Taking inspiration from nature, researchers from Princeton Engineering have improved crack resistance in concrete components by coupling architected designs with additive manufacturing processes and industrial robots that may precisely control materials deposition.
In an article published Aug. 29 within the journal Nature Communications, researchers led by Reza Moini, an assistant professor of civil and environmental engineering at Princeton, describe how their designs increased resistance to cracking by as much as 63% compared to traditional forged concrete.
The researchers were inspired by the double-helical structures that make up the scales of an ancient fish lineage called coelacanths. Moini said that nature often uses clever architecture to mutually increase material properties corresponding to strength and fracture resistance.
To generate these mechanical properties, the researchers proposed a design that arranges concrete into individual strands in three dimensions. The design uses robotic additive manufacturing to weakly connect each strand to its neighbor. The researchers used different design schemes to mix many stacks of strands into larger functional shapes, corresponding to beams. The design schemes depend on barely changing the orientation of every stack to create a double-helical arrangement (two orthogonal layers twisted across the peak) within the beams that is vital to improving the fabric’s resistance to crack propagation.
The paper refers back to the underlying resistance in crack propagation as a ‘toughening mechanism.’ The technique, detailed within the journal article, relies on a mix of mechanisms that may either shield cracks from propagating, interlock the fractured surfaces, or deflect cracks from a straight path once they’re formed, Moini said.
Shashank Gupta, a graduate student at Princeton and co-author of the work, said that creating architected concrete material with the mandatory high geometric fidelity at scale in constructing components corresponding to beams and columns sometimes requires the usage of robots. It is because it currently could be very difficult to create purposeful internal arrangements of materials for structural applications without the automation and precision of robotic fabrication. Additive manufacturing, during which a robot adds material strand-by-strand to create structures, allows designers to explore complex architectures that will not be possible with conventional casting methods. In Moini’s lab, researchers use large, industrial robots integrated with advanced real-time processing of materials which might be capable of making full-sized structural components which might be also aesthetically pleasing.
As a part of the work, the researchers also developed a customized solution to handle the tendency of fresh concrete to deform under its weight. When a robot deposits concrete to form a structure, the burden of the upper layers may cause the concrete below to deform, compromising the geometric precision of the resulting architected structure. To deal with this, the researchers aimed to higher control the concrete’s rate of hardening to forestall distortion during fabrication. They used a sophisticated, two-component extrusion system implemented on the robot’s nozzle within the lab, said Gupta, who led the extrusion efforts of the study. The specialized robotic system has two inlets: one inlet for concrete and one other for a chemical accelerator. These materials are mixed inside the nozzle just before extrusion, allowing the accelerator to expedite the concrete curing process while ensuring precise control over the structure and minimizing deformation. By precisely calibrating the quantity of accelerator, the researchers gained higher control over the structure and minimized deformation within the lower levels.
