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The problem with reinforced concrete (2016)

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Re: The problem with reinforced concrete (2016)

#171

Post by KMag »

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.

At least those samples to be mixed just right to survive over 1,000 years had a mixture that got stronger with age. There's a big element of survivorship bias.

Also, due to a lack of reinforcement, Roman concrete structures, at least those that survived, avoided putting concrete in tension. Roman concrete won't last very long in areas of buildings that are under tension. Edit: the implication being that using Roman concrete would make many modern building designs unworkable, particularly taller thinner designs that sway a bit in the wind.

Re: The problem with reinforced concrete (2016)

#172

Post by culturestate »

WalterBright wrote: post #168
culturestate wrote: post #125

Earlier quoted context omitted.

There's nothing wrong with having long eaves if that's your preference; I'm just pointing out that there are a lot of factors that go in to building a long-lasting structure, and the answer to most questions around best practices is "it depends." If you have a two-storey house in a wet area that gets a lot of storm activity coming from the northeast, for example, and you have an exposed northeast-facing wall, the eav…

> it might be good advice in Seattle Jeez, of course one pays attention to the local climate. I don't worry about tornadoes in Seattle, but would if in the midwest.

> Jeez, of course one pays attention to the local climate.

Believe it or not, this kind of thing isn't just immediately obvious to everyone.

Re: The problem with reinforced concrete (2016)

#174

Post by sgtnoodle »

frosted-flakes wrote: post #93
sgtnoodle wrote: post #44

Earlier quoted context omitted.

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.

Like zinc anodes on a boat?

Yep, I believe that's the same mode of operation. The definition of galvanic is, "relating to or involving electric currents produced by chemical action."

Re: The problem with reinforced concrete (2016)

#175

Post by dan-robertson »

sokoloff wrote: post #129
dan-robertson wrote: post #97

Earlier quoted context omitted.

Yeah I think this is a better way to put it. By incentivising long-lasting buildings you are better pricing in the amortised (environmental) negative externalities of tearing down and rebuilding. I see two arguments against: 1. Future buildings will be so much better for the environment that increasing costs today for long lasting buildings or having to wait longer for environmentally better buildings is a net negati…

> Old buildings are typically not useful. My 95 year old brick house would beg to differ on utility of old buildings. My prior house was over 230 years old and provided 14 years of excellent utility to me.

Old is certainly relative. A 200 year old house fits more into point 1 than 2 above. A 230 year old office block tends to not be such a well suited building.

Re: The problem with reinforced concrete (2016)

#176

Post by pgrddy »

It's also important to note that not all medieval and historic structures survived the test of time. A case of Survival-Bias. As the utility requirements of the structure may change over time,there is no incentive for engineers and clients to design a structure that would last more than 50-100 years. As far as the current building design provisions and policies go by, rebar does it's job.

What needs intervention is to find a suitable replacement for concrete/cement citing it's increasing contribution to global warming.

Re: The problem with reinforced concrete (2016)

#177

Post by triggercut »

Animats wrote: post #127
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…

Stainless steel rebar is quite real, and becoming more common for bridges. It's essential for concrete exposed to salt water, which includes bridged de-iced with sale. Order now.[1][2] There's epoxy-coated rebar, but that's on the way out. Quebec has already banned it. One scratch, water gets in, and corrosion starts. Also, the epoxy can be damaged by UV, like when there's a stack of rebar out in the sun. [1] https:/…

To build on your very important last point. Material handling procedure is something that I haven't seen mentioned here that is a very real issue too. Similar to agriculture or pharma where entire stocks can be thrown out if stored incorrectly, in many construction and manufacturing contexts your steel can be thrown out for not being stored correctly too (i.e. left at the port in the open for extended periods, or mixed with other metals). Not just steel, but lots of building products (like membranes) will usually be specd with how they should be stored before use.

Re: The problem with reinforced concrete (2016)

#179

Post by sidewndr46 »

ggcdn wrote: post #164
LegitShady wrote: post #158

Earlier quoted context omitted.

if you need to weld the rebar into cages (like you often do) then the cost goes up even more as welding ss is harder. But you're not wrong in general. There will still be corrosion in the concrete eventually but less likely from rebar oxidation.

Welding rebar is almost never used in North American building construction, and is actually forbidden in high seismic zones. But then again so is stainless steel rebar and carbon fibre rebar and most of these other types of products because they lack ductility

This is kind of what I was thinking while reading comments here.

I'm sure stainless rebar is easy to make. We could turn out huge amounts of it. But I don't see it ever having the same useful properties. All manner of stainless I've worked with is incredibly stiff and hard compared to regular steel. It's actually desirable in most applications, but rebar in particular needs to be flexible.

Re: The problem with reinforced concrete (2016)

#180

Post by jaclaz »

tomc1985 wrote: post #131
0xbadcafebee wrote: post #37

Earlier quoted context omitted.

There is no way to know other than to ask the architect. You can make educated guesses but that still won't tell you. Even then it's up to the contractors to have done everything properly. Or if it's made of stone. Stacking giant stones on top of each other is a sure-fire way to make a building outlive you. After that, the longest-lived buildings that I am aware of are made of wood. The catch is they've been rebuilt…

Didn't they figure out that Roman concrete was made or infused with ash from a volcano or something? https://en.wikipedia.org/wiki/Roman_concrete

Yes, but it is not that we don't use (or at least it is possible to use) ashes in "modern" concrete, typically we use ashes that are a by-product of (carbon based, yes I know) electrical generation plants.

The bigger difference in components is the kind of cement the Romans (and we "moderns" until a few years ago) used, i.e. pozzolanic cement, nowadays everything is "portland" cement.

BUT the definite difference is the kind of structures, Romans did not use "reinforced" concrete, only various types of "plain, non-reinforced" concrete, and all their structures are based on the main characteristic of concrete, which is its resistance to compression.

The idea of reinforced concrete is all about adding to a material with excellent compression resistance (but no resistance on tension/traction) a material (steel) with excellent resistance to tension/traction and relatively poor (in the quantities used in reinforced concrete) resistance to compression, obtainining a composite material that excels in both.

About ashes, overall it is more about their size that about their nature, concrete is a composite and if you have all possible sizes of aggregates (ashes are very, very small sized particles) in the "right" amount you essentially fit "better" the space, i.e. you have a higher density of the resulting composite, and, particularly when compression resistance is the goal, the higher the density the better the resistance.

Imagine (say) that you have to fill a 100x100x100 mm box with 10 mm balls, you can fit in them a certain amount of these balls (roughly 10x10x10=1000), but you are leaving lots of "air" between them, a single 10 mm ball is 2/3x3.1416x5^3=262 mm3, so the 1000 balls total 262,000, but the volume of the box is 100x100x100= 1,000,000, now if you have some 2 mm balls you can add them in the same volume, and then if you have some 0.5 mm balls you can put some of them in that same box as well, etc.

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