Paul Shepherd On Thin Shell Concrete Floor - hero

Changing floor shape could cut concrete usage by 75 per cent

Image credit: William McManus (University of Bath)

Swapping solid slab floors for a ‘thin shell’ vaulted alternative could help the construction industry towards its net-zero targets, according to a concept presented by a UK research team.

An interdisciplinary team of structural engineers, mathematicians and manufacturing experts from the Universities of Bath, Cambridge and Dundee has unveiled a full-scale demonstration of a thin-shell floor, which uses 60 per cent less carbon in its construction than an equivalent flat slab that could carry the same load.

The new vaulted style of floor, developed in the UK, uses 75 per cent less concrete than a traditional flat slab floor and could help the construction industry reduce its carbon footprint. 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 innovative vault-shaped floor design takes advantage of concrete’s inherent natural properties and strengths.

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The team has demonstrated that the new process could significantly reduce the carbon footprint of our built environment.

Dr Paul Shepherd, a reader in Bath’s Department of Architecture and Civil Engineering and the principal investigator for Acorn, 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 7 per cent of global CO2 emissions, the easiest way for construction to begin its journey to net zero is to use less concrete.

“That has been the driving force behind this project, which we hope could make a major difference to the impact of construction.”

Innovations in robotics, automated design and off-site fabrication are also key aspects of the project.

Most building floors use thick flat slabs of solid concrete, which are inefficient since they rely on the bending strength of concrete to support loads. Concrete isn’t very good at resisting the tension induced by bending, so these floors also need lots of steel reinforcement. Acorn’s approach is to use concrete for what it is inherently good at - resisting compression.

By putting the material only where it is needed, and ensuring that it works in compression, the Acorn design uses much less concrete. The new shape might prove impractical to make using traditional temporary formwork, so the Acorn team has in parallel developed an automated adaptable mould and a robotic concrete-spraying system that can be used in an off-site factory setting.

Alongside this new style of fabrication, the team has also developed bespoke software to seamlessly 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 site and then assembled. This created fresh challenges for the team, who had to split the large floor into nine transportable pieces and develop a connection system to join the pieces together. However, this approach also brought some advantages, in terms of reducing the time needed on-site for construction.

The Acorn team was also able to incorporate reversible joints, so that the floor can be disassembled and reused elsewhere at the end of the building’s life, promoting a circular economy for the construction industry.

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The practicality of this integrated system has been demonstrated to Acorn’s industry partners, with a full-scale 4.5m x 4.5m thin-shell building constructed in the NRFIS Laboratory of Cambridge University’s Civil Engineering Department.

Early results have suggested that Acorn’s approach of using material sparingly can already deliver significant carbon savings, with future research likely to lead to even more as the various processes are optimised further. Despite being the first of its kind, each piece took only half an hour to make and the whole floor took a week to assemble – future commercial versions could be manufactured in dedicated industrial facilities much more quickly, with site erection times much reduced accordingly.

Dr Shepherd added: “After three years of research, it is amazing to see the fruits of all our hard work dominating the laboratory and drawing interested looks from all who passed by. It’s not every day you can jump on top of your research! I just hope that one day soon this type of low-carbon automatically manufactured building becomes so widespread that people walk by without noticing.”

Adam Locke, programme leader of the Europe Hub Technology and Innovation at Laing O'Rourke, one of Acorn's industry partners, added: “The Acorn demonstrator is a very useful stepping-stone in the progressive pathway to decarbonising our solutions and complements very well our own work in this area.”

Decarbonisation of the construction industry and its heavy reliance on using concrete is a popular topic for research.

In May 2021, a joint venture between graphene specialists at The University of Manchester and alumni-led construction firm Nationwide Engineering unveiled graphene-enhanced concrete that could revolutionise the concrete industry and its impact on the environment.

Meanwhile, in April 2021, the inaugural tenants of Holland's first 3D-printed concrete home received their house keys. The house is the first of five such structures planned as part of ‘Project Milestone’ - a joint construction and innovation project of Eindhoven University of Technology, Van Wijnen, Saint-Gobain Weber Beamix, Vesteda, the Municipality of Eindhoven and Witteveen+Bos.

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