All the building structures are composed of different
types of materials. These materials are either called building
materials or materials of construction. It is very essential for a
builder, may be an architecture or engineer or contractor, to
become conversant thoroughly with these building materials.
The knowledge of different types of material, their properties
and uses for different purposes provides and important tool in
the hands of the builders in achieving economy in material
cost. The material cost in a building ranges 30 to 50 percent
cost of total cost construction. In addition to material
economy, the correct use of material results in better
structural strength, functional efficiency and esthetic
Classification of Rocks
Building stones are obtained from rocks occurring in
nature and classified in three ways.
- Geological classification
- Physical classification
- Chemical classification
According to this classification, the rocks are of the
a. Igneous rocks: Rocks that are formed by cooling of Magana
(molten or pasty rocky material) are known as igneous rocks.
Eg: Granite, Basalt and Dolerite etc.
b. Sedimentary rocks: these rocks are formed by the deposition
of production of weathering on the pre-existing rocks.
Examples: gravel, sandstone, limestone, gypsum, lignite etc.
c. Metamorphic rocks. These rocks are formed by the change
in character of the pre-existing rocks. Igneous as well as
sedimentary rocks are changed in character when they are
subject to great heat and pressure. Known as metamorphism.
Examples: Quartzite, Schist, Slate, Marble and Gneisses.
This classification based on general structure of rocks.
According to this, the rocks are classified into three types
a. Stratified Rocks: These rocks posses planes of stratification
or cleavage and such rocks can be easily split along these
Ex: sedimentary rocks
b. An stratified rocks: The structure may be crystalline
granular or compact granular. Examples: Igneous rocks and
Sedimentary rocks affected by movements of the earth.
c. Foliated Rocks: These rocks have a tendency to split up in a
definite direction only. Ex: Metamorphic rocks.
According to this classification rocks are classified into three
a. Siliceous rocks: In these rocks, silica is predominates. The
rocks are hard; durable and not easily effected by weathering
agencies. Ex: Granite, Quartzite, etc.
b. Argillaceous Rocks: In these rocks, clay predominates. The
rocks may be dense and compact or may be soft.
Ex: slates, Laterites etc.
c. Calcareous rocks: In these rocks, calcium carbonate
predominates. The durability to these rocks will depend upon the
constituents present in surrounding atmosphere. Ex: Lime Stone,
Uses of stones:
- Structure: Stones are used for foundations, walls, columns,
lintels, arches, roofs, floors, damp proof course etc.
2.Face works. Stones are adopted to give massive appearance
to the structure. Wall are of bricks and facing is done in stones
of desired shades. This is known as composite masonry.
- Paving stones: These are used to cover floor of building of
various types such as residential, commercial, industrial etc.
They are also adopted to form paving of roads, foot paths etc.
- Basic material: Stones are disintegrated and converted to
form a basic material for cement concrete, morum of roads,
calcareous cements, artificial stones, hallow blocks etc.
5.Misalliances: Stones are also used for (i) ballast for
railways (ii) flux in blast furnace (iii) Blocks in the
construction of bridges, piers, abutments, retaining walls,
light houses, dams etc.
Qualities of a good building stone:
The following are the qualities or requirements of a good building
- Crushing strength: For a good building stone, the crushing
strength should be greater than l000kg per cm2.
- Appearance: Good building stone should be a uniform
colour, and free from clay holes, spots of other colour bands
etc capable of preserving the colour for longtime.
- Durability: A good building stone should be durable. The
factors like heat and cold alternative wet and dry, dissolved
gases in rain, high wind velocity etc affect the durability.
- Fracture: For good building stone its fracture should be
sharp, even and clear.
- Hardness: The hardness greater than 17, treated as hard used
in road works. It is between 14 to 17, medium hardness, less
14 said be poor hardness.
- Percentage wear: For a good building stone, the percentage
wear should be equal to or less then 3 percent.
- Resistance to fire: A good building stone be fire proof.
