Transportation engineering Pavements and it's type. Flexible pavements and rigid pavements Difference between flexible and rigid pavements

1. NATIONAL

2. WHAT IS A PAVEMENT ?
 A multi layer system that distributes the vehicular loads over a
larger area .
OR
 It can also be defined as “structure which separates the tires of
vehicles from the under lying foundation.”
 Pavement is the upper part of roadway, airport or parking
area structure.
 It includes all the layers resting on the original ground.
 It consist of all structural elements or layers,including
shoulders.

3. FUNCTIONS OF THE PAVEMENT
The primary function of a pavement is to
transmit loads to the sub-base and underlying
soil
Reduce and distribute the traffic loading so as
not to damage the subgrade
Provide vehicle access between two points
under all-weather conditions
Provide safe, smooth andcomfortable ride to
road users without undue delays and excessive
wear & tear
Meet environmental and aesthetics requirement
Limited noise and airpollution
Reasonableeconomy

4. REQUIREMENTS OF PAVEMENT
STRUCTURE
• Sufficient thickness to spread loading to a pressure
intensity tolerable by subgrade
• Sufficiently strong to carry imposed stress due to traffic
load
• Sufficient thickness to prevent the effect of frost susceptible
subgrade
• Pavement material should be impervious to penetration of
surface water which could weaken subgrade and
subsequently pavement
• Pavement mat. shd be non-frost susceptible
• Pavement surface shd. be skid resistant

5. CLASSIFICATION OF PAVEMENTS
CLASSIFICATION OF PAVEMENT
Airport Pavement Highway & Freeway
Pavements
Parking & Street
Pavements
Classification by Structure
Rigid(Concret
e) Pavements
Flexible Pavements
(Asphalt Concrete
Composite
pavements
Gravel(unpave
d)
pavements

6. TYPES OF PAVEMENT
Flexible Pavements Rigid Pavements
PAVEMENTS

7. TYPES OF PAVEMENTS

8. TYPES OF PAVEMENTS

9. Flexible Pavement
Flexible pavements are those , which on the whole have low or
negligible flexural strength and are rather flexible in their structural
action under the loads . The flexible pavement layers may reflect
the non-recoverable as well as recoverable deformations pavement
surfaces.

10. Flexible Pavement
Flexible Pavements
• Elastic
• Three main layers.
Surfacing .
Wearing course.
Base course.
• Road Base
• Sub Base
• Supported by Sub grade.

11. TYPES OF FLEXIBLE PAVEMENT
Dense-graded
Open-graded Gap-graded

12. STRUCTURE OF FLEXIBLE PAVEMENT
In order to take maximum advantage of this property, material layers are usually
arranged in order of descending load bearing capacity with the highest load
bearing capacity material (and most expensive) on the top and the lowest load
bearing capacity material (and least expensive) at the bottom.

13. STRUCTURE OF FLEXIBLE PAVEMENT
• Surface Course: This is the top layer and the layer that comes in contact
with traffic.
• Base Course: This is the layer directly below the surface course and
generally consists of aggregates (either stabilized or un-stabilized).
• Sub-base Course: This is the layer (or layers) under the base layer. A
sub- base is not always needed.
• Sub-grade Course: The "sub-grade" is the material upon which the
pavement structure is placed. Although there is a tendency to look at
pavement performance in terms of pavement structure and mix design
alone. The sub-grade can often be the overriding factor in pavement
performance.

14. SURFACE COURSE
The surface course is the layer in contact with traffic loads and normally
contains the highest quality materials. It provides characteristics such as
friction, smoothness, noise control, rut and shoving resistance and
drainage.

15. BASE COURSE
The base course is immediately
beneath the surface course. It provides
additional load distribution and
contributes to drainage and frost
resistance. Base course are usually
constructed out of :
• Aggregates: Base courses are most
typically constructed from durable
aggregates that will not be damaged
by moisture or frost action.
Aggregates can be either stabilized
or un-stabilized.
Fig. Lime rock Base Course Undergoing Final
Grading

16. SUB-BASE COURSE
The sub-base course is between the base course and the sub-grade. It
functions primarily as structural support but it can also:
• Minimize the intrusion of fines from the sub-grade into the pavement
structure.
• Improves drainage.
• Minimize frost action damage.
• Provides a working platform for construction.
• The sub-base generally consists of lower quality materials than the
base course but better than the sub-grade soils.
• 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 so it may be omitted from design.

17. SUB-GRADE
Sub-grades be composed of a wide range of materials although some are much
better than others. This subsection discusses a few of the aspects of sub-grade
materials that make them either desirable or undesirable and the typical tests used
to characterize sub-grades.
Sub-grade Preparation Sub-grade Failure Crack

18. RIGID PAVEMENTS
• Rigid pavements are those, which contain
sufficient beam straight beam strength to be
able to bridge over the localized sub-grade
failures and areas of in adequate support.
• Load is transmitted through beam action
of slab in rigid pavements.

19. RIGID PAVEMENTS
• Rigidity – does not deform under stress.
• Concrete – air entrained increases resistance to frost damage and de-icing salt
corrosion.
• Reinforcement – may be bars or mesh. Continuous rigid pavements have heavy
reinforcement.
• Joints – used in non-continuous pavements to, allow for thermal movement.
Includes a ‘filler’ and surface sealant.
• Rigid Pavements – laid as single layer by ‘Concrete paver’

20. LOAD DISTRIBUTION IN RIGID
PAVEMENTS

21. STRUCTURE OF RIGID PAVEMENT
Surface course :This is the top layer , which consists of the PCC
slab, reinforced or continuously reinforced slabs.
Base course : This is the layer directly below the PCC layer and
generally consists of aggregate or stabilized sub- grade.
Sub-base course : This is the layer under the base layer .A sub-
base is not always needed and therefore may often be omitted.

