Additive manufacturing (AM) has begun to affect nearly every industry, from healthcare to aerospace, making it possible to create unique geometries with unique properties. One industry where 3D printing’s impact is at an even more nascent stage in construction. There are firms and research groups exploring the use of 3D printing as a building technology, but additive construction is still so young that its exact purpose and benefits remain speculative and unclear. Why, other than for sheer novelty, squeeze concrete out of a nozzle to fabricate a building when you can rely on traditional methods?

Here we explore the various technologies currently being developed in additive construction to understand what the purpose, benefits, drawbacks and hurdles are to the technology.

Large-Scale Binder Jetting

Among the first large-scale 3D printers for construction was the D-Shape 3D printer, made up of a 6m x6m aluminum frame and 300 nozzles that spray a binding agent onto masonry material, such as sand. While D-Shape has printed some large-scale objects, including a 3m x 3m x 3m sculpture, the company has struggled to realize the vision of its founder, Enrico Dini.

Dini’s largest construction project to date, a 12-meter-long, 1.75-meter-wide pedestrian bridge, was performed in conjunction with ACCIONA and the Institute of Advanced Architecture of Catalonia (IAAC). The bridge is made up of concrete powder micro-reinforced with polypropylene and reflects a parametric design meant to optimize the distribution of material, while minimizing waste through the use of recycling raw material during the manufacturing process.

A bridge 3D printed by ACCIONA and the Institute of Advanced Architecture of Catalonia in Spain. (Image courtesy of the Institute of Advanced Architecture of Catalonia.)

Rick Rundell, technology and innovation strategist, startup mentor and senior director at Autodesk, explained that the process used to fabricate the bridge might be more accurately described as 2.5D printing.

“Any of the companies that are making a go at 3D printing concrete really are kind of 2.5D printing concrete. They’re making custom panels by printing on a flat surface and giving it some dimension. Those panels are then intended to be tipped up and made into something,” Rundell said. “The railings of the bridge were 3D printed flat and tipped up, and then the bridge was cemented into place.”

3D Printing Metal

A pedestrian bridge is a good place to start when venturing into the world of 3D printing publicly used structures. Not as large as a single-family home, but not as small as an art object, a bridge can actually serve a useful purpose while demonstrating additive technology’s potential.

The MX3D bridge is near completion. (Image courtesy of MX3D.)

An additive construction that has received a great deal of attention is the MX3D Bridge, from Dutch firm MX3D. The project was unveiled in 2015 with an ambitious video depicting two industrial robotic arms standing on either side of a canal and welding a metal bridge until the two devices met in the middle.

Several years have passed since then, but the bridge is nearing completion. In the process, however, MX3D realized that the vision promoted in its initial video could not be created exactly as envisioned. Instead of printing the bridge live, on-site, the bridge has been fabricated off-site in a facility, where the industrial robotic arms would not be subjected to the elements.

“The MX3D Bridge project is a classic moonshot project,” Gijs van der Velden, CEO of MX3D, told engineering.com. “This means that we knew what we wanted to achieve, namely print a 12-meter bridge in stainless steel. We also knew that a lot of innovation was needed to bring the early stage technique up to the required level. We understood that our plan might have to be changed due to city permits or regulations. And it was clear that engineers, material researchers and other unforeseen external factors were going to change the original project plan.”

The MX3D Bridge has a unique shape to demonstrate the geometric possibilities of additive construction. (Image courtesy of MX3D.)

Unlike other projects that rely on plastics or masonry, the MX3D Bridge uses metal, introducing new advantages and challenges. van der Velden explained that the firm performed work with resin and concrete in the project’s early stages, before attempting metal.

“The form liberty that metal printing offers is greater,” he said. “Where concrete and resins only allow for a slight overhang as they require a longer 'drying' time, metal instantly solidifies and allows real 3D forms to be produced. The metals we use are 100 percent recyclable—not that I would want to recycle the bridge. Metal printing is relatively slow, but that will increase the drive on innovation to create more lightweight objects. Lighter equals faster equals cheaper.”

Like other additive construction projects, the MX3D Bridge promises a reduction in material usage, with van der Velden hoping for a 30 percent or more decrease in material usage. “In a world where material scarcity and footprint become bigger issues, a technology like 3D printing comes right on time,” he said.

Unlike other projects, the bridge also incorporates sensors to inform the physical properties and lifecycle of the structure. Created with Autodesk and The Alan Turing Institute, the sensor system built into the bridge will be used to conduct load testing—performed by Arup and Imperial College London—to determine how it behaves under dynamic loads and how the shape deforms when the bridge is overloaded. Additionally, the sensors will monitor the health of the bridge during operation, both while in use and underchanging environmental conditions.

