Bricks

Building Materials

CE-306

Bricks

Introduction

Definition : Structural units of rectangular shape and convenient size made from suitable

types of clays

Introduction


types of clays

Size of a modular brick : 19cm X 9cm X 9 cm

Introduction


types of clays


Nominal size of a modular brick : 20cm X 10cm X 10 cm

Introduction


types of clays



Weight of a brick: 3-3.5kg

Steps for manufacture of bricks:

Introduction


types of clays





1. Preparation of clay

Introduction


types of clays






2. Moulding

Introduction


types of clays






2. Moulding

3. Drying

Introduction


types of clays






2. Moulding

3. Drying

4. Burning

Introduction


types of clays






2. Moulding

3. Drying

4. Burning

Composition of suitable brick earth/clay

1. Alumina (20-30%)


1. Alumina (20-30%)Imparts plastic character to clays in wet condition.


1. Alumina (20-30%)Imparts plastic character to clays in wet condition.Excess alumina

makes clay more plastic,shrinkage cracks produced on drying, become too hard

when burnt.




when burnt. Less alumina content makes it difficult to mould bricks to proper shape.





2. Silica (50-60%)





2. Silica (50-60%)Imparts hardness and strength. Provides resistance against shrink-

age and durability against weather. High proportion of silica makes it difficult to

mould and also burn. After burning they will become brittle and porous.








3. Iron oxides (4-6%)








3. Iron oxides (4-6%)Acts as flux. Lowers softening temperature of silica and other

clay components during firing.Imparts characteristics red colour to the bricks.









clay components during firing.Imparts characteristics red colour to the bricks.Excess

makes the brick blackish in colour.Less iron oxide content makes the bricks yellowish

in colour.











in colour.

4. Lime (4%)











in colour.

4. Lime (4%)Makes burning and hardening of bricks quicker.











in colour.

4. Lime (4%)Makes burning and hardening of bricks quicker.Should not be more than

5% as it results in excessive softening of clays.











in colour.


5% as it results in excessive softening of clays.Must be present in finely powdered

and thoroughly dispersed form. Lime present as nodules it may give rise to slaking

which eventually causes disintegration.











in colour.





5. Magnesia











in colour.





5. Magnesia In small quantity it helps reducing shrinkage.Excess leads to decay of

bricks.











in colour.





5. Magnesia In small quantity it helps reducing shrinkage.Excess leads to decay of

bricks.

Harmful Substances in Brick Earth

1. Lime :


1. Lime :Excess of lime changes the colour of the brick from red to yellow.When present

in lumps, it absorbs moisture, swells and causes disintegration of bricks.




2. Pebbles and gravels :




2. Pebbles and gravels :Do not allow the clay to be mixed thoroughly and spoil the

appearance of the brick.May crack while working.






3. Iron Pyrites :






3. Iron Pyrites :Oxidise and decompose the brick during burning. The brick may split

into pieces.Pyrites discolourise the bricks.








4. Alkali :








4. Alkali :Excess of alkali melt clay on burning and make bricks unsymmetrical. When

bricks come in contact with moisture, water is absorbed and the alkalis crystallise.

On drying, the moisture evaporates, leaving behind grey or white powder deposits

which spoil the appearance. This phenomenon is called efflorescence.












5. Organic matter :












5. Organic matter :On burning green bricks, the organic matter gets charred and leave

pores making the bricks porous; the water absorption is increased and the strength

is reduced.














is reduced.

6. Sulphur :














is reduced.

6. Sulphur :If insufficient time is given during burning for proper oxidation of carbon

and sulphur, the latter will cause the formation of a spongy, swollen structure in the

brick.














is reduced.

6. Sulphur :If insufficient time is given during burning for proper oxidation of carbon

and sulphur, the latter will cause the formation of a spongy, swollen structure in the

brick.

Classification of Bricks based on field Practice

First Class Bricks :

1. These are thoroughly burnt and are of deep red, cherry or copper colour.

2. The surface should be smooth and rectangular, with parallel, sharp and straight

edges and square corners.

3. These should be free from flaws, cracks and stones and have uniform texture.

4. No impression should be left on the brick when a scratch is made by a finger nail.

5. The fractured surface of the brick should not show lumps of lime.

6. A metallic or ringing sound should come when two bricks are struck.

7. Water absorption should be 12–15% (not more than 20%)of its dry weight when

immersed in cold water for 24 hours.

8. The crushing strength of the brick should not be less than 14 N/mm2.

Uses: First class bricks are recommended for pointing, exposed face work in masonry

structures, flooring and reinforced brick work.

contd.

