Rigidpavement 2
Rigidpavement 2
Rigidpavement 2
ON
RIGID PAVEMENT
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INTRODUCTION
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India has one of the largest road networks in the world
(over 3 million km at present).For the purpose of
management and administration, roads in India are
divided into the following five categories:
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WHAT IS ROAD ?
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What is a Pavement?
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What is a Pavement?
OR
• Highway pavement is a structure consisting of
superimposed layers of selected and processed
materials whose primary function is to distribute
the applied vehicle load to the sub grade.
OR
• It can also be defined as “structure which
separates the tyres of vehicles from the under
lying foundation.”
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Requirements of pavement structure
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History of Road Development
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Classification of Pavements
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Types of Pavement
PAVEMENTS
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Comparison
Properties Flexible Rigid
Design Empirical method Designed and analyzed by using the elastic
Principle Based on load distribution theory
characteristics of the
components
Material Granular material Made of Cement Concrete either plan,
reinforced or prestressed concrete
Flexural Low or negligible flexible Associated with rigidity or flexural strength
Strength strength or slab action so the load is distributed over
a wide area of subgrade soil.
Normal Elastic deformation Acts as beam or cantilever
Loading
Excessive Local depression Causes Cracks
Loading
Stress Transmits vertical and Tensile Stress and Temperature Increases
compressive stresses to the
lower layers
Flexible pavements:
• Deep foundations / multi layer construction
• Energy consumption due to transportation of materials
• Increasing cost of asphalt due to high oil prices
Rigid pavements
• Single layer
• Generally last longer
• May require asphalt topping due to noise / comfort
issues
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Pavements Comparison
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Flexible Rigid
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RIGID PAVEMENT
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RIGID PAVEMENT
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RIGID PAVEMENT
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Basic Components of Concrete Pavement
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Rigid Pavements
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Types of Concrete Pavements
Types of concrete
pavement
Jointed Continuously
Jointed un – reinforced
Jointed dowelled Reinforced
dowelled concrete concrete
concrete pavements
concrete pavements pavements
pavements (JRCP) (CRCP)
(JUDCP)
(JDCP or
JPCP)
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Un Reinforced Concrete Pavements
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JPCP
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Jointed Plain Concrete Pavement (JCPC)
Reinforced Concrete Pavement
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JRCP
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Continuous Reinforced Concrete Pavement:
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CRCP
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Precast Prestressed Pavement
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Factors Governing Design of Pavements
• Subgrade soil
Thickness of pavement required.
Stress- strain behaviour under load.
Moisture variation.
• Design Period .
• Design commercial traffic volume.
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• Composition of commercial traffic in terms of single ,
tridem , tandem.
• Axle load spectrum.
• Tyre pressure.
• Lateral placement characteristics.
• Pavement component materials.
• Climatic factors.
• Required Cross sectional elements of the alignment.
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Axle load
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Truck Configuration
5 Axle Truck
2 Axle Truck
LCV
Tridem Axle
Standard Axle
10.2 Tonnes
Standard Axle
DESIGN LIFE
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Traffic consideration
Design lane
The lane carrying the maximum number of heavy
commercial vehicle is termed as design lane . each lane of
the two way lane highways are the outer lane of multi lane
highways can be considered as design lane .
• Lateral placement characteristics.
It is recommended that 25 percent of the total two –way
commercial traffic may be considered as design traffic for
two- lane two – way roads for the analysis of BUC. In
case four lanes and other multi lane divided highways 25
percent of the total traffic in the direction of predominant
traffic may be considered for design of pavement for
bottom up cracking. For TDC those vehicles with the
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spacing between transverse joint.
Temperature Consideration
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Concrete strength
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Modulus of elasticity and poission ratio of
concrete
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Environmental factors
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Precipitation :
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• COMPONENTS AND ALSO
GOVERNING FACTORS OF
PAVEMENT DESIGN
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Subgrade
• In winkler model it is assumed that the foundation is
made up of springs supporting the concrete slabs the
strength of subgrade is expressed in terms of modulus
of subgrade reaction K .
• Which is defined as the pressure per unit deflection of
the foundations as determined by plate load test The
modulus of subgrade reaction (k) is used as a primary
input for rigid pavement design. It estimates the
support of the layers below a rigid pavement surface
course (the PCC slab). The k value can be determined
by field tests or by correlation with other tests. There is
no direct laboratory procedure for determining k value.
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• Westergaard considered the rigid pavement slab as a thin
elastic plate resting on soil subgrade,which is assumed as
a dense liquid. The upward reaction is assumed to be
proportional to the deflection. Base on this assumption,
Westergaard defined a modulus of subgrade reaction in
kg/cm given by where is the displacement level taken as
0.125 cm and is the pressure sustained by the rigid plate
of 75 cm diameter at a deflection of 0.125 cm.
