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The problem with reinforced concrete (2016)

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Re: The problem with reinforced concrete (2016)

#141

Post by strken »

wahern wrote: post #29
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 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 .

I went and googled the most obvious solutions I could think of for protecting rebar from rust.

- dipping rebar in epoxy is sometimes done, but a single nick in the coating causes all the erosion to concentrate in that one spot, so it can be more dangerous than just uncoated rebar

- galvanised rebar works much better than epoxy, and resists corrosion at lower pH levels than normal iron, but may result in more metal loss under some conditions

- sacrificial anodes (as per the article) can and are used, but exactly how is quite complicated: if they're embedded in the concrete, the zinc breaks down into substances that can weaken it

- concrete is naturally alkaline, with cement being manufactured partly from lime, and this protects the rebar, but too high a pH causes other problems in the concrete itself, so you can't just dump alkaline substances into the mixture forever

- you can apparently use fibreglass as rebar, but I have no idea if it's any good, or what happens to fibreglass if you leave it embedded in concrete for a century

Re: The problem with reinforced concrete (2016)

#142

Post by ihsw »

mrfusion wrote: post #133
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 .

What are car mufflers made of that they resist rust so well?

Usually galvanized steel, you can tell by the speckling pattern.

Re: The problem with reinforced concrete (2016)

#143

Post by windthrown »

quickthrowman wrote: post #88
singlow wrote: post #84

Earlier quoted context omitted.

But on big projects, doesn't the architect often work for the bidder?

No, the architect works for the building owner (or tenant). The bidder is typically a general contractor.

I think that comment was asking about "Design-Build" projects which are becoming more and more common.

Re: The problem with reinforced concrete (2016)

#144

Post by 0xbadcafebee »

geoffmunn wrote: post #124
rootusrootus wrote: post #96

Earlier quoted context omitted.

> Roman concrete that we can't reproduce. That claim seems to date to a particular article written in 2017 that wasn't well sourced. Roman concrete is interesting stuff and has useful properties, but humans have since created concrete mixtures that are far superior. But they're expensive, so it's not too surprising we don't see them getting used in buildings that compare less than favorably to a temple built a couple…

I asked my dad about this a while back - he spent his entire career in civil engineering and he said almost exactly what you just did. Basically; modern concrete is far better, but often not built that way.

I haven't seen that theory tested. I can't find any tests or studies anywhere of replicated Roman concrete. And no tests of genuine Roman concrete, either. We don't know how it actually performs. So to make a comparison to modern concrete is specious.

Modern concretes can do a whole lot of stuff Roman concrete can't, because there are so many formulations of it. But if you want to stick a building literally in the ocean and have it never ever disappear, nobody has shown that we can actually do it today.

There's a whole lot of theory and talk by experts, about how we don't need to make it, but if we wanted to, boy would it be easy, but don't worry, modern concrete is just so amazing, you should just use that, for modern use cases, and oh by the way, it would be too expensive to make, even though we haven't actually made it or tried to bring the price down.

There's a world of practical experience needed to claim for a fact that modern concrete is legitimately better, much less that we can actually make it and that it would hold up as we expect. I'm still waiting for concrete evidence.

Re: The problem with reinforced concrete (2016)

#145

Post by ClumsyPilot »

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".

"First world country" does not correlate well with housing quality. UK has some of the worst housing in Europe, with 35% in need of repair. Many Ex Soviet states like Czech Repulbic are doing better.

UK also has a history of major failured in construction practices and inspection, where chunks of a new apartment block suddenly collapse like in Ronan Point, or a recently renovated tower block goes up in flames and half of residents die despite them warning about issues for years.

I wish living in first world country guaranteed sensible things are happening, but it doesn't

https://www.theguardian.com/environment/damian-carrington-bl... https://en.wikipedia.org/wiki/Ronan_Point https://en.wikipedia.org/wiki/Grenfell_Tower_fire

Re: The problem with reinforced concrete (2016)

#146

Post by Jerry2 »

kortex wrote: post #90
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/

> Namely, it can be toxic to humans Uhhhh the rest of the stuff in Concrete isn't great for human health, either, or as my cousin likes to say, "it sure ain't vitamins." Quartz dust and silica sand are really bad for the lungs, likely carcinogens. Lime is caustic. Dust in general is bad to breathe. These are well-known hazards in demolition and mitigation techniques already exist.

I never said it was. I'm saying that adding carbon nonoparticles will only make matters much worse.

Re: The problem with reinforced concrete (2016)

#147

Post by rsj_hn »

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…

With 30 year fixed rate mortgages at 3%, I'd say the present value of a building that lasts 100 years is 23% more than the present value of a building that lasts 50 years. It's certainly worth it to spend more for a longer lasting building.

Re: The problem with reinforced concrete (2016)

#148

Post by courtf »

samatman wrote: post #63
ConcernedCoder wrote: post #33

Tangentially related. The romans figured out that volcanic ash and salty sea water made cement that actually gets stronger with age instead of breaking-down after 50 years: https://www.sciencemag.org/news/2017/07/why-modern-mortar-cr...

I'm not sure, but this probably fits the facts better: the Romans figured out how to make cement with volcanic ash and salty sea water, and it turns out that it gets stronger with age. It's not clear to me that the Romans knew that, or that it informed their choice of that building material. I suspect it's more that they built with what they had, and got lucky that it turns out to be incredibly durable stuff.

The Roman scholar Pliny the Elder described underwater concrete structures that become "a single stone mass, impregnable to the waves and every day stronger."

https://www.nature.com/news/seawater-is-the-secret-to-long-l...

Sounds like they knew.

Re: The problem with reinforced concrete (2016)

#149

Post by ClumsyPilot »

LegitShady wrote: post #122
teh_klev wrote: post #58

Earlier quoted context omitted.

> Reinforced concrete seems to do exactly what it's intended to do for the designed life of that intent Until there's apparently "no money" to replace the structure after its design life time. Thinking in decades of life span for many of these structures is very short sighted. I think the article mostly gets that across i.e. re-enforced concrete is hard to recycle and their life span is often within that of a human l…

Municipal and other budgets are already highly strained all over. If the cost of an interchange or large culvert goes up 2x to increase its lifespan, you can do less work now. Your level of service goes down now. There are trade offs to everything. Build something much more durable, pay twice as much, do half the work in a season and get more complaints. We already aim to build infrastructure based on estimates of fu…

Budgets are strained precisely because they are saddle with 50 year old structures in need of maintenance. Only a small % of the budget goes to new construction.

Saving a little on the upfront cost only to pay a lot more for maintenance is a false economy. Stainless steel rebar does not double the cost of construction, and neither does high quality concrete.

We need to stop buying subscribtion to "bridge as a service"

Re: The problem with reinforced concrete (2016)

#150

Post by mrfusion »

naikrovek wrote: post #140
mrfusion wrote: post #133

Earlier quoted context omitted.

What are car mufflers made of that they resist rust so well?

plain steel, I believe, but they get very hot on trips of even a few km, which drives off any resting moisture and prevents exhaust moisture from condensing for a while after the engine is stopped. cars that make many short trips, which never give the exhaust system time to fully warm up, often have extremely compromised exhaust systems, because the moisture simply can't be driven away effectively.

Still crazy to think they drive through salted roads for a decade and are basically ok.

Btw were Deloreans pretty rust resistant? How will the cyber truck do living by the beach?

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