Post on 17-Jan-2023
The final version of this paper was published in:
Transportation Research Record: Journal of the Transportation Research Board, 2014
VOL 2370, Pages 84-91. DOI: 10.3141/2370-11
http://trb.metapress.com/content/b135086hu5444244/?genre=article&id=doi%3a10.3141%2f2370-11
Critical Problems with Using the Asphalt Ductility Test as a Performance
Index for Modified Binders
Paper #13-4125
Revised Version Submission date: February 28, 2013
Word count: 5386 plus 8 Table and Figures (250 words)
Total number of words: 7386
Hassan A. Tabatabaee, Ph.D. (Corresponding Author)
Research Associate
Department of Civil and Environmental Engineering
University of Wisconsin - Madison, 53706
Email: tabatabaee@wisc.edu
Phone: (608)-890-3321
Cristian Clopotel, Ph.D.
Graduate Research Assistant
Department of Civil and Environmental Engineering
University of Wisconsin - Madison, 53706
Email: clopotel@wisc.edu
Amir Arshadi
Graduate Research Assistant
Department of Civil and Environmental Engineering
University of Wisconsin - Madison, 53706
Email: arshadi@wisc.edu
Hussain Bahia, Ph.D.
Professor
Department of Civil and Environmental Engineering
University of Wisconsin - Madison, 53706
Email: bahia@engr.wisc.edu
Submitted for publication in the
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 1
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Transportation Research Record: Journal of the Transportation Research Board
February, 2013
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 2
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ABSTRACT
Despite the adaptation of advanced binder rheology characterization methods by many
agencies, the asphalt ductility test is still under use in some specifications in the USA and
a few countries as a performance indicator for asphalt modification. In the present study a
set of binders modified with two types of commonly used elastomeric polymer modifiers
were characterized in terms of fundamental, well-defined, binder properties known to
reflect rutting and fatigue resistance, results of which showed no correlations with binder
ductility.
Additionally, a test procedure was developed using a Dynamic Shear Rheometer (DSR) as a
surrogate to the conventional ductility test, results of which showed that both elastomeric
modified binders are much more ductile than conventional binders, even when conventional
ductility showed a loss of ductility. Finite Element Modeling (FEM) was used to show the
significant effects of decreasing true strain rates with elongation on the sample’s stress and strain
state due to the constant cross head speed in the conventional ductility test. Due to the well-
known dependency of failure stress and strain of viscoelastic material on strain-rate and
temperature, comparing binders with varying ductility values measured in the conventional test
is essentially flawed as it is equivalent to comparing them at different temperatures, thus
fundamentally unreliable as an indicator of the asphalt’s performance in the pavement. It is
therefore strongly recommended that the practice of using low temperature conventional ductility
be removed from modified binder specifications, or the DSR procedure proposed in this paper be
used to evaluate modified asphalts as a preferable test method.
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 3
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INTRODUCTION
The asphalt ductility test, as currently carried out in accordance to the ASTM D113-07
specification (1), is a measure of the ultimate elongation of an asphalt binder sample at a
constant rate and a specific temperature before breaking. Despite the adaptation of advanced
binder rheology characterization methods by many agencies, the asphalt ductility test is still
under use in some specifications in the USA and a few countries as a performance indicator for
asphalt modification, especially at lower service temperatures.
The significance of the results of the ductility test as a measure of asphalt performance
has been debated due to its empirical nature, low reproducibility, and unclear relationship
between the measured results and any fundamental material properties (2). Historically in
absence of advance characterization methods, some researchers have used the ductility test as a
qualitative measure for determining the level of aging in asphalt binders after laboratory aging or
extraction from the field (3,4,5,6,7). Doyle tested four asphalt binders recovered from field
section using the ductility at 13°C and noticed that binders that cracked more seemed to have a
lower ductility at this temperature, although the results did not correlate with any other low
temperature properties in the binders. Doyle suggested that elongation rate as low as 1°C/min
may still be too high to relate to low temperature shrinkage in pavements (4).
Halstead performed an extensive research on the relation of asphalt ductility to pavement
performance. Although he noticed that in some cases combining ductility and penetration data
may be useful for characterization asphalt binders, especially with regards to age hardening, he
was unable to define the exact role of the ductility measure on asphalt pavement durability,
concluding that more research was needed to define the significance of ductility for pavement
durability. Based on the results he further concluded that “it is most likely that the ability of
asphalt to undergo elongation is not the primary characteristic affecting durability.” He
suggested that ductility may be a function of the internal phase relationship of the asphaltic
constituents (5).
