Chapter 1
The Problem and Its Background
1.1
Introduction
Plastic is a non-biodegradable material created from a wide range of organic
polymers. Its unique chemical structure makes it highly resistant to many
processes of degradation. It is durable, easy to produce in large quantities and
can be found almost anywhere. Generally, plastic takes 10 to 1,000 years to
decompose. In 2017, more than 54,200 pieces of plastic waste were recovered
from Manila Bay in total, including some 9,000 from Nestle products, the most
frequently seen brand, according to a tally kept by Greenpeace (France-Presse,
2017, p. 1). In addition, plastic beverage bottles ranked fourth in the top 10 most
common items collected during the 2017 International Coastal Cleanup (ICC)
(Sloan, 2018, p. 1).
With the advent of the “Build, Build, Build” project under the Duterte
administration, the Philippines is expected to experience an infrastructure boom.
The construction industry in the country is projected to grow, but because of
bursting population and decrease in available land, more and more building and
non-building structures must be built on unused land with poor shear strength.
Occasionally, some soil may be found to be expansive and can often be
problematic, because it causes rigorous structural damage. To compensate, it
becomes necessary to employ a suitable method of low capital soil stabilization
using locally made materials to improve the performance of existing soil
(subgrade) and reliability of construction without spending too much money.
Aside from that, converting plastic bottles into soil stabilizers can also help
reduce plastic pollution. Therefore, plastic waste in the form of plastic bottles
must be recycled and used as alternative soil stabilizer, because it is free, widely
available and effective in enhancing the physical properties of subgrade.
1.2
Background of the Study
Plastic pollution is one of the problems that the Philippines is currently facing
today. The presence of huge numbers of plastic waste in the land and bodies of
water proves problematic. Drink bottles are the second most common type of
plastic waste found in the environment. Street flooding, which commonly occurs
in cities during heavy rains, is the result of plastic waste clogging the storm
drains. Plastic waste also negatively impacts the marine life. A study conducted
by Dutch researchers in the North Sea reported that the local seagull population
has ingested so much plastic, that an average of 30 plastic pieces could be found
in one seagull’s stomach (Effects of Plastic on Marine Life, n.d.). However,
despite its detrimental effects on the environment, plastic can still be useful.
Traditionally accepted materials used for soil stabilization, such as cement, are
still prevalent, but they can often be expensive. Plastic, on the other hand, is free
and widely available. If the effectiveness of plastic as good soil stabilizer is
proven, soil stabilization can be accomplished more economically, given the
abundance of plastic bottles in the surroundings, and plastic pollution can be
minimized at the very least.
1.3
Statement of the Problem
The following problems have been identified in this study:
•
Can plastic be used to increase the load-bearing capacity of subgrade?
•
What is the best mix of plastic and soil that will produce the maximum
load-bearing capacity?
•
1.4
How effective is plastic compared to other soil stabilizers?
Objectives of the Study
1.4.1 General Objective
The general objective of this study is to determine if plastic bottles can be
effectively used as substitute to commercial soil stabilizers to reduce the cost of
soil stabilization and help reduce plastic pollution at the same time.
1.4.2 Specific Objectives
The following are the specific objectives of this study:
•
To investigate the effect of plastic on the load-bearing capacity of
subgrade
1.5
•
To formulate an optimal plastic and soil mix
•
To provide an economic solution for soil stabilization
•
To help minimize plastic pollution
Scope and Limitation of the Study
The study will focus on the effect of plastic on the physical properties of soil,
specifically, its load-bearing capacity. The researchers will establish a cause and
effect relationship between varying amounts of plastic, starting from 0% up to
1.25% in 0.25% increments, and the load-bearing capacity of soil, which is
indicated by its California bearing ratio (CBR) value. The researchers will only
use plastic bottles made of polyethylene terephthalate (PET) for soil
reinforcement. They will be collected from various sources, such as waste
containers at school, or bought from junk shops or people who are collecting
plastic bottles for a living. The researchers may also collect spare plastic bottles
at home. More than 30 kg of disturbed sample of dry sandy soil will be collected
from a vacant lot in Valenzuela under sunny weather. More will be collected if it is
not enough.
