Effect of Grain Distribution on Resin Consumption and Mechanical Performance of GRP Pipes

Abstract

It was aimed to produce GRP pipes, having less resin consumption and higher mechanical properties by changing the grain distribution of fillers used in the core region. American Foundry Society (AFS) grain fineness number currently used in GRP pipe production, and the grain distribution determined to the Fuller equation, the exponent of which is 0.8 (F0.8), were used in the study. Chopped glass fibers, unsaturated polyester resin, and silica filler were used. It was manufactured three GRP pipes having 6m length and nominal diameter (DN) of 350mm by centrifugal casting technique. Initial specific ring stiffness and longitudinal tensile strength (LTS) tests were conducted on GRP pipes. After the longitudinal tensile tests of the produced GRP pipes, SEM images were taken from the core region and the morphological analyzes of the images were made. As a result of the study, when GRP pipes are produced using 14% less resin in F0.8 grain distribution, 44.11% higher stiffness and 50.4% higher LTS was obtained than the minimum value required in the standard.

Full text

Sakarya University Journal of Science
SAUJS
ISSN 1301-4048 e-ISSN 2147-835X Period Bimonthly Founded 1997 Publisher Sakarya University
http://www.saujs.sakarya.edu.tr/
Title: Effect of Grain Distribution on Resin Consumption and Mechanical Performance of
GRP Pipes
Authors: Şevki EREN, Özcan ÇAĞLAR, Neslihan GÖKÇE, Azime SUBAŞI, Serkan SUBAŞI
Recieved: 2021-02-16 00:00:00
Accepted: 2021-08-15 00:00:00
Article Type: Research Article
Volume: 25
Issue: 5
Month: October
Year: 2021
Pages: 1136-1147
How to cite
Şevki EREN, Özcan ÇAĞLAR, Neslihan GÖKÇE, Azime SUBAŞI, Serkan SUBAŞI; (2021),
Effect of Grain Distribution on Resin Consumption and Mechanical Performance of
GRP Pipes. Sakarya University Journal of Science, 25(5), 1136-1147, DOI:
10.16984/saufenbilder.878809
Access link
http://www.saujs.sakarya.edu.tr/en/pub/issue/65589/878809
New submission to SAUJS
http://dergipark.gov.tr/journal/1115/submission/start

Effect of Grain Distribution on Resin Consumption and Mechanical Performance
of GRP Pipes
Şevki EREN*
1
, Özcan ÇAĞLAR2, Neslihan GÖKÇE2, Azime SUBAŞI2, Serkan SUBAŞI2
Abstract
It was aimed to produce glass fiber reinforced pipes (GRP), having less resin consumption and
higher mechanical properties by changing the grain distribution of fillers used in the core
region. American Foundry Society (AFS) grain fineness number currently used in GRP pipe
production, and the grain distribution determined to the Fuller equation, the exponent of which
is 0.8 (F 0.8), were used in the study. Chopped glass fibers, unsaturated polyester resin, and
silica filler were used. It was manufactured three GRP pipes having 6 m length and nominal
diameter (DN) of 350 mm by centrifugal casting technique. Initial specific ring stiffness and
longitudinal tensile strength (LTS) tests were conducted on GRP pipes. After the longitudinal
tensile tests of the produced GRP pipes, SEM images were taken from the core region and the
morphological analyzes of the images were made. As a result of the study, when GRP pipes
are produced incorporating 14 % less body resin in F 0.8 grain distribution, 44.11 % higher
stiffness and 50.4 % higher LTS was obtained than the minimum value required in the standard.
Keywords: GRP pipe, filler materials, grain distribution, AFS grain fineness number, Fuller
equation.
1. INTRODUCTION
Glass fiber reinforced pipes (GRP) are generally
three-layered composite systems. These
composite systems consist of thin FRP layers on
the inner and outer surfaces of the pipe walls and
a polymer mortar layer in the center [1],[2],[3].
These pipes are produced by centrifugal casting
(CC) or filament winding (FW) methods
[2],[3],[4],[5]. GRP pipes must provide certain
design criteria, including short-term hydrostatic
failure strength, representing the longitudinal
* Corresponding author: seren@ahievran.edu.tr
1
Kırsehir Ahi Evran University.
ORCID: https://0000-0003-0773-4034,
2 Duzce University
E-Mail: ocaglar@superlit.com, nesligke@gmail.com, azimesubasi@duzce.edu.tr, serkansubasi@duzce.edu.tr
ORCID: https://0000-0002-6514-0691, https://0000-0001-5418-0551, https://0000-0002-1732-6686, https://0000-
0001-7826-1348
tensile strength (LTS) and initial specific ring
stiffness [2],[5]. The primary purpose of fillers is
to restrict the movement of the polymer chain,
thereby increasing hardness, abrasion resistance,
stiffness, and strength but reducing ductility [6],
[7],[8]. Glass fiber reinforced polymer composite
with particle-filled is formed by combining glass
fiber and mineral aggregates with a resin system
[9]. For this reason, GRP pipe manufacturers
prefer to apply a filling layer impregnated
between the FRP layers as an economical
alternative method [2]. AFS grain fineness
Sakarya University Journal of Science 25(5), 1136-1147, 2021

