Engineering Structures 206 (2020) 110176

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Engineering Structures
journal homepage: www.elsevier.com/locate/engstruct

Grouting and pull-out tests of hollow-type prestressing-strands for aninternal strengthening system

T

Takafumi Miharaa,b, Isamu Yoshitakea, , Ryosuke Anamia, Naoyuki Tsumurab,
Tatsuhiko Mimotob⁎ab

Department of Civil and Environmental Engineering, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi 755-8611, Japan
Kyokuto Kowa Corporation, Hikarimachi 2-6-31, Higashi-ku, Hiroshima, Hiroshima 732-0052, Japan

ARTICLE INFOABSTRACT

Keywords:
Internal anchorage
Strengthening
Hollow-type prestressing-strand
Grouting

The present study focused on creation of an internal strengthening system, which involved embedding a posttensioned PC tendon in a wedge-shaped anchorage of an existing concrete member. Under conditions withnarrow work spaces, it was difficult to employ the previous system using a post-tensioned prestressing bar, as
adequate backspace was required to install the bar. A flexible hollow corrugated pipe covered with steel wire
cables seemed applicable even in such narrow spaces. Interestingly, the hollow stranded tendon could also be
used as a grouting-pipe to fill the internal anchorage. The foci of this study were to develop a grouting material
suitable for passage through a hollow corrugated pipe, and to determine the applicability of the hollow-type
prestressing tendon for the internal strengthening system. In the study, a horizontal grouting test was first
conducted using 5 m-long corrugated pipes of 10 mm internal diameter. It was confirmed from the grout andstrength tests that some grouting materials were applicable for filling the hollow-type PC strands. In addition,
pull-out tests of the prestressing tendon embedded in the anchorage of mock-up RC blocks were conducted to
examine their load-bearing capacity. Furthermore, visible tests of the horizontal and upward grouting wereconducted to confirm the filling condition in the wedge-shaped anchorage. The test results confirmed adequateload-bearing capacity of the hollow prestressing tendon embedded in the anchorage when the filler applicable tohorizontal grouting was used.

1. Introduction
1.1. Objectives
General concrete is vulnerable to tensile forces, and cracks often
occur due to internal and external forces. Post-tensioning prestressing isa reliable method for reinforcing concrete structures. Post-tensioned
prestressed concrete (PC) members are generally employed in civil infrastructure such as bridges. Post-tensioning prestressing is also an effective method for strengthening existing concrete structures. The
strengthening system with external prestressing cables is widely used toincrease the load-bearing capacity of concrete bridge girders. However,it may be hard to arrange such prestressing cables for some concrete
members, because the workspace available may be inadequate for thestrengthening work. To avoid workspace issues, the authors [22,23]
developed an internal prestress strengthening system for existing concrete members, by which a post-tension prestressing tendon isembedded in a wedge-shaped internal anchorage (Fig. 1). Previous
studies confirmed that post-tensioned prestressing bars can be firmly
anchored in the internal wedge hole filled with high-strength fillingmaterial and that the system can contribute to the durability of jointed
concrete members. Rigid prestressing bars were used in previous investigations [22,23]. It should be noted that adequate backspace isoften required for installing the rigid bars in the existing concrete
members. Fig. 2 presents a typical application for strengthening thefooting of bridge piers. It may be hard to install conventional rigid bars
into such underground concrete members (Fig. 2a). On the other hand,a flexible prestressing tendon is more applicable, even in a narrow
workspace (Fig. 2b).
The present study focuses on use of the internal prestressing systemwith flexible prestressing tendons. In particular, the applicability of ahollow-type prestressing tendon (a flexible hollow corrugated pipe
covered with prestressing wire cables; Fig. 3) for this purpose wasstudied. Of interest is that the corrugated pipe can be used as a grouting

Corresponding author.
E-mail addresses: mihara@kkn.co.jp (T. Mihara), yositake@yamaguchi-u.ac.jp (I. Yoshitake), AnamiRyosuke@yucivil.onmicrosoft.com (R. Anami),n-tsumura@kkn.co.jp (N. Tsumura), mimoto@kkn.co.jp (T. Mimoto).
⁎

https://doi.org/10.1016/j.engstruct.2020.110176
Received 18 June 2019; Received in revised form 2 December 2019; Accepted 3 January 20200141-0296/ © 2020 Elsevier Ltd. All rights reserved.

