Remember me in your pray

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Assala mu alykum My Name is saqib imran and I am the student
of b.tech (civil) in sarhad univeristy of science and
technology peshawer.
I have written this notes by different websites and some by
self and prepare it for the student and also for engineer who
work on field to get some knowledge from it.
I hope you all students may like it.
Remember me in your pray, allah bless me and all of you
friends.
If u have any confusion in this notes contact me on my gmail id:
Saqibimran43@gmail.com
or text me on 0341-7549889.
Saqib imran.

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Rotary Intersection of Roads and its Design
Factors
What is Rotary Intersection of Roads?
The rotary intersection of roads is also called as traffic rotary which is nothing but
enlarged intersection of roads where vehicles cross roads or change their direction
without stopping.
All vehicles coming from different roads move in single direction around the central
island and diverges into required exit.
Design Factors for Rotary Intersection of Roads
There are many factors to be considered while designing traffic rotary as follows:

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1. Design speed
2. Shape of central island
3. Radius of rotary roadway
4. Weaving angle and weaving distance
5. Width of carriageway at entry and exit
6. Width of rotary roadway
7. Curves at entrance and exit
8. Capacity of rotary
9. Channelizing islands
10.Camber and super elevation
11.Sight distance
12.Lighting
13.Traffic signs
14.Pedestrian ways
Design Speed of Rotary Intersections
At rotary intersections, the vehicle can be moved without any breaking. So, there is
no chance to stop the vehicle while other vehicles can change their direction or
cross each other without stopping. But, the speed of vehicular movement should be
reduced.
Standard highway speed is not applicable at rotary intersection. It should be passed
with low speed which will results the safe carrying towards one’s direction without
any collision. Speed restriction board should be provided on the road towards rotary
intersection.
Shape of Central Island
The shape of Central Island provided for rotary intersection should not contain any
corners. It should be formed by curves to allow the comfortable rotations around it.

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The shape is particularly dependent upon number of roads meeting at that
particular junction. The shapes generally provided are circular, elliptical, turbine
and tangential. Circular shape island is shown below:
Radius of Rotary Roadway
The radius of roadway or pavement around the central island is dependent of shape
of Central Island. If it is circular shape, radii are similar at all points and if it is
elliptical or tangent radii is different at different points. The radius of rotary
roadway should be designed by just considering the friction force and super
elevation should be neglected.
Normal radius of roadway in curves
But super elevation (e) is neglected i.e., e = 0
Hence, radius of rotary

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Where f = coefficient of friction = 0.43 to 0.47
Weaving Angle and Weaving Distance of Rotary Intersections
Weaving angle is the angle formed by paths of vehicle entering the rotary and other
vehicle leaving the rotary at adjacent road. The exits of two vehicles may be
different but they travel in same way for some short distance in the rotary section
which is nothing but merging of vehicles and when the required exit is come two of
the vehicles diverged into different directions.
The length of which the two vehicles travel in same way is called as weave length.
The weaving angle should be small but minimum of 15o
is maintained. The weave
length should be at least four times the width of weaving section.
Width of Carriageway at Entry and Exit
The width of carriage way at entrance rand exits is dependent of volume of traffic in
that particular region or area. But, the minimum width of 5.0 meters should be
maintained for rotary intersections.
Width of Rotary Roadway
Vehicles coming from all directions may meet at a time at least for shorter distance
at rotary intersections. The width should be equal to the effective width of weaving
section. So, the width provided for rotary roadway should be as follows
Where e1 = width at entrance

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e2 = width of non-weaving section
Curves at Entrance and Exit
Entrance and exit curve is nothing but a curve traced by the rear inner wheel of
vehicle. Generally, at entrance the vehicle will slow down to design speed of rotary
intersection so, at the entrance curve radius can be provided as same as radius of
central island.
Coming to exit curves, the vehicle accelerates at exits hence the radius of curve at
exit should be greater than the radius of curve at entrance.
Capacity of Rotary Intersections
The capacity of rotary is derived from the below formula and it is mainly dependent
upon capacity of individual weaving section.
Where W = width of weaving section
e = average width of entry and width of non-weaving section for the range of e/W
L = weaving length for the range of W/L
Where p = proportion of weaving traffic = (b+c)/(a+b+c+d) = (0.4 < p < 1.0)
a = left turning traffic moving along left extreme lane
b = weaving traffic turning toward right while entering the rotary

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c = weaving traffic turning toward left while leaving the rotary
d = right turning traffic moving along right extreme lane
Channelizing Islands
Channelizing islands are provided at entrance or exit of road way to prevent the
vehicle from undesirable weaving.
Camber and Super Elevation
We already discussed that the super elevation for rotary roadways is neglected.
But, here if the vehicle is changing its direction to its opposite side it will travel
around the central island and changes the direction.
While changing, the vehicle may over turn or slip, to overcome this, minimum cross
slope is provided which is nothing but camber. This camber acts as super elevation
in case of rotary roadways.
Sight Distance
The sight distance provided at rotary intersections should be as higher as possible
and in no case the value must be less than the stopping sight distance.

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Lighting of Rotary Intersections
The edge of Central Island should be installed with lights which is mandatory.
Additional lights may also be provided at the kerbs if the diameter of Central Island
is more than 60 m. sometimes, entrance and exit curves can also be provided with
lights.
Traffic Signs at Rotary Intersections
Traffic signs should be installed on approaching roads to indicate the presence of
rotary intersection ahead to the roadway users. Kerbs at rotary intersections should
be coated with black and white strips to improve visibility. Traffic signals should be
placed 1 meter above road level to indicate the direction of exit.
Pedestrian Ways at Rotary Intersections
At rotary intersections, the vehicles will move consistently and will not stop. So, the
footpath is provided guard rails which will block the entrance of pedestrian into
roadway. If crossing of road is important and pedestrian traffic is higher, then
construction of subways, over bridges is good solution.

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Types of Concrete Pavements -Their
Construction Details and Applications
Concrete pavement which is occasionally called rigid pavement is a concrete layer
that is in contact with traffics directly and it is used for different purposes and
applications.
The concrete used for pavements can be modified and changed in various ways as
per the requirement. Not only does the concrete pavement need to be strong and
durable but also it must be workable and cost effective because it is commonly
prone to severe environmental conditions.
Concrete pavements offer several advantages which is not possessed by bituminous
pavement designs, for example, it is considerably suitable for large points loads,
withstand diesel spillage and other aggressive materials, suitable for cases where
sub-grade strength is low, resist high temperature, and many more benefits.

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There are different types of concrete pavement which are employed for various
applications and these will be discussed in the following sections.
Fig.1: Concrete Pavement Construction
Types of Concrete Pavements -Construction
Details and Applications
Following are the different types of concrete pavements and their applications and
advantages:
 Jointed unreinforced concrete pavement
 Jointed reinforced concrete pavement
 Continuously reinforced concrete pavement
Jointed Unreinforced Concrete Pavement

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As it can be observed from Figure-2, jointed unreinforced concrete pavement is
composed of batch work of concrete slab layers, which are small square units,
connected by employing tie bars and dowels or joints that is provided to prevent
cracks.
So, the joint layout detailing of jointed unreinforced concrete pavement is
important as it affects the design, construction, and services of the concrete
pavement.
Fig.2: Jointed Unreinforced Concrete Pavement
Fig.3: Details of Joints in Jointed Unreinforced Concrete Pavement

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The success of jointed unreinforced concrete pavements depends on the tensile
strength and flexural capacity of the concrete used which should withstand cracking
and support imposed loads.
The size of concrete pieces or panels is dependent on the concrete shrinkage strain
created due to concrete hardening. Shrinkage strain creates tensile force in
concrete and may cause cracks unless the tensile strength of concrete is greater
than the tensile stresses generated by shrinkage strains.
Designing, detailing and spacing of joints in the jointed unreinforced concrete
pavements are considerably significant and joints need to be organized in such a
way that produces square slab panels. This could be obtained when the 90 degree
between longitudinal joints and transverse joints are achieved as it can be seen in
Figure-2.
Additionally, the joint intervals in the jointed unreinforced concrete pavement is
dictated by concrete slab thickness. The joint spacing increases as the thickness of
the slab is increased and vice-versa.
It is recommended to use steel dowels in the joints otherwise the ability of the
joints to contain movements will be declined and eventually the slab thickness need
to be increased.
Table-1, which is taken with slight changes from American Concrete Pavement
Association, provides guidance on determining spacing in concrete pavements.
Table-1: Joint Spacing for Concrete Pavement
Pavement
thickness, cm
Maximum recommended joint
spacing, Limestone aggregate
(m)
Maximum recommended joint
spacing, Gravels and crushed
stone (m)
15 5.4 4.5

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20 5.9 4.9
25 6.4 5.3
30 7.2 6
Applications of Jointed Unreinforced Concrete Pavements
Jointed unreinforced concrete slabs can be used in different applications which
include airfield taxiway as it can be seen in Figure-4, airfield aprons see Figure-5,
and industrial yard as shown in Figure-6.
Fig.4: Use of Jointed Unreinforced Concrete Pavement in Construction of
Airfield Taxiway

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Fig.5: Airfield Apron

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Fig.6: Industrial Yard Constructed using Jointed Unreinforced Concrete
Pavement
Jointed Reinforced Concrete Pavement
The jointed reinforced concrete pavement is a modified or developed version of
jointed unreinforced concrete pavement. It is used instead of plain concrete
pavement when there is doubt regarding materials and workmanship and
differential settlement are anticipated.
Not only does thickness of jointed reinforced concrete pavement is thinner but also
its joint spacing is greater compared to that of jointed plain concrete pavement.
Generally, reinforced concrete slab with length of 10m are used but there are cases
in which the slab length can reach up to 20m.
Jointed reinforced concrete pavement can be designed as crack free slabs or
cracked slabs. The embedded steel reinforcement controls cracking and improves
concrete slab stiffness. By and large, steel bars are installed in the middle of the
slab but some designers locate reinforcements at both slab faces.
The most outstanding benefit of steel bar installation in the middle of the jointed
reinforced concrete pavement is balancing positive and negative moments equally
and as a result the slab is permitted to flex prior to cracking.
Added to that, the application of doweled joints in the jointed reinforced concrete
pavement is a must because the spacing is large, which means the movement in
the joint cannot be controlled if dowel ties are not used.
Commonly, pavement slab thickness of 150mm is employed and it is influenced by
number of practical parameters such as required concrete cover.

