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



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The 100 year old penetration grading system has been replaced by viscosity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.



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.



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.



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.



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.



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



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



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.



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‟.



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.



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.



Figure 3.Redwood viscometer



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.



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)



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.



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



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.



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



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.



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.



Figure 7. Figure 8.

Figure 9. Figure 10.



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.



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.