Lyles School researchers develop cement paste as strong as arthropod shells

Taking a page from nature, Purdue Civil Engineering researchers have created materials that get stronger when they crack.

A team led by Lyles School professors has developed a new technique for 3D-printing cement. Pablo Zavattieri, professor of civil engineering; Jan Olek, the James H. and Carol H. Cure Professor of Civil Engineering; and Jeffrey Youngblood, professor of materials engineering, have developed a material that gets tougher under pressure — much like the shells of arthropods such as lobsters and beetles. The technique eventually could contribute to more resilient structures during natural disasters.

"We are looking at how nature deals with interfaces and weak spots. The material in arthropod shells is very robust; it does not shatter like cement," Zavattieri explains.

How exoskeletons work

Arthropod exoskeletons have crack-propagation and toughening mechanisms that the team reproduces in 3D-printed cement. By incorporating designs from nature, the 3D-printed materials will give engineers more control over design and performance.

The team was inspired initially by the mantis shrimp, which conquers its prey with a "dactyl club" appendage that grows tougher on impact through twisting cracks that dissipate energy and prevent the club from falling apart.

The team uses micro-CT scans to understand the behavior of hardened 3D-printed, cement-based materials and therefore leverage their "weak" characteristics, such as pore regions found at the interfaces between the printed layers, which promote cracking. "We are studying the spatial arrangement of these interfaces to determine how these arrangements will influence crack propagation under load," says Olek. These findings were presented recently at the First RILEM International Conference on Concrete and Digital Fabrication in Zurich, Switzerland, and were published in the prestigious journal Advanced Materials.

The team's work was funded through a National Science Foundation grant. The acquisition of an X-ray microscope was supported by the 2017 Major Multi-User Equipment Program, offered by Purdue's Office of the Executive Vice President for Research and Partnerships.

PhD candidate Mohamadreza "Reza" Moini demonstrates the latest 3D-printed model, created in Hampton Hall.

Future of 3D-printed cement

"3D printing cement-based materials provides control over their structure, which can lead to the creation of more damage- and flaw-tolerant structural elements like beams or columns," says Mohamadreza "Reza" Moini, a PhD candidate in civil engineering and a member of the research team.

"The main applications for this, for now, are in structural research," Moini says. "We're still studying its characteristics and behaviors, but we see a lot of potential."

Zavattieri says, "There is still much to study, but what we have already been able to create and replicate has us very excited for the future. We hope to take what we have learned and expand it to many other  applications." In particular, the team plans to explore ways that cement-based elements could be designed for building more resilient structures.

The research project is funded through spring of 2020. Additional publications are expected to be released by the end of this year.