Effect of natural rubber on the properties of bitumen and bituminious mixes

International INTERNATIONAL Journal of Civil Engineering JOURNAL and OF Technology CIVIL (IJCIET), ENGINEERING ISSN 0976 – 6308 AND
(Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 10, October (2014), pp. 09-21 © IAEME
TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 5, Issue 10, October (2014), pp. 09-21
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9

IJCIET
©IAEME
EFFECT OF NATURAL RUBBER ON THE PROPERTIES
OF BITUMEN AND BITUMINIOUS MIXES
D. VASAVI SWETHA
Student (B.E. + M.E), civil engineering dept, Andhra University College of Engineering,
Visakhapatnam, INDIA
Dr. K. DURGA RANI
Professor, civil engineering dept, Andhra University College of Engineering, Visakhapatnam,
INDIA
ABSTRACT
In India the remnants of products of natural rubber latex are stockpiled every year often
uncontrollable causing sever environmental and other socio economic negative impacts. The
environmental solid waste like rubber, swim caps, gloves etc can be recycled in a better way so that
it is helpful for the future. Many studies have been done to find other alternative material to use as
modifiers in bitumen mixes on the improvement of its properties and highway quality. Studies still
today mainly focused on mechanical and physical characteristics of rubberized mixtures in which
balloon rubber is used either as alternative to natural aggregates or as additive. In this research
Natural Rubber latex (in the form of balloons) has been used as bitumen modifier. Bitumen when
compared to the rubberized bitumen is bit sensitive when exposed to traffic load and temperature.
The Rubberized bitumen formed reduces permanent deformations due to overload on the road and
thus unaffected by the changes in atmospheric temperature and improves skid resistance. Rubber
increases resistance to flow of bitumen at higher temperature and improves the resistance to brittle
fracture at low temperature. The upper surface layer of the pavement has been made of rubberized
bituminous mixtures. Rheological characteristics of rubberized bitumen as well as basic properties of
the implemented, rubberized bituminous mixture are presented. The behaviors of the two modifiers
were investigated by comprehensive laboratory testing and evaluation. It was observed that the
addition of natural rubber gave better overall performance in the bituminous mixes. Thus, this shows
natural rubber may contribute toward better flexible roads in the future. The above properties
increase the service life of rubberized roads in many cases to more than hundred percent when
compared to that of bituminous roads. Thus modified rubber bitumen of roads will combine savings
with safety.

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
Keywords: Balloon Rubber, Remnants of Environment, Natural Rubber Latex, Pavement, Traffic,
Rubberized Bituminous Mixture.
10
1. INTRODUCTION

Natural rubber modified bitumen is used for the prolongation of life of state roads. The need
to adopt rubber for the use of construction of the roads is mainly that it reduces the cost of
construction and also recycled rubber is used as it minimizes the environment pollution. The
utilization of recycled rubber in pavement construction sector can be a very promising and
environmentally friendly what to eliminate the nations stock of scrap. A steady stream of huge
volume of waste remnant or natural rubber is generated due to the continual increase in the
production of waste generated by the population. The availability of the Natural Rubber (Latex) is
enormous, as the rubber is a product obtained from Latex (e.g., mattresses, gloves, swim caps,
balloons) has become part of daily life. If it is not recycled, its present disposal is either by land
filling or by incineration. Both the processes have certain impact on the environment.
Various studies are being carried out to improve the quality of bitumen used in bituminous
road construction. One of the results of such studies is to use polymer-modified bitumen. Polymer
modified bitumen is emerging as one of the important construction materials for flexible pavements.
Use of polymers in the construction of flexible pavement is gaining importance because of the
several reasons. The polymer modified bitumen show better properties for road construction and
plastics waste, otherwise considered to be a pollution menace, can find its use in this process and this
can help solving the problem of pollution. Bitumen is a useful binder for road construction. Different
grades of bitumen like 30/40, 60/70 and 80/100 are available on the basis of their penetration values.
The steady increase in high traffic intensity in terms of commercial vehicles and the significant
variation in daily and seasonal temperature demand improved road characteristics. The studies on the
thermal behavior and binding property of the Natural Rubber promoted a study on the preparation of
Natural Rubber-bitumen blend and its properties to find the suitability of the blend for road
construction. “The initial cost is higher by around 20 per cent, but life-cycle cost is considerably
lesser than roads surfaced using modified bitumen”.
1.1 Natural Rubber (Latex)
Natural rubber is an elastomer that was originally derived from milky latex found in the sap
of some plants. The purified form of natural rubber is the chemical polyisoprene, which can also be
produced synthetically. Natural rubber is used extensively in many applications and products, as is
synthetic rubber. Natural rubber is an ideal polymer for dynamic or static engineering applications.
Natural rubber features:
• Excellent dynamic properties with a low hysteresis loss
• Good low temperature properties
• Strong bonding to metal parts
• High resistance to tear and abrasion and ease of processing
1.2 Properties of Natural Rubber
Natural rubber has been successfully used as an engineering material for many years. The
following range of properties shows just how versatile of a material natural rubber has proven to be
to engineers:
• Natural rubber combines high tensile and tear strength with an outstanding resistance to
fatigue.

