Civil Engineering Reference
In-Depth Information
Gypsum products are less well suited for re-use, but can be recycled through
the addition of 5-15 per cent waste gypsum to new products. The gypsum indus-
try is very centralized, which often makes recycling an uneconomic proposition.
There is chance of sulphur pollution from demolition and building waste
because of microbial breakdown.
Fossil meal products
Fossil meal is a sedimentary earth that can be used as fill or aggregate in cast
cement blocks or insulating mortars. Fossil meal products have good thermal
properties and a high moisture absorption rate, making them suitable for insula-
tion of high temperature equipment such as kilns, kettles, hot water tanks, bak-
ing ovens and high temperature equipment in industry. It can also be used in
walls between rooms as a fill. It has a powder-like consistency, and must be
placed between paper sheets so as not to leak out into the room.
Fossil meal mortars are made by mixing fossil meal with a cement, or even
with plant fibres up to 30 per cent by weight. Water is added and the ingredients
are well mixed together. The mortar is then ready for use on hot water pipes, for
example, preferably in several layers, each 1-2 cm thick. A canvas is bound over
the last layer, which can be painted or rendered with lime.
Blocks of fossil meal can be made using cement as a binder. It can also be used
as an insulating aggregate in brick products. Fossil meal contains large amounts
of silicium dioxide and can be superficially considered dangerous with respect to
silicosis. However, in fossil meal this substance is not the crystalline silicium
oxides as in quartz, but an amorphic version which is completely harmless.
Fossil meal is relatively widespread and causes considerable blemishes on the
countryside when extracted. The waste phase does not cause any problems.
Unmixed parts can be re-used or can even be left in the natural environment,
covered with earth.
Perlite and pumice products
Perlite is a natural glass of volcanic origin mined by open-cast methods in parts
of the world such as Iceland, Greece, Hungary and the Czech Republic. It is pul-
verized and expanded in rotating kilns at about 900-1200°C, which increases its
volume between five and twenty times. Expanded perlite was first produced in
the USA in 1953. It has the consistency of small popcorn and is used as loose fill
and aggregate in mortars, render and lightweight concrete blocks. It is also used
for the thermal insulation of buildings, the insulation of refrigerating rooms and
high temperature insulation.
Because the material absorbs a little moisture there is the risk of a reduced
insulation value and an increased settling problem within a wall. To avoid this,
