I use Atena 3D to modal

1. A Study on Behavior of Reinforcement Concrete Beam
using the Recycled Concrete
Anh-Thang Le1
, Thanh-Hung Nguyen1
, Cong-Vu-Duc Phan2
1
Faculty of Construction, HCMC University of Technology and Education, Vietnam
2
Student, Faculty of High Quality, HCMC University of Technology and Education, Vietnam
thangla@hcmute.edu.vn
Abstract. The demand for concrete materials in construction becomes huge due
to the development of the economy and urbanization in Vietnam. Recently, recy-
cled aggregate concrete has been studied for partly replacing natural stone of
concrete in the worldwide. It could save cost for land filling, and con-serve the
national resources such as river sand and aggregate. Recycling concrete gives the
benefit for environment. However, it may affect to the strength and performance
of the construction containing the concrete waste. The paper is a discussion based
on the experiments of reinforcement concrete beams with and without recycled
concrete. Testing results are simulated by the ATENA program on exploring the
behavior of beams. The analysis and experiment results show that replacing 20%
of natural stone with re-cycled aggregate concrete does not affect both the bear-
ing capacity and performance of beams.
Keywords: recycled concrete beams; simulation of a beam; ATENA 3D; the
flexural behavior of the beam.
1 Introduction
Construction demolition has created a huge amount of waste concrete, which raises
disposal cost due to the limited capacity of land filling. This has caused many other
issues such as the management of waste, environmental pollution, exhaustion of natural
resources. Therefore, many scientists in the world have focused on the use of recycled
aggregate concrete [1]. Waste from demolished building has been recycled around the
world. Especially in European Union countries, the waste from demolition building
could be up to 45% [2]. In Vietnam, the recycled concrete obtained from demolished
building is still limited due to lack of researching of this problem.
The early research on structural performance of the recycled aggregate concrete (RCA)
was published in Japan. KhaldounRahal [3] compared RCA and natural aggregate con-
crete (NAC). The concrete samples were tested with a compressive strength of 25 to
30Mpa. There were the conclusions that the compressive strength of the block after 28
days, and the direct shear strength of RCA achieved an average of 90% those of NAC
with the same mixing ratio. Sami W.Tabsh et al. [4] researched that using RCA with a
grade of 50 MPa that could give compressive strength and concrete tensile strength
equivalent to natural aggregate concrete.

2. 2
Researchers had various conclusions related the percent of RCA replacement that
causes reducing strength, wider cracks opening, larger deflection in the construction
components. Ajdukiewicz et al. [1] used partial and full recycled aggregate for rein-
forcement concrete beams. All the beams had the rectangle section of 200x300 and
2600 mm long. They tested with two longitudinal reinforcement ratios of 0.90% and
1.60%. It was reported that the RCA beams had slightly (3.5% in average) lower mo-
ment capacity and higher deflection compared with the conventional concrete (CC)
beams. Mahdi Arezoumandi et al. [5] investigated of the flexural strength of full scale
reinforced concrete beams constructed with both RCA (100%) and CC. The RCA
beams showed comparable flexural capacity of the CC beams.
Bai and Sun [6] used RCA of eight to ten years-old with different replacement levels
of 50%, 70%, and 100%. They observed similar crack pattern, but deflection and crack
width increased with the increment of RCA replacement level. Knaack and Kurama [7]
tested on the 150x230 mm cross section and 2000 mm long beams. They used RCA
from late 1920s with both 50% and 100% replacement level. They reported higher de-
flection for the RCA beams, but they concluded that the existing analytical models and
specification for CC beams can be used for the RCA beams. Based on the above liter-
atures, it is possible to use recycled concrete up to 100%. We always expected that
100% of RCA could be reused in new concrete structure because of environmental
benefit. However, specific deficiency of full-scale concrete beams needs to be investi-
gated in this article.
In this study, the 20% of RCA replacing natural stone are studied on both bending
strength of the beams and the beam performance. This ratio of RCA is selected because
experimental results on the testing samples indicate that there do not significantly dif-
ferences in compressive and tensile strength between concrete with 20% of RCA and
conventional concrete using natural stone. The considered grade of concrete is 25MPa,
a popular grade of concrete using in the building in Vietnam recently. The ATENA
software is used for the steel rebar exploration.
2 Experiments
Concrete mixtures are conducted according to TCVN 4453:1995 [8]. The considering
grade of concrete is 25 MPa, which is tested based on the compressive strength of con-
crete cubic samples of 150x150x150 after 28 days according to TCVN 3118:1993 [9].
The selected concrete grade is corresponding to the concrete of class C20/25 of Euro-
code 2.
2.1 RCA material
The tested cubic samples of 150x150x150, are milled to product the large particles of
RCA. Compressive strengths of all milled cubic samples are controlled above 30 MPa.
Natural aggregates are gradually replaced by aggregates from waste concrete at the
rates of 20%, 40%, 60%, 80%, and 100% of the aggregate weight. Compressive

