bulding materials iii

7/25/2019 Bulding Materials III

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UNIT I REQUIREMENTS OF INGREDIENTS FOR MORTAR/ CONCRETE:

Ordinary Portland Cement:

Definition of OPC

Cement can be defined as the bonding material having cohesive & adhesive properties which makes it capable to unite

the different construction materials and form the compacted assembly.

Ordinary/Normal Portland cement is one of the most widely used type ofPortland Cement.

The name Portland cement was given by Joseph Aspdin in 1824 due to its similarity in colour and its quality when it

hardens like Portland stone.Portland stone is white grey limestone in island of Portland, Dorset.

Composition of OPC

The chief chemical components of ordinary Portland cement are:

1.

Calcium

2. Silica

3. Alumina

4. Iron

Calcium is usually derived from limestone, marl or chalk while silica, alumina and iron come from the sands, clays & iron

ores. Other raw materials may include shale, shells and industrial byproducts.

Basic Composition:

Contents %

CaO 60-67

SiO2 17-25

Al2O3 3-8

Fe2O3 0.5-6.0

MgO 0.5-4.0

Alkalis 0.3-1.2

SO3 2.0-3.5

The chief compound which usually form in process of mixing:

1-triclcium silicate (3CaO.SiO2)

2-Dicalcium silicate (2CaO.SiO2)

3-tricalcium aluminates (3CaO.Al2O3)

4-tetracalcium aluminoferrite (4CaO.Al2O3.Fe2O3)


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Production & Manufacturing:

Manufacturing

Raw Materials

1. Calcareous (material having content of lime)

2. Argillaceous (material having contents of silica & alumina)

3. Gypsum

Process

Cement is usually manufactured by two processes:

1.

Wet process

2. Dry process

These two processes differ in operation but fundamentals of both these processes are same.

There are five stages in manufacturing of cement by wet process:

1. Crushing and grinding of raw material

2. Mixing the material in proportion

3. Heating the prepared mixture in rotary kiln

4.

Grinding the heated product known as clinker

5.

Mixing and grinding of cement clinker with gypsum

Crushing and Grinding:

In this phase, soft raw materials are first crushed into suitable size. This is done usually in cylindrical ball or tube mills

containing the charge of steel balls

Mixing the Material:

In this part, the powdered limestone is mixed with the clay paste in proper proportion (75%=lime stone; clay=25%)

The mixture is then grounded and made homogeneous by mean of compressed gas. The resulting material is known as

slurry having 35-40% water.

Heating the slurry in rotary kiln:

Slurry is then introduced in rotary kiln with help of conveyor. The rotary kiln consists of large cylinders 8 to 15 feet in

diameter & height of 300-500 feet. It is made with steel & is usually lined inside with firebricks.


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Kiln rotates at the rate of 1-2 revolution per minute. In rotary kiln, slurry is passed through different zones oftemperature. This whole process in kiln usually covers 2 to 3 hours.

Different temperature zones are as under:

Preheating Zone

In this zone, temperature is kept at 500 degree Celsius & usually the moisture is removed & clay is broken into silica,

aluminum oxide, iron oxide.

Decomposition Zone

Temperature is raised up to 800 degree Celsius. In this zone lime stone decomposes into lime and CO2.

Burning Zone

In this zone temperature is maintained up to 1500 degree Celsius and the oxides formed in above zones combine

together and form respective silicate, aluminates & ferrite.

Cooling Zone

This is last stage where the whole assembly cooled is up to 150 to 200 degree Celsius.

Clinker Formation

The product which is obtained from the rotary kiln is known as the cement Clinker. Clinker is usually in the form of

greenish black or grey colored balls.

Grinding the Clinker with Gypsum

The Cement Clinker is then air cooled. The required amount of Gypsum (5 %) is ground to the fine powder, and then

mixed with the Clinker. Finally cement is packed in bags and then transported to the required site.


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Setting and Hardening:

When ordinary Portland cement is mixed with water its chemical compound constituents undergo a series of chemical

reactions that cause it to set. These chemical reactions all involve the addition of water to the basic chemical

compounds. This chemical reaction with water is called "hydration". Each one of these reactions occurs at a different

time and with different rates. Addition of all these reactions gives the knowledge about how Ordinary Portland

cement hardens and gains strength. Those compounds and their role in hardening of cement are as under:

1. Tricalcium silicate (C3S):Hydrates and hardens rapidly and is largely responsible for initial set and early strength.

Ordinary Portland cements with higher percentages of C3S will exhibit higher early strength.

2.

Dicalcium silicate (C2S):Hydrates and hardens slowly and is largely responsible for strength increases beyond oneweek.

3. Tricalcium aluminate (C3A):Hydrates and hardens the quickest. It liberates a large amount of heat almost

immediately and contributes somewhat to early strength. Gypsum is added to Ordinary Portland cement to retard

C3A hydration. Without gypsum, C3A hydration would cause ordinary Portland cement to set almost immediately

after adding water.

4. Tetracalcium aluminoferrite (C4AF):Hydrates rapidly but contributes very little to strength. Most

ordinaryPortland cement color effects are due to C4AF.

Uses of OPC (Ordinary Portland cement):

It is used for general construction purposes where special properties are not required. It is normally used for thereinforced concrete buildings, bridges, pavements, and where soil conditions are normal. It is also used for most of

concrete masonry units and for all uses where the concrete is not subject to special sulfate hazard or where the heat

generated by the hydration of cement is not objectionable. It has great resistance to cracking and shrinkage but has less

resistance to chemical attacks.

Tests on Ordinary Portland cement

1. Fineness test

2. Soundness test

3.

Setting time test

4.

Strength tests1.

Compressive strength test

2. Tensile strength test

3. Flexural strength test

5. Specific gravity test

6.

Consistency test


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7.

Heat of hydration test

8. Loss of ignition test

Types of Cement

In addition to ordinary cement, the following are the other varieties of cement.

The main types cements are

i) Acid resistance cement

ii) Blast furnace cement

iii) Coloured cement

iv) Expanding cement

v) High alumina cement

vi) Hydrophobic cement

vii) Low heat cement

viii) Pozzolona cement

ix) Quick setting cement

x) Rapid hardening cement

xi) Sulphate resistance cement

xii) White resistance cement

a. Acid Resistance Cement: This is consists of acid resistance aggregates such as quartz, quartzites, etc,

additive such as sodium fluro silicate (Na2SiO6) and aqueous solution of sodium silicate. This is used for acid resistant

and heat resistant coating of installations of chemical Industry. By adding 0.5 percent of linseed oil or

2 percent of ceresil, its resistance to water is increased and known as acid water resistant cement.

b. Blast Furnace Cement: For this cement slag as obtained from blast furnace in the manufacture of pig iron and it

contains basic elements of cement, namely alumina, lime and silica. The properties of this cement are more or less the

same as those of ordinary cement and prove to be economical as the slag, which is waste product, is used in its

manufacture.

c. Coloured Cement: Cement of desired colour may be obtained by intimately mixing mineral pigments with

ordinary cement. The amount of colouring may vary from 5 to 10 percent and strength of cement if it is exceeds 10

percent. Chromium oxide gives brown, red or yellow for different proportions. Coloured cements are used for finishing

of floors, external surfaces, artificial marble, and windows.

d. Expanding Cement : This type of cement is produced by adding an expanding medium like sulphaaluminate and a

stabilizing agent to ordinary cement. Hence this cement expands where as other cement shrinks. Expanding cement is

used for the construction of water retaining structures and also for repairing the damaged concrete surfaces.

e. High alumina Cement: This cement is produced by grinding clinkers formed by calcining bauxite and lime. The total

content should not be less than 32 percent and the ratio by weight of alumina to lime should be between 0.85 and 1.30.

