Embed Size (px)
Citation preview
PERFORMANCE TESTING OF ASPHALT
PAVEMENTS
SPECIFYING LOW-TEMPERATURE
CRACKING PERFORMANCE FOR HOT-MIX ASPHALT
Tim Clyne, MnDOTJanuary 22,
2012TRB Workshop
Presentation Topics
Brief Project History Phase I Major Findings Phase II Research Mixture LTC Specification The Road Ahead
Affects Ride Quality
Project History
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
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 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%
Pooled Fund Project Phase I
Field Samples 13 pavement sections around region
Experimental Modeling
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
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
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
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
20
21
22
33
34
35
77
200
300
400
500
600
700
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
DCT vs. SCB
SCB = DCT if you remove creep!
0
100
200
300
400
500
600
700
800
900
1000
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
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
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 > 350 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/gravel 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 (begin
spring 2012) Extend to other types of cracking
Fatigue, Top Down, Reflective
