Even though construction is usually considered as originally the activity of men and machines in digging, moving, shaping, erecting, and so forth, the relative use of building materials by the construction industry far exceeds its share in the gross domestic product. Specifically is construction of great significance for that special class of materials – sometimes called as the “physical-structure” materials, which made major things of human civilization. Out of these “physical-structure” materials the more or less long-lasting and reliably shaped are wood and concrete.
They are basic building materials for thin-shell roof construction, walls, tanks, large-diameter pipes, runways, highway bridges and many other structures. Main Body Concrete is related to the most significant building technologies in twentieth and the early twenty first century. However, other important building materials, such as wood, also figure in the construction picture. The poured method of concrete building has been so improved that buildings of this material are now erected as rapidly as a wood structure.
Engineering departments all over the world are now prepared to assist engineers, architects and builders to apply concrete and wood to their construction work. Increasingly in the beginning of the twentieth century, when builders were asked how they should build the foundation possessing good physical strength, their answer was – concrete. Either by placing the steel frame upon concrete foundations or by placing it upon a more spacious concrete raft foundation, architectural constructors in most cases complement steel with concrete as a problem-solving building material.
By reinforcing concrete with steel rods, or by using steel machinery to form concrete blocks as prefabricated building blocks, builders further diversified their architectural techniques. The most approved composition of concrete for general construction consists of a mixture of broken limestone, granite or clean screened mixture of rock fragments, clean coarse sand and cement, in such proportions that the voids between the stone are completely filled by the sand and the voids in the sand completely filled with cement, with a slight excess of cement to guarantee a perfect connection with the stone.
To create top-quality concrete, manufacturers need equally high-grade cement. By 1900 approximately three-quarters of that material was Portland cement, named after the tiny island of Portland in the U. K. where a desirable limestone used in its manufacture was descovered. In 1824 Joseph Aspdin, from Leeds, was the first to provide the world with Portland cement, but after 1872 the material was produced in the United States and its popularity spread rapidly (Collins, 1998).
At the 1876 Philadelphia Exhibition, American Portland cement was displayed to the public as a useful and practical building material, but production only began in earnest in 1880 and domestic cement only began to overtake European imports in 1897, by which time American machinery for crushing aggregate and making concrete had also begun to substitute European machines, even in Europe itself (American Exporter, 1906, 58 (3), pp. 79-87). Wood structures can be constructed more quickly and inexpensively than other kinds.
Wood still is used for finish flooring in the living areas of about four out of five homes, although plastic tiles and other materials are gaining ground. Flooring generally involves both the visible flooring and a subflooring. Most frame houses utilize boards for subflooring, but plywood is gaining ground. In buildings which use concrete beams, concrete flooring slabs are generally poured right along with the beams. Steel structures may be floored with poured concrete or with precast concrete or gypsum slabs.
Roofs of houses, which have a timber framework and cladding, are likely to have as the foundation wooden board, plywood, or composition planking. However, the current general tendency in home building toward flat, or low-pitched, roofs has led to a partial shift from tile, wood, and asbestos tiles to concrete materials and poured concrete. Because of its important role in residential buildings, wood does only slightly less well than concrete. Although its relative cost has increased with time, it is still the most popular building material all over the world.
The open-grained wood of any of numerous coniferous trees, such as pine and cedar, as distinguished from that of a dicotyledonous tree, enters the English home as framing, siding, shingles, finishing panels, sash, millwork, and boarding, used to cover the wall studding or roof joists of a timber frame; the wood of any of numerous broad-leaved dicotyledonous trees, such as oak, beech, ash, etc. – principally as flooring, material used for making panels, and trim.
In non-residential buildings, wood is put to practice as the most widely used building material for concrete formwork, railroad ties, telephone poles, railings, fences, and many other purposes (BLAIRSLTD). The chief advantages of wood in construction industry include its ease of production and of process by which wood is packaged and transported, its low thermal conductivity, and its strength-to-weight ratio (which is greater than that of cast iron and is identical to that of the stronger concretes) (Rowell 9).
Yet, because of its peculiar weaknesses as an organic material, such as vulnerability to fungi and various insects, its relative lack of versatility in terms of design, and its long-term rise in price in comparison with concrete, the relative role of wood as a building material may to some degree decrease in the future, and further replacement may be projected. If considered as a structural material in large building construction, wood has already been largely replaced by concrete framing, brick or concrete walls, and concrete floors.
This trend will probably continue in the future. On the other part, wood framing probably will retain its dominating position in the residential building, although giving way a bit to steel, concrete, perhaps aluminium, and sandwich panel method of building. The advantages of metal roof frameworks are gradually reducing the amount of wood required for roof structures. Moreover, for exterior trimming wood is being increasingly substituted by brick exterior and by panels of such building materials as asbestos, metal, and organic materials with a polymeric structure.
Dry wall building and the utilisation of gypsum plasterboard and of metal lath are also considerably lessening the need for wood. The most important role for wood is probably in finished flooring, but there are modern trends toward replacement of composition and various types of synthetic materials even in living areas. Wood, like steel, is yielding to aluminum as the leading building material for window frames, door frames, doorways, trim, and other such purposes.