Sandstone, Argillaceous stone resists fire quite well
- Specific gravity: For a good building stone the specific
gravity should be greater then 8.7 or so.
- Texture: A good building stone should have compact fine
crystalline structure should be free from cavities, cracks or
patches of stuff or loose material.
- Water absorption: For a good building stone, the percentage
absorption by weight after 24 hours should not exceed 0.60.
- Seasoning: Stones should be well seasoned before putting
into use. A period of about 6 to 12 months is considered to be
sufficient for proper seasoning.
- Toughness Index: Impact test, the value of toughness less
than 13 – Not tough, between 13 and 19 – Moderate, greater
than 19- high
Characteristics of stones
In order to ensure suitable selection of stone of
particular work, one must be conversant with its composition,
characteristics, uses and place of availability.
- Igneous rock
- Composed of quart, felspar and mica and minerals
- Available in grey, green, brown and pink and red
- Hard and durable
- High resistance to weathering
- The texture varies with its quality
- Specify gravity 2.7 and compressive strength 700 to 1300
- Used for ornamental, road metal, railway ballast, aggregate
for concrete; for construction of bridges, piers and marine
- Igneous rock
- It is compact, hard and heavy
3.Available in red, yellow grey, blue and greenish black
- Specific gravity is 3 and compressive strength varies 1530
to 1890 kg/cm2.
- Used for ornamental, rail road ballast, aggregates for
1.4.3 Sand Stone:
- Sedimentary rock
- It is available in variety of formations fine grained, coarse
grained compact or porous
- Available in white, green, blue, black, red and yellow.
- Specific gravity 2.65 to 2.95
- Compressive strength is 650kgs / cm2
- Used for ashlar works
1.4.4 Lime Stone:
- Sedimentary rock: It is available in a variety of forms
which differ from one another in colour Compaction, texture,
hardness and durable
a. Compact lime stone
b. Granular lime stone
c. Magnesia lime stone
d. Kanker lime stone
f. Used for paving, road metal, etc
- Metamorphic rock
- Available in white, blue, green, yellow black and red colour
- High compactness,
- Suitable for decorative works, wall lining columns, pile,
table slabs, hearths, tiled floors, steps of stair case etc.
- Metamorphic rock
- Non absorbent, compact fine grained and produce metallic
ringing sound when struck
- Available in black, dark blue, grey, reddish brown etc.
- Used for providing damp proof course, paving dados etc
Selection of stones
In contemplating the use of stone for various
engineering works, the selection of the nature and quality of
stone is governed by the purpose in view, cost of stone, its
ornamental value and durability Suitability various types of
stones for different purposes and situation is briefly discussed
a. For face work, in general marble, granite and close-grained
sand stone are used in the form of thin slabs (veneers) where
the structure subjected to adverse weather effects.
b. For pillars, balustrade, pedestals, columns statues and door
and window sill and paving stone, granite marble and compact lime stone can be recommend because they can take
c. For ornamental works such as moulding and carvings, finegrained
sand stone, fine grained marble and fine grained
granite are used.
d. For bridges, piers, docks, break-waters and other marine
structures the stone should be very hard, heavy, strong and
durable granite and gneiss are recommended for this purpose
e. For road metal, stones should be hard, tough, resistant to
abrasion and durable. Basalt and course-grained granite are
generally recommended for this purpose.
f. For railway ballast, the stone should be hard, dense, durable,
tough and easily workable sandstone, compact lime stone,
trap and quartzite are commonly used
g. In situation like steps, doors sills, pavings etc where there is a
regular flow of traffic, stone should be hard, dense, easily
workable and durable. Marble, slates and sand stones are
commonly use in such places.
h. In fire proof construction, compact sand stone should always
Artificial stones: These are also known as cast stones or
reconstructed stones. Artificial stones may take up various
forms such as
a. Cement concrete: This is the mixture of cement, fine
aggregates, coarse aggregates and water. It may be cast in site or pre-cast if steel is used with cement concrete, it is known as
reinforced cement concrete.
b. Mosaic tiles: Pre-Cast concrete tiles with marble chips at
top surface are known as tiles. They are available in different
shades and widely adopted at present.
c. Terrazo : This is a mixture of marble chips and cement. It
is used for bathrooms residential buildings, temples etc.
