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Performance of Stone Matrix Asphalt and Asphaltic
Concrete Using Modifiers
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M. S. Ranadive, Ph.D., M.ASCE 1; H. P. Hadole 2; and S. V. Padamwar 3
Abstract: Waste plastic is harmful and affects the environmental cycle. This paper proposes the use of fiber extracted from refrigerator door
panels (FERD) and waste plastic in bituminous mixes for road construction. The effect of modification of bituminous mixes like stone matrix
asphalt (SMA) and asphalt concrete (AC) with FERD and processed waste plastic in granular form was studied. The FERD was used to
modify the SMA and AC, whereas waste plastic was used to modify AC. Different mixes of SMA and AC were prepared with and without
filler material. Furthermore, the study was done with varying lengths of fibers (2, 4, 6, and 8 mm), which were added to the SMA and
AC mixtures. Asphalt concrete mixtures with 0, 4, 6, 8, 10, and 12% waste plastic by weight of bitumen were prepared. The effect
of the preceding on drain down, Marshall stability, and indirect tensile strength was promising. DOI: 10.1061/(ASCE)MT.19435533.0002107. © 2017 American Society of Civil Engineers.
Author keywords: Stone matrix asphalt (SMA); Asphalt concrete (AC); Drain down; Marshall stability; Indirect tensile strength (ITS).
Introduction
In developing countries like India, it is necessary to strengthen the
infrastructure, which helps to fulfill the needs of an increasing population. Highway traffic in India is increasing at a fast rate. To
balance this increasing traffic rate, it is necessary to develop a good
road network. Due to the variation in, e.g., temperature, soil type,
and material used for road construction, the quality of roads can
vary greatly, which further leads to major distress in flexible pavements. Rutting is one of the main problems every road engineer
faces and needs to be resolved. Scientists and engineers have developed various techniques to overcome these problems, using data
pertaining to organizations such as the Central Pollution Control
Board. As per the report from the Central Pollution Control Board
(2015), in India nearly 12 million tons of plastic products are consumed every year, of which approximately 60% is converted into
waste. This report also discusses an action plan for plastic waste
management; its main action points; its setting, collection, and segregation at source; and its transportation to a place of disposal.
Stone matrix asphalt (SMA) is one of the bituminous mixes that
cause a minimum rutting problem, and is used in the construction
of road as a wearing course. Stone matrix asphalt was developed
in Germany in the mid-1960s and has been used successfully
by many countries in the world because it is highly rut-resistant.
Stone matrix asphalt is based on the concept of stone-to-stone
contact. In 1990, a European asphalt study brought the same
German-mix technology known as Splittmatrixasphalt, the English
translation of which is stone mastic asphalt. According to Prowell
1
Associate Professor, Dept. of Civil Engineering, College of Engineering, Pune, Maharashtra 411005, India. E-mail: msr.civil@coep.ac.in
2
M.Tech. Student, Dept. of Civil Engineering, College of Engineering,
Pune, Maharashtra 411005, India (corresponding author). E-mail:
hadole50@gmail.com
3
M.Tech. Student, Dept. of Civil Engineering, College of Engineering,
Pune, Maharashtra 411005, India. E-mail: santoshpadamwar214@gmail.com
Note. This manuscript was submitted on October 30, 2015; approved
on June 9, 2017; published online on October 25, 2017. Discussion period
open until March 25, 2018; separate discussions must be submitted for
individual papers. This paper is part of the Journal of Materials in Civil
Engineering, © ASCE, ISSN 0899-1561.
© ASCE
et al. (2002), the American version of this is stone matrix asphalt.
