Researchers Create Concrete from Local Soil

Scientists want to replace concrete with a more environment friendly material, and one candidate is soil. In one of the most recent iterations of these efforts, the Banerjee Research Laboratory at Texas A&M University has created a tool kit for using local soil to make construction materials. The modern form of concrete, a mixture of sand and gravel bonded by cement and water, has been used for only the past 150 years or so. The development of modern concrete reinforced with steel allowed builders to erect massive structures, giving us city skylines dominated by skyscrapers. With the growth of additive manufacturing, a process in which layers of concrete are 3D printed one on top of the other in a predetermined design, more complex building parts can be created more efficiently. Banerjee and Aayushi Bajpayee, a Ph.D. candidate in Banerjee’s lab, wanted to develop a sustainable material that could work with existing building codes and concrete-based construction methods. For their source material, the team settled on soil. That idea came from both nature and history. In nature, termites make impressive use of soil, building intricate and durable mounds. “That was one of our motivations, and the second one was ancient times,” said Bajpayee. “In ancient Rome and India, there are a lot of places [where people used] soil.” The difference between ancient earthen structures and a soil-based concrete alternative is that in ancient times, the main instinct for such construction was survival, said Bajpayee. “Now, our main instinct is sustainability.” Banerjee and Bajpayee used clay soil from a colleague’s backyard in College Station, Texas. They combined the clay, a water-repelling additive derived from beets, and sodium silicate to bind everything together. A 3D printer then extruded this material according to the desired design, forming a model a few inches tall. They hope that their method, presented at the 2020 ACS meeting and published in Frontiers in Materials, can serve as a chemical tool kit to be used at any construction site, particularly in remote or hostile environments. Once a construction team analyzes the local soil, they can tweak the ingredients in the tool kit, mix their material, and start printing. By cutting out the energy-intensive production steps, using local resources, and eliminating transport concerns, Banerjee predicts their material will have a much lower emissions profile than concrete, but they’re still running simulations to nail down the figures. “I think the numbers are going to be significant,” he said. But soil-based replacements have limited applications. Although they could prove valuable for building housing in remote areas, on the basis of the current work, Sant doesn’t think these materials are viable for larger structures.