Studies conducted by Kandhal in the 1960’s (8,9) showed that a pavement with ductility
above 10 cm at 15.6°C had relatively good performances in terms of thermal cracking. In
addition it was observed that when the ductility decreased to 3-5 cm at 15.6°C serious cracking
was observed.
An elaborate study regarding the correlation between the properties of the asphalt binders
and the properties of the asphalt concrete mixes was conducted by Goodrich (10). The author
showed that temperature susceptibility, forced ductility, toughness-tenacity and low temperature
ductility do not correlate with mixes performances.
Vonk et al (11), suggested that bitumen’s homogeneity is a condition for good ductility,
and the lower the asphaltene content, the better ductility. In addition the authors compared
ductility with Frass breaking point and concluded that ductility cannot be used as a surrogate for
the test. Citing Reese’s work (12), Vonk et al showed inconsistencies between ductility ranking
and reflective cracking ranking. The authors also showed that ductility highly sensitive to testing
temperature and rankings can be changed by simply altering the test temperature.
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 4
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An alternative methodology to the ductility was proposed by Ruan et al. (13,14), using
the Dynamic Shear Rheometer (DSR) by measuring G’/(η’/G’) for the binder. The parameter
correlated well with ductility when unmodified binders were tested and ductility was below 10
cm. However, the author showed a weak correlation between the ductility and G’/(η’/G’) for
modified binders.
In recent years researchers have focused on the applicability of ductility specification to
modified asphalt binders. Vonk and Korenstra in a detailed study reported that due to the different
structure in polymer modified binders; the ductility test would be inherently measuring different
properties of the asphalt binders depending on the presence of modification, thus concluding that
ductility is not a suitable performance indicator and binder selection tool (11).
Review of literature since the 1940s shows that limited work has focused on relating
ductility results to pavement performance, especially in terms of fundamental material
properties, with widely varying results and conclusions. The general lack of repeatable and
reliable correlation between ductility results and pavement performance in previous studies,
especially at lower temperatures, has limited the practical usage of this tool to specify suitability
of asphalt binders for pavement applications. On the other hand almost all studies in the literature
relating ductility to performance have been based on unmodified binders.
What is of utmost importance is that no fundamental analysis and interpretation of the
ductility test results has been presented to justify the use of this test, and the resulting ductility
measure, as a performance index. The objective of the present study was to identify and explain
the fundamental limitations of this test, to study the stress and strain development in the model
during elongation through finite element modeling, and to compare the ductility results to other
more fundamental binder damage resistance characterization parameters to further investigate the
applicability of this test as a reliable performance indicator, as well as introduce a preferable
alternative surrogate test method using the DSR.
EXPERIMENTAL DESIGN
In the present study a relatively large set of neat binders were modified with different dosages of
two commonly used elastomeric polymer modifiers, namely Elvaloy® and Styrene-Butadiene
Styrene (SBS). The studied materials are defined in TABLE 1.
Damage resistance testing of asphalt binders is recognized as a more direct method of
assessing performance of pavements based on engineering properties of the constituents. These
tests to some extent side step the complexity of non-linear viscoelasticity and stress dependency
of asphalt binder modulus by ranking binders based on ultimate failure parameters instead of
stiffness and modulus. This becomes especially advantageous when characterizing modified
asphalt binder for which non-linearity may be significantly affected by the modification type and
level. Such specification methods were suggested by researchers during the NCHRP 9-10 project
(15), and later used as a basis for the development of many new asphalt binder testing procedures
such as the Multiple Stress Creep and Recovery (MSCR) (16), and the Linear Amplitude Sweep
(LAS) (17). In the present study MSCR and LAS were performed at the high and intermediate
performance grade temperatures of the binders and compared to the ductility results to
investigate the potential relationship between ductility values and elongation failure through
ductility testing at 4°C.
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 5
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DUCTILITY AND DAMAGE RESISTANCE CHARACTERIZATION
FIGURE 1(a) and (b) plots the number of cycles to fatigue failure, Nf, against ductility results at
4°C. Nf was calculated based on the LAS results at the intermediate grade temperature, by
means of the Viscoelastic Continuum Damage framework (VECD), based on a 35% decrease in
modulus as the failure criteria. This parameter can be calculated assuming any inputted cyclic
strain amplitude, which for this study was set at 2.5 and 5%. The use of 4°C for the ductility
testing was historically based on practical limitations of testing at lower temperatures, especially
using a water bath. In reality, 4°C is closer to the low end of the fatigue damage temperature
range, rather than low temperature cracking, although it must be noted that fatigue damage
results from repeated loading and unloading, unlike the monotonic loading procedure used in the
ductility test. If ductility at 4°C is any indicator of crack resistance at that temperature, some
correlation with fatigue damage resistance would be expected. Contrary to this expectation, Nf
values at both strain levels show no correlation with ductility results. This lack of relationship
highlights the potential lack of any fundamental relationship between ductility and cracking
damage in asphalt binders.