• If the diameter of plate is not 75 cm then even then we
can find the value of k by using the following equations
K750=kΦ(1.21Φ+.078)
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• In case the plate bearing test could not be conducted,
the approximate k- value corresponding to CBR values
can be obtained from its soaked CBR value using
Table 2 (IRC:58-2011 )
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Sub Base
The main purpose of the sub base is to provide the
uniform ,stable,and the permanent support to the
concrete slab laid over it .It should have sufficient
strength so that it is not subjected to disintegration and
erosion under heavy traffic and adverse environment
conditions. For these sub base of Dry lean concrete
having 7 day strength of 10 Mpa determined is
recommended. The effective k value of different
combinations of subgrade and sub base can be
estimated from table 3.
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Drainage layer /Filtration layer
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Debonding layer
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• RIGID PAVEMENT
DESIGN
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Modulus of sub-grade reaction
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Relative stiffness of slab to sub-grade
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Equivalent radius of resisting section
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Critical load positions
Since the pavement slab has finite length and width, either
the character or the intensity of maximum stress
induced by the application of a given traffic load is
dependent on the location of the load on the pavement
surface. There are three typical locations namely the
interior, edge and corner, where differing conditions of
slab continuity exist. These locations are termed as critical
load positions.
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where h is the slab thickness in cm, P is the wheel load in
kg, a is the radius of the wheel load distribution in
cm, l the radius of the relative stffiness in cm and b is the
radius of the resisting section in cm
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Wheel load stresses - Westergaard's stress
equation
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Temperature stresses
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Temperature
stresses
Warping Friction
stresses stresses
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Warping stress
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• Based on the plate theory, westergaard (1926)
developed formula for calculating the warping stresses
in the concrete slab . In 1938 , Bradbury modifies his
formulae and developed the following equations for
calculating the maximum warping stress at the interior
and edge of the slab having finite dimensions
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Frictional stresses
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Critical Combination of Stresses
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Design of slab thickness
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• Figure shows the placement of axles load close to
transverse joint when there is negative temperature
gradient during night period causing high flexural
stress at the top of the slab leading to the Top – down
cracking (TDC)
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Calculation of flexural stress
BOTTOM – UP CRACKING
• Pavement with tied concrete shoulder for single rear
axle
• Pavement without tied concrete shoulder for single rear
axle
• Pavement with tied concrete shoulder for tandem axle
• Pavement without tied concrete shoulder for tandem
axle
TOP – DOWN CRACKING
• Paving with and without dowel bars having front
steering axles with the single tyres and the first axles of
the rear unit placed on the same panel. 82
CUMULATIVE FATIGUE DAMAGE
ANALYSIS
• For a given slab thickness and other parameter the
pavement will be checked for cumulative bottom up
and top down fatigue damage. For bottom up cracking
the flexural stress at the edge due to combined action
of single or tandem rear axle load and positive
temperature differential cycles are considered.
• The stress can be either selected from the stress charts
( as shown some sample figures) or by using the
equation ( shown some sample equations.. chart
explain clearly the interplay of thickness , modulus of
subgrade reaction, axle load and temperature
differential
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• Similarly for assessing the TDC fatigue damagef
caused by repeated cycles of axle load and negative
temperature , flexural stress can be estimated in same
manner.
• The flexural stress is divided by the design flexural
strength of the cement to obtain the stress ratio ( SR)
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Recommended procedure for slab design
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• Step-5: Estimate the axle load repetitions in the
specified six hours period during the day time . the
maximum temperature differential is assumed to be
remain constant during the 6 hrs for analysis of bottom
Up cracking.
• Step-6: Estimate the axle load repetitions in the
specified six hours period during the night time .
• The maximum negative temperature differential during
night is taken as half of day time maximum
temperature differential. Built in negative temperature
differential of 50 ˚c developed during the setting of the
concrete to be added to the temperature differential for
the analysis of top – down cracking . only those vehicle
whose front and first rear axle come between 87
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Load Transfer At The Joints
Types of
joints
Transverse Longitudinal
joints joints
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Longitudinal joints
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Distress In Rigid Pavement
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cracking Transverse cracking
Longitudinal cracking
Advantages of Concrete Pavement
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• Can be constructed over poor subgrades.
• Thinner overall pavement thickness = lower
consumption of raw materials.
• Resistant to abrasion from turning actions.
• No affected by weather, inert to spills and fire.
• High abrasion durability.
• Profile durability.
• Use of waste products like flyash and slag.
• Riding quality does not deteriorate.
• Saving of fuel costs of at least 1.1% over asphalt .
• Light colour enhances night visibility
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Disadvantages of Rigid Pavement
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REFRENCES
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