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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
1
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
2
Low Temperature Cracking (LTC) ProblemLTC is a major cause of pavement deterioration in regions with
severe winter climates
3
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
4
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)
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
6
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)
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)
Field Cracking Performancevs. Fracture Energy
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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)
Effects of Mix Composition on Fracture Energy
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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)
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
13
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
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)
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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.
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%
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
19
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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21
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)
22
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.
25
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;
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
• Study analyzing source of drop in fracture energy from mix design to production and placement
• Samples collected from 8 projects throughout the state
29
On-going Work
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
30
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
Thank you for your attention
Questions?
Acknowledgments:
– Bill Buttlar
– Dave Van Deusen
– Shongtao Dai
– Joe Voels
– Luke Johanneck
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Sponsoring agencies for present work:US Department of Transportation (FHWA)
Minnesota Department of TransportationTERRA
Contact:Eshan V. [email protected]
Chelsea [email protected]
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
34
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
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
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
37
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