Building materials in the hot climate zones

I. MODERN BUILDING MATERIALS

Some of the most important building materials are: timber, brick, stone, concrete, metal, plastics and glass.

Timberis provided by different kinds of trees. Timbers used for building purposes are divided into two groups called softwoods and hardwoods. Timber is at present not so much used in building construction, as in railway engineering, in mining and in the chemical industry where it provides a number of valuable materials.

However, timber is still employed as a building material in the form of boards. For the interior of buildings plywood and veneer serve a number of purposes.

A brick is best described as “building unit". It may be made of clay by molding and baking in kilns, of concrete, of mortar or, of a composition of sawdust and other materials. In shape it is a rectangular solid and its weight is from 6 ½ to 9 lb.

There exists variety of bricks for different purposes: ordinary, hollow or porous, lightweight, multicolor bricks for decorative purposes, etc. Bricks are usually laid in place with the help of mortar.

The shape and convenient size of brick enables a man to grip it with an easy confidence and, because of this, brick building has been popular for many hundreds of years. The hand of the average man is large enough to take a brick and he is able to handle more than 500 bricks in an eight-hour working day.

It is necessary, therefore, for the "would be" bricklayer to practice handling a brick until he can control it with complete mastery and until he is able to place it into any desired position.

The brick may be securely handled by placing the hand over the surface of the upper part of a brick and by placing the thumb centrally down the face of the brick with the first joints of the fingers on the opposite face. It is better to protect the thumb and the fingers with leather pads, which also prevent the skin from rough bricks.

Sometimes natural stones such as marble, granite, basalt, limestone and sandstone are used for the construction of dams and foundations. Marble, granite and sandstone are widely used for decorative purposes as well, especially with the public buildings.

Natural stone is used for foundations and for the construction of dams. The main varieties of building stone are basalt, granite, marble, sandstone and limestone.

Metals: Aluminium, principally in the form of various alloys, is highly valued for its durability and especially for its light weight, while brass is frequently used for decorative purposes in facing.

Steel finds its use in corrugated sheets for roofing, for girders, frames, etc. Various shapes are employed in construction.

Plastics are artificial materials used in construction work for a vast number of purposes. Nowadays plastics, which are artificial materials, can be applied to almost every branch of building, from the laying of foundation to the final coat of paint. Synthetic resins are the main raw material for plastics. Plastics have some good advantages as they are lighter than metals, not subject to corrosion, and they can be easier machined. Besides, they are inflammable, they can take any color and pattern, and they are good electrical insulators. Moreover, they possess a high resistance to chemical action.

A lot of decorative plastics, now available, have brought about a revolution in interior and exterior design. But plastics are used now not only for decoration. These materials are sufficiently rigid to stand on their own without any support. They can be worked with ordinary builders' tools.

Laminate is a strong material manufactured from many layers of paper or textile impregnated with thermosetting resins. This sandwich is then pressed and subjected to heat. Laminate has been developed for both inside and outside use. It resists severe weather conditions for more than ten years without serious deformation. As a structural material it is recommended for exterior work. Being used for surfacing, laminate gives the tough surface.

Foamed glass is a high-porosity heat insulating material, available in block made of fine-ground glass and a frothing agent.

Foamed glass is widely used in prefabricated house building, to ensure heat insulation of exterior wall panels, and in industrial construction. Foamed glass has a high mechanical strength, is distinguished by moisture, vapour and gas impermeability. lt is non-inflammable, offers resistance to frost, possesses a high sound adsorption, and it is easily sewn and nailed.

Structural foamed glass blocks designed to fill ceilings, and for making interior partitions in buildings and rooms, to ensure heat and sound insulation.

For insulation mineral wool or cinder wool is often resorted to.

II. Modern Building Materials

Concrete is perhaps the most widely spread building material used nowadays. Concrete is an artificial stone, made by thoroughly mixing such natural ingredients or aggregates as cement, sand and gravel or broken stone together with sufficient water to produce a mixture of the proper consistency. It has many valuable properties. It sets under water, can be poured into moulds so as to get almost any desirable form, and together with steel in reinforced concrete it has very high strength, and also resists fire. Prestressed concrete is most widely used at present while prefabricated blocks are employed on vast scale for skeleton structures.