Advantages

1. Initial setting time is about 31/2 hours therefore, allows more time for mixing and placing operations.

2. It can stand high temperatures.

3. It evolves great heat during setting therefore not affected by frost.

4. It resists the action of acids in a better way.

5. It lets quickly and attains higher ultimate strength.

Disadvantages:

1. It is costly

2. It cannot be used in mass construction as it evolves great heat and as it sets soon.

3. Extreme care is to taken to see that it does not come in contact with even traces of lime or ordinary cement.

f. Hydrophobic Cement: This type of cement contains admixtures, which decreases the wetting ability of cement grains.

The usual hydrophobic admixtures are acidol napthene soap, oxidized petrolium etc when hydrophobic cement is used,

the fire pores in concrete are uniformly distributed and thus the frost resistance

and the water resistance of such concrete are considerably increased.

g. Low Heat Cement: Considerable heat is produced during the setting action of cement. In order to reduce the amount

of heat, this type of cement is used. It contains lower percentage of tri calcium aluminates C3A and higher percentage of


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dicalcium silicate C2s. This type of cement is used for mass concrete works because it processes less compressor

strength.

h. Pozzuolona Cement: Pozzuolona is a volcanic powder and the percentage should be between 10 to 30.

Advantages

1. It attains compressive strength with age.

2. It can resist action of sulphates.

3. It evolves less heat during setting.

4. It imparts higher degree of water tightness.

5. It imparts plasticity and workability to mortar and concrete prepared from it.

6. It offers great resistance to expansion

7. It possesses higher tensile strength

Disadvantages:

1. Compressive strength in early days is less.

2. It possesses less resistance to erosion and weathering action.

i. Quick Setting Cement: This cement is prepared by adding a small percentage aluminum sulphate which reduce the

percentage of gypsum or retarded for setting action and accelerating the setting action of cement. As this cement

hardness less than 30 minutes, mixing and placing operations should be completed. This cement is used to lay concrete

under static water or running water.

j. Rapid Hardening cement: This cement has same initial and final setting times as that of ordinary cement. But it attains

high strength in early days due to

1. Burning at high temperature.

2. Increased lime content in cement composition.

3. Very fine grinding.

Advantages:

1. Construction work may be carried out speedily.

2. Form work of concrete can be removed earlier.

3. It is light in weight.

4. It is not damaged easily.

5. This cement requires short period of curing.

6. Use of this cement also higher permissible stresses in the design.

7. Structural member constructed with this cement may be loaded earlier.

k. Sulphate Resisting Cement: In this cement percentage of tri-calcium aluminates is kept below 5 to 6 percent and it

results in the increase in resisting power against sulphate. This cement is used for structure which are likely to be

damaged by sever alkaline condition such as canal linings, culverts, siphons etc.

l. White Cement: This is a variety of ordinary cement and it is prepared form such raw materials which are practically

free from colouring oxides of Iron, manganese or chromium. For burning of this cement, oil fuel is used instead of coal.

It is used for floor finish; plaster work, ornamental works etc.

3.3. Uses of Cement:

1. Cement mortar for masonry work, plaster, pointing etc

2. Concreter for laying floors, roofs and constructing lintels, beams, weather sheds, stairs, pillars etc.

3. Construction of important engineering structure such as bridges, culverts, dams, tunnels storage reservoirs, light

houses, deckles etc.

4. Construction of water tanks, wells, tennis courts, septic tanks, lampposts, roads, telephone cabins etc.

5. Making joints for drains, pipes etc.

6. Manufacture of pre cast pipes, piles, garden seats, artificially designed urns, flowerpots, etc dustbins, fencing posts

etc.

7. Preparation of foundations, watertight floors, footpaths etc.

SAND

Sand is an important building material used in the preparation of mortar, concrete, etc.

Sources of Sand: Sand particles consist of small grains of silica (Si02). It is formed by the decomposition of sand stones

due to various effects of weather. The following are the natural sources of sand.


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a. Pit Sand: This sand is found as deposits in soil and it is obtained by forming pits to a depth of about 1m to 2m from

ground level. Pit sand consists of sharp angular grains, which are free from salts for making mortar, clean pit sand free

from organic and clay should only be used.

b. Rive Sand: This sand is obtained from beds of rivers. River sand consists of fine rounded grains. Colour of river sand is

almost white. As the river sand is usually available in clean condition, it is widely used for all purposes.

c. Sea Sand: This sand is obtained from sea shores. Sea sand consists of rounded grains in light brown colour. Sea sand

consists of salts which attract the moisture from the atmosphere and causes dampness, efflorescence and disintegration

of work. Due to all such reasons, sea sand is not recommendable for engineering works. However be used as a local

material after being thoroughly washed to remove the salts.

Characteristics of sand:

1. It should be chemically inert

2. It should be clean and coarse. It should be free from organic matter.

3. It should contain sharp, angular and durable grains.

4. It should not contain salts, which attract the moisture from atmosphere.

5. It should be well graded (i.e.) should contain particles of various sizes in suitable proportions.

Grading of Sand:

According to the site of grains, sand is classified as fine, coarse and gravelly Sand passing through a screen with clear

opening of 1.5875mm is known as fine sand. It is generally used for masonry works.

Sand passing through a screen with clear openings of 7.62mm is known as gravely sand. It is generally used for

plastering. Sand passing through a screen with clear opening of 3.175mm is known as coarse sand. It is generally used

for masonry work..

Bulking of Sand:

The presence of moisture in sand increases the volume of sand. This is due to fact that moisture causes film of water

around the sand particles which result in the increase of volume of sand. For a moisture content of 5 to 8 percent, the

increase in volume may be about 5 to 8 percent, depending upon the grading of sand. The finer the material, the more

will be the increase in volume for a given moisture content. This phenomenon is known as bulking of sand. When

moisture content is increased by adding more water, sand particles pack near each other and the amount of bulking of

sand is decreased. Thus the dry sand and the sand completely flooded with water have practically the same volume. For

finding the bulking of sand, a test is carried out with following procedure as in the fig.

Fig. Bulking of Sand

I. A container is taken and it is filled two third with

the sample of sand to be tested.

II. The height is measured, say 20cm.

III. Sand is taken out of container

IV. The container is filled with water

V. Sand is then slowly dropped in the container and

it is thoroughly stirred by means of a rod.

VI. The height of sand is measured say 16cm, then

bulking of sand == -------------- = ------ or

25%.

SHORT ANSWER QUESTIONS

1. What are the main types of sand according to the natural source?

2. What is meant by bulking of sand?

3. What are the important characteristics of sand?

ESSAY TYPE QUESTIONS

1. Explain the sources of sand.

2. Explain the characteristics of sand.

3. Explain how bulking of sand is found using the experiment.

4. Explain the grading of sand.

5. Explain the bulking of sand.

Coarse aggregate: Sources, shape, size, grading, sampling and analysis, impurities


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Aggregates are the materials basically used as filler with binding material in the production of mortar and

concrete. They are derived from igneous, sedimentary and metamorphic rocks or manufactured from blast

furnace slag, etc. Aggregates form the body of the concrete, reduce the shrinkage and effect economy.

They occupy 70-80 per cent of the volume and have considerable influence on the properties of the concrete. It

is therefore significantly important to obtain right type and quality of aggregates at site. They should be clean,

hard, strong, durable and graded in size to achieve utmost economy from the paste.

Earlier aggregates were considered to be chemically inert but the latest research has revealed that some of

them are chemically active and also that certain types exhibit chemical bond at the interface of aggregates and

cement paste. To increase the bulk density of concrete aggregates are used in two markedly different sizesthe bigger ones

known to be coarse aggregate (grit) and the smaller ones fine aggregate (sand).