FIGURE 1(c) and (d) depicts the relationship observed for ductility at 4°C and MSCR
parameters at 3.2 kPa (Jnr and Percent recovery) at the binder high temperature grade for a
number of neat and elastomeric modified binders using both Elvaloy® and SBS. There does not
seem to be any correlation between the percent recovery and Jnr values and the corresponding
ductility values. Although stiffness and the ability to elongate are not fundamentally related, one
may expect that binders with higher ductility to tend to have lower stiffness (higher compliance).
FIGURE 1 shows that no such trend exists for the studied binders.
SAMPLE GEOMETRY EVOLUTION DURING ASPHALT DUCTILITY TEST
A point of concern when considering ductility of asphalt binders is the continuous change of
sample geometry during elongation. The change of geometry is governed by the Poisson ratio of
asphalt material, while the resulting stress in the sample will be affected by stiffness and rate of
relaxation in addition to the continuous cross sectional change of the sample. Binder
modification, especially with polymers, can potentially affect both of these aspects as the
elastomeric three dimensional networks may affect both the overall Poisson ratio of the asphalt
and the rate of stress relaxation as the sample elongates at the rate of 1 or 5 cm/min. Thus
comparison of the total elongation at any temperature using the ductility between different
modified and unmodified binders would be significantly affected by the varying stress states
between the samples.
The potential effect of change in ductility sample geometry in the test result ranking is
analyzed with two approaches. In one approach the dynamic shear rheometer (DSR) is used to
carry out a continuous rotation test on asphalt samples at 4°C. The test methodology follows that
of the Binder Yield Energy Test (BYET) (18). The strain rate experienced by the sample in the
ductility was calculated and converted to the appropriate strain rate to be used in the DSR
method. Such calculations were originally carried out for the development of the “Elastic
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Recovery – DSR” (ER-DSR) procedure at the University of Wisconsin-Madison (19). This DSR
BYET test was used as a comparison to the ductility test as it too imposes a continues
engineering strain on the sample to the point of apparent failure, while the sample geometry
evolution in this test may be better defined with a consistent effective cross section as opposed to
the asphalt ductility test. Multiple neat and two types of elastomer modified binders (Elvaloy®
and SBS) from different sources were tested using this method and compared to the ductility
results at 4°C. The results are shown in FIGURE 2. It should be mentioned that the DSR ductility
procedure was found to be very repeatable, with an average strain at peak stress coefficient of
variation of 8%.
The results shown in FIGURE 2 indicate that the conventional ductility test results show
erratic and inconsistent results for both elastomeric modification types for the six base binders
studied. However, conducting the ductility test on the same materials in a controlled geometry
condition in the DSR showed that both elastomeric modifiers significantly improved the ductility
at 4°C, regardless of the ductility test results. The addition of the elastomer clearly enhanced the
strain to peak stress by two to six times (200% - 600%), depending on base binder source, all
other conditions being identical. The difference in results between the conventional ductility and
the DSR ductility is attributed to the sample and load geometry difference.
Conventional ductility and DSR ductility results were plotted against each other in terms
of strain at respective failure criteria, as shown in FIGURE 3. A few notable observations are
made:
First, for the neat asphalt binders the strain at failure from the DSR-ductility and the
ductility test match up relatively well, confirming that the DSR procedure is capable
of capturing an equivalent response to that of the conventional ductility test.
Second, the DSR-ductility results from the Elvaloy-modified binders show much
higher strains at failure than that of the conventional ductility test, on the other hand,
SBS-modified binders seem to cover a range of responses from the conventional
ductility, while generally faring better in the DSR-ductility test.
Although the ductility test is used by some agencies as an indicator of the presence of
elastomeric modification, the results shown in FIGURE 2 and FIGURE 3 for two types
of elastomeric modification and various base binder types show that the conventional
ductility test is unable to consistently detect the presence of an elastomeric modification. On
the other hand, the DSR-Ductility methods consistently indicated the presence of elastomers
in the tested binders for both types of elastomeric modification and all base binder types.
