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Investigation of Flow Properties of Asphalt BindersContaining Polymer Modifiers
Yu-Hsun Nien,1 Pei-Hung Yeh,2 Wei-Chyum Chen,3 Wen-Tsung Liu,3 Jean-Hong Chen1
1Department of Polymer Materials, Kun Shan University, Yung-Kang City, Tainan Hsien 710, Taiwan
2Department of Applied Chemistry, Chaoyang University of Technology, Wufong Township, Taichung County41349, Taiwan
3Department of Civil Engineering, Kao Yuan University, Lujhu Township, Kaohsiung County 82151, Taiwan
Modified asphalts using polymeric additives, includingisotactic polypropylene (iPP) and different degrees ofchlorinated polypropylene (CPP), have been preparedand examined using differential scanning calorimetry(DSC), scanning electron microscopy (SEM), rotationalviscometer, and dynamic shear rheometer (DSR) in thisstudy. The results of DSC studies show that differentlevels of the crystallization occur in asphalt/iPP blendsbecause most of the crystallinity of iPP remain intact inthe blend, while those asphalt samples having CPPtend to affect the thermal behavior in the DSC thermo-grams because of increasing the amorphous region ofCPP. From the images of SEM, the distinctions of thephase distributions between the asphalt/iPP andasphalt/CPP blends illustrate that the chlorine contentin CPP is a significant factor in controlling its compati-bility with asphalt. The rheological studies show thatthe asphalt blends containing CPP (26 wt% of Cl) ex-hibit higher viscosity in terms of higher temperature toget Newtonian behavior and display superior rutting re-sistance to avoid permanent deformation at high tem-perature. POLYM. COMPOS., 29:518–524, 2008. ª 2008 Societyof Plastics Engineers
INTRODUCTION
Since the advent of asphalt blocks in paving industry,
efforts to improve the properties of asphalt surfacing
materials have centered on polymeric additives. Polymers
typically employed in polymer modified asphalt (PMA)
include plastics, elastomers, and fibers [1–5]. For instance,
the addition of styrene-butadiene-styrene copolymers
(SBS) block elastomer to asphalt increases the rutting
resistance of PMA at high temperature and improves the
ductility, elasticity, and cyclic loading properties of the
mixture at low temperatures [6]. It is known that additions
of polymers increase the cost of the corresponding PMA.
Therefore, recyclable polymers have been chosen as the
modifiers to provide the functions of improving the prop-
erties of asphalt surfacing materials within the past few
years [7–10]. If price and availability of various polymers
that have been proposed for asphalt modification are con-
sidered, it is obvious that polyolefins or vulcanized rubbers
would be more economical than other polymeric can-
didates. Further, polyolefins, either from virgin material or
from recycled waste, comprise approximately 60% of
plastic solid wastes. Therefore, incorporation of these ma-
terials into PMA can be an effective method of polymer
recycling and improve the properties of asphalt paving.
Thermoplastics, such as partially crystalline polyole-
fins, combine the advantages of rubber and fibers. The
crystalline segments of polyolefins serve as high strength
fillers in the asphalt/polymer blend and improve the blend
properties and overall service conditions [11]. However,
the polyolefins are only slightly compatible with asphalt;
thus, the blends tend to separate at high temperature. On
the contrary, amorphous segments of thermoplastics give
asphalts improved flexibility to improve resistance to per-
manent deformation and increase elastic modulus [1, 12].
For instance, ethylene–vinyl acetate copolymers (EVA)
are more compatible with asphalt, leading to the enhance-
ment of the blends tested in the areas of fatigue resistance
and field performance [13]. Unfortunately, the properties
of EVA blends may vary substantially depending upon
the asphalt used to prepare the PMA, and unsatisfactory
mixes may be produced. For any specific asphalt cement
(AC), the physical properties of the asphalt/polymer blend
are affected by the amount of polymeric material added,
its composition, its molecular weight, etc. However, the
most important variable is the compatibility of the AC
Correspondence to: Pei-Hung Yeh; e-mail: [email protected]
Contract grant sponsor: National Science Council, Taiwan.
DOI 10.1002/pc.20404
Published online in Wiley InterScience (www.interscience.wiley.com).