number is a grain distribution type used as a
general indication of sand fineness by most
foundries in the United States and calculated from
the grain distribution determined by standard
ASTM sieves [10]. Each fraction is multiplied
with a weighting factor, the results are added
together and divided by 100. AFS grain fineness
number gets bigger as the average size decreases
and is considered to be proportional to the number
of grains per unit weight [11]. AFS 35 (390 μm),
AFS 40 (340 μm), AFS 45 (300 μm), AFS 50 (280
μm), AFS 55 (240 μm), AFS 60 (220 μm), AFS
65 (210 μm), AFS 70 (195 μm), AFS 80 (170 μm),
AFS 90 (150 μm), etc. different AFS grain
fineness numbers have been currently using in the
industry [10]. GRP pipes and grain distributions
have been investigated by several researchers;
In the research conducted by Rafiee [2] it has been
reported that the effect of adding sand filler into
the polymer matrix as a core layer on the
mechanical properties of GRP pipes has not been
investigated enough by researchers. Kumar et al.
[12] has selected the silica sand with the range of
AFS 60-140 grain fineness number to explore its
potential effects on tensile properties of Al–7 %
Si alloy castings made by the EPC process. They
determined that the grain fineness number and
pouring temperature importantly affect the tensile
strength and elongation percentage after a
fracture. Fuller and Thompson [13] underlined the
important effect of aggregate grain distribution on
the physical and mechanical properties of
concrete. The problem of the best possible grain
distribution of aggregates and their contribution
to optimum proportioning for the concrete
mixture has been the issue of numerous
experimental and theoretical investigations. Shi
and Wei [14] examined the mechanical properties
of glass fiber reinforced plastic mortar pipes with
an inner diameter of 1500 mm under different
loading conditions. In their study, ring and axial
compressive strength and elastic modulus,
stiffness and fatigue test were carried out. It was
determined that the pipe stiffness was determined
as 2.3 MPa. As a result, it was concluded that the
composite with resin and quartz sand, increase the
compression strength and the effect of quartz sand
on compressive strength is more important than
the resin and glass fiber. Rafiee and Reshadi [15]
simulated and analyzed the functional failure in
composite pipes exposed to internal hydrostatic
pressure. A progressive damage modeling was
developed considering the effect of the core layer
added for increasing the pipe stiffness. The effect
of two primary parameters as core thickness and
the winding angles of cross plies were studied. It
was observed that first-ply-failure and functional
failure pressures increase linearly as the core
thickness increase. Gökçe et al. [16] analysed the
effects of the type of resin and fiber on the
mechanical behaviours of the polymer composite
pipe manufactured by the CC technic. Isophthalic,
ortophthalic, and vinyl ester resin were used as
matrix material, E and ECR glass fiber were used
as reinforcement material, and silica sand was
used as filler material. As a result, it was found
that the mechanical behaviours of the polymer
composite pipes changed with different types of
resin and fiber.
In this study, it was aimed to manufacture GRP
pipes having less resin consumption and higher
mechanical properties by changing the grain
distribution of the fillers used in the core region.
2. EXPERIMENTAL
2.1. Matrix Materials
Orthophthalic body resin (Boytek BRE 310) and
orthophthalic liner resin (BRE 816) were used in
GRP pipe production. Cobalt octoate (Co:
C16H30CoO4) (wt. 1 %) as an accelerator and
methyl ethyl ketone peroxide (MEKP: C8H18O6)
(wt. 1 %) as an initiator were used as additive
materials. Some mechanical properties of
orthophthalic body resin are given in Table 1.
Table 1 Physical and mechanical properties of
orthophtalic body resin
Property
Unit
Orthophthalic
Resin
Density
-
1.12
Viscosity
(cp)
250
Solid content
(%)
57
Tensile modulus
(MPa)
3550
Tensile strength
(MPa)
74
Flexural strength
(MPa)
125
Flexural modulus
(MPa)
3800
Elongation at Break (tensile)
(%)
3.15
Total volumetric shrinkage
(%)
8.0
EREN et al.
Effect of Grain Distribution on Resin Consumption and Mechanical Performance of GRP Pipes
Sakarya University Journal of Science 25(5), 1136-1147, 2021 1137

