Petroleum Science and Technology

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Use of Fourier transform infrared spectroscopy to

study ageing characteristics of asphalt binders

Bhupendra Singh, Nikhil Saboo & Praveen Kumar

To cite this article: Bhupendra Singh, Nikhil Saboo & Praveen Kumar (2017) Use of Fourier
transform infrared spectroscopy to study ageing characteristics of asphalt binders, Petroleum
Science and Technology, 35:16, 1648-1654, DOI: 10.1080/10916466.2017.1350710

To link to this article: http://dx.doi.org/10.1080/10916466.2017.1350710

Published online: 14 Nov 2017.

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 PETROLEUM SCIENCE AND TECHNOLOGY
, VOL. , NO. , –
https://doi.org/./..

Use of Fourier transform infrared spectroscopy to study ageing

characteristics of asphalt binders
Bhupendra Singha , Nikhil Saboob , and Praveen Kumarb
a
Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee, India; b Department of Civil
Engineering, Indian Institute of Technology (BHU), Varanasi, India
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ABSTRACT KEYWORDS
The present study aims at studying ageing characteristics of conventional bitu- ageing; ageing index (AI);
men, polymer modified bitumen (PMB) and warm mix asphalt (WMA) by using Fourier transform infrared
FTIR. Results of obtained FTIR spectrum were quantified by calculating differ- spectroscopy (FTIR); polymer
modified bitumen (PMB);
ent indices and finally based on these indices ageing index of the binders for
warm mix asphalt (WMA)
short- and long-term ageing were calculated. Results showed ageing increased
amount of complex and high molecular weight components of the binders.
PMB was found to have greater ageing resistance than conventional asphalt
binders. In case of WMA, results found to be inconclusive, requiring further
investigation.

1. Introduction
Ageing of asphalt binder is one of the most common causes of failures in flexible pavement. Ageing per-
tains to change in chemical, mechanical, and microstructural properties over the life time. Ageing starts
right from the construction of the pavement and continues throughout the service life. These changes can
be attributed to the loss of volatile components at elevated temperatures and oxidation of the binders.
Usually, ageing is broadly classified into two major categories: short-term ageing and long-term age-
ing. Short-term ageing includes the ageing that takes place during production of asphalt mix. Bitumen
at elevated temperatures exists as thin films over the aggregate particles, and hence, leads to oxidation
(Lu and Isacsson, 2002). Long-term ageing takes place during the service life the pavement, while it is
continuously exposed to traffic and change in climatic condition over years. Exposure to the environ-
mental oxygen causes oxidation of the binder and hardens it. Heavy vehicle loading and ultra-violet
(UV) rays sourcing from sun further accelerate this process. Ageing significantly affects the properties
of the asphalt binders. It reduces the elasticity of the binder making it hard, which results in cracking
of pavement under the application of repeated heavy loads (Cocurullo et al., 2004). Ageing causes the
formation of carbonyl compounds and sulphoxides, transformation of generic fractions (maltenes) to
larger molecules (asphaltenes) and hence increases molecular weight and polydispersity (Lu and Isacs-
son, 2002). Over the years researchers have used different methods to study and quantify the effect of
ageing on the asphalt binders. One such method is Fourier Transform Infrared Spectroscopy (FTIR).
Many studies have utilized it to study ageing characteristics of asphalt binders (Lu and Isacsson, 1998;
Lamontagne et al., 2001; Wu et al., 2009).
FTIR basically measures infrared (IR) absorption of the material. FTIR spectrometer consists of an IR
source that generates IR radiation. This radiation is passed through the sample that causes the bonds in
the molecules to vibrate and rotate at discrete frequencies, due to which some of the radiation is absorbed
by the material, while some passes through it. The transmitted IR radiation is absorbed by the detector

CONTACT Bhupendra Singh bhupendrasingh.iitr@gmail.com Department of Civil Engineering, Indian Institute of Technology,
Roorkee , India.
©  Taylor & Francis Group, LLC
 PETROLEUM SCIENCE AND TECHNOLOGY 1649

Figure . Working principle of FTIR spectroscopy.

that gives a spectrum of absorbance against wavelength. This spectrum is unique for each molecular
structure so with the help of it, functional groups present in the material can be identified. Figure 1
demonstrates the working principle of FTIR spectroscopy.
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This study aims at studying and comparing the ageing behavior of conventional binders with that of
polymer modified bitumen (PMB) and warm mix asphalt (WMA) using FTIR spectroscopy.

