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International Journal of Civil Engineering and Technology (IJCIET)
Volume 9, Issue 4, April 2018, pp. 1356–1369, Article ID: IJCIET_09_04_152
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=9&IType=4
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication Scopus Indexed
EFFECT OF AGED CRUMB RUBBER BITUMEN
ON PERFORMANCE DENSE GRADED MIX IN
MALAYSIA
Ayman Al Qudah, Mustaqqim Abdul Rahim, Zuhayr Md. Ghazaly
School of Environmental Engineering, Universiti Malaysia Perlis, 02600 Arau,
Perlis, Malaysia
Nuha Salim Mashaan
Noor Alawael Co., 3-5-11, Jalan 101C CBC, Taman Cherase, 50603 Kuala Lumpur, Malaysia
Suhana Koting
Center for Transportation Research, Department of Civil Engineering,
Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia
Madzlan Napiah
Department of Civil and Environmental Engineering, Universiti Teknologi PETRONAS,
32610 Seri Iskandar, Perak, Malaysia
Wan Mohd Sabki Wan Omar
School of Environmental Engineering, Universiti Malaysia Perlis, 02600 Arau,
Perlis, Malaysia
Yazan Issa
Department of Civil Engineering, Fahd Bin Sultan University, 71454 Tabuk, Saudi Arabia
ABSTRACT
To prevent pavement failure there are different solutions such as adopting new mix
methods or utilization of waste materials as additives. The main objective of this study
is to evaluate the effect of crumb rubber (CR) added to bitumen binder as a
reinforcing material on dense graded asphalt (DGA) mixture performance. The
performances of the DGA mixture were investigated by means of Marshall Stability
and flow test, stiffness test, indirect tensile strength test and cantabro test on DGA
samples before and after exposing unmodified and modified binders to aging process.
In this study, bitumen PEN (60/70) was utilized, modified with CR at three various
modification levels, namely, 5%, 10%, and 15%, respectively, by weight of the asphalt
binder. The optimum content of the added CR was found to be 5-10%. This percentage
results in the best level of stability and stiffness, maximum indirect tensile strength and
lower flow. The modified samples at different of CR contents were obviously better
Ayman Al Qudah, Mustaqqim Abdul Rahim, Zuhayr Md. Ghazaly, Nuha Salim Mashaan,
Suhana Koting, Madzlan Napiah, Wan Mohd Sabki Wan Omar and Yazan Issa
http://www.iaeme.com/IJCIET/index.asp 1357 [email protected]
properties in comparison with that of unmodified samples. It could be concluded that
reinforcement of binders by CR is a successful and beneficial technique.
Key words: Dense Graded Performance, Stability, Indirect tensile strength, Stiffness,
Abrasion loss, Crumb rubber, Bitumen Aging, Modified Bitumen
Cite this Article: Ayman Al Qudah, Mustaqqim Abdul Rahim, Zuhayr Md. Ghazaly,
Nuha Salim Mashaan, Suhana Koting, Madzlan Napiah, Wan Mohd Sabki Wan Omar
and Yazan Issa, Effect of Aged Crumb Rubber Bitumen on Performance Dense
Graded Mix in Malaysia, International Journal of Civil Engineering and Technology,
9(4), 2018, pp. 1356–1369.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=9&IType=4
1. INTRODUCTION
The Malaysian economy growth over the last few decades recorded a steady growth. This
economic growth in Malaysia has led to a population growth, as well as a great influx of
foreign workforces to cities. The increase in population causes increment in human activities
that lead to increase in a generated solid waste materials [1, 2]. In addition, this economic
growth has led to increase the infrastructure networks, thus, led to increase in the construction
of roads throughout the Malaysia. According to the environmental protection agency data,
there is a strong association between higher population density and higher traffic density and
this relationship is a statistically significant at the 99% level of confidence [3]. Traffic is one
of the most significant factors affecting performance of pavements. The pavement
performance is mostly affected by the loading magnitudes, configurations and the numbers of
load repetition by heavy lorries [4]. An increase in the traffic volume and vehicle loads leads
to distresses such as rutting and fatigue cracking that occur in asphalt pavement [5].
Additionally, flexible pavements are affected by surrounding environmental factors such as
temperature and moisture content [6], as well as the road pavement performance properties
are mainly impacted by the bitumen binder properties [7]. The flexible pavement is
commonly referred to Asphalt Concrete (AC) pavement and/or Hot Mix Asphalt (HMA).