AGGREGATES FOR CONCRETE

By the simple definition from the dictionary "aggregates are the materials, such as sand and small stones, that are mixed with cement to form concrete". In other words aggregates (or cushioning materials) can be defined as a mass of practically inert mineral materials, which, when surrounded and bonded together by an active binder, form the rock. This rock is denoted by the general term concrete.

Aggregates have three principal functions in the concrete: they provide a relatively cheap filler for the concreting material, or binder; they provide a mass of particles which are suitable for resisting the action of applied loads, of abrasion, of percolation of moisture through the mass, and of climate factors; they reduce volume changes resulting from the action of the setting and hardening of the concrete mass.

All aggregates, both natural and artificial, which have sufficient strength and resistance to weathering, and which do not contain harmful impurities may be used for making concrete.

As aggregates such natural materials as sand, pebbles, broken stone, broken brick, gravel, slag, cinder, pumice and others can be used.

PRESTRESSED CONCRETE

Prestressed concrete is not a new material. Its successful use has been developed rapidly during the last two decades, chiefly because steel of a more suitable character has been produced. Concrete is strong in compression but weak when used for tensile stresses.

If, therefore, we consider a beam made of plain concrete, and spanning a certain distance, it will at once be realized that the beam's own weight will cause the beam to "sag" or bend. This sagging at once puts the lower edge of the beam in tension, and if the cross-sectional area is small, causes it to break, especially if the span is relatively large.

If, on the other hand, we use a beam of similar cross-section, but incorporate steel bars in the lower portion, the steel will resist the tensile stress derived from the sag of the beam, and thus assist in preventing it from breaking.

In prestressed concrete steel is not used as reinforcement, but as a means of producing a suitable compressive stress in the concrete. Therefore any beam (or member) made of prestressed concrete is permanently under compression, and is consequently devoid of crack under normal loading, or so long as the "elastic limit" is not exceeded.

Prestressed concrete is not only used for beams but is now employed extensively for columns, pipes, and cylindrical water towers, storage tanks, etc.

 

Silicate Industry

Silicate industry is the industry processing the natural compounds of silicon. It embraces the production of cement, glass, and ceramics.

The production of ceramic goods is based on the property of clay when mixed with water to form putty, from which various articles can easily be molded. When these are dried and then for easily molding baked, that is, ignited at a high temperature, they become hard and retain their shape, no longer being softened by water.

In this way clay, mixed water and sand is molded into bricks, which are then dried and baked. The materials used to make silicate bricks are white sand and slaked lime.

Cement Production. Cement is made from limestone and clay, or from their natural mixture, marls. The materials roasted in cylindrical rotary kilns are charged into a slowly rotating kiln at its upper end and travel, mixing continuously, towards the lower end, while a current of hot gases, the products of the burning of fuel, flows in the opposite direction. During the period of their movement through the kiln the clay and the limestone react chemically, and the material emerging from the kiln in lumps of a caked mass is cement, which is then grounded.

When cement is mixed with water, it forms mortar, which hardens, binding various objects, such as bricks or stones, very firmly. It is for this reason that cement is used widely as binding materials in large-scale construction, including underwater construction.

Cement is often mixed with sand or gravel, in which case we get concrete. Concrete has roughly the same coefficient of thermal expansion as iron.

Glass Production. The initial materials for the production of ordinary glass are mainly soda, limestone, and sand. A mixture of these substances is heated in a bath-shaped furnace.

When it cools, the liquid mass of glass does not become hard at once. At first it becomes viscous and readily assumes any shape. This property of glass is used in making various articles out of it. Definite portions of the cooling semi liquid mass are taken from the bath, and these are blown or pressed to make various glassware. By machine methods glass sheets, tubes, etc., can be drawn continuously from the molten mass.

