Typically cracks or fissures in concrete are a sure sign that a structure is compromised or weakened. A team of researchers from Purdue University, however, are turning that idea on its head with the development of 3D printed cement structures that are actually made stronger by the material’s inherent weaknesses, especially during moments of extreme stress, like in a wildfire or earthquake.
The innovative project was inspired by nature and specifically arthropods (like lobsters and beetles), whose shells become stronger when pressure is applied. Using a bio-inspired approach, the team has managed to 3D print a cement paste that effectively becomes tougher when it is under pressure. The ultimate aim with the project is to advance it to the point where it can be used to make structures that can withstand natural disasters.
Jan Olek, a professor at Purdue’s Lyles School of Engineering, said of the work: ”Nature has to deal with weaknesses to survive, so we are using the ‘built-in’ weaknesses of cement-based materials to increase their toughness.”
More specifically, the researchers have studied arthropod shells and their crack propagation properties closely and have devised a technique wherein they can control how damage spreads through a cement paste structure between the printed layers. More specifically, the team was inspired by the mantis shrimp, a creature which subdues 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 project marks the first time researchers have 3D printed a bio-inspired structure using cement paste, and the implications of the achievement could be big. As the Purdue team explains, being able to 3D print cement-based materials like cement paste without the challenges previously brought about by inherent cracking and weaknesses, could open the doors for better structure designs and performance.
“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,” explained Jeffrey Youngblood, Purdue professor of materials engineering.
In studying the behaviour of the 3D printed cement structures, the team has relied on micro-CT scanning. The scanning has enabled the team to gain insight into the pore regions at the interfaces of printed layers, which encourage cracking. “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,” added Mohamadreza “Reza” Moini, a Purdue Ph.D. candidate of civil engineering.
So far, the researchers have explored various bioinspired design architectures, including “honeycomb,” “compliant,” and “Bouligand.” Each type of architecture showcased different behaviours once the 3D printed part had hardened. A structure printed with the Bouligand design, for instance, has good crack-resistance properties, while a compliant architecture gives the cement part a spring-like quality.