dct how it affects pavement mix design · dct –how it affects pavement mix design ... low...
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DCT – How it Affects Pavement
Mix Design
Eshan Dave, Chelsea Hanson, Chelsea Hoplin,
and Ben Helmer
59th Annual Asphalt Contractors’ Workshop
02/19/2015
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Outline
1. Low temperature cracking and fracture energy
2. Disk-shaped compact tension (DCT) test for
fracture energy
3. Low temperature cracking mix specifications
4. Current and future research
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Low Temperature Cracking (LTC) ProblemLTC is a major cause of pavement deterioration in regions with
severe winter climates
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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 and aggregate effects – voids, aggregate size and gradation
– Plant/field aging
– Structural effects of fracture process
Mix testing can provide:– Improved comparisons between cracking performance of asphalt
mixes
– Inputs for performance prediction models
– Input for maintenance decisions
– Insight for policy decisions
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Cracking of Asphalt Materials
5
Load
Load
CMOD
Crack
formation
CrackingDamage Zone
Onset of damage
δc
σt
Work, Wf
Lo
ad
Quasi-brittle fracture
Softening
Crack Mouth Opening Displacement (CMOD)
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Outline
1. Low temperature cracking and fracture energy
2. Disk-shaped compact tension (DCT) test for
fracture energy
3. Low temperature cracking mix specifications
4. Current and future research
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Disk-Shaped Compact Tension, DCT Test
ASTM D7313-13
Loading Rate:– Crack Mouth Opening Displacement
– CMOD = 1.0-mm/min
Measurements:– CMOD
– Load
7
P
P
CMOD, u
Wf
Crack Mouth Opening Displacement (CMOD), u
Lo
ad
, P
Quasi-brittle fracture
Softening(damage)
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Results for TH371 Sections
9
RPNorth Bound Crack
CountSouth Bound Crack
CountFracture Energy
[J/m2]
6 3 4 453.4417 12 8 356.18
21.5 10 57 330.59
0
50
100
150
200
250
300
350
400
450
500
RP 6 RP 17 RP 21.5
Frac
ture
En
erg
y [J
/m2]
Field Cores (TH371)RP6: Good performing section (2005 construction)RP17/21.5: Poor performing section (2004 construction)
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Field Cracking Performancevs. Fracture Energy
11
0
200
400
600
800
1000
0 10 20 30 40 50 60 70
Fra
ctu
re E
ne
rgy (
J/m
2)
TCTotal (%)
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8Pe
rce
nt
Cra
ck
ing
(M
nD
OT
)
Years in Service
RP 10
RP 5
182
326
0
50
100
150
200
250
300
350
400
450
500
550
Fra
ctu
re E
ne
rgy (
J/m
2)
RP 10 (PP)
RP 5 (GP)
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Effects of Mix Composition on Fracture Energy
12
0
200
400
600
800
1000
1200
PG 58-28 PG 64-28 PG 58-34 PG 70-34
Fra
ctu
re E
ne
rgy (
J/m
2)
0
100
200
300
400
500
4.3% 4.5% 4.7% 4.9% 5.1% 5.3% 5.5%
Fra
ctu
re E
ne
rgy (
J/m
2)
Asphalt Binder (%)
0
200
400
600
800
1000
1200
12.0% 14.0% 16.0% 18.0% 20.0%
Fra
ctu
re E
ne
rgy (
J/m
2)
VMA (%)
0
100
200
300
400
500
7.0 8.0 9.0 10.0 11.0
Fra
ctu
re E
ne
rgy (
J/m
2)
Adj. Asphalt Film Thickness (micron)
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Outline
1. Low temperature cracking and fracture energy
2. Disk-shaped compact tension (DCT) test for
fracture energy
3. Low temperature cracking mix specifications
4. Current and future research
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LTC Performance Specifications
Based on traffic levels
14
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
Marasteanu et al., 2012
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Refinement and Implementationof Specification
Implementation of
Performance-based
Specification (MnDOT)
Refinement Efforts (Spec. finalization,
conditioning process, training etc.)
