Driving down CO2 with carbon-capturing roads

One company transforms steel industry waste into green aggregate products

Spotted: In the US alone, there are over four million miles of paved public roadways. What if this massive expanse of infrastructure could do more than connect various locations? What if it could tackle climate change at the same time? Enter Alkali Earth.

The company uses steel slag, a calcium-rich industrial waste product that would likely otherwise be sent to landfills, to create carbon-capturing aggregate products for paving roads. The steel slag is crushed, and the extremely reactive minerals it contains readily combine with CO2 in the atmosphere to form stable carbonate minerals. According to Alkali Earth, this traps the carbon for thousands to millions of years.

At the end of last year, Alkali Earth was one of 12 companies to win a Frontier Climate Pre-Purchase contract, receiving funding from Stripe, H&M, and Shopify.

From 2025, Alkali Earth plans to offer carbon credits for the CO2 captured in its aggregates. The company continues to tweak its recipes for optimal carbon-capturing abilities and hopes to use steel slag in even more products in future to accelerate carbon sequestration across the built environment.

Buildings and infrastructure may have a massive environmental footprint, but they also have the potential to capture enormous volumes of carbon too, including in concrete and filler.

Written By: Matilda Cox