Performance Testing of Asphalt Pavements Specifying Low-Temperature Cracking Performance for Hot-Mix Asphalt

1. Performance Testing of Asphalt PavementsSpecifying Low-Temperature Cracking Performance for Hot-Mix Asphalt Tim Clyne, MnDOT January 22, 2012 TRB Workshop

2. Presentation Topics • Brief Project History • Phase I Major Findings • Phase II Research • Mixture LTC Specification • The Road Ahead

4. Affects Ride Quality

5. Project History

6. Initial Studies • Low Temperature Cracking of Asphalt Concrete Pavements • Introduced SCB test method • Developed models for crack spacing and propogation • Low Temperature Cracking Performance at MnROAD • Evaluated field performance of ML and LVR cells • Investigation of the Low-Temperature Fracture Properties of Three MnROAD Asphalt Mixtures • PG 58-28, 58-34, 58-40

7. Pooled Fund Project Phase I National TAP – August 2003

8. Pooled Fund Project Phase I • Investigation of Low Temperature Cracking in Asphalt Pavements National Pooled Fund Study TPF-5(080) • 16 Authors from 5 entities! • Large Laboratory Experiment • 10 Asphalt Binders • Neat and Modified, PG 58-40 to 64-22 • 2 Aggregate Sources • Limestone and Granite • 2 Air Void Levels • 4% and 7% • 2 Asphalt Contents • Optimum Design and + 0.5%

9. Pooled Fund Project Phase I • Field Samples • 13 pavement sections around region • Experimental Modeling

10. Laboratory Test Procedures • Indirect Tensile Test (IDT) • Test protocol AASHTO T 322-03 • Semi Circular Bend (SCB) • Proposed AASHTO Test • Disk Shaped Compact Tension • ASTM D 7313-06

11. Asphalt Binder Testing • Bending Beam Rheometer • Direct Tension • Double Edge Notched Tension • Dilatometric (Volume Change)

12. Phase I Major Findings

13. Fracture Mechanics Approach

14. Asphalt Mixture Testing • Binder gives a good start, but doesn’t tell whole story

15. Binder Grade • Modified vs. Unmodified • High temperature grade

16. Aggregate Type • Granite generally better than Limestone

17. Air Voids • Lower air voids = slightly better performance

18. Binder Content • More asphalt = better performance

19. Phase II Research

20. Objectives • Develop LTC mix specification • Test field additional field samples • Various mix types, binder grades & modifiers, RAP • Supplementary data from 12 MnROAD mixtures and 9 binders from 2008 • SCB, IDT, BBR, DTT, DENT • Porous, Novachip, 4.75 mm Superpave, WMA, Shingles • Improved modeling capabilities

21. DCT vs. SCB

22. DCT vs. SCB

23. DCT vs. SCB SCB = DCT if you remove creep!

24. Reproducibility

25. Equipment Cost

26. Phase II Major Findings • Conditioning / Aging • None > Long Term Lab = Field • Binder Modification • SBS > Elvaloy > PPA • RAP • No RAP > RAP = FRAP • Air Voids not significant • Test Temperature was significant

27. ILLI-TC Model • Modeling can provide: • True performance prediction (cracking vs. time) • Input for maintenance decisions • Insight for policy decisions

28. LTC Specification

29. Draft Mixture Specification • Prepare sample during mix design • Eventually perform on behind paver samples • Prepare specimens at 7% air voids • Long term condition per AASHTO R 30 • Perform 3 replicate tests at PGLT + 10°C • Average Gf > 350 J/m2 • Make adjustments if mix fails & retest

30. Specification Limit

31. Possible Mixture Adjustments • Binder grade • Reduce Low PG (-34 vs -28) • Different modifier or supplier • Aggregate source • Granite/taconite instead of limestone/gravel • Reduce RAP/RAS content • Aggregate gradation • Finer gradation • Increase binder content

32. What’s Next? • Use pilot spec on select projects in 2012 or 2013 • Implement in cooperation with Bituminous Office • HMA Performance Testing project – University of Minnesota Duluth • Phase I – Review of Literature & State Specifications • Phase II – Lab Testing & Field Validation (begin spring 2012) • Extend to other types of cracking • Fatigue, Top Down, Reflective

33. Thank You! • Tim Clyne • 651-366-5473 • tim.clyne@state.mn.us www.mndot.gov/mnroad