On the other hand, asphalt concrete (AC)–bituminous concrete
(BC) is commonly used as a wearing coat. Engineers are trying hard
to increase the performance of AC in different ways. As a result,
different types of fibers and polymers are added to the AC mix, which
gives better performance as compared to conventional mixtures. This
paper will focus on the investigation from the strength point of view
of bituminous material after the addition of fiber, filler, and processed
waste plastic. Here fiber extracted from refrigerator door panels
(FERD) and cement as filler material was used. Chowdary and
Raghuram (2013) explained that in artificial fiber, FERD gives better
results against rutting and deformation in flexible pavements. In this
work, an attempt is made to optimize the length of FERD with the
help of results obtained after performing various tests, like Marshall
stability, drain down, stripping value, and indirect tensile strength
(ITS). Because fiber extracted from waste door panels of refrigerators
can be used in an efficient manner, this will create awareness in the
market regarding waste management.
Scherocman (1991) followed the gradation of SMA according
to the 30–20–10 rule, whereby 30% should have pass through
a 4.75-mm sieve, 20% through a 2.36-mm sieve, and 10% through
a 0.075-mm sieve. According to Brown and Manglorkar (1993),
SMA is a gap-graded aggregate asphalt hot mix that maximizes
the asphalt content and course fraction, which provides stable
stone-on-stone contact that is held together by a rich mix of asphalt
content, filler, and stabilizing additives. Brown and Mallick (1994)
explained that as the percentage of aggregate passing through a
4.75-mm sieve decreases, the voids in the mineral aggregate
(VMAs) remain nearly constant and begin to increase when the
former reaches 30–40%. According to Brown et al. (1997a, b)
and Brown and Haddock (1997), the percentage of aggregate
passed through a 4.75-mm sieve must be lower than approximately
30% to ensure the formation of stone-on-stone contact. Marshall
hammer, Superpave gyratory compactor (SGC), dry rodded test,
vibrating table, and vibrating hammer are the tests discussed by
Brown et al. (1997a) to determine the stone-to-stone contact of
SMA. The gradation of SMA is considerably different from
dense-graded asphalt mixes, which is reported in Ministry of Road
Transport and Highways (MoRTH 2012). According to Chowdary
and Raghuram (2013), it is necessary to look again into the usage of
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fly ash in SMA mixes because it is observed that minimum drain
down is achieved when fly ash is used as a filler in combination with
fibers such as coconut, fiber extracted from refrigerator door panels,
and modified binders PMB-70 and CRMB-60. It was concluded that
FERD exhibited lower drain down than SMA mixes using other fibers, and added that FERD and jute fibers resulted in a higher stability value and showed improved properties of rut-resistance. Abtahi
et al. (2010) discussed the behavior and properties of various fibers
and their behavior on AC. This work pointed out that due to the use
of fibers in AC, there was a significant improvement in dynamic
modulus, moisture susceptibility, creep compliance, rutting resistance, and freeze-thaw resistance. Bahia and Anderson (1995) studied the viscoelastic nature of binders, and found that the complex
modulus and phase angles of the binders need to be measured at temperatures and loading rates that resemble different climatic and loading conditions. Shukla and Jain (1984) described that the effect of
wax in bitumen can be reduced by adding ethylene vinyl acetate
(EVA) and aromatic resin in the waxy bitumen. The addition of
4% EVA or 8% resin in waxy bitumen effectively reduces susceptibility and bleeding at high temperatures, or brittleness at low temperatures, of the mixes. According to Rajasekaran et al. (2013), waste
plastic from both the domestic and industrial sectors can be used in
the production of asphalt mix. Waste plastic used mainly for packaging is made up of polyethylene, polypropylene, and polystyrene.
Various food packaging plastics are used to coat hot aggregates at
160°C, and this becomes the raw material for construction of pavement. Khan et al. (2009) reported significant improvement in the
properties of the Marshall stability value, retained stability, and indirect tensile strength. In addition, control over rutting was observed
with the modification of AC using waste plastic in shredded form
(particle size diameter 2–3 mm). Vasudevan et al. (2007) and Yildrim
(2007) suggested the use of various polymers such as rubber, styrenebutadiene-styrene, styrene-butadiene-rubber, and elvaloy (ethylene
glycidyl acrylate) in AC.
