Emirates Journal for Engineering Research, 15 (1), 51-57 (2010)
(Regular Paper)
A STUDY ON CBR BEHAVIOR OF WASTE PLASTIC STRIP
REINFORCED SOIL
A.K. Choudhary1, J.N. Jha2* and K.S. Gill3
1
Department of Civil Engineering, National Institute of Technology, Jamshedpur, India,
E-mail: drakchoudharycivil@gmail.com
2
Department of Civil Engineering, Guru Nanak Dev Engineering College, Punjab, India
E-mail: jha@gndec.ac.in
3
Department of Civil Engineering, Guru Nanak Dev Engineering College, Punjab, India
E:mail: kulbirgillkulbir@yahoo.co.in
(Received August 2009 and accepted February 2010)
،ا ﺎ ت
و، اﻷ ﺎن ء ﺪ آ ر ﺎح ﻮ ﺔ
آ ﺮ
أداء ا ﺮق ا ﺮ ﺔ وﻏ ﺮ ا ﺮ ﺔ
ﻮا
ﻮ ﺔ اﻷر ﺔ
ﺮة
ت و ﻮارق
و ﺮ ﺎر ا، وا ﺮ، ﻬﺮ هﺬ اﻷر ﺔ ا ﻜ ﺮ
و ﺪ ﺬ.أداء هﺬ ا ر ﺔ
ﺎﺔو
وا ﺎء
ﻬ ﺔا
اﻷه ﺔ ا ﺮ
ﺈ، و ﺬ ﻚ.ﺔ
اﻷداء
ﺎ ﺔ ا ﻜ ﺎ ﺔ ا ﺪ ﺔ آ ﻮي ﺮ ﺔ
درا ﺔ إ ﻬﺎر إ ﻜﺎ ﺔ ﺮاﺋ ا ﻮ إ
ﺪة ﺎو ت
ﻚ
ﺎ ﺎت ا
ﻮل ﻬﺎ
ا
ﺎ ﺔ اﻜﺎ ﺔ ا ﺪﺔ ا
ﺮاﺋ ا ﻮ إ.ﺮ ﺔ ا ﺮ ﺔ
اﻬﺪ
ﻮ ﻬﺎ
ﻰ ﺮﺔ
أ ﺮ
ﺔ ا ﺎرات آﺎ ﻮر ﺎ ﻮﺿ ا
.ا ﺮ ﺔ
ﻮاﺋ
ﺔ ﻜ
آﺎ
أ ﻬﺮت ﺎﺋ ا ﺎرات آﺎ ﻮر ﺎ.ﺔ
ﺮاﺋ ا ﻮ ﺄ ﻮال وأ ﺎد
ﺔ
ﻮاﺋ
ﻜ
و ﻜ.ﻮة و ﻮك ا ﺮ ﺔ إ ﻰ ﺪ آ ﺮ
ا ﺮ ﺔ ﻜ ﺎت ﺎ ﺔ
أن إدراج ﺎ ﺎت ﺮاﺋ ا ﻮ إ
ﺎء ا ﺪود وا ﺮق
ا ﺪام هﺬ ا ﺔ ا ﺮ ﺔ ﺎﺋﺪ ﻬﺎ
The performance of paved and unpaved roads is often poor after every monsoon and, in most
cases; these pavements show cracking, potholes, wheel path rutting and serious differential
settlement at various locations. Therefore, it is of utmost importance considering the design and
construction methodology to maintain and improve the performance of such pavements. Attempts
have been made in the study to demonstrate the potential of reclaimed high density polyethylene
strips (HDPE) as soil reinforcement for improving engineering performance of subgrade soil.
HDPE strips obtained from waste plastic were mixed randomly with the soil. A series of
California Bearing Ratio (CBR) tests were carried out on randomly reinforced soil by varying
percentage of HDPE strips with different lengths and proportions. Results of CBR tests
demonstrated that inclusion of waste HDPE strips in soil with appropriate amounts improved
strength and deformation behavior of subgrade soils substantially. The proposed technique can be
used to advantage in embankment/road construction.
