California-based Heirloom, a developer of direct air capture (DAC) carbon removal, teamed up with CarbonCure, whose reclaimed water technology injects carbon dioxide (CO₂) into concrete wastewater, to demonstrate the permanent storage of captured CO₂ in concrete.

The captured gas was injected into the process wastewater at a Central Concrete batch plant in San Jose, California, where the CO₂-treated wastewater was tapped to make fresh concrete for use in regional construction projects. The gas is effectively sequestered in the concrete as calcium carbonate and will not be re-emitted to the atmosphere even if the concrete is demolished.

The cyclic DAC process engineered by Heirloom uses limestone to pull CO₂ from the air, after which the material is broken down into calcium oxide rock and CO₂ gas using heat from a renewable energy-poweredVertically stacked trays of limestone mineral powder absorb carbon dioxide. Source: Heirloom electric kiln. The calcium oxide is layered onto vertically stacked trays where it serves as a sponge, pulling CO₂ from the air before it is returned to the kiln to restart the process. The captured gas is then permanently stored safely underground or embedded in concrete.

The DAC-to-concrete solution also relies on CarbonCure’s technology to inject CO₂ into reclaimed water at concrete plants. Upon injection, the gas immediately reacts with cement in the water and mineralizes, permanently storing it and stabilizing the cement for reuse. The CO₂-treated slurry is then used in new concrete mixes. The company claims its technology can reduce the use of fresh water by up to 20%, lower virgin cement use by 10% and save 15 kg of CO₂ for every cubic meter of concrete.