effect of aged crumb rubber bitumen on performance … · samples before and after exposing...

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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


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

Effect of Aged Crumb Rubber Bitumen on Performance Dense Graded Mix in Malaysia


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.




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



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


10% CR


15% CR

Materials

CRMBBinders

RTFOat 163

oC

for 85 min

Aggregates

Aged CRMB Binder containing

5% CR


10% CR


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




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.



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




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.



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




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



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.




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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effect of aged crumb rubber bitumen on performance … · samples before and after exposing...

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