The following tests will take place at University of the East Caloocan using the
equipment provided by the university:
•
Free Swell Index Test
•
Sieve Analysis
•
Proctor Compaction Test
The CBR test, however, will take place at University of the East Manila.
1.6
Significance of the Study
The primary rationale of the study is to find a more economical method of soil
stabilization by providing data about the feasibleness of plastic as soil stabilizer.
The study is a significant endeavor in promoting the use of improperly disposedof plastic waste in the environment for subgrade improvement in the construction
of roads and other facilities. The result of the study will be especially useful to
construction firms specializing in building and road construction, because it will
encourage them to use plastic as alternative to more popular and costly soil
stabilizers and, hence, reduce construction costs. In addition, the study will help
alleviate plastic pollution in the country by encouraging construction firms to turn
plastic waste in the environment into more useful soil stabilizer for projects. This
will help reduce the amount of plastic waste in the environment.
1.7
Operational Definition of Terms
Free Swell Index. The increase in the volume of soil, without any external
constraints, when submerged in water.
Load-bearing Capacity. The capacity of soil to support the loads applied on the
ground.
Optimum Water Content. The water content at which a maximum dry unit weight
can be achieved after a given compaction effort.
Polyethylene Terephthalate (PET). The most common thermoplastic polymer
resin of the polyester family that is used as fibers for clothing, containers for
liquid and food, thermoforming for manufacturing and in combination with glass
fiber for engineering resins.
Soil Stabilization. A general term for any physical, chemical, biological or
combined method of changing a natural soil to meet an engineering purpose.
Chapter 2
Related Literature and Studies
Introduction
The increasing amount of plastic waste in the environment led the researchers to
explore other local and foreign literature for potential contributions of plastic to civil
engineering. This chapter will include finished literature, both local and foreign, that
investigate the feasibleness of plastic as soil stabilizer to support the study being
conducted by the researchers.
2.1
Local Literature
2.1.1 Utilization of Waste Tire Rubber Chips and Waste Plastic Strips for Soil
Stabilization
Dr. Grace O. Manlapas, Jenith L. Banaldia and Dr. Leovigildo E. Cardenas, in
their research, described the effectiveness of waste materials made of plastic
and tire rubber as agents of soil stabilization and how utilizing them as such
could help alleviate pollution. The study was conducted to determine the
difference between the two materials in terms of effectiveness. Several soil
samples were treated with varying amounts and aspect ratios of plastic and
rubber and underwent a series of California bearing ratio (CBR) tests to
determine the changes in their CBR values. The results indicated that adding
plastic and tire rubber to the soil significantly increased its CBR value, which
meant an improvement in its load-bearing capacity. However, it was found that
plastic performs better than tire rubber as soil stabilizer.
2.2
Foreign Literature
2.2.1 Stabilization of Soil by Using Plastic Wastes
Megnath Neopaney, Ugyen, Kezang Wangchuk and Sherub Tenzin, in their
research, treated several soil samples with plastic waste to enhance their
physical properties and increase their California bearing ratio (CBR) values. The
plastic waste used were plastic shopping bags that were collected from nearby
disposal sites. Strips of 10-mm width and 40-μm thickness were cut using aspect
ratios of 1, 2 and 3 and mixed thoroughly with the soil. The length of the strips
were 10 mm, 20 mm and 30 mm, respectively. The CBR value of soil
corresponding to 2.5-mm and 5-mm penetration and having 0%, 0.25%, 0.50%
and 1% plastic contents were determined by carrying out a series of laboratory
CBR tests. The results indicated that reinforcing the soil with plastic significantly
increased its CBR value as the aspect ratios and plastic contents also increased.
However, the continuous increase of its CBR value would stop at a certain limit,
and beyond that, the CBR value would decrease.
