section 1 - introduction to pavement

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    Tommy E. Nantung PhD PE

    Design and Construction of 

    LONG LIFE PAVEMENT

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    Introduction to Pavement

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    Roadmap to Presentation

    • Definition of Long Life Pavement

    • Why pavement failed

    A little history of pavement• Type of pavement distresses

    • AASHTO 1993/1998 Pavement Design

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    Definition of Long Life Pavement

    • A Long-Life Pavement is defined as apavement

     – no significant deterioration will develop in the

    foundations or the road base layers provided thatcorrect surface maintenance is carried out.

    • This definition implies that

     – all pavement layers, except the road surface layer

    are considered as permanent pavement layers andcommon distress mechanisms should, in principle,be eliminated completely.

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    Introduction to pavement structure

    • A pavement is a structure composed of

    structural elements, whose function is to

    protect the natural subgrade and to carry the

    traffic safety and economically.

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    Introduction to pavement structure

    • As a wheel passes:

     – Elastic deformations occur

     – Plastic deformations occur elastic deformations

    may lead to fatigue

     – Plastic deformation deformations may lead to

    excessive rutting.

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    Type of pavement based on structure

    • Rigid Pavement

     – A pavement structure of which the surface courseis made of Portland cement concrete

    • Flexible Pavement – A pavement structure of which the surface course

    is made of asphaltic concrete, that maintainsintimate contact with and distributes loads to the

    subbase or subgrade and depends upon aggregateinterlock, particle friction, and cohesion forstability

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    The difference between pavement structure

    • The essential difference between Flexible

    pavement and Rigid pavement is the manner

    in which they distribute the load

     – Flexible pavement is one which can adjust its

    position to the shape of the underlying layers

    without sustaining significant damage.

     –Rigid pavement tend (work as slab) to distributethe load over a relatively wide area of soil. Why?

    (High modulus of elasticity)

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    Definitions

    • Pavement Section

     – A layered system designed to distribute

    concentrated traffic loads to the subgrade.

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    Factors Affecting Pavement Performance

    3-10

    Traffic

    Subgrade

    Soil

    Materials

    Construction

    Variability

    Environment

    Maintenance

    and Rehabilitation

    Design

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    A Little History of Pavement Performance

    Roman Roads

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    Telford Road

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    Macadam Road

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    Macadam

     

    Regardless of thethickness of thestructure many

    of the roads in GreatBritain deteriorated

    rapidly

    when the subgradewas saturated.

     

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    Three Keys to Long Term Performance

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    Water Infiltration

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    Subgrade

    AC / PCC

    Base / Subbase

    Collector 

    Pipe

    To Outlet

    Shoulder 

    Permeable &

    Filter Layer 

    Water Infiltration

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    Source of Moisture

    Brand New Pavement Drought in the Summer

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    Variation of Resilient

    Modulus with Moisture Content

    3-1960 80100

    0

    2

    4

    6

    8

    10

    12

    14

    16

    % Saturation, S

    Resilient Modulus MR, ksi 100% AASHTO - T99

    95% AASHTO - T99

    402010 30 50 70 90

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    Another Key to Long Term Performance

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    Influence of Soil Compaction

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    Another Key to Long Term Performance

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    Flexible Pavement

    • Structure

     – Surface course

     – Base course

     – Subbase course

     – Subgrade

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    Types of Flexible Pavement

    Dense-graded

    Open-graded Gap-graded

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    Flexible Pavement – Construction

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    Types of Rigid Pavement

    • Jointed Plain Concrete Pavement (JPCP)

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    Types of Rigid Pavement

    • Continuously Reinforced Concrete

    Pavement (CRCP)

    Photo from the Concrete Reinforcing Steel Institute

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    Pavement types based on traffic

    • Low

     – Un-surfaced

     – Dust oil

     – Penetration macadam – Surface treatment

    • Intermediate

     – Dense cold mix

     –

    Cold mix – Open cold mix

     – Lime treated base - Soil cement

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    Pavement types based on traffic

    • High Type

     – Asphalt concrete surfaced

     – Portland cement concrete

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    Definition of Stress

    • Stress is defined as force per unit area. It has

    the same units as pressure, and in fact

    pressure is one special variety of stress.

