The 7th International Conference of Asian Concrete Federation“SUSTAINABLE CONCRETE FOR NOW AND THE FUTURE”
30 Oct – 02 Nov, 2016, Hanoi, Vietnam
www.acf2016.vn

INFLUENCE OF PLACING METHOD CONSIDERING FIBER ORIENTATIONTO BENDING CHARACTERISTICS OF DFRCC
K. Watanabe1, Y. Ozu1, M. Miyaguchi2, and T. Kanakubo3
1

Master Program, Dept. of Engineering Mechanics and Energy, University of Tsukuba, Tsukuba, Japan
2
Sumitomo Mitsui Construction Co.,Ltd., Tokyo, Japan
3
Professor, Dept. of Engineering Mechanics and Energy, University of Tsukuba, Tsukuba, Japan

ABSTRACT: Ductile fiber-reinforced cementitious composites (DFRCC) are cementitious materials
reinforced with short fibers to improve the tensile and bending ductility of mortar or concrete. It is wellknown that bending characteristics of DFRCC are influenced by fiber orientation. Controlling the fiber
orientation is one of the effective methodology to make DFRCC more practical. In this study, placing
methods considering fiber orientation using a vibrator and a device like a “comb” are newly proposed.
Beam specimens of which cross-sectional size is 180×280mm are manufactured using DFRCC reinforcedwith polyvinyl alcohol (PVA) fiber. The parameter is placing method of DFRCC. Four-point bending test iscarried out for these specimens. From the test result, the bending capacity and ductility increase inspecimens applied moving a comb and a vibrator axial direction. It is confirmed that the fiber
orientation tends to differ in each specimen and in positions of a cross-section by observing thespecimen section after loading. The bending capacity of each specimen is evaluated by section analysis
using the bridging law which expresses the difference of fiber orientation for the position of crosssection of the specimen.
1INTRODUCTION

Ductile fiber-reinforced cementitious composites (DFRCC) are cementitious materials with mixing fiberin mortar or concrete. DFRCC shows multiple cracks and deflection hardening behavior under thebending stress filed. DFRCC is expected as one of the new cementitious materials which show highductility for bending, tension, and compression behaviors those are improved largely than ordinary
concrete. It is known that the characteristics of fiber-reinforced cementitious composites are affected by
the distribution and orientation of fiber in matrix. To apply DFRCC for practical use, controlling of fiber
orientation is important to improve and stabilize the characteristics of DFRCC. In this study, placing
methods considering fiber orientation using a vibrator and a device like a “comb” are newly proposed.
Beam specimens of which sectional size is 180×280mm are manufactured using DFRCC reinforced with
polyvinyl alcohol (PVA) fiber. Four-point bending test is carried out for these specimens. The flow
analysis using a wide-use software based on finite-difference method (FDM) is also conducted tosimulate the flow of matrix and fiber orientation. The bending capacity of each specimen is evaluated bysection analysis considering the difference of fiber orientation in the cross-section of the specimen.

2OUTLINE OF PLACING METHOD

Placing methods of DFRCC proposed in this study are shown in Figure 1. While the normal placing (N)means that the DFRCC filled into the mold only by flow (self-compacting), the comb device is applied(CA) to arrange the fiber orientation longitudinally. A vibrator is applied with moving in the mold foraxial direction (VA) and perpendicular direction (VP).
Bucketyx

DFRCC

Φ6@36mm

Vibrator

Vibrator

CombMoldMoldMoldz

Normal(N)Moving Comb
To Axial Direction(CA)Moving Vibrator
To Axial Direction(VA)

Moving Vibrator
To Perpendicular Direction(VP)

Figure 1. Proposed placing method

3

BENDING TEST

3.1

Material properties

The mix proportion of DFRCC is shown in Table 1. Polyvinyl alcohol (PVA) fiber which length is 12mm,
diameter is 0.10mm is used. The fiber volume fraction is 2.0%. Fresh and mechanical property of DFRCC
are shown in Table 2. After sealed curing for 8 days, the specimens were cured in atmosphericenvironments. The testing age at bending test ranges 29 – 31 days.
Table 1. Mix proportion of DFRCC (kg/m3)
Water

Cement380678Fine
aggregate484

Fly ashPVA fiber

291

26High performance water
Thickening agent
reducing agent
62.52-3.03

Table 2. Fresh and mechanical property of DFRCC
Air content (%) Compressive strength (MPa) Elastic modulus (GPa)
1.8
45.6
13.9