Sand is the chief material used as a fine aggregate. It is required in mortar or concrete for economy and to prevent the excessive cracking. Mortar made without sand would be expensive.

The word "sand" is applied to any finely divided material which will not injuriously affect the cement or lime and which is not subject to disintegration or decay. Sand is almost the only material which is sufficiently cheap and which can fulfill these requirements.

A mixture of coarse and fine grains is very satisfactory, as it makes a denser and stronger concrete with a less amount of cement than when only fine-grained sand is used.

The following sands are used for mortars: pit or quarry sand, river sand and sea sand.

Lime is a calcium oxide. It is used in great quantities for mortar and plaster. Lime (quicklime) is a white solid that reacts violently with water to form calcium hydroxide. It is made by heating limestone in a special kind of furnace called a "kiln". Lime must be stored in a dry place, otherwise it will absorb moisture.

Limes may be divided into three distinct classes:

1.Rich limes that contain no more than 6 percent of impurities, slake very rapidly, and are entirely dependent on external agents for setting power. These are widely used for interior plasterer's works.

2.Poor limes that contain from 15 percent to 30 percent of useless impurities and possess the general properties of rich limes, only to a lesser degree.

3.Hydraulic limes that contain certain proportions of impurities, which when calcinated, combine with the lime and endow it with the valuable property of setting under water or without external agents.

Lime is a basic building material extensively used all over the world, but it was not until the later years of the 19th century that a greater appreciation of the fuel-burning problems involved became apparent. Until this time the requirement for lime was largely agricultural and it was produced by farmers or by small builders who used it for making mortar and plaster.

As industrial requirements increased "running" kilns were developed. These were lined with firebrick and charged at regular intervals with stone and fuel.

Around the world there are many different types of kilns and variations in lime-burning practice.

 

Asbestos

Asbestos has been known and used as a textile since the earliest times. The first written evidence of asbestos was recorded by Pliny in the first century A. D.

It is told that one of the Emperors of Rome delighted guests by throwing a tablecloth made of asbestos into fire and then removing it unchanged from the flame. A few centuries later Marco Polo told his friends in Italy about a substance he observed in Siberia. He told that it could be woven into attractive textiles, which did not burn even in direct flame.

Asbestos is one of the strangest of all the naturally occurring fibers. It is a rock, which has been subjected to unusual treatment during its formation. Asbestos is the only mineral substance used as a textile fiber in the form it is obtained from natural sources. There are many varieties of asbestos rocks but only chrysotile is widely used for textile products. Chrysotile is mined in many countries of the world. The soft, long, white fibers of this mineral can be spun into yarn by the usual processes. Pure asbestos being very difficult to spin, a proportion of cotton fiber is usually added to help to bind the asbestos fibers together. The strangest characteristic of asbestos fibers is their resistance to heat and burning. This property determines the ways in which they are used.

Early uses for asbestos included such articles as handkerchiefs and table coverings. We know commercial development of the fiber to have started in the 19th century. Asbestos was used in flameproof clothing of many kinds, for laboratory, industrial and military purposes.

Fabrics made of asbestos have good strength. Today the main applications are those in which non-inflammability is essential such as conveyor belting for hot materials, industrial packings, fireproof clothing, etc. Asbestos is sometimes used with glass fiber in making decorative fabrics for curtains used in hospitals, theatres and other buildings. Some grades of asbestos are used for electrical windings and insulation.

 

Text 1

Building materials are used in two basic ways. In the first way they are used to support the loads on a building and in the second way they are used to divide the space in a building. Building components are made from building materials and the form of a component is related to the way in which it is used. We can see how this works by considering three different types of construction:

1. In one kind of construction, blocks of materials such as brick, stone, or concrete are put together to form solid walls. These materials are heavy, however, they can support the structural loads because they have the property of high compressive strength. Walls made up of blocks both support the building and divide the space in the building.

2. In another type of construction, sheet materials are used to form walls which act as both space-dividers and structural support. Timber, concrete and some plastics can be made into large rigid sheets and fixed together to form a building. These buildings are lighter and faster to construct than buildings made up of blocks.

