Post on 30-Apr-2020
Journal ofTesting and Evaluation
Amir Hossein Sheikhmotevali1 and Mahmoud Ameri2
DOI: 10.1520/JTE20130306
Ranking of EVA ModifiedBitumens Based on AASHTOM320 Performance RelatedParameters
VOL. 44 NO. 4 / JULY 2016
Amir Hossein Sheikhmotevali1 and Mahmoud Ameri2
Ranking of EVA Modified BitumensBased on AASHTO M320 PerformanceRelated Parameters
Reference
Sheikhmotevali, Amir Hossein and Ameri, Mahmoud, “Ranking of EVA Modified Bitumens
Based on AASHTO M320 Performance Related Parameters,” Journal of Testing and Evaluation, Vol. 44,
No. 4, 2016, pp. 1–10, doi:10.1520/JTE20130306. ISSN 0090-3973
ABSTRACT
The AASHTO M320-10 bitumen specifications, and the measurements upon which they are
based, are designed to provide performance-related properties that can be related in a
rational manner to pavement performance. Some reports suggest that the AASHTO M320
specifications are well-suited for dealing with unmodified bitumens. However, a number of
studies question the validity of the AASHTO M320 specifications for modified systems. This
paper investigates the use and suitability of AASHTO M320 bitumen parameters for ranking
of plastomeric polymer modified bitumens. Two methods were used for the ranking of a
series of ethylene vinyl acetate (EVA) polymer modified bitumens (PMBs) in terms of the
three main distress modes associated with flexible pavements of low temperature cracking,
permanent deformation (rutting), and fatigue damage. AASHTO M320 bitumen parameters,
practical mechanical asphalt mixture properties were used for ranking of EVA PMBs then the
rankings were compared. Results show that AASHTO M320 bitumen parameters are valid for
EVA PMBs only at low polymer contents. It is an important conclusion because the high cost
of polymers makes the commercial use of modified bitumens only attractive for road
construction if the amount of polymer is relatively small.
Keywords
ethylene vinyl acetate, AASHTO M320, fatigue, rutting, low temperature cracking
Introduction
Fundamental, performance-based tests are not always easy to implement for acceptance. Many
agencies have found surrogate “performance-related” tests to be more convenient. Performance-
Manuscript received November 30, 2013;
accepted for publication December 15,
2014; published online January 27, 2015.
1 School of Civil Engineering, Iran Univ. of
Science and Technology, Narmak, Tehran
16846, Iran (Corresponding author),
e-mail: sheikhmotevalli@civileng.iust.ac.ir
2 Head of Center of Excellence for PMS,
Transportation and Safety, School of
Civil Engineering, Iran Univ. of Science
and Technology, Narmak, Tehran 16846,
Iran, e-mail: ameri@iust.ac.ir
Copyright VC 2015 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. 1
Journal of Testing and Evaluation
doi:10.1520/JTE20130306 Vol. 44 No. 4 / July 0000 / available online at www.astm.org
related tests and specifications closely simulate field conditions.
While not giving absolute answers, these performance-related
tests can be very effective at ranking materials and predicting
field failures. The AASHTO M320-10 [1] bitumen specifica-
tions, and the measurements upon which they are based, are
designed to provide performance-related properties that can be
related in a rational manner to pavement performance. Some
reports in the literature suggest that the AASHTO M320 specifi-
cations are well-suited for dealing with unmodified bitumens.
However, a number of studies question the validity of the
AASHTO M320 specifications for modified systems. Applica-
tion of polymers for bituminous pavement modification opens
new fields of application and research. The polymers that are
used for bitumen modification can be divided into two broad
categories, namely plastomers and elastomers. Despite consider-
able research about polymer modified bitumens (PMBs), plasto-
meric PMBs have still not been comprehensively characterized,
due to the complex nature and interaction of the bitumen and
polymer system. The literature on bitumen modification with
plastomeric polymers is quite scarce [2–6], especially with
respect to rheological properties. One of the principal plasto-
mers used in pavement applications is the semi-crystalline
copolymer, ethylene vinyl acetate (EVA). EVA polymers have
been used in road construction in order to improve both the
workability of the bitumen during construction and its defor-
mation resistance in service. This paper focuses on the use and
suitability of AASHTO M320 bitumen parameters for ranking
of polymer modified bitumens. The distress modes that are con-
sidered in this paper are rutting, load associated fatigue crack-
ing, and low temperature cracking.
