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CHAPTER 1
INTRODUCTION
1.1 Background
Failure in building structure is a critical matter that need to
be taken seriously. There are
many factors affecting the strength of the structure making it
essential for regular
maintenance. Besides error in building design, when the
structure in a building is
suppressed by load which exceeding its limit capacity, the
failure of structural may
occurred as well. Besides, the change in existing practice of
the building do also resulting
in new imposed loading that may exceed in the initial design. As
these failures may
produce cracks, they may also have been exposed to harsh
conditions which can weaken
the structure and causing it to deteriorate. Hence,
strengthening of structural will be
necessary in order to prevent these problems from getting
worse.
Researchers had developed few techniques and solutions to
overcome these
structural failures. At first, an external reinforcement using
epoxy bonded steel plates
have been introduced. This method consists of using steel plates
bonded to the tension
face of the subjected reinforced concrete beams using epoxy.
This steel plates were
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effectively strengthen the beams, however other materials are
sought to replace steel after
they discovered the disadvantages of using steel. It is found
that the steel is prone to
corrosion due to moisture content in air and the installation
process is rather difficult to
execute due to factors such as its heavyweight and abundantly
precautions.
Then, an alternative method using fibre reinforced composite
plate had been
developed to replace steel plate in external reinforcement. This
method is similar to the
steel plate method which involving epoxy resin bonding on the
surface of reinforced
concrete structural. The inherent properties of composite
materials in the plate include
high specific tensile strength, good fatigue, corrosion
resistance and simple installation.
Theoretically, these fibre composite plate do have a higher
ultimate strength and lower
density. Furthermore, the fibre reinforced composite plate takes
a lower cost and it does
not corrode. This bring more advantages in becoming external
reinforcement.
Years ago, the composite materials used in development of
composite plates are
man-made materials consisting two distinctive component
materials and the resulting
material being different from the component materials. Hence,
this material is generally
described as a rational combination of two or more materials to
yield a product that is
more efficient from its components. The components are fibre
phase which provides
strength, and the other one is fibre binder in matrix phase. The
matrix used in composite
materials like epoxy acts as a binder and bond the fibres in the
intended position which
provides the composite material its structural integrity by
giving shear transfer capability.
This leads to the development of glass and carbon fibre
reinforced plate, CFRP and
GFRP. Later in recent, biocomposite materials combining natural
or plant fibre with
polymer matrices is introduced to replace the man-made fibre due
to several factors
focusing on environment and sustainability, as biofibre plates
are eco-friendly.
In this research study, kenaf fibre is chosen as the materials
in developing biofibre
reinforced composite plate as an external reinforcement as they
are likely environmental
friendly and economical. It is clearly that this biocomposite
can help to reduce the
increasing cost of using petroleum-based material. Kenaf fibre
comes with high flexural
strength and tensile strength, making it as one of the choices
in extruded, moulded and
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non-woven products. The fibre has replace the glass fibres in
utilized as reinforcement
material for polymeric composites. Plant fibres are certainly
have more advantages
compared to glass and carbon fibres as they are cost effective,
have lower density,
renewable, recyclable, abrasive and biodegradable. This method
is the best solution to the
main problem as it promotes the sustainability development and
green development.
Recently, people are alert on the materials chosen for
structural upgrading has
additional function in efficiency and sustainability. The
materials should have fulfil these
criteria such as environmental friendly, sustainable,
recyclable, reusable, renewable and
beneficial to local economy by generating income along low in
cost. Waste disposal has
been a major issue in modern cities as more lands are required
in land filling. This
problem is due to the expansion world population and needs of
raw materials in satisfy
demands on world market is growing well. So, by practicing
sustainable development
along with green building, these problems stand a chance to be
reduced to minimum.
Figure 1.1 shows the general flow of the background on the
introduction of fibre
composite materials to the structural industry.
FIGURE 1.1: General flow of the background of natural fibre
composite plate
Strengthening of RC beam
Steel Plate
Carbon Fibre Composite Plate
Natural Fibre Composite Plate
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1.2 Statement of the Problem
Cracked and weakened reinforced concrete beams will disturb the
structure's stability and
worsen it. However, reconstructing or rebuilding the reinforced
concrete beam is not one
of the top choice because it will definitely increase the cost
and time. One of the best
solution would be rehabilitation of the cracked and weakened
beams, by means a suitable
repair is adequate enough to solve this matter. So, the
rehabilitation can be done by using
external reinforcement such as reinforced composite plate on the
beam.
Carbon fibre reinforced plate (CFRP) and glass fibre reinforced
plate (GFRP) are
able to replace steel plate effectively due to its high specific
tensile strength, lower
density, corrosion resistance and easier installation. In spite
of that, they have their own
disadvantages. When it comes to costing, these materials are
significantly expensive
compare to other fibres. Furthermore, this man-made materials
are not biodegradable,
brittle and hazardous as well.
Health hazardous due to manufacturing carbon fibre is one of the
major problems
in nowadays. The disadvantages of carbon are its high price and
brittle property. When it
compare to resins, fibres are distinctively inert. The main
hazard of carbon is the
mechanical irritation, either of the skin or the respiration.
The very small particle of
carbon can easily inhaled and thus respiratory problems or
worse. But the size of kenaf
fibre is relatively bigger than carbon, too large to be inhale.
Mechanical irritation
occurred when itching after direct contact with glass and
carbon. Most fibres have a
sizing that can cause chemical irritation.
The carbon is hazardous when it is subjected to a fire after a
crash. It produces
dangerous and hazardous compounds such as acids, cyanides and
any other threat
compounds that bond with the fibres, which are carried by the
smoke and flames into the
air. This poses a serious threat to anyone involving the fire
extinguishment or any other
people nearby. The fibres will infiltrate into the skin and
dissolve into the bloodstream.
Thus us compounded by the fact that the body does not recognize
carbon as a foreign
elements and will not attempt to repels it. This proves that the
carbon particle is
hazardous to human being and may bring harm to human health once
it is not handled in
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the right way. Moreover, these materials doubtlessly need extra
precaution when being
handled.
Thus, to overcome this issue, biofibres was introduced to the
industry. Biofibres
material do offer many advantages topping the problems
encountered by previous
solution. These biofibres are renewable, recyclable,
biodegradable, lightweight, non-
hazardous, higher flexural and tensile strength, relatively low
density and non-toxic.
Further investigation on the development of natural fibre has
been conducted by many
researchers in the world. Various green fibres are being used
including jute, hemp, coir,
sisal and also kenaf.
1.3 Purpose of the Study
External reinforcing of reinforced concrete structures has
slowly gained the popularity in
the industry because it is much easier and time effective
compared to reconstructing the
whole deteriorating structure. In the beginning, steel plate are
been used but some other
problems might occurred due to its natural properties.
The usage of steel plates might not be as efficient as expected,
leading to the main
purpose of the study, which is to assess the effectiveness of
kenaf fibre reinforced
composite plate as external reinforcement instead of steel
plates in strengthening the
structural beams.
1.4 Objectives of the Study
The main objectives of the research study are as follow:
1. To investigate the physical properties of kenaf fibre
reinforced composite plate.
2. To investigate the mechanical property of uncoated and coated
kenaf fibre
reinforced composite plates at different weathering
conditions.
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1.5 Research Question
The research questions of this research study are:
1. What is the factors affecting the strength of kenaf fibre
reinforced composite
plates?
2. How will kenaf fibre reinforced composite plates will be
affected its strength by
the presence of water content?
3. How effective the epoxy resin in resisting water molecule
from diffusing into
kenaf fibre reinforced composite plates?
4. What difference can be made by coated and uncoated kenaf
fibre reinforced
composite plate?
5. Does long exposure to water content surface can affected the
strength of kenaf
fibre reinforced composite plate?
1.6 Scope of Research
The scope of studies is determined in order to accomplish the
objective of the research
study. Many studies have been performed to investigate on the
structural properties of
natural fibre composite plates. However, the research study will
focus on kenaf fibre only.
The collected kenaf fibres are raw materials which were
purchased from LKTN
(Lembaga Kenaf dan Tembakau Malaysia).
On the other hand, the material chosen as bonding matrix phase
would be epoxy
resin, model EPOXY BBT-7892 purchased from Berjaya Bintang Timur
Sdn. Bhd. This
epoxy resin is consisting two liquid components which are resin
and hardener. This model
is specifically designated for hand lay-up fabricating process
in composite applications.
