International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol:12 No:06 53

Evaluation of Different Conditions on The Mixing

Bitumen and Carbon Nano-Tubes
Ziari Hasan 1* , Rahim-of Kamran2* , Fazilati Mohammad3* , Goli Ahmad1* , Farahani Hosein1*
1- Department of Civil Engineering, Iran University of Science and Technology, Tehran,
+989132677854 (Ahmad Goli) , E-mail address (agoli@iust.ac.ir)
2- Department of Civil Engineering, Islamic Azad University, Science and Research Branch
3- Department of Food Science and Technology, School of Agriculture, Isfahan University of Technology, Isfahan, Iran

Abstract-- Asphalt has been widely used for pavements building of the nanofibers. Carbon nanotubes (CNTs) are considered to
for long time. Actually, the increase in traffic loading and in the be one of the most beneficial nano-reinforcement materials.
number of vehicles together with the adverse environmental The combination of high aspect ratio, small size, low density,
conditions, conduce to a rapid structural damage of pavements. and unique physical and chemical properties makes them
In order to enhance the mechanical properties and the long time
perfect candidates for reinforcement in multifunctional and
behavior, a new generation of blend asphaltic has been developed
through the incorporation of different kind of polymers. smart cement-based materials. CNTs can be Structurally
Nano-reinforced materials hold the potential to redefine the field approximated to „„rolled-up‟‟ sheets of graphite (Fig.1). In this
of transportation materials both in terms of cost effectiveness graphite, sp2 hybridization occurs, where each carbon atom is
and long term pavement performance. This study focuses on the evenly connected to the other three carbon atoms (120º) in the
exploratory analysis of the mixing procedure of carbon nano- xy plane, and a weak π bond is present in the z axis. The sp2
tubes (CNTs) with asphalt cement (AC). In this paper, the impact set forms the hexagonal (honeycomb) lattice of a graphite
of different mixers on the mixture conditions of asphalt and sheet [14- 16].
carbon nano tube is investigated. CNT, having three percent of Nanoclay modification improves some characteristics of
asphalt weight, and asphalt are mixed together by using
asphalt binders and asphalt mixtures such as rutting. However,
mechanical, high shear and ultrasonic mixer, and then examined
by a scanning electronic microscope. According to the pictures of it has not mitigated the fatigue problem and hence, more
different samples, the ultrasonic mixer creates the best form of research is required before it can be utilized on a large scale
asphalt and CNT mixture. [18]. Research has shown that nanocalcium carbonate (nano -
CaCO3) modified asphalt [19, 20] can enhance asphalt rutting
Index Term-- Bitumen, Carbon Nano Tube (CNT), mixing, resistance and improve its low-temperature toughness.
S canning Electronic Microscope (S EM), Ultrasonic Mi xer Nanoclays such as sodium montmorillonite and organophilic
montmorillonite have shown improvements in viscosity,
1. INT RODUCT ION complex shear modulus and phase angles of styrene–
Asphalt has been widely used for pavements building for a butadiene–styrene (SBS) copolymer modified asphalt [21].
long time. Actually, the increase in traffic loading and the Varieties of CNTs include single-walled nanotubes (SWNTs)
number of vehicles together with the adverse environmental and multi-walled nanotubes (MWNTs). SWNTs only have one
conditions, conduce to a rapid structural damage to wall that constitutes a tube, whereas MWNTs are made up of
pavements. In order to enhance the mechanical properties and multiple walls that can slide against each other. The diameters
the long time behavior, a new generation of blend asphaltic of CNTs range from just a few nanometers in the case of
has been developed through the incorporation of different SWNTs to several tens of nanometers for MWNTs. The
kinds of polymers [1–6]. The application of nanotechnology in lengths of the tubes are usually in the micrometer range [14].
various applied fields is receiving widespread attention. It is
important to ensure that these applications address real
questions to allow the technology to improve general well-
being of the public, especially while evaluating application in
the area of civil engineering [7]. Nanoreinforced materials
hold the potential to redefine the field of traditional materials
both in terms of performance and potential applications [8–
13]. Hussain et al. [9] showed that the biggest challenge in
developing nanocomposite is the dispersion of nanoparticles
or chemical compatibility with matrix materials. They found
out that the issue of improving the carbon nanofibers
(CNFs)/matrix interfacial adhesion and complete dispersion
must be resolved before achieving the full potential of
nanoreinforced composite materials. Dispersion of nano-fibers
has been one of the biggest challenges due to the aggregation Fig. 1. T he structure of CNT s [17].