In concrete building the formwork is tending change from wood to steel and plywood and also to plastics. Growing popularity of plywood and of laminated structural members may slow down the trend away from wood. Laminated wood arches, structural frameworks of wood, and roof systems have proved appropriate for spanning distances up to 120 feet, and, because of their attractive and pleasant appearance, are today in frequent use in the building of churches and temples, buildings for public gatherings or meetings, shopping areas, and the similar places.
Plywood, which to some degree possesses more physical strength than lumber, may replace lumber in almost any of its uses; it is already extensively used in subflooring, boarding, interior panelling, concrete forms, and so forth. Thus, it may be expected to grow in total use at almost twice the rate predicted for lumber. Use of concrete in building is constantly increasing today. It is a changeable mixture of portland cement, fine aggregates (almost always sand), and coarse aggregates (crushed stone, gravel, cinder, slag, or whatever else is available within a particular area).
The proportions of these ingredients are influenced by the particular use to which the concrete is to be intended, but they are at most times 1:2:4. As can be seen, cement is the minor component in this mixture. The fact that concrete is the most extensively used building material can be explained by its advantages related to wood among which are versatility, its high breaking strength relative to bricks and other kinds of masonry materials, the low price which makes it comparatively inexpensive material relative to structural steel, and in essence the presence of concrete components almost in all areas (Classic Encyclopaedia).
The main uses of concrete in England are in dams, water tanks, pipes and sewers, heavy walls, piers, caissons, columns, and road and sidewalk pavements. In addition, concrete is utilised in the form of units cast in a particular form before being used in building, such as concrete blocks and cast stone, whose principal advantage over wood, brick, and structural tile is that they are costing relatively little.
Because of the low flexural strength of concrete, it is combined with steel in most of its construction applications (Classic Encyclopaedia). This combination is made possible by the match of coefficients of thermal expansion of these materials. The amount of reinforcing steel – rods, wire, wire-mesh, and so forth – needed for a concrete structure is only one-third to one-half the amount needed for a similar completely steel structure.
In England, the possibilities of this technique of construction are just beginning to extend its use beyond massive complex constructions. The chief disadvantages of reinforced concrete (also known as ferroconcrete or armoured concrete) in comparison with structural steel are the time and costs of construction, even if one takes account of the applying paints to the surface of steel members and their trimming. It is costly to build and remove forms, shores, and temporary metal or wooden frameworks.
Most of the developments, which been made not long ago, in methods of concrete building are somehow related to reducing expense on forms, First, as an alternative to the traditional lumber and plywood, steel – and more recently, plastic with fibrous matter to confer additional strength – forms have been experimented. Plastics are especially showing great promise, in view of the fact that they are smooth and easily utilised, able to keep water, may be given extraordinary shapes, and may be use again and again from fifteen to twenty times.
Second, “slip-form” pavers have been successfully employed in laying road pavements (Green 1-2). Third, precasting of concrete members has been used as a mass production technique and to provide solid and robust in construction, more unchanging in form concrete, but presents some transportation problems. Fourthly, so-called tilt-up construction and lift-slab construction has permitted walls, floors, and columns to be poured on a horizontal surface and then either tilted or lifted into place.
Finally, able to be used more than once, adjustable length steel trusses have removed the need for the multiple strengthening which differently has to be placed under the conventional built-up forms. The faster such form-saving processes are improved and used by engineers and constructors, the faster steel concrete is likely to be used as a structural material. One more limitation of usual concrete is its low heat insulation value.
That is why concrete walls are occasionally of a non-load bearing, sandwich type, being composed of a layer of insulating material cast between two concrete slabs. In this application, concrete is to a serious degree threatened by other types of curtain walls, including various types of sandwiches. Alternative way to give concrete protecting properties is to make it with relatively light weight aggregates – such as vermiculite, expanded clay, and so forth.
In this form, it not any more has sufficient quality of being physically strong to be used for load bearing purposes, although it has been very well utilised in long-span roof building. Prestressed concrete has gotten great significance as a building material. The basic characteristic of prestressed concrete is that, by compressing concrete and keeping it under compression, the tensile stresses caused by loads are neutralized (CEMENT). The compression is accomplished by casting the concrete around stretched rods or cables, the tension on which is released as the concrete sets.
A prestressed beam needs only one-fourth the weight of the steel and one-half the weight of concrete which is needed to support the same load by a usual reinforced concrete member. Although it was patented by a San Francisco engineer in 1886, prestressed concrete did not emerge as an accepted and effective building material until a half-century later. Since then it had been intensively used in Europe for structural purposes. Up to the present moment, prestressed concrete’s applications have been limited mostly to pipes, tanks, runways, and from time to time highway bridges.
As engineers and constructors gain experience and manage to reduce the manufacturing expenses, prestressing may become competitive with steel and with reinforced concrete building. After weighing up all the factors, the trend is more toward a substitution of concrete for other building materials than of other building materials for concrete. The use of portland cement which is made by heating a slurry of clay and crushed chalk should more than double in the next decades, may presumably triple, and at its lowest is expected to become greater by at least one-third.
Courtney from Study Moose
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