Different condition of kenaf fibre reinforced composite plate
are fabricated which
is correctively uncoated and coated composite plates. This is
carried out in order to
determine the best form of kenaf fibre composite plate is to use
as application on external
reinforcement. The kenaf fibres are uniformly distributed in one
direction during the
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fabrication process in order to provide a better tensile
strength. Tensile strength testing for
the mechanical property of the product will be based on ASTM
standard D3039. Physical
properties of the fibre plates, for example moisture content and
density will be also carry
out.
1.6 Outline of the Thesis
This thesis will provide an overview on the development of kenaf
fibre reinforced
composite plate and also focused on the investigation of the
tensile properties of kenaf
fibre reinforced composite plate, each uncoated and coated with
different weathering
conditions.
In the chapter one, a general idea on the background of fibre
reinforced plate will
be briefly explained with problems occurred. Reasons of the
application of this
technology on strengthening will stated as well. This chapter
summarizes the purpose and
gives an overview on this research study.
Chapter two will explain about the literature review of the
study, providing
relevant information to support the study. There would be a
deliberation on the
classification and characteristics of the natural fibres
including kenaf fibre including
applications of materials applied on the research. Several
methods of fabrication will be
discussed to clarify the execution of the study.
On the next chapter, a research methodology will be illustrate
as detailed
procedure on conducting the development of kenaf fibre
reinforced composite plate will
be explained thoroughly. The method used to fabricate the kenaf
fibre reinforced
composite plate is the hand lay-up method. Then, the methodology
will be continued with
the preparation on the physical properties test and the
mechanical property test of the
product. In the end of the chapter, a proper research plan will
be presented too.
Chapter four will focusing on the analyzing the results and
outcomes from the
experimental and laboratory work. The targeted output of this
study is mainly on the
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uncoated and coated kenaf fibre with various weathering
conditions. This resulted will be
recorded from the mechanical property test. Besides, physical
properties test will help the
study to elucidate the characteristics of kenaf fibre reinforced
composite plate,
concentrating at the density, water content and water
absorption. The analysis of results
will be explained fully with assistance of tables and graphs.
Next, problems occurred
during laboratory work will be discussed.
Finally, on chapter five, a conclusion will be made based on the
objective declared
in the thesis. Then, recommendations for improvement of future
research will be included
in this chapter.
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CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Nowadays, as an interest growth in green development, a quite
amount of researchers
have been study on the replacement of man-made fibres with green
or natural fibres.
Thus, the use of green fibres in building structural has further
accepted by the industries.
There are several properties that are required for construction
purposes such as high
specific strength and modulus, low cost, low density, absence of
health threats, easy
modifications and sustainability.
2.2 Natural Fibres
Natural fibres have become increasingly used in many
applications not only
because they are environmental friendly, but it is also because
of their various desirable
properties including stiffness. Natural fibres has been used on
many products such as
cloths, carpets, ropes, paper, mats and also building materials.
The synthetic fibres mostly
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produced from non-renewable resources and poses many problems.
For an example,
health risks rise up in the application of petroleum based
products either from direct or
indirect exposure such as water and air pollution. It is clearly
natural fibre is helping in
the needs of achieving sustainable development. Natural fibres
can be extracted from
leaves, bark and fruit of the plants itself. Natural fibres such
as cotton, hemp, kenaf, sisal
and others are widely used in numerous industries.
FIGURE 2.1: Hemp and cotton
The use of natural fibres and epoxy matrix is highly beneficial.
It is because its
strength and toughness of the resulting composites are greater
than those of the
unreinforced plastics. Plus, cellulose-based natural fibres are
technically durable, low in
cost, lightweight, abundant and renewable. Recently, natural
fibres reinforced polymer
materials are used commercially such as automotive, sporting
good, marine, electrical,
industrial, construction, household appliances and even
aerospace structure. Table 2.1
will show the advantages and disadvantages of natural fibre.
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TABLE 2.1: Advantages and disadvantages of natural fibres
Advantages Disadvantages
Producible with low investment at low
cost, which makes the material an
interesting product for low-wage
countries.
Thermal recycling is possible, as glass
causes problems in combustion
furnaces.
Low specific weight, resulting in a
higher specific strength and stiffness
than glass.
Benefits on being designated for
bending stiffness.
Renewable resources, the production
requires little energy as CO2 is used
while oxygen is given back to the
environment.
Price can fluctuate by harvest results or
agricultural politics.
Lower durability, fibre treatments can
improve this issue.
Have moisture absorption that causes
swelling of the fibres.
Lower strength properties, particularly
its impact strength.
2.3 Kenaf Fibre
Kenaf fibres have history of cultivation in some areas in the
world such as India,
Bangladesh, United States of America, South Africa, Vietnam,
Thailand, Indonesia, and
even in Malaysia. Known as Hibiscus Cannabinus, it is a tropical
crop related to jute or
cotton, and it has been incorporated in various applications,
successfully. The stems of
kenaf are able to produce two types of fibre, which are coarser
fibre in the outer layer
(bast fibre) and a finer fibre in the core. The harvesting time
of kenaf fibre only takes
about 150 days. This shows that this fibre are more efficient in
producing wood products,
reducing the demand of of timber, and leads to the solutions of
deforestation activities.
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It is an annual or biennial herbaceous plant growing to 1.5-3.5
m tall with a
woody base. The stems are 12 cm diameter, often but not always
branched.
The leaves are 1015 cm long, variable in shape, with leaves near
the base of the stems
being deeply lobed with 3-7 lobes, while leaves near the top of
the stem are shallowly
lobed or unlobed lanceolate. The flowers are 815 cm diameter,
white, yellow, or purple;
when white or yellow, the centre is still dark purple. The fruit
is a capsule 2 cm diameter,
containing several seeds.
Initially, kenaf leaves were consumed in human and animal diets,
and the bast was
used as bags and the sails for Egyptian boats. They were also
used as rope, twine, coarse
cloth and also paper. Other than that, in 1992, California,
Texas, Louisiana and
Mississippi used kenaf for animal bedding and food. Nowadays,
kenaf fibre is widely
used including in engineering wood, insulation, clothing-grade
cloth. soil-less potting
mixes, animal bedding, packing material, and also oil and liquid
absorbent.
FIGURE 2.2: Kenaf fibres
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2.3.1 Properties of Kenaf Fibre
The physical properties of natural fibres are depending on the
type of fibre itself. Kenaf
filament consist of discrete individual fibres sized 2-6 mm.
Their properties are
depending on the sources, age, separating technique and even the
history of the fibres.
The stem is straight and it is also unbranched, composed of an
outer layer, which is bark,
and a core. The process of separation of the stem into bark and
core is considerably easy,
either by chemical or enzymatic retting.
The performance of the materials is presented in terms of their
mechanical
properties. Tensile properties, flexural properties, compression
properties, impact
properties, and wear behaviour are important to determine and
for the sake of validity of
the kenaf ability, focusing under extreme and critical
conditions, which are the connection
between the material and the engineering performances. It is
proven that the kenaf fibre is
able to demonstrate an equivalent tensile strengths. Besides,
the flexural strength of kenaf
also is remarkably high compared to other fibres such as hemp,
coir, and sisal.
Plasticization is one of the sign of humidity aging, which
contributes to long-term
failure of an organic matrix. This is due to the water
absorption property of the fibre.
Plus, the humidity aging also may cause defects to the
mechanical properties and
dimensional stability of composites. Hence, this became one of
the major concerns in
developing solutions towards green technology. In kenaf side, it
will reach its equilibrium
at a certain specific immersion time. However, it will change
its magnitude of absorption
at a certain time, where it may solve few obstacles. This means
that the penetrability of
water, causing it to become active as water penetrating into the
interface through voids
induced by swelling of the kenaf fibres, resulting the ability
of the kenaf to neutralize the
acidity itself.
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TABLE 2.2: Advantages and disadvantages of kenaf fibres as
natural fibres
Advantage Disadvantage
High specific strength
Renewable
Low cost
Less health risk
Good heat conductor
Low impact strength
High moisture absorption
Low durability
Quality varies
Poor heat resistance
2.4 Epoxy Resin
Matrix materials have been used in structural industry for a
long time. However, they can
be classified into two main categories. The categories are
consist of thermoplastic
polymer and thermosetting polymers. Thermoplastic polymer is a
type of plastic that
changes its properties depending on temperature. It will become
soft when heated and
smoothly hardened when cooled. Under a certain temperature, they
have a significant
structural strength, but they will soften then melt upon
heating. Thermoplastic polymer
are such as polyethylene, polypropylene and vinyl.
