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Application of Recycled Polyethylene Terephthalate (PET) Fibers
to produce Fiber Reinforced Concrete pipes
R.M.M.P Rathnayaka1, De Silva Sudhira1 and De Silva Subashi1
1Department of Civil and Environmental Engineering Faculty of
Engineering University of Ruhuna
Hapugala, Galle Sri Lanka
E-mail:[email protected]
Abstract: Fiber reinforced concrete is one of the prominent
solutions for many problems that concrete had from its early stage.
Polyethylene terephthalate (PET) fiber is a sustainable solution
for fiber reinforced concrete since it is an eco-friendly material.
Manufacturing of the cage form of the conventional reinforcement
bars adjusted for concrete pipes requires special bending, welding,
and placement machinery, and also it is time-consuming. Objective
of this study is to investigate application of PET fibers as a
replacement material for steel reinforcement cage in reinforced
concrete pipe element. At the initial stage concrete cubes were
cast with different fiber compositions (i.e., 0%,1%,2% and 3%) for
water cement ratio of 0.3 and 0.45. Three sets of specimens (Plain
concrete, Reinforced concrete and PET fiber concrete) were
subjected to three-edge-bearing test. It was observed that 2% of
PET fiber content contributed to achieve optimum compressive
strength of 45.8 MPa for the concrete having 0.3 water cement
ratio. In addition, it was found that PET fiber reinforced concrete
is the most applicable method for production of concrete pipes.
PET-fibre concrete pipes seem to be an economical alternative to
the classically-reinforced-concrete pipes. Keywords: Recycled PET,
Compressive strength, Cylindrical pipes, Three edge bearing
test
1. INTRODUCTION
Fiber reinforced concrete (FRC) has become a prominent solution
for the drawbacks of ordinary concrete. For example, pavement
laying, shotcrete tunnel linings, blast resistant concrete,
overlays, and application to mine construction showed better
performance with FRC compared with ordinary concrete (Ochi et al,
2007). In experimental studies, Fraternali (2011) found that FRC
has improvement in the compressive strength compared with that of
the normal concrete. Further, it has been found that the
compressive strength depends on the fiber characteristics: length,
diameter and volume.
Cylindrical pipes, which can be manufactured using fiber
reinforced concrete, are often manufactured with steel
reinforcements and used to convey liquids. However, there are many
advantages of using steel fiber reinforced concrete over the
ordinary steel reinforcement pipes. Manufacturing of the cage form
of the conventional reinforcement bars requires special bending,
welding, and placement machinery, and time consuming. Steel fibres
of standard sizes, on the other hand, can be added to the pan-mixer
of any concrete plant as another aggregate or mineral admixture.
Without any extra process for modification, steel-fibre concrete
can be produced and cast in the moulds similar to the ordinary
plain concrete. Therefore, steel-fibre concrete pipes seem to be an
economical alternative to the classically-reinforced-concrete
pipes. Most of the times, these cylindrical pipes are used to
convey liquid, such as water and waste water. In the process of
conveying, steel fiber is exposed to the water. As a result, steel
fiber may corrode and durability of the pipe would reduce. To
overcome this problem an alternative type of fibers that are not
vulnerable to corrosion can be used.
Due to rapid development in technology, the use of PET materials
to manufacture containers has been increased. Among them, PET
bottles used for beverage containers has become very popular,
although PET bottles eventually become an environmental pollutant
due to their in proper recycling process (Kim et al, 2010).Use of
recycled PET fiber in fiber reinforced concrete pipes would provide
a
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mailto:[email protected]
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sustainable solution for the environment pollution while
increasing durability of the pipes. Objectives of this study
are
• To investigate the optimum mix proportion and strength
characteristics of PET fiber reinforced concrete.
• To investigate the mechanical and durability characteristics
of short PET fiber reinforced concrete made with short PET
fibres.
2. METHODOLOGY
2.1 Pet Fiber Material
PET fibers, used in this study, were collected from Beira Group,
Horana, Sri Lanka. PET fibber was added on the volume basis (0%,
1%, 2%, and 3% of total volume), and it would not replace any
material in the concrete. Each PET fiber addition was done for two
water cement ratios: 0.3 and 0.45.The diameter and the length of
the PET fiber was 0.7 mm and 50 mm, respectively (Figure 1).
Figure 1 PET fiber
2.2 Experimental Procedure
2.1.1. Compressive Strength
Cubes having the size of 150 mm x 150mm x 150 mm were cast
according to BS 1881 -108 (1988) and cured until the testing day as
described in BS1881-111(1988).Concrete was mixed based on the mix
design in accordance with BS 5328 .In order to achieve a workable
mix, Rheobuild 1000 was added to the concrete mix as a high-range
water-reducing admixture. Concrete crushing machine, available in
the Buildings Material Laboratory, was used to crush the cubes
(Figure 2(a)) at the age of 3, 7, 14, 21, and 28 days. At these
ages, the compressive strengths were determined.