Engineering Structures 206 (2020) 110176

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Special drilling device

A

A
I. Insertion of the special drilling device

II. Enlargement of the holeC

Abutment

A-A cross section

B

Segment for enlarging

B

B-B cross section

Footing

Wedge-shaped hole

PC tendon(a) Rigid prestressing bar

C-C cross section

C

Insert back-spacefor PC tendon

III . Removal of the device after drilling(a) Drilling for a wedge-shaped anchor
Flexible hollow
PC tendon[Step 1] Concrete core drillingfor internal anchorage(wedge-shaped hole)
Wedge-shaped hole

Existing concrete[Step 2] Install of a prestressing tendon
Fill high-strength grouting material into the anchorage holePrestressing tendon

Narrow back-space

Filler(b) Flexible hollow-type prestressing tendon[Step 3] Placing of new concrete (option)
Provide tensile force (pull) to the prestressing tendon
CouplerFig. 2. Schematics of bridge footing applications.

Tensiondeformations observed in experimental flexural tests. Saleem and Tsubaki [28] focused on a post-installed two-layered anchor system forstrengthening RC members and developed an analytical model for pullout responses. Park et al. [26] conducted flexural tests of post-tensioned
girders using high-strength strands. They reported that predictions ofcurrent design codes agreed well with the experiments while concrete
crack widths and stresses of reinforcement slightly exceeded the specified limits. Yurdakul and Avşar [35] investigated the retrofitting
technique by post-tensioning for an RC beam-column joint. Abela [2]reviewed investigations of a post-tension grouted anchor used for existing Tainter-gate anchorage systems. Faria et al. [8,7] investigatedpost-tension prestressing techniques for strengthening flat-slabs. The
structural responses of post-tensioned concrete slab/wall structures
have also been extensively reported [9,1,33,4,10].
Akiyama et al. [3] examined the flexural behaviors of cylindricalconcrete piles prestressed with unbonded bars. This paper showed thatthe load capacity of a prestressed concrete pile was greatly increased byconfining the pile between carbon fiber (CF) sheets. Kara et al. [13]conducted numerical analysis for estimating the curvature, deflection,and moment capacity of RC beams strengthened with prestressed NSM
FRP bars/strips. The numerical parametric study indicated that higher
prestressing levels improved structural performance; however, the levels decreased the beam ductility in comparison with beams strengthened with non-prestressed NSM FRP bars/strips. In addition, advanced
materials such as fiber reinforced polymers (FRPs) have been used asalternatives to conventional steel tendons [5,16,29,34,6,20,21,
17,18,36,19,27].
Grouting materials are also key factors for post-tensioning

New concrete[Step 4] Grouting

Grout(b) Post-tension prestressing
Fig. 1. Schematics of the developed strengthening system.

pipe to add filling materials to the anchorage. The objectives of thisstudy were to develop a grouting material suitable for passage througha hollow corrugated pipe, and to examine the pull-out loading capacityof the flexible prestressing tendon anchored in the wedge-shaped holewith the grouting material.
1.2. Review of research
Prestressing with an external and/or un-bonded tendon is a wellknown method for strengthening concrete effectively. Ng and Tan [24]developed a simple “pseudo-section analysis” method for externallyprestressed concrete beams subjected to flexure. In addition, Ng andTan [25] examined the flexural behavior of prestressed beams andconfirmed the applicability of the proposed analytical model. Vu et al.
[32] proposed a structural model of post-tensioned prestressed beams
with unbonded tendons. Their model accurately predicted the2Engineering Structures 206 (2020) 110176

T. Mihara, et al.

Table 2
Materials and mixture proportions of grouting material.
Materials

Type

Density

Water (W)
Cement (C)Tap-water
Ordinary Portland
cementSilica fume
Crushed sandPoly-carboxylic acid

1.00 g/cm3
3.16 g/cm3

Glycol ether

0.98 g/cm3

Manufacturer Sa
Manufacturer Sa
Manufacturer Ta

N/A
N/A
N/A

Micro filler (F)Fine aggregate (S)High-range water reducing
agent (HRWRA)
Shrinkage reducing agent(SRA)
Pre-mixed mortar (I)Pre-mixed material (II)Pre-mixed material (III)Dia.=27.9mm(a) Hollow corrugated pipe covered with steel-wire cables
h=1.2mmSteel-wires

