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TYPES
OF BITUMEN

  There are few types of bitumen that can be
found with different properties, specification and the uses are based on the
requirement of the industry. Bitumen is available in variety of grade types
which are penetration grade bitumen, oxidized bitumen grade, cut-back bitumen,
bitumen emulsion and polymer modified bitumen.

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  Penetration grade bitumen is refinery bitumen
that is manufactured at different viscosities. To characterise bitumen based on
their hardness, penetration test need to be carried out. Thus, it was named by
penetration bitumen. The range of penetration grade bitumen for road bitumen is
from 15 to 450. But the range that commonly used is 25 to 200. By fluxing the
residual bitumen with oils under partial control could bring the required hardness
of the bitumen. The BS EN 1426 and BS EN 1427 provide the penetration and
softening point values for the respective grades, as from Table-1. This will be
a big help in identifying the equiviscosity of the bitumen grade and its
hardness. Penetration values represent the grades for example, 40/60 as a penetration
value of 50 ± 10. The BS EN 13303 also gives the measure of loss on heating
with respective limits for all penetration bitumen grades. This measure is to
ensure that there are no volatile components present. So, no component whose
loss will contribute to the setting and hardening of bitumen during its
preparation or lay course is undergone. The BS EN 12592 provides the solubility values to ensure that there are
less or no impurities in the bitumen material. The advantages of penetration
grade bitumen are this bitumen may provide a better correlation with a low
temperature asphalt binder properties than the viscosity test, which is
performed at 60°C. Besides, the test is quick and inexpensive, thus it can be
used in the field. In contrast, there are also its disadvantages. This
bitumen’s shear rate is variable and high during the test. Since asphalt
binders typically behave as non-Newtonian fluid at 25° C, this will affect the
test results. The test also does not provide information with which to
establish mixing and compaction temperatures.

 

Table 1: Paving
Grade Bitumen Specification as per BS EN 12591

 

  Cut-back bitumen is bitumen that was blended
with more or less volatile hydrocarbon component. The viscosity of this bitumen
has been reduced by the addition of solvent which is normally derived from
petroleum. After the application is done, the bitumen’s original viscosity is
regained. The solvent that had been used in cutback bitumen is called the
“cutter” or “flux”. There are three types of solvents that
have been used for the blending process which are slow-curing, medium-curing or
rapid-curing solvents. The rate for bitumen to cure when get exposed to air can
be determined by the choice of the solvents. A rapid-curing (RC) solvent
evaporated much faster than a medium-curing (MC) solvent. The setting time of
bitumen is influenced by the evaporation rate of the solvent. The proportion of
solvent added determines the viscosity of the cutback bitumen at which the
higher the proportion of solvent, the lower the viscosity of the cutback. Cutbacks
are more workable than penetration grade bitumen at which they are more easily
reshaped. Only less amount of heat are required to liquefy cutback bitumen than
penetration bitumen, thus make it much easier to be used at lower temperatures.
Cutback bitumen can be applied at lower temperatures compared to penetration
grades due to its lower bitumen solvents viscosity. However, cutback bitumen
does have its own weakness which it consumes non-renewable energy resources
which are ultimately lost through evaporation. 

  Oxidized Bitumen is the refinery bitumen that
is further treated by the introduction of processed air. This process gives us
oxidized bitumen. Soft bitumen is being introduced by the air that is under
pressure into it by maintaining the controlled temperature. Compounds of higher
molecular weight are formed by the reaction of this introduced oxygen and
bitumen components. Thus, increases of asphaltenes and maltenes content
resulting in a harder mix. This makes the mix to have a lower ductility and
temperature susceptibility. Oxidised bitumen is commonly used for industrial
applications. They are specified and designated by reference to both the
softening and penetration test for example, 85 /40 is an oxidised bitumen with
softening point of 85 ± 5°C and penetration of 40 ± 5 dmm. Oxidised bitumen
also has to comply with solubility, loss on heating and flash point criteria. Some
of major advantages of oxidised bitumen are that it is completely water
resistant, highly flexible and durable. Further, it is chemically very stable.
It is a very flexible compound that is not only chemically stable but also very
durable compound apart from being completely water resistant. It also has some
prominent technical advantages that make it very sought after compound in
various applications. However, this modify bitumen has one determined
disadvantage to use in coating composition, considerably its tendency to
provide solutions that tend to extend in body on aging. These undesirable body
characteristics more pronounced in some solvents than in others and are
significantly unhealthy among the case of the additional volatile crude
solvents. The initial high body of modify bitumen solutions is of course
undesirable, visible of the subsequent low solid content of solutions having
viscosities sufficiently low for application by the while a substitute for slightly
of the latter, with none substantial increase in body of the answer.