Keywords: High Density Polyethylene, Pavement, Reinforcement, California Bearing Ratio.
1. INTRODUCTION
Nowadays, plastic containers usually made of high
density polyethylene (HDPE) are being increasingly
used for storage and marketing of various liquids.
Most of these containers are specifically made for spot
use, having short life span and are being discarded
immediately after use. Though, at many places HDPE
is being collected for recycling or reuse, however; the
secondary markets for reclaimed HDPE have not
developed as recycling program[1]. Therefore, the
quantity of HDPE that is being currently reused or
recycled is only a fraction of the total volume
produced every year[2]. According to the data
published by Environmental Protection Agency (US
Environmental Agency 1992), the solid waste
produced in the US in 1988 included 14.4 million tons
of plastic occupying 20% by volume of available
landfill spaces. Approximately 2.2 million tons of
HDPE are produced annually and only 7% are
currently being recycled. The estimated municipal
solid waste production in India up to the year 2000
was of the order of 39 million tons per year. This
figure is most likely to touch 56 million tons per year
by the end of 2010[3]. The typical percentage of
plastics in the municipal solid waste produced in India
is around 1%[4]. One of the main reasons cited for
2005 Mumbai city flood was choking of drains by
51
A.K.Choudhary et. al.
plastic wastes discarded/thrown indiscriminately by
the users. The best way to handle such wastes is to
utilize them for engineering applications. Some of the
civil engineering uses of recycled HDPE include fence
line posts of guard rail posts for highways[5] and light
weight reinforcing inclusions in concrete[6]. Soil
reinforcement technique can be a significant secondary
market for waste HDPE to improve the strength of
subgrade soils. This technique has been found
effective and reliable method to improve the strength
of subgrade soils[7]. A treated or stronger subgrade
soils shall require relatively thinner section of a
flexible pavement as compared to that of an untreated
and weaker sub-grade resulting in significant cost
advantage. Over the years, the use of geotextiles and
other polymeric reinforcements such as geogrids has
increased drastically in geotechnical engineering.
However; in certain cases; especially for low cost
embankment/road construction, their cost becomes a
prohibitive factor for their wide spread use. In
comparison with systematically reinforced soil,
randomly distributed fiber reinforced soils exhibit
some advantages. Preparation of randomly distributed
fiber-reinforced soils mimics soil stabilization by
admixture. Discrete fibers are simply added and mixed
with soils, much like cement, lime or other additives.
Randomly distributed fibers offer strength isotropy
and limit potential planes of weakness that can
develop parallel to oriented reinforcement. In recent
years applications of nontraditional materials either
natural or waste products have been tried in road
construction in many developing countries[8].
Traditional inert materials are replaced with materials,
which would otherwise be ecologically burdensome.
Towards this end; randomly reinforcing the soil by
using high density polyethylene strips obtained from
waste plastic containers may provide an easy and
sometimes an economical means to improve the
engineering performance of subgrade soils. On the
other hand, they are otherwise considered unsuitable
and if found effective can also reduce the problem of
disposal of this non biodegradable waste causing
environmental hazards. Prediction of pavement
performance becomes difficult if unconventional
materials are used as a part of pavement structure[9].
Therefore, in the present investigation an attempt has
been made to demonstrate the potential of reclaimed
HDPE strips as soil reinforcement for improving the
subgrade soils. The paper describes a series of CBR
tests carried out with varying percentage of HDPE
strips mixed uniformly with the soil .The results
obtained from the tests were presented and discussed.
It is also important to note that the choice of the
California Bearing Ratio (CBR) test apparatus as the
testing platform brings some inherent problems into
the experimental study. Small size of the CBR test
apparatus limits the size and amount of the fiber
inclusion. End effects in such a small sample size can
be more pronounced than that of the other large scale
model tests. When materials having maximum particle
52
sizes are to be tested, the test method provides for
modifying the gradation of the material. The modified
material may have significantly different strength
properties than the original material. Despite these
limitations, a large experience base has been
developed using the CBR test and some satisfactory
design methods are in use based on the test results.