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Applications of Jointed Reinforced Concrete Pavement
The jointed reinforced concrete pavement is used in the case where huge
concentrated loads are expected and the designer has doubt about labor force who
will build the concrete pavement.
Fig.7: Jointed Reinforced Concrete Pavement
Continuously Reinforced Concrete Pavement
This type of concrete pavement is built like long slab and reinforcement bars are
placed at the middle of the slab. The longitudinal reinforcements, which are
maintained at their position by transvers reinforcement bars, are employed to limit
shrinkage cracks.
Figure-8 shows embedded longitudinal reinforcements held by transverse
reinforcements.

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Fig.8: Arrangement of Longitudinal and Transverse Reinforcement in
Continuous Reinforced Concrete Pavement
Cracks in continuous reinforced concrete pavement are initiated in arbitrary manner
as can be observed in Figure 9.
It is required to provide anchors at the end of the continuous reinforced concrete
slabs otherwise huge ripple or bump will be formed at the beginning of bituminous
materials due to movements which are generated by temperature fluctuations.

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Fig.9: Cracking of Continuous Reinforced Concrete Pavement
Continuous reinforced concrete pavement operation is substantially influenced by
cracks spacing which is controlled by longitudinal reinforcement. Commonly,
longitudinal reinforcement ratio used in continuous reinforced concrete pavement is
specified to be 6 percent of sectional area. If spacing between cracks are
considerably small then it is likely that concrete blocks fail in shear.
There are various types of finished that may be applied for instance whisper
concrete and thin bituminous wearing course on the surface finish of continuous
reinforced concrete pavement.

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Fig.10: Continuous Reinforced Concrete Pavement with Successive Whisper
Concrete Resurfacing
Applications of Continuously Reinforced Concrete Pavement
Continuously reinforce concrete pavements may be employed for the construction
of airfield runways and highway projects and it is specifically cost effective when
massive quantity of aggregate is present at site.

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Fig.11: Airfield Runway, Liverpool Airport, UK
Types of Bitumen Mixes for Pavement
Construction and their Applications
There are various types of bitumen mixes with aggregates for pavement
construction. Applications of these bitumen mixes for pavements is discussed in this
article.
Types of Bitumen Mixes for Pavement
Construction and their Applications
Based on the nature of gradation selected for the bitumen mixes, they can be
classified into:
 Dense Graded Bitumen Mixes
 Semi-Dense Graded Bitumen Mixes
 Open Graded Bitumen Mixes
 Gap Graded Bitumen Mixes

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Fig.1: Gradation Chart for Dense, Open Graded and Gap Graded Bitumen
Mixes Density
The bitumen mix that is densely graded has continuous gradation, say in the
proximity of maximum density line. The bitumen mix with a large amount of fine
aggregate i.e. sand will form open graded bitumen mix.
When the mix lack materials of two or more sizes, it will form gap graded bitumen
mix. The semi-graded mix will have a gradation lying in between the open graded
and the gap graded. All the gradation variations are represented in figure-1.

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Dense Graded Bitumen Mixes for Pavements
These mixes possess continuous gradation of all primary aggregates. These
particles are packed together. Here inter-particle surface friction is the reason
behind their property of strength gain.
All most all possible flexible pavements constructed in the world employ dense
graded bitumen mixes.
There are two main types of dense graded mix used. They are:
 Dense Bitumen Macadam (DBM)
 Bituminous Concrete(BC)

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Dense Bitumen Mixes
This mix is mainly employed for base course and the binder course. This itself
consist of two gradations; Grading-1 and Grading-2. Grading-1 has 37.5mm as the
nominal maximum aggregate size (NMAS). While Grading-2 have NMAS of 25mm.
The fine aggregate percentages in both the grading are same in a range of 28 to
42%. The main criteria that differ both the grading are that the grading 1 consist of
large size particles i.e. 25mm to 45mm.
The grading-1 with NMAS of 37.5mm has many disadvantages like segregation.
This segregation will later result in honeycombing. At lower air-void levels, these
mixes become permeable compared to the grading 2, with NMAS of 25mm.
Hence, the grading-1 causes problems related to water exposure. With the increase
of NMAS, the permeability will increase the multi-fold at a present void level
condition.
Fig.2: Dense Bitumen Mixes Grade-1, NMAS mix of 37.5mm -Honeycombing
Defect due to Segregation

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The effect of the nominal maximum aggregate size on the permeability of the
flexible pavement is represented in the graph shown in figure-3.
The grade-1, have the advantage of rutting resistance compared to the grading-2.
During the rainy season, the pavement made of NMAS 37.5MM, Grade 1 must be
sealed or overlaid. This will avoid penetration of the water into the pavement and
reach the Wet mix macadam. This is the WMM course also called as crushed stone
base source.
Fig.3: Effect of Nominal Maximum Aggregate Size on Permeability of
Flexible Pavement
Bituminous Concrete Mixes (BC)
The bituminous concrete mix is used in two forms: Grade-1 and Grade-2. Grade-1
with NMAS of 19mm. The Grade-2 of 13mm as the NMAS.
From the above description about dense bitumen mixes, it was clear that dense
bitumen mix grade-2 have larger use as the base course due to its fewer
disadvantages compared to dense bitumen mix Grade-1. This hence was necessary
to determine a grade for the binder and the surface course.

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The bituminous concrete grading-1 with nominal maximum aggregate size 19mm
as the binder course binds the base course (dense bitumen mix Grade-1) as well as
the wearing course bituminous concrete grade-2 of nominal maximum aggregate
size 13mm, with NMAS 19 mm employed as a transition. The bituminous concrete
grading-2 is good to be used as a wearing course.
To facilitate medium and low traffic, a bituminous concrete grade of nominal
maximum aggregate size 9.5 mm was necessary to considered for the construction
of smooth and impermeable pavement in urban areas.
To facilitate thin asphalt lifts, bituminous concrete grading-3 is more suitable than
grade-2. The bituminous concrete grade-2 of NMAS 9.5mm has been efficiently
used in the highway construction for the US. For higher traffic BC grade-2 are
recommended.
Table-1: Recommended Bitumen Concrete(BC) Gradations

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Semi-Dense Bitumen Mixes
The two types of semi-bituminous mixes used in the pavement construction in India
are;
 Semi-Dense Bituminous Concrete (SDBC)
 Mixed Sealed Surfacing (MSS)
Semi-Dense Bituminous Concrete (SDBC)
The semi-dense bituminous concrete mixes have neither dense or open graded
characteristics. It consists of the so called pessimum voids when they are fully
constructed.
The word is an anonym of optimum. So, it is advised to make the mix get rid of
pessimum voids. These tend to capture moisture or water that will later cause
stripping.
When the semi dense bituminous concrete is employed above the bitumen
macadam (BM) layer, there is chances for the penetration of rainwater through the
SDBC and reach the BM.
This will create the separation of aggregate and the bitumen in the BM layer. This
will cause stripping and the scaling of SDBC. The scaling later with time will result
in the potholes on the road.

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Fig.4: Semi-Dense Bituminous Concrete Highways with Shallow Potholes
Mixed Seal Surfacing (MSS)
The Mixed Seal Surfacing design mix is based on the IRC: SP:78-2008. This is an
alternative used for the premix carpet (PMC). Both the PMC and the MSS are
employed in 20mm thickness.
There are two gradations that are specified for the mixed seal surfacing
mix. They are
 Type A – Closed Gradation with an NMAS value of 9.5mm
 Type B- Open Gradation with an NMAS value of 9.5mm or 12mm
The aggregate grading for the MSS mix is mentioned in table-2.
Table-2: Aggregate Grading for Mixed Seal Surfacing Mix

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Open Graded Bitumen Mixes
The open graded Bitumen Mixes have fine aggregates in a minimum amount, hence
they are very permeable to water. They are employed based on specific functions in
the base and for surface mixes.
Open Graded Bitumen Base Mixes
Three open graded mix types are employed as the base mixes. They are the
 Asphalt Treated Permeable Base (ATPB)
 Bituminous Macadam(BM)
 Built up Spray Grout (BUSG)
Asphalt Treated Permeable Base (ATPB)
Permeable asphalt treated base (PATB) is used extensively on major highway
construction in the US. This system will help to have sub surface drainage. The
PATB is also called as the Asphalt Treated Permeable Base (ATPB). The system
consists of separate course for the subsurface drainage. The thickness of the PATB
ranges from 75mm to 100mm.
The PATB is given between the granular sub-base (GSB) and the bituminous
course. The granular sub-base in flexible pavement too have the intention to
provide subsurface drainage.
The GSB consist of large quantity of fines that are passing through 0.075mm sieve,
which will let in providing excellent drainage system. A two-layer drainage system
is implemented by this system.
Bituminous Macadam (BM)

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The BM mix is open graded and highly permeable in nature. This is a recipe type
mix produced that gain no kind of quality in terms of strength and volumetric. The
void content is 20 to 25% higher than the dense graded bitumen (DBM). The DBM
have a void content of 3 to 5%. The BM have high potential to attract water and
moisture.
Built-up spray Grout (BUSG)
For flexible pavements, BUSG has been recommended as a base course. It is a two-
layer composite construction with single size aggregates, which are nicely
compacted. This has a hot bitumen layer applied after each layer. At the top, single
sized key aggregate is applied.
As the sprayed bitumen does not help in filling the voids that are created by the
coarse aggregate, these pavements behave to be highly permeable in nature. This
does have a property to attract moisture and water. The application of BUSG as a
remedy for the removal of potholes is stopped.
Open Graded Bitumen Surface Mixes
Three open graded mix types are employed as the surface mixes. They are:
 Open graded Friction course (OGFC)
 Premix Carpet (PMC)
 Surface Dressing
Open Graded Friction Course (OGFC)
The OGFC system consists of interconnected voids that help to improve the surface
drainage property. Here the rainwater will drain through the OGFC and reach the
bituminous concrete grade 2 (BC), that will later flow laterally within the OGFC.
Which is later ended at the shoulder. The last OGFC layer will have a thickness of
20mm.

