Journal of Wuhan University of Technology-Mater. Sci. Ed. Dec. 2010 1047

DOI 10.1007/s11595-010-0147-3

Analysis of Aging Mechanism of SBS Polymer Modified

Asphalt based on Fourier Transform Infrared Spectrum

ZHAO Yongli1, GU Fan1, XU Jing2, JIN Jing1

(1. School of Transportation, Southeast University, Nanjing 210096, China;

2. Jiangsu Bote New Materials Co., Ltd, Nanjing 210008, China)

Abstract: The aging mechanism of SBS modified asphalt during its aging process was studied.

The characterizations of base asphalt, SBS polymer and its modified asphalt were determined in dif-

ferent aging time by Fourier transform infrared spectrum (FTIR). FTIR shows that oxidative dehy-

drogenation reaction occurs in asphalt, and unsaturated carbon bond is generated under short-term

thermal aging condition. Additionally, SBS polymer was aged significantly under that condition, the

speed of which was faster than that of base asphalt. The aging laws of both asphalt and SBS polymer

during the aging process of SBS modified asphalt were similar to their aging laws respectively. Due to

the protective effect between asphalt and SBS polymer, the aging degrees of asphalt and SBS polymer

were lower than those aged independently.

Key words: SBS polymer modified asphalt; aging; FTIR

1 Introduction

Asphalt, the product after treatment of crude oil, is

composed of complex hydrocarbon and derivatives from

hydrocarbon replaced by non-metallic elements[1]

. The

aging process of asphalt material can be separated as

short term aging and long term aging phase[2-5]

. The

former phase is due to high temperature when asphalt

mixture is produced, starting from mixing process and

ending off the compacted asphalt mixture’s temperature

declining to natural degree. The latter one is formed by

the synthesis factors of light, temperature, precipitation,

and traffic load, beginning with the accomplishment of

pavement construction and ending when the pavement ser-

vice performance can not meet the requirements of traffic.

However, the aging process of modified asphalt

contains not only the aging of asphalt but also the aging

of modifier[6-9]

. At present, SBS (styrene-butadiene-

styrene) polymer modified asphalt is commonly used in

road project. Although numerous researches on SBS

polymer modified asphalt and its aging phenomena have

been studied, little research can explain the particular

aging phenomena of SBS polymer modified asphalt

comprehensively or SBS polymer’s aging influence on

SBS polymer modified asphalt’s aging process. There-

fore, an in-depth study on SBS polymer modified asphalt

is needed to establish the relationship between its

macro-phenomena and micro-characteristic. Thus, a ini-

tial understanding of the aging mechanism of SBS

polymer modified asphalt can be realized, which can

enhance life cycle of SBS polymer modified asphalt

pavement and provide a theoretical basis for researches

on pavement recycling.

2 Experimental

2.1 Materials

Shell 70# asphalt was chosen as base asphalt sample,

and SBS 1401 was used as modifier. The characteristic

properties are given in Tables 1-3.

2.2 Test methods

Normalized tests including penetration, softening

point and ductility were performed on the asphalt sam-

ples in terms of GB/T 4509-1998, GB/T 4507-1999,

GB/T 4508-1999 respectively, and rotary viscosity was

performed according to SH/T 0739-2003.

Table 1 Chemical composition of base asphalt

Chemical composition of base asphalt/%

Saturates Aromatics Resin Asphaltene

17.41 42.26 32.51 7.82

©Wuhan University of Technology and Springer-Verlag Berlin Heidelberg 2010

(Received: Mar. 12, 2010; Accepted: June 19, 2010)

ZHAO Yongli(赵永利): Assoc. Prof.; E-mail: yl.zhao@seu.edu.cn

Funded by the National Natural Science Foundation of China(No.50878054)

Vol.25 No.6 ZHAO Yongli et al: Analysis of Aging Mechanism of S… 1048

2.3 Measurement

The infrared spectra were recorded with Nicolet740,

whose resolution is 4 cm－1

, scanning frequency is 32

times and test range is 400-5000 cm－1

. The samples were

prepared by casting a film onto a sodium chloride (NaCl)

window from a 5% (w/v) solution in chloroform.

3 Results and Discussion

3.1 FTIR analysis of base asphalt and

SBS polymer modified asphalt

The FTIR analysis of Shell 70# base asphalt and its

SBS modified asphalt are given in Fig.1. In the figure,

horizontal axis is the wavenumber (cm－1

) and the vertical

axis is the transmission rate. The major band at 2920 cm－1

is identified as typical hydrocarbon stretching vibration,

C-H bond’s deformation vibration occurs in the 1460 cm－1

,

1600 cm－1

peak corresponds to C＝C bond in benzene

ring and C-H bond’s stretching vibration, and C＝C bond

in non-benzene ring appears in 966 cm－1

peak[10-14]

.