22. SURFACE COURSE
• The surface course is the layer in contact with traffic loads and is made of
PCC or RCC. It provides characteristics such as friction, smoothness,
noise control and drainage. In addition, it serves as a waterproofing layer to
the underlying base, sub-base and sub-grade.
• The surface course can vary in thickness but is usually between 150 mm (6
inches for light loading) and 300 mm (12 inches for heavy loads and high
traffic). Figure shows a 300 mm (12 inch) surface course.
Rigid Pavement Slab
(Surface Co45urse) Thickness
PCC Surface

23. BASE COURSE
The base course is immediately beneath the surface course. It provides:
• Additional load distribution,
• Contributes to drainage and frost resistance, Uniform support to the pavement and
• A stable platform for construction equipment. Bases also help and prevent sub grade
soil movement due to slab pumping. Base courses are usually constructed out of:
-Aggregates base. A simple base course of crushed aggregates has been a common option
since the early 1900s and is still appropriate in many situation.
-Stabilized aggregate or soil. Stabilizing agents are used to bind otherwise loose particles
to one another, providing strength and cohesion. Cement treated bases (CTB s) can be
built to as much as 20 - 25 percent of the surface course strength.
-Dense-graded HMA. In situations where high base stiffness is desired base courses can be
constructed using a dense-graded HMA layer.
-Permeable HMA. In certain situations where high base stiffness and excellent drainage is
desired, base courses can be constructed using an open

24. SUB-BASE COURSE
The sub-base course is the portion of the pavement structure between the base
course and the sub-grade. It functions primarily as structural support but it can
also:
• Minimize the intrusion of fines from the sub-grade into the pavement
structure.
• Improves drainage.
• Minimizes frost action damage.
• Provides a working platform for construction.
The sub-base generally consists of lower quality materials than the base
course but better than the sub-grade soils. Appropriate materials are aggregates
and high quality structural fill.

25. TYPES OF RIGID
PAVEMENT
 Joint plain concrete Pavement (JPCP)

26. TYPES OF RIGID
PAVEMENT
 Continuously Reinforced Concrete Pavement (CRCP)

27. Stresses in Rigid Pavement
TYPES OF STRESSES
•Different types of stresses are developed in CC pavement .The major types of stresses
in CC pavement consist of :
•Wheel load stresses caused by the heavy wheel loads of vehicles.
•Warping stresses caused by the temperature differential between the top and bottom of
the pavement due to daily variation in temperature.
OTHER FACTOR WHICH CAUSE ADDITIONAL STRESSES IN CC
PAVEMENTS
•Due to seasonal variation in temperature resulting in overall expansion and contraction
of the slab causing frictional stresses, as the friction force resists the slab movement.

28. Rigid Pavement Design Methods
•The design wheel load is first decided based on relevant axle load studies
and analysis.
•Based on the locality where the pavement is to be constructed and the data
on the topographic , climatic and other factors, the temperature
differentials for various pavement thicknesses are estimated.
•The supporting layers of the rigid pavement such as subgrade , sub-base
drainage layer and base course layers are decided and the subgrade
modulus is either determined or estimated.

29. Difference between Flexible and Rigid Pavement.
Flexible Pavement Rigid Pavement
It consists of a series of layers with the
highest quality materials at or near the
surface of pavement .
It consists of one layer Portland cement
concrete slab or relatively high flexural
strength.
It reflects the deformations of sub grade
and subsequent layers on the surface.
It is able to bridge over localized failure
and area of inadequate support.
Its stability depends upon the aggregate
interlock , particle friction and cohesion.
Its structural strength is provide by the
pavement slab itself by its beam action.
Pavement design is greatly influenced by
the sub grade strength .
Flexural strength of concrete is a major
factor for design.
It functions by a way of load distribution
through the component layers
It distributes load over wide area of sub-
grade because of its rigidity and high
modulus of elasticity.
Temperature variation due to change in
atmospheric condition do not produce
stress in flexible pavement.
Temperature changes induce heavy
stresses in rigid pavement.

30. Pavement Comparison
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

31. Pavements Comparison
• Heavy vehicles consume less fuel on rigid pavements
• Rigid pavements more economic when considering
environmental / lifee cycle costing

32. Types of Pavement Failure
Failure criteria
Flexible Pavements
• Fatigue Cracking
• Rutting
• Thermal Cracking
Rigid Pavements
• Fatigue Cracking
• Pumping or Erosion
• Others: Faulting, spalling, joint deterioration

33.  Flexible pavements are generally designed and
constructed for a design life of 15 years.
 The curing period for bituminous surface course is less
and hence the surface can be opened to traffic within 24
hours.
 It is possible to resort to ‘milling and recycling’ technique
and thus utilise substantial portion of damaged
bituminous pavement layers. This results in high salvage
value of deteriorated flexible pavement material.

34. Advantages of Rigid Pavement
 CC pavements do not get deteriorated under wet
weather conditions and when exposed to stagnant
water.
 CC pavements of major roads are generally
designed and constructed for 30 year period and
therefore the service life could be 30 years or even
more.
 Good night visibility even under wet weather
conditions.

35. Limitations of Flexible and
Rigid Pavements
Flexible Pavement :
 The bituminous pavement layers gat deteriorated when exposed to
stagnant water due to poor drainage of surface and subsurface water.
 It is essential to carry out routine and periodic maintenance of the
drainage system, shoulders and the pavement surface.
Rigid Pavement :
 Design of CC Pavements is to be carried out for a life of 30 years or
more in order to reduce the life cycle cost.
 It is not possible to restore a failed or badly cracked CC Pavement.

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