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 International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol:12 No:06 54
This paper focuses on the mixing conditions of CNT with proportion to asphalt is three percent, and asphalt are mixed
asphalt and the effect of various mixers on the CNF mixing together. This mixture is divided into three smaller mixtures
with asphalt cement (AC). (samples). Each sample is mixed by using a different mixer
and in different conditions. These mixers are mechanical, high
2. M AT ERIAL AND MET HODS
shear and ultrasonic mixers.
In the first stage, multi wall carbon nanotube, which its weight
T ABLE I
CHARACTERISTICS OF THE USED BITUMEN .
Ductility (cm) Softening point (0 c) Penetration at 25 0 c (0.1mm) Pure bitumen

Over 100 51 68 60/70

T ABLE II
CHARACTERISTICS OF THE USED CNT
lengh purity ash SSA Density
30 µm > 95% < 1.5 % 200 m2/gr 2.1 gr/cm2
Then, according to the capabilities of each mixer, which has a GRAP H 1
CONSIDERED CONDITIONS FOR COMBINATION OF ASP HALT AND CNT
different performance of mixing materials, the combination BASED ON THE KIND OF MIXER.
conditions are considered different for each of them.
Therefore, each mixer has its own specifications. For example,
due to the constant combination rate of a mechanical mixer, its
combination time is considered as a variable. The rotation rate
and the power of the mixer are supposed to be variables for
high shear and ultrasonic mixers, respectively.

2.1. Mechanical mixer

The mechanical mixers are often used in metallurgical and
mechanical laboratories. This kind of mixer is used to mix
several dry powder materials or combine solutions easily
mixed together or solve a solid material in a solution. The
mixer is used considering its time parameter a variable, while
its motor rotation is constant in each minute. In other words,
since the motor rotation is constant, the materials must be
mixed as long as a homogenized mix is obtained. One should
of course note that the time of mixing depends on the type of
matured materials and the operator‟s opinion.

Fig. 2. T he mixers which are used to mix asphalt and carbon nano tube (from
right to left: mechanical mixer, high shear mixer and ultrasonic mixer [22, 23]

Fig. 3. T hree kinds of mechanical mixer

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2.2. High shear mixer
High shear mixers are of the most applicable mixers which are
used in mixing asphalt and polymer. It is used to mix asphalt
with polymers and other additives Rotation rate of the mixer‟s
tip can be determined based on the kind of the polymer. This
mixer is used in mixing asphalt and polymer because of the
special structure of its tip. In fact, the special design of mixer
tip makes the mixture enter and move rapidly through the
space between two very close plates and leaves it through the
space between embedded slots in Outer layer. This procedure
results in making the mixture of asphalt and polymer more
homogeneous. Fig. 5. Different parts of an ultrasonic mixer and quality of its performance
[25].
3. Providing samples
As previously mentioned, it is necessary to determine how the
materials should be combined together. That is why, in this
test, three different kinds of mixers, with different conditions
considered for each of them, are used to mix CNT with
asphalt. Then, after sampling the mixture, these samples must
be tested by using a scanning electronic microscope to
determine the combination conditions of asphalt and CNT and
also the quality of dispersion of nano materials in nano scale.

