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By John Biggs
March 18, 2019
Nature is a common source of inspiration for builders and architects. They often turn to natural elements to incorporate them into their designs borrowing from their perfect symmetry, impeccable forms and strength developed over millions of years of evolution.
A Purdue University research team has developed the first-ever bioinspired 3D-printable cement paste that actually increases in strength as more pressure is applied to it, utilizing a technique that recreates the toughening mechanisms found in the shells of arthropods like lobsters or beetles. It is the team’s hope that their method could eventually be used to build structures more capable of withstanding natural disasters.
In nature, toughness is developed out of necessity. Arthropod shells are able to withstand a great deal of force because of the way pressure spreads across its surface. As they crack, twisted patterns spread across the material in a way that allows the layers to reorient themselves and strengthen, rather than fail structurally. Using a similar method, the researchers are studying how damage spreads through layers of 3D printed material and trying to replicate the natural resiliency of arthropod shells in their designs.
"Nature has to deal with weaknesses to survive, so we are using the 'built-in' weaknesses of cement-based materials to increase their toughness," said Jan Olek, a professor in Purdue's Lyles School of Civil Engineering.
For this, the team drew inspiration from another arthropod, the mantis shrimp, whose “dactyl club” appendage uses energy-dissipating twisting cracks to become stronger upon impact with its prey.
According to the university, using 3D-printed materials like cement paste, mortar and concrete would not only lead to stronger structures, it would also “give engineers more control over design and performance.”
"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," said Mohamadreza "Reza" Moini, a Purdue Ph.D. candidate of civil engineering.
Using micro-CT scans, the researchers have studied the behavior of hardened 3D printed concrete, specifically, what weaknesses are naturally built into the structure between the applied layers of paste. Taking note of those weak points, like pore clusters found between printed layers, the team can develop their unique printing forms, called “architectures,” to exploit those weaknesses, allowing the concrete to react to the pressure and better resist it.
Different architectures each provide a unique characteristic for a hardened 3D printed concrete element. For example, the team’s “Bouligand” architecture makes a material more crack resistant, while their “compliant” architecture gives cement elements, not traditionally known for their malleability, the ability to flex like a spring. Another, the “honeycomb” architecture, mimics one of the strongest forms in nature, enabling absorbed force to spread evenly to its corners.
The team is exploring other ways to incorporate their various architectures into cement-based elements that would make buildings more resilient. It would be especially useful in areas prone to earthquakes, wildfires and hurricanes. The enhanced design flexibility cement paste 3D printing allows frees the research team from the confines of traditional casting methods and makes the new designs and material behaviors possible.
"3D printing has removed the need for creating a mold for each type of design, so that we can achieve these unique properties of cement-based materials that were not possible before," said Jeffrey Youngblood, Purdue professor of materials engineering.
building materials technology
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