Yourskill Tricks: BUILDING MATERIALS

Building material is any material which is used for construction purposes. Many naturally occurring substances, such as clay, rocks, sand, and wood, even twigs and leaves, have been used to construct building.

I am discussing about building materials in following topics
1.Stones
2.Bricks
3.Cement
4.Concrete
5.Aluminium
6.Copper
7.Glass
8.Plastic
9.Bitumen
10. Asbestos
11.Paints
12.Roofing & Flooring tiles and wall tiles

Topic 1:
Stones :Stone is a ‘naturally available building material’ which has been used from the early age of civilization.It is available in the form of rocks, which is cut to required size and shape and used as building block.It has been used to construct small residential buildings to large palaces and temples all over the world.

Type of Stones

Stones used for civil engineering works may be classified in the following three ways:

•- Geological

•- Physical

•- Chemical

Geological Classification

Based on their origin of formation stones are classified into three main groups—Igneous, Sedimentary and Metamorphic Rocks.

(i) Igneous Rocks:

These rocks are formed by cooling and solidifying of the rock masses from their molten magmatic condition of the material of the earth. Generally igneous rocks are strong and durable. Granite, trap and basalt are the rocks belonging to this category, Granites are formed by slow cooling of the lava under thick cover on the top. Hence they have crystalline surface. The cooling of lava at the top surface of earth results into non-crystalline and glassy texture. Trap and basalt belong to this category.

(ii) Sedimentary Rocks:

Due to weathering action of water, wind and frost existing rocks disintegrates. The disintegrated material is carried by wind and water; the water being most powerful medium. Flowing water deposits its suspended materials at some points of obstacles to its flow.

These deposited layers of materials get consolidated under pressure and by heat. Chemical agents also contribute to the cementing of the deposits. The rocks thus formed are more uniform, fine grained and compact in their nature. They represent a bedded or stratified structure in general. Sand stones, lime stones, mud stones etc. belong to this class of rock.

(iii) Metamorphic Rocks:

Previously formed igneous and sedimentary rocks undergo changes due to metamorphic action of pressure and internal heat. For example due to metamorphic action granite becomes greisses, trap and basalt change to schist and laterite, limestone changes to marble, sandstone becomes quartzite and mudstone becomes slate.

Physical Classification

Based on the structure, the rocks may be classified as:

-• Stratified rocks

- •Unstratified rocks

(i) Stratified Rocks:

These rocks are having layered structure. They possess planes of stratification or cleavage. They can be easily split along these planes. Sand stones, lime stones, slate etc. are the examples of this class of stones.

(ii) Unstratified Rocks:

These rocks are not stratified. They possess crystalline and compact grains. They cannot be split in to thin slab. Granite, trap, marble etc. are the examples of this type of Rocks.

(iii) Foliated Rocks:

These rocks have a tendency to split along a definite direction only. The direction need not be parallel to each other as in case of stratified rocks. This type of structure is very common in case of metamorphic rocks.

Chemical Classification

On the basis of their chemical composition engineers prefer to classify rocks as:

• -Silicious rocks

• -Argillaceous rocks and

• -Calcareous rocks

(i) Silicious rocks: The main content of these rocks is silica. They are hard and durable. Examples of such rocks are granite, trap, sand stones etc.

(ii) Argillaceous rocks: The main constituent of these rocks is argil i.e., clay. These stones are hard and durable but they are brittle. They cannot withstand shock. Slates and laterites are examples of this type of rocks.

(iii) Calcareous rocks: The main constituent of these rocks is calcium carbonate. Limestone is a calcareous rock of sedimentary origin while marble is a calcareous rock of metamorphic origin.

Properties of Stones-

The following properties of the stones should be looked into before selecting them for engineering works:

(i) Structure:

The structure of the stone may be stratified (layered) or unstratified. Structured stones should be easily dressed and suitable for super structure. Unstratified stones are hard and difficult to dress. They are preferred for the foundation works.

(ii) Texture:

Fine grained stones with homogeneous distribution look attractive and hence they are used for carving. Such stones are usually strong and durable.

(iii) Density:

Denser stones are stronger. Light weight stones are weak. Hence stones with specific gravity less than 2.4 are considered unsuitable for buildings.

(iv) Appearance:

A stone with uniform and attractive colour is durable, if grains are compact. Marble and granite get very good appearance, when polished. Hence they are used for face works in buildings.

(v) Strength:

Strength is an important property to be looked into before selecting stone as building block. Indian standard code recommends, a minimum crushing strength of 3.5 N/mm2 for any building block. Table 1.1 shows the crushing strength of various stones.

Due to non-uniformity of the material, usually a factor of safety of 10 is used to find the permissible stress in a stone. Hence even laterite can be used safely for a single storey building, because in such structures expected load can hardly give a stress of 0.15 N/mm2. However in stone masonry buildings care should be taken to check the stresses when the beams (Concentrated Loads) are placed on laterite wall.

(vi) Hardness:

It is an important property to be considered when stone is used for flooring and pavement. Coefficient of hardness is to be found by conducting test on standard specimen in Dory’s testing machine. For road works coefficient of hardness should be at least 17. For building works stones with coefficient of hardness less than 14 should not be used.

(vii) Percentage wear:

It is measured by attrition test. It is an important property to be considered

in selecting aggregate for road works and railway ballast. A good stone should not show wear of more than 2%.

(viii) Porosity and Absorption:

All stones have pores and hence absorb water. The reaction of water with material of stone cause disintegration. Absorption test is specified as percentage of water

absorbed by the stone when it is immersed under water for 24 hours. For a good stone it should be as small as possible and in no case more than 5.

(ix) Weathering:

Rain and wind cause loss of good appearance of stones. Hence stones with

good weather resistance should be used for face works.

(x) Toughness:

The resistance to impact is called toughness. It is determined by impact test.

Stones with toughness index more than 19 are preferred for road works. Toughness index 13 to 19 are considered as medium tough and stones with toughness index less than 13 are poor stones.

(xi) Resistance to Fire:

Sand stones resist fire better. Argillaceous materials, though poor in strength, are good in resisting fire.

(xii) Ease in Dressing:

Cost of dressing contributes to cost of stone masonry to a great extent.Dressing is easy in stones with lesser strength. Hence an engineer should look into sufficient strength rather than high strength while selecting stones for building works.

(xiii) Seasoning:

The stones obtained from quarry contain moisture in the pores. The strength of

the stone improves if this moisture is removed before using the stone. The process of removing moisture from pores is called seasoning. The best way of seasoning is to allow it to the action of nature for 6 to 12 months. This is very much required in the case of laterite stones.

Tests on Stones

To certain the required properties of stones, the following tests can be conducted:

(i) crushing strength test

(ii) water absorption test

(iii) abrasion test

(iv) impact test

(v) acid test.

(i) Crushing Strength Test:

For conducting this test, specimen of size 40 × 40 × 40 mm are prepared from parent stone. Then the sides are finely dressed and placed in water for 3 days. The saturated specimen is provided with a layer of plaster of paris on its top and bottom surfaces to get even surface so that load applied is distributed uniformly. Uniform load distribution can be obtained satisfactorily by providing a pair of 5 mm thick playwood instead of using plaster of parislayer also.

The specimen so placed in the compression testing machine is loaded at the rate of 14 N/mm2 perminute. The crushing load is noted. Then crushing strength is equal to the crushing load divided by the area over which the load is applied. At least three specimen should be tested and the average should be taken as crushing strength.