AASHTOM320 BITUMEN RUTTING PARAMETER
The high temperature specification parameter for evaluating rut-
ting resistance (permanent deformation) in asphalt pavements
developed during the AASHTO M320 is a ratio of the complex
modulus and the phase angle (G*/sin(d)). The ineffectiveness of
the AASHTOM320 specification parameter G*/sin(d) in captur-
ing the high temperature performance of paving asphalts for rat-
ing their rutting resistance has been a significant concern [7,8].
There have been suggestions for refinement of the AASHTO
M320 specification parameter for the bitumens using new tests
and parameters such as repeated creep and recovery test [8],
G*/(1� (1/tan(d)sin(d))) [9], the zero-shear viscosity [8] and
multi stress creep recovery (MSCR) in AASHTO TP70-09 [10].
The zero-shear viscosity and permanent strain after repeated
creep test are difficult to run and determine, and have a lot of
questions as regards the accuracy of the measurements [7]. On
the other hand, the parameter G*/(1� (1/tan(d)sin(d))) needs a
change in the criterion requirement from the conventional 1000
Pa for unaged and 2200 Pa for rolling thin film oven test
(RTFOT)-aged at 10 rad/s to some other lower value at a lower
frequency in order to make it effective.
AASHTOM320 BITUMEN FATIGUE PARAMETER
The AASHTO M320 fatigue parameter was chosen to reflect
the energy dissipated per load cycle, which can be calculated as
G*sind. The specification prescribed a relationship whereby a
reduction in G*sind at 10 rad/s corresponds to improved fatigue
resistance. Validation of the AASHTO M320 bitumen fatigue
parameter with pavement performance has shown that,
although the bitumen properties are important, pavement struc-
tural effects may be equally or more important [11]. Bahia et al.
[8] reported that there was strong correlation between the
fatigue life of bitumen and that of mixture at intermediate tem-
perature and proposed cyclic fatigue test to replace the fatigue
parameter in the AASHTO M320 bitumen specification [8].
However, the testing time required to obtain the parameter was
too long to be an efficient specification test. Also, concerns
about repeatability and possible failures at boundaries of speci-
mens were raised by users of the test. Recent work by Martono
et al. [12] verified the suitability of using the dynamic shear rhe-
ometer for performing fatigue testing on bitumens and intro-
duced the concept of using a stress sweep or a strain sweep as
accelerated bitumen fatigue tests. Recently, Johnson et al. [13]
introduced a new fatigue testing protocol for bitumen, the mon-
otonic constant shear-rate test, which was demonstrated to have
great potential to be a fatigue test.
AASHTOM320 BITUMEN THERMAL CRACKING
PARAMETERS
Thermal cracking is widely recognized as a major cause of dis-
tress in asphalt pavements located in colder temperature cli-
mates. For a given pavement, the cracking temperature of the
bitumen used is considered to be a good indicator of the low
temperature cracking resistance of the whole pavement [14].
For unmodified bitumens, determination of cracking tempera-
ture is based on results from AASHTO T313 [15] bending
beam rheometer (BBR) test. Two bitumen parameters, i.e., the
stiffness and the m-value, are determined based on the BBR test
results at a loading time of 60 s. The cracking temperature is
defined as the temperature at which the stiffness reaches the
value of 300MPa or the m-value reaches the value of 0.3, or
moreover, the temperature at which one of the specification
thresholds is reached as temperature is decreased. The cracking
temperatures determined using BBR were found to be predictive
of low-temperature cracking in asphalt pavements constructed
using unmodified bitumens. However, it grossly over predicted
low-temperature cracking performance for modified bitumens.
