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Comment by greydius | Hacker News Reader

The only salient point this article mentions (but only briefly) is that concrete production generates a huge amount of CO2. Everything else is hogwash. In terms of strength, versatility, and cost, steel-reinforced concrete has proven to be the greatest building material humans have ever devised. It is by no means perfect, but nothing is. Concrete needs to be maintained just like anything else. With neglect it decays.

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I'm a fan of brutalism, so I do like concrete buildings and find them interesting, but there's also a good case to be made about mud bricks, which the author aludes to. Yes, you'll have issues building 10-storey high buildings out of mud-bricks, but it's definitely possible to build structures (like barns) out of them that can easily last more than 100 years, without the builder having to have a civil engineering degree. I've seen one such structure with my one eyes, built by my grand-grand-father who was a peasant. The only thing you have to be careful about when building stuff out of earth is water infiltrations, otherwise you're good.

Buildings made out of earth are also better heat insulators compared to concrete. My grandma's house was always cool in the summer, while my appartment which is part of a building made out of concrete wouldn't be livable in the summer without AC.

That's an apples to oranges comparison, though. Mud bricks are a good building material, and so are a lot of other things (e.g. wood, bamboo, paper), when the structure only has to support itself and a roof. But concrete enables structures that cannot (or should not) be built with those materials.

Mud/clay walls are OK to support roof or act as insulator, but they are weak when you need to attach something to wall. Moreover, outer layers can laminate out of wall if they are stronger than wall itself, so you will need to use lime stucco to paint wall, which is soft enough.

To solve these problems with mud/clay walls, wood and straw are used. To date, G.R.E.B.[1] technology is most advanced, cheap, and easy to use.

[1] http://www.approchepaille.fr/pdf/straw-bale-building-greb.pd...

>Everything else is hogwash.

Ongoing maintenance is an important energy and money sink for any society. I find it doubtful that concrete (at least, the modern versions and usage of it) will be sustainable beyond the fossil fuel era, simply because it will be too expensive to maintain.

EROEI for a given bit of infrastructure (ie how much energy is conserved or produced for a given energy expenditure in construction/maintenance) isn't as sexy, but it's just as much a thermodynamic constraint on sustainability as overusing the CO2 capacity of the oceans and atmosphere.

> Concrete needs to be maintained just like anything else

But how can this be done when the steel is enclosed within the concrete? What can be done once it started to rust?

There are several things that you can do.

0) Build using appropriate materials/design/construction. It's mostly a solved problem, it just takes wanting to spend enough money to do the process right.

1) Use epoxy coated rebar. It's commonly used in places where there's a large risk of cracking and rebar corrosion (e.g. roadways)

2) Use prestressing/posttensioning to put an overall compressive force on the concrete to prevent cracking.

The American Galvanizers association makes the case for hot-dipped, galvanized rebar, for what it's worth:

https://www.galvanizeit.org/uploads/publications/Galvanized_...

Small amounts of damage due to rust can be patched up with new concrete. Whether this involves welding in new elements of steel is a question I don't know the answer to.

http://www.cement.org/for-concrete-books-learning/concrete-t...

http://theconstructor.org/practical-guide/reinforcement-repa...

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