RTM Underground Pipes
-
Upload
mithileshmaverick -
Category
Documents
-
view
34 -
download
3
Transcript of RTM Underground Pipes
Composite Structures 68 (2005) 267–283
www.elsevier.com/locate/compstruct
Development of the trenchless rehabilitation processfor underground pipes based on RTM
Woo Seok Chin, Dai Gil Lee *
Mechanical Design Laboratory with Advanced Materials, Department of Mechanical Engineering, Korea Advanced Institute of Science and
Technology, ME3221, Guseong-dong, Yuseong-gu, Daejeon-shi 305-701, South Korea
Available online 26 April 2004
Abstract
In order to overcome the disadvantages of conventional excavation technology for repairing and replacing worn-out under-
ground pipes, various trenchless technologies have been developed and tried. But trenchless technologies so far developed have some
drawbacks such as high cost and inconvenience of operation.
In this study, a rehabilitation process for underground pipes has been developed using vacuum assisted resin transfer molding
(VARTM) with glass fiber fabric preform to overcome the disadvantages of present trenchless technologies. For the reliable
operation of the developed method, a simple method to apply pressure and vacuum to the reinforcement was devised with a flexible
mold technology.
From the investigation, it has been found that the developed process requires shorter operation time and lower cost with smaller
and simpler operating equipments than those of the conventional trenchless technologies.
� 2004 Elsevier Ltd. All rights reserved.
Keywords: Trenchless; Rehabilitation; Underground; RTM; CIPP; Dielectrometry
1. Introduction
Underground pipes, such as sewer and water-supply
pipes, gas pipes, shield pipes of communication cables
and electric power cables, etc., have been constructed all
over the world, and they are gradually increased in
proportion to industrialization and increase of income.
But these underground pipes have been undergone sev-eral problems such as cracks, breakages, or corrosion
due to the inappropriate design, careless management,
and the aging of pipe materials [1]. Since all of these
problems could lead to huge disaster and loss of social
fund, such as soil and water pollution, ground subsi-
dence, and explosion due to the gas leakage, the large-
scale rehabilitation of those damaged underground
pipes is very imminent. In order to solve these problems,the excavation technology has been used widely, which
replaces the damaged pipe with new one through the
*Corresponding author. Tel.: +82-42-869-3221; fax: +82-42-869-
5220/5221.
E-mail address: [email protected] (D.G. Lee).
URL: http://scs.kaist.ac.kr.
0263-8223/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.compstruct.2004.03.019
excavation of the ground. Since such a conventional
method has many drawbacks and irrationality induced
by the needless excavation of the ground, various
trenchless (sometime called excavation free or no-dig)
technologies without any excavation of the ground have
been developed and tried worldwide. However, these
technologies also have many disadvantages such as high
processing cost, inconvenience of operation and limitedapplications [1]. Since RTM has the capability to fab-
ricate large and complex three-dimensional anisotropic
fiber reinforced composite structures at the designed
position with low production cost, it may be plausible to
apply RTM to repair large underground pipes [2]. Al-
though there are many researches that are related to the
trenchless rehabilitation technologies and RTM [3–6],
the RTM process to repair underground pipes has notbeen attempted until now.
Therefore, in this study, a new trenchless rehabilita-
tion process of underground pipes to overcome such
problems of former trenchless technologies and ade-
quate to the situation of high traffic road, has been tried
and achieved with E-glass fiber fabric preform and
unsaturated polyester resin by vacuum assisted resin
transfer molding (RTM).
268 W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283
Also several different combinations of reinforcing fi-
ber preform have been tried through material tests and
experiments. In order to remove the micro void and
excessive resin within the reinforcing element and en-hance the resin wetting efficiency, the void removal
method using porous breathing tubes has been devised
and tested. For the reliable process, the wetting and
curing status of instilled resin were on-line monitored
using a dielectric sensor and a dielectrometer. After the
rehabilitation experiment on a small scale had been
performed successfully, actual repairing experiments
have been performed at the real concrete conduits. Fi-nally, the efficiency of the developed process was eval-
uated with respect to processing variables, such as
process cost and time, which were compared with those
of the conventional trenchless technology. Also, the
design criteria for the reinforcing element were sug-
gested to assure the sufficient reinforcing effect with
minimum material cost.
2. Trenchless rehabilitation process using RTM
2.1. Introduction of developed process
The rehabilitation process composed of four steps is
studied in this paper. Fig. 1 shows the process which is a
modification of the general RTM process. The range ofinternal diameter of the underground pipes for the
Fig. 1. Repairing processes of underground pipes with RTM: (a) preprocessin
sealing; (d) removal of wrinkles and twists of the reinforcing element; (e) inje
removing voids and excessive resin within the preform.
application of the developed process is 150–1000 mm,
and the length of pipe can be up to 50 m.
Step 1: After cleaning the interior of target conduits
(underground pipes), a wire is placed through conduits bythe mobile robot as shown in Fig. 1(a). Then, as shown
in Fig. 1(b), the reinforcing element of Fig. 2 is installed
at the designated position of conduits by a winding
machine. The adhesive of suitable viscosity is pasted on
the outer protection skin, which gives lubrication effect
during the dragging process as well as adhesion between
the reinforcing element and the target conduits.
Step 2: After placing the reinforcing element in theconduit, the both ends are closed and sealed as shown in
Fig. 1(c) using two specially designed covers. At this
time, the covers and the reinforcing element are clamped
with a band clamp that is tightly fitted into the groove of
the cover in the manner as shown in Fig. 3. After sealing
both ends of the reinforcing element, the compressed air
or nitrogen gas is supplied into the inside cavity through
the air inlet of covers to expand the inner protectionskin. This makes the outer protection skin and fiber
preform contact closely to the inner surface of the
conduits, and removes wrinkles and twists in the rein-
forcing element that might occur during the placing
operation as shown in Fig. 1(d). Then the pressure in the
cavity is removed, which helps the easy resin transfer at
the next stage.