2.2. Filling Materials
Silica sand with AFS 40-45 grain fineness number
(SiO₂: 98.94 %; Al₂O₃: 0.08 %; Fe₂O₃: 0.1 %)
currently used by Superlit Pipe Industry Inc. as
filling material in GRP pipe production were
used, and the grain distribution determined to the
Fuller equation was used in the study. The
physical properties of silica sand are given in
Table 2.
Table 2 Physical properties of silica sand
Physical properties
Silica sand
Moisture content (%)
0.002
Relative density
2.55
Burning loss (%)
1.3
Dry specific gravity
2.55
Specific gravity saturated with water
2.61
Loose unit weight (g/cm³)
1.616
Cramped unit weight (g/cm³)
1.791
Water absorption (%)
2.03
Specific surface area (m²/kg)
12.07
Average grain size (micron)
237
2.3. Fiber Materials
Chopped E-glass fiber was used in the study. The
physical and mechanical properties of E-glass
fiber are given in Table 3.
Table 3 Physical and mechanical properties of
chopped E-glass fiber
Properties
Glass fiber
Moisture content (%)
0.92
Fiber weight (g/km)
2400
Binder content (%)
2.1
Number of ends
60
Fiber diameter
(micron)
16-20
Specific weight
2.60
Tensile strength (MPa)
3400
Elasticity modulus
(GPa)
77
Fiber length (mm)
50
2.4. Optimization of Filler Particle
Distribution Used in GRP Pipe Production
Some early grain distribution design studies on
polymer composites were performed using silica
sands in different grain distributions determined
according to the Fuller equation and also in AFS
40-45 grain fineness number. As a result of the
tests on the polymer composites, the best grain
distribution, which has the minimum resin
consumption and the best compressive strength,
was determined as F0.8 [17]. It has been
concluded that the use of this distribution in GRP
pipe production will be appropriate. The Fuller
equation used in the study is given in Equation 1
[13].
P % = (d / D)n (1)
P%: total percent of particles passing through (or
finer than) sieve
d: diameter of the current sieve,
D: maximum size of aggregate (1000 µm)
n: exponent of the equation, (n=0.8 for this study)
However, since F 0.8 grain distribution is not
available in the market, silica sands with
AFS 40-45 and AFS 110-140 grain fineness
number that is available in the market were mixed
to obtain F 0.8 grain distribution. For this reason,
as a result of the grain distribution analysis, a new
optimized mixture was formed by taking the
proportion of 20 % of AFS 110-140 grain fineness
number and 80 % of AFS 40-45 grain fineness
number by weight and this mixture was called as
F 0.8 (optimization 1). It was concluded that the
new mixture optimized is the closest grain
distribution to F 0.8 grain distribution. The grain
sizes of the sands used are in the range of 0-1000
microns. F 0.8 filler grain-size distributions used
in the study are represented in Table 4 and
different AFS and F 0.8 (optimization 1) filler
grain-size distributions are represented in Table 5.
A visual of all filler grain-size distributions
graphic used in the study are represented in Figure
1.
EREN et al.
Effect of Grain Distribution on Resin Consumption and Mechanical Performance of GRP Pipes
Sakarya University Journal of Science 25(5), 1136-1147, 2021 1138

