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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

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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