Viscocity graded bitumen system
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Transcript of Viscocity graded bitumen system
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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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The 100 year old penetration grading system has been replaced by viscosity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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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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8. Viscosity Test
8.1 Apparatus Required: - Red Wood viscometer , stop watch, flask,
thermometer , filter paper.
8.2 Principle: -
Viscosity is the property of a fluid that determines its resistance to flow. It is
an indicator of flow ability of a bitumen l; the lowest the viscosity, greater
the flow ability. It is mainly due to the forces of cohesion
between the molecules of lubricating oil.
8.3. Description of the Redwood viscometer
It is divided in to three parts
8.3.1Oil Cup;
Material- Silver plated brass
Height-90mm
Diamtere-46.5mm
It holds the test sample of bitumen. The bottom of the cup is fitted
with polished-agate discharge tube containing an orifice of specified
dimension.
8.3.2. Water Bath: Bitumen cup is surrounded by water bath for
adjusting the temperature.
8.3.3. Kohlrausch Flask: It receives the bitumen from polished-agate
discharge tube.
8.4. Viscosity value
The time in second for 50ml of the test sample to flow through the orifice is
defined as the viscosity at a given test temperature.
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Figure 3.Redwood viscometer
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9. Features Of Viscosity System
The main features of VG System are as follows:-
In viscosity grading system, the principal test is absolute viscosity
measurement at 60˚C and also kinematic Viscosity measurement at
135˚C and penetration at 25˚C.
By measuring consistency at three different temperatures and
specifying the ranges, the slope of temperature vs-stiffness curve i.e.,
the temperature susceptibility of bitumen can be bound in a specified
range which is the key for better performances .It can be explained by
figure-4.
Figure 4. VG -30 grade of bitumen as per IS: 73 (2006)
Defining the range (minimum and maximum values) for penetration at 25˚C,
minimum value for absolute viscosity at 60˚C, and minimum value for
kinematic viscosity at 135˚C, the temperature susceptibility of bitumen can
be controlled in a better way towards better performance.
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Performance at high temperature
Earlier it was not possible to judge the performance of binder at high temp
with only penetration test at 25ºC. But with viscosity grades there is testing
of viscosity at 60ºC and at 135ºC which can predict the performance of
binder at high temperature.
Issues relating to compaction
During the compaction of mix on field, tender mix is common problem,
which is been addressed by having a requirement of minimum kinematic
viscosity at 135ºC.
Number of total test
There is considerable reduction in the number of tests required, as per the
viscosity grade the number of tests required are 7 compared to 13 as per the
penetration grade. In addition to this there is no compromising in the quality
of bitumen and also no new tests are required in implementing this
specification. Bitumen are classified as per the viscosity. The higher the
grade, the stiffer the Bitumen .To classify the bitumen as per the viscosity
grade following characteristics tests are carried out as per the IS: 73 2006.
1. Absolute viscosity at 60 ºC , poises
2. Kinematic viscosity at 135 ºC, cst
3. Flash point ºC
4. Solubility in trichloroethylene, %
5. Penetration test at 25 ºC, 1/10 th of mm
6. Softening point , ºC
7. Tests on residue from Rolling Thin Film Oven.
i ) Viscosity ratio at 60 ºC, ii) Ductility at 25 ºC (cm)
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The table-1 of IS:73 (2006) shows the requirements of different tests.
S.No Characteristics Paving
Grades
Methods Of
Test,
Ref. To Is No.
VG10 VG20 VG30 VG40
1 2 3 4 5 6 7
i) Absolute viscosity at
60oC, Poises, Min
800 1600 2400 3200 IS 1206(Part2)
ii) Kinematic viscosity at
135oC, cSt, Min
250 300 350 400 IS 1206(Part3)
iii) Flash point,
(Cleveland open cup),
˚ C, Min
220 220 220 220 IS 1209
iv) Solubility in
trichloroethylene,
percent, Min
99.0 99.0 99.0 99.0 IS 1216
v) Penetration at 25oC,
100g, 5 s, 0.1 mm
80-100 60-80 50-70 40-60 IS 1203
vi) Softening Point
(R & B ), o C, Min
40 45 47 50 IS 1205
vii) Tests on residue from
thin- film oven
tests/RTFOT
1) Viscosity ratio at
60 o C, Max
4.0 4.0 4.0 4.0 IS 1206(Part2)
2) Ductility at 25oC , cm,
Min,after thin-film oven
test
75 50 40 25 IS 1208
Table 1 : Requirements for Paving Bitumen (Clause 6.2 of IS 73 :2006)
It would have been ideal to adopt a truly, time-tested specification for
viscosity graded bitumen in India similar to ASTM. However, some
adjustments were made to facilitate the transition from penetration grades to
viscosity grades. It is hoped that the specifications will be fine tuned and
made more rational in near future.
