Global cement production accounts for approximately 7 per cent of annual greenhouse gas emissions, in large part through the burning of quarried limestone, and 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.

To make portland cement, the most common type of cement, limestone is extracted from large quarries and burned at high temperatures, releasing huge 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...