this digitally fabricated 'smart slab' is half the weight of a conventional concrete ceiling

researchers in switzerland have fabricated an 80-square-meter lightweight concrete slab, making it the world’s first full-scale architectural project to use 3D sand printing for its formwork. ‘smart slab’, which is just 20 millimeters at its thinnest point, has been realized as part of ‘DFAB house’ — a project underway in switzerland where ETH zurich professors are joining forces with industry experts to explore and test how digital fabrication can change architecture.

the smart slab shown resting on the mesh mold wall during the installation of the services above
image © NCCR digital fabrication / michael lyrenmann | video © NCCR digital fabrication / ETH zürich

the slab, which is less than half the weight of a conventional concrete ceiling, combines the structural strength of the material with the design freedom of 3D printing. developed by the research group of benjamin dillenburger, assistant professor for digital building technologies at ETH zurich, ‘smart slab’ is one of the core elements of DFAB HOUSE. the 80 sqm, 15 tonne ceiling consists of 11 concrete segments and connects the lower floor with the two-storey timber volume above.

the principal ribs of the smart slab showcase the free-form capabilities of concrete
image © digital building technologies (dbt), ETH zürich / andrei jipa

the research group developed a new software to fabricate the formwork elements, which is able to record and coordinate all parameters relevant to production. after planning on the computer is completed, the fabrication data can then be exported to the machines at the push of a button. the team then worked alongside several industry partners to realize the project. the first produced the high-resolution, 3D-printed sand formworks, which were divided into pallet-sized sections for printing and transport reasons, while another fabricated the timber formwork that gives shape to the upper part of the slab.

the hierarchical grid of structural ribs of the smart slab
image © digital building technologies (dbt), ETH zürich / andrei jipa

the two types of formwork for the concreting were then brought together by a third company, which first sprayed the fiber-reinforced concrete onto the sand formwork to produce the finely ribbed surface of the lower concrete shell and then casted the remaining concrete into the timber formwork. after a two-week hardening process, the 11 individual concrete segments were ready to be installed.

complex geometric features articulating the con- crete surface oft he smart slab
image © digital building technologies (dbt), ETH zürich / demetris shammas

the 3D sand printer used for the fabrication of the formwork has a build volume of 8 cubic meters
image © digital building technologies (dbt), ETH zürich / tom mundy

post-processing involves unconsolidated sand particles being removed from the print bed
image © digital building technologies (dbt), ETH zürich / tom mundy

the formwork parts are assembled seamlessly and prepared for concreting
image © digital building technologies (dbt), ETH zürich / andrei jipa

an oil-based release agent facilitates the removal of the formwork once the concrete hardens
image © digital building technologies (dbt), ETH zürich / andrei jipa

glass-fiber reinforced concrete being sprayed on the 3D printed formwork in several consecutive layers
image © digital building technologies (dbt), ETH zürich / andrei jipa

the smart slab segments being placed piece by piece on the 12cm wide mesh mold wall
image © digital building technologies (dbt), ETH zürich / tom mundy

the final and largest segment of the smart slab — weighing almost 2.5 tonnes — being installed on site
image © digital building technologies (dbt), ETH zürich / andrei jipa

the structural principle is a hierarchical grid of post-tensioned ribs cantilevering from the mesh mold wall
image © digital building technologies (dbt), ETH zürich / andrei jipa