The main finding from this comparison is important since it shows that the
conventional ductility test could be misleading due to the confounding effects of the
change in geometry during testing. This effect seems to bias results toward specific
types of modification systems, yielding results that cannot be supported by that of the
more robust DSR-ductility methodology. The DSR ductility results clearly show that
both elastomeric modifiers can indeed significantly improve the ductility of neat
binders.
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 7
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STRAIN RATE IN ELONGATION RHEOLOGY AND FAILURE PROPERTIES OF
VISCOELASTIC MATERIAL
Uniaxial elongational flows are believed to be strongly aligning flows in that a high degree of
orientational anisotropy in polymer chain segments can be induced (20). Thus the extreme test
conditions may result in widely varying responses for different polymer modification types, with
little relevance to realistic stress and strain states experienced by asphalt binders in the pavement.
Uniaxial elongation at constant strain rate is also classified as a strong flow because such a
deformation history has a tendency to stretch polymer chain segments. The high degree of chain
segment orientation and stretch induced by uniaxial elongation can result in rather dramatic
rheological responses including the phenomenon known as strain hardening, where the
elongational viscosity increases well above the linear viscoelastic prediction (20). In polymer
science, early attempts at extensional rheometry of polymer solutions were met with
disappointment due to the strong strain-rate and strain sensitivity of the extensional stresses
exhibited in polymer solutions and the widely disparate design of the instruments which resulted
in nonhomogeneous kinematics (21).
Material science studies have shown that true material failure properties can only be
achieved under constant-true-strain conditions (22,23,24). When experiments are carried out at a
constant crosshead speed condition (constant engineering strain), such as in the asphalt ductility
test, the specimen experiences a decreasing true strain rate during the test, thus making physical
interpretation of results difficult, especially in the non-elastic regimes (22,23). Thus material
scientists have gone to great length since early 1970s to maintain constant true strain rate in the
samples during elongational and tensile tests (25), such as detachable extensional rheometer
fixtures for torsional rheometers (21).
The study of stress and strain response in viscoelastic materials in not a new topic, and
has been investigated at length for many decades. Theoretical solutions and constitutive
equations have been developed for almost any loading geometry and time-temperature condition,
taking into account temperature and rate dependency, and more recently non-linear
viscoelasticity. Researchers have shown that for linear viscoelastic material time temperature
superposition is not only applicable to measurements of viscosity and stiffness, but to various
other physical properties, provided they involve the same molecular motions governing the
viscoelastic stiffness properties (26,27). Such observations have enabled researchers to plot
“failure strength envelope” as a function of ultimate strain for viscoelastic material (28). A
failure envelope is developed by plotting failure stress against strain at reduced strain rates
(26,28). Furthermore, the applicability of time temperature superposition to failure stress and
strain in viscoelastic material implies that the viscoelastic response of the amorphous chains
dominates failure properties (26). Many researchers studying viscoelastic fracture have shown
that there is a close dependency between failure stress and strain rate, such that the stress
decreases monotonically as the strain rate is decreased. On the other hand, researchers have
observed the existence of a “definite maximum strain at failure” for viscoelastic material tested
to failure at different strain rates (26,27,29,28). The strain at failure increases as the strain rate
decreases down to a certain strain rate, after which any decrease in strain rate will cause the
strain at failure decrease (27).
It has been shown that failure envelope in many instances works sufficiently well for
asphalt mixtures (30,31). Monismith et al. also showed that asphalt concrete failure stress at
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 8
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different temperatures, strain rates and test conditions behaved in a fashion similar to that
described by Smith (28,31), if tests are conducted at constant strain rates. In the failure envelope
for asphalt pavements tested at different temperatures and conditions, the higher failure stress
levels corresponded to lower test temperatures and higher strain rates. It was also be observed
that failure of samples tested under constant strain can be plotted on the same failure envelope as
those tested at the same temperature but under constant stress.
In the asphalt ductility test, due to the constant cross head speed conditions, the true-
strain-rate decreases with time and elongation. This decrease can cause the strain rate to change
by more than an order of magnitude only after a few cm of elongation. Equations 1 and 2 show
the formulation for calculation of “engineering strain” (also known as Cauchy strain) and “true
strain” (also known as natural strain). Mathematically, the true strain is the sum of all
instantaneous engineering strains and is calculated as follows:
[eq. 1]
∫
[eq. 2]
In which:
and are the “engineering” and “true” strain, respectively, and
l is the sample length, with l0 being the initial length.
