CE 251 Lecture 2

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Dr Rajib ChowdhuryDepartment of Civil Engineering

IIT Roorkee

Module CE-251

Building Materials,Construction and Estimation

Lecture 2: Clay Products - Bricks

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CE-251 - 2Clay products: Bricks

Clay products are one of the most important classes of structural materials.

The raw materials used in their manufacture are clay blended with quartz,sand, slag, sawdust and pulverized coal.

Structural clay products or building ceramics are basically fabricated bymoulding, drying and burning a clay mass.

Clay is the most important raw material used for making bricks.

Purest clays consist mainly of kaolinite (2SiO2.Al2O3.2H2O) with smallquantities of minerals such as quartz, mica, felspar, calcite, magnesite, etc.

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One of the oldest building material brick continues to be a most popular andleading construction material because of being cheap, durable and easy to

handle and work with.

Clay bricks are used for building-up exterior and interior walls, partitions,piers, footings and other load bearing structures.

The length, width and height of a brick are interrelated as below:

! Length of brick = 2 !width of brick + thickness of mortar

!

Height of brick = width of brick

Size of a standard brick (also known as modular brick) should be 19 !9 !9 cmand 19 ! 9 ! 4 cm. When placed in masonry the 19 ! 9 ! 9 cm brick withmortar becomes 20 !10 !10 cm.

Brickswith Frog

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Classification of Bricks

First Class Bricks

Second Class Bricks

Third Class Bricks

Fourth Class Bricks

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Classification of Bricks

Second Class Bricks are supposed to have the same requirements as the first classones except following:

! Small cracks and distortions are permitted.

! A little higher water absorption of about 1620% of its dry weight is allowed.

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

Third Class Bricks are underburnt. They are soft and light-coloured producing adull sound when struck against each other. Water absorption is about 25 per cent ofdry weight.

Fourth Class Bricks are overburnt and badly distorted in shape and size and arebrittle in nature.

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Use of different class of Bricks

First Class Bricks recommended for pointing, exposed face work in masonrystructures, flooring and reinforced brick work.

Third Class Bricks used for building temporary structures.

Fourth Class Bricks used for foundation and floors in lime concrete and roadmetal.

Second Class Bricks recommended for all important or unimportant hiddenmasonry works and centering of reinforced brick and reinforced cement concrete

(RCC) structures.

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Classification of Bricks according to Indian Standard (IS: 1077)

Class Av. Comp. Strength not less than (N/mm2)

35 35

30 30

25 25

20 20

17.5 17.5

15 15

12.5 12.5

10 10

7.5 7.5

5 5

3.5 3.5

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Characteristics of Good Bricks

Size and Shape The bricks should have uniform size and plane, rectangularsurfaces with parallel sides and sharp straight edges.

Texture & Compactness The surfaces should not be too smooth to cause slipping

of mortar. The brick should have pre-compact and uniform texture. A fracturedsurface should not show fissures, holes grits or lumps of lime.

Hardness & Soundness The brick should be so hard that when scratched by afinger nail no impression is made. When two bricks are struck together, a metallicsound should be produced.

Colour The brick should have a uniform deep red or cherry colour as indicative ofuniformity in chemical composition and thoroughness in the burning of the brick.

Water Absorption should not exceed 20 per cent of its dry weight when kept

immersed in water for 24 hours.

Crushing Strength should not be less than 10 N/mm2

Brick Earth should be free from stones, kankars, organic matter, saltpetre, etc.

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Ingredients of Good Brick Earth

Composition Amount

Silica 50-60%

Alumina 20-30%Lime 10%

Magnesia

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Functions of Various Ingredients

Silica It enables the brick to retain its shape and imparts durability, preventsshrinkage and warping. Excess of silica makes the brick brittle and weak on burning.

Alumina absorbs water and renders the clay plastic. If alumina is present in excessof the specified quantity, it produces cracks in brick on drying.

Lime

!

Reduces the shrinkage on drying.

! Causes silica in clay to melt on burning and thus helps to bind it.

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Functions of Various Ingredients

Iron

!