(ii) Water Absorption Test:

For this test cube specimen weighing about 50 grams are prepared and the test is carried out in the steps given below:

(a) Note the weight of dry speciment as W1.

(b) Place the specimen in water for 24 hours.

(c) Take out the specimen, wipe out the surface with a piece of cloth and weigh the specimen.Let its weight be W2.

(d) Suspend the specimen freely in water and weight it. Let its weight be W3.

(e) Place the specimen in boiling water for 5 hours. Then take it out, wipe the surface with cloth and weigh it. Let this weight be W4 . Then,

Percentage absorption by weight =(W2- W1)/(W1)x100 ---------(1)

Percentage absorption by volume =W2-W1/W2-W3X100--------(2)

Percentage porosity by volume =W4-W1/W2-W3X100-----------(3)

Density =W1/W2-W1----------------------------------------------------(4)

Specific gravity=W1/W2-W3-------------------------------------------(5)

∴ Saturation coefficient =Water absorption / Total porosity =W2-W1/W4-W1

(iii) Abrasion Test:

This test is carried out on stones which are used as aggregates for road construction. The test result indicate the suitability of stones against the grinding action under traffic. Any one of the following test may be conducted to find out the suitability of aggregates:

(i) Los Angeles abrasion test

(ii) Deval abrasion test

(iii) Dorry’s abrasion test.

However Los Angeles abrasion test is preferred since these test results are having good correlation with the performance of the pavements.

The Los Angeles apparatus consists of a hollow cylinder 0.7 m inside diameter and

0.5 m long with both ends closed.

It is mounted on a frame so that it can be rotated about horizontal axis. IS code has standardised the test procedure for different gradation of specimen. Along with specified weight of specimen a specified number of cast iron balls of 48 mm diameter are placed in the cylinder.Then the cylinder is rotated at a speed of 30 to 33 rpm for specified number of times (500 to 1000). Then the aggregate is removed and sieved on 1.7 mm. IS sieve. The weight of aggregate passing is found.

Then Los Angeles value is found as = Weight of aggregate passing through sieve/

Original weight × 100.

The following values are recommended for road works:

For bituminous mixes – 30%

For base course – 50%

(iv) Impact Test:

The resistance of stones to impact is found by conducting tests in impacting

testing machine It consists of a frame with guides in which a metal hammer weighing 13.5 to 15 kg can freely fall from a height of 380 mm.

Aggregates of size 10 mm to 12.5 mm are filled in cylinder in 3 equal layers; each layer being tamped 25 times. The same is then transferred to the cup and again tamped 25 times. The hammer is then allowed to fall freely on the specimen 15 times. The specimen is then sieved through 2.36 mm

(v) Acid Test:

This test is normally carried out on sand stones to check the presence of calcium

carbonate, which weakens the weather resisting quality. In this test, a sample of stone weighing about 50 to 100 gm is taken and kept in a solution of one per cent hydrochloric acid for seven days. The solution is agitated at intervals. A good building stone maintains its sharp edges and keeps its surface intact. If edges are broken and powder is formed on the surface, it indicates the presence of calcium

carbonate. Such stones will have poor weather resistance.

Uses of Stones:

Stones are used in the following civil engineering constructions:

(i) Stone masonry is used for the construction of foundations, walls, columns and arches.

(ii) Stones are used for flooring.

(iii) Stone slabs are used as damp proof courses, lintels and even as roofing materials.

(iv) Stones with good appearance are used for the face works of buildings. Polished marbles and granite are commonly used for face works.

(v) Stones are used for paving of roads, footpaths and open spaces round the buildings.

(vi) Stones are also used in the constructions of piers and abutments of bridges, dams and retaining walls.

(vii) Crushed stones with graved are used to provide base course for roads. When mixed with tar they form finishing coat.

(viii) Crushed stones are used in the following works also:

(a) As a basic inert material in concrete

(b) For making artificial stones and building blocks

Topic 2:

Bricks:Brick: is obtained by moulding good clay into a block, which is dried and then burnt. This is the oldest building block to replace stone. Manufacture of brick started with hand moulding, sun drying and burning in clamps.

A considerable amount of technological development has taken place with knowledge about to properties of raw materials, better machineries and improved techniques of moulding drying and burning.

The size of the bricks are of 90 mm × 90 mm × 90 mm and 190 mm × 90 mm × 40 mm. With mortar joints, the size of these bricks are taken as 200 mm × 100 mm × 100 mm and 200 mm × 100 mm

Types of Bricks

Bricks may be broadly classified as:

(i) Building bricks

(ii) Paving bricks

(iii) Fire bricks

(iv) Special bricks.

(i) Building Bricks:

These bricks are used for the construction of walls.

(ii) Paving Bricks:

These are vitrified bricks and are used as pavers.

(iii) Fire Bricks:

These bricks are specially made to withstand furnace temperature. Silica bricks belong to this category.

(iv) Special Bricks:

These bricks are different from the commonly used building bricks with respect to their shape and the purpose for which they are made. Some of such bricks are listed below:

(a) Specially shaped bricks

(b) Facing bricks

(d) Burnt clay hollow bricks

(e) Sewer bricks

( f ) Acid resistant bricks.

(b) Facing Bricks:

These bricks are used in the outer face of masonry. Once these bricks are provided, plastering is not required. The standard size of these bricks are 190 × 90 × 90 mm or 190 × 90 × 40 mm.

(c) Perforated Building Bricks:

These bricks are manufactured with area of perforation of 30 to 45 per cent. The area of each perforation should not exceed 500 mm2. The perforation should be uniformly distributed over the surface. They are manufactured in the size 190 × 190 × 90 mm and 290 × 90 × 90 mm.

(d) Burn’t Clay Hollow Bricks:

They are light in weight. They are used for the construction of partition walls. They provide good thermal insulation to buildings. They are manufactured in the sizes 190 × 190 × 90 mm,290 × 90 × 90 mm and 290 × 140 × 90 mm. The thickness of any shell should not be less than 11 mm and that of any web not less than 8 mm.

(e) Sewer Bricks:

These bricks are used for the construction of sewage lines. They are

manufactured from surface clay, fire clay shale or with the combination of these. They are manufactured in the sizes 190 × 90 × 90 mm and 190 × 90 × 40 mm. The average strength of these bricks should be a minimum of 17.5 N/mm2 . The water absorption should not be more than 10 per cent.

( f ) Acid Resistant Bricks:

These bricks are used for floorings likely to be subjected to acid attacks, lining of chambers in chemical plants, lining of sewers carrying industrial wastes etc. These bricks are made of clay or shale of suitable composition with low lime and iron content, flint or sand and vitrified at high temperature in a ceramic kiln.

Classification of Bricks

Properties of Bricks

The following are the required properties of good bricks:

(i) Colour:

Colour should be uniform and bright.

(ii) Shape:

Bricks should have plane faces. They should have sharp and true right angled corners.

(iii) Size:

Bricks should be of standard sizes as prescribed by codes.

(iv) Texture:

They should possess fine, dense and uniform texture. They should not possess fissures, cavities, loose grit and unburnt lime.

(v) Soundness:

When struck with hammer or with another brick, it should produce metallic sound.

(vi) Hardness:

Finger scratching should not produce any impression on the brick.

(vii) Strength:

Crushing strength of brick should not be less than 3.5 N/mm2. A field test for

strength is that when dropped from a height of 0.9 m to 1.0 mm on a hard ground, the brick should not break into pieces.

