The future will be printed in 3D. Lem Bingley talks to the experts at the forefront of construction’s digital transformation amid a global pandemic that has emphasised the need to find different ways of doing things
The coronavirus crisis “has opened the eyes of everyone who works in an office that we can work remotely”.
And, speaking to Construction News via video conference from his home in Dubai, Paul Mullett observes how commonplace this kind of link has become lately.
But the director of engineering and technology at consultant Robert Bird Group says it has also revealed how few people in construction can do the same.
“It’s raised awareness that we’re very dependent still on manual labour,” he says.
The result, Mullett argues, will be a strong surge of interest in “industrialised forms of construction, be it volumetric modular or flatpack modular, or whatever” as the industry adjusts to the new normal.
“Every contractor, every consultant, every standard we have is based around a certain way of doing things. 3D printing challenges all of those across a very broad spectrum: design, materials, methods, even the plant we use”
Paul Mullett, Robert Bird Group
Among the “whatever” category sits 3D printing with concrete, an additive-manufacturing approach where structures are built up from many thin layers of concrete applied robotically according to a digital design. As the layers are placed, they fuse together before curing to yield a finished material with qualities comparable to cast concrete.
Printing with concrete currently occupies a tiny niche, but one with enormous potential according to those working to develop the technology. Not least because it might cut out chunks of manual labour: “You’re replacing manual processes with a robot,” Mullett says.
In April last year, Robert Bird Group became a member of Dubai’s Centre for 3D Concrete Printing and Digital Construction, in collaboration with local partners the American University of Dubai, Arabtec Construction and 3DVinci Creations. The centre was set up to start filling in some of the “many knowledge gaps around what the technology is, what it can do and what the limitations are”, Mullett says.
He describes 3D printing as a key litmus test for the industry.
“If we can’t innovate with this technology, what hope do we have for the industry going forward?” he says, adding that construction currently suffers from many levels of technology lock-in.
“Every contractor, every consultant, every standard we have is based around a certain way of doing things,” he says. “3D printing challenges all of those across a very broad spectrum: design, materials, methods, even the plant we use.”
The future will be automated
Similar thoughts are set out by Jeroen Nuijten, innovation specialist at Bam Infra in the Netherlands. “If coronavirus has taught anything it’s that you’re absolutely dependent on your workforce,” he says, noting that increased use of robots during the execution phase could markedly reduce that dependence.
“We could save a lot of material – about 40 per cent – compared to the conventional way of working, and we learned that we could build much faster offsite”
Jeroen Nuijten, Bam Infra
He adds: “If I look at labour shortages […] climate change and housing shortages, there are so many different reasons why you would want to go in this direction, as a sector, an industry and a country.”
Bam began working with 3D printed concrete as part of a research consortium alongside the Technical University Eindhoven. An early practical project, begun in 2017, delivered a modest 8-metre bridge for cyclists and pedestrians.
“We learned a lot,” Nuijten says. “We could save a lot of material – about 40 per cent – compared to the conventional way of working, and we learned that we could build much faster offsite.”
In 2019, BAM raised its sights. Working with partner Saint-Gobain Weber Beamix, it shifted printing tasks from the university campus to its own commercial factory, visited by CN last spring. Nuijten says the factory has now printed components for a larger bridge and for other projects in the housing and transport sectors, including some used within the UK.
Major projects set to benefit
Bam sees a role for the technology in major projects such as Heathrow expansion. “We’re looking at how we can scale it to other parts of the business and other sectors,” says Nuijten.
Printing with concrete can achieve material savings because it provides strength only where it is actually needed, Nuijten says. “For the bridge, if you looked inside there are these hollows,” he explains. The components forming the span, for example, are printed out as hollow ‘towers’, which are turned through 90 degrees on site and strung together to lie horizontally, held in compression by post-tensioned steel cables running through the voids.
“Normally you would cast it and it becomes one complete concrete structure,” Nuijten says.
He explains that reduced weight due to the hollow span can unlock a virtuous circle with potential savings in cost as well as CO2 emissions. “We don’t really use formwork,” he adds. “That’s something that you save [that] is normally created and then wasted.”
For the larger bridge, Bam will print not just the span components but the anchor blocks for the steel cables. “We’ll print permanent formwork at the ends to cast the thrust blocks into,” says Mark Taylor, senior digital construction manager at Royal Bam Group.
