Researchers at Oregon State University have developed a quick-setting, environmentally friendly alternative to concrete they hope can one day be used to rapidly 3-D print homes and infrastructure.
Also known as additive manufacturing, 3-D printing is already being used to help solve construction challenges such as the global housing crisis that's emerged as the Earth's population approaches 8.5 billion.
But cement, the binding agent in concrete, accounts for about 8% of the planet's carbon dioxide emissions, and concrete's curing time - which can be multiple days - and required structural supports can inhibit progress on construction projects.
The new clay-based material developed by Devin Roach, Nicolas Gonsalves and collaborators at Oregon State cures as it's being extruded from the printer, thanks to its acrylamide-based binding agent, which undergoes a chemical reaction known as frontal polymerization. The material can even be printed across unsupported gaps, such as the top edge of an opening for a door or window.
"The printed material has a buildable strength of 3 megapascals immediately after printing, enabling the construction of multilayer walls and freestanding overhangs like roofs," said Roach, assistant professor of mechanical engineering in the OSU College of Engineering. "It surpasses 17 megapascals, the strength required of residential structural concrete, in just three days, compared to as long as 28 days for traditional cement-based concrete."
And because the new material consists largely of soil infused with hemp fibers, sand and biochar - carbon-rich matter made by heating wood chips and other organic biomass under low oxygen - its environmental footprint is much smaller than that of concrete. Concrete's binder, cement, is produced from carbon-releasing reactions in industrial kilns heated to more than 1,400 degrees Celsius, typically via energy produced by the burning of fossil fuels.
"I'm incredibly proud of our innovative, transdisciplinary team for coming up with a material that can make a difference in people's lives in multiple ways," Roach said. "Especially with the frequency of destructive natural disasters, we need to be able to get shelter and other structures built quickly - and we can do that with a material that's readily available and is associated with comparatively little emissions."
Gonsalves, a doctoral student, led the research, which also included Ashlei Morgan, Heidi Thiele, Andre Olarra and Adam Bischoff of the School of Mechanical, Industrial and Manufacturing Engineering; Pavan Akula of the School of Civil and Construction Engineering; Islam Hafez of the College of Forestry; and Yakun Zhang of the College of Agricultural Sciences.
Supporting the study, which was published in Advanced Composites and Hybrid Materials, were the U.S. Department of Agriculture, OSU's Global Hemp Innovation Center, and the College of Engineering.
"Currently, our material costs more than standard cement-based concrete, so we need to bring the price down," Roach said. "Before it can be used we also need to follow American Society for Testing and Materials standard tests and prepare a report that professional engineers can review and approve if it is proposed to be included in construction projects."