On the other hand, thermosetting, also known as thermoset, is a
type of polymer
material that irreversibly cures, as it takes heat to do the
curing. Other than that, this type
of polymer also cured by a chemical reaction, or irradiation,
such as electron beam
processing. Initially in liquid or malleable form, thermosetting
polymer cannot be
reheated and melted back to liquid form once it is hardened.
Example of thermosetting
polymers are epoxy, polyester, silicone and alkyd.
Thermoset materials are basically stronger than thermoplastic
materials. This can
be explained by the three dimensional network of bonds, which is
cross-linking. Also,
thermoset materials are better in withstand the higher
temperature applications up to the
decomposition temperature. However, since it is non-reformable,
the chances for
recycling the material is close to zero. Thus, for this
fabrication of kenaf composite plate,
thermosetting material, epoxy is used.
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In general, uncured epoxy resins have only poor mechanical,
chemical and heat
resistance properties. However, excellent properties can be
obtained by curing. Curing is
a process of reacting the linear epoxy resin with suitable
curatives to form three-
dimensional cross-linked thermoset structures, such as
hardeners. Curing of epoxy resins
is an exothermic reaction, hence it may produces sufficient heat
to cause thermal
degradation if not controlled. So, epoxy resins has becomes one
of the best option in
producing composite plate due to its better bonding between
fibres ad matrix, along with
compatible sizing, its ability to cure at room temperature and
good creep resistance.
As stated, epoxy can be cured by adding hardener and each
hardener gives
different cure profile and impacts different properties to
finish products. This can be
elaborated with the relation between the selection of hardeners
with the rate of curing
time, and also the volume ratio of epoxy resin and the hardener.
However, it cost higher
than other matrix materials. Epoxy also provides higher
viscosity then most polyester,
causing a slightly higher degree of difficulty in execution. The
table below shows the
advantages and disadvantages of epoxy resin.
TABLE 2.3: Advantages and disadvantages of epoxy resin
Advantage Disadvantage
Wider range of properties
Lower shrinkage during curing time
Absence of volatile elements during
cure
Ability to resist chemical and solvents
Provides great adhesion to wide variety
reinforcement
Higher cost
Longer curing time
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2.5 Natural Fibre Reinforced Composite
A composite material is made by mixing two or more materials or
elements or even by a
unique combination of properties. For thousand years ago, the
wattle and daub is a prove
of man-made composite materials that has been applied as
building materials, resulting
them one of the earliest composite materials been developed
ever. Besides, the most
common composite materials are Portland cement concretes and
asphalt concretes, which
are widely used in construction industries nowadays.
Practically, the natural fibre reinforced composites are
composite materials made
from natural fibres and polymer matrix such as epoxies.
Biocomposites are hybrid
materials made of polymer resin reinforced by natural fibres,
providing a significantly
high mechanical and physical performances. The short and
discontinuous natural fibre
composites can be considered as a success, but the application
of long continuous fibres
are widely encountered lately. The long continuous fibres is
basically more advanced for
capital-intensive materials and products. The structural
properties can be modified by
changing the direction of the fibres in the resin, increasing
the strength.
Within the bonding in the composite plate, the poor capabilities
and drawbacks of
the individual elements will be solved. This can be shown by its
high in stiffness and
strength with a low weight and excellent corrosion resistance.
Since the excellence
performance takes up a considerably long duration, this
technology gains a higher
demands compared to wool and metal.
2.6 Fabrication Methods
The fabrication methods are able to influence the performance of
composite that
produced, although the mixing product of fibres and matrix
itself resulting higher
performances in any properties. This shows the importance of
fabrication method in the
manufacturing of the composites. In a nutshell, there are so
many methods are used in the
industry, varying techniques, advantages, limitations and
specific characteristics of final
production. Nevertheless, these hand lay-up, resin transfer
moulding, Seemann composite
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resin infusion moulding process (SCRIMP) and compression
moulding can be considered
as the upfront in the industry as the fabrication methods.
2.6.1 Hand Lay-Up Method
This method is the simplest yet the most executed in the
industry. The hand lay-up
method is applied to manufacture a significant amount of fibre
reinforced polymer
composite products. The process consists of chopped or
continuous fabric which
impregnated or soaked with resin using handheld rollers,
brushers and other related
apparatus. The fabric layer are stacked on each other, with each
layer being applied with
matrix, which is the resin. Open mold is used for the hand
lay-up process. By this way, it
can save cost because it can be easily modifiedto develop
products with different shape
and surface texture.
In the open mold process, the surface of mold is applied with
several layers of
wax or glycerin so that the products are easily removed. It is
also sprayed with a
pigmented polyester resin called gel coat. On top of the gel
coat, fibre layers will be
saturated by resin and catalyst at the suitable room temperature
are located. To achieve a
proper and uniform wetting on the reinforcement, each fibres
will be pressed by using
hand rollers. "Prepreg", also known as pre-impregnated
reinforcement of resin is carried
out to ensure the consistent control over reinforcement to resin
ratio by weight or volume.
This method may take a longer time and it involves a lot of
labor-intensive steps even
though the procedures are simple. Still, there are possibilities
of the variation throughout
the process. In spite of its simplicity in the execution, a good
ventilation and protective
equipment are essential for the participated workers.
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FIGURE 2.3: Hand lay-up method
2.6.2 Resin Transfer Moulding (RTM)
Unlike the hand lay-up method, this resin transfer moulding is a
close mould process,
whereby the mould are kept under a low pressure. The preformed
fibre reinforcement is
placed in the mould throughout the fabrication process and they
will be infused with resin
and catalyst, as the fibres themselves will pumped into the
closed mould under low
pressure. Next, the mould is heated and cured in order to create
a composite part. The
surfaces of the mould is then utilized in the process by coating
it with gel coat, or even
applied with a veil to create a the best quality of smooth
surface of final product.
In the fabrication process, the complex shapes can be made in
one operation with
or without inserts. The process can be automated with limited
void content. On the
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brighter sides, this method can release the less hazardous
emissions. The resin commonly
used for this method are polyester, vinyl, ester, epoxies and
others. This process also
consisting a mineral fillers, which are nanoclays. The mineral
fillers will exfoliate to
enhance fire retardancy, mechanical properties, durability and
surface finish.
Furthermore, a good controlling system in the process under low
pressure
provides a high product strength with minimal fibre damages. Due
to its high production
rate and ability to produce complex shapes, it is more
preferable in the automobile
industry. Figure below shows the process of resin transfer
moulding method.
FIGURE 2.4: Resin transfer moulding process
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2.6.3 Seemann Composite Resin Infusion Moulding Process
(SCRIMP)
The Seemann composite resin infusion moulding process (SCRIMP)
is actually a
vacuum-assisted resin transfer moulding process that produces
parts for aerospace,
transportation, and infrastructure applications. SCRIMP is
applied for co-moulding
composite skins and core in one piece without using autoclave.
It is similar to the resin
transfer moulding which contributes in performing parts using
dry fibres and core.
However this process does not need two sided mould or resin
pressure, unlike the resin
transfer moulding.
Based on the figure below, the fibre layer including any core is
saturated, or
soaked in one infusion step, which leads to the elimination of
the weaker secondary bonds
and relatively longer times that are associated with the resin
transfer moulding process.
Fabric preform acts as an effective breather layer, eliminating
the trapped air voids in the
resin infusion process. Resin infused through the fibre layers
are spread evenly and the
fibres will be saturated. This method is applied in the
manufacturing of composite parts
like those with single skin and cored construction as well as
complex three-dimensional
truss parts.
FIGURE 2.5: Seemann composite resin infusion moulding process
(SCRIMP)
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2.6.4 Compression Moulding
The compression moulding is a technique off moulding which a
preheated polymer is
placed into an open, heated mould cavity. The good thing is,
this method can be used for
both thermosetting polymer, as well as thermoplastic polymer for
the sake of
manufacturing purposes. Throughout the process, matrix materials
including the fibres are
applied directly in the mould cavity and then will be compressed
under a certain pressure.
The mould is closed with a top plug and forces are applied to
perform the compression
process of the involving materials to contact all area of mould
evenly.
The thermosetting polymer will be cured through heating process.
On the other
hand, the thermoplastic polymer will soften up and form into the
mould cavity shape with
heat and pressure. The controlling of the temperature, pressure
and time residence are
depending on the properties of employed materials and the
dimension of product
required. The compression moulding is high in volume and
pressure plastic moulding
method, which is suitable for complex moulding and high strength
products. Thus, this
method can be considered as one of the top choices in the
automotive industry for
manufacturing parts, due to its time cnsuming and high
production rate.
