Civil Engineering Reference
In-Depth Information
are profiled to facilitate a good key to backing material. For tall
buildings, it is customary to use copper or stainless steel secur-
ing wire cramps at intervals. Because of potential problems
with drying shrinkage it is prudent to limit sizes of panels to
450 mm × 300 mm or 300 mm × 225 mm.
14.2.1.5 Pipes
Although the market is perhaps dominated by plastic pipes,
cylindrical clay pipes of 100-600 mm bore are used for domes-
tic drainage and other applications. These can be supplied in
200, 300 and 1000 mm lengths with spigot and socket factory-
fitted push fit flexible couplings. These units are of vitrified
clay fired at temperatures of 650°C to 1100°C which gives the
material a glass-like surface. In the UK, pipes are usually made
from coal measure shales. A variety of bends, bell-mouths,
adaptors, gullies and junction pieces are available. In the mod-
ern era the analysis of faults in underground drainage is greatly
enhanced by the use of closed circuit television. In some situ-
ations, it may be possible to insert new plastic liner tubes rather
than the more expensive technique of replacement.
14.2.2 Stone
14.2.2.1 Introduction
The dominant stones for construction purposes are:
■
Igneous.
These have crystallised from molten rock or magma. In the
UK the most frequently used igneous rock in construction is granite,
a coarse-grained material containing at least 66% silica consisting
mainly of quartz, mica and feldspar. These rocks are very resistant
to weathering due to their low porosity. Granite is typically found in
Cornwall, Cumbria, Ireland and Devon. As with other types of rock,
a great deal of material is imported through Italy although much of
it originates in Portugal, Spain, Turkey or Greece.
■
Metamorphic.
The origin of these rocks is that they have been
produced from re-crystallised sedimentary rock. Examples in
common use are slate and marble. Marble is typically found in
Connemara and Ledmore. Material described as Purbeck marble
is in fact a limestone which is capable of being polished. Slate is
quarried in Wales, Cumbria and Cornwall and is also imported
from Spain, China and Brazil.
■
Sedimentary.
These are the main UK building stones. They have
their origin in a two-stage process. For sandstones, sediment is
initially deposited; secondly, the compaction pressures from
movements of the earth's crust produce a hard rock. The cement-
ing agents may be siliceous (containing silica), calcerous (con-
taining calcium carbonate) dolomitic (containing dolomite and/or
magnesium), ferruginous (containing iron oxide) or argillaceous
(containing clay). These factors combine to give these rocks their
individual character and durability.
14.2.1.6 Terracotta and faience
Terracotta (see
Figure 14.3
) is normally a red coloured, dense,
hard ceramic formed from once-fired clay. The reddish colour
derives from the Etruria clay from which it is made. Alternative
colours such as buff and dark slate are available and can be
achieved using different types of clay. A variety of shapes are
produced by highly skilled hand moulders from the wet clay
and cast in plaster or rubber moulds. The finished products
may be used in decoration, cladding, ornate chimney pots, fini-
als and other applications. Although the use of terracotta dates
back to the mid-1800s (and perhaps as early as Roman times)
architects are still using the material in modern designs. An
example of this is the use of ventilated rain-screen cladding by
Renzo Piano for the Potsdammer Platz in Berlin.
Faience is terracotta that has been glazed prior to a second
firing. It is usually made into decorative panels which provide
attractive decorations to the elevations of buildings. Some units
Figure 14.3
Terracotta. Courtesy of Dr Geoffrey Edgell
