Note for BASICS OF CIVIL ENGINEERING - BCE By Suman Kumar Acharya

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BRICK A brick is building material used to make walls, pavements and other elements in masonry construction. Traditionally, the term brick referred to a unit composed of clay, but it is now used to denote any rectangular units laid in mortar. A brick can be composed of clay-bearing soil, sand, and lime, or concrete materials. Bricks are produced in numerous classes, types, materials, and sizes which vary with region and time period, and are produced in bulk quantities. Constituents of good brick earth: Bricks are the most commonly used construction material. Bricks are prepared by moulding clay in rectangular blocks of uniform size and then drying and burning these blocks. In order to get a good quality brick, the brick earth should contain the following constituents. 1.Silica 2.Alumina 3.Lime 4.Iron oxide 5.Magnesia Silica o Brick earth should contain about 50 to 60 % of silica. o It is responsible for preventing cracking, shrinking and warping of raw bricks. o It also affects the durability of bricks. o If present in excess, then it destroys the cohesion between particles and the brick becomes brittle. Alumina o Good brick earth should contain about 20% to 30% of alumina. o It is responsible for plasticity characteristic of earth, which is important in moulding operation. o If present in excess, then the raw brick shrink and warp during drying. Lime o The percentage of lime should be in the range of 5% to 10% in a good brick earth. 1

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o It prevents shrinkage of bricks on drying. o It causes silica in clay to melt on burning and thus helps to bind it. o Excess of lime causes the brick to melt and brick looses its shape. Iron oxide o A good brick earth should contain about 5% to 7% of iron oxide. o It gives red colour to the bricks. o It improves impermeability and durability. o It gives strength and hardness. o If present in excess, then the colour of brick becomes dark blue or blakish. o If the quantity of iron oxide is comparatively less, the brick becomes yellowish in colour. Magnesia o Good brick earth should contain less a small quantity of magnesia about1%) o Magnesium in brick earth imparts yellow tint to the brick. o It is responsible for reducing shrinkage o Excess of magnesia leads to the decay of bricks. Classification of Bricks as per common practice: Bricks, which are used in construction works, are burnt bricks. They are classified into four categories on the basis of its manufacturing and preparation, as given below. 1. First class bricks 2. Second class bricks 3. Third class bricks 4. Fourth class bricks First Class Bricks: These bricks are table moulded and of standard shape and they are burnt in kilns. The surface and edges of the bricks are sharp, square, smooth and straight. They comply with all the qualities of good bricks. These bricks are used for superior work of permanent nature. 2

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Second Class Bricks: These bricks are ground moulded and they are burnt in kilns. The surface of these bricks is somewhat rough and shape is also slightly irregular. These bricks may have hair cracks and their edges may not be sharp and uniform. These bricks are commonly used at places where brick work is to be provided with a coat of plaster. Third Class Bricks: These bricks are ground moulded and they are burnt in clamps. These bricks are not hard and they have rough surfaces with irregular and distorted edges. These bricks give dull sound when struck together. They are used for unimportant and temporary structures and at places where rainfall is not heavy. Fourth Class Bricks: These are over burnt bricks with irregular shape and dark colour. These bricks are used as aggregate for concrete in foundations, floors, roads etc, because of the fact that the over burnt bricks have a compact structure and hence they are sometimes found to be stronger than even the first class bricks. Tests on Bricks To know the quality of bricks following 7 tests can be performed. In these tests some are performed in laboratory and the rest are on field. Compressive strength test: This test is done to know the compressive strength of brick. It is also called crushing strength of brick. Generally 5 specimens of bricks are taken to laboratory for testing and tested one by one. In this test a brick specimen is put on crushing machine and applied pressure till it breaks. The ultimate pressure at which brick is crushed is taken into account. All five brick specimens are tested one by one and average result is taken as brick’s compressive/crushing strength. Water Absorption test: In this test bricks are weighed in dry condition and let them immersed in fresh water for 24 hours. After 24 hours of immersion those are taken out from water and wipe out with cloth. Then brick is weighed in wet condition. The difference between weights is the water absorbed by brick. The percentage of water absorption is then calculated. The less water absorbed by brick the greater its quality. Good quality brick doesn’t absorb more than 20% water of its own weight. Hardness test: In this test a scratch is made on brick surface with a hard thing. If that doesn’t left any impression on brick then that is good quality brick. Size, shape and colour test: In this test randomly collected 20 bricks are staked along lengthwise, width wise and height wise and then those are measured to know the variation of 3

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sizes as per standard. Bricks are closely viewed to check if its edges are sharp and straight and uniform in shape. A good quality brick should have bright and uniform colour throughout. Soundness test: In this test two bricks are held by both hands and struck with one another. If the bricks give clear metallic ringing sound and don’t break then those are good quality bricks. Some qualities of good brick are described below: Brick Earth: Brick earth should be free from stones, kankars, organic matter, saltpetre and harmful chemical etc. Size: The bricks should have uniform size, plain, rectangular surfaces with parallel sides and sharp straight edges. Whatever bricks are used for a construction but the bricks should be regular and uniform. Good bricks should not exceed 3 mm tolerances in length and 1.5 mm tolerances in width and height.Standard size of brick is 190x90x90mm Shape: Good bricks should have a uniform in shape. Edges of bricks should be a sharp, straight and right angle. Colour of Brick: Good brick should be well burnt and uniform copper colour. Over burnt and under burnt bricks are losses uniformity of colour on its surface and its strength. Good quality bricks should always be uniform colour throughout. Soundness: Well burnt brick should give a metallic sound when struck with a hammer or another brick. Hardness: The brick should be so hard that when scratched by a finger nail no impression is made. Strength: The Compressive strength of brick should be minimum 35 N/mm2 as per Is code. Texture and Compactness: The surfaces of brick should not be too smooth to cause slipping of mortar. The brick should have precompact and uniform texture. A fractured surface should not show cracks, holes grits or lumps of lime. Water Absorption: Water absorption of good brick should not exceed 20 percent of its dry eight when kept immersed in water for 24 hours. Frog in Brick: Brick should have proper frog, so that the mortar can be properly filled in the frog. The size of frog should be 100 mm in length, 40 mm in width and 10 mm depth. 4