> Given the survival of ancient structures,
Survivorship bias...
The problem with reinforced concrete (2016)
61–70 of 192 posts
Re: The problem with reinforced concrete (2016)
#62I 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…
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.
The problem, as per the article, isn't concrete. It's rusting steel inside reinforced concrete.
Re: The problem with reinforced concrete (2016)
#63Tangentially 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.
Re: The problem with reinforced concrete (2016)
#64This 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 .
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...
Re: The problem with reinforced concrete (2016)
#65Earlier quoted context omitted.
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.
In Spain buildings older than 50 years are required to be inspected and mandated to make reforms if necessary. I doubt it's much different in the rest of Europe/north America
Also, buildings don't fall all of sudden. You would get a lot of cracks and problems before your building collapses
Re: The problem with reinforced concrete (2016)
#66Reinforced concrete has achieved regulatory capture via the building codes. If you try to build with anything non-standard, prepare to deal with a mountain of red tape.
Given past "innovations" in the space of building materials, I think this is just about the last place people should be complaining about needing to comply with regulations...
Re: The problem with reinforced concrete (2016)
#67An 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 construct…
As a point of interest, recycled concrete is referred to as "urbanite".
https://www.concretenetwork.com/concrete/demolition/urbanite...
It's definitely a case of downcycling, though: there's a lot less we can do with urbanite than with cement and aggregate in their original forms.
Re: The problem with reinforced concrete (2016)
#68Fiber-reinforced cement composites are an interesting alternative:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/suco.2017001...
Some German researchers seem to think that carbon fiber-reinforced polymer "rebar" could be more durable than steel bars with similar cost and lower weight:
https://www.aboutcivil.org/carbon-reinforced-concrete-buildi...
Unfortunately, the terminology is not well standardized, and when you look up "carbon fiber reinforced concrete", you never know if you're going to get a fiber-reinforced cement composite (incorporating carbon fibers directly into the cement matrix) or a CFRP rebar system. Regardless, there do seem to be some improvements on the horizon.
Re: The problem with reinforced concrete (2016)
#69I 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…
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.
To be clear, the article is discussing reinforced concrete—concrete made with steel rebar, which rusts.
Unreinforced concrete can and does last for many hundred years. Reinforced concrete, not so much.
FTA:
“Early 20th-century engineers thought reinforced concrete structures would last a very long time – perhaps 1,000 years. In reality, their life span is more like 50-100 years, and sometimes less. Building codes and policies generally require buildings to survive for several decades, but deterioration can begin in as little as 10 years.”
Re: The problem with reinforced concrete (2016)
#70I took an engineering course on concrete 30 year ago. There were a lot of additives and techniques described which improve various properties but it seems like 30 years later cost is the biggest consideration.