MX3D and its partners, including the Lloyd’s Register Foundation, are also creating a digital twin of the bridge using “data from the FEA model, the material research, the testing data and the live feed” of the bridge, according to van der Velden.

“Combined, this data allows us to do thousands of additional tests in a virtual environment,” van der Velden said. “This way, we can generate much more development speed concerning the development of a data-centric design language.”

van der Velden believes that the biggest challenge for additive construction is design validation, before the start of production. “As all shapes are unique, a parametric method of validation needs to be built,” he explained. Without the need for preliminary destructive testing, we need to understand and prove the behavior of a tube with a variable thickness and changing organic geometry. For this, a data-centric design method is essential. The start will be hard, but as soon as we have a sizable amount of data, the development will speed up exponentially.”

The bridge is scheduled for completion in October 2018 before installation in its final location, likely spanning a canal in Amsterdam, in 2019. In addition to this project, MX3D is currently focusing on developing its 3D printing software and has several industrial, as well as infrastructural and art, projects underway in the Netherlands and the U.S.

Small-Scale Binder Jetting

San Francisco design firm Emerging Objects has relied on the material flexibility of binder jetting to conceive of new materials and design possibilities for additive construction. On its site, you’ll see a list of materials that include cement, ceramic, rubber, salt, sand, tea and wood.

In many cases, recycled objects were used as the feedstock, ground into a fine powder, and then printed into a new shape using a binding agent, thus giving new life to discarded goods. In a global social and economic system that overproduces and over consumes, recycling material is increasingly crucial. However, Emerging Objects also adds design elements to its 3D-printed objects that could bring new levels of sustainability to construction.

Emerging Objects utilizes the geometric complexity possible with 3D printing to create the Cool Brick, which features small cavities that collect moisture and allow air to pass through them. (Image courtesy of Emerging Objects.)

This enhancement is perhaps most evident in the “Cool Brick,” a ceramic brick designed to perform evaporative cooling. Made up of a network of lattices, the porous brick allows warm air to pass through it, where moisture passively collected from rainfall, cools the air and lowers the temperature within a building.

Unique to Emerging Objects’ approach to additive construction is its design of modular bricks and panels, which makes it possible to fabricate components with existing 3D printers. The firm has even gone so far as to use desktop 3D printers to demonstrate the feasibility of new construction methods with low-cost technologies. The Star Lounge is an example of a dome made from an assembly of modules 3Dprinted on MakerBot systems using biodegradable polylactic acid (PLA).

The Cabin of 3D Printed Curiosities features a number of 3D-printed elements, including a façade that features printed pots that contain small plants. (Image courtesy of Emerging Objects.)

3D Printing Walls

While Emerging Object is 3D printing bricks and other modular elements, Branch Technology, out of Chattanooga, Tenn., is 3D printing walls. Well, to be more exact, the startup is 3D printing the insides of walls. Using a large industrial robotic arm attached to rails, the firm’s C-FAB process 3D prints lattice structures that are then filled with spray foam and coated in concrete.

David Fuehrer, director of sales &new business development for Branch Technology, added, “In addition to the foam and concrete, we are looking into other fill and finish materials for our composite development, but currently we are not at liberty to offer further detail.”

By 3D printing weight optimized lattice structures, it’s possible to create very lightweight components, while maintaining structural integrity, three to four times the strength of wood stud construction. Other benefits, according to Fuehrer, include “direct digital fabrication, lightweight assemblies, faster on-site installations, unprecedented design freedom.”Fuehrer also suggested that, by 3D printing these elements off-site before shipping them to the build location, it’s possible to control the fabrication process.

Branch Technology is focused on using C-FAB for prefabrication purposes,” Fuehrer said. “This allows for more efficient and accurate production. We can maintain better quality in our manufacturing facility, translating to faster on-site installations.”

The firm has participated in a number of smaller projects as it works its way up to constructing a crowd-sourced, single-family home design. This includes a 1,600-cubic-foot pavilion made in part with Oak Ridge National Laboratory, Thornton Tomasetti CORE and Techmer PM, and designed by SHoP Architects.

The SHoP Pavilion is made up of two 3D-printed structures made by Branch Technology. Additional elements made from bamboo were 3D printed by Oak Ridge National Laboratory. (Image courtesy of Branch Technology.)

“Our previous projects showcase what is possible when combining parametric modeling with direct digital fabrication,” Fuehrer explained. “Each project pushes the boundaries of what is possible with this type of fabrication and provides us with opportunities to improve our processes in regard to moving projects from concept to final product.”

The pièce de résistance will be the 1,000-square-foot Curve Appeal home, designed by WATG’s Urban Architecture Studio and currently in development in Chattanooga. Selected through a crowd-sourcing competition, Curve Appeal will demonstrate the capabilities of C-FAB and freeform construction. WATG has tested a wall section for the design and the project’s groundbreaking is slated for 2018.