    However, stress is a much more complexquantity than pressure because it varies both

    with direction and with the surface it acts on

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    Definition of Stress

    • Compression Stress that acts to shorten an object.

    • Tension Stress that acts to lengthen an object.

    • Normal Stress Stress that acts perpendicular to asurface. Can be either compressional or tensional.

    • Shear Stress that acts parallel to a surface. It can causeone object to slide over another. It also tends todeform originally rectangular objects intoparallelograms. The most general definition is thatshear acts to change the angles in an object.

    f f

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    Definition of Strain

    • Strain is defined as the amount of

    deformation an object experiences compared

    to its original size and shape. For example, if a

    block 10 cm on a side is deformed so that itbecomes 9 cm long, the strain is (10-9)/10 or

    0.1 (sometimes expressed in percent, in this

    case 10 percent.) Note that strain isdimensionless.

    f f

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    Definition of Strain

    • Longitudinal or Linear Strain Strain that changes

    the length of a line without changing its direction.

    Can be either compressional or tensional.

    • Compression Longitudinal strain that shortens anobject.

    • Tension Longitudinal strain that lengthens an

    object.• Shear Strain that changes the angles of an object.

    Shear causes lines to rotate.

    fi i i f i

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    Definition of Strain

    H k’ L

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    Hook’s Law

    • Hook’s law is a quantitative relation betweenstress and strain – "Within elastic limit , strain produced in a body is

    directly proportional to stress"

     – i.e. Strain µ Stress – OR Strain =(Constant)(Stress)

     – Where 1/K = constant of proportionality

     – Strain =(1/K)(Stress)

     – OR Stress / Strain = KORStress / Strain = K

    Y ’ M d l

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    Young’s Modulus

    • "The ratio of stress to the longitudinal strain is

    called Young's modulus."

     – Young's Modulus = Stress / Longitudinal Strain

     – OR Y = s /

     – But s = F / A and = L / L

     – Putting these values in equation

    • Y or E =( F / A) / (  L / L)OR

    Y or E = F L / A L

    S S i D

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    Stress-Strain Demo

    • http://www.esm.psu.edu/courses/emch13d/d

    esign/animation/Fnecking.html

    • http://www.youtube.com/watch?v=mzb4Hpm

    rub4

    R l f P t S f

    http://www.esm.psu.edu/courses/emch13d/design/animation/Fnecking.htmlhttp://www.esm.psu.edu/courses/emch13d/design/animation/Fnecking.htmlhttp://www.esm.psu.edu/courses/emch13d/design/animation/Fnecking.htmlhttp://www.esm.psu.edu/courses/emch13d/design/animation/Fnecking.htmlhttp://www.youtube.com/watch?v=mzb4Hpmrub4http://www.youtube.com/watch?v=mzb4Hpmrub4http://www.youtube.com/watch?v=mzb4Hpmrub4http://www.youtube.com/watch?v=mzb4Hpmrub4http://www.youtube.com/watch?v=mzb4Hpmrub4http://www.esm.psu.edu/courses/emch13d/design/animation/Fnecking.html

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    Role of Pavement Surface

    Surface (PCC or HMA)

    Base Course

    Subbase Course

    Subgrade Soil

    4 Roles:

    3-39

    Smooth ride

    Skid resistance

    Moisture barrier 

    Distribute load

    Ri id t

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    Rigid pavement

    • One which will bridge minorundulations in underlyinglayers without failing.

    • Westergard theory or slab onelastic foundation.

    • Portland cement + aggregate(+ steel)

    • Types of failure

     – Polishing

     – Scaling

     –Joint needs filling

     – Fatigue

     – Pumping

    T ffi L di i Ri id P t

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    Traffic Loading in Rigid Pavement

    Ri id P t C iti l L di

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    Rigid Pavement Critical Loading

    42

    Subgrade Support

    LOAD

    Maximum Stress

    Bottom of Slab

    CRITICAL LOAD CONDITION ASSUMPTIONS

    Maximum stress at pavement edge

    25% Load Transfer to adjacent slab

    Ri id P t C iti l L di

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    Rigid Pavement Critical Loading