2. Experimental

2.1. Binders
This study was conducted on four different asphalt binders including VG-10, VG-30, PMB (S), and
WMA. VG 10 and VG 30 are the viscosity graded (VG) binders. Table 1 gives the details of the prepara-
tion of PMB (S) and WMA.

2.2. Binder ageing process

The short-term and long-term ageing of binders were studied using the two most common type of ageing
procedures: rolling thin film oven test (RTFOT) and pressure ageing vessel (PAV). Short-term ageing in
RTFOT was performed as per the procedure described in ASTM D2872. For long-term ageing, standard
procedure prescribed by ASTM D6521 was followed.

2.3. Conventional tests

The effects of ageing on the binders were initially quantified using different conventional tests including
penetration, softening point, and ductility; in addition, their penetration indexes (PIs) were calculated.
Dynamic mechanical analysis (DMA) using dynamic shear rheometer (DSR) was also done to evaluate
the high temperature performance grade (PG) of the binders.
Penetration, softening point, and ductility are one of the oldest tests to quantify the consistency of
asphalt binders. Though these are considered empirical, they do tend to provide some idea about the
hardness, stiffness, and tensile properties of the binder. PI measures temperature susceptibility of the
binders. Lower PI value indicates higher temperature susceptibility. The calculation of PI is based on
the work done by Pfeiffer and Van Doormal and mathematically presented as follows (John and
Whiteoak, 2003):
1,952 − 500. log(pen25 ) − 20.(SP)
PI = (1)
50. log(pen25 ) − SP − 120

Table . Modified binder preparation detail.

Modified binder Base binder Modifier used Modifier dosage Mixing temperature Mixing duration Shear rate

WMA VG- Zycotherm .% by wt °C  min  rpm

PMB (S) VG- SBS % by wt °C  min  rpm
 1650 B. SINGH ET AL.

where pen25 is the value of penetration at 25 °C and SP is the softening point of the binder.
With the introduction of Superpave binder grading protocol, many highway agencies have mandated
the use of DSR for quantifying rheological behavior of asphalt binders and evaluating PG for these
binders. In this study, high temperature PG has been evaluated to differentiate the binders in terms of
rheology.

2.4. Fourier transform infrared spectroscopy (FTIR)

FTIR was done for quantification and identification of the amount of functional groups present in the
asphalt binder before and after ageing. FTIR offers a fast and reliable determination of functional char-
acteristics of asphalt binders. To account the repeatability, FTIR was carried out on six samples for each
binder and ageing condition. Different indices were calculated for each test run. As the number of trials
were lesser than 30, repeatability limit for indices was calculated using t-test. Samples falling under the
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limit were used for further analysis.

3. Results and discussion

3.1. Conventional test measurements

The conventional properties of binders are presented in Table 2. In general, it is found that ageing
increases the overall stiffness of the binder as given by the increased softening point and decreased pen-
etration values. VG 10, VG 30, and WMA gave ductility values greater than 100 in un-aged and RTFOT
conditions, so the change in their ductility values due to short-term ageing could not be recorded. But
after ageing in PAV their ductility values reduced, which indicates increased brittleness of the binders.
Whereas in case of PMB (S) a decrease in ductility value was recorded due to short- and long-term ageing.
From PI values, WMA was found to be the most temperature susceptible, while PMB (S) the least.
All binders except WMA showed increased temperature susceptibility after RTFOT, whereas after PAV
temperature susceptibility decreased for all including WMA.

3.2. FTIR results

FTIR spectra of all the binders are shown in Figure 2(a–d). For all the binders, before and after ageing,
alike spectrum containing similar peaks and valleys were obtained, which indicates that ageing did not
introduce any new functionality. The only difference between un-aged, RTFOT, and PAV samples was
in the intensities of peaks. This demonstrates that ageing changes the contents of some of the functional
groups. In all the observed peaks listed in Table 3, peaks corresponding to carbonyl (1,700 cm−1 ) and
sulphoxide (1,030 cm−1 ) are mostly used to characterize ageing in asphalt binders (Petersen, 2009). All

Table . Conventional properties of binders.