HMA is defined as a mixture basically composed of bitumen binder and mineral aggregates,
include 5% of binder and 95% of mineral aggregates. By volume, a typical HMA is
approximately 85%, 10% and 5%, aggregates, bitumen and air void, respectively [8]. Due to
the asphaltic roads (HMA) in Malaysia dominates the overall surfacing layer at 87,626 km,
while the concrete roads are only 343 km and the other 3,651 km are gravel and earth roads
[9, 10], there is a need to improve materials in order to resist influence of internal or external
factors afflicting roads.
As the aggregate is one of the basic materials used in in the HMA mixture, the Aggregate
gradation is one of the most important properties of HMA, as well as stability, stiffness,
durability, resistance to moisture damages and resistance of fatigue cracking [11]. The
aggregate gradation (size) is increasingly important for providing an adequate skid resistance
and a higher abrasion resistance under heavy traffic. However, the HMA is mostly a dense
graded mix that is commonly used in Malaysia as road surfacing intended for general use. A
Dense graded (DG) mix generally consists of a uniform combined gradation of aggregates and
it has the most significant contribution in the load bearing capacity of the pavement. For the
DG mix, the air voids are typically ranged from 3% to 5% by volume of the total mix in a lab
compacted sample. Air voids are small pockets of air or airspaces which can be found
between the coated aggregate particles in the compacted sample. The goal of air voids in the
asphalt mixture is to permit for pavement to some external-additional compaction under
traffic loads and to provide space enough into which small amounts of asphalt binder can flow
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during this subsequent compaction. If HMA mixture is properly prepared, it will provide an
impermeable characteristic making the rainwaters to run away from the surface of pavement.
However, over time, pavement distress prevents the optimal function of road and contributes
to traffic accidents. Damaged pavements are considered as one of the significant factors that
contribute to the fatal motor vehicle crashes [12]. Due to the bitumen is the second basic
material used in the flexible pavements and is affected by external factors such as heavy rains
and temperature variations, there is a need to improve its properties to reduce the pavements
failure.
Asphalt cement also known as bitumen is considered as a thermoplastic, viscoelastic
adhesive material and its physical and rheological properties are very sensitive to temperature
changes and rate of loading [13]. Bitumen is widely used in roads pavements construction as a
glue or binder mixed with aggregates, primarily because of its excellent binding
characteristics and waterproof properties, as well as relatively low cost. But it is well known
that the physical and rheological properties of pure bitumen and its durability are not
sufficient to resist pavement distresses. Due to the inherent weaknesses of conventional
bitumen (unmodified) which has been leading to the high maintenance cost of the roads
network, there is a need to improve and modify the performance of an asphalt binder to
minimize the pavements failure. Reinforcement (modification) of asphalt binder is possible
during different stages of its usage, either in between binder production and mix processes or
before paving mix production [14]. Therefore, the use of scrap car tires (Crumb Rubber, CR)
in bitumen modification is considered to be one of the sustainable technologies which will
transform those vast-unwanted quantities of waste tires that accumulate in landfills and
stockpiles throughout the world, in particular Malaysia which produces about 10 million
pieces of scrap tire per year [15], into a new mixture which will help to dispose these solid
waste and avoid the disadvantages of bitumen which result during production and placement
of the asphalt mixtures, or during service lifespan through increasing the resistance to rutting
and fractures. Moreover, dealing with the growing problem of disposal of such materials is an
issue that requires coordination and involvement by all parties-involved, as well as it is both
financially and environmentally expensive. However, one of the major problems facing
bitumen during its service lifespan is the aging process [16]. The term aging was applied to
indicate multiple mechanisms in asphalt concrete mixtures. In many studies, the aging term is
applied to indicate only the effects of climate, which includes ultraviolet radiation, thermo-
oxidative aging, and moisture-related damages. In other cases, it may be applied to describe
the overall deterioration of the asphalt pavements from exposure to climatological and traffic
load factors. In general, the aging is a term the most used to describe the process of thermo-
oxidative aging only and it is this definition that is employed in this study. However, as
shown in field studies that CR has a significant effect in improving the bitumen performance
[17-20].
