Naked Science Forum
General Science => General Science => Topic started by: neilep on 23/11/2012 12:15:04
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Dearest Cityologists,
As a sheepy I of course luff cities ! Cities are my all time favourite metropolitan-large-town kind of place to dwell in. Out of all the large and densely populated areas with transport, commercial and residential infrastructures that exist out there..cities are my all time fave. Cities as ewe know were invented in 1957 and have enjoyed great success from then on.
Here is a picture of a city
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A City Last Night !
Nice eh ?...being delivered next Tuesday as an ornament for my train set !
Do not confuse a city with a grapefruit !!....This often happens so for your peace of mind please see view the below grapefruit so that ewe understand the differences. It's important to understand that one is a fruit served for consumption and the other is not !
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A Grapefruit Being NOT a City Just Moments ago !
Ok...so....say overnight all da humans on da planet decided they wanted to up and leave. All 7 billion just packed their stuff and high tailed it outer space chasing after the dinosaurs that decided to exit the planet 65 million years ago.
How Long Would Our Cities Remain Intact ?......What Would The Time-Scale Of Deterioration Be ?......What Would Be The First Signs That We Not There Anymore ?......... Would They Last As Long As Da Pyraminds ? When Would All Signs That We Were Even There Be Gone ?
Answering these kweschuns will help me know the answers to them ...cos....well...i just do not know......and I'd like to......
whajafink ?
hugs and shmishes
mwah mwah mwah !!
neil
Last One To Leave Turn The Lights Off
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Kwik Kwiz !..What City Is It ?
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Durban. BTW
There are quite magnificent cities from 500 years ago in UK that are barely noticeable now - Roxburgh was the de facto capital of Scotland and is almost completely gone
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I suppose that given the right sort of equipment and some knowledge of where to look todays major cities would be detectable for a very, very long time (even assuming that the archaelogical methods where only at today's level of technological development). It is hard to put a figure on it because we have no historical evidence of sufficiently old cities made with today's materials. I would guess 100s of thousands of years - although they would not be in a good state of repair and I would not want to rent a flat there. Note I say "detectable".
For a city to be largely recognisable with some buildings identifiable by eye, this would be much shorter. I would estimate that a modern city would be fairly recognisable for maybe 10,000 years. However, without repair a city would quite quickly decay to be a dangerous and unlivable environment. The life of some buildings being constructed today would be of the order of only 100 to 200 years. They may well survive much longer (depending on many factors) but 1000 years would be pushing it a lot - even for the best modern buildings.
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Most large buildings today use reinforced concrete construction, with iron reinforcing rods.
This takes advantage of the following complementary properties:
- Concrete is strong in compression, but weak in tension
- Iron rods are strong in tension, but weak in compression
The main problem is that it suffers from the following runaway effect, often nicknamed "concrete cancer":
- Concrete is somewhat permeable to oxygen and water, which allows:
- The Iron to slowly turn into Iron oxide
- The iron oxide consumes more volume than the iron
- This places the concrete under tension, so it fractures, and flakes off
- This allows ready access atmospheric oxygen and rain, leading to accelerated oxidation of adjacent areas
- Flaking off concrete reduces compressive strength; oxidising iron reduces tensile strength, and eventually the structure collapses.
- In some cases, the process is accelerated by using sea sand in the concrete mix. The salt in the sand accelerates the initial oxidation process
- It is thought that without frequent maintenance, most reinforced buildings, dams and bridges would collapse in about a century
- A long way short of the longevity of the pyramids, or even the Pantheon in Rome (a non-reinforced concrete structure).
Researchers are looking into alternatives to Iron rods, which will not suffer from concrete cancer; possibilities include alloys of nickel and aluminium/aluminum. This would extend the lifetime of structures significantly, but it is not clear if people will pay more now for a structure that might last longer far into the future.
A recent 4-part BBC series looked at this topic, and suggested that perhaps our plastic rubbish, radioisotope signature and species extinctions may give a significant clue to future archaeologists/geologists that we were here. http://downloads.bbc.co.uk/podcasts/worldservice/discovery/discovery_20121112-2000a.mp3
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Durban. BTW
There are quite magnificent cities from 500 years ago in UK that are barely noticeable now - Roxburgh was the de facto capital of Scotland and is almost completely gone
but that was 500 yrs ago
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DURBAN it is Imatfaal !!!.....lets rebuild Roxburgh (http://en.wikipedia.org/wiki/Roxburgh)!... would we need to get planning permission ?
Thank ewe all for your very informed answers !!
evan_au Thank ewe for the podcasts links and information, thanks also graham.d Guess my house of cards will need reinforcing somewhat!
Very grateful for all your information.