Basic Materials Used in Construction

1. Basic Materials Used in Construction • Several materials are required for construction. • The materials used in the construction of Engineering Structures such as buildings, bridges and roads are called Engineering Materials or Building Materials. • They include Bricks, Timber, Cement, Steel, Sand etc.

2. Some of the most important properties of building materials are grouped as follows

3. Definitions • Density: It is defined as mass per unit volume. It is expressed as kg/m3. • Specific gravity: It is the ratio of density of a material to density of water. • Porosity: The term porosity is used to indicate the degree by which the volume of a material is occupied by pores. It is expressed as a ratio of volume of pores to that of the specimen. • Strength: Strength of a material has been defined as its ability to resist the action of an external force without breaking.   • Elasticity: It is the property of a material which enables it to regain its original shape and size after the removal of external load.   • Plasticity: It is the property of the material which enables the formation of permanent deformation. • Hardness: It is the property of the material which enables it to resist abrasion, machining and scratching. • Ductility: It is the property of a material which enables it to be drawn out or elongated to an appreciable extent before rupture occurs.

4. Brittleness: It is the property of a material, which is opposite to ductility. Material, having very little property of deformation, either elastic or plastic is called Brittle.   • Creep: It is the property of the material which enables it under constant load to deform slowly but progressively over a certain period.   • Stiffness: It is the property of a material which enables it to resist deformation.   • Fatigue: The term fatigue is generally referred to the effect of cyclically repeated stress. A material has a tendency to fail at lesser stress level when subjected to repeated loading. • Impact strength: The impact strength of a material is the quantity of work required to cause its failure per its unit volume. It thus indicates the toughness of a material.   • Toughness: It is the property of a material which enables it to be twisted, bent or stretched under a high stress before rupture. • Thermal Conductivity: It is the property of a material which allows conduction of heat through its body. It is defined as the amount of heat in kilocalories that will flow through unit area of the material with unit thickness in unit time when difference of temperature on its faces is also unity. • Corrosion Resistance: It is the property of a material to withstand the action of acids, alkalis gases etc., which tend to corrode (or oxidize).

5. Stones • Stones are obtained from rocks. • A rock represents a definite portion of earth’s surface. • Process of taking out stones from natural rock beds is known as quarrying. • The term quarry is used to indicate the exposed surface of natural rocks. • Stones, thus obtained, are used for various engineering purposes. • Stone has been used to build small residential buildings to larges palaces, forts, temples and monuments. • RashtrapathiBhavan, Jaipur Palace, Red Fort, Birla Mandirsat Delhi, Banaras and Hyderabad, TajMahal, Gateway of India and India Gate etc. are the world famous stone buildings.

6. Uses of Stones: • Stones are used as a construction material for foundations, walls, columns and lintels. • Stones are used for face-work of buildings to give good appearance. • Thin stone slabs are used as roofing and flooring material. • Crushed stones are used for production of cement concrete. • Crushed stones are also used as ballast for railway track. • Aggregate of stone is used as a road metal.

7. Properties • A good building stone should have the following qualities. • Crushing Strength: For a good structure stone, the crushing strength should be greater than 100 N/mm2. • Hardness: For a good building stone, the coefficient of hardness should be more than 17. • Fracture: For a good building stone, its fracture should be sharp, even and clear. • Percentage wear: The percentage wear should be equal to or less than 3%. • Resistance to fire: Minerals composing stone should be such that shape of stone is preserved when a fire occurs. • Water absorption: For a good stone, percentage absorption by weight after 24 hours should not exceed 0.6. • Specific gravity: A good building stone should have a specific gravity more than 2.7. Compact and less porous building stones will have higher specific gravity.

8. Durability: A good build stone possesses higher resistance against the action of weathering agents. Durability is affected by chemical composition, resistance to atmospheric agents, physical structure etc. • Appearance: Stones which are used for face work should be decent in appearance and they should be capable of preserving their colour uniformly for a long time. • Seasoning:Stones should be well seasoned before putting into use i.e., they should be free of moisture content (quarry sap). Stones should be dried or seasoned before they are used in structural work.