 

Bitumen
emulsion is the products in which droplets of bitumen preparation are dispersed
in an aqueous medium. An emulsifier is used to stabilise the mixture. Bitumen emulsion
permits the handling, transport and application of bitumen at lower
temperatures and is mainly used in road surfacing applications.  This type of bitumen forms a two-phase system
consisting of two immiscible liquids, bitumen and water, stabilised by an emulsifier.
One of them is dispersed as fine globules within the other liquid. When
discrete globules of bitumen are dispersed in a continuous form of water,
bitumen emulsion is formed. Bitumen emulsion is used for laying purpose.
Basically, emulsions with low bitumen content and low viscosity are prone to
settlement. This settlement can be reduced by equalising the densities of two
phases. To achieve this, addition of calcium chloride to the aqueous phase is a
prime way. However, the coefficient of thermal expansion of bitumen and aqueous
phase are not the same, their densities can be made equal only at a specific
temperature. Increasing the viscosity of the phase behaviour can be made by
introducing a yield value, settlement can be eliminated completely. There are
many advantages of bitumen emulsion, one of them are bitumen emulsion provides
a convenient and environmentally friendly option as it is water based. Besides,
it doesn’t need extra heat while placing. It is also used in bituminous road
construction, maintenance and repair work. However, bitumen emulsions do have
its limitation. The setting time may vary due to temperature, wind and type of
emulsion. In addition, not a single type of bitumen emulsion can be used for
all works. It depends on the aggregate type setting time nature of work.

  Polymer modified bitumen is the type of
bitumen obtained by the modification of strength and the rheological properties
of the penetration graded bitumen. Here for this 2 to 8% of polymer is added. The
polymer used can be either plastic or rubber. These polymers vary the strength
and the viscoelastic properties of the bitumen. This is achieved by elastic
response increase, improvement in cohesive property, improvement in Fracture
strength and providing ductility. Some of the examples of rubber polymers used
are styrene block copolymers, synthetic rubbers, natural and recycled rubbers.
Plastics that are thermoplastic polymers are also used. Polymer modified
bitumen also one of the specially designed and engineered bitumen grades that
is used in making pavement, roads for heavy duty traffic and home roofing
solutions to withstand extreme weather conditions. It is normal bitumen with
added polymer which gives its extra strength, high cohesiveness and resistance
to fatigue, stripping and deformations, making it a favourable material for
infrastructure. When polymer is added to regular bitumen, it becomes more
elastomeric, which provides it with additional elasticity. The polymer that is
added is styrene butadiene styrene (SBS) which acts as a binder modification
agent. The primary objective of SBS polymer modified bitumen is to provide
extra life to pavement, roads and construction designs. Some of the qualities
exhibited by polymer modified bitumen are higher rigidity, increase resistance
to deformations, increase resistance to cracks and stripping, better water
resistance properties and high durability. Some popular plastomers and
thermoplastic elastomers in bitumen modification are discussed regarding their
advantages and disadvantages. Although polymers improve bitumen properties to
some extent, there are still some drawbacks limiting the future development of
bitumen polymer modification such as high cost, low ageing resistance and poor
storage stability of polymer modified bitumen.

 

 

 

 

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