Recipes for Zero-Carbon Cement

The quest for zero-carbon cement has sparked a wave of innovations aimed at reducing the significant carbon footprint of the world's most widely used building material. From carbon-neutral concrete using algae-grown limestone to novel electrochemical processes and the recycling of concrete and steel, researchers and companies are developing promising solutions to decarbonize cement production.

Seratech's Carbon-Neutral Concrete

Seratech, a London-based start-up, has developed a method for creating carbon-neutral concrete by replacing up to 40% of cement content with a type of silica made from captured industrial emissions and the carbon-absorbing mineral olivine. This approach is both low-cost and scalable, as it seamlessly integrates into existing production processes and leverages the abundance of olivine, unlike other cement substitutes like ground granulated blast-furnace slag (GGBS).

Biogenic Limestone by Minus Materials

Researchers from the University of Colorado in Boulder have developed a method to produce cement using limestone grown by algae through photosynthesis, rather than mined from the earth. This "biogenic limestone" emits only as much carbon as the microalgae absorbed from the atmosphere during its growth, potentially making the process carbon neutral or even carbon negative.

• Supported by a $3.2 million grant from the US Department of Energy
• Researchers are working to scale up manufacturing capabilities and lower the price of the material by using the coccolithophores microalgae to make more expensive items like cosmetics, biofuels, and food

Cambridge Researchers' Recycling Method

Cambridge researchers have developed a breakthrough method that recycles old concrete and steel simultaneously in steel-processing furnaces. The process purifies iron and produces "reactivated cement" as a byproduct, which could result in completely carbon-zero cement if powered by renewable energy.

• The technique has been trialed in furnaces producing a few dozen kilograms of cement, with the first industrial-scale trials underway this month, potentially producing about 66 tons of cement in two hours
• Researchers say the process could scale up to produce one billion tonnes of "electric cement" by 2050 without adding major costs to either concrete or steel production