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About building
There were a number of questions related to the subject of building 1) Do suspension bridges swing? Yes and no. See for example the Tacoma Narrows bridge collapse of 1940. This suspension bridge turned out to be sensitive to twisting caused by the wind. The swings got so bad that eventually the bridge was closed and it collapsed. After the disaster all new suspension bridges were designed to avoid this effect. The Millennium Bridge in London (2000) was a pedestrian bridge, which swung so badly that people got seasick walking on it, and it was closed less than one day after opening for modifications. The reason for the swinging was that when people walk on a moving surface, they 'catch' themselves to regain their balance. Unfortunately this extra push made the swing of this bridge worse, especially when thousands of people on the bridge were all trying to stay on their feet at the same time. The problem was fixed eventually and the bridge was reopened. Bridge designers try to limit the swings of suspension bridges to where they don't cause trouble, but sometimes unexpected things still happen. 2) How can concrete set up under water? For this, I made some concrete right there in the classroom. The recipe I used was 1 cup portland cement, 2 cups sand and 3 cups gravel. Mix in a big yoghurt container and pour into a 1-quart yoghurt container, right up to the top. Then I put plastic over the top, held in place with a rubber band, and put the whole thing into a bucket of water. How does the concrete get hard in a situation like that? The answer is that the mixture does not actually 'dry out' when it hardens. Rather, the water in the mixture undergoes a chemical reaction with the cement, which forms hard crystals which bind the sand and pebbles together - no water has to escape. In fact, if the mix dries out before it is cured, it turns back into the loose dry ingredients (sort of). That is why you have to cover up a freshly poured concrete sidewalk with plastic here in dry Santa Fe, to prevent the surface from drying out.
In the BBC science shack
Artist Andy Goldsworthy makes free-standing arches in the field from found stone.
Have a look here,
or here.
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Evaporation
The actual question was: "If you have water with color in it, will it evaporate that color?" |
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If you want to span a large distance out of say granite, you can try to
lay a granite beam between two columns. The weight of the beam will make it bow, and eventally it will snap in two.
The reason is that stone materials (natural rock, brick, concrete) have great compressiona strength, but low
tensional strength. That is, it is hard to crush a piece of blackboard chalk with your fingers, but you can easily break
it in two by pulling on the ends. This is the opposite of string: great tensional strength, but no compressional
strength at all.