Concrete slabs are something of an unsung hero in construction projects. All buildings have them, but they’re designed to be hidden, providing foundational support while tucked well out of sight. But if researchers at ETH Zurich have their way, concrete slabs will be as beautiful as they are functional.
The researchers have incorporated a 16.5-ton, 861 square-foot segment of “Smart Slab” ceiling into DFAB House, a Dübendorf, Switzerland-based complex that allows researchers to develop and test the latest innovations in 3D printing, robotics and automation. Its intricately textured ribbed design is only 20mm thick at its thinnest point, and less than half the weight of a conventional concrete ceiling without sacrificing on strength, the research team writes.
“We didn’t draw the slab, we programmed it,” noted Mania Aghaei Meibodi, Smart Slab project lead and senior researcher at ETH Zurich.
Indeed, every curve and detail of the Smart Slab ceiling came about thanks to a confluence of technologies, including a large-scale 3D sand printer and special new software that allows millimeter-precise measurements of each room’s dimensions and the curvature of every wall supporting the ceiling.
“We didn’t draw the slab, we programmed it.”
“It would not have been possible to coordinate all of these aspects with analogue planning, particularly with such precision,” Meibodi said.
The finished ceiling is an eye-catching patchwork of delicate swirling forms, with larger rib-like features for support and smaller ones for aesthetics and acoustics. The planning software even factored in the placement of fire sprinkler systems, seamlessly integrating them into the ceiling to minimize the amount of space they occupy.
“This saves only a few centimetres in the DFAB House project, but in high-rises this may mean a few extra floors could be fitted into the same height,” the research team wrote.
Using those computer-aided measuring techniques, the team was able to fabricate a reinforced concrete slab ceiling using only as much concrete as necessary. Since formwork is one of the most difficult parts of concrete construction, traditional methods rely heavily on sameness and uniformity, regardless of how much concrete is actually needed. This leads to excessive materials consumption and a larger carbon footprint.
“Digital fabrication methods can make a key contribution here: components can be optimized, enabling the necessary stability with far less material. The geometric complexity of a component does not matter in 3D printing, nor does it cause any additional costs – the printer simply prints what it is told to,” the team writes.
The Smart Slab coming together required the cooperation of several industry partners. First the design was created on a computer, and the resulting fabrication data was sent to a company to produce the high-res 3D printed sand frameworks. Another fabricated the timber formwork using CNC laser cutting, which gives the upper part of the Smart Slab its shape, including recesses to run electrical cables through while also reducing weight. Its ribbed surface comes from a third company which sprays fibre-reinforced concrete onto the sand formwork and casts it into the timber formwork.
With everything measured precisely and created to specification, installing the ceiling took less time than traditional methods would allow. The Smart Slab’s 11 individual segments were hardened, then transported to DFAB House by crane and put into place. Workers then prestressed the forms by criss-crossing the framework by running steel cables through pre-inserted channels, boosting its load capacity significantly.
A multitude of disciplines and technologies had to work together in harmony to make the Smart Slab possible. Benjamin Dillenburger, assistant professor for digital building technologies at ETH Zurich expressed excitement seeing the pieces come together.
“It was spectacular to see on the construction site how seamlessly our elements fitted with each other and with the existing components of the DFAB House,” said Dillenburger. “We owe this in part to the outstanding interdisciplinary collaboration with our partners. The meticulous work that we had invested into planning completely paid off.”