Second Class bricks : They are supposed to have the same requirements as the first class

ones except that

1. Well burnt ,slight overburning is allowed.

2. Small cracks,irregularities in shape and distortions are permitted.

3. A metallic or ringing sound should come when two bricks are struck.

4. A little higher water absorption of about 16–20%(not more than 22%) of its dry weight

is allowed.

5. The crushing strength should not be less than 7.0 N/mm2.

Uses: Second class bricks are recommended for all exterior work when plastering is done

and for interior walls.Not suitable for flooring.

contd.

Third Class bricks :

1. These are underburnt bricks .

2. They are soft and light-coloured producing a dull sound when struck against each

other.

3. Appearance, shape and size are non uniform and irregular.

4. Water absorption is about 25 per cent of dry weight.

Uses : It is used for building temporary structures and in dry weather conditions.

contd

Fourth Class or Jhamma bricks :

1. These are overburnt and badly distorted in shape and size .

2. Quite strong in compressive strength generally above 15N/mm2.

3. Low in porosity and water absorption.

Uses: Unfit for use in building construction.The ballast of such bricks is used for road

construction,foundation and floors as coarse aggregate.

Characteristics of good brick

The essential requirements for building bricks are sufficient strength in crushing, regularity

in size, a proper suction rate, and a pleasing appearance when exposed to view.

1. Size and shape : The bricks should have uniform size and plane, rectangular sur-

faces with parallel sides and sharp straight edges.

2. Colour :The brick should have a uniform deep red or cherry colour as indicative of

uniformity in chemical composition and thoroughness in the burning of the brick.

3. Texture and compactedness :The surfaces should not be too smooth to cause slip-

ping of mortar. The brick should have precompact and uniform texture. A fractured

surface should not show fissures, holes grits or lumps of lime.

4. The brick should be so hard that when scratched by a finger nail no impression is

made.

5. When two bricks are struck together, a metallic sound should be produced.

6. Water Absorption : Water absorption should not exceed 20 per cent of its dry weight

when kept immersed in water for 24 hours.

7. Crushing Strength : Crushing Strength should not be less than 10 N/mm2.

Standard tests for bricks (IS-1077-1970)

Compressive Strength Test:(IS-3495-I)

1. Five whole bricks are chosen randomly from a lot of brick samples and immersed in

water for 24hrs at room temperature.

2. After 24 hrs they are taken out,water is allowed to drain and surplus water cleaned.

3. Frogs are filled with 1:1 mortar, bricks are stored under damp sacks for 24hrs.

4. Bricks are placed in water for seven days.

5. Bricks are taken out of water to drain and remove surplus water.When surface dry

each brick is tested individually.

6. Bricks placed flat with frog end facing upward, between two plywood sheets, placed

on the testing machine and load applied axially at a uniform rate of 140 kg/cm2

7. Comp. Strength =Load/Area

8. Arithmetic mean of the compressive strenth of 5 bricks is taken as the compressive

strength of the lot.

Water Absorption Test(IS-3495-II)

1. Five whole bricks are chosen randomly from a lot of brick samples

2. Samples are dried in a oven at 110oC. Time taken is about 48hrs.

3. Specimens are weighed individually after cooling.

4. Dried samples are immersed in water for 24hrs at room temperature.

5. After 24 hrs, the samples are taken out,wiped dry and weighed individually within

three minutes after taken out.

6. Absorption value is calculated by , w=w2−w1

w1

X100 ,w1 = dryweight ,w2 = weight

after immersion.

7. Arithmetic mean of the water absorption of 5 bricks is taken as the water absorption

of the lot.

Efflorescence Test(IS-3495-III)

1. Five whole bricks are chosen randomly from a lot of brick samples.Place each brick

in a separate flat bottom dish containing distilled water.Depth of immersion of the

bricks should not be less than 2.5cm in each case.

2. The above dishes are kept in a warm room with adequate ventilation.Fresh distilled

water is added as the bricks appear dried.

3. At the end of second drying each brick is observed for efflorescence that is appear-

ance of any white patch of salt on the surface of the brick.

4. Efflorescence is reported by the following words as follows:

• Serious : Salt deposition is all around and quite heavy

• Heavy: Salt deposits cover more than 50% surface area

• Moderate: Salt deposits cover more than 10 to 50% surface area

• Slight: Salt covers surface area less than 10%

• Nil: No deposits after repeated wetting .

