A new vaulted style of floor developed in the UK uses 75% less concrete than a traditional flat slab floor and could – the team that has developed it believes – help the construction industry reduce its carbon footprint.
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 is said to use 60% less carbon in its construction than an equivalent flat slab that could carry the same load. 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 floor design exploits concrete’s inherent natural properties and strengths. The team says it 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 & Civil Engineering, and the Principal Investigator for ACORN (pictured standing on the ACORN concrete floor), 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 over 7% 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.”
The team added: “Currently, most building floors use thick flat solid concrete slabs, which are inefficient, since they rely on the material’s bending strength e 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 instead use concrete for what it is good at – resisting compression.”
The development teams says that by putting the material only where it is needed, and making sure it works in compression, the ACORN design uses ‘far less’ concrete. The new shape might prove impractical to make using traditional temporary formwork, so the team has developed an automated adaptable mould, and a robotic concrete spraying system, that can be used in an offsite factory setting. Alongside this new fabrication method, team members have 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 offsite, it also needs to be transported to site and then assembled. This brought some exciting challenges, entailing the team splitting the large floor into nine transportable pieces and developing a connection system to join them together. The team said: “However, this also brings some advantages – in terms of reducing time needed on site for construction.”
The ACORN team was also able to incorporate reversible joints, so that the floor can be disassembled and re-used elsewhere at the end of the building’s life, ‘promoting a circular economy for the construction industry’.
The practicality of this integrated system has just been demonstrated to ACORN’s industry partners, by making a full-scale 4.5 m x 4.5 m thin-shell building in the NRFIS Laboratory of Cambridge University’s Civil Engineering Department. Early results reportedly suggest ACORN’s approach of using material sparingly can already deliver significant carbon savings, with future research likely to lead to even more as processes are optimised. 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, and site erection times much reduced.
Dr Shepherd adds: “After three years of research, it’s 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 & Innovation at Laing O'Rourke, one of the ACORN partners, adds: “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.”
ACORN has received funding from UK Research and Innovation under the ISCF Transforming Construction programme.