Cocoon transforms steel production waste into a greener cement alternative

Slag is the molten waste produced during the production of steel in a traditional blast furnace. The material has been hailed as a greener cement alternative for making concrete, the most abundant man-made material on Earth. However, the waste has faced challenges in the supply chain as the steel industry seeks greener production methods.

Steelmakers in the US and Europe are increasingly turning to electric arc furnaces (EAFs), which are smaller, more energy-efficient and run on electricity instead of coal. Cocoon is a new startup based on the belief that greener steelmaking and the creation of concrete slag doesn’t have to be an either-or proposition.

Despite all the concerns surrounding concrete production, demand is only growing. Cement only makes up 10-15% of a concrete mix, while it accounts for about 90% of emissions. That’s why the industry is constantly looking for environmentally friendly alternatives. Cocoon is building a solution it calls “e-slag,” a processed byproduct of more energy-efficient steel production that serves as an alternative to cement.

“The challenge with steel slag is that it has a higher iron content. That’s one of the things that limits its ability to react as a cementitious material,” co-founder and CEO Eliot Brooks tells TechCrunch. “We have a two-step process that addresses that high iron content and the challenge that it creates, and also gets the cementitious reactivity at the other end of the process.”

The UK-based company’s technology is still in the testing phase and is designed to fit into existing steelmaking workflows. The standard system involves slag pots on rails or mounted on the front of a large truck, which dump the molten material into a large pit. The slag is then allowed to cool before being crushed and sent to cement producers. Cocoon’s solution is in a shipping container that sits in a pit and catches the molten material as it is poured out of the slag pots.

The company recently raised $5.4 million in pre-seed funding. The round includes Wireframe Ventures, Celsius Industries, Gigascale Capital and SOSV. The latter has been backing Cocoon for some time, with Brooks working part-time from SOSV’s recently opened HAX facility in Newark, New Jersey. The founder was on hand when TechCrunch toured the space in April.

The new funding will be used to build an R&D facility in London. Initial testing will be conducted at a steel mill in the north of England, followed by one in the U.S. Brooks hopes to have Cocoon’s technology integrated into a pilot plant sometime in late 2025.