2.1.2. Tensile Strength
Three cylindrical specimens having the standard size (150mm
diameter and 300mm height) (BS 1881:144 (1988)) were cast and split
tensile strength of concrete was determined. For each specimen,
split tensile strength was investigated by using the compression
testing machine as shown in Figure 2 (b). In addition, slump of the
mixture was measured for each mix proportion.
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Figure 2 Testing of specimens: (a) Compressive strength test,
(b) Split tensile strength test.
2.1.3. Cylindrical Culverts
Six cylindrical culverts were cast (Figure 3) using three
different mixtures: plain concrete, reinforced concrete and fiber
reinforced concrete (Table 1). The fiber reinforced cylindrical
culvert was cast using the optimum concrete mixture, which gave the
optimum value for compressive strength, tensile strength and
slump.
Figure 3 Procedure of casting cylindrical culverts; (a)
Assembling of the mould. (b) Steel reinforcement cage, (c)
Concreting, (d) Curing
a b
(a) (b)
(c) (d)
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(a) (b)
Figure 4 Schematic diagram of test apparatus (a) Front view, (b)
Side view
Table 1 Material composition of cylindrical culvert
Specimen Steel reinforcement PET fibers (Total volume)
Plain concrete - -
Reinforced concrete 6mm mild steel at
120mm c/c spacing
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Fiber reinforced concrete
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2%
Testing of cylindrical culverts was performed in accordance with
BS5911 Part 100 (1988). According to the standard, three edge
bearing test was performed as shown in Figure 4. The proof load was
obtained and ultimate load that the culvert can sustain was
calculated. Proof load is the line load that a pipe can sustain
without the development of cracks width exceeding 0.25 mm or more
over a distance exceeding 300mm in a three edge beading test [BS
5911 Part 100 (1988)]. The ultimate load was determined by
multiplying the proof load by 1.5. A 50x50mm grid was drawn on the
surface of the cylinder in order to locate the crack locations.
Crack widths were measured using the filler gauge.
3. RESULTS AND DISCUSSION
3.1 Compressive Strength
The variation of compressive strength of fiber reinforced
concrete is shown in Figure 5.It can be observed that for fiber
reinforced concrete, the compressive strength increases with the
age of the concrete for both water cement ratios of 0.30 and 0.45,
the similar behaviour that can be expected for normal concrete.
However, at each age, the compressive strength of the fiber
reinforced concrete is less compared with that for the normal
concrete for both water cement ratios of 0.3 and 0.45.For water
Actuator arm
Top support
Bottom supports
LVD
LVDT
Loading beam
500mm
300mm Diameter
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cement ratio 0.30, strength development in fiber reinforced
concrete, at 3,7,14 and 21 day is lesser than that for the normal
concrete. However, the compressive strength at 28 day is
considerably higher in normal concrete than that in fiber
reinforced concrete. Table 2 shows the reduction in 28 day
compressive strength with fiber percentage for water cement ratio
of 0.45 and 0.30. It can be seen that, for the water cement ratio
of 0.45, there is 42.35 % reduction in the compressive strength in
28 day comparing to the control specimen for a fiber 1%. However,
for a water cement ratio of 0.3, the variation of 28 day
compressive strength with the fiber percentage of 1% is 11.29%.
Ochi (2006) conducted similar test and identified that compressive
strength of PET FRC is increasing with increasing the fiber
content. This deference might be due to the properties of PET fiber
used in two studies: Ochi had used fibers which has 40mm length
whereas 50mm length PET fiber was used in the current study. Except
the length of the PET fibers all other properties were similar PET
fibre used in the current study. In is study, the maximum
improvement (i.e., 5.98 %.) was recorded for 1% of fiber content
using 0.55 water cement ratio. Beyond 1% of fiber, the compressive
strength decreases with the increment of fiber content. However,
the current study indicates a reduction in compressive strength
irrespective of the fiber contents (1%, 2%, & 3%) for both
water cement ratios of 0.30 and 0.45.
(a) (b)
Figure 5 Variation of compressive strength with age of the
concrete; (a) Water cement ratio 0.45, (b) Water cement ratio 0.30
[please edit the Figure 5(b) as in the Figure 5(a)]
Table 2 Reduction of compressive strength (%) with fiber
percentage for different water cement ratios: 0.3 and 0.45
3.2 Tensile Strength
Figure 6 shows the variation of tensile strength with the PET
fibre content. It can be found that there is an improvement in the
tensile strength in the fiber reinforced concrete for water cement
ratio 0.3 and 0.45. With the increment of fiber content the tensile
strength increases. Specimens with 0.3 water cement ratio exhibits
higher tensile strength than 0.45 water cement ratio.
