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Comment by elric | Hacker News Reader

Old bricks and old buildings are fine, they've already been made. But making bricks is pretty energy intensive. Brick laying requires mortar, which requires cement, which results in a lot of CO2. Brick houses are heavy, and require strong foundations. Usually concrete these days, again, lots of CO2. I have no idea at which point it makes sense to grow buildings out of fungi, but if they are a greener alternative to brick & mortar then it seems like an avenue worth investigating at least.

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Just to get a frame of reference: How much CO2? I'd assume that building once, and then not having to replace it for hundreds of years is the long con and more energy-efficient, if that's the metric we're going by.

Cement production accounts for ~7-8% of all global CO2 emissions. Wikipedia cites sources which claim ~900kg of CO2 is produced for every ton of cement. It's possible that frequent rebuilding could be more emission-efficient.

This entire debate is silly without numbers, but even worse it's missing the point - 38% of UK CO2 is from heating. Most of CO2 is produced to heat and cool building while the stand, not to build them.

Even tiniest improvements in quality of building, it's heating system and insulation will result in dramatic changes. This favours something well built, well insulated, with a heatpump, high thermal mass, and most importantly with heat recovery ventilation. Not hastily constructed crap that goes to shit in 30 years.

IMO the bigger question are: why does cement produce CO2? Could we use a different kind that doesn't? Could we capture CO2 from the atmosphere to produce cement, making it a closed loop?

Cement is a binder mostly made up of Ca and Si oxides. It produces CO2 mainly from the heat input required in production, pure and simple.

I have not heard of any carbon capture technologies that are more efficient than trees and oceans, so the best we can do is facilitate a process that generates less CO2 from fuels spent.

In order to produce CO2, the cement has to contain carbon. Where does that carbon come from? Potentially, we could use plants to capture carbon, and put plant matter in the cement. We could also use chemistry and catalysts to skip the plants. It might not be energy efficient, but maybe that doesn't matter. You can use solar panels and run your cement-generation-reactor only during the daytime, as well as put measures in place to cut back on cement usage. This problem is solvable, it just needs creative thinking and an active decision that we are going to solve it.

One of the inputs in cement manufacture is limestone which is Calcium Carbonate. That is ground and heated at high temperatures with clay minerals to produce portland cement.

So CO2 comes from the reaction between limestone and clay. And comes from burning natural gas or coal to generate the heat needed to drive the reaction.

So we use solar instead. We might not even need solar panels, we could potentially use one of those solar thermal reactors with an array of mirrors pointed to a central focal point. They can produce heat up to several hundred degrees C AFAIK.

Old brick buildings use a limestone based mortar, which actually absorbs CO2 as it cures.

Don't lime based mortar still require the O2 to be driven off through heating to very high temperatures? Isn't that the same reason portland cement production creates high levels of CO2? Or is the CO2 produced during the curing stage of cement?

Chemically they are net-neutral only if they are non-hydraulic lime, but hydraulic mortars do continue to absorb some CO2 over time.

Separately, they are nearly always heated with fossil fuels, but, unlike steel, it's not chemically helpful to do so.

Why aren't stone foundations more common? There's lots of modern cutting methods and everything is done anyway with an excavator. Why is it always concrete? Concrete can't handle water.

Labour. There's a reason CMUs are shaped like bricks. And concrete can handle water just fine if proper waterproofing and draining systems are included in construction.

> concrete can handle water just fine if...

Concrete itself doesn't handle the water, it's being protected. With quite brittle technology. In the long term these kind of ifs don't tend to work. You want to minimize the number of ifs if you want to build something that stays put for a long time.

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