M.Tech Assignment Report Civil engineering Department , N.I.T Hamirpur Page | 1 1.Introduction Bitumen is used as the binding material in highways and airfields most extensively in India and also in the rest part of the world. With the years, the mode of characterization of bitumen was felt to be changed. In fact, there is a huge gap in India between proper characterization of bitumen and its implementation in the refineries true to the specification and the ambitious planning of creation of important public assets in the highway sector whose durability and serviceability is very important towards the socioeconomic improvement of the country. In this paper review, an attempt has been made to find out the changes of characterization of bitumen mainly in Indian context with the technical justifications behind them. Nowadays there is intense road building going on in India. Most of the roads being built are with bitumen as a binder, so it is prime importance to use the appropriate bitumen. So we must use the bitumen which is best suited with Indian climatic and traffic condition, also whose physical characteristics are based on rational parameters rather than empirical. This has now been achieved by adopting the viscosity grading system for selecting paving bitumen in India. Adoption of viscosity-graded paving bitumen specification will also reduce the number of total tests to 7, which will reduce the cost of testing bitumen. This will result from eliminating empirical tests/parameters such as – penetration ratio, paraffin wax content, and Fraass breaking point without compromising the quality of bitumen .Since high penetration values are desirable for pavement durability, requirement for a minimum penetration value is adequate and has been retained in the viscosity-graded specification. Specifying a maximum value for penetration is undesirable and will reject
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M.Tech Assignment Report
Civil engineering Department , N.I.T Hamirpur Page | 1
1.Introduction
Bitumen is used as the binding material in highways and airfields most
extensively in India and also in the rest part of the world. With the years, the
mode of characterization of bitumen was felt to be changed. In fact, there is
a huge gap in India between proper characterization of bitumen and its
implementation in the refineries true to the specification and the ambitious
planning of creation of important public assets in the highway sector whose
durability and serviceability is very important towards the socioeconomic
improvement of the country. In this paper review, an attempt has been made
to find out the changes of characterization of bitumen mainly in Indian
context with the technical justifications behind them.
Nowadays there is intense road building going on in India. Most of the roads
being built are with bitumen as a binder, so it is prime importance to use the
appropriate bitumen. So we must use the bitumen which is best suited with
Indian climatic and traffic condition, also whose physical characteristics are
based on rational parameters rather than empirical. This has now been
achieved by adopting the viscosity grading system for selecting paving
bitumen in India.
Adoption of viscosity-graded paving bitumen specification will also reduce
the number of total tests to 7, which will reduce the cost of testing bitumen.
This will result from eliminating empirical tests/parameters such as –
penetration ratio, paraffin wax content, and Fraass breaking point without
compromising the quality of bitumen .Since high penetration values are
desirable for pavement durability, requirement for a minimum penetration
value is adequate and has been retained in the viscosity-graded specification.
Specifying a maximum value for penetration is undesirable and will reject
M.Tech Assignment Report
Civil engineering Department , N.I.T Hamirpur Page | 2
some good quality bitumen‟s unreasonably.
The 100 year old penetration grading system has been replaced by viscosity
grading system in India for paving bitumen. The new viscosity grading
system conforms to IS -73-2006 paving bitumen-specification (third
revision).
Viscosity grade bitumen is categorized according to viscosity. The higher
the grade, stiffer the bitumen. In viscosity grade ,viscosity test are conducted
at 60˚C and 135 ˚C which represents the temperature of road surface during
summer and mixing temperature respectively. As per the specifications there
are four grades VG-10, VG-20, VG-30, and VG-40.
The paper reviews the penetration grading system and viscosity grading
system with their respective advantages and disadvantages. An effort is
made to compare the specification of penetration grading with the new
viscosity grading.
Recommendation has been made for selection criterion of VG grades based
on climate and traffic.
Information about the new included tests like viscosity at 60˚C, kinematic
viscosity at 135˚C, solubility in trichloroethylene and the tests on rolling thin
film oven is given.
Further, 16 ongoing road construction projects in Pune, India were selected,
bitumen samples from these sites were collected and tested as per the
viscosity grading. The outcome as per the viscosity grade and their previous
penetration grades were compared. A statistical analysis of all these test
results were carried out which include descriptive statistics, and control
charts. The corresponding graphs were drawn and performance assessment
of each contractor was carried out.
