Classification and testing of bricks

Classification- storing- dimensions of bricks

1. Classification of Bricks

2. Types of Bricks Wired-cut bricks Pressed bricks Four types of brick in the market Ground moulded bricks fired in temporary clamps. Dimensions of bricks are not regular. Table moulded bricks fired in kilns and also called stock bricks. Machine moulded bricks fired in continuous kilns and also known as wire cut bricks. Pressed bricks made under pressure. These bricks are used of decorative works.

3. Dimensions of Bricks Bricks are made in traditional size and also in metric size prescribed by Bureau of Indian Standards. Depression made at the top of a brick is called “FROG”. Brickwork constructed with the frog laid facing upwards. It is a key to the mortar to bond bricks together.

4. Weight of Brickwork Deadweight 18 to 19 kN /m 3 Average weight 3 to 3.5kg depending on its denseness. Lightweight hollow bricks can be as low in weight as only 1/3 the weight of a common brick.

5. Storing of Bricks They are not stored for long periods, usually used up in construction as soon as they delivered at site. Each truckload should be piled in separate stacks on the ground. It should be stored in covered sheds during rainy season for weak bricks.

6. Bricks for special use Facing bricks Fireclay bricks Acid – Resisting bricks Forsterite bricks Silicon carbide bricks

7. Light – weight bricks In tall buildings, to reduce the deadweight of walls and thus, reduce the load on the foundation. In partition walls, to reduce weight and insulate them from sound. In walls above cantilever beams to reduce the weight. It can be made using by any one of the following methods, As solid bricks made from clay mixed with combustible materials which burn off during leaving a porous, light brick the fire. Hollow bricks contains hollow with ribs. Usually made from tile clay as the ribs have to be thin and strong. Available in many sizes including bricks of standard sizes.

8. Brick Substitutes As bricks made from clay excavated from earth, availability of good brickearth is less. So it is necessary to produce bricks from industrial waste or other raw materials. Flyash bricks Sandlime bricks (or) Calcium silicate bricks Cement and Concrete blocks

9. Flyash Bricks Made from flyash which is a raw materials from burning of coal or lignite from various industries especially in power house. Lime or cement is also added to give the bricks required strength. Government also encourages this use of the waste product by giving concessions in its manufacture.

10. Silicate bricks Made by autoclaving sandlime bricks (sand, lime, water and pigments for colour ) with high pressure steam in special chambers. High energy cost

11. Classification of bricks Mainly classified according to their use, physical requirements and I.S classification According to their use Common bricks Engineering bricks (Bricks carrying heavy loads) Fire bricks Specials (Special shapes)

12. According to general physical requirements Class I Class II Class III General requirements Uniform color, thoroughly burnt, rectangular faces with parallel sides and sharp straight right angled edges, compact and uniform texture. Uniform colour , and maybe slightly overburnt . Bricks are slightly distorted and have round edges. Fine compact and uniform texture. maybe slightly overburnt or overburnt . Distorted and have round edges. Defects in uniformity and shape Water absorption Not more than 20% by weight Not more 22% by weight Not more than 25% by weight Efflorescence Slight Slight Moderate

13. I.S classification of bricks according to strength Class Designation Compressive strength Additional requirements 10 10 N/mm 2 Dimensional tolerance _+ 3%, Surface must be smooth, Should have a ringing sound. 7.5 7.5 N/mm 2 Dimensional tolerance _+ 8%, 5 5.0 N/mm 2 Dimensional tolerance _+ 8%, 3.5 3.5 N/mm 2 Dimensional tolerance _+ 8%,

14. Tests for bricks Compressive Strength Five bricks are taken at random and their dimensions are measured Immersed in water of 25 C to 29 C for 24 hrs. Surplus moisture is allowed to drain and the frog, if any, is filled with mortar 1:3. It is kept under a jute bag for another 24hrs after which it is immersed in clean water for 3 days. At the time of testing, these bricks are removed from water, wiped dry and placed with the flat surface between plywood sheets each of 3mm thickness. This specimen is kept under UTM and load is applied. The compressive strength should note down.

15. Water absorption Five bricks taken for test. They are allowed to dry in an oven at 110 C to 115 C till they attain a constant weight usually takes place in 48 hrs. Then they are cooled at room temperature, which generally takes 4 to 6hrs without a fan and weight W 1 is measured. Then they kept in clear water at 29 C for 24 hrs and wiped dry with a damp cloth and weight W 2 is measured. The average percentage of water absorbed as percentage of dry weight is reported.

16. Efflorescence Five samples are taken and the bricks are placed vertically in a dish 30cmX20cm approximately in size with 2.5 cm immersed in distilled water. The water is allowed to be absorbed by the brick and evaporated through it. NIL – there is no perceptible deposit of salt. Slight – Not more than 10% of the area of brick is covered with salt Moderate – heavy deposit covering upto 50% of the area of the brick Heavy – Heavy deposit covering more than 50% of the area of the brick.

17. Dimensional tolerance: Bricks are selected at random to check measurement of length, width, height. Variations in dimensions are allowed only within narrow limits, -+3% for class one and -+8% for other classes Hardness: A scratch is made on the surface of the brick with the finger nail. In good brick, no impression will be left on he surface. Soundness : Two bricks are taken, one in each hand and they are struck with each other slightly. A clear ringing sound should be produced and the bricks should not get break.