Rheological properties of bitumen modified with ethylene butylacrylate glycidylmethacrylate

Rheological Properties of Bitumen Modified WithEthylene Butylacrylate Glycidylmethacrylate

Vesna Ocelic Bulatovic, Vesna Rek, Josipa MarkovicDepartment for Polymer Engineering and Organical Chemical Technology, Faculty of Chemical Engineeringand Technology, University of Zagreb, Marulicev trg 19, 10000 Zagreb, Croatia

This article presents experimental results related torheological viscoelastic properties of polymer modifiedbitumens, PmBs. Experiments were performed by adynamical shear rheometer before and after thermo-oxidative aging. Two types of bitumens with differentasphaltene contents were modified by the addition oftwo types of reactive ethylene terpolymers, Elvaloy AM,and Elvaloy 4170, with a different percentage of reactivefunctional group, glycidylmethacrylate, GMA. Results ofthe investigation indicate that the degree of reactivepolymer modification is a function of bitumen type,bitumen-polymer compatibility, and polymer concentra-tion. Polymer modification improves the following phys-ical properties of the base bitumen: penetration,softening point, temperature susceptibility, and elasticrecovery. Reactive polymers are effective binder modi-fiers that improve the susceptibility to high temperatureof asphalt mixes, and also their rutting resistance, con-tribute to their good storage stability and make themless sensitive to aging. This is a result of the formationof a chemical bond between the polymer and mole-cules of asphaltenes. POLYM. ENG. SCI., 54:1056–1065,2014. VC 2013 Society of Plastics Engineers

INTRODUCTION

Bituminous materials have been used in most highway

pavement and runway applications. The current traffic

loads and volume of vehicles considerably reduce the life-

time of pavements. In order to get longer periods between

repairs and to reduce the total cost of road pavements

polymer modified bitumens (PMBs) as new bituminous

materials have to be developed. This has contributed to a

large increase in the use of polymers as bitumen modi-

fiers [1]. Polymer modification of bitumens (BIT) is not a

new process, but interest in this technique has increased

considerably during the past decade due to the increased

performance-related requirements on roads [1]. A larger

number of researchers have been devoted to the study of

the effect of polymers on the properties of modified

bitumens and their road performance. Studies have con-

firmed the beneficial effects of polymer modification on

bitumen: decreased thermal susceptibility, reduced perma-

nent deformation (rutting), and increased resistance to

fatigue and to low temperature cracking [2–6].

Rutting is one of the most important types of deterioration

of asphalt pavements. It is a permanent deformation of the

paved road that occurs when an asphalt pavement is traffic-

loaded at temperatures of usually more than 40�C [7–9] At

high temperatures bitumen is not stiff enough and permanent

deformation occurs, leading to the formation of channels in

the traveling direction. This permanent deformation of the

asphalt layer occurs when both high temperatures and high

loads are present. In 1987, the United States Congress

authorized the Strategic Highway Research Program (SHRP)

[8–10] The Program was conceived to develop standard cri-

teria and systematical procedures to combine design with

good pavement performance. A final product of the SHRP is

Superpave, Superior-Performing Asphalt Pavements. Super-

pave deals with the most important causes of asphalt pave-

ment distress and low performance: rutting, low-temperature

cracking, fatigue cracking, moisture sensitivity, and aging.

The Program is based on rheological measurements. A

dynamic shear rheometer, DSR, is used to evaluate rheologi-

cal properties of the binder at higher temperatures. The

obtained results are directly related to permanent deforma-

tion, such as rutting [1, 10]. Superpave considers the complex

modulus (G*) as the stiffness of the binder including its vis-

cosity and its elastic properties. The phase angle d is used to

separate the viscosity from the elastic components. The stiff-

ness of a binder is directly related to rutting resistance: the

higher value of G* results in a longer life of asphalt in use

and in higher resistance to fatigue cracking [3, 8].

One of the primary causes of binder-related failures of

paved roads is the oxidative aging of bitumen [1]. Oxida-

tion is a very complex process which changes both the

chemical and the colloidal structure of bitumen and its

complexity increases when polymers are involved. As a

consequence, oxidation hardening of BIT is observed; polar

compounds react and covert to asphaltenes. Bitumen

increases its viscosity, loses its adhesivity and becomes

brittle [1, 3, 6].