FIGURE 2.6: COMPRESSION MOULDING
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CHAPTER 3
RESEARCH METHODOLOGY
3.1 Introduction
This chapter generally describes and discusses the overall plan
of the experiment program
to develop the kenaf fibre reinforced composite plate. The main
focus on this research
study is on the difference in strength between uncoated and
coated kenaf fibre composite
specimens. This will define the effects of water existence in
the reinforced fibre plate.
The research plan will includes the determination of kenaf fibre
reinforced composite
plate, physically and mechanically including its
development.
Data that have been gathered will be analyzed to detect the
effect of water
existence to kenaf fibre reinforced composite plate. Hence,
there would be various
conditions will be tested on the specimens, uncoated and
coated.
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3.2 Research Plan
The research plan in this study is primarily divided into three
main components which is
including the fabrication of kenaf and the testing upon the
specimens. Thus, the
components are fabrication of kenaf fibre reinforced composite
plate, physical properties
tests on the specimens, and mechanical property test on the
specimens. The proper
procedure will be explained thoroughly. Besides, the optimum
load for compaction will
calculated.
First of all, after kenaf fibres is purchased from LKTN (Lembaga
Kenaf dan
Tembaga Malaysia), after an appropriate preparation of the
fibre, the fabrication of kenaf
fibre reinforced composite plate will be carried out. The
execution of fabrication will be
done with using hand lay-up method. By this, the first objective
has been achieved.
After 16 plates have been developed, the plates will be tested
physically and
mechanically. In the beginning, physical properties tests will
be carried out. There would
be three tests in order to find the physical properties of kenaf
fibre reinforced composite
plates, which are density, moisture content and water
absorption. This step is tally with
the second objective of the research study. Furthermore, the
density test will be following
ASTM D3800 while moisture content and water absorption test will
be following ASTM
D5229.
Step three, another specimens of kenaf fibre composite plate
will be tested on its
mechanical property, which is tensile strength. In this study,
only tensile property will be
determined, since the main objective of the development of kenaf
fibre reinforced
composite plate is to overcome the external tension applied on
the concrete beam.
Concrete structure can withstand compression effectively, but
not tension force. To
investigate the tensile strength of the kenaf fibre plate
specimens, ASTM D3039 will be
followed. By this, the last objective of the research study is
achieved.
Throughout the fabrications and physical and mechanical
properties test,
observations will be made. The data will be monitored and
recorded for the next analysis.
The main target of the tests is to find the relation between the
strength of the kenaf fibre
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24
reinforced composite plate with the water existence. Ergo,
conclusion will be made
wholly. On the conclusion, further recommendations also will be
stated.
FIGURE 3.1: General flow of research plan
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25
3.2 Fabrication of Kenaf Fibre Reinforced Composite Plate
In fabricating kenaf fibre reinforced composite plate, the hand
lay-up method will be used
because it is the most suitable method among all.
For each plate, there will be five layer of kenaf fibre weighed
12g each, making it
total 60g of kenaf fibre for each plate. The size of plate is
400mm x 80mm x 6mm. The
mould used is made of steel, and matrix material is epoxy resin.
The fabrication process
will end with compaction of the plate with an optimum load.
3.3.1 Material Preparation
3.3.1.1 Kenaf Fibre
Kenaf bast fibres have been selected as the material of fibre
phase in the fabrication of
kenaf fibre reinforced composite plate. The bast is used due to
the distribution of the
fibres. The fibre composite plate bond on the tension surface of
beam must provide ample
tensile strength in order to achieve external reinforcement.
Hence, the fibres are preferred
to be long and continuous along the plate so that a better
tensile strength can be provided.
Moreover, the fibres are needed to uniformly distributed in one
direction. However, kenaf
core fibre does not obey the long and continuous characteristics
as they are short and thin
walled.
During the preparation of the fabrication process, the fibres
have to be handle
properly in order to accomplish the requirements; continuous,
uniformly distributed,
unidirectional. disintegrate and straighten. There are several
methods can be applied with
assisting tools such as clips, and comb. The fibre first is
cleaned to remove dirt and others
to maximize the quality. The discontinuous fibre is also need to
be removed, as tensile
strength may drop due to its existence. All the unwanted are
removed by combing. This
combing technique is also usable to straightening the curly
parts of the fibres. Despite
combing, there are still curly parts that need to be done,
hence, cellophane tape and clips
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26
are used by fixing the fibres at both ends by using this. Plus,
this fixing can ensure the
fibres are not overlapping each other, and they also won't be
twisted.
FIGURE 3.2: Kenaf fibre
The strength of kenaf fibre composite plate depends on the
bonding between
matrix and fibres. If fibres are not disintegrated properly,
gaps will existed between
fibres, causing the plate to inexact. There will be conditions
where some parts of fibre
will not fully soaked with epoxy, resulting air voids within
fibres.
3.3.1.2 Epoxy Resin
Matrix materials have been used in structural industry for a
long time. However, they can
be classified into two main categories. The categories are
consist of thermoplastic
polymer and thermosetting polymers. Thermoplastic polymer is a
type of plastic that
changes its properties depending on temperature. It will become
soft when heated and
smoothly hardened when cooled. Under a certain temperature, they
have a significant
structural strength, but they will soften then melt upon
heating. Thermoplastic polymer
are such as polyethylene, polypropylene and vinyl.
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27
On the other hand, thermosetting, also known as thermoset, is a
type of polymer
material that irreversibly cures, as it takes heat to do the
curing. Other than that, this type
of polymer also cured by a chemical reaction, or irradiation,
such as electron beam
processing. Initially in liquid or malleable form, thermosetting
polymer cannot be
reheated and melted back to liquid form once it is hardened.
Example of thermosetting
polymers are epoxy, polyester, silicone and alkyd.
Thermoset materials are basically stronger than thermoplastic
materials. This can
be explained by the three dimensional network of bonds, which is
cross-linking. Also,
thermoset materials are better in withstand the higher
temperature applications up to the
decomposition temperature. However, since it is non-reformable,
the chances for
recycling the material is close to zero. Thus, for this
fabrication of kenaf composite plate,
thermosetting material, epoxy is used.
The epoxy purchased consists of two component liquid, which is
the resin and the
hardener. For application in fabricating the kenaf composite
plate, the mixing ratio of
resin and hardener is 5:1. Averagely, 250g of resin will be
mixed to 50g of resin in a
suitable container. This measurement usually enough for making
one composite plate.
Safety precautions such as wear rubber gloves are required when
mixing the epoxy, as
skin irritation may occurred when directly contact to the skin.
Since the material is
corrosive, precaution needs to be taken seriously. Furthermore,
masks are needed as the
ammonia-like smell are definitely unpleasant. The epoxy is mixed
manually using stick
for about 5 minutes before applied to the fibres.
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28
FIGURE 3.3: Epoxy resin; a) Resin and b) Hardener
FIGURE 3.4: Mixing epoxy resin
A
B
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29
3.3.2 Steel Mould Preparation
In order to produce a well performance fibre composite plate
with required dimensions
using epoxy resin, a mould will be needed. Problems such as leak
of epoxy may occur
during fibre composite fabrication due to narrow spaces between
the middle frame and
bottom plate. This can cause the thickness of kenaf fibre
composite plate not constant
thus will affect the performance. Silicone sealant is one of the
best way to solve this. The
spaces will completely covered by this sealant. The silicone
sealant is applied before the
fabrication process started. Then the plate is applied with a
layer of grease to prevent the
fibre composite bonded on the steel mould surface and it also
makes it easier to remove
the plate once it is done.
FIGURE 3.5: Preparing the mould
3.3.3 Hand Lay-out Method
The hand lay-up method is used to produce a significantly large
number of fibres
reinforced polymer composite products in the industry. Thus,
before starting the
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30
fabrication, the fibre, epoxy resin and mould must be prepared
thoroughly. The following
will be details of procedures in fabricating the kenaf fibre
reinforced composite plate.
First step, the surface of the mould will applied with a thin
layer of grease. The
thin grease layer is essential because it would prevent the
completed kenaf fibre
reinforced composite plate from sticking to the mould and hard
to removed. Then, the
mould surface with thin layer of grease is pre-coated with
prepared resin mix. The epoxy
resin is spread evenly on the centre part of mould surface with
assisting tool such as
spatula and scrapper. The amount of epoxy resin used in this
first layer is depends on the
required fibre composite plate size.