Ravishankar et al. (2013) studied the effect of waste plastics
from garbage in shredded form in semidense bituminous concrete
(SDBC), and came to the conclusion that the optimum bituminous
content (OBC) for conventional mixes was found to be 4.93 and
5.1% for Grade 1 and Grade 2, respectively. Also, the optimum
plastic content (OPC) was observed as 10 and 12% for Grade 1
and Grade 2, respectively. The work done by Patekar and Ranadive
(2014) was referred to as guidelines for preparing the statistical
analysis, and the conclusions are reported in this paper.
Based on the preceding literature review, it is observed that the
areas related to SMA and AC modified with plastic and cellulose fiber
are usually focused and studied separately. From the report of the
Website Material on Plastic Waste Management (2013), it is seen that
an abundant quantity of waste products, such as plastic and refrigerator door panels, that are difficult to dispose of are available in India
and even worldwide. Pavements are one of the largest areas for the
consumption of such material, for its improvement in strength. This
paper aims to analyze the properties of SMA and AC modified with
FERD, AC modified mixture with use of granular plastic, and the
optimization of length of FERD for SMA and AC mixtures, and compare the results of SMA and AC fiber modification, as well as the
optimization of the percentage of plastic for the AC mixture with
a corresponding discussion on the behavior of fiber in SMA and AC.
Materials
It is always better to get all required aggregates from the same
quarry site. However, getting the aggregates from the same source
does not necessarily guarantee that properties of aggregates are the
same over time. In different seasons aggregates were collected and
tested for specific gravity, aggregate impact value, and soundness.
In addition, the Los Angeles abrasion test and shape test were performed, and it was observed that there was a deviation of 0.5% in
the results, so seasonal deviation in results is negligible. However,
the test results are not reported here. Hence, it was verified and
ensured that different batches in different seasons from the same
quarry site did not make much difference in their basic properties.
Aggregates were obtained from a local quarry located nearby the
city of Pune, Maharashtra, India, and the same source was used
throughout the research. Physical properties of the aggregate used
are shown in Table 1. In this work, cement was used as filler. As per
the guidelines provided by IRC: SP: 79 (IRC 2008), the mineral
filler should consist of finely divided mineral matter, and fly ash
should not be used as filler. The addition of filler reduces the drain
down of the asphalt binder, which is due to an increase in surface
area. A mineral filler of 5% by weight of aggregate was used, which
consisted of 3% stone dust and 2% cement. Bitumen of penetration
grade 60/70, i.e., VG30, was used as a binder. The physical properties of bitumen obtained from laboratory tests are given in Table 1.
Fibers used in this work were extracted from outdated and nonserviceable refrigerator door panels, which served as stabilizers; hence
these were waste fibers. The lengths of fibers used were 2, 4, 6, and
8 mm. The FERD making up the plastic matrix was epoxy, a thermosetting plastic, and most often polyethylene terephthalate (PET). The
study of properties of polyester was done by Yu and Sun (2010) and
Table 1. Physical Properties of Aggregate and Bitumen
Value (%)
Test sample
Aggregate
Property
Standard
Required as per IRC: SP: 79
Observed values
Impact value
Los Angeles abrasion value
IS 2386 (P-4) (IS 2007c)
IS 2386 (P-4) (IS 2007c)
ASTM C131 (ASTM 2006b)
IS 2386 (P-3) (IS 2007b)
ASTM C127-88 (ASTM 1988)
IS 2386 (P-1) (IS 2007a)
≤24
≤25
7.05
15.37
≤2
1.4
≤30
29.7
IS 1203 (IS 1978b)
ASTM D5 (ASTM 2013)
IS 1205 (IS 1978c)
ASTM D36 (ASTM 1995)
IS 1208 (IS 1978d)
ASTM D113 (ASTM 2007)
IS 1202 (IS 1978a)
ASTM D70 (ASTM 2009)
60–70
67
40–55
48
>75
78
Water absorption
Combined flakiness and elongation index
Bitumen
Penetration (100 g, 5 s at 25°C)
Softening point, ring and ball apparatus (°C)
Ductility at 27°C and 5 cm=min pull (cm)
Specific gravity at 27°C
© ASCE
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is referred to here. The physical and chemical properties of PET were
taken directly from the technical design guide provided by Molded
Fiber Glass Companies (2015) and were not investigated separately.