2.2.2 Utilisation of Polyethylene (Plastic) Shopping Bags Waste for Soil Improvement
in Sandy Soils
Kalumba D. and Chebet F. C., in their research, collected shopping bags made
of high-density polyethylene (HDPE) from a local supermarket and utilized them
for plastic reinforcement of embankments and road bases. Several samples of
Klipheuwel and Cape Flats sands having plastic contents of up to 0.3% were
subjected to a series of direct shear tests. Two types of strips (solid and
perforated) with length of 15 mm to 45 mm and width of 6 mm to 18 mm were
used. The diameter of perforations of the perforated strips were varied to
examine the effect of the openings on the strips. Based on the results obtained
from various tests, there had been an improvement in the peak friction angle of
soil after adding solid and perforated strips of varying lengths and concentrations
for both types of sands. The peak friction angle of soil was further enhanced
when perforations were introduced to the strips as compared to the samples with
solid strips. In addition, increasing the diameter of perforations resulted in an
increase in the peak friction angle of soil at an average of 2° for each mm of
perforation diameter. In conclusion, the study strongly supported the possibility of
utilizing plastic materials to increase the shear strength of sandy soil.
2.2.3 Comparative Study of CBR of Soil, Reinforced with Natural Waste Plastic
Material
Rajkumar Nagle, Prof. R. Jain and Prof. A. K. Shinghi, in their research,
described the advantages of using natural waste plastic material as soil
reinforcement to improve its properties because of its low cost, local availability,
biodegradability and eco-friendly nature. Significant enhancement in the soil’s
shear and tensile strengths was observed. In this study, different plastic
materials, which included plastic bottles made up of polyethylene terephthalate
(PET) and plastic sacks and carpets made of polypropylene, were used to treat
three different types of soil, namely black cotton soil, silty clay soil and sandy soil.
Plastic was added to several soil samples at varying concentrations, namely
0.25%, 0.50%, 0.75% and 1% of the total dry weight of each sample. Soaked
California bearing ratio (CBR) tests were then performed on the soil samples in
the laboratory. It was found that as the plastic contents of the soil samples
increased, their maximum dry densities (MDD) also increased, thereby
increasing their CBR values.
2.2.4 Experimental Study on Effect of Waste Plastic Bottle Strips in Soil Improvement
S. Peddaiah, A. Burman and S. Sreedeep, in their research, studied the potential
of plastic to be used as economical alternative to commercial soil stabilizers like
Portland cement and lime for improving the stability of embankments. Plastic
bottles made of polyethylene terephthalate (PET) were used in this study to treat
several samples of silty sand, which would undergo several tests, namely Proctor
compaction test, direct shear test and California bearing ratio (CBR) test, to
determine the effect of plastic on the soil’s maximum dry density (MDD), shear
strength and CBR values using varying aspect ratios and percentages of plastic
bottle strips (0.2%, 0.4%, 0.6% and 0.8%). The results of the Proctor compaction
test indicated that the maximum dry unit weight (MDU) of soil was maximum at
0.4% plastic content and began to decrease beyond that. In addition, based on
the results of the direct shear test, the angle of internal friction and cohesion was
found to increase up to 0.4% plastic content and began to decrease beyond that.
The CBR values also continued to increase up to 0.4% plastic content before
beginning to show signs of decline beyond that. The positive results of the
experimental works suggested that plastic could effectively replace expensive
soil stabilizers like Portland cement and lime.
2.2.5 Stabilization of Black Cotton Soil Using Plastic Waste
P. Harsha Vardhan and Mutluri Yamunna, in their research, described the
increasing cost of commercial agents used for soil stabilization, such as bitumen,
lime and Portland cement, and the need to find good alternatives like bamboo
and plastic, primarily, to reduce the cost of soil stabilization. It was also
mentioned that the disposal of plastic waste was becoming an issue, because of
the rapid accumulation of plastic waste (bottles, shopping bags, etc.) in the
environment, leading to plastic pollution. In this study, the researchers addressed
the problem of plastic pollution at Amravati, the state capital of Andhra Pradesh,
by utilizing plastic waste as soil stabilizing agent. The soil used was black cotton
soil, which was known to be expansive and unsuitable for construction of
structures because of its low load-bearing capacity. Several samples of black
cotton soil were treated with plastic, with concentrations ranging from 0% to
1.5%. A series of California bearing ratio (CBR) tests were then conducted to
determine the best plastic content that will give the highest possible CBR value.
The results indicated that the optimum percentage of plastic was 0.5%. The
addition of plastic in the soil reduced its optimum moisture content (OMC) and
increased its maximum dry density (MDD). In addition, it improved the physical
characteristics of black cotton soil.