11

• Excellent green strength and tack — has the ability to stick to itself and other materials,
making bonded natural rubber products easier to fabricate.
• Exhibits excellent dynamic properties with a low hysteresis which leads to low heat
generation.
• Adjustable hardness from very soft to very hard (ebonite).
• Appearance and color ranges from translucent (soft) to black (hard).
• Compounded to meet nearly any mechanical requirement.
• The ability to be electrically insulating or fully conductive.
• Protect, insulate and sealing properties.
• Absorb vibration and silence noise.
• Available in any surface roughness and shape.
To achieve the specific properties required for a given product, raw natural rubber has to be
compounded using ingredients such as carbon black, anti-degradants, softeners and a vulcanization
system.
1.3 Poly Isoprene
One of the most well known natural polymers is polyisoprene, or natural rubber.
Polyisoprene is diene polymer, which is a polymer made from a monomer containing two carbon-carbon
double bonds. Like most diene polymers, it has a carbon-carbon double bond in its backbone
chain. Polyisoprene can also be made by Ziegler-Natta polymerization. This is a rare example of a
natural polymer that we can make almost as well as nature does.
1.4 Environmental Concerns
Due to it being non-biodegradable rubber is very lethal to the environment. It is one of the
main contributions to land pollution. Besides plastic, glass, bottles, cans and other forms of litter.
Rubber release a lot of toxins that have even lead to severe skin diseases, pollution of drinking water
and fish being harmful to consume. If Rubber is burned it gives off chemicals into the surrounding
air and exhibit toxicity in the environment which has several effects in life.
1.5 Types of Bitumen Modifiers and Their Indicative Dose
Over the years, different types of materials have been investigated as additives for bitumen
modifications. Some of them, which are reported to have desired potential and their indicative dose
are given in table 1.

TABLE 1: TYPE OF ADDITIVES FOR BITUMEN MODIFICATION AND THEIR INDICATIVE
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DOSES
Sl. No. Types of Modifiers Examples
Indicative Dose
Level, per cent by wt.
of bitumen
1. Plastics
Thermoplastics
Thermosets
Low Density
Polyethylene(LDPE)
Ethylene Vinyl
Acetate (EVA)
Ethylene Butyl
Acrylate (EBA)
Epoxy Resins
3-6
3-5
2. Elastomers
Natural Rubber
Synthetic
Elastomers
Latex or Dry Rubber
Powder
Styrene Butadiene
Styrene
Block Copolymer
(SBS),
Styrene Butadiene
Rubber (SBR)
2-4
3-5
3. Reclaimed Rubbers Type Crumb Rubber
Powder from
discarded truck, tyres
further improved by
additives
10-12
1.6 Scope of the Study
This study aims the utilization of polyisoprene in bitumen blend for road construction.
Several tests are conducted on plain bitumen and bitumen blended with polyisoprene and the change
in the properties is observed. For the present study polymer used is Polyisoprene (Natural rubber) as
the availability of these materials is high and the preparation of blend is simple. Mix design for the
blend is also done for marshal stability value to determine the optimum binder content level.
The results obtained from plain bitumen are compared with those obtained from addition of
Polyisoprene polymer. The benefits obtained with addition are analyzed.
The experiments are done with 1%, 2%, 3%, 4%, 5%, 6% and 7% of bitumen modifier which
on further increase from 0.5% of bitumen modifier we can get better results.
2. TESTS ON BITUMEN
2.1 BITUMEN
Bitumen is a common binder used in road construction. It is principally obtained as a residual
product in petroleum refineries after higher fractions like gas, petrol, kerosene and diesel etc. are
removed. Indian Standard Institution (ISI) defines Bitumen as a black or dark brown non-crystalline
soil or viscous material having adhesive properties derived from petroleum crude either by or by
refinery process.

