Pavement Design CE 453 Lecture 28 1 Objectives

Pavement Design CE 453 Lecture 28 1

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

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

Two Categories of Roadway Pavements n n Rigid Pavement Flexible Pavement Rigid Pavement Typical Applications n High volume traffic lanes n Freeway to freeway connections n Exit ramps with heavy traffic 4

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

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

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

Advantages to Flexible Pavement n n n 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 8

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

Basic AASHTO Flexible Pavement Design Method n n n 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 10

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

Variables included in Nomographs n Reliability, R • • n 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 12

Variables included in Nomographs § Effective Modulus of Sub-Grade Reaction, k • Considers: 1. 2. 3. 4. 1. 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) • 13

14

15

16

17

18

19

20

21

22

23

24

25

Flexible Pavement Design n Pavement structure is a multi-layered elastic system, material is characterized by certain properties ¡ ¡ ¡ n 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 26

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 27

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

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 29

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

FAILURE EXAMPLES n n Primarily related to design or lifecycle, not construction All images from Distress Identification Manual for the Long. Term Pavement Performance Program, Publication No. FHWA-RD 03 -031, June 2003 31

FATIGUE CRACKING 32

RUTTING 33

SHOVING 34

PUMPING 35