Do=14mm

No.

w/cm

W

C

F

0
1
2
3
4
5

0.12
0.20
0.20
0.20
0.20
0.26

1.2 kg/mix
2.0 kg/mix
2.0 kg/mix
2.0 kg/mix
2.0 kg/mix
2.6 kg/mix

10 kg/mixI
10 kg/mix
N/A
9.5 kg/mix 0.5 kg/mix
9.0 kg/mix 1.0 kg/mix
10 kg/mixII
10 kg/mixIII

2.21 g/cm3
2.60 g/cm3
1.04 g/cm3

S

HRWRA

SRA

0
0
0
0
0

0
cm*1.4%
cm*1.5%
cm*1.5%0000W*1.5%
W*1.5%
00

a: the components and mixture proportions cannot be released.
I: Pre-mixed mortar (I); II: Pre-mixed material (II); III: Pre-mixed material (III).

Corrugated pipe

W=5mm

Di=10mm(b) Dimensions of hollow corrugated pipe
Fig. 3. Flexible prestressing tendon.
Table 1
Fundamental properties of prestressing tendons.
Materials

Rigid bar

Hollow-type tendon

Nominal diameter
Young’s modulus
Yield strength
Tensile strength
Standard

23 mm
202 GPa448.7 kN (1080 MPa)
511.0 kN (1230 MPa)
JIS G 3109

27.9 mm
162 GPa
N/A
588 kN (1732 MPa)
N/A

Fig. 4. Crim grip for flexible tendon.
Fig. 5. Grouting test.

prestressed concrete structures. Khayat et al. [14] conducted a laboratory test to develop a high-performance cementitious grout applicablein horizontal and vertical post-tensioning ducts. Schokker et al. [30]carried out a simulated field test on grouting materials for vertical andhorizontal applications and recommended a suitable grout mixture.
Schokker et al. [31] also conducted a pressure-filter test and reported arational post-tensioning grout material for bleed-resistance. Kim et al.
[15] examined fresh and hardened properties of steel-fiber reinforced
grout applicable to PC substructures. The study revealed positive effects
by ground, granulated blast-furnace slag (GGBS) on the chloride-penetration resistance and flowability of the grout. Kamalakannan et al.
[12] conducted tests on fresh and hardened properties of premixed

grouting materials for post-tensioned concrete. They evaluated the effect of binder fineness on the performance of the grouting materials.
Mimoto et al. [22] developed a new internal strengthening technique using post-tensioned tendons and a wedge-shaped anchorage. In
this study, a pull-out test was conducted to examine the load capacity ofa prestressing tendon fixed in the internal anchorage. In addition, Mimoto et al. [23] conducted a flexural test using full-scale beams jointed
by the post-tensioning technique. Rigid prestressing steel-bars(SBPR930/1080: yield strength of 1080 MPa) and a special pre-mixedmortar of high strength were used in these studies. The previous investigations confirmed the adequate load-bearing capacity of a rigid
3

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prestressing bar embedded in the grout-filled anchorage, even underpull-out and flexural loadings.

Table 3Grouting test results.
No.

Flowa
(mm)

5 m long
grouting

Segregation

0
1
2

189
> 300
244

Incomplete
Incomplete
Complete

N/A
Yes
No

3
4

193
265

Complete
Complete

Yes
No

5

163

CompleteNof′7d (MPa)

Filling
conditionb

109.6 /–
104.5b/–118.7b/132.7c90.1b/45.2c
113.0b/103.0c103.6b/98.4c

2. Hollow-type prestressing tendon

N/A
N/A
Full

As aforementioned, the footing of a bridge pier is one kind of application for the newly developed strengthening system. To install posttensioning tendons on the existing concrete members, adequate backspace is often required for the placement of rigid prestressing bars,
which was tested in previous studies [21,23]. The conventional prestressing rigid bars may not be applicable in narrow workspaces such asfootings under the ground, as shown in Fig. 2(a). On the other hand,flexible prestressing wire-cables can be installed in the existing concreteeven in such narrow work conditions, as illustrated in Fig. 2(b). The
flexible hollow-type prestressing tendon must be a useful material toextend the applicability of the new strengthening method. A hollowtype corrugated pipe covered with twisted steel-wire cable (Fig. 3a) is

N/A
Full
Full

a

Table flow-test.
The materials obtained from the mixer.
c
The grouted materials for 5 m long.
b(a) Pull-out test(b) Schematic of the test
1200

(mm)

7@50=350
U-1 U-3 U-5 U-7

65
35 160

65

93

400

280

U-2 U-4 U-6 U-8

100

BottomTop(c) Dimensions
Fig. 6. Detail of RC block for pull-out test.

