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Case Study
Case study of rutting performance of HMA modified
with waste rubber powder
G.H. Shafabakhsh *, M. Sadeghnejad, Y. Sajed
Faculty of Civil Engineering, Semnan University, Semnan, Islamic Republic of Iran
1. Introduction
Pavement construction is one of the most important costs in the field of transportation. In a study conducted in Canada it
has been found that the cost spent on the road pavement and streets, reach to 150$ million per year. Asphalt concrete is
among the materials which are widely used for roads and airports pavement. About 95% of all of the world pavements is of
asphalt type (Huang, 1993). These pavements over time suffer failure due to passing traffic loads and exposure to different
environmental conditions. Among the most important of these failures, we can mention rutting which is considered as the
main concern of transportation agencies in the field of pavement. Annually, millions of dollars have been spending to
compensate rutting failures in the pavement. The temperature and stress-induced by loading can be named as two main
parameters that lead to permanent deformation in asphalt pavements. When the traffic loading increases and temperatures
are high, rutting failure are more likely to occurring. Research in the field of improving the constituent materials of hot mix
asphalt (HMA), mix designs and methods of analysis and pavements design, including laboratory and field tests are needed
to cause providing more serves life for pavements and as a result, the loss of costs which are set to be spent to repair
pavement failures is prevented. Researchers and engineers are continuously trying to improve asphalt pavement
performance (Huang, 1993). A conventional asphalt system consisting of asphalt concrete layers and sub-layers on the
subgrade soil prepared are shown in Fig. 1 (Kok and Kuloglu, 2007).
Case Studies in Construction Materials 1 (2014) 69–76
ARTICLE INFO
Article history:
Received 16 February 2014
Received in revised form 18 April 2014
Accepted 20 April 2014
Available online 9 May 2014
Keywords:
Rubberized asphalt
Waste rubber powder
Wheel track test
Rutting depth
ABSTRACT
Low resistance against dynamic loads and short service life of pavement are the most
significant problems in the conservation and maintenance of roads, to the extent that,
annually enormous costs are spent in order to improve capabilities of road services in the
country. Research shows that the use of some wastes such as waste rubber powder in
asphalt mixtures not only increase its serves life but also cause to reduce production costs;
furthermore, recycling the crumb rubber has also considerably environmental benefits
environmental benefits such as reduced need for landfill, less atmospheric pollution from
burning. In this paper, the effect of adding waste rubber powder on the rutting
performance of asphalt mixtures has been studied. In order to compare the performance of
rubberized asphalt mixtures and conventional asphalt, wheel track test has been used. The
results of this study show that the use of rubber powder caused a significant decrease in
the rate of rutting depth of rubber asphalt mixtures compared to control samples.
ß2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND
license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
* Corresponding author. Tel.: +98 2313354302.
E-mail addresses: Shafabakhsh@Semnan.ac.ir (G.H. Shafabakhsh), Mostafa.sadeghnejad@yahoo.com (M. Sadeghnejad).
Contents lists available at ScienceDirect
Case Studies in Construction Materials
journal homepage: www.elsevier.com/locate/cscm
http://dx.doi.org/10.1016/j.cscm.2014.04.005
2214-5095/ß2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/
3.0/).
The presence of asphalt concrete layers is the main reason to create pavement structural capacity. HMA in the pavement
construction as the surface layer is used to distribute stress-induced by load and also protect unprotected sub layers from the
effect of water.
Asphalt mixture for efficiently performing both of these tasks during the life of pavement design, should be resistant
against the effects of climate and resist against the permanent deformation and cracking caused by load and environmental
factors. Constituent material properties play a significant role in pavement construction specifications (Haghi et al., 2005).
Failures that occur during the useful life of the pavement, mainly includes permanent deformations in the path of vehicles
wheel (rutting), fatigue cracking and thermal cracking. Since, enormous costs should be spent to repair and reconstruction of
shortcomings and defects, so early prevention often is more economical. To avoid this failure, pavement materials should be
selected so that they would have sufficient strength and stability. Aggregates must be broken, and applying excessive
bitumen and fine aggregate should be avoided (Tabatabaei, 2005).