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Viscosity Graded Bitumen and Equivalent Penetration Grade With
Their General Application to compare the specification of each
grading system, it is necessary to find the equivalent grade of other
system. As per the IS 73-2006 following table shows the equivalent
penetration grades of viscosity grades with their general application.
Table2. shows the equivalent penetration grade with respect to viscosity
grade.
Viscosity Grade
(Vg)
General Applications Equivalent
Penetration Grades
VG40 The area with high stress
concentration like intersections of
roads, truck parking, heavy traffic. It
can be used in higher temperatures
30-40
VG30 It is the most suitable for Indian road
condition.
60-70
VG20 It is used in areas of cold climate &
high altitude
……..
VG10 Used in spraying applications, and can
be used in very cold regions. Also
used for the manufacture of bitumen
emulsion & modified bitumen
80-100
Table 2.- VG Bitumen And Equivalent Penetration Grade
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10.Advantages of Viscosity Grade
Fundamental Engineering Properties: Fundamental engineering
properties are the base for viscosity grade.
Takes care of high as well low temperature: Both low & high temp
susceptibility of bitumen is dealt with the measurement of viscosity at
60 ºC and 135 ºC , which is not possible with Penetration value at
25ºC. Hence, road contractors can have better understanding of
Bitumen performance in the field.
Rutting performance of two same viscosity grades is identical which
is not possible in penetration grade.
Easy Mix Design: As viscosity value at two different temperatures is
available, there is greater ease in handling to customers. It is possible
to measure accurate mixing & compaction temperature.
Number of tests: Viscosity grading has 7 tests as compared to 14
tests of penetration grade system. Therefore there is considerable
reduction in time and cost.
Longer durability: The pavement made with Viscosity grade
bitumen is of longer durability.
Higher traffic capacity: The pavement made with appropriate VG
bitumen is of higher traffic capacity.
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11. Case Studies
Pune is one of the largest metropolitan city of India. Tremendous amount of
infrastructural work is under construction in Pune , it include construction
of bridges, rigid pavements, flexible pavements, under pass .Engineers
decide to carry out the testing of bitumen samples from the ongoing road
construction sites in and around Pune as per the Viscosity Grading. Then to
compare the specifications of Viscosity grading and Penetration grading.
They visited 16 ongoing flexible pavement construction sites and collected
the sample. There were in total 16 contractors, the names of contractors are
not disclosed here. The work of 16 sites is distributed among these
contractors. The data regarding contractors, latitude and longitude of site,
penetration grade claimed by the contractor, corresponding Viscosity
grading after testing is shown in table 3.
Sr.
No
Name of
contractor
Date of
visit
Grade of
bitumen(penetration)
claimed by
contractor
Viscosity
Grade
after
testing
Penetration
Grade after
testing
1 Contractor 1 7/2/2014 60-70 VG20 60-70
2 Contractor 2 10/2/2014 60-70 VG30 60-70
3 Contractor 3 13/2/2014 60-70 VG30 60-70
4 Contractor 4 17/2/2014 60-70 VG30 60-70
5 Contractor 5 18/2/2014 60-70 VG30 60-70
6 Contractor 6 22/2/2014 60-70 VG30 60-70
7 Contractor 7 26/2/2014 60-70 VG20 60-70
8 Contractor 8 25/2/2014 60-70 VG30 60-70
9 Contractor 9 26/2/2014 60-70 VG20 60-70
10 Contractor 10 6/3/2014 60-70 VG20 60-70
11 Contractor 11 7/3/2014 60-70 VG20 60-70
12 Contractor 12 7/3/2014 60-70 VG20 60-70
13 Contractor 13 8/3/2014 60-70 VG20 60-70
14 Contractor 14 14/3/2014 60-70 VG20 60-70
15 Contractor 15 20/3/2014 60-70 VG20 60-70
16 Contractor 16 26/3/2014 60-70 VG20 60-70
Table3. Data Collected By Engineers Of Ongoing Project
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Now from the above description it is clear that out of 16 samples 10 samples
belong to VG 20 and 6 samples belong to VG30 for all penetration value
60-70 .According to IS-73-2006 it is clear that equivalent grade for 60-70
penetration value is VG 30 therefore only 6 sites fulfill the requirement.