The coarse aggregate form the main matrix of concrete and the fine aggregate from the filler matrix between

the coarse aggregate.

Classification of aggregates:

The aggregates may be classified into natural aggregates and artificial aggregates.

Natural Aggregates:

These are obtained by crushing from quarries of igneous, sedimentary or metamorphic rocks. Gravels and sand reduced

to their present size by the natural agencies also fall in this category. The most widely used aggregate are from igneousorigin. Aggregates obtained from pits or dredged from river, creek or sea are most often not clean enough or well

graded to suit the quality requirement. They therefore require sieving and washing before they can be used in concrete.

Artificial Aggregates:

Broken bricks, blast furnace slag and synthetic aggregates are artificial aggregates. Broken bricks known as brick bats are

suitable for mass concreting, for example, in foundation bases. They are not used for reinforced concrete works. Blast

furnace slag aggregate is obtained from slow cooling of the slag followed by crushing. The dense and strong particles as

obtained are used for making precast concrete products. The sp. gr. of this range between 22.8 and bulk density 1120

1300 kg/m3. The blast furnace slag aggregate has good fire resisting properties but are responsible for corrosion of

reinforcement due to sulphur content of slag. Synthetic aggregates are produced by thermally processed materials such

as expanded clay and shale used for making light weight concrete.

On the basis of size:

According to size aggregates are classified as coarse aggregate, fine aggregate and all-in- aggregate

Coarse Aggregate:

Aggregate retained on 4.75 mm sieve are identified as coarse.

They are obtained by natural disintegration or by artificial crushing of rocks.

The maximum size of aggregate can be 80 mm. The size is governed by the thickness of section, spacing of

reinforcement, clear cover, mixing, handling and placing methods.

For economy the maximum size should be as large as possible but not more than one-fourth of the minimum

thickness of the member.

For reinforced sections the maximum size should be at least 5 mm less than the clear spacing between thereinforcement and also at least 5 mm less than the clear cover.

Aggregate more than 20 mm sizes are seldom used for reinforced cement concrete structural members.

Fine aggregate:

Aggregate passing through 4.75 mm sieve are defined as fine. They may be natural sanddeposited by rivers,

crushed stone sandobtained by crushing stones and crushed gravel sand.

All in- aggregate:

Naturally available aggregates of different fractions of fine and coarse sizes are known as all-in-aggregate. The

deficiency of any particular fraction can be corrected for use in the mix but they are not recommended for

quality concrete.

On the basis of size:Aggregates are classified as rounded, irregular, angular, and flaky.

Rounded:

These are generally obtained from river or sea shore and produce minimum voids (about 32 per cent) in the

concrete. They have minimum ratio of surface area to the volume, and the cement paste required is minimum.

Poor interlocking bond makes it unsuitable for high strength concrete and pavements.


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Irregular:

They have voids about 36 per cent and require more cement paste as compared to rounded aggregate. Because

of irregularity in shape they develop good bond and are suitable for making ordinary concrete.

Angular:

They have sharp, angular and rough particles having maximum voids (about 40 per cent). Angular aggregate

provide very good bond than the earlier two, are most suitable for high strength concrete and pavements; the

requirement of cement paste is relatively more.

Flaky:

These are sometimes wrongly called as elongated aggregate. However, both of these influence the concreteproperties adversely. The least lateral dimension of flaky aggregate (thickness) should be less than 0.6 times the

mean dimension. For example, the mean sieve size for an aggregate piece passing through 50 mm and retained

on 40 mm sieve is (50 + 40)/2 = 45.0 mm. If the least lateral dimension is less than 0.6 45 = 27.0 mm, the

aggregate is classified as flaky.

Elongated aggregate are those aggregate whose length is 1.8 times its mean dimension.

Flaky aggregate generally orient in one plane with water and air voids underneath. They adversely affect

durability and are restricted to maximum of 15 per cent.

Water:

The purpose of using water with cement is to cause hydration of the cement. Water in excess of that requiredfor hydration acts as a lubricant between coarse and fine aggregates and produces a workable and economical

concrete.

In case of excess water, the cement along with water comes to the surface by capillary action and forms a thin

layer over surface known as laitance. This weakens bond between the successive lifts of concrete.

The excess water may leak through the form work, resulting in honeycombed concrete and on evaporation

makes the concrete porous.

On the other hand lesser water makes it difficult to work with concrete and because of non uniform mixing the

resultant concrete is weaker in strength.

The amount of water must therefore be limited to produce concrete of the quality required for a job. Water is

also used for washing aggregates and curing.

Quality of water:

Almost any natural potable water that has no pronounced taste or odour is acceptable for the concrete mix.

Many sources of water unsuitable for drinking may also be used. In case of a doubt, water samples should be

tested for suitability. Excessive impurities may affect setting time, strength, durability and may cause

efflorescence, surface discolouration, and corrosion of steel.

The effects of impurities in water are mainly expressed in terms of setting time of Portland cement. The initial

setting time of the mixes with impure water and that with the pure water are obtained. Their difference in the

initial setting time of 30 minutes with initial setting time not less than 30 minutes is supposed to be

acceptable. The 7 day and 28 day compressive strengths of the cube/cylinder specimens prepared with impure

water should not differ by 10 per cent from that of cubes/cylinders prepared with pure water.

Effect of water in the mix depending on the source:

Natural ground water:

Natural ground waters seldom contain more than 20 to 30 ppm of iron. However, acid mine waters may carry

rather large quantities of iron. Iron salts in concentrations up to 40,000 ppm do not usually affect mortar

strengths adversely.

Sea water:

The sea water generally contains 3.5 per cent of salts with about 75 per cent of sodium chloride, about 15 per

cent of chloride and sulphate of magnesium.

It has been found to reduce the strength of concrete by 10-20 per cent and slightly accelerate the setting time.

Sea water may lead to corrosion of the reinforcement. Therefore, sea water may be recommended for concrete

without reinforcement. The chlorides in sea water may cause efflorescence restricting it to be used in making mortars for plastering.

The use of sea water is not recommended for pre stressed concrete because of stress corrosion and the small

diameter wires (if corroded may cause disaster).

Industrial waste water:

Most waters carrying industrial waste have less than 3,000 ppm of total solids.


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Waste waters from paint factories, coke plants, chemical and galvanizing plants may contain harmful impurities.

It is advisable to test any waste water that contains even few hundred parts per million of unusual solids before

using it for mixing concrete.

UNIT-II CEMENT CONCRETE AND ITS MANUFACTURE:

CONCRETE

Cement concrete is a mixture of cement, sand, pebbles or crushed rock and water. When placed in the skeleton of

forms and allowed to cure, becomes hard like a stone. Cement concrete is important building material because of thefollowing reasons.

1. It can be moulded into any size and shape of durable structural member.

2. It is possible to control the properties of cement concrete.

3. It is possible to mechanise completely its preparation and placing processes.

4. It possesses adequate plasticity for mechanical working.

The cement concrete has the following properties

1. It has high compressive strength

2. It is free from corrosion

3. It hardens with age and continues for a long time after concrete has attained sufficient strength

4. It is proved to be economical than steel

5. It binds rapidly with steel and it is weak in tension, steel reinforcement is placed in cement concrete at suitable places

to take up tensile concrete or simply R.C.C.

6. It forms a hard surface, capable of resisting abrasion stresses.This is called reinforced cement.

7. It has tendency to be porous to avoid this proper grading & consolidation of the aggregates, minimum water-cement

ratio should be adopted.

Constituents - Requirements.

The main constituents of concrete are

a) Cement / Lime: Before introduction of ordinary Portland cement, lime was used as cementing material. At present

most of the cement concrete works in the building construction is done with ordinary Portland cement. But other

special varieties of cement such as rapid hardening cement, high alumina cement are used under certain circumstances.

