Additive manufacturing, precise robotics, and architected design significantly enhance the crack resistance of concrete.
Drawing inspiration from nature, a team of researchers from Princeton Engineering has successfully boosted the crack resistance of concrete components through a combination of architected designs and cutting-edge additive manufacturing techniques, utilizing industrial robots that accurately manage material deposition.
In a study published on August 29 in the journal Nature Communications, the research led by Reza Moini, an assistant professor in civil and environmental engineering at Princeton, reveals that their innovative designs have enhanced crack resistance by up to 63% when compared to traditional cast concrete.
The researchers took cues from the double-helical structures found in the scales of a lineage of ancient fish known as coelacanths. Moini emphasized that nature often employs intelligent architectures to simultaneously improve material properties, including strength and resistance to fractures.
To establish these mechanical advantages, the researchers proposed a structure that organizes concrete into separate strands in a three-dimensional layout. This design employs robotic additive manufacturing to create loose connections between adjacent strands. Researchers experimented with various design configurations to assemble multiple stacks of strands into larger functional shapes like beams. These configurations involve slightly adjusting the orientation of each stack, creating a double-helical structure (two orthogonal layers twisted vertically) in the beams that is crucial for enhancing the material’s ability to resist crack propagation.
The article discusses the inherent resistance to crack propagation as a ‘toughening mechanism.’ The method outlined in the journal relies on a blend of processes that can either block cracks from spreading, interlock broken surfaces, or redirect cracks from their direct paths after they form, as explained by Moini.
Shashank Gupta, a graduate student at Princeton and co-author of the study, pointed out that producing architected concrete with the necessary high precision at scale—especially in components like beams and columns—often necessitates robotic assistance. This is because it is currently quite difficult to achieve intentional internal configurations of materials for structural purposes without the automation and accuracy that robotic fabrication provides. Additive manufacturing, where a robot applies materials strand-by-strand to build structures, enables designers to investigate complex architectures that traditional casting methods cannot achieve. In Moini’s lab, researchers utilize large industrial robots equipped with advanced real-time material processing capabilities to create full-sized structural components that also possess aesthetic appeal.
Furthermore, the team devised a tailored solution to tackle the issue of fresh concrete deforming under its own weight. When a robot lays down concrete to form a structure, the weight from the layers above can distort the concrete below, affecting the geometric accuracy of the finished architected form. To combat this, the researchers focused on regulating the rate of hardening of the concrete to prevent distortion during the fabrication process. They implemented a sophisticated, two-component extrusion system directly at the robot’s nozzle in their lab. Gupta, who led the extrusion segment of the study, described the specialized robotic setup that features two inlets: one for concrete and another for a chemical accelerator. These materials are combined within the nozzle just before extrusion, allowing the accelerator to speed up the concrete curing process while ensuring precise control over the structure and minimizing distortions. By accurately adjusting the accelerator’s quantity, the researchers achieved enhanced control over the structure and reduced deformation in the lower levels.