VVC 2008 Society of Plastics Engineers
POLYMER COMPOSITES—-2008
with the admixed polymer. The ability to enhance the
compatibility between asphalt and polymer is complicated
further by source dependent variations in asphalt composi-
tions within a given grade. Thus, the introduction of an
incompatible polymer into such a system generally results
in asphaltene flocculation and oil bleeding, which is the
main reason of a binder having no cohesion [14]. Even if
the phase separation of the asphalt components is not
apparent, extended mixing times will be required to
achieve acceptable mixes [15].
One of the various approaches to improve the compa-
tibility of asphalt/polymer blends is the utilization of
chemical modification of polymer additive to enhance the
interaction of the amorphous regions of the polymer with
the asphalt phase [16–20]. In this article, isotactic polypro-
pylene (iPP), with various degrees of chlorination, were
designed to increase the interaction between polymer and
polar components of asphalt. The asphalt blends were
compared with the unmodified asphalt to assess the ther-
mal transition properties of asphalt blends by differential
scanning calorimetry (DSC), the phase structures of the
asphalt blends by scanning electron microscopy (SEM),
and the rheologic properties of asphalt blends by rotational
viscometer and dynamic shear rheometer (DSR).
EXPERIMENTAL METHODS
Materials
Tank asphalt ACP-1 (tank asphalt) for the base mate-
rial in this study was obtained from the Chinese Petro-
leum Corporation, Taiwan. The physical properties of this
asphalt were as follows: penetration, 98 mm (258C,ASTM standard D5); Flash Point, 2198C (ASTM standard
D92); softening point, 488C (ASTM standard D36); and
solubility in trichloroethylene, 99.0% (ASTM standard
D2042). Polymers investigated as asphalt additives were
iPP (isotactic, spherical particles), and two types of
chlorinated polypropylene (26 wt% of Cl and 32 wt% of
Cl, noted as CPPA and CPPB, respectively), which were
purchased from Aldrich Co.
Preparation of PMA
Unless specified otherwise, the modified asphalt was
prepared by adding 3% or 5% by weight of polymer to
the tank asphalt. The asphalt was preheated to 1808C in a
small container, and then polymer was added into the
tank asphalt while the blend was mixed with a high shear
mixer. Then the polymer asphalt blend was stirred at
1608C for 40 min.
Microscopic Behavior of Asphalt/Polymer Blends
Images of asphalt samples were observed using a
scanning electron microscope (JSM-5610, model E-3) to
examine asphalt/polymer phase distribution. The structural
formation of asphalt samples was recorded using a camera
connected to the SEM. The SEM power was 0.5 keV and
the magnification ranged up to 250.
Measurement of DSC
Thermal analyses of tank asphalt and asphalt blends
were performed by DSC (Perkin Elmer Pyris Diamond) in
a nitrogen atmosphere at a flow rate of 20 ml/min. The
sample for DSC was sealed in aluminum sample pans
using an empty aluminum sample with cap as a reference.
The data were collected from �558C to 2008C at a heating
rate of 108C/min. The glass transition temperatures (Tg),melting points (Tm), and heat of fusion (Hf) of the blend
components were determined as previously described [21].
Measurement of Rotational Viscometer
Viscosity measured for each blend was based on
ASTM D4402-02 and AASHTO TP48-97 by a rotational
viscometer (Brookfield) at 608C (spindle no. 29) and at
1358C (spindle no. 27), respectively.
Measurement of DSR
A dynamic shear rheometer, CSR-500 model (Carri-
Med, Dorking, England), was used for dynamic mechani-
cal analysis of asphalt binders with 1,000 Pa stress at a
rate of 1.6 Hz to characterize the viscous and elastic
behavior of asphalt binders at intermediate and high
service temperatures. The samples were ‘‘sandwiched’’
between two parallel plates with a diameter of 25 mm
and a gap of 1 mm and the temperature was raised from
308C through one cycle before performing a temperature
sweep to 808C. The DSR measured the viscoelastic prop-
erties by measuring the strain response of the specimen to
a fixed torque, measuring the G*, G00, and G0 propertiesof asphalt binders as subjected to oscillator shear stress.
Under these conditions, the asphalt samples were also run
under a frequency sweep from 0.2 to 2.0 Hz at 308C to
comply with the asphalt binder specifications of Strategic
Highway Research Program (SHRP).