9. Bricks • Bricks are obtained by moulding clay in the rectangular blocks of uniform size and then by drying and burning these blocks. • Bricks are very popular as they are easily available, economical, strong, durable and reliable. • They are also reasonably heat and sound proof. • Thus, at places where stones are not easily available, but if there is plenty of clay, bricks replace stones. • The size of the bricks used are 190 mm × 90 mm × 90 mm. • Depth of a frog in a brick is 10mm to 20 mm. Frog

10. Bricks may defined as a small, solid or cored building unit in shape of rectangular block composed of inorganic, non-metallic substances of mineral origin and hardened by heat or chemical action. • Bricks may be divided into 3 types • Bricks made of Clay, burned or fired to hardness. Eg common brick, acid brick, sewer brick, fire brick, flooring brick etc. 2) Brick made of cementious materials that harden by chemical reaction. Eg sand-lime brick and cement brick. 3) Adobe Brick, which is simple fore-runner of burned brick, is dried out and hardened in sun. It is made of calcareous sandy clay or any alluvial desert clay with good plastic properties that dries to hard, uniform mass. Composition of Clay Bricks

11. Properties of bricks: • Good bricks which are used as building material should possess the following qualities. • Bricks should be uniform in shape and should be of standard size. • Bricks should be table moulded, well burnt in kilns, copper coloured, free from cracks and with sharp and square edges. • Bricks should give clear ringing sound when struck with each other. • Bricks when broken should show homogeneous and compact structure. • A brick should not absorb more than 15% of its weight of water when kept immersed for 24 hours. • The crushing strength should not be less than 5.5 N/mm2. • Bricks should be sufficiently hard such that no impression is left when scratched with finger nails and they should be free of soluble salts. • A brick should not break when dropped from a height of about one metre

13. Uses of Bricks: • Bricks are extensively used as a leading material of construction. • A fire brick (Refractory brick) is used for lining the interiors of ovens, chimneys and furnaces. • Broken bricks are used as a ballast material for railway tracks, and also as a road metal. • Bricks are extensively used for construction of load-bearing walls and partition-walls. • Bricks are also used for face-work when artistic effect is required.

14. Sand • It is natural product which is obtained from pits, river beds,shores,sea beds etc. • It is a form of silica (SiO2 ). • In construction works sand is mainly used as inert material in mortar and concrete.

15. Sea sand should not be used in making mortar and concrete for the following reasons: • It contains salt and hence structure remains damp. The mortar is affected by efflorescence and then blisters appear. • It contains shells and organic matter, which decompose after some time and reduce the strength and life of mortar and concrete. • Sand can be obtained artificially by crushing stones also. • In crushing stones to get coarse aggregates, it is obtained as a by-product. • The minute particles of crushed stones form artificial sand for construction activities. • In constructing dams and bridges, artificial sand is very commonly used.

16. Uses • Sand is used in mortar and concrete for the following purpose: • It subdivides the paste of binding material into thin films and allows it to adhere and spread. • It fills up the gap between the two building blocks and spreads the binding material. • It adds to the density of mortars and concrete. • It prevents shrinkage of cementing material. • It allows carbon dioxide from the atmosphere to reach some depth and thereby improves there by setting power. • The cost of cementing material per unit volume is reduced as this low cost material increases the volume of cementing material. • Silica of sand contributes to formation of silicates resulting into hardened mass.

17. Properties The properties of good sand are: • It should be chemically inert. • It should be free from organic or vegetable matter. • It should be free from salt. • It should contain sharp, angular and coarse grains. • It should be well graded. • It should be hard.

18. Cement • The cement is obtained by burning a mixture of calcarious (calcium) and argillaceous (clay) material at a very high temperature and then grinding the clinker so produced to a fine powder. • It was first produced by a mason Joseph Aspdinin England in 1924. • He patented it as portland cement.

