3 minute read
A renewable source of net zero concrete?
A renewable source
of net zero concrete?
Engineers at the University of Boulder, Colorado, have come up with the use of coccolithophores, a type of single-celled microalgae to grow calcium carbonate and turn it into a limestone alternative, with which it’s possible to make concrete. According to the university, cement production currently accounts for 7% of global carbon emissions so any reduction in traditional production methods would be significant.
Glenn Asakawa/CU Boulder and Pixabay
The university’s team of engineers has developed a way to make a sustainable concrete by adding living organisms to the mix.
“This is a really exciting moment for our team,” says Wil Srubar, lead principal investigator on the project and associate professor in Civil, Environmental and Architectural Engineering and CU Boulder’s Materials Science and Engineering Programme.
“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,” he says.
Concrete is one of the most ubiquitous materials on the planet, a staple of construction around the world. It starts as a mixture of water and portland cement, which forms a paste to which materials such as sand, gravel or crushed stone are added. The paste binds the aggregates together, and the mixture hardens into concrete.
Net carbon neutral way to make cement
In 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. In short, the carbon dioxide released into the atmosphere equals what the microalgae already captured.
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.
Prof Wil V Srubar, University of Boulder, Colorado
If all cement-based construction around the world was replaced with biogenic limestone cement, each year, a significant 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.
This could theoretically happen overnight, as biogenic limestone can “plug and play” with modern cement production processes, says Srubar.
“We see a world in which using concrete as we know it is a mechanism to heal the planet. We have the tools and the technology to do this today.”
The method is not only carbon neutral, but could even prove carbon negative because the material is able to sequester carbon and store it within the concrete. With only sunlight, seawater and dissolved carbon dioxide, the tiny organisms produce the largest amounts of new calcium carbonate on the planet and at a faster pace than coral reefs. coccolithophore blooms in the world’s oceans are so big, they can be seen from space.
“On the surface, they create these very intricate, beautiful calcium carbonate shells. It's basically an armor of limestone that surrounds the cells,” Srubar explains.
Students working in the Living Materials Laboratory, which uses calcifying microalgae to produce limestone and create a carbon neutral cement, as well as cement products which can slowly pull carbon dioxide out of the atmosphere and store it. The beauty of this process is that it is totally renewable and does not involve the extraction of non-renewable minerals from the ground. It’s currently unclear how costeffective the method would be compared to traditional cement production, so the road is still potentially long. Given however the skill and tenacity of some local cementitious materials manufacturers, it would be gratifying to see South African researchers becoming involved in this new opportunity also.
(https://www.weforum.org/videos/ carbon-neutral-cement-made-from-algaein-world-first),