As a result, for modified bitumens, additional testing using the
direct tension test (DTT) was proposed to address the case of
bitumens with a stiffness higher than 300MPa and with an
m-value greater than 0.3 [16,17]. In order to use the test, sophis-
ticated equipment (DTT and BBR) and analysis software are
required. Concerns were already raised about the expensive na-
ture of the approach because its use has become prohibitive to
Journal of Testing and Evaluation2
many practitioners. Shenoy [18] presented results that sug-
gested that BBR data alone may be sufficient for predicting
cracking temperature without the use of DTT data. Because of
the aforementioned issues, several surrogate test methods for
predicting cracking temperatures (Tcr) were developed by vari-
ous investigators. Roy and Hesp [19] used the thermal stress
restrained specimen test (TSRST) for predicting cracking tem-
peratures in both notched and un-notched bitumens. Kim [20]
and Mogawer et al. [21] developed the asphalt binder cracking
device (ABCD) for predicting cracking temperatures. The
authors reported a strong correlation between the cracking tem-
perature values using the ABCD method and the BBR and DTT
approach. It was, however, noted that use of the strain gauge
based method was cumbersome. In addition, the test provides
a narrow characterization of the low-temperature bitumen
properties [14].
Materials
The properties of aggregate and bitumen used in this research
study were presented in Tables 1 and 2, respectively. The poly-
mer used was EVA copolymer, which had melt indices (MI) of
2.5 g/10min, specific gravity of 0.938 g/cm3, and with a melting
point of 84�C (melting point is the temperature at which the
crystalline fractions of the EVA copolymer are melted) and
vinyl acetate (VA) content of 18 % by mass. Three levels of
EVA content were investigated namely 2, 4, and 6 % by weight
of bitumen. The polymer modified bitumens were prepared
using a low shear mixer at 180�C at a speed of 125 rpm. The
mixing time was 2 h. Table 4 shows bitumen codes used for
identification of test specimens.
The viscosity of bitumens at high temperature is an impor-
tant property since it reflects the bitumen’s ability to be pumped
through an asphalt plant, thoroughly coat the aggregate in hot
mix asphalt (HMA) mixture, and be placed and compacted to
form a new pavement surface. Table 4 shows the rotational vis-
cosity at 135�C according to AASHTO T316 procedure for all
bitumens. All bitumens satisfied the maximum limit for viscos-
ity of bitumens at 135�C set forth by AASHTO M320 (i.e.,
3.0 Pa s).
The aggregate gradation of all asphalt mixtures used in this
paper was shown in Fig. 1 and Table 3 which is typical for a
asphalt mixture wearing course with a maximum nominal
aggregate size of 12.5mm. The mixture design procedure was in
accordance with standard Marshall mix design procedure
(ASTM D1559-89 [22]) with compaction of specimens at
TABLE 1 Aggregate properties.
Properties Test Method Result Requirements
Coarse Aggregate
Los Angeles abrasion (%) AASHTO T96 20 maximum 30
Angularity (%) ASTM D5821 100 minimum 90
Elongation BS-812 11
Flakiness BS-812 22 maximum 25
Bulk specificgravity (gram/cm3)
AASHTO T85 2.654
Apparent specificgravity (gram/cm3)
AASHTO T85 2.709
Water absorption (%) AASHTO T85 0.8 maximum 2.5
Fine Aggregate
Plasticity Index AASHTO T89, T90 Non-plastic Non-plastic
Sand Equivalent AASHTO T1769 38
Bulk specificgravity (gram/cm3)
AASHTO T84 2.617
Apparent specificgravity (gram/cm3)
AASHTO T84 2.719
Water absorption (%) AASHTO T84 1.4 maximum 2.5
Filler (crushed limestone)
Plasticity index AASHTO T89, T90 Non-plastic
Specific gravity (gram/cm3) AASHTO T100 2.702
TABLE 2 Properties of unmodified bitumen.