At small strain levels the engineering strain and true strain do not significantly differ,
thus usable results may be derived from tests performed using constant engineering strain rates,
provided the strain levels remain low. But for the case of the asphalt ductility test, for which the
sample is elongated to many times its original length, such approximations lead to significant
error. This is demonstrated by using equations 1 and 2 to calculate the average engineering and
true strains and strain rates, assuming a 10 mm/min crosshead deflection rate and a 40 mm gage
length (defined as the uniform mid-section of the ductility dog-bone sample). FIGURE 4 shows
the results of the strain calculation for the ductility test. For a test run at a constant crosshead
speed, as is the case in the ductility test, the engineering strain increases proportionally to the
crosshead displacement rate, thus varies linearly as the sample elongates. It can be seen in
FIGURE 4(a) that when the elongation is small (i.e. less than 10 mm) the true and engineering
strain are very similar, but they rapidly diverge as the sample elongates. The linear increase of
engineering strain indicates a constant engineering strain rate as the sample elongates. On the
other hand, the true strain non-linearly varies and immediately decreases as the sample length
increases, as shown in FIGURE 4 (b).
In order to run an elongation test such as the asphalt ductility at a constant true strain rate
one must exponentially increase the crosshead speed to counteract the decreasing true strain rate.
This was done for the case of the asphalt ductility test by calculating the crosshead speed profile
needed to achieve constant true strain rates over 260mm of elongation (resulting in a 300 mm
sample mid-section). Three true strain rate levels, corresponding to the engineering strain rate,
the average true strain rate, and the terminal true strain rate, were targeted in these calculations.
The resulting crosshead deflection and strain rate profiles are shown in FIGURE 5. It can be seen
that there is a dramatic difference between strain at a constant cross head speed and the constant
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 9
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strain rates, potentially leading to significant variation in response of the viscoelastic medium at
different elongations, and consequently different strain rates.
Using the calculated crosshead deflection profiles, stress and strain curves were derived
for each true strain rate scenario using a finite element simulation. A model of a ductility sample
was developed in the FEM environment of ABAQUS, a powerful commercial FEM package.
Viscoelastic material properties of a typical asphalt binder were inputted using a 4-element
Prony series. FIGURE 6 shows the model geometry and simple stress distribution under a
constant crosshead speed.
Using the finite element model the four crosshead speed profiles shown in FIGURE 5(a)
were imposed upon the sample to assess the difference in stress-strain curves. As seen in
FIGURE 7, when testing at a constant crosshead speed (as in the ductility test), the slope of the
stress-strain curve will rapidly decrease as the true strain rate decreases, becoming relatively
constant at higher elongations where rate change becomes less pronounced. On the other hand,
performing the test at constant true strain rates using the cross head speed profiles shown in
FIGURE 5(a), the stress-strain curves build-up at a much more constant rate. Furthermore, the
simulation results presented in FIGURE 7 highlight the dramatic change in the rate of stress
build-up in the ductility sample for different true strain rates. For the constant crosshead
condition of the asphalt ductility test the rate of stress build-up is initially equal to that of the
high constant strain rate, but as the strain rate decreases with elongation the stress build-up rate
tends toward the lower constant strain level, as seen in the higher strains in the Figure.
An important consequence of the changing true strain rate in the ductility tests is the
continuous change of critical failure stress and strain in the sample due to strain-rate dependence
of failure criteria in viscoelastic material. Thus when comparing asphalt binders failing at
different elongation levels, one can’t simply rank the materials’ damage resistance based on
ranking of ductility results. This is due to the strain-rate dependency of failure criteria in
viscoelastic material, which results in significantly different failure conditions for samples failing
at different elongations and consequently different strain rates at the time of failure. Recall that
for asphalt and other viscoelastic materials failure stress and strain vary similarly with increasing
temperature or decreasing true strain rate, thus comparing the failure strain (or ductility) of two
binders at different elongation and strain rates will in essence be similar to comparing failure
properties of binders tested at two different temperatures. Thus the varying true strain-rate
conditions in the asphalt ductility test make any comparison between results for different binder
types and reliable interpretation of the results extensively difficult and fundamentally unsound.
CONCLUSIONS
A review of literature was conducted to show that there is no agreement among experts regarding
the value of the ductility test results in terms of defining pavement performance, with many
studies failing to find any reliable or consistent trend for the relationship between ductility and
pavement performance. Furthermore, ductility and fatigue and rutting performance tests were
conducted for a set of binders to compare ductility values with binder properties known to reflect
rutting and fatigue resistance. No correlations could be found to indicate the relevance of the
ductility in terms of fatigue or rutting resistance of asphalt.