13
2.2 General Uses of Bitumen
For Civil Engineering works

• Construction of roads, runways, platforms
• Water proofing to prevent water seepage
• Mastic floorings for factories and warehouse
• Canal lining to prevent erosion
• Dump-proof courses for masonry
• Tank foundation
• Joint filling material for mason
2.3 Properties of Bitumen
The bitumen should possess the following desirable properties
In presence of water the bitumen should not strip off from the aggregate. There has to be
adequate affinity and adhesion between the bitumen and aggregate used in the mix.
The viscosity of the bitumen at the time of mixing and compaction should be adequate. This
is achieved by heating the bitumen and aggregate prior to mixing or by use cut backs or emulsions of
suitable grade.
The bituminous should not be highly temperature susceptible. During the hottest weather of
the region the bitumen mix should not become too hard and brittle, causing of surface. The material
should be durable.
Bitumen main property that of very strong and durable adhesive that binds together a very
wide variety of other materials without affecting their properties. Bitumen is insoluble in numerous
organic solvents. As it is highly water proof, it can act as an effective sealant, it also resists action by
most acids, alkalis and salts. It does not contaminate water so it can be used to line water courses.
Bitumen given good controlled flexibility to mixtures of mineral aggregates.
2.4 Requirements of Bitumen
The desirable properties of bitumen depend on the mix type and construction. The general
problems while using bitumen in paving mixes are
1. Mixing
2. Attainment of desired stability under adverse weather conditions.
3. To maintain the stability under adverse weather conditions.
4. To maintain sufficient flexibility and thus avoid cracking of bituminous surface.
5. To have sufficient adhesion with the aggregates in the mix in the presence of water.
2.5 Tests on Bitumen
The various tests that have to be conducted of bitumen are
Penetration test
Softening point test
Viscosity test
Ductility test
Flash fire point
2.5.1 Penetration Test
The penetration test determines the hardness or softness of bitumen by measuring the depth
in tenths of a millimeter to which a standard loaded needle will penetrate vertically in five seconds.
The sample is maintained at a temperature of 25°C. The bitumen is softened to a pouring

consistency, stirred and poured into a container to depth of 15mm. then it is placed in a temperature
controlled water bath for one hour.. The sample with container is taken out and the needle is
arranged to make contact with the surface of the sample. The dial is set to zero or the initial reading
is taken and the needle is released for 5 seconds testing at a distance of 10mm apart. The final
reading is taken on dial gauge and mean value is reported as penetration value.
14
2.5.2 Softening Point Test

All semi-solid state bitumen grades need sufficient fluidity before they are used for
application with the aggregate mix and the procedure is done by heating.. A brass ring containing the
test sample of bitumen is suspended in liquid like water of glycerin at a given temperature. A steel
ball is placed upon the bitumen and liquid medium is then heated at a specified rate. The temperature
at which the softened bitumen touches the metal plate placed at a specified distance below the ring is
recorded as the softening point of particular bitumen. The apparatus and test procedure are
standardized by ISI. It is obvious that harder grade bitumen possess higher softening point than
softer grade bitumen.
2.5.3 Viscosity Test
Viscosity is defined as inverse of fluidity. High or low fluidity at mixing and compaction has
been used to result in lower stability values. One method by which viscosity is measured is by
determining the time taken by 50 CC of the material to flow from a cup through specified at a given
temperature. The sample material is heated at the temperature 20°C above the specified test
temperature and the material is allowed to cool. During this the material is continuously tirred. When
the material reaches slightly above test temperature, the same is poured in the tar cup, until the
leveling peg on the valve rod is just immersed. In the graduated receiver 20ml of mineral oil or one
percent by weight solution of soft soup is poured. The receiver is placed under the orifice. When the
sample material reaches the specified testing temperature within ±0.1°C and is maintained for 5
minutes, the valve is opened. The stop watch is started when cylinder records 25 ml. The time is
recorded for flow upto a mark of 75 ml.
2.5.4 Ductility Test
In the flexible pavement construction where bitumen films around the aggregates, this serves
as a satisfactory binder in improving the physical interlocking of the aggregates and if it does not
possess sufficient ductility would crack and thus provide pervious pavement surface.
The bitumen sample is melted to a temperature of 75 to 100°C above the approximate
softening point and poured in the casting assembly and placed on a brass plate, after a solution of
glycerin and dextrin is applied at all surfaces of the mould exposed to bitumen. 30 to 40 minutes
after the sample is poured the plate assembly along with the sample is placed in water bath
maintained at 27°C for 30 minutes. The sides of mould are removed and the clips are carefully
hooked on the machine without causing any initial strain. 2 or more specimens may be prepared in
the mould and clipped to the machines to as to conduct the tests simultaneously.
The pointer is set to read zero. The machine is started and the two clips are thus pulled apart
horizontally. While the test is in operation, it is checked whether the sample is immersed in water at
depth of at least 10 mm. The distance at which the bitumen thread of each specimen breaks, is
recorded (in cm) to report as ductility value.
2.5.5 Flash and Fire Point Test
Bituminous materials leave out volatiles at high temperatures depending upon their grade.
These volatile vapors catch fire causing a flash. The material is filled in the cup up to a filling mark.
The lid is placed to close the cup in a closed system. All accessories including thermometer of the

