Princeton University is deploying lasers to precisely assess the major shortcomings of 3D printed cement

Princeton University engineers are deploying lasers to accurately evaluate a major shortcoming of 3D-printed cement - the material's resistance to breakage. The researchers hope that advances in this area could lead to wider use of additive manufacturing in cement-based structures. The long-term goal is to use additive technology to develop better materials that enable innovative design and functionality.

Cement is a major component of the concrete that makes up most of modern construction, including buildings, roads, runways, Bridges and DAMS. In recent years, as the advantages of 3D printing in terms of efficiency and versatility have emerged, there has been a growing interest in the application of the technology to construction.

But compared to traditional cast concrete, 3D printed alternatives can crack, especially in areas between different layers of concrete. The researchers attribute this to the uneven microstructure introduced by the layering process used in 3D printing. Researchers at Princeton University used a new test to better understand this crack at a microscopic level. Their findings suggest that by properly characterizing fracturing characteristics, 3D-printed concrete could be as strong or even stronger than cast concrete.

In a study in the journal Cement and Concrete Composites, researchers at Princeton University demonstrate a new test method that uses lasers to cut precisely positioned grooves in 3D printed cement. By controlling the power and speed of the laser, the researchers can control key features such as the depth and shape of the grooves. This control allows for more accurate testing than traditional methods.

"We can now gain a more thorough understanding of the fracture properties of 3D-printed cement-based materials under various failure modes, which will be important for eventually scaling up this technology," said Reza Moini, assistant professor in the Department of Civil Engineering. Princeton University and the Department of Environmental Engineering, senior author of the study. "By taking advantage of the freedom in the design and manufacture of material structures that additive technology brings, stronger and tougher materials can be made."

The study's other Princeton authors, both members of Moini's lab, are Shashank Gupta and Arjun Prihar, both Ph.D. Student and former associate researcher Hadi Esmaeeli.

Unlike poured concrete, which is poured into a template and hardened, 3D-printed concrete contains a nozzle that extrudes a stick of cement slurry one at a time. The nozzles move back and forth, building the concrete strip by strip and eventually layer by layer.

"The advantage of this test for brittle 3D printed materials is that, using the same sample geometry, crack resistance under stretching, shearing, or any combination of the two can be captured," Moini said.

Shashank Gupta, first author of the paper, emphasizes that "this approach can help understand material properties as the researchers are working with industry to scale up additive manufacturing processes for concrete for both structural and non-structural applications."

Graduate students in Moini's lab are advancing these goals, studying building materials and fracture characteristics. Most recently, at the American Concrete Institute Spring Congress in San Francisco in April, co-author Arjun Prihar won third prize for the poster Award, and graduate student Krystal Delnoce won first place. Prihar's research focuses on understanding the fracture mechanics of sinusoidal structural design of concrete materials through experiments and simulations. Delnoce's research focuses on adopting a new method of fracture testing for 3D printed materials by developing a notch in the tool path.

"Our work helps to address fundamental questions about the fracture behavior of 3D-printed concrete," Moini said.

Source: Laser Network