The 2019 World Congress on
Advances in Structural Engineering and Mechanics (ASEM19)
Jeju Island, Korea, September 17 - 21, 2019

Evaluation of crack width in steel reinforced DFRCC members*Daiki Sunaga1), Keisuke Namiki2) and Toshiyuki Kanakubo3)1), 2)

3)

GSSIE, University of Tsukuba, Ibaraki, 305-8573, Japan
Dept. of Eng. Mechanics and Energy, Univ. of Tsukuba, Ibaraki, 305-8573, Japan1)s1920914@s.tsukuba.ac.jp

ABSTRACT
In order to evaluate crack width in steel reinforced Ductile Fiber-Reinforced
Cementitious Composites (DFRCC) members, uniaxial tension test was conducted forspecimens with one deformed steel rebar arranged. Polyvinyl Alcohol (PVA) fibers areused in DFRCC. The experimental parameters are cross-sectional area and fiber
volume fraction. According to the test result, larger tension stiffening effect is observedin specimens which have larger cross-sectional area and larger fiber volume fraction.
Crack width tends to widen in specimens which have larger cross-sectional area andsmaller fiber volume fraction.

1. INTRODUCTION
Ductile Fiber-Reinforced Cementitious Composite (DFRCC) is cementitious
material reinforced with short discrete fibers. DFRCC shows high ductility under tensile
and bending stress condition by bridging of fibers at crack. The previous studies havereported that structural members using DFRCC shows less damages and crack
opening compared with conventional concrete members (Sano et al. 2015, Kanakuboand Hosoya 2015). DFRCC can make it possible to improve durability and sustainable
use of structures. However, it is difficult to evaluate tensile characteristic of DFRCC andthere are only a few examples using DFRCC in structural members as actualapplications.
In order to use DFRCC in structural members and make the use of its highductility, it is needed to evaluate crack width precisely. At the level of DFRCC members,
bridging laws (tensile stress – crack width relationships) are used to evaluate crackwidth (Kanakubo et al. 2016). On the other hand, it is generally considered to use
DFRCC with steel reinforcing bars in structural members as steel reinforced DFRCC
members. In the case of evaluating crack width in steel reinforced DFRCC members,
not only bridging laws but also bond behavior between DFRCC and steel rebar should1),2)
3)

Graduate StudentProfessor

The 2019 World Congress on
Advances in Structural Engineering and Mechanics (ASEM19)
Jeju Island, Korea, September 17 - 21, 2019

be considered.
The objective of this study is to evaluate crack width in steel reinforced DFRCC
members. Uniaxial tension test is carried out for specimens using DFRCC byconsidering the influence of bridging effect and bond behavior between DFRCC andsteel rebar.

2. OUTLINE OF UNIAXIAL TENSION TEST
2.1 Specimen
Fig. 1 shows the dimension of specimens and Table 1 shows the specimens list.
The total length of the specimen is 800mm. One steel deformed rebar D16 (SD490)
was arranged in the center of square cross-section along the axial direction. PVA fibers
were used for DFRCC. The experimental parameters are cross-sectional area (Aseries:100mm×100mm and B series:150mm×150mm) and fiber volume fraction (1%,2% and no fiber). Three specimens were loaded for each parameter and 18 specimens
were tested in total.

Fig. 1 Specimen dimensions
Table 1 Specimen listTypeID

Common factor

No Fiber-A
PVA1%-A
PVA2%-ANo Fiber-B
PVA1%-B
PVA2%-B

1~31~3
1~3
1~3
1~3
1~3

Length: 800mm
Steel rebar: D16 (SD490)
Fiber: PVA

Cross-sectionalarea
100mm×100mm

150mm×150mm

Fiber
volumefraction
―1.0%
2.0%
―
1.0%
2.0%

The 2019 World Congress onAdvances in Structural Engineering and Mechanics (ASEM19)
Jeju Island, Korea, September 17 - 21, 2019

2.2 Materials
The mechanical properties of PVA fibers used in DFRCC are listed in Table 2 andthe visual appearance is shown in Fig. 2. The mix proportion of DFRCC is shown inTable 3. DFRCC is filled into the mold by pouring from one end of the mold to control
the fiber orientation.
Table 4 shows the mechanical properties of DFRCC at loading age of uniaxial
tension test. The results of tension test for reinforcing bar are shown in Table 5.

