10 ms·
How Cities Will Fossilise
- fnord77 5y agoI learned recently that reinforced concrete buildings only last about 50 years. Moisture and oxygen seeps into concrete and corrodes the rebar.
- karolist 5y agoMany WW2 era German bunkers and coastal batteries seem fine with no maintenance and erosive sea climate doing it's thing so not sure about that. https://www.tracesofwar.com/sights/12168/German-Coastal-Battery-Klaipeda.htm https://www.tracesofwar.com/sights/12168/German-Coastal-Batt...
- medium_burrito 5y agoYeah, German reinforced concrete structures like those and the flak towers are basically gonna last longer than the pyramids. They are the honey badger of architecture.
- hoseja 5y agoThere's difference between engineering for lowest possible cost and engineering to win a war.
- warmwaffles 5y agoUh no, axis and allies produced the cheapest/most effective means to win the war. Take for instance the Stg44, mostly stamped sheet metal. Russian PPSH, stamped sheet metal.
- labster 5y agoI think GP was trying to say that fortified buildings last longer than shoddy McMansions. Which seems true given the survival ratio of castles to hovels over a millennium or so. Of course to win a war you may want to fortify cheaply... but given the modern system armies we have now I’d have to say that part of the grand strategy is to simply outspend rival nations.
- hulitu 5y agoI think 50 years is a very pessimistic (and journalistic) value. There are whole towns in eastern europe build with reinforced concrete and they are still ok.
- Mediterraneo10 5y agoThey often aren’t OK. In many of those whole towns in Eastern Europe, the municipality is gradually pushing to move people out of the socialist-era concrete buildings and into newer ones. Their design means that, even if the structure itself does remain physically sound, they often struggle with ventilation, so mold forms.
- lucian1900 5y agoThat’s not universally true. In my home city the socialist-era blocks tend to be the ones without mould, when compared to some of the under-regulated new builds. If anything they’re sought after.
- dtgriscom 5y agoTrue, but unrelated to the point being made.
- PeterisP 5y agoThis seems to be mostly a construction quality issue of the time - in my corner of Eastern Europe, the 1960s buildings often are so bad to need reconstruction or replacement, but the 1900s/1910s/1920s/1930s buildings are structurally fine (with some exceptions due to total neglect) despite being twice as old. It's more of an indicator if you intentionally build mass cheap sloppy housing intended to be temporary just to allow faster urbanization ASAP (as arguably was the goal of 1960s soviet housing projects), then you're not getting proper long-term buildings - IIRC it was expected already when being built, the planned design lifetime of those buildings without major repair was just 30 years or so, and they've certainly met that bar.
- Quenty 5y ago
- WJW 5y agoThat seems super unlikely to be true. Easy counterexample: the Ingalls building in Manhattan was the first skyscraper to be built out of reinforced concrete and it was built in 1903. It still stands today. https://en.wikipedia.org/wiki/Ingalls_Building https://en.wikipedia.org/wiki/Ingalls_Building
- s_dev 5y agoIt's been maintained with constant supervision. Probably regular inspections and fixes. Watch what happens in as little as ten years once it has no human intervention at all.
- tokai 5y agoTen years of no-maintenance is unhealthy for any type of building.
- bruce343434 5y agoWhat does the maintenance look like? Try to spray wd40 in between the concrete cracks? I can't really find anything about this anywhere.
- Red_Leaves_Flyy 5y agoThe eli15 answer is that concrete is repaired by excising the damage and replacing what was removed. If you're really interested check out Sikas brochures.0 if you prefer video form I found this [1] that seems to cover a good variety of applications and can probably be comfortably watched at 2x speed. Maintaining concrete is a matter of having routine structural inspectors come out to poke and prod the concrete. Worn traffic areas get patches and sealants. Areas with a lot of runoff get seals to direct water in ideal ways. Etc. 0. https://www.sika.com/en/construction/structural-strengthening.html https://www.sika.com/en/construction/structural-strengthenin... 1. https://youtu.be/c0Pj5Qdy9IU https://youtu.be/c0Pj5Qdy9IU
- mr_overalls 5y ago
- todorstoyanov 5y agoThis can be the period the construction engineers are responsible or the worst possible exploitation conditions. My estimate is 200 - 300 years if roof is maintained well and no pipe leaks inside.