Step 3: A predetermined amount of unsaturatedpolyester resin is injected into the fiber preform with a
g; (b) placing of the reinforcing element; (c) attaching of the covers and
ction of polyester resin; (f) wetting of resin into the fiber preform and
Fig. 3. Clamping method of covers and the positions for pasting
adhesive.
Table 1
Material properties of the cured unsaturated polyester resin (Aekyung
PC670)
Property Value
Flexural strength (MPa) 104
Flexural stiffness (GPa) 3.9
Tensile strength (MPa) 54
Tensile modulus (GPa) 4.1
Tensile strain (%) 1.5
Curing conditions: MEKPO (of 55% peroxide) 1%+6% Co-Naph
0.1% Room temperature/24 h+ 60 �C/5 h.
Inner Protection Skin
Glass-fiber Preform
Outer Protection Skin
Fig. 2. Configuration of the reinforcing element.
W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283 269
RTM machine through the resin inlet of the cover as
shown in Fig. 1(e). Due to the low viscosity of the
unsaturated polyester resin, it is easy to transfer theresin into the fiber preform under low pressure.
Step 4: After injecting the resin, the compressed air or
nitrogen gas is fed into the cavity again to make the
injected resin wet the fiber preform uniformly as well as
bringing the reinforcing element into close contact with
the inner surface of the conduit as shown in Fig. 1(f).
The process is performed while a vacuum is applied to
the reinforcing element through the air vent of the cover,which helps the resin wetting and removes the micro
void and excessive resin within the fiber preform. Also
the volatiles produced during the cure of polyester are
evacuated through the air vent of the cover. When the
surplus resin and void within the fiber preform are
completely removed, the wetting of the fiber preform
and the resin flow are ceased, followed by resin cure. In
order to prevent the resin within the fiber preform fromflowing down due to the gravity, the pressure in the
cavity must be maintained. The temperature increase in
the cavity using some devices, such as the hot air blower
fan equipped with a compressor can decrease the curing
time of resin. After the injected resin is completelycured, the covers at both ends of the reinforcing element
are removed to complete the entire processes.
2.2. Material selection and tests
Since the underground structures are usually exposed
to chemically harsh environment and subjected to heavy
compressive load, the selection of repairing materials
considering reinforcing effects is very important. Also
the costs, such as material cost, processing cost, etc.,should be considered carefully because large amount of
material is required for repairing huge underground
structures and the short operation time is important not
to induce any traffic congestion. Therefore, in this study,
the unsaturated polyester resin with low viscosity, which
is five times cheaper than epoxy, was selected and used.
The PC670 (Aekyung Chemical, Daejeon, Korea) is
orthophthalic type unsaturated polyester resin with alow viscosity before cure (0.2 Pa s), which is transparent
and has the possibility of filler addition to reduce cost
and strengthen toughness. Table 1 shows the material
properties of PC670 used in this study.
The reinforcing element for repairing underground
pipes is composed of the reinforcing fiber preform and
two inner and outer protection skins as shown in Fig. 2.
These two protection skins protect the glass fiber pre-form from the internal surface of underground conduits
and subterranean water or sewage left within the con-
duit. Also the inner and outer skins encapsulate the fiber
preform in order to act as the mold during RTM pro-
cess. The protection films not only protect the fiber
preform but also sustain the tensile load up to 80 kN
that is induced by the air pressure of inside cavity (the
maximum air pressure applied to the conduit of 1000mm diameter is 0.1 MPa) and the traction force during
the process [7]. The material for protection skins should
have chemical stability when contacted to unsaturated
polyester resin because the styrene monomer used for
hardening of polyester, may react with the skin material.
In this study, the Pro-Sol film, a kind of tarpaulin films
270 W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283
(LG Chemical, Seoul, Korea), was used for the protec-
tion skins because the Pro-Sol film had superior tensile
properties as well as chemical stability when contacted
with the styrene monomer in polyester resin [1,7]. Thethickness of Pro-Sol film used in this study was 0.55 mm
with the tensile strength of 100 MPa.
Among the three stages of RTM process (preforming,
resin wetting, and curing), the resin wetting is the core
process of RTM because the product quality is mostly
governed by the degree of wetting [8]. The resin wetting
during RTM process, which is viscous flow through the
porous media, may be expressed by Darcy’s law as fol-lows.
U ¼ �KlrP ð1Þ
where, K is the permeability of fiber preform, l the
viscosity of resin, and DP the pressure gradient. There-
fore, the resin wetting time is dependent on the perme-
ability of fiber preform. When the viscosity of resin and
the available maximum pressure gradient are given, the
permeability of fiber preform, K, should be maximized
to reduce the overall process time. Also the strength offiber preform should be large because the fiber preform
forms a polymer matrix composite after the rehabilita-
tion process, which should sustain the external load
subjected by the ground and traffic.
In order to select the proper materials for fiber pre-
form, permeability and tensile strength of various E-glass
fiber mats, unidirectional mats (T800-E06; Dong-il
Industrial, Seoul, Korea), continuous strand mats(M8600; Keun-yung Industrial, Seoul, Korea), crowfoot
satin woven mats (Spec.#224; Hyundai Fiber, Kyoun-
gnam, Korea), chopped strand mats (CM450A; Hankuk
Fiber, Kyoungnam, Korea), and roving cloth mats
(WR580A; Hankuk Fiber, Kyoungnam, Korea) were
experimentally measured [9,10]. To reinforce the strength
Table 2
Measured permeabilities of the various E-glass fiber mats
Type of mat Volume fraction (%)
Unidirectional (T800-E06) 42.1
47.0
Continuous strand (M8600) 9.1
13.5
Stacked mat [UD/CSM/CSM/UD]T 25.8
Satin woven (Spec.#224) 42.4
48.5
54.6
Roving cloth (WR580A) 21.2
26.6
Chopped strand mat (CM450A) 18.2
22.4
UD (T800-E06): unidirectional mat, CSM (M8600): continuous strand mat.
of transverse direction of the preform, the stacked mat of
[Unidirectional mat 1 ply/continuous strand mat 2 plies/
unidirectional mat 1 ply]Total stacking sequence was em-
ployed. Tables 2 and 3 show the measured permeabilitiesof various fiber mats and the tensile strengths of cured
glass/polyester composites, respectively. From the test
results, the stacked mat with high permeability and
moderate tensile strength was selected for preform
materials.