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This system will have no trace of water on the surface. The OGFC system was
developed in 2002, by the US nationals. The safety and the environmental features
of OGFC are mentioned below:
 Improvement of frictional resistance of wet pavement
 Hydroplaning: Hydroplaning is the effect of skidding on ice and the loss of
control problems of the vehicles. This is due to the presence of water
during and after rain. The OGFC lets removal of water from the surface,
letting no water trace on the pavement.
 The splash and the spray are reduced: The high-speed movement of
vehicles will cause splashing and spraying of water to the nearby vehicles,
which will cause problems to the visibility. The OGFC results in no water
flooding in the road hence no splashing or spraying.
 Glare: The OGFC results in the reduction of glare from the headlights in
the wet conditions. This will help in better visibility and have reduced
driver fatigue.
 Noise Reduction
Premix Carpet (PC)
Here the PC is laid as a wearing course with a thickness of 20mm. The mix will
compose two single size aggregates. One is the aggregate that is passing through
22.5mm and that will retain in 11.2mm.
The second aggregate type will pass through 13.2mm and retain on 5.6mm sieve.
Here with respect to the climate and the traffic intensities, the viscosity grade
bitumen are employed. It can be either VG-10 or VG-30.
Based on the aggregate and aggregate application rates that are specified in IRC:
14-2004, in “Recommended Practice for Open Graded Premix Carpet”, the bitumen
content by weight of mix is 3.3%.
Surface Dressing

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As per IRC:110 -2005, ” Specification and Code of Practice for Design AND
Construction of Surface Dressing”, the surface dressing has the following
significances and objectives:
 The surface dressing will provide a dust free wearing course over a
granular base course that act similar to a water bound macadam (WBM)
or a wet mixed Macadam (WMM).
 The surface Dressing will help in providing impermeability for water
percolation for the road surface
 Surface Dressing provide high friction for the riding surface
 This will provide a renewal coat for periodic maintenance of bituminous
wearing surfaces.
 The surface dressing work involves the process of spraying of proper
grade paving bitumen mainly VG-10 or the rapid setting cationic emulsion.
This is applied over an aggregate layer of appropriate size and gradation.
Surface dressing does not increase the structural strength and the riding quality of
the pavement constructed.
Gap Graded Bitumen Mixes
The Stone Matrix Asphalt (SMA) is the most commonly used gap graded bituminous
mixes. With the increasing traffic and the high pressure of tires of the vehicles will
give large stresses to the road pavement. The roads are subjected to overloading
conditions in certain cases.
The stone matrix asphalt mix is tough, highly stable in structure and rut resistant
asphalt mix. These systems rely on the stone to stone contact that will facilitate in
strength. The rich mortar used in the system will provide better durability.
The advantages of stone matrix asphalt mix are:
 Surface Frictional Resistance are improved

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 The noise is reduced
 Compared to the conventional dense graded asphalt mix, the night
visibility is reduced.
The following steps are involved in the stone matrix asphalt mix design:
1. The selection of the materials i.e. aggregates, binder and the cellulose
fiber.
2. Three trial gradations are involved to ensure stone to stone contact.
3. Optimum binder content is used for the all the gradation chosen
4. The binder drains down as well as the moisture susceptibility is evaluated.
The performance of the stone matrix asphalt mix pavement as studied by the US,
based on the rutting effect seen in the road pavement. The figure-5 below shows
the rut depth caused for different ranges of the project conducted.
Fig.5: As per NCAT, the rutting performance of the stone matrix asphalt
mix pavement constructed in the US
The performance of the SMA pavements that are constructed in India has
performed well.
Compared to bitumen concrete, the cost for stone matrix asphalt mix has been
found to be 25 to 30% higher. The increased cost of the SMA material is due to its
composing materials like cellulose fiber, modified binder, and the binder content.

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In the US, the life cycle study conducted showed that the stone matrix asphalt mix
is more cost effective in terms of performance and lesser maintenance.
Bituminous Materials – Types, Properties and
Uses in Construction
Materials that are bound together with bitumen are called bituminous materials.
The use of bituminous materials were initially limited to road construction. Now the
applications have spread over the area of roof construction, for industrial purposes,
carpet tiles, paints and as a special coating for waterproofing.
History of Bituminous Materials
Before the era of bitumen, tar was used as the binder material for bituminous
materials.

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After the 20th century, the new types of vehicles with pneumatic tires came into its
existence in the UK. The time was when tar was used in road construction in larger
areas.
The road was constructed using water bound and graded aggregates as per the
principles that were developed by Macadam. Macadam roads produced large
amount of dust due to the action of the pneumatic tires and the speed of the
vehicles moving. This led to binding the surface of the road with this tar.
Tar would act as a dressing to coat the surface. It is well suited for the purpose as
it can be made semi-fluid and sprayed accordingly. This on cooling will get stiffened
and protects the road from water attacks.
The history of bitumen came from the refinery bitumen that was used in Mexican oil
fields in the UK, around 1913. But in 1920, the Shell Haven refinery was the one
who has a role in bringing the bitumen into road construction.
Difference between Bitumen and Tar
When compared to tar, bitumen is less temperature susceptible. So, for a given
temperature, the bitumen has larger stiffness compared to the tar at the same
temperature.
This proved higher deformation resistance and softening resistance compared to
the tar. In future, under high abrasion forces, they behave more brittle and highly
crack resistant.
With time, the vehicles increase, so the traffic. Hence it was essential to bring roads
with increasing performance. This lead to the complete use of bitumen than tar.
Types of Bitumen

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To go with a wide variety of circumstances, a wide variety of bituminous mixtures
were developed. The main variation is brought by the change in the bitumen
content, the bitumen grade, the aggregate type used and the size of the
aggregates.
Traditionally in UK, the bitumen is categorized into two. The first one is “asphalt”
and the second one is “macadam“. In North America, the asphalt is called as
bitumen itself.
Asphalts are bitumen mixture whose strength and stiffness is gained through the
mortar property. While in the case of macadam, the strength is dependent on the
aggregates that are used in the mix (i.e. grading of the aggregates).
For each case mentioned, the property of the bitumen change. It is found that the
asphalt properties are more governed by the bitumen properties than in the case of
macadam.
Fig.1: Representation of Asphalt Mix and its Characteristics

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Fig.2: A Representation of Macadam Mix and its Characteristics
Use of Bituminous Material in Flexible Pavement
The bituminous materials are mostly employed for the construction of flexible
pavement. When the road construction makes use of concrete slabs, we call it a
rigid construction.
The flexible pavement itself have several layers, each having specific functions to
be carried out, under loads. A general flexible pavement layer in a flexible
pavement is shown in figure.3.
Fig.3: Different Layers in a Flexible Pavement Construction

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Based on the position and the function of the material, the nature of the material
also varies. The surface course, the binder as well as the base may be of asphalt.
But the type and the properties of asphalt in each of these layers vary based on the
location and the function.
The asphalt in the surface course is different when compared with the asphalt that
is used in the binder course or in the base.
Constituents of Bituminous Materials
Graded aggregate and bitumen are the compositions of bituminous material. There
is a small proportion of air present in the same, which make the bituminous
material a three-phase material.
The whole property of the bituminous material is highly dependent on the individual
properties of each phase and their respective mix proportions. The two solid phases
i.e. the bitumen and the aggregate are different in nature.
The aggregate is stiff and hard in nature. The bitumen is flexible and vary under
temperature as they are soft. So, the whole performance of the material is greatly
influenced by the bitumen proportion in the whole mix.
The supply of bitumen can be carried out in a variety ways based on whether the
demand is for laying or is to facilitate some other performance. When the quality
and the performance of the bituminous material is concerned, the aggregate
constituent quality is also a primary factor.
We can either go for continuously graded aggregates, which are called as asphalt
concrete (Before in the UK, it was called as macadam as discussed in before
sections) or else the aggregates used can be gap graded, which are known as hot
rolled asphalts or stone asphalt (This was known before as asphalts in the UK).

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The filler is the fine component of the aggregates, that would pass through 63
microns. The graded aggregate mix might contain some quantity of fillers. But
when it is not adequate, extra filler either in the form of Portland cement, or
hydrated lime, or limestone dust are used.
Sources of Bitumen
The bitumen has mainly two sources, they are:
 Natural Bitumen
 Refinery Bitumen
Natural Bitumen or Natural Asphalts
The bitumen is obtained from petroleum naturally with the help of geological forces.
They are found to seen intimately connected with the mineral aggregates. They are
found deposited at bitumen impregnated rocks and bituminous sands that have
only a few bitumen in percentage.
The Val de Travers region of Switzerland and the ‘tar sand’ area of North America
gain notable range of bitumen deposits. The rock asphalts gain bitumen in 10%, in
the form of limestone or sandstone impregnated bitumen.
Lake asphalt composes of bitumen ‘lake’ that is found as dispersed finely divided
mineral matter in bitumen. The roads in the UK make use of bitumen from the
deposits of before mentioned lake deposits found in the Trinidad Lake.
The asphalt found from the lake are refined to a partial state by heating it to a
temperature of 1600
C. This is done in open skill to remove out the excess water.
Later the material is filtered. This is then barreled and transported.

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It is hard to use the material directly on the roads as it consists of 55% of bitumen,
mineral matter of 35% and 10% of organic matter. This even after treatment is
blended with refinery bitumen before use.
Refinery Bitumen
This bitumen is the residual material that is left behind after the crude oil fractional
distillation process. The crudes from different countries vary based on their
respective bitumen content.
It is found that crudes from Middle east and the North Sea have to undergo further
process even after distillation to get final bitumen. These sources have a very small
bitumen content.
But crude from the Caribbean and around countries give the higher content of
bitumen that can be extracted with great ease.
Manufacture of Bitumen
The manufacture of bitumen is a lengthy process which is represented briefly in the
below flowchart. The bitumen is a residual material. The final bitumen property will
depend upon the extent of extraction, the viscosity, and the distillation process.
The present refinery plant has the capability to extract bitumen more precisely as
the required viscosity and consistency.

