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

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Presentation on theme: "NCHRP Projects 9-25 & 9-31: Findings Related to Surface Cracking FHWA Mixture ETG Washington, DC February 2003 Advanced Asphalt Technologies, LLC “Engineering."— Presentation transcript:

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  (% LS) (VTM)  (Agg. S.A.) R 2 = 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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