日本建築学会大会学術講演梗概集	 （関東）	 2015 年	 9	 月	 1256

Bending Test of FRC Notched Beam with Various Polymer Fibers

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Polyvinyl alcohol
CMOD

Fig. 1 Used fibers
Table 1 Characteristics of used fiber
Diame- Tensile Elastic
Density LengthterStrength Modulus
ID(g/cm3)
(mm)
(mm)
(MPa)
（GPa）
Aramid-30 1.3930
0.53432
73
PVA-30
1.30
30
0.66
900
23
PVA-18
1.30
18
0.2
975
27
≧500
7-10.5
PP-30
0.91
30
0.7
Table 2 Mix proportion of base concrete
Unit weight (kg/m3)
Water cements/aratio
WCSG0.50
0.60
1853701006
676
Table 3 Fresh and compressive properties
AramidID
PVA-30 PVA-18 PP-30-30
Slump (cm)
14.5
15.5
6.5
23
Air (%)
5.7
3.9
1.3
6.5
Compressive
41.8
43.3
44.9
39.6
Strength (MPa)Elastic Modulus
25.8
27.4
27.1
25.2
(GPa)

Bending Test of FRC Notched Beam with Various Polymer
Fibers― 511 ―

NF
23
7.1
40.5
26.2

Ligament
30 70

1. INTRODUCTION
With the development of polymer material, various synthetic
fibers have become the best selection to improve concrete
capacity and failure resistance without corrosion of fibers1).
However, more research is necessary to study the contributionof synthetic fibers to concrete matrix. The objective of thisstudy is to make clear the influence of types of fibers to
fracture properties of fiber-reinforced concrete (FRC) by thebending test of notched beams.
2. EXPERIMENTAL PROGRAM
2.1 Specimen
Aramid, polyvinyl alcohol (PVA) and polypropylene (PP)fibers (Fig. 1) were used with 1% volume fraction. The
characteristics of the fibers are listed in Table 1. The mix
proportion for base concrete is shown in Table 2. The watercement ratio was set to 0.50 and sand aggregate ratio was 0.60.
The fresh and compressive properties are listed in Table3. The
notched beam specimens with 100mm square section (Fig. 2)
specified in JCI-S-001-2003 were used. The depth of the notch
was set to 30mm. For each fiber, 6 specimens were tested toobtain the average data. Plain concrete without fiber (NF) was
also tested.
2.2 Loading and measurement
As shown in Fig.2, three-point bending test was carried out.
Two π gauges were set on the side of the specimen to obtainthe crack mouth opening displacement (CMOD). For plain
concrete, clip gauge was set on the mid-bottom of beam tomeasure CMOD directly. One LVDT was set on the back tomeasure the load point deflection (LPD).
3. TEST RESULTS AND DISCUSSIONS
3.1 Failure progress
Examples of the final failure patterns after loading are shownin Fig. 3. Except for Aramid-30 specimens, the load showedremarkable drop when the crack appeared from the notch. The
maximum loads were observed as the matrix strength in thesespecimens. PP-30 and PVA-18 specimens showed the loadincrement after dropping with growing the crack. Aramid-30
specimens showed gradual failure through the loading.

5030050
LVDT

100
Ligament
30 70

AramidFracture energy

Toshiyuki KANAKUBO**70Bending Test
Polypropylene○Yu MU*

50300

50100

Fig. 2 Test specimen
MU Yu, KANAKUBO Toshiyuki

Fig. 3 Final failure patterns after loading
3.2 Load vs. CMOD relation
Examples of the load-CMOD curves are shown in Fig. 4.
Comparing to the plain concrete, FRCs show a high ductility
after cracking. The maximum load was observed after crack in
Aramid-30 specimens. More than 50% of the maximum load
can be remained until 8mm of CMOD. PP-30 specimen also
showed high deformability that the second peak load wasobserved approximately 3mm of CMOD.
3.3 Fracture energy
The fracture energy until several CMODs is shown in Fig. 5.
The error bars show the ranges of standard deviations by 6specimens. PVA fibers show the lowest standard deviation. The
fracture energy of Aramid-30 and PP-30 specimens increases
gradually with the increase of CMOD while the fracture energyof PVA specimens barely changed.
3.4 Evaluation of fiber stress
The equivalent fiber stress, which is defined as Eq.(1) and (2), isnewly introduced to evaluate the fiber effectiveness for crack
bridging. Eq.(1) is derived in similar with the modulus ofrupture for plain concrete. Stress distribution in the ligament
section is assumed to be linear one. Fracture energy till 15mm
CMOD is used for calculation. Fig. 6 shows the relationshipbetween tensile strength of fiber and equivalent fiber stress. The
straight line indicates the orientation factor 0.41 in case of the 3D random distribution. It is considered that the fiber, which isplotted near the line, had more effectiveness for bridging in thecapacity of its tensile strength.
G F (CMOD )  Alig 6
Sfb (1) 
0.75  15
4 b  h2

The maximum load was observed after cracking in aramid FRCspecimen. PP FRC specimen showed high deformability that thesecond peak load was observed in several millimeters of CMOD.
The equivalent fiber stress is newly introduced to evaluate thefiber effectiveness for crack bridging.

* 筑波大学大学院博士後期課程・修士（工学）**筑波大学システム情報工学研究科 准教授・博士(工学)Load (kN)
Fracture energy (N/mm)

510CMOD (mm)Fig. 4 Load-CMOD curve

15Aramid 30mm
PVA 30mm
PVA 18mm
PP 30mm+-

5

4.5

7.5
910
CMOD (mm)Fig. 5 Fracture energy(2)

4. CONCLUSIONS

10002

Where, f b : equivalent bending strength (N/mm ), GF(CMOD):
fracture energy (N/mm), Alig: area of ligament (mm2), S: span(mm), b: ligament width (mm), h: ligament height (mm),  f ,b :equivalent fiber stress (N/mm2) , Vf: fiber volume fraction.

Aramid 30mm
PVA 30mm
PVA 18mm
PP 30mm
w/o fiber
Plot : second peak

50Equivalent fiber stress (MPa) f ,b  f b V f

1015500
400

Orientation
factor : 0.410.1

300
200
1000

Aramid 30mm
PVA 30mm
PVA 18mm
PP 30mm

1000
2000
3000
4000
Tensile strength (MPa)Fig. 6 Equivalent fiber stress

5000

ACKNOWLEDGEMENT
This experiment was conducted under the committee activities
for JIS development of polymer fibers for concrete organized byJapan Chemical Fibers Association.
REFERENCES1) ACI Committee 544. 1R-96, State of the Art Reporton Fiber Reinforced Concrete, pp. 39-57, 1996
*Doctoral Program in GSSIE, University of Tsukuba, M. E.
**Associate Professor, GSSIE, University of Tsukuba, Dr. Eng― 512 ―