In what is being claimed as a world-first, Canada’s CarbonCure Technologies and Californian company Heirloom have announced they have permanently stored carbon dioxide from direct air capture into concrete, a “negative emissions” process.

Heirloom captured the carbon dioxide from the air at its headquarters in Brisbane, California, and then CarbonCure’s reclaimed water technology was used to inject the carbon dioxide into process wastewater at a Central Concrete concrete batching plant at San Jose. That concrete was then used in various construction projects across the Bay Area in California, the carbon dioxide being stored permanently as calcium carbonate.

The innovation could be a landmark in decarbonisation in a difficult-to-decarbonise industry – even if the potential decarbonisation would only be a fraction of the total carbon dioxide emissions of construction using concrete, every fraction is significant. Heirloom runs the USA’s only operational direct air capture facility, using limestone as the core substance. Renewable electricity powers a kiln, in which limestone is broken down into CO₂ and calcium oxide, the latter of which is then used to “pull” further CO₂ from the air, creating limestone, and the process then begins again, with the captured CO₂ either being stored geologically or used in products.

CarbonCure’s reclaimed water technology is also innovative in using water from the washing-down of concrete trucks, which contains some cement, so that injection of CO₂ can mineralise within the water, effectively using two waste products to create a commercial product.