DISSIPATED ENERGY STUDY OF FATIGUE IN AIRPORT PAVEMENTS

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DISSIPATED ENERGY STUDY OF FATIGUE IN AIRPORT
PAVEMENTS

• PHD Candidate Shihui Shen
• Advisor Prof. S. H. Carpenter
• FAA Working Group Meeting
• Feb 3, 2006

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PROJECT DEVELOPMENT

• Dissipated Energy (RDEC) Unifying Concept
• Load Modes, Gear Configurations, Load Pulse
  Duration, Load Levels
• Fatigue Endurance Limit
• Applicable to thick airport pavements
• Thickness below which no damage occurs
• Healing
• Recovery from Damage
• Impacts total loads to failure
• Damage Concept is Amenable to a Thickness Design
  Procedure

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DISSIPATED ENERGY CONCEPT REVIEW
Initial Load Cycle
STRESS
Second Load Cycle
STRAIN
Different Dissipated Energy Between First And
Second Load Cycle
Ratio of Dissipated Energy Change (RDEC)
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RDEC REVIEW
Ratio of Dissipated Energy Change, Log
I
III
II
Load Repetitions, Log
Plateau Value
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PV CALCULATION
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UNIQUE PV-Nf RELATIONSHIP
Data Points 546 Mixture types 98 Loading modes
2 Frequency 0.5-10 Hz Rest period 0- 0.4 sec.
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RDEC IN HEALING

• Best understood through energy behavior and
  viscoelastic properties of an HMA
• PV - energy based
• Can provide a unique indication of the impact of
  a load pulse followed by a rest period
• Research hypothesis
• Make rest period effect quantifiable through lab
  test
• Healing reduces the damage
• Reduced damage produces a lower PV, which
  translates into a longer fatigue life

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FATIGUE-HEALING TEST

• Four Point Bending Beam (SHRP T321-03)
• Mode of Loading Constant Strain _at_ 500
  microstrain
• Wave Shape Haversine
• Load Pulse Width 100ms (10 Hz)
• Rest Period 09 second
• Temperature 20o

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FATIGUE-HEALING TEST

• A short rest period between each load pulse to
  simulate rest between loads
• Intermediate strain level, 500 microstrain, is
  used

Haversine Load Pulse Sequence
The whole nature of energy change during a test
is continuous, thus the dissipated energy and the
PV can be obtained for each cycle to perform the
RDEC analysis,
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HEALING TEST PV vs. (RP1) FOR NEAT
BINDER
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HEALING TEST PV vs. (RP1) FOR POLYMER
BINDER
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PV-Nf FOR HEALING TEST
With 9 second rest period, the fatigue life
is extended 5 times for neat binder mix and 10
times for polymer binder mix

• Unique PV-Nf relationship for healing test

neat
polymer
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HEALING AND FEL

• Healing study using RDEC approach helps to
  understand the existence of FEL

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PV-IDE AT NORMAL STRAIN (DAMAGE)
At normal strain/damage condition and
continuous loading, the PV has a good correlation
with Initial Dissipated Energy (IDE).

• Under normal condition, load effect is dominant,
  while healing is negligible

• IDE, initial energy capacity of mixture
• PV, total effect on fatigue behavior (material
  fatigue resistance and load effect)

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PV-IDE FOR WHOLE LOADING RANGE
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UNIQUE PV-Nf RELATIONSHIP
Unique energy level at which no fatigue damage
exists
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PAVEMENT DESIGN

• Requires Relation to Standard Parameters
• Load Level
• Speed
• Repetition Interval
• Mix Variables
• Asphalt Grade

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PRELIMINARY PV PREDICTION MODEL

• Based on 19 IDOT mix
• Including neat binder and polymer binder mix
  various gradations 2 air voids levels
• Rich bottom binder mixes are included

• Where
• e controlled tensile strain
• S the flexural stiffness of HMA mix, MPa
• AV the air voids of mixture
• Vb the asphalt content by volume
• C the aggregate gradation parameter,
  C(PNMS-PPCS)/P200
• PNMS the percent of agg. passing nominal
  maximum size sieve
• PPCS the percent of agg. passing primary
  control sieve (PCS NMS 0.22)
• P200 the percent of agg. passing 200 sieve

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PV PREDICTION
R2 0.902
Line of equality
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BINDER FATIGUE TEST - DSR
Gemini 200 Dynamic Shear Rheometer
DSR Testing Geometry Schematic
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TYPICAL BINDER DE-N CURVE
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TYPICAL BINDER RDEC CURVE
III
Plateau Stage, II
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COMPARE PV-Nf CURVES FOR BINDER AND MIXTURE
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CONCLUSIONS

• RDEC provides a successful way to study HMA,
  fatigue, healing, and its role on fatigue
  endurance limit
• Healing does exist and its effect on fatigue
  behavior can be observed through lab accelerated
  fatigue-healing test

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CONCLUSIONS (cont.)

• The occurrence of healing is highly related to
  the level of damage healing effect can be
  dominant under low load damage condition.
• Healing under the low damage condition is a key
  to understand the existence of a fatigue
  endurance limit (FEL).
• Healing potential exceeds damage potential for
  any one load cycle.

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RECOMMENDATIONS

• PV can be predicted based on material properties,
  which can be integrated into pavement structural
  design.
• Combine this with PVL, the energy based FEL
  established before, provides a simple way to
  estimate the strain level that can reach
  unlimited fatigue life.
• The fatigue-healing test can be extended to
  different temperature, load levels, and more
  diversity of mix types.
• Asphalt binders energy recovery rates and
  healing capacity can be studied using the RDEC
  approach. It should provide an insight of the
  healing kinetics derived from the existing
  fatigue-healing study for mixture.

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THANK YOU !!
QUESTIONS ?