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INTRODUCTION

1. General

1.1. Importance is intense interaction, high quality

and quantity of materials

1.2. Romans, highways, three layered pavements

(compacted stones- small in mortar- massive

blocks embedded), continued till 1800.

1.3. Arabs no significant contribution.1.4. French (Pierre Tresaguet) small sized stones

used.

1.5. British (Mac Adam), comparatively large single

sized stones, drainage and compacted sub grade

emphasized.

1.6. Today, roads and airport pavements

2. Major Activities

2.1. Planning

2.2. Design

2.3. Construction

2.4. Evaluation

2.5. Maintenance

2.6. Rehabilitation3. Pavement Load Carrying Concept

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3.1. Flexible and Rigid Compared

Flexible Rigid

Essential difference is the way load is distributed

Structural capacity by loaddistribution characteristics of thelayered system, highest quality

material at or near the surface. Loadintensity reduces through depth andit is distributed over sub grade.

Most structural capacity by slabitself, major factor in design is

structural strength. Relatively minor

contribution to load carryingcapacity by sub base.

Deep deflection basin Shallow deflection basin

Low modulus of elasticity. High modulus of elasticity.

More role of sub grade strength Minor variation in Sub gradestrength, little influence.

Arbitrary, basic purpose was to distinguish between AC and PCCpavements.

Though generally AC (asphalt concrete) pavements are referred as flexibleand PCC or RCC as rigid yet it is not true

Thin PCC over granular behaves asflexible.

Full depth AC pavement & chip sealover PCC behaves as rigid

3.2. Definitions

3.2.1. Flexible Pavement . A flexible pavement

structure maintains intimate contact with and

distributes loads to the sub grade and depends

on aggregate interlock, particle friction, andcohesion for stability.

3.2.2. Rigid Pavement . Applied to wearing

surfaces constructed of Portland cement

concrete on sub grade or granular sub base

4. Pavement Design Procedures

4.1. Pre Road Test Design Procedures

4.1.1. General. Based upon experience, rule of

thumb, and soil mechanics principles.

Limitation - set traffic conditions. Over

designed, protecting sub grade.

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4.1.2. Group Index Method . Numerical indicator of

quality of sub grade, rugged, higher value more

thickness.

4.1.3. Pedological Methods . Soil classified based

upon formation and location. Poor soil requires

more thickness.

4.1.4. Strength Based Methods

4.1.4.1. CBR, estimates quality of RBS, baseand sub base materials- use empirical

charts/curves.

4.1.4.2. Hveem (R-value), Stabilometer,

measures horizontal pressure as a result of

vertical load,

4.1.4.3. Load deformation, Pavement

performance depends upon deformation and

not ultimate strength, Plate load test, vertical

deflection is related to load repetitions for

measured deflection.

4.1.4.4. Triaxial, confining pressure simulates

actual conditions, correlated to required

thickness through empirical equations andcharts

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4.2. Road Test Design Procedure

4.2.1. The most significant pavement research

initiative was the AASHTO road test in 1958. In

this project, special test sections of variable

thicknesses were constructed in Ottawa, Illinois,and subjected to repeated loadings from traffic

that included both single- and tandem-axle

vehicles. Each test section was subjected to

thousands of load repetitions. The research

project dealt with both flexible and rigid

pavements. The AASHO road test andsubsequent research led to the publication of a

series of guides for the design of pavements,

first in 1961

4.2.2. Mechanistic Empirical Design Procedures-

based upon mechanics of material equations,

input like wheel loads, output pavement

response (stress, stress, deformation), predictsdistress, improvement in procedure based upon

field data.

5. Pavement Designs and inputs

5.1. Structural Design

5.2. Materials Design5.3. Paving Mixture Design.

5.4. Joint Design for rigid pavement

5.5. Design inputs are grouped:

5.5.1. Traffic Loadings

5.5.1.1. Magnitude of axle loads. Studiedcontrolled and implemented for improvement

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in designs.

5.5.1.2. Volume and composition of axle loads.

Surveys, database and predictions.

5.5.1.3. Tire pressure and contact area.

5.5.2. Material Characteristics . May includegradation, strength or stability, and resistance to

the effects of repeated loadings.

5.5.3. Climate or Environment

5.5.3.1. Temperature and its fluctuations affect

asphalt concrete to lose stability whereas at

low temperatures asphalt concrete becomes

very hard and stiff. Also associated with frostheave freeze-thaw damage.

5.5.3.2. Moisture ; Sub grade soils and other

pavement materials weaken appreciably

when saturated, and certain clayey soils

exhibit substantial moisture-induced volume

change.6. Materials and Structural/ Functional Performance

6.1. What? Where?

6.2. Functional and structural performance

7. Causes of Failure

7.1. Inadequate Design . Base data, traffic, axle loads

tyre pressure etc,

7.2. Substandard Materials . Sampling, specifications,

test procedures, modern labs.

7.3. Construction Practices and Quality Control .Inspections, rolling, vibrators etc.

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8. Who are involved

9. Specifications