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Civil engineering Department , N.I.T Hamirpur Page | 3
2. History Of Bitumen Grading
(A) World Wide
The History of bitumen as binder in top layers of flexible pavement tells us
that In the late nineteenth century (1869 to 1876 AD) in Paris, London and
in United States compacted bituminous pavements were constructed, first of
its kind. At that time, all bitumen available was natural bitumen. At the
beginning of twentieth century (1902), bitumen was started being
commercially manufactured by refining crude petroleum oil in USA.With
the advent of motorized vehicles, the need for dust free, smooth, all weather
road was felt and for this reason, bituminous roads became a worldwide
need and popular also.In 1888, B.C Bowen invented Bowen Penetration
Machine which is called Penetrometer.
The temperature, at which bitumen was graded by chewing, was quite
naturally nearer to the normal human body temperature: (+) 37˚C.
After several modifications of the initial penetration machine, by 1910 in
USA, the penetrometer became the principal means of measuring and
controlling consistency of bitumen at 25˚C which is the average ambient
temperature in a year. American Society for Testing and Materials (ASTM)
Committee D04 on Road and Paving materials adopted the grading of
bitumen by penetration test at 25˚C.The next major change in USA was
initiated in early 1960, when bitumen was felt to be graded by viscosity at
60˚C, which is the maximum pavement temperature in summer.
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The principal reasons for this change were:
To replace the empirical penetration test with a rational scientific
viscosity test
To measure the consistency at 600C rather than 250C, which
approximates the asphalt
Pavement maximum surface temperature on a hot summer day when
rutting is likely to occur.
(B) In India Context
The first Indian Standard on bitumen was published in 1950 as
“Specification for asphaltic bitumen and fluxed native asphalt for
road making purpose” : IS:73. The first revision was
made to IS:73 in 1961 to change the grades of materials and incorporate
the methods of testing of bitumen and tar as per IS 1201 to IS 1220
(1958).
In this revision, the grades of fluxed native asphalt were deleted and the
paving grades were included. These standards were based on penetration
grades. The second revision was made on 1992 based on the revised
methods of test in IS 1201 to IS: 1220 (1978) and some additional data
on the properties of bitumen extracted from waxy crude and non-waxy
crude, were included.
In the second revision too ,penetration remained the principal test for
fixing gradation criteria. However, some new tests like penetration ratio,
paraffin wax content and viscosity at 60˚C and 135˚C and retained
penetration after thin film oven test (i.e, short term aging) had been
incorporated.
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The third revision of IS:73 was published in 2006, when the grading of
bitumen is changed from penetration grade to viscosity grade. In this
revision, the total numbers of tests have been reduced to 7 only
eliminating empirical tests/parameters such as penetration ratio, paraffin
wax content and Frass breaking point without compromising any quality
of bitumen.
Thus, before 2006, bitumen was graded in India mainly by penetration
grade and sometimes by softening point, which are empirical methods.
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3.Why Bitumen Needs Grading
Bitumen has got different uses. In fact, before used as the principal binder in
constructing highways ,bitumen was used in roofing, flooring, bridge,
sidewalk surfacing, waterproofing etc purposes.
Bitumen obtained by different ways, vary in property. Even bitumen
obtained by refining petroleum crude varies in property depending on the
source of crude petroleum and refining process.
Thus, bitumen needs grading, primarily for the different purposes for which
it is used, even in highway construction too, the purposes may be different.
Secondarily, bitumen refined from different crude oil source and by different
refining processes, varies in property. To categories that, bitumen needs to
be graded.
4.The Characteristics/Properties On Which Bitumen Needs
Grading.
For engineering and construction purposes, three properties of bitumen are
important :
(i) Consistency, (ii) Purity, (iii) Safety.
4.1 Consistency
Bitumen is a thermoplastic material which means it liquefy when heated and
solidify when cooled and its state of solidness (stiffness) or liquidness (i.e.,
ability to flow) is very much temperature sensitive. Consistency is the term
used to measure its degree of stiffness or ability to flow. Consistency of
bitumen can be judged by some empirical tests such as penetration,
softening point, ductility etc. and also by testing the fundamental property of
bitumen such as viscosity.