RESULTS AND DISCUSSION
Thermal Properties of Asphalt Binders
The applications of DSC analysis of asphalt blend to
evaluate the endothermic transitions from the melting/dis-
solution of crystalline and amorphous regions of asphalt
blends have been reported [22]. A comparison of DSC
thermograms of iPP, tank ACP-1, and ACP-1 blended
with 3% of the iPP, and chlorinated iPP is shown in
Fig. 1. In addition, the results of the effect of iPP, CPPA,
and CPPB contents on the melting points (Tm), heat of
DOI 10.1002/pc POLYMER COMPOSITES—-2008 519
fusion (DHf), and crystallinity (%) of the asphalt blend
components are also listed on Table 1 [23]. The results
show that there is no significant change in the glass tran-
sition of asphalt between the tank asphalt and the asphalt
blends at temperatures ranged between �308C and 308C.However, the thermogram of pure iPP (curve B) has melt-
ing peak at 1628C and the heat of fusion is 88.7 J/g, but
the melting transition of ACP-1/3% iPP blend (curve C)
is reduced to a broader less intense transition around
1568C and the heat of fusion (DHf ¼ 2.7 J/g) is close to
3% of the heat of fusion that observed from pure iPP (3%
of DHf of pure iPP ¼ 2.7 J/g). It shows that most of the
crystallinity of iPP remain intact in the blend, indicting
that there is insignificant interaction between the iPP and
the asphalt matrix when the iPP concentration is 3%.
When the concentration of iPP increases up to 5%, the
melting transition of the 5% iPP asphalt blend displays
the same as the melting transition of the 3% iPP/ACP-1
blend (Table 1). However, the heat of fusion (DHf ¼ 12.6
J/g) of 5% iPP asphalt blend is larger than 5% of pure
iPP (5% of DHf of pure iPP ¼ 4.4 J/g). The discrepancy
between the observed and calculated DHf implies that the
increasing DHf of 5% iPP asphalt blend may be referred
to the aggregation of iPP chains to crystallize in the
asphalt matrix, and induces the phase separation in the
blend as the iPP content reaches to 5%. On the contrary,
the melting point of asphalt blends having CPPA and
CPPB disappears in the DSC thermograms. This phenom-
enon points out that the introduction of chlorine atoms
into the iPP backbone changes the polarity and reduces
the crystallinity of the polymer (CPPA or CPPB), which
significantly affects the microstructure and thermal behav-
ior of the polymer by increasing the amorphous region
and enhancing the interaction between the polymer and
the asphalt matrix.
Phase Distribution of PMA Blend
The morphology of asphalt blends was viewed with
SEM to examine phase distribution and structure. Figure
2 shows the SEM images of tank asphalt ACP-1 without
any modifier, 3%, and 5% of the asphalt/polymer blends.
The SEM micrograph of ACP-1 blend with 3% iPP (Fig.
2B) or 5% iPP (Fig. 2C) shows that it obviously has two
phases, the asphalt phase and polymer phase, either in 3%
or 5% of the asphalt/iPP blends. It implies that phase sep-
aration severely occurs in the asphalt/iPP blend. However,
Fig. 2D shows the SEM image of 3% asphalt/CPPA dis-
plays no clear-cut interface between CPPA and asphalt,
while the ACP-1 blend with 3% CPPB shows a distinct
boundary between asphalt and CPPB in Fig. 2F. This
indicates that 3% of the asphalt/CPPA blend exhibits
more compatibility with asphalt matrix than 3% of the
asphalt/CPPB blend. In this study, the boundaries between
asphalt and CPP additives in 5% of the asphalt/CPPA
blend (Fig. 2E) as well as the asphalt/CPPB blend (Fig.
2G) are less observable than that in 3% of the asphalt/
CPPA blend (Fig. 2D) and the asphalt/CPPB blend (Fig.
2F). A comparison of the SEM micrographs of asphalt/
iPP blends and asphalt/CPP blends suggests that CPP
additives in asphalt blends result in better dispersion of
polymer into the asphalt phase than iPP additive and
affect the phase distribution of asphalt blends. It had been
reported that more highly dispersed polymer rich phases
are expected to improve the toughness of brittle asphalt at
low temperatures and reinforce asphalt at high tempera-
tures [24]. Therefore, the distinctions of the phase distri-
butions between the asphalt/iPP and asphalt/CPP blends
illustrate that the chlorine content in CPP is a significant
character in controlling its compatibility with asphalt.
