Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

The problem with reinforced concrete (2016)

theconversation.com

Post reply on HN
Print view View original

41–50 of 192 posts

Re: The problem with reinforced concrete (2016)

#41

Post by renewiltord »

nerdponx wrote: post #20
idoh wrote: post #18

I don't know if it is really a problem, more like a tradeoff. Reinforced concrete costs less and enables shapes that are impossible without it, with the downside that the buildings last 50 years instead of 100+ years. The present value of a building that lasts 50 years is not that much different that the same one that lasts 100 years. With that in mind, it makes perfect sense to make an office building out of reinfor…

> The present value of a building that lasts 50 years is not that much different that the same one that lasts 100 years. That's a problem in and of itself, IMO. Construction is tremendously resource-intensive. We should not be building "throwaway" buildings.

The classic problem is similar to that of that other famous future-proof thing: wifi in hotels. All the fancy hotels that got high-end wifi in the 2000s had shitty Internet for a long time because it was too hard to redo.

Sometimes, building to throw away is the best model. If something is so resource intensive in a way where the externalities are not appropriately mitigated, the right way is to tax the externalities, not to go after specific things.

If these builds were too expensive to build, they wouldn't be built.

Re: The problem with reinforced concrete (2016)

#42

Post by rdiddly »

Guessing at "the problem" before reading the piece, I figured it would be that it's weak in tension. Not quite what they said, but that does happen to be the reason you need rebar in the first place.

Concrete however does an excellent job of externalizing its costs: into the atmosphere, forward through time, and onto other people. So it will remain popular so long as those remain the expressed values of society.

Edit: Awww, boo hoo!

Re: The problem with reinforced concrete (2016)

#43

Post by quickthrowman »

alcover wrote: post #9

There are also interesting new methods to monitor corrosion Then what ? Can you repair or replace parts of a building ?

Yes, why wouldn’t you be able to repair replace parts of a building? You cut out the bad parts while reinforcing structural elements temporarily while the replacement work is performed, then you remove the temp supports.

New footings, beams, walls, etc are constructed or installed to replace old ones all the time.

Say you have a bad concrete footing for a post. You use jacks to support the beam on both sides of the post that sits on the footing, remove the post, remove the footing, pour a new footing, and then put a new post in and remove the beam jacks.

Re: The problem with reinforced concrete (2016)

#44

Post by sgtnoodle »

rsync wrote: post #13
quickthrowman wrote: post #5

Earlier quoted context omitted.

There’s also hot-dip galvanized and stainless steel rebar.

... with stainless being a much better (but much more expensive) choice. HD Galvanized is a coating whereas stainless steel is a different material - it is stainless all the way through ...

It's a coating, but my understanding is that it basically creates a battery that keeps the nearby iron from deteriorating. Small gaps in the coating therefore don't really matter as long as there is still some zinc nearby.

Re: The problem with reinforced concrete (2016)

#45

Post by hackeraccount »

nerdponx wrote: post #20
idoh wrote: post #18

I don't know if it is really a problem, more like a tradeoff. Reinforced concrete costs less and enables shapes that are impossible without it, with the downside that the buildings last 50 years instead of 100+ years. The present value of a building that lasts 50 years is not that much different that the same one that lasts 100 years. With that in mind, it makes perfect sense to make an office building out of reinfor…

> The present value of a building that lasts 50 years is not that much different that the same one that lasts 100 years. That's a problem in and of itself, IMO. Construction is tremendously resource-intensive. We should not be building "throwaway" buildings.

That's a bit like the one horse shay. It's not how long it lasts but what are the costs associated with it lasting any given length of time. Nothing lasts forever but say buildings lasted 500 years - Suddenly 500 years from now all buildings have to be replaced? And what's the cost of this 500 year building? Is it 10 times as much? Or is it 5 times as much?

Saying we shouldn't have buildings that only last 50 years but rather they should last 500 is like saying they shouldn't last 50 years but instead 5. Maybe. Maybe 5 makes sense.

My assumption would be - shocker - it's probably a complicated trade off that's best adjudicated by the people with the most skin in the particular game.

Re: The problem with reinforced concrete (2016)

#46

Post by renewiltord »

sesuximo wrote: post #10
minikites wrote: post #4

Earlier quoted context omitted.

Is it a good thing for society to directly incentivize the construction of longer lasting buildings?

IMO yes; if the materials cost a lot of time/carbon/resources to produce, then we should make them last!

No, time is not an externality: maybe time under construction yields to disruption to neighbours under construction and we can charge for that. Resources are fully internalized. If a building needs x sand and another needs 2x sand, the second will pay twice for sand. Carbon is externalized, but that's a general problem. How do we know that making a lasting building is better/worse than having the building not exist / exist and having people driver farther / closer?