Fig. 4. Quality of performance of high shear mixer [24]

2.3. Ultrasonic mixer
The term of ultrasonic waves is used for mechanical waves
whose oscillation frequencies are more than the upper limit of
human‟s hearing frequency range (20 Hz to 20 KHz).
Performing a simple calculation, it can be found out that if a Fig. 6. T he use of ultrasonic mixer in providing samples mixed with nano
point oscillates with the frequency and amplitude of 25 KHz materials
and 10  m , respectively, its acceleration will be 25000 times
as large as that of gravity. Such acceleration and, consequently
a high speed in liquids will result in cavitation and then, some
bulbs with the pressure of about 200 bars and the temperature
about 5000 k are formed during explosion. On the other
hand, if a relative movement with above specifications forms
between two solid surfaces, the resultant temperature increase
makes these surfaces weld together, called “ultrasonic
welding”. The applications of ultrasonic technology can
include accelerating chemical reactions, increasing fuel
efficiency, water purification, cell wall breaking and
disinfection, combining nano particles with water and other
Fig. 7. part of provided samples after mixing by using the ultrasonic mixer in
solutions homogeneously and so on. In fact, this apparatus different mixing conditions (right: samples provided for element analysis
produces a huge amount of energy by creating ultrasonic Left: samples provided for delivering to scanning electronic microscope)
waves and cavitation which can combine the mixture and also After providing samples according to graph 1 (different forms
separate nano particles from each other and finally, make a of mixture by using different mixers), all samples were tested
completely homogeneous mixture. by using a scanning electronic microscope to examine the
quality of asphalt and nano material combination. It should be
noted that the samples , before placing under the scanning
electronic microscope, were placed in a vacuum reservoir and
then covered with a thin layer of gold.

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Generally, the following points must be applied to observe the
provided samples under the scanning electronic microscope.
Size: size limitation is determined by the design of scanning
electronic microscopes. The samples whose sizes are 15 to 20
can be usually tested without sample movment.
Providing samples: Non-conductive materials are often
covered with a thin layer of carbon, gold or gold alloy. It is
necessary to make an electronic connection between sample
and base and spread the fine samples, like powders, on a
conductor film, like aluminum paint, and dry it completely.
The samples must be free of any liquid with high vapor
A
pressure like water, organic detergent solutions and residual
oil films.

Fig. 8. Asphalt sample, before (right) and after (left) preparation for placing
under the microscope (left sample: placement of sample in vacuum reservoir
and covering with gold) B

4. RESULT S ANALYSIS
The provided samples , with different mixers and in different
conditions, are placed under the microscope to examine
mixture conditions of asphalt and nano materials . Generally,
these samples, based on the mixer type, could be categorized
to three groups. The effect of mix by each mixer on the quality
of dispersion of nano materials was absolutely apparent. Thus,
the samples must be examined separately.

4.1. Mechanical mixer

Similar results were observed in almost all samples mixed by
the mechanical mixer. While there was a concentration of
nano materials in some parts of samples (Fig. 9, parts A, B,
D), there was almost no nano materials concentration in some C
other samples (Fig. 9, part c). The concentration of nano
materials indicates that the mechanical mixer is unable to
separate nano materials from each other. Therefore, these
materials were interlaced (Fig. 9, part D). In such conditions,
there were some concentrated micro materials instead of nano
dispersion. This indicates that the use of the mechanical
mixers, to mix nano materials, leads to forming a
heterogeneous mixture based on the materials dispersion in
asphalt. In addition, it cannot prevent nano materials from
becoming agglomerated.

