Members of the Penn State Den@Mars team, from University Park, Pa., with their completed 3D-printed dome structure on Aug. 25, 2017, at the Caterpillar Inc. Edwards Demonstration and Learning Center in Peoria, Illinois The team won second place and $150,000 in NASA's 3D-Printed Habitat Challenge, Phase 2: Level 3 competiiton. Credits: NASA/Joel Kowsky

Imagine a building optimized to have improved structural performance, a smaller ecological footprint, and seamless integration between transparent and non-transparent materials. In addition, the design of such a building allows architects more flexibility in terms of what they can create, as material and operational costs are lower.

How could this dream building be achieved? Researchers at the Pennsylvania State University, University Park think 3D printed concrete might be one solution.

The Penn State team— consisting of architects, structural engineers, electrical engineers, mechanical engineers, material scientists and other experts— is working to develop a type of printable concrete material that can be applied with a nozzle using a robotic 3D printer to create a viable, strong structure built layer-by-layer.

Their work is still ongoing, but the team recently made significant headway as participants in Phase 2 of NASA’s 3D-Printed Habitat Challenge. The challenge asked teams to develop the fundamental 3D printing technology necessary to produce a structurally sound habitat on Mars, including the printer itself and construction materials. The majority of the materials used had to be available on Mars. Competitors had to print beams, cylinders, and domes that were tested under compression load  to determine capacity at failure. Such capacity must have exceeded a minimum set by the competition rules to qualify passing the test. The scores in such tests would then determine the ranking of teams and identify the winning teams and the prize awards. At the final event, held Aug. 23-26 in Edwards, Illinois, the Penn State team came in second place, receiving a reward of $150,000. The first place prize of $250,000 went to architectural design and engineering firm Foster & Partners, in collaboration with startup Branch Technology.

Although their work specifically for the NASA 3D-Printed Habitat Challenge began approximately eight months prior to the competition, each of the members of the Penn State team had been studying different elements required to achieve 3D printed materials and structures for several years. It was the NASA contest that catalyzed them to work more collaboratively and diligently on the project.

This collaboration is critical to making 3D printed concrete a reality, said faculty team member Ali Memari, Ph.D., P.E., in an interview with R&D Magazine.

What makes this so interesting is the different layers of knowledge that are required to address the problem,” said Memari, the Bernard and Henrietta Hankin Chair of Residential Construction and Director of the Pennsylvania Housing Research Center at Penn State. “That is why we need a multidisciplinary team to be able to do something meaningful in this area. We work very well as a team together; each of us has a piece of the knowledge to make this happen.”

The advantages of 3D printing concrete

3D-printed concrete has several advantages. One significant advantage is its potential to decrease construction costs and open up opportunities for architects to be more creative, said Memari.

This is because 3D-printed concrete structures, unlike conventionally created concreate structures, do not require formwork—temporary or permanent molds into which concrete is poured.

“Formwork is very expensive, so if you had a way to actually make your concrete structure without the formwork it would be more economical,” said Memari. “Furthermore, because of the formwork, you have to come up with a detail and design that is simple and can be quickly poured, and you can’t do much variation, because any variation adds expense to the formwork.”

3D-printed concreate technology, if it can be made practical, would allow architects to basically come up with their ideal design and use a 3D printer to print it without as many limitations, explained Memari.

“Architects have been really restricted due to formwork expense and they are not always able to go with their dream design, instead having to choose a more simplified design,” he said. “Currently it is often very expensive to create what architects truly want to create.”

Another potential benefit of 3D printing concrete is the possibility of incorporating it with other materials to add additional benefits to a structure. Faculty team member Shadi Nazarian has been working on the concept of using 3D printing for seamless architecture for years. She has been working on joining materials, which are transparent, such as glass, with geopolymer concrete.

“We had designed this composition of geopoloymer concrete that could be joined seamlessly with glass, or can transition gradually to glass,” said Nazarian, associate professor of Architecture and affiliate faculty in the Materials Research Institutes (MRI) at Penn State, in an interview with R&D Magazine. “We designed a material that is basically a combination of geopoloymer and glass. On one side of a wall, if you can imagine, it could be structural concrete were the loads are greater, and then you can gradually transition, add more glass were you need translucency and reach 100 percent glass where you desire to have a picture window rendered that is transparent- that is a non-operable window.”