- lazide 5y agoWorst possible conditions usually involve seawater, acidic conditions, and/or moisture. Even without those factors it’s rare for reinforced concrete to last more than 50 years. The more protection from the elements, the better of course. Most concrete structures with long design lifetimes made of concrete (some dams, levees, bridges - but not all by any stretch) will use design techniques to minimize or remove the use of rebar, such as compression only designs , or ‘overbuilding’ so expected corrosion still leaves the structure strong enough over it’s design life. Generally, concrete is a strongly base compound and protects rebar from corrosion. Over time however it can be influenced by the environment, with those base compounds reacting and leaving a less protective environment. Some environments do it faster than others. If the covering concrete is strong enough/thick enough, the pressure caused by the rebar turning to rust inside the concrete won’t crack it - if the rebar was structurally important (pretty much always or why use it?) it still weakens the structure though, sometimes dangerously. Attempts to mitigate the risk where weatherproofing is not an option and rebar is essential for structural reasons like concrete roadways and bridges have had their share of disasters. epoxy coated rebar for instance can lead to unpredictable and sometimes rapid failures in exactly the types of environments it was expected to help in [https://www.fhwa.dot.gov/publications/publicroads/99novdec/rebars.cfm https://www.fhwa.dot.gov/publications/publicroads/99novdec/r...] https://partridge.com.au/concrete-cancer-what-is-it-and-what-does-it-mean/ https://partridge.com.au/concrete-cancer-what-is-it-and-what... Some other failure modes include the Alkali-Silica reaction (sometimes confusingly named concrete cancer too, though fundamentally different) [https://en.m.wikipedia.org/wiki/Alkali–silica_reaction https://en.m.wikipedia.org/wiki/Alkali–silica_reaction] The more dependent a design is on an element that can corrode, and the tighter it’s design tolerances, the more fragile it is. The more overbuilt it is, and more conservative the design, the more expensive it is. Taking a low margin design and then not maintaining it is a recipe for this kind of disaster [https://www.google.com/amp/s/www.independent.co.uk/news/world/europe/genoa-bridge-collapse-engineer-riccardo-morandi-warning-corrosion-rust-concrete-a8498716.html%3famp https://www.google.com/amp/s/www.independent.co.uk/news/worl...] and lots of dead people.
- marcosdumay 5y agoSteel does not corrode when embedded in concrete. The failure mode of reinforced concrete is when the rebar loses contact with the concrete. This condition can be detected and fixed before failure.
- refurb 5y agoApparently it depends on the climate. In Singapore, you need to maintain the surface of the concrete to keep water out or the rebar corrodes and the concrete spalls. Buildings only last 50 years or so before being torn down and rebuilt. https://www.mynicehome.gov.sg/article/dealing-with-spalling-concrete-in-your-flat https://www.mynicehome.gov.sg/article/dealing-with-spalling-...
- marcosdumay 5y agoIt doesn't depend on the climate, but it does depend on the concrete chemistry (that does vary geographically). Anyway, the sequence is that micro cracks form on the concrete and expose the steel, then the exposed steel rusts and pushes more concrete away, exposing more steel. This too can be fixed before it becomes a problem.
- bilbo0s 5y agoI think the material point is that, as engineers, we have to all concede that modern concrete has that fatal flaw. People are being hyperbolic here when they are saying these buildings won't last 60 years. In my opinion, most will definitely last 60 years, even with no maintenance. At the same time, I'm intellectually honest enough to concede that few reinforced concrete structures will last 500 years with no maintenance. And I'm confident that zero reinforced structures will last 1000 without maintenance. People on this thread claiming a collapse in 60 years are probably not civil engineers. People claiming that reinforced structures will outlast the Pyramids at Giza are definitely not civil engineers.
