Brick
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A brick is a ceramic block made of kiln-fired material, usually clay
or ground shale. Clay bricks are formed in a mould (the soft mud
method), or more frequently in commercial mass production by
extruding clay through a die and then wire-cutting them to the
desired size (the stiff mud process). Brick made from dampened clay
must be formed in molds with a great deal of pressure, usually
applied by a hydraulic press. These bricks are known as
hydraulic-pressed bricks, and have a dense surface which makes them
highly resistant to weathering, and thus suitable for facing work.
The shaped clay is then dried and fired to achieve the final,
desired strength. In modern brickworks, this is usually done in a
continuously fired kiln, in which the bricks move slowly through the
kiln on conveyors, rails, or kiln cars to achieve consistent
physical characteristics for all bricks. Bricks are also known in
the building trades as compressed earth blocks or CEBs. |
In the Near East and India, bricks have been in use for more than
five thousand years. The Tigris-Euphrates plain lacks rocks and
trees. Sumerian structures were thus built of plano-convex mudbricks,
not fixed with mortar or with cement. As plano-convex bricks (being
rounded) are somewhat unstable in behaviour, Sumerian bricklayers
would lay a row of bricks perpendicular to the rest every few rows.
They would fill the gaps with bitumen, straw, marsh reeds, and
weeds.
The Ancient Egyptians and the Indus Valley Civilization also used
mudbrick extensively, as can be seen in the ruins of Buhen,
Mohenjo-daro and Harappa, for example. In the Indus Valley
Civilization particularly, all bricks corresponded to sizes in a
perfect ratio of 4:2:1, and made use of the decimal system. The
ratio for brick dimensions 4:2:1 is even today considered optimal
for effective bonding.
The Romans made use of fired bricks, and the Roman legions, which
operated mobile kilns, introduced bricks to many parts of the
empire. Roman bricks are often stamped with the mark of the legion
that supervised its production. The use of bricks in Southern and
Western Germany, for example, can be traced back to traditions
already described by the Roman architect Vitruvius.
In the 12th century, bricks from Northern Italy were re-introduced
to Northern Germany, where an independent tradition evolved. It
culminated in the so-called brick Gothic, a reduced style of Gothic
architecture that flourished in Northern Europe, especially in the
regions around the Baltic Sea which are without natural rock
resources. Brick Gothic buildings, which are built almost
exclusively of bricks, are to be found in Denmark, Germany, Poland
and Russia. However, bricks were long considered an inferior
substitute for natural rock.
During the Renaissance and the Baroque, visible brick walls were
unpopular and the brickwork was often covered with plaster. It was
only during the mid-18th century that visible brick walls regained
some degree of popularity, as illustrated by the Dutch Quarter of
Potsdam, for example.
The transport in bulk of building materials such as bricks over long
distances was rare before the age of canals, railways, good roads
and large, reliable heavy goods vehicles. Before this time bricks
were generally made as close as possible to their point of intended
use (it has been estimated that in England in the eighteenth century
carrying bricks by horse and cart for ten miles over the poor roads
then existing could more than double their price). Bricks were made
using locally-available materials in regions that lacked stone and
other materials suitable for building close at hand, including for
example much of south-eastern England, large parts of the American
south-west and The Netherlands---all places lacking stone but
possessing the essential requisites for brick making: suitable clays
and fuel for firing.
Bricks can be mainly divided into three main categories which
include 1) clay bricks, (2) concrete blocks and (3) calcium silicate
bricks. The standard dimensions of clay and calcium silicate bricks
are the same; the standard dimensions are 230 x 110 x 76 mm. The
standard dimension for a concrete block modular is 390 x 190 x 190
mm.
Hard-burned brick should be used for face work exposed to the
weather, and soft brick for filling, foundations, and the like. The
mainstay standard US brick measures approximately 8 x 4 x 2.25
inches (203 x 102 x 57 millimeters), and has a crushing strength of
between 1000 and 15000 lbf/inē (7 to 105 megapascals) depending on
quality. The modern standard UK brick size is 215 x 102.5 x 65
millimetres.
A highly impervious and ornamental surface may be laid on brick
either by salt glazing, in which salt is added during the burning
process, or by the use of a "slip," which is a glaze material into
which the bricks are dipped. Subsequent reheating in the kiln fuses
the slip into a glazed surface integral with the brick base.ProportionsRegardless of size, bricks are usually manufactured with the depth
equal to half the length (assuming that the brick is laid
horizontally), in a 1:2:4 ratio. This allows for several convenient
layouts which must necessarily interweave the bricks in any
structure, often both at the corners and within the wall depth in
order to ensure the greatest possible durability of the structure.
Bricks are typically used for building and pavement. In the USA,
brick pavement was found incapable of withstanding heavy traffic,
but it is coming back into use as a method of traffic calming or as
a decorative surface in pedestrian precincts.
Bricks are also used in the metallurgy and glass industries for
lining furnaces. They have various uses, especially refractory
bricks such as silica, magnesia, chamotte and neutral (chromomagnesite)
refractory bricks. This type of brick must have a series of
properties such as good thermal shock resistance, refractoriness
under load, high melting point, satisfactory porosity (which can
influence several other properties), all of which are
high-temperature properties. There is a large refractory brick
industry, especially in the United Kingdom, Japan and the U.S.A.. |
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