As per Brown et al. (1997a), it was suggested to use 0.3% of fiber by
weight of total mix of aggregates because aggregates begin to force
apart as the fiber content exceeds this percentage, affecting various
properties of SMA. As per IRC: SP: 79, the dosage rate for fiber
suggested was 0.3% minimum by weight of total mix of aggregates
because it gives draindown test results within permissible limits for
the design mix of SMA, as per ASTM D6390 (ASTM 2005). These
are the main reasons for fixing the dosage rate at 0.3% by weight of
total mix of aggregate so that an investigation could be undertaken to
optimize the length of fibers.
Processed granular plastic from plastic waste was used in this
investigation. The granular plastic was 3–5 mm size, so that the
process of mixing with aggregates with ease was possible, and there
were no emissions at the time of mixing waste plastics with
aggregates.
2006a). The MSN is representative of the strength of the bituminous mixture. The bituminous mixture design was performed to
determine the OBC of the mixtures. As per the previous discussion,
with reference to Brown and Mallick (1994) and and Brown et al.
(1994) the SMA mixture was prepared with 50 blows. The mixing
and compaction temperatures were 160 and 150°C, respectively.
Gradation of Aggregates
Indirect Tensile Strength Test
The gradation for mix design of SMA and AC mix is as per guidelines,
provided by MoRTH (2012), IRC 29 (IRC 1988), AASHTO PP 41-02
(AASHTO 2004), and AASHTO MP 8-05 (AASHTO 2005).
In this test, a uniform tensile stress was developed perpendicular to
the direction of applied load and along the same vertical plane,
causing the specimen to fail by splitting. This test is also otherwise
known as the splitting test. The test was conducted using a Marshall
apparatus, with a deformation rate of 51 mm=min. A unidirectional
compressive load was applied, and corresponding failure load was
recorded, as per guidelines given in ASTM D6931 (ASTM 2012).
Methodology
The mix design procedure for SMA, as proposed in National Asphalt Technology Report by Brown and Cooley (1999) and by IRC:
SP: 79, was followed. The compaction process of SMA mixture
played a vital role in achieving proper density of the sample. According to the study by Brown and Mallick (1994), compaction
should be performed by a gyratory testing machine. The study
further concluded that air voids produced by gyratory compaction
and with the Marshall stability test with 50 blows are the same.
In the AC mixture, plastic in granular form was used. Initially,
aggregates were heated at approximately 170°C, followed by bitumen and granular plastic at approximately 170°C each. Then bitumen and plastic were mixed thoroughly and added to aggregates.
For each bitumen content, three samples of the Marshall stability test and ITS were prepared and tested. The mean values are
reported in Tables 2 and 3.
Experimental Investigation
Various tests like the draindown test, Marshall stability test, boiling
test, and indirect tensile strength were performed and brief descriptions for these are given below.
Boiling Test
The test was carried out as per ASTM D36 (ASTM 1995). A 250-g
sample of clean, oven-dried aggregate passed through a 20-mm
sieve and retained on a 12.5-mm sieve was heated to 160°C,
and 14 g of bitumen, heated separately to 150°C, was mixed
with the aggregates. The mixture was allowed to cool down to
80–100°C, and then was added to boiling water. The content
was boiled for 10 min and results were recorded for its stripping
value and are discussed subsequently.
Results and Discussion
The preceding test results are reported in Tables 2 and 3, while
graphical presentation of the properties of AC are presented in
Figs. 2–13. Test results for the SMA mixture are reported in Table 2.
