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Transcript of 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?
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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
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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
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COV = 4%
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Test Procedure - DTT
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DTT Results
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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
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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
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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)
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-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
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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
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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
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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