specified range are suitably fixed. The bitumen sample is then heated. The test flame is lit and
adjusted in such a way that the size of beed is of 4mm diameter. The heating is done at the rate of 5°-
6°C per minute. The stirring is done at a rate of approximately 60 revolutions per minute. The test
flame is applied at intervals depending upon the expected flash and fire points. First application is
made atleast 17°C below the actual flash point and then at every 1° to 3°C. The stirring is
discontinued during the application of the test flame.
15
3. TESTS ON BITUMINOUS MIXES
3.1 Bituminous Mixes

Bituminous concrete or asphaltic concrete is one of the highest and costliest types of flexible
pavement layers used in the surfacing course. The desirable properties of a good bituminous mix are
stability, durability, flexibility, skid resistance and workability.
Stability is defined as resistance of the paving mix to deformation under load and thus it is a
stress which causes a specified strain depending upon anticipated field conditions.
Durability is defined as the resistance of the mix against weathering and abrasive actions.
Tensile strain is introduced in the top layer consisting of bituminous mix when wheel loads ply over
it. Excessive strain causes cracking or plastic failure.
Flexibility is a property of the mix that measures the level bending strength. Skid resistance is
defined as the resistance of the finished pavement against skidding and is a function of surface
texture and bitumen content. Workability is the ease with which the mix can be laid and compacted
3.2 Properties of Bituminous Mixes
• Mix design methods should aim at determining the properties of aggregates and bituminous
material which would give a mix having the following properties.
• Sufficient stability to satisfy the service requirements of the pavement and the traffic
conditions, without undue displacements. Sufficient bitumen to ensure a durable pavement by
coating the aggregate and bonding them together and also by water-proofing the mix.
• Sufficient voids in the compacted mix as to provide a reservoir space for a slight amount of
additional compaction due to traffic and to avoid flushing, bleeding and loss of stability.
• Sufficient flexibility even in the coldest season to prevent cracking due to repeated
application of traffic loads.
• Sufficient workability while placing and compacting the mix.
• The mix should be the most economical one that would produce a stable, durable and skid
resistant pavement.
3.3 Marshalls Method of Mix Design
In this method, the resistance to plastic deformation of cylindrical specimen of bituminous
mixture is measured when the same is loaded at the periphery at a rate of 5cm per minute. The test is
extensively used in routine test programmed for the paving jobs. There are two major features of the
Marshall method of designing mixes namely,
Density-voids analysis
Stability-flow test
3.3.2 Gradation of Aggregates for Bituminous Macadam Mix
Sieve analysis is conducted on the supplied samples of 20mm, 10mm, 6mm and stone dust.
The specifications given by morth for bituminous macadam are presented in table 2.