2.3. Resin flow and wetting analysis
The resin flow during the rehabilitation process was
modeled as the circumferential flow in the fiber preform
as shown in Fig. 4 on the assumption that the radial and
longitudinal resin flows were neglected. Since the outside
pressure and inside vacuum are applied to the rein-
forcing element to wet the fiber preform with the resin,
the net pressure for the resin flow was constant during
the whole process. Considering the pressure drop due togravity, the net pressure, P , in the fiber preform may be
expressed as follows.
P ¼ Pair � Pvacuum � qgh ð2Þwhere Pair and Pvacuum represent the air and vacuum
pressures, respectively, q is the density of resin, and h is
the height difference of the resin front that can be ex-
pressed as follows.
h ¼ r � r cos h ¼ rð1� cos hÞ ð3ÞSince the resin flows in the r and z directions can be
neglected due to the thin fiber preform, the velocity uh ofthe resin front in the h direction is expressed as
uh ¼ �Khh
lrP ¼ �Khh
l@Pr@h
¼ �Khh
ld
dl½Pair � Pvacuum � qgrð1� cos hÞ� ð4Þ
Kxx (m2) · 10�10 Kyy (m
2)· 10�10
45.5 39.2
7.52 5.32
17.8 17.6
9.96 9.99
41.1 40.0
0.602 0.497
0.368 0.267
0.204 0.151
25.3 23.4
20.3 19.8
44.3 43.3
17.5 17.2
Fig. 4. Model for resin flow in the fiber preform used for resin wetting
analysis.
Table 4
Viscosity of the uncured polyester resin (PC670) w.r.t. the environ-
mental temperature
Temperature Viscosity (Pa s)
Room temperature (25 �C) 0.25
10 �C 0.75
5 �C 1.0
Table 3
Tensile properties of the glass/polyester composite materials
Type of mat Fiber volume fraction (%) Tensile strength (MPa) Young’s modulus (GPa)
Unidirectional (T800-E06) 47 630 33.9
Continuous strand (M8600) 10 55 6.87
14.5 77.2 7.4
Stacked mat [UD/CSM/CSM/UD]T 29.5 340 18.2
26.6 288 16.6
Satin woven (Spec.#224) 42.4 471 28.2
Roving cloth (WR580A) 28.5 259 13.5
UD (T800-E06): unidirectional mat, CSM (M8600): continuous strand mat.
W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283 271
where l is the length of the resin front measured along
the circumference of conduit and 06 h6 p.Using Eq. (4) and the measured values of perme-
abilities of various fiber mats, the movement of resin
front and complete wetting time were calculated with
respect to environmental temperature (viscosity of re-sin), types of fiber preform, and diameters of conduits
on the assumption that inside vacuum and outside air
pressure of 30 kPa were applied to the reinforcing ele-
ment. Tables 4 and 5 show the measured viscosity of
uncured polyester resin (PC670) with respect to the
environmental temperature and the permeabilities of
fiber mats used in the analysis, respectively. Fig. 5 shows
the predicted resin wetting time calculated under the
Table 5
Permeabilities of the various E-glass fiber mats used in the resin flow analys
Type of mat Volume fraction
Unidirectional (T800-E06) 47.0
Continuous strand (M8600) 13.5
Stacked mat [UD/CSM/CSM/UD]T 25.8
Satin woven (Spec.#224) 54.6
Roving cloth (WR580A) 26.6
Chopped strand mat (CM450A) 22.4
UD (T800-E06): unidirectional mat, CSM (M8600): continuous strand mat.
assumptions of constant viscosity of resin at a certain
experimental temperature and uniform permeability of
fiber preform.
As shown in Fig. 5, the stacked mat of [Unidirectional
mat 1 ply/continuous strand mat 2 plies/unidirectional
mat 1 ply]Total stacking sequence was the most appro-
priate for the shortest processing time because it assured
the shortest resin wetting time. In order to verify theseanalysis results, small-scale rehabilitation experiments
were performed in the transparent acryl pipes of inner
diameters of 180 and 300 mm using the preforms of
stacked mats and satin woven mats, respectively. From
the experiments, it was found that the predicted wetting
times had an error less than 7% [11]. Since the resin
wetting time should be regulated by controlling the
process variables, such as temperature and pressureduring the actual rehabilitation process, diagrams relat-
ing these process variables are required in order to
accomplish the repairing process reliably and effectively.
Therefore, the resin flow analysis was performed with
respect to the environmental temperature and applied
net pressure (vacuum+air pressure) for the conduit of
specified internal diameter. Fig. 6 shows the predicted
resin wetting time of the preform of stacked mats whose
is
(%) Kxx (m2)· 10�10 Kyy (m
2)· 10�10
7.52 5.32
9.96 9.99
41.1 40.0
0.204 0.151
20.3 19.8
17.5 17.2
0
30
60
90
120
150
180
0 200 400 600 800 1000 1200Diameter (mm)
Diameter (mm)Diameter (mm)
Diameter (mm)
Diameter (mm)
Wet
ting
Tim
e (m
in)
Wet
ting
Tim
e (m
in)
Wet
ting
Tim
e (m
in)
Wet
ting
Tim
e (m
in)
0
10
20
30
40
50
60
0 200 400 600 800 1000 1200
UD
CSM
Roving
Chopped
Stacked
UD
CSM
Roving
Chopped
Stacked
0
40
80
120
160
200
240
0 200 400 600 800 1000 1200
UD
CSM
Roving
Chopped
Stacked
0
20
40
60
80
100
120
140
160
100 300 500 700 900 1100
25
10
0
(a) (b)
(d)(c)
Fig. 5. Predicted resin wetting time of the rehabilitation process with respect to environmental temperature, types of fiber perform, and diameters of
conduits: (a) at 25 �C; (b) at 10 �C; (c) at 5 �C; (d) the resin wetting time of the preform of satin woven mat with respect to environmental temperature
and diameters of conduits.
