COMMON MATERIALS USED IN CONSTRUCTION, WOODWORK, METAL WORK AND ELECTRICAL AND ELECTRONICS TECHNOLOGY
This Unit is about some of the common materials used in construction and engineering work. The notes that have been given here are meant to help students familiarize or refresh their knowledge about the materials used for work in Technical Skills Education. The notes are meant for identification purposes; however, students are entreated to learn more about the uses, advantages and disadvantages, defects of the materials and safety precautions that would safeguard the value and utility of the materials. The materials to be introduced include the following.
- Gypsum and other building plasters
- Bricks, blocks and clay products
- Timber, Bamboo, Raffia, Formica
- Plywood, chipboard and slab materials
- Adhesives and mastics
- Painters’ materials
- Bituminous materials
- Metals and their products
Cements are binding substances used for mainly for construction work. The properties that make cements useful is that they set, harden, and adhere to other materials to bind them together. They are seldom used alone. They go mostly with stones and sand in various ratios depending on the required usage. However, many people have found innovative uses for cement by adding other components to do different jobs. The commonest type of cement for construction purposes is the ordinary Portland cement. What are the main constituents of Portland cement? Why is it called Portland cement? What are some of the safety threats cements face which can mare their usage and how can such threats be avoided? How are cements stored? To read more about cements, please follow this link. https://www.britannica.com/technology/cement-building-material https://www.quora.com/How-many-types-of-cement-are-there
Gypsum plasters are binders with gypsum used as its main binding material instead of Portland cement. Gypsum plaster is a white cementing material made by partial or complete dehydration of the mineral gypsum. Like Portland cement, when dry gypsum powder is mixed with water it gets hardened. This material can be applied over block, brick or concrete surface to form a smooth surface. They are mostly available in ready to use formats. Builders just add water and do not need sand. Gypsum has been found to offer excellent acoustic and thermal properties and gives levelled walls with the best finish. To find more about gypsum, its advantages and precautions while using it, please refer to Duggal (2008) pp 458 onwards.
Gypsum building plaster provides a smooth interior finish and is an ideal base for good quality paints and wallpaper finishes. It can be applied on both smooth and rough surfaces of the wall. Gypsum plaster is easy to apply and requires less skilled manpower unlike the traditional cement mortar. The preparation of surface and application of gypsum plaster should be apt to prevent cracks and peel offs.
Storage: When surfaces are exposed to moisture, there is a reduction of the setting time of gypsum plaster. So, gypsum bags have to be stored on elevated as well as a dry platform made of timber, brick or concrete. The shelf life of gypsum plaster is usually 3-4 months from the date of manufacture. If stored properly under suitable conditions of temperature and humidity, its shelf life can be increased by another 6 months.
Limes for Building and Construction Purposes
Lime is also a building material used mainly as lime mortar. There are two types of lime – hydraulic lime and non hydraulic lime. The non-hydraulic limes are also called quick lime. Hydraulic limes set under water while non-hydraulic limes do not set under water. Lime is a form of binder. All binders must not come into contact with its solvent unless the user is ready to apply it. When water or the appropriate solvent come into contact, they tend to harden. This reduces its workability. To learn more about limes, their uses, advantages and properties of lime, please visit the link below. https://theconstructor.org/building/lime-properties-uses-advantages-construction/15740/
Aggregates are the materials basically used as filler with binding material in the production of mortar and concrete. They are derived from igneous, sedimentary and metamorphic rocks or manufactured from blast furnace slag, etc. Aggregates form the body of the concrete, reduce the shrinkage and effect economy. They occupy 70-80 per cent of the volume and have considerable influence on the properties of the concrete. It is therefore significantly important to obtain right type and quality of aggregates at site. Their values are affected by dirt, impurity and other foreign materials. They should be clean, hard, strong, durable and graded in size to achieve utmost economy from the paste. Earlier aggregates were considered to be chemically inert but the latest research has revealed that some of them are chemically active and also that certain types exhibit chemical bond at the interface of aggregates and cement paste. To increase the bulk density of concrete aggregates are used in two markedly different sizes—the bigger ones known to be coarse aggregate (grit/stones) and the smaller ones fine aggregate (sand). The coarse aggregate forms the main matrix of concrete and the fine aggregate from the filler matrix between the coarse aggregate.