I. Problem Analysis
1. More Economical
Soil
Stabilization
2. Plastic Waste
Management
II. Material Resources
Requirements
1. Plastic Bottles
2. Soil
I. Preparation of Materials
1. Gathering of Raw
Materials
(Plastic Bottles, Soil)
II. Testing of Samples
1. Free Swell Index Test
2. Sieve Analysis
3. Proctor Compaction
Test
4. CBR Test
Output
Conceptual Framework
Process
Input
2.3
I. Result of Test of
Raw Materials
1. Free Swell Index
2. Classification of
Soil
3. Optimum Water
Content and
Maximum Dry
Density
4. CBR Value
In problem analysis, the researchers considered many possibilities for
economical soil stabilization. Over the past few years, other researchers had
been conducting studies about soil stabilization using different materials. Steel
strips (Miyata, Y. and Bathurst, R. J., 2012) and natural and synthetic fibers
(Hejazi, S. M., Sheikhzadeh, M., Abtahi, S. M. and Zadhoush, A., 2012) were
successfully used as soil stabilizers. However, these materials were limited and
could only be obtained from caves by extracting ores, which was not very
economic. Because of the increasing amount of plastic waste in the environment,
the researchers considered plastic as potential soil stabilizer. Today, plastic
products all over the world are known to be one of the leading causes of
pollution, but by putting them to good use, plastic pollution can be reduced, and
at the same time, soil stabilization can be more economical.
The process will include gathering the necessary materials and equipment for
experimental works like the free swell index test, sieve analysis, Proctor
compaction test and, finally, the California bearing ratio (CBR) test. The
researchers will then analyze the results of tests of raw materials and draw
conclusions based on them.
Chapter 3
Research Methodology
Introduction
This chapter will include the action plan on how the researchers will accomplish the
study within a particular time frame, procedures for conducting the experiments and
evaluating the results.
3.1
Research Method
The type of research used to conduct this study was quantitative, because
numerical data was the main basis for making generalizations about the effect of
plastic on the load-bearing capacity of soil. Of the four different approaches to
quantitative research, experimental design was used, because it is the most
appropriate design for demonstrating whether one or more factors cause a
change in an outcome. In this case, using experimental design, they would be
able to determine the relationship between plastic and the load-bearing capacity
of soil by manipulating the soil’s plastic content.
3.2
Project Planning and Management
3.2.1 Work Breakdown Structure per Proponent
The study of the viability of plastic as soil stabilizer of subgrade will be divided
into four phases. The first one shall begin in late November. The researchers will
collect more than 30 kg of disturbed sample of dry sandy soil. Plastic bottles
made of polyethylene terephthalate (PET) will also be collected.
The second one shall begin in late December, which will involve performing
experiments that will focus on characterizing the soil, because it is important to
determine the physical properties of soil first before subjecting it to further tests.
These will include the free swell index test, sieve analysis and Proctor
compaction test. It will take about 2-3 weeks to complete.
The third stage shall begin on early February, focusing on investigating the effect
of plastic on soil using the California bearing ratio (CBR) test. The plastic bottles
will be cut into strips of 20-mm length and 4-mm width and placed in a container.
The strips will be mixed with soil in varying percentages: 0%, 0.25%, 0.50%,
0.75%, 1% and 1.25%. All trials will be done in a single day, each with varying
amounts of plastic content.
Lastly, the fourth and final stage will solely focus on analyzing the results that
were obtained from the experiments. The researchers will create visual
representations of data and attempt to establish a plausible cause and effect
relationship between plastic and soil. They will determine if plastic influences the
CBR value of soil enough to consider it as good soil stabilizer. Conclusions will
be drawn, and facts will be checked before finalization to ensure reliability.
3.3
Testing and Evaluation Procedures
More than 30 kg of disturbed sample of dry sandy soil will be gathered and
equally divided into two groups: control and experimental. Soil samples from the
control group will have no plastic content and will be used for conducting tests
involving soil characterization. On the other hand, soil samples from the
experimental group will be used for conducting California bearing ratio (CBR)
tests to determine the CBR value of soil for varying plastic contents.
