1. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
STUDY OF DESIGN OF THE
2. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Flexible pavements are widely used despite some doubts regarding their economics
under different conditions. Lack of research, less construction technology and high cement
rates compared with asphalt in the past are the main reasons for not implementing concrete
pavement in Sudan. The purpose of this study is to conduct comparison in total present cost
between flexible pavement and jointed plain concrete pavement to locate a feasible long term
good performance pavement type. The principles and cost comparison were applied for the
two case study roads. The two most important parameters that govern pavement design,
namely sub -grade strength and traffic loading was determined in this study from Road A and
Road B material laboratory tests reports and traffic surveying data.
The design traffic in term of million ESAL was obtained from AASHTO equation for
20 year design life. The rigid pavement design used modified modulus of sub-grade reaction
k as measure of sub-grade strength, while design traffic was also million ESAL. The
AASHTO and PCA methods were applied for rigid pavement design in comparative manner
with AASHTO and Asphalt Institute (AI) methods for flexible pavement design. Typical
standard pavement cross sections obtained by AASHTO design for flexible and jointed plain
concrete pavements were adopted for life-cycle cost analysis (LCCA). The two components
of LCCA, construction and maintenance costs were calculated for the entire roads using 2014
rates. The total present-worth of cost for each road pavement cost were used for comparison.
It was found that the feasible long term pavement performance can be achieved by using
jointed plain concrete pavement with saving of (28 %) for road A and (6 %) for road B.
3. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Sl .no Page. no
1. Introduction 8
2. Methods of flexible pavement design 14
3. Design of flexible pavements as per guidance of
IRC: 37-2001 16
4. Design procedure 18
5. Pavement composition 20
6. Aggregate testing in pavement design 21
7 .Bitumen materials 29
8 .Geometric standards of BT roads 37
9 .Cross sectional elements of BT roads 40
10. Process in BT roads construction 43
11 .WBM road construction 46
12 .Project preparation of BT Roads 48
13 .Conclusion 61
4. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
A highway pavement is a structure consisting of superimposed layers of processed
materials above the natural soil sub-grade, whose primary function is to distribute the applied
vehicle loads to the sub-grade. The pavement structure should be able to provide a surface of
acceptable riding quality, adequate skid resistance, favorable light reflecting characteristics,
and low noise pollution. The ultimate aim is to ensure that the transmitted stresses due to
wheel load are sufficiently reduced, so that they will not exceed bearing capacity of the sub-
grade. Two types of pavements are generally recognized as serving this purpose, namely
flexible pavements and rigid pavements. This chapter gives an overview of flexible
pavements, layers, and their functions, and pavement failures. Improper design of pavements
leads to early failure of pavements affecting the riding quality.
One of the main purposes of pavement design is to produce a soil structure system
that will carry traffic smoothly and safely with minimum cost. The increase in axle load and
phenomenal growth of traffic warrant is much important in design, construction and
maintenance of roads. In this chapter, a glimpse of different approaches of flexible pavement
design is narrated. State of the art practice of pavement design with geo-synthetic is also
discussed. For sub grade, CBR values are ranging from 2% to 10% and design traffic ranging
from 1 msa to 150 msa for an average annual pavement temperature of 35° C. The layer
thicknesses obtained from the analysis have been slightly modified to adapt the designs to
stage construction. Using the following simple input parameters, appropriate designs could be
chosen for the given traffic and soil strength:
- Design traffic in terms of cumulative number of standard axles; and
- CBR of sub grade.
Road connectivity is a key component of rural and urban development, since it
promotes access to economic and social services, thereby generating increased agricultural
productivity, non-agriculture employment as well as non-agricultural productivity, which in
turn expands rural and urban growth opportunities and real income through which poverty
can be reduced
5. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
.A study (Fan et al. 1999) carried out by the International Food Policy Research
Institute on linkages between government expenditure and poverty in rural India has revealed
that an investment of Rs 1 crore in roads lifts 1650 poor persons above the poverty line.
Public investment on roads impacts rural poverty through its effect on improved agricultural
productivity, higher non-farm employment opportunities and increased rural wages.
Improvement in agricultural productivity not only reduces rural poverty directly by
increasing income of poor households, it also causes decline in poverty indirectly by raising
agricultural wages and lowering food prices (since poor households are net buyers of food
Similarly increased non-farm employment and higher rural enhance incomes of
the rural poor and consequently, reduce rural poverty. This study estimated that while the
‘productivity effect’ of government spending on rural roads accounts for 24 per cent of total
impact on poverty, increased non-farm employment accounts for 55 per cent and higher rural
wages accounts for the remaining 31 per cent.
Further, of the total productivity effect on poverty, 75 per cent arises from the direct impact
of roads in increasing incomes, while the remaining 25 per cent arises from lower food prices
(15 percent) and increased wages (10 per cent).
Similar results are found in other developing countries.
Thus, a Social Analysis of those who are affected and benefited by the road connectivity
should be conducted. The assessment and recommendations, both, demand-people oriented
approach and micro-planning.
1.1 Requirements of a pavement:
An ideal pavement should meet the following requirements:
Sufficient thickness to distribute the wheel load stresses to a safe value on the sub-
Structurally strong to withstand all types of stresses imposed upon it.
Adequate coefficient of friction to prevent skidding of vehicles.
Smooth surface to provide comfort to road users even at high speed.
6. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Produce least noise from moving vehicles.
Dust proof surface so that traffic safety is not impaired by reducing visibility.
Impervious surface, so that sub-grade soil is well protected.
Long design life with low maintenance cost.
1.2 Types of pavements
The pavements can be classified based on the structural performance into two,
flexible pavements and rigid pavements. In flexible pavements, wheel loads are transferred
by grain-to-grain contact of the aggregate through the granular structure. The flexible
pavement, having less flexural strength, acts like a flexible sheet (e.g. bituminous road). On
the contrary, in rigid pavements, wheel loads are transferred to sub-grade soil by flexural
strength of the pavement and the pavement acts like a rigid plate (e.g. cement concrete roads).
In addition to these, composite pavements are also available. A thin layer of flexible
pavement over rigid pavement is an ideal pavement with most desirable characteristics.
However, such pavements are rarely used in new construction because of high cost and
complex analysis required.
1.3 Flexible pavements:
Flexible pavements will transmit wheel load stresses to the lower layers by grain-to-
grain transfer through the points of contact in the granular structure (see Figure 1).
7. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Figure 1: Load transfer in granular structure
1.4 Deflectionon flexible pavement:
The wheel load acting on the pavement will be distributed to a wider area, and the
stress decreases with the depth. Taking advantage of these stress distribution characteristic,
flexible pavements normally has many layers. Hence, the design of flexible pavement uses
the concept of layered system. Based on this, flexible pavement may be constructed in a
number of layers and the top layer has to be of best quality to sustain maximum compressive
stress, in addition to wear and tear. The lower layers will experience lesser magnitude of
stress and low quality material can be used. Flexible pavements are constructed using
bituminous materials. These can be either in the form of surface treatments (such as
bituminous surface treatments generally found on low volume roads) or, asphalt concrete
surface courses (generally used on high volume roads such as national highways). Flexible
pavement layers reflect the deformation of the lower layers on to the surface layer (e.g., if
there is any undulation in sub-grade then it will be transferred to the surface layer). In the
case of flexible pavement, the design is based on overall performance of flexible pavement,
and the stresses produced should be kept well below the allowable stresses of each pavement
8. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
1.5 Types of Flexible Pavements:
The following types of construction have been used in flexible pavement:
1. Conventional layered flexible pavement,
2. Full - depth asphalt pavement, and
3. Contained rock asphalt mat (CRAM).
1. Conventional flexible pavements:
These are the layered systems with high quality expensive materials are placed in the
top where stresses are high, and low quality cheap materials are placed in lower layers.
2. Full - depth asphalt pavements:
These are constructed by placing bituminous layers directly on the soil sub-grade.
This is more suitable when there is high traffic and local materials are not available.