20. Oxide Composition Of Cement Some types of Cement are listed below: 1)Ordinary Portland Cement 2) Coloured Cement 3)White Cement 4) Quick Setting Cement 5) Rapid Hardening Cement 6) Low Heat Cement 7) Pozzolana Cement

21. Chemical properties of Cement • Portland cement consists of the following chemical components: • There may be small quantities of impurities present such as calcium oxide (CaO) and magnesium oxide (MgO). • When water is added to cement, C3A is the first to react and cause initial set. It generates great amount of heat. • C3S hydrates early and develops strength in the first 28 days. It also generates heat. • C2Sis the next to hydrate. It hydrates slowly and is responsible for increase in ultimate strength. • C4AF is comparatively inactive compound.

22. Physical properties of Cement • The following physical properties should be checked before selecting a portland cement for the civil engineering works. • IS 269–1967 specifies the method of testing and prescribes the limits: 1) Fineness: • It is measured in terms of percentage of weight retained after sieving the cement through 90 micron sieve or by surface area of cement in square centimeters per gram of cement. • According to IS code specification weight retained on the sieve should not be more than 10 per cent. 2) Setting time: • A period of 30 minutes as minimum setting time for initial setting and a maximum period of 600 minutes as maximum setting time is specified by IS code, provided the tests are conducted as per the procedure prescribed by IS 269-1967.

23. 3) Soundness: • Once the concrete has hardened it is necessary to ensure that no volumetric changes takes place. • The cement is said to be unsound, if it exhibits volumetric instability after hardening. • IS code recommends test with Le Chateliermould for testing this property. • At the end of the test, the indicator of Le Chateliermould should not expand by more than 10 mm. 4) Crushing strength: • For this mortar cubes are made with standard sand and tested in compression testing machine as per the specification of IS code. • The minimum strength specified is 16 N/mm2 after 3 days and 22 N/mm2 after 7 days of curing

24. Uses of Cement • Cement is used widely for the construction of various structures • Cement slurry is used for filling cracks in concrete structures. • Cement mortar is used for masonry work, plastering and pointing. • Cement concrete is used for the construction of various structures like buildings, bridges. water tanks, tunnels, docks, harboursetc. • Cement is used to manufacture lamp posts, telephone posts, railway sleepers, piles etc. • For manufacturing cement pipes, garden seats, dust bins, flower pots etc. cement is commonly used. • It is useful for the construction of roads, footpaths, courts for various sports etc.

25. Reinforcing Steel • Steel is an alloy of ferrous metal with 0.25 to 1.5 per cent of carbon. • Higher the carbon content, harder is the steel. Steel bars of circular cross sections are mainly used as reinforcement to strengthen concrete structures. • There are three types of reinforcing steel • Mild steel • High Yield Strength Deformed bars (HYSD)/TOR steel • High tensile steel.

26. Mild steel • It contains carbon up to 0.23 to 0.25%. • Higher value is permitted for bars of 20 mm and above diameter. • It is available in diameters of 6, 10, 12, 16, 20, 25 and 32 mm. • Its yield strength is 250 N/mm2 and young’s modulus is 2 × 10 ^5 N/mm2. • It was very commonly used reinforcement in concrete. It is used as window bars, for grills and for making steel gates.

27. High Yield Strength Deformed bars (HYSD)/TOR steel • Two types of TOR steel bars are available. • They are Fe-415 and Fe-500. • The number associated with the designation indicates the tensile strength of bar in N/mm2. • These bars are provided with ribs deformation on surface so that bond between concrete and steel improves. • These bars are available in diameters 8, 10, 12, 16, 20, 22, 25, 28 and 32 mm. • Nowadays these bars are replacing mild steel bars as reinforcement since their strength in tension and bond is higher.

28. High Tensile Bars • High tensile steel bars are made with 0.8 % carbon and 0.6 % manganese apart from small percentages of silicon, sulphur and phosphorous. • The process of making these wires involve cold drawing and tempering. • They are usually available in 2, 3, 4, 5, 6, 7 mm diameters. They may be bundled with number of them to form a strand. • These bars are having tensile strength as high as 1400 N/mm2 to 1900 N/mm2. • The young’s modulus of steels is also same as that of mild steel. • High tensile bars are used as reinforcement in prestressed concrete.

