Civil Engineering Reference
In-Depth Information
Fossil meal is a type of earth which is rich in silicium dioxide. It consists of
petrified and closed shells from silicious algae. Fossil meal is used as poz-
zolana, or as insulation for high temperatures, alone or mixed with brick or
mortar.
Perlite is a volcanic type of earth with a high content of silicium dioxide is
usually expanded for use as insulation. The deposits in Iceland are the largest
in the world. In most types of clay there is usually a high concentration of sili-
cium.
Potassium chloride and sodium chloride
These are extracted from salt water and used to produce two important base
materials, potash and soda, which in turn are the starting point for the manufac-
ture of glass and waterglass.
Potassium waterglass is produced by smelting potash and quartz at a temper-
ature of more than 1710°C. Potash, K
2
CO
3
, was once produced from the ash of
deciduous trees. It is now more common to produce it from potassium chloride.
Sodium waterglass is produced by allowing soda to replace potash in a com-
bination with quartz. The soda is made by passing carbon dioxide and ammonia
through a concentrated solution of sodium chloride.
Chlorine is produced electrolytically from a solution of sodium chloride. This
substance is very important in the production of chlorinated hydrocarbons for
the plastics industry. Hydrochloric acid is made industrially by igniting hydro-
gen and chlorine gas and is used in the production of PVC.
Sulphur
Sulphur occurs in its natural state and can be used independently for casting by
smelting and then pouring into a mould. It is most practical to use it when it is
an industrial by-product (see 'Sulphur', p. 184) or it occurs naturally, as in
Iceland.
Mica
This consists of aluminium silicates and is used in windows of oven doors.
Vermiculite is also a form of mica which can be expanded to make an insulation
material for high temperatures.
Montmorillonite
This is found mainly in bentonite clay. Its most important use is as a waterproofer
or watertight membrane. By adding water, the clay expands up to twenty times
its own volume. There are many sources on the European continent, but the USA
is the main producer.