- marcosdumay 5y ago
- yosito 5y agoThis was an interesting read, but it was written mostly as if cities were just surrendered to the forces of nature. In many or most cases, I would assume that when a building starts to succumb to the forces of nature, the city would either reinforce it or demolish it, and the city itself will continue to evolve. In some cases, I supposed cities may be abandoned, but in most cases, it will probably be a slow, evolving change barring some dramatic catastrophe.
- anamexis 5y agoI think it's plausible that we could see entire cities abandoned in our lifetime due to climate catastrophe.
- TedDoesntTalk 5y agoEspecially coastal cities.
- yosito 5y agoSome cities, yes. Jakarta comes to mind as a likely example. But if you look at photos of the areas of Jakarta that are submerged in water, it's clear that they weren't wealthy areas to begin with. I think wealthier cities like Shanghai or Miami will take a very different route.
- bobthepanda 5y agoIIRC Miami's issue is that a good deal of Florida is built on porous limestone, so water will just go under traditional flood barriers.
- caseysoftware 5y agoDepends on how it comes about. In some places - Detroit is an example - people start leaving, the tax base dwindles, and by the time they realize the need to demolish things, the funds aren't there. In some cases, the city pulls in its borders and declares the former-city areas someone else's problem. Here's a Detroit residential neighborhood suffering it now: https://www.msn.com/en-us/news/us/eerie-images-of-detroits-most-abandoned-neighborhood/ss-BB1cbqO7 https://www.msn.com/en-us/news/us/eerie-images-of-detroits-m...
- davidw 5y agoI was expecting it to be about rigid zoning laws or HOAs or something else preventing cities from changing or adapting.
- pratik661 5y agoI always wondered how you go from a thriving city to an 'ancient ruin'. A lot of cities in India have been continuously occupied for over 2000 years (Kalyan, Ujjain, Bharuch, Patna). A lot of them don't have any obvious ruins from that era (most old buildings tend to be from the medieval era or rock cut caves/temples/monasteries that were forgotten about in later eras) compared to a place like Hampi or Angkor (although both cities were abandoned in the medieval era). My guess is that for a city to have relatively well preserved ruins, it has to be completely abandoned due to some calamity. If a city is continuously occupied, old buildings get incrementally replaced by newer buildings, and very few old buildings get preserved. Even with Rome, my theory checks out. We have a lot of Roman ruins because Rome was heavily depopulated after the Roman empire collapsed. A lot of buildings were probably abandoned and then buried by dirt over time (like the Roman Forum). The only other preserved ruins were buildings that were repurpose d (Agrippa's Pantheon, Colessium, aqueducts, etc).
- twelvechairs 5y agoBig difference in cities built of masonry and those built of wood. Eastern Asia had many of the largest cities through history but they were often wooden and thus much less has survived than Rome
- pratik661 5y agoThat makes sense. Hampi and Angkor had a lot of buildings made out of stone. But what about Patna and Mathura? Ancient primary source accounts mention lots of buildings made out of stone.
- hackerbabz 5y agoAngkor Wat is not nearly as old as your Indian examples. It's similar age to Notre Dame cathedral. The main temple complex is the best preserved building in the area with some others that I think came later less well preserved. There are many many smaller temples very poorly preserved. As for a "city" of Angkor, it's now Siem Reap and there isn't much of the ancient city within the modern city.
- rmason 5y agoSome Detroit skyscrapers sat abandoned for 50-60 years with no heat or electricity. Sure some were falling apart and became a hazard with chunks of brick or concrete hitting the unwary pedestrian but the majority held up fairly well. When the billionaire Dan Gilbert bought them to rehabilitate he few major structural problems. So I think if major cities are abandoned their skyline may look somewhat familiar centuries from now.
- Lindn182 5y agoPlease upvote
- dirtyid 5y agoI was big proponent for mass timber until engineer told me the lifespan might be poor due to adhesives in fabrication. Can't find any solid analysis though.