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Road Materials and Mixture Design to prevent Permanent Deformation- Rutting

Hussain U. Bahia, PhD University of Wisconsin–Madison

November 5th, 2014, Buenos Aires, Argentina

Rutting: The most

damaging Pavement

Failure

1. Mechanism

2. Modeling

3. Binder Testing

4. Mixture Testing

5. Imaging and Micro

structure

Mechanics of Permanent Deformation for Rutting Modeling

•Volume change vs. Shape distortion

*Kim, R. Modeling of Asphalt Concrete (2009)

Str

ain

Time

load Distortion

Volume change

Mechanisms of Rutting: Volume and Shape changes

Factors Affecting Rutting

1. Traffic loading (cyclic).

2. Temperature: Most

critical at high.

3. Un-aged binder: Early

in pavement life

4. Permanent dislocation

of aggregate.

5. Accumulate gradually

with traffic.

Importance of Air Voids in Rutting: High voids = less traffic to same rut


Mechanistic Empirical Rutting Models

Asphalt Mixture Permanent Strain Model – Witczak et al.

Mechanistic Empirical Rutting Models MEPDG

Permanent to Resilient Strain Ratio Model

–NCHRP 1-37A

Mechanistic Empirical Rutting Models

Good correlation with Field - Strain Ratio Model

–NCHRP 1-37A=> Predicted vs. Estimated


How to Measure Rutting Resistance

Option A: Rheology

Option B: Damage Resistance

The focus in Rheology is on Linear Visco-Elasticity: G*, delta

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

45 50 55 60 65 70 75 80 85 90

Co

mp

lex

Mo

du

lus

(Pa

)

<< Viscous Phase Angle delta (°) Elastic >>

Low SBS %

No polymer network

Viscous above 60°C

Reasonably workable

High SBS %

Polymer network

Elastic during compaction

Workability problem

Courtesy of Nynas

Rheology of Binders and Mixtuers Dynamic Modulus /E*, G*/ Phase Angle,

Time, t

osint

osin(t-

0

0|*|

E

it

Rheology of Binder and Mixture

1E+00

1E+02

1E+04

1E+06

1E+08

1E-04 1E-02 1E+00 1E+02 1E+04 1E+06 1E+08

Reduced Frequency (Hz)

Co

mp

lex

Mo

du

lus

(k

Pa

)Binder fit

Mix fit

Binder

Mixture

G*

, M

Pa

Reduced Frequency, Hz

0

15

30

45

60

75

90

1E-04 1E-02 1E+00 1E+02 1E+04 1E+06 1E+08

Reduced Frequency (Hz)

Ph

ase A

ng

le (

deg

)

Binder fit

Mix fit

Mixture

Binder

Rheology of Binder and Mixture

Need for Bitumen Damage Resistance Characterization

•Linear VE (Small strain) is

not sufficient (NCHRP 9-10)

•Bitumen damage resistance

is very important

•Modified bitumen best

in damage resistance

Strain f

f

Rheology

LVE

Non-Linear /

Damage

Rutting: Repeated Load

Permanent Deformation Test

Flow Number

• Creep rate:

- Flow Number (FN) at High Temp

TIME

Mixture Rutting Resistance Same mix different Binders: SBS, FPE, Hybrid

Titan

More than 10 times

=> Traffic

Damage Testing for Rutting (Repeated Creep Test for Binders)

Creep Tests at 70C, 300 Pa shear stress

(Loading 1s Recovery 9s) 100 cycles

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 200 400 600 800 1000

Time (s)

Accu

mu

late

d S

train

PG82- PEs

PG 82- Oxidized

PG-82- SBSr



0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 200 400 600 800 1000

Time (s)

Accu

mu

late

d S

train

PG82- PEs

PG 82- Oxidized

PG-82- SBSr

Binder Rutting Testing – Creep and Recovery

Mixture Model for Rutting

Average of All Aggregates

Mix = 0.201 Binder + C

R 2

= 0.68

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 0.1 0.2 0.3 0.4

Binder rutting slope, (1/Kpa)

Mix

ture

ru

ttin

g s

lop

e S

Binder Damage Resistance

Role of Binders and how to test them

Need for Bitumen Damage Resistance Characterization

•Linear VE is not

sufficient Bitumen damage

resistance

is very important

•Modified bitumen best

in damage resistance

Strain f

f

LVE

G*,d

Non-Linear /

Damage

The new tests : Creep and Recovery (Multiple Stress Creep & Recovery- MSCR)

DSR

Dynamic Shear

Rheometer

0.1

68

Shear Stress, kPa

0.7 1.4

0.1

Shear Stain, mm/mm

0.7 1.4

Accumulated Strain

To Separate Non-Recoverable Response (Jnr) Four-Element (Burgers) Model

G0

t

t

G1

Strain

Time

Elastic Response

Delayed -Elastic Response

Viscous Response

More viscous ( non-recoverable) = more rutting Polymers Can Reduce Rutting Damage



0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0 200 400 600 800 1000

Time (s)