The aging of bitumen binders is one of the main factors determining the lifetime of asphalt
pavements. Aging causes the asphalt to stiffen and become brittle which leads to a higher
potential for fatigue and thermal cracking [21]. There are many factors might contribute to
hardening of the bituminous binder such as oxidation, polymerization, volatilization and
thixotropic. This is because bitumen is an organic compound, capable of reacting with oxygen
in the surrounding environment. The bitumen composite changes with the reaction of
oxidation developing a rather brittle structure. This reaction is referred to as an oxidative
hardening and/or age hardening [22]. To sum up the age hardening is a term used to describe
the phenomenon of hardening. Hardening is mainly associated with loss of volatile
components in asphalt aging during its services [23]. The effect of bitumen aging on the
performance of HMA mixtures is experimentally investigated using two different approaches.
Ayman Al Qudah, Mustaqqim Abdul Rahim, Zuhayr Md. Ghazaly, Nuha Salim Mashaan,
Suhana Koting, Madzlan Napiah, Wan Mohd Sabki Wan Omar and Yazan Issa
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The first approach is to subject the bitumen binders to the different aging conditions, and then
measure the resultant changes in physical and rheological properties to evaluate the aging
potential of the binder. The other is to subject loose asphalt mixture to aging condition prior
compaction, and then measure the properties of the aged mixtures. The first approach is the
most common from view of experimental investigation, thus, it was employed in this study.
Generally, aging of bituminous materials takes place in two major processes (phases) that
affect their properties and performance are namely short-term aging and long-term aging. The
short-term aging phase occurs at elevated temperatures during production, transportation, and
placement of the bituminous mixtures. In this phase, the bitumen binder is subjected to high
temperatures during its mixing and elevated the degree of exposure to air in a relatively short
period of time during its placement. Whereas long-term aging occurs at ambient temperature
due to exposure of the in-place asphalt to solar radiations and heating, in addition, to
progressive oxidation over several years in the life of the pavements [24]. However, the
proper use of bituminous binder as paving material is depended on its resistance to the
physical changes across the range of temperatures encountered in the unmodified pavements.
Aging was largely able to change the chemical and physical properties of bituminous binders
[25]. However, the problem with early pavement failure and the steady increase in used tires
created an idea for road designers to incorporate rubber tires in asphalt mixtures to bypass the
pavements distresses resulting from overloads and environmental factors. This idea leads to
improve asphalt performance and helps to dispose the vast quantities of waste tires, as well as
environmental-friendly.
Worldwide, there are many additives used as a reinforcing material into the asphalt
mixtures, one of among these additives is the CR [26-28]. Many good characteristics have
reported by the researches and applications of use the CR in the reinforcement of binders; to
mention but a few, improved resistance to surface initiated, improved durability, improved
resistance to rutting due to high viscosity, better resilience and high softening point, reduction
in pavement maintenance costs, minimize temperature susceptibility, reduce fatigue cracks
and saving in energies and natural resources (raw materials) by using waste products [29]. In
general, the fatigue resistance has enhanced by using CR as a modifier additive material in
bituminous binders [30, 31]. In addition, Lee et al. [32] pointed that the use CR in the bitumen
binders can improve properties of the binder by reducing the inherent temperature
susceptibility of binders. Hence, the improved CRMB binder pavements performance
compared with a neat bitumen pavements is primarily a result of improved and physical and
rheological properties of CRMB binder. However, in this study, CR was blended with
bitumen binder as an additive to evaluate effect of CR on the performance of Dense graded
Asphalt (DGA) mixture.
The bitumen PEN (60/70) is currently used in the construction of Malaysian roads
recommended in the new Public Works Department of Malaysia (JKR) standard
specifications for road works [33]. Moreover, it is subjected to high traffic loading and hot
weather condition. The weather condition in Malaysia leads to changes in temperatures of
about 55 oC at the surface to 25
oC at the subgrade during hot days. Due to an increase in
service traffic density, axles loading, and low maintenance service, the road structures have
been deteriorating and are therefore subjected to failure more rapidly. This study embarks on
the two following objectives. The first objective is to evaluate effect of bitumen aging on the
performance of HMA mixture. The second objective is to determine and evaluate the
influence of modified bitumen with CR on the performance of HMA before and after
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exposing modified bitumen to aging process, thus, reveal the possibility of bitumen modified
in improving the HMA mixture.