Table 4 F 0.8 filler grain-size distributions
Grain sizes
(µm)
P, %
F 0.8
1
0.4
10
2.5
100
15.8
150
21.9
180
25.4
250
33
300
38.2
500
57.4
600
66.5
710
76
850
87.8
1000
100
Table 5 Different AFS and F 0.8 (optimization 1) filler
grain size distributions
Grain sizes
(µm)
P, %
AFS
40-45
AFS
110-140
F0.8 (optimization 1)
[AFS 110-140 (%20)
+ AFS 40-45 (%80)]
1
0
0
0
63
0
22
4
90
0
75
15
125
1
97
20
180
2
99.5
22
250
19
100
35
355
61
100
68
500
89
100
91
600
94
100
95
710
98
100
99
850
99
100
99
1000
100
100
100
Figure 1 Different filler grain size distribution graphics used in the study
EREN et al.
Effect of Grain Distribution on Resin Consumption and Mechanical Performance of GRP Pipes
Sakarya University Journal of Science 25(5), 1136-1147, 2021 1139

2.5. Manufacture of GRP Pipe
In this study, the CC method was preferred to
produce GRP pipes in a standard way when the
optimized mineral filling material mixture is
started to mass production. It was produced three
GRP pipes, having 6 m length and DN of 350 mm.
GRP pipes were aimed to be exposed to a nominal
pressure (PN) of 6 bar, have a nominal stiffness
(SN) of at least 10.000 N/m2, and the LTS value
of at least 135 N/mm. The pipe production
process by the CC method can be seen in Figure
2.
Figure 2 GRP pipe production process by the CC
method
Since the grain distributions of each pipe
produced are different, the pipe types were
numbered from 1 to 3. Necessary explanations
regarding the raw material usage amounts of the
related pipes produced using different grain
distributions are described below.
Pipe No (1) (Reference Pipe):
The reference pipe has been currently
manufacturing by Superlit Pipe Industry Inc.
chopped E-glass has been using as fiber
reinforcement, and silica sand with AFS 40-45
grain fineness number has been using as filler
material in this reference pipe production.
Pipe No (2):
In pipe no 2, chopped E-glass was used as fiber
reinforcement, and silica sand with
F0.8 (optimization 1) grain distribution was used
as filler material. In this pipe type, the pipe
production was carried out by incorporating 3.5 %
less body resin than the amount of resin used in
the reference pipe.
Pipe No (3):
In pipe no 3, chopped E-glass was used as fiber
reinforcement, and F 0.8 (optimization 1) grain
distributed silica sand was used as filler material.
In this pipe type, the pipe production was carried
out by incorporating 14 % less body resin than the
amount of resin used in the reference pipe.
The pipe no 1 was called as the reference pipe.
Initial specific ring stiffness and the LTS tests
were performed on the produced pipes. The
schematic representation of the pipe section
produced by the CC method and a visual of the
part cut from the produced pipes are shown in
Figure 3. The duties of the layers specified in the
pipe section are given in Table 6 [18].
Figure 3 The schematic representation of the pipe section produced by the CC method and a visual of the part
cut from the produced pipes
EREN et al.
Effect of Grain Distribution on Resin Consumption and Mechanical Performance of GRP Pipes
Sakarya University Journal of Science 25(5), 1136-1147, 2021 1140

