Building materials, as the name suggests, are construction materials used to build houses or other structures. The use of these materials initiated a long time ago when people used to think of ways to provide themselves with shelter.
The idea of using mud or clay and mold into blocks and use them as building materials triggered the quest of humans to explore more such materials and customize their living.
In contemporary construction practices, we have a lot such materials that can conveniently be used for construction purposes. The choice of materials for a particular scheme depends on a lot of factors, the governing among which is probably the climatic background.
- 1. Rocks and Stones
- 2. Structural Clay Products
- General Properties
- Composition of Bricks
- Manufacturing Process
- Classification of Bricks
- Based on Field Practice
- First-Class Bricks
- Second-Class Bricks
- Third-Class Bricks
- Overburnt Bricks
- Uses of Bricks
- Based on The Purpose They Serve
- Common Bricks
- Facing Bricks
- Engineering Bricks
- Based on Overall Shape and Geometry
- Solid Bricks
- Perforated or Hollow Bricks
- Cellular Bricks
- What are the Characteristics of Good Bricks?
- Applications of Clay Products
- 3. Glass
- 4. Wood and Wood Products
- 5. Building Materials for Concrete
- 6. Ceramic Materials
- 7. Polymeric Materials
- 8. Plastic
- 9. Ferrous and Non-Ferrous Metals
- 10. Paints, Varnishes, and Enamels
- 11. Bitumen, Asphalt, and Tar
1. Rocks and Stones
Dating back to the stone age, rocks and stones are the oldest natural building materials discovered. A stone is a natural hard material comprising minerals from the earth and a rock is a portion of the Earth’s crust that gets detached and has an no definite structure or shape.
Around the world, we see some masterpieces of architecture made from stones and rocks. These include the famous Taj Mahal in India, the Great Pyramids of Egypt, the Great Wall of China, etc. The use of stone was not just confined to imparting aesthetics, it is an equally-good load-bearing building material and its use served a twofold purpose.
However, the use of stones as building materials became obsolete and they gradually lost their importance. This is because of the advent of cement and steel that replaced stones as better building materials having high strength and predictable performance.
In addition, the arduousness in dressing work required for stones made their use a less preferable option for builders.
Types of Rocks
Based on geological formation, there as 3 types of rocks namely igneous rocks, sedimentary rocks and metamorphic rocks.
These rocks are formed by solidification of magma within cracks and fissures in the Earth’s surface or hardening of lava on the Earth’s surface. Therefore, these rocks are formed as a result of a volcanic event.
Granite, syenite, diorite, and gabbro are a few igneous rocks. All rocks are composed of minerals that are derived from the Earth’s surface or crust.
Granite offers high resistance to weathering and forms an excellent building material for exterior works of a building exposed to tough climatic conditions. It can easily be polished and worked.
These rocks are formed by layers of sediments that get deposited atop each other for years and get compacted and cemented together. These rocks, therefore, usually have a stratified structure and serve as good building materials.
Examples of sedimentary rocks are slate, sandstone, limestone, etc.
Slate is a hard, tough, and fine-grained rock that can be used to make tiles and serve as an excellent roof-covering material.
Sandstone is a durable rock very well-suited for ashlar works, carving, etc.
Limestone is used in large quantities in blast furnaces and can also be used for stone masonry works particularly for walls. Kankar is impure limestone that is often used in foundations of buildings.
These rocks are formed when high temperature and pressure act on igneous and sedimentary rocks (metamorphic action). They may have a foliated structure (e.g., slate, gneiss, schist) or non-foliated structure (e.g., marble, quartzite, serpentine etc.).
Gneiss is a good material for street paving purposes and can easily be worked unlike granite.
Marble is a hard rock available in many colors. It takes a fine polish and is used for carving and decoration work of structures.
Uses of Stones
The use of stones as building materials depends upon the nature of construction work and the purpose it will serve. For structural purposes, a durable, non-porous and tough stone is selected such as granite, gneiss, marble, quartzite etc.
For facing and architectural purposes, finished stones such as granite, marble, limestone, sandstone, gabbro etc. are used. The finish imparted to the stones can be glossy, dull, ground, sawn, pointed, fluted or rock finish. They are generally used for facing slabs, stairs and landings as well as parapet walls.
