obtaining mix performance with high rap and modified binders
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Obtaining Mix Performance with High RAP and Modified Binders
Tanya Nash, P.E.
Asphalt Testing Solutions & Engineering
Objectives• Review of “Performance Tests” being used
• Performance Components of Asphalt Mixtures
• Performance Mix Design
“Performance Tests”
• Additional tests beyond volumetric properties
• Intend to indicate a mix’s resistance to particular distresses (i.e. field performance)
• May or may not yield an engineering property that can be used in pavement design or analysis.
NCAT Balanced Mix Design Workshop
History of Mix Design
1890•Barber Asphalt Paving Company
•Asphalt cement 12 to 15% / Sand 70 to 83% / Pulverized carbonite of lime 5 to 15%
1905
•Clifford Richardson, New York Testing Company
•Surface sand mix: 100% passing No. 10, 15% passing No. 200, 9 to 14% asphalt
•Asphaltic concrete for lower layers, VMA terminology used, 2.2% more VMA than current day mixes or ~0.9% higher binder content
1920s
•Hubbard Field Method (Charles Hubbard and Frederick Field)
•Sand asphalt design
•30 blow, 6” diameter with compression test (performance) asphaltic concrete design (Modified HF Method)
1927
• Francis Hveem (Caltrans)
•Surface area factors used to determine binder content; Hveem stabilometer and cohesionmeter used
•Air voids not used initially, mixes generally drier relative to others, fatigue cracking an issue
1943
•Bruce Marshall, Mississippi Highway Department
•Refined Hubbard Field method, standard compaction energy with drop hammer
•Initially only used air voids and VFA, VMA added in 1962; stability and flow utilized
1993
•Superpave
•Level 1 (volumetric)
•Levels 2 and 3 (performance based but never implemented)
http://asphaltmagazine.com/history-of-asphalt-mix-design-in-north-america-part-2/
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Stability
Stability + Durability
Stability + Durability
25 Years Without the Promised Performance Test!
The Good Ol’ Days
Photo Courtesy of Florida Memory (1955) Marshall Stability Marshall FlowHubbard Field Stability
Hveem StabilometerHveem Cohesionmeter
Rutting & Moisture Susceptibility Tests
• Tensile Strength Ratio - AASHTO T 283
• Hamburg Wheel Tracking - AASHTO T 324
• Asphalt Pavement Analyzer – AASHTO T 340
Texas Overlay TestTEX-248-F
Bending Beam FatigueAASHTO T 321
Direct Tension Cyclic Fatigue, S-VECD
SCB- LTRC – Jc- IFIT - FI
IDEAL-CT, Nflex Factor
Texas Overlay Test
Superpave IDT- Energy Ratio Cantabro
IDT Creep Compliance
AASHTO T 322
TSRSTSCB at Low TempAASHTO TP 105
Disk Shaped Compact Tension (DCT)
Fatigue (Cyclic Loading)Top-Down Cracking
Low Temperature Cracking
What’s with all the testing?
What’s Really in Your Asphalt Mix?