Starting in the second phase, the researchers will conduct soil characterization
tests on soil samples from the control group to obtain information about the
physical properties of the soil. These tests will include the free swell index test,
sieve analysis and Proctor compaction test.
In the third phase, the researchers will gather all plastic bottles and cut them into
strips of 20-mm length and 4-mm width. A single California bearing ratio (CBR)
test will be performed on a soil sample from the control group to determine the
CBR value of soil without plastic content. Next, CBR tests will be carried out on
soil samples from the experimental group. In each test, plastic bottle strips will be
mixed with the soil in different percentages, namely 0.25%, 0.50%, 0.75%, 1%
and 1.25%. The effect of plastic on the load-bearing capacity of soil will then be
analyzed after a series of tests, and conclusions will be drawn based on the
obtained data.
For evaluating the results, the researchers will arrange the data using the
following table:
Trial Number
Percentage of
CBR Value at
CBR Value at
Plastic Bottle Strips
2.5-mm
5-mm
Penetration
Penetration
1
2
3
4
5
6
They will then assess if adding an increasing percentage of plastic bottle strips to
the soil increases its load-bearing capacity, which is specified by its CBR values
at 2.5-mm and 5-mm penetration. If applicable, they will also determine the
percentage of plastic bottle strips that will give the highest possible strength gain
to the soil. This will allow the researchers to formulate an optimal plastic and soil
mix and to determine if the addition of more plastic bottle strips to the soil beyond
its percentage of maximum gain will show a decreasing pattern in its CBR values
at 2.5-mm and 5-mm penetration.
To give a general idea of the change in the soil’s load-bearing capacity based on
its plastic content, the researchers will also plot the data like the following graph:
Behavior of Sandy Soil at Varying Plastic Contents
1.2
1
Load (kN)
0.8
0.6
0.4
0.2
0
0
0.2
0.4
0.6
0.8
1
1.2
Penetration (mm)
The graph will show the different CBR values of soil at 0.5 mm, 1.0 mm, 1.5 mm,
2.0 mm, 2.5 mm, 4.0 mm, 5.0 mm, 7.5 mm, 10.0 mm and 12.5-mm penetration.
Chapter 4
Presentation, Analysis and Interpretation of Data
Introduction
The results of the different tests conducted by the researchers in support of their study,
namely the free swell index test, sieve analysis, Proctor compaction test and California
bearing ratio (CBR) test, will be given primary focus in this chapter. The data are
tabulated and arranged accordingly.
4.1
Project Results
Trial Number
Volume in
Volume in Water
Free Swell Index
14 mL
7.69%
Kerosene
1
13 mL
Table 1. Free swell index test.
The free swell index is a measurement of the change in the volume of soil
soaked in distilled water with respect to the volume of soil soaked in kerosene.
Sieve Size
Mass of Soil
% of Soil
Cumulative
% Finer (%
Retained
Retained
% of Soil
Passing)
Retained
4.75 mm
17.3 g
17.49%
17.49%
82.51%
2.00 mm
24.9 g
25.18%
42.67%
57.33%
1.18 mm
15.7 g
15.87%
58.54%
41.46%
425 μm
27.4 g
27.70%
86.24%
13.76%
250 μm
6.3 g
6.37%
92.61%
7.39%
75 μm
7g
7.08%
99.69%
0.31%
Pan
0.3 g
0.30%
99.99%
0.01%
98.9 g
Table 2. Sieve analysis.
In this table we gather data of Mass of soil retained, Percent of soil Retained,
Cumulative percent of soil Retained and the Percent Finer
To get the result we will used some formulas.
The results are presented in a graph of percent passing versus the sieve size.
1
2
3
4
5
Volume of
2211.7
2211.7
2211.7
2211.7
2211.7
Mold
cm3
cm3
cm3
cm3
cm3
Weight of
5955 g
5955 g
5955 g
5955g
5955 g
Weight of
7768.594
7901.296
7967.647
7945.53 g
7901.296 g
Mold and
g
g
g
Weight of
1813.594
1946.296
2012.647
1990.53 g
1946.296 g
Compacted
g
g
g
Mold
Compacted
Soil
Soil
Bulk
0.82
𝑔
𝑐𝑚3
0.88
𝑔
𝑐𝑚3
0.91
𝑔
𝑐𝑚3
0.90
𝑔
𝑐𝑚3
0.88
𝑔
𝑐𝑚3
Density
Water
4.84%
6.71%
8.80%
11.63%
14.05%
Content
Dry Density
0.78
𝑔
𝑐𝑚3
0.82
𝑔
𝑐𝑚3
0.84
𝑔
𝑐𝑚3
0.81
𝑔
𝑐𝑚3
0.77
𝑔
𝑐𝑚3
Table 3. Proctor compaction test.