Dimension test

• 20 pieces out of selected pieces are taken from the sample and are laid flat as shown

• The tolerance for class A & B should be as given in the

table

Dimension(mm) Tolerance(mm)A/B

Length 3800 ±12/± 30

Width 180 ±6/± 15

Height 180 ±6/± 15

Warpage Test(IS-3495-IV)

• Warpage of the brick is measured with the help of a flat steel or glass surface and

measuring ruler graduated in 0.5 mm divisions

• The sample consists of 10 bricks from a lot.

• For measuring concave warpage,the flat surface of the brick is placed along the

surface to be measured selecting the location that gives the greatest deviation from

straightness. The greatest distance of brick surface from the edge of straightness is

measured by a steel ruler

• The brick is place on the plane surface with the convex surface in contact with the flat

surface and the distances of four corners of brick are measured from the flat surface.

The largest distance is reported as warpage.

• The higher of the distance measured in concave and convex warpage tests is re-

ported as warpage.

Different forms of bricks

• Round ended and bull nosed bricks (a, f)) are used to construct open drains.



• Cant brick, also called splay brick are most suitable for door and window jambs, (b,

c). Double cant brick (c) is used for octagonal pillars.





• Cornice brick (d) is used from architectural point of view.






• Compass brick tapering in both directions along length used to construct furnaces(e).







• Perforated brick (g) is well burned brick, but is not sound proof. Hollow bricks (h)are

about l/3rd the weight of normal bricks and are sound and heat proof, but are not

suitable where concentrated loads are expected.










• Coping bricks are used as the top most bricks course of parapets (i). These drain off

the water from the parapets.












• Brick shown in (j) is used at plinth level and for door and window jambs.













• Split bricks are shown in (k, 1). When cut along the length, it is called queen closer

and when cut at one end by half header and half stretcher, it is known as king closer.













• Split bricks are shown in (k, 1). When cut along the length, it is called queen closer

and when cut at one end by half header and half stretcher, it is known as king closer.

Pictures of different forms of bricks





(a) (b) (c) (d)


(a) (b) (c) (d)


(a) (b) (c) (d)


(a) (b) (c) (d)


(a) (b) (c) (d)

(e) (f) (g) (h)


(a) (b) (c) (d)

(e) (f) (g) (h)


(a) (b) (c) (d)

(e) (f) (g) (h)


(a) (b) (c) (d)

(e) (f) (g) (h)


(a) (b) (c) (d)

(e) (f) (g) (h)

(i) (j) (k) (l)

Defects of bricks

• Overburning

Defects of bricks

• Overburning :Bricks should be burned at temperatures at which incipient, complete

and viscous vitrification occur. If overburnt, a soft molten mass is produced and the

bricks loose their shape.

Defects of bricks




• Underburning

Defects of bricks




• Underburning:When bricks are not burnt to cause complete vitrification, the clay is

not softened because of insufficient heat and the pores are not closed. This results

in higher degree of water absorption and less compressive strength.

Defects of bricks







• Bloating

Defects of bricks







• Bloating:Observed as spongy swollen mass over the surface of burned bricks is

caused due to presence of excess carbonaceous matter, sulphur in brick-clay.

Defects of bricks









• Efflorescence

Defects of bricks









• Efflorescence:This defect is caused because of alkalies present in bricks. When

bricks come in contact with moisture, water is absorbed and the alkalis crystalise.

On drying grey or white powder patches appear on the brick surface.

Defects of bricks












• Chuffs

Defects of bricks












• Chuffs:The deformation of the shape of bricks caused by the rain water falling on hot

bricks is known as chuffs.

Defects of bricks














• Laminations

Defects of bricks














• Laminations: Caused by the entrapped air in the voids of clay. Laminations produce

thin lamina on brick faces which weather out on exposure.

Defects of bricks














• Laminations: Caused by the entrapped air in the voids of clay. Laminations produce

thin lamina on brick faces which weather out on exposure.

Special Bricks

Burnt Clay Perforated Bricks(IS-2222)

Special Bricks


• Perforated Bricks contain cylindrical holes throughout thier thickness,have high com-

pressive strength and less water absorption.

Special Bricks




• These bricks are light in weight, require less quantity of clay and drying and burning

of these bricks is easy and economical.

Special Bricks






• The direction of perforations can be vertical or horizontal.

Special Bricks







• These are used in building walls and partitions. The area of perforations should not

exceed 30 to 45% of the area of face.