For road construction works, paving stones, cobble stones or curb stones are used. Depending upon the required level of performance, the choice of sedimentary or metamorphic rock may be made.
2. Structural Clay Products
A brick is a construction or building unit made from tampered clay molded into the desired shape while it is plastic and workable, air dried and burnt in the kiln.
Bricks are the most common building materials. The reason they are widely used in construction works is that they are cheap, readily available, durable and easy to handle and work with.
Bricks are usually rectangular in shape and are available in a number of sizes.
- The most common dimensions of a brick are 9” *4.5” *3” including the mortar thickness.
- The average weight of a brick is around 3 kg.
- The top face of a brick has a depression or indentation 1-2 cm deep that serves two purposes. Firstly, it serves to improve the bond between two bricks when they are glued by a mortar paste. Secondly, it informs about the manufacturer of the brick.
- The density of a brick ranges between 1600 kg/m3 to 1900 kg/m3.
- The specific gravity of a brick may range from 2.2 to 4 depending upon their composition.
- Bricks are brittle materials having a value of Young’s modulus of around 20MPa.
Composition of Bricks
Bricks around the world show a variety in their composition and are usually made up of three different materials.
- Burnt clay bricks
- Bricks made from a mixture of sand and lime
- Bricks made from Portland cement concrete
Bricks made from the last two types are normally termed as blocks and are normally available in the following sizes.
Length of brick = 2(Width of Brick) + Mortar Thickness
Height of brick = Width of Brick
The brick earth or clay that is molded and burnt to get bricks comprises many ingredients that are given below.
- Silica is present around 50-60 percent in the brick earth. It enables the brick to retain its shape and imparts durability to it while reducing shrinkage. However, if excess silica is present in the brick earth, it will make the bricks brittle and weak.
- Alumina is present in the range of 20-30 percent. It absorbs water and makes the brick earth plastic and workable. Excess alumina causes shrinkage cracking in the bricks upon drying.
- Lime is added as less than 10 percent. However, it serves some important functions. It reduces drying shrinkage and helps silica in the clay to melt and bind. Excess lime in the brick earth makes the brick unsound.
- Magnesia content in brick earth is limited to 1 percent. It affects the color of the brick and makes it yellow while burning.
- Iron Oxide content is confined to 7 percent of clay. It imparts the red color to bricks and improves their durability, strength and hardness.
- Alkalis and sulphur trioxide are present in trace amounts.
- Water is added to the brick earth and to bring it to a plastic or workable state and later mold it into the desired shape.
The brick earth comprising the afore-mentioned ingredients in properly tampered with to attain the required level of plasticity. Later on, the plastic clay is placed in the mold and are burned in the kiln at a scorching temperature of 1500 degree Celsius.
Upon burning in the kiln, the bricks get the desired color, shape and hardness and are cooled once taken out. They can then be used to serve the desired purpose.
Classification of Bricks
The classification of bricks can be based on a number of parameters and these categories are explained herewith.
Based on Field Practice
The field practice of classifying bricks is based on their physical and mechanical properties. On this basis, we have three types of bricks namely first-class brick, second-class brick and third-class brick.
- They are thoroughly burnt in the kiln and this burning imparts a deep red, cherry or copper color to them.
- They have smooth and plane surfaces, all rectangular in shape with sharp edges and square corners.
- They are free from cracks, dents, flaws or any form of exterior imperfections.
- They have a uniform texture and are hard enough to leave no impression when scratched by a finger nail.
- They give a metallic ringing sound when struck against each other.
- The water absorption of a first-class brick is less than 12-15 percent of its dry weight when immersed in cold water for 24 hours.
- The compressive strength or crushing strength of first-class bricks is not less than 10MPa.
- These bricks are not used for facing purposes since they have small cracks and a little distorted geometry.
- They also produce a ringing sound when struck against each other.
- The water absorption of second-class bricks is about 16-20 percent of their dry weight when soaked for a period of 24 hours.
- Their crushing strength is not less than 7MPa.
- These bricks are under-burnt and are light in color and relatively less hard.
- They produce a dull sound when struck against each other.
- Their water absorption is about 25 percent of their dry weight when soaked for a day.
Prolonged burning in the kiln sometimes over-burns the bricks and these are called overburnt bricks. They are badly distorted in shape and geometry and are very brittle in nature. However, they possess substantially good compressive or crushing strength and are therefore, crushed and used a ballast for road works.
