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