The soil compacted into the mold to a certain amount layer each receiving the
number of blows. In compaction test the soil was compacted to determine the
Optimal moisture content and to achieve the maximum dry density.
Penetration (mm)
0.5
Proving Ring
Reading
Load (kN)
1
0.252
1.0
2
0.505
1.5
2.6
0.656
2.0
3
0.757
4.0
3.7
0.934
5.0
4.5
1.136
7.5
5
1.262
10.0
7.5
1.894
12.5
8
2.020
Table 4. Trial 1 of CBR test (0% plastic content).
Penetration (mm)
Proving Ring
Reading
Load (kN)
0.5
4.5
1.136
1.0
6
1.515
1.5
6.5
1.641
2.0
6.75
1.704
4.0
6
1.515
5.0
5.5
1.389
7.5
6
1.515
10.0
9.3
2.348
12.5
11.7
2.954
Table 5. Trial 2 of CBR test (0.25% plastic content).
Penetration (mm)
Proving Ring
Reading
Load (kN)
0.5
2.5
0.631
1.0
4.3
1.086
1.5
5.7
1.439
2.0
6.5
1.641
4.0
8.1
2.045
5.0
8.7
2.196
7.5
10.7
2.701
10.0
13
3.282
12.5
15
3.787
Table 6. Trial 3 of CBR test (0.50% plastic content).
Penetration (mm)
Proving Ring
Reading
Load (kN)
0.5
3
0.757
1.0
6.1
1.540
1.5
8.2
2.070
2.0
10
2.525
4.0
14.3
3.610
5.0
16
4.040
7.5
14.9
3.762
10.0
22.4
5.655
12.5
34.2
8.634
Table 7. Trial 4 of CBR test (0.75% plastic content).
Penetration (mm)
Proving Ring
Reading
Load (kN)
0.5
2.8
0.707
1.0
4.9
1.237
1.5
6
1.515
2.0
6.5
1.641
4.0
7.4
1.868
5.0
8
2.020
7.5
10
2.525
10.0
11.9
3.004
12.5
13.6
3.434
Table 8. Trial 5 of CBR test (1% plastic content).
Penetration (mm)
Proving Ring
Reading
Load (kN)
0.5
1.5
0.379
1.0
3.8
0.959
1.5
5.5
1.389
2.0
6.2
1.565
4.0
6.2
1.565
5.0
6.1
1.540
7.5
6.9
1.742
10.0
8.5
2.146
12.5
10.1
2.550
Table 9. Trial 6 of CBR test (1.25% plastic content).
100
GRAVEL
90
100
#4 Coarse 100
#10
SAND
Medium
SAND
100
#40
100
#200
Fine
SAND
SILT/CLAY
82.51
% Passing
80
70
60
50
57.33
41.46
40
30
20
13.75
7.38
10
0.30
0
10.00
1.00
0.10
Particle Diameter (mm)
Figure 1. Particle size distribution curve of sandy soil.
0.01
Proctor Compaction Test
Dry Density (kN/m3)
8.4
8.2
8
7.8
7.6
7.4
7.2
4.84%
6.71%
8.80%
11.63%
14.05%
Water Content (%)
Dry Density
Figure 2. OMC and MDD of the soil.
Trial Number
Percentage of
CBR Value at
CBR Value at
Plastic Bottle Strips
2.5-mm
5-mm
Penetration
Penetration
1
0
6.050
5.637
2
0.25
12.516
6.892
3
0.50
13.158
10.897
4
0.75
21.119
20.047
5
1
12.826
10.023
6
1.25
11.821
7.642
Table 10. CBR values at 2.5-mm and 5-mm penetration.