272 W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283
fiber volume fraction is 25.8% as the temperature and
applied pressure are changed. By using these analysis
results, diagrams shown in Fig. 6 were prepared to
control the process variables.
3. On-line process monitoring with dielectrometry
The resin wetting and curing are two major process of
RTM because the product quality is dependent on thedegree of wetting [8] and its cure process [12]. Therefore,
it is necessary to monitor the wetting and curing status of
resin continuously during the rehabilitation process in
order to yield a satisfactory reinforcing quality in the
shortest process time. Since the Pro-Sol films used in this
study are not only opaque but also placed underground,
it is difficult to check them with the naked eye. For this
reason, dielectrometry and dielectric sensors were em-ployed to on-line monitor the resin flow and cure status
in this work, from which the applied pressure and tem-
perature were adjusted. The dielectrometry has been
known as a promising technique to in situ monitor the
entire cure process of thermosetting resin continuously.
When an alternating electric field is applied to the two
electrodes of the dielectric sensor embedded in the
composite material as shown in Fig. 7(a), the dipole and
ions within the resin, which is a dielectric material, are
aligned following an applied alternating electric field. At
this time, the combination of two electrodes and poly-
meric resin can be modeled as a parallel equivalent circuit
composed of resistance Rm and capacitance Cm as shown
in Fig. 7(b). The mobility of dipoles and ions has closerelations with the cure state and the viscosity of resin
within the composite material as shown in Fig. 7(c), and
can be expressed by the dissipation factor D, which
represents the ratio of the energy loss by movements of
dipoles and ions to the supplied electric energy. The
dissipation factor for the equivalent circuit shown in Fig.
7(b) can be obtained as follows [12].
D ¼ IR � VmIC � Vm
����
���� ¼IRIC
����
���� ¼ZC
ZR
����
���� ¼1
x � Rm � Cm
ð5Þ
where
IR electric current in resistance (A)
IC electric current in capacitance (A)
Vm voltage applied to equivalent circuit (V)
ZR equivalent impedance of resistance ðXÞZC equivalent impedance of capacitance ðXÞ
0
1
2
3
4
5
Tim
e(m
in)
10
20
30Temperature (degree C)
100
120
140
160
180
200
Pressure (kPa)
4.404.133.873.613.353.082.822.562.302.031.771.511.250.980.72
Temperature (degree C)
Pre
ssur
e(k
Pa)
10 20 30100
110
120
130
140
150
160
170
180
190
200
0
5
10
15
20
Tim
e(m
in)
10
20
30Temperature (degree C)
100
120
140
160
180
200
Pressure (kPa)
18.0416.9615.8914.8113.7312.6511.5710.50
9.428.347.266.185.104.032.95
Temperature (degree C)
Pre
ssur
e(k
Pa)
10 20 30100
110
120
130
140
150
160
170
180
190
200
0
20
40
60
Tim
e(m
in)
10
20
30Temperature (degree C)
100
120
140
160
180
200
Pressure (kPa)
51.8748.7745.6642.5539.4536.3433.2330.1227.0223.9120.8017.7014.5911.48
8.38
Temperature (degree C)
Pre
ssur
e(k
Pa)
10 20 30100
110
120
130
140
150
160
170
180
190
200
(a)
(b)
(c)
Fig. 6. Variation of resin wetting time with respect to environmental temperature and applied net pressure for the specified inner diameter of
conduits: (a) diameter of 0.3 m; (b) diameter of 0.6 m; (c) diameter of 1.0 m.
W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283 273
x frequency of an applied alternating electric field
(Hz; 1 kHz was used in this study)
The principle of dielectrometry is to monitor the cure
state by measuring this dissipation factor [1,12]. Since
the value of the dissipation factor changes when the
dielectric sensor contacts the resin, it is possible tomonitor the resin wetting as well as the cure status by
measuring the dissipation factor continuously.
In this work, a 1-channel dielectrometer and an
interdigital capacitance (IDC) dielectric sensor were
used to monitor the resin wetting and curing during the
rehabilitation process. In order to check the availability
of the proposed monitoring method, the resin wetting
experiments were performed in the transparent acryl
pipe of 180 mm diameter (the smallest inner diameterof the conduit in this study) with 1 m length and 5 mm
thickness using the reinforcing element in which one
Polymer Composite
Electrode
AC Electric Field
CmRm
ICIR
Vm
Cure state
Curing
Uncured
Fully cured
Behavior ofDipoles & Ions
Fully oriented
Random
Partially oriented
+ Dipoles - + Ions -
(a) (b)
(c)
Fig. 7. Principle and measuring method of cure status of composite with dielectric sensor: (a) measuring method; (b) equivalent circuit of dielectric
sensor and composite; (c) behavior of dipoles and ions w.r.t. the cure status of composite materials.
274 W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283
dielectric sensor was embedded in the middle upper
portion of fiber preform as shown in Fig. 8. In order to
observe the flow of resin with the naked eye, trans-
parent PVC film of 1.0 mm thickness was used for theouter protection skin. After manufacturing the rein-
forcing element in the manner shown in Fig. 2, it was
placed in the acryl pipe, and the two covers were at-
tached at the both ends of the reinforcing element.
Then the resin wetting experiment was performed fol-
Fig. 8. Reinforcing element with a breathing tube and a dielec
lowing the general rehabilitation process of Fig. 1.
From the experiments, it was found that the proposed
monitoring method detected well the resin wetting as
well as curing as shown in Fig. 9, in which the increaseof measured dissipation factors at the initial stage oc-
curred when the dielectric sensor contacted the resin.
The resin wetting time measured by the dielectric sensor
was about 7.5 min and it took about 3 h to complete
the resin curing at 50 �C.
tric sensor whose dimension is 9 mm· 250 mm· 168 lm.