Test Method
Parameters Unit ASTM AASHTO Results
Specific gravity gram/cm3 D70 T228 1.011
Penetration 0.1mm D5 T49 55
Softening point �C D36 T53 51
Ductility cm D113 T51 >100 cm
Solubility (%) D2042 T44 99.5
Flash point (Cleveland) �C D92 T48 303
Kinematic viscosity @ 120�C centistokes D2170 T201 1051
Kinematic viscosity @ 135�C centistokes D2170 T201 361
Kinematic viscosity @ 160�C centistokes D2170 T201 170
Heating loss — D1754 T179 �0.002Penetration after heating loss 0.1mm — — 47
Penetration after heatingloss to original penetration
% — — 85.4
Ductility after heating loss cm — — >50 cm
Penetration index — — — �0.73PVN (25–135) — — — �0.39
FIG. 1 Aggregate gradation of asphalt mixtures.
SHEIKHMOTEVALI AND AMERI ON PAVEMENT PERFORMANCE 3
75 blows on each side of cylindrical samples (10.16 cm in diam-
eter and 6.35 cm thick). Samples were prepared with bitumen
contents of 4.0, 4.5, 5.0, 5.5, 6.0, and 6.5 % by weight of the total
mix. The optimum bitumen content was found to be 5.6 % by
total weight of mixture for the asphalt mixture containing origi-
nal base bitumen. An optimum bitumen content of 5.6 % was
chosen for all mixtures so that the amount of bitumen would
not influence the analysis of the test data. For the dynamic
creep, creep compliance, and indirect tensile fatigue tests, the
specimens were compacted in a similar way. Table 4 shows mix-
ture codes used for identification of test specimens.
Methods
AASHTOM320 BITUMEN TESTS
In this research study, the properties of bitumens were eval-
uated using AASHTO M320 bitumen tests including the BBR
test (AASHTO T313) and the dynamic shear rheometer (DSR)
test (AASHTO T315-09 [23]). Three duplicate samples were
tested and the results were reported as the average of these tests.
In the DSR rutting test, the bitumens were tested at 58�C and a
frequency of 10 rad per second. In the DSR fatigue test, the bitu-
mens were tested using an 8mm parallel plate at 25�C. The
BBR test was conducted using each beam (125 by 6.35 by
12.7mm) at�12�C, and creep stiffness (S) and creep rate (m) of
the bitumens were measured at a loading time of 60 s.
ASPHALT MIXTURE PERFORMANCE TESTS
Dynamic Creep Rutting Test
For evaluating rutting resistance of asphalt mixtures, a dynamic
creep test under haversine shape load pulse was conducted for
all mixtures in accordance with NCHRP 9–19 [24]. In this
research study, dynamic creep test consists of 10 000 load cycles
with 0.1 s duration followed by a 0.9 s rest period and maximum
axial stress of 210 KPa at a test temperature of 54�C.
Indirect Tensile Fatigue Test
The indirect tensile fatigue test (ITFT) was used as a practical
method to estimate the resistance to cracking [25]. The test was
carried out at 250, 350, and 450 KPa stress levels in controlled
stress mode at 20�C with haversine wave shape. The load was
applied for 0.25 s followed by a rest period of 1.25 s. The failure
was established as the complete fracture of the specimen.
Creep Compliance Test at Low Temperature
Based on NCHRP-Report 530 [26], compliance values as deter-
mined using the indirect tensile procedure tend to agree very well
with those determined in uniaxial compression but not with val-
ues determined using uniaxial tension. Uniaxial compression is
suitable for determining creep compliance for research purposes;
thus, in this research study, a creep compliance test was per-
formed in uniaxial compression at �10�C. During this test, the
specimen was loaded with a constant load for 1000 s.
Results
RANKING OF POLYMER MODIFIED BITUMENS BASED
ON AASHTO M320 BITUMEN PARAMETERS
Result of DSR Rutting Test
The AASHTO M320 specifications specify minimum values of
1.0 and 2.2 KPa for the G*/sind of unaged and RTFOT-aged bitu-
mens, respectively, at the high performance grade temperature.
In general, the higher G*/sind values indicate that the bitumens
will be less susceptible to permanent deformation at high
pavement temperatures. The rutting resistance parameter, the
TABLE 3 Aggregate blending and gradation.
AggregateGravel
12–19 in.Gravel6–12 in.