FIGURE 3.6: Fabrication process of kenaf fibre reinforced
composite plate
Step two, the prepared kenaf fibre layer will be applied on the
epoxy resin mix
surface. Minor forced is applied on the centre part which
covered with epoxy resin using
scrapper. Gentle movement is recommended in this procedure to
avoid fibres from comes
off. The kenaf fibre layer is pressed from centre to both sides
of plate in order to spread
the epoxy resin mix into each part of mould. This is also to
ensure the kenaf fibres are
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31
completely soaked with epoxy. Besides, this will increase the
bonding between epoxy
resin and fibres as well as preventing air voids trapped in the
composite plate. The air
voids in the plate can definitely decrease the strength of the
composite plate. Throughout
the execution, the fibres must kept in the same direction.
Step one and two can be repeated four more times to complete the
plate. However,
before proceed to the next step, kenaf fibres are pulled from
both ends to ensure that
fibres are straighten by pulling the ends in opposite directions
during the epoxy resin mix
is in elastic form. This is to ensure the direction of the kenaf
fibres, preventing them from
curled up and disturb the strength of the product.
For step three, once the fibres are totally applied with epoxy
resin mix, the mould
is closed and sealed with top plate. The designated holes on top
of plate allow the trapped
air voids within mould released from the epoxy resin mix.
Additional loads applied on the
top plate gives compression force on fibre composite to ensure
the fibres and epoxy resin
are compressed. This will increase the performance of fibre
composite plate produced.
Heavy objects such as bricks are place on top plate of mould to
give external loadings.
FIGURE 3.7: Summary of fabrication process of kenaf fibre
reinforced composite plate
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Lastly, the fibre composite is left to dry for about 24 hours
with room temperature.
The plate will be removed from the mould gently. Figure 3.7 is a
summary of the
procedure of the fabrication of a kenaf fibre reinforced
composite plate.
3.3.4 Load Compression
After the fabrication process is done, the mould filled with
kenaf fibre and epoxy resin
mix must be compressed until the product is dry. Therefore, an
optimum load of
compression must be set in order to standardize the compression
criteria. The optimum
load of compression is important to maintain the quality of the
product kenaf fibre
reinforced composite plate along with preventing the mould from
break or damage due to
excessive load applied.
To determine the optimum compression load, in the beginning of
the compression,
the weight of the load must be applied gradually. Starting from
10kg, another load will be
added increasingly until the top plate is touched the mould.
Right after they are in contact,
there will be no more loads need to be applied, by means, the
total load applied is the
optimum load for compression. Figure 3.8 shows the illustration
when the top plate is
touched the mould.
FIGURE 3.8: Determination of optimum compression load
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From the compression process, it is found that the optimum
compression load for
a plate is 50kg. Hence the compression pressure acting on the
steel mould can be
calculated.
Compressive Pressure =
=
= 20.83 kN/m2
3.3.5 Lessons Learnt and Precautions
In producing the kenaf fibre reinforced composite plate, there
are few lessons that I have
learnt from the errors and problems that I have faced.
It is clear that the compaction process is very important in
producing high strength
of kenaf composite plate. However, since the plate has a long
dimension, then the
compaction occurred is possibly uneven. This will affected the
strength of the plate since
there will be still air bubbles trapped in the epoxy mix resin
and kenaf fibres. The error
that I have made is, I put loads at the center of the top plate.
This caused the compaction
focused on the center part of the plate, leading to uneven
compaction of the plate. Thus,
the solution is, to do the compaction, the first load has to be
on both end sides of plate, or
the first load has to be as long as the top plate. Then the
other load can be placed as usual.
This will guarantee the even compaction of the kenaf fibre
reinforced composite plate.
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34
FIGURE 1.9: Error; load focused on the center of the top
plate
FIGURE 3.10: The proper way; the first load is as long as the
top plate
FIGURE 3.11: The first loads are placed at the end of plates
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35
In compaction of the fibre, there are possibilities that the
fibres spilled out. This is
due to the amount of kenaf fibre used in fabricating the fibre
reinforced composite plate.
The spilled fibres can cause the plate to decrease its strength,
due to lacking amount of
kenaf fibre in the composite plate. This happened when the loads
are pressed the top
plate, the kenaf fibres at the top are dispersed to the sides.
Supposedly, with a proper
procedure and a great, ample pressure in compaction, this
problem can be prevented. The
reality stated that the dispersed fibres cant be prevented since
it will move to side since
the epoxy is not fully hardened yet. So, the solution is, when
preparing the epoxy and
kenaf fibre in the plate, it is best to leave spaces at both
sides inside the plate. This will
help the dispersed kenaf at the top to fill the space provided.
Hence by this way, the
strength of the plate can still maintained.
FIGURE 3.12: Spilled fibres
FIGURE 3.13: Leaving spaces at sides to prevent fibre spills
Spilled Fibres
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36
When opening the plate and separate the kenaf fibre composite
plate from the
mould, it would be hard to separate them especially when
removing the top plate. This is
because the epoxy resin have a very high cohesion strength and
the dry product of epoxy
will make it harder to remove as it is very high in strength
resistance. Apparatus such as
scrapper, nail and hammer are needed to remove the plate from
the mould. This can cause
the metal mould scratched off, or even worse, the fibre plate to
break. So, to solve this,
after the mould is applied with grease, gently cover them with
plastic cover. This is also
need to apply on the top plate. When the curing time is
completed, they will be easier to
remove.
Safety is very important. It is a compulsory for us to make sure
the safety is
guaranteed throughout the fabrication of the plate. Precautions
can be taken to prevent
from any problems. When it comes to handling the epoxy resin,
precautions such as
wearing gloves, goggle and face mask are strictly compulsory.
This is because the epoxy
resin is an exothermic material. It produces heat and gas when
the hardener is mixed with
the epoxy resin. The gas produces may cause problem when it is
inhaled directly
especially to asthmatic patient. When laying the fibres in the
plate, spread the epoxy resin
using scrapper instead of bare hands. Besides from protecting
hand from possible
irritation, the scrapper do provides a better, even spread on
the fibres. When placing the
load on the plate for the compaction process, precautions also
need to take. The plate
mould need to be placed on the ground so that it is easy to
place the loads, and it would
cause less problem if the loads fall, because the ground is
near.
3.3.6 Sample Specimens
After all composite plates have been developed, which the total
is 12 plates, the plates
will be sent to timber factory to cut them into specimens. There
are three specimens are
produced from one plate, making 48 specimens in total. The
dimensions for each
specimens is 250mmx15mmx6mm. Then, 18 specimens will be coated
with a layer of
epoxy resin mix. These specimens will be used in mechanical
property test which is
tensile strength test, in a category 'Coated'. The other 18
uncoated specimens are also will
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37
be tested on the same test. The rest of the specimens will be
tested on the physical
properties test, which are density, moisture content and water
absorption. Three
specimens for the water absorption test are also coated.
FIGURE 3.14: Sample specimens
3.3.7 Uncoated and Coated Specimens
From these 18 specimen plates, they will be divided by half.
Half of them will directly be
tested in various environment, which they will be left at
indoor, outdoor and in the water
for 7 days, 14 days and 28 days. After they undergo these
conditions then they will be
tested its strength. These sample plates are in category
Uncoated specimens.
When the plate is cut into smaller size of specimen plates,
there would be exposed
surface area(s) occurred at the sample plate. Hence, for the
other half plates, they will be
coated by epoxy resin to cover the exposed surface. This will be
carried out to determine
the effects of exposed area to the strength of the kenaf fibre
reinforced composite plates.
After that the Coated specimens will undergo the same procedure
as the Uncoated
specimens. All data will be recorded and tabulated for analysis
of the kenaf fibre
reinforced composite plate.
Theoretically, water content does affect the strength of the
kenaf fibre. The
presence of water will weaken the inner bond in the fibres thus
make it easier to break.
So, the exposed surface area will exposed to water moisture in
the air as well. The
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38
comparison will be made between the coated specimens and the
uncoated specimens to
determine the effect of moisture content in the air towards the
exposed surface area of
kenaf fibre reinforced composite plate. Figure 3.15 shows the
flow chart of the tensile
test.
FIGURE 3.15: Flow chart for physical properties tests and
mechanical property test
3.4 Physical Properties Tests
The physical properties of composite varies based on the
materials and fabrication
method have been applied for the manufacturing process.
Application of composite for
industrial is depending on the physical properties which gives
unique features to
composite. So, physical tests are performed in order to
determine the required physical
properties including density, moisture content and water
absorption of the kenaf fibre
reinforced composite plates.
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39
3.4.1 Density
The density of the kenaf fibre reinforced composite plate is
important to compare its
usefulness with other external reinforcement in the industry.
Theoretically, when the
density of a material is high, the weight of the material
definitely will be high. As
mentioned before, lightweight materials are preferable for an
easy installment and
maintenance. For this research study, the density test procedure
is applying Archimedes's
method.