Uses of Bricks
- First-class bricks are recommended for pointing, exposed facework in masonry structures, for flooring works and reinforced brickwork.
- Second-class bricks are avoided for facing purposes and are recommended for all hidden masonry works as well as centering of reinforced brick and RCC structures.
- Third-class bricks are only used for temporary structures.
Based on The Purpose They Serve
The use of bricks in construction can serve purposes other than strength and based on the purpose they serve; they can be classified as follows.
Common bricks serve manifold purposes and can be used where considerations of strength and durability are the top priority and no special importance is given to the appearance. They can be used for filling and backing walls.
These bricks are designed with due consideration to aesthetics, both color and texture. Therefore, they are used in exposed masonry works to create an attractive and pleasing appearance using masonry units.
These bricks have sound mechanical properties and they are hard, strong, durable and impermeable. They are used for all load-bearing structures.
Based on Overall Shape and Geometry
Based on the overall shape of a brick, we have four sub-categories as follows.
As the name indicates, these bricks may have small holes not exceeding 25 percent of the volume of a brick. Alternatively, the indentation volume must not exceed 20 percent of the total volume of the brick.
Perforated or Hollow Bricks
These bricks have small holes exceeding 25 percent of the volume of the brick.
Cellular bricks have holes closed at one end and the total volume of holes exceeds 20 percent of the brick volume.
What are the Characteristics of Good Bricks?
- When we talk about size and shape, a good brick has a uniform shape with plane sides, sharp edges and square corners.
- A good brick has a uniform deep red color which indicates its thorough burning in the kiln.
- The surface texture of a good brick is not too smooth to cause slippage of the mortar. However, it has a uniform texture and the sides have no imperfections and are compact.
- It is hard enough to resist any scratching done by finger nails.
- It is sound enough to give a ringing sound when struck against another brick.
- The water absorption of a good brick is less than 20 percent of its dry weight when immersed in water for a period of 24 hours.
- A good brick serves equally well the purpose of strength, durability, aesthetics and economy.
- It is made from brick earth that is free from stones or any organic matter.
- The crushing or compressive strength of a good brick is in excess of 10MPa.
Tiles are thin slabs made from tampered clay used for engineering construction works. They give a pleasing appearance and enhance the aesthetics of an interior or exterior work wherever they are used.
They are available in a plethora of designs, types, shapes, and colors, suiting the need of the hour. Roofing tiles, flooring tiles, wall tiles, and partition tiles are a few examples.
Tiles are durable building materials that are impervious to water, resist abrasion and can easily be washed or cleaned. The ingredients that make up tiles depend upon the purpose the tiles have to serve.
- For making tiles for roofs (which is not common in contemporary construction), white burning and red burning clays along with shale are used.
- For the surface of walls, the type of tiles used varies and depends on the degree of burning. Wall tiles are burned at a relatively low temperature followed by glazing and finally, they are fired again in a kiln at a lower temperature.
Properties of a Good Tile
- It has a uniform texture.
- The size and shape of the tile is accurate with no distorted dimensions.
- It is free from defects such as cracks, non-uniform burning in the kiln, etc.
- The water absorption of a good tile is less than 15 percent.
- It is resistant to water ingress and weather harshness.
- It is a durable product as a whole.
The term terracotta refers to burnt clay. Quite literally, terracotta is a refractory clay product of superior quality that is used for ornamental purposes in buildings. It is available in a variety of colors that can be tailored as per need.
- This superior quality burnt clay product is used for ornamental works.
- It is also used in cornices and arches.
- Hollow blocks of terracotta can be used in masonry construction.
- Porous terracotta can serve sound proofness.
- Since it is fireproof, it is a great choice as casting for steel columns and beams.
Porcelain is a building material from a high-grade ceramic ware that has a white color and glazed surface. It has nil water absorption and can be soft or hard.
Porcelain is used for manufacturing of reactor chambers, electric insulators, containers and crucibles, etc.
Just like porcelain, stoneware is also a hard ceramic material but possesses a different color, usually grey or brownish. It is made from refractory clay that is blended with crushed pottery, stones and sand and the mix is burned at high temperatures followed by slow cooling.
Stoneware is used in flooring tiles and wall tiles for kitchens and bathrooms. It is also used as a road paving material and in drain pipes and fittings.