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Fig.4: Flowchart Showing Preparation of Refinery Bitumen
Structure of Bitumen
The hydrocarbons and its derivatives formed in a complex colloidal system will
compose to form the bitumen structure.
Bitumen is a colloidal system that dissolves in trichloroethylene. This solvent is
used to determine the constituents that are present in the bitumen.
The bitumen constituents can be subdivided as follows:
 Asphaltenes: These are found to be insoluble in light aliphatic
hydrocarbon solvents
 Maltenes: These are soluble in n-heptane
The colloidal system of bitumen is a system with solid particles of Asphaltenes, that
together form a cluster of molecules or these can be micelles; a continuum of
Maltenes.
Based on the micelles dispersion, the bitumen can either exist in the form of a sol
or in the form of a gel. Sol is formed when there is complete dispersal. The gel is
formed when the micelles undergo flocculation to become flakes.
The bitumen take a gel character, when it has a higher quantity of saturated oil of
molecular weight less. That bitumen with aromatic oils show sol character. This is
one with more Asphaltenes.
Influence of Bitumen Constituents in the Material
Properties

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The individual fractions that form a bitumen surely have some contribution towards
the properties of the bitumen material.
 The Asphaltenes is the fraction that shapes body for the material.
 The resin in the bitumen contributes to adhesiveness and ductility of the
material.
 The viscosity and the rheology of the material are taken care by the oils
present in the bitumen material.
 The stiffness of the material is governed by the sulfur that is present in
significant amounts mainly in high molecular weighed fractions.
 The presence of a certain complex of oxygen will affect the acidity of the
bitumen. The acidity of the bitumen is a factor whose determination will
help in knowing the adhering capability of the bitumen with the aggregate
particles.
Roof Waterproofing Using Bituminous
Waterproofing Membrane Sheet
A bituminous waterproofing membrane is used for reinforced concrete roof
waterproofing. This waterproofing membrane comes on site in the form of rolls
manufactures and packed in the factory properly sealed.
The specifications and safety manuals of this membranes provided by manufacturer
should be read before installation process. Fire safety and prevention is the most
important while using this membrane.
All inflammable materials from roofs to be removed and good roofing practices
should be followed.
The bituminous waterproofing membranes are unfolded on the site and laid firmly
on surface with tar based adhesives using blowtorches.

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A layer of bituminous water proof membrane is laid over the structural roof which
acts as a shield against the seepage of water onto the roof. Roof tiles & membrane
is applied over the filler material laid to slope to pass the flow of water into drains.
A proper slope is necessary to allow the water to flow steadily to drains.
These membranes have 2 to 4 mm thick water proof materials. Membrane should
be flexible with elongation 150 % to cover any small cracks, strong, chemical & UV
resistant, flexible enough to take any shape over which it is laid.
Procedure for Roof Waterproofing Using
Bituminous Waterproofing Membrane

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Roof Surface Preparation
The surface to be membrane should be clear from dirt, dry and clean. Must not be
installed during adverse weather and below 450
F. For slope up to 3 inch the
membrane should be laid perpendicular to slab and more than 3 inch slope should
be laid parallel to slope. This ensures that water is never be running at joint lap
edge.
Torch Equipment
Torch equipments should be properly connected and hoses to be in good working
condition. Check the equipment against gas leakage by using soapy water. When
torch is opened it should be at lowest possible settings to avoid sudden gush of fire.
Roll Alignment
No wrinkles should be allowed while laying membrane and proper alignment is
necessary.

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Bituminous Waterproofing Membrane installation
The torch fire should be applied uniformly and slow over the roll while laying. The
best movement of the torch is as shown in the picture.
Compound flow out
While torching membrane on joints, approximately 1-inch chemical from the
waterproofing membrane should be flowing out to ensure proper filling of gaps.
More than 1-inch flow out signals to overheating of membrane.
Roller should be laid over joints along with torching so that compound sets properly
and no gap is created in joints.
Check Joints between Waterproofing Sheets
Ensure perfect joint between two sheets is the most crucial part. Check all the
edges of joints properly to ensure proper adhesion of end laps of membrane, air
gaps is not acceptable. At gaps the sheets should be lifted and heated with the
torch and resealed again.
End Laps in Waterproofing Membrane Sheets
At the end of sheet should be heated properly as to bitumen starts appearing over
the sheet. Heat the underside of membrane properly to ensure proper bond at laps.
The bituminous waterproofing membrane sheets are overlapped 3 inches at the
sides and 6 inches at the ends for proper grip and waterproof joint and block water
seepage. Staggered end laps must be 18 inches apart so that no adjacent end laps
coincide
Granules Applications

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Granules applications matching the sheet at the end laps and roller is spread to set
it properly. This all applications will give roof an enhanced professional finish.
DESIRABLE PROPERTIES OF ASPHALT
MIXES FOR PAVEMENTS
Bituminous mixes (some times called asphalt mixes) are used in the surface layer
of road and airfield pavements. The mix is composed usually of aggregate and
asphalt cements. Some types of bituminous mixes are also used in base coarse.
The design of asphalt paving mix, as with the design of other engineering materials
is largely a matter of selecting and proportioning constituent materials to obtain the
desired properties in the finished pavement structure.
Fig: Asphalt Mixes for Pavements
The desirable properties of Asphalt mixes are:
1. Resistance to permanent deformation: The mix should not distort or be
displaced when subjected to traffic loads. The resistance to permanent deformation
is more important at high temperatures.

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2. Fatigue resistance: the mix should not crack when subjected to repeated loads
over a period of time.
3. Resistance to low temperature cracking.This mix property is important in cold
regions.
4. Durability:the mix should contain sufficient asphalt cement to ensure an
adequate film thickness around the aggregate particles. The compacted mix should
not have very high air voids, which accelerates the aging process.
5. Resistance to moisture-induced damage.
6. Skid resistance.
7. Workability:the mix must be capable of being placed and compacted with
reasonable effort.
8. Low noise and good drainage properties:If the mix is to be used for the surface
(wearing) layer of the pavement structure.
Marshall stability and Hveem stabilometer tests are largely used for the routine
testing. Criteria for the suitable mix design have been specified by the Asphalt
Institute.
Penetration Value of Bitumen -Determination for
Road Construction
Penetration value test on bitumen is a measure of hardness or consistency of
bituminous material. A 80/100 grade bitumen indicates that its penetration value
lies between 80 & 100.

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Penetration value is the vertical distance traversed or penetrated by the point of a
standard needle into the bituminous material under specific conditions of load, time
and temperature. This distance is measured in one tenths of a millimeter.
Penetration test is used for evaluating consistency of bitumen. It is not regarded as
suitable for use in connection with the testing of road tar because of the high
surface tension exhibited by these materials.
Penetration test on bitumen is carried to determine:
1. Consistency of bituminous material
2. Suitability of bitumen for use under different climatic conditions and
various types of construction.
Determination of Penetration Value of Bitumen

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Apparatus for Penetration Test
Container
A flat bottomed cylindrical metallic dish 55 mm in diameter and 35 mm in depth is
required. If the penetration is of the order of 225 or more, dish of 70mm diameter
and 45mm depth is required.
Needle
A straight, highly polished, cylindrical hard steel rod.
Water bath
Water bath maintained at 25° ± 0.1 °C, containing not less than 10 litres of water,
the sample being immersed to a depth not less than 100mm from top and
supported on perforated shelf not less than 50mm from bottom of the bath.
Transfer dish or tray
Should provide support to the container & should not rock it. It should be of such
capacity as to completely immerse container during test.
Penetration apparatus
Should be such that it allows needle to penetrate without much friction& is
accurately calibrated to give results in one tenth of a millimeter.
Thermometer
Range 0- 44 °C and in readable upto 0.20 C.
Time measuring device
With an accuracy of l second.

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Procedure for Bitumen Penetration Test
(i) Preparation of test specimen: Soften the material to a pouring consistency at
a temperature not more than 60°C for tars and 90°C for bitumen above the
approximate softening point and stir it thoroughly until it is homogeneous and is
free from air bubbles and water.
Pour the melt into the container to a depth at least 10mm in excess of the expected
penetration. Protect the sample from dust and allow it to cool in an atmosphere at a
temperature between 15° to 30° C for one hour. Then place it along with the
transfer dish in the water bath at 25° ± 0.1 °C, unless otherwise stated.
(ii) Fill the transfer dish with water from the water bath to depth sufficient to cover
the container completely, place the sample in it and put it upon the stand of the
penetration apparatus.
(iii) Clean the needle with benzene, dry it and load with the weight. The total
moving load required is 100 ± 0.25 gms, including the weight of the needle, carrier
and super-imposed weights.
(iv) Adjust the needle to make contact with the surface of the sample. This may be
done by placing the needlepoint in contact with its image reflected by the surface of
the bituminous material.
(i) Make the pointer of the dial to read zero or note the initial dial reading.
(ii) Release the needle for exactly five seconds.
(vi) Adjust the penetration machine to measure the distance penetrated.
(vii)Make at least 3 readings at points on the surface of the sample not less than 10
mm apart and not less than l0mm from the side of the dish. After each test return

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the sample and transfer dish to the water bath and wash the needle clean with
benzene and dry it.
In case of material of penetration greater than 225, three determinations on each
of the two identical test specimens using a separate needle for each determination
should be made, leaving the needle in the sample on completion of each
determination to avoid disturbance of the specimen.
Precautions during Penetration Test
1. There should be no movement of the container while needle penetrates
into sample.
2. The sample should be free from any extraneous matter.
3. The needle should be cleaned with benzene and dried before penetration.
Observations for Penetration Test
Actual test temperature = °C
Penetration dial reading Test 1 Test 2 Test 3
(a) Initial
(b) Final
Penetration Value
Result of Test
Mean Penetration Value =
Recommended Penetration Value of Bitumen