(viii) Water Absorption:

After immersing the brick in water for 24 hours, water absorption should

not be more than 20 per cent by weight. For class-I works this limit is 15 per cent.

(ix) Efflorescence:

Bricks should not show white patches when soaked in water for 24 hours and

then allowed to dry in shade. White patches are due to the presence of sulphate of calcium, magnesium

and potassium. They keep the masonry permanently in damp and wet conditions.

(x) Thermal Conductivity:

Bricks should have low thermal conductivity, so that buildings built with them are cool in summer and warm in winter.

(xi) Sound Insulation:

Heavier bricks are poor insulators of sound while lightweight and hollow

bricks provide good sound insulation.

(xii) Fire Resistance:

Fire resistance of bricks is usually good. In fact bricks are used to encase

steel columns to protect them from fire.

Tests on Bricks

The following laboratory tests may be conducted on the bricks to find their suitability:

(i) Crushing strength

(ii) Absorption

(iii) Shape and size and

(iv) Efflorescence.

(i) Crushing Strength:

The brick specimen are immersed in water for 24 hours. The frog of the

brick is filled flush with 1:3 cement mortar and the specimen is stored in damp jute bag for 24 hours and then immersed in clean water for 24 hours. The specimen is placed in compression testing machine with 6 mm plywood on top and bottom of it to get uniform load on the specimen. Then load is applied axially at a uniform rate of 14 N/mm2 . The crushing load is noted. Then the crushing strength is the ratio of crushing load to the area of brick loaded. Average of five specimen is taken as the crushing strength.

(ii) Absorption Test:

Brick specimen are weighed dry. Then they are immersed in water for a

period of 24 hours. The specimen are taken out and wiped with cloth. The weight of each specimen in wet condition is determined. The difference in weight indicate the water absorbed. Then the percentage absorption is the ratio of water absorbed to dry weight multiplied by 100. The average of five specimen is taken. This value should not exceed 20 per cent.

(iii) Shape and Size:

Bricks should be of standard size and edges should be truely rectangular with sharp edges. To check it, 20 bricks are selected at random and they are stacked along the length, along the width and then along the height. For the standard bricks of size 190 mm × 90 mm × 90 mm.

IS code permits the following limits:

Lengthwise: 3680 to 3920 mm

Widthwise: 1740 to 1860 mm

Heightwise: 1740 to 1860 mm.

The following field tests help in ascertaining the good quality bricks:

(i) uniformity in size

(ii) uniformity in colour

(iii) structure

(iv) hardness test

(v) sound test

(vi) strength test.

(i) Uniformity in Size:

A good brick should have rectangular plane surface and uniform in size.

This check is made in the field by observation.

(ii) Uniformity in Colour:

A good brick will be having uniform colour throughout. This observation may be made before purchasing the brick.

(iii) Structure:

A few bricks may be broken in the field and their cross-section observed. The

section should be homogeneous, compact and free from defects such as holes and lumps.

(iv) Sound Test:

If two bricks are struck with each other they should produce clear ringing sound.

The sound should not be dull.

(v) Hardness Test:

For this a simple field test is scratch the brick with nail. If no impression is marked on the surface, the brick is sufficiently hard

(vi) Efflorescence:

The presence of alkalies in brick is not desirable because they form patches of gray powder by absorbing moisture. Hence to determine the presence of alkalies this test is performed as explained below: Place the brick specimen in a glass dish containing water to a depth of 25 mm in a well ventilated room.

After all the water is absorbed or evaporated again add water for a depth of 25 mm. After second evaporation observe the bricks for white/grey patches. The observation is reported as ‘nil’, ‘slight’,

‘moderate’, ‘heavy’ or serious to mean

(a) Nil: No patches

(b) Slight: 10% of area covered with deposits

(c) Moderate: 10 to 50% area covered with deposit but unaccompanied by flaking of the surface.

(d) Heavy: More than 50 percent area covered with deposits but unaccompanied by flaking of

the surface.

(e) Serious: Heavy deposits of salt accompanied by flaking of the surface.

Topic 3:
Cement:A cement is a binder, a substance used in construction that sets, hardens and adheres to other materials, binding them together. Cement is seldom used solely, but is used to bind sand and gravel (aggregate) together. Cement is used with fine aggregate to produce mortar for masonry, or with sand and gravel aggregates to produce concrete.

Cement is a commonly used binding material in the construction. The cement is obtained by burning a mixture of calcareous (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 Aspdin in England in 1924. He patented it as portland cement.

Types of Cement

In addition to ordinary portland cement there are many varieties of cement. Important varieties are briefly explained below:

(i) White Cement:

The cement when made free from colouring oxides of iron, maganese and chlorium results into white cement. In the manufacture of this cement, the oil fuel is used instead of coal for burning. White cement is used for the floor finishes, plastering, ornamental works etc. In swimming pools white cement is used to replace glazed tiles. It is used for fixing marbles and glazed tiles.

(ii) Coloured Cement:

The cements of desired colours are produced by intimately mixing pigments with ordinary cement. The chlorium oxide gives green colour. Cobalt produce blue colour.Iron oxide with different proportion produce brown, red or yellow colour. Addition of manganese dioxide gives black or brown coloured cement. These cements are used for giving finishing touches to floors,walls, window sills, roofs etc.

(iii) Quick Setting Cement:

Quick setting cement is produced by reducing the percentage of gypsum and adding a small amount of aluminium sulphate during the manufacture of cement. Finer grinding also adds to quick setting property. This cement starts setting within 5 minutes after adding water and becomes hard mass within 30 minutes. This cement is used to lay concrete under static or slowly running water.

(iv) Rapid Hardening Cement:

This cement can be produced by increasing lime content and burning at high temperature while manufacturing cement. Grinding to very fine is also necessary. Though the initial and final setting time of this cement is the same as that of portland cement, it gains strength in early days. This property helps in earlier removal of form works and speed in construction activity.

(v) Low Heat Cement:

In mass concrete works like construction of dams, heat produced due to hydration of cement will not get dispersed easily. This may give rise to cracks. Hence in such constructions it is preferable to use low heat cement. This cement contains low percentage (5%) of tricalcium aluminate(C3A) and higher percentage (46%) of dicalcium silicate (C2S).

(vi) Pozzolana Cement:

Pozzolana is a volcanic power found in Italy. It can be processed from shales and certain types of clay also. In this cement pozzolana material is 10 to 30 per cent. It can resist action of sulphate. It releases less heat during setting. It imparts higher degree of water tightness. Its tensile strength is high but compressive strength is low. It is used for mass concrete works. It is also used in sewage line works.

(vii) Expanding Cement:

This cement expands as it sets. This property is achieved by adding expanding medium like sulpho aluminate and a stabilizing agent to ordinary cement. This is used for filling the cracks in concrete structures.

(viii) High Alumina Cement:

It is manufactured by calcining a mixture of lime and bauxite. It is more resistant to sulphate and acid attack. It develops almost full strength within 24 hours of adding water. It is used for underwater works.

(ix) Blast Furnace Cement:

In the manufacture of pig iron, slag comes out as a waste product. By grinding clinkers of cement with about 60 to 65 per cent of slag, this cement is produced. The properties of this cement are more or less same as ordinary cement, but it is cheap, since it utilise waste product. This cement is durable but it gains the strength slowly and hence needs longer period of curing.