Applications of Clay Products
Clay products are universally used in profusion owing to easy availability of their raw materials, manufacturing and handling.
- Clay bricks (perforated or common) are abundantly used as wall materials around the world. In addition, ceramic facing tiles are used for wall finishing purposes in buildings.
- For pavement works, crushed bricks can be used to serve as road aggregate.
- For façade decoration, glazed or non-glazed varieties of ceramic stones, facing bricks, ceramic tiles, etc. can be used.
Glass is a mixture of a number of metallic silicates, one of which is normally a silicate of an alkali metal. It is amorphous in shape and is either transparent or translucent.
Glass has extensively been used in building construction for a long time now. For glazing doors, windows, curtains; for insulation purposes and for decorative work, the use of glass is not new in the building industry.
The most common types of glass used in construction activities are glass sheets, plates, laminates, insulation materials as well as tempered, wired and patterned glass (used to control the amount of light that can pass through).
Common Properties of Glass
- Glass absorbs, refracts or transmits light and can take up high polish and may be used as substitute for very costly gems.
- It has no definite crystalline structure and no sharp melting point.
- It is affected by alkalis and is an excellent electrical insulator.
- It is capable of being worked in many ways and can easily be tampered with.
- It is a very brittle material.
- It is not usually affected by air or water.
- Some of the properties of glass can be altered or tampered such as its fusibility, hardness, refractive power. The
- It is possible to alter some of its properties such as fusibility, hardness, refractive power, etc. to suit different purposes.
- Glass is not easily attacked by ordinary chemical reagents.
- It is possible to get glass with diverse colors and properties.
- It is even possible to weld pieces of glass by fusion. This is because it becomes softer and softer with a rise in temperature when heated.
- Glass can be made lighter, softer or stronger by using advanced techniques.
Classification of Glass
It is also called soft glass and is the most common type of glass used in doors, windows, and for making glass wares such as bottles.
This type of glass has high shining appearance and can take polish. It is not affected by temperature and is therefore used in electric bulbs, ornamental glass works, cut glass, etc.
This type of glass can withstand high temperatures and is most suitable for making laboratory equipment and cooking utensils.
Commercial Forms of Glass
Sheet glass is the most commonly used commercial form in engineering works. It is available in varying thicknesses that may range from 2 mm to 6.5 mm. It is used for glazing of doors, windows and for partitions.
Plate glass is manufactured in thicknesses varying from 3 mm to 22 mm. It is stronger and more transparent than sheet glass. It is mostly used making screens of vehicles and mirrors.
Tempered Plate Glass
It is a modified form of plate glass and is obtained by when plate glass is heated and suddenly cooled to temper it. Tempered glass is 3 to 5 times stronger than plate glass and is used in making table tops, shelves counters, etc.
It is produced by embedding wire nets 0.46 to 0.56 mm into the center of sheet glass during casting. It is used for fire-resisting doors and windows, for sky lights and roofs.
Laminated glass comprises two or more glass plates with intervening layers of transparent plastics, bound together by heat and pressure. This type of glass does crumble to tiny pieces that fly off when it breaks. It is used in glazing windows and doors of buildings and transport vehicles.
It comprises two or l=more glass layers separated by 6 mm to 12 mm of dehydrated air, hermetically sealed to provide heat insulation and to ensure transmission of light. It is also used in glazing doors and windows.
Bullet Proof Glass
It is produced by sandwiching vinyl plastic in alternate glass layers and pressing them with outer layers of glass. It is mostly used in display windows, banks, jewelry stores, etc.
This type of glass is used for decoration works during building construction. It is made by adding oxides of metals to molten glass.
Ground glass has its one face made rough by grinding. The purpose of doing so is to render the glass translucent so that it transmits light but obstructs visions and provides privacy. It is therefore recommended to be used for glazing doors and windows of toilets and bedrooms.
It is an optical glass which shines and takes up good polish. It is used for making electric bulbs and valves, etc.
Heat Absorbing Glass
Where heat of sun is desired to be cut off, heat-absorbing glass is the right choice. It is used in glazing windows of railway carriages and in buildings to serve the cause.
When two halves of pressed glass are fastened together, hollow sealed glass blocks are formed. They can be made 10 cm thick and are available in square sizes. They are used to provide heat and sound proof partitions.
