Brimstone, which claims to make portland cement in a carbon-negative process, announced that it obtained third-party ASTM C150 certification, an industry requirement. The company said that the certification "validates that the cement Brimstone produces is ordinary portland cement, the type of cement used in virtually all construction today."

"Cement production is a substantial driver of climate change, accounting for 7.5% of global CO2 emissions and 5.5% of total greenhouse gas (GHG) emissions," it said. "The Brimstone process is carbon-negative across a range of energy scenarios, providing a pathway to eliminate this footprint."

Key to the process is a significant change in making cement. Rather than using limestone, which releases CO₂ in the manufacturing process, Brimstone replaces the mineral with carbon-free calcium silicon rock. The company has claimed that the result is chemically and physically identical to conventional portland cement while remaining cost-competitive.