3.2

Loading and measurements

Outline of four-point bending test is shown in Figure 2. The displacement controlled 2MN universal
testing machine was used. The loading speed was set to 0.5mm/min. The measuring items were appliedload, the displacements at loading points (2 points) and local deformation to calculate the crack widthand curvature. After loading, number of cracks generated in pure bending section was counted visually.
5501680280

550

180280

LVDTs for deflection

LVDTs for local deformation

Figure 2. Specimen

4EXPRIMENTAL RESULT

4.1

Placing observation

Figure 3 shows the example of photos in placing for the specimen N and CA. During self-compacting,
DFRCC matrix are spreading in concentric circles around the placing point. Near the vertical mold walls,
DFRCC matrix are flowing along the walls. When the comb device moved, tracks of the comb device areobserved. In specimens VA and VP, tracks due to moving a vibrator are also observed.

Figure 3. Placing and moving a comb device

4.2

Bending moment-deflection curve

Bending moment – deflection curves are shown in Figure 4, the test results are summarized in Table 3.
Deflection is obtained as the average of two LVDTs at the loading points. The bending capacity andductility of specimens CA and VA are larger than those of specimen N. It is considered that fibers arearranged toward the longitudinal direction as the result of moving the vibrator and the comb, andresistance performance to crack opening increases. While bending capacity of specimen VP is similar asthat of specimen N, ductility is larger than specimen N.

Bending moment [kNm]

10NVACAVP

86420051015Deflection [mm]Figure 4. Bending moment – deflection curve
Table 3. Bending test resultsSpecimenNVACAVP

4.3

At maximum load
Max. Load (kN) Deflection (mm) Bending moment (kNm)
26.0
3.04
7.14
31.0
8.13
8.52
31.0
6.63
8.53
26.5
5.85
7.28

Crack pattern observation

The crack patterns after loading are shown in Figure 5. The number of cracks generated in pure bending
section is listed in Table 4. The cracks at the tension zone of 42mm (specimen depth 280mm×0.15) fromthe bottom were counted. In all specimens, after four or five cracks taking place, one of them is mainlyopened. The average crack spacing is calculated as pure bending span 280mm divided by the number ofcracks in each specimen.

NVACAFigure 5. Crack patterns after loading (triangles show loading points)

VP

Table 4. Number of cracks and average crack spacing
Specimen Number of cracks Average crack spacing (mm)
N
470
VA
556
CA
556
VP
470

4.4

Fracture surface observation

Specimen was ruptured into two pieces after loading at the major crack, and the fracture surface wasobserved visually. The photos of fracture surfaces are shown in Figure 6. The black-light was used foreasiness of visual observation. The dotted straight lines in the figure indicate the mold surfaces. The
matrix was poured from the upper surface in the photos. In specimen N, while fibers near the mold tend
to be along the mold surface, fibers at the central section tend to be arranged toward the perpendicular
direction for specimen axis (shown by arrows). Fibers in specimen VP are observed like swirling. In
specimens CA and VA, fibers have tendency to be rearranged to longitudinal direction. It is observedthat fibers in the center of section orient more axial direction of specimen. As the result of the surface
observation, fiber orientation can be controlled by the moving vibrator and comb longitudinally.

NVA
Figure 6. Fracture surfaces observation

5FLOW ANALYSIS

5.1

Simulation method

CAVP

The flow analysis is conducted using a general-purpose computational fluid dynamics (CFD) software
based on finite-difference method (FDM) by controlling volume (FLOW-3D). The fibers are replaced by
the unit vector in each calculated mesh, the vector is obtained as the results of fluid flow calculation
which is given by the coordinates of x, y and z of direction vector. So, collisions of fibers and influence offlow of fibers themselves cannot be considered. The difference of fiber volume fraction also cannot betaken account. Analysis conditions are listed in Table 5. To simulate the actual DFRCC placing carried out
in manufacturing the bending specimens, a flow-out hole was considered in the analysis. The position of

the flow-out hole is shown in Figure 7. Fluid density was set to be the same as DFRCC, and fluid viscosity
was decided from the flow test result of DFRCC as similar as described in the previous study (Kanakuboet al.(2016)). The radius of flow-out hole and the flow speed was decided to show the same filling timein manufacturing the bending specimen. The position of the hole is set as same as the actual DFRCC
placing.
Table 5. Analysis conditions
Parameter
Fluid viscosity (Pa*s)
Fluid density (g/cm3)
Flow time (s)Input value
4.36
1.96
240

