Building materials

The principal early building material of civilization was brick, most often unfired. According to Wikipedia, the free encyclopedia, brick is an artificial stone made by forming clay into rectangular blocks which are hardened, either by burning in a kiln or sometimes, in warm countries, by sun-drying.
History. The history of bricks dates back 7,500 B.C, when the oldest shaped bricks were found in the upper Tigris area in south east Anatolia. The inven¬tion of the fired brick as opposed to the coonsid¬erably earlier sun-dried mud brick is believed to have arisen in about the third millennium BC in the Middle East. This kind of bricks enabled the construction of permanent buildings in regions of the harsher climate because it was much more resistant to cold and moist weather conditions than mud bricks. By 1200AD brick making was to be found across Europe and Asia. The Romans made use of fired bricks, and the Roman legions, which operated mobile kilns, introduced bricks too many parts of the empire. 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 style of Gothic architecture that flourished in Northern Eu

urope, especially in the regions around the Baltic Sea which are without natural rock resources. 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. Bricks were often used, even in areas where stone was available, for reasons of speed and economy. In the late-20th century brick was confined to low or medium-rise structures or as a thin decorative cladding over concrete-and-steel buildings or for internal non-load bearing walls.
Methods of manufacture. Bricks may be made from clay, shale, soft slate, calcium silicate, concrete, or shaped from quarried stone. The most common material is clay and cllay bricks may be formed in one of the three processes – soft mud, dry press or wire cut.
The soft mud method is the most common, as it is the most economical. The clay is first ground and mixed with water to the desired consistency for forming in a mould. The clay is pressed into steel moulds with a hydraulic press. The shaped clay is then fired (“burned”) at 900-1000°C to achieve strength. In modern brickworks, this is usually done in a
continuously fired tunnel kiln, in which the bricks move slowly through the kiln on conveyors, rails, or kiln cars to achieve consistent physical characteristics for all bricks. The bricks often have added lime, ash and organic matter to speed the burning.

The dry press method is similar to mud brick but starts with a much thicker clay mix, so forming more accurate, sharper-edged bricks. The greater force in pressing and the longer burn make this method more expensive.
In wire cut the clay mix is 20-25% water, this is forced through a die to create a long cable of material of the demanded width and depth. This cable is then cut into bricks of the desired length by a wall of wires. The majority of structural bricks are made by this method as hard dense bricks are the result and any needed holes or other perforations can be introduced by the die. The introduction of holes reduces the needed volume of clay through the whole process, with the consequent reduction in costs per brick. The bricks are also lighter and so easier to handle and have different thermal properties compared to solid bricks. The cut bricks are hardened by drying for be
etween 20 and 40 hours at 50-150°C before being burned. The heat for the drying is often the waste heat of the burning process.
Mineral content and colour. The colour of the finished bricks depends on the mineral content of the bricks and the temperature at which they are burned. Pink bricks are the result of high iron content, white or yellow bricks have higher lime content. Most bricks burn to various red hues, if the temperature is increased the colour moves through dark red, purple and then to brown or grey at around 1300°C. A wider range of shades is produced from calcium silicate bricks. White is common but a wide range of “pastel” shades can be achieved. Only a few stones are suitable for bricks, common materials are granite, limestone and sandstone. Other stones, such as marble, slate, quartzite, etc. can be used in brick making but this tend to be limited to a particular locality.

Characteristics. Bricks must be small enough and light enough to be picked up by the bricklayer using one hand. In most cases, the length of a brick is about twice its width, about eight inches (about 200 mm) or slightly more. This allows bricks to be la
aid bonded in a structure to increase its stability and strength. The correct brick for a job can be picked from a choice of colour, surface texture, density, weight, absorption and pore structure, thermal characteristics, thermal and moisture movement, and fire resistance. Bricks may also be classified as solid (less than 25% perforations by volume, although the brick may be “frogged,” having indentations on one of the longer faces), perforated (containing a pattern of small holes through the brick removing no more than 25% of the volume), cellular (containing a pattern of holes removing more than 20% of the volume, but closed on one face), or hollow (containing a pattern of large holes removing more than 25% of the brick’s volume). Blocks may be solid, cellular or hollow.
Use of bricks. Bricks are usually used for building and pavement. Bricks have been used in construction for centuries, however, many houses and buildings are now being built from concrete blocks and other materials. 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 refractory bricks.
To sum up, brick has been the most popular building material for many ages and it still has not lost its popularity for reasons of speed and economy.

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