Sand0–6 in. Filler
Blending (%) 8 23 68 1
SieveSize (mm) Percent Passing (%)
Job MixFormula
19 100 100
12.5 28 100 94
9 0 86 100
4.75 2 97 67
2.4 0 60 100 41
0.3 14 77 10
0.075 9 51 6.3
0.02 19
0.005 8
0.002 5
FIG. 2 Result of DSR rutting test at 58�C (unaged bitumens).
TABLE 4 Mixture and bitumen codes and compositions.
BitumenCode
Polymer Content byWeight of Base Bitumen (%)
Brookfield ViscosityPass @ 135�C
MixtureCode
O.B. 0 0.348 Control
EVA2 2 0.511 MEVA2
EVA4 4 1.04 MEVA4
EVA6 6 1.934 MEVA6
Journal of Testing and Evaluation4
G*/sind, of all bitumens, was measured at 58�C and the results
were shown in Figs. 2 and 3. For all bitumens, there is an increase
in G*/sind with an increase in EVA content. Therefore, the rut-
ting resistance is in the order EVA6>EVA4>EVA2>O.B.
Result of DSR Fatigue Test
In the AASHTO M320 bitumen specification, the product of
the complex shear modulus, G*, and the sine of the phase angle,
d, is used to help control the fatigue of flexible pavements. The
AASHTO M320 bitumen specification has a maximum value of
5000 KPa for G*sind and lower G*sind values are generally con-
sidered desirable attributes from the standpoint of resistance to
fatigue cracking. The G*sind values of all bitumens were
depicted in Fig. 4. This trend shows fatigue resistance is in the
order EVA4>EVA6>EVA2>O.B.
Result of BBR Test
The creep stiffness modulus (S) and creep rate (m) of all bitu-
mens were determined by the BBR software at 60 s loading time
and shown in Figs. 5 and 6, respectively. Stiffness modulus and
m-value of all bitumens in this research study meet AASHTO
M320 requirements. The S-value is no more than 300MPa and
m-value is larger than 0.3. Figure 5 indicates that the values of
stiffness modulus (S) of bitumens decrease with the increase of
EVA content, whereas the m-values shows its respective change
law (Fig. 6). As the stiffness modulus (S) increases, the thermal
stresses developed in the pavement due to thermal shrinking
also increase, and thermal cracking becomes more likely. On
the other hand, as the m-value decreases, the rate of stress relax-
ation decreases and the ability of the flexible pavement to relieve
thermal stresses by flow decreases. Therefore, bitumens with the
smaller stiffness modulus and the larger m-value have a good
low temperature anti-cracking property. The smaller the S/m,
the better the low temperature performance is. The relationship
between S/m and EVA content (Fig. 7) shows low temperature
cracking resistance is in the order of EVA4>EVA2>O.B.
>EVA6.
RANKING OF POLYMER MODIFIED BITUMENS BASED
ONMECHANICAL TESTING OF MIXTURES
Because the same aggregate gradation was used for all mixtures,
the test results could directly represent the effects of bitumens
used in the mixtures on their performance and rank them.
Result of Dynamic Creep Test
Figure 8 shows the relationship between the number of cycles
and the axial accumulated permanent deformation for the
tested groups. The relationship between the accumulated
FIG. 3 Result of DSR rutting test at 58�C (RTFOT aged bitumens).
FIG. 4 Result of DSR fatigue test at 20�C (PAV aged bitumens).
FIG. 5 Result of BBR test S-value variation at �12�C (PAV aged bitumens).
FIG. 6 Result of BBR test m-value variation at �12�C (PAV aged bitumens).
SHEIKHMOTEVALI AND AMERI ON PAVEMENT PERFORMANCE 5
permanent strain and the number of load repetitions are
expressed generally in the form:
e ¼ a Nð Þb(1)
where:
e¼ the accumulated permanent strain due to dynamic ver-
tical loading,
N¼ the number of load applications that produced e, and
a and b¼ regression constants that depend on the material
and stress state conditions.
