4. BITUMEN:
Bitumen is a hydrocarbon in composition
containing 85% carbon, 12%hydrogen and
3% oxygen. It is a product derived during the
distillation of petroleum from the residue left
behind. It may occur in gaseous, liquid, semi-
solid or solid form. When in liquid form, it is
designated as naphtha of petroleum. The solid
form is commonly designated as Bitumen.
Being a hydrocarbon it is completely
dissolved by carbon disulphide.
5. Characteristics:
Following are the main characteristics of
Bitumen:
(i) Its colour is black.
(ii)Often it is in solid or semi-solid form.
(iii)It is a sticky substance.
(iv)It is a light material with specific
gravity 1.10.
(v)It is completely dissolves in carbon
disulphide.
6. Uses of Bitumen:
The main large-scale use of bitumen is
for the making of flexible pavements,
i.e. roads and high ways. It is also
used as water proofing agent in
building construction. Due to flexible
and water proof material, it is also
used for filling joints between
concrete slabs.
7. Types of Bitumen:
The main types of bitumen are given as
under:
(1) Straight-Run Bitumen:
This is the bitumen obtained straight from the
petroleum distillation. It is an oily substance
with comparatively lesser viscosity and can
be even sprayed.
8. (2) Blown Bitumen:
This variety is comparatively thick and
elastic. It is obtained by blowing air
through bitumen at a high temperature.
In doing so, the bitumen is partly oxides
and becomes thick and elastic. It has
high binding power; therefore it is
extensively used in the constructional
works.
9. (3) Bitumen Emulsion:
This type of bitumen is a liquid with aqueous
medium containing 50 to 60 % bitumen in a
finely divided form. It is prepared by
stirring and mixing vigorously the mixture
of hot water, molten bitumen and some
resinous substances which acts as the
emulsifying agent. It is used for making
and repairing roads. It is also used for
coating cast iron pipes (being water proof).
10. (4) Cut-back Bitumen:
This is a solution of the bituminous material in
a volatile solvent. Actually the volatile
products are removed by distillation of
petroleum. In this case the volatile
component called cut is added back to the
solid bitumen. It contains about 20% solvent
and 80% bituminous materials. The solvents
used include kerosene oil, petrol. It is used
for road making, more commonly for road
repair work.
11. (5) Plastic Bitumen:
It is mix consisting of bitumen, inert
filler and a thinner. It is suitable for
filling joints in the concrete slabs as it
has a good binding power and it has a
good binding power and it is water
repellent.
12. ASPHALT:
Asphalt is a solid or semi-solid product
left behind during the distillation of
petroleum. In composition, it is actually
a mixture of bitumen and certain inert
mineral matter, like silica, alumina and
lime. As such, it is only partly soluble in
carbon disulphide.
13. Characteristics of Asphalt:
Main characteristics of Asphalt are as under:
(1) It has a brownish-black colour.
(2) It is solid or semi solid material.
(3) It is moderately elastic.
(4) It is partly soluble in carbon disulphide.
(5) It does not absorb water.
(6) It has resistance to acids.
(7) It is soft, plastic, and workable when heated.
(8) It has high binding power.
(9) It is good insulator for heat, electricity and
sound.
(10) It is never solid hard and brittle.
14. Uses:
Main uses of Asphalt are as under:
It is mainly used for the construction of flexible
pavements i.e. Roads (highways).
To give ling to the swimming pools and other
water tanks.
As D.P.C in the building construction works.
It is used as water - proof cover for the roofs.
It is also used in the preparing of paints.
15. Types:
There are two main types known as Natural Asphalt and
Residual Asphalt.
Natural Asphalt:
It is the asphalt that occurs in nature. It is just collected
and used. If at all any purification is required, it is done
by simple melting and boiling. At some places it is found
in the lakes, as in South Africa, described as Lake
Asphalt. It contains as much as 70% bitumen and some
water and other impurities. It is easily purified by heating
and boiling. In doing so, the water content escapes, the
impurities rise up, leaving the bituminous matter beneath.
This refined asphalt is suitable for making flexible
pavements.
16. Another type of natural asphalt is known
as rock asphalt, found in the rocks. It is a
mix of rocky matter and bitumen. The
%age of bitumen is about 10 to 15 %. It
can be used as such for road making. The
rock asphalt is just crushed and spread
along the road. It is then heated and
processed by rolling.
17. (2) Residual Asphalt:
This is the solid or semi-solid material
left behind after the distillation of
petroleum. It is commonly known as
artificial asphalt.
In addition to the above two types on the
basis of mode of occurrence, there are
few more types which are actually the
finished products prepared from raw
asphalt. These include:
19. TAR:
Tar is a highly viscous black coloured sticky
substance derived from coal, wood or shales. It
contains 70 % to 95% bituminous matter.
However, its characteristics depend upon the
raw material from which it is extracted and the
amount of residual matter present in it. The
method of distillation is used for the extraction
of tar from its raw materials.
This is also used for the making of roads
(flexible pavements), also used as a preservative
for the timber.
20. Types:
Depending upon the raw materials
from which the tar is derived, there
are three types described as:
Coal Tar,
Wood Tar,
Mineral Tar.
