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LOW TEMPERATURE CRACKING
Tim Clyne, MnDOTDec 7, 2011MAAPT
Presentation Topics
Project History Phase I Major Findings Phase II Research Mixture LTC Specification The Road Ahead
Affects Ride Quality
We’re Making Progress
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Med
ian
No
. of T
ran
s. C
rack
s p
er 3
05 m
(p
er 1
000
ft.)
BAB Age, years
PG XX-34 Avg.
1971 to 1980
1981 to 1990
1991 to 1994
1995 to 1999
Current specCurrent spec
Initial SuperpaveInitial Superpave
Project History
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
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
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
Pooled Fund Project Phase I
National TAP – August 2003
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%
Pooled Fund Project Phase I
Field Samples 13 pavement sections around region
Experimental Modeling
Indirect Tensile Test
Developed during SHRP program
In current MEPDG Determines Creep Stiffness &
Tensile Strength Test protocol AASHTO T 322-
03
Creep & Strength Data
Semi Circular Bend
Apply constant Crack Mouth Opening Displacement
Determines Fracture Energy & Fracture Toughness
Proposed AASHTO Test Method
SCB Data
Disk Shaped Compact Tension
Similar to SCB except for geometry and loading rate
Determines Fracture Energy Test protocol ASTM D 7313-06
DCT Data
Asphalt Binder Testing
Bending Beam Rheometer Direct Tension Double Edge Notched Tension Dilatometric (Volume Change)
Phase I Major Findings
Fracture Mechanics Approach
Asphalt Mixture Testing
Binder gives a good start, but doesn’t tell whole story
Binder Grade
Modified vs. Unmodified High temperature grade
Aggregate Type
Granite generally better than Limestone
Air Voids
Lower air voids = slightly better performance
Binder Content
More asphalt = better performance
Phase II Research
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
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
DCT vs. SCB
Item DCT SCB EvenEquipment
needed x
Cost of test setup
x
Test time requirement
x
Ease of sample
preparation x
Repeatability of results
x
Loading mode ?Loading rate ?Lab vs. Field x Ability to test
thin lifts in field
x
OVERALL CHOICE
DCT vs. SCB
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21
22
33
34
35
77
200
300
400
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800
200 300 400 500 600 700 800
SC
B [J
/m2 ]
DCT [J/m2]
DCT vs SCB for 4% void specimens
PGLT+10C
Pearson's r = 0.41
2021
22
33
34
35
77
200
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SC
B [J
/m2 ]
DCT [J/m2]
DCT vs SCB 4% void specimens
PGLT
Pearson's r = 0.32
DCT vs. SCB
Equipment Cost
Item CostLoading 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 $1,500 Labview Programming $3,000 Dual water cooled masonry saws $10,000 Dual saw system for flat face and notching $7,000 TOTAL $50,000
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20-7-18 21-4-18 21-4-28 22-7-24 22-7-34
Gf[J
/m2 ]
Reproducibilty of DCT test
UIUC UMN
Reproducibility
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1000
20 21 22 33 34 35 77 WIS NY
Gf[J
/m2 ]
DCT Fracture Energy Conditioned and Field vs., Non-Conditioned
Non-ConditionedConditionedField
Aging Plays a Role
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
ILLI-TC Model
Modeling can provide: True performance
prediction (cracking vs. time)
Input for maintenance decisions
Insight for policy decisions
LTC Specification
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
Specification Limit
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
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