Viscosity of Asphalt Blends
The effect of the iPP and CPP additives with various
concentrations on viscosity for each of the asphalt blends
is listed in Table 2. The data illustrate that the viscosity
of asphalt blends is higher than the asphalt matrix and
FIG. 1. DSC thermograms of ACP-1 (curve A), pure iPP (curve B),
3% iPP blend (curve C), 3% CPPA blend (curve D), and 3% CPPB
blend (curve E).
TABLE 1. Influence of iPP, CPPA, and CPPB contents on the thermal
thermograms of the asphalt blends.
Sample Content (%) Tm (%C) DHf, (J/g) Crystallinitya (%)
iPP 0 162.4 88.7 42.4
ACP-1/iPP 3 156.4 2.7 1.3
ACP-1/iPP 5 156.6 12.6 6.0
CPPA 0 27.8 1.8 0.9
ACP-1/CPPA 3 –b – –
ACP-1/CPPA 5 – – –
CPPB 0 42.0 1.2 0.6
ACP-1/CPPB 3 – – –
ACP-1/CPPA 5 – – –
a The percent crystallinity of the modified samples was based upon
the reported theoretical DHf of iPP of 209 J/g.b The Tm and DHf in the thermal thermograms of ACP-1/CPPs
blends are not obvious and can not be detected by DSC.
520 POLYMER COMPOSITES—-2008 DOI 10.1002/pc
increases with the varied modifiers and their concentra-
tions at medium and high temperature ranges. Note that
in no case does the viscosity of a blend exceed the SHRP
criterion of 3 Pa s upper limit, in order to ensure that the
binder can be adequately pumped and mixed with the
aggregates at 1358C [25]. The asphalt with 5% of CPPA
increases the viscosity significantly than those 3% and 5%
of iPP as well as those CPPB at 60 and 1358C. Further,
as confirmed by SEM observation, asphalt blends contain-
ing CPPA exhibit higher viscosity. However, the observa-
tion from Table 2 shows the presence of the higher chlo-
rine content of CPPB in asphalt blends displays lower
viscosity than the asphalt blends containing iPP and
CPPA. Contrary to the expectation, the higher the chlo-
rine content of modified iPP, the lower is the viscosity of
the asphalt blend. Therefore, controlling the degree of
chlorination in modification of iPP can be considered as
an important factor to control the asphalt flow behavior.
Rheological Properties of Asphalt Blends
The linear viscoelastic moduli of asphalt binder under
oscillating conditions to yield dynamic mechanical prop-
erties can be measured by DSR to simulate traffic loading,
because the data can be acquired within the linear range
of the asphalt in a loading mode. In analyzing the rheo-
logic properties of asphalt binder, G*, the ratio of the
peak stress to the peak strain, reflects the total stiffness.
The in-phase component of jG*j is the shear storage
FIG. 2. SEM of (A) tank ACP-1 without any modifier (B) ACP-1% þ 3% iPP (C) ACP-1% þ 5% iPP (D)
ACP-1% þ 3% CPPA, (E) ACP-1% þ 5% CPPA (F) ACP-1% þ 3% CPPB (G) ACP-1% þ 5% CPPB;
magnification �250.
TABLE 2. Influence of iPP, CPPA, and CPPB contents on the
viscosity (Z; Pa s at 60 and 1358C) of modified asphalts.
