Eshan Dave Department of Civil Engineering University …ncaupg/Activities/2013... · Eshan V....
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Eshan V. Dave, University of Minnesota Duluth Eshan Dave Department of Civil Engineering University of Minnesota Duluth NCAUPG Technical Conference, St. Louis MO 01/24/2013
Transcript of Eshan Dave Department of Civil Engineering University …ncaupg/Activities/2013... · Eshan V....
Eshan V. Dave, University of Minnesota Duluth
Eshan Dave Department of Civil Engineering University of Minnesota Duluth
NCAUPG Technical Conference, St. Louis MO
01/24/2013
Eshan V. Dave, University of Minnesota Duluth
Outline
1. Low temperature cracking and fracture energy
2. Fracture energy tests
3. Effectiveness of fracture energy as low temperature cracking performance predictor
4. Low temperature cracking mix specifications
5. Current and future research
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Eshan V. Dave, University of Minnesota Duluth
Low Temperature Cracking (LTC) Problem LTC is a major cause of pavement deterioration in regions with
severe winter climates
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Eshan V. Dave, University of Minnesota Duluth
Mechanism of Thermal Cracking
SUPERPAVE: Binder properties at low-temperatures are used as the main
criteria to address thermal cracking
Asphalt pavement contraction during cooling induces tensile thermal stresses
Thermal stresses are greatest at
critical low temperatures or very fast cooling rates
Thermally induced stresses well in
excess of material strength result in onset of thermal cracking
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Eshan V. Dave, University of Minnesota Duluth
Why do we need specify LTC performance of asphalt mix?
Binder is important, but does not completely control material behavior: – Aggregate/mastic effects on mixture creep/fracture properties – Effects of RAP, RAS, WMA, and other additives – Mixture volumetrics – voids, aggregate structure – Plant/field aging – Structural effects of fracture process
Mix testing can provide:
– Improved comparisons between LTC performance of asphalt mixes – Inputs for performance prediction models – Input for maintenance decisions – Insight for policy decisions
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Eshan V. Dave, University of Minnesota Duluth
Cracking of Asphalt Materials
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Cracking Damage Zone
Crack formation
Onset of damage
δc
σt
Gf
Crack Mouth Opening Displacement (CMOD)
Load
Quasi-brittle fracture
Softening
Load
Load
CMOD
Eshan V. Dave, University of Minnesota Duluth
Fracture Energy, Gf
Sf
Crack Mouth Opening Displacement (CMOD), u
Load
, P
Quasi-brittle fracture
Softening (damage)
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P
P
CMOD, u
Fracture Energy, Gf: Energy required to create unit fracture surface Fracture work: Area under Load-Displacement curve Gf = Fracture Work Fracture Area
Eshan V. Dave, University of Minnesota Duluth
Tensile Strength-Fracture Energy Comparison
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103
104
100
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Fracture Energy (J/m2)
Indi
rect
Ten
sile
Stre
ngth
(MP
a)
Data from Iowa ProjectData from Other Projects
More Ductile (Compliant)
• Fracture energy appears to disseminate between mixes better than IDT strength
• Especially prevalent with modified binders
• Data supports need for true fracture mechanics approach
8 Source: Wagoner and Buttlar, 2007
Eshan V. Dave, University of Minnesota Duluth
-40 -30 -20 -10 0 100
500
1000
1500
2000
2500
Temperature, T (oC)
Frac
ture
Ene
rgy,
Gf (J
/m2 )
PG58-28PG64-22
Gf=627.1Exp0.041*T
r2 = 0.564
Gf =1299.3Exp0.047*T
r2 = 0.564r2 = 0.507
Test Temperature and Fracture Energy
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In terms of fracture energy the temperature spread is consistently greater than 6ºC
Eshan V. Dave, University of Minnesota Duluth
Outline
1. Low temperature cracking and fracture energy
2. Fracture energy tests
3. Effectiveness of fracture energy as low temperature cracking performance predictor
4. Low temperature cracking mix specifications
5. Current and future research
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Eshan V. Dave, University of Minnesota Duluth
Disk-Shaped Compact Tension (DCT ) Test ASTM D7313-08 Loading Rate:
– Crack Mouth Opening Displacement – CMOD Rate = 1.0 mm/min
Measurements: – CMOD – Load
Wagoner, Buttlar and Paulino, Experimental Mechanics, 45:270, 2005. ASTM D7313: Standard Test Method for Determining Fracture Energy of Asphalt-Aggregate Mixtures Using the Disk-Shaped Compact Tension Geometry (2008)
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P
P
CMOD, u
Eshan V. Dave, University of Minnesota Duluth
Semi-circular Bend, SC(B) Test Test Control: Constant CMOD Measurements:
– CMOD – Load
Li and Marasteanu, J. Asphalt Pav. Tech., 73:401-426, 2004.