Analyses from laboratory tests were successful in identify-
ing parameters that could be considered suitable indicators of
mixture sensitivity to permanent deformation. For repeated
loading compression tests, they include the coefficients a and b
from the best-fit line on the log–log plot of accumulated strain
versus load repetitions and the flow number. The b and a values
were obtained for all mixtures and presented in Figs. 9 and 10,
respectively. Lower b values suggest mixes with lower rutting
susceptibility; hence the rutting resistance is in the order
MEVA4>MEVA6>MEVA2>Control.
Result of Indirect Tensile Fatigue Test
Figure 11 shows the number of cycles to failure in the force
(stress)-controlled mode. Figure 12 shows the constants of the
regression equations relating the fatigue life to stress levels. The
general equation for the relationship is in the form of Eq 1:
Nf ¼ k1 rð Þ�k2(2)
where:
Nf¼ the fatigue life of the asphalt mixture,
r¼ the tensile stress, and
k1, k2¼ the fatigue coefficients.
There is an increasing trend in the resistance to fatigue
damage with increasing EVA content so the fatigue resistance is
in the order MEVA6>MEVA4>MEVA2>Control.
Result of Creep Compliance Test
In rheological theory, the Burger model is a classical four-unit
mode (two spring components and two dashpot components)
and very suitable to describe the viscoelasticity of bituminous
material. Equation 3 shows the relationship between creep com-
pliance and four Burgers model parameters at time t.
DðtÞ ¼ 1E1þ t
g1þ 1E2
1� e�E2g2t
� �(3)
FIG. 7 S/m-value variation at �12�C (PAV aged bitumens).
FIG. 8 Result of dynamic creep test at 54�C.
FIG. 9 Creep strain slope of all mixtures at 54�C.
FIG. 10 Intercept of creep curves of all mixtures at 54�C.
Journal of Testing and Evaluation6
where:
D(t)¼ creep compliance, 1/MPa,
E1 and E2¼ instantaneous and delayed elastic modulus,
MPa, respectively, and
g1 and g2¼ both viscous coefficient, MPa s.
The four Burgers’ parameters in Eq 3, relaxation time
(k1 ¼ E1=g1), and delay time (k2 ¼ E2=g2) were calculated
based on the results of creep compliance test (Fig. 13). The
results were shown in Table 5.
For viscoelastic materials, the external work can transform
into the energy of the following forms: elastic strain energy
stored in materials, dissipation energy caused by the material
flow, and surface energy caused by crack occurrence and devel-
opment [27]. During the creep test, the load applied to the spec-
imen is constant and small, and the specimen cannot be broken
until test time is over. Therefore, the external work can be trans-
formed as stored energy and dissipation energy, which mainly
makes the material flow. Considering the nature of Burger’s
model components, springs are associated with storage and
dashpots with dissipation of deformation energy; therefore, the
Burger’s model parameters are used to calculate dissipated and
stored energy. The energy per volume, W, is integrated for each
spring and dashpot in the model with the general relation
W ¼Ð
rde, which is based on the definition of mechanical
work as force times path. For stored and dissipated energy, Eq 4
and Eq 5 are obtained [27]:
Wstored tð Þ ¼ r20
1E1þ 12E2
1� 2e�E2g2t þ e�
2E2g2t
� �� �(4)
Wdissipated tð Þ ¼ r20
tg1þ 12E2
1� e�2E2g2t
� �� �(5)
In order to fully investigate the influence of EVA on the low tem-
perature performance, the concept of dissipation energy ratio
(DER), which is defined as a ratio between dissipation energy
and stored energy, was used in the analysis. The larger dissipation
energy or DER implies the material has a good internal flow, i.e.,
material has a good ability to relax the stresses in material [27].
DER ¼
tg1þ 12E2
1� e�2E2g2t
� �1E1þ 12E2
1� 2e�E2g2t þ e�
2E2g2t
� �(6)
The DERs of control and EVA modified mixtures were calculated
by Eq 6 (t¼ 60 s) according to Ref. [27]. Change of DERs with
EVA content was plotted in Fig. 14 so the low temperature cracking
resistance is in the order MEVA4>MEVA2>Control>MEVA6.
