Civil Engineering Reference
In-Depth Information
out for at least 5000 years. Iron was not used in building until the eighteenth cen-
tury, and then it was used for balustrades, balconies, furniture and various dec-
orative items. The first structural iron girder was manufactured by Charles Bage
in 1796, in England, and was used in a five-storey linen mill.
While cast iron contains a large proportion of carbon, steel is an iron alloy with a
carbon content of less than 2 per cent. Towards the end of the nineteenth century
steel became a serious rival to, and gradually replaced, brittle cast-iron. Buildings
with a steel structure started to appear just before the turn of the century. Today
steel is the only iron-based material used in the building industry. It is possible to
use about 20 different alloys in steel and up to 10 can be used in the same steel.
Normal building steel such as reinforcement, structural steel and most wall and roof
sheeting does not usually contain any alloy. A particularly strong steel quality is
formed through alloying it with small amounts of nitrogen, aluminium, niobium,
titanium and vanadium. Sheeting products are protected against corrosion by a pro-
tective layer of aluminium or zinc. Facing panels in aggressive environments are
often made of stainless steel which is 18 per cent chrome alloy and 8 per cent nick-
el. By adding 2 per cent molybdenum alloy an acid-resistant steel can be produced.
Ninety-five per cent of the cast iron manufactured is used in the production of
steel. Even if materials are known as iron reinforcement, iron beams, ironmon-
gery etc., they are all basically steel products.
As a resource iron is a very democratic material. Iron ore occurs spread even-
ly over the surface of the earth, and is extracted in over 50 countries. But the con-
sumption of iron in certain parts of the world is so high that there are very high
transport costs, from Australia, India or Brazil to Japan, from West Africa and
Brazil to Europe and from Venezuela to USA. Rapidly diminishing iron ore
reserves are also a problem, and the alloy metals required (nickel and zinc) also
have very limited reserves.
Together with iron resources carbon is also an important element, and is gen-
erally a prerequisite for the production of cast iron from iron ore. The exception
to the rule, where the reduction process uses natural gas, requires ore with a very
high iron content. Rock iron ore is normally extracted by mining.
Bog iron ore lies in the soil and is much more easily accessible: it was the dom-
inant source in earlier times. It lies in loose agglomerations in swamps or bogs.
To find it, the bog is probed with a spear or pole. Where there is resistance to the
spear, it can be assumed that there is ore. There may even be small traces of iron
filings when the pole is removed.
Extraction of iron ore usually occurs in open quarries and extends over large
areas, which means that the groundwater situation can change and the local
ecosystem can be damaged. A large amount of waste is produced, usually about
5-6 tons for 1 ton of iron ore. Extraction of coal takes place either in open quar-
ries or mines and causes the same environmental damage as the extraction of
iron ore.
