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

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 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
Semi Circular Bend (SCB)
Proposed AASHTO Test
Disk Shaped Compact Tension
ASTM D

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 Item DCT SCB Even Equipment needed x Cost of test setupx
Cost of test setup
Test time requirement
Ease of sample preparation
Repeatability of results
Loading mode ?
Loading rate
Lab vs. Field
Ability to test thin lifts in field
OVERALL CHOICE

22. DCT vs. SCB

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

24. Reproducibility

25. Equipment Cost Item Cost Loading fixtures $3,000
X‐Y Tables to facilitate coring and sawing
$1,500
CMOD Extensometer (Epsilon)
$1,400
Temperature‐Chamber
$20,000
Temperature modules and thermocouples
$400
PC for Data Acquisition
$1,000
Labview Based Interface Board
$700
Coring barrels (qty = 5)
$500
Labview Software for Data Acquisition
Labview Programming
Dual water cooled masonry saws
$10,000
Dual saw system for flat face and notching
$7,000
TOTAL
$50,000

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