The resting procedure is referred to standard testing method
ASTM D3800 and
apparatus are including thermometer, stirrer, balance, balance
stand, suspension wire and
water are used. The specimen size for this test are not
specifically stated, but I have used
the specimens with the same size as other tests which is 250mm x
15mm x 6mm. The
suspension wire is weighed in the air first. Then, the weight of
suspension wire with the
specimen is weighed. The suspension wire with specimen is then
immersed in the water
and weighed again. All the readings are recorded in a table. The
weight of the suspension
wire in the water is also recorded. Three specimens are used and
average density is
calculated.
FIGURE 3.16: Weighing the specimen in the air
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40
FIGURE 3.17: Weighing specimen in the water
3.4.2 Moisture Content and Water Absorption
Moisture content test is conducted to investigate the initial
water content in the fibre
plate. The apparatus used for the testing including oven,
measuring weight, glove and
container, besides the specimen itself. The initial weight of
three specimens are measured
and later on oven-dried at 150C temperature for 24 hours. Once
the oven-dried
specimens are removed from the oven, the specimens are weighed
again and the average
moisture content of kenaf fibre reinforced composite plate can
be determined.
Moisture absorption test is a crucial test which is to determine
the amount of
moisture can the kenaf fibre reinforced composite plate absorb.
The specimens will be
tested within two conditions, which are uncoated and coated.
This is also to determine the
effectiveness of epoxy resin mix in coating the exposed surface
of the fibre plate and the
ability of the epoxy resin in water resistance. So for this
test, three uncoated and three
coated specimens are used and then the average moisture
absorption of uncoated and
coated specimens are determined separately.
The specimens prior to testing were dried in an oven at 150C and
then were
allowed to cool to a room temperature. They then are kept in
desiccators. The weights of
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41
the specimens are then recorded before being submerged into the
water for 48 hours.
After that, the specimens were taken out from the moist
environment and all surface
moisture was removed with a clean dry cloth or any drying
materials. The specimens
weights are measured again. The weight difference before and
after submerging in the
water is calculated as it is representing the water absorption.
Hence, the percentage
weight gain or the water absorption of the specimens is measured
by this equation:
Water Absorption. % Mt = ( )
From the equation, the Wo and the Wt denote the oven-dry weight
and the weight
after the specimens being submerged in the water for 48 hours
respectively.
3.5 Mechanical Property Test
The performance of a material can be determined by its
properties and behavior under
mechanical properties which includes tensile, compressive, shear
and other properties in
the environment. These properties will be a critical criteria
when selecting the suitable
materials in a given application as well as designing a
structure with the selected
materials. These mechanical properties are measured by a
laboratory tests first before
being used in the industry. Thus for this kenaf fibre reinforced
composite plate, only
tensile property will be determine. By book, the concrete is
able to withstand compression
force effectively, but poorly in resisting tension. When applied
tension on concrete, the
structure will break or damage. In other words, concrete beam
can withstand a big
compression but very small tension. This is leading to the
invention of the external
reinforcement, to externally withstand tension force of the
structure.
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42
3.5.1 Tensile Strength
Tensile testing is a material test where the sample is subjected
to tension force until
reaching the failure state. The test result will be used to
select the material whether it is
appropriate for the application in the structure industry.
However, understanding on the
background theory of tensile test is crucial before conducting
the test. It is because it is
challenging to obtain a valid tensile property from a tensile
test. The conduction of tensile
test will be based on standard ASTM D3039.
According to the standard, minimum of five straight sided
specimens for each test
condition is required. The width of straight sided specimen is
15 mm and overall length
must be 250mm. These explains the dimension of the specimens
which is mentioned
before. The tab material used in this test will be aluminium
with 1mm thick and 50mm
length. The fibre composite plate is cut to 250mm x 15mm x 6mm
as stated previously.
Each test conditions is conducted with at least three specimens
to obtain an accurate
average reading. The testing of tensile strength will be using
the Universal Testing
Machine (UTM) model INSTRON 8801.The composite plate specimens
are subjected to
the testing machine to ensure that the specimens is tight to
prevent errors during the
testing.
FIGURE 3.18: Specimen for tensile test
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43
FIGURE 3.19: Universal testing machine (UTM) INSTRON 8801
FIGURE 3.20: Consequences when the composite plate are not well
made
3.6 Presence of Water
As mentioned before, water plays a crucial role in weaken the
strength of kenaf fibre
reinforced composite plate. Humidity aging is initially known
for being a main factor of
long-term failure of organic matrices when they are exposed to
atmosphere or when
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44
having a contact in liquid form. The presence of water that have
been absorbed into the
composite plate may cause the plate to swell, causing
degradation of the intermolecular
strength by hydrolysis, osmotic cracking and also changes of
water state that leads to
hydrothermic shock. These will disturb the durability of the
plate gradually.
The penetration of water is done by three mechanisms. The first
mechanism is
consisting the diffusion of water into the very small voids that
are already present in
between the polymer chain. Then, the voids are becoming some
sort of capillary transport
which transmit the water molecules to all voids to fill. This is
because the voids
represents the incomplete moisture. Lastly, when the fibre plate
starts swelling, the
transportation of micro-cracks in the plate. Although matrix
such as epoxy resin are
completely water resistant, the epoxy is possible to
moisturized, thus provides a higher
moisture to be transported throughout the plate, internally.
Focusing internally, when talking about kenaf fibre material,
the fibre is
hydrophilic, meaning that the material is likely to contact with
water. Although the rate of
absorption will reach its equilibrium at a certain stage, with a
small amount of water
presence will weaken the internal strength right away.
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45
CHAPTER 4
RESULT AND ANALYSIS
4.1 INTRODUCTION
This chapter basically elaborates the collected data and
discussion on the analysis from
the laboratory testing. The tests are divided into two main
categories which are physical
tests and mechanical test on both uncoated and coated kenaf
fibre reinforced composite
plate specimens. The physical test is conducted to measure the
physical properties of the
kenaf fibre reinforced composite plate which are density,
moisture content and water
absorption, while only tensile strength test is conducted for
mechanical property.
4.2 Physical Properties of Kenaf Fibre Reinforced Composite
Plate
4.2.1 Density
The density of kenaf fibre is determined by using Archimedes's
Method based on ASTM
D3800.
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46
4.2.1.1 Procedures
1. The suspension wire is weighed in the air.
2. The weight of suspension wire with the specimen is weighed
and recorded.
3. The suspension wire with specimen is immersed in the water
and weighed again.
The data is recorded.
4. The weight of the suspension wire in the water is
recorded.
5. All the readings are recorded in a table.
6. Three specimens are used and average density is
calculated.
4.2.1.2 Results
Results are observed and recorded. The density is calculated by
using these equations:
Vspecimen (cm3) = Wspecimen - Wsubmerged
water
specimen = Wspecimen
Vspecimen
where
Wspecimen = Weight of the specimen in the air, in g.
Wsubmerged = Weight of the specimen in the water, in g.
water = Density of water, 1 g/cm3
specimen = Density of the specimen in g/cm3
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47
TABLE 4.1: Density of kenaf fibre reinforced composite plate
Sample Weight in air (g) Weight in water (g) Density (g/cm3)
Density
(kN/m3)
1 27.32 8.83 1.477 14.77
2 31.38 8.43 1.367 13.67
3 30.29 6.75 1.286 12.86
Average 1.376 13.76
Steel usually have a density range between 77.50 kN/m3 to 80.50
kN/m
3 [_]. Due
to high density, leading to higher weight, the application of
the steel plate too reinforced
the beam externally would be rather difficult and intricate, as
an advanced machineries is
required to lift and move the steel plates.
Carbon fibre reinforced plate (CFRP) rather have much lower
density than steel,
ranged 17.50 kN/m3 to 19.50 kN/m
3 [_]. This explains the broad uses of this plate in the
industry nowadays. CFRP has a very high water resistant,
electrically conductive and
does not creep. These values promise a long term in aging the
stability of the building. It
is known that water does play an important role in weaken the
structure of a building. As
for steel, the presence of water will make it rust, and thus
corrodes to failure. Along with
its high weight due to its density, making it as a second
choice, after fibre reinforced plate
even though steel has a very high tensile strength. Furthermore,
CFRP is highly resistant
to many chemical solutions. The installation process then would
be so much easier as
there would not be any restrictions to the surface of the fibre
plate.
