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NCHRP Projects 9-25 & 9-31: Findings Related to Surface Cracking

NCHRP Projects 9-25 & 9-31: Findings Related to Surface Cracking. FHWA Mixture ETG Washington, DC February 2003. Advanced Asphalt Technologies, LLC. “Engineering Services for the Asphalt Industry”. Fatigue Testing and Analysis. Continuum damage approach

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NCHRP Projects 9-25 & 9-31: Findings Related to Surface Cracking

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  1. NCHRP Projects 9-25 & 9-31:Findings Related to Surface Cracking FHWA Mixture ETG Washington, DC February 2003 Advanced Asphalt Technologies, LLC “Engineering Services for the Asphalt Industry”

  2. Fatigue Testing and Analysis • Continuum damage approach • Normalization to reduce or eliminate effect of mixture stiffness • Produces single continuum damage fatigue constant “C**2” characteristic of intrinsic fatigue resistance • Independent of stress- vs. strain-control

  3. Effective Binder Content

  4. WesTrack Cracking Vs. Vbe

  5. Mixture Stiffness • Increased mixture stiffness decreases strains • Decreased strains increases fatigue life • HOWEVER…

  6. Binder Viscosity & Healing • Healing more rapid with low viscosity binders • Generally, fatigue resistance will decrease with increased high-temperature binder grade

  7. Healing and Binder Viscosity(after Little et al., 1999)

  8. Age Hardening |G*|aged / |G*|unaged = 1.76  0.0037(% LS) + 0.028 (VTM)  0.068 (Agg. S.A.) R2 = 74 %

  9. Age Hardening:Aggregate Type and Permeability • Limestone fines appears to significantly retard age hardening • Age-hardening also decreases with decreasing permeability • Increasing aggregate surface area • Decreasing air voids

  10. Summary: Factors Affecting Fatigue Cracking • Effective binder content • Structural stiffness • Mixture stiffness • Binder viscosity & healing • Mixture age hardening

  11. Ways to Increase Fatigue Life • Increase binder content • Decrease binder viscosity • Increase pavement thickness • Use limestone/hydrated lime fines and/or filler

  12. Controlling Rut Resistance • Rut resistance a function of • Binder grade • N-design • VMA relative to aggregate fineness • To maintain rut resistance with increased binder, increase proportion of fines/mineral filler

  13. Mix Resistivity

  14. Recommendations • Use 9.5 and 12.5-mm mixtures for wearing courses • Increase binder 0.5 % by weight • Maintain filler/binder ratio • Avoid unnecessary grade bumping • Use limestone/hydrated lime fines and mineral filler

  15. What Can 0.5 % Change in Binder Content Do?

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