Graphs were drawn but are not reported here.
Draindown Test Results
Fig. 1 shows the results of the draindown test for the different mixtures of SMA, and shows draindown as a function of the filler and
length of fiber. It is observed that the mix without filler shows a
higher draindown percentage. A draindown reduction is observed
with an increase in surface area due to the use of cement as a filler,
resulting in higher bitumen content. The draindown is less than
0.3% when the filler and fibers are used as stabilizers. As the length
of fiber increases, the draindown percentage decreases, but for
study purposes every sample of SMA was tested for MSN and
for indirect tensile strength to ascertain the strength of the mix.
For AC samples, this test was not conducted because the percentage
of fine aggregates was higher.
Schellenberg Draindown Test
The test developed by the Schellenberg Institute in Germany was
adopted for drain down. Using this test, the draindown percentage
of binder was discovered, as per the procedure outlined in ASTM
D6390 (ASTM 2005).
Marshall Stability Test
Bituminous samples were prepared for the Marshall stability number (MSN), as per guidelines provided in ASTM D6926 (ASTM
2010), and testing was done as per ASTM D6927 (ASTM
© ASCE
Marshall Test Results
The observed values of MSN, flow value, and volumetric properties, like percentage air voids, voids in mineral aggregate, and voids
filled with bitumen, for the different bituminous mixtures are given
in Tables 2 and 3. The three minimum values in a set were observed, and the average of the same is reported in these tables.
The results of the MSN of AC mixes modified with fibers are
shown in Fig. 2. From the results, it can be clearly observed that
the MSN of AC mixes is also a function of filler material and fiber
length and percentage of bitumen in the mix. One can observe that
04017250-3
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Table 2. Test Results for SMA and AC Modified with Fibers and Statistical Analysis
Engineering and
statistical parameters
Without
filler and
no fiber
Cement
as filler
and no fiber
Cement as filler
and 2-mm
fiber length
Cement as filler
and 4-mm
fiber length
Cement as filler
and 6-mm
fiber length
Cement as filler
and 8-mm
fiber length
For SMA mix
Optimum binder content (%)
Stability (kN)
Mean
Standard deviation
UCL
LCL
Drain down at OBC (%)
Mean
Standard deviation
UCL
LCL
Flow values
Mean
Standard deviation
UCL
LCL
VMA (%)
Mean
Standard deviation
UCL
LCL
Air voids filled by bitumen (%)
Mean
Standard deviation
UCL
LCL
Air voids (%)
ITS (kPa)
7.1
8.9
8.58
0.94
11.38
5.77
1.1
1.05
0.15
1.5
0.6
4.2
3.66
0.59
5.43
1.89
22.37
20.54
1.84
26.08
15
81.39
78.96
4.30
91.86
66.05
4
492
6.5
12.2
11.08
1.12
14.46
7.69
0.4
0.38
0.03
0.48
0.28
2.6
2.62
0.34
3.66
1.57
19.96
20
1.27
23.82
16.19
76.71
77.90
4.37
91.03
64.77
4
510
6.5
12.8
11.64
1.16
15.12
8.15
0.12
0.12
0.02
0.1
0.05
2.8
2.94
0.49
4.43
1.46
19.5
19.68
1.36
23.77
15.62
78.94
79.92
4.63
93.81