4

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often used in mining and related activities. This material has the uniquefeatures of higher flexible and ductility. In the study reported herein,
the focus was on the use of this material as a prestressing tendon for thestrengthening system.
The hollow-type prestressing tendon had an outer diameter of
27.9 mm. The PC tendon consisted of corrugated steel-pipe of 10 mm
inner diameter and 9 wires of 6.9 mm diameter. Fig. 3(b) describes thedetails of the corrugated pipe, which served as the inner material of theprestressing tendon. The inner pipe was used as a grouting pipe foradding filling material to the wedge-shaped anchorage.
The load capacity and the designed Young’s modulus of the flexible
tendon were 588 kN and 162 GPa, respectively. The fundamental
properties of rigid and flexible tendons are summarized in Table 1. A
crimp grip, a sort of steel-sleeve, was attached to the cable-end to resist
the pulling force by the prestressing tendon (Fig. 4).

400

50 150

400

150

50

(mm)

(d) Rebars arrangement -top view-

3. Grouting test with the hollow corrugated pipe

1200

3.1. Materials and mixture proportions(mm)

Adequate flowability and pumpability are required for the grouting
materials. In addition, high strength (90 MPa or higher) is required forthe hardened grout in the internal anchorage. To achieve the required
properties, the conventional materials given in Table 2 were prepared.
Pre-mixed materials (I, II, III) were also tested. Furthermore, Table 2
shows the mixture proportions of the grouting materials. Mixture No. 0
is the grouting material used for the rigid bar in the previous investigations [21,23]. Mixtures No.4 and No.5 are pre-mixed grouting
materials provided by different manufacturer. The primary components
in these grouting materials are cementitious binder, expansive andviscous additives, water-reducing chemical agent while the mixture
proportion cannot be revealed in public. Further information about
these pre-mixed materials such as physical and chemical components
cannot be released herein because of the commercial contract with the
manufactures.

400

93

65

50

11@100=110050(e) Rebars arrangement -side viewFig. 6. (continued)
Table 4
Materials and concrete-mixture proportion for pull-out test.
Materials

Properties

Reinforcing bar

JIS G-3112; Nominal diameter: 13 mm (D13) Yield
strength: 345 MPa; Young’s modulus: 206 GPa
See Table 1

Hollow-type PC
tendonSteel-sleeve
Bearing plate with aholeFig. 5(a) presents the grouting test conditions. To consider thegeneral application, a grouting test for a corrugated pipe 5 m long was
conducted using an electric pump (maximum rate: 2000 cm3/min). The
corrugated pipe was arranged horizontally to simulate transverse
strengthening of concrete members. In such cases, air-removal and fullgrouting at the anchorage should be examined carefully. To achieveadequate strength, segregation of the filling material after grouting
cannot be allowed. Compressive strength was examined using grouting
materials that traveled 5 m without material segregation, even at theend of the corrugated pipe. The dimensions of the cylindrical test specimens were 50 mm diameter and 100 mm length.

Crimp grip: 57 mm dia × 159 mm long
JIS G-3101; Dimensions: 120 × 120 × 25 mm
Yield strength: 235 MPa; Young’s modulus: 206 GPa

Concrete materials

Type

Density

Water (W)
Cement (C)Tap water
Ordinary Portland
cementCrushed sand
Crushed stone
WRA

1.00 g/cm3
3.16 g/cm3

Fine aggregate (S)Coarse aggregate (G)Admixture (AD)3.2. Grouting test method2.64 g/cm3
2.68 g/cm3
1.04 g/cm3

Type

w/cm

W kg/m3

C kg/m3

S kg/m3

G kg/m3

AD kg/m3

Air %3.3. Test results and discussion

Conc.