Wheel track groove (rutting) is the permanent deformation of pavement layers that can be increased over time. Pictures
of wheel track groove are shown in Fig. 2. Generally, three factors led to create rutting in the asphalt pavement include
permanent deformation accumulation in the surface of asphalt layer, permanent deformation of the subgrade, and erosion or
wear of asphalt at the wheels place due to the passing of vehicles. In the past it was believed that deformation of the subgrade
is the main reason of occurring grooves in the pavement and many of the design methods were built based on limiting the
vertical strain. However, research in recent years has indicated that the main reason of rutting is related to the upper part of
asphalt surface layer or surface layer (Rabbira, 2002).
Surface rutting of wheel path can cause to jeopardize road safety. Consequently, excessive rutting which is usually
considered as the main cause of premature failure and repairing operations and maintenance of road network, will lead to
the reduction in pavement serves life (Brock et al., 2003).
The evaluation of asphalt concrete mixtures to protect them against rutting phenomenon of wheel track has turned to the
important research area in recent years. This type of failure occurs as a result of the consolidation and compaction of asphalt
mixture after manufacturing and the plastic deformation caused by wheel passing vehicles over time. In recent years in order
to enhance pavement flexibility as well as their resistance against destructive factors such as fatigue, cracks induced by
extreme changes in temperature and permanent deformation of asphalt pavement, the utilization of waste materials that
[(Fig._2)TD$FIG]
Fig. 2. Rutting phenomenon occurrence in asphalt pavement.
[(Fig._1)TD$FIG]
Fig. 1. Asphalt pavement system under vehicles loading.
G.H. Shafabakhsh et al. / Case Studies in Construction Materials 1 (2014) 69–76
70
have the potential to improve the mechanical properties of the asphalt pavement, has been common in the construction of
HMA (Kandhal, 1992). Improvement of the pavement properties is possible by applying two methods:
Improve properties by using the modified bitumen
Improve properties by using the modified asphalt mixtures
In recent years, ascending trend of costs of repairing and reconstruction of roads and airports pavements which is creating
due to the increasing the amount and repetition of traffic loads on the pavements, has caused that a comprehensive research
is conducted on the use of additives in manufacturing of asphalt mixtures to enhance their capabilities against dynamic
loads. Low resistance of pavement against dynamic loads and their short life of serves are the most significant existing
problems in the field of conservation and maintenance of roads.
2. Literature review
Using recyclable materials in road construction is one of the cases that its related industries have obtained extensive
experience about the use of by-products in asphalt. Examples of wastes that have been used in asphalt mixtures, including
glass baking furnace dross, ash obtained the incineration of municipal waste, crushed brick, plastic, rubber obtained from
waste tires, waste glass and waste rubber powder. However, successful use of these products is depending on a full
investigation of the sources and their characteristics and usually is done at a low level.
According to the available reports, annually, about one billion, equivalent 9 million tons waste tires are produced in the
world. Due to the shortage of landfill space and environmental issues, recycling old tires seem necessary.
The value is 290 million rings in the U.S. and 110 in Japan. Collecting and storing these tires not only create pollution but
also contain high costs and in addition, there is the possibility of fire in the location as well. In Iran, the annual rate of worn
tires is nearly 7 million rings, approximately 220 thousand tons. On the other hand for a single truck tire, about 22 gallons of
oil is used. In the U.S. and Canada, only 30% of waste tires is transferred to the sanitary centers of landfill and the rest are
abandoned in the nature that make a suitable habitat for vermin and rodent such as rat and a suitable place for the growth of
mosquitoes and the spread of the agent of types of diseases such as viruses. Fig. 3 shows the accumulation of waste tires in
landfill. Given that the tire pieces are slowly decomposed, finding a solution for their use and reducing the environmental
risks caused by their burial in the environment is essential (Bidaki et al., 2012).
The utilization of waste crumb rubber as a modifier material in the asphalt has been considerable for researchers over the
recent four decades. Carried out researches in the manufacture of rubber asphalt pavement indicate the reduction of
[(Fig._3)TD$FIG]
Fig. 3. A landfill for accumulation of waste rubber.
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71
pavement thickness, increase of pavement life, becoming less light refraction reflection rate, becoming less traffic noise, the
reduction of maintenance costs, reduction of pollution and improve environmental issues.
