A New Way to Build
Housing projects from Mexico to California to Texas are utilizing 3DCP — three-dimensional construction printing or three-dimensional concrete printing — to rapidly erect durable homes. (click here for an article on this topic from the March/April issue of Standardization News). However, while use of this technology continues to expand in small, measured steps, it is becoming increasingly clear that concrete-based mixtures are not the only options for additive manufacturing (AM) in building construction.
Enter polymeric UV (ultraviolet)-cured material. It is similar to concrete-based alternatives in the way that it is extruded to shape walls and other structural elements. However, there are some important differences as well.
Polymeric UV-cured material could play an important role in helping AM gain broader acceptance as a viable tool for residential and commercial construction. But, as is often the case with new technologies, standards are needed to facilitate the evaluation of its performance, safety, and sustainability. ASTM International’s committee on additive manufacturing technologies (F42) — and in particular the group on construction (F42.07.07) — is working hard to meet that need.
A Unique Approach
Most current 3D construction printing (3DCP) is carried out with cement-based mixtures, although materials such as metals and organics (clay, for example) have been used successfully as well.
READ MORE: The Shape of Concrete to Come
Polymer-based thermoset composites are another option. Alexey Dubov, chief operating officer for Mighty Buildings, believes his firm is the only one currently using this type of material, and he notes that patents have been filed for the company’s 3D-printing process. Eighty percent of production is automated and takes place at the company's facility; modular wall panels and other components are then assembled on-site.
But what exactly is a manufactured polymeric UV-cured material? Dubov describes a blend consisting of an inorganic hydrate, an acrylate methacrylate monomer, and a light-induced polymerization agent, which is needed to activate the thermal reaction that begins the polymerization process. “After the polymerization reaction, the material as a thermoset forms a solid, stone-like material that is perfect for buildings,” he says.
According to Dubov, benefits of using polymers in 3DCP include the ability to form more complex geometries, which can improve the structural properties of the final building components, and increased energy efficiency, as polymers offer lower thermal conductivity. He also notes that polymers allow his company to eliminate most of the exterior weatherproofing materials and significantly reduce the number of exterior layers.
Mighty Buildings has completed more than nine structures, with others on the way. Some are referred to as accessory dwelling units — similar to tiny homes — while others are single-family units ranging from 864 to 1,440 square feet (80 to 134 m2) in size. A planned community in Rancho Mirage, California, will feature 15 “eco-friendly” homes with a striking mid-century design.
Stephan Mansour, vice chair of F42.07.07, agrees that the company is forging its own path. “They’re the only ones that are actually taking it that far and using this specific material for construction. Everybody else is going the traditional way of using concrete- or cement-based materials, or even adobe, like clay or mud, to print,” he says.
The sustainability component of polymeric materials could turn out to be even more significant than its design flexibility and other benefits. Mansour highlights the abundance of potentially recyclable material that could be processed and repurposed in polymer-based 3D-printing applications.
“When it comes specifically to construction, you don’t want to focus on a material that is hard to get and is very expensive, especially if you have to ship it from different locations,” Mansour explains. “So when it comes to polymers, they could be a material that is easily available on the market and that can be recycled and reused. It could be a construction-based material or something coming out of the manufacturing industry. And this is not just having a solution available in one location or one region of the globe. You can take that solution and implement it in different locations based on the different raw material or recycled material that’s available locally.”
Ready access to local material is crucial to the economics of 3DCP. Mansour previously worked for Consolidated Contractors Company, a large firm based in the Middle East, and managed CCC’s construction of a 3D-printed prototype housing unit in Saudi Arabia, which was completed in 2018. The availability of necessary supplies was limited.
Polymer-based thermoset composites are becoming part of the 3D printing construction process. Photos courtesy of Mighty Buildings.
“We had to ship the material from the Netherlands, and that took about six weeks, plus customs and all the logistical issues we ran into,” he says. “It makes no sense, especially when you want to focus on affordable housing or environmentally impactful solutions, when you have to bring your material from abroad.”
With the global population projected to approach 10 billion over the next 30 years according to a 2019 United Nations report, the shortage of affordable housing — already a serious issue — will become more acute in the future. Mansour likes to put it this way: “A city the size of Paris has to be built every year for the next 40 years.”
3DCP could be one solution to the problem.
A project located in an economically depressed area of Mexico illustrates the technology’s potential. Tabasco, a Mexican state on the southwestern edge of the Yucatán peninsula, might seem like an unlikely location for a groundbreaking achievement in residential construction. But thanks to the efforts of several dedicated organizations and the continuing evolution of 3DCP, the village of Nacajuca is already a showcase for the potential of this unique technology. Two 500-square-foot (46 m2) single-story houses have been built so far; the goal is to eventually complete a total of 50 such residences.
New Story is a nonprofit dedicated to tackling the worldwide housing crisis, with an emphasis on the use of innovative construction technologies. The organization partnered on the Nacajuca project with Échale, a Mexican affordable housing developer, and ICON, the Texas-based developer of the Vulcan 3DCP system. The Vulcan system prints with ICON’s proprietary high-strength concrete, which is blended with water and additives on-site, taking current weather conditions into account to achieve optimum performance.