0.4
0.6
0.8
1
0 100 200 300
Dis
sipa
tion
Fact
orD
issi
patio
n Fa
ctor
Time (min)
Time (min)
0.4
0.5
0.6
0.7
0 5 10 15 20
Curing Completed
Wetting Completed
Fig. 9. Dissipation factor of unsaturated polyester resin during the
rehabilitation process measured by the dielectrometer and dielectric
sensor.
W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283 275
4. Rehabilitation experiments with developed process
Using the above results and the developed process,
several real rehabilitation experiments, whose schematicdiagram is shown in Fig. 10, were performed at the
concrete pipe (reinforced spun concrete pipe) used for
Fig. 10. Schematic diagram of the repairing-reinforcing experiment with g
electrometry.
underground applications. The diameter and length of
the three concrete pipes were 300 mm and 10 m, 600 mm
and 10 m, 600 mm and 30 m, respectively. After the
reinforcing elements were prepared using the stackedmats and Pro-Sol films in the manner of Fig. 2 consid-
ering the dimensions of the target concrete pipes, a
porous breathing tube of 8 mm inside diameter was in-
serted into the upper position of the reinforcing element
as shown in Fig. 11 [7]. The breathing tube was con-
nected to the air vent of the reinforcing element to apply
a vacuum, which enhanced the efficiency of void re-
moval much. For the process monitoring, one dielectricsensor was embedded in the fiber preform and connected
to the dielectrometer whose sensor line was connected
through the breathing tube. Since the length of the pipes
is somewhat long, the method for supplying the resin
uniformly along the reinforcing element was needed.
For this end, two resin injection pipes with small pin-
holes were installed along the reinforcing element as
shown in Fig. 11, which was connected to RTM ma-chines to inject unsaturated polyester resin into the fiber
preform. By regulating the distance between pinholes,
the resin injection amount per unit length was made
uniform [7]. Since the breathing tube and the resin
injection tube were installed in the reinforcing element in
the manner as shown in Fig. 12, they could be easily
removed by pulling out one end of them before curing of
resin.After installation of the reinforcing element, its both
ends were closed using specially designed cover assembly
that are composed of a steel ring, a steel disk, and an
acryl disk as shown in Fig. 13. Fig. 14 shows the cross
sectional view of the reinforcing element after installa-
tion. The cover assembly is equipped with the pressure
gauge for checking an internal air pressure as well as the
lass fiber fabric and unsaturated polyester resin using RTM and di-
Fig. 11. Configuration of the reinforcing element containing the porous breathing tube and the resin injection pipes with pinholes.
Fig. 12. Pipe removal after the completion of resin wetting.
276 W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283
air inlet for pressurizing the internal cavity. After
attaching the cover assembly to the reinforcing element,
the multi-joint clamp made of chain-link as shown in
Fig. 15 was tightened using the steel ring with inner and
outer protection films by fitting into the groove of steel
ring. The groove on the circumferential face of the steel
ring increased the load transfer capability and sealing
effect of the resin, and the transparent acryl disk offeredthe visibility of inside status. In order to seal the gap
between the inner and outer protection skins and the
internal cavity of reinforcing element, thermosetting
adhesive, DP460 of 3M whose material properties are
given in Table 6, was pasted on the interface of two
skins, and a circumferential groove of steel ring. The
resin reservoir shown in Fig. 10, which was placed be-
tween the reinforcing element and a vacuum pump,prevents the expelled resin from going into a vacuum
pump directly and separates voids from the resin
through breathing tube. Since the amount of the bleeded
resin could be measured by the gauge on the resin res-
ervoir, it was possible to predict a fiber volume fraction
of the cured reinforcing element through a simple cal-
culation. After removing the wrinkles and twists in the
reinforcing element by expanding the inner protectionfilm, a predetermined amount of unsaturated polyester
resin (130% of the required amount) was injected into
the fiber perform with the RTM machine, which mixed
the resin with cure catalyst (MEKPO; methyl-ethyl-ke-
tone-peroxide) at predetermined rate. Then the resin
wetting and curing were followed in sequential order to
complete the entire rehabilitation process. The RTMmachines (high volume H.I.S.e hand-held casting unit;
Venus-Gusmer, Washington, USA) were actuated by
high pneumatic pressure and their detailed specifications
are given in Table 7. Test conditions and specifications
of each experiment are depicted in Table 8. Since the
long pipes with large diameters were tested, fairly long
times were required to finish the resin wetting. There-
fore, a little amount of the cure retardant for slowingdown the cure reaction was used in order to obtain the
sufficient process time considering the gelation time of
the unsaturated polyester resin (PC670) listed in Table 9.
From the experiments, it was found that large three-
dimensional composite structures could be constructed
inside of the large concrete pipes without any dry region
as shown in Fig. 16. Also, it was found that the void
removal method through the porous breathing tubesand the resin injection pipes with small pinholes were
very effective to expel the micro-void.
5. Comparison of processing cost and time
There are about 80 sorts of trenchless technologies so
far developed all over the world and largely classified
into four kinds: slip-lining, cured-in-place pipes (CIPP)
lining, close-fit lining, and spirally wound pipes lining
[11]. Among them, CIPP has been very successful
through the achievements of Insituform (Insituform�
Technologies, Ltd., Chesterfield, United Kingdom) andPaltem/Phoenix, and has attracted many modifications
and improvement. Since the CIPP products probably
take 35–40% of the global sewer market, the trenchless
rehabilitation method developed in this study was
compared with the two conventional CIPP lining pro-
cesses (one was Paltem/Phoenix lining process and the
other was D-Ins� lining process) with respect to cost,
Fig. 13. Photographs of cover for sealing the both ends of the reinforcing element for 600 mm pipe: (a) steel ring, (b) assembly of steel ring and steel
disk, (c) assembly of cover (steel ring+ steel disk+acryl disk) and multi-joint clamp.
Fig. 14. Cross sectional view of the reinforcing element and concrete pipes after installation.
