Cornell tests underwater 3D printing of concrete with a sediment fraction for marine repairs

Additive manufacturing of concrete is now proven on land, but in the ocean conventional methods often fail due to logistics and environmental influences. A team at Cornell University is therefore working on a process that extrudes concrete layer by layer directly underwater. The goal is repairs and construction work on maritime infrastructure—for example on foundations, port facilities, or connections that carry traffic between continents. The key is to build on site without large-scale dredging or washing in prefabricated components.

“We want to be constructing without being disruptive,” said Sriramya Nair, assistant professor of civil and environmental engineering, who leads the effort. “If you have a remotely operated underwater vehicle that shows up on site with minimal disturbance to the ocean, then there is a way to build smarter and not continue the same practices that we do on the land.”

The impetus was a call for proposals from the U.S. agency DARPA in fall 2024. It called for a 3D-printable concrete that can be deposited at depths of several meters—within a tight one-year timeframe. Nair’s group brought in experience from large-format concrete printing: they work with an industrial robot weighing around 6,000 pounds and adapted the recipe to account for continuous water exposure during deposition.

“When the call for proposals came out, we said, ‘Hey, let’s just do this and see, so that we will at least understand what the challenges are,” said Nair, whose group had already been working with a roughly 6,000-pound industrial robot to 3D-print large-scale concrete structures. “And it turned out, with our mixture we could actually 3D-print underwater by making adjustments to account for continuous water exposure.”

The main technical hurdle is “washout”: cement particles can wash out as they exit the nozzle before they bind, reducing strength and interlayer adhesion. Anti-washout admixtures help, but they increase viscosity.

“When you add those chemicals, it makes your mixture really viscous, and you can’t pump. So you’re balancing that pumpability with these anti-washout agents,” Nair said. “When it extrudes, even if you don’t have washout, you still want it to be able to hold the shape and bond well with the other layers. There are multiple parameters at play.”

DARPA is also pushing for material sourced from the seafloor: the mix is meant to consist mostly of sediment and contain only a small amount of cement to reduce transport needs.

“Nobody is doing this right now,” she said. “Nobody takes seafloor sediment and prints with it. This is opening up a lot of opportunities for reimagining what concrete could look like.”

In September, the team showed demonstration prints to DARPA representatives that come close to the sediment target. In a second phase, multiple groups are expected to print an underwater arch in March; Cornell is testing regularly in a large water tank to systematically measure deposition behavior, geometry, and strength.