3. Contained rock asphalt mats:
These are constructed by placing dense/open graded aggregate layers in between two
asphalt layers. Modified dense graded asphalt concrete is placed above the sub-grade will
significantly reduce the vertical compressive strain on soil sub-grade and protect from surface
1.6 Typical layers of a flexible pavement:
Typical layers of a conventional flexible pavement includes seal coat, surface course,
tack coat, binder course, prime coat, base course, sub-base course, compacted sub-grade, and
natural sub-grade .
Seal coat is a thin surface treatment used to water-proof the surface and to provide
9. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Tack coat is a very light application of asphalt, usually asphalt emulsion diluted with
water. It provides proper bonding between two layers of binder course and must be thin,
uniformly cover the entire surface, and set very fast.
Prime coat is an application of low viscous cutback bitumen to an absorbent surface
like granular bases on which binder layer is placed. It provides bonding between two layers.
Unlike tack coat, prime coat penetrates into the layer below, plugs the voids, and forms a
water tight surface.
Figure 2: Typical cross section of a flexible pavement
Surface course is the layer directly in contact with traffic loads and generally contains
superior quality materials. They are usually constructed with dense graded asphalt concrete
(AC). The functions and requirements of this layer are:
It provides characteristics such as friction, smoothness, drainage, etc. Also it will
prevent the entrance of excessive quantities of surface water into the underlying base,
sub-base and sub-grade,
10. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
It must be tough to resist the distortion under traffic and provide a smooth and skid-
resistant riding surface,
It must be water proof to protect the entire base and sub-grade from the weakening
effect of water.
This layer provides the bulk of the asphalt concrete structure. It's chief purpose is to
distribute load to the base course .The binder course generally consists of aggregates having
less asphalt and doesn't require quality as high as the surface course, so replacing a part of the
surface course by the binder course results in more economical design.
The base course is the layer of material immediately beneath the surface of binder
course and it provides additional load distribution and contributes to the sub-surface drainage.
It may be composed of crushed stone, crushed slag, and other untreated or stabilized
The sub-base course is the layer of material beneath the base course and the primary
functions are to provide structural support, improve drainage, and reduce the intrusion of
fines from the sub-grade in the pavement structure If the base course is open graded, then the
sub-base course with more fines can serve as a filler between sub-grade and the base course
A sub-base course is not always needed or used. For example, a pavement constructed over a
high quality, stiff sub-grade may not need the additional features offered by a sub-base
course. In such situations, sub-base course may not be provided.
The top soil or sub-grade is a layer of natural soil prepared to receive the stresses from
the layers above. It is essential that at no time soil sub-grade is overstressed. It should be
compacted to the desirable density, near the optimum moisture content.
11. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
1.7 Failure of flexible pavements:
The major flexible pavement failures are fatigue cracking, rutting, and thermal
cracking. The fatigue cracking of flexible pavement is due to horizontal tensile strain at the
bottom of the asphaltic concrete. The failure criterion relates allowable number of load
repetitions to tensile strain and this relation can be determined in the laboratory fatigue
test on asphaltic concrete specimens. Rutting occurs only on flexible pavements as indicated
by permanent deformation or rut depth along wheel load path. Two design methods have
been used to control rutting: one to limit the vertical compressive strain on the top of sub
grade and other to limit rutting to a tolerable amount (12 mm normally). Thermal cracking
includes both low-temperature cracking and thermal fatigue cracking.
12. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
2. METHODS OF FLEXIBLE PAVEMENT DESIGN
Modified Boussinesq’s equation limited the deflection of sub grade to 2.54mm
(O.linch). The US Navy (1953) applied Bur mister’s theory (Burmister, 1943) and limited the
surface deflection to 6.35mm (0.25 inch). There exist a number of methods for the design of
flexible pavements as summarized by Rao, 2007.
These are empirical method with or without a soil strength test. Limiting shear failure
method, limiting deflection method, regression method .Based on pavement performance,
mechanistic-empirical method and design based on theoretical studies .The use of empirical
method without a strength test dates back to the development of Public Roads (PR) soil
classification system, in which the sub grade was classified as uniform from A-l to A-8 and
non-uniform from B-l to B-3. This System was later modified by the Highway Research
Board (HRB,1945), in which soil were grouped from A-l to A-7 and a group Index was added
to differentiate the soil within each group .The empirical method with a strength test was first
used by California Highway Department in 1929 (Porter, 1950).
The thickness of the pavement was related to the California Bearing Ratio, defined as
the penetration resistance of a sub grade soil relative to standard crushed rock. The CBR
method of design was studied extensively by the US167 corps of engineers during the World
War II and became a very popular method of pavement design after the war.
The IRC also used this method to determine the thickness of individual layer of
pavement. The disadvantage of this empirical method is that it can be applied only to a given
set of environmental, material and loading condition. In this limiting shear failure method the
thickness of pavement is determined so that shear failure will not occur .The major properties
of sub grade soil considered are cohesion and angle of internal friction.
Me Leod (1953) advocated the use of logarithmic spirals to determine the bearing
capacity of pavement .The limiting deflection method is used to determine the thickness of
pavements so that the vertical deflection will not exceed the allowable limit. The Kansas
State Highway Commission the apparent advantage that it can be easily measured in the field.
A good example of the use of regression equations for pavement designs is the AASHTO
method based on the result of the road tests.
13. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
The disadvantage of the method is that the design equation can be applied only to the
conditions at the road test site .The mechanistic-empirical methods of design are based on the
mechanics of materials that relate an input, such as a wheel load, to an output or pavement
response such as stress and strain. The response values are used to predict distress based on
laboratory test and field performance data.
Dependence on observed performance is necessary because theory alone has not
proven sufficient to design pavements16 8realistically. The horizontal tensile strain at the
bottom of the bituminous layer and the vertical compressive strain (ez) on the sub grade are
identified as the critical parameters for fatigue and rutting failures respectively. The
mechanistic-empirical method is more theoretical in approach, through it needs calibration
based upon the performance of in-service pavements.
This approach is increasingly popular amongst various countries. In India too, the
Pavement Design Guidelines IRC: 37 have been updated in 2001 where the design
methodology has changed from empiricism to mechanistic pavement design principles. The
mechanistic-empirical approach is being successfully used in the design of reinforced
sections also, as it tries to relate the stress-strain parameters with the expected life of the
pavement. Figure 5.1 shows a layered bituminous pavement structure subjected to a set of
standard dual wheel load system.
14. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
3. DESIGN OF FLEXIBLE PAVEMENTS AS PER GUIDE LINES OF
These guidelines are applied to design flexible pavements for Expressway, National
Highways, State Highways, Major District Roads, and other categories of roads. Flexible
pavements are considered to include the pavements which have bituminous surfacing and
granular base and sub-base courses conforming to IRC standards. These guidelines apply to
3.2 Design criteria:
The flexible pavements has been modeled as a three layer structure and stresses and
strains at critical locations have been computed using the linear elastic model. To give proper
consideration to the aspects of performance, the following three types of pavement distress
resulting from repeated (cyclic) application of traffic loads are considered:
1. Vertical compressive strain at the top of the sub grade which can cause sub-grade
deformation resulting in permanent deformation at the pavement surface.
2. Horizontal tensile strain or stress at the bottom of the bituminous layer which can cause
fracture of the bituminous layer.
3. Pavement deformation within the bituminous layer.
While the permanent deformation within the bituminous layer can be controlled by
meeting the mix design requirements, thickness of granular and bituminous layers are
selected using the analytical design approach so that strains at the critical points are within
the allowable limits. For calculating tensile strains at the bottom of the bituminous layer, the
stiffness of dense bituminous macadam (DBM) layer with 60/70 bitumen has been used in the
15. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
3.3 Failure Criteria:
Figure 3: Critical Locations in pavement
3.4 Fatigue Criteria:
Bituminous surfacing of pavements display flexural fatigue cracking if the tensile
strain at the bottom of the bituminous layer is beyond certain limit. The relation between the
fatigue life of the pavement and the tensile strain in the bottom of the bituminous layer was
N f =2.21*10-4*(
)*0.854 Eq - 5.1
in which, N f is the allowable number of load repetitions to control fatigue cracking, e is the
tensile strain and E is the Elastic modulus of bituminous layer. The use of the above equation
would result in fatigue cracking of 20% of the total area.