In 2007, Wang et al. study on the effect of crumb rubber modifier on the sensitivity of high temperature of the surface
mixture. In this paper, they evaluated the effect of different sizes of crumb rubber on high temperature sensitivity of three
type of surface mixture. The evaluation was conducted in two parts: first, the properties of the modified and unmodified
bitumen in a wide range of test temperatures and aging conditions have been compared. Then rutting resistance of modified
mixtures is compared with conventional. The results of this research showed that the bitumen modified with crumb rubber
have better performance to resist against rutting (Wong and Wong, 2007).
Tortum and colleagues in 2005 used the results of Marshall Test to determine the optimal conditions for the use of tire
rubber in Asphalt Concrete. They considered granulated crumb rubber, fusion temperature, aggregate gradation, the amount
of crumb rubber, density temperature, the amount of bitumen and fusion time as experimental variables. In this study, the
method of dry mixing crumb rubber in asphalt concrete was used. The results of this research showed that rubber asphalt
mixtures have more favorable Marshall’s resistance than conventional mixtures (Tortum et al., 2005).
In another study, Celik and Atis (2008), studied on the phenomenon of compressibility of HMA made with bitumen
modified with crumb rubber. In this paper they tried to find a link between performance and compressibility of asphalt
mixtures. They used gyrating testing machine (GTM) in order to determine the performance of asphalt mixtures. The results
of this study indicated that gyrating compactor can be used for evaluating the performance and compressibility of HMA
(Celik and Atis, 2008).
According to the above research, necessity of conducting more complete and comprehensive investigation regarding the
utilization of waste rubber powder to improve the behavioral performance of asphalt mixtures is felt. This study examines
the rutting phenomenon in rubberized asphalt mixtures by wheel track test.
3. Research methodology
3.1. Materials
Used materials in the experiments consist of aggregates, waste rubber powder and pure bitumen. Aggregates gradation is
mediocrity continuous gradation of HMA related to the stratum of Topeka (type 4) in accordance with Iranian standard,
publication No. 101 of technical and public specifications of roads. The sizes of this grading are presented in Table 1. Bitumen
used is the bitumen 70-60 of Isfahan refinery which its characteristics have listed in Table 2. Moreover, the tire crumb rubber
used in this study was prepared from Yazd Tire Company. Granulated crumb rubber used is shown in Table 3.
3.2. Marshall test
This method of testing has been inserted in Standard No. ASTM-D1559, entitled ‘‘Standard Testing Method for
determination of asphalt mixtures resistance against plastic deformation with Marshall Method’’. Manufacturing and
preparing methods of specimens of asphalt mixture for asphalt mix design is performed based on Standard Method (ASTM-
D1559). In this method, the cylindrical compacted asphalt mixture specimens with a height of about 63.5 and diameter of
101.6 mm are provided. Compaction action is performed by a metal hammer having a circular cross-sectional surface
(diameter 98.4 mm) and weigh of 4.5 kg that freely falls from the clear height of 45 cm.
Table 2
Characteristics of bitumen used in this study.
Degree of
purity (%)
The weight
loss (%)
Degree of
combustion (8C)
Plasticity
(cm)
Softening
point (8C)
Penetration
degree 10 mm
Density
in 25 8C
99 0.75 262 112 51 66 1.02
Table 1
Continuous gradation of HMA related to the stratum of Topeka (type 4).
0.075 mm 0.3 mm 2.36 mm 4.75 mm 12.5 mm 19 mm Sieve size
2–10 5–21 28–58 44–74 90–100 100 Regulation range
6 13 43 59 95 100 Used weight percentage
Table 3
Crumb rubber gradation used in this study.
0.075 mm 0.3 mm 0.6 mm 1.18 mm 2 mm Sieve size
2.5 22.5 60 82.5 100 % passing the sieves
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72
According to previous studies, the optimal percentage of the utilization of waste rubber powder as a modifier of bitumen,
10% of bitumen weight has been determined; therefore, in this study, waste rubber powder has replaced 10% of the bitumen
used. To mix bitumen and crumb rubber, the mixer equipped with a thermocouple and thermostat is used until fusion occurs
at the desired temperature. Mixing is done with a speed of 1200 rpm.
