Brick Masonry

Bricks are still one of the most popular materials for construction of walls on account of its ready availability, ease of handling and construction, and economy. 

Bricks 

Bricks are made from ordinary clay, moulded and burnt in kilns. They can be hand moulded or machine pressed or extruded and wire cut. They should be well burnt, of uniform colour, free from cracks and nodules of free lime. They have, generally, a depression on one flat face, known as a 'frog'which  enables better keying of the mortar joint.  Bricks are available in the traditional nominal dimensions of 22.9 x 11.4 x 7.5 cm (actual 22.5 cm x 11.1 cm x 7 cm) or modular nominal sizes of 20 cm x 10 cm x 10 cm (actual 19 cm x 9 cm x 9 cm). 

The traditional brick sizes vary in different parts of the country with length from21 to 25 cm, width 10 to 13 cm and height 7 to 7.5 cm. With a view to achieve uniformity of size throughout the country, the modular size of bricks was standardised by Indian Standards Institution (now the Bureau of Indian Standards). 

Classification of Bricks 

Common burnt clay bricks are classified on the basis of compressive strength as given in Table. 

  Classification of Bricks

Tolerance on bricks dimension shall be 3% for designation 10 and above and 8% for lower designations. Dimensional accuracy of bricks is necessary for ensuring proper bond. This is tested by selecting 20 bricks at random and laying them on a level surface in touch with each other in a straight line and measuring the total length and calculating the variation with respect to the standard dimension. 

Other important tests to be conducted on bricks are for compressive strength, water absorption and efflorescence. For bricks of designation 10 and above one test each shall be done for every 50,000 bricks, while for lower designations the tests can be carried out for every 1 lakh bricks. 

Compressive strength shall be taken as the average strength of five specimens. However, no value shall be less than 20% of the specified value. The bricks shall be immersed in water for 24 hrs at 27 + 2. The surplus water is allowed to drain off. The frog of the bricks should be filled with 1 : 3 cement mortar flush to the surface and shall be cured under jute bags for 24 hr. The bricks shall then be immersed in water for 72 hr. The bricks after removal shall be wiped clean. Then the brick shall be placed in the compression testing machine with the flat face horizontal and mortar filled frog upward. Load shall be applied at a uniform rate of 

140 kg/cm2 after placing a plywood sheet on its top . The compressive strength is the load at failure of the brick, divided by surface area of the brick and is expressed as kg/cm2. Average of five results shall be taken as the relevant value. 

Water absorption shall not exceed 20% by weight upto class 12.5 and 15% by weight for upper classes. Five bricks shall be tested for water absorption. The bricks shall be dried m an oven at 110' to 115'C till they attain a constant weight. They shall be allowed to cool at room temperature. The cooled bricks shall be weighed. Then they shall be immersed in water at 27'C + 2'C  for 24 hrs. After removal they shall be wiped clean and weighed again. The difference between the two weights as a percentage of the dry weight shall be calculated and the average of the results for five bricks shall be reported as the value of water absorption. 

Efflorescence is the crystallisation of water soluble salts in the bricks and results in white powder on the surface of the bricks, which may result in surface disintegration of the brick work. It is therefore necessary to test the bricks for efflorescence. Distilled water is partially filled in a shallow pan and five bricks are placed on their end so that they are immersed in the water to a depth of 2.5 cm. The bricks are allowed to absorb the whole water. Distilled water is again poured into the dish to a depth of 2.5 cm and the water allowed to get absorbed and evaporate as before. Bricks shall be examined after the second evaporation for efflorescence. Efflorescence shall be classified as 'nil' if there is no perceptible deposit of salts, 'slight'  when not more than 10% of the area is covered with a thin deposit of salt, 'moderate' when there is heavier deposit covering upto 50% of the area, but unaccompanied by powdering or flaking of the surface, 'heavy' when heavy deposit covers 50% or more of the surface but unaccompanied by powdering or flaking, and 'serious'  when there is heavy deposit of salts accompanied by powdering and/or flaking of the surface. Bricks having efflorescence beyond 'moderate' shall not be used.