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 10
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A detailed analysis of the conventional ductility test indicated that one of the fundamental
problems with the test is the variation of sample geometry during the test. It is clear that this
confounding effect can cause significant problems leading to erroneous evaluation and ranking
of binder performance, in particular with respect to modified binders. To prove this point
specialized testing in the DSR was designed to measure true ductility at 4°C while carefully
controlling the geometry of the samples. Results of the DSR ductility test clearly show that
modified binders are more ductile than conventional binders, and that the results of conventional
ductility can be misleading for modified binder systems. Through this specialized testing it was
found that both elastomeric modifiers studied can improve ductility by a range of 200% to as
high as 600% while the conventional ductility is showing a loss of ductility for these modifiers.
The results for a large set of binders confirm this finding and show no correlation between the
conventional ductility test and the true ductility measured with the DSR.
Finite Element Modeling (FEM) was used to further highlight the fundamental
deficiencies of the use of the ductility test, especially with regards to the decreasing true strain
rate resulting from the constant cross head speed in the ductility test. A discussion of strain-rate
dependency of viscoelastic materials was used to conclude that comparing binders based on
ductility at failure is essentially similar to comparing failure strain between samples tested at
different temperatures, due to similar dependency of failure stress and strain of viscoelastic
material to strain-rate and temperature. Such conditions make any direct comparison of different
binders with different properties highly complex and fundamentally unreliable as an indicator of
the asphalt’s performance in the pavement.
Based on this study it is highly recommended that ductility test at 4 o C be removed from
modified binder specifications or requirements. If ductility of modified binders is still needed in
a specification, then the proposed method for using a test that can maintain a stable geometry,
such as the DSR, be used. The use of the conventional ductility test is misleading and could
unscientifically disqualify modified binders with superior ductility than the conventional binders.
REFERENCES
1. Standard Test Method for Ductility of Bituminous Materials; ASTM International: West
Conshohocken, PA, 2007.
2. Roberts, F. L., Kandhal, P. S., Brown, R. E., Lee, D.-Y., Kennedy, T. W. Hot Mix Asphalt Materials,
Mixture Design, and Construction, 2nd ed., National Asphalt Pavement Association Research and
Education Foundation: Lanham, MD, 1996, pp 47-48.
3. Clark, R. C. Practical Results of Asphalt Hardening on Pavement Life. Proceedings of the Association
of Asphalt Paving Technolgists, 1958, pp 196-208.
4. Doyle, P. C. Cracking Characteristic of Asphalt Cement. Association of Asphalt Pavement
Technologists, 1957, pp 581-597.
5. Halstead, W. J. The Relation of Asphalt Ductility to Pavement Performance. Association of Asphalt
Pavement Technologists, 1962, pp 247-270.
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 11
11
6. Lewis, R. H., Welborn, J. Y. Report on the Properties of the Residues of 50-60 and 85-100
Penetration Asphalts from Oven Tests and Exposeure. Association of Asphalt Pavement
Technologists, 1940, pp 12-68.
7. Skidmore, H. W. The Effect pf Oxidation Upon the Ductiloty of Asphalt Cements. Association of
Asphalt Pavement Technologists, 1940, pp 69-86.
8. Kandal, P., Koehler, W. C. Asphalt properties in relation to pavement performance. Transportation
Research Record 544, 1-13.
9. Kandal, P., Koehler., W. C. Significant studies on asphalt durability: Pennsylvania experience.
Transportation Research Record 999, 41-50.
10. Goodrich, J. Asphalt and Polymer modified asphalt properties related to the performance of asphalt
concrete mixes. Journal of the Association of Asphalt Paving Technologists 1988, 57.
11. Vonk, W. C., Korenstra, J. The Relevance of Ductility Specifications for Polymer Modified Bitumen.
Eurobitumen Congress, 2008.
12. Reese, R., Goodrich, J. Californian test road-A step close to performance based specifications.
Journal of the Association of Asphalt Paving Technologists 1993, 62.
13. Ruan, Y., Davidson, R. R., Glover, C. J. An investigation od asphalt durability: relationship between
ductility and rheological properties for unmodified asphalts. Petroleum Science and Technology 2003,
231-254.
14. Glover, C. J., Davidson, R. R., Domke, C. H., Ruan, Y.; Juristyarini, P.; Knorr, D. B. Development of
a new method for assessing asphalt binder performace durability; FHWA/TX-02/1872-1; Federal
Highway Administration, 2011.