“We’ll encase a reinforcement cage in those parts of the bridge, so that from a layman’s point of view it will all look exactly the same, because [the exterior] has been printed by a robot, but there will be elements where we’ve incorporated traditional reinforcement cages and mass concrete to give it the structural integrity we need.”
Taylor adds that beneath its layered surface, printed concrete is entirely homogenous. “It has the same shear capacity in all different directions,” he says. “Sometimes when people hear we’re printing in layers, they think it’s going to split along the layers. [But in tests] it performs the same as any normal lump of monolithic concrete.”
The 3D possibilities
The technique developed by Bam can employ fibre-reinforced concrete for additional strength and resilience, and can also add a steel cable into each layer. “We have developed a way to put the cable exactly in the centre of the layer,” Nuijten says.
“We found out specific ways to incorporate it and coat it, to make sure we have the benefit of putting steel in concrete.”
Because they are digitally controlled, 3D-printing techniques can be combined with generative or parametric design technologies to enable highly efficient structures that would be impossible to achieve by other means, Nuijten observes.
“You can print any shape you want,” he says. “Parametric design gives you the ability to design […] the best solution possible. Those two together are very powerful, because you can [employ] the optimal design for no extra cost.”
He adds: “It becomes very interesting for us, because now the complexity is not so much the creation of [the shape] – because the printer can do anything – but how you assemble it on site. [It’s] a big jigsaw puzzle.”
Taylor foresees many applications across construction that are a far cry from the firm’s initial modest bridge. “The civils sector [is] dumping big lumps of concrete everywhere for bridges, sea walls and river defences. There are more innovative ways to deliver those solutions in projects, that will reduce our carbon footprint.”
He adds: “The most successful projects are ones where we’re not trying to replace a traditional method with additive manufacturing, it’s where we’ve thought about it from the beginning, and we’ve worked with a customer to think of a better way to fix their problem.”
A concrete solution for cladding
Laing O’Rourke used 3D-printed moulds to create bomb-resistant concrete cladding for new Crossrail stations at Tottenham Court Road and Liverpool Street in London.
The contractor’s UK head of infrastructure, Declan McGeeney, explains that the first step was to scan and digitally model the tunnels and other spaces handed over by the tunnelling contractor. This phase determined the exact shape of the required cladding, which would be cast in sections offsite. The moulds were “really complex from an architectural perspective,” he says.
Working with its engineers in Australia, Laing O’Rouke came up with a new process for this stage, called FreeFab. The approach starts with a 3D printer, which translates a digital model of the complex mould into a physical shape by building up layers of wax. Next, a 5-axis milling machine, also guided by the digital model, gives the printed wax a smooth finish, rather than the stepped surface left by a 3D printer. Glass reinforced concrete (GRC) is then sprayed onto the mould to create the actual cladding section and, once the concrete has hardened, the wax can be melted away to reveal the finished piece.
David Shillito, operations director at Laing O’Rourke’s manufacturing business, says it would have been impossible to complete the work to schedule without this approach. “We had to produce 32,000 square metres of cladding [with] 2,300 different moulds,” he says. “If we’d had to go out and find the skilled labour to carve those moulds [by hand], because they were all double-curving shapes, we’d still be searching now.”
But Shillito adds that the Crossrail project would never have specified cast concrete cladding if it thought anyone would try to make the moulds manually. “They were aware that [3D printing] existed, though I don’t think they knew how to apply it,” he says.
Laing O’Rourke initially worked with a Yorkshire-based GRC specialist, but in 2014 it acquired its subcontractor to bring the work in-house. McGeeney says the resulting GRC division is now “a profitable venture employing 60 people” and that it is helping to “push the philosophy of offsite manufacturing and digital engineering out to a wider audience”.
The FreeFab process is suitable “where you’ve got really complex shapes that you need to put into place in difficult locations,” McGeeney says, adding that GRC cladding is likely to become a more widely chosen option post-Grenfell. “It’s becoming more prevalent because of its fire qualities, robustness, and bomb-blast [resistance],” he says, adding that it is suited to public spaces such as railway buildings and airport terminals.
Shillito adds that GRC allows substantial weight savings over conventional concrete cladding. “It’s a tenth of the thickness […] so you’re only using a tenth of the material,” he says. “As the fibres fly from the nozzle of the [spray] gun into the mould, they get all interwoven, and that gives it great strength and ductility. And that’s why it works so well in the bomb-blast scenario.”
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