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Penetration test is a commonly adopted test on bitumen to grade the material in
terms of its hardness. A 80/100 grade bitumen indicates that its penetration value
lies between 80 & 100.
Grading of bitumen helps to assess its suitability in different climatic conditions and
types of construction. For bituminous macadam and penetration macadam, IRC
suggests bitumen grades 30/40, 60/70, 80/100.
In warmer regions, lower penetration grades are preferred to avoid softening
whereas higher penetration grades like 180/200 are used in colder regions to
prevent the occurrence of excessive brittleness. High penetration grade is used in
spray application works.
Viscosity of Bituminous Materials –
Measurements and Factors
Introduction to Viscosity and Rheology of Bituminous Materials
The resistance of a liquid in flowing is defined as the viscosity of that fluid. Under
the action of force, the fluid reflects higher resistance when the viscosity is high.
The two factors that define the viscosity of bitumen are:
 Chemical Composition of Bitumen
 Structure of Bitumen
The bitumen is a composition of two factors (Structure of Bitumen) asphaltenes
miscelles and maltenes. In bitumen sol, the asphaltenes miscelles are dispersed in
maltenes continuum. As the asphaltenes content reduces, the viscosity of bitumen
also decreases. Aggregation is the factor that governs the viscosity of gel type
bitumen. Gel type bitumen have a higher viscosity.
Bitumen Structure Influence on Viscosity

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Bitumen consist of resins, aromatics and some form of saturated oil after their
manufacture. The asphaltenes dispersion is controlled by the above mentioned
elements in bitumen.
The aromatics in sufficient quantity provide a layer around the Asphaltenes. This
layer is stable and promotes dispersion. If it’s not sufficient the micelles will join as
shown in figure-1.
Fig.1. Sol Type Bitumen Schematic Diagram

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Fig.2.Schematic Diagram of Gel type bitumen
Now the saturated oil quantity will affect the maltenes continuum. This has a low
viscosity and low molecular weight. The increase in saturated oil quantity would
bring the viscosity down, but it increases the aggregation of asphaltenes with
aggregates, making the structure gel type.
This on other hand makes the aggregation of asphaltenes miscelles, causing
viscosity decrease. So, two opposing factors are said to exist. These effects are
depended on the aromatic stabilization.
The influence of asphaltenes on viscosity of bitumen can be summarized
as:
 The viscosity increases with increase in asphaltenes quantity
 The change in viscosity is governed by the asphaltenes particles
 The asphaltenes have aggregation tendency. Greater the aggregation,
greater is the viscosity.

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Measurement of Viscosity of Bitumen
The viscosity can be defined as the ratio of shear stress applied to the rate of shear
strain. It is measured in Pascal Seconds. The dynamic viscosity can also be
calculated in terms of kinematic viscosity in units m2
/s or mm2
/s.
1 mm2
/s = 1 cSt (Centistoke)
Based on absolute or kinematic viscosity requirement, the bitumen viscosity can be
measured by a variety of devices. The specifications kept for measurement is the
absolute viscosity at 60 degree Celsius and a Kinematic viscosity at 135 degree
Celsius.
The vacuum capillary tube viscometer is used to find absolute
viscosity. Atmospheric capillary tube viscometer is employed to measure the
kinematic viscosity.
The displacement happening on a thin layer of bitumen can be determined with the
help of a sliding plate test. The force in the layer is also calculated. The
arrangement involves keeping the bitumen layer between metal plates for different
combinations of loading time and temperature.
The resistance of force is represented by ‘F’, which is dependent on the:
 Area of the surfaces – A
 Distance between the surfaces – d
 Relative speed of movement of one plate with respect to other -V
Which gives,

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The coefficient of viscosity is represented by ?. This is also called the absolute
viscosity. And it is given by,
Now, the most practical means to measure the viscosity of bitumen is with the help
of rotational viscometer test (ASTM D4402 -02). The Brookfield and Thermocel
rotational viscometer let the measurement of bitumen viscosity at varying
temperatures.
Influence of Temperature on The Viscosity of
Bitumen
Bitumen tend to soften, when subjected to a temperature rise and will harden when
the temperature falls. Bases on different varieties of bitumen, the viscosity changes
with temperature also differs.
It is very essential to understand the viscosity variations of the bitumen used in the
construction process, with the temperature. This factor is also a governing factor
that assures the exposure of bitumen to open environment. The bitumen used for
an area having high temperature is not the same that is used in lower temperature
areas (cold regions). The serviceability, durability and maintenance factor is
dependent primarily on viscosity property of bitumen type used.
The change in viscosity of bitumen with temperature is represented by the value
of temperature susceptibility of bitumen. It is determined by the penetration
value, P and softening Point temperature, T.
The empirical relation can be given as:

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log P = AT +k
‘A’ is designated for temperature susceptibility of the logarithm of penetration
value. The value of A varies from 0.0015 to 0.06. This variation itself shows, there
would be variation in the response of bitumen with temperature. ‘k’ is a constant.
From the above expression, a relation has been developed by Pfeiffer and Van
Doormaal,1936. This new relation relates A to an index named as penetration
index, PI.
The relation tells that for road bitumen, the penetration index value PI =0;
It has been observed that most of the bitumen have a penetration of about 800, at
their softening point temperature. Thus, the PI can be evaluated, if the penetration
at 25 degree Celsius and softening point temperature are known.
Hence, Penetration Index of bitumen can be calculated
The figure below shows the Nomograph to prove the validity of above stated
expression by Pfeiffer and Van Doormaal,1936.

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Fig.3. Nomograph to evaluated the penetration Index of bitumen, with the
known values of softening point temperature and penetration value at 25
degrees.
Penetration Index for Bitumen
A quantitative measure of the response of the bitumen material to a given
temperature is represented by Penetration Index Value (PI). The PI index for
bitumen that is used for roads have a value ranging from -2 to +2.
When the PI index is low, the bitumen behaves like Newtonian fluids, that they
become very brittle at lower temperatures.

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When the bitumen has a higher value of Penetration Index, resistance to
permanent deformation is improved.
PI increases with the increase of asphaltenes (at the expense of aromatics). So, the
penetration index is affected by the bitumen chemical composition to a larger
extent. The figure below shows the variation of penetration index with each
chemical fraction of bitumen.
Fig.4: Graph showing variation of penetration index with respect to
chemical composition as per Lubbers, 1985
The behavior of bitumen after application in the construction can be predicted with
the help of PI. High penetration value asphalt binders are called as “soft”. These are
used in areas of cold climate. Low penetration numbers are called “hard”, which are
employed in hot climates.
Grading of Bitumen- Different Methods of
Bitumen Grading

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There are different methods of grading of bitumen such as chewing, penetration
grading, viscosity grading and superpave performance grading of bitumen which
are discussed in this article.
History of Bitumen Grading
The correlation between the bitumen stiffness and temperature varies with the type
of bitumen employed. The bitumen type varies based on their origin as well as a
method of refining.
The figure below explains this, where it is observed that bitumen A and Bitumen B
have different relationships with temperature.
Fig.1: Graph representing relationship between temperature and stiffness
for different bitumen
Due to these variations, it was necessary to fix a test temperature. A temperature
at which the grading of bitumen can be carried out. This will also give a way to
compare different binders of bitumen. For example, if we have bitumen A and B,
bitumen B at 25o
C is stiffer than bitumen A at the same temperature. But at 60
degree Celsius the condition is reversed.

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The bitumen stiffness at a lower temperature is also an essential criterion to have
resistance against thermal cracking. The above explanation of bitumen A and B are
from the estimates obtained for three temperatures 25, 60 and 135 degree Celsius
as shown in figure-1.
The temperature of 135 degrees is near to those temperatures at which the
bitumen mix is used for mixing and compacting during the construction. This
temperature would give bitumen possess a motor oil form; thin in layers. This state
makes them be easily mixed with aggregates.
To have proper mixing and compaction temperatures for asphalt mixtures, it is
necessary to find the stiffness of bitumen. Here the stiffness in terms of kinetic
viscosity must be determined.
The temperature 60 degree Celsius is similar to a temperature of the bituminous
pavement on an extremely summer day. Here the possible failure caused will be
rutting. The determination of stiffness at 60 degrees will be more useful in bringing
adequate resistance in the summer season. Based on this value, a minimum
stiffness value for the binder can be maintained. Here the stiffness is determined in
terms of viscosity.
Fig.2: Rutting Damage Caused in Bituminous Pavement Just after few
period of construction

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The average annual temperature of an asphalt pavement during a year is almost
near to 25 degree Celsius. The stiffness determination of bitumen at 25 degrees will
help us to find the maximum stiffness that is needed to resist the damages like
fatigue cracking or raveling.
These damages are caused after five to ten years of service life i.e. with age.
Rutting is caused just by construction. But raveling is caused after a duration
showing the inadequacy of the structure.
Fig.3: Fatigue Crack formed in Bitumen pavement after certain age
Different Methods of Grading of Bitumen

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Following are the different methods used for grading of bitumen
1. Grading by chewing
2. Penetration grading
3. Viscosity grading
4. Superpave performance grade
Grading of Bitumen by Chewing
During the 19th century, chewing was the method used to determine the stiffness
i.e. hardness if the bitumen. This was the time when no penetration test was
developed. It was carried out by experienced US inspectors. Based on the test
conducted, the sample was either accepted or rejected. The temperature of
bitumen tested was such that, it favors human body temperature.
Penetration Grading of Bitumen
The American Society for Testing Materials (ASTM) D 04 carried out bitumen
grading at a temperature of 25 degree Celsius for the testing of the road and
pavement materials in 1903.
The penetration test involves penetration of a needle that is loaded by 100g, into a
bitumen sample maintained at a temperature of 25-degree Celsius in a water bath
for a period of 5 seconds. The penetration value is measured in millimeters.
1 penetration unit = 0.1mm.
The greater the penetration value, the softer the bitumen become. The ASTM
standard D 946 gives 5 penetration grades for the bitumen binders. They are:
1. Hardest Bitumen Grade 40 –50
2. 60 –70
3. 85-100

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4. 120-150
5. Softest Bitumen Grade 200-300
The penetration grading system is 100 years old bitumen grading method. In India,
before 2006, the most widely used grade of bitumen was 60 to 70. For the
construction of low volume roads and to perform spraying, penetration value from
80 to 100 was used.
The disadvantages of penetration grading of bitumen are:
 The method of penetration grading is not a fundamental test. It makes
use of empirical tests.
 For polymer modified bitumen, this method cannot be employed
 At higher and lower temperatures during service, similitude at 25 degree
Celsius affects the performance. As shown in below figure, three bitumen
binders with 60 to 70 penetration grade is plotted against stiffness values.
Fig.4: Graph representing relationship between stiffness and temperature
of three binders A, B and C with penetration grade 60 -70
The three binders A, B, and C have same stiffness vale of 65 at 25 degree Celsius,
but different values at higher and lower temperatures. Hence the bitumen C is
subjected to rutting under higher service temperature, as its stiffness is low at
higher temperatures.