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48
FIGURE 4.1: Carbon fibre reinforced plate (CFRP)
Moving to glass fibre reinforced plate (GFRP), the density of
GFRP is 17.7 kN/m3
[_]. It also has a considerably low density compared to steel,
which also helps the
installation to be easier and faster. Comes with fairly high
Young's modulus and
strength, which are bonus in reinforcing the beam externally.
However, there are several
issues that have been carried along. GFRP is basically expensive
to produce, same as
CFRP, as it must be processed directly to shape by laying up
partially. Then they requires
hot pressing, which is also expensive, to cure the layers of the
glass fibres. Other than
that, it is difficult to shape, means the fabrication process is
rather complicated than other
fibre reinforced plate. It also cannot be recycled, showing the
uses of this GFRP is not
supporting sustainable development, which what are we fighting
for nowadays.
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49
FIGURE 4.2: Glass fibre reinforced plate (GFRP)
Based on the density test, kenaf fibre reinforced composite
plate has the lowest
density among all., which is 13.76 kN/m3. As we all know,
density is important in
indicating it usefulness regarding comfort, support and
durability. This result shows that
the kenaf fibre plate is lightweight, making it easy for
installation and other uses.
Although steel do have a huge difference of tensile strength,
but due to the steel's density,
it may cause a burden. Kenaf fibre is absolutely great
substitute for external
reinforcement because it also has high tensile strength. On the
other hand, CFRP and
GFRP have their own disadvantages that kenaf fibre plate can
overcome, making it
eligible to substitute them.
FIGURE 4.3: Kenaf fibre reinforced composite plate
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50
4.2.2 Moisture Content
The moisture content of fibre is determined by laboratory
testing based on the standard
testing method ASTM 5229. Three specimens are prepared during
the test in order to
determine the average value of moisture content of kenaf
fibre.
4.2.2.1 Procedures
1. The initial weight of three specimens are measured
separately.
2. The specimens are oven-dried at 150C temperature for 24
hours.
3. The specimens are weighed again.
4. The average moisture content of kenaf fibre reinforced
composite plate are
determined.
4.2.2.2 Results
The specimens need to be oven-dried for 24 hours to remove the
moisture content in the
plate initially. The moisture content of the three specimens are
calculated thoroughly
using these equations:
Moisture Content (%) = ( )
where
W0 = Initial weight of the specimen, in g.
Wt = Final weight of the specimen, after oven-dried, in g.
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TABLE 4.2: Moisture content of kenaf fibre composite plate
Sample Initial Weight (g) Final Weight (g) Moisture Content
(%)
1 32.5 31.59 2.88
2 30.4 29.6 2.70
3 33.2 32.33 2.69
Average 2.76
Based on the result, it is shown that the composite plate does
absorb water, and
this can cause swelling of the materials. This also shows the
possibilities of the
degradation of matrix or interfacial properties in the material.
Theoretically, low moisture
content composites resulting in a higher and better performance.
Inside the plate, the
existing moisture may leads to void development, and this may
weaken the structure as it
would interfere the bonding between the epoxy resin and the
fibre.
4.2.3 Water Absorption
Moisture absorption test is conducted in order to find the water
absorption behavior of the
composite plate. It is based on the standard ASTM 5229. These
specimens will be tested
under two conditions, which are coated and uncoated. Here we can
foresee the role of
epoxy resin in resisting water absorption.
4.2.3.1 Procedures
1. The uncoated and coated specimens are oven-dried at 150C and
then were
allowed to cool to a room temperature.
2. The weights of the specimens are then recorded.
3. The specimens are submerged in water for 48 hours.
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52
4. The specimens were taken out from the moist environment and
all surface
moisture was removed with a clean dry cloth
5. The specimens weights are measured again.
6. The water absorption of the specimens are calculated and
recorded.
4.2.3.2 Results
In this test, the differences of the water absorption between
uncoated and coated
specimens plays an important role, as it tells the effectiveness
of the epoxy resin as a
coater. The water absorption of the specimens are calculated
using this equations:
Water Absorption (%) = ( )
where
W0 = Initial weight of the specimen, in g.
Wt = Final weight of the specimen, after oven-dried, in g.
TABLE 4.3: Water absorption of uncoated and coated kenaf fibre
composite plate.
Type Sample Initial Weight (g) Final Weight (g) Water
Absorption(%)
Uncoated
1 29.9 29.96 0.2
2 32.52 32.56 0.12
3 29.37 29.91 0.13
Average 0.15
Coated
1 33.03 33.03 0
2 33.01 32.02 0.03
3 37.56 37.58 0.05
Average 0.03
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Water absorption is one important topic to discuss in developing
kenaf fibre
reinforced composite plate. Since the existence of moisture in
the fibre is able to disrupt
the strength of the product, as it would disturb the bonding
between the elements, an
addition of moisture or water content from surrounding is
something to prevent or reduce
to minimum. This concern is supported with the fact that the air
in the atmosphere does
contain moisture, Also when this external reinforcement
technique is applied, the plate
will be exposed to air and there are many possibilities that
this plate will be exposed to
other liquid forms of inert and thus nullified its function, not
mentioning other chemical
solution that have a high potential in spoil its strength.
In order to solve this issue, one needs to block the access of
water or any other
liquid form of inert to penetrate the external reinforcement.
One of the most effective way
is by coating the plate using its matrix, which is epoxy resin.
As discussed before, epoxy
resin, a thermosetting material has a wide usage since it is
waterproof, high specific
strength, heat resistance, strongly adhesive and chemical
resistance. In order to make it
cost effective and minimize the waste disposal, we can use the
excess epoxy resin used to
fabricate the kenaf fibre reinforced composite plate. This
supports the sustainable
development as well although epoxy resin cannot be recycled, by
using it to the
maximum. Thus, by coating the plate, it will increase the chance
of the plate's life. Water
absorption testing is mainly to determine the effectiveness of
coated kenaf fibre
composite plate in resisting water absorption.
So based on the results of the water absorption test, it clearly
shows that the epoxy
resin is effectively minimize the water absorption of the
composite plate. The water
absorption of uncoated kenaf fibre composite plate is 0.15%
while coated plate shows
0.03% of water absorption, which is close to zero. Technically,
if the fibre plate is coated
properly, it is possible that it will not absorb any water or
other liquid. In this case, the
reason that there is still water have been absorbed by the
coated kenaf fibre plate is
because it is not coated fully. Double coat would give a better
performance. Back to the
result, it clearly shows the impressive performance of coated
specimens compared to
uncoated one because there is a reasonably big gap between the
values.
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FIGURE 4.4: Differences of water absorption of uncoated and
coated specimens
From the chart above, it shows an obvious differences in water
absorption
between the two types of specimen. It became a matter because
this test only conducted
where the specimens are only submerged in the water for 48
hours. The usage of this
external reinforcement are meant to be effective for a long
time. Imagine that the coated
kenaf fibre reinforced composite plate is used for
reinforcement, logically it surely can
stand a higher load and last much longer than the uncoated type.
Thus, in my opinion it is
essential for kenaf composite plate to be coated before applied,
as it does not cause any
extra cost of materials.
4.3 Mechanical Properties of Kenaf Fibre Reinforced Composite
Plate
Besides physical properties such as density, moisture content
and water absorption,
mechanical properties is also important in determining the
capability of kenaf fibre
reinforced composite plate to be used as external reinforced in
construction. In fact,
mechanical properties will help to justify the strength and uses
of this fibre plate. This
mechanical properties test also will elaborate the effectiveness
of epoxy resin in
0.15
0.03
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Uncoated Coated
Wat
er
Ab
sorp
tio
n (
%)
Water Absorption
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preventing the specimens from weaken its inner strength due to
presence of water and
moisture. So for this mechanical property, only tensile strength
tests are conducted. I have
used approximately 36 specimens, uncoated and coated including
specimens as dummy,
for me to practice on how to use the machine for the testing and
for the trial. These
specimens are divided into two main components, which are indoor
and water condition.
Through this, it will emphasize and focus to the effects of
presence of water in the kenaf
fibre composite plate.
4.3.1 Tensile Strength Test
As mentioned above, only tensile strength test is conducted to
obtain the mechanical
property of the specimen. This is due to the reality that
concrete beam has a significantly
low tensile strength even though it can withstand a very high
compressive stress.
Concrete has a constant of elasticity at a low stress but it
will start to decrease gradually
at a higher stress levels as there would be developments of
matrix cracking. Tension also
contributes to the development of crack on the concrete besides
shrinkage. Tension
cracking on the concrete beam is commonly happened when a
transversely applied load is
placed on the surface of the beam causing compression, and the
opposite surface is
enforced by tension. This is due to induced bending. In such a
way, the surface that
enforced with tension would likely to crack.