Table 6 Duties of the layers specified in the pipe
section
Pipe
Layer
No
Function
Content
Thickness
1
An outer surface
protective layer
(outer barrier)
(UV, chemicals,
impact resistance,
etc.)
Resin and
sand
Min. 1 mm
2
Pressure layer
Resin and
chopped
fiber
While the wall
thickness is
increased to achieve
high pressure, the
thickness of the
layers in this region
is also increased.
3
CORE (filler zone)
- stiffness zone
Resin, sand
and small
amount of
chopped
fiber
4
Pressure layer
Resin and
chopped
fiber
While the wall
thickness is
increased to achieve
high pressure, the
thickness of the
layers in this region
is also increased.
5
Liner layer to
ensure sealing
Resin and
chopped
fiber
6
An inner surface
protective layer
(corrosion layer)
Pure Resin
Min. 1 mm
In GRP pipes, “resin + sand + chopped fiber”
materials are used in the third layer, which is
defined as the filling layer (CORE), to increase
the stiffness performance. In these GRP pipes, the
thicker pipe walls are necessary to increase the
apparent pipe stiffness [2],[18].
2.6. Initial Specific Ring Stiffness
Initial specific ring stiffness test was carried out
according to ISO 7685: 2019 was used as the
reference specified in the relevant standard [19].
In the study, the stiffness samples were cut from
the mold removal part and feeding part of GRP
pipes. The outer diameter of the pipe was
measured with a caliper on the stiffness samples
and measurements were recorded. Subsequently,
a deflection of 3 % was applied to the stiffness
samples and deflection values recorded 2 minutes
later and then the stiffness values were calculated.
The stiffness test samples of GRP pipes are given
in Figure 4.
Figure 4 The stiffness test sample images of GRP
pipes
2.7. Longitudinal Tensile Strength Test
ISO 8513: 2016 Method (A), was used to
determine the LTS value of the pipe samples [20].
5 longitudinal tensile test samples were cut in a
longitudinal direction from GRP pipes, and the
LTS test was carried out. A visual of specific ring
stiffness and the LTS test is given in Figure 5.
Figure 5 A visual of the specific ring stiffness and the
LTS test
EREN et al.
Effect of Grain Distribution on Resin Consumption and Mechanical Performance of GRP Pipes
Sakarya University Journal of Science 25(5), 1136-1147, 2021 1141

3. RESULTS AND DISCUSSIONS
3.1. Raw Material Usage Amounts in GRP
Pipes
Raw material usage amounts according to pipe
diameter and nominal pressure values of the GRP
pipes are given in Table 7.
Resin reduction amounts were determined by
foresight in this study. Of course, different resin
reduction ratios can be used.
3.2. Initial Specific Ring Stiffness Test Results
Average initial specific ring stiffness values of
GRP pipes, which are produced in different filler
grain distributions and numbered from 1 to 3, are
given in Table 8 and Figure 6.
Table 7 Raw material usage amounts of GRP pipes
DN/PN/SN
(mm/bar/N/m2)
Pipe No
Fiber
Grain
Distribution
Type
Body + Liner
Resin (kg)
Total
resin (kg)
Fiber
amount
(kg)
Filler
amount
(kg)
Total weight
(kg)
350/06/10.000
Pipe No: (1)
(Reference)
E- glass
AFS 40-45
29+14
43
16,6
77,1
136,7
Pipe No: (2)
E- glass
Fuller 0.8
28+14
(incorporating
3,5% less body
resin)
42
16,2
81
139,2
Pipe No: (3)
E- glass
Fuller 0.8
25+14
(incorporating
14% less body
resin)
39
16,2
79,8
135
Table 8 Average initial specific ring stiffness values of GRP pipes
DN/PN/SN
(mm/bar/N/m2)
Pipe No
Fiber
Grain
Distribution
Type
Stiffness (N/m2)
Range
Min.
Max.
Std.
Error
Std.
Dev.
Average
350/06/10.000
Pipe No: (1)
(Reference)
E glass
AFS 40-45
1626
14581
16207
334
668
15.369
Pipe No: (2)
E glass
Fuller 0.8
2271
15361
17632
494
988
16.697
Pipe No: (3)
E glass
Fuller 0.8
1710
13453
15163
339
758
14.411
Figure 6 Change of the stiffness values according to the pipe type
It was determined that all GRP pipes produced
within the scope of the study reached the minimum stiffness value of 10.000 N/m2 required
in the standard and even higher stiffness values.
EREN et al.
Effect of Grain Distribution on Resin Consumption and Mechanical Performance of GRP Pipes
Sakarya University Journal of Science 25(5), 1136-1147, 2021 1142