Parameter
Radius of flow-out hole R (mm)Height of flow-out hole h (mm)Position of flow-out hole d (mm)Flow speed V (mm/s)

Input value
124025078

Figure 7. Position of flow-out hole

5.2

Result of flow analysis

Figure 8 and 9 shows the analysis results for xy plane and zx plane, respectively. The results for xy plane(Figure 8) show the phenomenon that fluid spread in concentric circles around the placing point likeactual DFRCC pouring. As far from the placing point, fibers tend to orient randomly in the center of themold. After finishing placing (t=240s), many fibers which lie perpendicularly are observed from enlarged
view (right figure). From the results for zx plane (figure 9), fibers tend to orient along parabolic curvearound the placing point. It is assumed that fluid rebounds up from the bottom of the mold when fluid
placed. Rebounding fibers flow to the pure bending section remaining those orientations. While fibers
tend to orient perpendicularly around the upper surface due to fluid pouring, fibers orient longitudinallyat the bottom section.
t=80s
280

t=240s280

280

t=160s280

t=240s
280

1680

mmmm

180

Figure 8. Analysis results for xy plane (right: enlarged view at 240s)t=80s

t=240s180180t=160s

180t=240s

1680mmFigure 9. Analysis results for zx plane (right: enlarged view at 240s)

280mm

6SECTION ANALYSIS CONSIDERING FIBER ORIENTATION

6.1

Model for DFRCC

It is confirmed that the fiber orientation tends to differ in each specimen and in positions of a crosssection by observing the fracture surface of the specimens after loading. To evaluate the bending
capacity of each specimen, section analysis is conducted. The different bridging laws (tensile stress –crack width relationship) are applied to each position of divided 8 sections as shown in Figure 10.
Employed relationships between the stress and the strain are shown in Figure 10. The parabolic model isadopted in the compression side, the trilinear model is adopted in the tension side. In the parabolicmodel, σB is 45.6 MPa, εc is 0.0046 from the compression test result of test pieces of DFRCC. The
procedure of building up the trilinear model for tension side is shown in Figure 11. The bridging law isderived from the test result of pulling out of single PVA fiber considering the probability density function(PDF) which gives the fiber orientation distribution (Kanakubo et al.(2016)). The pullout model of single
fiber is also shown in Figure 11. The values of Pa and Pmax are assumed to be 1.5N and 3.0N, respectively.
The values of δa and δmax are set to 0.2mm and 0.45mm, respectively, as same as previous study(Kanakubo et al.(2016)). The elliptic function is adopted as the PDF for fiber orientation distribution(Kanakubo et al.(2016)). The orientation intensity, which is defined as the ratio of two radii, k(=a/b), andthe principal orientation angle θr can indicate the intense of the fiber orientation tendency toward theprincipal orientation angle. In this study, θr is set to 0 (longitudinal direction). The fiber orientation isexpressed by difference of the orientation intensity k. If k=1, it means fibers exist randomly. k>1 meansthat fibers tend to orient longitudinal direction, k<1 means fibers tend to orient to perpendiculardirection. The input value for the parameters are listed in Table 6. The coefficients to show snubbingeffect and the fiber strength degradation are set to 0.5 and 0.3, as same as those in the previous study(Kanda and Li (1999)). The rupture strength is 569MPa that is the average of rupture strength obtainedin previous pullout test of single fiber (Asano (2014)). The bridging law is calculated as the summation ofpullout load of fibers that exist on a crack surface. After that, the bridging law is modeled to trilinear
model, which is characterized by two points corresponding to the maximum stress and the point toshow remarkable changing of the slope. In order to use the bridging law in the section analysis, the crack
width is converted to strain, namely, crack width is divided by the average crack spacing observed in thebending test (Table 4). The values for the first point (σbs, εbs) and the second point (σ2, ε2) are listed inTable 7.
tension side(trilinear)

σσbsεc← k=0.4← k=0.2Eεεuεbs ε2ⅠⅡⅢⅣⅣⅢPLACED FACE

σ2

←k=1
← k=0.6moldⅡ
σBcompression side(parabola)

