complete testing suite for hma performance...
TRANSCRIPT
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Complete Testing Suite for HMA Performance
Prediction
Presenter: Imad L. Al-Qadi, PhD, PE, Dist.M.ASCE
H. Ozer, P. Singhvi, J. Rivera, A. El Khatib, M. Mueller,
and J. Trepanier,
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Loaded Flexible Pavement
Aggregate Base Deflection
Free Water
Wedge
Hydrostatic
Pressure
Subgrade Deflection
Direction of Travel
2
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Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Source: Nunn and Ferne (2001)
Pavement DistressesHeavy traffic
Segregation due to
paver operation
Aging and thermal loads
3
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Rutting/ Cracking in HMA
4
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Flexible Pavement System
Long-Lasting
Pavement
5
Materials
Pavement
StructureSustainability
Material Characterization
Asphalt concreteGranular Materials
Recycled Material
RAP, RAS, REOB
Rolling ResistanceRoughness, Texture, Def.,
Heat Exchange
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Contribution of Asphalt Binder• An analysis of over 1000 mixes shows
increased energy with increased binder %
Binder (40-91%)
Other Materials
Transportation
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Contribution of Asphalt Binder• An analysis of over 1000 mixes shows
increased energy with increased binder %
Binder (40-91%)
Other Materials
Transportation
Recycled Asphalt Shingles
Recycled Asphalt Pavement
Asphalt Binder Replacement (ABR)
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0.7
0.8
0.9
1.0
1.1
1.2
1.3
0 10 20 30 40 50 60
Rela
tive E
nerg
y &
GW
P
%ABR
Energy
GHG
Environmental Savings from ABR
20% Energy
Savings
22% CO2
Savings
60% ABR
MIX:
SMA
mix
SMA
mix
Virgin
mix
Yang et al. (2014). Environmental impacts from producing asphalt mixtures with varying degrees of recycled asphalt materials.
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Challenges with RAP/RAS (ABR)
• Fatigue cracking issue: stiffer mixes with high ABR may exhibit early fatigue cracking
• Thermal/Block cracking issue: Stiffer mixes have reduced relaxation potential
• Shingle asphalt is air blown to harden asphalt (PG 112+02) then additional aging on the roofs
• RAP AC can be hard or soft – depends on project(s) milled
• Counteracting binder selection of virgin binder becomes arbitrary
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Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Superpave™
-40°C -20°C 20°C 40°C
Low Temperature
CrackingFatigue/Block/Other
Forms of Cracking
Permanent
Deformation
Volumetrics Rut Test Cracking Test
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Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Pavement Cracking
• Traffic loading, temperature, AC material properties all play a role VERY COMPLEX
• We can’t afford running a battery of tests to simulate these conditions SUCH TESTS DO NOT EVEN EXIST
• We need a simple, affordable (money AND time), and meaningful test as a best approximate to overall cracking related damage THERMAL, FATIGUE, BLOCK,…
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IL-SCB Test• Modified SCB fracture test
conducted at 25˚C
• LVDT control load rate @ 50 mm/min
• Parameters calculated:• Fracture energy (Gf)
• Peak load (Pmax) & corresponding displacement (uo)
• Critical displacement (u1)
• Slope at inflection point (m)
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
SCB Simulations
• Perform numerical simulations of SCB test with bulk characteristic from complex modulus tests
10
100
1000
10000
1.E-06 1.E-04 1.E-02 1.E+00 1.E+02 1.E+04
E*,
ksi
Loading Frequency, Hz
54 38 21 4 -10 Master Curve
Duplicate Nodes
CZ Element
Bulk Properties from
Complex Modulus Test
Fracture Properties
Using Cohesive Zone
Model
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Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
FEM Results
• FEM simulations of SMA with 25% ABR
0
500
1000
1500
2000
2500
3000
3500
4000
0 1 2 3 4
Load
CMOD (mm)
N80 - 25 T = 25 C
Experimental - 6.25mm/minNumerical - 6.25mm/minExperimental - 50mm/minNumerical - 50mm/min
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DIC: Full Field Measurements
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FPZ (Temperature Effect)eyy
25°C
-12°C
0%RAS (64-22)
7%RAS (64-22)
5mm
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Fracture Energy Ambiguities
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Development of Flexibility Index
Flexibility Index (FI) = 𝑮𝑭 ×𝟏
𝒂𝒃𝒔(𝒎)
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Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Applicability and Seamless Implementation
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Applicability and Implementation
• Can use AASHTO T-283 (TSR) equipment
• Two low-costprototypes were already manufactured (9-18K)
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Conditioning Method
• Water bath conditioning allows the use of AASHTO T-283 (TSR) set up
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IL-SCB Tool
• A software tool was developed to process IL-SCB results
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Provide a Significant and Meaningful Spread in Test Output
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Case Study: High ABR Mixes
• Goal: Identify a difference in the performance of:
Mix ABR Binder Constant
Properties
Expected
Behavior
L4 0% 64-22 AC (%): 6
VMA (%):
15.3
Increment
in ABR
Decreases
Toughness
L7 20% 58-28
L9 30% 58-28
L10 60% 52-34