0.90

190

211

993

930

0.63

4.5

Table 3 summarizes the test results. All the test materials obtained
from the mixing-bowl achieved compressive strength of 90 MPa or
higher, which is what was required for the wedge-shaped anchorage.
The conventional high-strength mortar (No. 0) and the plain cement
paste (No. 1) hardly passed through the corrugated pipe 5 m long because of material-segregation in the pipe. The cement pastes incorporating silica-fume (No. 2, 3) completely passed to the end of thepipe 5 m long; however, material segregation at the pipe-end (Fig. 5b)
was observed in grouting test No. 3. The compressive strength of fillingmaterial No. 3 obtained from the pipe-end, was only about half of therequired minimum strength (90 MPa). It is remarkable that the other

Table 5Fundamental properties of filling materials and concrete.
Filling material

FlowComp. strength

Young’s mod.

Poisson’s ratio

No.2
No.4
No.5
ConcreteConc.

244 mm
225 mm
160 mmSlump
80 mm

118.3 MPa89.2 MPa95.7 MPa
Comp. strength25.1 MPa26.7 GPa
20.2 GPa
21.8 GPa
Young’s mod.
25.3 GPa

0.25
0.24
0.26
Poisson’s ratio
0.20

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(c) Hollow-type PC strand(a) Drilling(d) Grouting(b) Drilling device

Fig. 7. Preparation of RC block for pull-out test.

grouting materials (No. 2, 4, and 5) passed through the 5 m corrugatedpipe without segregation and achieved the required strength.
The filling test using the hollow-type prestressing tendon confirmedthat the required conditions were met, even in the horizontal wedgeshaped anchorage. Based on the grouting tests, three filling materials(No. 2, 4, and 5) were employed in the pull-out tests shown in the next
section.

previous study [22]. Fig. 6(a)–(e) describes the pull-out test and dimensions of the concrete blocks. The materials used in the RC blocks
and the mixture proportions of the concrete are summarized in Table 4.
The specified compressive strength of the concrete was 24 MPa at
28 days. To simulate a deteriorated concrete member, concrete wasmade with a relatively high water-cementitious material ratio (w/cm = 0.90). It should be noted that concrete with such high w/cm-ratio
was employed only for this experimental study and is hardly used inany practical application in Japan. Fundamental properties of thegrouting materials (No.2, No.4, No.5) and the concrete for RC block
were summarized in Table 5.
The wedge-shaped hole for the PC anchorage was made by drillingand enlarging. The diameter and length of the wedge-shaped hole was
93–65 mm and 100 mm, respectively. Fig. 7(a)–(d) describe the preparation of the tested RC blocks. The water and concrete shavings left
after the drilling were removed with a vacuum (340 W), and the holesize was confirmed by a microscopy (8 mm diameter, 300,000 pixels).
A hollow-type corrugated tendon, with a steel sleeve attached to thetendon end, was installed in the wedge-shaped hole. The filling material

4. Pull-out test of the hollow-type prestressing tendon
4.1. Test specimens
The study prepared 8 RC blocks for the pull-out test. Three specimens made by vertical grouting were used for each test (No.2 andNo.4), and a specimen made by vertical grouting (No.5) was also tested.
The last RC block was used for horizontal grouting and pull-out tests(described later). The dimensions of the mock-up RC blocks were
400 × 400 × 1200 mm. To avoid splitting failure, the cross section(400 × 400 mm) of the RC blocks was designed by referring to a6

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700

700
Pu (588 kN)

600

500
0.8Pu (470 kN)

400

Load (kN)

Load (kN)

500

300

300
200

100

100
0.0

1.0

2.0

3.0

4.0

Slip of tendon (mm)05.0(a) Pull-out load – slip responses
0

0.8Pu (470 kN)

400

200

0

Pu (588 kN)

600

0.0

1.0

2.0

3.0

4.0

Slip of tendon (mm)5.0(a) Pull-out load – slip responses

0

50

100

150

200

250

300

350

U-1

U-2

U-3

U-4

U-5

U-6

U-7

U-8

400
mm

0

-20

0

50

100

150

200

250

300

350

U-1

U-2

U-3

U-4

U-5

U-6

U-7

U-8

400
mm

-20
-40

-60

Strain (10-6)

Strain (10-6)

-40

-80
-100

0.7Pu

-120

0.8Pu

-140

0.9Pu

-160

1.0Pu

-60
-80

0.7Pu
0.8Pu

-100

0.9Pu
1.0Pu

-120

-180

-140

(b) Axial strain of concrete(b) Axial strain of concreteFig. 8. Pull-out test results (No.2).

Fig. 9. Pull-out test results (No.4).

