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May 26, 2023

Research team redesigns shape of floors to cut concrete use by 75%

Described as a ‘stepping stone’ in the industry’s efforts to decarbonise, the experimental structural technique has been drawn up by the universities of Bath, Cambridge and Dundee. According to the

Described as a ‘stepping stone’ in the industry’s efforts to decarbonise, the experimental structural technique has been drawn up by the universities of Bath, Cambridge and Dundee.

According to the team, composed of engineers, mathematicians and manufacturing experts, the new vaulted-style floor uses 75 per cent less concrete than a traditional flat slab floor and 60 per cent less carbon in its construction, yet can still carry the same load.

A 4.5m x 4.5m full-scale demonstration of the thin-shell floor has been set up in the NRFIS laboratory at Cambridge University’s civil engineering department. The curved structure is covered by standard raised floor panels to create a level surface.

The three-year Acorn (automating concrete construction) research project is backed and funded by the UKRI (UK Research and Innovation).

Paul Shepherd, reader at Bath’s department of architecture and civil engineering and principal investigator for Acorn said: ‘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.’

Currently, most building floors use thick flat slabs of solid concrete, which rely on lots of steel reinforcement to allow them to resist tension.

Shepherd said the new technique did not require additional supports and that the columns and foundations could actually be ‘significantly smaller’ given there would be ‘about a quarter of the concrete compared to a solid slab’.

He told the AJ: ‘There are some tie-rods between the columns to stop the arches spreading. But their embodied carbon is more than made up for by the reduction in concrete and removal of steer rebar.’

Asked whether the arched shape would affect building heights and design, Shepherd responded: ‘We don’t see the raised floor as “lost space”.

‘Many office buildings have a raised floor to run services through with easy access, and we just bought a standard raised floor system with adjustable height feet. We designed the shell to make sure you can get a 30cm air duct under it along the edge.’

He added: ‘You might say that, because it weighs so much less, you could actually build taller if the strength of the foundations was the limiting factor.’

However, the new shape would be trickier to make using traditional formwork, so the team has developed, in parallel, an automated adaptable mould and robotic concrete spraying system that can be used in an off-site factory setting.

Alongside this, the team has also created bespoke software to seamlessly optimise floors for a given building design – and control the automated manufacturing system to produce them.

As the floor is made off-site, it will need to be transported to site and assembled. The prototype demonstrates how this can be done by being split into nine pieces with a connection system devised to join the pieces together. Reversible joints have been incorporated to allow the floor to be disassembled and reassembled elsewhere.

You could actually build taller if the strength of the foundations was a limiting factor

Each piece of the prototype only took 30 minutes to make with the whole floor taking a week to assemble.

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.'

Acorn has received funding from UK Research and Innovation under the ISCF Transforming Construction programme.

In terms of the next steps, Shepherd said: ‘[We’ve] collected a lot of questions we still need to answer, and [we] feel it needs a second phase of research before it could be adopted by industry.

‘To this end, we have an application in for research council funding that is being assessed in early April. If funded, we will be researching the connections between shell segments, a more optimised strategy for reinforcement and improving the material properties with automated fabrication in mind, plus doing a whole package of work on life-cycle assessment to gather better data on the embodied carbon reductions possible.’

Shepherd also said the team would also be collaborating with others on aspects such as fire, acoustics, pedestrian loading and earthquake resistance.

‘Our approach is to tackle [these issues]with technical innovation and not by throwing concrete at them!’ he said.

Cross-section through prototype floor

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TagsConcrete Sustainability University of Bath