2. MATERIAL AND EXPERIMENTAL PROGRAM
The bitumen PEN (60/70), granite aggregates, and crumb rubber (CR) are the materials used
in this study. This section of study illustrates in detail experimental program and methods that
have been employed to prepare and evaluate samples of mixtures in accordance with ASTM
standard specifications. The flowchart of experimental work is presented in Figure 1.
2.1. Aggregates
Crushed granite aggregates were selected for this study because only granite aggregates are
permissible for use for asphalt wearing course [10]. The dense graded mix (ACW 14) is
recommended by Public Works Department of Malaysia (JKR) Standard specifications [33]
for road works. Aggregates was supplied from Pens Industries Sdn. Bhd. located at Perlis,
Malaysia. Table 1 indicates the properties of aggregates used in this study. Aggregate particle
size distribution according to JKR specifications is shown in Figure 2.
CR Bitumen PEN (60/70)
Marshall Stability Marshall Flow Indirect Tensile Strength Stiffness Cantabro
5 % of CR
10 % of CR
15 % of CR
Unaged CRMB Binder containing
5% CR
Unaged CRMB Binder containing
10% CR
Unaged CRMB Binder containing
15% CR
Materials
CRMBBinders
RTFOat 163
oC
for 85 min
Aggregates
Aged CRMB Binder containing
5% CR
Aged CRMB Binder containing
10% CR
Aged CRMB Binder containing
15% CR
Unaged RA Samples
Unaged RA
Samples containing
5% CR
Unaged RA
Samples containing
15% CR
Unaged RA
Samples containing
10% CR
Aged RA Samples
Aged RA
Samples containing
5% CR
Aged RA
Samples containing
15% CR
Aged RA
Samples containing
10% CR
Bitumen PEN (60/70)
Materials
Aggregates
Aged Binder
Control Mixture Samples
Aged control Mixture Samples
Aphalt mixtures Samples Testing
ConventionalModified
Processes
Figure 1 Flowchart of experimental work
Table 1 Properties of crushed granite aggregate utilized in this study
Property Unit Specification Result
Coarse Aggregate
Los Angeles abrasion Apparent specific gravity
Bulk specific gravity
Absorption
%
-
-
%
< 25
-
-
< 2
19.35
2.62
2.56
0.84
Fine Aggregate
Apparent specific gravity
Bulk specific gravity
Absorption
-
-
%
-
-
< 2
2.67
2.63
0.48
Ayman Al Qudah, Mustaqqim Abdul Rahim, Zuhayr Md. Ghazaly, Nuha Salim Mashaan,
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Figure 2 Aggregate gradation of DGA mixture with specification limits of JKR.
2.2. Bitumen
The bitumen PEN (60/70) extracted from the vacuum distillation residue collected from crude
oil is currently used in the construction of Malaysian roads as recommended in the new JKR
Standard [33] in order to reduce damages caused by fatigue failures. In this study, bitumen
PEN (60/70) used was obtained from Stolthaven (Westport) Sdn. Bhd. at Port Klang,
Malaysia. Table 2 shows the properties of base bitumen PEN (60/70) utilized in this study.
Table 2 Physical and rheological properties of bitumen PEN (60/70) utilized in this study
Property Unit Test Method Specification Result
Penetration at 25 ºC
Ductility at 25 ºC
Softening Point
Viscosity at 135 ºC
Specific gravity at 25 ∘C
0.1mm
cm
ºC
mPa.s
g/cm3
ASTM D5
ASTM D113
ASTM D36
ASTM D4402
ASTM D70
60 - 70
> 100
48 - 56
-
1.01 - 1.06
63
110
52
491
1.03
2.3. Crumb Rubber
The untreated CR utilized in this study was obtained by the mechanical shredding at an
ambient temperature supplied by Gcycle Company located at Kedah, Malaysia. The CR used
was originally produced from recycled vehicle tires. CR sized 0.6mm (30 mesh) was selected
for entire research.
2.4. Preparation of CRMB Binders
The wet process has been employed in this study to prepare CRMB binders. In the wet
process, CR is blended with base bitumen as an additive material. The bitumen PEN (60/70)
was used as base bitumen to produce the CRMB binders. The CR sized 0.60 mm (30-mesh)
and three different CR contents (ranged from 5% to 15%, with a 5% increment by weight of
base bitumen) were selected for this study. Three CRMB binders were produced by first
heating the bitumen PEN (60/70) up to 180 ºC before adding the CR. The required amount of
CR was slowly added to the heated bitumen and then bitumen was blended with CR using the
propeller blade mixer at a rotation speed of 4000 rpm and blending temperature was
maintained at 180 oC for an hour.