COMPARISON OF BITUMEN RANKING METHODS
G*/sin d— b Value Diagram
The bitumen high temperature parameter, G*/sind was plotted
against rutting parameter, b value. As seen in Figs. 15 and 16, the
FIG. 11 Result of indirect tensile fatigue test of all mixtures.
FIG. 12 Constants of asphalt mixtures fatigue life equation.
FIG. 13 Creep compliance curve of all mixtures at �10�C.
TABLE 5 Variation of burger model parameters with polymer
content.
Control MEVA2 MEVA4 MEVA6
E1 (MPa) 132 110 370 231
E2 (MPa) 111 141 672 1133
g1 (MPass) 3833 1318 3912 14 124
g2 (MPass) 178 137 157 198
Relaxtion time (s) 29 12 11 61
Delay time (s) 1.61 0.97 0.23 0.17
SHEIKHMOTEVALI AND AMERI ON PAVEMENT PERFORMANCE 7
relationship is linear except at 6 % polymer. This indicates that
the current AASHTO M320 high temperature bitumen specifi-
cation is valid for low polymer contents and does not capture
the complete performance characteristics of the modified sys-
tems at high polymer contents.
G*sin d—K2 Diagram
Using the hypothesis that a reduction in G*sind will correspond
to improved fatigue resistance, the G*sind values were com-
pared with the K2 values (Fig. 17). It is observed that with the
increase in EVA content, the fatigue resistance is improved,
while the G*sind values of corresponding bitumens is decreased
except at 6 % polymer and so AASHTO M320 intermediate
temperature bitumen specification is valid for low polymer con-
tents and it is not possible to use AASHTO M320 for fatigue
evaluation of EVA PMBs at high polymer contents.
S/m—DER Diagram
The ranking as a function of the mixture DER parameter and
bitumen S/m value was presented in Fig. 18. It is observed that
FIG. 14 Variation of DER parameter with polymer content at �10�C.
FIG. 15 Comparison of bitumen G*/sin(d) ranking and mixture b value
ranking (unaged).
FIG. 16 Comparison of bitumen G*/sin(d) ranking and mixture b value
ranking (RTFOT aged).
FIG. 17 Comparison of bitumen G*sin(d) ranking with mixture fatigue K2
ranking.
FIG. 18 Comparison of bitumen S/m ranking with mixture DER ranking.
Journal of Testing and Evaluation8
except at 6 % EVA, by decreasing S/m-value, the mixture DER
parameter is increased. From the above analysis, one can con-
clude that thermal cracking performance of EVA PMBs at high
polymer contents is mixture-dependent and cannot be pre-
dicted from bitumen properties.
Conclusions
In present paper, two methods were used for performance rank-
ing of a series of EVA PMBs in terms of the three main distress
modes associated with flexible pavements of low temperature
cracking, permanent deformation (rutting), and fatigue damage.
AASHTO M320 bitumen parameters, practical mechanical
asphalt mixture properties were used for the ranking of EVA
PMBs, and then the rankings were compared. The following
conclusions were obtained:
• AASHTO M320 bitumen parameters, G*/sind andG*sind, give a good indication of relative rutting andfatigue resistance for polymer modified bitumens at lowpolymer contents; however, it is not possible to evaluatefatigue and rutting resistance of PMBs at high polymercontents from the bitumen properties correctly.
• AASHTO M320 bitumen parameters, S- and m-values,show good relation to thermal cracking performance ofPMBs at low polymer contents. Mixture characteristicsmay have a significant effect on the thermal cracking per-formance of polymer modified bitumens at high polymercontents.
• AASHTO M320 bitumen parameters are valid for PMBsonly at low polymer contents. It is an important conclu-sion because the high cost of polymers makes the com-mercial use of modified bitumens only attractive for roadconstruction if the amount of polymer is relatively small.For evaluation of polymer modified bitumens at highpolymer contents, tests should be conducted on mixturesto provide a reasonable expectation of the performance ofthe polymer in the mixture, and AASHTO M320 bitumenparameters may result in misleading ranking.
References
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