This document discusses pavement design methods. It outlines the AASHTO pavement design method which considers factors like traffic, materials, environment and reliability. It describes two categories of pavement - rigid and flexible. Rigid pavement is suited for high traffic areas while flexible is used for other applications. The advantages and disadvantages of each are provided. It then details the basic AASHTO design methods for calculating the required thickness of rigid and flexible pavements based on factors like traffic loads, soil properties, layer coefficients and desired serviceability. Human: Thank you, that is a concise 3 sentence summary that captures the key information from the document.

1. 1
Pavement Design
CE 453 Lecture 28

2. 2
Objectives
 Understand and complete ESAL
calculation
 Know variables involved in and be
able to calculate required thickness
of rigid and flexible pavements

3. 3
AASHTO Pavement Design
Method Considerations
 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
 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
 Good durability
 Long service life
 Withstand repeated flooding and
subsurface water without deterioration

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Disadvantages of Rigid Pavement
 May lose non-skid surface with time
 Needs even sub-grade with uniform
settling
 May fault at transverse joints
 Requires frequent joint maintenance

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Flexible Pavement Typical
Applications
 Traffic lanes
 Auxiliary lanes
 Ramps
 Parking areas
 Frontage roads
 Shoulders

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Advantages to Flexible Pavement
 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
 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
 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
 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
 Reliability, R
• 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. Sub-base type
2. Sub-base thickness
3. Loss of support
4. 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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16. Other Growth Rates
 Multiple payment compound amount
factor, with i = growth rate
 G = [(1+i)n
-1]/i
16

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Flexible Pavement Design
 Pavement structure is a multi-layered elastic
system, material is characterized by certain
properties
 Modulus of elasticity
 Resilient modulus
 Poisson ratio
 Wheel load causes stress distribution (fig 20.2)
 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 skid-
resistant driving surface, prevent penetration of surface water
3 inches to > 6 inches

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Economic Analysis
• Different treatments results in
different designs
• Evaluate cost of different
alternatives

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Sensitivity Analysis
• 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
 Drainage
 Joints
 Grooving (noise vs. hydroplaning)
 Rumble strips
 Climate
 Level and type of usage

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FAILURE EXAMPLES
 Primarily related to design or life-
cycle, not construction
 All images from Distress
Identification Manual for the Long-
Term Pavement Performance
Program, Publication No. FHWA-
RD-03-031, 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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EXAMPLES
 http://training.ce.washington.edu/wsdot
 http://training.ce.washington.edu/wsdot