Comment by gjem97 | Hacker News Reader

Comment by gjem97 | Hacker News Reader

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I for one would love to see something like this happen, but I think ultimately this will always be limited to niche applications.

A developer recently built a 20 story apartment building next to my office window using entirely a reinforced concrete frame. I was incensed to find out that because of "concrete cancer" [1], the lifespan of that building may be less than 70 years. But the more I thought about it, the more I began to believe that maybe the additional lifespan is not an asset. The building is attractive today, but might not (probably won't) appeal to people 40 years from now. Furthermore, buyers are going to want different things from their homes (look at the popularity of open kitchens 40 years ago vs now). And I began to realize that it would be quite difficult to design and build a building that would be useful beyond 70 years from now.

Another way to look at it is that the marginal value of 10 years of longevity is not that large out 80-90 years. I think you'd have a difficult time finding a developer who would pay 10% extra to get a building that lasts 100 years instead of 90.

This line of reasoning leads to an icky "planned obsolescence" approach, but I think these are the economic realities.

[1] http://www.remedial.com.au/structural-repairs/concrete-cance...

A properly designed concrete structure will include enough clear cover (that is the distance between the surface and the reinforcement) to avoid water reaching the reinforcement. It should also take precautions such as roofing to avoid water interacting with the concrete in the first place.

LEED certification includes a credit called "good bones" which recognizes that although exterior trends change, the concrete bulk of a building can be reused if kept in good condition. A new facade can completely rejuvinate an otherwise dated structure. Most concrete building construction focuses on creating large open floors with columns to provide the largest flexibility in floor plan.

An additional interesting trend I've been seeing in Chinese construction is the construction of structures with double the standard height between floors. These buildings can be finished with units with features such as high ceilings and loft spaces that most high-rise units cannot accommodate.

It's not always the reinforcement. It can also be the accumulated result of decades of very slow reactions happening in the cement binder, or between the binder and the aggregate, generally also driven by moisture and gases penetrating the pores in the concrete, so cracks and spalling accelerate the process.

If it was just the rebar, we could replace the iron rebar with drawn basalt fiber rebar.

Perhaps in the future, structural concrete will be covered in an outer layer of ceramic that is subsequently vitrified at a certain stage in curing. You keep your building from collapsing by burning it in a towering inferno first.

That's good context, thanks. We're quite near a salt water estuary here, I imagine the humidity and salt in the air also makes a difference...

Another thing you can do relatively cheaply (I think) is powered cathodic protection. I don't know if they bothered to do that on this building.

You might want to Google Images for Brasília (Brazil's capital), built in the 50's with godzilions of reinforced concrete. It's still spectacular but it's high maintenance and you can see concrete cancer everywhere. I'm not sure if it was a good idea to use it there but surely it is gorgeous due to the architectural possibilities of reinforced concrete.

It seems that the term "Concrete Cancer" has been somewhat watered down since I studied Civ Eng at Plymouth Polytechnic (Devon, UK) in '89-91. I think you are referring to spalling.

It was a while back but I recall that the characteristic map cracking and eventual failure need salty water as well as the correct chemical composition of the cement used. I think there are something like three conditions needed. Stop one and you fix the problem. I seem to also recall that PP's Civ Eng dept did a lot of work on this in the '80s. Plymouth is a sea side city and has a lot of concrete structures that suffered eg Charles Cross multistory car park.

To be honest I would find it hard to believe that a structure that size would be designed to that short time scale. I'm not familiar with Aussie building regs (I'm not familiar with anyone's outside the UK and saw a.com.au link!) but it would be very hard to design for so short a lifespan. There will be a minimum conc. depth to the reinforcing bars, just for fire regs, let alone spalling. If the weather is a bit fierce then the other design criteria like being able to withstand a 1 in 100 or 200 or whatever year event will also play a part in the lifespan. Obviously there will also be a factor of safety applied which could be as high as 1.4. Take a close look at the final finish, it may have been sealed in some way. Keep the water and freeze/thaw and the like away and conc. can last a bloody long time.

I think you're both right and wrong :)

You're right in that certain buyers are going to be looking for certain elements that might not make much sense from a long-standing building point of view. Architectural shapes and trends change over time.

On the other hand, its also true that a lot of these trends are just bad architectural design. Period.

Sunken lounges of the 70's. Media-rooms and conspicuous consumpition-esque cavernous entrances and questionable elements in macmansions. These are designs that are incredibly difficult to repurpose into anything but their original purpose.

In my country (Aus), there is a now a common suburban design that almost entirely ignores long term elements and lessons of the environment that have been known for at least 100 years: see https://en.wikipedia.org/wiki/Queenslander_(architecture). Now we have a poor relation of the generic american style: dark roofs and colours, no overhangs/shelter/verandahs, directly western facing living areas and frontages, all designed to maximize internal sq meters/price.

Now, i appreciate that my queenslander example is a style built of wood traditionally. But there is another style example of highly valued real-estate with long term potential in the urban centres: victorian terraces and townhouses. Aside from the regrettable wealth signaling effect of owning one, its an architectural form that has lasted the test of time and is arguably constructible via concrete. And one of the reasons it has done so is because that form is the complete opposite of the media room/sunken lounge/mcmansion: almost universally flexible and readjustable. A proper Victorian townhouse in its context can be reclaimed and used as a bar, as a restaurant, as a residence, as an office or a place of business. Though like all succesful architecture, this is only because it works in the context of its environment.

As an example, here's a strange eyesore on an otherwise nice landscape that probably looked futuristic or something back when it was made, the concrete square tower to the right of the turquoise pyramid thing. http://www.newpaltz.edu/media/stock-images/slides/12308197_9...

That may just be a dormant Vogon spaceship.

Stranger Things

As someone who lives in a building that is 70 years old, I can tell you pipes (brass?) only last about 70 years.. redoing piping in place is a major pain. If the location wasn't so good I'd be gone long ago..

Pipes can last centuries or only years, depending on the material, the temperature, and the solutes in the water — even without getting into cases where the pipes actually break. Both lead and copper (which is more common than brass!) can last centuries in cold water that isn't chemically aggressive. Heck, in Boston a few years back, they dug up some wood pipes that were installed in the 1700s.

We tore our house apart somewhat about eight years ago and had all the pipe work replaced, amongst other things. We also (I did this bit because builder/plumbers generally take the path of least resistance) removed the last two lots of re-plumbing. The house was built in the '20s which is pretty modern hereabouts.

Brass is unlikely, copper is the material. The oldest pipe work I found was steel in our place - it was hard and weighed a fair bit. Copper is maleable, easy to bend and braze joints on to. It does corrode eventually but I think the thin layer of copper oxide that forms then seals in the pure copper, protecting it. The longevity of copper can be seen in the green roofs of some churches which must have looked absolutely stunning before oxidizing.

AFAIK pipes are usually replaced every 50 years. That's the common timespan around here at least. And yeah it's expensive.

I believe copper piping is most-common, it's always the first thing building-site thieves go for!

Which means my investment in the property will only last what? 50 Years?

70... 80-90... 100...

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