4. Wood and Wood Products
Wood is a natural building material and when used for construction or engineering works such as doors, windows, beams, battens, roofs, partition walls, etc., it is termed as timber.
When wood is a part of a living tree, it is termed as standing timber, when the tree has been felled it is called rough timber. When it is sawn to form various market forms used for construction works, it is called converted timber.
Wood, as a building material, is preferred because of
- Reasonable cost
- Ease of working
- Attractive appearance
- Good service life if protected from moisture and insect attack.
Uses of Wood
- As a building material, wood can be used for flooring, ceiling, paneling works and in the construction of partition walls.
- It can also be used in the form of piles, posts, beams, lintels, door/window frames etc.
- Wooden formworks for concrete casting are very common and frequently used. In addition, wood is also used for the timbering of trenches and other excavations, scaffolding, poles and fencing works.
- Wood can also be used as the main construction material for bridges. However, for longer spans, a wooden bridge is not preferred.
- Wood is also used to make railway sleepers that bear the load from the transiting trains.
What are the Characteristics of a Good Timber?
- A good timber is obtained from the heart of a sound tree and is free from sap.
- It has straight and close fibers and is uniform in color.
- It gives a clear ringing sound when struck. A dull sound is a sign of internal decay.
- It has regular annual rings. Timbers with narrow annual rings are generally the strongest.
- In case of a good timber, if you freshly cut the surface, it should give off a sweet smell.
- The teeth of saw do not get clogged while sawing a good timber.
- When a good timber is made plane, it has a bright and smooth surface. A dull appearance upon planning the surface is a sign of defective timber.
- If you see some variety of timber, the darker and heavier pieces are usually the stronger ones.
- A good timber is free from defects such as knots, shakes or other defects. It has firm adhesion of fibers and compact medullary rays.
Preservation of Timber
For proper utilization and functioning of timber, it ought to be protected from the attack of insects such as white ants etc. and from internal decaying caused by dry and wet rots. Therefore, the most effective way of preserving timber is by seasoning it.
Timber that is used for building or construction works should either be wholly dry and properly ventilated or wholly under water. In the latter case, it will not decay but will become soft and weak.
Adequate and proper damp proofing of the building and providing free circulation of air around the built-in portions of timber are essential for the preservation of timber. If such precision is hard to obtain, the timber can be preserved by applying preservatives.
Timber can be preserved by either of the following ways.
- Charring of timber includes applying an open flame to the surface of wood to char it. Doing so makes the wood resistant to fire and other deteriorations.
- Tarring includes coating the timber surface with tar or tar mixed with pitch. It is usually done on members that are embedded and is avoided in case of those structural members that are open to view because of the unpleasant black color.
- Painting the timber surface not only preserves it but also enhances its appearance.
- Creosoting is a preservation technique that involves pumping creosote oil from a chamber and saturating the timber with it. Creosote oil is a dark brown, thick, oily liquid that preserves timber from rot and attack of white ants. It is used in case of railway sleepers, piles and transmission poles.
- Wolman salt consists of creosote and sodium fluoride and is soluble in water. It renders the timber fire-resistant and immune from the attacks by fungi.
- Fire proofing of timber can be done to preserve it. This involves soaking it in ammonium sulphate, ammonium chloride, ammonium phosphate, sodium arsenate, or zinc chloride.
Veneers are thin sheets of wood that are peeled off, sliced or sawn from a log of wood having an attractive arrangement of grains. Rotary veneer cutters or veneer slicing machines are used to convert wooden logs into veneers.
Thickness of veneer sheets varies from 0.4 mm to 6 mm. These sheets are glued on the surface of inferior timber to improve their appearance and impart and aesthetic look.
The most common timbers used to make veneers are walnut, teak and rosewood. Veneers can also be used to manufacture plywood, laminboards and battenboards.
Plywood is obtained by gluing together veneers in odd number to the required thickness. The veneers used to make plywood are termed as plies. These are usually three-ply, five-ply, seven-ply or multi-ply depending upon the number of plies used.
The purpose of using an odd number of plies if to make the shrinkage stresses symmetric about the center ply and minimize the warping tendency of plywood. The plies are arranged in such a way that the grains of one layer are at right angles to the grains of the adjacent one.
Plywood is generally available up to 1.5 meters in width, 3.4 meters in length and their thickness may vary from 3 to 6mm. They are not prone to cracking or splitting easily when exposed to rain or sunlight.