High temp.
Penetration values Softening point Ductility value (as performance grading
Binder (as per IS:) (°C) (as per IS:) per IS:) Penetration index (as per AASHTO R)

VG-   > − . PG -XX

VG- RTFOT   > − .
VG- PAV    − .
VG-   > − . PG -XX
VG- RTFOT   > − .
VG- PAV    − .
WMA   > − . PG -XX
WMA RTFOT   > − .
WMA PAV    − .
PMB (S)    . PG -XX
PMB (S) RTFOT    .
PMB (S) PAV    .
 PETROLEUM SCIENCE AND TECHNOLOGY 1651
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Figure . FTIR Spectrum of a) VG ; b) VG ; c) WMA and d) PMB (S).

binder except WMA gave similar spectrums to each other; WMA spectrum curves were found to be dif-
ferent than others. They did not show significant carbonyl and sulphoxide functionalities after RTFOT.
The peaks intensified after PAV, but compared to other binders, those were still minor. Further morpho-
logical study is required to study the effect of zycotherm on the base binders. In case of PMB (S), peaks
corresponding to butadiene double bond (C–C) was observed at a wave number of 968 cm−1 . The spec-
trum of PMB (S) was found to be similar to the base binder, containing additional peaks for butadiene
double bonds. This is in agreement with the previous research work, which concludes that the interac-
tion of SBS with base binder is purely physical in nature (Masson et al., 2003). For PMB (S), carbonyl
and sulphoxide peaks of aged samples were found to be insignificant as compared to the conventional
binders. This indicates better ageing resistance of PMB (S).
In order to quantify the effect of ageing on the different components of asphalt binder, different
indexes were calculated using following equations (Lamontagne et al., 2001):

Aromatic index : IAr = A1600 A (2)

Aliphatic index : IAl = (A1460 + A1370 ) A (3)

Carbonyl index : IC=o = A1700 A (4)

Sulphoxide index : IS=o = A1030 A (5)

Table . Observed peak of FTIR spectrum.

Wavenumber (cm− ) Type of peak

, Carbonyl (C=O) absorption peak of aldehydes, ketones, and acids

, Aromatic (C=C) absorption peak
, Branched (C–H) shear vibration due to bending
, Branched (C–H) umbrella type vibration
, Sulfoxide group (S=O) stretch vibration absorption
 Butadiene double bond (C=C)
 1652 B. SINGH ET AL.
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Figure . Different Indexes of different Un-aged, RTFOT and PAV Binders.

Trans-butadiene index of PMB (S) was calculated using following equation (Wu et al., 2009):

ISBS = A968 A (6)

where A1600 = Area of spectral band around 1,600 cm−1 , A1460 = Area of spectral band around
1,460 cm−1 , A1370 = Area of spectral band around 1,370 cm−1 , A1700 = Area of spectral band
around 1,700 cm−1 , A1030 = Area of spectral band around 1,030 cm−1 , A968 = Area of spectra
l band around 968 cm−1 , and ƩA = summation of area of spectral bands between 600 and 2,000 cm−1 .
Functional indexes of un-aged, RTFOT, and PAV samples are shown below in Figure 3(a–d). Aro-
maticity and aliphatic indexes are inter-linked with each other. Ageing causes an increase in the forma-
tion of aromatic compound but it results in an equivalent reduction of aliphatic compounds. This behav-
ior was observed in conventional as well as modified binders, which can be seen from Figure 3(a–d). The
formation of aromatic compounds in aged binders can be credited to two major mechanisms, aromatiza-
tion of alkyl substituted naphthenic rings and aromatization of perhydroaromatic ring (Petersen, 2009).
Aromatization of perhydroaromatic ring takes place to make it more stable. In the process, aromatic rings
get associated with each other forming a cluster. This cluster formation results in increased viscosity of
the binders after ageing (Nivitha et al., 2016). Carbonyl index and sulphoxide index increased in both the
conventional binders. This may be attributed to oxidation, dehydrogenation, and crosslinking reactions,
which occur simultaneously during the ageing process (Siddiqui and Ali, 1999). In oxidation process,
oxygen reacts with perhydroaromatics and forms hydroperoxides. Formation of hydroperoxides results
in faster production of sulphoxides (Petersen, 2009). Greater carbonyl and sulphoxide index indicates
greater oxidation reaction, which further indicates increased hardness of the asphalt binders. This was
also observed in the results of conventional tests conducted on the binders.
In PMB, ageing causes the degradation of polymer network. Degraded polymer network along-
side increased polarity of bitumen molecules, changes molecular association, and hence compatibil-
ity between polymer and bitumen. In un-aged condition, the properties of PMB were found to be far
more superior than the conventional binders. However, after RTFOT the difference between these two
decreased and after PAV, the properties of PMB were found to be closer to the conventional binders.
 PETROLEUM SCIENCE AND TECHNOLOGY 1653

Table . Ageing index of the binders.