3.5 Rutting Criteria:
The contribution of rutting from various layers could be different. It is reported that(
Chakroborty et al,2003), 46% of rutting take place from bituminous surface and granular base
course, while the sub-base and sub grade contribute 54% of the total rutting. The vertical
strain at sub-grade is assumed as the index of rutting to occur in a pavement.
16. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
4. DESIGN PROCEDURE
Based on the performance of existing designs and using analytical approach, simple
design charts and a catalogue of pavement designs are added in the guideline. The pavement
designs are given as
The method considers traffic in terms of the cumulative number of standard axles
(8160 kg) to be carried by the pavement during the design life. This requires the following
1. Initial traffic in terms of CVPD
2. Traffic growth rate during the design life
3. Design life in number of years0
4. Vehicle damage factor (VDF)
5. Distribution of commercial traffic over the carriageway
1. Initial traffic:
Initial traffic is determined in terms of commercial vehicles per day (CVPD). For the
structural design of the pavement only commercial vehicles are considered assuming laden
weight of three tons or more and their axle loading will be considered. Estimate of the initial
daily average traffic flow for any road should normally be based on 7-day 24- hour classified
traffic counts (ADT). In case of new roads, traffic estimates can be made on the basis of
potential land use and traffic on existing routes in the area.
2 .Traffic growth rate:
Traffic growth rates can be estimated
By studying the past trends of traffic growth, and
By establishing econometric models.
17. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
If adequate data is not available, it is recommended that an average annual growth rate of 7.5
percent may be adopted.
3. Design life:
For the purpose of the pavement design, the design life is defined in terms of the cumulative
number of standard axles that can be carried before strengthening of the pavement is
necessary. It is recommended that pavements for arterial roads like NH, SH should be
designed for a life of 15 years, EH and urban roads for 20 years and other categories of roads
for 10 to 15 years.
4 .Vehicle Damage Factor:
The vehicle damage factor (VDF) is a multiplier for converting the number of
commercial vehicles of different axle loads and axle configurations to the number of standard
axle-load repetitions. It is defined as equivalent number of standard axles per commercial
vehicle. The VDF varies with the axle configuration, axle loading, terrain, type of road, and
from region to region. The axle load equivalency factors are used to convert different axle
load repetitions into equivalent standard axle load repetitions. For these equivalency factors
refer IRC: 37-2001.
5 .Vehicle distribution:
The exact VDF values are arrived after extensive field surveys affects the total
equivalent standard axle load application used in the design. Until reliable data is available A
realistic assessment of distribution of commercial traffic by direction and by lane is necessary
as it directly, the following distribution may be J ft assumed.
4.2 Single lane roads:
Traffic tends to be more channelized on single roads than two lane roads and to allow
for this concentration of wheel load repetitions, the design should be based on total number of
commercial vehicles in both directions.
4.3 Two-lane single carriageway roads:
The design should be based on 75 % of the commercial vehicles in both directions.
18. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
4.4 Four-lane single carriageway roads:
The design should be based on 40 % of the total number of commercial vehicles in
4.5 Dual carriageway roads:
For the design of dual two-lane carriageway roads should be based on 75 % of the
number of commercial vehicles in each direction. For dual three-lane carriageway and dual
four-lane carriageway the distribution factor will be 60 % and 45 % respectively.
4.6 Pavement thickness design charts:
For the design of pavements to carry traffic in the range of l to 10 ms a, use chart 1
and for traffic in the range 10 to 150 msa, use chart 2 of IRC: 37-2001. The-design curves
relate pavement thickness to the cumulative number of standard axles to be carried over the
design life for different sub-grade CBR values ranging from 2 % to 10 %. The design charts
will give the total thickness of the pavement for the above inputs. The total thickness consists
of granular sub-base, granular base and bituminous surfacing. The individual layers are
designed based on the recommendations given below and the subsequent tables.
19. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
5. PAVEMENT COMPOSITION
Sub-base materials comprise natural sand, gravel, laterite, brick metal, crushed stone
or combinations there-of meeting the prescribed grading and physical requirements. The sub-
base material should have a minimum CBR of 20% and 30% for traffic up to 2 msa and
traffic exceeding 2 msa respectively. Sub-base usually consist of granular material or WBM
and the thickness should not be less than 150 mm for design traffic less than 10 msa and-200
mm for design traffic of 10-msa and above.
5.2 Base course:
The recommended designs are for unbounded granular bases which comprise conventional
water bound macadam (WBM) or wet mix macadam (WMM) or equivalent confirming to
MOST specifications. The materials should be of good quality with minimum thickness of
225 mm.For traffic up to 2mmfor traffic-exceeding 2msa.
5.3 Bituminous surfacing:
The surfacing consists of a wearing course or a binder course plus wearing course. The most
commonly used wearing courses are surface dressing, open graded premix carpet, mix seal
surfacing, semi-dense bituminous concrete and bituminous concrete. For binder course,
MOST specifies, it is desirable to use bituminous macadam (BM) for traffic up to 5 msa and
dense bituminous macadam (DBM) for traffic more than 5 msa.
20. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
6. AGGREGATE TESTING IN PAVEMENT DESIGN
Aggregate is a collective term for the mineral materials such as sand, gravel, and
crushed stone that are used with a binding medium (such as water, bitumen, Portland cement,
lime, etc.) to form compound materials (such as bituminous concrete and Portland cement
concrete). By volume, aggregate generally accounts for 92 to 96 percent of Bituminous
concrete and about 70 to 80 percent of Portland cement concrete. Aggregate is also used for
base and sub-base courses for both flexible and rigid pavements. Aggregates can either be
natural or manufactured. Natural aggregates are generally extracted from larger rock
formations through an open excavation (quarry). Extracted rock is typically reduced to usable
sizes by mechanical crushing. Manufactured aggregate is often a bye product of other
manufacturing industries. The requirements of the aggregates in pavement are also discussed
in this chapter.
6.2 Desirable properties
The aggregates used in top layers are subjected to (i) Stress action due to traffic wheel
load, (ii) Wear and tear, (iii) crushing. For a high quality pavement, the aggregates should
possess high resistance to crushing, and to withstand the stresses due to traffic wheel load.
The aggregates used in the surface course are subjected to constant rubbing or
abrasion due to moving traffic. The aggregates should be hard enough to resist the abrasive
action caused by the movements of traffic. The abrasive action is severe when steel tyred
vehicles moves over the aggregates exposed at the top surface.
21. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Resistance of the aggregates to impact is termed as toughness. Aggregates used in the
pavement should be able to resist the effect caused by the jumping of the steel tyred wheels
from one particle to another at different levels causes severe impact on the aggregates.
Shape of aggregates:
Aggregates which happen to fall in a particular size range may have rounded cubical,
angular, flaky or elongated particles. It is evident that the flaky and elongated particles will
have less strength and durability when compared with cubical, angular or rounded particles of
the same aggregate. Hence too flaky and too much elongated aggregates should be avoided as
far as possible.
Adhesion with bitumen:
The aggregates used in bituminous pavements should have less affinity with water
when compared with bituminous materials, otherwise the bituminous coating on the
aggregate will be stripped off in presence of water.
The property of aggregates to withstand adverse action of weather is called
soundness. The aggregates are subjected to the physical and chemical action of rain and
bottom water, impurities there-in and that of atmosphere, hence it is desirable that the road
aggregates used in the construction should be sound enough to withstand the weathering
Freedomfrom deleterious particles:
Specifications for aggregates used in bituminous mixes usually require the aggregates
to be clean, tough and durable in nature and free from excess amount of flat or elongated
pieces, dust, clay balls and other objectionable material. Similarly aggregates used in
Portland cement concrete mixes must be clean and free from deleterious substances such as
clay lumps, chart, silt and other organic impurities.
22. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
6.3 Aggregate tests:
In order to decide the suitability of the aggregate for use in pavement construction,
following tests are carried out:
1. Crushing test
2. Abrasion test
3. Impact test
4. Soundness test
5. Shape test
6. Specific gravity and water absorption test
7. Bitumen adhesion test
One of the model in which pavement material can fail is by crushing under
compressive stress. A test is standardized by IS: 2386 part-IV and used to determine the
crushing strength of aggregates. The aggregate crushing value provides a relative measure of
resistance to crushing under gradually applied crushing load. The test consists of subjecting
the specimen of aggregate in standard mould to a compression test under standard load
conditions (Figure 1). Dry aggregates passing through 12.5 mm sieves and retained 10 mm
sieves are filled in a cylindrical measure of 11.5 mm diameter and 18 cm height in three
layers. Each layer is tampered 25 times with at standard tamping rod. The test sample is
weighed and placed in the test cylinder in three layers each layer being tampered again. The
specimen is subjected to a compressive load of 40 tonnes gradually applied at the rate of 4
tonnes per minute. Then crushed aggregates are then sieved through 2.36 mm sieve and
weight of passing material (W2) is expressed as percentage of the weight of the total sample
(W1) which is the aggregate crushing value.
A value less than 10 signifies an exceptionally strong aggregate while above 35 would
normally be regarded as weak aggregates.
23. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Figure 4: Crushing test setup
2. Abrasion test:
Abrasion test is carried out to test the hardness property of aggregates and to decide
whether they are suitable for different pavement construction works. Los Angeles abrasion
test is a preferred one for carrying out the hardness property and has been standardized in
India (IS: 2386 part-IV). The principle of Los Angeles abrasion test is to find the percentage
wear due to relative rubbing action between the aggregate and steel balls used as abrasive
Los Angeles machine consists of circular drum of internal diameter 700 mm and
length 520 mm mounted on horizontal axis enabling it to be rotated (see Figure 2). An
abrasive charge consisting of cast iron spherical balls of 48 mm diameters and weight 340-
445 g is placed in the cylinder along with the aggregates. The number of the abrasive spheres
varies according to the grading of the sample. The quantity of aggregates to be used depends
upon the gradation and usually ranges from 5-10 kg. The cylinder is then locked and rotated
at the speed of 30-33 rpm for a total of 500 -1000 revolutions depending upon the gradation
After specified revolutions, the material is sieved through 1.7 mm sieve and passed
fraction is expressed as percentage total weight of the sample. This value is called Los
Angeles abrasion value.
24. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
A maximum value of 40 percent is allowed for WBM base course in Indian
conditions. For bituminous concrete, a maximum value of 35 is specified.
Figure 5: Los Angeles abrasion test setup
The aggregate impact test is carried out to evaluate the resistance to impact of
aggregates. Aggregates passing 12.5 mm sieve and retained on 10 mm sieve is filled in a
cylindrical steel cup of internal diameter 10.2 mm and depth 5 cm which is attached to a
metal base of impact testing machine. The material is filled in 3 layers where each layer is
tamped for 25 numbers of blows. Metal hammer of weight 13.5 to 14 Kg is arranged to drop
with a free fall of 38.0 cm by vertical guides and the test specimen is subjected to 15 numbers
of blows. The crushed aggregate is allowed to pass through 2.36 mm IS sieve. And the
impact value is measured as percentage of aggregates passing sieve (W1) to the total weight
of the sample (W2).
25. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Figure 6: Impact test setup
Aggregates to be used for wearing course, the impact value shouldn't exceed 30
percent. For bituminous macadam the maximum permissible value is 35 percent. For Water
bound macadam base courses the maximum permissible value defined by IRC is 40 percent.
Soundness test is intended to study the resistance of aggregates to weathering action,
by conducting accelerated weathering test cycles. The Porous aggregates subjected to
freezing and thawing is likely to disintegrate prematurely. To ascertain the durability of such
aggregates, they are subjected to an accelerated soundness test as specified in IS: 2386 part-
V. Aggregates of specified size are subjected to cycles of alternate wetting in a saturated
solution of either sodium sulphate or magnesium sulphate for 16 - 18 hours and then dried in
oven at 105-110℃ to a constant weight. After five cycles, the loss in weight of aggregates is
determined by sieving out all undersized particles and weighing. And the loss in weight
should not exceed 12 percent when tested with sodium sulphate and 18 percent with
magnesium sulphate solution.
26. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
The particle shape of the aggregate mass is determined by the percentage of flaky and
elongated particles in it. Aggregates which are flaky or elongated are detrimental to higher
workability and stability of mixes.
The flakiness index is defined as the percentage by weight of aggregate particles
whose least dimension is less than 0.6 times their mean size. Test procedure had been
standardized in India (IS: 2386 part-I)
Figure 7: Flakiness gauge
The elongation index of an aggregate is defined as the percentage by weight of
particles whose greatest dimension (length) is 1.8 times their mean dimension. This test is
applicable to aggregates larger than 6.3 mm. This test is also specified in (IS: 2386 Part-I).
However there are no recognized limits for the elongation index.
Figure 8: Elongation gauge
27. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
6.Specific Gravity and waterabsorption:
The specific gravity and water absorption of aggregates are important properties that
are required for the design of concrete and bituminous mixes. The specific gravity of a solid
is the ratio of its mass to that of an equal volume of distilled water at a specified temperature.
Because the aggregates may contain water-permeable voids, so two measures of specific
gravity of aggregates are used: apparent specific gravity and bulk specific gravity.
Apparent Specific Gravity:
Gapp , is computed on the basis of the net volume of aggregates i.e., the volume
excluding water-permeable voids. Thus
Where, MD is the dry mass of the aggregate, VN is the net volume of the aggregates
excluding the volume of the absorbed matter, W is the density of water.
Bulk Specific Gravity:
Gbulk, is computed on the basis of the total volume of aggregates including water
permeable voids .Thus
Where, VB is the total volume of the aggregates including the volume of absorbed water.
Water absorption, the difference between the apparent and bulk specific gravities is nothing
but the water-permeable voids of the aggregates. We can measure the volume of such voids
by weighing the aggregates dry and in a saturated, surface dry condition, with all permeable
voids filled with water. The difference of the above two is MW. MW is the weight of dry
aggregates minus weight of aggregates saturated surface dry condition. Thus
28. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
The specific gravity of aggregates normally used in road construction ranges from
about 2.5 to 2.9. Water absorption values ranges from 0.1 to about 2.0 percent for aggregates
normally used in road surfacing.
7 .Bitumen adhesiontest:
Bitumen adheres well to all normal types of road aggregates provided they are dry and
free from dust. In the absence of water there is practically no adhesion problem of bituminous
construction. Adhesion problem occurs when the aggregate is wet and cold. This problem can
be dealt with by removing moisture from the aggregate by drying and increasing the mixing
temperature. Further,the presence of water causes stripping of binder from the coated
aggregates. These problems occur when bitumen mixture is permeable to water. Several
laboratory tests are conducted to arbitrarily determine the adhesion of bitumen binder to an
aggregate in the presence of water. Static immersion test is one specified by IRC and is quite
simple. The principle of the test is by immersing aggregate fully coated with binder in water
maintained at 40℃ temperature for 24 hours. IRC has specified maximum stripping value of
aggregates should not exceed 5%.
29. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Table 1: Tests for Aggregates with IS codes
Property of aggregate Type of Test Test Method
Crushing strength Crushing test
IS : 2386 (part 4) -
Hardness Los Angeles abrasion test
IS : 2386 (Part 5)-
Toughness Aggregate impact test
IS : 2386 (Part 4)-
Soundness test- accelerated durability
IS : 2386 (Part 5)-
Shape factors Shape test
IS : 2386 (Part 1)-
Specific gravity and
Specific gravity test and water
IS : 2386 (Part 3)-
Adhesion to bitumen Stripping value of aggregate IS : 6241-1971
Aggregates influence, to a great extent, the load transfer capability of pavements.