Plywood is used for covering or paneling walls, for doors and shuttering in RCC (reinforced cement concrete) structures.
A laminboard comprises a laminae core more than 8mm thick that is glued between two or more plies. The grains of the core should be at right angle to the outer plies.
Laminboards are available up to 1.5m in width, 2.5 to 3 meters in length and 1cm to 5cm thick. They are light and strong and do not crack easily.
They are used for the construction of partition walls, in ceilings and doors, etc.
Block boards are similar to laminboards with the exception that the core is made from blocks having thickness less than 2.5 cm. these blocks are glued between two or more outer plies.
In block boards, too, the direction of grains of the core should be at right angles to that of the outer plies. Blockboards are cheaper than laminboards and are used for partition walls and doors.
Batten boards are similar to block boards. However, the core consists of close-grained battens not exceeding 8 cm in width, 2 to 3 cm thick and are edge-glued between two or more outer plies.
It is important to keep the direction of grains of the core perpendicular to that of the plies’ present adjunct. Batten boards are also used for partition walls, ceilings as well as doors and windows. They are light and strong and do not split or crack easily.
Hardboard is an important wood-based product. It is manufactured from wood wastes that are obtained from saw mills, low-quality or inferior timber or small wooden logs.
The raw materials are firstly converted into chips that are softened with steam and converted into fibers. To increase the strength, water repellant and synthetic resins are added. These are then pressed into boards of uniform thickness using a hydraulic press.
To tailor the properties of hardboards, other material may be added during manufacture. Owing to their homogeneous composition, hardboards have uniform strength in all directions. They are also free from natural defects such as shakes, knots, etc.
Hardboards are used for interior and exterior wall panels, ceilings, siding, countertops and much more. They can be given an aesthetic finish like embossed, perforated, wood-grained, plastic-faced, veneer finish, enameled, etc.
5. Building Materials for Concrete
The role of cement in concrete is that of a confining agent. It holds together all the other ingredients and provides strength to the hardened concrete by the hydration reaction. It is available in a number of types that are delineated in the ASTM standard.
Aggregates in concrete are of two types. The coarse aggregates or crushed stones are added to make the concrete strong and durable and also help improve its impact resistance. Fine aggregates are usually added as a filler material to fill in the voids of concrete and also to reduce the overall cost.
Lime acts as a substitute of cement or may be added in some portion along with cement in the concrete mix. Just like cement, lime is capable of reacting with water to product compounds that impart strength to the hardened product.
However, excess lime eventually leads to unsoundness in the final product which becomes prone to volumetric expansion.
6. Ceramic Materials
Ceramic materials are polycrystalline products of natural clays that are subjected to baking and burning at high temperatures with the addition of metal oxides and other inorganic substances having a high melting point.
As a building material, ceramics may comprise bricks, concrete, glass, porcelain, high temperature refractories, etc. In other words, clay products can be summed up to form the family of ceramics. In addition, refractory units made from other minerals are also a class of ceramics.
7. Polymeric Materials
Polymers such as rubber and rubber-based products are in conveyor belts, tank linings, etc. In addition, polymers also serve as insulating coatings and some may combine with waste rubber to make flooring tiles.
Chlorinated rubber is used in the production of protective coatings and adhesives used in construction and finishing works.
Plastics, mostly being synthetic materials, are available in market in a variety of forms to suit various structural and non-structural requirements. By varying the proportions of the constituents, the properties of plastic show great variations.
Over 40 groups or families of plastics have been produced so far, each with its own characteristics such as lightweight, heavyweight, heat-resistant, hard, soft, clear or opaque.
An important behavior of plastic that needs special consideration is in to heat. Based on this, we have two categories of plastics as follows.
- Thermoplastics become soft when heated and hard when cooled, irrespective of the number of heating and cooling cycles. They generally comprise acrylic, polyvinyl chloride (PVC), poly ethylene, polyvinyl acetate, cellulose acetate, poly propylene, etc.
- Thermosetting plastics have a chain-like structure having cross-links between molecules in adjacent chains. As a consequence, this type of plastic retains strength even on heating and fail by charring under prolonged heating.
Compared to thermoplastics, thermosetting plastics are hard, strong and more brittle. They cannot be reused and require great pressure and momentary heat during molding and finally get hardened on cooling.
