Rowan University engineers have found a way to measure how 3D-printed concrete deforms while it is still being printed and cured, by starting with images of the finished structure and analyzing the build in reverse. The method shows how lower layers respond to the weight of fresh material, which is where a printed wall can fail before it is finished.
Digital image correlation normally tracks deformation against a reference image taken before loading, and a structure that is still being printed has no such image. Led by Islam Mantawy and Behrad Koohbor of the Henry M. Rowan College of Engineering, the team took thousands of images during printing and curing, then worked backward from the cured structure, using the concrete’s natural surface roughness as the pattern to track. They also built a mathematical approach to validate the reverse-time method and explain how the concrete deforms, shrinks, and cures, even in the first moments after a layer is laid down. The work is published in Experimental Mechanics.
“If you’re building an 8-foot-tall wall and the bottom layer starts to crack and collapse, the entire structure can fail before you reach the final layer,” said Mantawy, an assistant professor of civil and environmental engineering who heads Rowan’s Additive and Robotic Construction Laboratory. “What was supposed to be a faster, more efficient construction method becomes slower and less efficient because you have to start over from scratch.”
Temperature, humidity, and the mix’s chemistry all change how a print behaves as it cures, and the researchers say measuring those effects could help engineers spot problems earlier. Koohbor, an associate professor of mechanical engineering affiliated with Rowan’s Advanced Materials & Manufacturing Institute, said the reverse-time approach could also serve other additive manufacturing processes where conventional quality checks fall short because the part does not exist when production begins.
Mantawy sees it as a step toward printers that run themselves. “Without knowing what’s happening inside the structure, you won’t be able to achieve self-operating 3D printing,” he said. “It’s a way to have an eye on the structure as it evolves.”
Rowan engineering students Nicholas Pagliocca, Anthony Mackin, Aly Ahmed, and Jenna Migliorino contributed. The research was supported in part by a U.S. Department of Education Graduate Assistance in Areas of National Need (GAANN) grant through Rowan’s Center for Research & Education in Advanced Transportation Engineering Systems.
Source: Rowan Today