In the pipe number 2 with F 0.8 (optimization 1)
grain distribution, which is used as an alternative
to AFS 40-45 grain fineness number, 8.64 %
higher stiffness was obtained by incorporating 3.5
% less body resin compared to the reference pipe
production.
In the pipe number 3 with F 0.8 (optimization 1)
grain distribution, a reduction of 6.23 % in the
stiffness was obtained by incorporating 14 % less
body resin compared to the reference pipe
production, but 44.11 % higher stiffness value
was obtained than the minimum stiffness value of
10.000 N/m2 required in the standard.
As the stiffness test results, it was concluded that
it is possible to produce GRP pipes with F 0.8
(optimization 1) grain distribution at a lower cost
by providing up to the ratio of 14 % resin
consumption.
3.3. LTS Test Results
Average LTS values of GRP pipes are given in
Table 9 and Figure 7.
It was determined that all GRP pipes produced
within the scope of the study reached the
minimum LTS value of 135 N/mm required in the
standard and even higher strength values.
Table 9 Average LTS values of GRP pipes
DN/PN/SN
(mm/bar/N/m2)
Pipe No
Fiber
Grain
Distribution
Type
LTS (N/mm)
Range
Min.
Max.
Std. Error
Std. Dev.
Average
350/06/10.000
Pipe No: (1)
(Reference)
E glass
AFS 40-45
57
190
247
16.895
29.263
214.97
Pipe No: (2)
E glass
Fuller 0.8
32
199
231
8.010
16.020
212.98
Pipe No: (3)
E glass
Fuller 0.8
26.1
185.8
211.9
8.6834
15.0401
203.167
Figure 7 Change of the LTS values according to the
pipe type
In pipe number 2 with F 0.8 (optimization 1) grain
distribution, 57.8 % higher LTS value was
obtained than the minimum LTS value of 135
N/mm required in the standard by incorporating
3.5 % less body resin.
In pipe number 3 with F0.8 (optimization 1) grain
distribution, 50.4 % higher LTS value was
obtained than the minimum LTS value of 135
N/mm required in the standard by incorporating
14 % less body resin.
As the LTS test results, it was concluded that it is
possible to produce GRP pipes with F 0.8
(optimization 1) grain distribution at a lower cost
by providing up to the ratio of 14 % resin
consumption.
Kumar et al. [12] determined that the grain
fineness number and pouring temperature
importantly affect the tensile strength. Fuller and
Thompson [13] underlined the important effect of
aggregate grain distribution on the physical and
mechanical properties of concrete. In this study, a
better grain distribution was obtained by using the
F 0.8 (optimization 1) grain distribution in the
core region in GRP pipe production and for this
reason, it was concluded that F 0.8 (optimization
1) grain distribution is effective in reducing resin
consumption.
EREN et al.
Effect of Grain Distribution on Resin Consumption and Mechanical Performance of GRP Pipes
Sakarya University Journal of Science 25(5), 1136-1147, 2021 1143

3.4. SEM Images and Morphological Analysis
of GRP Pipes
• After the longitudinal tensile tests of the
produced GRP pipes, SEM images were taken
from the core region and the morphological
analyzes of the images were made. SEM images
in the core region of AFS 40-45 and F 0.8
(optimization 1) grain distributed GRP pipes are
shown in Figure 8 and Figure 9 respectively.
When the SEM images in the core region of AFS
40-45 grain distributed GRP pipes in Figure 8
were examined, it was observed that there were
air gaps and matrix cracks. However, it has been
observed that the fillers are homogeneously
distributed, and the random orientation of the
fibers is good. The increase in tensile strength of
composites is due to the increase in fiber content,
due to the fact that fibers play an important role in
tensile strength and their ability to resist crack
propagation. When the Initial Specific Ring
Stiffness and LTS test results of AFS 40-45 grain
distributed GRP pipes are evaluated, it is thought
that the amount of fiber used for this mixture is
enough to fulfill this task.
When the SEM images in the core region of
F 0.8 (optimization 1) grain distributed GRP pipes
in Figure 9 were examined, it was observed that
the fillers were homogeneously distributed, and
the random orientation of the fibers is good. In
addition, it was observed that the matrix structure
was adhered on the surface of the broken fiber
pieces and fiber cavities were formed on the
broken matrix surface. When this situation is
evaluated together with the Initial Specific Ring
Stiffness and LTS test results of GRP pipes with
Figure 8 SEM images in the core region of AFS 40-45 grain distributed GRP pipes
Figure 9 SEM images in the core region of F0.8 grain distributed GRP pipes
EREN et al.
Effect of Grain Distribution on Resin Consumption and Mechanical Performance of GRP Pipes
Sakarya University Journal of Science 25(5), 1136-1147, 2021 1144

