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Design Concepts and Perpetual Pavement Mike Mamlouk Arizona State - - PowerPoint PPT Presentation
Design Concepts and Perpetual Pavement Mike Mamlouk Arizona State - - PowerPoint PPT Presentation
Design Concepts and Perpetual Pavement Mike Mamlouk Arizona State University Asphalt Pavement Why is it hard to design pavement? Hard to estimate service life Different load magnitudes, configurations & speeds Multilayer system
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Why is it hard to design pavement?
- Hard to estimate service life
- Different load magnitudes, configurations & speeds
- Multilayer system
- Viscoelastic, non-linear materials
- Material properties are affected by environmental
conditions
- Unconventional definition of failure
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Distresses vs. Failure
When a distress or a combination of distresses reaches a certain unacceptable level it is considered failure
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Distresses in Asphalt Pavement
Rutting Fatigue Cracking Thermal Cracking Roughness Shoving Bleeding/Flushing
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Pavement Condition Age or Load Applications
Good Poor
Empirical Nature of Pavement Design
Performance
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Major Research Projects
- AASHO Road Test
- Strategic Highway Research Program
(SHRP)
- Mechanistic-Empirical Pavement
Design Guide (AASHTOWare Pavement ME Design)
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Factors Affecting Pavement Performance
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Factors Affecting Pavement Performance
- 1. Traffic
2.Soil and pavement materials 3.Environment 4.Construction and maintenance
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Traffic
Traffic has a major effect on pavement performance ➢Traffic volume ➢Traffic load ➢Tire pressure ➢Rate of applying load
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Severe Traffic Conditions
Heavy load and high traffic volume High tire pressure Slow moving vehicles
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Effect of Changing Tire Pressure
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Effect of Changing Load
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Effect of Tire Pressure & Loads
- Changing tire pressure affects upper layers
- Changing load affects deeper layers
- Required quality of surface is mostly
determined by tire pressure
- Required pavement thickness is mostly
determined by load magnitude
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Factors Affecting Pavement Performance
- 1. Traffic
2.Soil and pavement materials 3.Environment 4.Construction and maintenance
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Wheel Load Hot-mix asphalt Aggregate Base Natural soil
Material quality affects performance
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Factors Affecting Pavement Performance
- 1. Traffic
2.Soil and pavement materials 3.Environment 4.Construction and maintenance
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Environmental Factors
- Moisture
- Temperature
- Freeze and thaw
- Aging
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Factors Affecting Pavement Performance
- 1. Traffic
2.Soil and pavement materials 3.Environment 4.Construction and maintenance
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- Construction and maintenance practice
largely affects performance
Construction and maintenance
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Design Objective
To determine the required layer materials and thicknesses so that the pavement would last for a certain design life before failure.
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Pavement Design Approaches
- 1. Based on experience (ie., standard sections)
- 2. Based on simple strength tests or soil formula
- 3. Based on statistical evaluation of pavement
performance (1993 AASHTO method)
- 4. Based on structural analysis of layered systems
with some empirical relations (AASHTOWare ME design)
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Concept of Perpetual Pavement
➢Extended-life HMA pavement ➢Limit distresses in the surface layer ➢Has been used in Europe
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Example of Perpetual Pavement
SMA 1.5” – 3” High Modulus Rut Resistant Material 4” – 7” Flexible Fatigue Resistant Material 3” – 4” Pavement Foundation
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Endurance Limit
➢ Strain level below which HMA would endure indefinite load repetitions without accumulating fatigue cracks
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Healing Concept
➢Capability of material to self-recover its stiffness or strength upon resting due to closure of cracks ➢Traffic loads are separated by “rest periods” may allow for partial or full healing of damage ➢It increases the number of load applications before failure
Microstrain Time (sec) Field Measurement
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NCHRP Report 762 Tests w/ & w/o Rest Period
Time
Rest Period
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Model Development
0.2 0.4 0.6 0.8 1 1.2 20000 40000 60000 Stiffness Ratio, SR Loading Cycles, N Test w/o Rest Period Test w/ Rest Period Healing
SR =
𝐷𝑣𝑠𝑠𝑓𝑜𝑢 𝑇𝑢𝑗𝑔𝑔𝑜𝑓𝑡𝑡 𝐽𝑜𝑗𝑢𝑗𝑏𝑚 𝑇𝑢𝑗𝑔𝑔𝑜𝑓𝑡𝑡
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How to get EL
Healing
➢When SR = 1 Full healing ➢Strain becomes EL ➢EL is not a single value ➢N is not a significant factor ➢EL is based on healing
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EL Values
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Incorporation in Pavement Design
➢Layer thicknesses and material properties can be controlled so that strain does not exceed the EL ➢Field validation is still needed
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