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