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4.2 Purity
By definition, bitumen is entirely soluble in trichloroethylene. Nowadays,
almost entire bitumen is obtained by refining petroleum crude, which are
usually more than 99.5% soluble in trichloroethylene. This test is carried out
to check the presence of organic materials and impurities in bitumen.
4.3 Safety
For using bitumen in HMA, it needs to be heated up. But bitumen being a
petroleum product, there is chance of fire hazard.
The temperature at which a heated bitumen sample will instantaneously
flash in the presence of an open flame is called flash point and is considered
as the level of safe temperature. [The temperature at which bitumen supports
combustion is called fire point and in much higher temperature than flash
point].
The flash point of all bitumen are usually well above the temperature
normally used in paving operations.
Thus, it can be concluded that there is no point to grade bitumen on purity
and safety aspect. It is the consistency property of bitumen by which it can
be graded.
5.Penetration Grading
Grading of bitumen by penetration test at 25 °C was adopted by the
American Society for Testing and Materials(ASTM) Committee D04 on
Road and Paving Materials in 1903. To quantify the Penetration grading the
following asphalt concrete characteristics are to be evaluated as per the
standard IS: 73-1992.
Penetration depth of a 100 g needle; 25° C
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Flash point, °C
Softening point °C
Penetration ratio
Ductility at 25 °C, cm
Paraffin wax content
Fraass breaking point
Solubility in trichloroethylene
Loss on heating (TFOT)
Retained penetration after Thin Film Oven Test (TFTO)
Viscosity at 60 °C and 135 °C
Water content
Specific gravity at 27 °C
Penetration of a bituminous material is the distance in tenths of millimeter
that standard needle will penetrate vertically into a sample under standard
conditions of temperature, load and time.
In penetration grade, the bitumen is classified as per the values of
penetration test. Other tests have just to fulfill the minimum requirement as
per the IS. IS 73-1992 specifies five penetration grades of bitumen as
20-30
30-40 (hardest bitumen)
40-50
60-70
80-100 (softest bitumen)
Fig.1 shows schematic of the penetration test. In this procedure, a needle is
loaded with a 100-g weight and allowed to penetrate into an asphalt sample
for 5 sec. Prior to conducting the test, the asphalt cement sample is brought
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to the testing temperature of 25°C. Measures the depth of penetration in
tenths of millimeters.
The greater the penetration, the softer is the bitumen. The most widely used
penetration grade in India is 60-70. The softer 80-100 penetration
grade has been used for low-volume roads and spray applications (such
surface dressing) in India
6.What Was Wrong With Penetration Grading?
6.1 The two main disadvantages of penetration grading system
The penetration test is an empirical test not fundamental test.
Testing the consistency of bitumen by penetration test at 25˚C is very
deceptive to judge its performance at higher and lower temperature.
It will be evident from following example :
Figure 1. Schematics of penetration test.
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In figure-2, there are three, bitumen A, B & C whose penetration at
25˚C is same i.e, 65.
But these bitumen are having different stiffness values at higher
(say60˚C) temperature and at lower (say 40˚C) temperature.
Figure 2. Stiffness versus temperature for different bitumen
The slope of the stiffness vs. temperature curve is called temperature
susceptibility.
Steeper is the slope, more will be the temperature susceptibility of the
bitumen.
In this figure, bitumen „C‟ is most temperature susceptible , in other words
more prone to rutting at higher temperatures and more prone to cracking at
low temperatures (due to higher stiffness)compared to bitumen „B‟ and „A‟.
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6.2 The other disadvantages of penetration grading system
The penetration grading system is not sufficient to control the
temperature susceptibility of bitumen within a specified range for a
better control over the performance of the bituminous mix.
penetration grading system can not be used effectively for
Polymer-modified bitumen too.
No guidance is available for appropriate viscosity of bitumen for
mixing and compaction.
(This should be 170±20 & 280±30 centistokes respectively).
7. Why Viscosity Grading System Was Needed
Since 1970, in USA, bitumen was started to be graded by its fundamental
property i.e, viscosity (absolute) at 60˚C which approximates the maximum
temperature during hot summer when rutting is likely to occur. The main
point behind this is, same viscosity grade bitumens gave similar rutting
performance in hot summer. Viscosity graded bitumens were suitable for a
wide range of temperatures:- 25˚C for raveling/fatigue cracking, 60˚C for
rutting and 135˚C for construction.
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