1. Transportation Engineering II
The Pavement

2. What is a Pavement?
A multi layer system that distributes the vehicular loads over a larger area

3. 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.
It can also be defined as “structure which separates the tires of vehicles from the under lying foundation.”

4. What is a Pavement?
Pavement is the upper part of roadway, airport or parking area structure
It includes all layers resting on the original ground
– It consists of all structural elements or layers, including shoulders

5. Functions of the Pavement
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 and comfortable ride to road users without undue delays and excessive wear & tear
– Meet environmental and aesthetics requirement
– Limited noise and air pollution
– Reasonable economy

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

7. Classification of Pavements

8. Types of Pavement
PAVEMENTS
Flexible Pavements
Rigid Pavements

9. Flexible Pavements Asphalt Concrete Aggregate Base Course
Natural Soil (Subgrade)
Aggregate Subbase Course
Aggregate Base Course
Asphalt Concrete

10. Flexible Pavements 150 psi Wearing C. Base Sub-base 3 psi Sub-grade
Given Wheel Load
150 psi
Wearing C.
Base
Sub-base
3 psi
Sub-grade
Load Distribution in Flexible Pavements

11. Rigid Pavements

12. Rigid Pavements
Load Distribution in Rigid Pavements

13. Pavements Comparison Flexible pavements: Rigid 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
Heavy vehicles cause greater deflection on flexible pavements rather than on rigid pavements. When the pavement deflects or moves, it absorbs a portion of the vehicle energy that otherwise would be available to propel the vehicle forward.
Concrete’s rigid design reduces the pavement’s deflection and corresponding fuel consumption. Also smoothness of concrete pavements is less affected by seasonal changes, which could also contribute to lower fuel consumption.

14. Pavements Comparison
Heavy vehicles consume less fuel on rigid pavements
Rigid pavements more economic when considering environmental / life-cycle costing
Heavy vehicles cause greater deflection on flexible pavements rather than on rigid pavements. When the pavement deflects or moves, it absorbs a portion of the vehicle energy that otherwise would be available to propel the vehicle forward.
Concrete’s rigid design reduces the pavement’s deflection and corresponding fuel consumption. Also smoothness of concrete pavements is less affected by seasonal changes, which could also contribute to lower fuel consumption.

15. Flexible Pavement
“A flexible pavement is a structure that maintains intimate contact with and distributes load to the sub grade and depends on aggregate interlock, particle friction and cohesion for stability”

16. Flexible Pavement OR
It is a structure which distributes the traffic loading stresses to the soil (sub grade) at a magnitude that will not shear or distort the soil i.e., from 150 psi to 3 psi
Pavement which reflects deformation of sub grade & the subsequent layers on to the surface” i.e.; load is transmitted from grain to grain through contact points of granular material, i.e. in a compressive way.

17. Flexible Pavement Flexible pavements Elastic Three main layers
Surfacing
Wearing course
Base course
Road base
Sub base
Supported by Sub-grade

18. Flexible Pavement Introduction
Flexible pavements are so named because the total pavement structure deflects, or flexes, under loading.  A flexible pavement structure is typically composed of several layers of different materials. 

19. Flexible Pavement
Each layer receives the loads from the above layer, spreads them out, then passes on these loads to the next layer below.  Thus, the further down in the pavement structure a particular layer is, the less load (in terms of force per unit area) it must carry.

20. Load Distribution In Flexible Pavements

21. 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.

22. 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.

23. Structure of Flexible Pavement
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.

24. 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.

25. Surface Course
  In addition, it serves to prevent the entrance of excessive quantities of surface water into the underlying base, sub-base and sub-grade. This top structural layer of material is sometimes subdivided into two layers.

26. Wearing Course
This is the layer in direct contact with traffic loads.  It is meant to take the brunt of traffic wear and can be removed and replaced as it becomes worn.  A properly designed (and funded) preservation program should be able to identify pavement surface distress while it is still confined to the wearing course.  This way, the wearing course can be rehabilitated before distress propagates into the underlying intermediate/blinder course

27. Intermediate/Binder Course
Intermediate/Binder Course: This layer provides the bulk of the HMA structure.  It's main purpose is to distribute load.

28. Base Course
The base course is immediately beneath the surface course.  It provides additional load distribution and contributes to drainage and frost resistance.  Base courses 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. 

29. HMA: In certain situations where high base stiffness is desired, base courses can be constructed using a variety of HMA mixes.  In relation to surface course HMA mixes, base course mixes usually contain larger maximum aggregate sizes, are more open graded and are subject to more lenient specifications.

