Next to water, concrete is the most widely used substance on earth in the civil construction industry.. The concrete material is the base foundation of modern development, fortifying buildings and structures. But owing to their large-scale use, the production of concrete results in substantial emission of greenhouse gasses and places strain on the availability of natural resources. The concrete manufacturing process accounts for about 5% CO2 (carbon dioxide) released into the atmosphere. In response to growing environmental and economic forces, regulatories, engineers, developers and owners are seeking efficient, innovative concrete solutions that conserve non-renewable resources. Global demands for regulating concrete production waste arise from the growth of these environmental and economic issues.
Various efforts have been conducted by researchers to arrive at some alternatives that can significantly reduce the high energy consumed and environmental impacts during the fabrication process of concrete. Cement plants have also started testing carbon capture technologies and electric kilns to slash emissions. But carbon capture is expensive, and scaling the technology to meet the demand of the cement and concrete industry is no easy feat. Algae have been used as an alternative biofuel for heating cement kilns, and algae cultivation systems have also been linked with cement production to capture carbon. Algae naturally use sunlight, water, and dissolved carbon dioxide to produce the largest amounts of new calcium carbonate, the primary material in limestone.
The team at the University of Colorado Boulder and their colleagues at the Algal Resources Collection at the University of North Carolina Wilmington (UNCW) and the National Renewable Energy Laboratory (NREL) are figuring out ways to use all-natural microalgae to solve concrete’s biggest emissions problem – cement. They have been rewarded for their innovative work with a $3.2 million grant from the U.S. Department of Energy’s (DOE) Advanced Research Projects Agency-Energy (ARPA-E). The research team was recently selected by the HESTIA program (Harnessing Emissions into Structures
“This is a really exciting moment for our team,” says Wil Srubar, lead principal investigator on the project and an associate professor at the University of Colorado and the lead researcher of the project. “For the industry, now is the time to solve this very challenging problem. We believe that we have one of the best solutions, if not the best solution, for the cement and concrete industry to address its carbon problem,” he further says.
The concept of growing limestone came to Srubar while snorkeling in Thailand in 2017. He saw the calcium carbonate, the main component of limestone, grown naturally in the ocean.
To make Portland cement, the most common type of cement, limestone is extracted from large quarries and burned at high temperatures, releasing large amounts of carbon dioxide. The research team found that replacing quarried limestone with biologically grown limestone, a natural process that some species of calcareous microalgae complete through photosynthesis (just like growing coral reefs), creates a net carbon-neutral way to make portland cement.
Ground limestone is also often used as a filler material in Portland cement, typically replacing 15% of the mixture. By using biogenic limestone instead of quarried limestone as the filler, Portland cement could become not only net neutral but also carbon negative by pulling carbon dioxide out of the atmosphere and storing it permanently in concrete.
‘If all cement-based construction around the world was replaced with biogenic limestone cement, each year, a whopping 2 gigatons of carbon dioxide would no longer be pumped into the atmosphere and more than 250 million additional tons of carbon dioxide would be pulled out of the atmosphere and stored in these materials,’ said Srubar.
The researchers are also working on algae growth optimization and the startup Minus Materials, born from the research, has already made small quantities of the material available with plans to expand. Minus Materials previously won the university-wide Lab Venture Challenge pitch competition and secured $125,000 in seed funding for the enterprise.
“We see a world in which using concrete as we know it is a mechanism to heal the planet,” Srubar says. The team hopes that replacing quarried limestone with a homegrown version can also improve air quality, reduce environmental damage and increase equitable access to building materials around the world.