Determine sensitivity of fracture energy to
thermal cracking performance
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DCT Spec. Implementation
DCT based specifications are currently being implemented:
– Minnesota DOT (discussed here)
– Wisconsin DOT (next presentation)
– Chicago DOT (ASTM version)
– Illinois Tollways (ASTM version)
16
ASTM D7313-13 MnDOT Modified WisDOT Modified
Specimen Prep Minor Differences
Test Equipment No Difference
Specimen
Conditioning: AgingN/A AASHTO R30 (oven aging)
Specimen
Conditioning:
Temperature
8 - 16 hr @ test temp.
± 0.2ºCDiscussed later
Initial Cond.: 8 - 16 hr @
-12ºC±5ºC
Final Cond.: 1.5±0.5 hr @
test temp.
Data Analysis No Difference
Test Temperature
Recommendation:
PGLT + 10ºC
No requirement
98% Reliability Low
Temperature + 10ºC
(Use LTPPBind 3.1 software)
10±0.5ºC warmer than
WisDOT plan specified lower
temperature grade.
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MnDOT DCT Specifications
“MnDOT Modified”
– Current version used by MnDOT
GOAL: Improve ease, practicality and repeatability of
test procedure
Several changes/additions to ASTM specification
Revisions made to temperature conditioning
of specimens:
– Specimens must reach test temperature in no faster than
0.75 hours, but within 1.5 hours.
– Specimens must stay in conditioning chamber for a minimum
of 2 hours before testing.
– All testing must be finished within 5 hours of initial placement
into conditioning chamber
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Temperature Conditioning and InterlabVariability Studies
18
Field sampled material (I-94)
Samples tested at MnDOT and UMD
Temperature conditioning: Room to Chamber is
comparable to 1/3 deg. C/minute
Interlab differences:
– Fracture Energy: 2.4 – 8.1%
– Peak Load: 0.7 – 4.6%
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Outline
1. Low temperature cracking and fracture energy
2. Disk-shaped compact tension (DCT) test for
fracture energy
3. Low temperature cracking mix specifications
4. Current and future research
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Projects
Variety of climates,
binders, construction
– D2 – TH 310, FDR +
Overlay, PG 58-34
– D3 – TH 371,
Reconstruct, PG 64-34
– Metro – TH 10, Mill &
Overlay, PG 64-28
– D6 – TH 56, SFDR +
Overlay, PG 58-34
– D6 – TH 69, Mill &
Overlay, PG 58-28
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334292 310
195
318
257
317
627
444
324
549 543
470
0
100
200
300
400
500
600
700F
rac
ture
En
erg
y (
J/m
2)
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334292 310
195
318
257
317
627
444
324
549 543
470
0
100
200
300
400
500
600
700F
rac
ture
En
erg
y (
J/m
2)
TH 56 – SPWEA340C, tested @ -24CNote production decrease relative to mix design;Adjustment made: 0.1% additional binder.
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334292 310
195
318
257
317
627
444
324
549 543
470
0
100
200
300
400
500
600
700F
rac
ture
En
erg
y (
J/m
2)
TH 310 – SPWEB340C, tested @ -30CNote low value in first mix design;Adjustment made: eliminate 20% RAP, stockpile feeds adjusted.
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334292 310
195
318
257
317
627
444
324
549 543
470
0
100
200
300
400
500
600
700F
rac
ture
En
erg
y (
J/m
2)
TH 10 – SPWEB440E, tested @ -24CNo adjustment made;Note drop in fracture energy at mix production.
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334292 310
195
318
257
317
627
444
324
549 543
470
0
100
200
300
400
500
600
700F
rac
ture
En
erg
y (
J/m
2)
TH 69 – SPWEA440F, tested @ -24CNo mix design data;Adjustment made: reduce RAP from 30% to 20%, stockpile feeds adjusted.
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334292 310
195
318
257
317
627
444
324
549 543
470
0
100
200
300
400
500
600
700F
rac
ture
En
erg
y (
J/m
2)
TH 371 – SPWEB340B, tested @ -18CNo adjustment required;Note drop in fracture energy at mix production;
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Summary
2 projects (TH10 and TH371) passed at mix design
– Both Level 4 designs (Higher amounts of crushed agg.)
