Future Direction for Specs'

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Future Direction for Specs.

• John DAngelo
• Federal Highway Administration
• AMAP 2006

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Modified Binders Affect Performance

• Study same mix different binders.

PG 63-22 mod. no rutting
PG 67-22 unmod. 15mm rutting
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Proposed MSCR TEST Protocol
Creep Stress
1
10
time
Creep Strain
time
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High Temperature Binder Test

• New test criteria
• Perform multiple stress levels on the same sample
  at reduced number of cycles.
• Stress levels 25, 50, 100, 200, 400, 800, 1600,
  and 3200 Pa.
• Run 10 cycles at each stress level no rest
  periods
• Total cycles per test 80.

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ALF and CR ranking
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High Temperature Binder Criteria

• Study
• Refine the Multi-Stress Creep and Recovery Test
• Evaluate multiple binders
• Evaluate binder and mix properties to develop
  specification criteria.

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Development of Standard Practice for Superpave
Plus Specifications

• Use of DSR in Place of ER and Ductility

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Why Superpave Plus Specs.

• The existing specifications do not identify the
  performance characteristics of modified binders.
• The existing specifications do not have a
  criteria for fatigue or durability.
• Agencies look to other tests to identify
  modifiers
• Elastomeric polymer modifiers are desired

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State DOTs Specifying Polymer PG (PG)
Ductility
ER
SB/SBS Required
ER
ER
PA
ER TT
ER
ER
ER
ER
ER
ER
ER FD
ER PA
ER
Ductility, TT ER
FD
TT DT
ER TT
ER
ER
ER
SB/SBS Required
ER
ER PA
ER-Elastic Recovery FD-Force Ductility TT-Toughnes
s Tenacity PA-Phase Angle
PA
FD ER
ER
PA
PG modifier
PG
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Toughness Tenacity
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Elastic Recovery
AC doesnt recover SB modified AC recovers
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Problem Statement

• Provide Users with alternatives to the empirical
  Superpave Plus tests
• Elastic Recovery
• Ductility/ Force Ductility
• Toughness and Tenacity
• Approach Develop AASHTO/ASTM Standard Practice
  for Superpave Plus Specifications
• DSR
• Multiple Stress Creep Recovery

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So What Do We Do? Use DSR Approach

• Use DSR
• Muti Stress Creep Recovery Test
• Two creep stress levels
• Ten cycles per stress level
• For Elastomeric modifiers Specify
• strain recovery gt 15 or 20
• Overall change between stress levels
• Run on the RTFOT
• Run on the same sample as RTFOT grading

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Proposed MSCR TEST Protocol
3200 Pa
Creep Stress
100 Pa
1
10
time
Creep Strain
time
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What criteria? recovered strain
(Peak Strain - recovered Strain)/Peak Strain
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PG 64-34 1101 SBS 83 recovery 100Pa
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PG 64-34 1101 SBS 21 recovery 3200Pa
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70-22 3SBR 26 recovery 100Pa
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70-22 3SBR 15 recovery 3200Pa
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67-34 28 recovery 100Pa
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67-34 9 recovery 3200Pa, 75 ER
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Difference between low stress and high stress
shows how sensitive the formulation is to stress
Differential 9
Differential 66
Differential 59
Unknown
LDPE
EVA
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Two 70-22s with SBS. Not all binders are the
same.
Differential 30
Differential 18
SBS
SBS
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General relationship between ER and MSCR
Incompatible SBS
Special EVA
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Findings to date

• The DSR MSCR percent strain recovery criterion
  can replace the FD, ER, or TT.

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Future Steps

• Analyze available MSCR percent recovered strain
  data to finalize creep stress level and test
  protocol
• Where available, show relationships with existing
  ER, FD, Duct., and TT data

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NCHRP 9-36 Improved Procedure for Laboratory
Aging of Asphalt Binders

• Improved procedure for short-term laboratory
  aging usable in a purchase specification such as
  AASHTO M320.
• Apply to neat and modified binders.
• Quantify binder volatility.
• Extend to long-term aging.
• Mimic PP2 mix aging.
• Advanced Asphalt Technologies (August 2005)

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Original SAFT Apparatus (Glover)

• Aging Conditions
• 163C
• 30 minutes
• Atmospheric air
• 2 liters /minute

Heating Mantle
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SAFT by COX
Vessel top fully enclosed
Sits on bench at convenient height
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(4) Verification Study

• Mixtures with 12 binders
• Mixtures aged in laboratory
• Physical properties
• Binders aged with SAFT and RTFOT
• Physical properties
• Volatile collection and analysis
• Binder and mixture aging to be compared
• Comparison using Hirsch model
• Status
• Mixture work underway
• Binder aging to follow optimization study

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Questions