Correspondence to: Vesna Ocelic Bulatovic; e-mail: [email protected]

Contract grant sponsor: Ministry of Science, Education and Sport of the

Republic of Croatia; contract grant number: 125-1252971-2578.

DOI 10.1002/pen.23649

Published online in Wiley Online Library (wileyonlinelibrary.com).

VC 2013 Society of Plastics Engineers

POLYMER ENGINEERING AND SCIENCE—2014

Also, it is important for the modified bitumen that the

dispersion remains stable during storage and transporta-

tion at high temperatures to avoid the segregation of the

polymer [8, 10].

Three types of polymers are used for bitumen modifi-

cation, that is, thermoplastic elastomers, plastomers, and

reactive plastomers. Thermoplastic elastomers and plasto-

mers form a physical network between the bitumen and

the polymer. The polymer is swollen by light aromatic

components from the bitumen, that is, by maltenes. Con-

sequently, the polymer rich phase occupies between 4 and

10 times higher volume than that of the added polymer

[1–6]. When reactive polymers are used, the polymeric

phase is usually homogeneously dissolved in the asphaltic

phase. This is due to three reasons: reactive polymers are

added in small quantity; they have a highly polar nature;

and the formation of a chemical bond between the poly-

mer and the bitumen [11]. This chemical bond improve

mechanical behavior, storage stability and temperature

susceptibility of the PMBs [3, 5, 7].

This article presents the characterization of properties

of PMBs modified with two types of reactive polymers,

both are ethylene butylacrylate glycidylmethacrylate,

Elvaloy AM and Elvaloy 4170 with a different percentage

of reactive functional group, glycidylmethacrylate, GMA.

The characterization was carried out using conventional

methods, that is, rheological measurements performed by

a DSR and determination of the critical temperature in

accordance with the SHRP to prove the resistance to per-

manent deformation. The rheological properties of unaged

PMBs and PMBs after artificial thermo-oxidative aging in

the rolling thin film oven test (RTFOT) were determined.

EXPERIMENTAL

Materials

Two bitumens, BIT 70/100 (marked as B1) and BIT

50/70 (marked as B2), were used to produce blended,

polymer-modified bitumens, PMBs. The BITs used in this

study are supplied by INA Refinery Rijeka, Croatia.

The polymers used as modifiers both are terpolymers

ethylene – butylacrylate – glycidylmethacrylate, Elvaloy

AM (containing butylacrylate 28 wt%, glycidylmethacry-

late 5.3 wt%) and Elvaloy 4170 (containing butylacrylate

20 wt%, glycidylmethacrylate 9 wt%), supplied by

DuPont, Belgium.

Sample Preparation

The modified bitumens were prepared by mixing poly-

mers with base bitumens using a Silverson L4R mixer

based on the information gained from the manufacturer,

the DuPont Company.

First, the base bitumen was adequately heated (160�C)

and stirred for about 2 h to obtain homogeneity and was

then poured into 1 L aluminum cans. The cans of bitumen

were subsequently heated to 180–185�C and stirred for 10

min before adding a polymer. A given part of polymers

was then added slowly to the bitumen under high speed

stirring for 4 h until the blend became essentially homog-

enous. The content of reactive polymers Elvaloy AM and

Elvaloy 4170 was 1.6 and 1.9 wt%. A higher polymer

content cannot be used because of gel formation [1, 12].

A constant temperature was kept while the mixing pro-

cess continued. For the preparation of PMB, the softening

point was checked after 1 h of stirring to make sure that

the reaction between the polymer and bitumen had

started. When the reaction started, the cans were trans-

ferred to an oven and were kept at 180�C for 24 h under

controlled conditions and in an oxygen-free environment

to ensure a complete reaction. After the desired period of

curing, the blends were removed from the aluminum cans

and were divided into small containers covered with alu-

minum foil and stored for testing at ambient temperature.

The prepared samples are marked as B1/AM 1.6 (for

example), the first mark is bitumen type, B1, second is

Elvaloy type, Elvaloy AM, and third is content of Elva-

loy, 1.6 wt%.

