ADVANCES IN MATERIAL TESTING FOR LONG LIFE ASPHALT PAVEMENTS

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ADVANCES IN MATERIAL TESTING FOR LONG LIFE
ASPHALT PAVEMENTS

• Samuel H. Carpenter
• University of Illinois Urbana-Champaign
• Rhode Island Transportation Forum
• November 5, 2004

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NCHRP 1-37A

• AASHTO 2002 Design Guide - Driving Research
• Performance Models
• Verification
• Calibration
• New Material Testing
• Dynamic Modulus
• Fatigue

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TESTING

• Stiffness Dynamic Modulus
• Temperature
• Rate of Loading
• Key Element in Structural Thickness Design
• Seasonal Variations
• Regional Variations
• Fatigue Gradual Failure Under Repeated Loadings

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ASPHALT PAVEMENT FATIGUE
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Full Depth Asphalt
Subgrade
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STRUCTURAL DESIGN FOR FATIGUE

• Reduce Bending Reduce Strain
• Increase Thickness of Asphalt Layer
• Increase Stiffness of Asphalt Layer
• Improve Material Behavior

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DYNAMIC MODULUS
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SAMPLE PREPARATION
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SAMPLE PREPARATION
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(No Transcript)
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ILLINIOS DOT TESTING

• 21 Mixtures Sampled From Field Construction
  Projects
• Specimens Compacted, Prepared, and Tested at 4
  and 7 Percent Air Voids
• Develop Typical Values Examine Models

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DYNAMIC MODULUS - STIFFNESS
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FATIGUE DESIGN

• Tensile Strain at Bottom of Asphalt
• Tensile Strain in Flexural Beam Test
• Other Configurations

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FATIGUE TESTING

• Tensile Strain in Flexural Beam Test
• Other Configurations
• 10 Hz Haversine Load, 20o C, Controlled Strain

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FLEXURAL FATIGUE TEST
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SAMPLE PREPARATION
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FLEXURAL FATIGUE TEST
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MODULUS DECREASE - DAMAGE
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IDOT MIX - TYPICAL FATIGUE
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FATIGUE COEFFICIENTS
y -0.3269x 1.1879 R2 0.9354
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INDIRECT TENSILE STRENGTH
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FATGUE IN THICKNESS DESIGN
0.01
Unique Curve for Every Mixture
0.001
Strain (Strain/1E6)
0.0001
Thicker HMA
0.00001
1.0E02
1.0E04
1.0E06
1.0E08
1.0E10
1.0E12
1.0E14
Load Cycles to 50 Stiffness (Failure)
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Perpetual Pavement ?
0.01
0.001
Strain (Strain/1E6)
0.0001
0.00001
1.0E02
1.0E04
1.0E06
1.0E08
1.0E10
1.0E12
1.0E14
Load Cycles to 50 Stiffness (Failure)
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FATIGUE ENDURANCE LIMIT
0.01
0.001
Strain (Strain/1E6)
0.0001
FATIGUE ENDURANCE LIMIT
0.00001
1.0E02
1.0E04
1.0E06
1.0E08
1.0E10
1.0E12
1.0E14
Load Cycles to 50 Stiffness (Failure)
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DISSIPATED ENERGY
INITIAL LOAD CYCLE
STRESS
STRAIN
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DISSIPATED ENERGY

• Dissipated Energy Ratio - Damage

INITIAL LOAD CYCLE
STRESS
SECOND LOAD CYCLE
STRAIN
DIFFERENT DISSIPATED ENERGY BETWEEN FIRST AND
SECOND LOAD CYCLE
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70 MICRO STRAIN TEST
Projected Life 1 E13
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70 MICRO STRAIN
Plateau Value
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UNIQUE FATIGUE LIFE PLOT
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PLATEAU VALUE LOAD CYCLES
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FATIGUE

• 60 Different Mixtures Tested to Date
• FAA Project Damage Approach Energy Based
• 11 Illinois Mixtures Sampled for IDOT Project
  22 Mixtures Tested
• Neat Binders
• Polymer Modified
• Rich Bottom Base Mixtures

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LOW STRAIN TESTING
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FATIGUE ENDURANCE LIMIT
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LABORATORY FIELD SHIFT

• Field Life is 4 to 50 Times Longer Than the
  Laboratory Fatigue Test Predictions
• Illinois DOT Test Sections
• Response to wheel loads
• ATLaS
• FWD, HWD
• Field fatigue comparison to lab

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PERPETUAL PAVEMENT SECTIONS
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IN-SITU STRAIN GAGES
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ATLaS FULL SCALE TESTER
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RECORDED TENSILE STRAINS
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DISSIPATED ENERGY APPROACH

• Laboratory Testing to Demonstrate Field Shift
  Factor
• HEALING
• Add a Rest Period Between Each Individual Load
  Cycle
• Not after a set number of cycles

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LABORATORY HEALING
5 Second Rest 10x Life Increase
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PLATEAU VALUE LOAD CYCLES
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DISSIPATED ENERGY

• Validates Fatigue Endurance Limit
• Provides Mechanistic Damage-Based Fatigue
  Analysis
• Is a Fundamental Material Property
• Allows Study of Healing in Pavement

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FATIGUE ENDURANCE LIMIT

• Crucial for Perpetual Pavements
• Limit to HMA Thickness
• Unique fatigue curves
• Independent of Traffic Level
• Crucial structural design element
• Questions necessity of rich bottom layer