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Characterization of Damage Resistance to Rutting Using IPAS2 Software
Pouya Teymourpour, Hussain Bahia
ARC Deliverables/Products Presentation and Workshop
TRB 2015, Thursday, January 15, 2015Marriott Marquis, Washington DC.
Work completed with the generous help of
Dr. Nima Roohi Sefidmazgi
Dr. Raul Velasquez
Dr. Aaron Coenen
Funding supported by Federal Highway Administration (FHWA)
Acknowledgements
2
Outline• Overview
• Background– Aggregate structure role in Asphalt Concrete (AC) performance
– Imaging methods in AC characterization
• iPas2
• Internal structure analysis– Aggregate structure and rutting performance
– Factors affecting aggregate structure Gradation
Binder rheology
Compaction conditions on
• Conclusions and future work
Aggregate structure role in AC performance
•Rutting mechanisms:– Densification ( V 0
– Shearing ( V 0
•Current mix design procedures: target density
Depending on Aggregate interlock
Flow Number at Equal Density
SampleStress (kPa)
= 1034% AV
Coarse Mix 210 7Fine Mix 400 7
Almost 100% difference
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Image analysis of AC:Background
•Yue et al. 1995: Primary indices, major and minor axis, orientation
•Masad et al. 1998: Efficiency of 2D analysis, concept of anisotropy (
•Masad et al. 1999: Introduced X-ray computed tomography, initial method of contact characterization
•Tashman et al. 2001, 2007: Characterized asphalt mixtures based on air void distribution, aggregate orientation, segregation
•Zelew and Papagiannakis (2009, 2011) : focused on automation of processing and analysis
However, there is no agreement on how to quantify
and describe aggregates’ structure
Evaluating Performance - Rutting
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Flow Number (Rutting) vs. Density
Density ≠ Performance
Defining Aggregate Structure
AC Rutting Performance
?per area
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Can we measure aggregate structure?iPas2 (Image analysis and processing software)
• iPas2 is tool to identify aggregate proximity during and aftercompaction.
• Outputs:– Packing– Connectivity– Orientation– Spatial Distribution
Introduction
• iPas : Image Processing and Analysis System
• Two components:– Image Processing Filters
Enhancing
Result: Black and White Image
– Microstructure Analysis Area Fraction
Gradation
Other Micromechanical Characteristics> Proximity zones, total proximity length, contact orientation, aggregate
orientation, segregation
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iPas overviewStep 1 -Image processing
Original image Median Filtered Hmax Filtered
After watershed transform After thresholding
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Labeled image
After Coenen et al. 2011
iPas overviewStep 2- Microstructure analysis
G1
G2
G3
Segregation Orientation Number of proximity zones
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New approach for aggregate skeleton characterization: iPas2
Proximity zones Proximity length
New approach for aggregate skeleton characterization: iPas2
Performance
No. of Contact zones
Contact length
Contact orientation
Skeleton
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Example 1: Effect of aggregate Gradation on Rutting
Wide range of gradations used
Effect of aggregate structure on rutting:Testing
Mixture Flow Number
(1034 kPa) 506 340 520 3400 523 1275
F-CBE 400 F-SBS 430 F-GTR 240 F-Neat 150 C-CBE 210 C-SBS 260 C-GTR 160 C-Neat 100
Range of rutting performance
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Example 2: Effect of Binder Modification on Rutting
0
10000
20000
30000
40000
50000
60000
0 1000 2000 3000 4000 5000
Per
man
ent
Str
ain
(m
icro
stra
in)
No. of Cycles
Neat S C H
• H mixture has the best mixture performance• Lower m-value implies a lower rate of permanent
deformation accumulation with number of cycles
0
400
800
1,200
1,600
2,000
Neat S C H
FN
Coarse Fine
0
20
40
60
80
100
Neat S C H
m-v
alu
e
Coarse Fine
Effect of Aggregate Structure on Rutting
• Structure dictates how load is carried through mix
• Targeting density (AV at Ndes)as indicator of performance is not effective– Mixes of the same air voids have very different laboratory performances
R² = 0.96
0
1000
2000
3000
4000
5000
0 500 1000 1500 2000Pro
xim
ity
Len
gth
(m
m/1
00 c
m2 )
FN
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Effect of Compaction Temperature on Evolution of Aggregate Structure
50 C Difference
200
1,200
2,200
3,200
4,200
5,200
60 85 110 135 160Tot
al P
roxi
mit
y L
engt
h (
mm
/100
cm
2 )
Compaction Temp. (°C)
Neat C S H
High viscosity effectDry contact effect
• Different binders show a peak at different temps– Optimum compaction – Optimum mastic viscosity
Different mixtures could achieve similar packing levels, but at different temperatures
Remarks: Effect of Aggregate Packing on Performance
•Density is not sufficient to estimate packing of aggregates
•Internal structure of mixtures have significant effect on performance
•Mixture with low connectivity generally show poor rutting and thermal performance
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Conclusions
•Aggregate structure of asphalt mixtures can be characterized successfully using analysis of 2D images
•Rutting resistance ~ Aggregate structure
•Effect of compaction effort and method, temperature, gradation, binder rheology on inherent aggregate structure is successfully captured
Thank you