Conventional Tests

The base bitumen and PMBs were subjected to the fol-

lowing conventional bitumen tests according to standards:

penetration test (HRN EN 1426), ring and ball technique

to determine the softening point temperature (HRN EN

1427), elastic recovery test (HRN EN 13398). The storage

stability of the PMBs was determined from the difference

between the softening point temperatures of PMBs taken

from the top and the bottom of a cylindrical mould after

they had been stored vertically at 163�C in an oven for

48 h (HRN EN 13399). The temperature susceptibility of

the PMBs has been calculated in terms of penetration

index (PI) [13].

Fourier Transform Infrared Spectroscopy

FT-IR analysis was performed by means of a Perkin

Elmer Instruments—Spectrum One FT-IR Spectrometer,

MA. Sample solutions (10% by weight) were prepared in

carbon disulfide. Sample scans were performed using

NaCl cells. IR spectra were obtained by 15 scans with 4

cm21 resolution in wave numbers ranging from 2000 to

650 cm21.

The spectroscopy of pure polymers was performed in

the attenuated total reflection (ATR) mode with a Dia-

mond Durascope ATR Accessory.

Iatroscan Thin Film Chromatography, TLC-FID

Iatroscan thin film chromatography or Thin-layer chro-

matography with flame ionization detector, TLC-FID

IATROSCAN. The TLC-FID was used to separate bitu-

men into four generic fractions-SARA fractions: saturates,

DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—2014 1057

aromatics, resins, and asphaltenes. The bitumen solutions

were prepared in dichloromethane, and 1 lm of the sam-

ple solution was spotted on chromarods-S III (dimensions

are 0.9 mm in diameter with particle size of 5 lm and

micropores of 60 A).The separation into fractions were

performed by a three-stage development using different

solvents: (a) saturates in n-heptane, (b) aromatics in tolu-

ene, and (c) resins in a 95:5 (vol:vol) dichloromethane-

methanol mixture. Asphaltenes were quantified as those

compounds detected at the point of origin on the chro-

marods. The fractions were determined by means of Iatro-

scan MK-6s analyzer, Analysesysteme, Germany.

Rheological Measurements

Rheological properties were determined by a dynamic

shear rheometer, MCR 301, Anton Paar, with the Peltier

temperature control system, using the parallel-plates

geometry. The dynamic rheometer is a type of testing

equipment applying oscillatory loading to a material sam-

ple. The tests were conducted over a range of tempera-

tures at a fixed frequency in order to provide a complete

characterization of the viscoelastic properties of the

binder.

The Dynamic Shear Rheometer (DSR) tests were per-

formed under controlled strain loading conditions, using

the temperature sweep test applied in the temperature

range 25 to 80�C at a fixed traffic frequency of

10 rad s21 and variable strain. Preliminary tests were car-

ried out at different temperatures in order to determine

the strain range in which the BIT remains in the linear

viscoelastic range (LVE). In this range, the stress

response is directly proportional to the strain value and

the complex modulus is independent of the strain level

[14, 15]. The temperature sweep tests were done with a

parallel plate testing geometry of 25 mm in diameter and

a 1 mm gap. Before the temperature sweep test, all the

samples were tempered at 80�C for 10 min and then the

measurements started [16]. The viscoelastic parameters

obtained from the DSR were the complex modulus G*,

the complex viscosity g*, and the phase angle d.

Aging Procedure

Short term laboratory aging of the base bitumens and

Elvaloy PMBs was performed using the Rolling Thin

Film Oven Tests (RTFOT) according to ASTM D 2872.

The bitumens and Elvaloy PMBs were exposed to ele-

vated temperatures to simulate the conditions during the

production, mixing and laying of asphalt mixes. Sam-

ples of specific weights were placed into glass contain-

ers heated to 163�C for about 15 min and were then

placed into a rotating oven at 163�C for 85 min with

the air on, and with the flow rate of 4 L/min. All meas-

urements were performed before and after the simulated

aging in the laboratory, that is, before and after the

RTFOT test.