Hence it is essential that they should be thoroughly tested before using for construction. Not
only that aggregates should be strong and durable, they should also possess proper shape and
size to make the pavement act monolithically. Aggregates are tested for strength, toughness,
hardness, shape, and water absorption
30. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
7. BITUMEN MATERIALS
Bituminous materials or asphalts are extensively used for roadway construction,
primarily because of their excellent binding characteristics and water proofing properties and
relatively low cost. Bituminous materials consists of bitumen which is a black or dark colored
solid or viscous cementitious substances consists chiefly high molecular weight hydrocarbons
derived from distillation of petroleum or natural asphalt, has adhesive properties, and is
soluble in carbon disulphide. Tars are residues from the destructive distillation of organic
substances such as coal, wood, or petroleum and are temperature sensitive than bitumen.
Bitumen will be dissolved in petroleum oils where unlike tar.
7.2 Production of Bitumen:
Bitumen is the residue or by-product when the crude petroleum is refined. A wide
variety of refinery processes, such as the straight distillation process, solvent extraction
process etc. may be used to produce bitumen of different consistency and other desirable
properties. Depending on the sources and characteristics of the crude oils and on the
properties of bitumen required, more than one processing method may be employed.
7.3 Vacuum steamdistillation of petroleum oils:
In the vacuum-steam distillation process the crude oil is heated and is introduced into
a large cylindrical still. Steam is introduced into the still to aid in the vaporizations of the
more volatile constituents of the petroleum and to minimize decomposition of the distillates
and residues. The volatile constituents are collected, condensed, and the various fractions
stored for further refining, if needed. The residues from this distillation are then fed into a
vacuum distillation unit, where residue pressure and steam will further separate out heavier
gas oils. The bottom fraction from this unit is the vacuum-steam-refined asphalt cement. The
consistency of asphalt cement from this process can be controlled by the amount of heavy gas
oil removed. Normally, asphalt produced by this process is softer. As the asphalt cools down
to room temperature, it becomes a semi solid viscous material.
31. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
7.4 Different forms of bitumen
Normal practice is to heat bitumen to reduce its viscosity. In some situations
preference is given to use liquid binders such as cutback bitumen. In cutback bitumen
suitable solvent is used to lower the viscosity of the bitumen. From the environmental point
of view also cutback bitumen is preferred. The solvent from the bituminous material will
evaporate and the bitumen will bind the aggregate. Cutback bitumen is used for cold weather
bituminous road construction and maintenance. The distillates used for preparation of cutback
bitumen are naphtha, kerosene, diesel oil, and furnace oil. There are different types of
cutback bitumen like rapid curing (RC), medium curing (MC), and slow curing (SC). RC is
recommended for surface dressing and patchwork. MC is recommended for premix with less
quantity of fine aggregates. SC is used for premix with appreciable quantity of fine
Bitumen emulsion is a liquid product in which bitumen is suspended in a finely
divided condition in an aqueous medium and stabilized by suitable material. Normally
cationic type emulsions are used in India. The bitumen content in the emulsion is around 60%
and the remaining is water. When the emulsion is applied on the road it breaks down
resulting in release of water and the mix starts to set. The time of setting depends upon the
grade of bitumen. The viscosity of bituminous emulsions can be measured as per IS: 8887-
1995. Three types of bituminous emulsions are available, which are Rapid setting (RS),
Medium setting (MS), and Slow setting (SC). Bitumen emulsions are ideal binders for hill
road construction. Where heating of bitumen or aggregates are difficult. Rapid setting
emulsions are used for surface dressing work. Medium setting emulsions are preferred for
premix jobs and patch repairs work. Slow setting emulsions are preferred in rainy season.
In bituminous primer the distillate is absorbed by the road surface on which it is
spread. The absorption therefore depends on the porosity of the surface. Bitumen primers are
32. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
useful on the stabilized surfaces and water bound macadam base courses. Bituminous primers
are generally prepared on road sites by mixing penetration bitumen with petroleum distillate.
Certain additives or blend of additives called as bitumen modifiers can improve
properties of Bitumen and bituminous mixes. Bitumen treated with these modifiers is known
as modified bitumen. Polymer modified bitumen (PMB)/ crumb rubber modified bitumen
(CRMB) should be used only in wearing course depending upon the requirements of extreme
climatic variations. The detailed specifications for modified bitumen have been issued by
IRC: SP: 53-1999. It must be noted that the performance of PMB and CRMB is dependent on
strict control on temperature during construction. The advantages of using modified bitumen
are as follows
1. Lower susceptibility to daily and seasonal temperature variations.
2. Higher resistance to deformation at high pavement temperature.
3. Better age resistance properties.
4. Higher fatigue life for mixes.
5. Better adhesion between aggregates and binder.
6. Prevention of cracking and reflective cracking.
7.5 Requirements of Bitumen:
The desirable properties of bitumen depend on the mix type and construction. In
general, Bitumen should posses following desirable properties.
The bitumen should not be highly temperature susceptible: during the hottest weather
the mix should not become too soft or unstable, and during cold weather the mix
should not become too brittle causing cracks.
The viscosity of the bitumen at the time of mixing and compaction should be
adequate. This can be achieved by use of cutbacks or emulsions of suitable grades or
by heating the bitumen and aggregates prior to mixing.
There should be adequate affinity and adhesion between the bitumen and aggregates
used in the mix.
33. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
7.6 Tests on bitumen:
There are a number of tests to assess the properties of bituminous materials. The
following tests are usually conducted to evaluate different properties of bituminous materials.
1. Penetration test
2. Ductility test
3. Softening point test
4. Specific gravity test
5. Viscosity test
6. Flash and Fire point test
7. Float test
8. Water content test
9. Loss on heating test
It measures the hardness or softness of bitumen by measuring the depth in tenths of a
millimeter to which a standard loaded needle will penetrate vertically in 5 seconds. BIS had
standardized the equipment and test procedure. The penetrometre consists of a needle
assembly with a total weight of 100g and a device for releasing and locking in any position.
The bitumen is softened to a pouring consistency, stirred thoroughly and poured into
containers at a depth at least 15 mm in excess of the expected penetration. The test should be
conducted at a specified temperature of 25℃. It may be noted that penetration value is largely
influenced by any inaccuracy with regards to pouring temperature, size of the needle, weight
placed on the needle and the test temperature. A grade of 40/50 bitumen means the
penetration value is in the range 40 to 50 at standard test conditions. In hot climates, a lower
penetration grade is preferred. The Figure 4.1 shows a schematic Penetration Test setup.
34. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Figure 9: Penetration Test Setup
2 .Ductility test:
Ductility is the property of bitumen that permits it to undergo great deformation or
elongation. Ductility is defined as the distance in cm, to which a standard sample or briquette
of the material will be elongated without breaking. Dimension of the briquette thus formed is
exactly 1 cm square. The bitumen sample is heated and poured in the mould assembly placed
on a plate. These samples with moulds are cooled in the air and then in water bath at 27 C
temperature. The excess bitumen is cut and the surface is leveled using a hot knife. Then the
mould with assembly containing sample is kept in water bath of the ductility machine for
about 90 minutes. The sides of the moulds are removed, the clips are hooked on the machine
and the machine is operated. The distance up to the point of breaking of thread is the ductility
value which is reported in cm. The ductility value gets affected by factors such as pouring
temperature, test temperature, rate of pulling etc. A minimum ductility value of 75 cm has
been specified by the BIS. Figure 4.2 shows ductility moulds to be filled with bitumen.
35. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
3. Softening point test:
Softening point denotes the temperature at which the bitumen attains a particular
degree of softening under the specifications of test. The test is conducted by using Ring and
Ball apparatus. A brass ring containing test sample of bitumen is suspended in liquid like
water or glycerin at a given temperature. A steel ball is placed upon the bitumen sample and
the liquid medium is heated at a rate of 5 C per minute. Temperature is noted when the
softened bitumen touches the metal plate which is at a specified distance below. Generally,
higher softening point indicates lower temperature susceptibility and is preferred in hot
climates. Figure 4.3 shows Softening Point test setup.