(x) Acid Resistant Cement:

This cement is produced by adding acid resistant aggregated such as quartz, quartzite, sodium silicate or soluble glass. This cement has good resistance to action of acid and water. It is commonly used in the construction of chemical factories.

(xi) Sulphate Resistant Cement:

By keeping the percentage of tricalcium aluminate C3A below five per cent in ordinary cement this cement is produced. It is used in the construction of structures which are likely to be damaged by alkaline conditions. Examples of such structures are canals, culverts etc.

(xii) Fly Ash Blended Cement:

Fly ash is a byproduct in thermal stations. The particles of fly ash are very minute and they fly in the air, creating air pollution problems. Thermal power stations have to spend lot of money to arrest fly ash and dispose safely. It is found that one of the best way to dispose fly-ash is to mix it with cement in controlled condition and derive some of the beneficial effects on cement. Nowadays cement factories produce the fly ash in their own thermal stations or borrow it from other thermal stations and further process it to make it suitable to blend with cement. 20 to 30% fly ash is used for blending.Fly ash blended cements have superior quality of resistance to weathering action. The ultimate strength gained is the same as that with ordinary portland cement. However strength gained in the initial stage is slow.

Properties of Cement:

(i) Chemical properties: Portland cement consists of the following chemical compounds:

(a) Tricalcium silicate 3 CaO.SiO2 (C3S) 40%

(b) Dicalcium silicate 2CaO.SiO2 (C2S) 30%

(d) Tetracalcium aluminate 4CaO.Al2O3.Fe2O3 (C3AF) 11%

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. C2S is the next to hydrate. It hydrates slowly and is responsible for increase in ultimate strength. C4AF is comparatively inactive compound.

(ii) Physical properties:

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:

(a) Fineness (b) Setting time

(a) 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 gramme of cement. According to IS code specification weight retained on the sieve should not be more than 10 per cent. In terms of specific surface should not be less than 2250 cm2/gm.

(b) 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.

(c) 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 Chatelier mould should not expand by more than 10 mm.

(a) 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.

Physical Tests on Cement:

(a) Soundness Test:

It is conducted by sieve analysis. 100 gms of cement is taken and sieved through IS sieve No. 9 for fifteen minutes. Residue on the sieve is weighed. This should not exceed 10 per cent by weight of sample taken.

(b) Setting Time:

Initial setting time and final setting time are the two important physical properties of cement. Initial setting time is the time taken by the cement from adding of water to the starting of losing its plasticity. Final setting time is the time lapsed from adding of the water to complete loss of plasticity.

Vicat apparatus is used for finding the setting times Vicat apparatus consists of a movable rod to which any one of the three needles shown in figure can be attached. An indicator is attached to the movable rod. A vicat mould is associated with this apparatus which is in the form of split cylinder.

Before finding initial and final setting time it is necessary to determine water to be added to get standard consistency. For this 300 gms of cement is mixed with about 30% water and cement paste prepared is filled in the mould which rests on non porous plate. The plunger is attached to the movable rod of vicat apparatus and gently lowered to touch the paste in the mould. Then the plunger is allowed to move freely. If the penetration is 5 mm to 7mm from the bottom of the mould, then cement is having standard consistency. If not, experiment is repeated with different proportion of water fill water required for standard consistency is found. Then the tests for initial and final setting times can be carried out as explained below:

Initial Setting Time: 300 gms of cement is thoroughly mixed with 0.85 times the water for standard consistency and vicat mould is completely filled and top surface is levelled. 1 mm square needle is fixed to the rod and gently placed over the paste. Then it is freely allowed to penetrate. In the beginning the needle penetrates the paste completely.

As time lapses the paste start losing its plasticity and offers resistance to penetration. When needle can penetrate up to 5 to 7 mm above bottom of the paste experiment is stopped and time lapsed between the addition of water and end if the experiment is noted as initial setting time.

Final Setting Time. The square needle is replaced with annular collar. Experiment is continued by allowing this needle to freely move after gently touching the surface of the paste. Time lapsed between the addition of water and the mark of needle but not of annular ring is found on the paste. This time is noted as final setting time.

(c) Soundness Test:

This test is conducted to find free lime in cement, which is not desirable. Le Chatelier apparatus shown in is used for conducting this test. It consists of a split brass mould of diameter 30 mm and height 30 mm. On either side of the split, there are two indicators, with pointed ends. The ends of indicators are 165 mm from the centre of the mould.

Properly oiled Le Chatelier mould is placed on a glass plate and is filled completely with a cement paste having 0.78 times the water required for standard consistency. It is then covered with another glass plate and a small weight is placed over it. Then the whole assembly is kept under water for 24 hours.

The temperature of water should be between 24°C and 50°C. Note the distance between the indicator. Then place the mould again in the water and heat the assembly such that water reaches the boiling point in 30 minutes. Boil the water for one hour. The mould is removed from water and allowed to cool. The distance between the two pointers is measured. The difference between the two readings indicate the expansion of the cement due to the presence of unburnt lime. This value should not exceed 10 mm.

(d) Crushing Strength Test:

For this 200 gm of cement is mixed with 600 gm of standard sand confirming to IS 650–1966. After mixing thoroughly in dry condition for a minute distilled potable water P4+ 3 percentage is added where P is the water required for the standard consistency.

They are mixed with trowel for 3 to 4 minutes to get uniform mixture. The mix is placed in a cube mould of 70.6 mm size (Area 5000 mm2) kept on a steel plate and prodded with 25 mm standard steel rod 20 times within 8 seconds. Then the mould is placed on a standard vibrating table that vibrates at a speed of 12000 ± 400 vibration per minute.

A hopper is secured at the top and the remaining mortar is filled. The mould is vibrated for two minutes and hopper removed. The top is finished with a knife or with a trowel and levelled. After 24 ± 1 hour mould is removed and cube is placed under clean water for curing.After specified period cubes are tested in compression testing machine, keeping the specimen on its level edges.

Average of three cubes is reported as crushing strength. The compressive strength at the end of 3 days should not be less than 11.5 N/mm2 and that at the end of 7 days not less than 17.5 N/mm2.

Topic 4:
Concrete:Concrete is a composite material composed of coarse aggregate bonded together with a fluid cement that hardens over time. Most concretes used are lime-based concretes such as Portland cement concrete or concretes made with other hydraulic cements, such as ciment fondu. However, asphalt concrete, which is frequently used for road surfaces, is also a type of concrete, where the cement material is bitumen, and polymer concretes are sometimes used where the cementing material is a polymer.

Plain concrete, commonly known as concrete, is an intimate mixture of binding material, fine aggregate, coarse aggregate and water. This can be easily moulded to desired shape and size before it looses plasticity and hardens. Plain concrete is strong in compression but very weak in tension.

The tensile property is introduced in concrete by inducting different materials and this attempt has given rise to RCC, RBC, PSC, FRC, cellular concrete and Ferro cement. In this chapter proportioning, mixing, curing, properties, tests and uses of plain concrete is dealt in detail. The other improved versions of concrete are explained and their special properties and uses are pointed out.

PLAIN CONCRETE

Major ingredients of concrete are:

1. Binding material (like cement, lime, polymer)

2. Fine aggregate (sand)

3. Coarse aggregates (crushed stone, jelly)

4. Water.

A small quantity of admixtures like air entraining agents, waterproofing agents, workability agents etc. may also be added to impart special properties to the plain concrete mixture. Depending upon the proportion of ingredient, strength of concrete varies.