Permanent Deformation

To provide a more profound insight into rheological

properties, the critical temperature at which permanent

deformation (rutting) occurs was determined according to

the SHRP program [9]. The critical temperature, TC, is

both the temperature at which G*/sin d is equal to or less

than 1 kPa (strain value is 10%) before aging and that at

which G*/sin d is equal to or less than 2.2 kPa after aging

at a frequency of 10 rad s21 [8, 17]. The critical tempera-

ture was determined automatically by the DSR software.

RESULTS AND DISCUSSION

Conventional Properties

When the bitumen B2 is mixed with Elvaloy 4170, the

only possible addition of the polymer is 1.6 wt%. When

1.9 wt% of Elvaloy 4170 is added to B2, the PMB sam-

ple becomes a gel after 24 h of curing, that is, the mate-

rial becomes insoluble and infusible (B2/4170 1.9). In

this case, it must be emphasized that the polymer content

was such that it could be able to partially segregate and

give rise to local semicrystalline domains that can give a

physical contribution to the polymeric network [18]. In

the case of B1 modified with 1.9 wt% of Elvaloy 4170,

the gel formation is observed after storage stability test.

Table 1 shows the chemical, fractional composition of the

BITs, including saturates, aromatics, resins, and asphal-

tenes (SARA fractions) that were obtained using the

Iatroscan thin film chromatography. These two bitumens

have similar softening point, but they differ in their pene-

tration value and in their chemical composition. In the

bitumen modified with reactive polymers, a reaction took

place between the asphaltenes in BIT and the GMA

groups in Elvaloy, so the percentage of the asphaltenes is

very important. The B2 has a higher percentage of asphal-

tenes, which indicates a more likely chemical reaction.

The Colloidal Indices (CIs) of the two bitumens were cal-

culated in order to determine the potential compatibility

of the base bitumens with a polymer [14]. It is clear that

different percentages of the SARA fractions allow the CIs

of the two base bitumens to differ considerably. This will

inevitably result in differences in the compatibility and

rheological performance of the PMBs. B2 (greater per-

centage of asphaltenes) exhibits a higher CI value, which

TABLE 1. Chemical composition of base bitumens.

Binder

Saturates

(%)

Aromatics

(%)

Resins

(%)

Asphaltenes

(%) CIa

B1 4.06 44.07 36.54 15.33 0.241

B2 3.86 40.64 36.34 19.60 0.305

aColloidal index (CI) 5 (asphaltenes 1 saturates)/(resin 1 aromatics).

1058 POLYMER ENGINEERING AND SCIENCE—2014 DOI 10.1002/pen

may lead to a more compatible system with a reactive

polymer.

The effect of reactive polymers, Elvaloy AM and Elva-

loy 4170, on the conventional properties of the base bitu-

mens can be seen in Table 2. The addition of reactive

polymers increases the softening point temperatures and

decreases penetration. But, increasing the content of Elva-

loy the penetration little increase in the case of modifica-

tion B1, in modification of B2 with higher content of

Elvaloy the penetration is similar. The increase in soften-

ing point temperature, which is an indicator of the stiffen-

ing effect of PMBs is favorable since the bitumen with a

higher softening point may be less susceptible to perma-

nent deformation (rutting) [12, 18]. To improve the PMB

performance, a polymer should be able to increase the

softening point value and to improve the elastic behavior

of the bitumen without decreasing the penetration range

too much [18]. The best compromise between these

requirements is reached by the PMBs combining B2 and

Elvaloy 4170 (Table 2, B2/4170 1.6)

Bitumens have a low penetration index (PI), indicating

their susceptibility to temperature changes [13]. As previ-

ously noted, the modification of bitumens with Elvaloy

AM or Elvaloy 4170 polymers reduces the temperature

susceptibility of the resulting PMBs, and improves their

quality. Asphalt mixture containing bitumen with a higher

PI is more resistant to low temperature cracking and to

permanent deformation [13]. Elvaloy 4170 modified sam-

ples yield higher PI values compared to Elvaloy AM

modified samples (Table 2, B1/ 4170 1.9 and B2/4170

1.6). As expected, following the aging process, a higher

softening point and lower penetration values are found.

The penetration index has increased (except in the case of

B1 modified with Elvaloy AM) which confirms that the

temperature susceptibility is improved. It may be attrib-

uted to composition changes. As many researchers have

proved, the content of asphaltenes increases after aging.