2. BACKGROUND
Soil fiber composites have been found effective in
improving the CBR value as reported in the
literature[10-14]. These studies indicated that stressstrain-strength properties of randomly distributed fiber
reinforced soil are a function of fiber content and
aspect ratio. Considerable improvement in frictional
resistance of fine grained soil was also reported by
roughened HDPE[15]. In addition, use of polyethylene
fiber (plastic waste) improved peak and ultimate
strength of both cemented and un-cemented soil[16].
Strength and load bearing capacity of soil was
enhanced considerably when the soil is stabilized
mechanically with short thin plastic strips of different
length and content[4, 7]. The feasibility of reinforcing
soil with strips of reclaimed high density polyethylene
has also been investigated to a limited extent[17-19]. It
has been also reported that the presence of a small
fraction of HDPE fiber can increase the fracture
energy of the soil. Although, a few studies on the
subject of engineering behavior of HDPE reinforced
soil as described earlier are available in literature but a
detailed study pertaining to its use in real life problems
is still quite meager. In view of the above limited
studies, present study has been taken up with special
reference to its feasibility for application in
embankment/road construction.
3. EXPERIMENTAL WORK
A brief description of the materials and methods [as
per IS-2720-Part-XVI (1987)] used in this
investigation is given in the following paragraphs:
Materials
Sand: Locally available sand collected from Kharkai
River, Jamshedpur, Jharkhand (India) was used in this
study having specific gravity of 2.62, mean particle
diameter (D50) of 0.55 mm, coefficient of uniformity
(Cu) of 2.40 and coefficient of curvature (Cc) of 1.67.
The grain size distribution of the soil is shown in
Figure 1. The sand was classified as ‘SP’ as per the
Unified Classification System. The maximum and
minimum dry densities of sand as determined from the
relative density test were 16.5kN/m3 and 14.6kN/m3
respectively.
HDPE: The waste plastic strips used in the present
study were purchased from a rag picker, who collects
recycling material from the waste dump around
Jamshedpur, Jharkhand (India) at a price of INR 100
per kg (approximately $2per kg). They are made of
Emirates Journal for Engineering Research, Vol. 15, No.1, 2010
A study on CBR behavior of waste plastic strip reinforced soil
Emirates Journal for Engineering Research, Vol. 15, No.1, 2010
Percent finer (%)
80
70
60
50
40
30
20
10
0
0.1
1
10
Grain size (mm)
Figure 1 Grain size distribution of sand
4. RESULTS AND DISCUSSION
The most important engineering parameter to evaluate
a sub-grade or sub-base materials for pavement design
is the CBR value. Deformation of the soil specimen
being predominantly shear in nature, the CBR value
can be regarded as an indirect measure of strength[21].
The load-penetration curves obtained from the CBR
tests for un-reinforced and randomly reinforced system
with strip contents ranged from 0.025% to 4.0% for
different aspect ratios (AR=1 to 3) are shown in Figure
2 through Figure 4. It can be observed from these
figures that mixing of randomly distributed HDPE
strips in sand increased the piston load at a given
penetration considerably. The figures further reveals
that the initial slope of the load-penetration curve is
significantly improved due to the incorporation of
strips in sand. It is also evident from these figures that
inclusion of waste plastic increased the CBR value
significantly.
Strip content
12
AR = 1
0%
0.25%
0.50%
1%
2%
4%
10
8
6
4
2
10
12.5
8.5
5
7.5
4
3
2
2.5
1
1.5
0
0
The experimental study involved performing a series
of laboratory CBR tests on unreinforced and randomly
oriented HDPE strip reinforced sand specimen.
