Bricks | CE 010

Preamble

In the previous post CE 009, a preliminary discussion was made on building materials. Some 20 groups of building material was presented, of which, the first one was Brick. Actually, the name of this group would have been well suited as Bricks and Allied Products but the term Brick was kept only to easily memorize the list. Bricks and Allied Products contain three major items, viz., Bricks, Brick Products and Special Bricks.

Burnt clay bricks and heavy duty burnt clay bricks are very popular in construction and will be discussed under section Bricks. Brick bats and dust will be discussed under section Brick Products. Apart from that, a few special types of bricks like fire bricks, fly ash bricks, hollow clay bricks, acid resistance bricks and refractory bricks etc. are also used for some special purpose. These will be discussed under section Special Bricks.

Bricks

General: Brick is a specific and uniform size hard burnt clay unit used as basic building block for civil construction. Bricks are laid in multiple layers with mortars in between each other to form a load bearing or non load bearing wall unit. Wall units constructed in particular plan and design form a building or other brick built structures or structural elements.

Types of Brick

There are two types of burnt clay bricks, viz., Modular brick and Conventional brick. Modular bricks are manufactured by systematic and fully mechanized process whereas conventional bricks are manufactured by comparatively easier and long practiced method of open burning and kiln burning. Modular and Conventional bricks are different both in quality and size. The use of modular bricks has not yet been popularized much in India. Conventional bricks still hold the major share since the manufacturing of it is much easier.

Size of Bricks

The nominal size of a modular brick is 8 in x 4 in x 4 in i.e., 200 mm x 100 mm x 100 mm whereas the nominal size of a conventional brick is 10 x 5 x 3 in i.e., 250 x 125 x 75 mm. But one should keep in mind that it is the nominal size and not the actual size of the brick. Actual size of the brick is always a little less than the nominal size and varies from one place to another. This is intentionally made so that the thickness of the finished wall after plastering becomes 10 in (250) or 5 in (125) or 3 in (75).

Frog of Bricks

The frog of a brick is a cut portion or groove of a brick of about 125 length x 50 width x 3 mm depth. During brick laying work of building construction, this side always appears up. Brick manufacturing companies use to emboss their brand names over here. Technically, mortar placed on this space is used to bind the brick of the next upper layer.

Basic Ingredients of Bricks:

The basic ingredients of bricks are clay, silt and silty sand. They are used in different proportions for manufacturing of different types of bricks. Clay, silt and silty sand are first mixed in a specified proportion and then put to moulds to achieve desired shape. The same are then sun dried in open air for a good bonding and afterwards burnt in fire to obtain a finished brick.

Brick Burning System

There are two types of brick burning system, viz., open burning system and kiln burning system. In open burning system, dry bricks are kept in an open field in such a way that makes a huge perforated stack. These stacks are locally called Open Bhatta or Open Bhatti. Small sized coals are kept in the perforations and fired for a desired time – normally for three to four days. In kiln burning system, dry bricks are kept in regular arrangement in a closed kiln specially designed for burning of bricks. Here, the coal firing is done for a few hours in a very high but controlled temperature of 900 to 1200 degree centigrade so that most of the bricks get more or less equal burning.

Factors Affecting Quality of Bricks

Quality of bricks depends on a number of factors. The first thing that influences the quality of conventional bricks is the quality of its basic ingredients. Good quality and composition of basic materials are not available in all places. Hence, quality of bricks depends on place of manufacturing. The quality of bricks also depends on the burning quality of the kiln or bhatta. Since, temperature in a bhatta is beyond control, kiln bricks are normally better than bhatta bricks. All kilns are not of same quality too. Hence, quality of bricks also varies from one kiln to another. Finally, workmanship is also a factor to build good quality of bricks.

Types of Conventional Brick

Depending on quality, four types of bricks are available in the market, viz., (a) First class bricks, (b) Second class bricks (c) Third class bricks and (d) Heavy duty burnt clay bricks or Jhama bricks.

Quality of Good First Class Bricks

Good first class bricks should be very sound, hard, properly burnt, free from any flaw or crack and homogeneous in texture. These should have uniform shape, size and deep red or copper red color. Good first class bricks should emit metallic sound when struck together and should not absorb water more than 15 % of its own weight.

Engineering Properties of Bricks

Crushing strength and water absorption are considered as common engineering properties of bricks. These are determined in laboratory maintaining standard testing conditions. Crushing strength of brick is determined with the help of a compression testing machine. Load taken by a brick at it's crushing point divided by flat area yields the crushing strength of that brick. The measuring units of crushing strength are Newton per sq mm in SI system, kg per sq cm in MKS system and pounds per square inch in FPS system.

The crushing strength of a third class brick should be at least 3.5 MPa (500 psi). It will be called third class until it attains a value of 7 MPa (1000 psi). A brick of 7 - 10 MPa (1000 - 1500 psi) strength is called second class brick. For a first class brick, the crushing should further increase - ranging from 10 to 12.5 MPa (1500 - 1800 psi). A brick may be called very good first class brick if it attains a crushing strength of 14 MPa (2000 psi).

Water absorption is measured in percentage of brick weight. An oven dried brick is kept immersed in water for 24 hours. The weight of brick increases due to absorption of water. This weight increase divided by the original weight of the brick, expressed in percentage is called water absorption of brick.

A brick with 20% or more water absorption capacity is designated as third class brick. In case of second class brick, this capacity ranges from 20 to 15%. If it further reduces and varies from 15 to 10%, then it is a first class brick. A brick may be called very good first class brick if the capacity further decreases down 10% and attains a value up to 7%.

Heavy Duty Burnt Clay Bricks

All bricks are never burnt equally during the burning process. A few bricks always become over burnt. Due to over burning, these bricks attain more strength but loses uniformity in size and shape. Such bricks are called heavy duty burnt clay bricks. We locally call it Jhama bricks. These are not used for normal wall construction but owing to more strength, these are used as a sub-base of foundation or road pavement.

Brick Products

Heavy duty burnt clay bricks or Jhama bricks are broken into pieces. Many of these pieces are altogether called brick ballast or brick bats. We locally call it Jhama khoa. These materials are independently used as a sub-base of foundation or road pavement. Sometimes, these are also used as a coarse aggregate of lime concrete or cement concrete.

Owing to low engineering properties, third class bricks are seldom used in wall construction. Instead, these bricks are converted to dust and are then call Brick Dust. Locally, we call these Surkhi. Brick dust or Surkhi is used as fine aggregate of lime concrete or lime mortar.

Please Subscribe and Share