So for any two samples having same penetration grade may show different
behavior at high & low temperatures.
12. Statistical Analysis of Data Statistics is the science of gathering, analyzing, interpreting and presenting
data. It is branch of Mathematics. Statistics teaches us how to summarize,
analyze and draw meaningful inferences from data that then lead to improve
the functioning of a particular department, entire company etc. In this work
software is used to analyze the data.
12.1 Descriptive Analysis
N Minimum Maximum Mean Std
Deviation
Variance
Absolute viscosity at
60˚c poise
16 1615.35 2813.45 2143.1
0
407.21 165821.1
kinematic viscosity
at 135˚C cst
16 310.8 388.54 342.21 24.59 605.019
viscosity by tar
viscometer secs
16 51 76 63.62 7.164 51.317
Flash point ˚C 16 270 305 286.81 10.71 114.69
FIRE point _ ˚C 16 285 315 301.81 11.11 123.89
Ductility at 27˚C in
cm
16 69 87.66 80.61 4.91 24.204
solubility in
(%)trichloroethylen
e
16 95.86 99.6 99.27 0.21516 .046
Penetration at 25 _
C in 1/10 th of mm
16 55.0 76 63.28 5.05 25.566
softening point _ C 16 46.0 53.0 49.01 1.99 3.96
Table 4. Descriptive Analysis Of Collected Data.
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12.2 Control Charts
All the processes exhibit variation .Conrol charts help to minimize process
variation. Control limits identify the normal operating zone of a process. A
control charts contains a set of limits around the hypothesized normal
distribution of common cause. Any observation falling outside these limits
indicates the presence of a special cause.
The control charts used in statistical quality control represents a picture of a
process. When used and continuously updated, control charts represent a
moving picture of the process. Control limits represents three standard
deviation either side of the mean, so 99.7% of points are within these limits.
Process is not under control, if one or more points are found outside the
control limits. Following charts are the outcome from software, control
chart is drawn for each test.
Figure 5. Figure 6.
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Figure 7. Figure 8.
Figure 9. Figure 10.
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Figure 11. Figure 12.
From the above analysis ,it is clear that all the tests are under control as no
points are found outside the control limits.
13. Conclusion
Out of 16 samples, 10 samples belong to VG 20 & 6 samples belong
to VG 30, though their penetration grade lies between 60-70. So any
two samples of same viscosity grade would give similar performance
but the possibility of the same in penetration grade is less. In another
words two samples having same penetration grade may show different
behavior at high & low temperatures.
Viscosity is measured at 60˚C & 135˚C , which takes care of both low
and high temperature susceptibility of binder, which is not possible
with only penetration value @ 25˚C.
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Greater ease in handling for users as viscosity value at two different
temperatures (@60 ˚ C & 135˚C ) is available which would enable
users to measure accurate mixing & compaction temperatures.
Penetration test was developed in times of significantly lower
pavement loading. Today there is almost 10 %increase in pavement
loading which contributes to 40 % increase in stresses applied to
pavements & further heavy traffic and change in weather conditions.
Therefore to cope up with the change, there is need to shift
frompenetration to viscosity grade.
14. References
[1] International journal of innovations in engineering and
technology(IJIET).
[2] Paper published by “AshutoshPatekar ,Mtech student COEP”.
[3] Paper published by”RajibChattaraj” on “A step toward better quality
control”.
[4] Indian road congress publications (IRC-73-2006)
[5] Indian road congress publications (IRC-73-1992)
[6] S.K.Khanna, C.E.G.Justo Book of Highway engineering.