Editorial Feature

What is Algae-Grown Limestone?

A new research project led by Colorado University (CU) Boulder engineers has developed a carbon neutral – and potentially even carbon negative – cement production method that uses microalgae to capture and sequester carbon dioxide from the atmosphere.

cement, limestone, carbon dioxide, carbon, limestone, concrete, biogenic

Image Credit: MZinchenko/Shutterstock.com

The CU Boulder team is working with scientists at the Algal Resources Collection, located at the University of North Carolina Wilmington, as well as National Renewable Energy Laboratory (NREL) to develop a biogenic limestone-based Portland cement.

The United States Department of Energy (DoE) recently rewarded the group with an Advanced Research Projects – Energy (ARPA–E) grant of $3.2 million for its work.

The Harnessing Emissions Into Structures Taking Inputs from the Atmosphere (HESTIA) program also recently selected the team to scale up their algae cement to help tackle the significant environmental impact of the construction industry.

Tackling the Cement Problem

Currently, the manufacture of cement is singularly responsible for 8% of the world’s greenhouse gas emissions. But the research team sees this as an opportunity.

Will Srubar, who is the project’s lead principal investigator as well as fulfilling duties as associate professor in CU Boulder’s Materials Science and Engineering program, said:

“This is a really exciting moment for our team. For the industry, now is the time to solve this very wicked 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.”

Concrete is among the most commonly manufactured materials on Earth. It is a construction industry staple in every part of the world.

To make concrete, cement is required. It is mixed with water and possibly also aggregate materials like sand, gravel, or stone, binding them together before hardening the entire mixture as it sets into concrete.

The most common type of cement used around the world is Portland cement. Portland cement is made out of limestone, which must be quarried in large quantities and then burned at very high temperatures.

Extracting limestone from large quarries with all of the infrastructures that must accompany them is environmentally costly – in terms of land use changes, material use and wastage, and energy requirements.

The process of burning limestone to make cement also releases large quantities of carbon dioxide into the atmosphere.

Biologically Grown Limestone

The team is discovering that taking quarried limestone out of the equation for construction projects and replacing it with a carbon-negative alternative can significantly reduce the project’s environmental impact.

The team is developing biologically grown limestone, which exploits a natural phenomenon whereby calcareous microalgae calcify the limestone through photosynthesis. This is the same photosynthesis method that coral reefs use to grow into hard, durable structures.

The same amount of carbon dioxide is pulled out of the atmosphere with this method as is released back into the atmosphere, researchers said, so the limestone cement it creates is net neutral.

But the biogenic limestone could also be used as a filler material for cement, replacing quarried limestone. This would make the resulting concrete carbon negative, as carbon dioxide pulled down or captured from the air would be relatively permanently stored or sequestered in concrete.

The Potential Impact

The team estimated that their biogenic limestone cement product could save two gigatons of carbon dioxide emissions in a year if it replaced the cement used in all cement-based production around the world.

In addition to this, over 250 million tons of air borne carbon dioxide would be captured and sequestered from the atmosphere.

The group has ensured the biogenic limestone product is compatible with all common cement production practices today, and that it could be immediately scaled up and deployed to replace any cement manufacturing process in the world.

“We see a world in which using concrete as we know it is a mechanism to heal the planet,” said Srubar. “We have the tools and the technology to do this today.”

Cultivating Carbon Capture Coccolithophores

While snorkeling in Thailand in 2017, Srubar noticed how nature grows hard, durable calcium carbonate based structures in coral reefs – which are predominately made up of limestone – and got the idea for the team’s biogenic cement product.

Working with his team at CU Boulder’s Living Materials Laboratory, Srubar then began cultivating a cloudy white microalgae called coccolithophore.

Coccolithophores capture carbon dioxide and sequester it in hard, mineral form through photosynthesis, removing it from the atmosphere and storing it safely away.

The microalgae produce the newest calcium carbonate matter on the planet, much faster than any coral reefs. And they only use sunlight, seawater, and carbon dioxide dissolved in the sea to do it.

The coccolithophores can live in most conditions on the planet: in hot and cold temperatures, in salt and fresh waters, in cities, on land, and at sea.

The team estimated that up to 2 million acres of open ponds filled with them could produce all of the United States’s annual cement requirements. This is just 0.1% of the country’s entire land area.

The researchers are seeking out ways to commercialize the technology now.

More from AZoBuild: How Can Moss Contribute to Urban Greening?

References and Further Reading

Hempstead, M. (2022). Algae-Grown Limestone Could Be the Key to ‘Carbon Negative’ Cement Production. [Online] Springwise. Available at: https://www.springwise.com/innovation/property-construction/algae-grown-limestone-for-cement (Accessed on 11 July 2022).

Heveran, C.M., et al. (2020). Biomineralization and Successive Regeneration of Engineered Living Building Materials. Matter. doi.org/10.1016/j.matt.2019.11.016.

Simpkins, K. (2022). Cities of the future may be built with algae-grown limestone. [Online] CU Boulder. Available at: https://www.colorado.edu/today/2022/06/23/cities-future-may-be-built-algae-grown-limestone 

Shin, B., et al. (2020) Mitochondrial Oxidative Phosphorylation Regulates the Fate Decision between Pathogenic Th17 and Regulatory T Cells. Cell Reports. doi.org/10.1016/j.celrep.2020.01.022.

Websites should be referenced as below:

Pesheva, E. (2020). Tackling Coronavirus. [Online] Harvard Medical School. Available at: https://hms.harvard.edu/news/tackling-coronavirus 

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Ben Pilkington

Written by

Ben Pilkington

Ben Pilkington is a freelance writer who is interested in society and technology. He enjoys learning how the latest scientific developments can affect us and imagining what will be possible in the future. Since completing graduate studies at Oxford University in 2016, Ben has reported on developments in computer software, the UK technology industry, digital rights and privacy, industrial automation, IoT, AI, additive manufacturing, sustainability, and clean technology.

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