Sample Content (%) 608C 1358C
ACP-1 0 116 0.31
ACP-1/iPP 3 274 0.74
ACP-1/iPP 5 407 1.13
ACP-1/CPPA 3 391 0.80
ACP-1/CPPA 5 921 1.58
ACP-1/CPPB 3 162 0.34
ACP-1/CPPB 5 230 0.51
DOI 10.1002/pc POLYMER COMPOSITES—-2008 521
modulus, G0 (the elastic portion), the out-phase compo-
nent of jG*j is the loss modulus, G00 (the viscous portion),
and tan is a mechanical damping or internal friction, i.e.
tan d ¼ G00/G0, sin d ¼ G00/G*, and G* ¼ G0 þ iG00. Ifthe isochronal sin d value is 1, the system is considered
as a Newtonian fluid, i.e. the storage modulus vanishes
since sin d % 1, G*/sin d % G00. The isochronal sin
curves are a function of temperature for asphalt blends, as
illustrated in Fig. 3. It displays that sin d value of the
tank ACP-1 approaches unity and the asphalt blends ex-
hibit less than 1 at 528C. A sin d of unity confirms that
tank ACP-1 exhibits a Newtonian flow at temperatures
equal to or greater than 528C, while the other asphalt
blends display the viscoelastic properties at 528C. How-ever, the isochronal sin curves of the blends approach
unity above 708C as the viscoelastic asphalt binders begin
to flow as Newtonian fluids except the asphalt/CPPA
blends. In addition, as the polymer concentration in-
creases, higher temperatures are required for all of asphalt
blends to attain Newtonian behavior. As can be seen in
Fig. 3, CPPA modified asphalt blends exhibit lower sin dthan those of asphalt blends above 308C. It illustrates thatthere is an increased viscoelastic component in the CPP
modified asphalt blends over a wide temperature range,
which could be responsible for the good interaction of
chlorinated iPP with the polar fractions of asphalt matrix.
Increasing viscoelastic properties in asphalt/CPPA blends
at higher temperatures should improve their pavement
performance at maximum in-service temperature.
The effect of frequency sweeps on the sin d values of
asphalt binders at 308C is illustrated in Fig. 4. The addi-
tion of polymeric additives leads to decrease in sin d val-
ues of asphalt blends than the tank asphalt at all frequency
ranges. It suggests that all of the PMAs blends exhibit
more elastic behavior than tank asphalt in frequency stud-
ies. In addition, it can be seen that the sin d values of
asphalt binders decrease significantly with increasing both
the polymer concentrations and frequencies. Note that
there is no difference of sin d value between 3% and 5%
of the asphalt/iPP blends at 0.2 Hz. However, the differ-
ence of sin d values between both 3% and 5% of asphalt/
iPP blends changes gradually as the frequency increases.
This phenomenon reveals that the flow property of the
asphalt/iPP blend is not related to the polymer concentra-
tion at low frequency, but is associated with the volume of
iPP at high frequency. Besides, the asphalt blend contain-
ing 5% CPPA has the lowest sin d value at all frequencies.
It indicates that the blend has the best viscoelastic property
among all of the asphalt binders in this study.
To evaluate the permanent deformation of asphalt
binder, G*/sin d is selected to express the contribution of
asphalt binder to rutting properties. From the SHRP sug-
gestions, the G*/sin d value should be larger than 1 kPa
at 10 rad/s for the original binder at a maximum pave-
ment design temperature. Higher values of G*/sin d value
are expected to result in high resistance to permanent de-
formation. Figure 5 shows the isochronal plot of G*/sin dthat reveals distinct differences because of the polymeric
modifiers, which may interact with asphalt. The results of
polymer additions leading to improvement on the per-
formance grade of the PMAs are listed in Table 3. It can
be observed that the in-service temperature of the asphalt
blend is enhanced by the effects of polymeric modifier
and concentration, with increasing the benefit of road per-
formance. Note that all the modified asphalt binders are
qualified according to SHRP suggestions of the stiffness
parameter at 648C, except the asphalt matrix. However,
only the asphalt blends containing chlorinated iPP meet
the SHRP suggestions at 708C or higher service tempera-
tures. As an in-service temperature of asphalt binder,
when the temperature is below 708C, the G*/sin d value
of the asphalt/CPPA binder to the qualification of the
SHRP suggestions is up to 908C, which is enough to
avoid permanent deformation. These observations imply
that introduction of chlorine atoms may enhance the
FIG. 3. Variation of sin d with temperature for ACP-1 and the blends
of ACP-1 with 3% and 5% of polymer additives. Dash lines are set at
sin d ¼ 1.0, T ¼ 528C and 708C.
FIG. 4. Variation of sin d with frequency sweeps for ACP-1 and the
blends of ACP-1 with iPP and CPPs at 308C.