The cement should comply with all standard specifications

b) Fine Aggregates: The material, which is passed through 4.7625mm B.S.test sieve, is termed as fine aggregates.

Usually natural river sand is used as fine aggregates. But places where natural sand is not available economically, finely

crushed stone may be used as fine aggregates.

c) Coarse Aggregates: The material retained on 4.7625mm size B.S.test sieve is termed as coarse aggregates. Broken

stone is generally used as coarse aggregates. For thin slabs, and walls, the maximum size of coarse aggregates should be

limited to one third the thickness of the concrete section.

d) Water: Water to be used in the concrete work should have the

following properties.

1) It should be free from oils

2) It should be free from acids or alkalies

3) It should be free from Iron, Vegetables matter or other substance, which is likely to have adverse effect on

concrete.

4) It should be fit for drinking purpose

Function of Water

1. It acts as lubricant for fine and coarse aggregates.

2. It acts chemically with cement to form binding paste with coarse aggregates and reinforcement.

3. It is necessary to flux the cementing material over the surface of the aggregates.

4. It is employed to damp the concrete in order to prevent them absorbing water vitally necessary for chemical action

5. It enables the concrete mix to blow into moulds.


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Uses and types

Uses of Concrete:

1:2:2 - For heavy loaded R.C.C columns and R.C.C arches of long spans

1:2:2 - For small pre cast members of concrete like fencing poles, telegraph poles etc. watertight construction.

1:2:3 - For water tanks, bridges, sewers etc.

1:2:3 - For foot path, concrete roads

1:2:4 - For general work of RCC such as stairs, beams, columns, slabs, etc

1:4:8 / 1:5:10 For mass concrete for heavy walls, foundation footings etc.

Preparation of concrete mix:

There are two types of concrete mixing

(i) Hand mixing

(ii) Machine mixing

1. Hand Mixing: This method of mixing concrete is resorted to when the quantity if concrete to be used in a work is

insufficient to warrant the necessity of machine. This is used with advantage in places where

machinery cannot be used on account of their non-availability or in works near a hospital where the noise of machine is

not desirable. Hand mixing is done on a clean, hard and impermeable surface. Cement and sand are first mixed dry with

the help of shovels until the mixture attains a uniform colour. Aggregative are then added to this mixture and the whole

mixture is then turned by shovels until the stone pieces uniformly spread throughout. After this, desired are quantity of

water is poured into the heap from a can fitted with a rose. The mass is then turned until a workable mixture is

obtained. It is advised to add 10% extra cement to guard against the possibility of inadequate mixing by this method.

2. Machine Mixing: - The machine used for mixing concrete is termed as concrete mixer. Two types of concrete mixers

are in common are

1. Continuous mixers

2. Batch mixers

Continuous mixers are employed in massive construction where large and continuous flow of concrete is desired. The

process of feeding the mixing is more or less automatic. The machine requires careful supervision so as to obtain the

concrete mix of desired consistency. In batch type of concrete mixer. The desired proportion of materials are fed into

the hopper of a drum in which the materials get mixed by the series of blades or baffles inside the mixer.

Batch mixers are further two types

1. Tilting drum type

2. closed drump type.

In the first type, components are fed in the revolving drum in a tilted position and after sometime the concrete mix is

discharged by tilting the drums in the opposite direction. In the latter type the drum remains rotating in one direction

and emptied by means of hopper which tilts to receive the discharge. While using the mixer, coarse aggregates should

be fed first, sand and cement should be put afterwards. In this revolving state, the components get mixed while water is

poured with the help of can. The concrete should be for atleast 2 minutes, the time being measured after all the

ingredients including water have been fed into the drum. The batch type concrete mixer is as shown in the fig.

Fig., Batch type Concrete Mixer

Compaction - Methods:

Concrete should be placed and compacted immediately after mixing.

The concrete should be placed within 30 to 40 minutes to prevent the danger of concrete getting its initial set,before laying the concrete; the shuttering should be cleaned of all of dust or debris. Crude oil or grease etc is

usually applied to the shuttering before concreting to prevent the shuttering absorbing the water from the

concrete or getting stuck to it.


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In placing the concrete, care should be taken to see that it should not be thrown from heights. Concrete should

be laid in layers 15 to 30 cm (6 to12) in thickness and each layer should be properly compactedbefore laying

the next one.

Compaction of concrete should be proceeding immediately after placing.

The function of compaction of concrete is to expel the air bubbles in the mass and make it impermeable in

addition to its securing the desired strength.

The concrete mass should be consolidated or compacted till the cream of the cement starts appearing on the

surface. Over compaction may lead to segregation of concrete while-under-compaction may leave air voids in

concrete and results in honey combing. Compaction may be done by hand or mechanical device.

(i) Hand compaction: The hand compaction may be done by Roding, tamping or hammering. Tamping is

usually adopted for compacting concrete for slabs or other such surfaces. Roding is done for thin vertical members.

Hammering is done for massive plain concrete works and for compact an almost dry concrete the surface is beaten with

heavy flat bottom rammers till the thin film of mortar start appearing on the surface.

(ii) Mechanical compaction: Mechanical compaction is done by the use of vibrators. Vibrators are of three types

1. Internal

2. External

3. Surface.

Internal vibrators are commonly used in large works for flat surface compaction. In this the vibrator is immersed

in the full depth of concrete layer. The vibrator should be kept in one position for about 3 minutes and thenremoved and placed another position.

External vibrators are placed against the form work and are only adopted for thin section of members or in

places where internal vibrators cannot be used with ease.

Surface vibrators are generally employed in concrete road construction. Compaction of concrete by use of

vibrators permits the use of stiff concrete mix of high strength and ensure better compaction than that obtained

by the method of hand compaction

6.5 Curing of concrete:

Curing of concrete is one of the essential requirements of process of concreting. Curing is process of keep the set

concrete damp for some days in order to enable the concrete gain more strength

Purposes:

(i) Curing protects concrete surfaces from sun and wind(ii) Presence of water is essential to cause the chemical action which a companies the setting of concrete

Definition of Concrete Curing

Curing is a procedure that is adopted to promote the hardening of concrete under conditions of humidity and

temperature which are conducive to the progressive and proper setting of the constituent cement. Curing has a major

influence on the properties of hardened concrete such as durability, strength, water-tightness, wear resistance, volume

stability, and resistance to freezing and thawing.

Concrete that has been specified, batched, mixed, placed, and finished can still be a failure if improperly or inadequately

cured. Curing is usually the last step in a concrete project and, unfortunately, is often neglected even by professionals.

Methods of Curing Concrete

The best curing method depends on:

Cost

Application equipment required

Materials available

Size and shape of the concrete surface

1. Keep concrete in water

Keep the concrete immersed in water during the curing period to fulfill the moisture requirements of concrete. This can

be done by:


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Ponding or immersion

Spraying or fogging

o Fogging minimizes moisture loss during and after placing and finishing of concrete.

Saturated wet coverings

Such methods provide some cooling through evaporation, which is beneficial in hot weather.

2. Prevent the loss of the existing water

Prevent the loss of the mixing water from concrete by sealing its surface. This can be done by:

Covering the concrete with impervious paper or plastic sheets.

o Polyethylene film is an effective moisture barrier for curing concrete and easily applied to complex as well as simple

shapes. To minimize discoloration, the film should be kept as flat as possible on the concrete surface.

