Civil Engineering Reference
In-Depth Information
1
Resources
The earth's resources are usually defined as being 'renewable' or 'non-renew-
able'. The renewable resources are those that can be renewed or harvested regu-
larly, such as timber for construction or linseed for linseed oil. These resources
are renewable as long as the right conditions for production are maintained.
Thinning out of the ozone layer is an example of how conditions for the majori-
ty of renewable resources can be drastically changed. All renewable resources
have photosynthesis in common. It has been estimated that man uses 40 per cent
of the earth's photosynthetic activity (Brown, 1990).
Non-renewable resources are those that cannot be renewed through harvesting,
e.g. iron ore, or that renew themselves very slowly, e.g. crude oil. Many of these
are seriously limited - metals and oil are the most exploited, but in certain regions
materials such as sand and aggregates are also becoming rare. The approximate
sizes of different reserves of raw materials are given in Table 1.1, though there are
many different estimates. Everyone, however, is quite clear about the fact that
many of the most important resources will be exhausted in the near future.
Fresh water is a resource that cannot be described either as a renewable or non-
renewable resource. The total amount of water is constant if we see the globe as
a whole, but that does not present a drastic lack of water in many regions. This
is especially the case for pure water, which is not only necessary in food produc-
tion but also essential in most industries. Water is often used in industry in sec-
ondary processes, e.g. as a cooling liquid, and thereafter is returned to nature,
polluted and with a lower oxygen content.
Usable and less usable resources
It is also normal to divide resources into 'usable' and 'less-usable'. The crust of the earth
contains an infinite amount of ore. The problem of extracting ore is a question of econo-
my, available technology, consequential effects on the landscape and environment and
energy consumption. Around 1900 it was estimated that to make extraction of copper a
viable process, there should be at least 3 per cent copper in the ore; by 1970 the level had