66.01
4
515
6.3
14.1
12.36
1.39
16.53
8.18
0.09
0.09
0.01
0.14
0.03
2.2
2.32
0.48
3.76
0.88
19.12
19.91
1.02
22.97
16.84
80.78
78.05
4.94
92.87
63.23
4
527
6
15.6
14.24
1.05
17.39
11.08
0.07
0.074
0.0054
0.09
0.05
2.1
2.3
0.32
3.24
1.35
18.28
19.53
1.54
24.14
14.92
77.91
79.43
3.71
90.58
68.28
4
603
6.5
14.8
13.12
1.26
16.92
9.31
0.034
0.047
0.011
0.08
0.01
2.4
2.4
0.52
3.97
0.83
19.7
19.45
1.53
24.04
14.86
79.32
78.09
4.98
93.06
63.12
4
477
For AC mix
Optimum binder content (%)
Stability
Mean
Standard deviation
UCL
LCL
Flow values
Mean
Standard deviation
UCL
LCL
VMA (%)
Mean
Standard deviation
UCL
LCL
Air voids filled by bitumen (%)
Mean
Standard deviation
UCL
LCL
Air voids (%)
ITS (kPa)
5.5
13.2
11.86
1.54
16.50
7.21
4
4.16
0.3
5.05
3.27
18.02
17.47
0.93
20.22
14.59
68.67
77.60
6.78
98
57
5.64
419
5.5
13.5
12.8
1.33
16.17
8.18
3.4
3.94
0.29
4.8
3.08
18.83
18.84
1.23
22.54
15.14
69.26
75.026
5.85
92.60
57.40
5.78
447
6
14.8
13.8
0.85
16.39
11.28
2.8
3.7
0.32
4.58
2.66
19.4
19.32
1.23
23
15.61
71.61
72.11
6.65
92.18
52.23
5.5
477
6
14.2
13.84
0.54
16.73
0.99
2.3
2.6
0.62
4.73
0.99
18.98
18.89
1.22
22.58
15.20
73.10
73.81
6.77
94.14
53.49
5.1
496
6
15.1
13.48
0.79
16.62
22.82
3.16
2.7
0.59
4.47
0.92
19.01
18.9
1.38
22.95
14.67
73.14
74.23
5.96
92.14
56.33
5.1
501
6
14.4
14.20
0.64
15.40
11.55
2.6
2.4
0.48
30.86
26.06
18.85
18.71
1.036
21.87
15.66
73.55
74
6.53
93.60
54.40
3.87
477
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Bituminous
mix test sample
Note: LCL = lower control limit; UCL = upper control limit.
Table 3. Test Results for AC Modified with Waste Plastic
Engineering parameters of AC mix 0% waste plastic 4% waste plastic 6% waste plastic 8% waste plastic 10% waste plastic 12% waste plastic
Optimum binder content (%)
Stability (kN)
Flow values
Air voids (%)
VMA (%)
Air voids filled by bitumen (%)
ITS (kPa)
© ASCE
5.5
13.2
2.9
5.64
18.07
68.75
410
5.5
14
2.6
5.24
17.62
70.25
503
6
14.8
2.9
4.48
17.84
74.84
634
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5.5
16.8
2.4
4.85
17.22
71.79
587
5.5
15.4
2.8
4.45
16.84
73.55
603
5.5
12.2
3
4.06
16.45
75.29
477
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Fig. 1. Draindown percentage for SMA
Fig. 4. Flow value for AC modified with fiber
Fig. 2. Marshall stability for AC modified with fiber
Fig. 5. Flow value for AC modified with waste plastic
Fig. 3. Marshall stability for AC modified with waste plastic
Fig. 6. Percentage air voids for AC modified with fiber
the MSN of the AC mix is greatest for the sample having filler and
6-mm fiber length for 6% bitumen content by total weight of mix.
Hence, the OBC of cement- and fiber-modified mixtures is higher
than the unmodified mixture. From Fig. 3, it is clearly observed that
the MSN of AC mixes is also a function of the plastic modifier. One
can observe that the MSN for the AC mix modified with waste plastic
is greatest for the sample with a bitumen content of 5.5% by weight
of aggregate and 8% waste plastic by weight of bitumen.
