Pavement Design
CE 453 Lecture 28
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Objectives
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Understand and complete ESAL
calculation
Know variables involved in and be
able to calculate required thickness
of rigid and flexible pavements
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AASHTO Pavement Design
Method Considerations
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Pavement Performance
Traffic
Roadbed Soil
Materials of Construction
Environment
Drainage
Reliability
Life-Cycle Costs
Shoulder Design
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Two Categories of Roadway Pavements
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Rigid Pavement
Flexible Pavement
Rigid Pavement Typical Applications
 High volume traffic lanes
 Freeway to freeway connections
 Exit ramps with heavy traffic
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Advantages of Rigid Pavement
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Good durability
Long service life
Withstand repeated flooding and
subsurface water without deterioration
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Disadvantages of Rigid Pavement
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May lose non-skid surface with time
Needs even sub-grade with uniform
settling
May fault at transverse joints
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Flexible Pavement Typical
Applications
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Traffic lanes
Auxiliary lanes
Ramps
Parking areas
Frontage roads
Shoulders
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Advantages to Flexible Pavement
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Adjusts to limited differential
settlement
Easily repaired
Additional thickness added any time
Non-skid properties do not deteriorate
Quieter and smoother
Tolerates a greater range of
temperatures
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Disadvantages of Flexible Pavement
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Loses some flexibility and cohesion with
time
Needs resurfacing sooner than PC
concrete
Not normally chosen where water is
expected
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Basic AASHTO Flexible
Pavement Design Method
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Determine the desired terminal
serviceability, pt
Convert traffic volumes to number of
equivalent 18-kip single axle loads (ESAL)
Determine the structural number, SN
Determine the layer coefficients, ai
Solve layer thickness equations for
individual layer thickness
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Basic AASHTO Rigid Pavement
Design Method
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Select terminal serviceability
Determine number of ESALs
Determine the modulus of sub-grade
reaction
Determine the slab thickness
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Variables included in
Nomographs
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Reliability, R
•
•
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Incorporates a degree of certainty
into design process
Ensures various design alternatives will
last the analysis period
Resilient Modulus for Roadbed Soil,
MR
•
Generally obtained from laboratory
testing
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Variables included in
Nomographs

Effective Modulus of Sub-Grade
Reaction, k
•
Considers:
1.
2.
3.
4.

Sub-base type
Sub-base thickness
Loss of support
Depth to rigid foundation
Drainage Coefficient, mi
•
Use in layer thickness determination
Applies only to base and sub-base
•
See Tables 20.15 (flexible) and 21.9 (rigid)
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Flexible Pavement Design
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Pavement structure is a multi-layered elastic
system, material is characterized by certain
properties
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Modulus of elasticity
Resilient modulus
Poisson ratio
Wheel load causes stress distribution (fig 20.2)
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Horizontal: tensile or compressive
Vertical: maximum are compressive, decrease with
depth
Temperature distribution: affects magnitude of
stresses
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Components
Sub-grade (roadbed) course: natural material that serves as the
foundation of the pavement structure
Sub-base course: above the sub-grade, superior to sub-grade course
Base course: above the sub base, granular materials such as crushed
stone, crushed or uncrushed slag, gravel, and sand
Surface course: upper course of the road pavement, should withstand
tire pressures, resistant to abrasive forces of traffic, provide skidresistant driving surface, prevent penetration of surface water
3 inches to > 6 inches
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Economic Analysis
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Different treatments results in
different designs
Evaluate cost of different
alternatives
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Sensitivity Analysis
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Input different values of traffic
volume
Compare resulting differences in
pavement
Fairly significant differences in ADT
do not yield equally significant
differences in pavement thickness
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OTHER ISSUES
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Drainage
Joints
Grooving (noise vs. hydroplaning)
Rumble strips
Climate
Level and type of usage
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FAILURE EXAMPLES
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Primarily related to design or lifecycle, not construction
All images from Distress
Identification Manual for the LongTerm Pavement Performance
Program, Publication No. FHWA-RD03-031, June 2003
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FATIGUE CRACKING
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RUTTING
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SHOVING
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PUMPING
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