According to the research results, asphaltenes exhibit the

lowest temperature susceptibility among the separated

fractions in BIT and PMBs [19, 20].

Also, it is very important to find the best compromise

between the above mentioned parameters after thermo-

oxidative aging. After aging, the elastic recovery is

reduced, but still improves the elastic behavior of the

PMBs. The results of the RTFOT, which simulates the

hardening of bitumen, indicate that the Elvaloy AM

PMBs are more affected by aging than the Elvaloy 4170

PMBs [1, 3, 10, 21].

Permanent Deformation

Pavement deformation (rutting) behavior of paving

materials is an important factor in the design and analysis

of flexible pavements [8, 22]. As shown in Table 3, when

the value of G*/sin d � 1 kPa before aging, and the value

of G*/sin d � 2.2 kPa after aging, then the critical tem-

peratures are obtained according to SHRP. The Elvaloy

PMBs have a higher critical temperature than base bitu-

mens. This means that Elvaloy PMBs have better temper-

ature resistance to permanent deformation (rutting) under

frequencies equal to traffic frequencies, which means bet-

ter properties when used in road construction. It is due to

the formation of chemical bonds between asphaltenes

from BIT and reactive functional groups, GMA, from

Elvaloy. The Elvaloy PMB with B2 has a higher critical

temperature than the Elvaloy PMBs with B1. The

TABLE 2. Conventional properties of BITs and Elvaloy PMBs.

Properties B1 B2

B1/AM

1.6

B1/AM

1.9

B1/4170

1.6

B1/4170

1.9

B2/AM

1.6

B2/AM

1.9

B2/4170

1.6

B2/4170

1.9

Before RTFOT

Penetration (25�C, 1/10 mm) 71.1 62.9 64.6 66.7 60.6 62.7 55.4 55.4 54.8

Softening point (�C) 46.7 48.6 55.5 55.0 57.2 66.0 55.2 57.0 59.6

Penetration index, PI (2) 21.24 21.03 0.77 0.72 0.95 2.77 0.27 0.67 1.18

Elastic recovery (%) – – 68.0 69.0 72.5 74.5 68.5 72.0 72.5

After RTFOT GEL

Penetration (25�C, 1/10 mm) 44.0 38.7 38.2 40.8 38 GEL 34.0 36.0 35.9

Softening point (�C) 51.1 54.7 59.0 59.2 64.0 GEL 61.0 65.5 67.7

Penetration index, PI (2) 21.22 20.67 0.19 0.38 1.12 GEL 0.32 1.26 1.69

Elastic recovery (%) – – 70.0 62.5 70.5 GEL 60.0 61.0 68.5

TABLE 3. The critical temperature according to SHRP Program.

Samples

B1 B2 B1/AM 1.6 B1/AM 1.9 B1/4170 1.6 B1/4170 1.9 B2/AM 1.6 B2/AM 1.9 B2/4170 1.6

TBefore RTFOT (�C) 65.1 67.8 71.5 70.4 71.6 73.6 73.6 73.8 75.7

TAfter RTFOT (�C) 64.4 66.1 70.5 68.9 69.0 GEL 71.7 72.9 75.0

TC (�C) 64.0 64.0 70.0 64.0 64.0 GEL 70.0 70.0 70.0


difference between the temperature before and after aging

is small for Elvaloy PMBs, which contributes to the good

stability and less sensitivity to thermo-oxidative aging

[1, 8]. Sample B2/4170 1.6 shows the highest critical

temperatures. This means that the rutting resistance per-

formance of the bitumen B2/4170 is better than that of

the B1/4170. Also, the modification with the reactive

polymer Elvaloy 4170 results in a better rutting perform-

ance than the modification with the Elvaloy AM polymer.

It is due to a higher percentage of asphaltenes in B2, and

a higher percentage of the reactive functional group in

Elvaloy 4170, which contributes to a higher occurrence

probability of a chemical reaction.

