Incredible! They use a massive arc furnace (used for steel recycling) to recycle concrete. They suggest that solar power could power the arc furnaces, resulting in zero emission concrete. As concrete currently constitutes 7.5% of anthropogenic carbon emissions, this tech could make a big difference.

Arc furnaces are crazy energy intensive. But if solar power keeps doubling every 2 years, we will very soon have way more power than we know what to do with (at certain times in the day). Arc furnaces are a good way to suck up the negative electricity spot prices!

This is a very cool discovery, but it's not like "used cement" ends up in landfills today.

Most cement ends up as concrete.

Crushed concrete of various sizes is a valuable aggregate used as a cheaper alternative to crushed stone for road building etc.

In my area any time I see an ad selling crushed concrete it's gone by the time I ring. Perhaps because we have clay and sand soils around here there is a permanent shortage of such things.

Seems like the "big if feasible" part is reducing concrete to hydrated cement paste.

From actual paper: https://www.nature.com/articles/s41586-024-07338-8

Recovered cement paste (RCP) is not commercially available at scale at present. . . . The value of the improved recovered aggregates is not at present high enough to cover the extra cost of processing, so RCP is currently landfilled. However, the know-how and the technologies required to produce RCP at scale exist. [22]

22. Thermomechanical beneficiation of recycled concrete aggregates (RCA): https://www.sciencedirect.com/science/article/pii/S095006182...

The cited paper does not support the assertion that tech to recycle concrete into RCP exists. The paper discusses removing adhered mortar (AM) from recycled concrete aggregate (RCA).

Nice to see this topic survive the flagging process on HN..

Would be great to have a discussion of some other promising non-carbon energy sources, such as drilled geothermal.

Slightly off-topic - gen pop are often surprised when I mention that NET-ZERO == MAX-CO2 == MAX-HEAT. People often assume that getting to net-zero is 'mission accomplished' .. but its the area under the curve that counts, the total CO2/GHG equiv put up there, as it stays around for a long time.

If we are nearing +1.5C today, with temp rising at around 0.25C to 0.3C per decade, at current long plateau of max emissions.. we will likely be somewhere in range +2.5C to +3.0C by the time we reach net-zero, possibly by 2050.

I'm not sure that +2.5C is survivable for large human populations .. hence the above concerns prompt one to look at things like SRM - putting up sulphur particulates to increase cloud cover, so less sunlight is absorbed by the oceans, exerting a net cooling effect [ as we did with container shipping fuels until recently - until the fuel was mandated to contain less Sulphur ]

IMHO, we engineered our way into this mess by geo-engineering a CO2-rich hot biosphere, and we will need to engineer our way out of it - it could be worse, we seem to have a lot of technologies that can replace carbon-fuel and store energy and arguably reduce heat.

Another way is to build stuff that doesn't have to be torn down after 10 years. Quite a lot of large concrete buildings in town have been torn down less than 20 years, some just 10.

Seems quite wasteful, surely there's a better way with some planning and foresight.

Nice, this was one of the bigger things I have on my "I hope someone knows how to solve this" pile.
There was some discussion yesterday [0] (21 points, 4 comments)

[0]: https://news.ycombinator.com/item?id=40446764

They replace the flux used in steel recycling with used concrete, and instead of useless slag they get recycled cement.

This is a really good idea, but it is important to keep in mind that even if all of the steel production in the world (~100 Mton/y) shifted to this method, it would only have a negligible impact on the cement production (~ 4 Gton/y).

>>The Cambridge researchers found that used cement is an effective substitute for lime flux

So they can only "recycle" this concrete as a substitute ingredient during steel making? That cannot scale. We would have to start making epically more amounts of steel in order to process even 1% of the concrete that we would want to recycle.

Cement production is a significant contributor to global carbon dioxide emissions. Amazing that the development of effective cement recycling methods is in process.
It may not be a panacea, but using busted up chunks of concrete in gabions is a great way to re-use an otherwise worthless material. For those who don't like the aesthetic of post-industrial wasteland, just use the concrete chunks in the interior of the gabion and put the pretty rocks on the exterior faces so that no-one will ever know your beautiful gabions are filled with demolition debris.
How costly is it? How much energy is it going to consume? Aren't most concrete carbon emissions due to energy consumption?
I really appreciate all technical solutions to our battle against climate change. Yet I fear all these gains are without any value as long as any increase in efficiency is eaten by our economies relianze on constant growth.

This is the root climate challenge as it drives all the incentives to exceed our energy/CO2-budgets. Turns out we are witnessing what happens when you run exponentially growing feedback into the logistic function.

Many are sceptical whether we can solve this capitalism-problem without fundamental changes to the system, that would leave you with a system that is no longer about capital. I am convinced there are many ways to solve that, but first we have to acknowledge the driving force behind climate change isn't technology, it is the need to grow markets and populations.

This should be adopted slowly over time to learn more about the real life consequences. There may be no negatives, or there might be something significant.

It may take 10 - 30 years to observe changes. and if all is well it can be adopted at scale and/or possible problems detected can be mitigated.

Move fast and break things is not a real way to approach climate change.