Table 2 Mechanical properties of fiber
TensileLength Diameter
strength(mm) (mm)(MPa)
120.10
1200

Fiber
PVA

Elastic
modulus(GPa)28

Fig. 2 Visual appearance of fiber
Table 3 Mix proportion of DFRCC (kg/m3)
TypeNo Fiber
PVA1%
PVA2%

WaterCementSand

Fly ash380678484291

PVA fiber01326

Table 4 Mechanical properties of DFRCC
TypeNo Fiber
PVA1%
PVA2%

Compressive strength(MPa)
47.2
47.4
44.1

Elastic modulus(GPa)
17.0
16.8
15.9

The 2019 World Congress onAdvances in Structural Engineering and Mechanics (ASEM19)
Jeju Island, Korea, September 17 - 21, 2019

Table 5 Test results of tension test for reinforcing bar
Yield
TypeDiameter
strength(MPa)SD490 D16 (16mm) 491

Elastic Yield
modulus strain(GPa)(μ)
1882610

Tensilestrength(MPa)561

2.3 Loading and measurements
Uniaxial tension test was carried out by universal testing machine as shown in Fig.
3. Total deformation was measured by 2 LVDTs. Crack widths were measured by Pitype LVDTs spaced at 100mm on both side of the specimens.

Fig. 3 Test setup

3. TEST RESULTS AND DISCUSSIONS
3.1 Load – total deformation relationships
Fig. 4 shows the load – total deformation relationships measured from the loading
test. Since the deformation measured by LVDTs includes the elongation of steel rebar
at both ends of specimens (60mm), the deformation of the specimens in 800mm wasobtained by excluding the elongation of steel rebar in 60mm region. The elastic

The 2019 World Congress on
Advances in Structural Engineering and Mechanics (ASEM19)
Jeju Island, Korea, September 17 - 21, 2019

modulus obtained from tension test of reinforcing bars was used to calculate theelongation of steel rebar. The dotted line in Fig. 4 shows the load – deformation
relationships of steel bare rebar in 800mm length. The yielding strengths of all No
Fiber-A specimens and one of No Fiber-B specimens are lower than those of otherspecimens because some steel rebars showed lower yielding strength than specified
value.
In general, tensile load of steel reinforced concrete member is larger than that ofsteel bare rebar at same deformation. This phenomenon is called tension-stiffening
effect. Tension-stiffening effect is brought by tensile load carrying in surrounding
concrete being transmitted via bond between the rebar and concrete. In case ofDFRCC, tension-stiffening is caused not only by bond behavior between DFRCC andsteel rebar but also by bridging of fibers at cracks.
According to the test results, tension-stiffening effect is small in No Fiber
specimens without bridging. By comparing PVA1% specimens to PVA2% specimens inthe same series of cross-sectional area, tension-stiffening effect is larger in PVA2%specimens. By comparing A series (100mm×100mm) to B series (150mm×150mm) inthe same fiber-volume fraction, tension-stiffening effect is larger in B series specimens.
However, in No Fiber specimens, there is a few differences between A series and B
series. Therefore, tension-stiffening effect is mostly influenced by bridging of fibers.

012Total deformation (mm)35000

PVA1%-A1
PVA1%-A2
PVA1%-A3
Steel Rebar

12Total deformation (mm)3100

Load (kN)

Load (kN)

10050Load (kN)No Fiber-A1
No Fiber-A2
No Fiber-A3
Steel Rebar

100

No Fiber-B1
No Fiber-B2
No Fiber-B3
Steel Rebar

12Total deformation (mm)3500500

PVA2%-A1
PVA2%-A2
PVA2%-A3
Steel Rebar

12Total deformation (mm)3100

Load (kN)

50100

Load (kN)

Load (kN)

100

PVA1%-B1
PVA1%-B2
PVA1%-B3
Steel Rebar

12Total deformation (mm)3500Fig. 4 Load – total deformation relationship

PVA2%-B1
PVA2%-B2
PVA2%-B3
Steel Rebar

12Total deformation (mm)3The 2019 World Congress onAdvances in Structural Engineering and Mechanics (ASEM19)
Jeju Island, Korea, September 17 - 21, 2019

3.2 Crack patterns
Fig. 5 shows the examples of crack patterns at steel rebar yielding. Thespecimens with least axial cracks are picked up from each type of specimens. Table 6shows the number of cracks in each specimen shown in Fig. 5.
Comparing with the number of cracks in A series (100mm×100mm), increasingfiber volume fraction increased the number of cracks. However, in B series(150mm×150mm), there was few differences among No Fiber, PVA1% and PVA2%.
This tendency is also observed in the other two specimens for each type.

