Post on 07-Apr-2018
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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