W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283 277
time, and reinforcing effects. The Paltem/Phoenix liningprocess is a cured-in-place lining process that was
developed by Tokyo Gas (Tokyo Gas Co., Ltd., Tokyo,
Japan) and Ashimori Industry (Ashimori Industry Co.,
Ltd., Osaka, Japan) for lining gas pipes, in which a
polyethylene resin coated woven hose is bonded with
epoxy resin to the pipe to be repaired in inversed shape
by water or air pressure [13]. From the beginning, this
process was named Paltem (pipeline automatic liningsystem), and then became known as Phoenix in Europe
because Osaka Bosui (Osaka Bosui Construction, Co.,
Osaka, Japan) participated in this development shared it
with a French company Le Jointe Interne [13].
The D-Ins� lining process (Samil Setec, Seoul, Korea)
is a modified Insituform process, in which the polyester
fabric felts impregnated with polyester, or vinylester
Table 7
Specifications of the RTMmachine (Venus-Gusmer, Inc., Washington,
USA)
Property Value
Mass injection output 2.3–13.6 kg/min.
Injection capacity 0.408 kg/stroke
Air consumption 0.28 m3/min.
Catalyst mixing ratio (volume) 0.5–3.0%
Catalyst jug 2 gallon (7.57 l)
Fig. 15. Multi-joint clamp: (a) photograph of multi-joint clamp with roller chain links, (b) assembly of cover and clamp, (c) detailed drawing of the
multi-joint clamp, (d) roller chain rink and detailed draft of joining part.
Table 6
Material properties of the cured epoxy adhesive (3M DP460)
Properties Value
CTE (10�6 m/m �C) 59.0 (below Tg)159.0 (above Tg)
Poisson ratio 0.4
Density (kg/m3) 1100
Elastic modulus (GPa) 2.7
Tensile strength (MPa) 37
Tg: glass transition temperature.
278 W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283
resin are used and also installed in the conduit in the
inversed shape by water pressure.
The mechanical properties of reinforcing element
developed in this study (RTM liner) were tested and
compared with that of Paltem-SZ liner and D-Ins� liner,
and the production cost and processing time were com-
pared only with those of D-Ins� process. For the con-
venience, the reinforcing element of this study was named
‘‘RTM liner.’’ The tensile properties of the RTM linerwere measured with INSTRON 4206 according to
ASTM D3039 and their flexural properties were mea-
sured with the same machine according to ASTM D790.
Tables 10 and 11 show the comparison results of mecha-
nical properties and the production cost and processing
time, respectively. As listed in Table 10, it has been found
that the RTM liner of this study has much superior
mechanical properties to those conventional liners forsewer rehabilitation. The comparison results of produc-
tion cost and processing time in Table 11 were carried out
on the assumption that the extra cost was same for both
cases and the processes were applied to repair the conduit
of 300 mm inner diameter. From the results, it was found
that the margin of repairing cost of developed process
was about 85 US $, and the margin of repairing time was
about 16 h. Comparing with the excavation technology,this newly developed process could cut cost of excavation
technology by more than 40%. If the diameter of target
conduits is increased, the effect of cost saving will be
further enhanced.
Table 9
Gelation time of the unsaturated polyester resin (PC670) with respect to the amount of cure catalyst (MEKPO)
Temperature (�C) MEKPO (methyl-ethyl-ketone-peroxide) Remarks
0.6 0.8 1.0 1.26 Unit: %
20 46 41 32 28.5 Unit: min
25 31 25 21.5 17
30 18 14.5 12 10.5
36 11.5 9.5 8.5 8
Fig. 16. Real rehabilitation experiment using concrete pipes of 600 mm inner diameter: (a) initial setup of the equipments; (b) resin injection (RTM
machine#1) and application of vacuum; (c) resin injection (RTM machine#2); (d) photograph of the real construction experiment; (e) photograph of
the repaired concrete pipes; (f) inner surface of repaired concrete pipes.
Table 8
Test conditions of each rehabilitation experiment
Descriptions (diameter· length) 300· 1000 (mm) 600· 1000 (mm) 600· 3000 (mm)
Preform [UD1/CSM3/UD1] [UD2/CSM4/UD2] [UD2/CSM4/UD2]
Injected resin (kg) 44 120 400
Resin:MEKPO 100:1 (volume) 100:0.75 100:0.75
Retardant No No 15000 ppm
Environmental temperature (�C) 5 14 16
Viscosity of resin (Pa s) 0.8–1.0 0.4–0.5 0.3–0.4
Inner pressure (kPa) 20–30 20–30 20–30
UD (T800-E06): unidirectional mat, CSM (M8600): continuous strand mat.
W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283 279
Table 10
Comparison of the mechanical properties between the reinforcing element developed in this study and conventional liners for sewer rehabilitation
RTM liner Paltem-SZa D-Ins�b
Resin system Unsaturated polyester Unsaturated polyester Unsaturated polyester
Felt E-glass fiber Chopped strand glass
fiber+ polyester fabric
Unwoven polyester fabric
Tensile strength 340 60 23
Flexural strength 420 110 53
Flexural modulus 15.8 6.0 1.9
aMaterial data from Ashimori Industry, Japan.bMaterial data from Samil Setec, Korea.
Table 11
Comparison of repairing cost with CIPP (cured-in-place pipes) lining process
Cost RTM method (US $/m) D-Ins� lining process (US $/m)
Material 38 72
Process 95 146
Extra Same ðaÞ Same ðaÞTotal 133þ a 218þ aMargin 85
• Material cost: reinforcing element, resin, adhesive, tubes, etc.
• Extra cost: inspection, cleaning, perforation of junction, etc.
• Repairing cost of excavation technology: 380 US $/m.
• 1 US$ ¼ 1300 won.
280 W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283
6. Design criteria of the reinforcing element
As mentioned previously, the RTM liner of this study
has much higher mechanical properties than those of
conventional liners, which might be somewhat over-designed, consequently there is a possibility of further
material cost saving. Therefore, it is necessary to
develop some design criteria of the RTM liner which can
guarantee sufficient material properties with minimum
cost. On the assumption that the RTM liner is com-
posed of unidirectional mats (T800-E06) and continuous
strand mats (M8600) only, the design criteria of RTM
liner was suggested in order to reduce the material costwith sufficient reinforcing effect.