Specimens were prepared by compacting sand in dry
state in three equal layers to a dry density of
16.2kN/m3 (corresponding to a relative density of Dr=
85%) in a steel CBR mould of 150 mm diameter and
175 mm high. HDPE strip reinforced sand layers were
prepared at the same dry density as that of
unreinforced sand. Required amount of strips as well
as sand for each layer were first weighed and then the
strips were randomly mixed with dry sand and due
care was taken so as to have a homogeneous mix. The
mix was then transferred to the mould and a surcharge
base plate 148 mm in diameter and weighing 25 N was
placed over it in order to avoid segregation of strips
during vibration. The sand was compacted in the
mould by vibrating it on a vibration table for 2
minutes. Similar procedure was adopted for
compacting other two layers in the mould. The tests
were performed as per procedures described in IS2720-PartXVI-1987[20]. A surcharge plate of 2.44kPa
was placed on the specimen prior to testing. The loads
were carefully recorded as a function of penetration up
to a total penetration of 12.5 mm. Finally, loadpenetration curves were drawn for each case and
corrections were applied using the standard procedure.
From the load-penetration curves so obtained
california bearing ratio values as well as secant
modulus (defined as the ratio of load in kPa at a
penetration of 5.0 mm to the penetration of 0.005m)
were determined. Since for all the cases considered in
the present investigation, the CBR value at 5.0 mm
penetration was observed higher than that of 2.5 mm
penetration even on repetition. Therefore CBR values
reported in the present investigation are those of 5.0
mm penetration.
90
0.5
Test Procedure
100
Load (kN)
HDPE having a width of 12mm and a thickness of
0.40mm. These were cut into lengths of 12mm [Aspect
Ratio (AR) =1], 24mm (AR=2) and 36mm (AR=3). It
is important to ensure that mould diameter remains at
least 4 times the maximum strip length, which will
ensure that there is sufficient room for the strips to
deform freely and independent of mould confinement.
The waste plastic strips to be added to the soil were
considered a part of the solid fraction in the void solid
matrix of the soil. The content of the strip is defined
herein as the ratio of weight of strips to the weight of
dry sand. The tests were conducted at various strip
contents of 0.0%, 0.25%, 0.50%, 1.0%, 2.0% and
4.0%. In the absence of standards for testing strips, the
standard used for wide width tensile strength test
(ASTM D 4885) for geosynthetics were used. The
tensile strength of 100mm long waste plastic strip was
determined at a deformation rate of 10mm/min in a
computer controlled House field machine. The average
ultimate tensile strength of this strip was 0.36kN and
percent elongation at failure was 23%.
Penetration (mm)
Figure 2 Load penetration curve for varying strip
content having AR= 1
Increase in the CBR value due to the presence of strip
content has been expressed by a dimensionless term
California bearing ratio index (CBRI) and has been
defined as the ratio of the CBR value of reinforced soil
(CBRr) to the CBR value of unreinforced soil (CBRu).
53
A.K.Choudhary et. al.
CBRI = CBRr/CBRu
(1)
AR = 2
Strip content
12
55
Strip content
50
45
CBR (%)
The CBR value of the unreinforced sand
corresponding to 2.5mm and 5.0mm penetration were
found to be 14.01 % and 18.88 % respectively as
shown in Figure 2, which were increased to 24.23%
and 29.20% respectively when sand was reinforced
with 0.25% waste plastic strips having aspect ratio
equal to 1. Further increase in strip content from
0.25% to 1% without changing the aspect ratio again
enhanced the CBR value to 29.78% and 32.89%
respectively corresponding to 2.5mm and 5.0 mm
penetration. The trend remained unchanged even when
the percentage of waste plastic strip content is further
increased from 1% to 2% or 4% in the soil. The
maximum value of CBR at 5 mm penetration is
41.65% when 4% waste plastic strip content having
aspect ratio equal to 1 was mixed with the soil. Similar
results have been observed for other values of aspect
ratio as shown in Figure 3 and Figure 4.
noticeably attributed to strip inclusion in the soil and
strip length. Figure 5 reveals that the CBR value for 4
% strip content having 12 mm strip length is 41.65%
but this value increased to 48.85% when strip length
was increased from 12mm to 24 mm without changing
the strip content. When the strip length was further
increased to 36 mm again without changing the strip
content, the value of CBR increased further from
48.85% to 54.89%. Increase in CBRI value of a
reinforced system was found approximately 2.9 times
as high as that of an unreinforced system as shown in
Figure 6. A similar trend was also observed for other
strip content.