Ac

cu

mu

late

d S

tra

in

PG82- PEs

PG 82- Oxidized

PG-82- SBSr

More Polymer

(e.g. Elvaloy)

Some Polymer

No Polymer

Cycles, (time, sec)

12.0

2.5

~ 75%

less

Rutting

Using Burgers Model to Estimate Jnr

teGG

tJtJJtJ

tG

vdee

0

/

10

1)1(

11

)()()(

11

where

Je = elastic compliance,

Jde = delayed elastic compliance, and

Jv = viscous compliance => Jnr

SS

Steady State Viscosity

Multiple Stress Creep and Recovery (MSCR) - ASTM 7045-10, AASHTO TP70

• Creep stress:0.1

kPa, 3.2 kPa

• 10 cycles

– 1 sec constant creep

stress

– 9 sec zero stress

• Output: Creep

compliance (Jnr)

and Percent

Recovery (%R) at 0.1

kPa, and 3.2 kPa

MSCR B5 46ºC

0.001

0.01

0.1

1

10

0 25 50 75 100 125 150 175 200

time (s)

Data

Model PredictionStress: 0.1 kPa

Stress: 3.2 kPa S

tra

in

The New Bitumen Grading System- M332 – PG xx(z)-yy 1. Climate: xx-yy 2. Traffic conditions- Trucks (S,H,V,E) 3. Reliability , and 4. Modification

PG 64(V)-10 Performance

Grade Summer

Average 7-day

max pavement

design temp

Winter

Min pavement

design temp

Traffic

Volume &

Speed

Advanced Performance Grading System for Qatar – AASHTO MP19

•Direct and effective consideration of Traffic

Traffic Volume Design ESALsa

(Million)

Adjusting the Jnr limits Measured at Environmental Grade

Traffic Speed - Load Rate

Standingb Slowc Standardd

0.3 to < 3 H Standard S 3 to < 10 V High H

10 to < 30 E Very high V ≥ 30 E Extremely high E

b-Standing Traffic—Average traffic speed is < 20 km/h. C Slow Traffic—Average traffic speed >20 to <70 km/h, d Standard Traffic—average traffic speed is > 70 km/h.

Mixture Micro-structure: Aggregate Packing effects

Role of Aggregates

and how to measure it

0

0,01

0,02

0,03

0,04

0,05

0,06

0 1000 2000 3000 4000 5000 6000

Tota

l Pe

rman

en

t St

rain

Number of Cycles

Binder 519

Binder 520

Increasing flow number

Better rut resistance

Typical Results from FN - Mixtures

Low Flow Number High Flow Number

0

0,01

0,02

0,03

0,04

0,05

0,06

0 2000 4000 6000 8000 10000

Tota

l Pe

rma

ne

nt

Str

ain

Number of Cycles

Neat-Coarse

GTR-Coarse

Plastomer-Coarse

Elastomer-Coarse

Could be

aggregate

packing

and

structure

Bitumen + aggregate gradation + volumetrics ≠

Performance

Can we Measure aggregate structure ? iPas1 … iPas2 … (Image Processing and Analysis Software)

• iPas: A tool to identify

aggregate structure.

• Give statistics about

– Packing

– Connectivity

– Orientation

– Spatial segregation Contact Length

Contact Zone

Stress Path

Input Image

Intensity Distribution

181

0 255

Thresholded Black and white image

Input Image


176

0 255

12

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Input Image


176

0 255

12

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

(1) Image processing (2) Image analysis

Proximity points

Orientation

Segregation

iPas software includes 2-Parts

G1

G2

G3

Aggregate Packing Characterization 2D to represent 3D - Stereology

iPas output used to quantify packing: Aggr. Proximity Index

API= Total aggregate to aggregate Proximity length

Cutting sections

Internal Aggregate Structure (API) Can explain the differences in FN

Neat Binder

Elastomer Binder

GTR Binder

GTR Binder Lower Density

Plastomer Binder

More Results of Mixture Rutting: Effect of Aggregate Gradation

Elastomer- Coarse, Fine

,

Plastomer-Coarse, Fine

Neat- coarse , Fine

GTR-

Coarse,

Fine

Validation of Effect of Aggregate Packing and Skeleton

R² = 0,973

10

100

1000

10000

0 1000 2000 3000 4000

Ru

ttin

g -

FN

Proximity length (mm)

WCTG

Fine E1B1

Coarse E1B1

Projects

Technologies to Stop Rutting Damage Resistance Characterization + Imaging

Hard

Soft

Elastic

Viscous

Strong

Weak

Pen-Vis

Summary

•Both Binders and Aggregates play a major role in

rutting resistance

•Binder damage resistance should be measured

correctly ( large strain repeated creep)

•Voids can have an effect ( but aggregate structure

is more important

•Aggregate packing is very important

• Imaging and visualization can help

Same Problems but New Methods to Solve

Acknowledgments

•Conference Organizers

–Argentinean Road Association

•YPF organization

– Technical Manager Marcela Balige

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