It is possible to determine the proportion of the ingredients for a particular strength by mix design procedure. In the absence of mix design the ingredients are proportioned as 1:1:2, 1:1 ½ :3, 1:2:4, 1:3:6 and 1:4:8, which is the ratio of weights of cement to sand to coarse aggregate. In proportioning of concrete it is kept in mind that voids in coarse aggregates are filled with sand and the voids in sand are filled with cement paste.

Proportion of cement, sand and coarse aggregates in concrete

1:1:2 For machine foundation, footings for steel columns and concreting under water.

1:1 ½ : 3 Water tanks, shells and folded plates, for other water retaining structures.

1:2:4 Commonly used for reinforced concrete works like beams, slabs, tunnel lining, bridges

1:3:6 Piers, abutments, concrete walls, sill of windows, floors.

1:4:8 Mass concretes like dam, foundation course for walls, for making concrete blocks.

Functions of Various Ingredients

Cement is the binding material. After addition of water it hydrates and binds aggregates and the surrounding surfaces like stone and bricks. Generally richer mix (with more cement) gives more strength. Setting time starts after 30 minutes and ends after 6 hours. Hence concrete should be laid in its mould before 30 minutes of mixing of water and should not be subjected to any external forces till final setting takes place.

Coarse aggregate consists of crushed stones. It should be well graded and the stones should be of igneous origin. They should be clean, sharp, angular and hard. They give mass to the concrete and prevent shrinkage of cement. Fine aggregate consists of river sand. It prevents shrinkage of cement.

When surrounded by cement it gains mobility enters the voids in coarse aggregates and binding of ingredients takes place. It adds density to concrete, since it fills the voids. Denser the concrete higher is its strength. Water used for making concrete should be clean. It activates the hydration of cement and forms plastic mass. As it sets completely concrete becomes hard mass.

Water gives workability to concrete which means water makes it possible to mix the concrete with ease and place it in final position. More the water better is the workability. However excess water reduces the strength of concrete. To achieve required workability and at the same time good strength a water cement ratio of 0.4 to 0.45 is used, in case of machine mixing and water cement ratio of 0.5 to 0.6 is used for hand mixing.

Preparing and Placing of Concrete

The following steps are involved in the concreting:

1. Batching

2. Mixing

3. Transporting and placing and

4. Compacting.

1. Batching:

The measurement of materials for making concrete is known as batching. The

following two methods of batching is practiced:

(a) Volume batching

(b) Weight batching.

(a) Volume Batching:

In this method cement, sand and concrete are batched by volume. A gauge box is made with wooden plates, its volume being equal to that of one bag of cement. One bag of cement has volume of 35 litres. The required amount of sand and coarse aggregate is added by measuring on to the gauge box. The quantity of water required for making concrete is found after deciding water cement ratio.

For example, if water cement ratio is 0.5, for one bag of cement (50 kg), water required is 0.5 × 50 = 25 kg, which is equal to 25 litres. Suitable measure is used to select required quantity of water.Volume batching is not ideal method of batching. Wet sand has higher volume for the same weight of dry sand. It is called bulking of sand. Hence it upsets the calculated volume required.

(b) Weight Batching:

This is the recommended method of batching. A weighing platform is

used in the field to pick up correct proportion of sand and coarse aggregates. Large weigh batching plants have automatic weighing equipments.

2. Mixing:

To produce uniform and good concrete, it is necessary to mix cement, sand and

coarse aggregate, first in dry condition and then in wet condition after adding water.

The following methods are practiced:

(a) Hand Mixing

(b) Machine Mixing.

(a) Hand Mixing:

Required amount of coarse aggregate for a batch is weighed and is spread on an impervious platform. Then the sand required for the batch is spread over coarse aggregate. They are mixed in dry condition by overturning the mix with shovels. Then the cement required for the batch is spread over the dry mix and mixed by shovels. After uniform texture is observed water is added gradually and mixing is continued. Full amount of water is added and mixing is completed when uniform colour and consistency is observed. The process of mixing is completed in 6–8 minutes of adding water. This method of mixing is not very good but for small works it is commonly adopted.

(b) Machine Mixing:

In large and important works machine mixing is preferred. Required quantities if sand and coarse aggregates are placed in the drum of the mixer. 4 to 5 rotations are made for dry mixing and then required quantity of cement is added and dry mixing is made with another 4 to 5 rotations. Water is gradually added and drum is rotated for 2 to 3 minutes during which period it makes about 50 rotations. At this stage uniform and homogeneous mix is obtained.

3. Transporting and Placing of Concrete.

After mixing concrete should be transported to the

final position. In small works it is transported in iron pans from hand to hand of a set of workers. Wheelbarrow and hand carts also may be employed. In large scale concreting chutes and belt conveyors or pipes with pumps are employed. In transporting care should be taken to see that segregation of aggregate from matrix of cement do not take place.Concrete is placed on form works. The form works should be cleaned and properly oiled. If concrete is to be placed for foundation, the soil bed should be compacted well and is made free from loose soil.Concrete should be dropped on its final position as closely as possible. If it is dropped from a height, the coarse aggregates fall early and then mortar matrix. This segregation results into weaker concrete.

4. Compaction of Concrete:

In the process of placing concrete, air is entrapped. The entrapped air reduces the strength of concrete up to 30%. Hence it is necessary to remove this entrapped air. This is achieved by compacting the concrete after placing it in its final position. Compaction can be carried out either by hand or with the help of vibrators.

(a) Hand Compaction:

In this method concrete is compacted by ramming, tamping, spading or

by slicing with tools. In intricate portions a pointed steel rod of 16 mm diameter and about a metre long is used for poking the concrete.

(b) Compaction by Vibrators:

Concrete can be compacted by using high frequency vibrators.

Vibration reduces the friction between the particles and set the motion of particles. As a result entrapped air is removed and the concrete is compacted. The use of vibrators reduces the compaction time. When vibrators are used for compaction, water cement ratio can be less, which also help in improving the strength of concrete. Vibration should be stopped as soon as cement paste is seen on the surface of concrete. Over vibration is not good for the concrete.

The following types of vibrators are commonly used in concreting:

(a) Needle or immersion vibrators

(b) Surface vibrators

(d) Vibrating tables.

Needle vibrators are used in concreting beams and columns. Surface vibrators and form vibrators are useful in concreting slabs. Vibrating tables are useful in preparing precast concrete elements.

Curing of Concrete

Curing may be defined as the process of maintaining satisfactory moisture and temperature conditions for freshly placed concrete for some specified time for proper hardening of concrete. Curing in the early ages of concrete is more important. Curing for 14 days is very important. Better to continue it for 7 to 14 days more. If curing is not done properly, the strength of concrete reduces. Cracks develop due shrinkage.

The durability of concrete structure reduces. The following curing methods are employed:

(a) Spraying of water

(b) Covering the surface with wet gunny bags, straw etc.

(d) Steam curing and

(e) Application of curing compounds.

(a) Spraying of water:

Walls, columns, plastered surfaces are cured by sprinkling water.

(b) Wet covering the surface:

Columns and other vertical surfaces may be cured by covering

the surfaces with wet gunny bags or straw.

The horizontal surfaces like slab and floors are cured by stagnating the water to a

height of 25 to 50 mm by providing temporary small hunds with mortar.

(d) Steam curing:

In the manufacture of pre-fabricated concrete units steam is passed over the

units kept in closed chambers. It accelerates curing process, resulting into the reduction of curing period.