Ⅰ
section of specimen

Figure 10. Relationship between stress versus strain and specimen section

PDF giving
fiber orientation

Set parameters by previous researches
Pullout load
相対度数0.2PmaxPaδa δmaxa
θr

0.1-45045
配向角（°）

lb

Bridging law

convertMaking bridging lawa each k

楕円分布
k=0.69r=-35.0°

0-90

constructby90x

k=Tensile Stress-Strain
Converting by
average crack spacing
Tensile stress+

Tensile stress

Pullout modelof single PVA fiber

Crack width

Tensile strain

Principle orientain angle θr=0°(Longitudinal orientation)

Figure 11. Procedure of building up the trilinear model for tension side
Table 6. Input values for bridging law
Parameter
Input value Parameter
Input valueFirst peak load, Pa (N)1.5
Fiber strength (MPa)569
Crack width at Pa, δa (mm)0.2
Snubbing coefficient, f
0.5
Maximum load, Pmax (N)
3.0
Fiber strength reduction factor, f’ 0.3
Crack width at Pmax, δmax (mm) 0.45
Table 7. Characteristic values for trilinear model for tension sidek σbs εbs
0.7 1.87 0.00325
0.6 1.78 0.00300
0.4 1.54 0.00300
0.2 1.15 0.00300

6.2

σ2ε2εu0.45 0.0075 0.100
0.39 0.0075 0.100
0.27 0.0075 0.100
0.14 0.0075 0.100

Result of section analysis

The different bridging laws are applied to each position of divided 8 sections of the specimen as shownin Figure 10. The orientation intensity is decided as the maximum bending moment measured in thebending test corresponds to that calculated by analysis. The employed orientation intensities and theanalysis results are shown in Table 8. As shown in the table, the employed orientation intensities forspecimen N shows lower values especially for the central section (k=0.2 for layer No.IV), because fibers
distribute perpendicularly around specimen center as observed in Section 4.4. In specimens VA and CA,
fibers around the central section tend to orient longitudinally. That corresponds to employing higher
orientation intensity such as 0.7 for the layer II-IV. In specimen VP, all orientation intensities are 0.4 thatis smaller than specimen N, because the fiber orientation to longitudinal direction tends to decrease due
to moving the vibrator perpendicular direction. The bending capacity calculated by section analysis cancatch the difference of obtained capacity by bending test. The difference can be expressed by thesection analysis considering the orientation intensity “k”.
Table 8. Analysis condition
Specimen Orientation intensity of each position of cross-section
NVA
CA
VP

I:k=0.6,II:k=0.4,III:k=0.4,IV:k=0.2
I:k=0.6,II-IV:k=0.7
I-IV:k=0.4

Maximum moment(kNm)
TestAnalysis
7.14
7.17
8.52
8.65
8.53
8.65
7.28
7.22

7CONCLUTION

1.

Placing methods of DFRCC considering fiber orientation using a vibrator and a device like a “comb”
are newly proposed. Beam specimens, in which the vibrator or the comb is applied with moving
longitudinal direction, show larger bending capacity and ductility.

2.

From the results of fracture section observation and flow analysis, the fiber orientation tends todiffer in each specimen and in positions of a cross-section.

3.

The bending capacity of each specimen is evaluated by section analysis using the bridging law which
expresses the difference of fiber orientation for the position of cross-section of the specimen. The
difference of bending capacity can be expressed by the section analysis considering the orientation
intensity.

8ACKNOWLEDGEMENTThe authors wish to express their gratitude and sincere appreciation to the Kuraray Co., Ltd. forproviding the PVA fiber. This study was supported by the JSPS KAKENHI Grant Number 26289188.
9REFERENCES

Asano, K. (2014) “Study on Fiber Orientation and Bridging Constitutive Law in High Performance Fiber Reinforced
Cementitious Composites”, Doctoral thesis, University of Tsukuba, pp.16-31, (in Japanese)
Kanakubo, T., Miyaguchi, M., and Asano, K. (2016) “Influence of Fiber Orientation on Bridging Performance ofPolyvinyl Alcohol Fiber-Reinforced Cementitious Composite”, Materials Journal, American Concrete Institute,Vol.113, No.2, pp.131-141
Kanda, T. and Li, V. C. (1999) “Effect of Fiber Strength and Fiber-Matrix Interface on Crack Bridging in CementComposites”, ASCE Journal of Engineering Mechanics, Vol.125, No.3, pp.290-299