Simple, for externalities, you directly charge for the externality.

All these stop-gap "it costs carbon, so we must make it last 50 years" is like placing massive `if-then-else` statements throughout your codebase and then being surprised when the emergent behaviour of your program somehow results in uglier, more carbon polluting, sicker buildings that are now 100 years old and imposing massive costs on society around them.

Re: The problem with reinforced concrete (2016)

#47

Post by rektide »

throwawaysea wrote: post #23

An interesting read, albeit with information that is likely familiar to many. Given the issues surrounding concrete with greenhouse gases, recycling, and landfill contribution, it seems that timber ( https://arstechnica.com/information-technology/2012/05/wood-... ) may actually be a more viable alternative. We have techniques to grow it sustainably, it can be a carbon sink within a city, and it is mostly natural wood…

This is the only post I found mentioning recycling, and I think that's a key factor in this all. My generation is going to be the first saddled with a lot of old buildings we have to deal with. We are going to have to get good at recycling buildings.

My understanding that the economics have already really pushed us massively forwards in the past decade or two, that we are far more aggressive about recycling construction aggregate[1].

The article has a nod midway through to these concerns,

> The many alternative materials for concrete reinforcement – such as stainless steel, aluminium bronze and fibre-polymer composites – are not yet widely used. The affordability of plain steel reinforcement is attractive to developers. But many planners and developers fail to consider the extended costs of maintenance, repair or replacement.

This definitely seems like a huge societal blind-side to me. As much as it's an issue of planners and developers, I feel like there's a consumer lack of understanding. The invisible hand can't push effectively here, can't reward the builders doing it right adequately. In part because society is not aware, doesn't know what to ask for, doesn't have standards, doesn't view & comprehend the role of maintenance & ultimately recycling. These are far off things.

As my generation starts to see the limits of sustainability, see where so very many many creations begin to become risks & hazards & losses rather than values, we may develop some sense, but switching over into a fear-based emotional reaction isn't necessarily a great fix. Trying to give us all a picture of the life-cycle, the costs, the trade-offs; that seems like the necessary task. Regulating our ability to see & ascertain.

Hopefully we just get better & better about recycling. It'd be so interesting to see how reinforcements are extracted from construction aggregate today. Stainless steel reinforcement isn't expensive... if you can safely view it not as a sunk construction cost, but as a semi-long term loan for a building. Where-as more advanced materials like fiber-polymer, I tend to imagine, may have wonderful characteristics in use, I also tend to imagine them as likely having less recoverability. Steel: material we know how to re-cast.

[1] https://en.wikipedia.org/wiki/Concrete_recycling

Re: The problem with reinforced concrete (2016)

#48

Post by raylad »

diegocg wrote: post #35
raylad wrote: post #31

Earlier quoted context omitted.

It will become a very big problem if/when buildings start collapsing with people in them. I grew up partly in an 18 story reinforced concrete building built in the 1920s. The apartment I lived in was recently sold for several million dollars. Once, when there was a leak and the plaster came off, the underlying concrete was exposed and it scraped away like very weak sandstone. How strong is the building and when will…

Unless you are living in a developing country, the answer to the second question should be "yes".

It should be but is it? I don't think anyone ever tested this building, which has a combined market value of probably close to $200M.

None of the owners want to know that their investments are worthless. So nothing will be checked unless its required by law.

Re: The problem with reinforced concrete (2016)

#49

Post by petertodd »

XorNot wrote: post #27
Jerry2 wrote: post #24

Earlier quoted context omitted.

> graphene Graphene has its own set of problems. Namely, it can be toxic to humans. [1] And who knows what massive quantities of graphene in concrete will do to an environment 10-20 years after the building's construction. Even demolition with explosives will probably be problematic due to potentially massive clouds of nanoparticles it could create. [1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5039077/

Graphene isn't persistent though - it burns.

So does plastic.

Re: The problem with reinforced concrete (2016)

#50

Post by quickthrowman »

brutusborn wrote: post #3

This should be an economics piece, not an environmental piece. The author states that "one of iron’s unalterable properties is that it rusts" yet further on acknowledges the existence of stainless steel. There's nothing wrong with reinforced concrete, but the incentives to produce long lasting buildings are not there. The cheapest bidder will generally win and their building will last the "design life" of the buildin…

> The cheapest bidder will generally win and their building will last the "design life" of the building, but often not much more. The simplest way to change this is to extend the design life, which would result in stainless steels or another more expensive material being used in this application.

Just FYI, on a ‘plan and spec’ construction project, all material is specified by the architect and engineers. If the project specs say you have to use stainless steel rebar, then even the low bidder will have it included.

Post reply on HN