30. Lime rock Base Course Undergoing Final Grading

31. 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.

32. Sub-base Course
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. 

33. However, a pavement constructed over a low quality soil such as a swelling clay may require the additional load distribution characteristic that a sub-base course can offer.  In this scenario the sub-base course may consist of high quality fill used to replace poor quality sub-grade.

34. Sub-grade
Although a pavement's wearing course is most prominent, the success or failure of a pavement is more often than not dependent upon the underlying sub-grade , the material upon which the pavement structure is built. 

35. 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.

36. Sub-grade Preparation
Sub-grade Failure Crack

37. Types of Flexible Pavement
Dense-graded
Open-graded
Gap-graded

38. Flexible Pavement – Construction

39. Types of Pavements

40. Types of Pavements

41. Types of Pavements

42. Types of Pavements

43. Types of Pavements

44. Types of Pavements

45. Types of Flexible Pavements

46. Types of Flexible Pavements

47. Types of Flexible Pavements

48. Typical Load Distribution in Flexible Pavement
Sub-grade
Bituminous Layer
Wheel Load

49. Typical Stress Distribution in Flexible Pavement.
Vertical stress
Foundation stress

50. Load Transfer Mechanism

51. Load Transfer Mechanism

52. Rigid Pavement
Rigid pavements are those, which contain sufficient beam strength to be able to bridge over the localized sub-grade failures and areas of in adequate support. OR
Load is transmitted through beam action of slab in rigid pavements.
Rigid pavements are those, which reduces the stress concentration and distributes the reduced stresses uniformly to the area under the slab.

53. Rigid Pavement 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’

54. Rigid Pavements

55. Basic Components of Concrete Pavement

56. Concrete paver

57. Rigid Pavements
Load Distribution in Rigid Pavements

58. Rigid Pavements Introduction
Rigid pavements are so named because the pavement structure deflects very little under loading due to the high modulus of elasticity of their surface course.  A rigid pavement structure is typically composed of a PCC surface course built on top of either
the sub-grade or
an underlying base course. 

59. Rigid Pavements
Because of its relative rigidity, the pavement structure distributes loads over a wide area with only one, or at most two, structural layers. 
There are other types of surfaces also i.e.; reinforced, continuously reinforced etc.

60. 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 (or layers) under the base layer.  A sub-base is not always needed and therefore may often be omitted.

61. 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.

62. Rigid Pavement Slab (Surface Course) Thickness
PCC Surface
Rigid Pavement Slab (Surface Course) Thickness

63. 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 situations.

64. Base Course
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 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 graded HMA. 

65. Base Course
Lean concrete.  Contains less Portland cement paste than a typical PCC and is stronger than a stabilized aggregates.  Lean concrete bases (LCB s) can be built to as much as percent of the surface course strength.  A lean concrete base, functions much like a regular PCC surface course and therefore, it requires construction joints and normally cracks over time.  These joints and cracks can potentially cause reflection cracking in the surface course.

66. Completed CTB with Curing Seal
Lean Concrete Base Material

67. 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. 

68. Sub-grade
Sub grade provides support to the overlying concrete slab. If it is of good quality then slab can be laid over it without providing sub-base otherwise if it is extremely poor then a sub-base layer should be incorporated .
For design purpose the only thing to know about sub-grade is its classification and the unit pressure coming from slab to sub-grade should be calculated for its selection. However, it must be resistant to moisture damages.

69. Types of Rigid Pavement
Jointed Plain Concrete Pavement (JPCP)

70. Types of Rigid Pavement
Continuously Reinforced Concrete Pavement (CRCP)
Photo from the Concrete Reinforcing Steel Institute

71. Rigid Pavement – Construction
Slipform
More in pavement guide interactive
Stevens Way will be fixed form starting in May
Fixed form

72. Pavements Comparison Flexible pavements: Rigid 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
Heavy vehicles cause greater deflection on flexible pavements rather than on rigid pavements. When the pavement deflects or moves, it absorbs a portion of the vehicle energy that otherwise would be available to propel the vehicle forward.
Concrete’s rigid design reduces the pavement’s deflection and corresponding fuel consumption. Also smoothness of concrete pavements is less affected by seasonal changes, which could also contribute to lower fuel consumption.

73. Pavements Comparison

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

75. Flexible vrs. Rigid Pavements

76. Flexible vrs. Rigid Pavements

77. Airport-Highway Pavements