Comment by anfilt | Hacker News Reader

Comment by anfilt | Hacker News Reader

Depends on the resources. I would say if we can get a handle on the energy. That goes a long way. For building materials we are not going to really run out of steel, clay for bricks, and concrete. Wood is renewable if managed properly.

I remember reading something that said the population will peak around 10 to 10.5 billion, and not really grow beyond that. So when it comes to housing for that many people there is plenty of land.

That mainly leaves food. I have heard some people say meat is quite inefficient, but how much land do we need to feed 10.5 billion people?

It would be interesting to see other resource like copper plotted as how much is needed per person vs world supply. I do know aluminum is 3rd most abundant element in earths crust and iron is the 4th most abundant.

Really, for energy we should just be using renewable, and nuclear. Also when reading about how much the fuel for nuclear is actual used only like a few percent we need better reactors.

>concrete

Concrete is staggeringly carbon-intensive. You need to burn a lot of fuel to produce cement, which itself emits carbon during the calcination process. Every ton of cement produces about 900kg of CO2, making up about 5% of global carbon emissions.

http://blogs.ei.columbia.edu/2012/05/09/emissions-from-the-c...

If you do some quick and dirty calculations of a 3000 sqft concrete house with 5 people lasting 100 years then the CO2 burden comes out to around 43kg/yr/person. An average american produces about 1000kg/yr so that's around 5% of a person's total CO2.

Ha, and they're living in some shabby plywood houses, at that.

> You need to burn a lot of fuel to produce cement, which itself emits carbon during the calcination process.

The CO2 emitted by the calcination process is reabsorbed when the Portland cement sets. You won't get back the CO2 expended in the heating process, but the calcination itself is more or less CO2-neutral.

It's roughly this:

Making cement: CaCO3 (limestone) + (some other stuff, varying with the type of cement) + lots of heat -> CaO + CO2.

Setting cement: CaO + H2O -> Ca(OH)2 ("portlandite").

Ca(OH)2 + CO2 (from atmosphere) -> CaCO3 + H20 (chemically much the same as the original limestone, but now set into a useful form).

I'm too lazy to balance all the equations, and there are a lot of other things mixed into modern cements, but that's the basic idea.

It seems unfair to charge cement with the CO2 driven off during manufacture, while ignoring the fact that an equal amount of CO2 is absorbed during setting.

I did say if we get a handle on the energy that fixes a lot of things. If that furnace was powered by a CO2 free source the chemical reaction is neutral once the concrete is used.

> concrete

Actually we have been depleting the planets sand resources for a good while now, and could be facing a "sand crisis" in the not distant future, largely thanks to concrete:

https://www.smithsonianmag.com/science-nature/world-facing-g...

It sounds like the main issue in that article is local shortages. It doesn’t say anything about global supply (e.g., how long would it take to deplete the Sahara, and would that be considered land reclamation?)

Well I don't claim to be an expert, but I've read elsewhere that there are a lot of different qualities of sand, and that desert sand is not (as) useful as building material due to its shape and structure.

https://www.quora.com/Why-is-desert-sand-not-used-for-constr...

Just asked a friend of mine who is a civil engineer. He said desert sand is a bad idea for standing concrete structures. However, mixing a bit with supported concrete structures like a concrete pad or roads makes them less prone to cracking.

For particular demanding applications all sand is sifted and structure/shape of the sand checked.

For evening more demanding application sand may be produced via crushing to get long flat sand grains.

Also the checking of the quality of sand is called sieve analysis.

Interesting article. However sand is just mostly ground up quartz (silicon dioxide). It is the second most abundant mineral in earths crust.

We could just grind rocks instead of causing erosion in water ways. However, we would need a good energy source to run a grinder/crusher. We are improving along those lines of energy production. Natural, sand is made by wind and hydro power. So if we keep it that way we should fine.

Also it seems to more of we are collecting sand and other aggregate in haphazard way. I am not sure I would call that running out? Unless sources with low environmental impact are running out?

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