University of Colorado Boulder researchers found that a seaweed-based ingredient used in foods like ice cream could make natural earthen materials such as clay and sand easier to 3D-print into durable structures. The discovery could help turn construction waste into lower-impact building materials.
The research was led by scientists at CU Boulder, with researchers from Columbia University also contributing.
The team studied biopolymers, which are large biological molecules that can act like glue. In nature, termites, wasps, and honeycomb worms use biopolymers to bind materials such as soil and clay into strong structures without relying on cement.
Inspired by these natural systems, the researchers tested five biopolymers to understand which could help bind earthen materials and make them suitable for 3D printing.
The tested materials included guar gum, locust bean gum, cassia gum, sodium alginate, and xanthan gum. Guar gum, locust bean gum, and cassia gum are derived from legumes and are commonly used in foods such as salad dressings to keep ingredients from separating.
The researchers found that locust bean gum could bind soil particles into a stronger network. But that same strength made the material harder to push through a 3D-printer nozzle.
Sodium alginate, which is derived from seaweed and is often used in ice cream and popping boba, produced a different effect. Rather than acting like glue, the polymer changed the electrical charges on clay particles and caused them to repel each other.
This allowed clay and sand particles to remain suspended in a stable mixture while still flowing smoothly through a 3D printer.
The team then searched for the best formulation. By adding just 0.12% sodium alginate to natural earth excavated from a granite quarry near Golden, Colorado, the researchers produced a material that was both stronger and easier to print.
The resulting material could withstand 25% more pressure than earth without the biopolymer and could be printed 33% faster.
Using the formula, the team printed an 8-millimeter-thick wall that leaned outward at dramatic angles. The structure remained stable even when tilted to 60 degrees, which is far steeper than the Leaning Tower of Pisa.
While the current study primarily focuses on improving printability, the researchers said the same framework could be used to test other biopolymers for additional properties such as strength and durability.
The findings could also support more sustainable construction practices. Construction projects often generate large amounts of excavated soil from foundations, basements, and parking structures, and much of that material ends up in landfills.
By reusing waste earth material onsite, builders could reduce the environmental footprint of construction while taking advantage of widely available local materials.
KEY QUOTES:
“From termite mounds to adobe buildings, humans and animals have been building with earth since the dawn of time. But there hasn’t been a lot of science to how earthen builders design the materials. So, we wanted to use scientific knowledge and tools to understand it.”
Wil Srubar, Professor in the Department of Civil, Environmental and Architectural Engineering at CU Boulder
“There are some good indoor environmental benefits of having earth in a building. It can regulate indoor moisture and uptake air pollutants. It can also serve as a thermal insulator, keeping things cool in the summer and warm in the winter.”
“Our study suggests that there are ways to reuse waste earth material onsite, and that could largely reduce the environmental footprint of construction.”
Samuel Armistead, Research Associate in the Department of Civil, Environmental and Architectural Engineering at CU Boulder
“Clay and sand are among the most abundant building materials on Earth. The science and engineering we’re developing can be applied almost anywhere in the world.”
Wil Srubar, Professor in the Department of Civil, Environmental and Architectural Engineering at CU Boulder
