Elsefi, Mostafa2(1)

8/10/2019 Elsefi, Mostafa2(1)

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Evaluation of the Ductility

Specifications for

Straight Asphalt Binder in

Louisiana

Mostafa Elseif i

Louisiana State University

1


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Introduction

Louisiana Binder Specifications: PG 64-22 is allowed on base course

Conventional SuperPave criteria are required(RV, DSR, and BBR)

Ductility at 25oC (RTFO-residue): minimum100cm

Ductil ity test is not required in

neighboring states (Texas, MS): How does ductility complement current binder

specifications?

2/17/2009 LOUISIANA STATE UNIVERSITY 2


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Research Objectives

Establish the relationship between the

ductility and pavement performance.

Suggest possible modifications tocurrent binder specifications by

adopting a SuperPave test indicative of

mix performance for straight binders



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Asphalt Binders Tested

Nine straight binders classified as PG 64-22 wereobtained from two asphalt suppliers (labeled A to I).

Selected binders have contrasting levels ofductility.

Experimental program: Ductility for RTFO and PAV residues

DTT on PAV residues

Gel Permeation Chromatography (GPC) on all binders

Dynamic Mechanical Analysis and DifferentialScanning Calorimetry

Multiple Stress Creep Recovery Test

Indirect Tensile Strength on Asphalt Mixtures



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Asphalt Binders Tested


Binder IDG*/sind (64oC)

Original kPa

G*/sind (64oC)

RTFO kPa

G*sind (25oC)

PAV kPa

BBR Stiffness

(MPa)m-value

Brookfield

@135oC

A 1.74 4.66 2430 113 0.350 0.550

B 1.73 5.22 2120 87 0.355 0.560

C 1.67 4.31 2460 107 0.334 0.530

D 1.77 5.79 1793 127 0.332 0.530

E 1.55 4.60 2520 94 0.351 0.520

F 1.57 4.29 3000 108 0.333 0.530

G 2.09 4.81 4855 229 0.311 0.545

H 2.03 4.67 4550 218 0.313 0.563

I 1.89 3.90 4804 231 0.312 0.588


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Test Procedure - Ductility


COV = 4%


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Test Procedure - DTT



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DTT Results


COV = 19%


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Test Procedure - MSCR

Apply a constant shearstress for 1sec followed bya rest period for 9sec

10 consecutive loading

cycles are applied at twoloads

Introduced to predict binderrutting resistance at high

temperature Conducted at 25oC on RTFO

residues



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MSCR Results

Three parameters are calculated:

Non-recoverable creep compliance (Jnr):

Percentage recovery (r)

Stress dependency


r =110

1

x100

Jnr =

nr

rdifference =r100r3200

r100

x100


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MSCR Test



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DTT vs. Ductility



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DTT vs. Ductility

An inverse correlation between binder

ductility and the measured failure strain

A binder that provides a high ductility

would be characterized by poor elongationproperties at low temperature

Two hypothesis:

Effect of aging Effect of temperature



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Effect of Aging

High ductility binders may lose more lightcomponents during the aging process



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Effect of Aging - GPC

GPC separates the components ofasphaltic materials based on theirdifferences in molecular weights

GPC determines the fractions of: Polymer (high molecular weight),

Asphaltenes (medium molecular weight),

Maltenes (low molecular weight), and

Very light oils (very low molecular weight)



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Effect of Aging


12.8 14.6 13.8 14.5 16.3 16.6

11.7 12.1 11.4

80.7 78.7 79.8 78.8 77.4 77.1

82.9 83.1 84.1

6.5 6.7 6.4 6.7 6.4 6.3 5.4 4.8 4.6

0.0

20.0

40.0

60.0

80.0

100.0

A B C D E F G H I

M

o

l

e

c

u

l

a

r

F

r

a

c

t

i

o

n

(

%)

Binder ID

Oth er LMW MMW

15.9 16.8 16.9 16.9 18.3 18.1 14.0 17.5 16.5

77.7 76.6 76.9 76.5 75.6 75.7 80.7 78.1 79.4

6.4 6.6 6.2 6.6 6.1 6.1 5.3 4.4 4.2

0.0

20.0

40.0

60.0

80.0

100.0

A B C D E F G H I

M

o

l

e

c

u

l

ar

F

r

a

c

t

i

o

n

(

%)

Binder ID

Oth er LMW MMW


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Effect of Temperature

Employed two testmethods on three binders:

Differential Scanning

Calorimetry (DSC): To characterize content of

crystallizable materials

Dynamic mechanical

analysis (DMA): To characterize the glass

transition temperature (Tg)


-20 -16 -12 -8 -4 0 4 8

1000

2000

10M

15M

20M

E',E"(Pa)

Temperature,oC

E"

Sample Breaking Tg 0.2oC

E'

E"

5M

E'

Time(sec)

Time


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Effect of Temperature

Asphalt Binder Glass TransitionTg (C) CrystallizableSpecies

Below 25C (%)*

CrystallizableSpecies

Above 25C (%)*

D original

D RTFO

D PAV

-4.5

-3.3

3.5

Not detected

Not detected

Not detected

0.18

0.41

0.37

G original

G RTFO

G PAV

-7.5^

0.2

7.4

0.48

0.41

0.86

0.12

0.33

Not detected

I original

I PAV

5.0

8.3

0.03

Not detected

0.12

0.10


Binders with high duct ility (G and I) have a higher

glass transition temperature and greater content of

crystallizable materials


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Relationship between Molecular

Compositions and Binder Physical Properties


LMW vs. G*/sin

(rutting

criterion)

LMW vs. BBR Stiffness


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Effect on Mix Performance

A limited number of HMA sampleswere prepared with three binders(B, F, and G).

Design for low-cost asphalt-treated

base: 25% sand

75% Marietta Limestone

3% binder

Samples were tested using indirect-tensile strength test setup (agedand unaged)



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Effect on Mix Performance


R l ti hi b t MSCR


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Relationship between MSCR

and Binder Ductility



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Conclusions

An inverse correlation exists betweenbinder ductility at 25oC and themeasured failure strain at -12oC:

An increase in the binder content of LMWresults in an increase in its ductility atintermediate temperature

An increase in the binder content of

crystallizable LMW results in crystallizationof these molecular fractions at lowtemperature



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Conclusions

Using a binder with a high ductility resultsin a mixture with greater indirect tensilestrength

A binder characterized with a high level ofductility would exhibit poor performance inthe MSCR test

Current SuperPave specifications failed todifferentiate between these binders interms of performance



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Recommendations

The ductility test should be kept in the

state binders specifications as it

correlates well with mix performance at

intermediate temperature.



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Acknowledgements

This paper is based on the results of LTRC08-2P.

The author would like to acknowledge: Project Review Committee (PRC)

Zhongjie Doc Zhang

Louay Mohammad

Chris Abadie

Ionela Glover

Ioan Negulescu

William Daly

T. Naidoo and S. Bradley



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Thank You

Documents

Elsefi, Mostafa2(1)