    43

    LOAD

    TOP DOWN CRACKING DUE TO EDGE OR CORNER LOADING NOT

    INCLUDED IN DESIGN

    Maximum stress due to corner or edge loading condition

    Risk increases with large multi-wheel gear configurations

    These conditions may need to be addressed in future procedures

    Maximum Stress

    Top of Slab

    C li t

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    Curling stress

    Curling stress

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    Curling stress

    JPCP Bottom-Up Cracking –

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    Base

    Subgrade

    Critical stress region at

    bottom of slab

    JPCP Bottom Up Cracking (Mid-slab Load + Positive Curl/Warp Condition)

    JPCP Top Down Cracking

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    Base

    Subgrade

    Critical stressregion at top of slab

    JPCP Top Down Cracking(Joint Load + Negative Curl/Warp Condition)

    JPCP Top down Cracking

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    Top of slab(crack initiation)

    JPCP Top-down Cracking

    Flexible pavement

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    Flexible pavement

    • Can adjust its position to theshape of the underlying layerswithout damage.

    • Based on layered systemconcept.

    • Asphalt cement or liquidasphalts + aggregate

    • Failure types

     – Bleeding

     – Polishing

     –

    Deformation (rutting) – Fatigue

    Traffic Loading in Flexible Pavement

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    Traffic Loading in Flexible Pavement

    Stress and strain in flexible pavement

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    Stress and strain in flexible pavement

    Chapter 3 Section 2 Flexible Pavement Design

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    Chapter 3 Section 2 – Flexible Pavement Design

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    Subgrade Support

    Wearing Surface

    Subgrade

    Subbase

    Base Course

    Approximate Line ofWheel-Load Distribution

    Area of Tire Contact

    Wheel LoadHorizontal Strain and Stressat the bottom of the asphalt

     Vertical Subgrade Strain

    Must also guardagainst potentialfailure in baselayers

    Importance of stresses in pavement

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    Importance of stresses in pavement

    • To understand

     – The mechanism of load distribution

     – To use in improved design methods

     – To evaluate the performance of materials.

    Stress – strain analysis in pavement

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    Stress – strain analysis in pavement

    • Flexible Pavements:

     – Layered elastic theory

     – Finite element analysis

     – Visco elastic analysis

    • Rigid Pavements:

     – Slab on elastic foundation (Westergard)

     – Others (finite element).

    Pavement loading

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    Pavement loading

    Pavement loading

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    Pavement loading

    • Wheel can be single or dual

    • Axle can be single or Tandem

    • Legal axle loads are (18 kip to 20 kip) for more

    load add more axles

    • Allowable is 32 kip with spacing of 40"-48".

    Pavement loading – tire pressure

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    Pavement loading  tire pressure

    • If tire is inflated correctly – The contact pressure between pavement and tire is

    equal to the tire pressure.

    • If tire has low pressure, then edge pressure ishigher than center.

    • If tire has high pressure, then center pressure ishigher than edge pressure.

    • For correct inflation, and assuming a uniformcontact pressure, the tire imprint may beassumed circular.

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    PAVEMENTS ARE DESIGNEDTO FAIL

    (IN A PREDICTABLE WAY)

    Performance vs Design Life

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    Performance vs Design Life

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    AND WHY PAVEMENT FAILSPREMATURELY

    (IN AN UNPREDICTABLE WAY)

    Two Measures of Pavement Performance

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    Two Measures of Pavement Performance

    • Functional performance:

     – present serviceability index, pavement surface

    friction, and wet-weather safety index

    • Structural performance: – pavement structural capacity to accommodate

    future traffic

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    Attributes of a Pavement in Good Condition

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    Attributes of a Pavement in Good Condition

    • High level of service (LOS)• Safe

    • High customer satisfaction

    Exceeds target performance indicators or haslimited deterioration; e.g., – IRI < 15 cm/km (95 in/mi)

     – PCI > 70 or PCR ≥ 3.5• Surface Distress (cracks, faulting, etc.)