Applying membrane-forming curing compounds.

o Penetrating sealers help protect reinforcing steel in bridge decks from corrosion due to chloride infiltration without

reducing surface friction

3. Steam Curing

Strength gain can also be accelerated with:

CURING OF CONCRETE BY COVERING ITS SURFACE

WITH A SHEET LAYER

Live steam

Heating coils

Electrically heated forms or pads

Requirements for curing

Time- 3-7 Days

Temperature- 50-100 F

Moisture- Saturated at all times

Effect of Curing on concrete performance: The purpose of curing is to ensure that the concrete does not dry out

prematurely, but retains moisture so that it will build up strength and gain durability and resistance to wear. The

concrete should be kept continuously damp for at least 7 days to achieve satisfactory curing. The easiest method is to

cover the concrete with plastic sheeting immediately after finishing. It

Increases Strength

Increases Water tightness

Increases Abrasion resistance

Increases Freeze-thaw resistance

Increases Volume stability

Decreases permeability.


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UNIT - III: TYPES OF CONCRETE AGGREGATES AND CONCRETE:

Lightweight Aggregate:

Lightweight aggregates are used to make lightweight concrete.

Lightweight aggregates can be processed natural materials (for example expanded clay or expanded shale),

processed by-products (for example foamed slag or sintered pulverized fuel ash) or unprocessed materials (forexample pumice).

Lightweight aggregate is a type of coarse aggregate that is used in the production of lightweight concrete

products such as concrete block, structural concrete, and pavement.

Most lightweight aggregate is produced from materials such as clay, shale, or slate. Blast furnace slag, natural

pumice, vermiculite, and perlite can be used as substitutes.

Applications where lightweight aggregates are used include:

Lightweight concrete masonry,

Structural lightweight and semi-lightweight cast-in-place concrete ,

Low-density precast concrete units,

Low-density mortars for radiant heat floor and refractory,

Geotechnical low-density engineered fill,

Insulating concrete fill,

Concrete roofing tile and ballast and

Ground cover and soil-less mix.

Lightweight Aggregate:

Advantages:

Minimizing the need for repair and replacement of the Infrastructure

Reduced heat island effect in urban areas :

The magnitude of the heat island effect is the temperature difference between a citys hot built-up core and its

surrounding cool rural areas which can amount to 6C or more.

By incorporating vesicular aggregates into the soil, the tiny pores act as reservoirs that hold and release as

needed water and soluble nutrients for the vegetation to absorb.

The porous cellular lightweight aggregates help manage water by acting as a moisture flywheel absorbing

moisture during wet periods and slowly releasing it along with soluble nutrients during dry spells.

In addition to minimizing the need for irrigation, it also reduces the amount of runoff. As in wastewater

treatment plants a gravel bed can be an important component in improving the quality of the groundwater.

Horticulture uses such as green roofs.

Usage of recycled by products :

By-products such as fly ash and bottom ash from power generating plants can be processed into lightweight

aggregates.

Filter beds:


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In the treatment of municipal waste, filter beds are used where a bacterial film anchors and develops on

aggregate surfaces. The surface of lightweight aggregates provides an ideal medium for the development of this

bacterial growth and is particularly effective in lowering the phosphates content. With a vesicular aggregate

even more surface area is available for the beneficial organisms to form as compared to normal weight

aggregates.

Examples: Litex brand lightweight aggregate is well suited for concrete masonry, structural

and non-structural concrete, soil stabilization, and horticulture and landscapingapplications.

True Lite Lightweight Aggregate brand aggregate ("True Lite") is a co-product of the iron

production process. It is well suited for lightweight concrete masonry, lightweight

structural and non-structural concrete, and lightweight engineered fill applications. True Lite offers excellent

fire resistance, thermal insulating, and sound absorption capabilities.

In cement, Vitrex brand pelletized slag offers:

Low moisture content. Vitrex brand pelletized slag typically has a moisture content of less than 8 percent.

Some cement producers grind Vitrex brand pelletized slag directly without further drying.


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Reinforced cement concrete:

Reinforced cement concrete is a composite material made

up of cement concrete and reinforcement in which the concreteresists compression with reinforcement resisting the tension and

shear. It is the most versatile building material available and is

extensively used in the construction industry ranging from small

structural elements such as beams and columns to massive

structures like dams and bridges.

The idea of reinforcing concrete with steel has resulted in a

composite material, having the potential of resisting significant

tensile stresses. The steel bars are embedded in the tensile zone of

concrete to compensate the poor tensile resistance of concrete.

The bond between steel and the surrounding concrete

ensures strain compatibility. Moreover, the reinforcing steel impartsductility to this composite material.

The reinforcing steel also supplements concrete in bearing

compressive forces, as in the case of columns. Here the bars are

confined with lateral ties, in order to maintain their positions and to

prevent their local buckling. In addition, the lateral ties also serve to confine the concrete, thereby enhancing its

compression load bearing capacity.

Prestressed concrete:

One of the serious limitation of reinforced cement concrete is the cracking which is a natural phenomenon for concrete

constructions. Once cracks occur they do not disappear even after removal of load. If the width of these cracks is to be

kept within permissible limits, the steel stress has to be kept low.

Presence of cracks lowers the capacity of structure to bear reversal of stresses, impact vibration and shocks. Also, thereinforcing bars may get corroded in due course of time and the concrete deteriorates. Besides these disadvantages, the

presence of cracks makes theory of reinforced concrete quite irrational.

Efforts were made to eliminate the cracking of concrete by artificially introducing in it either before or simultaneously

with the application of external loads, a compressive force of permanent nature. This force is so applied that it causes

compressive stresses in that zone of the member where tensile stress will be caused by external loads. The tensile stress

in concrete will thus be neutralized and it will not crack.

A prestressed concrete may thus be defined as a concrete in which stresses of suitable magnitude and distribution are

introduced to counteract, to a desired degree, the stresses resulting from external loads. The concept of prestressing

concrete was first used by Mandl of France in 1896. In prestressed concrete high strength concrete and steel are

desirable.

The former is required because of following:1. The use of high strength concrete results in smaller cross-section of member and hence smaller self weight; longer

spans become technically and economically practicable.

2. High bearing stresses are generated in anchorage zones.

3. The shrinkage cracks are reduced, with higher modulus of elasticity and smaller creep strain resulting in smaller loss

of prestress.


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The loss of prestress at the initial stages is very high and for this reason high strength steel is required. High tensile

strength wires with ultimate tensile strength up to 2010 N/mm2 are the choice. For prestressed concrete members, the

high tensile steel used generally consists of coires, bars or strands.

Prestressing is achieved by either pre-tensioning or post-tensioning. In the former the wires or cables are anchored,

tensioned and concrete is cast in the moulds. After the concrete has gained strength the wires are released. This sets up

compression in concrete which counteracts tension in concrete because of bending in the member.

In the post-tensioning prestressing force is applied to the steel bars or cables, after the concrete has hardened

sufficiently. After applying the full prestress the cable passages are grouted. The minimum 28-day cube compressive

strength for concrete is 40 N/mm2 for pre-tensioned members and 30 N/mm2 for post-tensioned members.Advantages:

1. The cracking of concrete is eliminated enabling the entire cross-section of the member to take part in resisting

moment.

2. As dead load moments are neutralized and the shear stresses are reduced, the sections required are much smaller than

those for reinforced concrete. This reduces the dead weight of structure.

3. In ordinary reinforced concrete (RCC) the economy is not as pronounced as in prestressed concrete (PSC). The

prestressing force in most cases is computed strictly from dead load of the structure; consequently, a weight reduction of

25% results in a substantial reduction in the weight of prestressing tendons. It is widely used for construction of precast

units such as beams, floors, roofing systems, bridges, folded plate roofs, marine structures, towers and railway sleepers

Fibre reinforced concrete:Conventional concrete is modified by random dispersal of short discrete fine fibres of asbestos, steel, sisal, glass,

carbon, poly-propylene, nylon, etc. Asbestos cement fibres so far have proved to be commercially successful. The

improvement in structural performance depends on the strength characteristics, volume, spacing, dispersion and

orientation, shape and their aspect ratio (ratio of length to diameter) of fibres. A fibre-reinforced concrete requires a

considerably greater amount of fine aggregate than that for conventional concrete for convenient handling.