Hence the reinforced concrete beams are invented to support the
beam from
failure due to tensile stress applied. Along with the fact that
concrete needs to reinforced
at the tension area, kenaf fibre reinforced composite plate is
designed to reinforced the
concrete beam form tension externally. In such a degree, kenaf
composite plate will
provide an extra reinforcement from the surface to hold the
tensile stress.
To obtain tensile strength of the specimen, A tensile strength
test tallied to ASTM
D3039 is carried out. The specimens are subjected to tension
force until it reached the
state of failure, which is breaking. Machinery that responsible
in finding the tensile
strength of the composite plate is Universal Testing Machine
(UTM) model INSTRON
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56
8801. The size of specimens each is 250mm x 15mm x 6mm and it is
crucial to have a
specimen with thickness of less than 10mm, because that's the
maximum size of specimen
the machine can hold.
FIGURE 4.5: Universal Testing Machine (UTM) INSTRON 8801
The UTM INSTRON 8801 is connected to computer nearby, as the
results of the
tensile strength of specimens are directly transferred to the
compute using a specific
software. In the software, a basic set up is needed such as
setting up the size of specimen,
type of specimen, and also the rate of tension force applied on
the specimens. The rate is
definitely versatile as we can decide what rate to be used.
Theoretically, the lower the
rate, the more accurate the reading. However, if the rate is too
small, the graph of result
obtain will not be smooth and too disturbed, thus a proper rate
is essential. Also, the stress
and strain needs to be reset prevent the zero errors. For this
test, I have used 5mm/min of
rate for the tension force. After the result is procured, we can
save them into a desirable
folder.
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FIGURE 4.6: Specimens for tensile strength test
FIGURE 4.7: Zero error happened when the stress and strain is
not reset
4.3.1.1 Procedures
Conducting tensile strength test using UTM INSTRON 8801 can be
considered as quite
intricate. This is because first, the specimen must be placed
vertically without any slant as
Zero error
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58
it would disrupt the results. Secondly, we have to reset the
tensile strain and stress few
times as they would normally unstable. So the strain and stress
must be at the initial value
which is zero, then the testing can be proceed. Plus, if the
specimens aren't placed
properly or the characteristics disobey the requirements, the
machine will shut off
immediately resulted from a gradually decreased pressure.
However, thanks to the lab
technician for helping my partner and I in guiding us to conduct
the test properly.
Therefore, the procedure of the testing for each specimen is
described below.
1. The specimen holders are set at ample length suit for the
specimen.
2. The upper and lower grip holder are aligned in parallel.
3. The specimen is gripped firmly.
4. The stress and strain of tension is reset to zero value.
5. The testing started until the specimen reach its failure
state.
6. The 'finish' button is clicked and the graph of tensile
development is obtained.
7. The files are saved in a specific folder.
FIGURE 4.8: The technician guided us to set up the machine.
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FIGURE 4.9: Setting up the rate of tension, specimens' dimension
and type of specimens.
FIGURE 4.10: The specimens after failure
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60
4.3.2 Effects of the Presence of Water
As mentioned before, water plays a crucial role in weaken the
strength of kenaf fibre
reinforced composite plate. The disruption of the structure of
the plate happens when the
presence of water is exist between the fibres and the matrix
resin. It will disturb the
cohesion and bonding between the fibres and the epoxy resin, and
leading to decrease of
stability of the plate. Initially, when there is no water
molecule, the cohesion and bonding
are in completely stable. The plate would not stand a higher
tension when there is a
presence of water molecules. Thus, a further steps need to be
taken in order to prevent the
plate from absorbing water.
4.3.3 Uncoated and Coated Specimens
Since water is likely to disrupt the stability of the strength
of the composite plate, a proper
solution for this problem should be made. There are various ways
to prevent the
composite plate from being affected by water molecules, such as
pretreatment of the
fibres, and as well as by coating the specimens.
For the properties determination by various testing, after the
curing of the
fabricated kenaf fibre reinforced composite plate, the plate
needs to be cut into smaller
specimens. Initially when the plate is completely dried, there
are also exposed inner fibre
to the atmosphere. This increases the chances of moisture
absorption. It worsen the case
when the plate is cut into smaller pieces as bigger surface area
is exposed. So, the water
molecules even from the atmosphere would easily diffused into
the fibres in the plate.
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FIGURE 4.11: Cross section of kenaf fibre composite plate after
being cut into smaller
pieces
FIGURE 4.12: Penetration of water into the exposed surface
By coating the cut specimens, the water absorption can be
prevented because of
the epoxy's characteristics. Besides having a high flexural
strength and others, epoxy
resin is effectively waterproof. The covered exposed surface
will prevent from the water
to be absorbed. Besides prevent the inner structure of the plate
being filled with water
molecules, it will also acts as an extra shield and strengthener
for the plate. This
theoretically will increase the tensile strength of the
plate.
This explains the effectiveness and advantages of using epoxy
resin as addition
coating. Although there are many other choices such as polyester
and silicone, epoxy
resin provides a better strength. Besides, we can reuse the
excessive epoxy resin that has
been used of the fabrication of the kenaf fibre reinforced
composite plate. The fact that
the epoxy resin is not recyclable, at least we can decrease its
waste disposal to the
minimum.
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FIGURE 4.13: When the specimen is coated, the water cannot
penetrate the specimen
4.3.4 Indoor Condition
As stated before, for the mechanical property test, the tensile
strength test are conducted
under two conditions, indoor and water. For the indoor
condition, 6 uncoated and 6
coated specimens are used, excluding the dummy specimens. The
specimens are placed in
indoor for 7, 14 and 28 days. Although the specimens are not
exposed to water directly,
the atmosphere itself contains water moisture. So, this test
will determine whether the
moisture from the atmosphere can affect the strength of the
plate or not. A definition of
textbook tells that the rate of water absorption from the air is
not as slow as in the water,
due to the quantity of water molecules in the air. For the
testing, I have placed the
specimens in my room, as it is indoor. We are neglecting the
outdoor condition because
theoretically the water content in the air indoor and outdoor
are likely the same.
4.3.5 Water Condition
For this condition 20 specimens, uncoated and coated are used,
excluding the dummy
specimens. The specimens are submerged in water for 1, 3, 7, 14
and 28 days. Since the
water molecules are in maximum capacity in this condition, it is
decided that we test them
in more variables of days. The results according to days of
testing will make it clearer in
justifying the effects of water absorption in disturbing the
strength structure of kenaf fibre
reinforced composite plate.
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63
4.3.6 Results
The result obtained from the tensile strength test are tabulated
in two different table
according to the indoor and water conditions. For each state of
specimen, let say for this
kenaf fibre reinforced composite plate, in indoor condition for
7 days testing per se, there
would be 2 specimens will be tested and a higher value of
tensile stress is chosen. This is
because there are possibilities of error that can be made, such
as zero error and others.
Thus it would be safe to have more than one specimens for each
conditions. Furthermore,
a backup specimens are essential since the UTM INSTRON 8801 is
rather sensitive to
handle. The table below shows parts of the tensile strength
test's result.
TABLE 4.4: Results obtained from the tensile strength test
Maximum
Load (kN) Modulus (Mpa)
Maximum Tensile
Extension (mm)
Tensile Strain at Break
(%)
9.5 9807.46 2.16568 0.86627
TABLE 4.5: Maximum tensile stress for specimens under INDOOR
condition
Condition: Indoor
Days of testing Condition Specimen Max. Tensile Stress (MPa)
7
Uncoated KIU7-1 69.36
Uncoated KIU7-2 51.37
Coated KIC7-1 75.09
Coated KIC7-2 60.6
14
Uncoated KIU14-1 63.19
Uncoated KIU14-2 59.63
Coated KIC14-1 73.16
Coated KIC14-2 67.96
28
Uncoated KIU28-1 51.61
Uncoated KIU28-2 36.25
Coated KIC28-1 74.77
Coated KIC28-2 40.53
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From the results from the table above, the shaded result is the
chosen one, as the
value is higher. Note that for uncoated specimens, as the days
of testing increase, the
tensile stress can handled by the specimens is decrease. This
shows that the longer the
surface exposed to the atmosphere, the weaker the specimens can
be. The decrease of the
value in the results explains the role of water moisture content
in weaken the structure of
the plate. The next tables will show a clearer vision of the
decreasing tensile stress by
day. However, the maximum tensile stress for coated specimens to
endure are almost
constant by days.
TABLE 4.6: Simplified result for UNCOATED specimens under INDOOR
condition
Days of Testing