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Fig. 10. Voids filled with bitumen for AC modified with fiber
Fig. 7. Percentage air voids for AC modified with waste plastic
Fig. 8. Voids in mineral aggregate for AC modified with fiber
Fig. 11. Voids filled with bitumen for AC modified with waste plastic
Fig. 9. Voids in mineral aggregate for AC modified with waste plastic
Fig. 12. ITS for AC modified with fiber
Figs. 4 and 5 show that the flow value for AC modified with
fiber and waste plastic is within the permissible limits, i.e., 2–
4 mm (MoRTH 2012) at OBC. Because the length of fiber is longer,
there is a tendency to obstruct the flow of the bituminous mixtures.
Therefore, the flow value decreases, which does not occur in the
case of plastic. This is due to the addition of plastic in granular size.
As per Brown et al. (1997a, b), the air voids should be designed
close to 4% to minimize rutting and spots. For samples of AC,
© ASCE
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Fig. 14. Comparison of stability between SMA and AC
Fig. 13. ITS for AC modified with waste plastic
as per MoRTH (2012), the percentage of air voids should be within
3–6%. Figs. 6 and 7 show the percentage of air voids for different
mixes of AC, with fiber and plastic as the modifiers. For SMA, as
per IRC: SP: 79, VMAs should be a minimum of 17%. The variation of VMAs with a variation in filler and length of fiber is shown
in Figs. 8 and 9. All the SMA and AC mixes under study modified
with fiber and plastic satisfy the minimum requirement of VMAs.
The variation in air voids filled by bitumen (VFB) with filler, type
of fiber, and waste plastic content can be seen in Figs. 10 and 11. It
is expected to fill 65–75% of the air voids with bitumen. Hence the
limit is satisfied. From the preceding discussion, as well as Figs. 6–11,
it is clear that various mixes are within permissible limits.
Fig. 15. Comparison of flow value between SMA and AC
Boiling Test
Stripping values were observed for various bituminous mixes
modified with waste plastic. As per MoRTH, the stripping value
should not be greater than 5%. For the AC mix without plastic,
the stripping value was observed as 4%. However, for AC with
4, 6, 8, and 10% plastic, the stripping observed was 2, 0, 0, and
0%, respectively.
Indirect Tensile Strength Test
The ITS of the bituminous mixture helps assess the resistance to
thermal cracking of given mixtures. In this study, the effect of
the length of fiber on ITS was studied at a temperature of 25°C.
From Figs. 12 and 13, it is clear that for AC mixtures the ITS
is greatest for the sample with filler and 6-mm fiber length, as compared with the samples of different lengths. For the sample with
plastic as a modifier, the ITS increased up to 6% by addition of
waste plastic, and thereafter it decreased.
Comparison between SMA and AC Modified with
Fibers
From Fig. 14, it is clear that the sample with cement as the filler and
6-mm fiber length gives a higher MSN as compared with other
bituminous mixes. From Fig. 15, it can also be observed that
the MSN of the SMA mix is more than that of the AC mix. As
the length of fiber increases, the MSN also increases in the case
© ASCE
Fig. 16. Comparison of VMA between SMA and AC
of SMA mixtures. The flow in the Marshall stability analysis is
the deformation caused during loading. From Fig. 15, it is very
clear that deformation of the SMA mixture is less when compared
with the AC mix. For all SMA mixtures the flow values are within 2
to 4 mm. A comparison of VMAs in Marshall stability analysis for
both SMA and AC mixes is shown in Fig. 16. A comparison of ITS
for both SMA and AC mixes is shown in Fig. 17. The final observations and corresponding conclusion are discussed in the next
section.
04017250-7
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Fig. 17. Comparison of ITS between SMA and AC
Comparison between AC Modified with Plastic
and Fibers, and SMA
The variation in the MSN and flow value for the different bituminous mixtures is observed for 6% bitumen content from Tables 2
and 3. The MSN is the smallest for plastic (although it is more than
the minimum requirement) in comparison to the SMA and AC with
fibers, and is less by 5 and 2%, respectively. The flow value is comparatively greater for the use of plastic as compared with the SMA
and AC fiber-modified mixtures, by 20 and 7%, respectively. This
may be due to the fact that plastic makes bitumen less viscous than
the original mixture, but in the case of the fiber-modified bituminous mixes the bitumen must have been held by fibers.