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2.5. Rolling Thin Film Oven Test
The Rolling Thin Film Oven (RTFO) test was performed according to ASTM D2872 [34].
This test is used to simulate short-term aging of bituminous material in addition to provide a
quantitative measure of the volatiles lost during the aging process. During the RTFO test, the
bitumen binders are exposed to high temperature to simulate manufacturing and placement of
the HMA mixture. The RTFO test was started by heating the RTFO oven at 163°C for 2
hours. Besides, a sufficient amount of binder was heated and poured into the glass RTFO
bottles with 35 g of binder. These bottles were immediately positioned in the rotating carriage
inside a heated RTFO oven. The carriage was then rotated at a rotation speed of 15 rpm. The
airflow was allowed to flow into each bottle at a uniform rate of 4000 ml/min. Bitumen
samples were maintained in the RTFO oven at 163°C for 85 min to expose to accelerated
aging.
2.6. Preparation of Asphalt Mixture Specimens
In this study, all the Asphalt Concrete (AC) mixture specimens were designed according to
JKR standards [33] to meet the Malaysian road works conditions. As stated in JKR standards,
the Marshall mix design method in accordance to ASTM D1559 [35] was certified as a design
method for AC mixtures in Malaysia. In this study, the combined aggregates with 14mm
(ACW 14) was used. According to JKR standards, mineral filler should be incorporated as
part of the combined aggregate. The content of required of filler in the AC mixtures should be
included an Ordinary Portland Cement (OPC) or hydrated lime as filler to resistance of
stripping. If OPC is used, the amount is not exceed 2% by total weight of the combined
aggregates. The AC mixture specimens have been prepared with 1156.6 g of aggregates
including 2% of OPC.
Preparation of the specimens were started by heating the combined granite aggregates in
the oven for one hour at 160 ºC before mixing with bitumen binder. Aggregate was then
transferred to the pan heated at 150 oC. Besides, the bitumen PEN (60/70) and CRMB binder
were heated to a temperature of 160 ºC and 180 oC, respectively. In order to obtain binder
more homogeneous, the CRMB binder was agitated vigorously before it was poured onto the
aggregates. Then, bitumen was poured to the heated aggregate as per the required amount. In
this study, the mixing process continued until all the aggregate have been coated totally by the
bitumen and the mix temperature was maintained at 150 °C. All AC samples were
automatically compacted by applying 75 blows for each face of specimen with a Marshall
hammer at temperature of 145 oC. The specimens in molds were left to cool at room
temperature for 24 hours. Then cylindrical specimens were removed from molds using
specimen extractor, and weighed and tested. In this study, two different types of asphalt
mixtures were prepared and these mixtures are unaged and aged asphalt mixtures. The unaged
asphalt mixture included four asphalt mixtures that prepared with unaged bitumen PEN
(60/70) as control sample and the three rest are designed were with unaged CRMB binders
containing 5%, 10% and 15% CR; whereas the aged asphalt mixture were produced with aged
bitumen PEN (60/70) and aged CRMB binders containing 5%, 10% and 15% CR as well.
Moreover, all AC mixtures were prepared at Optimum Bitumen Content (OBC). For the
determination of OBC, the conventional asphalt mixtures were prepared at five different
contents of unaged bitumen PEN (60/70) ranged from 4% up to 6% with a 0.5% increment by
total weight of the asphalt mixture as recommended by JKR standard [33]. In addition, five
graphs, namely, stability, flow, bulk specific gravity ( , voids in mix ( ), and voids
filled with bitumen ( ) of the compacted specimen were plotted versus the percentages of
PEN (60/70) binder. The OBC was found 5.2% and it was calculated as the numerical average
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of binder values based on the ACW 14 mix requirements [33]: peak stability, median flow,
peak , median and at 75%.
3. RESULTS AND DISCUSSION
3.1. Marshall Stability
The Marshall test was carried out by using a Marshall apparatus in accordance with ASTM
D1559 [35]. The Marshall stability refers to the maximum load resistance escalated during
applying 50.8 mm/min of deformation loading rate at 60 oC before failure of the compacted
cylindrical specimen. The Marshall stability can be defined as a measurement of the
susceptibility of an asphaltic mixtures to deformations ensuring from frequent and heavy
traffic loads. The Marshall Stability results obtained from asphalt mixture specimens are
presented in Figure 3.