(No. 2, 4, or 5) was grouted into the anchorage through the internal
corrugated pipe. To ensure complete filling in the experimental study,
vertical grouting was performed as shown in Fig. 7(d).

previous study [22]. The observed elongations of the tendon were
proportional to the load up to a load of approximately 490 kN. The
prestressing tendons did not yield and were firmly fixed in the wedgeshaped anchorage by the filling material. The results confirm that theload-bearing capacity of the anchoring system was adequate for theprestressing tendon used in this study. The loading test for each of thethree filling materials used is described below. Note is that the loadcapacity (Pu = 588 kN) is the maximum tensile force guaranteed by the
manufacturer and the criterion force (0.8 Pu) shown below is defined in
the Japanese specification [11].

4.2. Test method
The pull-out load of the embedded PC tendon was provided to thetest specimens by a center-hole hydraulic jack system. The load wasstatically increased to 588 kN, which is the capacity of the hollow-type
prestressing tendon. A schematic of the pull-out test is illustrated inFig. 6(b). A center-hole load cell (Max. 1000 kN) and 4 Linear Variable
Differential Transformers (LVDT (A)-(D)) having the capacity of
100 mm were set as shown in the schematic figure. In addition, wirestrain gauges (120 ohm, 60 mm long) were arranged on the concretesurface as shown in Fig. 6(c). The pull-out test was conducted at thegrouting-material age of 12 days.

4.3.1. Filling material No. 2
Fig. 8(a) and (b) show pull-out load-slip responses and concrete
strains, respectively. Obvious increases of the tendon slip were observed at the pull-out load of 490 kN. The total slips of the tendon werein the range 0.7–0.8 mm at the load of 470 kN (=0.8 Pu). The maximum strain at the concrete surface was −147 micro-strain at U-7(300 mm from the anchorage edge) and was almost equal to the designed value (−145 micro-strain). Note is that the designed strain was
calculated using the load and apparent Young's modulus of the RC
block. The observed strain distribution confirms a constant compressive
strain at U-6 (250 mm from the anchorage edge) or higher positions.

4.3. Pull-out load capacity and slip
The maximum loads of all test specimens exceeded the nominal
load-capacity (Pu = 588 kN) of the flexible tendon. For safety in theexperiment, the pull-out loads were maintained for a while (about
1 min. for observing cracks); then removed immediately when themeasurement using the load-cell was 588 kN or higher. It is certain thatthe actual maximum loads were higher than the designed load-capacity(Pu = 588 kN). It is noteworthy that the observed loads were almost
100 kN higher than the maximum loads of the rigid tendon used in a

4.3.2. Filling material No. 4
Fig. 9(a) and (b) show pull-out load-slip responses and concrete

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5. Experimental verifications

Load (kN)

700
600

Pu (588 kN)

500

0.8Pu (470 kN)

5.1. Visible test for horizontal and upward grouting
The greatest concern with horizontal grouting is having a void in theupper part of the anchorage. Grouting material may flow out of theanchorage because high fluidity is required to pass through the corrugated pipe. Hence, it may be hard to achieve adequate anchoring for theprestressing tendon. To examine complete filling even in horizontal
grouting, a visible test was conducted using a transparent acrylic pipethat simulated the wedge-shaped anchorage (Fig. 11(a)). The fillers
tested were the cementitious grouting materials (No. 2, 4, and 5) that
achieved the fluidity appropriate for passing through the 5 m corrugated pipe and the capacity adequate for the (vertical) pull-out loading.
Transparent pipes 1 m long were used in the visible test (Fig. 11(b)).
To prevent outflow of the filling material, steel-wool (sw) was set at theedge of the anchorage in some test cases (Fig. 11(c)). In addition to thehorizontal grouting, upward grouting of 0.35 rad was also carried out inthe visible test. A schematic of the visible filling test is illustrated inFig. 11(d).
Fig. 12(a)–(c) illustrates grout-filling conditions of 0 rad,0 rad + sw, and 0.35 rad + sw, respectively. In addition, the visible
test results are summarized in Table 6. The test result confirms thatgrouting material No. 5 entirely filled the wedge-shaped acrylic pipe
without the use of steel-wool. On the other hand, grouting materials No.
2 and 4 flowed out from the edge of the wedge-shaped pipe, and upper
voids were observed in the pipe. The different results were due to thepaste-flow, that is, 163 mm for filler No. 5 and over 200 mm for theother fillers (No. 2 and 4).
In the test using steel-wool, the grouting materials (No. 4 and 5)
entirely filled the simulated anchorage. For filling material No. 2, an
upper void was observed while the outflow was slightly reduced by thesteel-wool. One remarkable observation was that the pseudo wedgeshaped anchorage of 0.35 rad (upward grouting) was entirely filledusing material No. 5 and steel-wool. Filler No. 5 is a commercial premixed material that contains Portland cement, an expansive material, athickener, and a high-range water reducing agent (HRWRA).