     – Skid Number > 35

     – Deflection < 305 microns (12 mils)

    3-62

    Typical HMA Pavement Distresses

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    Typical HMA Pavement Distresses

    • Fatigue cracking• Bleeding

    • Polishing

    • Edge cracking

    • Roughness• Longitudinal and transverse cracking

    • Reflection cracking

    • Raveling/weathering/oxidation

    • Potholes

    • Rutting (stable/unstable)

    3-63

    Primary HMA Deterioration Load

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    Primary HMA Deterioration Load

    Plastic

    Deformation

    Rutting

    Load

    Fatigue

    Cracking

    Primary HMA Deterioration Traffic

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    Primary HMA Deterioration Traffic

    Friction Loss

    Polishing

    Surface

    Wear 

    Traffic

    Primary HMA Deterioration Environment/Aging

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    Primary HMA Deterioration Environment/Aging

    Block Cracking

    Raveling/Weathering Asphalt

    Hardening

    or 

    Oxidation

    Environment / Aging

    Primary HMA Deterioration Material/Mix

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    Primary HMA Deterioration Material/Mix

    Material Problems

    Friction Loss

    Bleeding/Flushing

    Secondary HMA Deterioration Moisture

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    Secondary HMA Deterioration Moisture

    Infiltration

    Breakdown of

    Existing Cracks

    Deteriorated CracksCracks+

    Moisture

    Infiltration

    Composite Pavement Deterioration

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    Composite Pavement Deterioration

    Horizontal

    Movement

    (environmental)+Vertical

    Movement

    (load)

    3-69

    Reflection Cracking

    Composite Pavement Deterioration

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    p

    Cracking

    +

    Moisture

    Infiltration

    3-70

    Delamination

    Typical Rigid Pavement Distresses

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    yp g

    • Blow-ups

    • Transverse cracking

    • Longitudinal cracking

    • Corner breaks

    • Materials-related distress

    Transverse joint faulting• Joint spalling

    Joint seal damage

    Loss of fines(pumping)

    Polishing (loss offriction)

    Map cracking andscaling

    Roughness

    3-71

    PCC Pavement Deterioration - Load

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    Loads

    Slab Fatigue

    Transverse Cracking

    PCC Pavement Deterioration - Traffic

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    Traffic

    Surface Wear 

    Friction Loss

    Polishing

    PCC Pavement Deterioration - Environment/Material

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    Material

    Joint

    Problems

    3-74

    Joint Seal Damage

    Environmental/Materials

    PCC Pavement Deterioration - Construction

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    Joint and

    SurfaceProblems

    3-75

    ScalingPoorConstruction

    Quality

    PCC Pavement Deterioration - Construction

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    Joint and

    SurfaceProblems

    3-76

    Map Cracking

    PoorConstruction

    Quality

    PCC Pavement Deterioration - Construction

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    Joint andSurface

    Problems

    3-77

    Longitudinal Cracking

    PoorConstruction

    Quality

    PCC Pavement Deterioration - MoistureInfiltration

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    Infiltration

    Breakdown of

    Existing Cracks

    3-78

    Deteriorated Cracks

    Cracks/Joints+

    Moisture

    Infiltration

    PCC Pavement Deterioration - MoistureInfiltration

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    Infiltration

    Cracks/Joints+

    Moisture

    Infiltration

    Subgrade

    Softening

    3-79

    Loss of Fines (Pumping)

    PCC Pavement Deterioration - MoistureInfiltration

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    Infiltration

    Cracks/Joints+

    Moisture

    Infiltration

    Subgrade

    Softening

    3-80

    Corner Breaks

    PCC Pavement Deterioration - MoistureInfiltration

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    Infiltration

    Cracks/Joints+

    Moisture

    Infiltration

    Subgrade

    Softening

    3-81

    Transverse Joint Faulting

    PCC Pavement Deterioration - Incompressibles

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    Cracks/Joints+

    Incompressible

    Material

    3-82

    Blow-Ups

    PCC Pavement Deterioration - Incompressibles

    http://training.ce.washington.edu/PGI/Modules/09_pavement_evaluation/Images/rigid_distress/sr195_blowup2.JPGhttp://training.ce.washington.edu/PGI/Modules/09_pavement_evaluation/Images/rigid_distress/sr195_blowup2.JPG

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    Cracks/Joints+

    Incompressible

    Material

    3-83

    Joint Spalling

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    Mystic Connecticut