3. Rod materials, on the other hand, can be used for structural support but not for dividing spaces. Timber, steel and concrete can be formed into rods and used as columns. Rod materials with high tensile and compressive strength can be fixed to form frame structures. The spaces between the rods can be filled with light sheet materials which act as space dividers but do not support structural loads.

Text 2

The external walls are made of brick cladding, wall planks, windows, doors, heads and sills, stanchion and inner lining panels. While the steel frame is being erected, the wall planks and floor units are fixed. At the same time, the stanchions are enclosed in castings which serve the function of resisting fire. The precast concrete floor units are capable of carrying a load of up to 5kN/sq m. The wall planks are designed to be weatherproof and to support the outer cladding. The aluminum heads, sills and windows are then fixed from inside the building. After this, the 900 mm and 1,800 mm wide external doors are installed. These doors are either aluminum framed and pre-glazed or hardwood framed and glazing is done on site. Finally, the internal sills and lining panels are installed. These form a cavity for the heating and electrical services. A grill underneath the sill, together with an intake at skirting level, enables air to circulate up past the finned heating element. The lining panels are capable of being removed to give access to the services.

Text 3

The thermal resistance of a material and the thickness of that material used in roof determine the loss of heat through a roof. Poor insulants have high k-values whereas good insulants have very low k-values. Increasing the thickness of the insulation laid on a roof will increase its resistance to heat loss in direct proportion. Thus the thermal resistance (r) of each element of the roof structure is directly proportional to the thermal conductivity (k) of the material, i.e.

If the resistance of all elements of the roof structure are added, this gives the total or overall thermal resistance (R).

R=r1+r2+r3+r4+…

where r1 is the resistance of the waterproof membrane, etc.

The overall thermal conductance of the whole roof structure (U) is the reciprocal of the overall thermal resistance (R), i.e.

The U-value is a measure of the overall rate of heat loss through the total roof structure. A well insulated roof has a low U-value. The higher the U-value, the greater the heat loss through the roof. U-value is defined as the heat loss (w) per unit area (m) per degree Celsius temperature difference (˚C) between the warm interior of the building and the cold exterior.

Text 4

The gravitational force on a structure can be divided into dead loads and live loads. Dead loads can be calculated accurately because they rarely change with time and are usually fixed in one place. Live loads are always variable and movable, so no exact figures can be calculated for these forces.

Structures must also resist other types of forces, such as wind, earthquakes, which are extremely variable. It is impossible to predict accurately the magnitude of all the forces that act on a structure during its life; we can only predict from past experience the probable magnitude and frequency of the loads.

Engineers never design a structure so that the applied loads exactly equal the strength of the structure. This condition is too dangerous because we can never know the exact value of either the applied loads or strength of the structure. Therefore, a number called a ‘factor of safety’ is used. The safety factor is defined as a ratio of the probable strength of the structure and the probable loads on the structure. This factor may range from 1·1 (where there is little uncertainty) to perhaps 5 or 10 (where there is great uncertainty).

Text 5

Building materials in the hot climate zones

Cane and leaves are available in the warm-humid zones and grass in the intermediate and subtropical zones. Vine, bamboo and palm-fronds are used for buildings in the warm-humid zones. Because these materials are light, do not store heat, and allow the free passage of air, they are frequently used for making roofs. However, they have a relatively short life span because they deteriorate rapidly due to termite attack. They are also highly combustible.

Both hardwoods and softwoods are found in most tropical and subtropical areas with the exception of the hot dry zones. On external woodwork preservative stains should be used rather than paints which tend to deteriorate fairly rapidly in the hot zones. Extremes of climatic conditions cause dimensional changes producing cracks, splits and warping. Wind-blown sand and grit gradually erode exposed timber. In warm-humid zones timber is liable to wet and dry rot and to attack by termites and beetles.