Concrete is made up of different ingredients, which have various functions. The properties of concrete mainly depend on the mixing of concrete ingredients i.e. cement, coarse aggregates, fine aggregates (sand), and water. Various other concrete ingredients can also be used such as admixtures, pigments, fibers, polymers and reinforcement. All these ingredients help in modifying the properties of the fresh as well as hardened concrete. In short, these materials are like members of family and they perform their individual role in such a manner that they contribute to overall success of the concrete as a whole family. The main threat that mares the utility of concrete is adding too much water and or too much sand. This reduces the strength of the concrete. Impurities in the materials used for making concretes (e.g. the water, the sand and the stones) can also be a threat. There are other defects too that can be discussed. Can you think of any? Read more about concretes from Duggal (2008) pp 144 onwards.
Bricks, blocks and clay products
One of the oldest building material brick continues to be a most popular and leading construction material because of being cheap, durable and easy to handle and work with. Clay bricks are used for building-up exterior and interior walls, partitions, piers, footings and other load bearing structures. Brick, blocks and all other clay products including engineering bricks also have their threats and disadvantages. To find out more, read Duggal (2008) pp. 8 onwards
Timber, Bamboo, Raffia, Formica
Timber, bamboo and raffia are all plant products. Timber is obtained from wood logs, bamboo comes from a subfamily of the perennial evergreen grass family and raffia is a type of fibre made from the palm some of the palm family of plants. The three materials have their uses. How different are they from each other? How are timber, bamboo and raffia stored? What are some of the safety threats of timber, bamboo and raffia? Are timber, bamboo and raffia different from each other? How different are they from formica?
Formica is a plastic product named after a New Zealand–based company called Formica Group. It is a heat-resistant, wipe-clean laminate. They come under a group of materials known as composites. Composite materials are combination of two or more materials in which one of the materials called the reinforcing phase is in the form of fibers, sheets or particles and is embedded in the other material called the matrix phase. The reinforcing material and the matrix material can be metal, ceramic, or polymer. Typically, reinforcing materials are strong with low densities while the matrix is usually a ductile or tough, material. If the composite is designed and fabricated correctly, it combines the strength of the reinforcement with the toughness of the matrix to achieve a combination of desirable properties not available in any single conventional material. For example, the design situation may demand both the strength and toughness, which have inverse relation, and are not exhibited by one material. When no single conventional material is able to satisfy the competing design specifications for a given application, the solution may be a composite material.
Because of the variety of available reinforcement and matrix materials, as well as the ability to combine them in wide range of volume fraction, composites can be produced with a broad range of elastic modulus, strength, and toughness combinations. The flexibility of tailoring to a specific need is one of the most important attributes of composites. Another advantage over conventional material is that composites can be designed to exhibit specific properties in specific directions (their anisotropy can be beneficial). The only drawback of the composites is that these are often more expensive than the conventional materials.
Application of composite materials in civil infrastructure and engineering systems is not only technologically sound but also economically justifiable. The economic impact to evolve from the use of composite infrastructure is:
- Reduction in installation and construction cost
- Reduction in maintenance cost
- Reduction in insurance liability
- Market expansion for the raw
- Development and sale of the service equipment for inspection of composites structures
Technically, Plywood, chipboard and all slab materials are classified under composites. Read more about composites from Duggal (2008) pp 515 – 518.
Plastic and Rubber Materials
Plastics are a wide range of synthetic or semi-synthetic materials that usually use polymers as a main ingredient. The plasticity during production makes it possible for plastic to be moulded, extruded or pressed into solid objects of various shapes, making them an adaptable material for many different uses. Currently, rubber is harvested mainly in the form of the latex from the rubber tree or others. The latex is a sticky, milky colloid drawn off by making incisions in the bark and collecting the fluid in vessels in a process called “tapping”. The latex then is refined into rubber that is ready for commercial processing. Read more on plastics and rubbers under polymeric materials. Look for their main characteristics, types, uses, threats, advantages and disadvantages. Refer to Duggal (2008) pp 402 – 422.