F 0.8 (optimization 1) grain distribution, it is
understood that the matrix and fiber interface
bond strength is strong. Considering these results,
it was concluded that it is possible to use lower
rates of resin in GRP pipes with F 0.8
(optimization 1) grain distribution in this study.
4. CONCLUSIONS
In this study, silica sands with AFS 40-45 grain
fineness number currently used in GRP pipe
production were used, and alternatively, F 0.8
grain distributions were used to reduce the resin
consumption and increase the mechanical
properties. As a result of the study;
It was determined that mechanical properties such
as stiffness and longitudinal tensile strengths
decreased as a result of reducing the amount of
resin. However, all GRP pipes produced within
the scope of the study reached the minimum
stiffness, and the LTS value required in the
standard and even higher values.
In the pipe number 2 with F 0.8 (optimization 1)
grain distribution, 8.64 % higher stiffness was
obtained compared to the reference GRP pipe
production and 57.8 % higher LTS value was
obtained than the minimum LTS value of 135
N/mm required in the standard by incorporating
3.5 % less resin.
In the pipe number 3 with F 0.8 (optimization 1)
grain distribution, 44.11 % higher stiffness value
was obtained than the minimum stiffness value of
10.000 N/m2 and 50.4 % higher LTS value was
obtained than the minimum LTS value of 135
N/mm required in the standard by incorporating
14 % less resin.
As a result of the study, when GRP pipes are
produced incorporating 14 % less resin in F 0.8
(optimization 1) grain distribution, 44.11 %
higher stiffness and 50.4 % higher LTS value was
obtained than the minimum value required in the
standard.
In other words, it was concluded that F 0.8
(optimization 1) grain distribution is effective in
reducing resin consumption, and it is possible to
produce GRP pipes with F 0.8 (optimization 1)
grain distribution at a lower cost by providing up
to the ratio of 14 % resin consumption.
Acknowledgments
The authors gratefully acknowledge the financial
support of the Scientific and Technological
Research Council of Turkey (TUBITAK) and like
to thank Superlit Pipe Industry Inc. for carrying
out GRP pipe productions.
Funding
This work was supported by The Scientific and
Technological Research Council of Turkey
(TUBITAK), TUBITAK 1505: University-
Industry Cooperation Project [Grant Number:
5140058], and GRP pipe productions were carried
out by Superlit Pipe Industry Inc., at Kaynaşlı /
DÜZCE factory in Turkey.
The Declaration of Conflict of Interest/
Common Interest
The authors declare that they have no known
competing for financial interests or personal
relationships that could have appeared to
influence the work reported in this paper.
Authors' Contribution
The authors contributed to the study as follows.
Şevki EREN: Investigation, Writing- Original
draft preparation, Methodology, Formal analysis
(35 %), Özcan ÇAĞLAR: Conceptualization,
Methodology (20 %), Neslihan GÖKÇE:
Conceptualization, Methodology (15 %), Azime
SUBAŞI: review & editing, Visualization,
Validation (15 %), Serkan SUBAŞI:
Methodology, Supervision, Project
administration (15 %).
The Declaration of Ethics Committee Approval
This study does not require ethics committee
permission or any special permission.
EREN et al.
Effect of Grain Distribution on Resin Consumption and Mechanical Performance of GRP Pipes
Sakarya University Journal of Science 25(5), 1136-1147, 2021 1145

The Declaration of Research and Publication
Ethics
The authors of the paper declare that they comply
with the scientific, ethical and quotation rules of
SAUJS in all processes of the paper and that they
do not make any falsification on the data
collected. In addition, they declare that Sakarya
University Journal of Science and its editorial
board have no responsibility for any ethical
violations that may be encountered, and that this
study has not been evaluated in any academic
publication environment.
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Effect of Grain Distribution on Resin Consumption and Mechanical Performance of GRP Pipes
Sakarya University Journal of Science 25(5), 1136-1147, 2021 1147