Earth is one of the most widely used traditional building materials in hot-dry lands. Earth is used not only for walls but also for roofs; mud brick vaults and domes are common in countries like Iran and Egypt. Because mud has les strength than most other construction materials, walls are built thicker. Partly due to the thickness of mud walls and partly due to its low thermal conductivity, rooms built of mud are much cooler in hot climates than those of any other material. Mud bricks are brittle and do not withstand tension well. For this reason the vault and the dome were evolve in the East. There is a risk of termite damage in some areas. Walls exposed to weathering and rain require frequent repair work.

Concrete and reinforced concrete are widely used throughout the non-temperate zones. Cement is manufactured locally in many places. Sand is found almost everywhere but it may be contaminated with soluble salts. Suitable aggregate may be difficult to find. Concrete is most frequently used for the structure, foundations and floor slabs of buildings. Care must be taken when using concrete for walls and roofs. Heat builds up on the exterior of concrete walls and roofs due to solar radiation and surface temperatures usually exceed air temperatures. Then, because concrete walls tend to be thin and concrete has a low resistance to the passage of heat, heat is conducted into the interior. Salts in aggregates and water can cause corrosion of the reinforcement and subsequent spalling of the concrete cover. In hot-dry areas the rapid evaporation and shortage of water can result in low strength, cracking and high permeability.

Text 6

The house is a single-storey building with a square-shaped plan. It contains seven rooms. The entrance which is located on the south side leads into a hall. On the left of the hall is the living room and beyond that in the north-west corner is the dining area. The kitchen is adjusted to the dining area. A terrace is situated outside the living room on the west side. A toilet is located in the centre of the house. Access to the toilet is from the hall. The two bedrooms are located on the east side with a bathroom between them. There is also an entrance to the kitchen on the north side.

Text 7

The single-storey structure consists of three frames. These frames are made up of steel stanchions and beams. The frames are placed between end walls and spaced at 3 meter centres. The stanchions carry the beams. These beams support the roof. The roof beams cantilever a short distance beyond the stanchions. This means that they extend over the profiled sheet steel cladding. The cladding can then be placed outside the line of the stanchions.

The beams are bolted to steel stanchion caps. The stanchion caps are welded to the top of each stanchion. The load on each beam is transmitted through these plates to the stanchions.

The upper face of the steel base plates and the ends of the stanchions are machined flat. The bottom of each stanchion is welded to a base plate. Each base plate is fixed to a concrete column base by two holding-down bolts.

Steel angles are fixed across the ends of the beams and built into the brick walls. These angles tie the frames together and also provide a place to fix the top of the cladding.

Text 8

Looking at the building from across the river, you can see the two main elements of the building. The first element you notice is a series of horizontal band of concrete on four levels. These are external walkways around the perimeter of the building. The second element consists of two vertical bands of concrete. These are lift towers which are located at each end of the building. They both extend above the roof of the building. However, the tower on the left is higher than the tower on the right. The ground floor of the building may be entered on the right from a broad paved terrace on the river shore. It may also be entered on the first floor from the road which runs parallel to the river on the other side of the building. Entry form the terrace is through double glass door, set in glazed panels in aluminum frames which in turn are set in the concrete structural elements.

Text 9

When an architect receives a commission for a building, he meets the client and discusses his requirements. After visiting the site, the architect draws up preliminary plans and, together with a rough estimate of the cost, submits them to the client for his approval. If the client suggests changes, the architect incorporates them into the final design which shows the exact dimension of every part of the building. At this stage, several building contractors are invited to bid for the job of constructing the building. When they submit their tenders or prices, the architect assists his client in selecting the best one and helps him to draw up a contract between the client and the contractor.

Work now starts on the building. As construction proceeds, the architect makes periodic inspections to make sure that the building is being constructed according to his plans and that the materials specified in the contract are being used. During the building period, the client pays the bills from the contractor. Subsequently, the contractor completes the building and the client occupies it. For six months after completion there is a period known as the ‘defects liability period’. During this period, the contractor must correct any defects that appear in the fabric of the building. Finally, when all the defects have been corrected, the client takes full possession of the building.

 


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