Algae-grown limestone could be the key to ‘carbon negative’ cement production

Limestone, the key ingredient in portland cement, could be created using a process similar to coral reef formation

Spotted: Look around yourself in any city and you will almost certainly see buildings made using Portland cement. It is one of the world’s most common building materials but one of the most environmentally damaging.

Cement has such a negative impact because its production involves heating limestone to extremely high temperatures. And today, the limestone used in cement is quarried from the earth, which means that the heating process releases carbon dioxide into the atmosphere that would otherwise be locked away underground.

But what if there was another way to produce limestone?

This was the key question addressed by a research team at the University of Colorado Boulder. Wil Srubar, lead principal investigator on the project, was inspired by coral reefs – durable, long-lasting structures made from calcium carbonate, a main component of limestone. “If nature can grow limestone, why can’t we?” he asked, and it was this key insight that led to the creation of a new cement that is ‘grown’ using the power of microalgae – tiny plant-like microorganisms.

To make their algae-grown cement, the researchers selected a species of white algae called Coccolithophores. These microscopic creatures capture carbon dioxide from the air through photosynthesis and convert it into calcium carbonate, which can be used in place of quarried limestone.

The reason why an algae-derived ‘biogenic’ limestone could be a game-changer is because heating it only releases carbon dioxide that was previously extracted from the atmosphere during the algae’s lifetime. The net effect on the total amount of carbon dioxide in the atmosphere is therefore neutral. This stands in contrast to the production of cement from quarried limestone, which releases carbon that had previously been in the ground for millions of years.

But the story doesn’t end here. Ground limestone is often used as a filler material in portland cement. In other words, a proportion of the cement mixture – typically around 15 per cent – is not cement at all but ‘raw’ limestone. If the quarried limestone filler was replaced with the researchers’ biogenic limestone, the cement mixture as a whole could even be considered ‘carbon negative’. This means that its production would actually result in a net reduction in carbon dioxide in the atmosphere.

So could microscopic creatures transform the building industry? The research is certainly promising if it can be commercialised.

Cement production is an important area of innovation. Springwise has previously spotted cement made from fruit and vegetable scraps, a carbon-capture solvent for cement production, and a process that harnesses microbes to produce cement.

Written By: Matthew Hempstead