Behavior of Sandy Soil at Varying Plastic Contents
10
9
8
7
Load (kN)
6
5
4
3
2
1
0
0.5
1
0%
Plastic
1.5
0.25%
Plastic
2
4
5
Penetration (mm)
0.50%
Plastic
0.75%
Plastic
7.5
1%
Plastic
10
12.5
1.25%
Plastic
Figure 3. Loads (kN) at different penetration and plastic content.
CBR Values at 2.5-mm and 5-mm Penetration
25
CBR Value (%)
20
15
10
5
0
0
0.25
0.5
0.75
1
1.25
Percentage of Plastic Strips (%)
CBR Value at 2.5-mm Penetration
CBR Value at 5-mm Penetration
Figure 4. CBR values at 2.5-mm and 5-mm penetration.
As you can see in this graph in trial 4 having a percentage of 0.75% of plastics
strips increased it’s load up to 8-9 KN (load) at the peak penetration of 12.5. Unlike on the other sample 3-4 KN (load) at the peak penetration of 12.5.
Chapter 5
Summary of Findings, Conclusions and Recommendations
Introduction
This chapter mainly entails the researchers’ findings based on the tests that were
conducted in controlled environments and their conclusions with respect to the
objectives stated in the first chapter. Graphs, which were created using the data from
the tests, will be analyzed thoroughly to reach the best possible conclusion. In addition,
they will also recommend small adjustments to the study’s methodology, if applicable, to
yield more accurate results in the most optimal condition possible.
5.1
Summary
The result obtained from the free swell index test has shown that the free swell
index of soil is 7.69%, which indicates that it has low degree of expansion. On
the other hand, the results obtained from sieve analysis have shown that the soil
used is poorly graded sand, containing 82.20% sand, 17.49% gravel and 0.31%
silt. The soil was also found to have an optimum moisture content (OMC) of 9%
and maximum dry density (MDD) of 0.84
𝑔
𝑐𝑚3
.
In addition, the results obtained from a series of California bearing ratio (CBR)
tests have shown that the CBR value of soil kept increasing but only up to a
certain point. When the plastic content of soil reached 1%, the CBR value of soil
showed decline up to 1.25% for the 2.5-mm and 5-mm penetration.
5.2
Findings
The free swell index of soil was found to be 7.69%. It was also found to have a
low degree of expansion, because its free swell index was far below 35%. The
researchers classified the soil as poorly graded sand or SP according to the
Unified Soil Classification System (USCS). It consisted of 82.2% sand, 17.49%
gravel and 0.31% silt and clay. The optimum moisture content (OMC) of soil was
9%, while its maximum dry density (MDD) was 8.24
𝑘𝑁
𝑚3
. The maximum California
bearing ratio (CBR) value of soil was attained at 0.75% plastic content at 2.5-mm
and 5-mm penetration. The CBR values were 21.119% and 20.047%,
respectively. On the other hand, the minimum CBR value was at 6.050% and
5.637% at 2.5-mm and 5-mm penetration, respectively.
5.3
Conclusions
It can be concluded from this study that plastic bottle strips made of polyethylene
terephthalate (PET) can be effectively used as reinforcement for improving the
load-bearing capacity of existing soil (subgrade), because the addition of plastic
into the soil considerably increases its California bearing ratio (CBR) value at 2.5mm and 5-mm penetration. The optimal plastic and soil mix is achieved at 0.75%
plastic content, which gives the maximum CBR value. However, adding more
plastic to the soil caused its CBR value to decrease. In addition, using plastic as
soil stabilizer is more economical than cement because of the latter’s cost. It will
also help in reducing plastic waste in the environment, because they will be
turned into soil stabilizer.
5.4
Recommendations
It is recommended that the researchers conduct at least 14 trials of California
bearing ratio (CBR) test with plastic contents ranging from 0% to 1.3% in 0.1%
increments (0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%,
1.1%, 1.2% and 1.3%) to obtain a more accurate result about the effect of plastic
on the load-bearing capacity of soil and the optimal plastic content that will give
the highest CBR value to the soil. Through this, the researchers will be able to
know how the load-bearing capacity of soil will behave in more tightly packed
concentrations of plastic and determine a potentially better optimal plastic
content as opposed to just considering 6 trials of plastic content used in this
study.