400
300
Vertical grouting

200

Horizontal grouting

100
0

0.0

1.0

2.0

3.0

4.0

Slip of tendon (mm)5.0(a) Pull-out load – slip responses
0

0

50

100

150

200

250

300

350

U-1

U-2

U-3

U-4

U-5

U-6

U-7

U-8

400
mm

-20

Strain (10-6)

-40
-60
-80

0.7Pu

-100

0.8Pu

-120

0.9Pu

-140

1.0Pu

-160
-180

(b) Axial strain of concreteFig. 10. Pull-out test results (No.5).

strains, respectively. As well as the test mentioned above, this test
confirms that the tendon-slip significantly increased at the load of
490 kN. The total slips of the tendon were greater than the test results of
No. 2, and were in the range 1.1–1.7 mm at the load of 470 kN (=0.8Pu). The maximum strain at U-7 was −141 micro-strain, and the strain
was almost equal to the maximum strain of No. 2 and the designed
value. Hence, constant strain distributions were also observed in thistest.

5.2. Horizontal pull-out loading test
In the visible test, material No. 5 was selected as the material suitable for horizontal grouting. To confirm the capacity of the material, ahorizontal pull-out loading test was conducted as well as a vertical pullout loading test. The loading and measurement systems were the same
as for the pull-out test mentioned earlier. The horizontal grouting andthe loading test are described in Fig. 13(a) and (b), respectively.
The load-slip responses shown in Fig. 10(a) represent the comparative test results of vertical (full) and horizontal grouting. The slip
(approximately 4.0 mm) at the ultimate load of the horizontal grouting
test was 1.1 mm greater than the slip with full grouting, while the slip
(approximately 1.5 mm) at the load of 470 kN (=0.8 Pu) was almost
equal to the slip at the same load in the full-grouting test.
Fig. 14(a) and (b) show pull-out load-deformation responses andconcrete strains, respectively. As in the previous tests, the pull-out test
confirmed that the maximum load exceeded the load-capacity(Pu = 588 kN) of the flexible tendon. The comparative test result
confirmed that the maximum load and elongation of the flexible tendon
were greater than the rigid prestressing tendon (steel-bar). It is noteworthy that the gradient of the load-elongation response was significantly lower than the test result with a rigid steel-bar. The observation implies that the flexible tendon can provide higher
prestressing force and possibly decrease loss of the force caused fromvolume change of concrete. Furthermore, the elongation characteristic
contributes to decrease the loss of prestressing force when the

4.3.3. Filling material No. 5
Fig. 10(a) and (b) show pull-out load-slip responses and concrete
strains, respectively. For comparison, the result obtained from thehorizonal grouting test (discussed later) is shown in Fig. 10(a). The nonlinear response to the pull-out load was almost same as the test results(No. 2 and 4), the obvious increase of slip was observed at approximately 490 kN. The total slip of the tendon was 1.24 mm at the load of
470 kN (=0.8 Pu). The maximum strain was −161 micro-strain at U-7,
and it was slightly greater than the designed value.
The test results (No. 2, 4, 5) showed that the load capacities wereadequate for fixing the tendon and that the slips were little different. It
is noted that these test results were obtained from the specimens having
the tendon anchorage filled with high-strength materials. Therefore,horizontal and upward grouting into the anchorage was examined toinvestigate their practical application for the horizontal strengtheningof concrete structures.