Compared with base asphalt and SBS modified as-

phalt spectra, SBS modified asphalt spectra includes not

only all peaks of base asphalt, but also two special peaks

at 966 cm－1

and 723 cm－1

. In order to determine whether

these two characteristic peaks can identify SBS polymer,

SBS polymer was determined by FTIR independently,

whose spectrum is given in Fig.2. The spectra of SBS

polymer show that bands at 2920 cm－1

and 1460 cm－1

identify C-H bond’s stretching vibration and deformation

vibration respectively. Besides that, characteristic peaks

at 966 cm－1

and 700 cm－1

can still be found. Thus, these

two characteristic peaks can identify the existence of SBS

polymer. Moreover, peak at 966 cm－1

corresponds to

C＝C bond in butadiene and peak at 700 cm－1

identifies

the existence of styrene.

3.2 FTIR analysis of aging base asphalt

In order to analyze base asphalt’s aging law, RTFOT

was adopted to age three AH-70 asphalt, sample b, c, and

d, and their corresponding aging time were 85 minutes,

200 minutes and 480 minutes respectively. After aging,

three samples and original one (a) were analyzed by FTIR.

The results were given in Fig.3.

In Fig.3, it is shown that with the increase of aging

time, new absorption peak occurs at 3095 cm－1

. In addi-

tion, peaks at 1600 cm－1

and 1065 cm－1

enhance ap-

parently. Thus, dehydrogenated type of oxidation oc-

curred and new unsaturated bonds were generated during

the asphalt aging process. However, characteristic peak at

1700 cm－1

corresponding to C＝O bond did not appear,

that is carbonyl did not existence during the thermal ag-

ing process.

Table 2 Physical characteristic properties of base asphalt

Material Softening point/℃ Penetration/0.1 mm(25 ℃) Ductility/cm(15 ℃) Rotary viscosity/(Pa·s)(135 ℃)

Base asphalt 47.3 72.0 >100 0.375

Table 3 Physical characteristic properties of SBS polymer

Material Tensile strength/MPa 300% stretching stress/MPa Elongation at break/% Tensile set at break/% S/B ratio

SBS 16.0 3.0 750 40 40/60

Fig.1 FTIR of base asphalt and SBS modified asphalt

Fig.2 FTIR of SBS polymer

Fig.3 FTIR of base asphalt in different aging time

Journal of Wuhan University of Technology-Mater. Sci. Ed. Dec. 2010 1049

Hitherto oxidation is widely considered as the aging

mechanism of asphalt[15-17]

, but concrete explanations are

different among the scholars. Mohamed Ali Dhalaan

divided oxidation of asphalt into two sorts. One is hy-

drogen in light component emitted from asphalt in high

temperature condition and unsaturated bonds were

formed by dehydrogenation with the generation of mac-

romolecule material. The other is asphalt absorbed oxy-

gen and generated asphaltene, water-soluble salt and

some acid in normal temperature. The results of Fig.3

show that in addition to light component volatilizing,

oxidative dehydrogenation reaction forming unsaturated

bonds mainly occurred during the aging process of base

asphalt.

3.3 FTIR analysis of aging SBS polymer

modified asphalt

Due to the addition of SBS modifier, SBS polymer

is bound to have variations during the aging process of

SBS modified asphalt. In order to analyze these varia-

tions of functional groups during the aging process,

original SBS modified asphalt and its short term and long

term aging samples were determined by FTIR, whose

results are given in Fig.4.

Fig.4 shows that new characteristic peak at 1030 cm－1

,

appeared both in short term and long term aging SBS

modified asphalt, identifies S＝O bond in sulfoxide.

Characteristic peak at 1650 cm－1

in short term aging SBS

modified asphalt identifies C＝O in carboxyl and peak at

1700 cm－1

in long term aging sample also corresponds to

C＝O in carboxyl. Thus, oxidative reaction mainly oc-

curred in the aging process of SBS modified asphalt. New

C＝O bond in carboxyl is due to the absorption of oxygen

in the unsaturated carbon chain and S＝O bond is gen-

erated by the absorption of oxygen in sulfur element.

Transform those transmission spectra into absorp-

tion spectra, and calculate the absorption-peak area of

carbonyl, sulfoxide, C＝C bond in butadiene and satu-

rated C-H bond by integral. According to formulas (1) to

(3), the calculating results are given in Table 4[18]

.