Advantages of artificial stones:
- Cavities may be kept in artificial stones to convey pipes,
electric wires etc.
- Grooves can be kept in artificial stone while it is being cast
which are useful for fixing various fittings.
- It can cast in desired shape
- It can be made in a single piece and hence trouble of getting
large blocks of stone for lintels, beams etc is avoided.
- It can be made stronger than natural stone
- It is cheap and economical
- It is more durable than natural stone
- Natural bed is absent in artificial stones and hence, the
question of taking precautions with respect to the natural bed
of stones does not arise.
Aggregates – Grading: Aggregates is derived from igneous,
sedimentary and metamorphic rocks or is manufacture from
clays, slag etc. The properties of concrete are directly related
to those of its constituents and should be hard, strong, durable, and free from clay, loam, vegetables and other such
foreign matters. The presence of clay or dirt coating prevents
the adhesion of cement on the surface of aggregates and
ultimately retards the setting and hardening of cement and
reduces the strength, durability and soundness of concrete.
Depending upon their size, the aggregates are classified as (i)
Fine Aggregative (ii) coarse aggregates.
(i) Fine Aggregates: The material, most of when passes through
4.75mm I.S. sieve size, is termed as fine aggregates. It should
not contain more than 1 to 8% of fine particles, which may be
obtained from sea, river, lake or pit may be used as fine
aggregates but care should be taken all its impurities must be
(ii) Coarse Aggregates: The material whose particles are of such
size as are retained on 4.75mm, I.S sieve are called coarse
aggregates. The size of the coarse aggregates used depends
upon the nature of work. The maximum size may be 23mm
for mass concrete such as dams etc. and 63mm for plain
concrete. Crushed hard stone and gravel is the common
materials used as coarse aggregates for structural concretes.
Coarse aggregates usually obtained by crashing granite,
gneiss, crystalline lime stone and good variety of sandstone
Grading of Aggregates:
Grading of aggregates consists of proportionating the
fine and coarse aggregates in such a ratio, so as to get
strongest and densest mix with the least amount of cement
Grading the aggregates is so graded as to have minimum
voids when mixed with all ingredients, and water should
render a concrete mass of easy workability.
The grading of aggregates are done by the following methods
(i) By trail – In this method, proportionating of aggregates
as to give heaviest weight for same volume, yield the
(ii) By finesse modules method (sieve analysis method): in
this method, the samples of both coarse and fine
aggregates are passed through a set of nine standard sieve
and the percentage of sample retained on each of the said
sieves is determined. The total of these percentages
divided by 100 gives the finesses modulus of sample
(iii) By minimum voids method: This method is based on the
fact, that so obtain dense concrete the quantity of cement
should also be slightly in excess of voids more that the
fine aggregates. In this method the voids in the fine and
coarse aggregates are separately found out with the help of
graduated cylinder and water. The percentage of voids I
aggregate, “X” given by the equation.
X = (V1 – V2)/ V2 x 100
Where v1, volume of water filled
Where v2, volume of aggregates.
(iv) By arbitrary standards: It is a commonly adopted
method of propitiating the aggregates in a concrete mix for small works of moderate importance. This method is
not recommended for large works or important works in
this method, the volume of cement, sand and coarse
aggregates are taken in the proportion of 1:n:2n
respectively. The quantity of water to be used a varied suit
the workability descried.
Ex: 1:1:2 M250 rich mix for columns, beams
1:1:3 – M200 Water retaining structures etc
1:3:6 – M150 slab’s columns roads etc
1:3:6 – M100 – foundations,
1:4:8 – For mass concrete.