AMS Spring 2023

FreeFAB 3D Printing Technique Comes to Life in the Crossrail Project


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The largest construction project in Europe right now involves digging a new railway system, running east to west across London. Called Crossrail, the ambitious project will result in a railway that runs over 100 km, passing through 40 stations. It’s expected to carry 200 million passengers a year, increasing central London’s rail capacity by 10 percent and adding an estimated £42 billion to the city’s economy. But it’s not just the size and scale of the railway that makes Crossrail so impressive; it’s the advanced construction techniques that are being used.

Last year, we were introduced to FreeFAB, a construction technique developed by Dr. James Gardiner of construction firm Laing O’Rourke. The large-scale 3D printing technology is a bit different than other forms of construction 3D printing, in that it combines the benefits of old and new construction technology. A giant robotic 3D printer, with a build volume of 30 x 3.5 x 1.5 meters, prints large molds from a specially designed wax; those molds are then used to cast concrete panels, which right now are being installed by the hundreds in the passenger tunnels of what will become the Elizabeth line when the Crossrail project is finished.

While 3D printing is being touted as the next big thing in construction, there are flaws in the technology, according to engineer Bill Baker. 3D printing can cause weaknesses in structures due to poor adhesion or gaps between layers, so the FreeFAB technique doesn’t 3D print structures directly, instead creating panels from 3D printed molds and then fusing those panels together using traditional construction techniques. The advantages are numerous, compared to conventional ways of producing molds.

[Image: Bechtel]

One of the advantages is that 3D printing makes it easier, faster and cheaper to create even complex shapes. The Crossrail project involves panels that curve along two different axes, and typically creating a mold for that kind of shape would take about eight days, according to Alistair O’Reilly, general manager at GRCUK, the construction firm in whose factory the FreeFAB system is installed. 3D printing it, on the other hand, takes three hours.

Curved panels such as these could be used for various kinds of building projects – for example, they could be installed in houses in order to create a soundproofing effect, but it would be far too expensive and time-consuming to do something like that using traditional construction methods. The panels created using the FreeFAB method are also extremely strong, as has been proven in testing – the panels have withstood twice the required force in bomb-proofing tests.

[Image: Bechtel]

The technique is also much more eco-friendly and less wasteful than conventional mold-making technologies. Typical molds are made from wood and polystyrene, and can only be used to produce one shape; once they’re no longer needed, they’re thrown out. FreeFAB wax molds, however, can be melted and the wax re-used again and again. Dr. Gardiner, an environmentalist, made sure that would be possible, though it took him three years to come up with a wax formula that could be 3D printed, milled and recycled.

Sustainability is a priority for everyone involved in the Crossrail project. 84% of the construction machinery used in the central rail section has been fitted with pollutant-reducing emission controls, and 98% of the material excavated from the tunnels and other sites has been reused, incredibly. Overall, the project has been highly beneficial for London and the UK as a whole – more than 4,500 local workers have been employed on Crossrail, while over 550 apprenticeships have been created. 96% of the contracts awarded by Crossrail went to local companies.

“Bechtel has placed sustainability right at the heart of our infrastructure business,” said Steven Kay, infrastructure operations manager of Bechtel, which is working as a project delivery partner on Crossrail. “We have played a central role in the development of low carbon energy, through solar power, nuclear, liquefied natural gas and lower carbon coal. We have taken a lead in supporting the communities we work in through local sub-contracting and local hiring…We want to help create a lasting and beneficial legacy through our projects here in the UK. Ultimately, there is nothing more rewarding than completing something that’s not just a project for a customer, but actually handing over the know-how that you’ve helped to create to prepare and inspire the next generation to take on the infrastructure challenges to come.”

The next generation should be well-equipped to take on those infrastructure challenges, thanks to the development of technologies such as 3D printing and FreeFAB. FreeFAB has gained a number of high-profile fans, such as Dr. Philippe Block, an architectural engineer at ETH Zurich. Dr. Block is known for the design and construction of membrane-like floors built under compression, which use that compression to hold each other up rather than relying on steel reinforcement. Each floor section is carefully designed to bear a certain amount of weight, allowing for the construction of thin but strong structures out of material that is normally weaker than reinforced concrete.

According to Dr. Block, his thin floors require only about a third as much material as is required for a typical floor slab, and allow more floors to be fit into buildings without making the buildings any larger. He has already tested the technique in several projects, and plans to use it for the experimental HiLo House, part of ETH Zurich’s NEST project, which also includes the multi-technology DFAB House. Dr. Block will work with Dr. Gardiner to 3D print molds for the floors using FreeFAB. The HiLo unit is expected to be completed in 2018. That’s also when Crossrail should be complete. The new railway will open in phases beginning in December of 2018, and will be fully operational by December 2019.

HiLo and the Crossrail project are just two examples of how radically construction is changing, and how integral a role 3D printing is playing in the new generation of construction techniques. People are beginning to build very differently, and it’s exciting to watch as the construction industry evolves into something more efficient and effective. The places where we live, work, and travel are starting to look and operate differently than ever before, and we may soon see an infrastructure that’s stronger than we’ve ever experienced. Discuss in the Crossrail forum at

The HiLo unit [Image courtesy of ETH Zurich]

[Sources: The Economist / Civil Service World]


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