(1)

(2)

(3)

Table 4 indicates that with the increase of aging time,

carbonyl index and sulfoxide index enhance obviously,

but butadiene index declines at the same time. Carbonyl

was generated on the whole aging process of asphalt.

Oxidation was occurred in the unsaturated carbon chain

by the absorption of oxygen with the generation of C＝O

bond. On the contrary, the generation of sulfoxide mainly

occurred in short-term aging stage. Thus it is proved that

sulfur atom has a stronger ability to absorb oxygen than

carbon atom. Meanwhile, the declination of butadiene

index, that is the decrease of C＝C content in butadiene

shows that C＝C bond has been fractured in the aging

process and C＝O bond was generated on the ther-

mal-oxidation aging condition. The variation of butadi-

ene index shows that butadiene content in SBS declines

to 70 percentage of the original one after short term aging

and 22 percentage of the original one after long term

aging process, that is, approximately 30 percentage of

SBS polymer aged during the short term aging process,

and after long term aging process, SBS polymer lost its

modified effect totally.

Thus, oxidative reaction mainly occurred in the ag-

ing process of SBS modified asphalt, with the generation

of carbonyl and sulfoxide. In addition, C＝C bond con-

tent in butadiene decreased gradually, which shows that

SBS polymer’s low temperature modified effect declines

sharply to the asphalt.

Comparison of the results of Fig.3 and Fig.4, the

addition of SBS polymer makes asphalt’s aging behavior

and mechanism different from before. As for base asphalt,

C=O

C H

ACI

A−

=

S O

C H

ASI

A

=

−

=

C C

C H

ABI

A

=

−

=

Table 4 Absorption-peak area of SBS modified asphalt in different aging time

Aging category AC=O AS=O AC=C AC-H CI SI BI

Original 0.000 0.032 0.790 2.809 0.000 0.011 0.281

Short term aging 0.336 0.093 0.433 2.252 0.149 0.041 0.192

Long term aging 1.843 0.132 0.182 2.850 0.647 0.046 0.064

Fig.4 FTIR of SBS modified asphalt in different aging time

Vol.25 No.6 ZHAO Yongli et al: Analysis of Aging Mechanism of S… 1050

in addition to the volatilization of light component, de-

hydrogenation of asphalt molecular mainly occurred in

the aging process with the generation of C＝C bond, but

few C＝O bond was formed in the process. While SBS

polymer added into the asphalt, large amount of C＝O

bond was formed due to the oxidation. The addition of

SBS polymer only modified the physical property of

asphalt without any chemical characteristic changed, thus

C＝O bond must be formed in SBS polymer, that is, the

stability of carbon atom in SBS polymer is lower than

that in base asphalt.

The results of macro-test also show that SBS

polymer has little ability to resist oxidation, which was

given in Fig.5.

Fig.5 shows that appearance of SBS polymer

changed sharply only after 1 hour in TFOT aging condi-

tion. When aging time increases to 5 hours, which is the

standard aging time, SBS polymer has cross-linked

sharply with snuff color appearance. Table 5 shows that

the weight of SBS polymer increases significantly during

the aging process, which is due to the intensive oxidation.

When the aging time is only 1 hour, the weight increase

reached to the upper limit of base asphalt’s weight

variation (0.8%) allowed in JTG F40-2004. Thus, it is

proven again that the aging resistance of SBS polymer is

much lower than that of base asphalt.

3.4 Analysis of interaction mechanism

between SBS polymer and base as-

phalt in aging process

From above tests and analysis, it is shown that SBS

polymer has lower ability to resist oxidation. Provided

that SBS polymer in asphalt rapidly aged, the perform-

ance of SBS modified asphalt would be seriously affected.

However the aging environment of SBS polymer in as-

phalt is different from that of SBS in air, because of ab-

sorption and swelling reaction when SBS added into

asphalt.

In order to further evaluate the variation of SBS

polymer and asphalt respectively in the aging process of

SBS modified asphalt, four SBS modified asphalt aging

samples were made from different methods. Sample 1

was made from base asphalt and 8 percent of original

SBS mixed by high-speed sheering machine. Sample 2

was made from 8 percent of original SBS and short term

aged base asphalt which was aged in 5-hour TFOT aging

condition. Sample 3 was made by sample 1 aged in

5-hour TFOT aging condition. Sample 4 was made from

short term aging SBS polymer and short term aging as-

phalt mixed by high-speed sheering machine.

