In this paper, the authors will investigate the effect of reinforced concrete beams strengthened with high-strength fiber reinforced concrete (SFRC) at the tensile zone. The experiments are tested at the University Structural Engineering Laboratory HCMC Technical Education. The assessments are given by the experimental model with reinforced concrete beams corresponding to concrete grades of M20, M25, M30 in compressive zone and the high-strength fiber concrete in the tensile zone. Comparison results of the steel-reinforced concrete beams reinforced with high-strength fiber concrete and normal reinforced concrete beams shows the increasing the bearing capacity of beams, and the behavior of beams changed significantly compared to conventional concrete beams.

1. © Springer Nature Singapore Pte Ltd. and Ho Chi Minh City University of Technology Press 2019
J.N. Reddy et al. (eds.), Proceedings of the International Conference on Sustainable Civil Engineering
and Architecture 2019, Springer Series in Civil Engineering and Architecture,
https://doi.org/...
Experimental Study of Reinforced Concrete Beams Strengthened
by High-Strength Fiber Reinforced Concrete
N. T. Hung1
, L. A. Thang1*
, K. G. Phat2
, P. C. V. Duc2
1
Faculty of Civil Engineering, Ho Chi Minh City University of Technology and Education, Ho Chi Minh City,
Vietnam
2
Student Faculty of High Quality, Ho Chi Minh City University of Technology and Education, Ho Chi Minh
City, Vietnam
*
thangla@hcmute.edu.vn
Abstract. In this paper, the authors will investigate the effect of reinforced concrete beams
strengthened with high-strength fiber reinforced concrete (SFRC) at the tensile zone. The
experiments are tested at the University Structural Engineering Laboratory HCMC Technical
Education. The assessments are given by the experimental model with reinforced concrete beams
corresponding to concrete grades of M20, M25, M30 in compressive zone and the high-strength
fiber concrete in the tensile zone. Comparison results of the steel-reinforced concrete beams
reinforced with high-strength fiber concrete and normal reinforced concrete beams shows the
increasing the bearing capacity of beams, and the behavior of beams changed significantly
compared to conventional concrete beams.
Keywords: Steel fiber reinforced concrete, reinforced concrete beam, experiment of beam,
concrete beam strengthened with fiber concrete.
1 Introduction
Recently, there has been a topic in Vietnam related to the precast structure of which steel fibre reinforced
concrete (SFRC) having the role of the form works. The efficiency of existing reinforced concrete structures
strengthening with SFRC have been studied by many authors (Brühwiler & Denarié, 2013; Habel, Denarié, &
Brühwiler, 2006; Lampropoulos, Paschalis, Tsioulou, & Dritsos, 2016; Noshiravani & Brühwiler, 2013; 2014).
High price of SFRC causes many limits to carry out the application and experiment, especially in the developing
countries.
In contrast to concrete, the tensile strength of SFRC enhances significantly with the existing of steel fiber.
The tensile strength depending on a number of factors as mix components, the amount of steel fibers, mixing
equipment and mixture procedure. Steel fiber keeps the concrete maintains the loading capacity after load
reaching to the peak of load. The tensile test could be found in various literatures (Graybeal, 2014; Wille, El-
Tawil, & Naaman, 2014).
The reinforcement concrete beams strengthened by a SFRC layer at the bottom of beams can exhibit the
better the structural performance (Brühwiler & Denarié, 2013; Habel, Denarié, & Brühwiler, 2006;
Lampropoulos, Paschalis, Tsioulou, & Dritsos, 2016; Noshiravani & Brühwiler, 2013; 2014; Hussein, 2015).
Besides, it is also reported that SFRC enhances flexural behavior of the beam, increased stiffness, and reduced
crack widths. SFRC could serve as protection function for reinforcement due to its low-water permeability
(Hussein, 2015). There were experiments carried out by other researches in order to measure the bonding
strength between the ordinary concrete and SFRC (Harris, Muñoz, Gheitasi, Ahlborn, & Rush, 2015; Muñoz,
Harris, Ahlborn, & Froster, 2014; Tayeh, Bakar, & Johari, 2013).
The article is a study of the behavior and performance of reinforcement concrete beams strengthened by an
SFRC layer in the beam's tension zone. Several conventional concrete grades combined with the same type of