Figure 3 Stability results versus CR content before and after bitumen aging
Figure 3 was plotted between the Marshall Stability value versus different CR contents
before and after aging process. The diagram shows effect of CR on the stability values of
unaged and aged HMA mixtures containing 0%, 5%, 10% and 15%, respectively. As shown
clearly in Figure 3, the addition of CR to the asphalt cement generally led to increase stability
of HMA mixture with CR content increased, where the higher stability value for the
rubberized HMA mixtures before aging process was at 10% CR. This similar finding was
revealed by Issa [36] and Kök et al [37]. As expected, the stability values for control (asphalt
mixture without CR) and rubberized mixtures increased after aging process. In the comparing
the stability of aged rubberized mixtures with aged-control mixture, the stability values of
aged rubberized mixtures have significantly increased as CR content increased. It can be
explained that aged HMA mixtures became stiffer and harder due to the aged binder lost the
volatile materials and became more viscous after exposure to high temperature, therefore, led
to better adhesion between the materials, aggregates and binders, in the mix. Based on the
results, the rubberized mixture can resist the permanent deformations and rutting under heavy
traffic loads. However, the stiffness and hardness alone are do not give the full picture
however, because the ductility and/or brittleness of the mixture will also affect its
performance with respect to cracking. Thus, though the 15% aged-rubberized mixture has the
highest stability value after aging process but this gives a negative indicator. Where the
stability value of 15% rubberized mixture largely increased as a result of exposure to aging,
this means it became very brittle and higher stiffness, thus, less resistance to cracks.
According to Izaks et al. [38], the combination of higher stiffness and more brittle behaviour
will likely result in a shorter fatigue life and a higher probability of thermal cracking
occurring in the field.
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3.2. Marshall Flow
Marshall Flow is a measure of permanent deformation of the asphalt mixtures determined
during the Marshall Stability test. However, it can be seen obviously in Figure 4 that Marshall
flow value decreased with CR addition up to 10%, and increases at higher percentage; and the
same result mentioned by Issa [36]. As shown at same the figure, the Marshall flow values for
control and rubberized mixtures decreased after aging process, this is explained physically
that aged mixtures became more harden and also could be related to the good adhesion
offered by aggregates and binder and the reduction in fluidity of the binder. Accordingly, the
CR has a significant effect on the Marshall flow of DGA mix; and the CRMB binder will
improve the performance of DGA mix.
Figure 4 Flow results versus CR content before and after bitumen aging
3.3. Stiffness
The ratio of stability (KN) to flow (mm), stated as the Marshall quotient (MQ), as an
indication of the stiffness of the asphalt mixtures. It is well recognized that the MQ is a
measure of the materials resistance to shear stress, permanent deformations and thus rutting.
However, high MQ values indicate a high stiffness mix with a greater ability to spread the
applied load and resistance to creep deformation [37].
In current study, the stiffness of asphalt mixture samples was calculated using Eq. (1)
specified in JKR standard [33].
(1)
Figure 5 Stiffness results versus CR content before and after bitumen aging
Figure 5 shows the stiffness ( increases with CR content increased and then it started
to decrease at higher percentage of the waste CR. But still shows higher than that of
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control mixture. This is due to increase in the Marshall Stability value. Additionally, in
comparison the of mixtures before and after aging condition, the values of control
and rubberized after aging are higher. It is related to increase in the stability and reduction in
the Marshall Flow. However, high values indicate a high stiffness mix with a greater
ability to spread the applied load and resistance to creep deformation.
3.4. Indirect Tensile Strength
The indirect tensile strength (ITS) test is very useful in indication to the performance of HMA
mixtures which depend on the cohesion of asphalt films. It was carried out in accordance with
ASTM D6931 [39]. The asphalt mixture samples were cured at 40 oC for 72 hours. After
samples cool to a room temperature, samples were then immersed in water at 25 oC for 24
hours prior to testing. The ITS test was performed by loading a compacted cylindrical
specimen across its diametric vertical plane at 50.8 mm/min deformation rate and 25 oC
temperature. The ultimate load at failure was recorded and utilized to calculate the ITS of the
specimen as illustrated in Eq. (2).