Provides red colour on burning when excess of oxygen is available and darkbrown or even black colour when oxygen available is insufficient, however,excess of ferric oxide makes the brick dark blue.

!

Improves impermeability and durability.

! Tends to lower the fusion point of the clay, especially if present as ferrousoxide.

! Gives strength and hardness.

Magnesia exceeding 1%, affects the colour and makes the brick yellow, in burning;it causes the clay to soften at slower rate than in most case is lime and reduceswarping.

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Additives in Bricks

Certain additives such as fly ash, sandy loam, rice husk ash, basalt stone dust, etc. areoften required:

! To modify the shaping, drying and firing behavior of clay mass,

! To help conserve agricultural land and utilize waste materials available inlarge quantities.

Some of the basic physio-chemical requirements of conventional additives are asfollows:

! Fly Ash

! Sandy Loam

! Rice Husk Ash

! Basalt Stone Dust

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Processes in Brick Manufacturing

Unsoiling Digging Weathering Blending Tempering

Moulding

Drying

Burning

Brick

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Testing of Bricks

Water Absorption Test [IS: 3495 (Part III)]

" The existence of minute pores confers marked capillary properties on brick ceramics.In particular all bricks absorb water by capillary action.

" The percentage of water absorption is a very valuable indication of the degree ofburning.

"

Water absorption does not necessarily indicate the behavior of a brick in weathering." Low absorption (< 7 %) usually indicates a high resistance to damage by freezing,

although some type of bricks of much higher absorption may also be frost resistance.

" 24 Hours Immersion Cold Water Test:

=

Ws

!Wd

Wd

"100The water absorption in %

This should not be more than 20% for First Class brick and not more than 22% for Second Classbrick.

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Testing of Bricks

Compressive Strength Test [IS: 3495 (Part I)]

" This can be determined by subjecting a brick to compressive loads in a compressiontesting machine.

" Determine the load at which the brick breaks down.

" The load producing fracture, divided by the area of surface taking the load gives

crushing strength of the brick." This varies from 70 140 kg/cm2for First Class bricks. Minimum crushing strength is

35 kg/cm2.

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Testing of Bricks

EfflorescenceTest [IS: 3495 (Part III)]

" The ends of the brick are kept in a 150 mm diameter porcelain or glass dishcontaining 25 mm depth of water at room temperature (20 30C) till the entire wateris absorbed or evaporated.

" The water is again filled to 25 mm depth in the dish and allowed to be absorbed bythe brick or evaporated. Presence of efflorescence is classified as below.

Nil When the deposit of efflorescence is imperceptible.

Slight When the deposit of efflorescence does not cover more than 10%of the exposed area of the brick

Moderate When the deposit of efflorescence is more than 10% but less than50% of the exposed area of the brick.

Heavy When the deposit of efflorescence is more than 50% but thedeposits do not powder or flake away the brick surface.

Serious When the deposits are heavy and powder or flake away thebrick surface

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Defects of Bricks

Over-burning bricks Under-burning bricks

Black Core When brick-clay contains bituminous matter or carbon and they arenot completely removed by oxidation, the brick results in black core mainly because ofimproper burning.

BloatingThis defect observed as spongy swollen mass over the surface; caused dueto the presence of excess carbonaceous matter and sulphur in brick-clay.

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.

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Defects of Bricks

Checks/Cracks This defect may be because of lumps of lime or excess of water.

ChuffsThe deformation of the shape of bricks caused by the rain water falling onhot bricks is known as chuffs.

Blisters Broken blisters are generally caused on the surface of sewer pipes and draintiles due to air imprisoned during their moulding.

Spots Iron sulphide, if present in the brick clay, results in dark surface spots on thebrick surfaces. Such bricks though not harmful are unsuitable for exposed masonrywork.

Laminations Caused by the entrapped air in the voids of clay.

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Questions

What are properties of First Class bricks?

Describe how bricks are classified?

Write short note on process of brick manufacturing.

What are the constituents of good brick-earth?

Describe the common defects in bricks?

Describe briefly the tests to which bricks may be put before using them forengineering purposes.

What is a frog? State its importance in clay bricks.

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CE 251 Lecture 2