The American Society for Testing Materials (ASTM)
has produced the specifications drafted by committees
of engineers drawn from users and suppliers. These
specifications are issued provisionally and revised in
accordance with the comments of the industry received
by ASTM. In 1989 ASTM produced F1216-89 which
was subsequently revised in 1991 and 1993. The currentissue ASTM F1216-93 covers the design and installation
issues and performance of installed liners [13]. Under-
ground pipes are largely classified into two kinds by
their application: gravity pipes and pressure pipes, and
each of them are divided into partially deteriorated pipes
and fully deteriorated pipes according to their damaged
condition. ASTM F1216 suggests some design consid-
erations to determine the thickness of CIPP (liner) forrepairing underground pipes case-by-case (totally four
cases). In this study, the RTM liner for rehabilitating the
fully deteriorated gravity pipes of 300 mm inner diam-
eter was considered and its design criteria were sug-
gested. Since a fully deteriorated pipe is structurally
unsound and cannot support soil and outside load, the
RTM liner for this case should be designed to supporthydraulic, soil and outside loads. ASTM F1216 suggests
that the following equation should be used to calculate
the minimum thickness of CIPP liner for repairing the
fully deteriorated gravity pipes [14].
E
12ðD=tÞ3P 0:00064 ðSI unitsÞ ð6Þ
where E is the initial modulus of elasticity (MPa), D is
the mean inside diameter of original pipe (mm) and t isthe thickness of CIPP liner (mm).
Since the RTM liner is basically the combination ofthe unidirectional mat and continuous strand mat, its
total thickness is the summation of the thickness of used
mats. However, since the thicknesses of fiber mats be-
fore resin wetting are different from those after curing
followed by resin wetting, their effective thicknesses (the
thickness that each fiber mat occupies within the cured
composite made of those mats) after curing should be
known to design the liner using Eq. (6). The elasticmodulus of the arbitrarily stacked composite made of
unidirectional mats and continuous strand mats can be
calculated through the rule of mixture (ROM) if their
effective thicknesses are known, because the fiber vol-
ume fractions of each layer can be determined from their
effective thicknesses. To obtain the effective thickness of
each fiber mat, the following procedure was devised.
y = 8.9755E-09x - 5.3147E-09
5.0E-10
1.5E-09
2.5E-09
3.5E-09
4.5E-09
0.6 0.7 0.8 0.9 1.0 1.1 1.2
Per
mea
bilit
y (
m2 )
Per
mea
bilit
y (
m2 )
e
ex
+=
1
3
y = 1.4203E-11x + 4.9486E-10
5.0E-10
1.5E-09
2.5E-09
20 40 60 80 100
e
ex
+=
1
3
(a)
(b)
Fig. 17. Plot of the permeabilities versus x ¼ e3=ð1þ eÞ: (a) unidirec-tional mat (T800-E06); (b) continuous strand mat (M8600).
W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283 281
The most well-known permeability modeling for
Newtonian flow through various porous media is the
Kozeny–Carman equation which considers the porous
medium as a bundle of capillaries, which was knownthat this equation could predict the permeability in the
fiber direction pretty well [15]. Generally, the Kozeny–
Carman equation is
Ki ¼r2f4Ci
ð1� vfÞ3
v2f¼ r2f
4Ci
e3
1þ eð7Þ
where Ki is the permeability in the i-directionði ¼ x; y; zÞ, rf is the fiber radius, Ci is the Kozeny con-
stant to be determined experimentally, vf is the fibervolume fraction, and e is the void ratio which is ex-
pressed by the following equation.
e ¼ 1
vf� 1 ð8Þ
Since the permeability is proportional to the function of
void ratio, it was possible to derive the empirical relation
between the permeability and void ratio using the per-meabilities and the fiber volume fractions of unidirec-
tional mats and continuous strand mats listed in Table
2. From the plot of the permeabilities versus x ¼ e3=ð1þ eÞ shown in Fig. 17, two experimental equations for
K (one is for unidirectional mat and the other is for
continuous strand mat) were obtained as follows.
KUD ¼ 8:9755� 10�9x� 5:3147� 10�9
KCST ¼ 1:4203� 10�11xþ 4:9486� 10�10ð9Þ
Since the ply weight of each glass fiber mat and the
density of E-glass fiber are known, the fiber volume
fractions of the unidirectional mat and continuous
strand mat with an arbitrary thickness can be calculated.
Then the permeabilities of each fiber mat at the specifiedthickness can be determined from Eq. (9).
In order to determine the effective thickness of two
fiber mats, the measured permeability of the stacked mat
listed in Table 2 and the concept of equivalent perme-
ability were used. When the permeability for flow in the
horizontal direction changes from layer to layer as shown
in Fig. 18, which is similar to the flow in the stacked mat,
the equivalent permeability of n layers can be formulatedas follows [16].
Keq ¼1
h
Xn
i¼1
Kihi ð10Þ
where, Keq and h are the equivalent permeability andtotal thickness of n layers and Ki and hi are the perme-
ability and thickness of the individual layers, respec-
tively. It was known that Eq. (10) agrees pretty well to
the experimental result irrespective of staking sequence
when the total thickness of preform is relatively thin and
the through-thickness flow is negligible [6]. If the per-
meabilities of the individual layer are known, the
equivalent permeability of the layered preform can be
determined from Eq. (10). After transforming the vari-
able x in Eq. (9) into the function of thickness of each
mat because the void ratio can be expressed by means of
the effective thickness, it can be combined with the Eq.
(10). Since the permeability ðKeqÞ and the total thickness
ðhÞ of stacked mat are known, the effective thickness of
unidirectional mat and continuous strand mat can bedetermined by solving Eqs. (9) and (10) simultaneously.
From the calculation, it was found that 1 ply of the
unidirectional mat (T800-E06) and the continuous
strand mat (M8600) have the effective thickness of 0.868
and 1.132 mm, respectively.
In order to determine the thickness of RTM liner
using the Eq. (6), its modulus should be known. Since
the cured RTM liner is the mixture of unidirectionalmats, continuous strand mats and polyester resin, its
equivalent modulus can be formulated by employing the
rule of mixture (ROM) as following.
