Carbon dioxide (CO2) captured via direct air capture (DAC) has been permanently stored in concrete for the first time, in a demonstration project led by Canadian business CarbonCure Technologies and Californian outfit Heirloom.
The project was successfully completed earlier this month and saw Heirloom capture CO2 from the atmosphere using its DAC technology at its headquarters in Brisbane, California. Then CarbonCure’s reclaimed water technology injected the captured CO2 into the process wastewater at a Central Concrete batch plant in San Jose, California. Central Concrete used the CO2-treated wastewater to make fresh concrete, which was produced for a range of construction projects across the Bay Area of California.
The technology deployed means the CO2 is durably sequestered in the concrete as calcium carbonate. It would not be returned to the atmosphere even if the concrete were demolished.
Heirloom runs the US’s only operational DAC facility. It uses limestone, an abundant material, to pull CO2 from the air. Harnessing a cyclic process, the limestone is broken down into calcium oxide rock and CO2 gas using heat from a renewable energy-powered electric kiln. The calcium oxide is spread onto vertically stacked trays where it acts like a sponge – pulling CO2 from the air before it is returned to the kiln and the process begins again. The captured CO2 gas is then permanently stored safely underground or – as was the case with this first-of-its-kind project – embedded in concrete.
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