GATE Civil Engineering (CE) 2027 Test: Bricks & Brick Masonry - 1 Free

It is present either free as sand or in combination as silicate of alumina. Presence of silica prevents shrinking, cracking or warping of green brick. In the presence of lime and oxide of iron, silica fuses at lower temperature and provides the brick its hardness and durability.

A brick of standard size - (190 mm x 90 mm x 90 mm) is recommended by BIS with mortar thickness, the size of such brick becomes (200 mm x 100 mm x 100 mm) and it is known as nominal size of modular brick.

The ingredients of good brick clay (percent) are:
(i) Silica (50 to 60)
(ii) Alumina (20 to 30)
(iii) Lime (2 to 5)
(iv) Oxide of iron  
(v) Magnesia (< 1)

For good bonding in brick masonry-
(A) All bricks need to be uniform in size.
(B) Bats must be used in each course wherever required to provide adequate bonding.
(C) The vertical joints in alternate courses should fall in plumb.
(D) Surkhi that is finely powdered broken bricks act as adulterant and is usually not used as an additive.

Presence of silica prevents shrinking, cracking or warping of green brick.
A small quantity of lime in finally divided or powdered state is desirable as it reduces shrinkage on drying and acts as flex during burning process enact enabling silica to fuse and bend the brick particles together, The colour of the brick ranges from light yellow to red depending upon the quantity of oxide of iron in clay.