Chemical
• Anti-Strips
• Warm Mix
• Stiffening / Softening Agents
Rejuvenators
• Crude Oil
• Flux
• Bio Oils
• Corn Oils
• Tall Oil
Recycled
• Vacuum Tower Asphalt Extender (VTAE)
• Ground Tire Rubber (GTR)
Polymers
• Elastomers (SBS)
• Plastimers(Elvaloy)
• Latex
• SBR
Mixture
• Fibers
• Lime
• GTR
• Pelletized Polymers
• RAP
• RAS
Grading system based on climate
PG 67-22
Materials – Asphalt Binder
PerformanceGrade
Average 7-daymax pavementdesign temp
Min pavementdesign temp
Asphalt Binder Additives
Polymers
Waxes, PPA, Warm Mix Additives…
SBSElvaloy® RET
Rejuvenators
Anti-Strips
Sulfur
Recycled Materials
Recycled Binder Characterization
Materials – Asphalt Binder
8
25
DSR
No Aging(Original)
RTFO(Short-Term)
PAV Aging(Long-Term)
Construction Rutting Fatigue Low Temperature Cracking
Performance Beyond PG
• Delta Tc – method for measuring the loss of relaxation properties of asphalt binders
• Ductility – Ability of a material to be stretched without breaking
• Glover-Rowe – simplified equation for the ductility estimated from DSR data
𝐺 − 𝑅 = 𝐺∗ (cos 𝛿) ×2
sin 𝛿@ 15°C and 0.005 rad/sec
Performance Beyond PG
• Cross-Over Temperature (Twc): binder transitions from a viscous material to an elastic material• lower the temperature the less prone the binder is to cracking
• Rheological Index (R-Value): log of the glassy modulus of the binder minus the log of the modulus where the phase angle is 45• Larger the R value, the more brittle and prone to cracking• NCHRP 9-59 uses BBR data to calculate
𝑅 =log(
𝑆
3000)
log(1−𝑚)
Recommended: 1.5 > R > 2.5
Important for the virgin binder and the blended binder
What about the mix?
Superpave Volumetrics
Performance Beyond Volumetrics
As a Contractor, how do I get there?
Step #1: Know what your agency wants
• Must meet Superpave Volumetrics AND performance
• Start with SP Volumetrics to determine optimum with performance
• Just get performance
As a Contractor, how do I get there?
Step #2: Know where you are from a company and mixture standpoint
• Understand the impact of BMD on asphalt binder demand, recycle
potential / availability
• Evaluate your readiness (e.g., capabilities / needs). Do you need to more
people, training, equipment?
• Establish baseline (test your mixes to see where you are at)
• Optimize mixes (performance + economics)
What’s after the baseline testing?
Remember, it’s still aggregate, asphalt, and air…
• Asphalt Content
• Gradation
• Higher / Lower additive dosage
Is it that simple?
Increasing Asphalt Content
• Reduce Gyrations?• ONLY if Gradation remains constant
Gyrations VMA, % Air Voids, %Volume of Effective
Asphalt (Vbe), %
Asphalt Content, %
75 15.31 4.0 11.31 5.72
100 15.40 4.0 11.40 5.74
125 15.22 4.0 11.22 5.78
Design gyration experiment of 9.5mm example from NAPA Back 2 Basics: Volumetric by Gerry Huber, Heritage Group
Increasing Asphalt Content
• Reduce Design Air Voids?• Add more asphalt to fill in the air voids… i.e. 3.0% air voids may
increase the binder content ~0.4%
• BUT VMA must be the same• Change gradation to keep the asphalt content the same
Increasing Asphalt Content
• Increase VMA?
YES!• 1.0% of VMA ~ 0.4% asphalt binder
• Total Asphalt Content and Effective Asphalt Content Increase
Effective Asphalt Content
• Specific Gravity (aggregate and mix) has the largest effect of on Binder Content
• Make sure the Gsb is correct• Negative absorption –
not OK.
NAPA Back 2 Basics: Volumetric by Gerry Huber, Heritage Group
NCHRP 9-58: Rejuvenator Dosage
NCHRP 9-58: Binder Blend Evaluation
NCHRP 9-58: Mixture Evaluation
As a Contractor, how do I get there?
Step #1: Characterize your material
Step #2: High RAP or Modified Binder / Mix or BOTH
Step #3: Baseline
Step #4: What’s available? Look at the economics
Step #5: Start balancing
First Steps
• Rutting: Hamburg / APA
• Cracking: IDEAL-CT
• Durability: Cantabro
Questions?
Tanya Nash, P.E.
tnash@ats.consulting
(904) 510-3072
Asphalt Testing Solutions & Engineering
7544 Philips Hwy
Jacksonville, Florida 32256
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