Sofia Lopez volunteers with New Story. “For each community, New Story develops one technology further. The outcome integrates diverse innovative solutions to create the lowest cost and most effective way of building for affordable housing. And that’s a pretty amazing mission,” says Lopez, who is an architect with an AM specialization.
One of the challenges that the New Story team has faced in Nacajuca is “selling” the unique aesthetics of 3D-printed structures to the people for whom the houses are being built. Lopez points out that just because a home is “free” doesn’t mean potential residents will rush to embrace it. Education and community involvement, and homes designed with feedback from the families who will live in them,
“If we present to you a house that is 3D printed, it’s not going to look like all the houses you’ve seen in your life, because it has the lines,” Lopez says. “The community design team has to be very conscious of explaining to people that these houses are special and that they’re actually pretty cool.”
Another way to gain local buy-in has been to ensure that the houses in Nacajuca were designed to reflect the needs of the community. They feature a porch in front, like traditional homes in the area. This space creates a type of corridor and a visual interaction with the community. Because cooking with fire is common in the area, a wok-type installation is incorporated into the back of the house.
Finding the Gaps
Projects like those described above — and others, like TECLA in Italy and a two-story home recently completed in Germany — provide an exciting glimpse of the role 3DCP could play in ameliorating the global housing shortage. It is also a reminder that this technology is evolving quickly, whether it is using concrete-based materials, polymeric materials, or even local soil, as in the TECLA example, and that standards need to keep pace.
The first step in developing such standards, especially for a new technology like three-dimensional construction printing, is to figure out where, exactly, they are required. Another is to ensure that any new standards are in harmony with existing ones that operate in the same space.
“F42.07.07 is the subsection dedicated to the application of additive manufacturing to construction,” notes Sam Ruben, chair of that section and co-founder and chief sustainability officer at Mighty Buildings. “In order to make sure that we are complementing the standards work of the various other efforts related to three-dimensional printing construction, we have embarked on a gap analysis to understand where additional standards are needed.”
Ruben goes on to explain that once the analysis is completed (in a few months), the subcommittee will move forward with developing standards that address a number of materials with potential for use in 3DP construction, including polymers, composites, metals, and concrete. “We will also focus on specific materials where needed, or identify existing standards or opportunities for collaboration with other committees,” he says.
Ruben is particularly interested in standards related to polymer-based alternatives. He also emphasizes how important the standards his group has underway are to both sides of the construction equation.
“On the one hand, building officials need standards and specifications that they can trust in order to properly evaluate the safety and code compliance of 3DP construction,” he says. “On the other hand, standards are needed that enable to producers to demonstrate that they are doing things the right way. Without such standards, the adoption of this promising technology will be delayed due to the conservative nature of building officials.”
One such standard is in the early stages of development. The proposed specification for additive manufacturing for construction — process characteristics and performance — specification for manufactured polymeric UV cured structures for residential applications (WK74302) is F42.07.07’s first effort to focus specifically on polymer-based materials used in 3DCP.
Dubov sees other areas that will require standards, including sustainability, safety, and design processes. His section’s next initiative will address post-processing steps like milling, coating, and polyurethane foam injection. “These standards will help ensure the final product’s quality — a 3D-printed building component with coating and insulation,” he asserts.
Joint Group 80
Even as ASTM committees continue to work on standards related to various aspects of AM in construction, they are also involved in a parallel effort to advance international development of 3DCP standards.
Joint Group 80 (JG80) is a collaboration between ASTM and the International Organization for Standardization (ISO), officially launched in March 2020. Mansour was instrumental in recruiting relevant stakeholders from the 3DCP sector to participate, and he describes an agenda that encompasses different material options even as it moves forward with measured urgency.
“Joint Group 80 is not just concrete-based, but will also include polymers and compound materials,” Mansour explains. “The biggest focus now is that 3D construction printing is moving forward, especially in North America in the last few months. So we are rushing to get standards in place to make sure that the printed elements are actually safe and that the quality is up to standards.”
Mansour emphasizes that JG80 is “agnostic” in terms of both material and technology. “We are trying to encompass as many different players in the market as possible,” he says. And though the group includes companies vying for market share in this new technology, they are working together because the development of strong, consensus-based standards ultimately benefits the entire industry.
Ruben applauds this inclusive approach. “Building out the standards framework to account for the existing diversity of materials, and in a way that allows for new innovations, is important to supporting this young but growing sector.”
“Joint Group 80 aims to bridge the gap between conventional methods and 3DCP,” says Mansour. “It doesn’t touch in detail on specific standards when it comes to, for example, safety, material handling, sustainability, architectural design, approval. Those are out of the scope of the existing standards. But that’s where our section can come into play, to actually address those detailed standards topic by topic.”
The end result, it is hoped, will be a menu of test methods, specifications, guides, and other standards that will make it easier for general contractors to accept and begin to utilize 3DCP as another tool in construction. “Nothing happens in construction without standards,” Mansour concludes.
Jack Maxwell is a freelance writer based in Westmont, New Jersey.