15. Bahia, H. U.; Hanson, D. I.; Zeng, M.; Zhai, H.; Khatri, M. A.; Anderson, M. R. Project NCHRP 9-
10, Superpave Protocols for Modified Asphalt Binders; Final Report; National Cooperative Highway
Research Program, 2001.
16. ASTM D7405 - 10a Standard Test Method for Multiple Stress Creep and Recovery (MSCR) of Asphalt
Binder Using a Dynamic Shear Rheometer, American Society of Testing Materials, 2010.
17. Hintz, C., Velasquez, R., Johnson, C., Bahia, H. Modification and Validation of the Linear Amplitude
Sweep Test for Binder Fatigue Specification. Transportation Research Record: Journal of the
Transportation Research Board 2011.
18. Standard Method of Test for Yield Energy of Asphalt Binders Using the Dynamic Shear Rheometer
(Draft), University of Wisconsin Madison, 2009.
19. Clopotel, C. Modification of the Elastic Recovery Test of Binders and Its Relationship to Performance
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 12
12
Properties of Asphalt Binders, M.Sc. Thesis, University of Wisconsin-Madison, 2010.
20. Venerus, D. C., Zhu, S.-H., Ottinger, H. C. Stress and birefringence measurements during the uniaxial
elongation of polystyrene melts. Journal of Rheology 1999, 43 (3), 795-813.
21. Sentmanat, M., Wang, B. N., McKinley, G. H. Measuring the transient extensional rheology of
polyethylene melts using the SER universal testing platform. Journal of Rheology 2005, 49 (3), 583-
606.
22. Davis, J. R. Tensile Testing, 2nd ed., ASM International, 2004, pp 225-226.
23. G'sell, C., Jonas, J. J. Determination of the plastic behaviour of solid polymers at constant true strain
rate. Journal of Materials Science 1979, 14 (3), 583-591.
24. Baudelet, B., Suery, M. Constant stress creep and constant true strain-rate tensile tests of the
superplastic alloy PbSn. Journal of Materials Science 1972, 7 (5), 512-516.
25. Stevenson, J. F. EIongationaI Flow of Polymer Melts. AlChE Journal 1972, 18 (3), 540-547.
26. Roland, C. M. Viscoelastic Behavior of rubbery Materials, Oxford Press Inc.: New York, 2011.
27. Zak, A. R. Multiaxial Failure of viscoelastic Materials, United States Air Force, 1964.
28. Smith, T. L. Stress-strain-time-temperature Relationships in Polymers. Symposium on Stress-strain-
time-temperature Relationships in Materials, 1962, pp 60-89.
29. Dong, R. G. Description of Tensile Failure of Viscoelastic Materials Under Multiaxial Loading.
Polymer Engineering and Science 1970, 10 (2).
30. Bynum Jr., D., Traxler, R. N. Failure Envelopes for Asphaltic Concrete. Materiaux Et Constructions
1973, 6 (36).
31. Monismith, C. L., Secor, G. A., Secor, K. E. Temperature Induced Stresses and Deformations in
Asphalt Concrete. Proccedings of the Association of Asphalt Pavement Technologists Annual
Meeting,, pp 248-286.
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 13
13
List of Table Titles:
TABLE 1 Crude sources and modification types used in present study
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 14
14
List of Figure Captions:
FIGURE 1 (a) and (b) show relationship between LAS and Ductility at 4°C; (c) and (d) show the
relationship between MSCR parameters at 3.2 kPa and Ductility at 4°C.
FIGURE 2 (a) Effect of elastomeric modification on ductility at 4°C for different base binders,
(b) effect of elastomeric modification on real ductility ( % strain at Peak stress) at 4°C for
different base binders], (c) DSR-ductility shear stress against shear strain at 4°C.
FIGURE 3 Relation between ductility engineering strain at failure (assuming a 4 cm gauge
length) and DSR-ductility strain at peak stress, both measured at 4°C.
FIGURE 4 (a) True strain and engineering strain variation with ductility sample elongation, (b)
true strain rate and engineering strain rate variation as ductility sample elongates.
FIGURE 5 (a) Crosshead deflection curve with test time, and (b) true strain rate profile,
calculated for the asphalt ductility tests
FIGURE 6 FEM of asphalt ductility sample under elongation
FIGURE 7 Stress vs. Strain curve from finite element simulation using different crosshead speed
profiles.