Fiber percentage (%) Compressive strength reduction (%)
0.45 W/C ratio 0.30 W/C ratio
1 42.35 11.29
2 42.14 8.92
3 37.61 11.12
0
10
20
30
40
50
3 7 14 21 28
Com
pres
sive
Str
ess
(MPa
)
Days Control Specimen 1% PET
2% PET 3% PET
0
10
20
30
40
50
3 7 14 21 28
Com
pres
sive
Str
engt
h (M
Pa)
Days Control Specimen 1% PET
2% PET 3% PET
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Sandaruwani et al (2012) identified that fiber content can be
increased up to 2% with an improvement in the tensile strength in
concrete. The tensile strength will reduce as the fiber content
increase beyond 2%. However, Arful (2015) observed that the
inclusion of PET fiber above 1.0% decreases the tensile strength in
concrete. The inclusion of PET fiber improved the tensile property
and showed the ability in absorbing energy in the post-cracking
state due to the bridging action imparted by the fibers during
cracking.
Figure 6 Variation of tensile strength with fiber content for
water cement ratio 0.3 and 0.45
3.3 Slump
The variation of the slump values with the fiber content is
shown in Figure 7. With increasing the fiber content, slump value
of the concrete mixture decreases. In the case of 0.3 water cement
ratio,3% of PET fiber content the slump value is 45mm. For domestic
applications such a water cement ratio is not recommended, because
of low workability.
Figure 7 Variation of slump with the fiber content
3.4 Load Bearing Test
Reinforced concrete cylinder shows an improvement in ultimate
load over the plain concrete (Figure7). It was identified that PET
fiber concrete performs well in bearing test comparing to the steel
reinforced concrete and plain concrete: there is a significant
reduction in the crack length and width in the fiber reinforced
cylinder.
0.00.51.01.52.02.53.03.54.0
control 1% PET 2% PET 3% PET
Tens
ile S
tren
gth
(MPa
)
0.45 w/c ratio 0.3 W/C ratio
0
50
100
150
200
250
300
Control 1% PET 2% PET 3% PET
Slum
p (m
m)
0.45 W/C Ratio 0.3 W/C Ratio
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Figure 8 Crack patterns (a) Plain concrete, (b) Reinforced
concrete, (c) Fiber reinforced concrete
Figure 9 Load vs. deflection curve for cylindrical culverts
Plain concrete pipe do not comply with the BS 5911 Part 100
requirements in terms of ultimate load (Figure 8). Both reinforced
concrete culverts and fiber reinforced culverts satisfy the
requirement of BS 5911 Part 100.Comparing to a previous study by
Tefarul et al (2007) , , current study shows a significant
improvement in ultimate load, crack width reduction and also the
length of the crack. In addition, PET fiber reinforcement has an
advantage over normal steel fibers because corrosion can be
eliminated by using PET fiber reinforced concrete to produce
cylindrical culverts.
4. CONCLUSIONS
For water cement ratio of 0.3 and 0.45, the workability of fresh
concrete decreases with the addition of PET fiber, although the
geometry of fibers has a small effect on the workability of
concrete.The reduction in 28 day compressive strength in PET fiber
reinforced concrete is less for water cement ratio of 0.3 compared
to that for water cement ratio of 0.45, indicating that 0.3 water
cement ratio can be considered as the optimum water cement ratio.
In addition, 2% of PET fiber percentage was identified as the
optimum fiber content for PET fiber reinforced concrete.
Load
(kN
/m)
35 30 25 20 15 10 5 0
0 1 2 3 4 5 6
Deflection (mm)
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The tensile strength that is required for cylindrical culverts,
increases with the inclusion of PET fiber showing the ability in
absorbing energy in the post-cracking state due to the bridging
action imparted by the fiber. During cracking there is a
significant reduction in the crack length and width in the fiber
reinforced cylindrical culverts.
ACKNOWLEDGEMENT
The authors would like to express their gratitude to Faculty of
Engineering Research Grant 2015 for providing necessary financial
support and Department of Civil and Environmental Engineering,
Faculty of Engineering, University of Ruhuna for the supports to
carry out the research work successfully. The authors also wish to
thank Lal Construction for the support extended in preparation of
specimens.
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Young-Chul, 2010. Material and structural performance evaluation of
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pp. 448-455. Tefarul Haktanir, Kamuran Ari, Fatih Altun,Okan
Karahan, 2007. A comparative experimental investigation of concrete
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