1. Pavement Design
CE 453 Lecture 28

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

3. AASHTO Pavement Design Method Considerations
Pavement Performance
Traffic
Roadbed Soil
Materials of Construction
Environment
Drainage
Reliability
Life-Cycle Costs
Shoulder Design

4. 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

5. Advantages of Rigid Pavement
Good durability
Long service life
Withstand repeated flooding and subsurface water without deterioration

6. Disadvantages of Rigid Pavement
May lose non-skid surface with time
Needs even sub-grade with uniform settling
May fault at transverse joints

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

8. 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

9. Disadvantages of Flexible Pavement
Loses some flexibility and cohesion with time
Needs resurfacing sooner than PC concrete
Not normally chosen where water is expected

10. 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

11. Basic AASHTO Rigid Pavement Design Method
Select terminal serviceability
Determine number of ESALs
Determine the modulus of sub-grade reaction
Determine the slab thickness

12. 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

13. Variables included in Nomographs
Effective Modulus of Sub-Grade Reaction, k
Considers:
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 (flexible) and 21.9 (rigid)

26. 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

27. 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

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

29. 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

30. OTHER ISSUES Drainage Joints Grooving (noise vs. hydroplaning)
Rumble strips
Climate
Level and type of usage

31. 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 , June 2003

32. FATIGUE CRACKING

33. RUTTING

34. SHOVING

35. PUMPING