(e) Application of curing compounds:

Compounds like calcium chloride may be applied on the curing surface. The compound shows affinity to the moisture and retains it on the surface. It keeps the concrete surface wet for a long time.

Properties of Concrete:

Concrete has completely different properties when it is the plastic stage and when hardened. Concrete in the plastic stage is also known as green concrete. The properties of green concrete include:

1. Workability

2. Segregation

3. Bleeding

4. Harshness.

The properties of hardened concrete are:

1. Strength

2. Resistance to wear

3. Dimensional changes

4. Durability

5. Impermeability.

Properties of Green Concrete

1. Workability:

This is defined as the ease with which concrete can be compacted fully without

segregating and bleeding. It can also be defined as the amount of internal work required to fully compact the concrete to optimum density. The workability depends upon the quantity of water, grading, shape and the percentage of the aggregates present in the concrete. Workability is measured by

(a) The slump observed when the frustum of the standard cone filled with concrete is lifted and removed.

(b) The compaction factor determined after allowing the concrete to fall through the compaction testing machine.

(c) The time taken in seconds for the shape of the concrete to change from cone to cylinder when tested in Vee-Bee consistometer.The suggested values of workability

2. Segregation:

Separation of coarse particles from the green concrete is called segregation.

This may happen due to lack of sufficient quantity of finer particles in concrete or due to throwing of the concrete from greater heights at the time of placing the concrete. Because of the segregation, the cohesiveness of the concrete is lost and honeycombing results. Ultimately it results in the loss of strength of hardened concrete. Hence utmost care is to be taken to avoid segregation.

3. Bleeding:

This refers to the appearance of the water along with cement particles on the

surface of the freshly laid concrete. This happens when there is excessive quantity of water in the mix or due to excessive compaction. Bleeding causes the formation of pores and renders the concrete weak.Bleeding can be avoided by suitably controlling the quantity of water in the concrete and by using finer grading of aggregates.

4. Harshness:

Harshness is the resistance offered by concrete to its surface finish. Harshness is due to presence of lesser quantity of fine aggregates, lesser cement mortar and due to use of poorly graded aggregates. It may result due to insufficient quantity of water also. With harsh concrete it is difficult to get a smooth surface finish and concrete becomes porous.

Properties of Hardened Concrete

1. Strength:

The characteristic strength of concrete is defined as the compressive strength of

150 mm size cubes after 28 days of curing below which not more than 5 per cent of the test results are expected to fail. The unit of stress used is N/mm2. IS 456 grades the concrete based on its characteristic

Till year 2000, M15 concrete was permitted to be used for reinforced concrete works. But IS 456–2000 specifies minimum grade of M20 to be used for reinforced concrete works.Strength of concrete depends upon the amount of cement content, quality and grading of aggregates, water cement ratio, compaction and curing.

Strength of concrete is gained in the initial stages. In 7 days the strength gained is as much as 60 to 65 per cent of 28 days strength. It is customary to assume the 28 days strength as the full strength of concrete. However concrete gains strength after 28 days also.

2. Dimensional Change:

Concrete shrinks with age. The total shrinkage depends upon the constituents of concrete, size of the member and the environmental conditions. Total shrinkage is approximately 0.0003 of original dimension.

The permanent dimensional change due to loading over a long period is termed as creep. Its value depends upon the stress in concrete, the age of the concrete at the time of loading and the duration of the loading.

The ultimate creep strain may be estimated from the values of creep coefficient. The creep coefficient is defined as ultimate creep strain divided by the elastic strain at the age of loading.

The size of concrete may change due to thermal expansion also. The coefficient of thermal expansion depends upon the nature of cement, the type of aggregates, cement content, relative humidity and the size of the sections of the structural elements. Table 3.6 shows the coefficient of thermal expansion of concrete with different types of aggregates.

3. Durability:

Environmental forces such as weathering, chemical attack, heat, freezing and

thawing try to destroy concrete. The period of existance of concrete without getting adversely affected by these forces is known as durability. Generally dense and strong concretes have better durability. The cube crushing strength alone is not a reliable guide to the durability. Concrete should have an adequate cement content and should have low water cement ratio.

4. Impermeability:

This is the resistance of concrete to the flow of water through its pores.Excess water during concreting leaves a large number of continuous pores leading to the permeability.Since the permeability reduces the durability of concrete, it should be kept very low by using low water cement ratio, dense and well graded aggregates, good compaction and continuous curing at low temperature conditions. The cement content used should be sufficient to provide adequate workability with low water cement ratio and the available compaction method

Tests on Concrete:

The following are some of the important tests conducted on concrete:

1. Slump test.

2. Compaction factor test.

3. Crushing strength test.

1. Slump Test:

This test is conducted to determine the workability of concrete. It needs a slump

cone for test Slump cone is a vessel in the shape of a frustum of a cone with diameter at bottom 200mm and 50mm at top and 300 mm high. This cone is kept over a impervious platform and is filled with concrete in four layers. Each layer is tamped with a 16 mm pointed rod for 25 times. After filling completely the cone is gently pulled up. The decrease in the height of the concrete is called slump. Higher the slump, more workable is the concrete.

2. Compaction Factor Test:

This is another test to identify the workability of concrete. This test is conducted in the laboratory. The test equipment consists of two hoppers and a cylinder fixed to a stand, the dimensions and the distances between the three vessels being standardized.

Vessel A and B are having hinged bottoms whereas cylinder C is having fixed bottom. Top vessel A is filled with the concrete to be tested. As soon as it is filled, the hinged door is opened. Concrete is collected in vessel B. Then the hinged door of B is opened to collect concrete in cylinder C. The concrete in cylinder C is weighted.

Let it be W1.Now cylinder is again filled with the sample of concrete in 50 mm layers, which is compacted by ramming and vibrating. Then the weight of compacted concrete is determined. Let this weight be W2. The ratio W1/W2 is termed as compaction factor.

3. Crushing Strength Test: Metallic moulds of size 150 mm × 150 mm × 150 mm are used for

casting concrete cubes. Before filling mould, it is properly oiled on its inner surfaces, so that cubes can be easily separated. Fresh cube is filled with concrete to be tested in 3 layers and kept in the room. After 24 hours, cube is removed from the mould and kept under water for curing.

After 28 days of curing cubes are tested in the compression testing machine. In this test cubes are placed over the smooth surface which is in contact with side plates of mould. The crushing load is noted and crushing strength is found as load divided by surface area (150 × 150 mm2).

Code specify the desirable strength of concrete for 3 days and 7 days for quick assessment of strength of concrete.Desirable Properties of Concrete Appropriate quality and quantity of cement, fine aggregate, coarse aggregate and water should be used so that the green concrete has the following properties:

(a) Desired workability

(b) No segregation in transporting and placing

(d) No harshness.

Hardened concrete should have

(a) required characteristic strength

(b) minimum dimensional changes

(d) impermeable

(e) good resistance to wear and tear.

Uses of Concrete

1. As bed concrete below column footings, wall footings, on wall at supports to beams

2. As sill concrete

3. Over the parapet walls as coping concrete

4. For flagging the area around buildings

5. For pavements

6. For making building blocks.

However major use of concrete is as a major ingredient of reinforced and prestressed concrete. Many structural elements like footings, columns, beams, chajjas, lintels, roofs are made with R.C.C. Cement concrete is used for making storage structures like water tanks, bins, silos, bunkers etc. Bridges,dams, retaining walls are R.C.C. structures in which concrete is the major ingredient.