For FRC to be fully effective, each fibre needs to be fully embedded in the matrix, thus the cement paste requirement is

more. For FRC the cement paste required ranges between 35 to 45 per cent as against 25 to 35 per cent in conventional

concrete.

The first flexural cracking load on a FRC member increases due to crack arresting mechanism of the closely spaced

fibres. After the first crack fibres continue to take load provided the bond is good. Thereafter the fibres,reaching the

breaking strain fracture. The neutral axis of the section shifts and the fibres of adjacent layers fracture on reaching thebreaking strain. Failure occurs when the concrete in compression reaches the ultimate strain.

Advantages:

1. Strength of concrete increases.

2. Fibres help to reduce cracking and permit the use of thin concrete sections.

3. Mix becomes cohesive and possibilities of segregation are reduced.

4. Ductility, impact resistance, tensile and bending strength are improved.

Disadvantages:

1. Fibres reduce the workability of a mix and may cause the entrainment of air.

2. Steel fibres tend to intermesh and form balls during mixing of concrete.

Types of Frcs:

Steel Fibre Reinforced Concrete (SFRC) Aspect ratios of 30 to 250

Diameters vary from 0.25 mm to 0.75 mm

Hooks are provided at the ends to improve bond with the matrix

Introduction of steel fibres

modifies:

1. Tensile strength

2.

Compressive strength

3. Flexural strength

4. Shear strength

5.

Modulus of Elasticity

6. Shrinkage

7. Impact resistance

8. Strain capacity/Toughness

9. Durability


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10.

Fatigue

Applications:

Fibre reinforced concrete is useful in hydraulic structures, airfield pavements, highways, bridge decks, heavy duty floors,

and tunnel linings.

Highway and airport pavements

Refractory linings Canal linings

Industrial floorings and bridge-decks

Precast applications - wall and roof panels, pipes, boats, staircase steps & manhole covers

Structural applications.

Polypropylene Fibre Reinforced Concrete (PFRC) :

Glass Fibre Reinforced Concrete (GFRC)

Ready mixed concrete:

Ready mixed concrete (RMC) is a concrete, delivered at site or into the purchasers vehicle, in plastic condition and

requires no further treatment before being placed in a position in which it is to set and harden.

It is a high quality concrete of required grade produced under strictly controlled conditions in a centralised automatic

batching plant and supplied to the customer in a transit mixer truck for its placement at site.

The concrete can be mixed either dry at the batching plant, loaded into agitator truck mixers and water added during

transportation; or it can be mixed wet at the batching plant, discharged into the agitator truck mixers and transported

to site.

Use of RMC to its full advantage requires more careful planning on the site as compared to the site mixing. Due tobetter quality control measures adopted, RMC can be considered to be almost a factory-made product, yet it is not. It is

advantageous not only for mass concreting but also for small quantities of concrete to be placed at intervals.

RMC is extremely useful on congested sites or in road construction where limited space is available for aggregate stock

piling and mixing plant.

The major setback to the use of RMC is its cost. Though a little bit expensive, the increasing emphasis on quality, with

skilled labour becoming expensive, and its inherent advantages outweigh the cost.

Admixtures in RMC:

Generally RMC is transported to sites which are located at long distances from the batching plants. At the delivery point,

concrete should be workable and plastic. The transit period is sometimes four to five hours. The ordinary concrete will

suffer slump loss due to the time lost in transit and evaporation of water due to atmospheric conditions such as high

temperature. Therefore, admixtures will be required to extend the setting time and, retention of specified slump ofconcrete.

Two types of admixtures are in usethe high performance water reducing admixtures and a high range water-reducing

super-plasticizers.

The advantages of using high performance water reducing admixtures are:

1. Improved cohesion and reduced bleeding and segregation.

2. Makes the mix cohesive even if the aggregates are of slightly poor grading.

3. Since chloride free it is safe for use in reinforced and prestressed concrete.

4. Improved workability and workability retention with controlled extended setting time and hence ideal for use in hot

weather condition.

5. Workability increases without extra water addition.

6. Assists in producing dense, close textured, low permeability concrete thus enhancing durability.7. Water reduction helps in improvement of compressive strength at all ages.

The advantages of using high range water-reducing super plasticizers are:

a) Speedy construction.

b) Increased workability and reduced segregation.

c) Longer placing time.


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d) Improved pumpability.

e) Chloride free.

f) Safe for use in prestressed and marine structures.

g) Safe for use with sulphate resisting cement and marine aggregate.

h) Higher ultimate strength.

i) Improved workability.

Advantages of using RMC:

1. Enhanced quality and durability resulting in lower maintenance costs and increased speed of construction.

2. Ready mix concrete is consistently of the same quality and provides a high quality of construction material;

construction time is also reduced.

3. It reduces congestion at the site and prevents traffic jams.

4. It hastens infrastructure development and thus provides more employment opportunities.

5. It is an environmentally safer alternative.

6. With ready mixed concrete, modern construction techniques can be followed.

7. ConvenienceReady Mix Concrete is delivered at the site with minimum logistical hassles.

8. Different types of concretes can be made for different applications.

9. Use of RMC obviates the need to set up the infrastructure required for site manufactures of concrete. This also

reduces the working capital to be invested by the customers, as they will not be required to maintain stock of

aggregates, cement, plant and machinery etc.

UNIT IV SURFACE FINISHING, FLOORING AND DAMP-PROOFING

Paints:

Paint is a liquid surface coating. On drying it forms a thin film (60150 _) on the painted surface. Paints are

classified as oil paints, water paints, cement paints, bituminous paints and special paints such as fire proof

paints, luminous paints, chlorinated rubber paints (for protecting objects against acid fumes), etc. The functions of the paints are: to protect the coated surface against possible stressesmechanical or chemical;

deteriorationphysical or environmental; decorate the structure by giving smooth and colourful finish; check

penetration of water through R.C.C; check the formation of bacteria and fungus, which are unhygienic and give

ugly look to the walls; check the corrosion of the metal structures; check the decay of wood work and to varnish

the surface to display it to better advantage.

Characteristics of an ideal paint:

The requirements are uniform spread as a thin film, high coverage, good workability and durability, sufficient

elasticity to remain unaffected by expansion or contraction of the surface to be painted or by weathering action

of atmosphere. The paints should also be: impervious to air and water, cheap and economical to form a hard

surface.

Enamel:

Enamels consists of bases like zinc oxide, etc. ground in varnish. If desired colouring pigments may be added.

They dry quickly and furnish a hard glossy surface. Enamel can be used for internal as well as external works and


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are generally recommended for application on wood work. These are acid resistant, not affected by alkalis,

gases and, are waterproof.

Application:

The surface of the wood is rubbed with a sand paper and cleaned. A primer coat consisting of titanium white in

pale linseed oil is followed by two to three coats of enamel paint.

Distempers:

Distemper is made with base as white chalk and thinner as water. Some colouring pigments and glue are added.

They are available in powder and paste forms and are substantially cheaper than paints. They are most suitable for plastered surfaces as well as white washed surfaces of interior walls.

Oil bound washable distemper, washable oil free distemper, and non washable distemper or emulsion paints

are some of the types of distemper. In the oil bound distemper, the drying oil is rendered mixable with water.

While using they are thinned by adding water. On drying, the oil content in distemper hardens and yields a

comparatively durable coating.