Storage Stability

The samples are stored at elevated temperatures, which

accelerate the phase separation of PMBs into bitumen and

polymer rich phases [6, 8, 23]. All the samples investi-

gated in this study were homogeneous and there was no

difference in the softening point value between the top

and the bottom of the tube (Fig. 1). Thanks to a chemical

reaction between the polymer and the bitumen, the phase

separation was avoided. From the results, we can con-

clude that all Elvaloy PMB samples improved their stor-

age stability because of the chemical reaction between the

polymer and bitumen, contributing to the phase stability

during storage and transport.

Fourier Transform Infrared Spectroscopy

The IR spectra of Elvaloy AM and Elvaloy 4170 terpoly-

mers show noticeable peaks at 1732 and 1640 cm21, which

is assigned to the carbonyl stretching (C@O) of glycidyl

methacrylate (GMA) and (C@C) of butyl acrylate (BA)

groups, respectively [4, 24–26]. The absorption bands of

high intensity are observed at 1160, 943, 907, and

849 cm21, which corresponds to the epoxy group represent-

ing the reactive functionality in glycidyl methacrylate,

GMA [4, 25–27]. Figure 2 presents the IR spectra of sample

B1/AM 1.6. In IR spectra of Elvaloy PMB (B1/AM 1.6),

the bands characteristic of the epoxy groups at 943, 907,

and 849 cm21 disappear, while the intensity of the band at

1163 cm21 is decreased [5, 17, 24]. This indicates that the

epoxide ring is open and chemical reactions between the

carboxylic acid group in asphaltenes from BIT and Elvaloy

occur. The same reaction is present in all investigated Elva-

loy PMBs. The reactions are given in Fig. 3.

Rheological Properties

The temperature dependency, as one of the most

important rheological properties of bituminous binders, is

investigated. Dynamic temperature sweep tests with linear

viscoelastic range were performed between 25 and 80�Cand results are shown in Figs. 4–9. The rheological

parameters, complex modulus (G*), complex viscosity

(g*), and phase angle (d), in a broad temperature range at

a fixed traffic frequency (10 rad s21), for the base bitu-

mens and bitumens modified with reactive terpolymers

(Elvaloy AM and Elvaloy 4170) are presented.

From Figs. 4–7 one can see that G* and g* of the

base bitumens decrease sharply with the increasing tem-

perature and are very low at high temperatures. The two

bitumens used had very similar G* and g* behavior in

the medium temperature range (20–40�C) (Figs. 4–7). At

high temperatures, B2 has about a 10–20% higher values

of G* and g* compared to B1, showing grater stiffness,

which is expected. A large difference is noted at low

temperature range 25�C to ambient temperature, where

FIG. 1. Storage stability. [Color figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com.]


the opposite trend was found. B1 has a higher values of

G* and g* compared to B2. As seen in Figs. 4–7, for

Elvaloy PMB samples, G* and g* are reduced by

increasing the temperature. The G* and g* values of

Elvaloy PMBs are higher than the same values of the

base BITs. Bitumen modification improved the visco-

elastic properties with higher values of the complex

modulus and complex viscosity with respect to the base

bitumen. It means that the added polymer gives stiffness

and enough rigidity to the bitumen so that it does not

flow at high temperatures [12, 15]. The G* and g* in

Elvaloy PMBs increases significantly at higher tempera-

tures, and this increase was higher for high Elvaloy con-

tent (Fig. 5 and 7). At higher temperatures, the influence

of polymer content on G* and g* were more

pronounced. A high values of G* and g* indicated high

rutting resistance at higher temperatures, and better

resistance to melting at higher temperature [24]. The

samples of BIT 70/100 modified with a lower content of

reactive polymers Elvaloy AM and Elvaloy 4170 (1.6

wt%, Samples B1/AM 1.6 and B1/4170 1.6), show very

similar behavior of G* and g* to that of the base bitu-

men at low and medium temperatures. At high tempera-

tures, Elvaloy PMBs show higher values of G* and g*

than B1. This was expected because the influence of

bitumen modification by polymers is mainly manifested

at elevated temperatures, while the low temperature

behavior is known to be less influenced by polymer

modifiers [5]. Samples B1/AM 1.9 and B1/4170 1.9

show the opposite trend at low temperatures (25–25�C),

the values of G* and g* are lower in comparison with

the base bitumen (Fig. 4). The largest increase in stiff-

ness is achieved for sample B1/4170 1.9. But at this

content of Elvaloy 4170, some results indicated that this

bitumen-polymer system tended to chemical gelation.

