Poured concrete actually is a passive remover! The issue is the process of baking carbonate rocks at high temperatures to form the cement. This not only takes a lot of energy, but it inherently drives off CO2 from the rock. Over the decades as concrete slowly gets stronger and stronger it absorbs back a small but substantial fraction of the CO2 it emitted.

The way to make this better is to be able to have mixes with lower fractions of cement for a similar level of strength - hence using graphene in this case.

I found out the hard way that the older concrete gets, the stronger it gets.

Was trying to make a 30cm x 60cm hole in a DIY concrete wall that the last owner of my house had placed over the mains pipe that was leaking from two joints underneath it (I suspect he also DIYed the piping, given its rather unorthodox setup). I had to make room for a plumber to access it.

It was poured in the early 70s, looked pretty, well, homemade, so I figured, easy! Borrowed a concrete breaker, got to it.

3 weeks, very painful wrists from the vibration, and a hired concrete saw, later, I finished my hole.

But holy crap, I had vastly underestimated concrete.

It takes about 40 years for concrete to reach about max strength. I've also experienced the fun of it having lived in a concrete building from the 70s :)

Couldn't this be addressed best by driving the heat on green energy and directly siphoning off the produced CO2 into either underground capture or even green fuels?

I'm still a bit at loss why Climeworks or Prometheus Fuels would pump ginormous amounts of normal air through their respective setups to extract the 0,0004% of CO2 instead of feeding from pure CO2 by industrial processes like this one.

It seems like an easy win on the low hanging fruit to me, and I think there's work on making that practical from Noya Labs: https://techcrunch.com/2021/02/24/noya-labs-turns-cooling-to...

CO2 was actually too expensive for enhanced oil recovery for which it is often used since in many cases capturing it in an effective way from industry is just not possible or nowhere near economically viable even at high prices. Hence trump signed a subsidy for co2 sequestration to fight the climate change he didn't believe in.

Since pumping CO2 into the ground is technically just that (even if they don't really care much whether it actually stays there and oil comes out in the process).

Generally the solution to these problems whether it's co2 capture or power to gas at scale is not some future way to defy physics or edge our way up in efficiency towards a distant future where it might be viable but to just emit less. I suspect we'll look at this in the future the same way many look at the plastics industry's takes and propaganda about recycling.

good point, but CO2 is ~415ppm = 0.4 per thousand = 0.04%

It could in theory, but as you say, nobody has created a practical way doing either of those things yet.

If the CO2 from cement production is mostly sequestered, it ends up being a net negative CO2 emitter. But that's not cheap.

A passive remover but still a net emitter?

Yes, the concrete manufacturing process emits more CO2 than aging concrete absorbs.

Maybe the solution is dense, high rise concrete buildings surrounded by woodland. The size of the woodland being determined by the net emissions from the concrete.

The emissions occur during production. Concrete itself doesn't emit CO2, it's the cement being made from limestone that generates emissions.

I might even prefer that to living in suburbia if you also added room for commercial zoning.

I think the way we designed cities around cars could really stand a serious second look. Cars are really a necessary evil for me. I just bought one after 6 years of not having a car. I wish I didn't need it.

I hear that. We can put bike lanes and a tram track beside the building, shops and amenities at the bottom, and room for food trucks to come and go. It'll be perfect.

More seriously, sorry to hear about the car. It sucks to be that way. I've always been lucky enough to arrange my life around access to public transport (I don't drive) but I've been tempted many, many times.

> Or, hear me out, devise a concrete that reacted with atmospheric co2 to produce something more benign. That way it changes from an emitter to being a passive remover

Good propertyy. It would be even better if the material acted as a good insulator. And be re- or upcyclabe when we need to tear down the building. And while we're at it: it would be nice if the product would just grow...

That sounds like a tree to me...

So true...

Geopolymer concrete pretty much fits the bill for this. From my layman’s understanding the main reason we don’t use geopolymers instead of Portland cement is because we already have so much infrastructure for Portland cement

That's similar to how we already had so much steel infrastructure. The existing infrastructure didn't hold back the people who owned none of it.

https://www.nytimes.com/1981/09/23/business/the-rise-of-mini...

This is a dream scenario, but something a bit more achievable...I would like to see more buildings designed with a longer design life, so we don't have to pour concrete on the same block multiple times a century. I wonder if current emissions calcs for "Green" buildings include demolition and reconstruction when they are past their use-by date.

Like wood ;)

We should use more wood.

Rot is the main issue, I think.

Not if the wood is glulam:

https://en.wikipedia.org/wiki/Glued_laminated_timber

Consider this picture:

https://en.wikipedia.org/wiki/Glued_laminated_timber#/media/...

Your picture link should be https://en.wikipedia.org/wiki/File:Mj%C3%B8st%C3%A5rnet.jpg eh?

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The "Glulam versus steel" section is really interesting!

> A 2002 case study comparing energy use, greenhouse gas emissions, and costs for roof beams found it takes two to three times more energy and six to twelve times more fossil fuels to manufacture steel beams than it does to manufacture glulam beams. It compared two options for a roof structure of a new airport in Oslo, Norway: steel beams, and glulam spruce wood beams. The life cycle greenhouse gas emission is lower for the glulam beams. If they are burned at the end of their service life, more energy can be recovered than was used to manufacture them. If they are landfilled, the glulam beams are a worse alternative than steel because of the methane emission.[9] A more recent study by Chalmers University of Technology was not so optimistic. Nevertheless, it showed that while the absolute greenhouse emissions are strongly dependent on the method used to calculate them, the environmental profile of glulam is typically as good as or better than steel in an example structural application.[10] The cost of the glulam beams is slightly lower than the steel beams.

I'm also curious about the flammability. I did some Googling and wasn't able to find a concise answer. It seems like the beams themselves can be fireproofed with a non-wood cladding, or another study said they can be over-specced to give a 1 hour fire resistance rating. Another study said that steel connectors are typically used, and cladding for the wood-steel connection is an unresolved issue.

It seems like people are using them, so I presume it's safe. I don't think I would want to live in them until we've seen a bunch of them catch on fire. I'd probably be fine with it up to 3 stores, but anything higher would make me concerned.