2. Instruction for Authors for International Conference on Sustainable Civil Engineering and Architecture 2019 2
SFRC and steel reinforcement in a beam were tested in the laboratory. The bending strength and performance of
the beam were observed and discussed in the paper.
2 Experimental investigations
2.1 Test program
Experimental investigations were carried out on purpose to determine the flexural behavior of the composite
beams of conventional concrete-SFRC. Test program consisted of property's characterization tests of concrete,
SFRC and steel reinforcement. The determination of structural behavior was done on four intermediate-scale
beams using 4-point bending tests (Fig. 1).
Figure 1. Detailing of the RC beams and the concrete-SFRC composite beams
2.2 Mixtures and material properties
All beams were reinforced with the same manner. Longitudinal reinforcement of Ø14 mm (grade AII) placing in
the lower part, upper reinforcement Ø12 mm (grade AII) and the stirrup rebar of Ø6 mm was arranged uniformly
along the beam (grade AI) as shown in Fig. 1. Average yielding strength of steel rebar (fsy) is 300 MPa and
modulus of elasticity (Es) is 200 GPa. In the study, steel fibers (1.6% by volume) with the tensile strength (ffb,u )
of 135 MPa were used for the SFRC mixture. Fiber length (lf) is 35 mm, diameter (df) is 0.55 mm, and the ratio
(lf/df) is 64. The elastic modulus of steel fiber (Efb,s) is 200 Gpa (Fig.2a). Mixture of compositions in the
experiment is presented in Table 1.
Table 1. Mix compositions of conventional concrete and SFRC
Materials
Quantity (kg/m3)
M200 M250 M300 M800
Cement 297.0 346.0 378.0 690.0
Aggregate 5x10 1050.0
Aggregate 10x20 1164.8 1150.8 1142.4
Sand 522.0 501.0 477.0 310.0
Water 195.0 195.0 195.0 195.0
Fly ash 35.0
Silica fume 80.0
Plasticizer 16.5
Steel fibers - 3Dmax 40.0
The material composition used in SFRC is shown in Fig. 2. In which silica fume (Fig. 2e) and plasticizer
(Fig. 2f) are additive for strengthen and workability of the concrete mixture.

3. (a) (b) (c)
(d) (e) (f)
Figure 2. Materials: (a) Steel fibres, (b) Aggregate, (c) Fine sand from Binh Dinh province, (d) Fly ash, (e)
Silica fume, (f) Plasticizer
The compressive strengths of conventional concrete and SFRC were tested at the age of 28 days. Average
values of compressive strength are presented in Table 2.
Table 2. Compressive strength of conventional concrete and UHPFRC
TT M20 M25 M30 M80
Compressive strength (MPa) 22.4 29.2 33.4 87.0
2.3 Preparing specimens
The conventional reinforcement concrete beams and the composite beams of concrete and SFRC are cast in the
laboratory as shown in Fig. 1. There are two types of beam section with and without 10cm of SFRC layer
thickness (Fig. 1). SFRC is placed in the tension area of beams.. The concrete grades of beams are summarized
in Table 3. Each cross section types have two beams.
Table 3. The concrete grades of beams
Beam type Beam description Concrete normal UHPFRC
Type 1 B1-CC20 M20
Type 2 B2-20 M20 M80
Type 2 B3-25 M25 M80
Type 2 B4-30 M30 M80
3 Experimental results
3.1 Deflection
Fig. 3 shows the curves of the relationship between load and deflection at mid-span of the beams. It can be seen
that there is a difference in mid-span displacement of the beams with and without SFRC. The elastic stiffness of
reinforcement concrete beams with SFRC is the same and higher than the elastic stiffness of conventional
reinforcement concrete beams. As increasing the grade of the concrete in the beam's upper part from 20 MPa, 25
MPa, and 30 MPa, the bending load capacity of the beam increases 17.7%, 20.0% and 40.2%, respectively,
comparing to the conventional reinforcement concrete beam. The difference between the beam of B2-20 and B1-
CC20 is 17.7%. It indicates that the bearing capacity of the reinforced concrete beam increases significantly with
the strengthening of SFRC.