Figure 11: Softening Point Test Setup
Figure 10: Ductility Test
36. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
4. Specific gravity test:
In paving jobs, to classify a binder, density property is of great use. In most cases
bitumen is weighed, but when used with aggregates, the bitumen is converted to volume
using density values. The density of bitumen is greatly influenced by its chemical
composition. Increase in aromatic type mineral impurities cause an increase in specific
The specific gravity of bitumen is defined as the ratio of mass of given volume of bitumen of
known content to the mass of equal volume of water at 27℃. The specific gravity can be
measured using either pycnometer or preparing a cube specimen of bitumen in semi solid or
solid state. The specific gravity of bitumen varies from 0.97 to 1.02.
Viscosity denotes the fluid property of bituminous material and it is a measure of
resistance to flow. At the application temperature, this characteristic greatly influences the
strength of resulting paving mixes. Low or high viscosity during compaction or mixing has
been observed to result in lower stability values. At high viscosity, it resists the compactive
effort and thereby resulting mix is heterogeneous, hence low stability values. And at low
viscosity instead of providing a uniform film over aggregates, it will lubricate the aggregate
particles. Orifice type viscometers are used to indirectly find the viscosity of liquid binders
like cutbacks and emulsions. The viscosity expressed in seconds is the time taken by the 50
ml bitumen material to pass through the orifice of a cup, under standard test conditions and
specified temperature. Viscosity of a cutback can be measured with either 4.0 mm orifice at
25℃ or 10 mm orifice at 25 or 40℃.
37. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Figure 12: Viscosity Test
6. Flashand fire point test:
At high temperatures depending upon the grades of bitumen materials leave out
volatiles. And this volatile catches fire which is very hazardous and therefore it is essential to
qualify this temperature for each bitumen grade. BIS defined the flash point as the
temperature at which the vapour of bitumen momentarily catches fire in the form of flash
under specified test conditions. The fire point is defined as the lowest temperature under
specified test conditions at which the bituminous material gets ignited and burns.
Normally the consistency of bituminous material can be measured either by
penetration test or viscosity test. But for certain range of consistencies, these tests are not
applicable and Float test is used. The apparatus consists of an aluminum float and a brass
collar filled with bitumen to be tested. The specimen in the mould is cooled to a temperature
of 5 C and screwed in to float. The total test assembly is floated in the water bath at 50 C
and the time required for water to pass its way through the specimen plug is noted in seconds
and is expressed as the float value.
38. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
It is desirable that the bitumen contains minimum water content to prevent foaming of the
bitumen when it is heated above the boiling point of water. The water in bitumen is
determined by mixing known weight of specimen in a pure petroleum distillate free from
water, heating and distilling of the water.
9. Loss on heating test:
When the bitumen is heated it loses the volatility and gets hardened. About 50gm of
the sample is weighed and heated to a temperature of 163 C for 5hours in a specified oven
designed for this test. The sample specimen is weighed again after the heating period and loss
in weight is expressed as percentage by weight of the original sample.
Table 1: Tests for Bitumen with IS codes
Type of test Test Method
Penetration Test IS: 1203-1978
Ductility test IS: 1208-1978
Softening Point test IS: 1205-1978
Specific gravity test IS: 1202-1978
Viscosity test IS: 1206-1978
Flash and Fire Point test IS: 1209-1978
Float Test IS: 1210-1978
Determination of water content IS: 1211-1978
Determination of Loss on heating IS:1212-1978
39. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
8 .GEOMETRIC STANDARDS OF BT ROADS
There may be geometric deficiencies in the alignment, either horizontally or
vertically. These would have to be seen on a case-by-case basis depending on the severity of
the problem, road safety implications, availability of land etc.
Up gradation may require widening of the carriageway to 3.75 m in case the earlier
width was less. This will also require corresponding road way width of 7.5 m and land width
of 11-12 m. While formation width may not always be available it must be ensured that in all
up gradation cases roadway width of 7.5 m is available (except in habitation portion). The
design of the pavement must take into account the difference in the over lay crust thickness
over the existing pavement and in the widened portion. Due to changes in centre line etc.
appropriate changes in the surface profile and camber will also have to be designed, where
It is possible that the road to be upgraded may suffer from inadequate side drains or
lack of integration of the drains with the cross drainage. In adequate cross drainage (in terms
of number of CDs, their proper siting or their capacity) may also need to be addressed.
Inspection of the road will generally reveal the nature of the deficiency and necessary
hydrological investigations may be made in the case of CD Work analysis.
8.2 Some important issues in the design:
It has been indicated that the geometric standards for Rural Roads are to be as given
in IRC SP 20:2002. However, practical difficulties sometimes normally arise in providing the
recommended geometrics due to non-availability of land, with no scope even for acquisition.
In such cases, efforts must be made to provide the geometrics within the land available by
shifting the centre line to the extent possible.
40. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
If even after this, Standard Geometrics like Radius of Curvature, gradient etc. cannot
be provided for the normal design speed, the geometrics are to be designed as per the ground
conditions and the corresponding safe speed determined.
Appropriate signboards must be erected on either side indicating the safe speed at
which the vehicles can travel in such stretches. In addition at accident prone locations, speed
reducing devices such as rumble strip should be provided.
Pavement Design: –
The estimation of design parameters is the most important issue in the design of
pavement. It has been noticed quite often that there is a tendency to estimate the
design CBR on the conservative side and also to inflate the amount of traffic
expected. The combined effect of this is over design of the pavement, which in turn is
reflected in higher costs of construction. This engineering skill of the PIU lies in
ensuring quality with economy.
Not only must CBR be estimated properly, the conditions in which it is to be
estimated also need to be consciously determined. It is always not necessary to adopt
4 day soaked CBR for design, since this represents the worst condition of design.
Depending upon the pattern of conditions prevailing at the site, the CBR may be
determined at the equilibrium moisture content (Annexure 5.6) in cases where the sub
grade is not likely to come in contact with water either due to capillarity or through
percolation from the top.
Similarly, the estimation of base year traffic should be done judiciously taking
guidance from the recently constructed roads in similar conditions. The traffic must
have some correlation with the agricultural surplus of the area and its expected growth
When marginal aggregates and locally available material are used, special care should
be taken in material characterization. While adopting a particular method of
stabilization, the efficacy of use of the most suitable stabilizing agent is to be
established and accordingly used in the design. Detailed specifications are available
for various methods of stabilization in the publication ‘Specification for Rural Roads’
published by the IRC.
41. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
9. CROSS SECTIONAL ELEMENTS OF B.T ROADS
9.1 Carriage way:
It is basically the traveled way which is used for movement of vehicles, it takes the
vehicular loading and predominant vehicle loads is shared by this component which is called
It may be cement concrete road or it may be bituminous pavement. In case of bituminous
pavement it is the black top portion which is the carriageway. The width of the carriage way
depends on the number of traffic lane; minimum lane is a single lane road which is supposed
to be used for movement of one vehicle at a time. the width of road or width of carriage way
for single lane road is .75, for intermediate lane road 5.5 m, two lanes without raised kerb is
7 m, two lane with raised kerb is 7.5 m and for multi-lane road width per lane is 3.5 m
Next is shoulder. You might have seen a black top of surface and on each side some
extra width or extra portion of the road which we call a ‘shoulder’. Basically it gives
support to carriageway and provides a space for stop vehicle in case there is a
necessity for a vehicle to stop, if there is no shoulder then it will stop right on the
carriageway and it will block the entire carriageway.
So, a shoulder is kept on each side of the carriage way which can be used by vehicle
for stopping the vehicle and for parking.
So it is basically one half the differences between the road way width and the
The carriageway including separator or median, in case it is a divided road plus
shoulders on both sides together is known as roadway width.