Thermosetting plastics comprise polyester, epoxy resin, Bakelite, etc.
Properties of Plastics
- Plastics are light in weight.
- They have a low thermal conductivity as well as electrical conductivity.
- Plastics have great resistance to moisture and provide impermeable films for moisture barriers.
- These are easy to work upon and can be molded to any desired shape or form.
- Plastics are available in a wide range of colors and shades.
- Plastics can be transparent, translucent or opaque.
- They offer good resistance to attack by organic acids, bases, salts and living organisms.
- Plastics are slow burning, self-extinguishing or even non-inflammable.
- They can be formed or molded into any shape. They can be cast, molded, extruded, sawn, machined, riveted and glued to make products of desired shape and form.
- Plastics are rust-proof.
- An advantage of using plastic is that it can be reused after reprocessing. However, with regard to its environmental impact, plastic takes a way longer time to decompose and remains in landfills or is dispensed on other sites where it harms the existing creatures and the environmental as a whole.
- They have dimensional stability.
- Plastics are cheap due to their light weight, adaptability, low maintenance and have aesthetic value.
- They have good sound and heat absorption properties
Constituents of Plastics
Plastics consist of the following constituents.
- Plasticizer imparts workability and desired combination of strength, flexibility and toughness.
- Fillers (in the form of saw dust, mica, corn husk, etc.) are added to augment the hardness, tensile strength, bond opacity, and workability and also helps reduce the cost and shrinkage on setting.
- Pigment is added to achieve the desired color in hardened plastic and it must be resistant to the action of sunlight and weathering action.
- Lubricant is added to make the molding of plastic easier and prevents sticking of plastic to the mold.
- Catalyst is only added for thermosetting plastics and it helps accelerate the polymerization of fusible resin during molding operation.
- Fibers may be added for augmenting the strength and durability properties of plastics.
- Blowing agent (in the form of sodium bicarbonate and ammonium carbonate) are sometimes added to produce porous articles made from plastics.
The process of lamination involves impregnating thin sheets of paper, cloth, wood, glass fiber or asbestos with thermosetting resin and passing it through rollers, subjecting it to heavy pressures.
These sheets under the effect of heavy pressure and temperature are bonded together to form sheets of varying thicknesses. The resultant product is called “laminate” and these laminates are extensively used for decorative and ornamental purposes.
Structural Applications of Plastics
Plastics have innumerable applications either to substitute or protect other building materials, or to improve the comfort conditions. However, because of relatively low stiffness, they are not used as the primary load bearing materials. Some of the structural uses of plastics are as follows.
- In order to use plastics in structural applications, they need to be reinforced with glass fibers, jute, cotton, sisal, asbestos, and synthetic and metallic fibers.
- Flat sheets made from plastic can be used glazing purposes.
- In structural members that are susceptible to corrosion, glass fiber structural shapes can effectively be used to keep a check on and inhibit the commencement of corrosion.
- Plastic foam boards can be used a decking and roofing material.
- Insulating materials can also be made from plastics.
Non-Structural Applications of Plastics
Apart from contributing in structural applications, plastics can also serve non-structural purposes as given below.
- Resilient flooring can be obtained from plastics. These include vinyl tile, vinyl-cushioned flooring, linoleum, cork-tile, rubber flooring, etc.
- Non resilient flooring that primarily serves an aesthetic purpose can also be made from plastics. This may include plastic terrazzo and other plastic toppings.
- Plastic also contributes in making carpets such as tufted carpets, woven carpets, loomed and knitted carpets, all of which make an aesthetic floor finish.
- Interior and exterior finishes such as wall coverings can be made from plastic and are available in a plethora of designs and thicknesses.
- In areas where a barrier is to be provided for moisture control, a plastic membrane-type material or plastic sheeting can effectively serve as vapor barriers.
- Plastic is used to make plastic pipes, PVC sealing compounds, paints and varnishes, and lights.
- Sunscreens, adhesives and material coatings can also be made from plastic.
9. Ferrous and Non-Ferrous Metals
The use of metals in building works is very common and we come across their use in our daily lives too. A metal is a solid material which is typically hard, shiny, malleable, fusible, and ductile with excellent electrical and thermal conductivity.