4. Instruction for Authors for International Conference on Sustainable Civil Engineering and Architecture 2019 4
Figure 3. Load and deflection at the mid-span of a beam
3.2 Crack patterns
As the crack occurring, there is the difference in the crack pattern of beams with and without SFRC. Looking to
Fig. 4, it could be said that the SFRC had a significant effect to crack propagation. The distances of cracks of
beams with SFRC are closer than that of beams without SFRC. There is the phenomenal that the steel fiber was
pulled out the concrete matrix.
Through Fig. 4, we could see that B4-30 appears fewer cracks than beams of B2-20, and B3-25. This
indicates that the bonding between concrete of various grades and SFRC may cause the difference in the crack
pattern.
On the other hand, it could be seen that there are more cracks in the SFRC. The phenomenon of sliding
between the two layers of concrete that may cause the number of cracks in the SFRC part is more than the
number of cracks in the normal concrete. Besides, there is the restart crack in the normal concrete. The crack not
goes through the contact face, the crack in the normal concrete start at a distance away from the crack in SFRC.
(a)
(b)
0
10
20
30
40
50
60
70
80
90
100
110
120
0 10 20 30 40 50
Totalload(kN)
Beam deflection (mm)
B4-30
B3-25
B2-20
B1-CC20

5. (c)
(d)
Figure 4. Cracking patterns of different type of tested beams at failure load: (a) B1-CC20, (b) B2-20, (c) B3-25
and (d) B4-30
Fig. 4 shows that B1-CC20, B2-20, B-25 and B4-0 have the number of cracks of 16, 15, 16 and 14,
respectively. The maximum crack widths measured on the specimens of B2-20, B-25 and B4-0 are 9.6 mm, 8.7
mm, 6.5 mm, correspondingly. This indicates that the higher the grade of concrete combined with SFRC, the
more the crack width resistance of the beam.
3.3 Curvature and ductile of beams
Based on the image processing, the radius of curvature of B1-CC20, B2-20, B3-25 and B4-30 are estimated as
9.9 m, 6.1 m, 6.5 m and 5.4 m, respectively. The curvature of reinforcement concrete beams with SFRC is higher
that of conventional reinforcement concrete beams.
Figure 5. The curvature of B2-20
Due to the limit of LVDT of 50 mm, the displacement of the beams cannot be measured up to 50mm. The
relationship curve of load and displacement went down as shown in Fig.3. B1-CC20 cannot maintain the bearing
load after the displacement above 45mm. On the other hands, the reinforcement concrete beams with SFRC can
maintain the bearing load up to displacement of 150mm (Fig. 5). Thus, the curvatures of beams with SFRC are
higher than the curvature of conventional beams without SFRC. It could be said that the ductility of the beam
increases as the beam is strengthened by an SFRC layer.
3.4 Layer separation
The phenomenon of slippage at the contact face between conventional concrete and SFRC could be observed
easily (Fig. 4). The gap between two concrete layers of the beams of B2-20, B3-25 and B4-30 are 4.1 mm, 3.9
mm and 3.5 mm, respectively. Those gaps are measured at the mid-span of the beam. The beams have the higher
the load-bearing capacity leading the smaller the gap between two concrete layers of the beam. Gaps may be
caused by difference in the stiffness of various layers. The stiffness of SFRC layer is higher than that of
conventional concrete layer.

6. Instruction for Authors for International Conference on Sustainable Civil Engineering and Architecture 2019 6
4 Conclusions
The experimental results show the efficiency in loading capacity of the composite beams between the
conventional concrete and SFRC. Besides, there are some conclusions related to the behavior and performance
of beams:
- The performance of beams having the SFRC layer could also be enhanced as bending. The composite
beams have the increased stiffness, and the crack widths reduced. SFRC layer could help the reinforcement
concrete beams increasing curvature and ductile.
- The behavior of the beam is affected significantly by concrete's grade working with SFRC. The
performance of B4-30 is better than the performance of B2-20 and B3-25. Thus, the closer the grade of
conventional concrete to the grade of the concrete matrix in SFRC, the better performance of the bending beams
could be observed.
- The phenomenon of slippage at the contact face between conventional concrete and SFRC could be
observed easily in every case of beams having the SFRC layer.
Acknowledgement. The authors are grateful for the financial support as well as the experimental equipment of
the HCM University of Technology and Education, and the unconditional help of the faculty of construction so
that we can complete this research.
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