Carriageway width plus shoulder on both sides together is known as roadway width. This
width of the roadway varies depending on the terrain condition.
We are already familiar with the type of terrains, so, for difficult terrain that value is
lesser and also it varies depending on the type of road namely NH national highways, state
highways to major district road, other district road and the village road.
Obviously the values are higher for higher category road namely national highway and
state highway and the value reduces as we move from national highway state highway to
42. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
MDR to ODR and for village road. Again the requirement for single lane and two lanes are
The next element is camber. You might have observed that the carriageway or the black
top portion of the road is not really flat. There is a transfer slope which is provided and that
transfer slope is known as camber.
The rain water during monsoons should be drained off immediately from the carriageway.
It is essential to drain off the water from the road surface to keep the pavement in good
condition. So, to drain of the water easily and reasonably in a faster manner there is a cross
slope which is provided and it is known as camber.
Different possible shapes are there which are also used like parabolic camber, straight
line camber or it may be a combination of both parabolic and straight line.
Parabolic camber is generally preferable for faster moving traffic particularly on two
lane road because if we use straight line camber then it is not convenient for vehicles
particularly faster moving vehicles on two lane roads to complete the overtaking maneuver.
Because for overtaking on two lane road a faster vehicle has to occupy the lane which
is supposed to be used for opposing traffic and then it completes the overtaking operation
and comes back to its original lane. So it has to cross the central line of the carriageway
which essentially will not be convenient if we provide straight line camber.
Therefore, for fast moving vehicles on two lane roads where overtaking is very
common parabolic shape of camber is preferable because it keeps the shape, the carriageway
will be flatter near the center of the road and it will be steeper towards the edges.
However, when cement concrete road or high type pavement surface is used then the
requirement of camber or the cross slope is generally lesser and we do not require really very
a steep slope or the camber. in that case where it is a very flat slope one can also provide
straight line camber because the actual difference a between the edge and the center will be
negligible so even when there is a need for overtaking it will not be that uncomfortable for
the faster moving vehicle.
So where the requirement is lesser particularly for high type pavement surface like
cement concrete pavement one can also use straight line camber.
43. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Kerb is essentially a vertical or sloping member along the edge of a pavement or paved
Kerb is normally desirable for urban roads. It facilitates and controls drainage, it
strengthens and protects pavement edge, and it also helps to delineate pavement edge and
presents a more finished appearance for the road. It also encourages orderly roadside
development. So there are many functions for kerb. But it is a common feature for
urban roads. Normally for non-urban situations or the rural environment kerb is not provided.
There are different shapes of kerb as shown here: barrier type kerb, semi-barrier type
kerb and mountable kerb. Mountable kerbs are provided where we want the vehicle to cross
the kerb with very minimum difficulty. Yes, there is kerb, there is a barrier but vehicle can
easily cross that barrier. So wherever we feel that there should be provisions for vehicle to
cross the barrier easily there we use mountable kerbs.
9.2 Side drain:
Proper drainage of water is essential. We have talked about the camber but also one
has to look into the need for surface drainage and sub-surface drainage. Surface drainage is
required to efficiently move surface water and lead them to natural water channels.
They are normally provided along the toe of embankment, they may be of V shape or
trapezoidal shape. So the water which is coming out through camber should be channelized to
natural water channels so we need to provide surface drainage.
Also, there is requirement for sub surface drainage particularly it is the drainage of
underground water which is dealt separately under pavement design because this directly
does not come under cross section elements.
44. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
10.PROCESSES IN BITUMINOUS ROAD CONSTRUCTION
10.1 Bituminous road constructions steps:
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.
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.
The premix is prepared in a hot mix plant of a required capacity with the desired
quality control. The bitumen may be heated upto 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
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 tonnes tandem roller.
45. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
Figure 13: Tandem Roller
The routine checks are carried out at site to ensure the quality of the resulting pavement
mixture and the pavement surface.
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 atleast 95% of the density obtained in the laboratory. The
variation in the thickness allowed is 6mm per 4.5m length of construction.The AC surface
should be checked by a 3.0 m straight edge.
46. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
11. WBM ROAD CONSTRUCTION
WBM Stands for Water Bound Macadam which is the most commonly used road
construction procedure for over more than 190 years pioneered by Scottish Engineer John
Loudon Macadam around 1820. Macadam is a type of Road Construction. The broken stones
of base and surface course, if any are bound by the stone dust are presence of moisture is
Macadam means the pavement base course made of crushed or broken aggregate
mechanically interlocked by rolling and the voids filled with screening and binding material
with the assistance of water.WBM may be used as a sub-base, base course or a surface
course. The thickness of each compacted layer of WBM ranges from 10cm to 7.5cm
depending on size and the gradation of aggregate used.
Figure 14: FINISHED WBM ROAD
47. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
11.1 Construction Procedure:
1. Prepare the foundation for receiving the WBM course.
2. Lateral confinement may be done by compacting the shoulder to advance, to a thickness
equal to that of the compacted WBM layer and by trimming the inner side vertically.
3. Spreading of Course Aggregate.
4. Compaction of coarse aggregate is done by wheeled power roller of capacity 6 to 10 tonnes
or alternately by an equivalent vibratory roller
5. Dry screening is applied gradually over the surface to fill the interstices in these.
6. The surface is sprinkled with water, swept and rolled.
7. Binding material is applied at a uniform and slow rate at two and more layers.
8. WBM Coarse is allowed to set overnight.
Figure 15: BINDING MATERIAL SCREENING MATERIAL
48. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
12. PROJECT PREPARATION FOR BT ROADS
12.1 Steps involved in project preparation:
The various steps involved and the agency responsible for the Project Preparation are
Detailed project report (DPR):
Each Road Project (whether a new link or up-gradation of an existing road) should
have a separate Detailed Project Report (DPR).
The DPR should be based on detailed survey and investigations, design and
technology choice and should be of such detail that the quantities and costs are accurate, and
no cost over-run takes place due to changes in scope of work or quantities at the time or
execution. Guidance may be taken from IRC: SP: 19 for preparing the DPR.
If needed, they will associate in the investigations of special nature. The Engineers
also will be apprised of the need for appropriate Designs with respect to Geometrics,
Pavement Crust, Surface Drainage, CD Works as well as the measures for Environmental
The steps involved in the preparation are as under:
1. Selection of
: The suitability of the existing track as the final alignment is
examined, and need for avoiding sharp kinks and dwellings is
: The topographical survey is carried out with a plane table/
Compass/ theodolite, designing the horizontal curves. A line
of levels is run along the centre line and cross-sections are
3. Soil survey : Samples of local soils are collected and tests like grain-size
analysis, moisture-density relationships and CBR are carried
49. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
: The source of materials for forming the embankment,
pavement layers and cross-drainage structures are identified
and their leads established.
: The sites for bridges are selected and hydrological survey to
determine the discharge and HFL is carried out.
: On existing roads, traffic survey is done. On new roads, the
traffic likely to ply is estimated. The growth rate is
: Considering the soil strength, traffic and design life,
pavement thickness is determined. Its composition is selected
after exploring the ways to maximize the use of local
8. Drainage Plan : A drainage plan is made for the road giving a scheme for the
effective drainage of water into natural channels, supported
9. Design of
: The type of culverts, bridges and causeways is selected and
design of the various elements like foundations, substructure
and superstructure is done.
10. Preparation of
: Plans showing the land holdings and the selected alignment
are made to a scale of 1:8000 to 1:2000, depending upon the
availability of maps. The existing village plans available with
the revenue authorities are generally used.
11. Preparation of: Alignment Plans, Longitudinal Sections and Cross-sections
50. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
road drawings are prepared.
12. Selection of
: The specifications for various items of work are selected,
keeping in view need to adopt intermediate technology.
13. Estimation of
items of work
: Detailed quantities of each item of work are worked out.
14. Analysis of
: The rates for each item of work are analyzed.