Characteristics:

1. The coatings are thick and more brittle compared to paints.

2. They are workable, easy in application but less durable.

3. The film being porous can be applied on even newly plastered surface.

Distempers are applied in the following manner:Preparation of surface: The surface is thoroughly rubbed and cleaned. In case of a new plastered surface, the surface is

kept exposed, to weather, for drying before the application of distemper. If an existing (old) distempered surface is to

be redone, surface is cleaned with profuse watering. The efflorescence and patches, if any, should be wiped out by a

clean cloth. Cracks, if any should be filled with putty.

Priming coat: A priming coat as recommended by the manufacturer is applied on the prepared surface.

Final coat: Two or three coats of distemper are applied. Each coat should be applied only after the previous coat has

dried.

Defects:

A painted building with full colour effects gives complete satisfaction. But the appearance of defects becomes a ready

source of complaint. Unfortunately painting defects are by no means uncommon. They may arise from a variety of

causes but the principal reasons behind them are incorrect choice of paint in relation to backing materials, application

of paint to a damp surface or one to which moisture may have access and; poor workmanship.

Effects of background:

The factors affecting durability are dampness, cleanliness, movements, chemical reactions,etc.

Dampness: The traditional construction in brick, cement, etc. involves the use of wet procedures.

If paint is applied on an insufficiently dry background the moisture is trapped and in the process of subsequent drying

the adhesion of the paint breaks down. Emulsion paints are somewhat better in this respect.

Cleanliness:

Paint will not adhere to the surface if it is not cleaned of dirt or dust.

Movements:The painting processes can be delayed for proper results for movements caused by shrinkage and special paints should

be used for thermal movements.

Chemical reactions:

Between backing material and paint film may push the paint off the backing material and lead to softening or

decolourise the paint. This effect generally occurs only if moisture is present and is noticeable in oil paints over

materials containing cement or lime. The breakdown of bond is because of the crystallization of salts below the paint

film and the discolouration is usually due to action of free lime on the pigments.

Effects of weather:

The paint film is subjected to chemical attack of atmosphere, sunlight and heat, all deteriorating it. Special chemical

resistant paints should be applied in industrial areas. Alkali resistant paints weather well in coastal areas. Blue and greencolours tend to fade when exposed to bright light. In addition the fierce heat of sun may breakdown the paint film

because of the disintegration of the material itself and also because of the thermal movement. The most common

defects noticed after painting, are as follow:

1.

Swelling of the paint film and can be defined as localized loss of adhesion between one or more coatings or between

primer and parent surface.


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When swelling is because of oil or grease on the surface it is known as blistering and in case of moisture it is

called peeling. It occurs in nonporous coatings such as oil based paints and enamels. A special heat-resisting

type of paint should be used for hot surfaces such as radiators.

It is brought about by moist air, oily or greasy surface, or imprisoned gases between the painted surface and the

paint film, which expand under the influence of heat.

2. Emulsion paints provide a porous coating and allow the moisture to pass through. If hair cracks produced enclose

small area it is known as crazing.

In case the enclosed area is large the defects is called crocodiling.

It is caused when the paint film lacks in tensile strength and occurs when paint is applied during very coldweather or because of insufficient drying of undercoat.

When cracks are very small and do not enlarge with time, the top coating is flattened with emery paper and a

fresh coat of paint is applied.

3. The cracks extend throughout the entire paint system extending right down to the original surface.

Cracks in the plaster or masonry do not let the paint to remain intact.

Paint applied on glossy surface.

Premature application of top coat before the previous coat has completely dried.

Painting improperly seasoned wood.

4.

Flaking is detachment of paint film from the surface.

The moisture penetrates through the cracks on the coatings and the bond between surface and paint film is lost.

Cures:1. Use of plastic emulsion paints.

2. Surface should be rubbed with emery paper before applying a fresh coat.

3. All dirt or dust on surface should be removed prior to painting.

5. Chalking: Paint film becomes powder due to insufficient oil in primer.

6.

Alligatoring: One layer of paint films sliding over the other one, when a hard paint is applied over a soft one or vice

versa.

7. Wrinkling: or crawling appears when the paint film is quite thick or the oil in the paint is more than required. The

lower portion of the paint does not dry due to greater thickness of the paint film which shrinks due to drying in

course of time.

8. Running & sagging: Paints applied over smooth and glossy surface do not stick and flow back or towards the

unpainted area. This is known as running and sagging. The surface to-be painted should, therefore, be rubbedwith an emery paper before painting.

9.

Mild dew: Mildew thrives in warm, moist and dark places. Zinc oxide and phenol mercury oleate are very useful to

check its growth.

10.Bloom: is identified as dull patches on the finished, polished or painted surface due to defect in the quality of paint

or poor ventilation.

11.Flashing: is characterized by the appearance of certain glossy patches on the painted surface. The reasons attributed

to this defect are weathering actions, use of cheap paint, and poor workmanship.

12.

Grinning: is due to the imperfect opacity of the paint film even after the final coat. The background and its defects

can be clearly visible in such a case.


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UNIT V - GLASS

Glass is an inorganic, homogeneous and amorphous substance obtained through the cooling of a molten mass. Its main

qualities are the transparency and hardness. The glass has uncountable applications in the most varied industries, given

its inalterability characteristics, hardness, resistance and thermal, optical and acoustic properties, becoming one of the

few materials yet irreplaceable, being every time more present in the technological development researches for the

well-being of the man.

Qualities & Features:

Recyclability

Transparence (permeable to light)

Hardness

Non absorbance

Great dielectric insulator

Low thermal conductivity

Abundant resources in the nature

Durability

Composition of Glass

-

its not a single compound and its difficult to give it a particular chemical formula- commonly expressed as combination of alkali oxides, metal oxides and silica dioxides aX2O, bYO, 6SiO2

Where,

a, b are no. of molecules;

X is an atom of an alkali metal i.e. Na, K etc.

Y is an atom of a bivalent metal i.e. Ca, Pb etc.

For example,

Soda-lime Glass - Na2O, CaO, 6SiO2

Potash-lead Glass - K2O, PbO, 6SiO2

Important properties of glass


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1.

Absorbs, refracts and transmits light

2. Amorphous substance having no definite crystalline structure which makes it easy to fuse it and mould it as

many times as possible

3. No sharp melting point

4.

Does not react with water and other atmospheric agentsbut is affected by alkalis

5.

Characteristics, both physical and chemical, vary considerably with addition of other materials (B2O3, if added

with glass makes its alkali resistant)

6. Excellent electrical insulator at elevated temperatures

7. Easy to clean and maintain it from stains

8.

Easy to add colour to glass

9. Considerable compressive strength up to certain point but does not deform but breakshighly brittle substance

10.

Thermal conductivity is less

Manufacturing of Glass

Stage ICollection of raw materials depending on the type of the glass:

Say, Soda-lime Glass preparation needs Chalk (CaO), Soda ash (Na2O) and Clean sand (SiO2)

Cullet in the form of waste glass or broken glass is added to increase the fusibility as well as to prevent the loss of alkali

through volatilisation.

Decolourisers are also added to eliminate the yellowish tint of Ferric Oxides and greenish tint of Ferrous Oxides

Antimony Oxide, Arsenic Oxide, Cobalt Oxide, Manganese Oxide, Nickel Oxide are the most commonly used

decolourisers.

Stage IIPreparation of batch

- By adding ingredients in correct proportion, and mixing them uniformly.

Stage IIIMelting in furnace

- In pot furnace or tank furnace depending on the scale of operationsmall scale in pot and large scale in tank furnace

- Refractory lining of fire clay.

Stage IVFabrication of glass

Float Glassmakes the molten glass float over liquid tin;


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Plate Glassrolled over either two layers of roller or combination of plate and rolled

Cast glasscast by pouring molten glass or pressing them in moulds.