8Engineering Structures 206 (2020) 110176

T. Mihara, et al.

(a) Transparent acrylic pipe
1m(b) Schematic of grouting test

Crimp grip (φ57x159 mm)
Hollow corrugated pipewith steel-wire cables

I. 0radSteel-wools
Steel-wools

III. 0.35rad+sw

II. 0rad+sw(c) Schematic of test parameters
FillerFillerAir
Steel-wools

Viscous grouting material(d) Air-removal from the wedge-shaped holeFig. 11. Visible grouting test.

prestressing strand is set at the end of concrete member. Note is that alonger hydraulic jack system is needed for prestressing with the flexible
strand compared to the rigid bar.
The maximum elongation of the tendon was about 55 mm under theload capacity (Pu = 588 kN), the maximum axial strain was −160
micro-strain at U-8 (350 mm from the anchorage edge). In addition,
Fig. 14(b) confirms that the strains in the range of U-6 to U-8(250–350 mm from the anchorage edge) were hardly different. Theseobserved results were not different from the test using the specimens
with an entirely filled anchorage. Based on the visible and pull-out
tests, the study results indicated that filler No.5 was the most suitable
grouting material for the post-tension strengthening system with aflexible hollow-type prestressing tendon.
Fig. 15 presents a cross-section of the anchorage exposed by sawcutting a post-test specimen. It was confirmed that the grouting material in the anchorage was hardly damaged by the pull-out load. The

photograph shows the tilted head of the prestressing tendon. The tilted
head was due to the deadweight of the flexible tendon, the slant wasobserved to be 0.052 rad. Further research on the impact of such eccentricity should be done though a pull-out test to confirm adequate
anchoring capacity for the tendon.
6. Conclusions
To develop an internal strengthening system using the hollow-type
prestressing-strand, this study examined the grouting materials applicable for a horizontal hollow duct. A pull-out test of the PC tendon
was conducted using 8 mock-up RC specimens. The remarkable findingsin the experimental study are listed below.

• The high-strength mortar used for the rigid prestressing tendon
barely passed through the corrugated pipe 5 m long because

9Engineering Structures 206 (2020) 110176

T. Mihara, et al.

Table 6
Visible test results.
Case

Test parameters

Void

Upper-air void
I
II
III

Flow-out

0 rad
0 rad + sw
0.35 rad + sw

Flow-out

yes

no

yes

no

No.2, 4
No.2
No.2

No.5
No.4, 5
No.4, 5

No.2, 4
No.2
No.2

No.5
No.4, 5
No.4, 5(a) I. 0rad

Steel-wools(a) Horizontal grouting(b) II. 0rad+sw

0.35rad(c) III. 0.35rad+sw(b) Pull-out test

Fig. 12. Visible test results.

••

Fig. 13. Verification test.

segregation of the mortar occurred at the pipe-end.
The grouting test confirmed that cement pastes without fine aggregate are an appropriate filling material for passage through thecorrugated pipe.
The pull-out test revealed that adequate load capacity and negligible
slip of the flexible prestressing tendon embedded in the internal
wedge-shaped anchorage can be provided by using filling materials
that can pass through the corrugated pipe.

• One filling material (No. 5) was applicable even in the upward

grouting (0.35 rad), so it was selected as the material most suitable
for the post-tension strengthening system using the flexible hollowtype tendon.

10

Engineering Structures 206 (2020) 110176

T. Mihara, et al.

Declaration of Competing Interest

700
Pu (588 kN) for flexible tendon

600

Load (kN)

The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence the work reported in this paper.

Pu' (511 kN) for rigid tendon

500

0.8Pu (470 kN)

400

Flexible tendon

Rigid tendon

300

Acknowledgments
The authors thank Dr. Era (Kyokuto Kowa Co.) and Dr. Kawakane(Kyokuto Kowa Co.) for their assistance. We would also thank Editage(www.editage.com) for English language editing.

200
100
0

0

20

40

Elongation of tendon (mm)60

Appendix A. Supplementary material

80

Supplementary data to this article can be found online at https://doi.org/10.1016/j.engstruct.2020.110176.

(a) Pull-out load – deformation responses
0

0

50

100

150

200

250

300

350

U-1

U-2

U-3

U-4

U-5

U-6

U-7

U-8

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-20

Strain (10-6)

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CRediT authorship contribution statement
Takafumi Mihara: Conceptualization, Methodology, Validation,
Investigation, Writing - original draft, Visualization, Project administration. Isamu Yoshitake: Validation, Writing - original draft, Writing review & editing, Supervision, Visualization, Project administration.
Ryosuke Anami: Methodology, Validation, Investigation. Naoyuki
Tsumura:Methodology,
Investigation.
TatsuhikoMimoto:Conceptualization, Supervision.
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12