0%
40
0.25%
35
0.50%
30
1%
25
2%
4%
20
0%
0.25%
0.50%
1%
2%
4%
Load (kN)
10
8
6
15
10
20
30
40
Strip length (mm)
Figure 5 Variation of California Bearing Ratio (CBR)
with strip length at different strip content
4
2
10
12.5
8.5
5
7.5
4
3
2
2.5
1
1.5
0
0.5
0
Penetration (mm)
Figure 3 Load penetration curve for varying strip
content having AR = 2
Strip content
20
18
0%
0.25%
16
14
0.50%
1%
2%
12
10
2.9
2.7
4%
8
2.5
CBRI
Load (kN)
AR = 3
6
4
2
AR=1
2.3
AR=2
2.1
AR=3
1.9
12.5
10
8.5
7.5
5
4
3
2.5
2
1
1.5
0
0.5
0
Penetration (mm)
Figure 4 Load penetration curve for varying strip
content having AR = 3
The variation of CBR for strip reinforced sand with
different strip lengths at various strip contents is
shown in Figure 5. On the other hand, Figure 6 shows
the variation of CBRI with different strip contents at
various aspect ratios. The increase in CBRI is
54
Increase in strength of soil due to the inclusion of
waste plastic can also be expressed in terms of piston
load. Increase in piston load due to the presence of
waste plastic strip has
been expressed by a
dimensionless term known as piston load ratio (PLR),
which is defined as ratio of maximum piston load
at12mm penetration for HDPE strip reinforced sand
(Lr) to the maximum piston load at same penetration
for unreinforced sand(Lu).
PLR = Lr/Lu
(2)
1.7
1.5
0
1
2
3
4
Strip Content (%)
Figure 6 Variation of California Bearing Ratio Index
(CBRI) with strip content at different aspect ratio
Figure 7 shows the relationship between PLR and
strip content at different aspect ratios. It is seen that
the piston load increases with increase in strip content
Emirates Journal for Engineering Research, Vol. 15, No.1, 2010
A study on CBR behavior of waste plastic strip reinforced soil
and strip length. It can be also observed that the piston
load of reinforced system having aspect ratio 3 is
almost three times as high as that of an un-reinforced
system.
The variation in secant modulus of strip reinforced
sand with strip length at various strip content is shown
in Figure 8. As expected the increase in secant
modulus is noticeably attributed to strip inclusion in
soil and strip length. For example, the secant modulus
of the un-reinforced sand of 395.2MPa can be
increased to 611.2 MPa when 0.25% of waste plastic
strip having strip length of 12mm is added. When the
strip content was increased to 2% without changing
the strip length, the secant modulus became
712.9MPa. Similar trend was observed when strip
content was further increased to 4%. Figure 8 further
reveals that secant modulus also increases with the
increase in strip length even when there is no change
in the strip content. For example, when the strip length
was increased from 24 mm to 36 mm without change
in strip content, the secant modulus at 4 % strip
content was increased from 1022.5 mPa to 1149.0
Mpa. A similar trend was also observed for other strip
contents.