Because 3D printing offers a layer-by-layer printing approach, it could also be used to create building components that are optimized for better structural or environmental performance.

If you have a wall, you can use different materials to set off the composition of the wall,” explained faculty team member José Pinto Duarte, Ph.D, Stuckeman Chair in Design Innovation and director of the Stuckeman Center for Design Computing, in an interview with R&D Magazine. “For instance, you could use concrete with cork so you have optimized structural performance and optimized environmental performance. You could change the grading of the concrete relative to the cork, so when the wall needs to be stronger you could use more concrete, and where the wall can be weaker, you could use more cork and improve the environmental performance.”

Tests utilizing this approach demonstrated that the operational cost of a building could potentially be lowered 30 percent if it were designed and build in this manner, according to Duarte.

Learning from the competition

Participating in NASA’s 3D-Printed Habitat Challenge required the Penn State team to take on some challenges regarding 3D printing concrete that they had not tackled before.  

We were initially thinking of this for Earth-use but once we heard about the NASA competition we had to rethink it for space,” said Memari. “We had to come up with the proper robot, proper mixers, and new materials. These were the biggest challenges that we had to work toward solving.”

Faculty team member Sven Bilén, professor engineering design, electrical engineering, and aerospace engineering and head of SEDTAPP in the College of Engineering, agreed.

"The pulling together of all of these elements into a system was our biggest challenge, said Bilén in an interview with R&D Magazine. "As individual elements, we addressed the materials, the fabrication method, the robot, but getting all of these to work together seamlessly required a systems approach, and without that approach, we likely would not have been as successful."

The team developed a new formulation for concrete that was made from 80 to 90 percent materials that could be found on Mars and didn’t require much water. This material, if perfected, could be used on Earth as well, said Duarte.

“The interesting thing is that the material we developed has many advantage over traditional concrete, he said. “For instance, it has a smaller ecological footprint, so it could actually be used on Earth with many advantages.”

Creating a type of concreate that could flow though a nozzle, print quickly, and be strong enough before it was completely dry to not collapse under the weight of the next layer, was a challenge for the team.

Typical concreate is made up of cement, sand, aggregates such as pebbles or small stones, and water. The cement serves as a bonding material, the sand as a filler, and the aggregates give it strength. But in 3D printing, pebbles or small stones can’t be used, as they won’t be able to flow out of a nozzle. The team had to look to alternative reinforcements, including glass fiber and carbon fiber reinforcements. 

Concrete is also a difficult material to 3D print with, due to how the material sets, said faculty team member Nicholas Meisel, Ph. D, in an interview R&D Magazine.

“In 3D printing, we need support material, which is typically a sacrificial scaffolding that is going to hold up any sort of printed overhangs in our structure, otherwise our structure ends up drooping down. The challenge with concrete is that you can’t really make that support structure in the traditional sense because you’d have to go in and chip away at all of this solidified concrete that you don’t need printed in place,” said Meisel, Emmert H. Bashore Development Professor and assistant professor of engineering design and mechanical engineering. “So we had to come up with a solution for that. Existing concrete printing systems really just avoid this problem; they print straight walls that you don’t have worry about solving those support material problems.”

Next Steps

The Penn State team is unsure if they will be able to participant in Phase 3 of NASA’s 3D-Printed Habitat Challenge —which requires teams to create a full-scale 3D printed shelter— as participating would require them to raise nearly $2 million in funding.

Either way, they plan to continue their work to develop 3D printed concrete technology.

We are interested in this technology, not just for building shelters on Mars, but for building houses on Earth,” said Duarte. “We are very interested in understanding what the architecture enabled by this technology is going to look like. We are interested in understanding the best possible shapes for a building to take advantage of this technology.”

The faculty leaders for the Penn State team also included Aleksandra Radlińska, assistant professor of civil and environmental engineering.

In addition, the team included Jamie Heilman, digital fabrication and specialized technologies coordinator in the Stuckeman School and undergraduate and graduate students in architecture and engineering. Traveling to the competition included two of the team’s engineering undergraduates, Andrew Przyjemski and Nathan Watson.

Other students from various departments who contributed to the development of the project included: Maryam Hojati, Flávio Craveiro, Negar Ashrafi, Minhyeok Ko, Jivtesh Khurana, Keunhyoung Park, Juliana Neves, Mehrzad Zahabi, Arman Nasr; as well as Randall Bock- who is an instructor in agricultural and Biological engineering.