‘Thin shell’ floors could cut carbon in construction

The ‘thin shell’ vaulted floor was developed by a team of structural engineers, mathematicians and manufacturing experts at the Universities of Bath, Cambridge and Dundee. Compared with a traditional flat slab floor, the innovation is said to use 75 per cent less concrete and 60 per cent less carbon in its construction.

The curved vault-shaped structure is covered by standard raised floor panels to create a level surface. Created by the UKRI-funded ACORN (Automating Concrete Construction) research project, the vault-shaped floor design takes advantage of concrete’s ‘inherent natural properties and strengths’, the team said.

Dr Paul Shepherd, principal investigator for ACORN and a reader in Bath University’s Department of Architecture and Civil Engineering, said: “Achieving the net-zero targets recently ratified at the COP26 conference will require significant change by the construction industry, which is responsible for about half of the UK’s total emissions.

“Since concrete is the world’s most widely consumed material after water, and its production contributes more than seven per cent of global CO2 emissions, the easiest way for construction to begin its journey to net-zero is to use less concrete.”

Currently most building floors use thick flat slabs of solid concrete, which rely on the bending strength of concrete to support loads. Concrete isn’t good at resisting the tension induced by bending, so these floors need steel reinforcement. Instead, ACORN’s approach is to use concrete for what it is good at — resisting compression.

By putting the material only where it is needed, and making sure it works in compression, the ACORN design uses less concrete. Researchers noted that the shape may prove impractical to make using traditional temporary formwork, so they have also developed an automated adaptable mould and robotic concrete spraying system that can be used in an off-site factory setting.

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Alongside this new style of fabrication, the team has developed bespoke software to optimise floors for a given building design and control the automated manufacturing system to produce them.

Since the floor is made off-site, it also needs to be transported to the site and then assembled. The team split the large floor into nine transportable pieces and developed a connection system to join the pieces together.

The ACORN team said they also incorporated reversible joints, so the floor can be disassembled and reused elsewhere at the end of the building’s life, promoting a circular economy in construction.

Practicality of the system has just been demonstrated to ACORN’s industry partners by making a full-scale 4.5m x 4.5m thin-shell building in the NRFIS Laboratory of Cambridge University’s Civil Engineering Department.

Early results suggest that ACORN’s approach can deliver ‘significant carbon savings’ according to the team, with future research likely to lead to more as processes are optimised. Each piece took only half an hour to make despite being the first of its kind, and the whole floor took a week to assemble — future commercial versions could be manufactured in dedicated industrial facilities more quickly, researchers believe.