E ¼ vf ;UDEf ;UD þ vf;CSTEf ;CST þ vmEm ð11Þ
where, vf ;UD and Ef;UD are the fiber volume fraction and
modulus of unidirectional mats, respectively, vf ;CST and
Ef ;CST are those of continuous strand mats, respectively,
and vm and Em are those of matrix (polyester resin),
respectively.
Fig. 18. Horizontal resin flow through the porous media composed of n layers with different permeabilities.
282 W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283
From the material properties given in Tables 1 and 3,
Ef ;UD (¼ 67 GPa) and Ef ;CST (¼ 30 GPa) were obtained
through ROM. Since the effective thickness of each mat
is known, the equivalent modulus of RTM liner com-posed of those mats can be determined if the number of
each mat is specified. Using Eqs. (6) and (10) and the
previous result, other stacking sequences for RTM liner
were suggested. When one ply of the unidirectional mat
and two plies of the continuous strand mats were se-
lected, vf;UD and vf;CST are 0.107 and 0.116, respectively.
This gives the equivalent modulus of 14 GPa and
E=12ðD=tÞ3 of 0.001341, which is two times larger thanthe limit value of 0.00064. Another solution is to use
three plies of the continuous strand mats. This gives the
equivalent modulus of 8.2 GPa and E=12ðD=tÞ3 of
0.000997, which is also larger than the limit value. Since
the price of unidirectional mat ($2.4/m2) is about 1.5
times more expensive than that of continuous strand
mat, it is evident that the newly suggested stacking se-
quences are more cost effective than the original one.Because large amount of fiber mats are required to re-
pair huge and long underground conduits, the effect of
cost saving will be large.
Since the design criteria of RTM liner suggested in
this study uses just two materials, such as unidirectional
mats and continuous strand mats, it will be possible to
extend the range of design parameter (wide variance of
materials) by performing the previous design procedurewith more diverse materials, which will lead to the fur-
ther enhanced cost saving.
7. Conclusions
In this study, a new trenchless rehabilitation process
of underground pipes, which not only overcomes the
problems of former trenchless technologies, but also is
adequate to the situation of high traffic road, has been
tried with E-glass fiber fabric and unsaturated polyester
resin by vacuum assisted resin transfer molding (RTM).
E-glass fiber reinforced composites were used for rein-
forcing damaged underground pipes and the RTM
technology was modified for fabricating large under-
ground composite structures. Also the reinforcing ele-ment for repairing the interior of damaged underground
pipes has been developed through various material tests
and experiments. For the reliable rehabilitation process,
the glass fiber preform was covered with tarpaulin films
that worked as a flexible mold and protection skins and
a porous breathing tube was used to remove the volatile
and micro void within the reinforcing element. After
actual repairing experiments have been performed atthe real concrete pipes, the efficiency of the developed
process was evaluated and compared with those of the
conventional trenchless technology. From the compar-
ison of processing cost and processing time, it was
found that the developed process was very effective in
view of cost and time. Finally, the design criteria of the
reinforcing element which assure the sufficient rein-
forcing effect with minimum material cost have beensuggested.
Acknowledgements
This work was supported financially by the Korean
Government under NRL (National Research Labora-
tory) projects and, in part, by BK 21 Project. The au-thors would like to thank to their financial support.
References
[1] Lee DG, Chin WS, Kwon JW, Yoo AK. Repair of underground
buried pipes with glass fiber composites using RTM. Comp Struct
2002;57(1–4):67–77.
[2] Mallick PK. Fiber-reinforced composites. Marcel Dekker; 1988.
p. 3–4.
[3] Kang MK, Lee WI. Analysis of resin transfer/compression
molding process. Polym Comp 1999;20(2):293–304.
[4] Toutanji H, Dempsey S. Stress modeling of pipelines strengthened
with advanced composites materials. Thin-Walled Struct 2001;39:
153–65.
W.S. Chin, D.G. Lee / Composite Structures 68 (2005) 267–283 283
[5] Skordos AA, Kahnanas PI, Partridge IK. A dielectric sensor for
measuring flow in resin transfer molding. Measure Sci Technol
2000;11:25–31.
[6] Diallo ML, Gauvin R, Trochu F. Experimental analysis and
simulation of flow through multi-layer fiber reinforcements in
liquid composite molding. Polym Comp 1998;19(3):246–56.
[7] Chin WS, Kwon JW, Lee DG. Trenchless repairing of under-
ground pipes using RTM based on the axiomatic design method. J
Comp Mater 2003;37(12):1109–26.
[8] Advani SG. Flow and rheology in polymer composites manufac-
turing. Elsevier; 1994. p. 466–8.
[9] Adams KL, Russel WB, Rebenfeld L. Radial penetration of a
viscous liquid into a planar anisotropic porous medium. Int J
Multiphase Flow 1988;14:203–15.
[10] Standard test method for tensile properties of polymer matrix
composite materials. American Society for Testing and Materials
D3039/D3039M-95a. 1995.
[11] Chin WS, Kwon JW, Lee DG. Trenchless repairing of under-
ground pipes using RTM and dielectrometry. 3rd International
Conference on Composites in Infra-Structures, San Francisco,
USA, June 2002.
[12] Kwon JW, Chin WS, Lee DG. In-situ cure monitoring of
adhesively bonded joints by dielectrometry. J Adhes Sci Technol
2003;17(16):2111–30.
[13] Downey DB. Trenchless methods for sewer renovation. In:
International Seminar for the Expansion of Sewer Rehabilitation
and Trenchless Technologies, vol. 1. 1999. p. 1–10.
[14] Standard practice for rehabilitation of existing pipelines and
conduits by the inversion and curing of a resin-impregnated tube.
American Society for Testing and Materials F1216-93. 1993.
[15] Gutowski TG. Advanced composites manufacturing. John Wiley
& Sons; 1997. p. 416–8.
[16] Das BM. Principles of geotechnical engineering. PWS Publishing
Company; 1993. p. 148–50.