Civil Engineering Reference
In-Depth Information
the high pH of the cement. The sawdust has to be treated in the same way as the
wood in woodwool slabs before production (see 'Woodwool cement - produc-
tion and use', p. 282).
Raw material for concrete with light aggregate is widely available. The pollu-
tion caused by the processes involved is the same as for concrete (see 'Concrete
structures' p. 192). To attain acceptable thermal insulation levels, considerable
thicknesses are necessary, and the primary energy consumption is high. Erecting
a fully-insulated wall of light expanded clay block insulated with expanded
polyurethane uses 75 per cent more energy than for an equivalent construction
in timber (Fossdal, 1995).
Except for possible pollution from granules and the use of plastic sheeting, the
production and use of concrete products usually causes no problems. The use of
steel reinforcement with these products may increase the electromagnetic fields
within a building.
Light expanded clay blocks are initially inert and the waste from them can be
used as fill for road building, as ground insulation or as insulating aggregate in
smaller concrete structures, light mortars and render. Lightweight concrete
blocks can easily be re-used if they are held together by weak mortar, as can larg-
er concrete units that have been bolted or placed without fixing. Lightweight
concrete products can be produced in local small and medium-sized factories.
Gypsum products
Gypsum is used mainly for sound-proofing and wind-proofing boards which are
also very good moisture regulators. The products are cast from 90-95 per cent
gypsum which has fibreglass added (0.1 per cent by weight) as reinforcement.
The following constituents are also added, to a total weight of 1 per cent: calci-
um ligno-sulphate, ammonium sulphate and an organic retardant. In the wind-
proofing boards the additives include silicon (0.3 per cent by weight). The boards
are often covered in cardboard which is glued with a potato flour paste or PVAC
glue. Acoustic boards have a covering of woven fibreglass on the surface.
Gypsum is sourced from power stations as a by-product, or from nature. In
both cases the raw material situation is good, even if it is hoped that polluting
coal power stations become less active in future. The materials needed for the
additives are renewable or obtained from fossil resources. The cardboard cover-
ing is produced from a minimum of 90 per cent recycled cellulose. Extraction of
gypsum has a large impact on the natural environment, and the use of gypsum
from power stations improves the waste situation.
Apart from dust, the use of gypsum has no particular problems, except when
additives, e.g. the retardant diethyl triamine, are used. When silicon is added,
methyl chloride is used. Once in the building, however, the products cause no
problems.