.Topic 5

ALUMINIUM

It is present on the surface of earth crust in most of the rooks and clay. But to produce the metal bauxite (Al2O3. 2H2O) is ideally suited ore.

Properties of Aluminium

1. It is having silver colour and bright lustre.

2. It is very light in weight.

3. It is good conductor of electricity.

4. It has very good resistance to corrosion.

5. It melts at 66°C.

6. It is highly ductile and malleable.

7. It has high strength to weight ratio.

Uses of Aluminium

1. It is used to make door and window frames.

2. Aluminium structural members are becoming popular.

3. Aluminium wires are used as conductors of electricity.

4. It is used as a foil.

5. Aluminium powder serves as pigments in paints.

.Topic 6:

COPPER

It is a naturally available metal in the form of ores which contain small amount of iron and sulphur. After removing impurities, it is processed electrolytically to get purest metal. This metal is almost indestructible. Copper scrap can be processed to get original copper.

Properties of Copper

1. It is having reddish brown colour.

2. Its structure is crystalline.

3. It is highly ductile and malleable.

4. It resists corrossion.

5. It can be welded easily at red heat condition.

6. Dents on the copper can be hammered out.

7. It has high electric and thermal conductivity.

8. Its melting point is at 1083°C.

Uses of Copper

1. It is used as electric wire and cable.

2. It is used as lighting conductor.

3. For water proofing the construction joints copper plates are used.

4. Copper tubes are used for hot and cold water supply, gas and sanitation connections.

5. It forms a major constituent of brass and bronze.

Topic 7:

GLASS

Silica is the main constituent of glass. But it is to be added with sodium potassium carbonate to bring down melting point. To make it durable lime or lead oxide is also added. Manganese oxide is added to nullify the adverse effects of unwanted iron present in the impure silica. The raw materials are ground and sieved. They are mixed in specific proportion and melted in furnace. Then glass items are manufactured by blowing, flat drawing, rolling and pressing.

Important Properties of Glass

1. It absorbs, refracts or transmits light. It can be made transparent or translucent.

2. It can take excellent polish.

3. It is an excellent electrical insulator.

4. It is strong and brittle.

5. It can be blown, drawn or pressed.

6. It is not affected by atmosphere.

7. It has excellent resistance to chemicals.

8. It is available in various beautiful colours.

9. With the advancement in technology, it is possible to make glass lighter than cork or stronger than steel.

10. Glass panes can be cleaned easily.

Types of Glass

The glass may be broadly classified as:

1. Soda-lime glass

2. Potash lime glass

3. Potash lead glass

4. Common glass and

5. Special glasses.

1. Soda Lime Glass: It is mainly a mixture of sodium silicate and calcium silicate. It is fusible at low temperature. In the fusion condition it can be blown or welded easily. It is colourless. It is used as window panes and for the laboratory tubes and apparatus.

2. Potash Lime Glass: It is mainly a mixture of potassium silicate and calcium silicate. It is also known as hard glass. It fuses at high temperature. It is used in the manufacture of glass articles which have to withstand high temperatures.

3. Potash Lead Glass: It is mainly a mixture of potassium silicate and lead silicate. It possesses bright lustre and great refractive power. It is used in the manufacture of artificial gems, electric bulbs, lenses, prisms etc.

4. Common Glass: It is mainly a mixture of sodium silicate, calcium silicate and iron silicate. It is brown, green or yellow in colour. It is mainly used in the manufacture of medicine bottles.

5. Special Glasses: Properties of glasses can be suitably altered by changing basic ingredients and adding few more ingredients. It has now emerged as versatile material to meet many special requirement in engineering. The following is the list of some of the special glasses:

(a) Fibre glass

(b) Foam glass

(d) Structural glass

(e) Glass black

(f) Wired glass

(g) Ultraviolet ray glass

(h) Perforated glass.

Topic 8:

PLASTICS

Plastic is an organic material prepared out of resin. It may or may not contain fillers, plasticisers and solvents. Plastic may be defined as a natural or synthetic organic material which are having the property of being plastic at some stage of their manufacture when they can be moulded to required size and shape.

Shellac and bitumen are the natural resins used as plastic for a long time. In 1907, Blackland produced synthetic resin from the reaction of phenol and formaldehyde. The resin was hardened under pressure and heat to produce useful plastic articles.

Types of Plastics

Primarily there are two types of plastics:

1. Thermosetting and

2. Thermoplastic.

1. Thermosetting Plastics: It needs momentary heated condition and great pressure during shaping. When heated cross linkage is established between the molecules and chemical reaction takes place. During this stage shape can be changed with pressure. This change is not reversible. The scrap of such plastic is not reusable. Bakelite is an example of such plastic.

2. Thermoplastic: In this variety, the linkage between the molecules is very loose. They can be softened by heating repeatedly. This property helps for reuse of waste plastic. These plastic need time to cool down and harden. These plastics are to be kept in moulds till cooling takes place completely. Bitumen, cellulose and shellac are the examples of this variety of plastics.

Properties of Plastics

1. Colour: Some plastics are completely transparent. Using pigments plastics of any attractive colour can be produced.

2. Dimensional Stability: It is dimensionally stable to a great extent.

3. Durability: Plastic offers great resistance to moisture and chemicals and hence more durable.

4. Electrical Insulation: The plastics possess excellent electrical insulating property.

5. Fire Resistance: The phenol-formaldehyde and urea-formaldehyde plastics resist fire to a great extent and hence they are used as fire proofing materials.

6. Strength: The plastics are reasonably strong. Their strength may be increased by reinforcing with various fibrous materials. Attempts are being made to produce structurally sound plastics.

7. Specific Gravity: The specific gravity of plastics is very low and hence convenient to handle.

8. Ductility: The plastics are not ductile and hence they fail without giving warning.

9. Fixing: Plastics can be bolted, drilled, glued, clamped or simply push fitted in position.

10. Maintenance: There is no maintenance cost for plastic articles i.e., they do not need painting and polishing.

Topic 9:

BITUMEN

Ashalt, bitumen and tar are referred as bituminous materials, which are essentially hydrocarbon materials.The asphalt is a mixture of inert mineral matter lime alumina, lime, silica etc. and a hydrocarbon known as asphaltic bitumen. In some places like Trinidad and Bermudez, asphalt is available in nature at a depth of 3 to 60 metres. It is known as natural asphalt.

Common variety used all over the world is residual asphalt, which is obtained by fractional distillation of crude petroleum oil. Bitumen is the binding material which is present in asphalt. It is a hydrocarbon.

It is obtained by partial distillation of crude oil. It contains 87 per cent carbon, 11 per cent hydrogen and 2 per cent oxygen.Tar is obtained in the distructive distillation of coal, wood or other organic materials. When coal or wood is heated to redness in an closed chamber, it yields volatile product and residue coke. After separating and cooling volatile product gives tar.

Topic 10:

ASBESTOS

Asbestos is a general name for several varieties of fibrous minerals which are available in nature. But presently, most of the commercial asbestos produced is ‘chriotile’ [Mg6SiO11(OH)6.H2O].