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 To guide the contractors for asphalt mixing and to know the temperature
of compaction, no bitumen viscosity is available.
 The temperature susceptibility of the binders is not controlled by the
penetration grading. The temperature susceptibility is the slope of
temperature v/s stiffness line. Steep slope curve represents high
temperature susceptible binders, which are not appreciated. This is
because, at high temperatures, they are very soft and low temperatures
they are stiff.
Viscosity Grading of Bitumen
In the 1970s, US introduced the method of viscosity grading at 60 degree Celsius.
This was to ensure a solution for construction problems and to have high
temperature performance. These were tender mixes that must undergo mix
pushing and shoving under the roller, without which it cannot be rolled properly.
Prior to 1970s, the US construction used 60 to 70 penetration grade that shows
variation towards rutting action. They showed lower viscosity at 135 degree Celsius.
This caused tender mix problems during the construction process.
The viscosity test, unlike penetration grading, is a fundamental test carried out at
60 degree Celsius. This temperature is the maximum temperature to which the
road pavement is subjected to at summer. The measurement is in terms of Poise.
In India, the equipment for testing the viscosity at 60 and 135 degrees are
available. They are very simple to handle with. In the US, Six Asphalt Cement (AC)
viscosity grades were specified. They are,
Grade Viscosity at 60 degree Celsius, Poises
AC -2.5 SOFTEST 250±/-50
AC-5 500±/-100
AC-10 1000±/-200
AC-20 2000±/-400

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AC-30 3000±/-600
AC-40 HARDEST 4000 ±/-800
In the US, Bitumen is mentioned as asphalt cement or asphalt. The grades with
lower viscosity i.e. AC-2.5 and AC-5 were used for cold service temperatures; areas
like Canada. In Northern tier states, AC-10 was used. Mostly in the US, AC-2- was
used.
Only five grades excluding AC-30 was initially determined. These have a mean
viscosity that will double from grade to grade. This resulted in no overlap in
viscosity range. But the problem of AC-20 to be too soft and AC-40 to be too hard,
that was faced by countries Florida, Georgia, and Alabama made AC-30 to be
incorporated and hence six grades.
The figure below shows the AC-30 bitumen viscosity grade which is equivalent to
VG-30 in India.
Fig.5: Graph representing temperature and stiffness (in terms of viscosity)
relationship of AC-30 (VG-30) Bitumen
Advantages of Viscosity Grading of Bitumen
The advantages of viscosity grading system are:

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1. Same rutting performance is given by the binders of same viscosity grade,
unlike the case of penetration grades.
2. The viscosity grading system retains minimum performance in terms of
fatigue cracking. This will enable acceptable performance. This is for an
average yearly temperature of 25 degrees.
3. The potential on tender mixes can be minimized with the minimum
specified values of kinematic viscosity at a temperature of 135 degrees
Celsius.
4. The maximum allowable temperature susceptibility can be established by
specifying the minimum value of penetration at 25 degrees and the
kinematic viscosity at 135 degrees.
5. For a wide variety of temperatures, the viscosity binders were employed.
A temperature of 60 degrees for rutting, 25 degrees for raveling or fatigue
problems or 135 degrees for construction activity.
6. The suppliers can provide the users with accurate asphalt mixing and
temperature values for construction. This is possible because of the
measurement of viscosity at two temperatures.
Superpave Performance Grading of Bitumen
The performance grading of bitumen is based on the evaluation of the material
performance when in use, unlike being rational as in viscosity grading system. The
viscosity grading system is more into experience based method of grading. And this
has proved to have excellent performance for over 20 years in US pavement
construction.
The Superpave grading was developed as a part of a 5year strategic highway
research planning (SHRP) from 1987 to 1992, to have a performance based grading
system for bitumen. These were developed based on the engineering features that
will help in solving many of the engineering problems.

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Features of Superpave Performance Grading of Bitumen
The Superpave performance grading system make use of a new set of bitumen
tests. The method incorporates the following salient features:
 The system includes tests and specification for bitumen binders. This
bitumen binder may have either modified or unmodified bitumen.
 The field performance by the engineering principles will influence the
physical properties determined from the Superpave bitumen tests. That is,
it is not achieved by experience alone.
 The bitumen simulation for a period of 5 to 10 years, to understand its
performance with age was developed. This is a long-term bitumen aging
test.
 The tests and specification of Superpave system intend to avoid three
main damages in bitumen i.e. raveling, fatigue cracking and thermal
cracking. These failures happen at high, intermediate and low temperature
respectively.
 The pavement is taken for testing for the entire range of temperature as
shown in the figure below. A rotational viscometer is taken to determine
the viscosity at 135 degree Celsius. The viscoelastic property of bitumen
at two temperatures is determined with the help of a dynamic shear
rheometer. The first temperature is “high temperatures” maximum 7-day
temperature during a hot summer day of the project site. The second one
is “intermediate temperature”, which is the average annual temperature of
the pavement at the project site.
 During Winter a bending beam rheometer and direct tension tester are
used to measure the bitumen rheological properties at the project site.

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Fig.6: The testing carried on the pavement at project site for entire range
of temperature in a Superpave grading system (As per FHWA)
The performance of Superpave is dependent on climate. The Superpave
performance grade (PG) for project location where the temperature during 7 days is
greater than 64 degree Celsius and a minimum temperature of -22 degrees are PG
64 to 22.
The available higher grades are PG 52, PG 58, PG 64, PG 70, PG 76 and PG 82. The
lower grades are -4, -10, -16, -22, -28, -34 and so on. Both the temperature levels
increment at a rate of 6 degrees.
If in Rajasthan the project site has maximum 7-day record temperature of
pavement as 70 degrees and a minimum temperature of -3 degree, PG 70 to 4
bitumen will be specified for that project.
Steps in Bituminous Road Construction
Bitumen road construction consists of various steps such as preparation of base
course, application of bituminous coat, placement of bituminous mix, rolling and
check for quality etc. which are discussed.
Steps in Bituminous Road Construction

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1. Preparation of the existing base course layer
The existing surface is prepared by removing the pot holes or rust if any. The
irregularities are filled in with premix chippings at least a week before laying
surface course. If the existing pavement is extremely way, a bituminous leveling
course of adequate thickness is provided to lay a bituminous concrete surface
course on a binder course instead of directly laying it on a WBM.
2. Application of Tuck Coat
It is desirable to lay AC layer over a bituminous base or binder course. A tack coat
of bitumen is applied at 6.0 to 7.5 kg per 10 sq.m area, this quantity may be
increased to 7.5 to 10 kg for non-bituminous base.
3. Preparation and placing of Premix
The premix is prepared in a hot mix plant of a required capacity with the desired
quality control. The bitumen may be heated up to 150 – 177 deg C and the
aggregate temperature should not differ by over 14 deg C from the binder
temperature.
The hot mixed material is collected from the mixture by the transporters, carried to
the location is spread by a mechanical paver at a temperature of 121 to 163 deg C.
the camber and the thickness of the layer are accurately verified.
The control of the temperatures during the mixing and the compaction are of great
significance in the strength of the resulting pavement structure.
4. Rolling

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A mix after it is placed on the base course is thoroughly compacted by rolling at a
speed not more than 5km per hour.
The initial or break down rolling is done by 8 to 12 tonnes roller and the
intermediate rolling is done with a fixed wheel pneumatic roller of 15 to 30 tonnes
having a tyre pressure of 7kg per sq.cm. the wheels of the roller are kept damp
with water.
The number of passes required depends on the thickness of the layer. In warm
weather rolling on the next day, helps to increase the density if the initial rolling
was not adequate. The final rolling or finishing is done by 8 to 10 tonne tandem
roller.
Fig: Tandem Roller
5. Quality control of bituminous concrete
construction
The routine checks are carried out at site to ensure the quality of the resulting
pavement mixture and the pavement surface.

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Periodical checks are made for
a) Aggregate grading
b) Grade of bitumen
c) Temperature of aggregate
d) Temperature of paving mix during mixing and compaction.
At least one sample for every 100 tonnes of the mix discharged by the hot mix
plant is collected and tested for above requirements. Marshall tests are also
conducted.
For every 100 sq.m of the compacted surface, one test of the field density is
conducted to check whether it is at least 95% of the density obtained in the
laboratory. The variation in the thickness allowed is 6mm per 4.5m length of
construction.
6. Finished surface

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The AC surface should be checked by a 3.0 m straight edge. The longitudinal
undulations should not exceed 8.0 mm and the number of undulations higher than
6.0 mm should not exceed 10 in a length of 300 m. The cross-traffic profile should
not have undulations exceeding 4.0mm.
Various Lab Tests on Bitumen for Pavement
Construction
Various laboratory tests on bitumen is conducted to check quality and different
properties of bitumen for pavement construction. Bitumen is a black or brown
mixture of hydrocarbons obtained by partial distillation of crude petroleum.
Bitumen is insoluble in water. It composes 87% carbon, 11% hydrogen and 2%
oxygen by weight. It is obtained in solid or semi-solid state. It is generally used as
surface coarse for roads, roof coverings etc.
Tests on Bitumen to Check Quality and
Properties for Pavement
To ensure the quality of bitumen several tests are performed which are as follows.
 Ductility test
 Flash and Fire point test
 Float test
 Loss on heating test
 Penetration test
 Softening point test
 Specific gravity test
 Viscosity test
 Water content test

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Ductility Tests on Bitumen
The property of bitumen which allows it to undergo deformation or elongation is
called ductility of bitumen. The ductility of bitumen is measured by the distance in
Cm (centimeter), to which the bitumen sample will elongate before breaking when
it is pulled by standard specimen at specified speed and temperature.
Firstly the bitumen sample is heated to 75-100o
C and melted completely. This is
poured into the assembled mold which is placed on brass plate. To prevent sticking
the mold and plate are coated with glycerin and dextrin. After filling the mold,
placed it in room temperature for 30-40 minutes and then placed it in water for 30
minutes.
Then take it out and cut the excess amount of bitumen with the help of hot knife
and level the surface. Then place the whole assembly in water bath of ductility
machine for 85 to 95 minutes. Then detach the brass plate and the hooks of mold
are fixed to machine and operate the machine.
The machine pulls the two clips of the mold horizontally and then bitumen
elongates. The distance up to the point of breaking from the starting point is noted
as ductility value of bitumen. The minimum value should be 75cm.