Ferrous metals have iron as the principal constituent and are produced in larger quantities than any other metallic material. Examples include;
- Cast Iron
Steels are alloys of carbon iron plus other alloying materials. The mechanical properties of steel are sensitive to the carbon content and based on this we have three categories of steel.
This type of steel is produced in the largest quantities when compared with other alloys. It is used in the construction of structural steel shapes and possess very high toughness.
They are stronger than low-carbon steel but are less ductile. They are used in railway tracks and wheels and provide a good combination of strength and toughness.
High-carbon steel is the strongest among all as far as the ultimate strength is concerned. However, it is least ductile and fails with no prior warning. Therefore, its use in load-bearing structural components is avoided.
Uses of Steel in Construction
- Structural steel is used in framed construction works where steel beams and columns are connected together in a certain geometry to form a structural system that bears the applied loading.
- In concrete members, steel is used as a reinforcing material to improve the tensile strength of concrete, which otherwise may cause a brittle, instantaneous failure of the member.
- Steel fibers can be accommodated in a concrete mix to improve its mechanical properties post its ultimate strength.
The main problem with steel is corrosion which drastically reduces its service life. To offset this problem, stainless steel can be used. It possesses high corrosion resistance i.e., it is rust-free.
This property of corrosion resistance can be imparted to steel by the addition of alloying elements especially a minimum of 12% Cr along with Ni and Mo. This type of steel is used in razor blades, cutlery, etc.
Non-ferrous metals contain lesser or no quantity of iron in their composition. Therefore, they do not rust and can be picked up my magnets. They are strong and lighter than ferrous metals and cannot suspend similar loads.
They can be easily fabricated and have high electrical and thermal conductivities. A few examples of non-ferrous metals include,
- Aluminum is used in road signs, household piping, etc.
- Copper is a reddish-brown metal used in electrical fittings and wires, domestic water pipes, etc.
- Zinc is a silvery-blue metal that is used batteries, rust-proof paints, etc.
10. Paints, Varnishes, and Enamels
Paints, varnishes and enamels are surface coatings that upon drying form a thin film of the surface they are applied.
In general, paints can be classified as follows.
- Oil Paints consist of a base, vehicle, coloring pigments, solvent or thinner, drier and inert filler. By varying the type and proportion of the constituent ingredients, the painted surface can be made to look dry, glossy or flat as desired.
- Water Paints are also termed as white wash.
- Cement Paints are water-based coatings applied to the exterior or interior masonry works or concrete structures.
- Bituminous Paints comprise bitumen that is diluted with mineral spirits and is used as an exterior coating or sealant for damp-proofing.
When a base such as zinc oxide is ground in varnish, enamels are prepared. The desired coloring pigment may be added to impart color to the enamel. Enamels dry slowly and leave a hard, tough, and elastic film which is smooth and durable.
They are used in painting or coating the surface of glass, metal, wood as well as interior and exterior walls of a room. Enamels are durable coatings and are extensively used because of their versatility.
White wash is a coating of a surface by a mixture of fresh lime slaked with water and screened through a fine cloth, followed by the addition of a glue.
White wash is not a superior quality coating and therefore, it is recommended for low and medium-class houses. Normally, ceilings are white washed and walls are generally color washed.
Distempers (also called water paints) simply comprise a base such as white chalk mixed with a thinner such as water. It is used for the treatment of masonry walls; however, distemper gets affected by weather and is likely to come off if washed.
It forms a cheap, durable and easy finish for interior works. For exterior works, exposed to weather affects, the use of distempers is avoided because upon alternate wetting and drying, they flake off easily.
Varnish is a solution of resin in oil or turpentine or alcohol. Upon drying, it leaves behind a hard, transparent and glossy film of resin over the surface it is applied.
If you look forward to increasing the brilliance of a surface and to protect it from environmental conditions, a varnish is the apt choice. It is resistant to wear, retains its color, and gives a pleasing appearance.
11. Bitumen, Asphalt, and Tar
Bitumen, asphalt, tar are residual compounds of destructive distillation of coal. They are extensively used in pavement works, for their construction, maintenance and repair. In ancient times, tar was used a binding material to hold together stones or other construction units or as a water-proof coating for baths and pools.
In contemporary construction practices, the use of bitumen and bituminous compounds is not confined to damp proofing works of basement, floors and roofs. They are also used for painting timber and structural steel members and as binders in road works.