Stage VAnnealing of glass

- Itsof process of making glass objects cool down gradually from a very high temperature

- Due to high thermal insulation of glass rapid cooling creates thermal stress between inner and outer layers of glass

leading to a state of strain

- Makes glass highly vulnerable to minor shocks and disturbancesthus annealing is a crucial process

Flue method of annealingglass objects being passed through a flue with varying temperature allowing it to cool down

graduallya constant process applied for large scale annealing.

Oven method of annealing temperature variation achieved by cooling the oven itself from high temperature an

intermittent process suitable for small scale annealing.

Test for waviness

- Apply a coating of silver on one surface protected by metallic copper film (similar to making of mirror out

of glass)

-

Sketch comprising broad straight bands at 45 to the horizontal in a rectangle waved in front of the mirror

which should be vertically placed.

- Image of bands free from distortion means that the glass is free from waviness or distortion free.

Types of glass

A. Soda lime glass

- contains 70-74 percent Silica, 8-13 percent calcium oxide and 13-28 percent sodium oxide

-

comprises of 90 percent of the glass manufactured

- used for flat glass panels, window glass and tableware

B. Lead Glass

- composition similar to soda lime glass but lead oxide replaces calcium oxide

- highly resistant to electricity

- refractive index around 2.2characteristic sparkle in cut glass

-

extensively used in manufacturing luminaries and shielding nuclear radiation

C. Boro-silicate glass

-

contains 10-20 percent of boron oxide, 80-87 percent silica, and sodium oxide less than 10 percent

-

possess high shock resistance and electrical insulation properties- low co-efficient of thermal expansion and excellent chemical stability

D. Laminated glass

-

made of two or more layers of glass which are laminated to an interlayer of clear or tinted Poly Vinyl

Butyral (PVB)

- resistant to shattering as the pieces remain in places after breaking

E. Tinted glass

- used for reflecting or absorbing solar radiation

- green glass has highest day light transmittance and grey glass has the lowest

F. Coated glass

- clear glass panel with a very thin metallic coating

- reflects heat and thermally insulates the internal space


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G. Wired Glass

- molten glass rolled with a wire mesh embedded

- resist splintering of glass even after breaking

- wired glass has application in high temperature environment

- should satisfy flameproof requirements as per the IS

H. Coloured glass

- various colours by incorporating Ti, V, Cr, Mn, Fe, Co, Ni, Se etc.

Application of Glass in Door and Window shutters

Transparent or translucent glass sheets, clear or tinted are used as door and window shutters in various sizes

Classification of transparent glass used as door/window glazing

1. AA Quality or Special Selected Quality (SSQ)for safety glass in door/window or wind shields.

2. A Quality or Selected Quality (SQ)for selected glazing and wind shields.

3.

B Quality or Ordinary Quality (OQ)for general purpose glazing and framing.4. C Quality or Greenhouse Quality (GQ)For green house glazing but varied suitably for doors and windows.

Glass Tiles

- made for the purpose of glazing, wall finish, partions, ceilings, curtain walls and swimming pool application

-

Wide variety ranging from clear to tinted glass, plain, polished, textured, roughened, laminated with

interlays of polymers, wired etc.

Glass Fibres

-

fibres made out of glass and drawn into threads

-

diameter up to 5 micron.

- contains silica 50-55 percent, calcium oxide 15-20 percent, boron oxide 8-12 percent and sodium and

potassium oxide less than 1 percent

- used in gypsum plaster with epoxy resin or cement as binders

- low silica content makes them alkali resistant suitable for cement matrix composites

-

glass fibre reinforced composites are extensively used in preparation of water pipes, tanks and panels

Glass Wool

- composition similar to boro-silicate glass

- glass melted at 1500-1600 C and blown through holes of a platinum alloy plate molten material after

passing through holes is subjected to high speed gaseous jets and the resultant woolly mass is moved over a conveyor

belt- glass wool is more cost effective than rock wool

- extensively used for thermal insulation and acoustic insulation

- glass wool used as core material in ply woods and metallic sheets or plastics used for ceiling and partition

wall panels, door shutters etc.

Glass Blocks

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glass blocks typically have compressive strength in the range of 3-4 MPa

- can be either hollow (made of two pressed glass shapes fused together into a single unit at an elevated

temperature with the air trapped inside dehydrated and partially evacuated) or solid

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chemical composition similar to the glass used in door/window panels-

can have various colours, textures, transparency and dimension

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used mostly as partition walls where light transmission, insulation and glare control are of major importance

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mortar used in glass block masonry is cement lime mortar where cement in 1 part, lime in 0.5 part and

sand in 3 parts are used


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Waste Utilisation

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glass manufacturing is a relatively environment friendly process and its offers ample scope for reuse

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waste glass in form of cullet is fed back to glass furnaces for reuse

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this leads to significant waste minimization and lower mining of raw materials

- broken glass in powdered form is mixed with clay for moulding bricksimparting high strength

- waste glass has application in special grade concrete the chemical resistance increases but the

compressive strength decreases

Types of glass:

There are 2 types of flat glass: The float and the printed glass.

Float Glass

The float glass is a transparent, colorless or colored glass, with uniform thickness and homogeneous mass. It is the ideal

glass for application that demand perfect visibility, as it does not present optical distortion and has high light

transmission.

It constitutes the raw material for the processing of all the other flat glasses, being applied to different segments and it

can be: laminated, tempered glass, curved, screen-printed glass and used in double glazing. It is used in automotive

industry, of household appliances, civil construction, furniture and decoration.

Printed GlassThe printed glass is a translucent flat glass, colorless or colored, which receives the printing of a pattern (drawing) when

is leaving the furnace. It is used in civil construction, household appliances, furniture and decoration.

Casted Glass

Glass castingis the process in whichglass objects arecast by directing molten glass into amould where

it solidifies. The technique has been used since theEgyptian period. Modern cast glass is formed by a

variety of processes such as kiln casting, or casting into sand, graphite or metal moulds.

Glass block:

When it comes todesigning and building with glass, one of the simplest yet most versatile

ways of utilising glass is in the form of glass blocks. Glass blocks can be used both internally

and externally and wherever they are placed the way in which they transmit and refract light

allows the designer to maximise the sense of light and space creating beautiful and

alwaysunique living and working spaces.Where privacy is paramount opaque glass blocks can

be selected, retaining light and vibrancy whilst protecting privacy.

Glass blocks are suitable for both commercial and residential purposes and can be used to fill window openings, form

dividing walls, external walls, in the creation of shower cubicles, bars, terraces, and desks. In fact the design potential

for the use of glass blocks in any construction is limited only by your imagination.

The foamed glass aggregate is produced from cleaned recycled glass. The product is especially suited for usage in the

construction of roads, as frost-heave insulation as well as a bulk lightening material. It is also excellent as an all-round

building insulator (foundation and frost heave insulator, flat roof insulator in the structure of inverted roofs), as well as a

bulk lightening material for foundations. Crushed foamed glass can also be used as a capillary blocker.
http://en.wikipedia.org/wiki/Glasshttp://en.wikipedia.org/wiki/Castinghttp://en.wikipedia.org/wiki/Molding_(process)http://en.wikipedia.org/wiki/Ancient_Egypthttp://www.glassblocks.ie/glassblocks_technicaldetails.phphttp://www.glassblocks.ie/glassblocks_lifestyle_gallery.phphttp://www.glassblocks.ie/glassblocks_lifestyle_gallery.phphttp://www.glassblocks.ie/glassblocks_technicaldetails.phphttp://en.wikipedia.org/wiki/Ancient_Egypthttp://en.wikipedia.org/wiki/Molding_(process)http://en.wikipedia.org/wiki/Castinghttp://en.wikipedia.org/wiki/Glass

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