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Performance Mix Design
Stacey Diefenderfer, Ph.D., P.E.
Virginia Pavement Research and Innovation Symposium
June 26, 2018
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What Is PMD?
• Designing mixes using performance tests
on appropriately conditioned specimens to
address multiple modes of distress taking
into consideration mix aging, traffic,
climate and location within the pavement
structure.
– from FHWA Balanced Mix Design Task Force
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Why PMD?
• Volumetrics do not tell the whole story
– Change performance without changing
volumetrics
• Goal of PMD
– Design mixes for the application and service
requirement
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PMD for Innovation
• Address technologies / methodologies in
mix design that cannot be handled within
current specs
• Tailor mixtures for in-service applications
• Designers can have space to innovate
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MIX DESIGN
APPROACHES
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Volumetric
Design w/
Performance
Verification
Select trial gradation
Validate JMF. Go to production
Perform volumetric analysis;
select design binder content and
volumetric properties
Conduct performance tests
Perform moisture damage test
Improve moisture
susceptibility
Redesign mix
Moisture
damage
passed?
Performance
passed?No
No
Yes
Yes
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Volumetric Design w/
Performance Verification
• Superpave design approach
• Verification of performance properties
– If do not meet performance properties, re-
design the mix
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Performance-
Modified
Volumetric Design
Select trial gradation
Validate JMF. Go to production
Perform volumetric analysis;
select initial binder content
Conduct performance tests
Perform moisture damage test
Improve moisture
susceptibility
Adjust mix proportions
and/or binder content
Moisture
damage
passed?
Performance
passed?No
No
Yes
Yes
Verify volumetric properties
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Performance-Modified
Volumetric Design
• Use Superpave approach to select initial
design binder content
• Performance test results could modify
mixture proportions and/or adjust the
binder content
• Final volumetric properties may be allowed
to fall outside volumetric spec
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Performance
DesignSelect trial gradation
Validate JMF. Go to production
Conduct performance tests;
select design binder content
Perform moisture damage test
Perform volumetric analysis;
determine & report volumetric
properties at design binder
content
Improve moisture
susceptibility
Moisture
damage
passed?
No
Yes
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Performance Design
• Run performance tests at varying binder
contents and select the design binder
content from results
• Volumetrics determined afterward and
reported
• No spec requirements on volumetrics
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MOVING FROM VOLUMETRIC
DESIGN TO PMD
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Developing PMD Specifications
• Know mix/pavement performance
• Develop a baseline for performance
• Select appropriate test procedure
• Develop testing and specification structure
• Re-evaluate and validate
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Selecting Test Procedures
• Correlates to field performance
• Sensitivity to mix properties
• Repeatability
• Ease of use
• Availability/cost
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Where Are We Going?
VTRC Projects
• PMD – Phase I
– Benchmark current mixtures
– Shadow testing during production
– Develop & validate spec recommendations
– Validate process during design
• High RAP Trials
– Trial production of >40% RAP mixtures
– Use PMD for design and production
evaluation
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PMD – Phase I
• Benchmarking / Shadow testing
– Cracking test
• IFIT/SCB, Overlay test, Nflex, IDEAL-CT
– Rutting
• APA, Hamburg
– Other
• Cantabro - durability
• Volumetrics
• Binder grading Photo: Cox et al. (2017)
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PMD – Phase I
• Mix Design Shadowing
– Cracking test
• IDEAL-CT, IFIT/SCB, Overlay test, Nflex
– Rutting
• APA
– Other
• Cantabro – durability
• Volumetrics
• Binder grading
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High RAP Trials
• Focused on mixes with RAP ≥ 40%
• Mix Types
– Control
– Volumetric design + Performance testing
– Performance design
• Mix acceptance still based on volumetrics
– Performance will be evaluated
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High RAP Trials – Performance Testing
Test Procedure Specimens Criteria
APA rutting 8,000 passes
64ºC
120lb, 120psi
4 pills (APA Jr)
150 mm dia.
75 ± 2 mm ht.
7±0.5% air voids
Rutting ≤ 8.0mm
Cantabro 300 rotations
30-33 rot/min
3 pills
150 mm dia.
115 ± 5 mm ht.
Ndesign, report air voids
Mass loss ≤ 7.5%
IDEAL-CT Condition (25±1°C for 2±0.5 hr)
Contact load - 0.1kN at 0.05 kN/s
Load to failure - 50 mm/min
3 pills
150mm dia.
62 ± 2mm ht.
7±0.5% air voids
CTindex ≥ 70
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Future Considerations in PMD
• Acceptance protocols
• Aging (laboratory vs. in-service)
• Relationships between performance criteria
and service life
• Calibrating performance criteria to
mixture/pavement type (traffic level)
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Thank you!