Binders RTFOT PAV

VG- . .

VG- . .
WMA . .
PMB (S) . .

Comparing carbonyl and sulphoxide indexes of conventional binders with that of PMB (S), it was seen
that although ageing degraded the properties of PMB (S) but still during ageing, PMB (S) resists the for-
mation of sulphoxide and carbonyl compounds much more as compared to conventional binders. The
reason behind this improved behavior can be attributed to the blending process of the base binder with
the polymer modifier. During the blending process, SBS absorbs the light oily fractions of the binders
and swells 8–9 times its original volume. This hinders the interaction of oxygen and bitumen molecules
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and reduces the oxidation process. Previous studies have also concluded that better dispersibility of
asphaltenes leads to greater formation of carbonyl compounds. However, modifiers interrupt the asphal-
tene network resulting in decreased carbonyl formation (Nivitha et al., 2016). In case of WMA, the car-
bonyl and sulphoxide indexes were even lower than PMB (S). This indicates greater ageing resistance
as compared to PMB (S). Though this is a general observation based on the spectral analysis, a further
morphological and microscopical investigation is needed to understand its behavior completely.
In PMB (S) it was found that after RTFOT, ISBS decreased from 0.0154 to 0.0122, which further
decreased to 0.0063 after PAV. This is an indicator of the degraded chain segment of butadiene in SBS.
Due to oxidation free radicals are generated, which causes double bond reactions in the unsaturated
mid-block of SBS, i.e. polybutadiene (Wang et al., 1995).
To quantify the effect of ageing on the binders, ageing index (AI) of the binders with respect to RTFOT
and PAV, was calculated. For conventional binders, i.e. VG-10 and VG-30, carbonyl and sulphoxide com-
pounds are major influencing factors, which cause significant changes in the binder property. AI of these
binders was calculated using following equation:
(Is=o + Ic=o )aged
AI = (7)
(Is=o + Ic=o )unaged

PMB (S) resists the formation of sulphoxide and carbonyl compounds. Degradation in binder prop-
erty occurs due to the degraded chain segment of butadiene which is represented by trans-butadiene
index (ISBS ). AI for PMB (S) was calculated using following equation:
(ISBS )unaged
AI = (8)
(ISBS )aged

AI of conventional binders and PMB are given in Table 4. From the obtained values, PMB (S) was
found to be most ageing resistance with respect to both kind of ageing. Among conventional binders,
VG-10 performed better than VG-30 in RTFOT, whereas in PAV, VG-30 performed better. Although AI
of WMA was lowest, but further morphological and chemical investigations are required to draw a firm
conclusion.

4. Conclusions
This paper examined the ageing characteristics of conventional, WMA and PMB with the help of FTIR
spectroscopy. From the absorbance spectrum, it was observed that the interaction between binder and
PMB was purely physical in nature. Ageing influences binder chemical and physical characteristics sig-
nificantly. Increased binder hardness as a result of ageing was evident with increased softening point
and decreased penetration values. Short-term ageing increased temperature susceptibility of the binders,
whereas long-term ageing decreased it. Aromatic and aliphatic compounds were found to be inter-linked
 1654 B. SINGH ET AL.

with each other. Ageing increased aromatic compounds of the binders, which on the other hands resulted
in a decrease in aliphatic compounds. Carbonyl and sulphoxide compounds increased after ageing, which
attributes to the increased hardness of the binders. PMB (S) resisted the formation of these compounds,
which indicates better ageing resistance. Although SBS was effective in decreasing the formation of other
functionalities, at higher temperature chain segments of butadiene decreases that causes degradation in
the binder properties. This degradation was clear from decreasing trans-butadiene index of PMB (S)
after RTFOT and further after PAV. As indicated by ageing resistance, PMB (S) showed better resistance
to ageing than conventional binders VG-10 and VG-30. In case of conventional binders, VG-10 showed
better resistance during RTFOT but in PAV, VG-30 was found to be better. Although WMA showed better
ageing resistance than all the other binders but it needs further morphological and chemical investigation
to understand its behavior properly.

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