7
Investigation of Flow Properties of Asphalt Binders Containing Polymer Modifiers Yu-Hsun Nien, 1 Pei-Hung Yeh, 2 Wei-Chyum Chen, 3 Wen-Tsung Liu, 3 Jean-Hong Chen 1 1 Department of Polymer Materials, Kun Shan University, Yung-Kang City, Tainan Hsien 710, Taiwan 2 Department of Applied Chemistry, Chaoyang University of Technology, Wufong Township, Taichung County 41349, Taiwan 3 Department of Civil Engineering, Kao Yuan University, Lujhu Township, Kaohsiung County 82151, Taiwan Modified asphalts using polymeric additives, including isotactic polypropylene (iPP) and different degrees of chlorinated polypropylene (CPP), have been prepared and examined using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), rotational viscometer, and dynamic shear rheometer (DSR) in this study. The results of DSC studies show that different levels of the crystallization occur in asphalt/iPP blends because most of the crystallinity of iPP remain intact in the blend, while those asphalt samples having CPP tend to affect the thermal behavior in the DSC thermo- grams because of increasing the amorphous region of CPP. From the images of SEM, the distinctions of the phase distributions between the asphalt/iPP and asphalt/CPP blends illustrate that the chlorine content in CPP is a significant factor in controlling its compati- bility with asphalt. The rheological studies show that the asphalt blends containing CPP (26 wt% of Cl) ex- hibit higher viscosity in terms of higher temperature to get Newtonian behavior and display superior rutting re- sistance to avoid permanent deformation at high tem- perature. POLYM. COMPOS., 29:518–524, 2008. ª 2008 Society of 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). V V C 2008 Society of Plastics Engineers POLYMERCOMPOSITES—-2008

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Page 1: Investigation of flow properties of asphalt binders containing polymer modifiers

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

Page 2: Investigation of flow properties of asphalt binders containing polymer modifiers

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

Page 3: Investigation of flow properties of asphalt binders containing polymer modifiers

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

Page 4: Investigation of flow properties of asphalt binders containing polymer modifiers

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

Page 5: Investigation of flow properties of asphalt binders containing polymer modifiers

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

Page 6: Investigation of flow properties of asphalt binders containing polymer modifiers

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

Page 7: Investigation of flow properties of asphalt binders containing polymer modifiers

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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