29. Cement concrete • Cement concrete is an artificial product obtained by hardening of the mixture of cement, sand, gravel and water in pre-determined proportions. • The hardening of cement-concrete is due to chemical reaction between cement and water and the process is also called ‘setting’.

30. Properties of cement-concrete • Properties of concrete are different when it is in plastic stage (green concrete) and hardened stage. • Properties of Green/Fresh Concrete: • Workability: The workability of a freshly prepared concrete is the ease with which it can be mixed, placed, compacted and finished without affecting homogeneity. • Segregation: A good concrete is a homogeneous mixture of cement, sand, coarse aggregates and water. Segregation during mixing, placing and compacting affects strength, durability and water tightness. • Bleeding: Bleeding is the separation of water cement slurry from coarse and fine aggregates either due to excessive quantity of water in fresh concrete or due to excessive vibration during compaction process. Bleeding of concrete causes formation of pores and reduces compressive strength. • Harshness: Harshness of concrete is due to use of poorly graded aggregates in concrete mix. A harsh concrete is porous and difficult to get smooth surface finish.

31. Properties of hardened Concrete: • Strength: Hardened concrete should have high compressive strength. Compressive strength is the most important parameter considered in the design of concrete structures. • Durability: Concrete should be capable of withstanding the adverse effects of weathering agents such as wind and water. In addition, it should resist temperature variation, moisture variation, freezing and thawing. • Impermeability: Hardened concrete should be impermeable or water-tight. This property of concrete is considered in the construction of water tanks and bins. • Resistance to wear and tear: Hardened concrete should be capable of with standing abrasive action during its usage. When concrete is used as a flooring material, or for constructionof cement concrete roads, it should withstand abrasive action.

32. Uses of Cement Concrete • It is used for making Reinforced Cement Concrete (R.C.C.) and Prestressed Cement Concrete (P.S.C.). • It is used for mass concrete works such as dams and bridges. • It is used for making electric poles, railway sleepers and high rise towers. • It is used for the construction of silos and bunkers. • It is used for the construction of water tanks and under water construction. • It is used for the construction of road pavements and air port pavements. • It is used for construction of arches and ornamental structures. • It is one of the best universally accepted construction material and used in various civil Engineering works.

33. Reinforced Cement Concrete (R.C.C.) • Plain concrete can withstand very high compressive loads. • But it is very weak in resisting tensile loads. • Steel, on the other hand can resist very high tensile force. • Hence, steel is embedded in concrete whenever tensile stresses are expected in concrete. • Such a concrete is called ‘Reinforced Cement Concrete.

34. Properties of R.C.C. • R.C.C. is highly economical when compared to other engineering materials. • R.C.C. is durable and can effectively resist moisture variation and temperature variation. • R.C.C. is a fire resistant construction material. • Water-tight structures such as water tanks can be constructed of R.C.C. • R.C.C. can be moulded to any shape and size before setting and hardening of concrete.

35. Uses • R.C.C. is used for construction of structural elements such as beams, columns and slabs. • R.C.C. is used for the construction of water tanks, storage bins, bunkers, tall chimneys, towers etc., • R.C.C. is used in making raft foundations and pile foundations. • R.C.C. is used in the construction of bridges, marine structures, aqueducts, high rise buildings and many other civil engineering works.

36. Plain Cement Concrete (P.C.C.) • The intimate mixture of cement, sand, coarse aggregate and water is known as plain cement concrete. • A small quantities of admixtures like air entraining agents, water proofing agents, workability agents may also be added to impart special properties to the plain cement concrete.

