Building stones & bricks ..

 1. General Introduction:
The engineering structures are composed
of materials. These materials are known
as the engineering materials or building
materials. It is necessary for an engineer
to become conversant with the properties
of such materials. A building demand wide
range of materials with various properties
such as water-resistance, strength, durability, temp-resistance, appearance,
permeability etc. So these are to be properly studied before making final
selection for any building material for a particular use. As many materials
are used for a single infrastructure to come up. So the grouping of

building materials for construction is done by considering these before
mentioned specific properties of the materials such as stones, ceramics,
cement concrete, timber, metals and bricks etc. So out of all these
materials we will further study in this chapter in detail about the building
stones and bricks.

 Following are the some characteristics of a good building stone:
 Durability (They are durable enough to dress and fit it in structure
easily)
 Hardness (Stones are harder
than other materials)
 Resistance to fire
 Resists Weathering (capable of
withstanding the adverse effects of rain, frost, wind etc.)
 Appearance and Textures (Provides different styles to the
structure)

Possessing such characteristics still stones with
exposed faces when are acted upon by
atmospheric and external agencies gets
deteriorated. Following are the causes of decay of
stones:
Alternate wetness and drying by rain and
sunshine wear out stones quickly.
Frost in cold places makes the moisture present
in the atmosphere deposited in pores of stones.
At freezing temperature it expands and causes
splitting of stones.

 Living Organisms like worms and bacteria act upon stones and
deteriorate them. These organisms makes holes in them and thus weaken
them.
 Impurities in Atmosphere have adverse effects on stones for instance, the
acids and fumes are predominant in
atmosphere in industrial areas in cities
which deteriorates the stones.
 Rain Water has chemical action also
on stones as when it descends through
atmosphere it absorbs CO2 and H2S
gases. These gases acts adversely on
stones and deteriorate them.

 Temperature Variations such as rise and fall of temperature causes
expansion and contraction in stones respectively and frequent
changes like this may result in deterioration of stones.
 Vegetable Growth occurs in stones such as creepers and certain
trees develop with there roots in joints between them. They absorb
moisture and make the stone surface dump and expand to break it
resulting in deterioration.
 Wind contains fine particles of dust.
If it is blowing with high velocity
such particles will strike against
the stone surfaces and thus the
stones will get decayed with the
high pressure.

 The decay of building stones are to some extent prevented, if they
are properly preserved. For this purposes, the preservatives are
applied on the stone surfaces. An ideal preservative has the
following properties:
 It does not allow moisture to penetrate the stone surface.
 It does not develop objectionable colour.
 It is easily penetrated in stone surface.
 It is economical.
 It is non-corrosive and harmless.
 It remains effective for a long time
after drying.
 Its application on stone is easy.

 Following are the preservatives which are commonly used to
preserve the stones:
 Coal Tar: If coal tar is applied on stone surface it preserves stone but the
colour of coal tar produces objectionable
appearance and surface coated with
coal tar absorbs heat of the sun So it
is not generally used.
Paint: An application of paint on stone
surface serves as a preservative.
The paint changes the original colour of
stones. It is applied under pressure if deep penetration is required.
 Paraffin: This preservative may be used alone or it may be dissolved in
neptha and then applied on stone surface. It changes the original colour of
stone.

 Artificial stone is a name for various kinds of synthetic stone
products used from the 18th century onward. They have been
used in building construction and civil engineering work
and industrial uses such as grindstones.

1. A good cast stone should resemble a
natural stone fully to achieve it white
cement with aggregate of the crushed
stone and sand selected to have
matching colour are used.
2. Aggregate must be clean and durable.
3. Pigments used for colouring the cast
stone should be judiciously chosen, so
that they do not interfere with the
setting of cement.
4. They should not be used in a
proportion greater that 15% by
volume of the cement used.
5. Cement and aggregates are usually
mixed in 1:3 proportion.