522 POLYMER COMPOSITES—-2008 DOI 10.1002/pc
compatibility between the polymer additives and asphalt
depending upon the degree of chlorination. Therefore, the
rheological response of blends with CPPA may have im-
portant benefits as road paving binders on improving
binder resistance to rutting.
Figure 6 displays the influence of frequency sweeps on
the G*/sin d values of asphalt binders at 308C. It exhibitsthat the G*/sin d values of all modified asphalt binders
increase with frequency and concentration. An increase in
frequency yields an increase in the G*/sin d value for all
asphalt binders in this study. As may be seen in Fig. 6,
the lowest G*/sin d value of asphalt blend is observed for
the blend containing 3% CPPB in the whole frequency
range, even when the CPPB concentration up to 5%
exhibits the same performance of the asphalt matrix at
high frequency range. Unlike the results of the rutting
parameter under the temperature sweep at constant
frequency (Fig. 5), the presence of CPPB modifier in tank
asphalt does not expect to enhance the rutting resistance
in the frequency studies. A comparison of the asphalt
blends containing CPPA and CPPB in Fig. 6 shows that
the G*/sin d values of 3% asphalt/CPPA blend is higher
than that of 5% asphalt/CPPB blend. The difference
between the G*/sin d values of CPPA and CPPB modified
asphalt binders may explain that the degrees of chlorina-
tion in iPP play an important role on the reinforcement of
asphalt binder in rutting properties. On the other hand, an
inspection of Fig. 6 illustrates that there is no significant
difference between 3% asphalt/iPP blend and 3% asphalt/
CPPA blend at all frequency ranges. However, the G*/sind value of the 5% iPP modified blend is higher than that
of the blend containing 5% CPPA at high frequencies.
This observation implies, unlike the influence of tempera-
ture on rutting properties, that the presence of the higher
crystalline component of iPP in the asphalt matrix exhib-
its better performance on responding to rutting properties
in the frequency studies.
CONCLUSIONS
Modified asphalts using polymeric additives, including
iPP and different degrees of chlorinated polypropylene
(CPP), have been prepared and reported in this study.
Chlorination of polypropylene at different levels is an
effective means to change the properties of the iPP as a
modifier for improving the thermal and rheological prop-
erties of asphalt binder. The results of DSC studies show
that different levels of the phase separations occur in
asphalt/iPP blend, while those asphalt samples having
CPPA or CPPB tend to disappear with the endothermic
transition in the DSC thermograms because of the
increase of the amorphous region of CPPA or CPPB. The
images of the SEM, which show the phase distribution of
asphalt blends, exhibit that the blends containing chlori-
nated iPP are more compatible than the corresponding
blends with pure iPP. The viscosity of asphalt blend
increases, resulting in improvement of its high tempera-
ture properties, in terms of higher temperature to attain
Newtonian behavior. However, the asphalt blends contain-
ing CPPB (32 wt% of Cl) display lower viscosities and
higher sin d values than the asphalt blends containing iPP
and CPPA in this study. It is also found the enhancement
FIG. 5. Comparison between rutting factor of tank ACP-1 and the
modified asphalt blends. Dash lines are set at G*/sin d ¼ 1 kPa, T ¼648C and 708C.
TABLE 3. Influence of iPP, CPPA, and CPPB contents on the G*/
sin d 5 1 kPa of modified asphalts.
Sample Content (%)
Temperature (8C)when G*/sin d ¼ 1 kPa
ACP-1 0 61.5
ACP-1/iPP 3 66.8
ACP-1/iPP 5 69.2
ACP-1/CPPA 3 93.2
ACP-1/CPPA 5 98.8
ACP-1/CPPB 3 83.8
ACP-1/CPPB 5 86.2
FIG. 6. The effects of frequency sweeps on the G*/sin d values of the
asphalt binders at 308C.
DOI 10.1002/pc POLYMER COMPOSITES—-2008 523
of the rutting resistance of the asphalt blend as reflected
by G*/sin d parameter is correlated to the compatibility
between the polymer modifier and the asphalt matrix at
high temperatures. As results, the asphalt/CPPA blends
exhibit superior rutting resistance in high temperature
ranges to avoid permanent deformation, while the asphalt/
iPP blends present better performance on the rutting
resistance in the frequency studies.
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