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 15
15
TABLE 1 Crude sources and modification types used in present study
Crude Source Modification Types Base Performance Grade Modified Performance Grades
Russian Elvaloy 4170® (1 levels) PG 64-28 PG 70-28
Czech Republic Elvaloy AM® (2 levels) PG 64-22 PG 70-22, PG 76-22
Flint Hills SBS (2 Levels) PG 64-22 PG 70-22, PG 76-22
Valero Elvaloy 4170® (1 levels) PG 58-28 PG 64-28
Nustar SBS (2 Levels) Elvaloy
AM® (2 levels) PG 64-22 PG 70-22, PG 76-22
BP Elvaloy 4170® (2 levels) PG 58-28 PG 64-28, PG 70-28
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 16
16
(a) (b)
(c) (d)
FIGURE 1 (a) and (b) show relationship between LAS and Ductility at 4°C; (c) and (d)
show the relationship between MSCR parameters at 3.2 kPa and Ductility at 4°C.
0.0E+00
2.0E+05
4.0E+05
6.0E+05
8.0E+05
1.0E+06
1.2E+06
0 10 20 30 40
LA
S N
f (2
.5%
Str
ain
)
Ductility @4⁰C (cm)
0.0E+00
5.0E+03
1.0E+04
1.5E+04
2.0E+04
2.5E+04
0 10 20 30 40
LA
S N
f (5
% S
tra
in )
Ductility @4⁰C (cm)
0
10
20
30
40
50
60
70
80
0 20 40 60MS
CR
%R
eco
ver
y a
t 3
.2 k
Pa
Ductility @4⁰C (cm)
0
1
2
3
4
5
6
0 20 40 60MS
CR
Jn
r a
t 3
.2 k
Pa
(1
/kP
a)
Ductility @4⁰C (cm)
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 17
17
(a) (b)
(c)
FIGURE 2 (a) Effect of elastomeric modification on ductility at 4°C for different base
binders, (b) effect of elastomeric modification on real ductility ( % strain at Peak stress) at
4°C for different base binders], (c) DSR-ductility shear stress against shear strain at 4°C.
0
5
10
15
20
25
30
35
40
A B C D E F
Du
ctil
ity
at
4°C
(cm
)
Base Binder Type
Base Elastomeric ModificationX
0
200
400
600
800
1000
1200
1400
A B C D E FDS
R-D
uct
ilit
y P
eak
Str
ain
at
4°C
(-)
Base Binder Type
Base Elastomeric Modification
SBS
Modified Elvaloy
Modified
X
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 500 1000 1500 2000 2500
Str
ess
(MP
a)
Strain (%)
Nustar 76-22(ELV) Nustar 76-22(SBS)Nustar 70-22(SBS) Nustar
Elvaloy
Modified
SBS
Modified
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 18
18
FIGURE 3 Relation between ductility engineering strain at failure (assuming a 4 cm gauge
length) and DSR-ductility strain at peak stress, both measured at 4°C.
0
200
400
600
800
1000
1200
1400
0 200 400 600 800 1000 1200 1400
DS
R S
tra
in t
o P
eak
Str
ess
(%)
Ductility Engineering Strain at Failure (%)
Line of Equality SBS Modified
Elvaloy Modified Neat
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 19
19
(a) (b)
FIGURE 4 (a) True strain and engineering strain variation with ductility sample
elongation, (b) true strain rate and engineering strain rate variation as ductility sample
elongates.
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0 100 200 300
Str
ain
(-)
Elongation (mm)
True Engineering
0.000
0.001
0.002
0.003
0.004
0.005
0 100 200 300
Str
ain
Ra
te (
1/s
)
Elongation (mm)
True Engineering
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 20
20
(a) (b)
FIGURE 5 (a) Crosshead deflection curve with test time, and (b) true strain rate profile,
calculated for the asphalt ductility tests
0
50
100
150
200
250
300
0 500 1000 1500 2000 2500 3000 3500
Elo
ng
ati
on
(m
m)
Elapsed Test Time (sec)
Constant True Strain Rate (High)Constant True Strain Rate (Ave)Constant True Strain Rate (Low)Constant Crosshead Speed
0.000
0.001
0.002
0.003
0.004
0.005
0 50 100 150 200
Tru
e S
tra
in R
ate
(1
/s)
Elongation (mm)
Constant True Strain Rate (High)
Constant True Strain Rate (Ave)
Constant True Strain Rate (Low)
Constant Crosshead Speed
Tabatabaee, Clopotel, Arshadi, Bahia, 2013 21
21
(a)
(b)
FIGURE 6 FEM of asphalt ductility sample under elongation