow spheres is standardised in areas subject to similar stresses. This enables accelerated construction through the installation of the hollow bodies in batches.

The hollow elements were produced using a centrifugal casting process. This machine can produce up to 12 mineral hollow spheres in six-strand bundles on two frames simultaneously. The strands were placed within the structural element between the upper and lower reinforcement layers on a temporary framework made of reinforcing steel. They were then secured with binding wire to keep them in place during concreting. To reveal the internal structure of the mesograded reinforced concrete slab to exhibition visitors, the underside was not completely filled with concrete. To achieve this, the slab was turned upside down in the formwork compared to its later position in the museum and concreted at a slight angle.

PROJECT PARTNERS
Institute for Lightweight Design and Construction (ILEK)
Werner Sobek AG

DESIGN AND PROJECT COORDINATION
Daria Kovaleva, Carl Niklas Haufe, Lucio Blandini

STRUCTURAL ENGINEERING
Oliver Gericke (Werner Sobek AG), Carl Niklas Haufe and Olga Miller (ILEK)

PRODUCTION SUPPORT
Laurin Weiss, Maximilian Nistler, Niklas Mauch, Felix Wagner, Henry Hammley, Espen Vetter, Elias Kirchgässler, Julian Klemm, Max Serper, Markus Berndt, Thomas Tronsberg, Materials Testing Institute of the University of Stuttgart.

SUPPORTED BY
SIKA Deutschland GmbH, C-Con GmbH, carl wiedenmann GmbH.

FUNDING
This project was funded by the European Commission under the ‘Horizon Europe’ framework programme (Grant Agreement No.: 101092339).