Civil Engineering Reference
In-Depth Information
native metals. There are in fact alternatives for all metals/alloys except for
chrome, which is a part of stainless steel.
Recycling
Metal materials corrode, and 16-20 per cent of the total iron content effectively
disappears. Chemical corrosion occurs mainly in the presence of water and oxygen;
it is an oxidation process. Copper, aluminium and chrome are relatively resistant to
corrosion. Metals are also attacked by acids: carbonic acid from carbon dioxide and
water, and sulphuric acid. Iron, aluminium and magnesium are the metals most
commonly affected. Base materials such as lime solution and concrete can attack
metals, particularly aluminium, zinc and lead. Electro-corrosion can occur with cer-
tain combinations of metals.
The remaining metals can in theory be recycled or re-used.
Pure steel structures in heavy sections are usually easy to remove; as they are
standardized, they are quite easy to re-use. In reinforced concrete, where the steel
content can be up to 20 per cent, recycling is the only alternative, even if the
process is relatively difficult.
A differentiation must be made between industrial and domestic waste.
Industrial waste is usually pure and can be recycled without difficulty, where-
as domestic waste may contain a whole variety of substances and therefore can
cause problems. Copper in the electric cables of old cars and tin from tin cans
make it impossible to recycle the steel in these products. Another problem is
that waste metal often has a surface treatment, which can lead to complica-
tions.
All metals and metal alloys used in the building industry can be melted down
and recycled. The metal can be added to new processes in varying proportions,
from 10-100 per cent depending upon the end product and its quality require-
ments. Steel and aluminium alloys can only be used for similar alloy products,
whereas copper, nickel and tin can be completely reclaimed from alloys in which
they are the main component. Copper, for example, can be removed from brass
through an electrolytic process.
The technology for smelting is relatively simple. A normal forge is all that is
necessary. Breaking down alloys electrolytically and further refining, casting or
rolling techniques, require much more complex machinery.
Metals in building
Iron and steel
Iron was used in prehistoric times. Pure iron has been found in meteorites and
could be used without any refining. Smelting iron from iron ore has been carried
