Civil Engineering Reference
In-Depth Information
water on the surface, but also within the mineral structure. It therefore has the
capacity of taking up large amounts of water and swelling to twenty times in
volume. This absorption occurs quickly, and when the surroundings dry out
again, the clay releases its moisture. It is therefore useful as an absorbent water-
proof membrane on foundation walls made of brick and concrete. Bentonite clay
can be purchased in panel form, packed between two sheets of corrugated card-
board: the clay is approximately 0.5 cm thick and the cardboard gradually rots
away. The panels should be under a certain pressure, which can be achieved by
a compressed layer of earth of at least 0.4 m.
There is an abundance of montmorillonite clay, but in very few places, so high
levels of transport energy are needed. The environmental problems of this prod-
uct are otherwise of no consequence.
Fired clay materials
Fired clay in the form of bricks is mainly a structural material and has a low ther-
mal insulation value. However, it is possible to add substances to the clay which
burn out during the firing and leave air pockets in the structure. The lighter
product that results can be found in slab or block form.
Clay can also be expanded to light expanded clay pellets for use as loose fill, or
it can be cast with cement to form blocks or slabs. By exposing light expanded clay
to even higher temperatures, the light, airy granules cohere into a solid mass
which can be used to form blocks known as Zytan blocks. This type of block is no
longer in production because of the very high primary energy use required.
All fired clay products are chemically inactive. In the indoor climate there are
no particular problems with these products.
Certain types of brick are good moisture regulators. The more developed the
microporous structure, the better the moisture regulation. Low-fired brick and
brick with a high proportion of lime give the best results. Because of their high
primary energy use, all fired clay products should be recycled, preferably in their
original undamaged state. Coloured and glazed clay products may contain
heavy metal pigments, and as a result can cause problems when they are finally
disposed of.
Fired clay
Blocks of porous clay are fired at temperatures of 1000°C or more. The organic
ingredients in the block (sawdust, pieces of cork, etc.) are burnt away to leave an
internal structure with isolated air holes. In one particular product, granules of
polystyrene are used as the aggregate for burning out the clay. During the firing
the polystyrene granules vapourize. The vapours from the polystyrene have a pol-
luting effect, whereas the completed product is probably free from polystyrene.
