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Low Temperature Cracking

Low Temperature Cracking. Tim Clyne, MnDOT. Dec 7, 2011 MAAPT. Presentation Topics. Project History Phase I Major Findings Phase II Research Mixture LTC Specification The Road Ahead. Affects Ride Quality. We’re Making Progress. Initial Superpave. Current spec. Project History.

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Low Temperature Cracking

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  1. Low Temperature Cracking Tim Clyne, MnDOT Dec 7, 2011 MAAPT

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

  3. Affects Ride Quality

  4. We’re Making Progress Initial Superpave Current spec

  5. Project History

  6. Initial Project • Low Temperature Cracking of Asphalt Concrete Pavements (1999-2004) • Mihai Marasteanu, Xue Li, Timothy Clyne, Vaughan Voller, David Timm, David Newcomb • Introduced SCB test method • Developed two models • Crack spacing • Damage and crack propagation

  7. Phase I Field Performance • Low Temperature Cracking Performance at MnROAD • Brief for 2007 MnROAD Lessons Learned project • Tim Clyne, Ben Worel, Mihai Marasteanu • Evaluated field performance of ML and LVR cells

  8. LVR Superpave Cells • Investigation of the Low-Temperature Fracture Properties of Three MnROAD Asphalt Mixtures • University of Minnesota • Xinjun Li, Adam Zofka, Xue Li, Mihai Marasteanu, Timothy R. Clyne

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

  10. Pooled Fund Project Phase I • Investigation of Low Temperature Cracking in Asphalt Pavements National Pooled Fund Study 776 • 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%

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

  12. Indirect Tensile Test • Developed during SHRP program • In current MEPDG • Determines Creep Stiffness & Tensile Strength • Test protocol AASHTO T 322-03

  13. Creep & Strength Data

  14. Semi Circular Bend • Apply constant Crack Mouth Opening Displacement • Determines Fracture Energy & Fracture Toughness • Proposed AASHTO Test Method

  15. SCB Data

  16. Disk Shaped Compact Tension • Similar to SCB except for geometry and loading rate • Determines Fracture Energy • Test protocol ASTM D 7313-06

  17. DCT Data

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

  19. Phase I Major Findings

  20. Fracture Mechanics Approach

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

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

  23. Aggregate Type • Granite generally better than Limestone

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

  25. Binder Content • More asphalt = better performance

  26. Phase II Research

  27. Work Plan • Updated literature review • Test additional field samples • Various mix types, binder grades & modifiers, RAP • Develop LTC mix specification • Improved modeling capabilities • Model thermal cycling effects • Validate new mixture specification • Final Report

  28. Supplementary Data • Asphalt Mixture and Binder Fracture Testing for 2008 MnROAD Construction • University of Minnesota • Mihai Marasteanu, Ki Hoon Moon, Mugurel Turos • Tested 12 MnROAD mixtures and 9 binders, reported data • SCB, IDT, BBR, DTT, DENT • Porous, Novachip, 4.75 mm Superpave, WMA, Shingles

  29. DCT vs. SCB

  30. DCT vs. SCB

  31. DCT vs. SCB

  32. Equipment Cost

  33. Reproducibility

  34. Aging Plays a Role

  35. 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

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

  37. LTC Specification

  38. 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 > 400 J/m2 • Make adjustments if mix fails & retest

  39. Specification Limit

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

  41. 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 (proposed fall 2011) • Extend to other types of cracking • Fatigue, Top Down, Reflective

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

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