Fig. 9. Microscopic picture of samples mixed with nano materials by using a

mechanical Mixer (heterogeneous dispersion of nano materials and
agglomeration of nano materials)

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4.2. High shear mixer
High shear mixer combined and provided the samples with
three different angular velocities. First, asphalt and CNT were
mixed by the mixer with the angular velocities of 1000, 1500
and 2000 rpm for 15 minutes at 120 c and then, the mixture
were sampled. In contrast to the provided samples by the
mechanical mixer, the dispersion of nano materials in the
whole sample mixed by the high shear mixer (Fig. 10, parts A,
B) was homogeneous. But unfortunately, this mixer, like the
previous one, could not disperse nano materials in nano scale
and these materials were dispersed in micro scale. Therefore,
agglomeration of nano materials in the sample was observed C
(Fig. 10, part C, D).
High shear mixer is used to homogeneously mix asphalt and
additive due to its nature and designed shape which combines
the materials with high speed and pressure between two near
plates (That is why it is used to mix asphalt and polymer). It
should be noted that the materials used in this test are in nano
scale. Consequently, they normally become agglomerated and
approach micro scale. Therefore, this mixer cannot separate
these nano materials from each other. Based on the observed
samples under the scanning electronic microscope, it is clearly
concluded that the high shear mixers are not capable of
separating nano materials from each other. One should of
course note that since this problem has been caused in the case
of CNT, other nano materials may not encounter this problem.
Thus, they would be considered useful for mixing with D
asphalt.

Fig. 10. microscopic picture of samples mixed with nano by using a high
shear mixer (homogeneous dispersion of nano materials and their
agglomeration)

4.3. Ultrasonic mixer:

The samples mixed by an ultrasonic mixer are generally
categorized into three groups. The samples provided with the
power of 60 watt for 10 and 15 minutes and the one provided
with the power of 65 watt for 15 minutes at 12 c are placed
under the scanning electronic microscope. For these samples,
A and particularly for the sample provided with the power of 65
watt for 15 minutes, nano materials are observed
homogeneously and separately dispersed in asphalt (without
agglomeration) (Fig. 11, part A,B). Also, as it can be seen in
Fig. 11, CNT particles are separated from each other and
easily recognizable.

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walls. This point shows that not only is the carbon nano-tube
an add-on to bitumen, but also it is capable of reacting to
bitumen molecules. As a result, final composition is not a
physical one.

6. CONCLUSION
Polymeric and non-polymeric materials are used to improve
CNT the characteristics of asphalt and its mixtures and
consequently, to increase and improve their life and
performance. CNT, as a new material possessing some unique
characteristics and having a similar molecular structure to
asphalt, was used in this test. Since appropriate conditions of
combination of asphalt and nano materials must be provided
to make a modified asphalt with CNT, three kinds of mixers
A and three mixture conditions for each mixer were considered.
Observing the samples obtained from nano materials and
asphalt combination under the scanning electronic microscope
indicates that a mechanical mixer is not useful for mixing
these nano materials, because it not only cannot separate nano
materials from each other, but also cannot homogeneously
disperse this material in the asphalt samples.
High shear mixer, because of the type of the mixture, can
homogeneously disperse nano materials in asphalt, but like
mechanical miner, it cannot separate the agglomerated nano
carbon tubes from each other.
In spite of two previous mixers, the ultrasonic mixer can make
a homogeneous mixture and separate nano particles from each
other. This is because of its capability in creating cavitations
and producing energy throughout ultrasonic waves.
Samples elemental analysis shows that combining carbon
nanotubes with bitumen to increase the percentage of carbon
B combined with carbon nanotube-based bitumen is typical. The
reason for this statement is that carbon nanotube as an additive
is not without reaction with tar and bitumen to create a
Fig. 11. microscopic picture of samples combining with nano materials by chemical reaction occurs with this material.
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Ahmad Goli
- PhD Student in Civil Engineering, T ransportation Engineering.
- PhD T hesis title: Laboratory analysis of HMA mixes characteristics
modified with Carbon Nano T ube (CNT ).
- Extensive experience in preparing different test specimens and performing
experimental tests to characterize the performance of different types o f
modified asphalt and use of CNT in other technology. In this research analysis
of HMA mixes characteristics modified with Carbon Nano T ube (CNT ).
- Research interests:
 Bitumen modifier with different polymers
 Mechanical and performance properties of asphalt concretes

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