B1 modified with various contents of both Elvaloy

polymers has higher values of the complex modulus and

complex viscosity over a wide temperature range than

pure B2 (Fig. 6). The behavior of the Elvaloy PMBs

shown by the G*/T curve is almost the same (Fig. 6).

Slighter higher values are exhibited by sample B2/4170

1.6 at high temperatures. A bigger increase in complex

modulus is noted in the modification of B2.

The phase angle is more sensitive to the chemical struc-

ture and its change is more pronounced in Elvaloy PMBs

than the changes in G* and g* (Fig. 8 and 9) [23]. To pre-

vent high temperature rutting, bitumen should be more

elastic at elevated temperatures. However, as the

FIG. 2. FT-IR spectrum for bitumen modified with ELVALOY. [Color figure can be viewed in the online

issue, which is available at wileyonlinelibrary.com.]

FIG. 3. The typical reaction between carboxylic acid groups in asphaltene and GMA funtional group in Elvaloy [5].


temperature increases, the phase angle for the base bitu-

mens approaches 90�. The base BITs show predominantly

viscous behavior. B2 shows somewhat lower values of

phase angle than B1. The addition of Elvaloy 4170 and

Elvaloy AM to BITs decreased the phase angle values.

This indicates that reactive polymers significantly improve

the elasticity of modified binders. These increases in elas-

ticity at high temperatures can be attributed to the viscosity

of the base bitumens being low enough to allow the elastic

network of the polymer to influence the mechanical prop-

erties of modified binders [28].

The d/T curves for Elvaloy PMBs are very similar to

the same curves for the base bitumens up to a tempera-

ture of 25�C. After this temperature, the phase angle

decreases and approximates to a relatively constant value,

which may be due to the formation of chemical bonds

between the polymer and bitumen. The modification with

Elvaloy 4170 has the lowest d values and a more pro-

nounced plateau region on the d/T curve than the modifi-

cation with Elvaloy AM. It may be explained by a higher

percentage of reactive functional groups, GMA, which

will react with the asphaltenes from bitumen. This indi-

cates the formation of a chemical network, what is

improved by IR measurements (Fig. 2) [29]. The chemi-

cal network contributed to the better elasticity. As we can

see from Figs. 7 and 8, the influence of Elvaloy 4170 on

the elastic response of both bitumens is more noticeable

at high temperatures. But, for the same reason, Elvaloy

FIG. 4. Temperature dependence of G* for B1 modified with Elvaloy, before and after RTFOT. [Color

figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

FIG. 5. Temperature dependence of g* for B1 modified with Elvaloy, before and after RTFOT. [Color fig-

ure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]


4170 has a greater tendency toward inter-chain reactions

between polymer macromolecules, which leads to the for-

mation of gel [24, 30] To avoid the risk of the insoluble

bitumen gel creation, the amount of Elvaloy 4170 must

be carefully chosen to prevent the network from forming

the gel below the chemical gel point. The effectiveness

regarding the elastic response of reactive polymers at

high temperatures may be ranked as B2/4170 1.6>B1/

4170 1.9>B2/AM 1.9>B1/4170 1.6> B2/AM 1.9>B1/

AM 1.9>B1/AM 1.6.

Figures 4–9 also illustrate the effect of thermo-

oxidative aging on the rheological properties of modified

bitumens containing reactive polymers. The changes in

rheological properties, that is, in G* and g*, and in d, are

noted after aging under RTFOT conditions. Evidently, the

process of aging increases the G* and g* values and

improves the elastic response (decreased phase angle).