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Low Temperature SCB (-12ºC):
0
0.01
0.02
200 400 600 800 1000
Pro
babili
ty D
ensity
Fracture Energy (J/m2)
L4
L7
SCB (-12ºC, 1 mm/min, CMOD Control)
ABR
0% vs 20%
Overlap:
43%
μ = 742 σ = 57
μ = 795 σ = 22
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Low Temperature SCB (-12ºC):
0
0.01
0.02
200 400 600 800 1000
Pro
ba
bili
ty D
en
sity
Fracture Energy (J/m2)
L7
L9
SCB (-12ºC, 1 mm/min, CMOD Control)
ABR
20% vs 30%
Overlap:
11%
μ = 795 σ = 22μ = 677
σ = 55
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Low Temperature SCB (-12ºC):
0
0.01
0.02
200 400 600 800 1000
Pro
babili
ty D
ensity
Fracture Energy (J/m2)
L4
L7
L9
L10
SCB (-12ºC, 1 mm/min, CMOD Control)
ABR
30% vs 60%
Overlap:
58%
μ = 677 σ = 55
μ = 635 σ = 130
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Low Temperature SCB:
• High Repeatability:
• ~ 9% COV
• Low
Discrimination:
• 40% Overlap
30 %
40%
Normal Distribution Overlap:
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
0
0.002
0.004
0.006
0.008
0.01
700 1200 1700 2200
Pro
ba
bili
ty D
en
sity
Fracture Energy (J/m2)
L4
L7
SCB (25ºC, 50 mm/min)
Intermediate Temperature SCB (25 ºC):
ABR
0% vs 20%
Overlap:
3%
μ = 1622 σ = 51
μ = 1895σ = 73
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
0
0.002
0.004
0.006
0.008
0.01
700 1200 1700 2200
Pro
ba
bili
ty D
en
sity
Fracture Energy (J/m2)
L7
L9
SCB (25ºC, 50 mm/min)
Intermediate Temperature SCB (25 ºC):
ABR
20% vs 30%
Overlap:
37%
μ = 1622 σ = 51
μ = 1703 σ = 174
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
0
0.002
0.004
0.006
0.008
0.01
700 1200 1700 2200
Pro
ba
bili
ty D
en
sity
Fracture Energy (J/m2)
L4
L7
L9
L10
SCB (25ºC, 50 mm/min)
Intermediate Temperature SCB (25 ºC):
ABR
30% vs 60%
Overlap:
21%
μ = 1280 σ = 164
μ = 1703 σ = 174
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
30 %
40%
Intermediate Temperature SCB:
• Intermediate
Repeatability:
• ~ 10% COV
• Intermediate
Discrimination:
• ~ 25%
Overlap
Normal Distribution Overlap:
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Flexibility Index SCB (25 ºC):
0
0.3
0.6
0.9
1.2
1.5
0 5 10 15 20
Pro
babili
ty D
istr
ibution
Flexibility Index
L4
L7
L9
L10
SCB (25ºC, 50 mm/min)
Overlaps:
< 3%
Increase in ABR = Reduction in FI
60% 30% 20% 0%
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
30 %
40%
Flexibility Index SCB (25 ºC):
• Reduced
Repeatability:
• ~ 15% COV
• High
Discrimination:
• ~ 3% Overlap
Normal Distribution Overlap:
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Correlation to FieldPerformance
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Accelerated Loading Facility• Simulates truck traffic with controlled loading and pavement
temperatures.
• Up to 35,000 cycles can be applied per week.
• Wheel load can be varied from 33 kN (7,500 lb) representing a light
truck to 84 kN (19,000 lb) simulating a heavy axle.
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Lane Properties
ABR Group Lane WMA Binder Grade
Control 1 - PG64-22
20%
(w/ RAP)
9 Water PG64-22
4 Chemical PG64-22
40% (RAP)
8 - PG58-28
11 Chemical PG58-28
5 - PG64-22
20%
(w/ RAS)
7 - PG58-28
3 - PG64-22
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IL-SCB vs. Fatigue Cracking
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Field Cores
• Field cores were obtained from nine IDOT districts
• Flexibility index values were compared to field performance data obtained from districts
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Field Correlation (D1)District 1
Section #Field Perf. FI
Thickness
(mm)
5 Bad 1.3 40
10 Bad 1.4 41
4 Bad 1.8 41
7 Good 2.3 38
6 Bad 2.9 38
2 Bad 3.1 38
11 Good 3.4 26
12 Bad 3.9 38
3 Good 4.9 41
1 Good 5.0 37
8 Good 6.0 25
13 Bad 10.4 41
9 Good 10.9 26
Increasing
FI
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Effect of Construction Year
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Balanced Mix
0 5 10 15 20 25
Fle
xib
ility
In
de
x
Rut Depth (mm) @ Maximum Allowable Passes
SOFT & FLEXIBLE
UnstableStiff & Brittle
Stiff & FLEXIBLE
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Balanced Mix
0 5 10 15 20 25
Fle
xib
ility
In
de
x
Rut Depth (mm) @ Maximum Allowable Passes
SOFT & FLEXIBLE
UnstableStiff & Brittle
Stiff & FLEXIBLE
High
Performance
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Final Remarks• Asphalt mixture brittleness can result from
mixture volumetrics as well as adding recycled materials (RAP and RAS)
• Low temperature fracture tests could not distinguish between AC mixes
• IL-SCB test is a practical, affordable, and reliable test to distinguish between mixes’ cracking resistance
• The method is supported by extensive lab and field testing, theoretical, and numerical methods, and DIC technique
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Findings and Remarks
• IL-SCB test method and the proposed Flexibility Index have successfully screened hundreds of AC mixes for changes in brittleness
• Implementation of a balanced mix design and field performance validation is underway• Simple interaction plots combining Hamburg and IL-
SCB tests
• A life-cycle approach is needed to assess sustainability impact of recycled materials• Pavement performance and traffic volumes are critical
“Where Excellence and Transportation Meet”
Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
Acknowledgements
• ICT R27-128 Project Technical Review Panel
• Undergrad and graduate students involved
• ICT research engineers
ICT.illinois.edu
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Illinois Center for TransportationUniversity of Illinois at Urbana Champaign
HMA Testing “Book Ends”
HMA
HARD SOFT
Courtesy of David Lippert