6. BRICK EARTH:
A. Composition: A good brick
earth should be such that when
prepared with water it can be easily
moulded, dried and burnt without
cracking or warping. It should
contain a small quantity divided
lime to help in binding the particles
of brick together by melting the
particles of sand. A little oxide of
iron should also be present which
would give the brick its peculiar red
colour.
Alumina - 20-30%
Silica - 50-60%
Magnesia - Small
quantity
Lime - Small quantity
Oxide of Iron - Small quantity

 The bricks should be table-moulded, well burnt in kilns, copper
coloured, free from cracks and with sharp and square edges. The
colour should be uniform and bright.
 The bricks should be uniform in shape and should be of
standard size.
 The bricks should give a clear metallic ringing sound when
struck with each other.
 The brick should not absorb water more than 20 percent by
weight for first class bricks and 22 percent by weight for second
class bricks, when soaked in cold water for a period of 24 hours.
 The bricks should have low thermal conductivity and they
should be sound proof.

 The brick earth is classified into following three categories:
1. Loamy, mild or sandy clay: This type of earth consists of
considerable amount of free silica in addition to alumina. The
addition of lime in such clay helps to fuse sand and thereby to
increase hardness of bricks. Also the presence of sand helps in
preventing cracking, shrinking and warping of bricks.
2. Plastic, strong or pure clay: This clay consists of alumina and
silica and it is referred to as strong clay or fat clay. The raw bricks
will crack, shrink and warp during drying if pure clay alone is
used in making bricks

Hence such clay is corrected by the addition of sand and ash.
The sand prevents shrinkage and the ash provides lime to act
as flux.
3. Marls, chalky or calcareous clay: This clay consists of
considerable amount of chalk in addition to alumina and silica.
Such clay generally makes good bricks. But to avoid
undesirable effects of excess lime, the sand is sometimes added
to such clay.

 A brick is generally subjected to the following tests to find out its
suitability for construction work:
 Absorption: A brick is taken and it is weighed dry. It is then immersed in
water for a period of 16 hours. It is weighed again and the differences in
weight indicates the amount of water absorbed by the brick. It should not
in any case exceed 20 percent of weight of dry brick.
 Crushing Strength: The crushing strength
of a brick is found out by placing it in a
compression testing machine. It is pressed
till it breaks. As per BIS: 1077-1957, the
minimum crushing strength of bricks is
3.50 N/mm square. The bricks with crushing strength of 7 to 14 N/m

m square are graded as A and those having above 14 N/mm square are
graded as AA.
 Hardness: In this test, a scratch is made on brick surface with the help of a
finger nail. If no impression is left on the surface, the brick is treated to be
sufficiently hard.
 Soundness: In this test, the two bricks
are taken and they are struck with each
other. The bricks should not break and
a clear ringing sound should be produced.
 Structure: A brick is broken and its structure is examined. It should be
homogeneous, compact and free from any defects such as holes, lumps
etc.

 These bricks are made from fire-clay. These bricks are usually white or
yellowish white in colour. The weight is about 30 to 35 N. They can resist
high temperature without softening and melting. Hence they are used for
linings of interior surfaces of furnaces, chimneys, kilns etc. The
compressive strength for these is between 200 to 220 N/mm square.
Following are three varieties of fire bricks:
1. Acidic Bricks: These bricks are used for acidic lining. Following are the
types of acidic bricks:
 Ordinary fire-bricks
 Silica bricks

2. Basic Bricks: These bricks are used for basic lining and basic refractory
materials are used in the manufacture of such bricks. The magnesia bricks
are prepared from lime and magnesia rocks. The dolomite may also be
adopted for the manufacture of these bricks.
3. Neutral Bricks: These bricks are used for neutral lining. They offer
resistance to the corrosive action of slag's and acid fumes. As compared to
the basic bricks, the neutral bricks are more inert to the slag's. Following
are the types of neutral bricks:
 Chromic bricks
 High alumina bricks

Building stones & bricks ..

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