Adhesives and mastics
Adhesives are natural or synthetic binders used for surface coatings. Natural binders like plant juices, glues, etc. have been in use since prehistoric age but have gradually lost their social acceptance and have been replaced by synthetic binders derived from plant minerals or mineral oil. These may be applied hot, or as an emulsion, or with a solvent. High load bearing adhesives have been developed for engineering applications. Structural adhesives are based on specially cured rubber-toughened epoxies, acrylics and silanes. Silane resins are used to prevent moisture penetration.
Adhesives have an advantage over rivets and bolts by distributing stress over larger areas ot
a joint. This reduces galvanic corrosion between dissimilar metals and provides the ability to cement together extremely thin sheets. The process of bonding with adhesives is economical.
Adhesives lose stability at high temperatures and the resistance to peeling is poor. Special care is to be exercised in their application. They take lot of time to form the bond.
Adhesives should have high tensile strength. The important physical properties of adhesives are cohesive strength, adherence, ﬂuidity, and wettability of the substrate.
Paint is a liquid surface coating. On drying it forms a thin film (60–150 µ) on the painted surface. Paints are classified as oil paints, water paints, cement paints, bituminous paints and special paints such as fire proof paints, luminous paints, chlorinated rubber paints (for protecting objects against acid fumes), etc. The functions of the paints are: to protect the coated surface against possible stresses—mechanical or chemical; deterioration—physical or environmental; decorate the structure by giving smooth and colourful finish; check penetration of water through R.C.C; check the formation of bacteria and fungus, which are unhygienic and give ugly look to the walls; check the corrosion of the metal structures; check the decay of wood work and to varnish the surface to display it to better advantage.
Bitumen and bituminous materials
Bitumen and bituminous materials have been known and used in construction works since ancient times; approximately 6000 B.C. Asphalts were used as cements to hold stonework together in boat building and as waterproofing in pools and baths. Some asphalt was mixed with stand and used to pave streets and palace floors.
Bitumens are mainly composed of a mixture of high-molecular hydrocarbons, methane, napthane and other aromatic series and their oxygen or sulphur derivatives. Tar and asphalt are the two varieties of bituminous materials. Tars are bituminous condensates obtained in the process of destructive distillation of coal, petroleum, wood and other organic materials at high temperature without access of air. They are composed of hydrocarbons and their sulphurous, nitrous and oxygen derivatives. Asphalt on the other hand is a naturally occurring bitumen which is a combination of an inorganic mineral matter either calcareous or siliceous and an organic matter—a chemical compound of carbon and hydrogen. Bitumens and bituminous materials are being extensively used in damp proofing the basements, floors, roofs, damp proof courses; painting timber and steel structural elements;
Glass and Ceramics
Ceramics refer to polycrystalline materials and products formed by baking natural clays and mineral admixtures at a high temperature and also by sintering oxides of various metals and inorganic substances having high melting point. The word is of Greek origin and derives its name from Keromos meaning potter’s earth or clay. But, nowadays the term ceramic is applied to a wide range of silicates, metallic oxides and their combinations. Carbon, boron, silicon, certain carbides, silicates, refractory hydrides and sulphides are also considered to be ceramics. As a building material, ceramics may include brick, stone, concrete, glass, abrasives, porcelain, high temperature refractories, etc. Clay is the most common example of ceramic materials.
Magnesium oxide can withstand high temperatures (1650–2500°) without melting and is used
extensively as a refractory. Ceramics are usually hard and brittle and are in the form of amorphous (non-crystalline) or glassy solids. The bond in these materials is mixed ionic and covalent and while these can be made in single crystal forms, their more common structure is glassy. Because of covalent ionic bond the electrons are not free which makes the ceramics, thermal and electrical insulators. At low temperatures, ceramics behave elastically. However, under proper conditions of stress and temperature these deform by viscous flow.
Glass is a non-crystalline, often transparent amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling of the molten form; some glasses such as volcanic glass are naturally occurring. There are other sources too. See Duggal (2008) pp 391 – 401 for more details.
Metals are opaque, lustrous elements that are good conductors of heat and electricity. Most metals are malleable and ductile and are, in general, denser than the other elemental substances. Metals can be classified under ferrous and nonferrous metals. Ferrous metals include iron products while nonferrous metals are non-iron products. Ferrous metals tend to rust easily however they are easy to weld and common to find in greater quantities. When two or more metals are combined, the resulting metal is an alloy. Metals are seldom used without alloying.