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The problem with reinforced concrete (2016)

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Re: The problem with reinforced concrete (2016)

#71

Post by soperj »

peteradio wrote: post #64
wahern wrote: post #29

Earlier quoted context omitted.

> The author states that "one of iron’s unalterable properties is that it rusts" yet further on acknowledges the existence of stainless Even stainless steel rusts, just more slowly. Roughly 10-100x more slowly, judging by https://www.nrc.gov/docs/ML1124/ML112490377.pdf and https://www.mdpi.com/2076-3417/10/23/8705/pdf .

That doesn't smell right. I've got 15 year old knives that have never once shown signs of rust. A pair of old scissors left in the rain rusted in under a day. That puts the factor to closer to >10000 than 10 or 100...

You leave your knives outside?

Re: The problem with reinforced concrete (2016)

#72

Post by sgillen »

peteradio wrote: post #64
wahern wrote: post #29

Earlier quoted context omitted.

> The author states that "one of iron’s unalterable properties is that it rusts" yet further on acknowledges the existence of stainless Even stainless steel rusts, just more slowly. Roughly 10-100x more slowly, judging by https://www.nrc.gov/docs/ML1124/ML112490377.pdf and https://www.mdpi.com/2076-3417/10/23/8705/pdf .

That doesn't smell right. I've got 15 year old knives that have never once shown signs of rust. A pair of old scissors left in the rain rusted in under a day. That puts the factor to closer to >10000 than 10 or 100...

Maybe if you want to invalidate those studies you can try leaving the knives out in the rain 10-100 days in a row!

Re: The problem with reinforced concrete (2016)

#73

Post by robocat »

raylad wrote: post #31
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…

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…

> Does anyone know? Is anyone testing?

In first-world countries/states with earthquakes, the answer to this is often yes and yes.

A good article from 2000 in Christchurch discusses the issues: https://www.canterbury.ac.nz/media/documents/event/Hopkins-L...

The article is relevant because Christchurch had a major earthquake in 2011. I know of quite a few older buildings that were retrofitted that did not even need to be demolished (most buildings are designed to just survive a major earthquake, but often they need to be demolished due to damage, similar to writing off cars after accidents).

Christchurch did have regulatory failures because many older buildings were known to be unsafe (e.g. only meeting 10% of current code/regulations), but owners could defer fixing them up to code almost indefinitely. But that regulatory failure is being addressed in other parts of the country e.g. Wellington.

The South Island of New Zealand is overdue for a magnitude 8.2 Earthquake which will devastate many towns on the West Coast, and will affect the whole country indirectly. https://www.stuff.co.nz/the-press/news/90364889/magnitude82-...

You can sometimes see where concrete of a building has been tested for example a circular hole about 10cm across is left where a sample was taken.

If interested, next time you meet a civil engineer or someone working in the relevant department that deals with the building codes will often know relevant details about your location.

Re: The problem with reinforced concrete (2016)

#74

Post by mardifoufs »

peteradio wrote: post #64
wahern wrote: post #29

Earlier quoted context omitted.

> The author states that "one of iron’s unalterable properties is that it rusts" yet further on acknowledges the existence of stainless Even stainless steel rusts, just more slowly. Roughly 10-100x more slowly, judging by https://www.nrc.gov/docs/ML1124/ML112490377.pdf and https://www.mdpi.com/2076-3417/10/23/8705/pdf .

That doesn't smell right. I've got 15 year old knives that have never once shown signs of rust. A pair of old scissors left in the rain rusted in under a day. That puts the factor to closer to >10000 than 10 or 100...

There are different grades of stainless steels. The common, "construction" grade stainless steels usually rust albeit very slowly. And while some of them are basically impervious to corrosion, they are usually way more expensive or have a lot less tensile strength. I don't know about knives specifically but it wouldn't surprise me if those more corrosion resistant grades are what's used to make them.

Re: The problem with reinforced concrete (2016)

#75

Post by scythe »

gonzo41 wrote: post #60

Surely this could be the moment for glass fiber reinforced concrete to take center stage. It really should just last forever.

My understanding is that alkali-resistant glass is required, but the 18% ZrO2 used means that it isn't much cheaper than using carbon fiber, which seems to have slowly taken over. But GFRC is bright white, while carbon fiber makes a greyish product, so the former is preferred for decoration.

Re: The problem with reinforced concrete (2016)

#76

Post by dominojab »

peteradio wrote: post #64
wahern wrote: post #29

Earlier quoted context omitted.

> The author states that "one of iron’s unalterable properties is that it rusts" yet further on acknowledges the existence of stainless Even stainless steel rusts, just more slowly. Roughly 10-100x more slowly, judging by https://www.nrc.gov/docs/ML1124/ML112490377.pdf and https://www.mdpi.com/2076-3417/10/23/8705/pdf .

That doesn't smell right. I've got 15 year old knives that have never once shown signs of rust. A pair of old scissors left in the rain rusted in under a day. That puts the factor to closer to >10000 than 10 or 100...

they rust if you have stainless still that havent been chrome or nickel plated leave them in the rain for a season or two.

Re: The problem with reinforced concrete (2016)

#77

Post by phkahler »

soperj wrote: post #71
peteradio wrote: post #64

Earlier quoted context omitted.

That doesn't smell right. I've got 15 year old knives that have never once shown signs of rust. A pair of old scissors left in the rain rusted in under a day. That puts the factor to closer to >10000 than 10 or 100...

You leave your knives outside?

Knives tend to get washed.

Re: The problem with reinforced concrete (2016)

#78

Post by lovemenot »

hackeraccount wrote: post #45
nerdponx wrote: post #20

Earlier quoted context omitted.

> 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 b…

I understand your reasoning. The problem is that this line is seldom used in the opposite direction.

You want a flimsy shell and to externalise the environmental impact? Sure thing, whatever the market will bear and is legal.

I think it is fair enough for people to put pressure on current practices. Zara and H&M will persist, but their customers should be and, thanks to outside voices, are now aware that social and environmental factors are involved in fast fashion.

Sure, it's arbitrary. But we still have alternatives. All else being equal, less entropy is better than more.

Re: The problem with reinforced concrete (2016)

#79

Post by gamblor956 »

wonder_er wrote: post #56
GoToRO wrote: post #40

Earlier quoted context omitted.

I spoke with a builder, and the concrete starts to decay in 50 years. Until then it's like new. It lasts much longer than that, 100+ years is not a problem.

I suggest the builder may have suffered from some motivated reasoning. Concrete not starting to decay until 50 years has passed is the exception, not the rule.

Only if you have poorly mixed concrete.

The kind of concrete they use in buildings is not the same as the concrete they use in sidewalks.

Re: The problem with reinforced concrete (2016)

#80

Post by bombcar »

lurquer wrote: post #51
minikites wrote: post #4

Earlier quoted context omitted.

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

Good point. What hubris for a landowner to assume there will be a need for a building 1000 years hence. Buildings aren’t usually demolished and replaced because they are dilapidated; rather, it’s because the new owner has a different need (and a different aesthetic.) A building that takes 1000 to crumble is just as a much a blight — maybe more — as a plastic bottle that takes 10,000 years to crumble.

Arguably for many buildings we should be going the other way - if the average house is remodeled or torn down in 30-40 years perhaps we should be building out of renewable materials that are designed to last long and no more (think hay bales covered with mud).
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