3-D printing of ‘greener’ buildings with local soil

The construction sector currently faces two major challenges: the demand for sustainable infrastructure and the need to repair inferior buildings, bridges and roads. While concrete is the material of choice for many construction projects, it has a large carbon footprint, resulting in high waste and energy expenditures. Today, researchers report progress toward a sustainable building material made from local soil, using a 3-D printer to create a portable structure.

The researchers will present their results today at the American Chemical Society (ACS) Fall 2020 Virtual Meeting & Expo.

“The environmental impact of the construction sector is a matter of growing concern,” said Sarbajit Banerjee, Ph.D., the project’s lead researcher. “Some researchers have become accustomed to additive manufacturing, such as building structures layer by layer, which is often done with a 3-D printer. That progress has begun to transform this sector in terms of waste reduction, but the materials used it must be sustainable in the process. “

For example, construction projects using extruded layers of concrete have highlighted the potential of additive fabrication for building structures quickly and inexpensively. However, concrete production is responsible for about 7% of carbon dioxide emissions according to the International Energy Agency, and can not be recycled.

“Historically, people built with locally sourced materials, such as Adobe, but the move to concrete has raised many environmental issues,” said Aayushi Bajpayee, a student in Banerjee’s lab at Texas A&M University. She presents the work at the meeting. “Our idea was to turn back the clock and find a way to adapt materials from our own backyards as a potential replacement for concrete.”

An advantage of using local soil in construction is that the materials do not have to be produced and transported to the construction site, thus reducing both costs and environmental damage. Banerjee and Bajpayee also say that soil supplementation could one day be used outside of Earth, to make settlements on the moon or even Mars.

Soil is typically classified by the layers of materials it contains, starting with the top organic layer where plants grow and ending at the hard bedrock of the earth’s crust. Beneath the initial organic layer lies clay, which gives the soil its plastic, shaped character that the researchers capitalized on in their project.

The researchers began collecting soil samples from a colleague’s backyard and modifying the material with a new eco-friendly additive so that it would bind together and be easily extruded through the 3-D printer. Because soils differ greatly by location, their goal was to have a “toolkit” for chemistry that could convert any type of soil into printable building materials. From there, Bajpayee built small-scale test structures, cubes measuring two inches on each side, to see how the material performed when extruded in stacked layers.

The next step was to make sure the mixture is portable, which means it will stand up to the weight of the layers, but also other materials used in construction such as rebar and insulation. To help with this, the researchers reinforced the clay mixture by “zipping” the microscopic layers on the surface to prevent it from absorbing and expanding, which compromised the print structure. Using this method, the researchers showed that the material could hold twice as much weight as the unmodified clay mixture.

Next, the team plans to improve the load-bearing capabilities of the soil to scale up their test structures and get as close to a concrete replacement as possible. In addition, they have been collecting data to see if these 3-D-print structures are as environmentally friendly as they suggest, especially in terms of carbon footprint and recycling potential. Once they have a better idea of ​​the chemistry, functionality and usability of building with local lands, they plan to further explore how this technology can be used outside our own planet.