Bricks Flashcards
Composition of good bricks
- ALUMINA ( 20 to 30 % )
- SILICA ( 50 to 60 % )
- LIME
- OXIDE OF IRON ( 5 to 6 % )
- MAGNESIA
This constituent imparts plasticity to earth so
that it can be molded if present in excess, raw bricks
shrink and warp during drying and burning
Alumina
prevents cracks, shrinking
and warping of raw bricks.
Silica
A small quantity desirable in a
finely powdered state to prevent shrinkage
of raw bricks.
Lime
Excess makes bricks dark blue or blackish, 5 to 6 percent is desirable in good
brick to impart red color to bricks
Oxidation of Iron
A small quantity in brick earth
imparts yellow tint to bricks, and decreases
shrinkage.
But excess may decreases and shrink
leads to the decay of brick.
Magnesia
These bricks can only be used in the
constructions of temporary and cheap
structures.
●
Such bricks should not be used at places
exposed to heavy rains
Sundried bricks
FIRST CLASS BRICKS - these bricks are
table molded and of standard shape
SECOND CLASS BRICKS - these bricks
are ground molded and they are burnt in
kilns. T
THIRD CLASS BRICKS - these bricks are
ground molded and they are burnt in clamps
Burnt bricks
Tests for bricks
- Absorption
- Crushing Strength or Compressive Strength
- Hardness
- Shape and size
- Soundness
A good brick should not absorb more than
20% of water by weight, when placed in
water for 24 hours
Water absorption
found by placing it in a compression testing
machine. It is pressed till it breaks.
Minimum crushing strength of brick is
35kg/cm2 and for superior bricks, it may
vary from 70 to 140kg/cm2.
Crushing strength
Good bricks should be hard and should not
be scratched by fingernails.
Hardness
A good brick should have a uniform
rectangular shape with even surfaces and
sharp corners. It should be free from cracks.
It should have a uniform brick-red color.
Shape and size