15. Estimate : The estimated cost is arrived.
16. Preparation of
: The DPR documents are prepared.
The following drawings should accompany the DPR as Volume II:
1. Key Map, showing the State in relation to India, District in relation to State, and a
district map showing all the Blocks, with the names of each Block marked.
2. A Block road map showing the Master Plan and the Core network and the proposed
3. An Index Map of the road showing the full road to a suitable scale, topographical
features like rivers, canals, streams, railway lines, villages, Market Centres, other
roads and Legend.
4. Plan and Longitudinal Sections of the road, showing 1 km in each sheet.
5. Typical cross-sections.
6. Detailed cross-sections.
7. Drawings of culverts, submersible bridges, paved dips and High Level Bridges, giving
General Arrangement Drawings (GAD), structural details.
8. Drawings of protective works like retaining walls, breast walls, check walls, drains.
9. Miscellaneous Drawings like kilometer stones, Traffic signs.
51. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
12.3 Choice of technology:
Since there is readily available labour in most rural areas of the country, and Rural
Road construction and maintenance can be efficiently implemented by labour oriented or
appropriate technology, the DPR should be prepared keeping this important consideration in
The use of modern highway construction equipment like large capacity Hot Mix
Plants, Paver Finishers, Wet Mix Macadam Plants, Vibratory Rollers, Earthmoving and
excavating equipment may not be insisted upon where it is not cost and/or time-effective.
The estimates shall reflect the true scope, quantum and cost of works, based
on detailed surveys and investigations. The following points may be kept in view
while framing the estimates:
The borrow areas must be located accurately. It is not advisable to borrow earth from
the road land. Temporary earth from adjacent fields may be borrowed with the
consent of the farmers. Otherwise, fallow land, and non-agricultural land, near to the
project may be identified. The lead and lift involved may be accurately assessed and
accounted for. The haulage method should also be identified.
The sources of gravel, sand, stone aggregates, bricks and marginal materials should be
accurately identified, and the availability of the required quantity and quality of
materials established. The leads involved, and the condition of roads leading to the
sources shall be determined.
The rates shall be based on the State’s updated Schedule of Rates based on Standard
Data Book: Analysis of Rates for Rural Roads 2004.
No provision for escalation shall be allowed.
For externally funded projects, contingencies supervision charges may be allowed as
12.7 Economic analysis:
While providing new links to unconnected habitations is a social responsibility, the
investments on up gradation of existing roads should result in economic benefits. Proposals
52. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
for up gradation should be subjected to economic analysis. The specifications for up
gradation and maintenance interventions should be so selected that the IRR is at least 12
The benefits that may be considered for the analysis may include
(i) Agricultural producer surplus
(ii) Savings in vehicle operating costs
(iii) Savings in travel time of passengers.
12.8 Extension of intended completed date:
The Engineer is empowered to extend intended completion date in the following events:
If a compensation event occurs.
If it is impossible for completion to be achieved by intended completion date because
of a variation order issued by the Engineer.
The Engineer shall decide within 21 days of the request of the Contractor whether,
and by how much time, the extension is to be granted. The Contractor is required to
give full and detailed proposal for extension of time along with supporting
It should be noted that if the Contractor fails to cooperate in dealing with a delay, the
delay because of the failure shall not be considered in assessing the new intended
completion date. The Engineer as per clause 28 of the GCC is empowered to instruct
the Contractor to delay the start or progress of any activity within the works.
However, the Engineer will have to obtain a written approval of the Employer for
ordering delay totaling more than 30 days.
12.9 Payments and deposits:
As per clause 38 of the GCC, the Contractor is required to submit fortnightly/
monthly statements of value of the work done including variations and compensation events,
if any, supported with detailed measurement of each item.
53. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
The Engineer within 14 days is required to check the Contractor’s statement and
certify the amount. It is to be noted that the value of work executed shall be determined on
the basis of measurements by the Engineer.
Payments shall be adjusted for various deductions and the Engineer shall pay the
Contractor amounts certified within 15 days of date of each certification.
The rates quoted by the Contractor shall be deemed to be inclusive of the sales and
other levies, duties, royalties, toll, taxes of Central and State Governments, local bodies and
authorities that the Contractor will have to pay for the performance of this Contract.
The Engineer shall deduct a security deposit of 5% from each running payment due to
the Contractor. The security deposit and performance security, aggregating to 10%, of the
Contract price shall be released to the Contractor, after completion of defect liability period
provided that the Contractor has corrected defects notified to him during the period of
performance guarantee and the Contractor has satisfactorily completed the routine
maintenance of roads as per the conditions of Contract.
The Engineer would convert security deposits for the defect liability period into
interest bearing securities of a scheduled commercial bank in the name of Employer if so
desired by the Contractor.
The Contractor shall request the Engineer to issue a certificate of completion of the
construction of the works, and the Engineer will do so upon deciding that the works is
completed. In case of Routine Maintenance the Contractor shall request the Engineer to issue
the certificate of completion of the Routine Maintenance and the Engineer will do so upon
deciding that the Routine Maintenance is completed.
12.11 Final account:
The Contractor shall supply the Engineer with a detailed account of the total amount
that the Contractor considers payable for works under the contract within 21 days of issue of
certificate of completion of construction of works. The Engineer shall issue a defect liability
54. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
certificate and certify any payment that is due to the Contractor for works within 42 days of
receiving the Contractor’s account if it is correct and complete.
If the account is not correct or complete, the Engineer shall issue within 42 days a
schedule that states the scope of the corrections or additions that are necessary. If the Account
is still unsatisfactory after it has been resubmitted, the Engineer shall decide on the amount
payable to the Contractor and issue a payment certificate within 28 days of receiving the
Contractor’s revised account. The payment of final bill for construction of works will be
made within 14 days thereafter.
In case the account is not received within 21 days of issue of Certificate of
Completion as provided in clause 50.1 above, the Engineer shall proceed to finalize the
account and issue a payment certificate within 28 days. The payment of final bill for
construction of works will be made within 14 days thereafter.
In case of Routine Maintenance, the Contractor shall supply the Engineer with a
detailed account of the total amount that the Contractor considers payable under the contract
21 days before the end of the Routine Maintenance Period. The Engineer shall issue a
Routine Maintenance Completion Certificate and certify any final payment that is due to the
Contractor within 42 days of receiving the Contractor’s account if it is correct and complete.
If it is not, the Engineer shall issue within 42 days a schedule that states the scope of
the corrections or additions that are necessary.
If the Final Account is still unsatisfactory after it has been resubmitted, the Engineer
shall decide on the amount payable to the Contractor and issue a payment certificate within
28 days of receiving the Contractor’s revised account. The payment of final bills for routine
maintenance will be made within 14 days thereafter. In case the account is not received
within 21 days of issue of Certificate of Completion as provided in clause 50.3 above, the
Engineer shall proceed to finalize the account and issue a payment certificate within 28 days.
55. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
During the MINI PROJECT for a period of 45 days I have undergone field training in
construction, execution and maintenance of rural roads.
During the MINI PROJECT, I observed following points:
Construction procedure of B.T road
Different layers in B.T road construction , i.e., prime coat, tack coat and seal coat
Procurement of skilled labour, who plays a vital role for completing the project
Procurement of materials near by the work site ,which reduce the transportation
About the tender and contract processes.
The maintenance of the roads sanctioned is the responsibility of the contractor whom
the work was entrusted for a period of 5 years from the date of completion of the
56. STUDY OF DESIGN OF THE FLEXIBLE PAVEMENTS
1. ”TRANSPORTATION ENGINEERING and planning ” by C.S Papacostas and P.D
2. “Introduction to TRANSPORTATION ENGINEERING by J.H Banks.
3. “HIGHWAY ENGINEERING” by P.H Wright and K.Dixon.
4. “HIGHWAY ENGINEERING” by S.K Khanna and C.E.G Justo.
5. “Principles and practices of HIGHWAY ENGINEERING ” by L.R Kadiyali.
6. “TRANSPORTATION ENGINEERING” by Arora.