In order to conducting the Marshal Test on the specimens, first the specimens are placed in a warm water bath for 30 min
at 60 8C and after this period, the specimens are withdrawn from the bath and their outer surface dries. Jaws of the Marshall
Apparatus lubricated and then the specimens are placed in the Marshall apparatus. With turning on the machine, loading on
specimens is performed.
According to the Marshall Test results, in the conventional asphalt specimens, optimum percentage of bitumen is 6%.
Moreover, according to the Marshall Test results, optimal amount of bitumen modified with rubber powder for rubberized
asphalt specimens, with optimum percentage of additive 5/5 percent is obtained.
3.3. Wheel track test
Wheel track rutting Test is applied to determine the resistance of asphalt mixtures against permanent deformation at
critical temperatures and under loading similar to what the pavement surface is applied. This test can be done on the
cylindrical kernels taken from the asphalt road as well as asphalt slab made in the laboratory. Wheel track rutting test with
the reciprocating motion of loaded wheel on asphalt specimens determine the potential of asphalt pavement rutting. This is
done by measuring the rut depth created in the sample along the moving of apparatus’s wheel at specified intervals by rut-
gauge. Desired rut-gauges should have sufficient accuracy at least 0.1 mm. The maximum rut depth measured by wheel track
apparatus is 20 mm and then the machine turns off. This test is carried out according to the Standard instructions of Great
Britain BS 598: Part 110 (British Standards Institution, 1996).
Acceptable segment dimensions for the construction of asphalt samples are 300 mm 300 mm which is its most
common state. Also, acceptable thickness for specimens made in the laboratory is 75 mm 50 mm. While, for samples which
are made of existing pavement, these dimensions are 35 mm 110 mm. In this study, specimens with dimensions
300 mm 300 mm 50 mm were used. Given the dimensions of the mold in which slab is built
(300 mm 300 mm 50 mm) and also the specific gravity of asphalt specimens (G
mb
) which is calculated in the Marshall
test, weight of materials required for the manufacture of asphalt slab is calculated. To perform the test, the sample should be
placed into the wheel track machine and after performing the necessary setting through existing software on the computer
attached to the machine, start the test. According to the Standard, the load applied to the specimen through apparatus’s
wheel should be 710 N but this amount can be changed. Temperatures at which these tests can be measured are in the range
of 30–70 8C. Schematic view of the manner of implementing wheel track test and wheel track test apparatus is shown In
Fig. 4. In this study, in order to evaluate the effect of temperature and stress on the asphalt mixtures and assess the impact of
the utilization of rubber powder on improving the behavior of these mixtures in different loading conditions, wheel track test
is conducted at temperatures of 40, 50 and 60 8C and applied load is equivalent to 100 and 200 kPa.
4. Wheel track test results
Wheel track test results are shown in Tables 4 and 5. As can be seen from the results, rut depth measured in samples
modified with rubber powder is to a large extent lower than the amount of rut depth in the conventional asphalt specimens.
This theorem is the proof of the claim of the high power of crumb rubber in reducing permanent deformation of asphalt
mixtures.
[(Fig._4)TD$FIG]
Fig. 4. Schematic view of the wheel track test and wheel track test apparatus.
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73
Figs. 5–7 show the results of rut-depth for different temperatures and stresses applied. In these figures, C represents
unmodified and R crumb rubber modified and 200/100 kPa applied pressure. As was expected, increasing the stress level, rut
depth in asphalt mixtures is increased but the important matter is the manner of increasing as in rubber asphalt mixtures
due to the high impact of rubber powder on improving the behavior of asphalt mixtures, the rate of increase is less than
control mixtures. The important point is occurred at 50 8C, so that rut depth in rubber asphalt mixture in applied stress of
200 kPa is less than rut depth in control asphalt mixture in applied stress of 100 kPa. A very important point is this that
rutting phenomenon mostly occurs at high temperatures; therefore, using waste rubber powder, the amount of permanent
deformation in the asphalt mixtures could be greatly reduced. This effect can be due to the improving the behavior of
bitumen modified with rubber powder than conventional asphalt. Adding crumb rubbers to the bitumen cause increase its
stiffness and viscosity. Improving both of these features in bitumen can lead to increase the stiffness of asphalt mixtures and
the rate of rut depth in them is considerably reduced. Figs. 5–7 also illustrate the effect of temperature on the behavior of
asphalt mixes. The results show that with increasing temperature, the values of rut depth either in modified specimens or in
Table 4
The results of wheel track tests on the rubberized asphalt samples.
