Ever wondered what is Bitumen? What is Asphalt? What is difference between these two? What is MC 30 Bitumen? What is cutback bitumen? We will learn all these in this blog. You can watch YouTube video tutorial here.
Bitumen and Asphalt
ü Asphalt = Aggregate + Bitumen {In India}
ü Asphalt = Bitumen {In America}
So, meaning of Asphalt and bitumen varies according to
country as well. Beware where you use this term. We will follow Asphalt =
Aggregate + Bitumen throughout this blog.
Bitumen is binding material like cement and Asphalt is
obtained by mixing aggregate and bitumen. So, you can say, bitumen is analogous
to cement while asphalt is analogous to concrete.
Bitumen vs Coal tar
ü Bitumen is produced from
fractional distillation of crude oil (i.e., raw oil or oil in natural state).
In fractional distillation, different material distills as different temperature
and get separated from mixture.
ü Coal tar is produced destructive
distillation of coal and wood in absence of air. Destructive distillation means
by burning.
ü Both are black in color.
Requirement of Bitumen
ü Not more sensitive to temperature
i.e., should not
become too soft or unstable during hottest weather and should not become too
brittle causing crack during cold weather.
ü Adequate viscosity at the time of mixing which can
be achieved by using cutback bitumen or emulsion bitumen of suitable grades or
by heating bitumen and aggregate before mixing.
ü Adequate adhesion i.e., when bitumen is too fluid,
it losses adhesion and when bitumen is too viscous, it is adhesive but cannot
be applied effectively.
Bitumen as last end product
LPG à Gasoline à Petrol à Kerosene à Diesel à Lubricant à Oil à Wax à Bitumen
As you
move towards right, viscosity increases while as you move towards left in the
list, viscosity decreases. It means LPG is least viscous while bitumen is most
viscous in the above list.
Cutback Bitumen
ü It is a type or grade of bitumen
ü It is liquid bitumen
ü Cutback means reduce something
and in Cutback bitumen, Viscosity is temporarily reduced by adding volatile oil
ü After application, the oil
evaporates and bitumen gains its original viscosity
Types of Cutback Bitumen
ü If oil is highly volatile then it
evaporates quickly and vice-versa. Based on how quickly, the oil evaporates,
there are three types-
1.
Rapid Curing (RC)
2.
Medium Curing (MC)
3.
Slow Curing (SC)
The types are described below-
1.
RC à
Manufactured by solving bitumen in gasoline. It is recommended for surface
dressing and patchwork.
2.
MC à
Manufactured by solving bitumen in kerosene. It is recommended for premix with
less quantity of fine aggregate.
3.
SC à
Manufactured by solving bitumen in Gasoil or fuel oil or directly from
distillation of crude oil. It is recommended for premix with appreciable
quantity of fine aggregate.
Generally,
MC is used in road. So, we will discuss about MC here.
Medium Curing (MC)
ü Now we know that MC-30 is grade of cutback bitumen.
ü MC-30 means Medium Curing 30. But
what does 30 represents here?
ü MC grades are of following types:
Ø MC-30, MC-70, MC-250, MC-800, and MC-3000
ü The number in grade indicates
viscosity. Hence 30 represents minimum viscosity of bitumen.
ü MC grades do not immediately
break when comes in contact with aggregate so, it is designed to be mixed with
aggregates.
ü Of the above-mentioned grades, we
will discuss about MC-30 and MC-70.
MC-30 and MC-70
ü MC-30 has the lowest viscosity
ü MC-70 is commonly used as prime
coat
ü MC-30 is used for WBM (Water
bound Macadam)
ü MC-70 is used for stabilized soil
base/crusher run Macadam
The table below shows viscosity of the above-mentioned
grades.
|
Grade of Cut back Bitumen |
Kinematic viscosity at 60oC (140oF) (mm2/s) |
|
|
Minimum |
Maximum |
|
|
MC-30 |
30 |
60 |
|
MC-70 |
70 |
140 |
Advantage of Cutback Bitumen
ü Cutback bitumen reduces viscosity
so that it can penetrate pavements more effectively or it can be sprayed at
cold temperature where neat bitumen cannot be successfully sprayed
ü Penetration grade bitumen has a
thermoplastic property which causes material to soften at higher temperature
and harden at lower temperature
ü Fluidity of bitumen is obtained
by raising temperature but when it is needed to have fluidity at lower
temperature, cutback bitumen is employed
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