PhD student Fabian Rodriguez monitors the progress of the latest 3D printing.

3D-printed concrete is speeding up the construction industry

Purdue researchers are utilizing 3D concrete printing to potentially improve the stability of structures, reduce their construction time and overall cost and to enable new functionalities.

Pablo Zavattieri, the Jerry M. and Lynda T. Engelhardt Professor in Civil Engineering, is involved in a pair of research teams that are studying new uses for 3D printing that could have a wide impact in materials, architectural and structural engineering. One team is researching reinforced concrete structures and another is researching how new, architected materials can mimic modern shape-memory alloy.

“With 3D concrete printing, research conducted over the last few years has taken giant leaps into a new era of building homes and other civil structures,” Zavattieri said. “This emerging technology allows for the creation of more complex structures and has shown to be both more costeffective and faster to build.”

The Purdue concrete 3D printing research team, led by Jan Olek, the James H. and Carol H. Cure Professor in Civil Engineering; Jeffrey Youngblood, professor of materials engineering; Zavattieri; and PhD students Fabian Rodriguez, Reza Moini and Yu Wang; has partnered with the Lyles School of Civil Engineering’s Robert L. and Terry L. Bowen Laboratory for large-scale civil engineering research. At Bowen Lab, the research team, in collaboration with Amit Varma, the Karl H. Kettelhut Professor of Civil Engineering; Christopher Williams, assistant professor of civil engineering; and graduate student Shubham Agrawal; has been producing prototypes of reinforced 3D-printed structural elements and comparing the mechanical performance with conventional cast concrete.

“We started working in small-scale 3D printing of cement and mortar and have spent the past few years understanding the materials used and developing the process to make it more efficient,” Rodriguez said. “We are now ready to apply what we have learned, into a largescale process that, we hope, will make a giant impact on structural engineering.”

Zavattieri said that the 3D printing of cement-based materials is being intensively explored as a time and costeffective alternative to conventional cast concrete in the construction industry. Its development relies on the successful integration of structural engineering, material design, the extrusion system, testing procedures and, more recently, the use of techniques to incorporate reinforcing components as an important step to develop viable alternatives for large-scale construction with the aim to satisfy the performance requirements of conventional methods.

The research team has created cement-based mixtures to be used in 3D printing systems at different size scales using controlled architectures that significantly influence the performance of the material. Simultaneously, the team has developed a reinforcing alternative that allows an enhanced mechanical response of 3D-printed cement-based materials by using a 3D-printed steel plate to promote composite action between the reinforcement and cementitious matrix.

“We are looking to produce larger elements with a size-scale closer to structural applications to replicate what the team has learned so far at the prototype scale and demonstrate the advantages not only from a mechanical point of view but also from the efficiency and economy of the use of this technology,” Zavattieri said.

Architected materials can mimic shape-memory alloy

In the realm of architected materials, Zavattieri’s team is researching shape-memory alloy that could potentially be used in a wide variety of fields, including civil engineering materials and structures.

What, exactly, is shape-memory alloy? As the name suggests, shape-memory alloy (SMA) is a material that can be deformed and returned to its original shape when heat is applied. Stents that are inserted and then expanded in arteries are made of shape-memory alloy.

Shape-memory alloy is made from nitinol — a mix of nickel and titanium — and is both expensive to buy and produce. Zavattieri’s research into 3D materials with nitinol’s properties, however, could lead to a dramatic reduction in cost for both producers and consumers, and even enable new properties and applications that were not possible before with nitinol.

“Currently, shape-memory alloy is very expensive and would make using it for any large-scale project almost impossible through cost alone,” Zavattieri said. “So, what we are doing is playing with the geometry of 3D-printed materials to mimic the behavior. With this we can use these materials for larger projects such as adding them to buildings and bridges to make them more earthquake resistant.”

Additionally, these architected materials can be made from a wide variety of polymers, made by many different low-cost production processes as well as 3D printing, and are designed to respond to various stimuli such as heat, magnetic fields and solvent absorption. These architected materials offer a lower-cost alternative that can expand the design space for SMA-like material behavior to include larger-scale (e.g., self-compacting dunnage) or lower-cost applications (e.g., medical implants).

Postdoctoral researcher Yunlan Zhang said that the applications for the research are as flexible as the material itself.

“This is truly cutting-edge research being done,” Zhang said. “We’re already exploring its effectiveness in protective equipment for both land-based vehicles and in aerospace vehicles.”

Civil engineering PhD student Kristiaan Hector echoed Zhang, adding their work is surely just the beginning and will lead to even greater leaps in the near future.

“With the structure of these materials, energy can be absorbed and dissipated in a way that it can protect a person or object without sacrificing itself,” Hector said. “Research into this has only really just begun, but — in a few years — you’ll probably see this cause a major shift in architectural and structural applications.”