This is related to higher stiffness, which is a consequence

of the oxidation process of BIT [19]. As many researchers

have shown, the oxidative aging of BIT increases the con-

tent of asphaltenes and increases molecular weight [31,

32]. Both bitumens show an increase in G* at medium

and high temperatures, but the behavior differs at low

temperatures. For B1, instead of an increase, there is a

decrease in G* at low temperatures after ageing (25–

15�C). Consequently, Elvaloy PMBs with B1 also show a

decrease in G* at low temperature, which means that the

degree of aging is to a great extent determined by the

FIG. 6. Temperature dependence of G* for B2 modified with Elvaloy, before and after RTFOT. [Color fig-


FIG. 7. Temperature dependence of g* for B2 modified with Elvaloy, before and after RTFOT. [Color fig-



corresponding base bitumen. The addition of Elvaloy to

B2 does not cause changes at low temperatures after

aging. If we compare the results of our previous research

into bitumen modified with nonreactive polymers, it is

evident that the modification with Elvaloy shows no large

increase in the values of G* and g* after aging [6, 29].

From our previous research, in the case of bitumen modi-

fied with nonreactive polymer after aging, the d values of

PMBs on the d/T curve are evidently lower, and the elas-

tic plateaus (indicator of formed polymer network) are

affected. It means that chemical processes which include

degradation reactions as well as secondary processes of

crosslinking take place during the aging of PMBs. Minor

changes after aging with Elvaloy modification is

associated with the resulting chemical bond which con-

tributes to the retention of the properties and good stabil-

ity. All Elvaloy PMB samples show a similar increase in

G* and g* after aging. The phenomena are mainly due to

the oxidative hardening of bitumens. For the same reason,

the d values on the d/T curve show little changes after

aging for all Elvaloy PMB samples. All the aged samples

exhibit an enhanced elasticity as compared with the base

bitumen [19, 32]. After aging, the d values of BITs on

the d/T curve are lower as well as the values of Elvaloy

PMBs. At medium and high temperatures the aged sam-

ples are characterized by higher stiffness and elasticity,

whereas at low temperatures, the rheological properties

G* and d are not affected by aging.

FIG. 9. Temperature dependence of d for B2 modified with Elvaloy, before and after RTFOT. [Color figure

can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

FIG. 8. Temperature dependence of d for B1 modified with Elvaloy, before and after RTFOT. [Color figure

can be viewed in the online issue, which is available at wileyonlinelibrary.com.]


CONCLUSIONS

Based on the results of conventional tests, it was con-

cluded that the addition of reactive polymers Elvaloy AM

and Elvaloy 4170 improved the temperature susceptibility

of both BIT 70/100 and BIT 50/70. All Elvaloy PMB

samples show good storage stability due to the chemical

reaction with asphaltenes from the bitumen.

The reactive polymer modifications increase the com-

plex modulus and the complex viscosity of both bitumens,

mainly at high temperature, while very little change is

noted at lower temperatures. It means that a reactive

polymer gives stiffness and enough rigidity to the bitu-

men so that it does not flow at high temperatures. The

addition of reactive polymers to both bitumens reduces

the phase angle, and Elvaloy PMBs show better elasticity

at higher temperatures. All Elvaloy PMB samples have

higher critical temperatures, i.e. better resistance to per-

manent deformation. Elvaloy PMBs with BIT 50/70 have

higher critical temperatures compared to PMBs with BIT

70/100.

Both bitumens modified with Elvaloy 4170 have

higher critical temperatures than bitumens modified with

Elvaloy AM.

After aging, the hardening of BITs and Elvaloy PMBs

occurred and the phase angle decreased as a consequence

of oxidation of the base bitumens. The influence of aging

on Elvaloy PMBs is less strong compared to PMBs with

nonreactive polymers as modifiers. Elvaloy 4170, due to

its higher GMA content with respect to Elvaloy AM,

exhibits a better ability to crosslink via either asphaltene

groups or interchain mechanisms in the network

formation.

Summarizing the results, we can conclude that the

modification of bitumen with a higher content of asphal-

tenes (BIT 50/70) by a reactive polymer with a higher

content of reactive group (GMA group) will give the best

rheological behavior, but the amount of Elvaloy 4170

must be carefully chosen to prevent the network from

forming the gel below the chemical gel point. The fact

that the use of different bitumens led to different rheolog-

ical behaviors and different gelation conditions suggests

that asphaltenes played an important role in the network

formation.

To conclude, it seems that reactive polymers are effec-

tive binder modifiers that improve the high temperature

properties of asphalt mixes and which contribute to good

storage stability because of chemical bond formation

between the polymer and bitumen.

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