No Fiber-A

PVA1%-A

PVA2%-ANo Fiber-B

PVA1%-B

PVA2%-B

Fig. 5 Examples of crack patterns at steel rebar yielding

Table 6 Number of cracks
TypeNumber

No Fiber-A PVA1%-A
710

PVA2%-A No Fiber-B
134

PVA1%-B
5PVA2%-B
53.3 Crack width
In each LVDT measurement section with one crack, crack width is calculated byaveraging two values measured by both sides of LVDTs. The number and occurrenceof cracks are checked by visual observation and measurement values of LVDT. The
section which has axial cracks, two or more cracks, and cracks taking place on theboundary of sections or across two sections are excluded from the evaluation.

The 2019 World Congress on
Advances in Structural Engineering and Mechanics (ASEM19)
Jeju Island, Korea, September 17 - 21, 2019

0.1
0.2
0.3
Crack width (mm)

0.4

2000

1000
No Fiber-B
Test resultsAverage
00.1
0.2
0.3
Crack width (mm)0.4

Steel strain ()No Fiber-A
Test results
Average

2000

1000
PVA1%-A
Test results
Average00.1
0.20.3Crack width (mm)

0.4

2000

1000
PVA1%-B
Test results
Average
00.1
0.2
0.3
Crack width (mm)

0.4

2000

1000
PVA2%-A
Test results
Average
0Steel strain ()

1000

0

Steel strain ()Steel strain ()2000

Steel strain ()Steel strain ()Fig. 6 shows steel strain – crack width relationship. The test results of eachsection in the same type of specimens are shown in the same graph. Tension load isconverted to steel strain by using the elastic modulus obtained from the tension test ofreinforcing bars. The dotted line in Fig. 6 shows the average of test results in each typeof specimens. The test results of each section are evaluated by the least square
method to obtain slopes and Y-intercepts. The dotted line is determined by averagevalues of them in the same type of specimens.
According to the test results, by comparing A series (100mm×100mm) to B series(150mm×150mm) in the same fiber volume fraction, the slope of average line is smallerin specimens which have larger cross-section. Crack width tends to widen withincreasing of cross-sectional area. Since the number of cracks becoming fewer inlarger specimens, crack width of each crack also becomes to widen at the same valueof steel strain. On the other hand, by comparing PVA1%, PVA2% to No Fiber
specimens in the same cross-sectional area, the slope of average line is larger in
specimens which have larger fiber volume fraction. Crack width tends to narrow withincreasing of fiber volume fraction. That is because the bridging force of fibers
increases with cross-sectional area.

0.1
0.2
0.3
Crack width (mm)

0.4

2000

1000
PVA2%-B
Test results
Average
00.1
0.2
0.3
Crack width (mm)0.4

Fig. 6 Steel strain – crack width relationship

4. CONCLUSIONSIn this study, to evaluate crack width in steel reinforced DFRCC members,
uniaxial tension test is carried out for specimens with one steel deformed rebar
arranged. Polyvinyl alcohol (PVA) fiber is used in DFRCC. The experimentalparameters are cross-sectional area and fiber volume fraction. The test results areThe 2019 World Congress on
Advances in Structural Engineering and Mechanics (ASEM19)
Jeju Island, Korea, September 17 - 21, 2019concluded as follows;(1) Larger tension stiffening effect is observed in specimens which has larger crosssection and larger fiber volume fraction.
(2) Crack width tends to widen in specimens which have larger cross section andsmaller fiber volume fraction.

5. ACKNOWLEDGMENT
This study was supported by the JSPS KAKENHI Grant Number 18H03802

6. REFERENCES
Kanakubo, T. Miyaguchi, M. Asano, K. (2016), “Influence of Fiber Orientation onBridging Performance of Polyvinyl alcohol Fiber-Reinforced Cementitious
Composites”, Material Journal, American Concrete Institute, Vol.113, No.2, pp.131141
Kanakubo, T., Hosoya, H. (2015), “Bond-Splitting Strength of Reinforced StrainHardening Cement Composite Elements with Small Bar Spacing”, Structural Journal,
American Concrete Institute, Vol.112, No.2, pp.189-198
Sano, N., Yamada, H., Miyaguchi, M., Yasojima, A., Kanakubo, T., (2015), “StructuralPerformance of Beam-Column Joint using DFRCC”, 11th Canadian Conference onEarthquake Engineering -Facing Seismic Risk-, Paper ID 94163