2. OBJECTIVES
• UNDERSTAND AND COMPLETE THICKNESS CALCULATION BASED ON
PREVIOUS CONCEPTS
• KNOW VARIABLES INVOLVED IN AND BE ABLE TO CALCULATE REQUIRED
THICKNESS OF RIGID AND FLEXIBLE PAVEMENTS
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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
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5. ADVANTAGES OF RIGID PAVEMENT
• GOOD DURABILITY
• LONG SERVICE LIFE
• WITHSTAND REPEATED FLOODING AND SUBSURFACE WATER
WITHOUT DETERIORATION
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6. DISADVANTAGES OF RIGID PAVEMENT
• MAY LOSE NON-SKID SURFACE WITH TIME
• NEEDS EVEN SUB-GRADE WITH UNIFORM SETTLING
• MAY FAULT AT TRANSVERSE JOINTS
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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
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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
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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
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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
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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
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13. 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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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
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27. COMPONENTS
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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
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
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30. OTHER ISSUES
• DRAINAGE
• JOINTS
• GROOVING (NOISE VS. HYDROPLANING)
• RUMBLE STRIPS
• CLIMATE
• LEVEL AND TYPE OF USAGE
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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-03-031, JUNE 2003
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