16

TABLE 2: GRADATION OF AGGREGATES
S.NO SIEVE SIZE (mm) RECOMMENDED GRADATION AS PER
%FINER (MORTH SPECIFICATION)
1 26.5 100
2 19 90-100
3 13.2 56-88
4 4.75 16-36
5 2.36 4-19
6 300μ 2-10
7 75μ 0-8
Approximately 1200g of the mixed aggregates and the filler are taken and heated to a
temperature of 175-190°C. The bitumen is heated to a temperature of 121 to 145°C and the required
quantity of the first trial percentage of bitumen is added to the heated aggregates and thoroughly
mixed at desired temperature of 154-160°C. The mix is placed in a pre-heated mould and compacted
by a rammer with 75 blows on either side at a temperature of 130-149°C(suitable heating, mixing
and compacting temperatures are chosen depending upon the grade of bitumen). Number of blows on
each side of marshall specimen is taken as 75. Three specimens are prepared using each trial bitumen
content and cooled to room temperature.. The specimens are kept immersed in water in a
thermostatically controlled water bath at 60±1°C for 30-40 minutes. The specimens are taken out one
by one, placed in the Marshall Test head and tested to determine Marshall Stability value which is
the maximum load in kg before failure and the flow value which is the deformation of the specimen
in 0.25mm units up to the maximum load. The corrected Marshall Stability value of each specimen is
determined by applying the appropriate correction factor. The optimum content for the mix design is
found by taking the average value of the following bitumen contents found from the graphs of the
test results.
• Bitumen content corresponding to maximum stability
• Bitumen content corresponding to maximum unit weight
The Marshall Stability value, Flow value at the average value of bitumen content is checked
with the Marshall mix design criteria/ specifications given in table 3.
TABLE 3: SPECIFICATIONS FOR MARSHALL STABILITY TEST
Test Property Specified value
Marshall Stability, kg 340(minimum)
Flow value, 0.25mm units 8 to 16
Mix with very high Marshall Stability values and low Flow values are not desirable as the
pavements constructed with such mix are likely to develop cracks due to heavy moving loads, if the
pavement components permit relatively high deflection values.
4. TEST RESULTS AND DISCUSSIONS
The results of the above tests are presented in the following tables and figures.
4.1 Table 4 shows the penetration values of ordinary bitumen (O.B) and bitumen mixed with natural
rubber (N.R)

17

TABLE 4: PENETRATION VALUES OF O.B AND POLYMER MODIFIED BITUMEN
TEST PROPERTY O.B O.B+
1%N.R
O.B+
2%N.R
O.B+
3%N.R
O.B+
4%N.R
O.B+
5%N.R
O.B+
5.5%N.R
O.B+
6%N.R
O.B+
7%N.R
Penetration
Value(1/10th)mm
69
71
66
61
62
69
64
65
68
69
71
67
67
65
68
62
69
66
60
66
78
69
65
73
63
70
75
72
71
79
63
76
76
79
76
78
72
71
66
73
74
66
82
74
72
75
78
69
78
66
77
79
69
76
78
74
83
76
79
78
75
82
71
72
78
68
83
79
65
72
83
74
76
81
80
84
80
78
72
84
81
79
76
79
75
76
79
71
80
79
73
77
80
81
83
81
74
77
80
80
82
82
79
76
83
85
83
82
79
81
82
73
81
78
77
81
78
81
83
75
80
79
81
79
80
77
84
86
76
79
75
76
79
71
80
79
73
77
80
81
83
74
71
81
77
70
79
71
83
77
79
67
80
82
75
78
73
64
82
71
74
67
72
73
79
77
80
77
77
64
80
72
73
76
71
64
74
66
70
79
Average
Value(1/10th)mm
67 72 75 77 78 80 78.6 76 73
After conducting the penetration value test it is observed that there is gradual increase in
penetration value upto 5% and the value gradually decreased. This indicates that initially the bitumen
got softened upto 5% and then it got hardened. Henceforth bitumen with 1-4% binder content is
suitable in colder regions and from 4-7% it is suitable in warmer regions.
4.2 Softening Point and Viscosity Results
Table 5 shows the softening point and viscosity point results of ordinary bitumen (O.B) and
bitumen mixed with natural rubber (N.R).
TABLE 5: SOFTENING POINT RESULTS OF ORDINARY POLYMER MODIFIED
BITUMEN
TYPE OF SAMPLE SOFTENING
POINT VALUE(°C)
VISCOSITY POINT
VALUE(°C)
Ordinary Bitumen 52 293
Ordinary Bitumen + 1% (N.R) 48 222
Ordinary Bitumen + 5.5% (N.R) 56 648
After conducting the softening point test it is observed that the base bitumen softening point
value is 52°C and decreases at 1% of bitumen modifier to 48°C which is not beneficial. Perhaps 1%
Binder content values can be ruled out. As there is steady increase from 2% we can limit our study to
2-7% of Binder content.

