Civil Engineering Reference
In-Depth Information
highly refined products are, the more energy they consume in production, with
associated pollution during the process. Most mineral-based climatic materials
are often chemically stable in the indoor climate. However, in many cases organ-
ic material additives can cause problems by emitting irritating gases and
encouraging the growth of micro-organisms. Some of the materials produce
dust problems during the building process and even after the building is fin-
ished. Some raw materials include radioactive elements which lead to a high
concentration of radon in the indoor air.
As waste, mineral-based climatic materials can be considered chemically neu-
tral - the main problem can be their volume. Attention must be given to coloured
products, as the pigments may contain heavy metals.
Clean loose aggregates can be re-used, as can blocks and prefabricated units.
They can also be crushed into insulating granules, which are particularly well-
suited to use as underlay for roads.
Cement products
Cement can be used as an insulating material in three forms:
• As foamed concrete
• As aerated concrete
• As binder for light mineral and organic aggregates
Foamed concrete
Foamed concrete has considerably better thermal insulation properties than nor-
mal concrete - as high as 0.1 W/mK for densities of approximately 650 kg/m
3
. It
consists of Portland cement and fine sand in proportions of about half and half.
The foaming agent is either tensides or protein substances. The latter can cause
considerable problems in the indoor climate if it reacts with cement. The use of
tensides, however, causes no such problems. Foamed concrete is seldom used in
building construction because of its relatively low thermal insulation and low
load-bearing capacity. It is used nowadays mostly for the levelling of floors,
sprayed onto horizontal surfaces or into hollow cavities from mobile tanks trans-
ported by lorry. The environmental aspects of this concrete are the same as
in situ
concrete (see 'The composition of concrete', p. 193).
Aerated concrete
Aerated concrete is produced by reacting finely powdered quartz (about 50 per
cent by weight) with lime, gypsum and cement. A yeast constituent such as alu-
minium powder is added to a proportion of about 0.1 per cent. Aluminium reacts
to release hydrogen. When the substance is almost stiff, it is cut into blocks and