– Both polymer modified
3 failed at mix design
– TH 69, 58-28, 30% RAP, 324 J/m2
Adj. 58-34, 20% RAP, 549 J/m2
– TH 56, 58-34, 20 % RAP, 292 J/m2
Adj. + 0.1% new AC, 310 J/m2
– TH 310, 58-34, 20% RAP, 257 J/m2
Adj. 58-34, 0% RAP, 317 J/m2
Old oil in mix design, 195 J/m2
Need to make sure that same materials are used for
mix design and production (esp. binder)
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• Training of lab staff
• Round robin (inter-laboratory) repeatability study
• Samples collected this fall, with testing to start this
spring
• Participating labs include AET, Braun, MnDOT,
and UMD
28
On-going Work
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• Study analyzing source of drop in fracture energy from mix design to production and placement
• Samples collected from 8 projects throughout the state
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On-going Work
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Future Efforts
• State Transportation Innovation Councils (STIC) project
• FHWA program through TERRA
• Review state of practice and current studies being
undertaken by neighboring states
• Performance reviews of pilot implementation sections
of 2013 and for samples from 2014 construction
season
• Database of DCT results
• Continued implementation efforts
• Additional pilot projects
• Training of lab staff
• Workshops and webinars
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Summary In light of newer asphalt technologies (high recycling,
WMA, additives) performance based specifications
are becoming necessary
– Low risk on agencies, high innovation from industry
Fracture energy has and is continuing to show high
potential as cracking performance indicator
Stay tuned:
– 2015: Improve breadth of DCT result
database
– 2016: Continue with pilot projects
– 2017: Goal of implementation
Plan to target wear courses
New and re-construction
Possibly on thick overlays
Stand-alone testing equipment
is available 31
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Thank you for your attention
Questions?
Acknowledgments:
– Bill Buttlar
– Dave Van Deusen
– Shongtao Dai
– Joe Voels
– Luke Johanneck
32
Sponsoring agencies for present work:US Department of Transportation (FHWA)
Minnesota Department of TransportationTERRA
Contact:Eshan V. [email protected]
Chelsea [email protected]
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Objective: Determine the allowable variability
in fracture energy for purposes of job specification
– Req. fracture energy = 400 J/m2 (if actual is
375 J/m2 is it too low?)
Approach:
– Simulate performance of various fracture energies
using IlliTC and different combinations of:
Minnesota climates
Asphalt mixtures
Pavement structures
Use of IlliTC to Determine Sensitivity of Thermal Cracking to Fracture Energy
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Simulation Variables
35
Asphalt Mix PG28R PG34R PG34
MnROAD Cell Cell 21 Cell 22 Cell 35
Virgin Binder
GradePG 58-28 PG 58-34 PG 58-34
Total Percent AC 5.2% 5.2% 5.6%
Recycled Binder as
Percent of Total AC28% 28% 0%
Amount of RAP 30% 30% 0%
Fracture Energy (J/m2)
Pavement Thickness (in.)
Climate
Asphalt Mix PG28R
Cold
4
300 350 375 400 425 450
6 8
Intermediate Warm
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Results from Sensitivity Study
Variation of fracture energy by 25 J/m2 might be
sufficient in changing the thermal cracking performance
of the pavement
36
Asphalt Mix PG28R PG28R PG34R PG34
Climate Warm Case-1 Warm Case-2 Intermediate Cold
Pavement Thickness (cm) 10 15 20 15
Fracture Energies (J/m2) Corresponding to Thermal Cracking Performance Levels
No Damage (ND) No data No data No data ≥425
Damaged (D) 450 425-450 375-450 300-375
Cracked (C) ≤425 ≤400 ≤350 No data
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MnDOT 2013 Implementation Project
Contractor provide samples at mix design
– TSR pucks, 7% AV, +/- 0.5%
UMD perform DCT tests
– If mix passes, approve for paving
Passing value of Gf > 400 J/m2
If mix fails, adjust mix & try again
– MnDOT paid for difference in
cost (D-I funds)
– Adjusted mix was used for paving
a section of project
Testing is also conducted on
production mixes
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Possible Mixture Adjustments
Binder grade
– Reduce low PG (-34 vs -28)
Different modifier or supplier
Aggregate source and crushing
– Granite/taconite instead of
limestone
Aggregate Gradation
– Finer gradation
– Increase binder content
38