37. Uses of plain cement concrete • Uses of plain cement concrete is listed below: • As bed concrete below the wall footings, column footings and on walls below beams. • As sill concrete to get a hard and even surface at window and ventilator sills. • As coping concrete over the parapet and compound walls. • For flagging the area around the buildings. • For making pavements. • For making tennis courts, basket ball courts etc

38. Precast Concrete (P.C.C.) • Usually concrete structures are built by casting them in their final position in the site by providing form work, pouring concrete and then removing the form work. It is called as cast-in-situ construction. • If concrete elements are cast in factories or elsewhere and transported to their final destination, they are called precast elements. • Since the elements are cast in factories where controls are better, they are superior to cast in situ elements. • However, the disadvantage is cost of transportation and achieving desired connections on site.

39. Uses Precast concrete is used in the following: • Pipes and tanks • Poles, piles, sleepers and pavement • Lintel beams • Beams and girders • Building blocks • Wall panels • Manhole covers

40. Prestressed Concrete (PSC) • Prestressed concrete is a method for overcoming concrete's natural weakness in tension. • It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. • Prestressing tendons (generally of high tensile steel cable or rods) are used to provide a clamping load which produces a compressive stress that balances the tensile stress that the concrete compression member would otherwise experience due to a bending load. • Traditional reinforced concrete is based on the use of steel reinforcement bars, rebar's, inside poured concrete. • ACI committee defines prestressed concrete as the one in which internal stresses have been introduced such that the stresses resulting from given external loadings are counter-acted to a desired degree.

42. Uses • Prestressed concrete is commonly used in making the following structural elements. • Beams and girders. • Slabs and grid floors. • Pipes and tanks • Poles, piles, sleepers and pavements. • Shell and folded plate roofs.

43. Introduction to smart materials • These are the materials which exhibit considerable changes in their mechanical properties like strain (Deformation) and viscosity, when subjected to changes in thermal, electrical or magnetic field changes. • These properties can be exploited to develop sensors and devices which can respond to changes automatically. • Hence such materials are called as intelligent/active/adaptive materials also. • Currently available smart materials are : • Shape Memory Alloy (SMA) • MagnetostrictiveMaterials • Piezoelectric Materials • ElectrostrictiveMaterials and • Electro-rheological Fluids.

44. Shape Memory Alloy (SMA) • They are the smart materials which have the ability to return to some previously defined shape or size when subjected to appropriate thermal changes • Materials that exhibit shape memory only upon heating are referred to as having one way shape memory. • Some materials undergo a change in shape upon cooling also. • These materials are said to have two way shape memory. • However for commercial exploitation only Niti (Nickel alloys) and the copper base alloys such as CuZn Al (Copper-Zinc- Aluminium) alloys are found useful.

45. Magnetostrictive Materials • They are the smart materials which have the ability to undergo deformation when subjected to magnetic field. • The higher known magnetostriction are those of iron alloys containing rare earth elements Dysposium (Dy Fe2) or Terbium (TbFe2). Cut-away of a transducer comprising: magnetostrictive material (inside), magnetising coil, and magnetic enclosure completing the magnetic circuit (outside)

46. Piezoelectric Materials • These are the materials which have capability to produce a voltage when surface strain is introduced. • Conversely, the material undergo deformation (stress) when an electric field is applied across it. • Example are quartz, Rochelle salt Polyvinylidenefluid (PVDF)

47. Electrostrictive Materials • These materials are identical to piezoelectric materials, with better strain capacity but very sensitive to temperature

48. ElectrorheologicalFluids • They are the colloidal suspensions that undergo changes in viscosity when subjected to an electric field. Such fluids are highly sensitive and respond instantaneously to any change in the applied electric field.

49. Applications • Smart materials are used in aircrafts and spacecrafts to control vibrations and excessive deflections. • Smart concrete is used in smart structures. Smart concrete (a composite of carbon fibres and concrete) is capable of sensing minute structural cracks / flaws. • Smart materials have good potential to be used in health care markets. Active control drug delivery devices such as Insulin Pump is a possibility. • Smart materials have applications in the design of smart buildings and state of art vehicles. Smart materials are used for vibration control, noise mitigation, safety and performance.