Temperature (8C) Applied pressure (kPa) Rut depth (mm)
Number of wheel passes
250 500 750
40 100 0.116 0.133 0.160
200 0.263 0.296 0.365
50 100 0.357 0.414 0.541
200 0.516 0.631 0.774
60 100 0.530 0.730 1.010
200 0.880 1.150 1.410
Table 5
The results of wheel track tests on the conventional asphalt samples.
Temperature (8C) Applied pressure (kPa) Rut depth (mm)
Number of wheel passes
250 500 750
40 100 0.146 0.180 0.219
200 0.346 0.487 0.514
50 100 0.725 0.905 1.240
200 0.834 0.940 1.512
60 100 1.240 1.550 1.620
200 1.450 2.020 2.430
[(Fig._5)TD$FIG]
Fig. 5. Results of wheel track test for asphalt specimens at 40 8C.
G.H. Shafabakhsh et al. / Case Studies in Construction Materials 1 (2014) 69–76
74
conventional is increased, but the rut depth growth with increasing temperature in the rubberized asphalt samples is less.
This phenomenon occurs due to the reducing thermal sensitivity of asphalt mixtures affected by the addition of crumb
rubber. Softening point of bitumen is greatly improved by the addition of crumb rubber that this factor can lead to the
reduction of thermal sensitivity of modified bitumen and thus asphalt rubber mixtures.
The important point in Fig. 6 is that rut-depth of control specimens in the stress of 100 kPa is greater than mastic asphalt
mixtures even in the stress of 200 kPa. This result suggests that by replacing 10% of the bitumen used in asphalt mixes with
waste rubber powder in addition to reducing production costs of asphalt mixtures, rubberized asphalt mixtures at high
temperatures and stresses will have better performance compared to the control specimens.
The results at 50 8C show that for conventional asphalt, persistent strain rate is rapidly increasing while specimens
modified with rubber powder have normal slope and thus the rut-depth is less than conventional asphalt mixtures.
Fig. 8 illustrates the effect of waste rubber powder on rut depth of samples in different stresses 100 and 200 kPa and
temperatures 40, 50 and 60 8C at 750 passes of wheel. In these figures, C represents unmodified and R crumb rubber modified
and 200/100 kPa applied pressure. Results show that temperature has large effect on rut depth of conventional and modified
samples. For example, in conventional sample and by applying stress 200 kPa, rut depth in 50 8C is approximately 3 times
[(Fig._6)TD$FIG]
Fig. 6. Results of wheel track test for asphalt specimens at 50 8C.
[(Fig._7)TD$FIG]
Fig. 7. Results of wheel track test for asphalt specimens at 60 8C.
G.H. Shafabakhsh et al. / Case Studies in Construction Materials 1 (2014) 69–76
75
larger in comparison with 40 8C. This shows high sensitivity of asphalt samples to temperature. In conclusion, by adding
waste rubber powder to specimens, rut depth of asphalt samples is reduced significantly.
5. Conclusion
In this research, the effect of waste rubber powder on the improvement of asphalt mixtures performance and reduce rut
depth caused by wheels passing by wheel track test has been examined. This experiment is carried out at two different
temperatures and stresses to conduct examinations in different situations. The main results of this research are:
Waste rubber powder has high impact on reducing rut depth of asphalt mixtures at different temperatures and stresses.
Asphalt mixtures containing 10% waste rubber powder has better performance at higher temperatures. Rubber powder
with reducing thermal sensitivity of asphalt mixtures can increase its resistance against permanent deformation.
The results show that by replacing 10% of the bitumen used in asphalt mixes with waste rubber powder in addition to
reducing production costs of asphalt mixtures, rubberized asphalt mixtures at high temperatures and stresses will have
better performance compared to the control specimens.
The results at 50 8C show that for conventional asphalt, persistent strain rate is rapidly increasing while specimens
modified with rubber powder have normal slope.
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[(Fig._8)TD$FIG]
Fig. 8. Rut depth of asphalt samples at different stresses and temperatures at 750 passes.
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