Those samples were tested by FTIR to analyze the

variation of characteristic peak corresponding to C＝C

bond and C＝O bond. The test results are given in Table

6.

Comparison the characteristic peak area of sample 1

and sample 2, it is shown that the peak area of C＝C bond

and C＝O bond has little change when base asphalt was

aged, that is, the content of C＝C and C＝O has few

variation. Thus it also presents that dehydrogenation is

mainly occurred during the aging process of base asphalt

without C＝O bond formed.

Comparison the characteristic peak area of sample 1

and sample 3, it is shown that the peak area of C＝C bond

decreased and that of C＝O bond increased gradually.

Thus it presents that the main aging behavior of SBS

modified asphalt is the fracture of C＝C bond and the

generation of C＝O bond, that is, carbonyl was formed

when C＝C bond in butadiene absorbed oxygen and

fractured. Because C＝C bond in butadiene can improve

asphalt’s low temperature deformability resistance well,

SBS modified asphalt’s low temperature crack resistance

declined sharply with the fracture of C＝C bond in the

aging process.

Table 5 Weight variation of SBS polymer in different TFOT

aging time

Aging time 1 h 2 h 3 h 5 h 10 h

Increase weight ratio 0.77% 0.95% 1.38% 1.65% 1.83%

Table 6 FTIR analysis of different SBS modified asphalt

aging samples

Material

Characteristic peak area

AC=C AC=O

Sample 1 0.176 0.5611

Sample 2 0.179 0.5591

Sample 3 0.167 0.6411

Sample 4 0.074 0.7524

Fig.5 Appearance of SBS polymer in different TFOT aging time

Journal of Wuhan University of Technology-Mater. Sci. Ed. Dec. 2010 1051

The difference of characteristic area between sam-

ple 3 and sample 4 indicates that when SBS polymer and

base asphalt were aged separately, the loss of C＝C bond

and the generation of C＝O bond increased significantly.

Thus SBS polymer was protected by base asphalt and its

aging speed was lower in asphalt than that in air, which

made sure good performance of SBS modified asphalt in

the long working period.

In order to make sure the variation of SBS modified

asphalt’s macro performance, those samples above were

determined by force ductility test. The force extension

curves are given in Fig.6 and the corresponding data are

given in Table 7. Fig.6 indicates that the curve of SBS

modified asphalt is different from that of base asphalt

apparently. After the initial tension increased, the tension

of base asphalt’s force extension curve declined rapidly

to nearly 0. On the contrary, after a period of decline, the

tension of SBS modified asphalt’s force extension curve

increased significantly and lasted for a long distance. In

this tension rising stage, SBS polymer exerts an impor-

tance effect.

Table 7 indicates that SBS added into asphalt im-

proved its tension and ductility significantly and in-

creased its area surrounded by force extension curve,

which presents the energy absorbed by asphalt during its

tensile process. Thus the energy absorbed by SBS modi-

fied asphalt was 50 times than that of base asphalt indi-

cating SBS asphalt has a better deformability resistance.

Comparison the force ductility test data between

sample 1 and sample 2, it is shown that the aging of base

asphalt has little influence on the fracture energy of SBS

modified asphalt. While the difference between sample 2

and sample 3 indicates that the aging of SBS polymer

makes the attenuation of SBS modified asphalt’s per-

formance. Force ductility test data between sample 2 and

sample 4 shows that the fracture energy of sample 4 ac-

counts for only 5 percentage of that of sample 2 when

SBS polymer was aged, which is cater to the results in

Table 6 that large amount of C＝C bond was fractured.

Comparison the difference between sample 3 and sample

4, it is also indicated that the protection of SBS polymer

in asphalt reduces the attenuation of SBS modified as-

phalt’s performance significantly, which is consistent to

the conclusion in Table 6.

4 Conclusions

Base asphalt and SBS modified asphalt were de-

termined by aging tests and FTIR in different aging

conditions. The aging mechanism of SBS modified as-

phalt was understood further.

a) Dehydrogenation is mainly occurred in the aging

process of base asphalt with the generation of C＝C bond,

but few C＝O bond is generated because there is no re-

action between carbon chain and oxygen in this process.

b) SBS polymer has little ability to resist oxidation.

In the thermal aging process, C＝C bond in SBS polymer

fractured and C＝O bond is generated due to large ab-

sorption of oxygen. Thus SBS polymer’s modified effect

to asphalt’s low temperature crack resistance declined

sharply in this process.

c) SBS polymer is protected by asphalt apparently

after it is added into asphalt to make modified asphalt.