3.5
3
2.5
PLR
AR = 1
AR = 2
AR = 3
2
1.5
1
0.25
0.5
1
2
4
Strip content (%)
strips showed elongation, thinning and clear
impression of sand particles. Apparently, as the soil
sheared during penetration, strip fixed in the sand by
friction elongated as the soil deformed. Generally the
CBR value at 2.5mm penetration is higher. However
in the present study, the CBR value of HDPE strip
reinforced sand at 5.0mm penetration are found to be
higher than those at 2.5mm penetration. This indicates
that at higher deformation the HDPE strip
reinforcement is more effective in improving the
strength of sand by increasing the resistance to
penetration. The resisting action of the strips can be
visualized by Figure 9 (a) and (b). In situation (a) the
plunger pushes down particle ‘C’ to occupy position in
between particle ‘A’ and ‘B’. The strip resists the
downward movement of particle ‘C’ until slippage
between soil and strip occurs resulting into a
development of situation (b). Thus, it is the interaction
between soil and strips which causes the resistance to
penetration of the plunger resulting into higher CBR
values. Kumar et al. (1999) based on their laboratory
investigations conducted on silty sand and pond ash
specimens reinforced with randomly distributed
polyester fibers, concluded that fibers increased the
peak compressive strength, CBR value, peak friction
angle and ductility of the specimen. Authors further
reported that the optimum fiber content for both silty
sand and pond ash was approximately 0.3-0.4 % of dry
unit weight[12]. Santoni et al. (2001) based on their
laboratory unconfined compression tests conducted on
sand specimen reinforced with randomly oriented
discrete fibers, concluded that the fibers inclusions
significantly improved the unconfined compression
strength of sand specimens and the maximum benefit
was achieved at a fiber content rate between 0.6% and
1% of dry weight[22]. The disagreement among the
reported results is attributed to the difference in the
material properties and testing conditions.
Figure 7 Variation of Piston Load Ratio (PLR) with strip
content at different aspect ratio
Strip
1250
Strip content
Secant modulus,
(Mpa)
1150
1050
0%
950
0.25%
850
0.50%
750
1%
650
2%
4%
550
450
(a)
(b)
Figure 9 Schematic diagram showing position of strip
(a) before and (b) after slippage between soil and strip
Thickness of Base Course:
350
10
20
30
40
Strip length (mm)
Figure 8 Variation of secant modulus with strip length
at different strip content
After the completion of each test, specimens were
dissected and the strips were examined. Many of the
Emirates Journal for Engineering Research, Vol. 15, No.1, 2010
For the cost benefit analysis of the reinforcement
(plastic waste as strip) function, it is necessary to
evaluate the pavement thickness reduction that is
achievable by use of HDPE strips. As per
recommendation of IRC-37-1984, the sub-base
material should have minimum CBR of 20% for
cumulative traffic up to 2 million standard axle (msa)
and 30% for traffic of greater than 2msa. Since the
55
A.K.Choudhary et. al.
inclusion of 4% HDPE strips with aspect ratio 3
increased the value of CBR from 18.88% to 54.89%,
so it can be safely concluded that the sub-base made of
sand mixed with randomly oriented HDPE strips can
be used for the traffic greater than 2msa particularly
for situations where good quality conventional sub
base materials (gravel, moorum, kankar, brick mortar,
crushed stone etc) are not available locally.
5.
6.
5. CONCLUSIONS
The feasibility of reinforcing soil with strips of
reclaimed HDPE was investigated in this study. Strips
of HDPE were mixed with local sand and tested to
determine CBR values and secant modulus. The tests
show that reinforcing sand with waste HDPE strips
enhances its resistance to deformation and its strength.
Based on the results, the following conclusions can be
drawn:
7.
8.
1. The addition of reclaimed HDPE strips, a waste
material, to local sand increases the CBR value and
secant modulus.
9.
2. The maximum improvement in CBR and secant
modulus is obtained when the strip content is
4% and the aspect ratio 3.
10.
3. The reinforcement benefit increases with an
increase in waste plastic strip content and length.
4. The maximum CBR value of a reinforced system is
approximately 3 times that of a unreinforced
system.
5. Base course thickness can be significantly reduced
if HDPE strip reinforced sand is used as sub-grade
material. This suggests that the strips of
appropriate size cut from reclaimed HDPE may
prove beneficial as soil reinforcement in highway
sub-base if mixed with locally available granular
soils in appropriate quantity.
The results of this study suggest that strip cut from
reclaimed HDPE may prove useful as soil
reinforcement in highway application. However
further study is needed: (i) to optimize the size and
shape of strips and (ii) to assess the durability and
aging of the strip. Large scale test is also needed to
determine the boundary effects influence on test
results.
11.
12.
13.
14.
15.
16.
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