3. 3
strengths are investigated and summarized in Figure 1a. The diagram shows the com-
pressive strength of the recycled concrete specimen decrease as the ratio of RCA in-
creasing. In case of 20% RCA, the compressive strength reduced a little, about 1.7%.
The maximum reduction is 28.9% as the rate of RCA reaching 80%. As increasing the
rate of RCA up to 100%, experimental results show the compressive strength of con-
crete slightly improved. The compressive strength of recycled concrete with 100%
RCA higher that of 80% RCA is due to the homogeneous use of aggregate.
The average tensile strengths of concrete with and without 20% RCA was 1.81 and 1.93
Mpa, respectively. Thus, there were 6% reducing of tensile strength as 20% RCA re-
placing for natural aggregate in the concrete mixture. The ratio of 20% RCA in concrete
beams was selected in this study.
Fig. 1. (a) Concrete aggregate after milling and the compressive strength of concrete specimens
according to the ratios of RCA, (b) Deflection of beams according to load levels.
2.2 Beam testing results
The tested reinforcement concrete beams with size of 200x300x3300mm, Figure 2a.
Two beams with 20% of RCA are named as RCA1 and RCA2. The beam with 100%
natural aggregate is named as CC.
Fig. 2. (a) Diagram of the reinforcement concrete beam (sizes in mm), (b) steel rebar
numbering.
The ultimate loads of the beams of RCA1, RCA2, and CC are 136 KN, 138.8 KN, and
145.1 KN, respectively. Figure 1b shows the relationship between the displacement at
the mid-span of beams and total loading. The error between the ultimate load of the
beam with 100% natural aggregate and the lowest ultimate load of the beam with 20%
of RCA is 6.27%.
0
50
100
150
200
250
300
0 20 40 60 80 100
CompressiveStrength
(daN/cm²)
RCA (%)
0
20
40
60
80
100
120
140
160
0 5 10 15 20 25 30 35 40
Totalload(kN)
Beam deflection (mm)
RCA1
RCA2
CC
5
72
31
6
4
(a)
(a) (b)

4. 4
2.3 Crack patterns
Figure 3 presents the failure modes of beams. RCA1 and RCA2 have a total of 12 cracks
and 10 cracks, respectively, while the CC has a total of 9 cracks. The cracks are almost
located in the middle zone of beams. The crack paths are developed following the per-
pendicular path to the tension stress caused by bending. It indicates that the small
amount RCA could cause more cracks in the failure mode caused by bending. It could
be said that the performance of a beam in long term could be affected by the present of
RCA.
Fig. 3. Crack patterns
Fig. 4. Stress distribution of reinforce-
ments in the beam.
3 Model of the Beam
The finite-element analysis software, ATENA, has been selected for the modeling of
the testing beams. The layout of reinforcement inside the beam and the stress
distribution in the concrete beams after analyzing are captured in Figure 4.
The input parameters of both concrete and steel materials are summarized in Table
1. Those values are selected based on the concrete of class C20/25 (Eurocode 2).
Table 1. The input parameter of the models
Parameter Symbol RCA CC
Compressive strength of concrete
(MPa)
fc 19.55 21.25
Tensile strength of concrete (MPa) ft 1.941 2.052
Concrete elastic modulus (MPa) E 27070 28060
Yield strength of steel (MPa)
fy(Φ16) 300 300
fy (Φ14) 300 300
Elastic modulus of steel (GPa) E 200 200
3.1 Verification for the beam models
Figure 5 shows the comparison of the relationship between total load and deflection at

