Carbon-negative is a long stretch, it's just using waste material that is usually used as fuel. It's at best low-carbon compared to concrete, which honestly is already a good thing.

At around the same time, Meyer learned about the large amount of waste lignin that is produced every year, primarily from pulp and paper processes, which is also expected to be produced from biorefineries in the future.

[...] During the production of pulp and paper products, roughly 100 million tons of lignin are produced annually as a waste byproduct and subsequently burned as low-value fuel.

Meyer saw lignin as a polymer that could be used as a material instead of a fuel and sought to crosslink it like an epoxy resin. Using lignin allowed Meyer to sequester CO2 captured from the air in the form of biomass that would otherwise be burned.

(Emphasis mine)

Cement contributes to ~8% of the Earth's CO2 emissions. Almost 4x aviation, and not too far off all of the Earth's combined agriculture.

If concrete was a country, it'd be the 3rd highest polluting country on Earth, after China and the US.

Even if this headline is overly ambitious, any improvement is a good one.

Roman concrete would cure by reacting with the carbon dioxide in the air, fixing it into the concrete. It doesn't sound like that's how this concrete works, but I wonder if a methodology like that would be carbon negative.

The real problem is that we're still paving over the planet for the sake of car dependency. We don't need more concrete. We should be tearing it up and banning cars.