18

After conducting the viscosity point test it is observed that the base bitumen viscosity value is
293 seconds and decreases at 1% of bitumen modifier which is 222 seconds and then it increases.
This trend is also similar to softening point trend but there is steep increase upto 7%. Since it is
softer at 1% it is ruled out and from 2-4% it is optimum criterion for determining optimum binder
content from Marshall Stability Test.
4.3 Ductility and Flash Fire Test Results
Table 6 shows the ductility value and flash fire point results of ordinary bitumen (O.B) and
bitumen mixed with natural rubber (N.R).
TABLE 6: DUCTILITY RESULTS OF ORDINARY POLYMER MODIFIED BITUMEN
TYPE OF SAMPLE DUCTILITY
VALUE (CM)
FLASH
POINT(°C)
FIRE
POINT(°C)
Ordinary Bitumen 120 260 270
Bitumen + 1% natural rubber latex 120 230 240
Bitumen + 5.5% natural rubber latex 53 280 310
After conducting ductility value test it is observed that the base bitumen ductility value is
120cm. There is sudden decrease in ductility value from 2 to 3%. Then it gradually decreases and
goes less than 50 cm at 6% and continues upto 7%. According to ISI specifications ductility values
below 50 cm are not suitable for road construction.
Flash fire point test is conducted on 60/70 bitumen grade mixed with Natural Rubber
(Latex) and graph is drawn between % of bitumen modifier added on x-axis and temperature in
degrees on y-axis. In Flash point from 1-3% we can see steady graph and after 3% it is increasing.
Even though from 1-3% it is decreasing it is not much lower so it is suitable for working conditions
without causing fire hazards from safety point of view. The minimum value of flash point specified
by ISI is 175°C for all grades of bitumen.
4.4 Marshall Stability Test Results
Table 7 shows the marshall stability test results are presented below.
TABLE 7: MARSHALL STABILITY RESULTS FOR BITUMINOUS MACADAM MIX
SAMPLE MARSHALL STABILITY
VALUE (kg)
FLOW VALUE (mm)
Sample with 3.3% Ordinary
bitumen
601 2.88
Sample with 3% bitumen
containing 3% natural rubber
589 2.8
Sample with 3% bitumen
616 2.9
Sample with 3.5% bitumen
545 3.1
Sample with 3.5% bitumen
528 3.3

For ordinary bitumen of 60/70 grade, maximum strength is obtained at 3.3%.
19

3% and 4% natural rubber is added to two percentages of bitumen levels (3% 3.5). 3.5% is
selected because for normal 60/70 bitumen the optimum binder content is obtained at 3.3%. From
Marshall Stability test maximum strength 616kgs is obtained for 4% natural rubber at 3% bitumen
level. By adding 4% bitumen modifier, the bitumen content can be decreased considerably, thereby
the cost of road construction is reduced. As 1% and 5% above binder contents are ruled out, 2%, 3%
and 4% are taken as optimum binder content for the calculation of Stability and flow tests.
4.7 Figures of Various Tests are Presented Below

20
5. CONCLUSIONS

Huge amount of scrap rubber is generated from surroundings which can totally be used for
this purpose by reusing it and solving the problem of disposal of rubber and its waste generation.
Penetration test at 25°C is the most commonly adopted test on bitumen to grade the material in terms
of hardness. So, in warmer regions lower penetration grades are preferred and in colder regions
higher penetration values are used. Since the obtained value is in between 60mm (1/10thmm) and
80mm (1/10thmm), it can be used for both regions in pavement construction.
Softening point test gives an idea of temperature at which the bituminous material attains a
certain viscosity. So bitumen with higher softening point preferred in warmer place and it is also
used to specify hard bitumen. Since the obtained value is between 50°C and 55°C, it can be preferred
in warmer places.
From the viscosity values, it can be concluded that resistance to flow increases with increase
of % bitumen modifier. So, higher the duration more viscous is the material. As viscosity value is
more, it can be used in pavement construction.
The minimum value specified by Indian Standards Institution is 50cm, % of bitumen
modifier more than 5.5 should not be used in pavement construction. As it is less than 50cm after
5.5% of bitumen modifier, due to its low ductility value, the pavement may crack especially in cold
weather.
Flash fire point has no significance about strength of bitumen. They are used to know the
working temperatures of the bitumen. If the working temperatures are more than flash fire point
values, then fire hazards may occur.
Since Bitumen gets soften at 1% it is ruled out and percentages above 5.5% are ruled out in
ductility. Hence from 2-4% we can get the optimum binder content value for determining Marshall
stability test.
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[11] Highway Engineering Materials by Khanna and Justo.

21

[12] Recommended Practice for Bituminous Penetration Macadam (Full Grout), IRC.
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