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Eshan V. Dave, University of Minnesota Duluth
Outline
1. Low temperature cracking and fracture energy
2. Fracture energy tests
3. Effectiveness of fracture energy as low temperature cracking performance predictor
4. Low temperature cracking mix specifications
5. Current and future research
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Eshan V. Dave, University of Minnesota Duluth
Low Temperature Cracking Pooled Fund Study
Investigation of Low Temperature Cracking in Asphalt Pavements – TPF-5(132) – Phase II
Participating States: – Minnesota (Lead State) – Connecticut – Iowa – New York – North Dakota – Wisconsin
LTC performance specifications for asphalt mixes Final Report:
http://www.pooledfund.org/Document/Download/3690
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Eshan V. Dave, University of Minnesota Duluth
Results from Phase-I of Pooled Fund Study
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Eshan V. Dave, University of Minnesota Duluth
Results for Phase-II of Pooled Fund Study
Results for validation sections:
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Eshan V. Dave, University of Minnesota Duluth
Results from other Minnesota Mixes
Field Cores (TH371) – RP6: Good performing section (2005 construction) – RP17/21.5: Poor performing section (2004 construction)
Plant Produced Mixes (TH9 and TH70)
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TH9 TH70 Gradation coarse fine Design Traffic Level 1 – 3 Million ESALs Design Gyrations 60 Binder PG58-34 RAP [%] 20 20 Total AC [%] 4.0 5.2 New AC Ratio [%] 73 76
Eshan V. Dave, University of Minnesota Duluth
Results for TH371 Sections
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RP North Bound Crack Count
South Bound Crack Count
Fracture Energy [J/m2]
Wear 6 3 4 453.44
17 12 8 356.18 21.5 10 57 330.59
050
100150200250300350400450500
RP 6 RP 17 RP 21.5
Frac
ture
Ene
rgy
[J/m
2 ]
Eshan V. Dave, University of Minnesota Duluth
TH371 Recovered Binder Grade and Fracture Energy
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250
300
350
400
450
500
-40-35-30-25-20
DC
T Fr
actu
re E
nerg
y (J
/m2)
Low Temperature Grade of Recovered Binder (ºC)
Eshan V. Dave, University of Minnesota Duluth
DCT Testing: TH9 & TH70 Samples
• TH9 Coarse Gradation – Total AC = 4.0%
• TH70 Fine Gradation • Total AC = 5.2%
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100
200
300
400
500
600
700
800
TH9 TH70
Frac
ture
Ener
gy [J
/m2 ]
Tested at -24CTested at -18C
Eshan V. Dave, University of Minnesota Duluth
Outline
1. Low temperature cracking and fracture energy
2. Fracture energy tests
3. Effectiveness of fracture energy as low temperature cracking performance predictor
4. Low temperature cracking mix specifications
5. Current and future research
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Eshan V. Dave, University of Minnesota Duluth
LTC Performance Specifications
Based on traffic levels Limits based on:
– Fracture energy test @ 10ºC above 98% reliability Superpave Low Temperature PG (PGLT)
– Low temperature cracking performance model (IlliTC)
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Limits
Project Criticality / Traffic Level High
(> 30M ESALs) Medium
(10 – 30M ESALs) Low
(< 10M ESALs) DCT Fracture Energy
(J/m2) 690 460 400
IlliTC Cracking Prediction (m/km) < 4 < 64 Not required
Eshan V. Dave, University of Minnesota Duluth
IlliTC: Low Temperature Cracking Model
Self contained user-friendly software for conducting low temperature cracking simulations
Simulations are based on the fracture mechanics principles
Accounts for pavement structure, non uniform temperature profiles, and mix viscoelastic and fracture properties
Has intuitive graphical user interface
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Eshan V. Dave, University of Minnesota Duluth
Overview
1. Low temperature cracking and mix tests
2. Fracture energy tests
3. Effectiveness of fracture energy as low temperature cracking performance predictor
4. Low temperature cracking mix specifications
5. Current and future research
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Eshan V. Dave, University of Minnesota Duluth
MnDOT DCT Low Temperature Fracture Testing Pilot Project
Develop DCT specimen fabrication and testing capabilities at MnDOT
Between 3 – 5 pavement projects will be used for pilot implementation/trial of LTC mix specifications
Lab testing will be conducted during mix design and production
Testing will be conducted during 2013 construction season
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Eshan V. Dave, University of Minnesota Duluth
MnDOT Study on Asphalt Performance Test
Phase-I: Synthesis of Asphalt Performance Tests – Several cracking tests are available
Two most promising tests:
– Disk Shaped Compact Tension Fracture Test (DCT)
– Dry Indirect Tensile Strength (ITS) from TSR
Phase-II: Currently Underway – Task-1: Analysis of Laboratory Test and Field Performance Data – Task-2: Laboratory Testing and Field Performance Evaluation of
Field Sections DCT versus Field Performance
– Task-3: Analysis of Lab Testing and Field Performance Data Preliminary Performance Specification
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Eshan V. Dave, University of Minnesota Duluth
Summary
Low temperature cracking performance of pavements show very good correlation to mix fracture energies
Fracture energy based low temperature cracking mix specifications have been developed through Pooled Fund Study
The fracture energy based specifications are supplemented with thermal cracking prediction model (IlliTC) for high traffic roadways
Currently studies are underway to: – Conduct pilot implementation of fracture energy based
specifications – Further validate the fracture energy recommendations and
develop performance based specifications
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Eshan V. Dave, University of Minnesota Duluth
Thank you for your attention
Questions? Contributors:
– Bill Buttlar – Tim Clyne – Mihai Marasteanu – Luke Johanneck
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Acknowledgements: US Department of Transportation (FHWA) Minnesota Department of Transportation Connecticut Department of Transportation Iowa Department of Transportation North Dakota Department of Transportation New York State Department of Transportation Wisconsin Department of Transportation Nextrans Research Center
Contact: Eshan V. Dave [email protected]