The aging speed of SBS polymer is lower than that in air.

Thus SBS modified asphalt can keep a better road per-

formance in a long time.

References

[1] Maria da Conceicao Cavalcante Lucena, Sandra de Aguiar

Soares, Jorge Barbosa Soares. Characterization and Thermal

Behavior of Polymer Modified Asphalt[J]. Materials Re-

search, 2004: 529-534

[2] Qian Chun-xiang,Xie Jie-guang, Wang Hong-bo. Anti-aging

Capability of SBS and SEBS Modified Asphalt and Mix-

ture[J]. Journal of Southeast University (Natural Science

Edition), 2005, 35(6): 945-949

[3] Robert Y. Liang, Suckhong Lee.Short-term and Long-term

aging Behavior of Rubber Modified Asphalt Paving Mix-

ture[J]. Transportation Research Record, 1996, 1530: 11-17

[4] Prithvi S Kandhal, Sanjoy Chakraborty. Effect of Asphalt

Fig.6 Different samples’ force tension curves

Table 7 Different samples’ force ductility test data in 15 ℃

Material Total area

/(N·cm) Ductility/cm

Maximum

tension/N

70#A base asphalt 86 83 17.21

Sample 1 4413 100 38.12

Sample 2 4522 72.2 75.22

Sample 3 2449 75.8 48.23

Sample 4 277 8.2 52.09

Vol.25 No.6 ZHAO Yongli et al: Analysis of Aging Mechanism of S… 1052

film Thickness on Short-and Long-term Aging of Asphalt

Paving Mixtures[J]. Transportation Research Record, 1996,

1535: 83-90

[5] Bell C A, Wieder A J, Felin M J. Laboratory Aging of As-

phalt T-aggregate Mixtures field Validation[J]. Transporta-

tion Research Board, 1994-4

[6] Zanzotto L, Stastna J, Vacin O. Thermomechanical proper-

ties of Several Modified Asphalts[J]. Appl. Rheol., 2000, 10:

124-44

[7] Sengoz B, Isikyakar G. Evaluation of Properties and Micro-

structure of SBS and EVA Polymer Modified Bitumen[J].

Construction Building Material, 2007, 22: 1897-905

[8] Xiaohu LU, Ulf Isacsson. Chemical and Rheological Evalu-

ation of Aging Properties of SBS Polymer Modified Bitu-

mens[J]. Fuel, 1998,77: 961-972

[9] M S Cortizo, D O Larsen, H Bianchetto, et al. Effect of the

Thermal Degradation of SBS Copolymers During the Age-

ing of Modified Asphalts[J]. Polymer Degradation and Sta-

bility, 2004(86): 275-282

[10] Codrin Daranga. Characterization of Aged Polymer Modi-

fied Cements for Recycling Purposes[D]. USA, Louisiana

State University, 2005

[11] Diego O. Larsen, Jose Luis Alessandrini, Alejandra Bosch.

Micro-structural and Rheological Characteristics of

SBS-asphalt Blends during Their Manufacturing[J]. Con-

struction and Materials,2009: 2769-2774

[12] Masson JF, Pelletier L, Collins P. Rapid FTIR Method for

Quantification of Styrene-butadiene Type Copolymers in

Bitumen[J]. Appl. Polym. Sci., 2001, 79: 1034-41

[13] Lu X, Isacsson U. Modification of Road Bitumens with

Thermoplastic Polymers[J]. Polym. Testing, 2001, 20(1):

77-86

[14] Wang S, Chang J, Tsiang R. Infrared Studies of Thermal

Oxidative Degradation of Polystyrene-block-polybutadiene-

Block-polystyrene Thermoplastic Elastomers[J]. Polymer

Degradation and Stability, 1996, 52: 51-7

[15] Peterson JC. A dual, Sequential Mechanism for the Oxida-

tion of Petroleum Asphalt[J]. Petroleum Sci. Technol., 1998;

16(9-10): 1023-1259

[16] Ali MF, Siddiqui MN. Changes in Asphalt Chemistry and

Durability During Oxidation and Polymer Modification[J].

Petroleum Sci. Technol., 2001, 19(9-10): 1229-1249

[17] Mohamed Ali Dhalaan. Characterization and Design of

Recycled Asphalt Concrete Mixture Using Indirect Tensile

Test Methods[D]. The University of Texas at Austin, 1982

[18] L Y He, J W Button. Methods to Determine Polymer Con-

tent of Modified Asphalt[J]. Transportation Research

Record, 1991, 1317: 23-31