Properties of Asbestos

1. It is flexible, soft and non-porous.

2. It is fireproof and acid proof material.

3. It is a good insulator of heat and electricity.

4. When it is mixed with cement and water, it retains shape firmly.

5. Its colour is brown or grey.

6. It can be cut into pieces or can be drilled.

7. It possesses high tensile strength in the direction of its fibres.

8. Its specific gravity is 3.10.

Uses of Asbestos

1. Asbestos cement sheets are the cheapest roofing materials.

2. Asbestos cement pipes are used as down take pipes of rain water from the roof.

3. With bitumen it forms good damp proof layer.

4. It is used for preparing fire proof ropes and clothes.

5. It is used as covering material for fuse and electric switch boxes.

6. It is useful for insulating boilers, furnaces etc.

Topic 11:

PAINTS

Paints are applied on the surfaces of timber, metals and plastered surfaces as a protective layer and at the same time to get pleasant appearance. Paints are applied in liquid form and after sometime the volatile constituent evaporates and hardened coating acts as a protective layer.

Constituents of Paint

The essential constituents of paints are:

1. Base

2. A vehicle

3. A pigment

4. A drier

5. A thinner.

1. Bases: It is a principal constituent of paint. It also possesses the binding properties. It forms an opaque coating. Commonly used bases for paints are white lead, red lead, zinc oxide, iron oxide, titanium white, aluminium powder and lithophone. A lead paint is suitable for painting iron and steel works, as it sticks to them well. However it is affected by atmosphere action and hence should not be used as final coat. While zinc forms good base but is costly.

Lithophone, which is a mixture of zinc sulphate and barytes, is cheap. It gives good appearance but is affected by day light. Hence it is used for interior works only.

2. Vehicles: The vehicles are the liquid substances which hold the ingredients of a paint in liquid suspension and allow them to be applied on the surface to be painted. Linseed oil, Tung oil and Nut oil are used as vehicles in paints. Of the above four oils, linseed oil is very commonly used vehicles. Boiling makes the oil thicker and darker. Linseed oil reacts with oxygen and hardens by forming a thin film.

3. Pigment: Pigments give required colour for paints. They are fine particles and have a reinforcing effect on thin film of the paint. The common pigments for different colours are:

Black—Lamp black, suit and charcoal black.

Red—venedion red, red lead and Indian red.

Brown—burned timber, raw and burned sienna

Green—chrome green, copper sulphate.

Blue—prussian blue and ultra marine

Yellow—ochre and chrome yellow.

4. The Drier: These are the compounds of metal like lead, manganese, cobalt. The function of a drier is to absorb oxygen from the air and supply it to the vehicle for hardening. The drier should not be added until the paint is about to be used. The excess drier is harmful because it destroys elasticity and causes flaking.

5. The Thinner: It is known as solvent also. It makes paint thinner and hence increases the coverage. It helps in spreading paint uniformly over the surface Terpentine and neptha are commonly used thinners. After paint applied, thinner evaporates and paint dries.

Properties of an Ideal Paint

1. It should be possible to apply easily and freely.

2. It should dry in reasonable time.

3. It should form hard and durable surface.

4. It should not be harmful to the health of workers.

5. It should not be easily affected by atmosphere.

6. It should possess attractive and pleasing appearance.

7. It should form a thin film of uniform nature i.e., it should not crack.

8. It should possess good spreading power.

9. It should be cheap.

Types of Paints

Depending upon their constituents there are various types of paints. A brief description of some of them which are commonly used are given below:

1. Oil Paint: These paints are applied in three coats-primer, undercoat and finishing coat. The presence of dampness while applying the primer adversely affect the life of oil paint. This paint is cheap and easy to apply.

2. Enamel Paint: It contains white lead, oil, petroleum spirit and resinous material. The surface provided by it resists acids, alkalies and water very well. It is desirable to apply a coat of titanium white before the coat of enamel is applied. It can be used both for external and internal walls.

3. Emulsion Paint: It contains binding materials such as polyvinyl acetate, synthetic resins etc. It dries in 1 1 2  2 hours and it is easy to apply. It is more durable and can be cleaned with water. For plastered surfaces, first a coat of cement paint should be applied and then the emulsion point. Emulsion paint needs sound surfaces.

4. Cement Paint: It is available in powder form. It consists of white cement, pigment and other additives. It is durable and exhibits excellent decorative appearance. It should be applied on rough surfaces rather than on smooth surfaces. It is applied in two coats. First coat is applied on wet surface but free from excess water and allowed to dry for 24 hours. The second coat is then applied which gives good appearance.

5. Bituminous Paints: This type of paint is manufactured by dissolving asphalt or vegetable bitumen in oil or petroleum. It is black in colour. It is used for painting iron works underwater.

6. Synthetic Rubber Paint: This paint is prepared from resins. It dries quickly and is little affected by weather and sunlight. It resists chemical attack well. This paint may be applied even on fresh concrete. Its cost is moderate and it can be applied easily.

7. Aluminium Paint: It contains finely ground aluminium in spirit or oil varnish. It is visible in darkness also. The surfaces of iron and steel are protected well with this paint. It is widely used for painting gas tanks, water pipes and oil tanks.

8. Anti-corrosive Paint: It consists essentially of oil, a strong dier, lead or zinc chrome and finely ground sand. It is cheap and resists corrosion well. It is black in colour. Application of Paint Preparation of surface for application of paint is the most important part in painting. The surface to be painted should not be oily and it should be from flakes of the old paint. Cracks in the surface should be filled with putty and then with sand paper. Then primer is applied. Painting work should be carried out in dry weather. The under coats and first coats must be allowed to dry before final coat is applied.

Topic 12:

ROOFING AND FLOORING TILES

These are also clay products like brick but are thin. Depending upon their use, building tiles may be further classified as

1. Roofing tiles

2. Flooring tiles and wall tiles.

1. Roofing Tiles: Roofing tiles are used to cover sloping roofs. They are supported on wooden reapers. Sometimes light gauge steel or steel rods are also used as reapers. After supporting on reapers these tiles should be strong enough to take load of a man safely. The tiles should he leak proof. Normally these tiles are having curved surface having ribbed sections, so that with thin section they are sufficiently strong to resist the load. However many times flat tiles are used under curved/ribbed tiles.

These tiles are not subjected to load directly. They serve in reducing adverse thermal effects. Corrugated tiles satisfy the requirements of appearance and leak proof but they can be easily blown away by wind.

The desirable properties of the roofing tiles are:

1. They should not absorb moisture more than 20 per cent by weight.

2. They should give pleasing look.

3. They should be capable of taking load of a man safely, after they are supported on reapers.

4. They should be durable.

5. They should be uniform in shape and size.

6. Warpage should not exceed 2% along the edges and 1.5% along the diagonal.

2. Flooring Tiles and Wall Tiles: These tiles are manufactured by burning pressed green tiles twice. First they are burnt at 700°C. Then they are dipped in the glaze solution and again burnt at 1250°C to fuse them with glaze. The thickness of these tiles vary from 15 to 20 mm. These tiles are flat and they have pleasing appearance. There are two types of flooring tiles:

(a) Glazed Tiles: These tiles are used as finish surfaces for floors and walls in kitchen and bathrooms.These tiles are glazed and are provided with attractive colours and designs.

(b) Mosaic Tiles: These are precast concrete tiles with marble chips on the top surface. Afterfixing these tiles polishing is done.

The desirable properties of flooring and roofing tiles are:

1. Tolerance for length = ± 5 mm.

2. Tolerance for thickness = ± 2 mm.

3. Should be uniform in shape and colour.

4. They should be sound, hard and durable.

5. They should have very low percentage of water absorption.

6. They should give a clear ringing sound when struck with each other.

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BUILDING MATERIALS