Building Materials- BRICKS Basic Civil Engineering Industrial Extension officer Coaching
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Basic Civil Engineering-set 4
BRICKS
Contents
Brick
๏ฑobtained by moulding good clay into a block, which is dried and then burnt.
๏ฑoldest building block to replace stone
๏ฑManufacture of brick started with hand moulding, sun drying and
burning in clamps
Size
The size of the bricks are of 90 mm ร90 mm ร90 mm and 190 mm ร90 mm ร40 mm.
With mortar joints, the size of these bricks are taken as 200 mm ร100 mm ร100 mm and 200 mm ร100 mmร50 mm
Types of Bricks
Bricks may be broadly classified as:
(i) Building bricks
(ii) Paving bricks
(iii) Fire bricks
(iv) Special bricks
(i) Building Bricks: These bricks are used for the construction of walls.
(ii) Paving Bricks: These are vitrified bricks and are used as pavers.
(iii) Fire Bricks: These bricks are specially made to withstand furnace temperature. Silica bricks
belong to this category.
(iv) Special Bricks: These bricks are different from the commonly used building bricks with
respect to their shape and the purpose for which they are made. Some of such bricks are listed below:
(a) Specially shaped bricks
(b) Facing bricks
(c) Perforated building bricks
(d) Burnt clay hollow bricks
(e) Sewer bricks
( f ) Acid resistant bricks.
Properties of Bricks
(i) Colour: Colourshould be uniform and bright.
(ii) Shape: Bricks should have plane faces. They should have sharp and true right angled corners.
(iii) Size: Bricks should be of standard sizes as prescribed by codes.
(iv) Texture: They should possess fine, dense and uniform texture. They should not possess fissures, cavities, loose grit and unburnt lime.
(v) Soundness: When struck with hammer or with another brick, it should produce metallic sound.
(vi) Hardness: Finger scratching should not produce any impression on the brick
. (vii) Strength: Crushing strength of brick should not be less than 3.5 N/mm2. A field test for strength is that when dropped from a height of 0.9 m to 1.0 mm on a hard ground, the brick should not break into pieces.
(viii) Water Absorption: After immercingthe brick in water for 24 hours, water absorption should not be more than 20 per cent by weight. For class-I works this limit is 15 per cent.
(ix) Efflorescence: Bricks should not show white patches when soaked in water for 24 hours and then allowed to dry in shade. White patches are due to the presence of sulphateof calcium, magnesium and potassium. They keep the masonry permanently in damp and wet conditions
. (x) Thermal Conductivity: Bricks should have low thermal conductivity, so that buildings built with them are cool in summer and warm in winter.
(xi) Sound Insulation: Heavier bricks are poor insulators of sound while light weight and hollow bricks provide good sound insulation.
(xii) Fire Resistance: Fire resistance of bricks is usually good. In fact bricks are used to encase steel columns to protect them from fire.
Tests on Bricks
to find their suitability:
(i) Crushing strength
(ii) Absorption
(iii) Shape and size and
(iv) Efflorescence.
(i) Crushing Strength:
The brick specimen are immersed in water for 24 hours.
The frog of the brick is filled flush with 1:3 cement mortar and the specimen is stored in damp jute bag for 24 hours
and then immersed in clean water for 24 hours.
The specimen is placed in compression testing machine with 6 mm plywood on top and bottom of it to get uniform load on the specimen.
Then load is applied axially at a uniform rate of 14 N/mm2 .
The crushing load is noted. Then the crushing strength is the ratio of crushing load to the area of brick loaded. Average of five specimen is taken as the crushing strength.
(ii) Absorption Test:
Brick specimen are weighed dry. Then they are immersed in water for a period of 24 hours. The specimen are taken out and wiped with cloth. The weight of each specimen in wet condition is determined. The difference in weight indicate the water absorbed. Then the percentage absorption is the ratio of water absorbed to dry weight multiplied by 100. The average of five specimen is taken. This value should not exceed 20 per cent.
(iii) Shape and Size:
Bricks should be of standard size and edges should be truelyrectangular with sharp edges. To check it, 20 bricks are selected at random and they are stacked along the length, along the width and then along the height.
For the standard bricks of size 190 mm ร90 mm ร90 mm.
IS code permits the following limits:
Lengthwise: 3680 to 3920 mm
Widthwise: 1740 to 1860 mm
Heightwise: 1740 to 1860 mm
field tests help in acertainingthe good quality bricks:
(i) uniformity in size
(ii) uniformity in colour
(iii) structure
(iv) hardness test
(v) sound test
(vi) strength test
Classification of Bricks Based on their Quality
(i) First class bricks
(ii) Second class bricks
(iii) Third class bricks and
(iv) Fourth class bricks
(i) First Class Bricks:
These bricks are of standard shape and size. They are burnt in kilns. They fulfill all desirable properties of bricks.
(ii) Second Class Bricks:
These bricks are ground mouldedand burnt in kilns. The edges may not be sharp and uniform. The surface may be some what rough. Such bricks are commonly used for the construction of walls which are going to be plastered.
(iii) Third Class Bricks:
These bricks are ground mouldedand burnt in clamps. Their edges are somewhat distorted. They produce dull sound when struck together. They are used for temporary and unimportant structures.
(iv) Fourth Class Bricks:
These are the over burnt bricks. They are dark in colour. The shape is irregular. They are used as aggregates for concrete in foundations, floors and roads
Uses of Bricks
Bricks are used in the following civil works:
(i) As building blocks.
(ii) For lining of ovens, furnaces and chimneys.
(iii) For protecting steel columns from fire.
(iv) As aggregates in providing water proofing to R.C.C. roofs.
(v) For pavers for footpaths and cycle tracks.
(vi) For lining sewer lines
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