Researchers at University of Colorado Boulder in the US have developed a method to make cement production carbon neutral or even carbon negative by pulling CO2 out of the air with the help of microalgae.

Concrete is one of the most ubiquitous materials on the planet. One of the main ingredients, and the one causing most emissions, is cement. Cement is made of limestone that is burned at high temperatures, which releases large amounts of CO2. Global cement production accounts for 7% of annual greenhouse gas emissions.

Some species of calcareous microalgae make their own limestone through photosynthesis. The research team found that replacing quarried limestone with this biologically grown, or biogenic, limestone is a carbon neutral way to make Portland cement. Not only that, but the concrete in which this biogenic limestone is uses pulls CO2 from the atmosphere and stores it, making the material carbon negative.

According to the team, “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.”

The microalgae are not picky, able to live in both warm and cold water, salt and fresh, and all around the world. According to the team’s estimates, about 4000 to 8000 square kilometres (1 to 2 million acres) of open ponds would be required to produce all of the cement that the U.S. needs, which is between 0.05% and 0.10% of all land area in the U.S. and only 1% of the land used to grow corn. In addition, the microalgae’s lipids, proteins, sugars and carbohydrates can be used to produce biofuels, food and cosmetics, meaning these microalgae could also be a source of other, more expensive co-products, helping to offset the costs of limestone production.

Photos: University of Colorado Boulder