Conclusions
The following conclusions are drawn based on the results obtained
from the bituminous mixes modified with FERD.
The MSN is mainly affected by the extent of the aggregate proportion. Longer fibers push the aggregate apart in the mixture, resulting in a decrease in the MSN. Furthermore, it was noted that at
the time of compaction of the mixture, the fibers may break due to
the long length. Using short fibers, the VMA increases for an increase in OBC, which results in a loss of MSN, but at an 8-mm fiber
length the VMA increases, which may be due to the same fact.
Hence, fiber should be used up to its optimum length. It is logical
that when the length of fiber increases, the tensile strength will also
increase, but for 8-mm fiber length it decreases, which may be due
to a loss of density. However, a study done by Brown and
Manglorkar (1993) noted that when mineral fibers were used there
was no loss in density. The MSN of the SMA mixes is increased by
75.28%, whereas for the AC mixes it increased by 14.39% as compared with conventional mixes. For both mixes, the optimum dosage of fiber is found to be 0.3% of total weight of mix, with a length
of 6 mm. The flow value is within the limits for SMA and AC
mixes, as per specifications provided by MoRTH and IRC: SP: 79
(i.e., 2–4 mm). The ITS value increased by 22.57 and 19.57% for
the SMA and AC mixes, respectively, at optimum dosage, as compared with conventional to mixes.
As compared with other samples of SMA, the sample prepared
with 6-mm fiber length was compacted properly so that a 4% void
ratio was achieved at the minimum bitumen percentage. For the
SMA, proper compaction was the main criteria to maintain
stone-to-stone contact and the MSN of the sample. As per the study
by Qiu and Lum (2006), in the case of SMA the volume of coarse
© ASCE
aggregate has a significant influence on the percentage of air voids
and VMA achieved.
The following conclusions are drawn based on the results obtained on the bituminous mixes modified with waste plastic: The
maximum MSN was obtained for the mix with 8% waste plastic,
and it increased by 21.73% as compared with conventional mixes.
The flow value was also within the permissible limits. The optimum
bitumen contents for the conventional AC mix and the AC mix with
8% plastic were found to be equal, but the MSN achieved in the
modified mixes was larger. Thus, 8% waste plastic can be used to
enhance the pavement quality compared with the conventional AC
mix. The ITS value increased by 42.97% for the AC mix with 6%
waste plastic, as compared with the ITS of the conventional mix.
The ITS of the bituminous mixes increased with an increase in plastic content of up to 6%, and decreased with a further increase in the
plastic content. The boiling test results showed that the mixes modified with waste plastic were strip-resistant, even when subjected to
the worst moisture condition. The modification of AC will further
help to maximize the use of waste plastics in the construction of
pavements, and will also avoid its disposal by incineration and
landfill. In general, the MSN required, as per MoRTH, is 9 kN.
However, by using waste plastic the MSN achieved is much greater,
which may result in a reduction of the bitumen content, saving the
cost of the work. The average air voids of each mixture type at
different binder contents are shown in Fig. 7. By comparing the
mixtures’ mechanical or physical properties, the air void content
should be within 0.5%, according to the standard, but in this case
the air void variation is bit high, which might affect the comparison
of results, especially the ITS.
The following conclusions are drawn based on the statistical
analysis: The process was found to be more stable for the AC modified with fiber than for the AC modified with both plastic and SMA.
The process was controlled, and results were predictable from the
run chart (not shown here) for AC. For SMA, the results of flow
values bounced about its center in random fashion, which implies
that its process was stable and predictable, but from a stability point
of view the mean level drifting upward implies that the process was
unstable.
Acknowledgments
The authors would like to thank the reviewers for their helpful comments and suggestions on improving this paper.
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