Civil Engineering Reference
In-Depth Information
looked. The percentage by weight of environmentally-damaging material in
demolition and building waste is relatively small, but is still a large quantity and
has a considerable negative effect on the environment. Waste that has a particu-
larly damaging environmental effect and cannot be recycled is usually burned or
dumped.
While some materials can be burned in an ordinary incinerator with no partic-
ular purifying treatment, others need incinerators with highly efficient smoke
purifiers. Far too few incinerators can do this efficiently - many still emit envi-
ronmentally-damaging materials such as sulphur dioxide, carbon fumes, hydro-
gen chloride, heavy metals or dioxides.
Depending on the environmental risk of the materials that are to be dumped,
the disposal sites must ensure that there is no seepage of the waste into the water
system. This is the most serious type of environmental damage that can occur at
such depots when the constituents of the materials are washed out by rain, sur-
face water or groundwater.
The most dangerous materials are those containing heavy metals and other
poisons, and also plastics which are slow to decompose and cause problems
because of their sheer volume. Organic materials contain enzymes that break
down materials, but synthetic materials do not. They take a long time to decom-
pose, so they have to be broken down mechanically before further treatment.
Synthetic materials tend to be deposited in the most remote places, and become
very difficult to eradicate.
There is an evident relationship between the natural occurrence of a material
and its potential to damage the environment. If the amount of a substance is
reduced or increased in the environment (in air, earth, water or inside organ-
isms), it can be assumed that this increases the risk of negative effects on the
Table 2.1:
Pollution in the material life cycle
Stages of the material life cycle
Material pollution
Energy pollution
1.
Extraction of raw materials
x
x
2.
Production process
x
x
3.
Building process
x
x
1
4.
Transport between stages 1, 2, 3 and 7
x
1
x
5.
Materials in use
x
x
2
6.
Materials in combustion
x
7.
Materials during demolition
x
Notes:
x
1
: Very small proportions, e.g. accidents during the transport of building materials, though such accidents
can lead to leakage of highly dangerous chemicals such as construction glue, which contains phenol.
x
2
: Highly polluting building materials give rise to higher use of energy through the increased ventilation
required in the building.
