Civil Engineering Reference
In-Depth Information
Another step in the right direction is pozzolana mixing, which is now standard
in many European factories, but this requires a local resource of pozzolana.
The greatest gains can be achieved through developing cements requiring less
energy in production, where lower temperatures are required. The most prof-
itable cements with the greatest potential are probably the lime pozzolana mix-
tures.
Glass
Glass surfaces bring in views, light and solar warmth. However, like the rest of
the wall, they must protect the inhabitants against rain, cold, heat and noise. Few
materials can satisfy these different demands at the same time. There have been
many alternatives throughout history: shell, horn, parchment, alabaster, oiled
textiles, crystalline, gypsum (selenite) and thin sheets of marble. Eskimos have
used the skin of intestines. In Siberia mica is cut into sheets for windows. This is
known as Russian glass.
None of these seriously rival glass, and the only alternative commonly in
use is rice paper, used in Japan for letting light pass from room to room inter-
nally. More recently, plastic alternatives have been developed, such as plexi-
glass.
Normal clear glass lets about 85-90 per cent of daylight through. There are
many other types of glass on the market: diffuse, coloured, metal-coated, rein-
forced, etc. Glass has also been developed to perform other functions, e.g. as
insulation, such as foamglass and glasswool, the latter having a very large pro-
portion of the insulation market nowadays.
History
The Phoenicians were probably the first to produce glass, about 7000 years ago. But the
oldest known piece of glass is a blue coloured amulet from Egypt. Glass painting began
in the Pharaohs' eighteenth dynasty (1580-1350 BC), but it is difficult to say if glass win-
dows were produced during this period.
A broken window measuring 70
100 cm and 1.7 mm thick, opaque and probably cast
in a mould was excavated from the ruins of Pompeii. It was originally mounted in a bronze
frame in a public bathhouse.
Flat glass technology spread very slowly through Europe. Glass craftsmen kept their
knowledge close, and only the Church, with a few exceptions, was allowed to share the
secrets. Early glass was blue-green or brown, partly because ferrous sand (containing
iron) was used as a raw material. Later it was discovered that adding magnesium oxide,
'glassblowers' soap', neutralized the effect.
During the eighteent century glass became affordable for use as windows in all hous-
es. Glass was still very valuable and far into the nineteenth century it was normal to put
many small pieces together to make one pane. From 1840 the methods of glass plate pro-
duction became modernized and glass became even cheaper. The methods of production
were still basically manual - glass spheres were blown, then divided.
