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