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Flash and Fire Point Tests on Bitumen
Flash point of bitumen is defined as the point of lowest temperature at which
bitumen catches vapors of test flame and fires in the form of flash. Fire point of
bitumen is defined as the point of lowest temperature at which the bitumen ignites
and burns at least for 5 second under specific conditions of test.
Flash and fire point test helps to control fire accidents in bitumen coated areas. By
this test we can decide the bitumen grade with respect to temperature for particular
areas of high temperatures.

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Float Tests on Bitumen
Float test is used to determine the consistency of bitumen. But we generally use
penetration test and viscosity test to find out the consistency of bitumen except for
certain range of consistencies. The float test apparatus consists of aluminum float
and brass collars as shown in below figure.
These collars are filled with melted bitumen sample and cooled to 5o
C and then
attached them into aluminum floats and this assembly is placed in water bath at a
temperature of 50o
C. Note down the time in seconds from the instant the float is
put on the water bath until the water breaks the material and enters the float.

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Loss on Heating Tests on Bitumen
When the bitumen is heated, water content present in the bitumen is evaporated
and bitumen becomes brittle which can be damaged easily. So, to know the amount
of loss ness we will perform this test. In this test, take the bitumen sample and
note down its weight to 0.01gm accuracy at room temperature.
Then place the sample in oven and heat it for 5 hours at 163o
C. After that take out
the sample and cooled it to room temperature and take the weight to 0.01gm
accuracy and note down the value. Then for the two values of weight before and
after heating we can compute the loss of mass. The loss should be less than 5% of
total weight otherwise it is not preferred for construction.

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Penetration Test on Bitumen
The penetration value of bitumen is measured by distance in tenths of mm that a
standard needle would penetrate vertically into bitumen sample under standard
conditions of test. By this test we can determine the hardness or softness value of
bitumen.
In this test, firstly heat the bitumen above its softening point and pour it into a
container of depth attest 15mm. bitumen should be stirred wisely to remove air
bubbles. Then cool it to room temperature for 90 minutes and then placed it in
water bath for 90 minutes.
Then place the container in penetration machine adjust the needle to make contact
with surface of sample. Make dial reading zero and release the needle for exactly 5
seconds and note down the penetration value of needle for that 5 seconds. Just
repeat the procedure thrice and note down the average value.

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Softening Point Test on Bitumen
Softening point of bitumen indicates the point at which bitumen attains a particular
degree of softening under specified conditions of the test. Take small amount of
bitumen sample and heat it up to 75-100o
C. Ring and ball apparatus is used to
conduct this test. Heat the rings and apply glycerin to prevent from sticking. Fill this
rings with bitumen and remove the excess material with hot sharp knife.
Assemble the apparatus parts, balls are arranged in guided position that is on the
top of bitumen sample. And fill the beaker with boiled distilled water. Then apply
temperature @ 5o
C per minute. At certain temperature bitumen softens and ball
slowly move downwards and touches the bottom plate, this point is noted as
softening point.

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Specific Gravity Test on Bitumen
Specific gravity of bitumen is the ration of mass of given volume of bitumen to the
mass of equal volume of water at specified temperature. Specific gravity is the
good indicator of quality of binder. It can be determined by pycnometer method.
In this method, take clean and dry specific gravity bottle and take its weight(w1).in
the 2nd
case, fill the bottle with distilled water and dip it in water bath for 30 minutes
and note down the weight(w2). Next, fill half the bottle with bitumen sample and
weigh (w3).
Finally fill the bottle with half water and half portion with bitumen and weigh (w4).
Now we can find out specific gravity from the formulae.

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Viscosity Test on Bitumen
Viscosity is the property of bitumen which influences the ability of bitumen to
spread, penetrate into the voids and also coat the aggregates. That is it influences
the fluid property of bitumen. If viscosity of bitumen is higher, compactive effort of
bitumen reduces and heterogeneous mixture arises.
If viscosity is lower, then it will lubricate the aggregate particles. Viscosity is
determined by using tar viscometer. The viscosity of bitumen is expressed in
seconds is the time required for the 50 ml bitumen sample to pass through the
orifice of a cup, under standard conditions of test and at specified temperature.

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Water Content Test on Bitumen
When bitumen is heated above the boiling point of water, sometimes foaming of
bitumen occurs. To prevent this bitumen should have minimum water content in it.
Water content in bitumen is determined by dean and stark method. In this method,
the bitumen sample is kept in 500ml heat resistant glass container.
Container is heated to just above the boiling point of water. The evaporated water
is condensed and collected. This collected water is expressed in terms of mass
percentage of sample. It should not more than 0.2% by weight.
Different Types of Bitumen, their Properties and
Uses

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There are different types of bitumen available with different properties,
specifications and uses based on requirements of consuming industry.
The specification of bitumen also shows variation with the safety, solubility, physical
properties, and the durability.
To understand the performance of the bitumen when it is on service, the design of
physical properties of the material is highly essential. The standard testing methods
are carried out to grade bitumen.
Types of Bitumen and their Properties and Uses
The bitumen can be classified into the following grade types:
 Penetration Grade Bitumen
 Oxidized Bitumen Grades
 Cut Back Bitumen
 Bitumen Emulsion
 Polymer Modified Bitumen
Penetration Grade Bitumen
The penetration grade bitumen is refinery bitumen that is manufactured at different
viscosities. The penetration test is carried out to characterize the bitumen, based on
the hardness. Thus, it has the name penetration bitumen.
The penetration bitumen grades range from 15 to 450 for road bitumen. But the
most commonly used range is 25 to 200. This is acquired by controlling the test
carried out i.e. the distillation process.
The partial control of fluxing the residual bitumen with the oils can help in bringing
the required hardness.

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The table below shows the penetration grade bitumen’s test carried out as per BS
EN 12591. This test is for bitumen that is for road application.
Table.1. Paving Grade Bitumen Specification As per BS EN 12591

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The BS EN 1426 and BS EN 1427 provides the penetration and softening point
values for the respective grades, as from Table-1. This will help in identifying the
equiviscosity and the hardness of the bitumen grade.
The grades are represented by the penetration values i.e. For example, 40/60 as a
penetration value of 50 ± 10.
The BS EN 13303 also gives the measure of loss on heating with respective limits
for all penetration bitumen grades. This measure is to ensure that there are no
volatile components present.
So, no component whose loss will contribute to the setting and hardening of
bitumen during its preparation or lay course is undergone. The BS EN
12592 provides the solubility values to ensure that there is less or no impurities in
the bitumen material.
Oxidized Bitumen
The refinery bitumen is further treated by the introduction of processed air. This will
give us oxidized bitumen. By maintaining a controlled temperature, the air is
introduced under pressure into soft bitumen.
Compounds of higher molecular weight are formed by the reaction of this
introduced oxygen and bitumen components. Thus, the Asphaltenes and the
Maltenes content increases resulting in a harder mix. This harder mix has a lower
ductility and temperature susceptibility.

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The oxidized bitumen is used in industrial applications such as roofing and coating
for pipes. By this method of processing, the bitumen that has a lower penetration
can be manufactured, which can be employed for paving roads.
Cutback Bitumen
These are a grade of bitumen that comes under penetration grade bitumen. This
type of bitumen has a temporarily reduced viscosity by the introduction of a volatile
oil. Once after the application, the volatile material is evaporated and bitumen gain
its original viscosity.
The penetration grade bitumen is a thermoplastic material. It shows the different
value of viscosity for different temperature. In areas of road construction, it is
necessary for the material to be fluid in nature at the time of laying i.e. during
surface dressing.
It is also essential for the material to regain back to its original hardness and
property after setting. This is ensured by cutback bitumen. The fluidity is obtained
for any bitumen by raising the temperature. But when it is necessary to have
fluidity at lower temperatures during surface dressing, cutback bitumen is
employed.

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The time for curing and the viscosity of cutback bitumen can be varied and
controlled by the
1. dilution of volatile oil, and
2. the volatility of the oil added.
70/100 or 160/220 pen bitumen that is diluted with kerosene are the main
composition of bitumen in the construction of roads in the UK. The standard tar
viscometer is used to test the standard viscosity.
The table-2, shows the cutback specifications based on BS 3690. This provides the
requirement of the bitumen to satisfy solubility property, distillation property as
well as recovery of properties after curing.
Table-2: The Cutback Bitumen Specification As per BS 3690: Part 1 & BS EN
12591

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Bitumen Emulsion
The this type of bitumen forms a two-phase system with two immiscible liquids.
One of them is dispersed as fine globules within the other liquid. When discrete
globules of bitumen are dispersed in a continuous form of water, bitumen emulsion
is formed.
This is a form of penetration grade bitumen that is mixed and used for laying
purposes.
An emulsifier having a long hydrocarbon chain with either a cationic or anionic
ending is used for dispersing the bitumen globules. This emulsifier provides an
electrochemical environment. The ionic part of the chain has an affinity towards
water and the bitumen is attracted by hydrocarbon part.