Special Bricks









• In case of rectangular perforations, larger dimensions should be parallel to longer

side of the brick.Dimension of perforation parallel to short side should not be more

than 20 mm in case of rectangular projection and 25 mm in case of circular projec-

tion.Area of each perforation should not exceed 500mm2

Special Bricks









• In case of rectangular perforations, larger dimensions should be parallel to longer

side of the brick.Dimension of perforation parallel to short side should not be more

than 20 mm in case of rectangular projection and 25 mm in case of circular projec-

tion.Area of each perforation should not exceed 500mm2

Burnt Clay Hollow Bricks(IS-3952)

• Hollow blocks, known as cellular or cavity blocks, are manufactured from a thoroughly

ground, lump free, well mixed clay mass of medium plasticity to allow moulding.




• These are used to reduce the dead weight of the masonry and for exterior as well as

partition walls.





partition walls.

• They also reduce the transmission of heat, sound and dampness.





partition walls.


• Minimum average value should be 3.5 N/mm2. Strength of individual block should

not fall below the average value by more than 20 per cent.





partition walls.




• Water Absorption should not be more than 20 per cent.





partition walls.




• Water Absorption should not be more than 20 per cent.

Fire Clay /Refractory Bricks

• Fire-clay bricks are made from fire-clay.



• Fire-clay is a term applied, to include those sedimentary or residual clays which vitrify

at a very high temperature and which, when so burnt, possess great resistance to

heat.are pure hydrated silicates of alumina and contain a large proportion of silica

55–75%, alumina 20–35%, iron oxide 2–5% with about 1 per cent of lime, magnesia

and alkalis. The greater the percentage of alumina, the more refractory the clay will

be. Fire clays are capable of resisting very high temperatures up to 1700°C without

melting or softening.










• The colour of the brick is whitish yellow or light brown. The water absorption of fire-

clay bricks varies from 4–10%.The minimum average compressive strength of the

bricks should be 3.5N/mm2.













• These are used for lining blast furnances, ovens, kilns, boilers and chimneys.













• These are used for lining blast furnances, ovens, kilns, boilers and chimneys.

Types of Fire Clay Bricks

• Acid Refractory Bricks


• Acid Refractory Bricksconsist of silica bricks (95–97% silica and 1–2% lime) used

in lining furnaces having siliceous and acidic slag, steel industry and coke oven.

The softening temperature ranges from 1700°to 1800°C. Sili ca bricks are hard and

also possess good refractoriness under load. But they have tendency to spall during

rapid temperature change therefore, these can not be used for lining of furnaces

which have to be cooled and reheated frequently.








• Basic Refractory Bricks








• Basic Refractory Bricksconsist of magnesia bricks (magnesia min. 85%, calcium

oxide max. 25% and silica max. 5.5%) and bauxite bricks (min 85% aluminium oxide

and max 20% clay). These are highly resistant to corrosion and are used for lining

furnances having basic slag. Due to high thermal expansion and consequent poor

resistance to spalling the use of these bricks is restricted to copper metallurgy and

basic open hearth.













basic open hearth.

• Neutral Refractory Bricks













basic open hearth.

• Neutral Refractory Bricksconsist of chromite bricks (50% chrome and iron ore con-

taining 30% iron oxide and bauxite containing 15% aluminium and 5% silica), chrome

magnesite bricks (Cr2O3 18%, MgO 30%), spinel and forsterite bricks. The neutral

refractory bricks are suitable at places where acidic and basic linings are to be sep-

arated, e.g. for lining copper reverberatory furnance.













basic open hearth.

• Neutral Refractory Bricksconsist of chromite bricks (50% chrome and iron ore con-

taining 30% iron oxide and bauxite containing 15% aluminium and 5% silica), chrome

magnesite bricks (Cr2O3 18%, MgO 30%), spinel and forsterite bricks. The neutral

refractory bricks are suitable at places where acidic and basic linings are to be sep-

arated, e.g. for lining copper reverberatory furnance.

Assignment

1. What are the constituents of good brick earth?

2. State the harmful ingredients in brick earth.

3. What are the characteristics of a good brick ?

4. Explain briefly the tests performed on bricks as per BIS.

5. Discuss the Classification of bricks.

6. What are the uses of various types of bricks?

7. Distinguish between First Class and Second Class Brick.

8. What are the defects of bricks.

9. Write shortnotes on (i) Bull nose brick (ii) Perforated bricks (iii) Hollow bricks (iv)

Refractory/Fire Bricks.

To be submitted on the next class.

Date post:	29-Nov-2014
Category:	Documents
Upload:	sandip-chandra
View:	223 times
Download:	4 times

Bricks

Documents