(
) (2)
Where is tensile strength of specimen; is max applied load to fail specimen; and
and are thickness and diameter of specimen, respectively. The effect of CR content on ITS
is depicted in Figure 6. The ITS values significantly increased with increasing of CR content.
As expected, and as was found by Sarsam et al. [40], Figure 6 shows that the ITS values for
control and rubberized asphalt mixtures also significantly increased after aging process.
Mixtures with higher ITS indicate that, apart from being stiffer and better adhesion due to
increase in viscosity, they are more resistant to deformations, thus, the CR is able to improve
the performance of DGA mix.
Figure 6 Indirect tensile strength results versus CR content before and after bitumen aging
2.5. Cantabro
Cantabro test was used to measure the resistance of the compacted asphalt mixtures to
ravelling. This test was conducted following a method adapted from ASTM C131 [41].
Samples were placed in a Los Angeles machine without the steel balls for 300 revolutions at
25±1 oC and speed of 30 to 33 rpm. The percentage of abrasion loss ( ) was calculated based
on Eq. (3).
(
) (3)
Where is the abrasion loss (%). and are the mass before and after test,
respectively. Figure 7 show effect of CR on abrasion loss of compacted sample. The higher
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value of abrasion loss indicates the lower ravelling resistance. The results show, abrasion loss
values increased as the CR contents increased except in the case of lowest CR content (5%),
the abrasion loss decreased slightly. This is due to the addition of CR with high percentages
make mixture more stiff and brittle, and shatters upon effect. Additionally, it can be observed
clearly in Figure 6 that the abrasion loss values of aged mixtures are higher compared to those
unaged mixtures. Aging process is expected to increase mixtures stiffness, making the
mixtures more brittle and therefore more susceptible to abrasion.
Figure 7 Indirect tensile strength results versus CR content before and after bitumen aging
4. CONCLUSIONS
In this research, the bitumen binder was modified by adding CR, which is considered a solid
waste material produced from scrap car tires. The unmodified and modified binders were
simulated to short-term aging by using RTFO oven. The effects of CR and aging on the
performance characteristics of DGA mix were investigated in this experimental study. Based
on the findings and discussions, the following conclusions can be drawn:
Stability is improved by adding CRMB binder to the DGA mix as better adhesion between
materials is developed. In comparing the Marshall stability of control mix with rubberized
mixes, the values stability of rubberized mixes were generally higher. The Marshall stability
of control and rubberized mixes were significantly increased after aging process.
The Marshall Flow values decreased before aging process as CR content increased except in
the case of the 15% of CR. Meanwhile the flow results after aging show decreased.
The stiffness of rubberized samples, in general, increased with increasing of CR content
compared with control sample. In addition, the stiffness of unmodified and modified asphalt
mixtures increased after aging process.
The ITS values of DGA samples containing different CR contents are higher in comparison
with that of control sample due to increase in viscosity that led to better adhesion. The ITS of
control and rubberized mixes were significantly increased after aging process.
Abrasion loss values significantly increased as the CR contents increased except in the case of
lowest CR content (5%), the abrasion loss decreased slightly. The Abrasion loss were
increased after aging process due to the mixes became stiffer.
The OBC of conventional asphalt mixture was found 5.2% by weight of total mix. Meanwhile
the optimum content of the added CR was found to be 5-10% by the weight of asphalt binder.
Ayman Al Qudah, Mustaqqim Abdul Rahim, Zuhayr Md. Ghazaly, Nuha Salim Mashaan,
Suhana Koting, Madzlan Napiah, Wan Mohd Sabki Wan Omar and Yazan Issa
http://www.iaeme.com/IJCIET/index.asp 1367 [email protected]
ACKNOWLEDGEMENTS
The authors would like to acknowledge the support from Ministry of Higher Education
Malaysia for the Research Acculturation Grant Scheme (RAGS) 2015, No. 9018-00088 and
SCHOOL OF ENVIRONMENTAL ENGINEERING, UNIVERSITI MALAYSIA PERLIS.
The authors would also like to thank the UNIVERSITI MALAYSIA PERLIS (UniMAP),
UNIVERSITI TENOLOGI PETRONAS (UTP) and UNIVERSITI MALAYA (UM) for their
laboratory assistance during the testing program.
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