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As shown in figure below, the hydrocarbon binds the bitumen globules strongly and
the ionic part is seen on the surface of the globules. Depending on the ions present,
the droplets take a charge.
The emulsions can be cationic (positive charge) or anionic (negatively charged).
The globules of the same charge hence repel each other, making the whole system
stable. To facilitate adhesion with the aggregates (that are negatively charged),
cationic emulsions are more preferred.

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Bitumen during Dispersion in an emulsifier
The stability of emulsions is dependent on the following factors:
 Types of bitumen emulsifier and its quantity
 Water evaporation rate
 Bitumen quantity
 Bitumen globules size
 Mechanical forces
The emulsions are applied by using sprays. For this viscosity is a primary concern.
With the increase of bitumen content, the mixture becomes more viscous. This is
found to be sensitive when the amount exceeds 60%.

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The BS 434: Part 1 and BS EN 13808 gives the specification for the viscosity of
road emulsions.
Polymer – Modified Bitumen
Polymer modified bitumen is the type of bitumen obtained by the modification of
strength and the rheological properties of the penetration graded bitumen. Here for
this 2 to 8% of polymer is added.
The polymer used can be either plastic or rubber. These polymers vary the strength
and the viscoelastic properties of the bitumen. This is achieved by:
1. Elastic response increase
2. Improvement in cohesive property
3. Improvement in Fracture strength
4. Providing ductility
Some of the examples of rubber polymers used are styrene block copolymers,
synthetic rubbers, natural and recycled rubbers. Plastics that are thermoplastic
polymers are also used.

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Types of Failures in Rigid Pavements and their
Causes and Repair Techniques
Failures in rigid pavements are caused by distresses due to various causes. Repair
techniques these types of failures in rigid pavements are discussed.
Types of Failures in Rigid Pavements
The different types of distresses responsible for failures in rigid pavements are:
1. Joint Spalling
2. Faulting
3. Polished Aggregate
4. Shrinkage Cracking
5. Pumping
6. Punch out
7. Linear Cracking
8. Durability Cracking
9. Corner Break

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Joint Spalling in Rigid Pavements
Excessive compressive stress causes deterioration in the joints, called as the
spalling. This may be related to joint infiltration or the growth of pavement, that
are caused by the reactive aggregates.
Poor quality concrete or construction technique will also result in joint spalling.
Small edges to large spalls in the back of the slab and down to the joints can be
observed.
Main causes of joint spalling in rigid pavements are:
 Joints subjected to excessive stress due to high traffic or by infiltration of
any incompressible materials
 The joint that are constructed with weak concrete
 Joint that is accumulated with water that results in rapid freezing and
thawing

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Fig.1: Joint Spalling in Rigid Pavement Slabs
The joint spalls can be avoided by using good construction techniques, or by sealing
the joints.
Faulting in Rigid Pavements
The difference in elevation between the joints is called as faulting. The main causes
of failures in rigid pavements due to faulting are:
 Settlement of the pavement that is caused due to soft foundation
 The pumping or the erosion of material under the pavement, resulting in
voids under the pavement slab causing settlement
 The temperature changes and moisture changes that cause curling of the
slab edges.

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Fig.2: Faulting with difference in elevations found between the joints
Polished Aggregate in Rigid Pavements
The repeated traffic application leads to this distress. These are the failures in rigid
pavements caused when the aggregates above the cement paste in the case of PCC
is very small or the aggregates are not rough or when they are angular in shape,
that it cannot provide sufficient skid resistance for the vehicles.
The polishing degree should be specified before the construction is carried out. This
study is included in the condition survey, where it is mentioned as a defect.
Fig.3: Polished Aggregates
Shrinkage Cracking in Rigid Pavements
These are hairline cracks that are less than 2m in length. They do not cross the
entire slab. The setting and curing process of the concrete slab results in such
cracks. These are caused due to higher evaporation of water due to higher
temperature cracks. Improper curing can also create shrinkage cracks in rigid
pavements.

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Fig.4: Shrinkage Cracking in Pavements
Pumping Effects
The expulsion of water from the under a layer of the pavement is called as
pumping. This distress is caused due to the active vehicle loads coming over the
pavement in a repetitive manner. This will result in the fine materials present in the
sub base to move along with water and get expelled out with the water.
Larger voids are created under the pavement due to repeated expulsion. The stains
on the pavement or on the shoulder surface are the method through which this
type of failure of rigid pavement is evidenced.
Pumping can be avoided by prevention of water accumulation at the pavement sub-
base interface. This can be achieved by reducing the deflection to a minimum value
and by the provision of a strong well constructed sub-base.
The constructed sub-base must have sufficient drainage facility so that the
subgrade below is not saturated. Modern pavement construction makes use of
underground drainage system that is the best solution for pumping distress.

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Fig.5: Pumping Effect
Corner Breaks in Rigid Pavements
These are the failures in rigid pavements that is caused due to pumping in
excessive rate. When the pumping completely remove the underlying support that
no more support exists below to taken the vehicle load, the corner cracks are
created. The repair method is either full slab replacement or the repair for the full
depth must be carried out.
Fig.6: Corner Break Failures in Rigid Pavement
Punch-out in Rigid Pavements

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A localized area of concrete slab that is broken into pieces will be named as punch
out distress. This distress can take any shape or form. These are mainly defined by
joints and cracks. The joints and cracks will mainly keep 1.5m width.
The main reason behind punch outs is heavy repeated loads, the slab thickness
inadequacy, the foundation support loss or the construction deficiency like
honeycombing.
Fig.7. Punch-out Failures in Rigid Pavements
Linear Cracking in Rigid Pavements
These types of failures in rigid pavements divides the slab into two or three pieces.
The reason behind such failures is traffic loads at repeated levels, the curling due to
thermal gradient and moisture loading repeatedly.

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Fig.8: Linear Cracking
Durability Cracking in Rigid Pavements
The freezing and thawing action will create regular expansion and contraction which
will result in the gradual breakdown of the concrete. This type of distress is patterns
of cracks on the concrete surface as layers that are parallel and closer to the joints.
Joints and cracks are the areas where the concrete seem to be more saturated.
Here a dark deposit is found and called the ‘D’ cracks. This failure of rigid pavement
will finally result in the complete disintegration of the whole slab.
Fig.9. Durability Cracking or ‘D’ Cracks Failure in Rigid Pavements

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Why is Bitumen Used in Road Construction?
Properties and Advantage of Bitumen for
Pavements
Bitumen is used in road construction due to various properties and advantages it
has over other pavement construction materials. Advantages of bitumen for road
construction is discussed.
Why is Bitumen Used in Road Construction?
Bitumen gain certain unique properties that are inbuilt in it during its manufacture.
The bitumen as a raw material in flexible road construction and bitumen as a mix
(composing other materials i.e. aggregates/ pozzolans) serves certain advantages,
that prompt to use bitumen widely in road construction.
Use of Bitumen in Flexible Road Construction

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The reason behind the significant application of bitumen in flexible pavements are
explained below:
1. Production of Bitumen is economical
Bitumen is a by-product of crude oil distillation process. Crude oil itself is a
composition of hydrocarbons. The primary products that are available are the
petrol, diesel, high octane fuels and gasoline.
When these fuels are refined from the crude oil, the bitumen is left behind. Further
treatment of by-product, to make it free from impurities give pure bitumen.
As the primary product demand is of utmost importance to the society, the bitumen
as a by product has survival for long. This by product is utilized as a new
construction material, without going for any other new resource.
2. Physical and Rheological Properties of Bitumen bring Versatility
The physical and the chemical properties of Bitumen are found to be a function of
load level, temperature and the duration of loading. It is a thermoplastic and
viscoelastic material.
These dependencies make us to truly access the traffic on the road so that a
bitumen mix properties can be varied based on the stress levels calculated. This
versatility of bitumen results in a large variety of bitumen mix, based on the road
application.
3. The Melting Point of Bitumen is low
It is highly appreciable about the fact that bitumen has a favorable melting point,
that helps in both surface dressing and wearing resistance with ease.

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The melting point of the bitumen should not be too high, that it can be melted
easily during laying the pavement. At the same time, bitumen has a melting point,
which would not let the already casted road pave to melt and deform under high
temperatures.
In areas of high temperatures, along with this quality of bitumen, the aggregate
composition helps to cover up the effect of large temperature.
4. Bitumen can undergo Recycling
As the melting point of bitumen is favorable, it can be melted back to its original
state. This is called as asphalt recycling process.
The torn-up asphalt pieces are taken up to the recycling plant, instead of sending
them to landfills. This recycled mix can be reused. If necessary, the old bitumen is
mixed with new bitumen and new aggregates to make the mix live again.
5. Bitumen gain Adhesive Nature
As explained in the production of bitumen, it is free from hydrocarbon and hence
not toxic. The by product is refined to maximum to get rid of organic materials and
impurities.
The bitumen has a highly adhesive nature, which keeps the materials in the road
mix bind together under strong bonds. These become stronger when the mix is set
i.e. ready for vehicle movement.
6. Bitumen has Color Variety
The traditional bitumen is black in color. This is because the dense organic material
within bitumen is black in color. Now, when certain pigments are added to bitumen,
the color of our choice can be obtained. These are colored bitumen.

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It is costly than the normal colored bitumen. The disadvantage of colored bitumen
is that it requires more chemical additives and materials.
Requirements of Bitumen Mixes for Road
Construction
An overall bitumen mix is used in the construction of flexible pavement to serve the
following needs.
 Structural Strength
 Surface Drainage
 Surface Friction
Structural Strength of Bituminous Pavements
The figure below shows a typical cross section of flexible pavement, that was
developed in the USA. The structural bitumen layer composes of:
 Bituminous surface or wearing course
 Bituminous binder course
 Bituminous base course
The primary purpose of these bitumen mixes is structural strength provision. This
involves even load dispersion throughout the layers of the pavement. The loads
involved are dynamic or static loads, which is transferred to the base subgrade
through the aggregate course.
A granular base with a bituminous surface course is only provided for roads of low
traffic. It is just sufficient and economical.
The rebounding effect of bitumen upper layers helps in having resistance against
high dynamic effect due to the heavy traffic. Rebounding property is reflected by