5. 5
mid-span of the beams of RCA and CC. It could be observed that there is not a big gap
between the curves of experience and those of modeling. It indicates that the models
created in the environment of ATENA software could be used for the further investiga-
tion.
Fig. 5. Comparison of experiment results and those obtained from modeling: (a) the curves of
RCA, and (b) the curves of CC.
3.2 Stress distribution in the reinforcement of the concrete beams
Table 2 summaries the distribution of stress in the beam models. The first column is
the numbering of longitudinal reinforcements, which are illustrated in Figure 2b. The
stresses showed in the table are the steel stress values obtained corresponding to the
ultimate loads. It could be observed that the steel bars in both the compressive zone and
tensile zone of the beam could be reached to the yield-point of steel. The difference of
steel stresses in models of RCA, and CC could be up to 80%. It shows that the stress
distribution inside the longitudinal steel bars was affected by the using 20% of RCA in
the beam.
Table 2. The stress in the longitudinal steel bars
No.
Steel stress in CC (MPa) Steel stress in RCA (MPa) Error (%)
Max Min Max Min Max Min
1 300.0 -8.9 300.0 -8.8 0 1
2 132.1 -300.0 26.9 -300.0 80 0
3 300.0 -19.3 300.0 -11.9 0 39
4 300.0 -11.0 300.0 -10.4 0 6
5 300.0 -5.8 300.0 -8.8 0 53
6 300.0 -15.0 300.0 -11.3 0 25
7 97.3 -300.0 46.4 -300.0 52 0
4 Conclusions
Study on recycled concrete aggregate partly replacing the natural aggregate in rein-
forcement concrete components is the current trend in Vietnam. A study on the beams
0
20
40
60
80
100
120
140
160
0 5 10 15 20 25 30 35 40
Totalload(kN)
Beam deflection (mm)
RCA1
RCA2
Model of RCA
0
20
40
60
80
100
120
140
160
0 5 10 15 20 25 30 35 40
Totalload(kN)
Beam deflection (mm)
CC
Model of CC
(a) (b)

6. 6
containing 20% of RCA is performed in which the qualities of RCA are carefully con-
trol. The following conclusions are made:
- Both compressive and tensile strengths of concrete are reduced a little even
though the compressive strength of concrete producing RCA has the higher
compressive strength of the desire concrete. The experimental results show
the reduction of compressive strength is 1.7%, while the reduction of tensile
strength is 6%.
- The performance of reinforcement concrete beam with 20% of RCA could
also be affected. The experimental results show that the deflections increase
comparing to that of the conventional beam. Besides, the number of cracking
appeared in the beams is also increased. On the other words, RCA could af-
fect to the long-term performance of the reinforcement concrete components.
- Based on the simulation models in the ATENA software, the distribution of
stress in the longitudinal steel bars of a beam changed in various models of
the beams with and without RCA. The maximum error of steel stresses could
be up to 80%. The longitudinal steel bars were affected by the using 20% of
RCA in the beam.
Acknowledgments
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 from
the faculty of civil engineering so that we can complete this research.
References
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cycled aggregate concrete and natural aggregate concrete. J Adv Concr Technol 5(2), 259–
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2. European Commission (DG ENV), Service contract on canagement of construction and
demolition waste -SR1: Final report task 2. BIO intelligence service, Paris, 2011.
3. KhaldounRahal.: Mechanical properties of concrete with recycled coarse aggregate. Build-
ing and Environment 42(1), 407-415 (2007).
4. Sami W.Tabsh, Akmal S.Abdelfatah.: Influence of recycled concrete aggregates on strength
properties of concrete. Construction and Building Materials 23(2), 1163-1167 (2009).
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study on flexural strength of reinforced concrete beams with 100% recycled concrete aggre-
gate. Engineering Structures 88, 154–162 (2015).
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concrete beam. Applied Mechanics and Materials 29, 543-548 (2010).
7. Knaack, Adam M., and Yahya C. Kurama.: Behavior of reinforced concrete beams with
recycled concrete coarse aggregates. Journal of Structural Engineering 141.3 (2014).
8. TCVN 4453:1995, Monolithic concrete and reinforced concrete structures - Codes for con-
struction, check and acceptance.
9. TCVN 3118:1993, Heavyweight concrete - Method for determination of compressive
strength.